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Sample records for dot interfacial layer

  1. Au Nanoparticles as Interfacial Layer for CdS Quantum Dot-sensitized Solar Cells

    Directory of Open Access Journals (Sweden)

    Zhu Guang

    2010-01-01

    Full Text Available Abstract Quantum dot-sensitized solar cells based on fluorine-doped tin oxide (FTO/Au/TiO2/CdS photoanode and polysulfide electrolyte are fabricated. Au nanoparticles (NPs as interfacial layer between FTO and TiO2 layer are dip-coated on FTO surface. The structure, morphology and impedance of the photoanodes and the photovoltaic performance of the cells are investigated. A power conversion efficiency of 1.62% has been obtained for FTO/Au/TiO2/CdS cell, which is about 88% higher than that for FTO/TiO2/CdS cell (0.86%. The easier transport of excited electron and the suppression of charge recombination in the photoanode due to the introduction of Au NP layer should be responsible for the performance enhancement of the cell.

  2. A layer-by-layer ZnO nanoparticle-PbS quantum dot self-assembly platform for ultrafast interfacial electron injection

    KAUST Repository

    Eita, Mohamed Samir

    2014-08-28

    Absorbent layers of semiconductor quantum dots (QDs) are now used as material platforms for low-cost, high-performance solar cells. The semiconductor metal oxide nanoparticles as an acceptor layer have become an integral part of the next generation solar cell. To achieve sufficient electron transfer and subsequently high conversion efficiency in these solar cells, however, energy-level alignment and interfacial contact between the donor and the acceptor units are needed. Here, the layer-by-layer (LbL) technique is used to assemble ZnO nanoparticles (NPs), providing adequate PbS QD uptake to achieve greater interfacial contact compared with traditional sputtering methods. Electron injection at the PbS QD and ZnO NP interface is investigated using broadband transient absorption spectroscopy with 120 femtosecond temporal resolution. The results indicate that electron injection from photoexcited PbS QDs to ZnO NPs occurs on a time scale of a few hundred femtoseconds. This observation is supported by the interfacial electronic-energy alignment between the donor and acceptor moieties. Finally, due to the combination of large interfacial contact and ultrafast electron injection, this proposed platform of assembled thin films holds promise for a variety of solar cell architectures and other settings that principally rely on interfacial contact, such as photocatalysis. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Efficacy of In2S3 interfacial recombination barrier layer in PbS quantum-dot-sensitized solar cells

    International Nuclear Information System (INIS)

    Basit, Muhammad Abdul; Abbas, Muhammad Awais; Bang, Jin Ho; Park, Tae Joo

    2015-01-01

    In 2 S 3 interfacial recombination barrier layer (IBL) via successive ionic layer adsorption and reaction (SILAR) was successfully employed between PbS quantum dots and mesoporous TiO 2 in quantum-dot-sensitized solar cells (QDSSCs). In 2 S 3 IBL significantly increased the resistance against back electron transfer from TiO 2 , resulting an increment in the photocurrent density (J SC ) for the cell with single SILAR cycle of In 2 S 3 IBL. Further increase in the number of SILAR cycles of In 2 S 3 IBL deteriorated the J SC , whereas open-circuit voltage sustained the increasing trend. Therefore, an optimal photo-conversion efficiency of ∼2.2% was obtained for the cell with 2 SILAR cycles of In 2 S 3 IBL, which strategically reached a value of ∼2.70% after annealing (increased by 40% compared to the control cell without IBL). In 2 S 3 IBL not only improved the recombination resistance and electron life time of the cells, but it also enhanced the photostability of the cells. - Highlights: • In 2 S 3 interfacial recombination barrier layer was deposited on TiO 2 photoanode via SILAR process. • Resistance against back electron transfer from TiO 2 (recombination) increased notably. • Fabricated PbS-QDSSCs were characterized using IPCE, OCVD and EIS techniques. • In 2 S 3 IBL improved chemical capacitance, electron life time and photostability of modified cells. • 2In 2 S 3 IBL showed optimal performance, yielding 40% improvement in PCE after heat treatment.

  4. Interfacial passivation of CdS layer to CdSe quantum dots-sensitized electrodeposited ZnO nanowire thin films

    International Nuclear Information System (INIS)

    Zhang, Jingbo; Sun, Chuanzhen; Bai, Shouli; Luo, Ruixian; Chen, Aifan; Sun, Lina; Lin, Yuan

    2013-01-01

    ZnO porous thin films with nanowire structure were deposited by the one-step electrochemical deposition method. And a CdS layer was coated on the as-deposited ZnO nanowire thin films by successive ionic layer adsorption and reaction (SILAR) method to passivate surface states. Then the films were further sensitized by CdSe quantum dots (QDs) to serve as a photoanode for fabricating quantum dots-sensitized solar cells (QDSSCs). The effect of the CdS interfacial passivation layer on the performance of the QDSSCs was systematically investigated by varying the SILAR cycle number and heating the passivation layer. The amorphous CdS layer with an optimized thickness can effectively suppress the recombination of the injected electrons with holes on QDs and the redox electrolyte. The newly formed CdS layer on the surface of the ZnO nanowire thin film obviously prolongs the electron lifetime in the passivated ZnO nanoporous thin film because of the lower surface trap density in the ZnO nanowires after CdS deposition, which is favorable to the higher short-circuit photocurrent density (J sc ). For the CdSe QDs-sensitized ZnO nanoporous thin film with the interfacial passivation layer, the J sc and conversion efficiency can reach a maximum of 8.36 mA cm −2 and 2.36%, respectively. The conversion efficiency was improved by 83.47% compared with that of the cell based on the CdSe QDs-sensitized ZnO nanoporous thin film without CdS interfacial passivation (0.39%)

  5. A layer-by-layer ZnO nanoparticle-PbS quantum dot self-assembly platform for ultrafast interfacial electron injection

    KAUST Repository

    Eita, Mohamed Samir; Usman, Anwar; El-Ballouli, AlA'A O.; Alarousu, Erkki Antero; Bakr, Osman; Mohammed, Omar F.

    2014-01-01

    solar cell. To achieve sufficient electron transfer and subsequently high conversion efficiency in these solar cells, however, energy-level alignment and interfacial contact between the donor and the acceptor units are needed. Here, the layer-by

  6. Influence of interfacial layer on contact resistance

    NARCIS (Netherlands)

    Roy, D.; In 't Zand, M.A.A.; Delhounge, R.; Klootwijk, J.H.; Wolters, Robertus A.M.

    2008-01-01

    The contact resistance between two materials is dependent on the intrinsic properties of the materials in contact and the presence and properties of an interfacial layer at the contact. This article presents the difference in contact resistance measurements with and without the presence of a process

  7. Enhanced interfacial contact between PbS and TiO2 layers in quantum dot solar cells using 2D-arrayed TiO2 hemisphere nanostructures

    Science.gov (United States)

    Lee, Wonseok; Ryu, Ilhwan; Lee, Haein; Yim, Sanggyu

    2018-02-01

    Two-dimensionally (2D) arrayed hemispherical nanostructures of TiO2 thin films were successfully fabricated using a simple procedure of spin-coating or dip-coating TiO2 nanoparticles onto 2D close-packed polystyrene (PS) nanospheres, followed by PS extraction. The nanostructured TiO2 film was then used as an n-type layer in a lead sulfide (PbS) colloidal quantum dot solar cell. The TiO2 nanostructure could provide significantly increased contacts with subsequently deposited PbS quantum dot layer. In addition, the periodically arrayed nanostructure could enhance optical absorption of the cell by redirecting the path of the incident light and increasing the path length passing though the active layer. As a result, the power conversion efficiency (PCE) reached 5.13%, which is approximately a 1.7-fold increase over that of the control cell without nanostructuring, 3.02%. This PCE enhancement can mainly be attributed to the increase of the short-circuit current density from 19.6 mA/cm2 to 30.6 mA/cm2, whereas the open-circuit voltage and fill factor values did not vary significantly.

  8. Interfacial Layer Engineering for Performance Enhancement in Polymer Solar Cells

    Directory of Open Access Journals (Sweden)

    Hao Zeng

    2015-02-01

    Full Text Available Improving power conversion efficiency and device performance stability is the most critical challenge in polymer solar cells for fulfilling their applications in industry at large scale. Various methodologies have been developed for realizing this goal, among them interfacial layer engineering has shown great success, which can optimize the electrical contacts between active layers and electrodes and lead to enhanced charge transport and collection. Interfacial layers also show profound impacts on light absorption and optical distribution of solar irradiation in the active layer and film morphology of the subsequently deposited active layer due to the accompanied surface energy change. Interfacial layer engineering enables the use of high work function metal electrodes without sacrificing device performance, which in combination with the favored kinetic barriers against water and oxygen penetration leads to polymer solar cells with enhanced performance stability. This review provides an overview of the recent progress of different types of interfacial layer materials, including polymers, small molecules, graphene oxides, fullerene derivatives, and metal oxides. Device performance enhancement of the resulting solar cells will be elucidated and the function and operation mechanism of the interfacial layers will be discussed.

  9. Impact of Interfacial Layers in Perovskite Solar Cells.

    Science.gov (United States)

    Cho, An-Na; Park, Nam-Gyu

    2017-10-09

    Perovskite solar cells (PCSs) are composed of organic-inorganic lead halide perovskite as the light harvester. Since the first report on a long-term-durable, 9.7 % efficient, solid-state perovskite solar cell, organic-inorganic halide perovskites have received considerable attention because of their excellent optoelectronic properties. As a result, a power conversion efficiency (PCE) exceeding 22 % was certified. Controlling the grain size, grain boundary, morphology, and defects of the perovskite layer is important for achieving high efficiency. In addition, interfacial engineering is equally or more important to further improve the PCE through better charge collection and a reduction in charge recombination. In this Review, the type of interfacial layers and their impact on photovoltaic performance are investigated for both the normal and the inverted cell architectures. Four different interfaces of fluorine-doped tin oxide (FTO)/electron-transport layer (ETL), ETL/perovskite, perovskite/hole-transport layer (HTL), and HTL/metal are classified, and their roles are investigated. The effects of interfacial engineering with organic or inorganic materials on photovoltaic performance are described in detail. Grain-boundary engineering is also included because it is related to interfacial engineering and the grain boundary in the perovskite layer plays an important role in charge conduction, recombination, and chargecarrier life time. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Compliant Interfacial Layers in Thermoelectric Devices

    Science.gov (United States)

    Firdosy, Samad A. (Inventor); Li, Billy Chun-Yip (Inventor); Ravi, Vilupanur A. (Inventor); Fleurial, Jean-Pierre (Inventor); Caillat, Thierry (Inventor); Anjunyan, Harut (Inventor)

    2017-01-01

    A thermoelectric power generation device is disclosed using one or more mechanically compliant and thermally and electrically conductive layers at the thermoelectric material interfaces to accommodate high temperature differentials and stresses induced thereby. The compliant material may be metal foam or metal graphite composite (e.g. using nickel) and is particularly beneficial in high temperature thermoelectric generators employing Zintl thermoelectric materials. The compliant material may be disposed between the thermoelectric segments of the device or between a thermoelectric segment and the hot or cold side interconnect of the device.

  11. Investigation on Interfacial Charge Transfer Process in CdSexTe1-x Alloyed Quantum Dot Sensitized Solar Cells

    International Nuclear Information System (INIS)

    Wei, Huiyun; Wang, Guoshuai; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

    2015-01-01

    Colloidal QDs, typically, alloyed QDs with extending light absorption range, exhibit prospective application on quantum dot-sensitized solar cells (QDSCs). In this work, CdSe 0.8 Te 0.2 alloyed QDs have been employed to assemble QDSCs, and the influence of the photoanode structure and film thickness on the cell performance has been investigated in detail. Further study on the charge transport and interfacial electron transfer processes reveals that with the film thickness increasing, recombination possibility will be remarkably enhanced. By careful control on the balance between the light absorption and carrier recombination, an optimal double-layer photoanode structure with 11.5 μm-thickness transparent and 6 μm-thickness scattering layers can present a power conversion efficiency of 7.55%, which is one of the best records for the sandwiched-type QDSCs

  12. Organic photovoltaic device with interfacial layer and method of fabricating same

    Science.gov (United States)

    Marks, Tobin J.; Hains, Alexander W.

    2013-03-19

    An organic photovoltaic device and method of forming same. In one embodiment, the organic photovoltaic device has an anode, a cathode, an active layer disposed between the anode and the cathode; and an interfacial layer disposed between the anode and the active layer, the interfacial layer comprising 5,5'-bis[(p-trichlorosilylpropylphenyl)phenylamino]-2,2'-bithiophene (PABTSi.sub.2).

  13. Quantum dot laser optimization: selectively doped layers

    Science.gov (United States)

    Korenev, Vladimir V.; Konoplev, Sergey S.; Savelyev, Artem V.; Shernyakov, Yurii M.; Maximov, Mikhail V.; Zhukov, Alexey E.

    2016-08-01

    Edge emitting quantum dot (QD) lasers are discussed. It has been recently proposed to use modulation p-doping of the layers that are adjacent to QD layers in order to control QD's charge state. Experimentally it has been proven useful to enhance ground state lasing and suppress the onset of excited state lasing at high injection. These results have been also confirmed with numerical calculations involving solution of drift-diffusion equations. However, deep understanding of physical reasons for such behavior and laser optimization requires analytical approaches to the problem. In this paper, under a set of assumptions we provide an analytical model that explains major effects of selective p-doping. Capture rates of elections and holes can be calculated by solving Poisson equations for electrons and holes around the charged QD layer. The charge itself is ruled by capture rates and selective doping concentration. We analyzed this self-consistent set of equations and showed that it can be used to optimize QD laser performance and to explain underlying physics.

  14. Quantum dot laser optimization: selectively doped layers

    International Nuclear Information System (INIS)

    Korenev, Vladimir V; Konoplev, Sergey S; Savelyev, Artem V; Shernyakov, Yurii M; Maximov, Mikhail V; Zhukov, Alexey E

    2016-01-01

    Edge emitting quantum dot (QD) lasers are discussed. It has been recently proposed to use modulation p-doping of the layers that are adjacent to QD layers in order to control QD's charge state. Experimentally it has been proven useful to enhance ground state lasing and suppress the onset of excited state lasing at high injection. These results have been also confirmed with numerical calculations involving solution of drift-diffusion equations. However, deep understanding of physical reasons for such behavior and laser optimization requires analytical approaches to the problem. In this paper, under a set of assumptions we provide an analytical model that explains major effects of selective p-doping. Capture rates of elections and holes can be calculated by solving Poisson equations for electrons and holes around the charged QD layer. The charge itself is ruled by capture rates and selective doping concentration. We analyzed this self-consistent set of equations and showed that it can be used to optimize QD laser performance and to explain underlying physics. (paper)

  15. Interfacial layering and capillary roughness in immiscible liquids.

    Science.gov (United States)

    Geysermans, P; Pontikis, V

    2010-08-21

    The capillary roughness and the atomic density profiles of extended interfaces between immiscible liquids are determined as a function of the interface area by using molecular dynamics and Lennard-Jones (12-6) potentials. We found that with increasing area, the interface roughness diverges logarithmically, thus fitting the theoretical mean-field prediction. In systems small enough for the interfacial roughness not to blur the structural details, atomic density profiles across the fluid interface are layered with correlation length in the range of molecular correlations in liquids. On increasing the system size, the amplitude of the thermally excited position fluctuations of the interface increases, thus causing layering to rapidly vanish, if density profiles are computed without special care. In this work, we present and validate a simple method, operating in the direct space, for extracting from molecular dynamics trajectories the "intrinsic" structure of a fluid interface that is the local density profile of the interface cleaned from capillary wave effects. Estimated values of interfacial properties such as the tension, the intrinsic width, and the lower wavelength limit of position fluctuations are in agreement with results collected from the literature.

  16. High reduction of interfacial charge recombination in colloidal quantum dot solar cells by metal oxide surface passivation.

    Science.gov (United States)

    Chang, Jin; Kuga, Yuki; Mora-Seró, Iván; Toyoda, Taro; Ogomi, Yuhei; Hayase, Shuzi; Bisquert, Juan; Shen, Qing

    2015-03-12

    Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar cells (CQDSCs). By coating thin TiO2 layers onto ZnO-NW surfaces, the open-circuit voltage and power conversion efficiency have been improved by over 40% in PbS CQDSCs. Characterization by transient photovoltage decay and impedance spectroscopy indicated that the interfacial recombination was significantly reduced by the surface passivation strategy. An efficiency as high as 6.13% was achieved through the passivation approach and optimization for the length of the ZnO-NW arrays (device active area: 16 mm2). All solar cells were tested in air, and exhibited excellent air storage stability (without any performance decline over more than 130 days). This work highlights the significance of metal oxide passivation in achieving high performance BHJ solar cells. The charge recombination mechanism uncovered in this work could shed light on the further improvement of PbS CQDSCs and/or other types of solar cells.

  17. Enhancement of device performance of organic solar cells by an interfacial perylene derivative layer

    KAUST Repository

    Kim, Inho; Haverinen, Hanna M.; Li, Jian; Jabbour, Ghassan E.

    2010-01-01

    We report that device performance of organic solar cells consisting of zinc phthalocyanine and fullerene (C60) can be enhanced by insertion of a perylene derivative interfacial layer between fullerene and bathocuproine (BCP) exciton blocking layer

  18. Effect of antiferromagnetic interfacial coupling on spin-wave resonance frequency of multi-layer film

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Rong-ke, E-mail: rkqiu@163.com; Cai, Wei

    2017-08-15

    Highlights: • A quantum approach is developed to study the SWR of a bicomponent multi-layer films. • The comparison of the SWR in films with FM and AFM interfacial coupling has been made. • The present results show the method to enhance and adjust the SWR frequency of films. - Abstract: We investigate the spin-wave resonance (SWR) frequency in a bicomponent bilayer and triple-layer films with antiferromagnetic or ferromagnetic interfacial couplings, as function of interfacial coupling, surface anisotropy, interface anisotropy, thickness and external magnetic field, using the linear spin-wave approximation and Green’s function technique. The microwave properties for multi-layer magnetic film with antiferromagnetic interfacial coupling is different from those for multi-layer magnetic film with ferromagnetic interfacial coupling. For the bilayer film with antiferromagnetic interfacial couplings, as the lower (upper) surface anisotropy increases, only the SWR frequencies of the odd (even) number modes increase. The lower (upper) surface anisotropy does not affect the SWR frequencies of the even (odd) number modes{sub .} For the multi-layer film with antiferromagnetic interfacial coupling, the SWR frequency of modes m = 1, 3 and 4 decreases while that of mode m = 2 increases with increasing thickness of the film within a proper parameter region. The present results could be useful in enhancing our fundamental understanding and show the method to enhance and adjust the SWR frequency of bicomponent multi-layer magnetic films with antiferromagnetic or ferromagnetic interfacial coupling.

  19. Two-Dimensional Layered Oxide Structures Tailored by Self-Assembled Layer Stacking via Interfacial Strain.

    Science.gov (United States)

    Zhang, Wenrui; Li, Mingtao; Chen, Aiping; Li, Leigang; Zhu, Yuanyuan; Xia, Zhenhai; Lu, Ping; Boullay, Philippe; Wu, Lijun; Zhu, Yimei; MacManus-Driscoll, Judith L; Jia, Quanxi; Zhou, Honghui; Narayan, Jagdish; Zhang, Xinghang; Wang, Haiyan

    2016-07-06

    Study of layered complex oxides emerge as one of leading topics in fundamental materials science because of the strong interplay among intrinsic charge, spin, orbital, and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials that exhibit new phenomena beyond their conventional forms. Here, we report a strain-driven self-assembly of bismuth-based supercell (SC) with a two-dimensional (2D) layered structure. With combined experimental analysis and first-principles calculations, we investigated the full SC structure and elucidated the fundamental growth mechanism achieved by the strain-enabled self-assembled atomic layer stacking. The unique SC structure exhibits room-temperature ferroelectricity, enhanced magnetic responses, and a distinct optical bandgap from the conventional double perovskite structure. This study reveals the important role of interfacial strain modulation and atomic rearrangement in self-assembling a layered singe-phase multiferroic thin film, which opens up a promising avenue in the search for and design of novel 2D layered complex oxides with enormous promise.

  20. Effect of interfacial layer on water flow in nanochannels: Lattice Boltzmann simulations

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Yakang [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266580 (China); College of Science, China University of Petroleum, Qingdao 266580, Shandong (China); Liu, Xuefeng, E-mail: liuxf@upc.edu.cn [College of Science, China University of Petroleum, Qingdao 266580, Shandong (China); Liu, Zilong [College of Science, China University of Petroleum, Qingdao 266580, Shandong (China); Lu, Shuangfang [Institute of Unconventional Oil & Gas and New Energy, China University of Petroleum, Qingdao 266580, Shandong (China); Xue, Qingzhong, E-mail: xueqingzhong@tsinghua.org.cn [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266580 (China); College of Science, China University of Petroleum, Qingdao 266580, Shandong (China); National Production Equipment Research Center, Dongying 257064, Shandong (China)

    2016-04-15

    A novel interfacial model was proposed to understand water flow mechanism in nanochannels. Based on our pore-throat nanochannel model, the effect of interfacial layer on water flow in nanochannels was quantitatively studied using Lattice Boltzmann method (LBM). It is found that both the permeability of nanochannel and water velocity in the nanochannel dramatically decrease with increasing the thickness of interfacial layer. The permeability of nanochannel with pore radius of 10 nm decreases by about three orders of magnitude when the thickness of interfacial layer is changed from 0 nm to 3 nm gradually. Furthermore, it has been demonstrated that the cross-section shape has a great effect on the water flow inside nanochannel and the effect of interfacial layer on the permeability of nanochannel has a close relationship with cross-section shape when the pore size is smaller than 12 nm. Besides, both pore-throat ratio and throat length can greatly affect water flow in nanochannels, and the influence of interfacial layer on water flow in nanochannels becomes more evident with increasing pore-throat ratio and throat length. Our theoretical results provide a simple and effective method to study the flow phenomena in nano-porous media, particularly to quantitatively study the interfacial layer effect in nano-porous media.

  1. Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

    NARCIS (Netherlands)

    Kim, N.H.; Han, D.S.; Jung, J.; Cho, J.; Kim, J.S.; Swagten, H.J.M.; You, C.Y.

    2015-01-01

    We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlOx and Ta/Pt/Co/AlOx structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy

  2. Interfacial chemistry and the design of solid-phase nucleic acid hybridization assays using immobilized quantum dots as donors in fluorescence resonance energy transfer.

    Science.gov (United States)

    Algar, W Russ; Krull, Ulrich J

    2011-01-01

    The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling the regeneration and reuse of solid-phase QD-FRET hybridization assays. FRET-sensitized emission from acceptor dyes associated with hybridization events at immobilized QD donors provides the analytical signal in these assays. The minimization of active sensing area reduces background from QD donor PL and allows the resolution of smaller amounts of acceptor emission, thus lowering the LOD. The association of multiple acceptor dyes with each hybridization event can enhance FRET efficiency, thereby improving sensitivity. Many previous studies have used interfacial protein layers to generate selectivity; however, transient destabilization of these layers is shown to prevent efficient regeneration. To this end, we report a protein-free interfacial chemistry and demonstrate the specific detection of as little as 2 pmol of target, as well as an improved capacity for regeneration.

  3. TFB:TPDSi2 interfacial layer usable in organic photovoltaic cells

    Science.gov (United States)

    Marks, Iobin J [Evanston, IL; Hains, Alexander W [Evanston, IL

    2011-02-15

    The present invention, in one aspect, relates to a solar cell. In one embodiment, the solar cell includes an anode; an active organic layer comprising an electron-donating organic material and an electron-accepting organic material; and an interfacial layer formed between the anode and active organic layer, where the interfacial layer comprises a hole-transporting polymer characterized with a hole-mobility higher than that of the electron-donating organic material in the active organic layer, and a small molecule that has a high hole-mobility and is capable of crosslinking on contact with air.

  4. Ultrasonic Guided Waves in Piezoelectric Layered Composite with Different Interfacial Properties

    Directory of Open Access Journals (Sweden)

    Xiao Chen

    2011-01-01

    Full Text Available Combining the propagation model of guided waves in a multilayered piezoelectric composite with the interfacial model of rigid, slip, and weak interfaces, the generalized dispersion characteristic equations of guided waves propagating in a piezoelectric layered composite with different interfacial properties are derived. The effects of the slip, weak, and delamination interfaces in different depths on the dispersion properties of the lowest-order mode ultrasonic guided wave are analyzed. The theory would be used to characterize the interfacial properties of piezoelectric layered composite nondestructively.

  5. Analysis on Interfacial Performance of CFRPConcrete with Different Thickness of Adhesive Layer and CFRP Plate

    Directory of Open Access Journals (Sweden)

    Guo Qingyong

    2018-01-01

    Full Text Available The bond behavior of CFRP-concrete interface is the analysis foundation for concrete structures with external strengthening CFRP. In the paper, the influences of the thickness of CFRP plate and adhesive layer on interfacial adhesive properties are investigated through the finite element program. The influence rules of the thickness on the interfacial ultimate bearing capacity and the effective bond length are performed. The results show that the thickness of adhesive layer and CFRP plate has a significant effect on the interfacial performance of CFRP-concrete.

  6. Ultrafast Interfacial Electron and Hole Transfer from CsPbBr3 Perovskite Quantum Dots.

    Science.gov (United States)

    Wu, Kaifeng; Liang, Guijie; Shang, Qiongyi; Ren, Yueping; Kong, Degui; Lian, Tianquan

    2015-10-14

    Recently reported colloidal lead halide perovskite quantum dots (QDs) with tunable photoluminescence (PL) wavelengths covering the whole visible spectrum and exceptionally high PL quantum yields (QYs, 50-90%) constitute a new family of functional materials with potential applications in light-harvesting and -emitting devices. By transient absorption spectroscopy, we show that the high PL QYs (∼79%) can be attributed to negligible electron or hole trapping pathways in CsPbBr3 QDs: ∼94% of lowest excitonic states decayed with a single-exponential time constant of 4.5 ± 0.2 ns. Furthermore, excitons in CsPbBr3 QDs can be efficiently dissociated in the presence of electron or hole acceptors. The half-lives of electron transfer (ET) to benzoquinone and subsequent charge recombination are 65 ± 5 ps and 2.6 ± 0.4 ns, respectively. The half-lives for hole transfer (HT) to phenothiazine and the subsequent charge recombination are 49 ± 6 ps and 1.0 ± 0.2 ns, respectively. The lack of electron and hole traps and fast interfacial ET and HT rates are key properties that may enable the development of efficient lead halide perovskite QDs-based light-harvesting and -emitting devices.

  7. Visualization and characterization of interfacial polymerization layer formation

    NARCIS (Netherlands)

    Zhang, Yali; Benes, Nieck Edwin; Lammertink, Rob G.H.

    2015-01-01

    We present a microfluidic platform to visualize the formation of free-standing films by interfacial polymerization. A microfluidic device is fabricated, with an array of micropillars to stabilize an aqueous–organic interface that allows a direct observation of the films formation process via optical

  8. The effect of interfacial layers on charge transport in organic solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Mbuyise, Xolani G.; Tonui, Patrick; Mola, Genene Tessema, E-mail: mola@ukzn.ac.za

    2016-09-01

    The effect of interfacial buffer layers in organic photovoltaic cell (OPV) whose active layer is composed of poly(3 hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend was studied. The electrical properties of OPV devices produced with and without interfacial layers are compared and discussed in terms of measured parameters of the cells. The charge transport properties showed significant difference on the mobility and activation factor between the two types of device structures. The life time measurements in the unprotected conditions are also presented and discussed.

  9. Evidence for possible quantum dot interdiffusion induced by cap layer growth

    International Nuclear Information System (INIS)

    Jasinski, J.; Czeczott, M.; Gladysz, A.; Babinski, A.; Kozubowski, J.

    1999-01-01

    Self-organised InGaAs quantum dots were grown on (001) GaAs substrates and covered with two different types of cap layers grown at significantly different temperatures. In order to determine quantum dot emission energy and dot size distribution, photoluminescence and transmission electron microscopy studies were carried out on such samples. Simple theoretical model neglecting effect of interdiffusion allowed for correlation between quantum dot size and photoluminescence emission energy only in the case of dots covered by cap layers grown at the lower temperature. For dots covered by layers grown at the higher temperature such correlation was possible only when strong interdiffusion was assumed. (author)

  10. Self-healing sandwich structures incorporating an interfacial layer with vascular network

    International Nuclear Information System (INIS)

    Chen, Chunlin; Peters, Kara; Li, Yulong

    2013-01-01

    A self-healing capability specifically targeted for sandwich composite laminates based on interfacial layers with built-in vascular networks is presented. The self-healing occurs at the facesheet–core interface through an additional interfacial layer to seal facesheet cracks and rebond facesheet–core regions. The efficacy of introducing the self-healing system at the facesheet–core interface is evaluated through four-point bend and edgewise compression testing of representative foam core sandwich composite specimens with impact induced damage. The self-healing interfacial layer partially restored the specific initial stiffness, doubling the residual initial stiffness as compared to the control specimen after the impact event. The restoration of the ultimate specific skin strength was less successful. The results also highlight the critical challenge in self-healing of sandwich composites, which is to rebond facesheets which have separated from the core material. (paper)

  11. A solution-processed binary cathode interfacial layer facilitates electron extraction for inverted polymer solar cells.

    Science.gov (United States)

    Zhang, Xinyuan; Li, Zhiqi; Liu, Chunyu; Guo, Jiaxin; Shen, Liang; Guo, Wenbin

    2018-03-15

    The charge transfer and separation are significantly affected by the electron properties of the interface between the electron-donor layer and the carrier-transporting layer in polymer solar cells (PSCs). In this study, we investigate the electron extraction mechanism of PSCs with a low temperature solution-processed ZnO/PEI as electron transport layer. The incorporation of PEI layer can decrease the work function of ZnO and reduce interfacial barrier, which facilitates electron extraction and suppresses bimolecular recombination, leading to a significant performance enhancement. Furthermore, PEI layer can induce phase separation and passivite inorganic surface trap states as well as shift the interfacial energy offset between metal oxide and organic materials. This work offers a simple and effective way to improve the charge transporting property of organic photovoltaic devices. Copyright © 2017 Elsevier Inc. All rights reserved.

  12. Cleaved-edge overgrowth of aligned quantum dots on strained layers of InGaAs

    International Nuclear Information System (INIS)

    Wasserman, D.; Lyon, S.A.

    2004-01-01

    Strain aligned InAs quantum dots were grown on the cleaved edges of first growth samples containing strained In x Ga (1-x) As layers of varying thickness and indium fraction. The formation of the cleaved-edge quantum dots was observed by means of atomic force microscopy. 100% linear alignment of InAs quantum dots over the InGaAs strain layers of the first growth sample is demonstrated. Linear density of the aligned dots was found to depend on the properties of the underlying InGaAs strain layers. Vertical alignment of an additional InAs quantum dot layer over the buried, linearly aligned, initial dot layer was observed for thin GaAs spacer layers

  13. Molecular dynamics simulation aiming at interfacial characteristics of polymer chains on nanotubes with different layers

    Science.gov (United States)

    Li, Kun; Gu, Boqin; Zhu, Wanfu

    2017-03-01

    A molecular dynamics (MD) simulations study is performed on multiwalled carbon nanotubes (MWNTs)/acrylonitrile-butadiene rubber (NBR) composites. The physisorption and interfacial characteristics between the various MWNTs and polymer macromolecular chains are identified. The effects of nanotube layers on the nanotubes/polymer interactions are examined. Each of the situation result and surface features is characterized by binding energy (Eb). It is shown that the binding energy (Eb) increase with the number of layers.

  14. A thermal conductivity model for nanofluids including effect of the temperature-dependent interfacial layer

    International Nuclear Information System (INIS)

    Sitprasert, Chatcharin; Dechaumphai, Pramote; Juntasaro, Varangrat

    2009-01-01

    The interfacial layer of nanoparticles has been recently shown to have an effect on the thermal conductivity of nanofluids. There is, however, still no thermal conductivity model that includes the effects of temperature and nanoparticle size variations on the thickness and consequently on the thermal conductivity of the interfacial layer. In the present work, the stationary model developed by Leong et al. (J Nanopart Res 8:245-254, 2006) is initially modified to include the thermal dispersion effect due to the Brownian motion of nanoparticles. This model is called the 'Leong et al.'s dynamic model'. However, the Leong et al.'s dynamic model over-predicts the thermal conductivity of nanofluids in the case of the flowing fluid. This suggests that the enhancement in the thermal conductivity of the flowing nanofluids due to the increase in temperature does not come from the thermal dispersion effect. It is more likely that the enhancement in heat transfer of the flowing nanofluids comes from the temperature-dependent interfacial layer effect. Therefore, the Leong et al.'s stationary model is again modified to include the effect of temperature variation on the thermal conductivity of the interfacial layer for different sizes of nanoparticles. This present model is then evaluated and compared with the other thermal conductivity models for the turbulent convective heat transfer in nanofluids along a uniformly heated tube. The results show that the present model is more general than the other models in the sense that it can predict both the temperature and the volume fraction dependence of the thermal conductivity of nanofluids for both non-flowing and flowing fluids. Also, it is found to be more accurate than the other models due to the inclusion of the effect of the temperature-dependent interfacial layer. In conclusion, the present model can accurately predict the changes in thermal conductivity of nanofluids due to the changes in volume fraction and temperature for

  15. Thermally oxidized formation of new Ge dots over as-grown Ge dots in the Si capping layer

    International Nuclear Information System (INIS)

    Nie Tianxiao; Lin Jinhui; Shao Yuanmin; Wu Yueqin; Yang Xinju; Fan Yongliang; Jiang Zuimin; Chen Zhigang; Zou Jin

    2011-01-01

    A Si-capped Ge quantum dot sample was self-assembly grown via Stranski-Krastanov mode in a molecular beam epitaxy system with the Si capping layer deposited at 300 deg. C. After annealing the sample in an oxygen atmosphere at 1000 deg. C, a structure, namely two layers of quantum dots, was formed with the newly formed Ge-rich quantum dots embedded in the oxidized matrix with the position accurately located upon the as-grown quantum dots. It has been found that the formation of such nanostructures strongly depends upon the growth temperature and oxygen atmosphere. A growth mechanism was proposed to explain the formation of the nanostructure based on the Ge diffusion from the as-grown quantum dots, Ge segregation from the growing oxide, and subsequent migration/agglomeration.

  16. Effects of interfacial layer on characteristics of TiN/ZrO2 structures.

    Science.gov (United States)

    Kim, Younsoo; Kang, Sang Yeol; Choi, Jae Hyoung; Lim, Jae Soon; Park, Min Young; Chung, Suk-Jin; Chung, Jaegwan; Lee, Hyung Ik; Kim, Ki Hong; Kyoung, Yong Koo; Heo, Sung; Yoo, Cha Young; Kang, Ho-Kyu

    2011-09-01

    To minimize the formation of unwanted interfacial layers, thin interfacial layer (ZrCN layer) was deposited between TiN bottom electrode and ZrO2 dielectric in TiN/ZrO2/TiN capacitor. Carbon and nitrogen were also involved in the layer because ZrCN layer was thermally deposited using TEMAZ without any reactant. Electrical characteristics of TiN/ZrO2/TiN capacitor were improved by insertion of ZrCN layer. The oxidation of TiN bottom electrode was largely inhibited at TiN/ZrCN/ZrO2 structure compared to TiN/ZrO2 structure. While the sheet resistance of TiN/ZrCN/ZrO2 structure was constantly sustained with increasing ZrO2 thickness, the large increase of sheet resistance was observed in TiN/ZrO2 structure after 6 nm ZrO2 deposition. When ZrO2 films were deposited on ZrCN layer, the deposition rate of ZrO2 also increased. It is believed that ZrCN layer acted both as a protection layer of TiN oxidation and a seed layer of ZrO2 growth.

  17. Interfacial layers in tape cast anode-supported doped lanthanum gallate SOFC elements

    Energy Technology Data Exchange (ETDEWEB)

    Maffei, N.; De Silveira, G. [Materials Technology Laboratory, Natural Resources Canada, CANMET, 405 Rochester Street, Ottawa, Ontario (Canada) K1A OG3

    2003-04-01

    Lanthanum gallate doped with strontium and magnesium (LSGM) is a promising electrolyte system for intermediate temperature solid oxide fuel cells (SOFCs). The reported formation of interfacial layers in monolithic type SOFCs based on lanthanum gallate is of concern because of its impact on the performance of the fuel cell. Planar anode-supported SOFC elements (without the cathode) were prepared by the tape casting technique in order to determine the nature of the anode/electrolyte interface after sintering. Two anode systems were studied, one a NiO-CeO{sub 2} cermet, and the other, a modified lanthanum gallate anode containing manganese. Sintering studies were conducted at 1250, 1300, 1350, 1400 and 1450 C to determine the effect of temperature on the interfacial characteristics. Scanning electron microscopy (SEM) revealed a significant diffusion of Ni from the NiO-CeO{sub 2} anode resulting in the formation of an interfacial layer regardless of sintering temperature. Significant La diffusion from the electrolyte into the anode was also observed. In the case of the modified lanthanum gallate anode containing manganese, there was no interfacial layer formation, but a significant diffusion of Mn into the electrolyte was observed.

  18. Nanoscopic characterization of the water vapor-salt interfacial layer reveals a unique biphasic adsorption process

    Science.gov (United States)

    Yang, Liu; He, Jianfeng; Shen, Yi; Li, Xiaowei; Sun, Jielin; Czajkowsky, Daniel M.; Shao, Zhifeng

    2016-08-01

    Our quantitative understanding of water adsorption onto salt surfaces under ambient conditions is presently quite poor owing to the difficulties in directly characterizing this interfacial layer under these conditions. Here we determine the thickness of the interfacial layer on NaCl at different relative humidities (RH) based on a novel application of atomic force spectroscopy and capillary condensation theory. In particular, we take advantage of the microsecond-timescale of the capillary condensation process to directly resolve the magnitude of its contribution in the tip-sample interaction, from which the interfacial water thickness is determined. Further, to correlate this thickness with salt dissolution, we also measure surface conductance under similar conditions. We find that below 30% RH, there is essentially only the deposition of water molecules onto this surface, typical of conventional adsorption onto solid surfaces. However, above 30% RH, adsorption is simultaneous with the dissolution of ions, unlike conventional adsorption, leading to a rapid increase of surface conductance. Thus, water adsorption on NaCl is an unconventional biphasic process in which the interfacial layer not only exhibits quantitative differences in thickness but also qualitative differences in composition.

  19. Engineering Interfacial Energetics: A Novel Hybrid System of Metal Oxide Quantum Dots and Cobalt Complex for Photocatalytic Water Oxidation

    International Nuclear Information System (INIS)

    Niu, Fujun; Shen, Shaohua; Wang, Jian; Guo, Liejin

    2016-01-01

    Graphical abstract: A cobalt complex engineers the interfacial energetics of metal oxide quantum dots (n- or p-type) and electrolytes for highly efficient O_2 generation under visible light irradiation. - Highlights: • A noble-metal-free hybrid photocatalytic system using a single-site cobalt catalyst was developed for O_2 generation. • Considerable activity and excellent stability for O_2 production were achieved by this novel system. • CoSlp engineered the QDs/electrolyte interfacical energetics for efficient hole transfer. - Abstract: Here we reported a novel hybrid photocatalytic water oxidation system, containing metal oxide (n-Fe_2O_3 or p-Co_3O_4) quantum dots (QDs) as light harvester, a salophen cobalt(II) complex (CoSlp) as redox catalyst and persulfate (S_2O_8"2"−) as sacrificial electron acceptor, for oxygen generation from fully aqueous solution. The n-Fe_2O_3 QDs/CoSlp and p-Co_3O_4 QDs/CoSlp systems exhibited good O_2 evolution performances, giving turnover numbers (TONs) of ca. 33 and ca. 35 over CoSlp after visible light irradiation for 72 h, respectively. The excellent photocatalytic performance could be ascribed to the efficient hole transfer from QDs to CoSlp catalyst, leading to reduced photogenerated charge recombination, as well as the CoSlp engineered interfacial band bending of QDs, increasing the driving force or decreasing the energy barrier for hole transfer and then benefiting the following O_2 generation at the QDs/electrolyte interface. The present work successfully demonstrated a novel hybrid system for photocatalytic O_2 evolution from fully aqueous solution; and the essential role of cobalt complexes in engineering the interfacial energetics of semiconductors (n- or p-type) and electrolytes could be informative for designing efficient systems for solar water splitting.

  20. Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell

    International Nuclear Information System (INIS)

    Shanmugam, Mariyappan; Jain, Nikhil; Jacobs-Gedrim, Robin; Yu, Bin; Xu, Yang

    2013-01-01

    Single crystalline, two dimensional (2D) layered insulator hexagonal boron nitride (h-BN), is demonstrated as an emerging material candidate for surface passivation on mesoporous TiO 2 . Cadmium selenide (CdSe) quantum dot based bulk heterojunction (BHJ) solar cell employed h-BN passivated TiO 2 as an electron acceptor exhibits photoconversion efficiency ∼46% more than BHJ employed unpassivated TiO 2 . Dominant interfacial recombination pathways such as electron capture by TiO 2 surface states and recombination with hole at valence band of CdSe are efficiently controlled by h-BN enabled surface passivation, leading to improved photovoltaic performance. Highly crystalline, confirmed by transmission electron microscopy, dangling bond-free 2D layered h-BN with self-terminated atomic planes, achieved by chemical exfoliation, enables efficient passivation on TiO 2 , allowing electronic transport at TiO 2 /h-BN/CdSe interface with much lower recombination rate compared to an unpassivated TiO 2 /CdSe interface

  1. Influences of interfacial properties on second-harmonic generation of Lamb waves propagating in layered planar structures

    International Nuclear Information System (INIS)

    Deng Mingxi; Wang Ping; Lv Xiafu

    2006-01-01

    This paper describes influences of interfacial properties on second-harmonic generation of Lamb waves propagating in layered planar structures. The nonlinearity in the elastic wave propagation is treated as a second-order perturbation of the linear elastic response. Due to the kinematic nonlinearity and the elastic nonlinearity of materials, there are second-order bulk and surface/interface driving sources in layered planar structures through which Lamb waves propagate. These driving sources can be thought of as forcing functions of a series of double frequency lamb waves (DFLWs) in terms of the approach of modal expansion analysis for waveguide excitation. The total second-harmonic fields consist of a summation of DFLWs in the corresponding stress-free layered planar structures. The interfacial properties of layered planar structures can be described by the well-known finite interfacial stiffness technique. The normal and tangential interfacial stiffness constants can be coupled with the equation governing the expansion coefficient of each DFLW component. On the other hand, the normal and tangential interfacial stiffness constants are associated with the degree of dispersion between Lamb waves and DFLWs. Theoretical analyses and numerical simulations indicate that the efficiency of second-harmonic generation by Lamb wave propagation is closely dependent on the interfacial properties of layered structures. The potential of using the effect of second-harmonic generation by Lamb wave propagation to characterize the interfacial properties of layered structures are considered. Some experimental results are presented

  2. Enhancement of device performance of organic solar cells by an interfacial perylene derivative layer

    KAUST Repository

    Kim, Inho

    2010-05-26

    We report that device performance of organic solar cells consisting of zinc phthalocyanine and fullerene (C60) can be enhanced by insertion of a perylene derivative interfacial layer between fullerene and bathocuproine (BCP) exciton blocking layer (EBL). The morphology of the BCP is influenced by the underlying N,N′-dihexyl-perylene-3,4,9,10-bis(dicarboximide) (PTCDI-C6), which promotes migration of the cathode metal into the BCP layer. Insertion of a PTCDI-C6 layer between fullerene and BCP layers enhances the power conversion efficiency to 2.5%, an improvement of 32% over devices without PTCDI-C6 layer. The enhancement in device performance by insertion of PTCDI-C6 is attributed to a reduction in series resistance due to promoted metal migration into BCP and optimized optical interference effects in multilayered devices. © 2010 American Chemical Society.

  3. Crystalline Molybdenum Oxide Thin-Films for Application as Interfacial Layers in Optoelectronic Devices

    DEFF Research Database (Denmark)

    Fernandes Cauduro, André Luis; dos Reis, Roberto; Chen, Gong

    2017-01-01

    The ability to control the interfacial properties in metal-oxide thin films through surface defect engineering is vital to fine-tune their optoelectronic properties and thus their integration in novel optoelectronic devices. This is exemplified in photovoltaic devices based on organic, inorganic...... or hybrid technologies, where precise control of the charge transport properties through the interfacial layer is highly important for improving device performance. In this work, we study the effects of in situ annealing in nearly stoichiometric MoOx (x ∼ 3.0) thin-films deposited by reactive sputtering. We...... with structural characterizations, this work addresses a novel method for tuning, and correlating, the optoelectronic properties and microstructure of device-relevant MoOx layers....

  4. Efficient organic photovoltaic cells on a single layer graphene transparent conductive electrode using MoOx as an interfacial layer.

    Science.gov (United States)

    Du, J H; Jin, H; Zhang, Z K; Zhang, D D; Jia, S; Ma, L P; Ren, W C; Cheng, H M; Burn, P L

    2017-01-07

    The large surface roughness, low work function and high cost of transparent electrodes using multilayer graphene films can limit their application in organic photovoltaic (OPV) cells. Here, we develop single layer graphene (SLG) films as transparent anodes for OPV cells that contain light-absorbing layers comprised of the evaporable molecular organic semiconductor materials, zinc phthalocyanine (ZnPc)/fullerene (C60), as well as a molybdenum oxide (MoO x ) interfacial layer. In addition to an increase in the optical transmittance, the SLG anodes had a significant decrease in surface roughness compared to two and four layer graphene (TLG and FLG) anodes fabricated by multiple transfer and stacking of SLGs. Importantly, the introduction of a MoO x interfacial layer not only reduced the energy barrier between the graphene anode and the active layer, but also decreased the resistance of the SLG by nearly ten times. The OPV cells with the structure of polyethylene terephthalate/SLG/MoO x /CuI/ZnPc/C60/bathocuproine/Al were flexible, and had a power conversion efficiency of up to 0.84%, which was only 17.6% lower than the devices with an equivalent structure but prepared on commercial indium tin oxide anodes. Furthermore, the devices with the SLG anode were 50% and 86.7% higher in efficiency than the cells with the TLG and FLG anodes. These results show the potential of SLG electrodes for flexible and wearable OPV cells as well as other organic optoelectronic devices.

  5. Interfacial Bonding Energy on the Interface between ZChSnSb/Sn Alloy Layer and Steel Body at Microscale

    Directory of Open Access Journals (Sweden)

    Jianmei Wang

    2017-09-01

    Full Text Available To investigate the performance of bonding on the interface between ZChSnSb/Sn and steel body, the interfacial bonding energy on the interface of a ZChSnSb/Sn alloy layer and the steel body with or without Sn as an intermediate layer was calculated under the same loadcase using the molecular dynamics simulation software Materials Studio by ACCELRYS, and the interfacial bonding energy under different Babbitt thicknesses was compared. The results show that the bonding energy of the interface with Sn as an intermediate layer is 10% larger than that of the interface without a Sn layer. The interfacial bonding performances of Babbitt and the steel body with Sn as an intermediate layer are better than those of an interface without a Sn layer. When the thickness of the Babbitt layer of bushing is 17.143 Å, the interfacial bonding energy reaches the maximum, and the interfacial bonding performance is optimum. These findings illustrate the bonding mechanism of the interfacial structure from the molecular level so as to ensure the good bonding properties of the interface, which provides a reference for the improvement of the bush manufacturing process from the microscopic point of view.

  6. Interfacial Bonding Energy on the Interface between ZChSnSb/Sn Alloy Layer and Steel Body at Microscale.

    Science.gov (United States)

    Wang, Jianmei; Xia, Quanzhi; Ma, Yang; Meng, Fanning; Liang, Yinan; Li, Zhixiong

    2017-09-25

    To investigate the performance of bonding on the interface between ZChSnSb/Sn and steel body, the interfacial bonding energy on the interface of a ZChSnSb/Sn alloy layer and the steel body with or without Sn as an intermediate layer was calculated under the same loadcase using the molecular dynamics simulation software Materials Studio by ACCELRYS, and the interfacial bonding energy under different Babbitt thicknesses was compared. The results show that the bonding energy of the interface with Sn as an intermediate layer is 10% larger than that of the interface without a Sn layer. The interfacial bonding performances of Babbitt and the steel body with Sn as an intermediate layer are better than those of an interface without a Sn layer. When the thickness of the Babbitt layer of bushing is 17.143 Å, the interfacial bonding energy reaches the maximum, and the interfacial bonding performance is optimum. These findings illustrate the bonding mechanism of the interfacial structure from the molecular level so as to ensure the good bonding properties of the interface, which provides a reference for the improvement of the bush manufacturing process from the microscopic point of view.

  7. Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy

    Science.gov (United States)

    Paradzah, Alexander T.; Diale, Mmantsae; Maabong, Kelebogile; Krüger, Tjaart P. J.

    2018-04-01

    Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the problem of fast electron-hole recombination, researchers have resorted to growth of nano-structured hematite, doping and use of under-layers. Under-layer materials enhance the photo-current by minimising electron-hole recombination through suppressing of back electron flow from the substrate, such as fluorine-doped tin oxide (FTO), to hematite. We have carried out ultrafast transient absorption spectroscopy on hematite in which Nb2O5 and SnO2 materials were used as interfacial layers to enhance hole lifetimes. The transient absorption data was fit with four different lifetimes ranging from a few hundred femtoseconds to a few nanoseconds. We show that the electron-hole recombination is slower in samples where interfacial layers are used than in pristine hematite. We also develop a model through target analysis to illustrate the effect of under-layers on electron-hole recombination rates in hematite thin films.

  8. Tungsten oxides as interfacial layers for improved performance in hybrid optoelectronic devices

    International Nuclear Information System (INIS)

    Vasilopoulou, M.; Palilis, L.C.; Georgiadou, D.G.; Argitis, P.; Kennou, S.; Kostis, I.; Papadimitropoulos, G.; Stathopoulos, N.A.; Iliadis, A.A.; Konofaos, N.; Davazoglou, D.; Sygellou, L.

    2011-01-01

    Tungsten oxide (WO 3 ) films with thicknesses ranging from 30 to 100 nm were grown by Hot Filament Vapor Deposition (HFVD). Films were studied by X-Ray Photoemission Spectroscopy (XPS) and were found to be stoichiometric. The surface morphology of the films was characterized by Atomic Force Microscopy (AFM). Samples had a granular form with grains in the order of 100 nm. The surface roughness was found to increase with film thickness. HFVD WO 3 films were used as conducting interfacial layers in advanced hybrid organic-inorganic optoelectronic devices. Hybrid-Organic Light Emitting Diodes (Hy-OLEDs) and Organic Photovoltaics (Hy-OPVs) were fabricated with these films as anode and/or as cathode interfacial conducting layers. The Hy-OLEDs showed significantly higher current density and a lower turn-on voltage when a thin WO 3 layer was inserted at the anode/polymer interface, while when inserted at the cathode/polymer interface the device performance was found to deteriorate. The improvement was attributed to a more efficient hole injection and transport from the Fermi level of the anode to the Highest Occupied Molecular Orbital (HOMO) of a yellow emitting copolymer (YEP). On the other hand, the insertion of a thin WO 3 layer at the cathode/polymer interface of Hy-OPV devices based on a polythiophene-fullerene bulk-heterojunction blend photoactive layer resulted in an increase of the produced photogenerated current, more likely due to improved electron extraction at the Al cathode.

  9. Interfacial stresses in a bi-material assembly with a compliant bonding layer

    International Nuclear Information System (INIS)

    Suhir, E; Vujosevic, M

    2008-01-01

    We examine an elongated bi-material adhesively bonded or soldered assembly with a continuous compliant attachment (bonding layer). The assembly is subjected to external tensile forces or to bending moments applied to one of the assembly components. We develop simple predictive analytical ('mathematical') models for the evaluation of interfacial shearing (in the case of external tensile forces) and peeling (in the case of external bending moments) stresses and strains in the bonding material. The developed models can be helpful in stress-strain analyses of assemblies of the type in question and particularly for printed-circuit-board (PCB)/surface-mounted-device (SMD) assemblies employed in electronic packaging. These models enable one to particularly evaluate the maximum interfacial stresses in the bonding material from the predicted or measured strains in the PCB in the vicinity of but still outside the surface-mounted package

  10. Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers.

    Science.gov (United States)

    Gan, Zecheng; Xing, Xiangjun; Xu, Zhenli

    2012-07-21

    We investigate the effects of image charges, interfacial charge discreteness, and surface roughness on spherical electric double layer structures in electrolyte solutions with divalent counterions in the setting of the primitive model. By using Monte Carlo simulations and the image charge method, the zeta potential profile and the integrated charge distribution function are computed for varying surface charge strengths and salt concentrations. Systematic comparisons were carried out between three distinct models for interfacial charges: (1) SURF1 with uniform surface charges, (2) SURF2 with discrete point charges on the interface, and (3) SURF3 with discrete interfacial charges and finite excluded volume. By comparing the integrated charge distribution function and the zeta potential profile, we argue that the potential at the distance of one ion diameter from the macroion surface is a suitable location to define the zeta potential. In SURF2 model, we find that image charge effects strongly enhance charge inversion for monovalent interfacial charges, and strongly suppress charge inversion for multivalent interfacial charges. For SURF3, the image charge effect becomes much smaller. Finally, with image charges in action, we find that excluded volumes (in SURF3) suppress charge inversion for monovalent interfacial charges and enhance charge inversion for multivalent interfacial charges. Overall, our results demonstrate that all these aspects, i.e., image charges, interfacial charge discreteness, their excluding volumes, have significant impacts on zeta potentials of electric double layers.

  11. Effect of ultrathin GeOx interfacial layer formed by thermal oxidation on Al2O3 capped Ge

    International Nuclear Information System (INIS)

    Han Le; Zhang Xiong; Wang Sheng-Kai; Xue Bai-Qing; Liu Hong-Gang; Wu Wang-Ran; Zhao Yi

    2014-01-01

    We propose a modified thermal oxidation method in which an Al 2 O 3 capping layer is used as an oxygen blocking layer (OBL) to form an ultrathin GeO x interfacial layer, and obtain a superior Al 2 O 3 /GeO x /Ge gate stack. The GeO x interfacial layer is formed in oxidation reaction by oxygen passing through the Al 2 O 3 OBL, in which the Al 2 O 3 layer could restrain the oxygen diffusion and suppress the GeO desorption during thermal treatment. The thickness of the GeO x interfacial layer would dramatically decrease as the thickness of Al 2 O 3 OBL increases, which is beneficial to achieving an ultrathin GeO x interfacial layer to satisfy the demand for small equivalent oxide thickness (EOT). In addition, the thickness of the GeO x interfacial layer has little influence on the passivation effect of the Al 2 O 3 /Ge interface. Ge (100) p-channel metal–oxide–semiconductor field-effect transistors (pMOSFETs) using the Al 2 O 3 /GeO x /Ge gate stacks exhibit excellent electrical characteristics; that is, a drain current on-off (I on /I off ) ratio of above 1×10 4 , a subthreshold slope of ∼ 120 mV/dec, and a peak hole mobility of 265 cm 2 /V·s are achieved. (condensed matter: structural, mechanical, and thermal properties)

  12. Evaluation of interlayer interfacial stiffness and layer wave velocity of multilayered structures by ultrasonic spectroscopy.

    Science.gov (United States)

    Ishii, Yosuke; Biwa, Shiro

    2014-07-01

    An ultrasonic evaluation procedure for the interlayer interfacial normal stiffness and the intralayer longitudinal wave velocity of multilayered plate-like structures is proposed. Based on the characteristics of the amplitude reflection spectrum of ultrasonic wave at normal incidence to a layered structure with spring-type interlayer interfaces, it is shown that the interfacial normal stiffness and the longitudinal wave velocity in the layers can be simultaneously evaluated from the frequencies of local maxima and minima of the spectrum provided that all interfaces and layers have the same properties. The effectiveness of the proposed procedure is investigated from the perspective of the sensitivity of local extremal frequencies of the reflection spectrum. The feasibility of the proposed procedure is also investigated when the stiffness of each interface is subjected to small random fluctuations about a certain average value. The proposed procedure is applied to a 16-layered cross-ply carbon-fiber-reinforced composite laminate. The normal stiffness of resin-rich interfaces and the longitudinal wave velocity of plies in the thickness direction evaluated from the experimental reflection spectrum are shown to be consistent with simple theoretical estimations.

  13. Wetting layers effect on InAs/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Sun Chao [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, P.O. Box 49(BUPT), Xitucheng Road No. 10, Beijing 100876 (China); Lu Pengfei, E-mail: photon.bupt@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, P.O. Box 49(BUPT), Xitucheng Road No. 10, Beijing 100876 (China); Yu Zhongyuan; Cao Huawei; Zhang Lidong [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, P.O. Box 49(BUPT), Xitucheng Road No. 10, Beijing 100876 (China)

    2012-11-15

    FEM combining with the K{center_dot}P theory is adopted to systematically investigate the effect of wetting layers on the strain-stress profiles and electronic structures of self-organized InAs quantum dot. Four different kinds of quantum dots are introduced at the same height and aspect ratio. We found that 0.5 nm wetting layer is an appropriate thickness for InAs/GaAs quantum dots. Strain shift down about 3%{approx}4.5% for the cases with WL (0.5 nm) and without WL in four shapes of quantum dots. For band edge energy, wetting layers expand the potential energy gap width. When WL thickness is more than 0.8 nm, the band edge energy profiles cannot vary regularly. The electron energy is affected while for heavy hole this impact on the energy is limited. Wetting layers for the influence of the electronic structure is obviously than the heavy hole. Consequently, the electron probability density function spread from buffer to wetting layer while the center of hole's function moves from QDs internal to wetting layer when introduce WLs. When WLs thickness is larger than 0.8 nm, the electronic structures of quantum dots have changed obviously. This will affect the instrument's performance which relies on the quantum dots' optical properties.

  14. A Novel, Diazonium-Phenolic Resin Two-Layer Resist System Utilizing Photoinduced Interfacial Insolubilization

    Science.gov (United States)

    Uchino, Shou-ichi; Iwayanagi, Takao; Ueno, Takumi; Hashimoto, Michiaki; Nonogaki, Saburo

    1987-08-01

    This paper deals with a negative two-layer photoresist system utilizing a photoinduced insolubilization process at the interface. The bottom layer is a phenolic resin either with or without aromatic azide and the top layer is a photosensitive layer comprised of an aromatic diazonium compound and a water soluble polymer. Upon exposure to light, the diazo compound decomposes to cause insolubilization at the interface between the two layers. The system exhibits high contrast due to the combination of interfacial insolubilization and contrast enhancement by photobleaching of the diazonium compound. Patterns of 0.5 um lines and spaces are obtained using an i-line stepper and a resist system containing 4-diazo-N,N-dimethylaniline chloride zinc chloride in the top layer and 3-(4-azidostyry1)- 5,5-dimethyl- 2-cyclohexen-1-one in the bottom layer. Resists with varying spectral responses from mid-UV to g-line can be designed by selecting the kind of diazo compound used in the top layer.

  15. Thermal conduction in polymeric nanofluids under mean field approximation: role of interfacial adsorption layers

    International Nuclear Information System (INIS)

    Nisha, M R; Philip, J

    2013-01-01

    Polymeric nanofluids of TiO 2 /PVA (polyvinyl alcohol) and Cu/PVA have been prepared by dispersing nanoparticles of TiO 2 or metallic copper in PVA. The thermal diffusivities and thermal conductivities of these nanofluids have been measured as a function of particle loading following a thermal wave interference technique in a thermal wave resonant cavity. It is found that in both cases thermal conductivity increases with particle concentration, with Cu/PVA nanofluids showing a much larger increase. The results have been compared with the corresponding values calculated following different theoretical models. Comparison of the results with model-based calculations shows that the thermal conductivity variations in these nanofluids are within the framework of the classical mean field theory including the formation of thin interfacial adsorption layers around nanoparticles. Although the molecular weight of PVA is very high, it is found that the adsorption layer thickness is limited by the hydrodynamic radius of the nanoparticles. It is found that particle clustering followed by interfacial layering accounts for the larger increase in thermal conductivity found for Cu/PVA compared to TiO 2 /PVA. (paper)

  16. Layer-by-layer assembly of multicolored semiconductor quantum dots towards efficient blue, green, red and full color optical films

    International Nuclear Information System (INIS)

    Zhang Jun; Li Qian; Di Xiaowei; Liu Zhiliang; Xu Gang

    2008-01-01

    Multicolored semiconductor quantum dots have shown great promise for construction of miniaturized light-emitting diodes with compact size, low weight and cost, and high luminescent efficiency. The unique size-dependent luminescent property of quantum dots offers the feasibility of constructing single-color or full-color output light-emitting diodes with one type of material. In this paper, we have demonstrated the facile fabrication of blue-, green-, red- and full-color-emitting semiconductor quantum dot optical films via a layer-by-layer assembly technique. The optical films were constructed by alternative deposition of different colored quantum dots with a series of oppositely charged species, in particular, the new use of cationic starch on glass substrates. Semiconductor ZnSe quantum dots exhibiting blue emission were deposited for fabrication of blue-emitting optical films, while semiconductor CdTe quantum dots with green and red emission were utilized for construction of green- and red-emitting optical films. The assembly of integrated blue, green and red semiconductor quantum dots resulted in full-color-emitting optical films. The luminescent optical films showed very bright emitting colors under UV irradiation, and displayed dense, smooth and efficient luminous features, showing brighter luminescence in comparison with their corresponding quantum dot aqueous colloid solutions. The assembled optical films provide the prospect of miniaturized light-emitting-diode applications.

  17. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures.

    Science.gov (United States)

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L; Zhang, Qianfan; Zhao, Weisheng

    2015-12-11

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

  18. Interfacial Shear Rheology of β-Lactoglobulin - Bovine Submaxillary Mucin Layers Adsorbed at Air/Water Interface

    DEFF Research Database (Denmark)

    Celebioglu, Hilal Yilmaz; Kmiecik-Palczewska, Joanna; Lee, Seunghwan

    2017-01-01

    The interfacial rheological properties of solutions of β-lactoglobulin (BLG), as a model food compound, mixed with bovine submaxillary mucin (BSM), a major salivary protein, have been investigated. Time, frequency, stress sweep and flow measurements have been performed at different pHs (7.4, 5.......0 and 3.0), to investigate the air/water interfacial properties. All protein layers (BLG, BSM, and BLG-BSM mixtures) formed an elastic network at the air/water interface with low frequency dependence of the interfacial modulus. The results indicated that BLG moves faster as smaller molecule than mucin...

  19. A brilliant sandwich type fluorescent nanostructure incorporating a compact quantum dot layer and versatile silica substrates.

    Science.gov (United States)

    Huang, Liang; Wu, Qiong; Wang, Jing; Foda, Mohamed; Liu, Jiawei; Cai, Kai; Han, Heyou

    2014-03-18

    A "hydrophobic layer in silica" structure was designed to integrate a compact quantum dot (QD) layer with high quantum yield into scalable silica hosts containing desired functionality. This was based on metal affinity driven assembly of hydrophobic QDs with versatile silica substrates and homogeneous encapsulation of organosilica/silica layers.

  20. MoO3–Au composite interfacial layer for high efficiency and air-stable organic solar cells

    DEFF Research Database (Denmark)

    Pan, Hongbin; Zuo, Lijian; Fu, Weifei

    2013-01-01

    Efficient and stable polymer bulk-heterojunction solar cells based on regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend active layer have been fabricated with a MoO3–Au co-evaporation composite film as the anode interfacial layer (AIL). The optical...

  1. Wetting layers effect on InAs/GaAs quantum dots

    International Nuclear Information System (INIS)

    Sun Chao; Lu Pengfei; Yu Zhongyuan; Cao Huawei; Zhang Lidong

    2012-01-01

    FEM combining with the K·P theory is adopted to systematically investigate the effect of wetting layers on the strain-stress profiles and electronic structures of self-organized InAs quantum dot. Four different kinds of quantum dots are introduced at the same height and aspect ratio. We found that 0.5 nm wetting layer is an appropriate thickness for InAs/GaAs quantum dots. Strain shift down about 3%∼4.5% for the cases with WL (0.5 nm) and without WL in four shapes of quantum dots. For band edge energy, wetting layers expand the potential energy gap width. When WL thickness is more than 0.8 nm, the band edge energy profiles cannot vary regularly. The electron energy is affected while for heavy hole this impact on the energy is limited. Wetting layers for the influence of the electronic structure is obviously than the heavy hole. Consequently, the electron probability density function spread from buffer to wetting layer while the center of hole's function moves from QDs internal to wetting layer when introduce WLs. When WLs thickness is larger than 0.8 nm, the electronic structures of quantum dots have changed obviously. This will affect the instrument's performance which relies on the quantum dots' optical properties.

  2. Probing the dielectric response of the interfacial buffer layer in epitaxial graphene via optical spectroscopy

    Science.gov (United States)

    Hill, Heather M.; Rigosi, Albert F.; Chowdhury, Sugata; Yang, Yanfei; Nguyen, Nhan V.; Tavazza, Francesca; Elmquist, Randolph E.; Newell, David B.; Hight Walker, Angela R.

    2017-11-01

    Monolayer epitaxial graphene (EG) is a suitable candidate for a variety of electronic applications. One advantage of EG growth on the Si face of SiC is that it develops as a single crystal, as does the layer below, referred to as the interfacial buffer layer (IBL), whose properties include an electronic band gap. Although much research has been conducted to learn about the electrical properties of the IBL, not nearly as much work has been reported on the optical properties of the IBL. In this work, we combine measurements from Mueller matrix ellipsometry, differential reflectance contrast, atomic force microscopy, and Raman spectroscopy, as well as calculations from Kramers-Kronig analyses and density-functional theory, to determine the dielectric function of the IBL within the energy range of 1 eV to 8.5 eV.

  3. Ultrasonic Measurement of Interfacial Layer Thickness of Sub-Quarter-Wavelength

    Energy Technology Data Exchange (ETDEWEB)

    Kim, No Hyu; Lee, Sang Soon [Korea University of Technology and Education, Cheonan (Korea, Republic of)

    2003-12-15

    This paper describes a new technique for thickness measurement of a very thin layer less than one-quarter of the wavelength of ultrasonic wave used in the ultrasonic pulse-echo measurements. The technique determines the thickness of a thin layer in a tapered medium from constructive interference of multiple reflection waves. The interference characteristics are derived and investigated in theoretical and experimental approaches. Modified total reflection wave g(t) defined as difference between total and first reflection waves increases in amplitude as the interfacial layer thickness decreases down to zero. A layer thickness less than one-tenth of the ultrasonic wavelength is measured using the maximum amplitude of g(t) with a good accuracy and sensitivity. The method also requires no inversion process to extract the thickness information from the waveforms of reflected waves, so that it makes possible to have the on-line thickness measurement of a thin layer such as a lubricating oil film in thrust bearings and journal bearings during manufacturing process

  4. Ultrasonic Measurement of Interfacial Layer Thickness of Sub-Quarter-Wavelength

    International Nuclear Information System (INIS)

    Kim, No Hyu; Lee, Sang Soon

    2003-01-01

    This paper describes a new technique for thickness measurement of a very thin layer less than one-quarter of the wavelength of ultrasonic wave used in the ultrasonic pulse-echo measurements. The technique determines the thickness of a thin layer in a tapered medium from constructive interference of multiple reflection waves. The interference characteristics are derived and investigated in theoretical and experimental approaches. Modified total reflection wave g(t) defined as difference between total and first reflection waves increases in amplitude as the interfacial layer thickness decreases down to zero. A layer thickness less than one-tenth of the ultrasonic wavelength is measured using the maximum amplitude of g(t) with a good accuracy and sensitivity. The method also requires no inversion process to extract the thickness information from the waveforms of reflected waves, so that it makes possible to have the on-line thickness measurement of a thin layer such as a lubricating oil film in thrust bearings and journal bearings during manufacturing process

  5. Interfacial reactions between indium tin oxide and triphenylamine tetramer layers induced by photoirradiation

    International Nuclear Information System (INIS)

    Satoh, Toshikazu; Fujikawa, Hisayoshi; Yamamoto, Ichiro; Murasaki, Takanori; Kato, Yoshifumi

    2008-01-01

    The effects of photoirradiation on the interfacial chemical reactions between indium tin oxide (ITO) films and layers of triphenylamine tetramer (TPTE) were investigated by using in situ x-ray photoelectron spectroscopy (XPS). Thin TPTE layers deposited onto sputter-deposited ITO films were irradiated with violet light-emitting diodes (peak wavelength: 380 nm). Shifts in the peak positions of spectral components that originated in the organic layer toward the higher binding-energy side were observed in the XPS profiles during the early stages of irradiation. No further peak shifts were observed after additional irradiation. An increase in the ratio of the organic component in the O 1s spectra was also observed during the photoirradiation. The ratio of the organic component increased in proportion to the cube root of the irradiation time. These results suggest that photoirradiation induces an increase in the height of the carrier injection barrier at the interface between TPTE and ITO in the early stages of the irradiation, possibly due to the rapid diffusion controlled formation and growth of an oxidized TPTE layer, which is considered to act as a high resistance layer

  6. Recombination barrier layers in solid-state quantum dot-sensitized solar cells

    KAUST Repository

    Roelofs, Katherine E.

    2012-06-01

    By replacing the dye in the dye-sensitized solar cell design with semiconductor quantum dots as the light-absorbing material, solid-state quantum dot-sensitized solar cells (ss-QDSSCs) were fabricated. Cadmium sulfide quantum dots (QDs) were grown in situ by successive ion layer adsorption and reaction (SILAR). Aluminum oxide recombination barrier layers were deposited by atomic layer deposition (ALD) at the TiO2/hole-conductor interface. For low numbers of ALD cycles, the Al2O3 barrier layer increased open circuit voltage, causing an increase in device efficiency. For thicker Al2O3 barrier layers, photocurrent decreased substantially, leading to a decrease in device efficiency. © 2012 IEEE.

  7. Multiscale structure, interfacial cohesion, adsorbed layers, miscibility and properties in dense polymer-particle mixtures

    Science.gov (United States)

    Schweizer, Ken

    2012-02-01

    A major goal in polymer nanocomposite research is to understand and predict how the chemical and physical nature of individual polymers and nanoparticles, and thermodynamic state (temperature, composition, solvent dilution, filler loading), determine bulk assembly, miscibility and properties. Microscopic PRISM theory provides a route to this goal for equilibrium disordered mixtures. A major prediction is that by manipulating the net polymer-particle interfacial attraction, miscibility is realizable via the formation of thin thermodynamically stable adsorbed layers, which, however, are destroyed by entropic depletion and bridging attraction effects if interface cohesion is too weak or strong, respectively. This and related issues are quantitatively explored for miscible mixtures of hydrocarbon polymers, silica nanospheres, and solvent using x-ray scattering, neutron scattering and rheology. Under melt conditions, quantitative agreement between theory and silica scattering experiments is achieved under both steric stabilization and weak depletion conditions. Using contrast matching neutron scattering to characterize the collective structure factors of polymers, particles and their interface, the existence and size of adsorbed polymer layers, and their consequences on microstructure, is determined. Failure of the incompressible RPA, accuracy of PRISM theory, the nm thickness of adsorbed layers, and qualitative sensitivity of the bulk modulus to interfacial cohesion and particle size are demonstrated for concentrated PEO-silica-ethanol nanocomposites. Temperature-dependent complexity is discovered when water is the solvent, and nonequilibrium effects emerge for adsorbing entangled polymers that strongly impact structure. By varying polymer chemistry, the effect of polymer-particle attraction on the intrinsic viscosity is explored with striking non-classical effects observed. This work was performed in collaboration with S.Y.Kim, L.M.Hall, C.Zukoski and B.Anderson.

  8. Inter-Layer Energy Transfer through Wetting-Layer States in Bi-layer InGaAs/GaAs Quantum-Dot Structures with Thick Barriers

    DEFF Research Database (Denmark)

    Xu, Zhang-Cheng; Zhang, Ya-Ting; Hvam, Jørn Märcher

    2009-01-01

    The inter-layer energy transfer in a bi-layer InGaAs/GaAs quantum dot structure with a thick GaAs barrier is studied using temperature-dependent photoluminescence. The abnormal enhancement of the photoluminescence of the QDs in the layer with a larger amount of coverage at 110K is observed, which...

  9. Smooth Interfacial Scavenging for Resistive Switching Oxide via the Formation of Highly Uniform Layers of Amorphous TaOx.

    Science.gov (United States)

    Tsurumaki-Fukuchi, Atsushi; Nakagawa, Ryosuke; Arita, Masashi; Takahashi, Yasuo

    2018-02-14

    We demonstrate that the inclusion of a Ta interfacial layer is a remarkably effective strategy for forming interfacial oxygen defects at metal/oxide junctions. The insertion of an interfacial layer of a reactive metal, that is, a "scavenging" layer, has been recently proposed as a way to create a high concentration of oxygen defects at an interface in redox-based resistive switching devices, and growing interest has been given to the underlying mechanism. Through structural and chemical analyses of Pt/metal/SrTiO 3 /Pt structures, we reveal that the rate and amount of oxygen scavenging are not directly determined by the formation free energies in the oxidation reactions of the scavenging metal and unveil the important roles of oxygen diffusibility. Active oxygen scavenging and highly uniform oxidation via scavenging are revealed for a Ta interfacial layer with high oxygen diffusibility. In addition, the Ta scavenging layer is shown to exhibit a highly uniform structure and to form a very flat interface with SrTiO 3 , which are advantageous for the fabrication of a steep metal/oxide contact.

  10. Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

    Science.gov (United States)

    Korotchenkov, Oleg; Nadtochiy, Andriy; Kuryliuk, Vasyl; Wang, Chin-Chi; Li, Pei-Wen; Cantarero, Andres

    2014-03-01

    The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si.

  11. Influence of wetting layer wave functions on carrier capture in quantum dots

    DEFF Research Database (Denmark)

    Markussen, Troels; Kristensen, Philip; Tromborg, Bjarne

    2005-01-01

    This work numerically solves the effective mass Schrodinger equation and shows that the capture times are strongly influenced by details of the continuum states not accounted for by the approximate wave functions. Results show that calculations of capture time for phonon mediated carrier capture...... from a wetting layer into a quantum dot depend critically on the approximations used for the wetting layer wave functions....

  12. Atomic Layer Deposition of Stable LiAlF4 Lithium Ion Conductive Interfacial Layer for Stable Cathode Cycling.

    Science.gov (United States)

    Xie, Jin; Sendek, Austin D; Cubuk, Ekin D; Zhang, Xiaokun; Lu, Zhiyi; Gong, Yongji; Wu, Tong; Shi, Feifei; Liu, Wei; Reed, Evan J; Cui, Yi

    2017-07-25

    Modern lithium ion batteries are often desired to operate at a wide electrochemical window to maximize energy densities. While pushing the limit of cutoff potentials allows batteries to provide greater energy densities with enhanced specific capacities and higher voltage outputs, it raises key challenges with thermodynamic and kinetic stability in the battery. This is especially true for layered lithium transition-metal oxides, where capacities can improve but stabilities are compromised as wider electrochemical windows are applied. To overcome the above-mentioned challenges, we used atomic layer deposition to develop a LiAlF 4 solid thin film with robust stability and satisfactory ion conductivity, which is superior to commonly used LiF and AlF 3 . With a predicted stable electrochemical window of approximately 2.0 ± 0.9 to 5.7 ± 0.7 V vs Li + /Li for LiAlF 4 , excellent stability was achieved for high Ni content LiNi 0.8 Mn 0.1 Co 0.1 O 2 electrodes with LiAlF 4 interfacial layer at a wide electrochemical window of 2.75-4.50 V vs Li + /Li.

  13. Effect of interfacial layers on dielectric properties in very thin SrBi2Ta2O9 capacitors

    International Nuclear Information System (INIS)

    Moon, Bum-Ki; Isobe, Chiharu; Hironaka, Katsuyuki; Hishikawa, Shinichi

    2001-01-01

    The effect of interfacial layers on the dielectric properties in very thin SrBi 2 Ta 2 O 9 (SBT) capacitors has been investigated using static measurements. Total permittivity (ε t ) decreased as the film thickness was reduced in both Pt/SBT/Pt and Ir/SBT/Pt capacitors. The contribution of the interfacial capacitance (C int ) and bulk capacitance to the total capacitance indicates that C int of the Ir/SBT/Pt structure was lower than that of the Pt/SBT/Pt structure, while the bulk permittivity (ε b ) was essentially the same. The dispersion of all capacitors followed the power law, while the Ir/SBT/Pt capacitor showed a larger dispersion of C int . These results suggest that the Pt/SBT/Pt capacitor is preferred for obtaining the high performance with less effect of the interfacial layers on the dielectric properties. [copyright] 2001 American Institute of Physics

  14. Self-aligned periodic Ni nano dots embedded in nano-oxide layer

    International Nuclear Information System (INIS)

    Doi, M.; Izumi, M.; Kawasaki, S.; Miyake, K.; Sahashi, M.

    2007-01-01

    The Ni nano constriction dots embedded in the Ta-nano-oxide layer (NOL) was prepared by the ion beam sputtering (IBS) method. After the various conditions of the oxidations, the structural analyses of the NOL were performed by RHEED, AES and in situ STM/AFM observations. From the current image of the conductive AFM for NOL, the periodically aligned metallic dots with the size around 5-10 nm were successfully observed. The mechanism of the formation of the self-organized aligned Ni nano constriction dots is discussed from the standpoint of the grain size, the crystal orientation, the preferred oxidation of Ta at the diffused interface

  15. Efficiency enhancement of solid-state PbS quantum dot-sensitized solar cells with Al2O3 barrier layer

    KAUST Repository

    Brennan, Thomas P.; Trejo, Orlando; Roelofs, Katherine E.; Xu, John; Prinz, Fritz B.; Bent, Stacey F.

    2013-01-01

    Atomic layer deposition (ALD) was used to grow both PbS quantum dots and Al2O3 barrier layers in a solid-state quantum dot-sensitized solar cell (QDSSC). Barrier layers grown prior to quantum dots resulted in a near-doubling of device efficiency (0.30% to 0.57%) whereas barrier layers grown after quantum dots did not improve efficiency, indicating the importance of quantum dots in recombination processes. © 2013 The Royal Society of Chemistry.

  16. MOVPE grown InGaAs quantum dots of high optical quality as seed layer for low-density InP quantum dots

    International Nuclear Information System (INIS)

    Richter, D; Hafenbrak, R; Joens, K D; Schulz, W-M; Eichfelder, M; Rossbach, R; Jetter, M; Michler, P

    2010-01-01

    To achieve a low density of optically active InP-quantum dots we used InGaAs islands embedded in GaAs as a seed layer. First, the structural InGaAs quantum dot properties and the influence of the annealing technique was investigated by atomic force microscope measurements. High-resolution micro-photoluminescence spectra reveal narrow photoluminescence lines, with linewidths down to 11 μeV and fine structure splittings of 25 μeV. Furthermore, using these InGaAs quantum dots as seed layer reduces the InP quantum dot density of optically active quantum dots drastically. InP quantum dot excitonic photoluminescence emission with a linewidth of 140 μeV has been observed.

  17. Organic-Inorganic Hybrid Interfacial Layer for High-Performance Planar Perovskite Solar Cells.

    Science.gov (United States)

    Yang, Hao; Cong, Shan; Lou, Yanhui; Han, Liang; Zhao, Jie; Sun, Yinghui; Zou, Guifu

    2017-09-20

    4,7-Diphenyl-1,10-phenanthroline (Bphen) is an efficient electron transport and hole blocking material in organic photoelectric devices. Here, we report cesium carbonate (Cs 2 CO 3 ) doped Bphen as cathode interfacial layer in CH 3 NH 3 PbI 3-x Cl x based planar perovskite solar cells (PSCs). Investigation finds that introducing Cs 2 CO 3 suppresses the crystallization of Bphen and benefits a smooth interface contact between the perovskite and electrode, resulting in the decrease in carrier recombination and the perovskite degradation. In addition, the matching energy level of Bphen film in the PSCs effectively blocks the holes diffusion to cathode. The resultant power conversion efficiency (PCE) achieves as high as 17.03% in comparison with 12.67% of reference device without doping. Besides, experiments also demonstrate the stability of PSCs have large improvement because the suppressed crystallization of Bphen by doping Cs 2 CO 3 as a superior barrier layer blocks the Ag atom and surrounding moisture access to the vulnerable perovskite layer.

  18. Confined methane-water interfacial layers and thickness measurements using in situ Raman spectroscopy.

    Science.gov (United States)

    Pinho, Bruno; Liu, Yukun; Rizkin, Benjamin; Hartman, Ryan L

    2017-11-07

    Gas-liquid interfaces broadly impact our planet, yet confined interfaces behave differently than unconfined ones. We report the role of tangential fluid motion in confined methane-water interfaces. The interfaces are created using microfluidics and investigated by in situ 1D, 2D and 3D Raman spectroscopy. The apparent CH 4 and H 2 O concentrations are reported for Reynolds numbers (Re), ranging from 0.17 to 8.55. Remarkably, the interfaces are comprised of distinct layers of thicknesses varying from 23 to 57 μm. We found that rarefaction, mixture, thin film, and shockwave layers together form the interfaces. The results indicate that the mixture layer thickness (δ) increases with Re (δ ∝ Re), and traditional transport theory for unconfined interfaces does not explain the confined interfaces. A comparison of our results with thin film theory of air-water interfaces (from mass transfer experiments in capillary microfluidics) supports that the hydrophobicity of CH 4 could decrease the strength of water-water interactions, resulting in larger interfacial thicknesses. Our findings help explain molecular transport in confined gas-liquid interfaces, which are common in a broad range of societal applications.

  19. Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells.

    Science.gov (United States)

    Zhou, Nanjia; Kim, Myung-Gil; Loser, Stephen; Smith, Jeremy; Yoshida, Hiroyuki; Guo, Xugang; Song, Charles; Jin, Hosub; Chen, Zhihua; Yoon, Seok Min; Freeman, Arthur J; Chang, Robert P H; Facchetti, Antonio; Marks, Tobin J

    2015-06-30

    In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor-inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance.

  20. Photon induced non-linear quantized double layer charging in quaternary semiconducting quantum dots.

    Science.gov (United States)

    Nair, Vishnu; Ananthoju, Balakrishna; Mohapatra, Jeotikanta; Aslam, M

    2018-03-15

    Room temperature quantized double layer charging was observed in 2 nm Cu 2 ZnSnS 4 (CZTS) quantum dots. In addition to this we observed a distinct non-linearity in the quantized double layer charging arising from UV light modulation of double layer. UV light irradiation resulted in a 26% increase in the integral capacitance at the semiconductor-dielectric (CZTS-oleylamine) interface of the quantum dot without any change in its core size suggesting that the cause be photocapacitive. The increasing charge separation at the semiconductor-dielectric interface due to highly stable and mobile photogenerated carriers cause larger electrostatic forces between the quantum dot and electrolyte leading to an enhanced double layer. This idea was supported by a decrease in the differential capacitance possible due to an enhanced double layer. Furthermore the UV illumination enhanced double layer gives us an AC excitation dependent differential double layer capacitance which confirms that the charging process is non-linear. This ultimately illustrates the utility of a colloidal quantum dot-electrolyte interface as a non-linear photocapacitor. Copyright © 2017 Elsevier Inc. All rights reserved.

  1. The role of interfacial water layer in atmospherically relevant charge separation

    Science.gov (United States)

    Bhattacharyya, Indrani

    Charge separation at interfaces is important in various atmospheric processes, such as thunderstorms, lightning, and sand storms. It also plays a key role in several industrial processes, including ink-jet printing and electrostatic separation. Surprisingly, little is known about the underlying physics of these charging phenomena. Since thin films of water are ubiquitous, they may play a role in these charge separation processes. This talk will focus on the experimental investigation of the role of a water adlayer in interfacial charging, with relevance to meteorologically important phenomena, such as atmospheric charging due to wave actions on oceans and sand storms. An ocean wave generates thousands of bubbles, which upon bursting produce numerous large jet droplets and small film droplets that are charged. In the 1960s, Blanchard showed that the jet droplets are positively charged. However, the charge on the film droplets was not known. We designed an experiment to exclusively measure the charge on film droplets generated by bubble bursting on pure water and aqueous salt solution surfaces. We measured their charge to be negative and proposed a model where a slight excess of hydroxide ions in the interfacial water layer is responsible for generating these negatively charged droplets. The findings from this research led to a better understanding of the ionic disposition at the air-water interface. Sand particles in a wind-blown sand layer, or 'saltation' layer, become charged due to collisions, so much so, that it can cause lightning. Silica, being hydrophilic, is coated with a water layer even under low-humidity conditions. To investigate the importance of this water adlayer in charging the silica surfaces, we performed experiments to measure the charge on silica surfaces due to contact and collision processes. In case of contact charging, the maximum charge separation occurred at an optimum relative humidity. On the contrary, in collisional charging process, no

  2. Minimizing performance degradation induced by interfacial recombination in perovskite solar cells through tailoring of the transport layer electronic properties

    Directory of Open Access Journals (Sweden)

    Liang Xu

    2018-03-01

    Full Text Available The performance of hybrid organic-inorganic metal halide perovskite solar cells is investigated using one-dimensional drift-diffusion device simulations. We study the effects of interfacial defect density, doping concentration, and electronic level positions of the charge transport layer (CTL. Choosing CTLs with a favorable band alignment, rather than passivating CTL-perovskite interfacial defects, is shown to be beneficial for maintaining high power-conversion efficiency, due to reduced minority carrier density arising from a favorable local electric field profile. Insights from this study provide theoretical guidance on practical selection of CTL materials for achieving high-performance perovskite solar cells.

  3. Analysis of Strain and Intermixing in a Single Layer Ge/Si dots using polarized Raman Spectroscopy

    OpenAIRE

    PEROVA, TANIA; MOORE, ROBERT

    2006-01-01

    PUBLISHED The built-in strain and composition of as-grown and Si-capped single layers of Ge?Si dots grown at various temperatures (460?800 ?C) are studied by a comparative analysis of the Ge-Ge and Si-Ge modes in the polarized Raman spectra of the dots. A pronounced reduction of the strain and Ge content in the dots after deposition of the cap layer at low temperatures is observed, indicating that strain-induced Si diffusion from the cap layer is occurring. For large dots grown at 700?800...

  4. Interfacial bonding stabilizes rhodium and rhodium oxide nanoparticles on layered Nb oxide and Ta oxide supports.

    Science.gov (United States)

    Strayer, Megan E; Binz, Jason M; Tanase, Mihaela; Shahri, Seyed Mehdi Kamali; Sharma, Renu; Rioux, Robert M; Mallouk, Thomas E

    2014-04-16

    Metal nanoparticles are commonly supported on metal oxides, but their utility as catalysts is limited by coarsening at high temperatures. Rhodium oxide and rhodium metal nanoparticles on niobate and tantalate supports are anomalously stable. To understand this, the nanoparticle-support interaction was studied by isothermal titration calorimetry (ITC), environmental transmission electron microscopy (ETEM), and synchrotron X-ray absorption and scattering techniques. Nanosheets derived from the layered oxides KCa2Nb3O10, K4Nb6O17, and RbTaO3 were compared as supports to nanosheets of Na-TSM, a synthetic fluoromica (Na0.66Mg2.68(Si3.98Al0.02)O10.02F1.96), and α-Zr(HPO4)2·H2O. High surface area SiO2 and γ-Al2O3 supports were also used for comparison in the ITC experiments. A Born-Haber cycle analysis of ITC data revealed an exothermic interaction between Rh(OH)3 nanoparticles and the layered niobate and tantalate supports, with ΔH values in the range -32 kJ·mol(-1) Rh to -37 kJ·mol(-1) Rh. In contrast, the interaction enthalpy was positive with SiO2 and γ-Al2O3 supports. The strong interfacial bonding in the former case led to "reverse" ripening of micrometer-size Rh(OH)3, which dispersed as 0.5 to 2 nm particles on the niobate and tantalate supports. In contrast, particles grown on Na-TSM and α-Zr(HPO4)2·H2O nanosheets were larger and had a broad size distribution. ETEM, X-ray absorption spectroscopy, and pair distribution function analyses were used to study the growth of supported nanoparticles under oxidizing and reducing conditions, as well as the transformation from Rh(OH)3 to Rh nanoparticles. Interfacial covalent bonding, possibly strengthened by d-electron acid/base interactions, appear to stabilize Rh(OH)3, Rh2O3, and Rh nanoparticles on niobate and tantalate supports.

  5. Charge transport in quantum dot organic solar cells with Si quantum dots sandwiched between poly(3-hexylthiophene) (P3HT) absorber and bathocuproine (BCP) transport layers

    Science.gov (United States)

    Verma, Upendra Kumar; Kumar, Brijesh

    2017-10-01

    We have modeled a multilayer quantum dot organic solar cell that explores the current-voltage characteristic of the solar cell whose characteristics can be tuned by varying the fabrication parameters of the quantum dots (QDs). The modeled device consists of a hole transport layer (HTL) which doubles up as photon absorbing layer, several quantum dot layers, and an electron transport layer (ETL). The conduction of charge carriers in HTL and ETL has been modeled by the drift-diffusion transport mechanism. The conduction and recombination in the quantum dot layers are described by a system of coupled rate equations incorporating tunneling and bimolecular recombination. Analysis of QD-solar cells shows improved device performance compared to the similar bilayer and trilayer device structures without QDs. Keeping other design parameters constant, solar cell characteristics can be controlled by the quantum dot layers. Bimolecular recombination coefficient of quantum dots is a prime factor which controls the open circuit voltage (VOC) without any significant reduction in short circuit current (JSC).

  6. Effect of Oxygen Inhibition Layer of Universal Adhesives on Enamel Bond Fatigue Durability and Interfacial Characteristics With Different Etching Modes.

    Science.gov (United States)

    Ouchi, H; Tsujimoto, A; Nojiri, K; Hirai, K; Takamizawa, T; Barkmeier, W W; Latta, M A; Miyazaki, M

    The purpose of this study was to evaluate the effect of the oxygen inhibition layer of universal adhesive on enamel bond fatigue durability and interfacial characteristics with different etching modes. The three universal adhesives used were Scotchbond Universal Adhesive (3M ESPE, St Paul, MN, USA), Adhese Universal (Ivoclar Vivadent, Schaan, Lichtenstein), and G-Premio Bond (GC, Tokyo, Japan). The initial shear bond strength and shear fatigue strength to enamel was determined in the presence and absence of the oxygen inhibition layer, with and without phosphoric acid pre-etching. The water contact angle was also measured in all groups using the sessile drop method. The enamel bonding specimens with an oxygen inhibition layer showed significantly higher (padhesive type and etching mode. Moreover, the water contact angles on the specimens with an oxygen inhibition layer were significantly lower (puniversal adhesives significantly increases the enamel bond fatigue durability and greatly changes interfacial characteristics, suggesting that the bond fatigue durability and interfacial characteristics of these adhesives strongly rely on its presence.

  7. Interfacial Microstructure and Its Influence on Resistivity of Thin Layers Copper Cladding Steel Wires

    Science.gov (United States)

    Li, Hongjuan; Ding, Zhimin; Zhao, Ruirong

    2018-04-01

    The interfacial microstructure and resistivity of cold-drawn and annealed thin layers copper cladding steel (CCS) wires have been systematically investigated by the methods of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and resistivity testing. The results showed that the Cu and Fe atoms near interface diffused into each other matrixes. The Fe atoms diffused into Cu matrixes and formed a solid solution. The mechanism of solid solution is of substitution type. When the quantity of Fe atoms exceeds the maximum solubility, the supersaturated solid solution would form Fe clusters and decompose into base Cu and α-Fe precipitated phases under certain conditions. A few of α-Fe precipitates was observed in the copper near Cu/Fe interfaces of cold-drawn CCS wires, with 1-5 nm in size. A number of α-Fe precipitates of 1-20 nm in size can be detected in copper near Cu/Fe interfaces of CCS wires annealed at 850°C. When annealing temperature was less than 750°C, the resistivity of CCS wires annealed was lower than that of cold-drawn CCS wires. However, when annealing temperature was above 750°C, the resistivity of CCS wires was greater than that of cold-drawn CCS wires and increased with rising the annealing temperature. The relationship between nanoscale α-Fe precipitation and resistivity of CCS wires has been well discussed.

  8. "Supersaturated" self-assembled charge-selective interfacial layers for organic solar cells.

    Science.gov (United States)

    Song, Charles Kiseok; Luck, Kyle A; Zhou, Nanjia; Zeng, Li; Heitzer, Henry M; Manley, Eric F; Goldman, Samuel; Chen, Lin X; Ratner, Mark A; Bedzyk, Michael J; Chang, Robert P H; Hersam, Mark C; Marks, Tobin J

    2014-12-24

    To achieve densely packed charge-selective organosilane-based interfacial layers (IFLs) on the tin-doped indium oxide (ITO) anodes of organic photovoltaic (OPV) cells, a series of Ar2N-(CH2)n-SiCl3 precursors with Ar = 3,4-difluorophenyl, n = 3, 6, 10, and 18, was synthesized, characterized, and chemisorbed on OPV anodes to serve as IFLs. To minimize lateral nonbonded -NAr2···Ar2N- repulsions which likely limit IFL packing densities in the resulting self-assembled monolayers (SAMs), precursor mixtures having both small and large n values are simultaneously deposited. These "heterogeneous" SAMs are characterized by a battery of techniques: contact angle measurements, X-ray reflectivity, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry, and DFT computation. It is found that the headgroup densities of these "supersaturated" heterogeneous SAMs (SHSAMs) are enhanced by as much as 17% versus their homogeneous counterparts. Supersaturation significantly modifies the IFL properties including the work function (as much as 16%) and areal dipole moment (as much as 49%). Bulk-heterojunction OPV devices are fabricated with these SHSAMs: ITO/IFL/poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][2-[[(2-ethylhexyl)oxy]carbonyl]-3-fluorothieno[3,4-b]thiophenediyl

  9. Ultimate Scaling of High-κ Gate Dielectrics: Higher-κ or Interfacial Layer Scavenging?

    Directory of Open Access Journals (Sweden)

    Takashi Ando

    2012-03-01

    Full Text Available Current status and challenges of aggressive equivalent-oxide-thickness (EOT scaling of high-κ gate dielectrics via higher-κ ( > 20 materials and interfacial layer (IL scavenging techniques are reviewed. La-based higher-κ materials show aggressive EOT scaling (0.5–0.8 nm, but with effective workfunction (EWF values suitable only for n-type field-effect-transistor (FET. Further exploration for p-type FET-compatible higher-κ materials is needed. Meanwhile, IL scavenging is a promising approach to extend Hf-based high-κ dielectrics to future nodes. Remote IL scavenging techniques enable EOT scaling below 0.5 nm. Mobility-EOT trends in the literature suggest that short-channel performance improvement is attainable with aggressive EOT scaling via IL scavenging or La-silicate formation. However, extreme IL scaling (e.g., zero-IL is accompanied by loss of EWF control and with severe penalty in reliability. Therefore, highly precise IL thickness control in an ultra-thin IL regime ( < 0.5 nm will be the key technology to satisfy both performance and reliability requirements for future CMOS devices.

  10. Numerical simulation of electronic properties of coupled quantum dots on wetting layers

    International Nuclear Information System (INIS)

    Betcke, M M; Voss, H

    2008-01-01

    Self-assembled quantum dots are grown on wetting layers and frequently in an array-like assembly of many similar but not exactly equal dots. Nevertheless, most simulations disregard these structural conditions and restrict themselves to simulating a pure single quantum dot. For reasons of numerical efficiency we advocate the effective one-band Hamiltonian with energy- and position-dependent effective mass approximation and a finite height hard-wall 3D confinement potential for computation of the energy levels of the electrons in the conduction band. Within this model we investigate the geometrical effects mentioned above on the electronic structure of a pyramidal InAs quantum dot embedded in a GaAs matrix. We find that the presence of a wetting layer may affect the electronic structure noticeably. Furthermore, we establish that, in spite of the large bandgap of the InAs/GaAs heterostructure, if the dots in a vertically aligned array are sufficiently close stacked there is considerable interaction between their eigenfunctions. Moreover, the eigenfunctions of such an array are quite sensitive to certain structural perturbations

  11. Ultrafast interfacial energy transfer and interlayer excitons in the monolayer WS2/CsPbBr3 quantum dot heterostructure.

    Science.gov (United States)

    Li, Han; Zheng, Xin; Liu, Yu; Zhang, Zhepeng; Jiang, Tian

    2018-01-25

    The idea of fabricating artificial solids with band structures tailored to particular applications has long fascinated condensed matter physicists. Heterostructure (HS) construction is viewed as an effective and appealing approach to engineer novel electronic properties in two dimensional (2D) materials. Different from common 2D/2D heterojunctions where energy transfer is rarely observed, CsPbBr 3 quantum dots (0D-QDs) interfaced with 2D materials have become attractive HSs for exploring the physics of charge transfer and energy transfer, due to their superior optical properties. In this paper, a new 0D/2D HS is proposed and experimentally studied, making it possible to investigate both light utilization and energy transfer. Specifically, this HS is constructed between monolayer WS 2 and CsPbBr 3 QDs, and exhibits a hybrid band alignment. The dynamics of energy transfer within the investigated 0D/2D HS is characterized by femtosecond transient absorption spectrum (TAS) measurements. The TAS results reveal that ultrafast energy transfer caused by optical excitation is observed from CsPbBr 3 QDs to the WS 2 layer, which can increase the exciton fluence within the WS 2 layer up to 69% when compared with pristine ML WS 2 under the same excitation fluence. Moreover, the formation and dynamics of interlayer excitons have also been investigated and confirmed in the HS, with a calculated recombination time of 36.6 ps. Finally, the overall phenomenological dynamical scenario for the 0D/2D HS is established within the 100 ps time region after excitation. The techniques introduced in this work can also be applied to versatile optoelectronic devices based on low dimensional materials.

  12. A Study on Organic-Metal Halide Perovskite Film Morphology, Interfacial Layers, Tandem Applications, and Encapsulation

    Science.gov (United States)

    Fisher, Dallas A.

    Organic-metal halide perovskites have brought about a new wave of research in the photovoltaic community due to their ideally suited optical and electronic parameters. In less than a decade, perovskite solar cell performance has skyrocketed to unprecedented efficiencies with numerous reported methodologies. Perovskites face many challenges with high-quality film morphology, interfacial layers, and long-term stability. In this work, these active areas are explored through a combination of studies. First, the importance of perovskite film precursor ratios is explored with an in-depth study of carrier lifetime and solvent-grain effects. It was found that excess lead iodide precursor greatly improves the film morphology by reducing pinholes in the solar absorber. Dimethyl sulfoxide (DMSO) solvent was found to mend grains, as well as improve carrier lifetime and device performance, possibly by passivation of grain boundary traps. Second, applications of perovskite with tandem cells is investigated, with an emphasis for silicon devices. Perovskites can easily be integrated with silicon, which already has strong market presence. Additionally, both materials' bandgaps are ideally suited for maximum tandem efficiency. The silicon/perovskite tandem device structure necessitated the optimization of inverted (p-i-n) structure devices. PEDOT:PSS, copper oxide, and nickel oxide p-type layers were explored through a combination of photoluminescent, chemical reactivity, and solar simulation results. Results were hindered due to resistive ITO and rough silicon substrates, but tandem devices displayed Voc indicative of proper monolithic performance. Third, replacement of titanium dioxide n-type layer with iron oxide (Fe 2O3, common rust) was studied. Iron oxide experiences less ultraviolet instability than that of titanium dioxide under solar illumination. It was found that current density slightly decreased due to parasitic absorption from the rust, but that open circuit voltage

  13. Interfacial layers evolution during annealing in Ti-Al multi-laminated composite processed using hot press and roll bonding

    Science.gov (United States)

    Assari, A. H.; Eghbali, B.

    2016-09-01

    Ti-Al multi-laminated composites have great potential in high strength and low weight structures. In the present study, tri-layer Ti-Al composite was synthesized by hot press bonding under 40 MPa at 570 °C for 1 h and subsequent hot roll bonding at about 450 °C. This process was conducted in two accumulative passes to 30% and to 67% thickness reduction in initial and final passes, respectively. Then, the final annealing treatments were done at 550, 600, 650, 700 and 750 °C for 2, 4 and 6 h. Investigations on microstructural evolution and thickening of interfacial layers were performed by scanning electron microscopes, energy dispersive spectrometer, X-ray diffraction and micro-hardness tests. The results showed that the thickening of diffusion layers corresponds to amount of deformation. In addition to thickening of the diffusion layers, the thickness of aluminum layers decreased and after annealing treatment at 750 °C for 6 h the aluminum layers were consumed entirely, which occurred because of the enhanced interdiffusion of Ti and Al elements. Scanning electron microscope equipped with energy dispersive spectrometer showed that the sequence of interfacial layers as Ti3Al-TiAl-TiAl2-TiAl3 which are believed to be the result of thermodynamic and kinetic of phase formation. Micro-hardness results presented the variation profile in accordance with the sequence of intermetallic phases and their different structures.

  14. Recombination Suppression in PbS Quantum Dot Heterojunction Solar Cells by Energy-Level Alignment in the Quantum Dot Active Layers.

    Science.gov (United States)

    Ding, Chao; Zhang, Yaohong; Liu, Feng; Nakazawa, Naoki; Huang, Qingxun; Hayase, Shuzi; Ogomi, Yuhei; Toyoda, Taro; Wang, Ruixiang; Shen, Qing

    2017-09-22

    Using spatial energy-level gradient engineering with quantum dots (QDs) of different sizes to increase the generated carrier collection at the junction of a QD heterojunction solar cell (QDHSC) is a hopeful route for improving the energy-conversion efficiency. However, the results of current related research have shown that a variable band-gap structure in a QDHSC will create an appreciable increase, not in the illumination current density, but rather in the fill factor. In addition, there are a lack of studies on the mechanism of the effect of these graded structures on the photovoltaic performance of QDHSCs. This study presents the development of air atmosphere solution-processed TiO 2 /PbS QDs/Au QDHSCs by engineering the energy-level alignment (ELA) of the active layer via the use of a sorted order of differently sized QD layers (four QD sizes). In comparison to the ungraded device (without the ELA), the optimized graded architecture (containing the ELA) solar cells exhibited a great increase (21.4%) in short-circuit current density (J sc ). As a result, a J sc value greater than 30 mA/cm 2 has been realized in planar, thinner absorption layer (∼300 nm) PbS QDHSCs, and the open-circuit voltage (V oc ) and power-conversion efficiency (PCE) were also improved. Through characterization by the light intensity dependences of the J sc and V oc and transient photovoltage decay, we find that (i) the ELA structure, serving as an electron-blocking layer, reduces the interfacial recombination at the PbS/anode interface, and (ii) the ELA structure can drive more carriers toward the desirable collection electrode, and the additional carriers can fill the trap states, reducing the trap-assisted recombination in the PbS QDHSCs. This work has clearly elucidated the mechanism of the recombination suppression in the graded QDHSCs and demonstrated the effects of ELA structure on the improvement of J sc . The charge recombination mechanisms characterized in this work would be

  15. Influence of interfacial scattering and surface roughness on giant magnetoresistance in Fe/Cr trilayers using ab initio layer potentials

    International Nuclear Information System (INIS)

    Pereiro, M.; Botana, J.; Baldomir, D.; Warda, K.; Wojtczak, L.; Man'kovsky, S.V.; Iglesias, M.; Pardo, V.; Arias, J.E.

    2005-01-01

    Ab initio full-potential linearized augmented-plane-wave (FP-LAPW) method combined with the semiclassical Boltzmann formalism was employed to calculate the giant magnetoresistance ratio in the trilayers nFe/3Cr/nFe (1=< n=<8). The present results emphasize the very important role of the ferromagnetic layer as well as the interfacial scattering and surface roughness on the giant magnetoresistance effect

  16. Direct self-assembling and patterning of semiconductor quantum dots on transferable elastomer layer

    Energy Technology Data Exchange (ETDEWEB)

    Coppola, Sara [Institute of Applied Sciences and Intelligent System- CNR, Via Campi Flegrei 34, Pozzuoli, 80078 (Italy); Vespini, Veronica, E-mail: v.vespini@isasi.cnr.it [Institute of Applied Sciences and Intelligent System- CNR, Via Campi Flegrei 34, Pozzuoli, 80078 (Italy); Olivieri, Federico [Institute of Applied Sciences and Intelligent System- CNR, Via Campi Flegrei 34, Pozzuoli, 80078 (Italy); University of Naples Federico II, Department of Chemical Materials and Production Engineering, Piazzale Tecchio 80, Naples 80125 (Italy); Nasti, Giuseppe; Todino, Michele; Mandracchia, Biagio; Pagliarulo, Vito; Ferraro, Pietro [Institute of Applied Sciences and Intelligent System- CNR, Via Campi Flegrei 34, Pozzuoli, 80078 (Italy)

    2017-03-31

    Highlights: • A quantum dots self-patterning on micrometrical polymeric array is proposed. • The effect of a quantum dots mix on the array is evaluated. • A PDMS membrane is exploited to transfer the pattern on it. - Abstract: Functionalization of thin and stretchable polymer layers by nano- and micro-patterning of nanoparticles is a very promising field of research that can lead to many different applications in biology and nanotechnology. In this work, we present a new procedure to self-assemble semiconductor quantum dots (QDs) nanoparticles by a simple fabrication process on a freestanding flexible PolyDiMethylSiloxane (PDMS) membrane. We used a Periodically Poled Lithium Niobate (PPLN) crystal to imprint a micrometrical pattern on the PDMS membrane that drives the QDs self-structuring on its surface. This process allows patterning QDs with different wavelength emissions in a single step in order to tune the overall emission spectrum of the composite, tuning the QDs mixing ratio.

  17. Interface feature characterization and Schottky interfacial layer confirmation of TiO{sub 2} nanotube array film

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hongchao [State Key Laboratory of Powder Metallurgy, Central South University, 410083 Changsha (China); Chongyi Zhangyuan Tungsten Industry Corporation Limited, 341300 Ganzhou (China); Tang, Ningxin; Yang, Hongzhi; Leng, Xian [State Key Laboratory of Powder Metallurgy, Central South University, 410083 Changsha (China); Zou, Jianpeng, E-mail: zoujp@csu.edu.cn [State Key Laboratory of Powder Metallurgy, Central South University, 410083 Changsha (China)

    2015-11-15

    Highlights: • Interfacial fusion of TiO{sub 2} nanotube film increases with annealing temperature. • Interface bonding force of the film increases with annealing temperature. • We report the forth stage of nanofibers formation in the growing mechanism. • TiO{sub 2} nanotubes grow from Schottky interface layer rather than from Ti substrate. • Schottky interface layer's thickness of 35–45 nm is half the diameter of nanotube. - Abstract: We report here characterization of the interfacial microstructure and properties of titanium dioxide (TiO{sub 2}) nanotube array films fabricated by anodization. Field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), nanoindentation, atomic force microscopy (AFM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the interface of the film. With increasing annealing temperature from 200 °C to 800 °C, the interfacial fusion between the film and the Ti substrate increased. The phase transformation of the TiO{sub 2} nanotube film from amorphous to anatase to rutile took place gradually; as the phase transformation progressed, the force needed to break the film increased. The growth of TiO{sub 2} nanotube arrays occurs in four stages: barrier layer formation, penetrating micropore formation, regular nanotube formation, and nanofiber formation. The TiO{sub 2} nanotubes grow from the Schottky interface layer rather than from the Ti substrate. The Schottky interface layer's thickness of 35–45 nm was identified as half the diameter of the corresponding nanotube, which shows good agreement to the Schottky interface layer growth model. The TiO{sub 2} nanotube film was amorphous and the Ti substrate was highly crystallized with many dislocation walls.

  18. Stable MoS2 Field-Effect Transistors Using TiO2 Interfacial Layer at Metal/MoS2 Contact

    KAUST Repository

    Park, Woojin; Min, Jung-Wook; Shaikh, Sohail F.; Hussain, Muhammad Mustafa

    2017-01-01

    dioxide (TiO2) interfacial layer between contact metal and MoS2 channel is suggested to achieve more stable performances. The reduced threshold voltage (VTH) shift and reduced series resistance (RSD) were simultaneously achieved.

  19. Carrier confinement in Ge/Si quantum dots grown with an intermediate ultrathin oxide layer

    Science.gov (United States)

    Kuryliuk, V.; Korotchenkov, O.; Cantarero, A.

    2012-02-01

    We present computational results for strain effects on charge carrier confinement in GexSi1-x quantum dots (QDs) grown on an oxidized Si surface. The strain and free carrier probability density distributions are obtained using the continuum elasticity theory and the effective-mass approximation implemented by a finite-element modeling scheme. Using realistic parameters and conditions for hemisphere and pyramid QDs, it is pointed out that an uncapped hemisphere dot deposited on the Si surface with an intermediate ultrathin oxide layer offers advantageous electron-hole separation distances with respect to a square-based pyramid grown directly on Si. The enhanced separation is associated with a larger electron localization depth in the Si substrate for uncapped hemisphere dots. Thus, for dot diameters smaller than 15-20 nm and surface density of the dots (nQD) ranging from about 1010 to 1012 cm-2, the localization depth may be enhanced from about 8 nm for a pyramid to 38 nm for a hemisphere dot. We find that the effect in a hemisphere dot is very sensitive to the dot density and size, whereas the localization depth is not significantly affected by the variation of the Ge fraction x in GexSi1-x and the aspect ratio of the dot. We also calculate the effect of the fixed oxide charge (Qox) with densities ranging from 10-9 to 10-7 C/cm2 for 10-Ωcm p-type Si wafers on the carrier confinement. Although the confinement potential can be strongly perturbed by the charge at nQD less than ≈4×1011 cm-2, it is not very sensitive to the value of Qox at higher nQD. Since, to our knowledge, there are no data on carrier confinement for Ge QDs deposited on oxidized Si surfaces, these results might be applicable to functional devices utilizing separated electrons and holes such as photovoltaic devices, spin transistors, and quantum computing components. The use of hemisphere QDs placed on oxidized Si rather than pyramid dots grown on bare Si may help to confine charge carriers deeper

  20. Interplay of Interfacial Layers and Blend Composition To Reduce Thermal Degradation of Polymer Solar Cells at High Temperature.

    Science.gov (United States)

    Ben Dkhil, Sadok; Pfannmöller, Martin; Schröder, Rasmus R; Alkarsifi, Riva; Gaceur, Meriem; Köntges, Wolfgang; Heidari, Hamed; Bals, Sara; Margeat, Olivier; Ackermann, Jörg; Videlot-Ackermann, Christine

    2018-01-31

    The thermal stability of printed polymer solar cells at elevated temperatures needs to be improved to achieve high-throughput fabrication including annealing steps as well as long-term stability. During device processing, thermal annealing impacts both the organic photoactive layer, and the two interfacial layers make detailed studies of degradation mechanism delicate. A recently identified thermally stable poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl

  1. Interfacial transduction of nucleic acid hybridization using immobilized quantum dots as donors in fluorescence resonance energy transfer.

    Science.gov (United States)

    Algar, W Russ; Krull, Ulrich J

    2009-01-06

    Fluorescence resonance energy transfer (FRET) using immobilized quantum dots (QDs) as energy donors was explored as a transduction method for the detection of nucleic acid hybridization at an interface. This research was motivated by the success of the QD-FRET-based transduction of nucleic acid hybridization in solution-phase assays. This new work represents a fundamental step toward the assembly of a biosensor, where immobilization of the selective chemistry on a surface is desired. After immobilizing QD-probe oligonucleotide conjugates on optical fibers, a demonstration of the retention of selectivity was achieved by the introduction of acceptor (Cy3)-labeled single-stranded target oligonucleotides. Hybridization generated the proximity required for FRET, and the resulting fluorescence spectra provided an analytical signal proportional to the amount of target. This research provides an important framework for the future development of nucleic acid biosensors based on QDs and FRET. The most important findings of this work are that (1) a QD-FRET solid-phase hybridization assay is viable and (2) a passivating layer of denatured bovine serum albumin alleviates nonspecific adsorption, ultimately resulting in (3) the potential for a reusable assay format and mismatch discrimination. In this, the first incarnation of a solid-phase QD-FRET hybridization assay, the limit of detection was found to be 5 nM, and the dynamic range was almost 2 orders of magnitude. Selective discrimination of the target was shown using a three-base-pairs mismatch from a fully complementary sequence. Despite a gradual loss of signal, reuse of the optical fibers over multiple cycles of hybridization and dehybridization was possible. Directions for further improvement of the analytical performance by optimizing the design of the QD-probe oligonucleotide interface are identified.

  2. Layer-by-layer-assembled quantum dot multilayer sensitizers: how the number of layers affects the photovoltaic properties of one-dimensional ZnO nanowire electrodes.

    Science.gov (United States)

    Jin, Ho; Choi, Sukyung; Lim, Sang-Hoon; Rhee, Shi-Woo; Lee, Hyo Joong; Kim, Sungjee

    2014-01-13

    Layer cake: Multilayered CdSe quantum dot (QD) sensitizers are layer-by-layer assembled onto ZnO nanowires by making use of electrostatic interactions to study the effect of the layer number on the photovoltaic properties. The photovoltaic performance of QD-sensitized solar cells critically depends on this number as a result of the balance between light-harvesting efficiency and carrier-recombination probability. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Predicting the mixed-mode I/II spatial damage propagation along 3D-printed soft interfacial layer via a hyperelastic softening model

    Science.gov (United States)

    Liu, Lei; Li, Yaning

    2018-07-01

    A methodology was developed to use a hyperelastic softening model to predict the constitutive behavior and the spatial damage propagation of nonlinear materials with damage-induced softening under mixed-mode loading. A user subroutine (ABAQUS/VUMAT) was developed for numerical implementation of the model. 3D-printed wavy soft rubbery interfacial layer was used as a material system to verify and validate the methodology. The Arruda - Boyce hyperelastic model is incorporated with the softening model to capture the nonlinear pre-and post- damage behavior of the interfacial layer under mixed Mode I/II loads. To characterize model parameters of the 3D-printed rubbery interfacial layer, a series of scarf-joint specimens were designed, which enabled systematic variation of stress triaxiality via a single geometric parameter, the slant angle. It was found that the important model parameter m is exponentially related to the stress triaxiality. Compact tension specimens of the sinusoidal wavy interfacial layer with different waviness were designed and fabricated via multi-material 3D printing. Finite element (FE) simulations were conducted to predict the spatial damage propagation of the material within the wavy interfacial layer. Compact tension experiments were performed to verify the model prediction. The results show that the model developed is able to accurately predict the damage propagation of the 3D-printed rubbery interfacial layer under complicated stress-state without pre-defined failure criteria.

  4. Luminescence spectra of CdSe/ZnSe double layers of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Reznitsky, Alexander; Permogorov, Sergei; Korenev, Vladimir V.; Sedova, Irina; Sorokin, Sergey; Sitnikova, Alla; Ivanov, Sergei [A.F. Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, 194021 St. Petersburg (Russian Federation); Klochikhin, Albert [B.P. Konstantinov Nuclear Physics Institute, St. Petersburg (Russian Federation)

    2009-12-15

    We have studied the emission spectra and structural properties of double CdSe/ZnSe quantum dot (QD) sheet structures grown by molecular beam epitaxy in order to elucidate the mechanisms of the electronic and strain field interaction between the QD planes. The thickness of the ZnSe barrier separating the CdSe sheets was in the range of 10-60 monolayers (ML) in the set of samples studied. We have found that coupling between dots in adjacent layers becomes relatively strong in CdSe/ZnSe double layers structures with 25-27 ML barrier, while it is rather weak when the barrier thickness exceeds 30 ML. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Graded GaAsSb strain reducing layers covering InAs/GaAs quantum dots

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Zíková, Markéta; Pangrác, Jiří; Oswald, Jiří; Kuldová, Karla; Vyskočil, Jan; Hulicius, Eduard

    2013-01-01

    Roč. 370, MAY (2013), s. 303-306 ISSN 0022-0248 R&D Projects: GA ČR GAP102/10/1201 Institutional research plan: CEZ:AV0Z10100521 Keywords : band alignment * photoluminescence * strain reducing layer * quantum dot * MOVPE * InAs/GaAs Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.693, year: 2013

  6. Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer.

    Science.gov (United States)

    Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J

    2016-06-09

    Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack.

  7. Production of three-dimensional quantum dot lattice of Ge/Si core-shell quantum dots and Si/Ge layers in an alumina glass matrix.

    Science.gov (United States)

    Buljan, M; Radić, N; Sancho-Paramon, J; Janicki, V; Grenzer, J; Bogdanović-Radović, I; Siketić, Z; Ivanda, M; Utrobičić, A; Hübner, R; Weidauer, R; Valeš, V; Endres, J; Car, T; Jerčinović, M; Roško, J; Bernstorff, S; Holy, V

    2015-02-13

    We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.

  8. Interfacial exchange, magnetic coupling and magnetoresistance in ultra-thin GdN/NbN/GdN tri-layers

    Science.gov (United States)

    Takamura, Yota; Goncalves, Rafael S.; Cascales, Juan Pedro; Altinkok, Atilgan; de Araujo, Clodoaldo I. L.; Lauter, Valeria; Moodera, Jagadeesh S.; MIT Team

    Superconducting spin-valve structures with a superconductive (SC) spacer sandwiched between ferromagnetic (FM) insulating layers [Li PRL 2013, Senapati APL 2013, Zhu Nat. Mat. 2016.] are attractive since the SC and FM characteristics can mutually be controlled by the proximity effect. We investigated reactively sputtered GdN/NbN/GdN tri-layer structures with various (SC) NbN spacer thicknesses (dNbN) from superconducting to normal layers. Magnetoresistive behavior similar to GMR in metallic magnetic multilayers was observed in the tri-layers with dNbN between 5-10 monolayers (ML), where thinner NbN layers did not show superconductivity down to 4.2 K. The occurrence of GMR signal indicates the presence of a ML of FM metallic layers at the GdN/NbN interfaces. Susceptibility and transport measurements in these samples revealed that the interface layers (ILs) are ferromagnetically coupled with adjacent GdN layers. The thickness of each of the IL is deduced to be about 1.25 ML, and as a result for dNbN magnetically coupled and switched simultaneously. These findings and interfacial characterization by various techniques will be presented. Work supported by NSF and ONR Grants.

  9. Coulomb Oscillations in a Gate-Controlled Few-Layer Graphene Quantum Dot.

    Science.gov (United States)

    Song, Yipu; Xiong, Haonan; Jiang, Wentao; Zhang, Hongyi; Xue, Xiao; Ma, Cheng; Ma, Yulin; Sun, Luyan; Wang, Haiyan; Duan, Luming

    2016-10-12

    Graphene quantum dots could be an ideal host for spin qubits and thus have been extensively investigated based on graphene nanoribbons and etched nanostructures; however, edge and substrate-induced disorders severely limit device functionality. Here, we report the confinement of quantum dots in few-layer graphene with tunable barriers, defined by local strain and electrostatic gating. Transport measurements unambiguously reveal that confinement barriers are formed by inducing a band gap via the electrostatic gating together with local strain induced constriction. Numerical simulations according to the local top-gate geometry confirm the band gap opening by a perpendicular electric field. We investigate the magnetic field dependence of the energy-level spectra in these graphene quantum dots. Experimental results reveal a complex evolution of Coulomb oscillations with the magnetic field, featuring kinks at level crossings. The simulation of energy spectrum shows that the kink features and the magnetic field dependence are consistent with experimental observations, implying the hybridized nature of energy-level spectrum of these graphene quantum dots.

  10. Interfacial rheological properties of adsorbed protein layers and surfactants : a review

    NARCIS (Netherlands)

    Bos, M.A.; Vliet, T. van

    2001-01-01

    Proteins and low molecular weight (LMW) surfactants are widely used for the physical stabilisation of many emulsions and foam based food products. The formation and stabilisation of these emulsions and foams depend strongly on the interfacial properties of the proteins and the LMW surfactants.

  11. Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

    Science.gov (United States)

    Bhattacharya, Debarati; Basu, Saibal; Singh, Surendra; Roy, Sumalay; Dev, Bhupendra Nath

    2012-12-01

    Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni-Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

  12. Strong and reversible modulation of carbon nanotube-silicon heterojunction solar cells by an interfacial oxide layer.

    Science.gov (United States)

    Jia, Yi; Cao, Anyuan; Kang, Feiyu; Li, Peixu; Gui, Xuchun; Zhang, Luhui; Shi, Enzheng; Wei, Jinquan; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai

    2012-06-21

    Deposition of nanostructures such as carbon nanotubes on Si wafers to make heterojunction structures is a promising route toward high efficiency solar cells with reduced cost. Here, we show a significant enhancement in the cell characteristics and power conversion efficiency by growing a silicon oxide layer at the interface between the nanotube film and Si substrate. The cell efficiency increases steadily from 0.5% without interfacial oxide to 8.8% with an optimal oxide thickness of about 1 nm. This systematic study reveals that formation of an oxide layer switches charge transport from thermionic emission to a mixture of thermionic emission and tunneling and improves overall diode properties, which are critical factors for tailoring the cell behavior. By controlled formation and removal of interfacial oxide, we demonstrate oscillation of the cell parameters between two extreme states, where the cell efficiency can be reversibly altered by a factor of 500. Our results suggest that the oxide layer plays an important role in Si-based photovoltaics, and it might be utilized to tune the cell performance in various nanostructure-Si heterojunction structures.

  13. White light emission from organic-inorganic hererostructure devices by using CdSe quantum dots as emitting layer

    International Nuclear Information System (INIS)

    Tang Aiwei; Teng Feng; Gao Yinhao; Li Dan; Zhao Suling; Liang Chunjun; Wang Yongsheng

    2007-01-01

    In this paper, white light emission was obtained from organic-inorganic heterostructure devices by using CdSe quantum dots as emitting layer, in which CdSe quantum dots were synthesized via a colloidal chemical approach by using CdO and Se powder as precursors. Photoluminescence of CdSe quantum dots demonstrated a white emission with a full wavelength at half maximum (FWHM) of about 200 nm under ambient conditions, and the white emission could be observed in both multilayer device ITO/PEDOT:PSS/CdSe/BCP/Alq 3 /Al and single-layer device: ITO/PEDOT:PSS/CdSe/Al. The broad emission was attributed to the inhomogeneous broadening. The CIE coordinates of the multilayer device were x=0.35 and y=0.40. The white-light-emitting diodes with CdSe quantum dots as the emitting layer are potentially useful in lighting applications

  14. Ultrathin ZnS and ZnO Interfacial Passivation Layers for Atomic-Layer-Deposited HfO2 Films on InP Substrates.

    Science.gov (United States)

    Kim, Seung Hyun; Joo, So Yeong; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

    2016-08-17

    Ultrathin ZnS and ZnO films grown by atomic layer deposition (ALD) were employed as interfacial passivation layers (IPLs) for HfO2 films on InP substrates. The interfacial layer growth during the ALD of the HfO2 film was effectively suppressed by the IPLs, resulting in the decrease of electrical thickness, hysteresis, and interface state density. Compared with the ZnO IPL, the ZnS IPL was more effective in reducing the interface state density near the valence band edge. The leakage current density through the film was considerably lowered by the IPLs because the film crystallization was suppressed. Especially for the film with the ZnS IPL, the leakage current density in the low-voltage region was significantly lower than that observed for the film with the ZnO IPL, because the direct tunneling current was suppressed by the higher conduction band offset of ZnS with the InP substrate.

  15. Interfacial mixing in double-barrier magnetic tunnel junctions with amorphous NiFeSiB layers

    International Nuclear Information System (INIS)

    Chun, B.S.; Ko, S.P.; Hwang, J.Y.; Rhee, J.R.; Kim, T.W.; Kim, Y.K.

    2007-01-01

    Double-barrier magnetic tunnel junctions (DMTJs) comprising Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO x /free layer (CoFe 4/NiFeSiB 2/CoFe 4, CoFe 10, or NiFeSiB 10)/AlO x /CoFe 7/IrMn 10/Ru 60 (nm) have been examined with an emphasis given on understanding the interfacial mixing effects. The DMTJ, consisted of NiFeSiB, shows low switching field and low bias voltage dependence because the amorphous NiFeSiB has lower M S (=800 emu/cm 3 ) and offers smoother interfaces than polycrystalline CoFe. An interesting feature observed in the CoFe/NiFeSiB/CoFe sandwich free layered DMTJ is the presence of a wavy MR transfer curve at high-resistance region. Because the polycrystalline CoFe usually grows into a columnar structure, diamagnetic CoSi, paramagnetic FeSi, and/or diamagnetic CoB might have been formed during the sputter-deposition process. By employing electron energy loss spectrometry (EELS) and Auger electron spectroscopy (AES), we were able to confirm that Si and B atoms were arranged evenly in the top and bottom portions of AlO x /CoFe interfaces. This means that the interfacial mixing resulted in a distorted magnetization reversal process

  16. Effects of interfacial transition layers on the electrical properties of individual Fe 30 Co 61 Cu 9 /Cu multilayer nanowires

    KAUST Repository

    Ma, Hongbin

    2016-01-01

    In this work, we accurately measure the electrical properties of individual Fe30Co61Cu9/Cu multilayered nanowires using nanomanipulators in in situ scanning electron microscopy to reveal that interfacial transition layers are influential in determining their transport behaviors. We investigate the morphology, crystal structure and chemistry of the Fe30Co61Cu9/Cu multilayered nanowires to characterize them at the nanoscale. We also compare the transport properties of these multilayered nanowires to those of individual pure Cu nanowires and to those of alloy Fe30Co61Cu9 nanowires. The multilayered nanowires with a 50 nm diameter had a remarkable resistivity of approximately 5.41 × 10-7 Ω m and a failure current density of 1.54 × 1011 A m-2. Detailed analysis of the electrical data reveals that interfacial transition layers influence the electrical properties of multilayered nanowires and are likely to have a strong impact on the life of nanodevices. This work contributes to a basic understanding of the electrical parameters of individual magnetic multilayered nanowires for their application as functional building blocks and interconnecting leads in nanodevices and nanoelectronics, and also provides a clear physical picture of a single multilayered nanowire which explains its electrical resistance and its source of giant magnetoresistance. © The Royal Society of Chemistry 2016.

  17. Thickness measurement of a thin hetero-oxide film with an interfacial oxide layer by X-ray photoelectron spectroscopy

    Science.gov (United States)

    Kim, Kyung Joong; Lee, Seung Mi; Jang, Jong Shik; Moret, Mona

    2012-02-01

    The general equation Tove = L cos θ ln(Rexp/R0 + 1) for the thickness measurement of thin oxide films by X-ray photoelectron spectroscopy (XPS) was applied to a HfO2/SiO2/Si(1 0 0) as a thin hetero-oxide film system with an interfacial oxide layer. The contribution of the thick interfacial SiO2 layer to the thickness of the HfO2 overlayer was counterbalanced by multiplying the ratio between the intensity of Si4+ from a thick SiO2 film and that of Si0 from a Si(1 0 0) substrate to the intensity of Si4+ from the HfO2/SiO2/Si(1 0 0) film. With this approximation, the thickness levels of the HfO2 overlayers showed a small standard deviation of 0.03 nm in a series of HfO2 (2 nm)/SiO2 (2-6 nm)/Si(1 0 0) films. Mutual calibration with XPS and transmission electron microscopy (TEM) was used to verify the thickness of HfO2 overlayers in a series of HfO2 (1-4 nm)/SiO2 (3 nm)/Si(1 0 0) films. From the linear relation between the thickness values derived from XPS and TEM, the effective attenuation length of the photoelectrons and the thickness of the HfO2 overlayer could be determined.

  18. Atomic Layer Deposition of CdS Quantum Dots for Solid-State Quantum Dot Sensitized Solar Cells

    KAUST Repository

    Brennan, Thomas P.; Ardalan, Pendar; Lee, Han-Bo-Ram; Bakke, Jonathan R.; Ding, I-Kang; McGehee, Michael D.; Bent, Stacey F.

    2011-01-01

    Functioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO 2, we are able to grow QDs of adjustable size which act as sensitizers for solid-state QDsensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1-10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2',7,7'-tetrakis-(N,N-di-p methoxyphenylamine) 9,9'-spirobifluorene (spiro-OMeTAD) as the solid-state hole conductor. The ALD approach described here can be applied to fabrication of quantum-confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Atomic Layer Deposition of CdS Quantum Dots for Solid-State Quantum Dot Sensitized Solar Cells

    KAUST Repository

    Brennan, Thomas P.

    2011-10-04

    Functioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO 2, we are able to grow QDs of adjustable size which act as sensitizers for solid-state QDsensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1-10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2\\',7,7\\'-tetrakis-(N,N-di-p methoxyphenylamine) 9,9\\'-spirobifluorene (spiro-OMeTAD) as the solid-state hole conductor. The ALD approach described here can be applied to fabrication of quantum-confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. All-solution processed composite hole transport layer for quantum dot light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiaoli [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Synergetic Innovation Center of Chemical Science and Engineering, Tianjin (China); Dai, Haitao, E-mail: htdai@tju.edu.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Zhao, Junliang; Wang, Shuguo [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Sun, Xiaowei [Department of Electrical & Electronic Engineering, South University of Science and Technology of China, Tangchang Road 1088, Shenzhen, Guangdong 518055 (China)

    2016-03-31

    In the present work, poly-TPD and TCTA composite hole transport layer (HTL) was employed in solution processed CdSe/ZnS quantum dot light emitting diodes (QLEDs). As the doping level of TCTA can determine the carriers transport efficiency of HTL, the proper mixing ratio of TCTA and poly-TPD should be found to optimize the performance of composite HTL for QLEDs. The doping of poly-TPD by low TCTA content can make its HOMO level lower and then reduce the energy barrier height from HTL to quantum dots (QDs), whereas the doping of poly-TPD by the concentrated TCTA results in the degraded performance of QLEDs due to its decreased hole transport mobility. By using the optimized composition with poly-TPD:TCTA (3:1) as the hole transport layer, the luminescence of the device exhibits about double enhancement compared with that of poly-TPD based device. The improvement of luminescence is mainly attributed to the lower energy barrier of hole injection. The Förster resonant energy transfer (FRET) mechanism in the devices was investigated through theoretical and experimental analysis and the results indicate that the TCTA doping makes no difference on FRET. Therefore, the charge injection mechanism dominates the improved performance of the devices. - Highlights: • Quantum dot light emitting diodes (QLEDs) were fabricated by all solution method. • The performance of QLEDs was optimized by varying the composite hole transport layer. • The blend HTL could promote hole injection by optimizing HOMO levels. • The energy transfer mechanism was analyzed by studying Förster resonant energy transfer process.

  1. Detection of Interfacial Debonding in a Rubber-Steel-Layered Structure Using Active Sensing Enabled by Embedded Piezoceramic Transducers.

    Science.gov (United States)

    Feng, Qian; Kong, Qingzhao; Jiang, Jian; Liang, Yabin; Song, Gangbing

    2017-09-01

    Rubber-steel-layered structures are used in many engineering applications. Laminated rubber-steel bearing, as a type of seismic isolation device, is one of the most important applications of the rubber-steel-layered structures. Interfacial debonding in rubber-steel-layered structures is a typical failure mode, which can severely reduce their load-bearing capacity. In this paper, the authors developed a simple but effective active sensing approach using embedded piezoceramic transducers to provide an in-situ detection of the interfacial debonding between the rubber layers and steel plates. A sandwiched rubber-steel-layered specimen, consisting of one rubber layer and two steel plates, was fabricated as the test specimen. A novel installation technique, which allows the piezoceramic transducers to be fully embedded into the steel plates without changing the geometry and the surface conditions of the plates, was also developed in this research. The active sensing approach, in which designed stress waves can propagate between a pair of the embedded piezoceramic transducers (one as an actuator and the other one as a sensor), was employed to detect the steel-rubber debonding. When the rubber-steel debonding occurs, the debonded interfaces will attenuate the propagating stress wave, so that the amplitude of the received signal will decrease. The rubber-steel debonding was generated by pulling the two steel plates in opposite directions in a material-testing machine. The changes of the received signal before and after the debonding were characterized in a time domain and further quantified by using a wavelet packet-based energy index. Experiments on the healthy rubber-steel-layered specimen reveal that the piezoceramic-induced stress wave can propagate through the rubber layer. The destructive test on the specimen demonstrates that the piezoceramic-based active sensing approach can effectively detect the rubber-steel debonding failure in real time. The active sensing

  2. Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

    International Nuclear Information System (INIS)

    Bhattacharya, Debarati; Basu, Saibal; Singh, Surendra; Roy, Sumalay; Dev, Bhupendra Nath

    2012-01-01

    Highlights: ► Room temperature diffusion in Si/Ni/Si trilayer detected through complementary x-ray and polarized neutron reflectometry. ► Analyses of XPNR data generated the construction of the layered structure in terms of physical parameters along with alloy layers created by diffusion. ► Scattering length density information from XPNR provided quantitative assessment of the stoichiometry of alloys formed at the Si/Ni and Ni/Si interfaces. - Abstract: Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni–Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

  3. Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharya, Debarati, E-mail: debarati@barc.gov.in [Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Basu, Saibal; Singh, Surendra [Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Roy, Sumalay; Dev, Bhupendra Nath [Department of Materials Science, Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Jadavpur, Kolkata 700032 (India)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer Room temperature diffusion in Si/Ni/Si trilayer detected through complementary x-ray and polarized neutron reflectometry. Black-Right-Pointing-Pointer Analyses of XPNR data generated the construction of the layered structure in terms of physical parameters along with alloy layers created by diffusion. Black-Right-Pointing-Pointer Scattering length density information from XPNR provided quantitative assessment of the stoichiometry of alloys formed at the Si/Ni and Ni/Si interfaces. - Abstract: Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni-Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

  4. ZnSe passivation layer for the efficiency enhancement of CuInS2 quantum dots sensitized solar cells

    International Nuclear Information System (INIS)

    Peng, Zhuoyin; Liu, Yueli; Zhao, Yinghan; Chen, Keqiang; Cheng, Yuqing; Kovalev, Valery; Chen, Wen

    2014-01-01

    Highlights: • ZnSe is employed as passivation layer in CuInS 2 quantum dots sensitized solar cells. • Slight red-shift has been occurred in UV–vis absorption spectra with ZnSe coating. • CuInS 2 based solar cells coated by ZnSe have better efficiency than that of ZnS. • Higher rate of charge transport can be produced after coating with ZnSe. -- Abstract: The effect of ZnSe passivation layer is investigated in the CuInS 2 quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS 2 quantum dot sensitized TiO 2 photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS 2 quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS 2 based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer

  5. Influence of wetting-layer wave functions on phonon-mediated carrier capture into self-assembled quantum dots

    DEFF Research Database (Denmark)

    Markussen, Troels; Kristensen, Philip Trøst; Tromborg, Bjarne

    2006-01-01

    Models of carrier dynamics in quantum dots rely strongly on adequate descriptions of the carrier wave functions. In this work we numerically solve the one-band effective mass Schrodinger equation to calculate the capture times of phonon-mediated carrier capture into self-assembled quantum dots. C....... Comparing with results obtained using approximate carrier wave functions, we demonstrate that the capture times are strongly influenced by properties of the wetting layer wave functions not accounted for by earlier theoretical analyses....

  6. Silicon dioxide with a silicon interfacial layer as an insulating gate for highly stable indium phosphide metal-insulator-semiconductor field effect transistors

    Science.gov (United States)

    Kapoor, V. J.; Shokrani, M.

    1991-01-01

    A novel gate insulator consisting of silicon dioxide (SiO2) with a thin silicon (Si) interfacial layer has been investigated for high-power microwave indium phosphide (InP) metal-insulator-semiconductor field effect transistors (MISFETs). The role of the silicon interfacial layer on the chemical nature of the SiO2/Si/InP interface was studied by high-resolution X-ray photoelectron spectroscopy. The results indicated that the silicon interfacial layer reacted with the native oxide at the InP surface, thus producing silicon dioxide, while reducing the native oxide which has been shown to be responsible for the instabilities in InP MISFETs. While a 1.2-V hysteresis was present in the capacitance-voltage (C-V) curve of the MIS capacitors with silicon dioxide, less than 0.1 V hysteresis was observed in the C-V curve of the capacitors with the silicon interfacial layer incorporated in the insulator. InP MISFETs fabricated with the silicon dioxide in combination with the silicon interfacial layer exhibited excellent stability with drain current drift of less than 3 percent in 10,000 sec, as compared to 15-18 percent drift in 10,000 sec for devices without the silicon interfacial layer. High-power microwave InP MISFETs with Si/SiO2 gate insulators resulted in an output power density of 1.75 W/mm gate width at 9.7 GHz, with an associated power gain of 2.5 dB and 24 percent power added efficiency.

  7. Strategy for synthesizing quantum dot-layered double hydroxide nanocomposites and their enhanced photoluminescence and photostability.

    Science.gov (United States)

    Cho, Seungho; Jung, Sungwook; Jeong, Sanghwa; Bang, Jiwon; Park, Joonhyuck; Park, Youngrong; Kim, Sungjee

    2013-01-08

    Layered double hydroxide-quantum dot (LDH-QD) composites are synthesized via a room temperature LDH formation reaction in the presence of QDs. InP/ZnS (core/shell) QD, a heavy metal free QD, is used as a model constituent. Interactions between QDs (with negative zeta potentials), decorated with dihydrolipoic acids, and inherently positively charged metal hydroxide layers of LDH during the LDH formations are induced to form the LDH-QD composites. The formation of the LDH-QD composites affords significantly enhanced photoluminescence quantum yields and thermal- and photostabilities compared to their QD counterparts. In addition, the fluorescence from the solid LDH-QD composite preserved the initial optical properties of the QD colloid solution without noticeable deteriorations such as red-shift or deep trap emission. Based on their advantageous optical properties, we also demonstrate the pseudo white light emitting diode, down-converted by the LDH-QD composites.

  8. RBS/channeling study of buried Ge quantum dots grown in a Si layer

    International Nuclear Information System (INIS)

    Fonseca, A.; Alves, E.; Barradas, N.P.; Leitao, J.P.; Sobolev, N.A.; Carmo, M.C.; Nikiforov, A.I.; Presting, H.

    2006-01-01

    In last decades we have been assisting to a crescent importance of low dimensional systems for the fabrication of nano- and opto-electronic devices. Ge quantum dots (QDs) are well suited for fulfilling these requirements. In this work we present and discuss Ge/Si multilayer and single layer samples grown by molecular beam epitaxy. RBS/channeling results reveal the evidence for the presence of Ge QD for the thickest (with 1 ML of SiO 2 and 0.9 nm of Ge) single layer sample. On the other hand Ge atoms are fully substitutional incorporated in the Si matrix for the thinner sample, excluding the formation of Ge QDs. Multilayer sample shows an angular deviation of the Ge curve (-0.48 o ) with respect to the Si ones, indicating the compressive strain of the films. A tetragonal distortion of (1.78 ± 0.19%) was calculated

  9. Multiplexed interfacial transduction of nucleic acid hybridization using a single color of immobilized quantum dot donor and two acceptors in fluorescence resonance energy transfer.

    Science.gov (United States)

    Algar, W Russ; Krull, Ulrich J

    2010-01-01

    A multiplexed solid-phase assay for the detection of nucleic acid hybridization was developed on the basis of a single color of immobilized CdSe/ZnS quantum dot (QD) as a donor in fluorescence resonance energy transfer (FRET). This work demonstrated that two channels of detection did not necessitate two different QD donors. Two probe oligonucleotides were coimmobilized on optical fibers modified with QDs, and a sandwich assay was used to associate the acceptor dyes with interfacial hybridization events without target labeling. FRET-sensitized acceptor emission provided an analytical signal that was concentration dependent down to 10 nM. Changes in the ratio of coimmobilized probe oligonucleotides were found to yield linear changes in the relative amounts of acceptor emission. These changes were compared to previous studies that used mixed films of two QD donors for two detection channels. The analysis indicated that probe dilution effects were primarily driven by changes in acceptor number density and that QD dilution effects or changes in mean donor-acceptor distance were secondary. Hybridization kinetics were found to be consistent between different ratios of coimmobilized probes, suggesting that hybridization in this type of system occurred via the accepted model for solid-phase hybridization, where adsorption and then diffusion at the solid interface drove hybridization.

  10. Role of the wetting layer in the enhanced responsivity of InAs/GaAsSb quantum dot infrared photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Guzmán, Álvaro, E-mail: guzman@die.upm.es; Yamamoto, Kenji; Ulloa, J. M.; Hierro, Adrian [Instituto de Sistemas Optoelectrónicos y Microtecnología y Dept. Ingeniería Electrónica, Universidad Politécnica de Madrid, ETSI de Telecomunicación, Avda. Complutense 30, 28040 Madrid (Spain); Llorens, J. M. [IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC), Isaac Newton 8, PTM, E-28760 Tres Cantos, Madrid (Spain)

    2015-07-06

    InAs/GaAs{sub 1−x}Sb{sub x} Quantum Dot (QD) infrared photodetectors are analyzed by photocurrent spectroscopy. We observe that the integrated responsivity of the devices is improved with the increasing Sb mole fraction in the capping layer, up to 4.2 times for x = 17%. Since the QD layers are not vertically aligned, the vertical transport of the carriers photogenerated within the QDs takes place mainly through the bulk material and the wetting layer of the additional QD regions. The lower thickness of the wetting layer for high Sb contents results in a reduced capture probability of the photocarriers, thus increasing the photoconductive gain and hence, the responsivity of the device. The growth of not vertically aligned consecutive QD layers with a thinner wetting layer opens a possibility to improve the performance of quantum dot infrared photodetectors.

  11. Graphene Quantum Dot Layers with Energy-Down-Shift Effect on Crystalline-Silicon Solar Cells.

    Science.gov (United States)

    Lee, Kyung D; Park, Myung J; Kim, Do-Yeon; Kim, Soo M; Kang, Byungjun; Kim, Seongtak; Kim, Hyunho; Lee, Hae-Seok; Kang, Yoonmook; Yoon, Sam S; Hong, Byung H; Kim, Donghwan

    2015-09-02

    Graphene quantum dot (GQD) layers were deposited as an energy-down-shift layer on crystalline-silicon solar cell surfaces by kinetic spraying of GQD suspensions. A supersonic air jet was used to accelerate the GQDs onto the surfaces. Here, we report the coating results on a silicon substrate and the GQDs' application as an energy-down-shift layer in crystalline-silicon solar cells, which enhanced the power conversion efficiency (PCE). GQD layers deposited at nozzle scan speeds of 40, 30, 20, and 10 mm/s were evaluated after they were used to fabricate crystalline-silicon solar cells; the results indicate that GQDs play an important role in increasing the optical absorptivity of the cells. The short-circuit current density was enhanced by about 2.94% (0.9 mA/cm(2)) at 30 mm/s. Compared to a reference device without a GQD energy-down-shift layer, the PCE of p-type silicon solar cells was improved by 2.7% (0.4 percentage points).

  12. The role of interfacial layers in the enhanced thermal conductivity of nanofluids: A renovated Hamilton-Crosser model

    International Nuclear Information System (INIS)

    Yu, W; Choi, S.U.S.

    2004-01-01

    We previously developed a renovated Maxwell model for the effective thermal conductivity of nanofluids and determined that the solid/liquid interfacial layers play an important role in the enhanced thermal conductivity of nanofluids. However, this renovated Maxwell model is limited to suspensions with spherical particles. Here, we extend the Hamilton--Crosser model for suspensions of nonspherical particles to include the effect of a solid/liquid interface. The solid/liquid interface is described as a confocal ellipsoid with a solid particle. The new model for the three-phase suspensions is mathematically expressed in terms of the equivalent thermal conductivity and equivalent volume fraction of anisotropic complex ellipsoids, as well as an empirical shape factor. With a generalized empirical shape factor, the renovated Hamilton--Crosser model correctly predicts the magnitude of the thermal conductivity of nanotube-in-oil nanofluids. At present, this new model is not able to predict the nonlinear behavior of the nanofluid thermal conductivity

  13. Interfacial Passivation of the p-Doped Hole-Transporting Layer Using General Insulating Polymers for High-Performance Inverted Perovskite Solar Cells.

    Science.gov (United States)

    Zhang, Fan; Song, Jun; Hu, Rui; Xiang, Yuren; He, Junjie; Hao, Yuying; Lian, Jiarong; Zhang, Bin; Zeng, Pengju; Qu, Junle

    2018-05-01

    Organic-inorganic lead halide perovskite solar cells (PVSCs), as a competing technology with traditional inorganic solar cells, have now realized a high power conversion efficiency (PCE) of 22.1%. In PVSCs, interfacial carrier recombination is one of the dominant energy-loss mechanisms, which also results in the simultaneous loss of potential efficiency. In this work, for planar inverted PVSCs, the carrier recombination is dominated by the dopant concentration in the p-doped hole transport layers (HTLs), since the F4-TCNQ dopant induces more charge traps and electronic transmission channels, thus leading to a decrease in open-circuit voltages (V OC ). This issue is efficiently overcome by inserting a thin insulating polymer layer (poly(methyl methacrylate) or polystyrene) as a passivation layer with an appropriate thickness, which allows for increases in the V OC without significantly sacrificing the fill factor. It is believed that the passivation layer attributes to the passivation of interfacial recombination and the suppression of current leakage at the perovskite/HTL interface. By manipulating this interfacial passivation technique, a high PCE of 20.3% is achieved without hysteresis. Consequently, this versatile interfacial passivation methodology is highly useful for further improving the performance of planar inverted PVSCs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. The interfacial tension of the mercury —1 M HClO4− solution interface at high potentials; comparison with double-layer capacitance measurements

    NARCIS (Netherlands)

    Sluyters-Rehbach, M.; Woittiez, W.J.A.; Sluyters, J.H.

    Interfacial tension values have been measured in order to calculate the electrical charge density as a function of potential. The results are in accordance with those obtained from double-layer capacitance data reported earlier2,3, also at highly positive potentials.

  15. Decreased Charge Transport Barrier and Recombination of Organic Solar Cells by Constructing Interfacial Nanojunction with Annealing-Free ZnO and Al Layers.

    Science.gov (United States)

    Liu, Chunyu; Zhang, Dezhong; Li, Zhiqi; Zhang, Xinyuan; Guo, Wenbin; Zhang, Liu; Ruan, Shengping; Long, Yongbing

    2017-07-05

    To overcome drawbacks of the electron transport layer, such as complex surface defects and unmatched energy levels, we successfully employed a smart semiconductor-metal interfacial nanojunciton in organic solar cells by evaporating an ultrathin Al interlayer onto annealing-free ZnO electron transport layer, resulting in a high fill factor of 73.68% and power conversion efficiency of 9.81%. The construction of ZnO-Al nanojunction could effectively fill the surface defects of ZnO and reduce its work function because of the electron transfer from Al to ZnO by Fermi level equilibrium. The filling of surface defects decreased the interfacial carrier recombination in midgap trap states. The reduced surface work function of ZnO-Al remodulated the interfacial characteristics between ZnO and [6,6]-phenyl C71-butyric acid methyl ester (PC 71 BM), decreasing or even eliminating the interfacial barrier against the electron transport, which is beneficial to improve the electron extraction capacity. The filled surface defects and reduced interfacial barrier were realistically observed by photoluminescence measurements of ZnO film and the performance of electron injection devices, respectively. This work provides a simple and effective method to simultaneously solve the problems of surface defects and unmatched energy level for the annealing-free ZnO or other metal oxide semiconductors, paving a way for the future popularization in photovoltaic devices.

  16. Stable MoS2 Field-Effect Transistors Using TiO2 Interfacial Layer at Metal/MoS2 Contact

    KAUST Repository

    Park, Woojin

    2017-09-07

    Molybdenum disulphide (MoS2) is an emerging 2-dimensional (2D) semiconductor for electronic devices. However, unstable and low performance of MoS2 FETs is an important concern. In this study, inserting an atomic layer deposition (ALD) titanium dioxide (TiO2) interfacial layer between contact metal and MoS2 channel is suggested to achieve more stable performances. The reduced threshold voltage (VTH) shift and reduced series resistance (RSD) were simultaneously achieved.

  17. Simply synthesized TiO2 nanorods as an effective scattering layer for quantum dot sensitized solar cells

    International Nuclear Information System (INIS)

    Samadpour, Mahmoud; Zad, Azam Iraji; Molaei, Mehdi

    2014-01-01

    TiO 2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (V oc = 497 mV, J sc = 11.32 mA/cm 2 , FF = 0.54), in optimized structures. High efficiency can be obtained just by tuning the photoanode structure without further treatments, which will make this system a promising nanostructure for efficient quantum dot sensitized solar cells. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  18. p-Type semiconducting nickel oxide as an efficiency-enhancing anode interfacial layer in polymer bulk-heterojunction solar cells

    Science.gov (United States)

    Irwin, Michael D.; Buchholz, D. Bruce; Hains, Alexander W.; Chang, Robert P. H.; Marks, Tobin J.

    2008-01-01

    To minimize interfacial power losses, thin (5–80 nm) layers of NiO, a p-type oxide semiconductor, are inserted between the active organic layer, poly(3-hexylthiophene) (P3HT) + [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), and the ITO (tin-doped indium oxide) anode of bulk-heterojunction ITO/P3HT:PCBM/LiF/Al solar cells. The interfacial NiO layer is deposited by pulsed laser deposition directly onto cleaned ITO, and the active layer is subsequently deposited by spin-coating. Insertion of the NiO layer affords cell power conversion efficiencies as high as 5.2% and enhances the fill factor to 69% and the open-circuit voltage (Voc) to 638 mV versus an ITO/P3HT:PCBM/LiF/Al control device. The value of such hole-transporting/electron-blocking interfacial layers is clearly demonstrated and should be applicable to other organic photovoltaics.

  19. Passivation effects on quantum dots prepared by successive ionic layer adsorption and reaction

    Science.gov (United States)

    Dai, Qilin; Maloney, Scott; Chen, Weimin; Poudyal, Uma; Wang, Wenyong

    2016-06-01

    ZnS is typically used to passivate semiconductor quantum dots (QDs) prepared by the successive ionic layer adsorption and reaction (SILAR) method for solar cell applications, while for colloidal QDs, organic ligands are usually used for this passivation purpose. In this study we utilized oleylamine and oleic acid ligands, besides ZnS, to passivate QDs prepared by the SILAR approach, and investigated their effects on the incident photon-to-current efficiency (IPCE) performance of the solar cells. It was observed that oleylamine passivation decreased device performance, while oleic acid passivation improved the IPCE of the cells. Redshift of the IPCE onset wavelength was also observed after oleic acid coating, which was attributed to the delocalization of excitons in the CdS QDs.

  20. GaAs droplet quantum dots with nanometer-thin capping layer for plasmonic applications

    Science.gov (United States)

    In Park, Suk; Trojak, Oliver Joe; Lee, Eunhye; Song, Jin Dong; Kyhm, Jihoon; Han, Ilki; Kim, Jongsu; Yi, Gyu-Chul; Sapienza, Luca

    2018-05-01

    We report on the growth and optical characterization of droplet GaAs quantum dots (QDs) with extremely-thin (11 nm) capping layers. To achieve such result, an internal thermal heating step is introduced during the growth and its role in the morphological properties of the QDs obtained is investigated via scanning electron and atomic force microscopy. Photoluminescence measurements at cryogenic temperatures show optically stable, sharp and bright emission from single QDs, at visible wavelengths. Given the quality of their optical properties and the proximity to the surface, such emitters are good candidates for the investigation of near field effects, like the coupling to plasmonic modes, in order to strongly control the directionality of the emission and/or the spontaneous emission rate, crucial parameters for quantum photonic applications.

  1. Formation of carbonaceous nano-layers under high interfacial pressures during lubrication with mineral and bio-based oils

    Energy Technology Data Exchange (ETDEWEB)

    Baltrus, John P. [U.S. DOE

    2014-01-01

    In order to better protect steel surfaces against wear under high loads, understanding of chemical reactions between lubricants and metal at high interfacial pressures and elevated temperatures needs to be improved. Solutions at 5 to 20 wt. % of zinc di-2-ethylhexyl dithio phosphate (ZDDP) and chlorinated paraffins (CP) in inhibited paraffinic mineral oil (IPMO) and inhibited soy bean oil (ISBO) were compared on a Twist Compression Tribotester (TCT) at 200 MPa. Microscopy of wear tracks after 10 seconds tribotesting showed much smoother surface profiles than those of unworn areas. X-ray photoelectron spectroscopy (XPS) coupled with Ar-ion sputtering demonstrated that additive solutions in ISBO formed 2–3 times thicker carbon-containing nano-layers compared to IPMO. The amounts of Cl, S or P were unexpectedly low and detectable only on the top surface with less than 5 nm penetration. CP blends in IPMO formed more inorganic chlorides than those in ISBO. It can be concluded that base oils are primarily responsible for the thickness of carbonaceous nano-layers during early stages of severe boundary lubrication, while CP or ZDDP additive contributions are important, but less significant.

  2. Interfacial engineering of two-dimensional nano-structured materials by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zhuiykov, Serge, E-mail: serge.zhuiykov@ugent.be [Ghent University Global Campus, Department of Applied Analytical & Physical Chemistry, Faculty of Bioscience Engineering, 119 Songdomunhwa-ro, Yeonsu-Gu, Incheon 406-840 (Korea, Republic of); Kawaguchi, Toshikazu [Global Station for Food, Land and Water Resources, Global Institution for Collaborative Research and Education, Hokkaido University, N10W5 Kita-ku, Sapporo, Hokkaido 060-0810 (Japan); Graduate School of Environmental Science, Hokkaido University, N10W5 Kita-ku, Sapporo, Hokkaido 060-0810 (Japan); Hai, Zhenyin; Karbalaei Akbari, Mohammad; Heynderickx, Philippe M. [Ghent University Global Campus, Department of Applied Analytical & Physical Chemistry, Faculty of Bioscience Engineering, 119 Songdomunhwa-ro, Yeonsu-Gu, Incheon 406-840 (Korea, Republic of)

    2017-01-15

    Highlights: • Advantages of atomic layer deposition technology (ALD) for two-dimensional nano-crystals. • Conformation of ALD technique and chemistry of precursors. • ALD of semiconductor oxide thin films. • Ultra-thin (∼1.47 nm thick) ALD-developed tungsten oxide nano-crystals on large area. - Abstract: Atomic Layer Deposition (ALD) is an enabling technology which provides coating and material features with significant advantages compared to other existing techniques for depositing precise nanometer-thin two-dimensional (2D) nanostructures. It is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. ALD is especially advantageous when the film quality or thickness is critical, offering ultra-high aspect ratios. ALD provides digital thickness control to the atomic level by depositing film one atomic layer at a time, as well as pinhole-free films even over a very large and complex areas. Digital control extends to sandwiches, hetero-structures, nano-laminates, metal oxides, graded index layers and doping, and it is perfect for conformal coating and challenging 2D electrodes for various functional devices. The technique’s capabilities are presented on the example of ALD-developed ultra-thin 2D tungsten oxide (WO{sub 3}) over the large area of standard 4” Si substrates. The discussed advantages of ALD enable and endorse the employment of this technique for the development of hetero-nanostructure 2D semiconductors with unique properties.

  3. Tunable UV-visible absorption of SnS2 layered quantum dots produced by liquid phase exfoliation.

    Science.gov (United States)

    Fu, Xiao; Ilanchezhiyan, P; Mohan Kumar, G; Cho, Hak Dong; Zhang, Lei; Chan, A Sattar; Lee, Dong J; Panin, Gennady N; Kang, Tae Won

    2017-02-02

    4H-SnS 2 layered crystals synthesized by a hydrothermal method were used to obtain via liquid phase exfoliation quantum dots (QDs), consisting of a single layer (SLQDs) or multiple layers (MLQDs). Systematic downshift of the peaks in the Raman spectra of crystals with a decrease in size was observed. The bandgap of layered QDs, estimated by UV-visible absorption spectroscopy and the tunneling current measurements using graphene probes, increases from 2.25 eV to 3.50 eV with decreasing size. 2-4 nm SLQDs, which are transparent in the visible region, show selective absorption and photosensitivity at wavelengths in the ultraviolet region of the spectrum while larger MLQDs (5-90 nm) exhibit a broad band absorption in the visible spectral region and the photoresponse under white light. The results show that the layered quantum dots obtained by liquid phase exfoliation exhibit well-controlled and regulated bandgap absorption in a wide tunable wavelength range. These novel layered quantum dots prepared using an inexpensive method of exfoliation and deposition from solution onto various substrates at room temperature can be used to create highly efficient visible-blind ultraviolet photodetectors and multiple bandgap solar cells.

  4. Band Offsets and Interfacial Properties of HfAlO Gate Dielectric Grown on InP by Atomic Layer Deposition.

    Science.gov (United States)

    Yang, Lifeng; Wang, Tao; Zou, Ying; Lu, Hong-Liang

    2017-12-01

    X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy have been used to determine interfacial properties of HfO 2 and HfAlO gate dielectrics grown on InP by atomic layer deposition. An undesirable interfacial InP x O y layer is easily formed at the HfO 2 /InP interface, which can severely degrade the electrical performance. However, an abrupt interface can be achieved when the growth of the HfAlO dielectric on InP starts with an ultrathin Al 2 O 3 layer. The valence and conduction band offsets for HfAlO/InP heterojunctions have been determined to be 1.87 ± 0.1 and 2.83 ± 0.1 eV, respectively. These advantages make HfAlO a potential dielectric for InP MOSFETs.

  5. Interfacial micromorphological differences in hybrid layer formation between water- and solvent-based dentin bonding systems.

    Science.gov (United States)

    Gregoire, Geneviève L; Akon, Bernadette A; Millas, Arlette

    2002-06-01

    Many dentin bonding systems of different compositions, and in particular containing different solvents, have been introduced to the market. Their effect on the quality of the interface requires clarification by means of comparative trials. This study investigated micromorphological differences in hybrid layer formation with a variety of commercially available water- or solvent-based dentin bonding products and their recommended compomers. Five bonding systems were used on groups of 10 teeth each as follows: group I, acetone-based system used with 36% phosphoric acid; group II, a different acetone-based system containing nano-sized particles for filler loading and used with a non-rinsing conditioner containing maleic acid; group III, the acetone-based system of group II used with 36% phosphoric acid (the only difference in the treatment for groups II and III was the acid etching system); group IV, a mixed-solvent-based system (water/ethanol) used with 37% phosphoric acid; and group V, a water-based system used with 37% phosphoric acid. Each bonding system was covered with the recommended compomer. Class I occlusal preparations were made in extracted teeth and restored with one of the above systems. Five specimens of each group were studied with optical microscopy after staining. Scanning electron microscopy was used to examine the interface of the bonding system/dentin of the other 5 teeth in each group. The optical microscopy measurements were made with a 10 x 10 reticle. A micron mark with scale was used for the scanning electron microscope. All measurements were made in microm. The following criteria were used to define a good interface: absence of voids between the different parts of the interface, uniformity of the hybrid layer, good opening of the tubuli orifices, and tag adherence to the tubuli walls. Morphological differences were found at the interface depending on dentin treatment and adhesive composition. The acetone-containing systems were associated

  6. Interfacial layers and semi-transparent electrodes for large area flexible organic photovoltaics

    DEFF Research Database (Denmark)

    Patil, Bhushan Ramesh

    the exciton recombination and charge carrier losses in the devices. I report on the implementation of a novel exciton blocking layer of an intrinsic organic material, ‘N,N'-di-1-naphthalenyl-N,N'-diphenyl [1,1':4',1'':4'',1‴-quaterphenyl]-4,4‴-diamine (4P-NPD)’, in organic small molecule-based OPVs. Using...... this interlayer, the efficiency of OPV devices increased by approx. 24 % compared to reference devices. I also report on the use the use of electron transport layer of organic material ‘2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine, BCP)’ for inverted small molecule-based lab-scale and up......-scaled OPVs. The pronounced clustering of the BCP layer lead to increasing discrepancies in the device performance with the increase in the device size, which disqualifies it for use of in the inverted large area OPVs. The second section deals with up-scaling of highly conductive semi-transparent electrodes...

  7. Enhanced ionic conductivity in composite materials due to interfacial space charge layers

    International Nuclear Information System (INIS)

    Dudney, N.J.

    1985-01-01

    The ionic conductivity of a number of salts (e.g., β-AgI, LiI, CuCl, HgI 2 , etc.) can be enhanced by one to three orders of magnitude with the addition of fine particles of an insoluble and nonconducting material such as Al 2 O 3 or SiO 2 . Typically the conductivity increases with addition of the inert particles and reaches a peak at 10-40 vol % of the particles. The mechanism responsible for the enhanced conductivity of the composite is not understood at this time. Some claim that this effect is due to an increased concentration of charge carriers in a diffuse space charge layer near the charged surface of the particle. The goal of the present study is to test this proposed mechanism by calculating the maximum space charge layer effect and then using this result to estimate the conductivity of a composite with a random distribution of Al 2 O 3 particles. Also, the conductivity of composite systems has been investigated assuming an ordered distribution of particles which are surrounded by a high conductivity layer

  8. Interfacial engineering of electron transport layer using Caesium Iodide for efficient and stable organic solar cells

    Science.gov (United States)

    Upama, Mushfika Baishakhi; Elumalai, Naveen Kumar; Mahmud, Md Arafat; Wright, Matthew; Wang, Dian; Xu, Cheng; Haque, Faiazul; Chan, Kah Howe; Uddin, Ashraf

    2017-09-01

    Polymer solar cells (PSCs) have gained immense research interest in the recent years predominantly due to low-cost, solution process-ability, and facile device fabrication. However, achieving high stability without compromising the power conversion efficiency (PCE) serves to be an important trade-off for commercialization. In line with this, we demonstrate the significance of incorporating a CsI/ZnO bilayer as electron transport layer (ETL) in the bulk heterojunction PSCs employing low band gap polymer (PTB7) and fullerene (PC71BM) as the photo-active layer. The devices with CsI/ZnO interlayer exhibited substantial enhancement of 800% and 12% in PCE when compared to the devices with pristine CsI and pristine ZnO as ETL, respectively. Furthermore, the UV and UV-ozone induced degradation studies revealed that the devices incorporating CsI/ZnO bilayer possess excellent decomposition stability (∼23% higher) over the devices with pristine ZnO counterparts. The incorporation of CsI between ITO and ZnO was found to favorably modify the energy-level alignment at the interface, contributing to the charge collection efficiency as well as protecting the adjacent light absorbing polymer layers from degradation. The mechanism behind the improvement in PCE and stability is analyzed using the electrochemical impedance spectroscopy and dark I-V characteristics.

  9. Interfacial characteristics of polyethylene terephthalate-based piezoelectric multi-layer films

    International Nuclear Information System (INIS)

    Liu, Z.H.; Pan, C.T.; Chen, Y.C.; Liang, P.H.

    2013-01-01

    The study examines the deformation between interfaces and the adhesion mechanism of multi-layer flexible electronic composites. Indium tin oxide (ITO), aluminum (Al), and zinc oxide (ZnO) were deposited on a polyethylene terephthalate (PET) substrate using radio frequency magnetron sputtering at room temperature to form flexible structures (e.g., ITO/PET, Al/PET, ZnO/ITO/PET, and ZnO/Al/PET) for piezoelectric transducers. ITO and Al films are used as the conductive layers. A ZnO thin film shows a high (002) c-axis preferred orientation at 2θ = 34.45° and excellent piezoelectric properties. Nanoscratching and nano-indention testing were conducted to analyze the adhesion following periodic mechanical stress. Additionally, two Berkovich and conical probes with a curvature radius of 40 nm and 10 μm are examined for the scratching test. A 4-point probe is used to measure the conductive properties. The plastic deformation between the ductile Al film and PET substrate is observed using scanning electron microscopy to examine the chip formation on the ITO/PET. Delamination between the ZnO and Al/PET substrate was not observed. The result suggests that ZnO film has excellent adhesion with Al/PET compared to ITO/PET. - Highlights: ► Interfaces and adhesion mechanism of multi-layer flexible electronic composites ► Polyethylene terephthalate (PET) based flexible structures ► Nano-scratching and nano-indention tests were used to analyze adhesion. ► Using two various probes of Berkovich and conical ► Piezoelectric zinc oxide film has excellent adhesion with aluminum/PET

  10. Supersaturated Self-Assembled Charge-Selective Interfacial Layers for Organic Solar Cells

    Science.gov (United States)

    2014-11-24

    layers (IFLs) on the tin-doped indium oxide (ITO) anodes of organic photovoltaic (OPV) cells, a series of Ar2N-(CH2)n-SiCl3 precursors with Ar = 3,4...Bulk- heterojunction OPV devices are fabricated with these SHSAMs: ITO/IFL/poly[[4,8- bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][2...phobicity,15,19,20 electrical conductivity,21−23 and charge in- jection/collection selectivity through the film.1,2,10 For example, on metal oxide substrates

  11. Interfacial Energy Alignment at the ITO/Ultra-Thin Electron Selective Dielectric Layer Interface and Its Effect on the Efficiency of Bulk-Heterojunction Organic Solar Cells.

    Science.gov (United States)

    Itoh, Eiji; Goto, Yoshinori; Saka, Yusuke; Fukuda, Katsutoshi

    2016-04-01

    We have investigated the photovoltaic properties of an inverted bulk heterojunction (BHJ) cell in a device with an indium-tin-oxide (ITO)/electron selective layer (ESL)/P3HT:PCBM active layer/MoOx/Ag multilayered structure. The insertion of only single layer of poly(diallyl-dimethyl-ammonium chloride) (PDDA) cationic polymer film (or poly(ethyleneimine) (PEI) polymeric interfacial dipole layer) and titanium oxide nanosheet (TN) films as an ESL effectively improved cell performance. Abnormal S-shaped curves were observed in the inverted BHJ cells owing to the contact resistance across the ITO/active layer interface and the ITO/PDDA/TN/active layer interface. The series resistance across the ITO/ESL interface in the inverted BHJ cell was successfully reduced using an interfacial layer with a positively charged surface potential with respect to ITO base electrode. The positive dipole in PEI and the electronic charge phenomena at the electrophoretic deposited TN (ED-TN) films on ITO contributed to the reduction of the contact resistance at the electrode interface. The surface potential measurement revealed that the energy alignment by the transfer of electronic charges from the ED-TN to the base electrodes. The insertion of the ESL with a large positive surface potential reduced the potential barrier for the electron injection at ITO/TN interface and it improved the photovoltaic properties of the inverted cell with an ITO/TN/active layer/MoOx/Ag structure.

  12. Charge separation in contact systems with CdSe quantum dot layers

    International Nuclear Information System (INIS)

    Zillner, Elisabeth Franziska

    2013-01-01

    Quantum dot (QD) solar cells are a fast developing area in the field of solution processed photovoltaics. Central aspects for the application of QDs in solar cells are separation and transport of charge carriers in the QD layers and the formation of charge selective contacts. Even though efficiencies of up to 7% were reached in QD solar cells, these processes are not yet fully understood. In this thesis the mechanisms of charge separation, transport and recombination in CdSe QD layers and layer systems were studied. Charge separation was measured via surface photovoltage (SPV) at CdSe QD layers with thicknesses in the range of monolayers. To determine the influence of interparticle distance of QDs and trap states on the surface of QDs on charge separation, QDs with four different surfactant layers were studied. Layers of CdSe QDs were prepared on ITO, Si, SiO 2 and CdS by dip coating under inert atmosphere. The layers were characterized by Rutherford backscattering spectrometry, UV-vis spectroscopy, step profilometry and scanning electron microscopy to determine the areal density, the absorption and thickness of CdSe QD monolayers. SPV measurements show that initial charge separation from the CdSe QDs on ITO only happened from the fi rst monolayer of QDs. Electrons, photo-excited in the fi rst monolayer of CdSe QDs, were trapped on the ITO surface. The remaining free holes were trapped in surface states and/or diffused into the neighboring QD layers. The thick surfactant layer (∼ 1.6 nm) of pristine QDs had to be reduced by washing and/or ligand exchange for separation of photo-excited charge carriers. Both, interparticle distance and trap density, influenced the processes of charge separation and recombination. SPV transients of CdSe monolayers could be described by a single QD approximation model, based on Miller-Abrahams hopping of holes between the delocalized excitonic state, traps on the surface of the QD and the filled trap on the ITO surface

  13. Charge separation in contact systems with CdSe quantum dot layers

    Energy Technology Data Exchange (ETDEWEB)

    Zillner, Elisabeth Franziska

    2013-03-06

    Quantum dot (QD) solar cells are a fast developing area in the field of solution processed photovoltaics. Central aspects for the application of QDs in solar cells are separation and transport of charge carriers in the QD layers and the formation of charge selective contacts. Even though efficiencies of up to 7% were reached in QD solar cells, these processes are not yet fully understood. In this thesis the mechanisms of charge separation, transport and recombination in CdSe QD layers and layer systems were studied. Charge separation was measured via surface photovoltage (SPV) at CdSe QD layers with thicknesses in the range of monolayers. To determine the influence of interparticle distance of QDs and trap states on the surface of QDs on charge separation, QDs with four different surfactant layers were studied. Layers of CdSe QDs were prepared on ITO, Si, SiO{sub 2} and CdS by dip coating under inert atmosphere. The layers were characterized by Rutherford backscattering spectrometry, UV-vis spectroscopy, step profilometry and scanning electron microscopy to determine the areal density, the absorption and thickness of CdSe QD monolayers. SPV measurements show that initial charge separation from the CdSe QDs on ITO only happened from the fi rst monolayer of QDs. Electrons, photo-excited in the fi rst monolayer of CdSe QDs, were trapped on the ITO surface. The remaining free holes were trapped in surface states and/or diffused into the neighboring QD layers. The thick surfactant layer ({approx} 1.6 nm) of pristine QDs had to be reduced by washing and/or ligand exchange for separation of photo-excited charge carriers. Both, interparticle distance and trap density, influenced the processes of charge separation and recombination. SPV transients of CdSe monolayers could be described by a single QD approximation model, based on Miller-Abrahams hopping of holes between the delocalized excitonic state, traps on the surface of the QD and the filled trap on the ITO surface

  14. Contrasting suspended covers reveal the impact of an artificial monolayer on heat transfer processes at the interfacial boundary layer.

    Science.gov (United States)

    Pittaway, P; Martínez-Alvarez, V; Hancock, N

    2015-01-01

    The highly variable performance of artificial monolayers in reducing evaporation from water storages has been attributed to wind speed and wave turbulence. Other factors operating at the interfacial boundary layer have seldom been considered. In this paper, two physical shade covers differing in porosity and reflectivity were suspended over 10 m diameter water tanks to attenuate wind and wave turbulence. The monolayer octadecanol was applied to one of the covered tanks, and micrometeorological conditions above and below the covers were monitored to characterise diurnal variation in the energy balance. A high downward (air-to-water) convective heat flux developed under the black cover during the day, whereas diurnal variation in the heat flux under the more reflective, wind-permeable white cover was much less. Hourly air and water temperature profiles under the covers over 3 days when forced convection was minimal (low wind speed) were selected for analysis. Monolayer application reduced temperature gain in surface water under a downward convective heat flux, and conversely reduced temperature loss under an upward convective heat flux. This 'dual property' may explain why repeat application of an artificial monolayer to retard evaporative loss (reducing latent heat loss) does not inevitably increase water temperature.

  15. Interfacial and Electrical Properties of Ge MOS Capacitor by ZrLaON Passivation Layer and Fluorine Incorporation

    Science.gov (United States)

    Huang, Yong; Xu, Jing-Ping; Liu, Lu; Cheng, Zhi-Xiang; Lai, Pui-To; Tang, Wing-Man

    2017-09-01

    Ge Metal-Oxide-Semiconductor (MOS) capacitor with HfTiON/ZrLaON stacked gate dielectric and fluorine-plasma treatment is fabricated, and its interfacial and electrical properties are compared with its counterparts without the ZrLaON passivation layer or the fluorine-plasma treatment. Experimental results show that the sample exhibits excellent performances: low interface-state density (3.7×1011 cm-2eV-1), small flatband voltage (0.21 V), good capacitance-voltage behavior, small frequency dispersion and low gate leakage current (4.41×10-5 A/cm2 at Vg = Vfb + 1V). These should be attributed to the suppressed growth of unstable Ge oxides on the Ge surface during gate-dielectric annealing by the ZrLaON interlayer and fluorine incorporation, thus greatly reducing the defective states at/near the ZrLaON/Ge interface and improving the electrical properties of the device.

  16. Effect of an Interfacial Layer on Electron Tunneling through Atomically Thin Al2O3 Tunnel Barriers.

    Science.gov (United States)

    Wilt, Jamie; Sakidja, Ridwan; Goul, Ryan; Wu, Judy Z

    2017-10-25

    Electron tunneling through high-quality, atomically thin dielectric films can provide a critical enabling technology for future microelectronics, bringing enhanced quantum coherent transport, fast speed, small size, and high energy efficiency. A fundamental challenge is in controlling the interface between the dielectric and device electrodes. An interfacial layer (IL) will contain defects and introduce defects in the dielectric film grown atop, preventing electron tunneling through the formation of shorts. In this work, we present the first systematic investigation of the IL in Al 2 O 3 dielectric films of 1-6 Å's in thickness on an Al electrode. We integrated several advanced approaches: molecular dynamics to simulate IL formation, in situ high vacuum sputtering atomic layer deposition (ALD) to synthesize Al 2 O 3 on Al films, and in situ ultrahigh vacuum scanning tunneling spectroscopy to probe the electron tunneling through the Al 2 O 3 . The IL had a profound effect on electron tunneling. We observed a reduced tunnel barrier height and soft-type dielectric breakdown which indicate that defects are present in both the IL and in the Al 2 O 3 . The IL forms primarily due to exposure of the Al to trace O 2 and/or H 2 O during the pre-ALD heating step of fabrication. As the IL was systematically reduced, by controlling the pre-ALD sample heating, we observed an increase of the ALD Al 2 O 3 barrier height from 0.9 to 1.5 eV along with a transition from soft to hard dielectric breakdown. This work represents a key step toward the realization of high-quality, atomically thin dielectrics with electron tunneling for the next generation of microelectronics.

  17. Adsorption of β-casein-surfactant mixed layers at the air-water interface evaluated by interfacial rheology.

    Science.gov (United States)

    Maestro, Armando; Kotsmar, Csaba; Javadi, Aliyar; Miller, Reinhard; Ortega, Francisco; Rubio, Ramón G

    2012-04-26

    This work presents a detailed study of the dilational viscoelastic moduli of the adsorption layers of the milk protein β-casein (BCS) and a surfactant at the liquid/air interface, over a broad frequency range. Two complementary techniques have been used: a drop profile tensiometry technique and an excited capillary wave method, ECW. Two different surfactants were studied: the nonionic dodecyldimethylphosphine oxide (C12DMPO) and the cationic dodecyltrimethylammonium bromide (DoTAB). The interfacial dilational elasticity and viscosity are very sensitive to the composition of protein-surfactant mixed adsorption layers at the air/water interface. Two different dynamic processes have been observed for the two systems studied, whose characteristic frequencies are close to 0.01 and 100 Hz. In both systems, the surface elasticity was found to show a maximum when plotted versus the surfactant concentration. However, at frequencies above 50 Hz the surface elasticity of BCS + C12DMPO is higher than the one of the aqueous BCS solution over most of the surfactant concentration range, whereas for the BCS + DoTAB it is smaller for high surfactant concentrations and higher at low concentrations. The BCS-surfactant interaction modifies the BCS random coil structure via electrostatic and/or hydrophobic interactions, leading to a competitive adsorption of the BCS-surfactant complexes with the free, unbound surfactant molecules. Increasing the surfactant concentration decreases the adsorbed proteins. However, the BCS molecules are rather strongly bound to the interface due to their large adsorption energy. The results have been fitted to the model proposed by C. Kotsmar et al. ( J. Phys. Chem. B 2009 , 113 , 103 ). Even though the model describes well the concentration dependence of the limiting elasticity, it does not properly describe its frequency dependence.

  18. The photovoltaic impact of atomic layer deposited TiO2 interfacial layer on Si-based photodiodes

    Science.gov (United States)

    Karabulut, Abdulkerim; Orak, İkram; Türüt, Abdulmecit

    2018-06-01

    In present work, photocurrent, current-voltage (I-V) and capacitance/conductance-voltage-frequency (C/G-V-f) measurements were analyzed for the photodiode and diode parameters of Al/TiO2/p-Si structure. The TiO2 thin film structure was deposited on p-Si by using atomic layer deposition technique (ALD) and its thickness was about 10 nm. The surface morphology of TiO2 coated on p-Si structure was observed via atomic force microscope (AFM). Barrier height (Φb) and ideality factor (n) values of device were found to be 0.80 eV, 0.70 eV, 0.56 eV and 1.04, 2.24, 10.27 under dark, 10 and 100 mW/cm2, respectively. Some photodiodes parameters such as fill factor (FF), power efficiency (%η), open circuit voltage (Voc), short circuit current (Isc) were obtained from I-V measurement under different light intensity. FF and η were accounted 49.2, 39,0 and 0.05, 0.45 under 10 and 100 mW/cm2 light power intensity, respectively. C-2-V graph was plotted from C-V-f measurements and zero bias voltage (V0), donor concentration (Nd), Fermi energy (EF), barrier height (Φb) and maximum electric field (Em) were determined from C-2-V data for different frequencies. The electrical and photocurrent values demonstrated that it can be used for photodiode, photo detector and photo sensing applications.

  19. Effect of various intermediate ceramic layers on the interfacial stability of zirconia core and veneering ceramics.

    Science.gov (United States)

    Yoon, Hyung-In; Yeo, In-Sung; Yi, Yang-Jin; Kim, Sung-Hun; Lee, Jai-Bong; Han, Jung-Suk

    2015-01-01

    The purposes of this study were to evaluate the effects of intermediate ceramics on the adhesion between the zirconia core and veneer ceramics. The polished surfaces of fully sintered Y-TZP blocks received three different treatments: (1) connector (C), (2) liner (L) or (3) wash layer (W). All the treated zirconia blocks were veneered with either (a) fluorapatite glass-ceramic (E) or (b) feldspathic porcelain (V) and divided into four groups (CE, CV, LE and WV). For the control group, the testing surfaces of metal blocks were veneered with feldspathic porcelain (VM). A half of the samples in each group (n = 21) were exposed to thermocycling, while the other half of the specimens were stored at room temperature under dry conditions. All specimens were subjected to the shear test and the failed surfaces were microscopically examined. The elemental distribution at the zirconia core/veneer interface was analyzed. The specimens in Groups CE and CV exhibited significantly greater mean bond strength values than those in Groups LE and WV, respectively (p ceramic substances into the zirconia surface. A glass-ceramic based connector is significantly more favorable to core/veneer adhesion than the other intermediate ceramics evaluated in the study. However, thermal cycling affected the bond strength at the core/veneer interface differently according to the intermediate ceramics.

  20. Photoelectrochemical Characterization of Sprayed alpha-Fe2O3 Thin Films : Influence of Si Doping and SnO2 Interfacial Layer

    NARCIS (Netherlands)

    Liang, Y.; Enache, C.S.; Van De Krol, R.

    2008-01-01

    a-Fe2O3 thin film photoanodes for solar water splitting were prepared by spray pyrolysis of Fe(AcAc)3. The donor density in the Fe2O3 films could be tuned between 10171020cm-3 by doping with silicon. By depositing a 5 nm SnO2 interfacial layer between the Fe2O3 films and the transparent conducting

  1. Effect of Al 2 O 3 Recombination Barrier Layers Deposited by Atomic Layer Deposition in Solid-State CdS Quantum Dot-Sensitized Solar Cells

    KAUST Repository

    Roelofs, Katherine E.

    2013-03-21

    Despite the promise of quantum dots (QDs) as a light-absorbing material to replace the dye in dye-sensitized solar cells, quantum dot-sensitized solar cell (QDSSC) efficiencies remain low, due in part to high rates of recombination. In this article, we demonstrate that ultrathin recombination barrier layers of Al2O3 deposited by atomic layer deposition can improve the performance of cadmium sulfide (CdS) quantum dot-sensitized solar cells with spiro-OMeTAD as the solid-state hole transport material. We explored depositing the Al2O3 barrier layers either before or after the QDs, resulting in TiO2/Al2O3/QD and TiO 2/QD/Al2O3 configurations. The effects of barrier layer configuration and thickness were tracked through current-voltage measurements of device performance and transient photovoltage measurements of electron lifetimes. The Al2O3 layers were found to suppress dark current and increase electron lifetimes with increasing Al 2O3 thickness in both configurations. For thin barrier layers, gains in open-circuit voltage and concomitant increases in efficiency were observed, although at greater thicknesses, losses in photocurrent caused net decreases in efficiency. A close comparison of the electron lifetimes in TiO2 in the TiO2/Al2O3/QD and TiO2/QD/Al2O3 configurations suggests that electron transfer from TiO2 to spiro-OMeTAD is a major source of recombination in ss-QDSSCs, though recombination of TiO2 electrons with oxidized QDs can also limit electron lifetimes, particularly if the regeneration of oxidized QDs is hindered by a too-thick coating of the barrier layer. © 2013 American Chemical Society.

  2. Tandem colloidal quantum dot solar cells employing a graded recombination layer

    KAUST Repository

    Wang, Xihua; Koleilat, Ghada I.; Tang, Jiang; Liu, Huan; Kramer, Illan J.; Debnath, Ratan; Brzozowski, Lukasz; Barkhouse, D. Aaron R.; Levina, Larissa; Hoogland, Sjoerd; Sargent, Edward H.

    2011-01-01

    Tuning of the electronic bandgap in colloidal quantum dots (CQDs) by changing their size enables the spectral response of CQD-based photodetectors and photovoltaic devices to be tailored. Multi-junction solar cells made from a combination of CQDs of differing sizes and thus bandgaps are a promising means by which to increase the energy harvested from the Sun's broad spectrum. Here, we report the first CQD tandem solar cells using the size-effect tuning of a single CQD material, PbS. We use a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine. Our tandem solar cell has an open-circuit voltage of 1.06Â V, equal to the sum of the two constituent single-junction devices, and a solar power conversion efficiency of up to 4.2%. © 2011 Macmillan Publishers Limited. All rights reserved.

  3. Tandem colloidal quantum dot solar cells employing a graded recombination layer

    KAUST Repository

    Wang, Xihua

    2011-06-26

    Tuning of the electronic bandgap in colloidal quantum dots (CQDs) by changing their size enables the spectral response of CQD-based photodetectors and photovoltaic devices to be tailored. Multi-junction solar cells made from a combination of CQDs of differing sizes and thus bandgaps are a promising means by which to increase the energy harvested from the Sun\\'s broad spectrum. Here, we report the first CQD tandem solar cells using the size-effect tuning of a single CQD material, PbS. We use a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine. Our tandem solar cell has an open-circuit voltage of 1.06Â V, equal to the sum of the two constituent single-junction devices, and a solar power conversion efficiency of up to 4.2%. © 2011 Macmillan Publishers Limited. All rights reserved.

  4. Efficient, air-stable colloidal quantum dot solar cells encapsulated using atomic layer deposition of a nanolaminate barrier

    KAUST Repository

    Ip, Alexander H.; Labelle, André J.; Sargent, Edward H.

    2013-01-01

    Atomic layer deposition was used to encapsulate colloidal quantum dot solar cells. A nanolaminate layer consisting of alternating alumina and zirconia films provided a robust gas permeation barrier which prevented device performance degradation over a period of multiple weeks. Unencapsulated cells stored in ambient and nitrogen environments demonstrated significant performance losses over the same period. The encapsulated cell also exhibited stable performance under constant simulated solar illumination without filtration of harsh ultraviolet photons. This monolithically integrated thin film encapsulation method is promising for roll-to-roll processed high efficiency nanocrystal solar cells. © 2013 AIP Publishing LLC.

  5. Efficient, air-stable colloidal quantum dot solar cells encapsulated using atomic layer deposition of a nanolaminate barrier

    KAUST Repository

    Ip, Alexander H.

    2013-12-23

    Atomic layer deposition was used to encapsulate colloidal quantum dot solar cells. A nanolaminate layer consisting of alternating alumina and zirconia films provided a robust gas permeation barrier which prevented device performance degradation over a period of multiple weeks. Unencapsulated cells stored in ambient and nitrogen environments demonstrated significant performance losses over the same period. The encapsulated cell also exhibited stable performance under constant simulated solar illumination without filtration of harsh ultraviolet photons. This monolithically integrated thin film encapsulation method is promising for roll-to-roll processed high efficiency nanocrystal solar cells. © 2013 AIP Publishing LLC.

  6. Enhanced performance of solution-processed broadband photodiodes by epitaxially blending MAPbBr3 quantum dots and ternary PbSxSe1-x quantum dots as the active layer

    Science.gov (United States)

    Sulaman, Muhammad; Yang, Shengyi; Jiang, Yurong; Tang, Yi; Zou, Bingsuo

    2017-12-01

    Organic-inorganic hybrid photodetectors attract more and more interest, since they can combine the advantages of both organic and inorganic materials into one device, and broadband photodetectors are widely used in many scientific and industrial fields. In this work, we demonstrate the enhanced-performance solution-processed broadband photodiodes by epitaxially blending organo-lead halide perovskite (MAPbBr3) colloidal quantum dots (CQDs) with ternary PbSxSe1-x CQDs as the active layer. As a result, the interfacial features of the hetero-epitaxial nanocomposite MAPbBr3:PbSxSe1-x enables the design and perception of functionalities that are not available for the single-phase constituents or layered devices. By combining the high electrical transport properties of MAPbBr3 QDs with the highly radiative efficiency of PbS0.4Se0.6 QDs, the photodiodes ITO/ZnO/PbS0.4Se0.6:MAPbBr3/Au exhibit a maximum photoresponsivity and specific detectivity of 21.48 A W-1 and 3.59 × 1013 Jones, 22.16 A W-1 and 3.70 × 1013 Jones at room temperature under 49.8 μW cm-2 532 nm laser and 62 μW cm-2 980 nm laser, respectively. This is higher than that of the layered photodiodes ITO/ZnO/PbS0.4Se0.6/MAPbBr3/Au, pure perovskite (MAPbBr3) (or PbS0.4Se0.6) QD-based photodiodes reported previously, and it is also better than the traditional inorganic semiconductor-based photodetectors. Our experimental results indicate that epitaxially-aligned nanocomposites (MAPbBr3:PbSxSe1-x) exhibit remarkable optoelectronic properties that are traceable to their atomic-scale crystalline coherence, and one can utilize the excellent photocarrier diffusion from PbSxSe1-x into the perovskite to enhance the device performance from the UV-visible to infrared region.

  7. Three-dimensional nanostructures on Ge/Si(100) wetting layers: Hillocks and pre-quantum dots

    International Nuclear Information System (INIS)

    Ramalingam, Gopalakrishnan; Floro, Jerrold A.; Reinke, Petra

    2016-01-01

    The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of these nanostructures, hillocks and pre-quantum dots, is studied by scanning tunneling microscopy. A wetting layer deposited at 350 °C is initially rough on the nanometer length-scale and undergoes a progressive transformation and smoothening during annealing at T < 460 °C when vacancy lines and the 2xn reconstruction are observed. The metastable Ge WL then collapses to form 3D nanostructures whose morphology is controlled by the WL thickness: first, the hillocks, with a wedding cake-type structure where the step edges run parallel to the 〈110〉 direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy controls the type of structure. The crossover thickness between the hillock and p-QDs regime is between 1.6 and 2.1 ML. The hillocks have larger lateral dimensions and volumes than p-QDs, and the p-QDs are exceptionally small quantum dots with a lower limit of 10 nm in width. Our work opens a new pathway to the control of nanostructure morphology and size in the elastically strained Ge/Si system.

  8. Inkjet-assisted layer-by-layer printing of quantum dot/enzyme microarrays for highly sensitive detection of organophosphorous pesticides.

    Science.gov (United States)

    Luan, Enxiao; Zheng, Zhaozhu; Li, Xinyu; Gu, Hongxi; Liu, Shaoqin

    2016-04-15

    We present a facile fabrication of layer-by-layer (LbL) microarrays of quantum dots (QDs) and acetylcholinesterase enzyme (AChE). The resulting arrays had several unique properties, such as low cost, high integration and excellent flexibility and time-saving. The presence of organophosphorous pesticides (OPs) can inhibit the AChE activity and thus changes the fluorescent intensity of QDs/AChE microscopic dot arrays. Therefore, the QDs/AChE microscopic dot arrays were used for the sensitive visual detection of OPs. Linear calibration for parathion and paraoxon was obtained in the range of 5-100 μg L(-1) under the optimized conditions with the limit of detection (LOD) of 10 μg L(-1). The arrays have been successfully used for detection of OPs in fruits and water real samples. The new array was validated by comparison with conventional high performance liquid chromatography-mass spectrometry (HPLC-MS). Copyright © 2016 Elsevier B.V. All rights reserved.

  9. Iridium Interfacial Stack (IRIS)

    Science.gov (United States)

    Spry, David James (Inventor)

    2015-01-01

    An iridium interfacial stack ("IrIS") and a method for producing the same are provided. The IrIS may include ordered layers of TaSi.sub.2, platinum, iridium, and platinum, and may be placed on top of a titanium layer and a silicon carbide layer. The IrIS may prevent, reduce, or mitigate against diffusion of elements such as oxygen, platinum, and gold through at least some of its layers.

  10. Inkjet-assisted layer-by-layer printing of quantum dot/enzyme microarrays for highly sensitive detection of organophosphorous pesticides

    Energy Technology Data Exchange (ETDEWEB)

    Luan, Enxiao; Zheng, Zhaozhu; Li, Xinyu; Gu, Hongxi [State Key Laboratory of Urban Water Resource and Environment, School of Life Science and Technology, Harbin Institute of Technology, Harbin 150080 (China); Micro- and Nanotechnology Research Center, Harbin Institute of Technology, Harbin 150080 (China); Liu, Shaoqin, E-mail: shaoqinliu@hit.edu.cn [Micro- and Nanotechnology Research Center, Harbin Institute of Technology, Harbin 150080 (China)

    2016-04-15

    We present a facile fabrication of layer-by-layer (LbL) microarrays of quantum dots (QDs) and acetylcholinesterase enzyme (AChE). The resulting arrays had several unique properties, such as low cost, high integration and excellent flexibility and time–saving. The presence of organophosphorous pesticides (OPs) can inhibit the AChE activity and thus changes the fluorescent intensity of QDs/AChE microscopic dot arrays. Therefore, the QDs/AChE microscopic dot arrays were used for the sensitive visual detection of OPs. Linear calibration for parathion and paraoxon was obtained in the range of 5–100 μg L{sup −1} under the optimized conditions with the limit of detection (LOD) of 10 μg L{sup −1}. The arrays have been successfully used for detection of OPs in fruits and water real samples. The new array was validated by comparison with conventional high performance liquid chromatography-mass spectrometry (HPLC-MS). - Graphical abstract: A fluorimetric assay for high-throughput screening of organophosphorous pesticides was developed based on the CdTe QDs/AChE microarrays via inkjet-assisted LbL printing techniques. - Highlights: • The large scale microarrays of CdTe QDs and AChE were fabricated by facile inkjet-assisted LbL printing technique. • The QDs/AChE microscopic dot arrays could be used quantitatively and rapidly for the sensitively visual detection of OPs. • A detection limit of 10 μg L{sup −1} was achieved, much lower than levels specified by standard tests and other colorimetric detection methods. • The low cost, short processing time, sufficient sensitivity, good stability and ease of use make it for a facile platform for on-site screening.

  11. Improving the Performance of PbS Quantum Dot Solar Cells by Optimizing ZnO Window Layer

    Science.gov (United States)

    Yang, Xiaokun; Hu, Long; Deng, Hui; Qiao, Keke; Hu, Chao; Liu, Zhiyong; Yuan, Shengjie; Khan, Jahangeer; Li, Dengbing; Tang, Jiang; Song, Haisheng; Cheng, Chun

    2017-04-01

    Comparing with hot researches in absorber layer, window layer has attracted less attention in PbS quantum dot solar cells (QD SCs). Actually, the window layer plays a key role in exciton separation, charge drifting, and so on. Herein, ZnO window layer was systematically investigated for its roles in QD SCs performance. The physical mechanism of improved performance was also explored. It was found that the optimized ZnO films with appropriate thickness and doping concentration can balance the optical and electrical properties, and its energy band align well with the absorber layer for efficient charge extraction. Further characterizations demonstrated that the window layer optimization can help to reduce the surface defects, improve the heterojunction quality, as well as extend the depletion width. Compared with the control devices, the optimized devices have obtained an efficiency of 6.7% with an enhanced V oc of 18%, J sc of 21%, FF of 10%, and power conversion efficiency of 58%. The present work suggests a useful strategy to improve the device performance by optimizing the window layer besides the absorber layer.

  12. GeO{sub x} interfacial layer scavenging remotely induced by metal electrode in metal/HfO{sub 2}/GeO{sub x}/Ge capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Taehoon; Jung, Yong Chan; Seong, Sejong; Ahn, Jinho, E-mail: jhahn@hanyang.ac.kr [Department of Materials Science and Engineering, Hanyang University, Seoul 04763 (Korea, Republic of); Lee, Sung Bo [Department of Materials Science and Engineering and Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 08826 (Korea, Republic of); Park, In-Sung, E-mail: parkis77@hanyang.ac.kr [Department of Materials Science and Engineering, Hanyang University, Seoul 04763 (Korea, Republic of); Institute of Nano Science and Technology, Hanyang University, Seoul 04763 (Korea, Republic of)

    2016-07-11

    The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeO{sub x} interfacial layer (IL) between HfO{sub 2} dielectric and Ge substrate in metal/HfO{sub 2}/GeO{sub x}/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeO{sub x} IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. The capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7 nm, 3.0 nm, and 3.5 nm, and each final remnant physical thickness of GeO{sub x} IL layer is 1.1 nm 1.4 nm, and 1.9 nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by oxidation reaction at the metal/HfO{sub 2} interface.

  13. The photoluminescence decay time of self-assembled InAs quantum dots covered by InGaAs layers

    International Nuclear Information System (INIS)

    Shu, G W; Wang, C K; Wang, J S; Shen, J L; Hsiao, R S; Chou, W C; Chen, J F; Lin, T Y; Ko, C H; Lai, C M

    2006-01-01

    The temperature dependence of the time-resolved photoluminescence (PL) of self-assembled InAs quantum dots (QDs) with InGaAs covering layers was investigated. The PL decay time increases with temperature from 50 to 170 K, and then decreases as the temperature increases further above 170 K. A model based on the phonon-assisted transition between the QD ground state and the continuum state is used to explain the temperature dependence of the PL decay time. This result suggests that the continuum states are important in the carrier capture in self-assembled InAs QDs

  14. ZnSe passivation layer for the efficiency enhancement of CuInS{sub 2} quantum dots sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Zhuoyin; Liu, Yueli; Zhao, Yinghan; Chen, Keqiang; Cheng, Yuqing [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China); Kovalev, Valery [Department of Mechanics and Mathematics, Moscow State University named after M.V. Lomonosov, Leninskie Gory 1, 119992 Moscow (Russian Federation); Chen, Wen, E-mail: chenw@whut.edu.cn [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China)

    2014-02-25

    Highlights: • ZnSe is employed as passivation layer in CuInS{sub 2} quantum dots sensitized solar cells. • Slight red-shift has been occurred in UV–vis absorption spectra with ZnSe coating. • CuInS{sub 2} based solar cells coated by ZnSe have better efficiency than that of ZnS. • Higher rate of charge transport can be produced after coating with ZnSe. -- Abstract: The effect of ZnSe passivation layer is investigated in the CuInS{sub 2} quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS{sub 2} quantum dot sensitized TiO{sub 2} photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS{sub 2} quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS{sub 2} based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer.

  15. Characterization of highly stacked InAs quantum dot layers on InP substrate for a planar saturable absorber at 1.5 μm band

    International Nuclear Information System (INIS)

    Inoue, Jun; Akahane, Kouichi; Yamamoto, Naokatsu; Isu, Toshiro; Tsuchiya, Masahiro

    2006-01-01

    We examined the absorption saturation properties in the 1.5 μm band of novel highly stacked InAs quantum dot layers. The transmission change at vertical incidence based on the saturable absorption of the quantum dots was more than 1%. This value is as large as the reflection changes of previously reported 1-μm-band quantum dot saturable absorber with interference enhancement. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Improving the electrical properties of lanthanum silicate films on ge metal oxide semiconductor capacitors by adopting interfacial barrier and capping layers.

    Science.gov (United States)

    Choi, Yu Jin; Lim, Hajin; Lee, Suhyeong; Suh, Sungin; Kim, Joon Rae; Jung, Hyung-Suk; Park, Sanghyun; Lee, Jong Ho; Kim, Seong Gyeong; Hwang, Cheol Seong; Kim, HyeongJoon

    2014-05-28

    The electrical properties of La-silicate films grown by atomic layer deposition (ALD) on Ge substrates with different film configurations, such as various Si concentrations, Al2O3 interfacial passivation layers, and SiO2 capping layers, were examined. La-silicate thin films were deposited using alternating injections of the La[N{Si(CH3)3}2]3 precursor with O3 as the La and O precursors, respectively, at a substrate temperature of 310 °C. The Si concentration in the La-silicate films was further controlled by adding ALD cycles of SiO2. For comparison, La2O3 films were also grown using [La((i)PrCp)3] and O3 as the La precursor and oxygen source, respectively, at the identical substrate temperature. The capacitance-voltage (C-V) hysteresis decreased with an increasing Si concentration in the La-silicate films, although the films showed a slight increase in the capacitance equivalent oxide thickness. The adoption of Al2O3 at the interface as a passivation layer resulted in lower C-V hysteresis and a low leakage current density. The C-V hysteresis voltages of the La-silicate films with Al2O3 passivation and SiO2 capping layers was significantly decreased to ∼0.1 V, whereas the single layer La-silicate film showed a hysteresis voltage as large as ∼1.0 V.

  17. Magneto-optical response of layers of semiconductor quantum dots and nanorings

    NARCIS (Netherlands)

    Voskoboynikov, O.; Wijers, Christianus M.J.; Liu, J.L.; Lee, C.P.

    2005-01-01

    In this paper a comparative theoretical study was made of the magneto-optical response of square lattices of nanoobjects (dots and rings). Expressions for both the polarizability of the individual objects as their mutual electromagnetic interactions (for a lattice in vacuum) was derived. The

  18. Forward-bias diode parameters, electronic noise, and photoresponse of graphene/silicon Schottky junctions with an interfacial native oxide layer

    Science.gov (United States)

    An, Yanbin; Behnam, Ashkan; Pop, Eric; Bosman, Gijs; Ural, Ant

    2015-09-01

    Metal-semiconductor Schottky junction devices composed of chemical vapor deposition grown monolayer graphene on p-type silicon substrates are fabricated and characterized. Important diode parameters, such as the Schottky barrier height, ideality factor, and series resistance, are extracted from forward bias current-voltage characteristics using a previously established method modified to take into account the interfacial native oxide layer present at the graphene/silicon junction. It is found that the ideality factor can be substantially increased by the presence of the interfacial oxide layer. Furthermore, low frequency noise of graphene/silicon Schottky junctions under both forward and reverse bias is characterized. The noise is found to be 1/f dominated and the shot noise contribution is found to be negligible. The dependence of the 1/f noise on the forward and reverse current is also investigated. Finally, the photoresponse of graphene/silicon Schottky junctions is studied. The devices exhibit a peak responsivity of around 0.13 A/W and an external quantum efficiency higher than 25%. From the photoresponse and noise measurements, the bandwidth is extracted to be ˜1 kHz and the normalized detectivity is calculated to be 1.2 ×109 cm Hz1/2 W-1. These results provide important insights for the future integration of graphene with silicon device technology.

  19. Effect of heat treatment on interfacial and mechanical properties of A6022/A7075/A6022 roll-bonded multi-layer Al alloy sheets

    Science.gov (United States)

    Cha, Joon-Hyeon; Kim, Su-Hyeon; Lee, Yun-Soo; Kim, Hyoung-Wook; Choi, Yoon Suk

    2016-09-01

    Multi-layered Al alloy sheets can exhibit unique properties by the combination of properties of component materials. A poor corrosion resistance of high strength Al alloys can be complemented by having a protective surface with corrosion resistant Al alloys. Here, a special care should be taken regarding the heat treatment of multi-layered Al alloy sheets because dissimilar Al alloys may exhibit unexpected interfacial reactions upon heat treatment. In the present study, A6022/A7075/A6022 sheets were fabricated by a cold roll-bonding process, and the effect of the heat treatment on the microstructure and mechanical properties was examined. The solution treatment gave rise to the diffusion of Zn, Mg, Cu and Si elements across the core/clad interface. In particular, the pronounced diffusion of Zn, which is a major alloying element (for solid-solution strengthening) of the A7075 core, resulted in a gradual hardness change across the core/clad interface. Mg2Si precipitates and the precipitate free zone were also formed near the interface after the heat treatment. The heat-treated sheet showed high strengths and reasonable elongation without apparent deformation misfit or interfacial delamination during the tensile deformation. The high strength of the sheet was mainly due to the T4 and T6 heat treatment of the A7075 core.

  20. Photoelectrochemical Characterization of Sprayed α-Fe2O3 Thin Films: Influence of Si Doping and SnO2 Interfacial Layer

    Directory of Open Access Journals (Sweden)

    Yongqi Liang

    2008-01-01

    Full Text Available α-Fe2O3 thin film photoanodes for solar water splitting were prepared by spray pyrolysis of Fe(AcAc3. The donor density in the Fe2O3 films could be tuned between 1017–1020 cm-3 by doping with silicon. By depositing a 5 nm SnO2 interfacial layer between the Fe2O3 films and the transparent conducting substrates, both the reproducibility and the photocurrent can be enhanced. The effects of Si doping and the presence of the SnO2 interfacial layer were systematically studied. The highest photoresponse is obtained for Fe2O3 doped with 0.2% Si, resulting in a photocurrent of 0.37 mA/cm2 at 1.23 VRHE in a 1.0 M KOH solution under 80 mW/cm2 AM1.5 illumination.

  1. Contribution to the study of low-energy X-ray-induced degradations on the oxide-silicon interfacial transition layer of MOS structures

    International Nuclear Information System (INIS)

    Boukabache, Ali

    1983-01-01

    The Si-SiO_2 interface is considered as a transition layer. Its thickness is typically about 10 A. It contains traps which exchange charges with silicon by a tunneling mechanism. Its influence on MOS capacitor, gate-controlled diode and MOS transistor is analyzed. Long channel MOST's (P-Substrate) are irradiated with low energy X-ray (between 0 and 240 Krads) in order to validate the model. Capacitance, recombination velocity and 1/f noise measurements indicate that the X- ray induce traps distributed in space and in energy. These traps provoke a decrease in mobility. Additionally, X-rays create a fixed oxide charge which induce a shift in the characteristics of MOS structures. Finally, under irradiation the behaviour of the gate-controlled diode and the MOS capacitor are in accordance with theoretical model of the interfacial layer. The overall noise behaviour cannot be explained by existing theoretical models. (author) [fr

  2. p-Type semiconducting nickel oxide as an efficiency-enhancing anodal interfacial layer in bulk heterojunction solar cells

    Science.gov (United States)

    Irwin, Michael D; Buchholz, Donald B; Marks, Tobin J; Chang, Robert P. H.

    2014-11-25

    The present invention, in one aspect, relates to a solar cell. In one embodiment, the solar cell includes an anode, a p-type semiconductor layer formed on the anode, and an active organic layer formed on the p-type semiconductor layer, where the active organic layer has an electron-donating organic material and an electron-accepting organic material.

  3. Physical and electrical characteristics of Si/SiC quantum dot superlattice solar cells with passivation layer of aluminum oxide.

    Science.gov (United States)

    Tsai, Yi-Chia; Li, Yiming; Samukawa, Seiji

    2017-12-01

    In this work, we numerically simulate the silicon (Si)/silicon carbide (SiC) quantum dot superlattice solar cell (SiC-QDSL) with aluminum oxide (Al 2 O 3 -QDSL) passivation. By exploiting the passivation layer of Al 2 O 3 , the high photocurrent and the conversion efficiency can be achieved without losing the effective bandgap. Based on the two-photon transition mechanism in an AM1.5 and a one sun illumination, the simulated short-circuit current (J sc ) of 4.77 mA cm -2 is very close to the experimentally measured 4.75 mA cm -2 , which is higher than those of conventional SiC-QDSLs. Moreover, the efficiency fluctuation caused by the structural variation is less sensitive by using the passivation layer. A high conversion efficiency of 17.4% is thus estimated by adopting the QD's geometry used in the experiment; and, it can be further boosted by applying a hexagonal QD formation with an inter-dot spacing of 0.3 nm.

  4. Physical and electrical characteristics of Si/SiC quantum dot superlattice solar cells with passivation layer of aluminum oxide

    Science.gov (United States)

    Tsai, Yi-Chia; Li, Yiming; Samukawa, Seiji

    2017-12-01

    In this work, we numerically simulate the silicon (Si)/silicon carbide (SiC) quantum dot superlattice solar cell (SiC-QDSL) with aluminum oxide (Al2O3-QDSL) passivation. By exploiting the passivation layer of Al2O3, the high photocurrent and the conversion efficiency can be achieved without losing the effective bandgap. Based on the two-photon transition mechanism in an AM1.5 and a one sun illumination, the simulated short-circuit current (J sc) of 4.77 mA cm-2 is very close to the experimentally measured 4.75 mA cm-2, which is higher than those of conventional SiC-QDSLs. Moreover, the efficiency fluctuation caused by the structural variation is less sensitive by using the passivation layer. A high conversion efficiency of 17.4% is thus estimated by adopting the QD’s geometry used in the experiment; and, it can be further boosted by applying a hexagonal QD formation with an inter-dot spacing of 0.3 nm.

  5. Mapping bound plasmon propagation on a nanoscale stripe waveguide using quantum dots: influence of spacer layer thickness

    Directory of Open Access Journals (Sweden)

    Chamanei S. Perera

    2015-10-01

    Full Text Available In this paper we image the highly confined long range plasmons of a nanoscale metal stripe waveguide using quantum emitters. Plasmons were excited using a highly focused 633 nm laser beam and a specially designed grating structure to provide stronger incoupling to the desired mode. A homogeneous thin layer of quantum dots was used to image the near field intensity of the propagating plasmons on the waveguide. We observed that the photoluminescence is quenched when the QD to metal surface distance is less than 10 nm. The optimised spacer layer thickness for the stripe waveguides was found to be around 20 nm. Authors believe that the findings of this paper prove beneficial for the development of plasmonic devices utilising stripe waveguides.

  6. All-inorganic quantum-dot light-emitting-diodes with vertical nickel oxide nanosheets as hole transport layer

    Directory of Open Access Journals (Sweden)

    Jiahui Li

    2016-10-01

    Full Text Available All-inorganic quantum dot light emitting diodes (QLEDs have gained great attention as a result of their high stability under oxygen-rich, humid and high current working conditions. In this work, we have fabricated an all-inorganic QLED device (FTO/NiO/QDs/AZO/Ag with sandwich-structure, wherein the inorganic metal oxides thin films of NiO and AZO were employed as hole and electron transport layers, respectively. The porous NiO layer with vertical lamellar nanosheets interconnected microstructure have been directly synthesized on the substrate of conductive FTO glass and increased the wettability of CdSe@ZnS QDs, which result in an enhancement of current transport performance of the QLED.

  7. Experiment on neutron transmission through depleted uranium layers and analysis with DOT 3.5 and MCNP

    International Nuclear Information System (INIS)

    Oka, Y.; Kodama, T.; Akiyama, M.; Hashikura, H.; Kondo, S.

    1987-01-01

    The reaction rates in the multi-layers containing depleted uranium were measured by activation foils and micro-fission chambers. The analysis of the experiment was carried out by using the multi-group transport calculation code, DOT 3.5 and the continuous energy Monte Carlo code, MCNP. The multi-group calculation overpredicted the low energy reaction rates in the DU layers, while the continuous energy calculation agreed well. The multi-group and continuous energy calculation was compared for the one-dimensional transmission of iron spheres. The results revealed overprediction of the multi-group calculation near the fast neutron source. The averaging of the resonance shapes in generating the multi-group cross sections made minima of the resonance valleys higher than that of the pointwise cross section. This increased the scattering of the neutrons inside and caused the overprediction of the multi-group calculation

  8. Recombination barrier layers in solid-state quantum dot-sensitized solar cells

    KAUST Repository

    Roelofs, Katherine E.; Brennan, Thomas P.; Dominguez, Juan C.; Bent, Stacey F.

    2012-01-01

    in situ by successive ion layer adsorption and reaction (SILAR). Aluminum oxide recombination barrier layers were deposited by atomic layer deposition (ALD) at the TiO2/hole-conductor interface. For low numbers of ALD cycles, the Al2O3 barrier layer

  9. First-Principles Investigations of the Working Mechanism of 2D h-BN as an Interfacial Layer for the Anode of Lithium Metal Batteries.

    Science.gov (United States)

    Shi, Le; Xu, Ao; Zhao, Tianshou

    2017-01-18

    An issue with the use of metallic lithium as an anode material for lithium-based batteries is dendrite growth, causing a periodic breaking and repair of the solid electrolyte interphase (SEI) layer. Adding 2D atomic crystals, such as h-BN, as an interfacial layer between the lithium metal anode and liquid electrolyte has been demonstrated to be effective to mitigate dendrite growth, thereby enhancing the Columbic efficiency of lithium metal batteries. But the underlying mechanism leading to the reduced dendrite growth remains unknown. In this work, with the aid of first-principle calculations, we find that the interaction between the h-BN and lithium metal layers is a weak van der Waals force, and two atomic layers of h-BN are thick enough to block the electron tunneling from lithium metal to electrolyte, thus prohibiting the decomposition of electrolyte. The interlayer spacing between the h-BN and lithium metal layers can provide larger adsorption energies toward lithium atoms than that provided by bare lithium or h-BN, making lithium atoms prefer to intercalate under the cover of h-BN during the plating process. The combined high stiffness of h-BN and the low diffusion energy barriers of lithium at the Li/h-BN interfaces induce a uniform distribution of lithium under h-BN, therefore effectively suppressing dendrite growth.

  10. Role of organically modified layered silicate both as an active interfacial modifier and nanofiller for immiscible polymer blends.

    CSIR Research Space (South Africa)

    Ray, SS

    2007-05-01

    Full Text Available ) revealed efficient mixing of the polymers in the presence of organically modified layered silicate. X-ray diffraction (XRD) patterns and transmission electron microscopic (TEM) observations showed that silicate layers were either intercalated or exfoliated...

  11. Probing and Manipulating the Interfacial Defects of InGaAs Dual-Layer Metal Oxides at the Atomic Scale.

    Science.gov (United States)

    Wu, Xing; Luo, Chen; Hao, Peng; Sun, Tao; Wang, Runsheng; Wang, Chaolun; Hu, Zhigao; Li, Yawei; Zhang, Jian; Bersuker, Gennadi; Sun, Litao; Pey, Kinleong

    2018-01-01

    The interface between III-V and metal-oxide-semiconductor materials plays a central role in the operation of high-speed electronic devices, such as transistors and light-emitting diodes. The high-speed property gives the light-emitting diodes a high response speed and low dark current, and they are widely used in communications, infrared remote sensing, optical detection, and other fields. The rational design of high-performance devices requires a detailed understanding of the electronic structure at this interface; however, this understanding remains a challenge, given the complex nature of surface interactions and the dynamic relationship between the morphology evolution and electronic structures. Herein, in situ transmission electron microscopy is used to probe and manipulate the structural and electrical properties of ZrO 2 films on Al 2 O 3 and InGaAs substrate at the atomic scale. Interfacial defects resulting from the spillover of the oxygen-atom conduction-band wavefunctions are resolved. This study unearths the fundamental defect-driven interfacial electric structure of III-V semiconductor materials and paves the way to future high-speed and high-reliability devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

    Directory of Open Access Journals (Sweden)

    Peng Xia

    2017-11-01

    Full Text Available A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF state to low resistance (ON state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

  13. Rational design of a bi-layered reduced graphene oxide film on polystyrene foam for solar-driven interfacial water evaporation

    KAUST Repository

    Shi, Le

    2016-12-20

    Solar-driven water evaporation has been emerging as a highly efficient way for utilizing solar energy for clean water production and wastewater treatment. Here we rationally designed and fabricated a bi-layered photothermal membrane with a porous film of reduced graphene oxide (rGO) on the top and polystyrene (PS) foam at the bottom. The top porous rGO layer acts as a light absorber to harvest and convert light efficiently to thermal energy and the bottom PS layer, which purposefully disintegrates water transport channels, acts as an excellent thermal barrier to minimize heat transfer to the nonevaporative bulk water. The optimized bi-layered membrane was able to produce water evaporation rate as high as 1.31 kg m−2 h−1 with light to evaporation conversion efficiency as high as 83%, which makes it a promising photothermal material in the literature. Furthermore, the experiments and theoretical simulation were both conducted to examine the relationship between the overall energy efficiency and the depth of the photothermal material underwater and the experimental and simulations results coincided with each other. Therefore, this work provides systematic evidence in support of the concept of the interfacial heating and shines important light on practical applications of solar-driven processes for clean water production.

  14. Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

    Science.gov (United States)

    Xia, Peng; Li, Luman; Wang, Pengfei; Gan, Ying; Xu, Wei

    2017-11-01

    A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

  15. Two-Step Physical Deposition of a Compact CuI Hole-Transport Layer and the Formation of an Interfacial Species in Perovskite Solar Cells.

    Science.gov (United States)

    Gharibzadeh, Saba; Nejand, Bahram Abdollahi; Moshaii, Ahmad; Mohammadian, Nasim; Alizadeh, Amir Hossein; Mohammadpour, Rahele; Ahmadi, Vahid; Alizadeh, Abdolali

    2016-08-09

    A simple and practical approach is introduced for the deposition of CuI as an inexpensive inorganic hole-transport material (HTM) for the fabrication of low cost perovskite solar cells (PSCs) by gas-solid phase transformation of Cu to CuI. The method provides a uniform and well-controlled CuI layer with large grains and good compactness that prevents the direct connection between the contact electrodes. Solar cells prepared with CuI as the HTM with Au electrodes displays an exceptionally high short-circuit current density of 32 mA cm(-2) , owing to an interfacial species formed between the perovskite and the Cu resulting in a long wavelength contribution to the incident photon-to-electron conversion efficiency (IPCE), and an overall power conversion efficiency (PCE) of 7.4 %. The growth of crystalline and uniform CuI on a low roughness perovskite layer leads to remarkably high charge extraction in the cells, which originates from the high hole mobility of CuI in addition to a large number of contact points between CuI and the perovskite layer. In addition, the solvent-free method has no damaging side effect on the perovskite layer, which makes it an appropriate method for large scale applications of CuI in perovskite solar cells. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Design and implementation of an efficient single layer five input majority voter gate in quantum-dot cellular automata.

    Science.gov (United States)

    Bahar, Ali Newaz; Waheed, Sajjad

    2016-01-01

    The fundamental logical element of a quantum-dot cellular automata (QCA) circuit is majority voter gate (MV). The efficiency of a QCA circuit is depends on the efficiency of the MV. This paper presents an efficient single layer five-input majority voter gate (MV5). The structure of proposed MV5 is very simple and easy to implement in any logical circuit. This proposed MV5 reduce number of cells and use conventional QCA cells. However, using MV5 a multilayer 1-bit full-adder (FA) is designed. The functional accuracy of the proposed MV5 and FA are confirmed by QCADesigner a well-known QCA layout design and verification tools. Furthermore, the power dissipation of proposed circuits are estimated, which shows that those circuits dissipate extremely small amount of energy and suitable for reversible computing. The simulation outcomes demonstrate the superiority of the proposed circuit.

  17. Confinement of carbon dots localizing to the ultrathin layered double hydroxides toward simultaneous triple-mode bioimaging and photothermal therapy.

    Science.gov (United States)

    Weng, Yangziwan; Guan, Shanyue; Lu, Heng; Meng, Xiangmin; Kaassis, Abdessamad Y; Ren, Xiaoxue; Qu, Xiaozhong; Sun, Chenghua; Xie, Zheng; Zhou, Shuyun

    2018-07-01

    It is a great challenge to develop multifunctional nanocarriers for cancer diagnosis and therapy. Herein, versatile CDs/ICG-uLDHs nanovehicles for triple-modal fluorescence/photoacoustic/two-photon bioimaging and effective photothermal therapy were prepared via a facile self-assembly of red emission carbon dots (CDs), indocyanine green (ICG) with the ultrathin layered double hydroxides (uLDHs). Due to the J-aggregates of ICG constructed in the self-assembly process, CDs/ICG-uLDHs was able to stabilize the photothermal agent ICG and enhanced its photothermal efficiency. Furthermore, the unique confinement effect of uLDHs has extended the fluorescence lifetime of CDs in favor of bioimaging. Considering the excellent in vitro and in vivo phototherapeutics and multimodal imaging effects, this work provides a promising platform for the construction of multifunctional theranostic nanocarrier system for the cancer treatment. Copyright © 2018 Elsevier B.V. All rights reserved.

  18. Broadband light sources using InAs quantum dots with InGaAs strain-reducing layers

    Energy Technology Data Exchange (ETDEWEB)

    Tsuda, Megumi; Inoue, Tomoya; Kita, Takashi; Wada, Osamu [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2011-02-15

    We fabricated broadband superluminescent diodes (SLDs) for optical coherence tomography (OCT). We used three kinds of quantum dot (QD) layers with different emission peak wavelengths in the active region of SLD. The emission wavelength was controlled by reducing the strain in QDs; by using the In{sub 0.1}Ga{sub 0.9} As strain-reducing layer, the peak wavelength shifted toward the longer-wavelength side, and the photoluminescence peak intensity becomes strong in contrast to QDs on GaAs. By stacking these strain-controlled QD layers, the SLD device shows a broad electroluminescence spectrum with the center wavelength of 1130 nm and the spectral linewidth of approximately 240 nm at the injection of 1A caused by the increased emission intensity from the excited states. This corresponds to an resolution of 2.3 {mu}m in OCT. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Highly efficient inverted organic light emitting diodes by inserting a zinc oxide/polyethyleneimine (ZnO:PEI) nano-composite interfacial layer

    Science.gov (United States)

    Kaçar, Rifat; Pıravadılı Mucur, Selin; Yıldız, Fikret; Dabak, Salih; Tekin, Emine

    2017-06-01

    The electrode/organic interface is one of the key factors in attaining superior device performance in organic electronics, and inserting a tailor-made layer can dramatically modify its properties. The use of nano-composite (NC) materials leads to many advantages by combining materials with the objective of obtaining a desirable combination of properties. In this context, zinc oxide/polyethyleneimine (ZnO:PEI) NC film was incorporated as an interfacial layer into inverted bottom-emission organic light emitting diodes (IBOLEDs) and fully optimized. For orange-red emissive MEH-PPV based IBOLEDs, a high power efficiency of 6.1 lm W-1 at a luminance of 1000 cd m-2 has been achieved. Notably, the external quantum efficiency (EQE) increased from 0.1 to 4.8% and the current efficiency (CE) increased from 0.2 to 8.7 cd A-1 with rise in luminance (L) from 1000 to above 10 000 cd m-2 levels when compared to that of pristine ZnO-based devices. An identical device architecture containing a ZnO:PEI NC layer has also been used to successfully fabricate green and blue emissive IBOLEDs. The significant enhancement in the inverted device performance, in terms of luminance and efficiency, is attributed to a good energy-level alignment between the cathode/organic interface which leads to effective carrier balance, resulting in efficient radiative-recombination.

  20. Effect of surface pretreatment on interfacial chemical bonding states of atomic layer deposited ZrO2 on AlGaN

    International Nuclear Information System (INIS)

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Ng, Serene Lay Geok; Ji, Rong; Liu, Zhi Hong

    2015-01-01

    Atomic layer deposition (ALD) of ZrO 2 on native oxide covered (untreated) and buffered oxide etchant (BOE) treated AlGaN surface was analyzed by utilizing x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy. Evidenced by Ga–O and Al–O chemical bonds by XPS, parasitic oxidation during deposition is largely enhanced on BOE treated AlGaN surface. Due to the high reactivity of Al atoms, more prominent oxidation of Al atoms is observed, which leads to thicker interfacial layer formed on BOE treated surface. The results suggest that native oxide on AlGaN surface may serve as a protecting layer to inhibit the surface from further parasitic oxidation during ALD. The findings provide important process guidelines for the use of ALD ZrO 2 and its pre-ALD surface treatments for high-k AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors and other related device applications

  1. MgO-hybridized TiO{sub 2} interfacial layers assisting efficiency enhancement of solid-state dye-sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Sakai, Nobuya; Ikegami, Masashi; Miyasaka, Tsutomu, E-mail: miyasaka@toin.ac.jp [Graduate School of Engineering, Toin University of Yokohama, 1614 Kurogane-cho, Aoba, Yokohama, Kanagawa 225-8502 (Japan)

    2014-02-10

    Interfacial modification of a thin TiO{sub 2} compact layer (T-CL) by hybridization with MgO enhanced the quantum conversion efficiency of solid-state dye-sensitized solar cells (ssDSSCs) comprising a multilayer structure of transparent electrode/T-CL/dye-sensitized mesoporous TiO{sub 2}/hole conductor/metal counter electrode. The Mg(CH{sub 3}COO){sub 2} treatment was employed to introduce a MgO-TiO{sub 2} CL (T/M-CL), which enhanced the physical connection and conduction between the CL and mesoporous semiconductor layer as a consecutive interface, owing to the dehydration reaction of Mg(CH{sub 3}COO){sub 2}. The photocurrent density of ssDSSC was increased 33% by the T/M-CL compared with the T-CL, using an equivalent amount of adsorbed dye. The ssDSSC with the T/M-CL yielded the highest efficiency of 4.02% under irradiation at 100 mW cm{sup −2}. The electrical impedance spectroscopy showed that the charge-transfer resistance (R{sub ct}) of the photoelectrode with T/M-CL was reduced by 300 Ω from the reference non-treated T-CL electrode. Characterized by the intrinsically low R{sub ct} of the compact layer, the T/M-CL is capable of improving the photovoltaic performance of solid-state sensitized mesoscopic solar cells.

  2. Nanocrystalline-Si-dot multi-layers fabrication by chemical vapor deposition with H-plasma surface treatment and evaluation of structure and quantum confinement effects

    Directory of Open Access Journals (Sweden)

    Daisuke Kosemura

    2014-01-01

    Full Text Available 100-nm-thick nanocrystalline silicon (nano-Si-dot multi-layers on a Si substrate were fabricated by the sequential repetition of H-plasma surface treatment, chemical vapor deposition, and surface oxidation, for over 120 times. The diameter of the nano-Si dots was 5–6 nm, as confirmed by both the transmission electron microscopy and X-ray diffraction analysis. The annealing process was important to improve the crystallinity of the nano-Si dot. We investigated quantum confinement effects by Raman spectroscopy and photoluminescence (PL measurements. Based on the experimental results, we simulated the Raman spectrum using a phenomenological model. Consequently, the strain induced in the nano-Si dots was estimated by comparing the experimental and simulated results. Taking the estimated strain value into consideration, the band gap modulation was measured, and the diameter of the nano-Si dots was calculated to be 5.6 nm by using PL. The relaxation of the q ∼ 0 selection rule model for the nano-Si dots is believed to be important to explain both the phenomena of peak broadening on the low-wavenumber side observed in Raman spectra and the blue shift observed in PL measurements.

  3. Sandwich-like singled-walled titania nanotube as a novel semiconductor electrode for quantum dot-sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Cunku; Li, Xin; Fan, Xiujuan [Department of Chemistry, Harbin Institute of Technology, Harbin 150090 (China); Qi, Jingyao [School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090 (China)

    2012-06-15

    A novel sandwich-like singled-walled titania nanotube is designed as a photoanode in quantum dot-sensitized solar cells. It acts as a hollow coaxial nanocable, in which the injected electron is confined in the conducting layer for transport, guarded from electron recombination by the protective layers. An ultrafast interfacial electron transfer is also expected in this photoelectric system due to the unique nanoarchitecture. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Effects of the thickness of NiO hole transport layer on the performance of all-inorganic quantum dot light emitting diode

    International Nuclear Information System (INIS)

    Zhang, Xiao Li; Dai, Hai Tao; Zhao, Jun Liang; Li, Chen; Wang, Shu Guo; Sun, Xiao Wei

    2014-01-01

    All-inorganic quantum dot light emitting diodes (QLEDs) have recently gained great attention owing to their high stability under oxygenic, humid environment and higher operating currents. In this work, we fabricated all-inorganic CdSe/ZnS core-shell QLEDs composed of ITO/NiO/QDs/ZnO/Al, in which NiO and ZnO thin film deposited via all-solution method were employed as hole and electron transport layer, respectively. To achieve high light emitting efficiency, the balance transport between electrons and holes play a key role. In this work, the effects of the thickness of NiO film on the performance of QLEDs were explored experimentally in details. NiO layers with various thicknesses were prepared with different rotation speeds. Experimental results showed that thinner NiO layer deposited at higher rotation speed had higher transmittance and larger band gap. Four typical NiO thickness based QLEDs were fabricated to optimize the hole transport layer. Thinner NiO layer based device performs bright emission with high current injection, which is ascribed to the reduced barrier height between hole transport layer and quantum dot. - Highlights: • All-inorganic quantum dot light emitting diodes (QLEDs) were fabricated. • Thinner NiO film can effectively enhance on–off properties of devices. • Improved performance of QLEDs is mainly attributed to energy barrier reduction

  5. Hydrothermal growth of double-layer TiO{sub 2} nanostructure film for quantum dot sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Feng Shuanglong; Yang Junyou, E-mail: jyyang@mail.hust.edu.cn; Liu Ming; Zhu Hu; Zhang Jiansheng; Li Gen; Peng Jiangying; Liu Qiongzhen

    2012-01-31

    A double-layer (DL) film with a TiO{sub 2} nanosheet-layer on a layer of TiO{sub 2} nanorod-array, was synthesized on a transparent conductive fluorine-doped tin oxide substrate by a two-step hydrothermal method. Starting from the precursors of NaSeSO{sub 3}, CdSO{sub 4} and the complex of N(CH{sub 2}COOK){sub 3}, CdSe quantum dots (QDs) were grown on the DL-TiO{sub 2} substrate by chemical bath deposition method. The samples were characterized by X-ray diffraction, Scanning electron microscopy, Energy dispersion spectroscopy, and their optical scattering property was measured by light reflection spectrometry. Some CdSe QDs sensitized DL-TiO{sub 2} films serve as the photoanodes, were assembled into solar cell devices and their photovoltaic performance were also characterized. The short circuit current and open-circuit voltage of the solar cells range from 0.75 to 4.05 mA/cm{sup 2} and 0.20 - 0.42 V under the illumination of one sun (AM1.5, 100 mW/cm{sup 2}), respectively. The photocurrent density of the DL-TiO{sub 2} film is five times higher than that of a bare TiO{sub 2} nanorod array photoelectrode cell. - Highlights: Black-Right-Pointing-Pointer A two-step hydrothermal deposition method was used to deposit TiO{sub 2} films. Black-Right-Pointing-Pointer Double-layer TiO{sub 2} films were synthesized on transparent FTO substrate. Black-Right-Pointing-Pointer The bi-functional character of the electrode were confirmed. Black-Right-Pointing-Pointer Photocurrent density of DL-film electrode was enhanced 5 times than a single film.

  6. Interfacial charge separation and recombination in InP and quasi-type II InP/CdS core/shell quantum dot-molecular acceptor complexes.

    Science.gov (United States)

    Wu, Kaifeng; Song, Nianhui; Liu, Zheng; Zhu, Haiming; Rodríguez-Córdoba, William; Lian, Tianquan

    2013-08-15

    Recent studies of group II-VI colloidal semiconductor heterostuctures, such as CdSe/CdS core/shell quantum dots (QDs) or dot-in-rod nanorods, show that type II and quasi-type II band alignment can facilitate electron transfer and slow down charge recombination in QD-molecular electron acceptor complexes. To explore the general applicability of this wave function engineering approach for controlling charge transfer properties, we investigate exciton relaxation and dissociation dynamics in InP (a group III-V semiconductor) and InP/CdS core/shell (a heterostructure beween group III-V and II-VI semiconductors) QDs by transient absorption spectroscopy. We show that InP/CdS QDs exhibit a quasi-type II band alignment with the 1S electron delocalized throughout the core and shell and the 1S hole confined in the InP core. In InP-methylviologen (MV(2+)) complexes, excitons in the QD can be dissociated by ultrafast electron transfer to MV(2+) from the 1S electron level (with an average time constant of 11.4 ps) as well as 1P and higher electron levels (with a time constant of 0.39 ps), which is followed by charge recombination to regenerate the complex in its ground state (with an average time constant of 47.1 ns). In comparison, InP/CdS-MV(2+) complexes show similar ultrafast charge separation and 5-fold slower charge recombination rates, consistent with the quasi-type II band alignment in these heterostructures. This result demonstrates that wave function engineering in nanoheterostructures of group III-V and II-VI semiconductors provides a promising approach for optimizing their light harvesting and charge separation for solar energy conversion applications.

  7. Interfacial reactions between titanium and borate glass

    Energy Technology Data Exchange (ETDEWEB)

    Brow, R.K. [Sandia National Labs., Albuquerque, NM (United States); Saha, S.K.; Goldstein, J.I. [Lehigh Univ., Bethlehem, PA (United States). Dept. of Materials Science

    1992-12-31

    Interfacial reactions between melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8--120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.

  8. Molecular Doping of the Hole-Transporting Layer for Efficient, Single-Step Deposited Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Kirmani, Ahmad R.

    2017-07-31

    Employment of thin perovskite shells and metal halides as surface-passivants for colloidal quantum dots (CQDs) have been important, recent developments in CQD optoelectronics. These have opened the route to single-step deposited high-performing CQD solar cells. These promising architectures employ a QD hole-transporting layer (HTL) whose intrinsically shallow Fermi level (EF) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a generalized approach to effectively balance band-edge energy levels of the main CQD absorber and charge-transport layer for these high-performance solar cells. Briefly soaking the QD HTL in a solution of the metal-organic p-dopant, molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), effectively deepens its Fermi level, resulting in enhanced band bending at the HTL:absorber junction. This blocks the back-flow of photo-generated electrons, leading to enhanced photocurrent and fill factor compared to undoped devices. We demonstrate 9.0% perovskite-shelled and 9.5% metal-halide-passivated CQD solar cells, both achieving ca. 10% relative enhancements over undoped baselines.

  9. Single step deposition of an interacting layer of a perovskite matrix with embedded quantum dots

    Science.gov (United States)

    Ngo, Thi Tuyen; Suarez, Isaac; Sanchez, Rafael S.; Martinez-Pastor, Juan P.; Mora-Sero, Ivan

    2016-07-01

    Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ~1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells.Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and

  10. Interfacial characterization of ceramic core materials with veneering porcelain for all-ceramic bi-layered restorative systems.

    Science.gov (United States)

    Tagmatarchis, Alexander; Tripodakis, Aris-Petros; Filippatos, Gerasimos; Zinelis, Spiros; Eliades, George

    2014-01-01

    The aim of the study was to characterize the elemental distribution at the interface between all-ceramic core and veneering porcelain materials. Three groups of all-ceramic cores were selected: A) Glass-ceramics (Cergo, IPS Empress, IPS Empress 2, e-max Press, Finesse); B) Glass-infiltrated ceramics (Celay Alumina, Celay Zirconia) and C) Densely sintered ceramics (Cercon, Procera Alumina, ZirCAD, Noritake Zirconia). The cores were combined with compatible veneering porcelains and three flat square test specimens were produced for each system. The core-veneer interfaces were examined by scanning electron microscopy and energy dispersive x-ray microanalysis. The glass-ceramic systems showed interfacial zones reach in Si and O, with the presence of K, Ca, Al in core and Ca, Ce, Na, Mg or Al in veneer material, depending on the system tested. IPS Empress and IPS Empress 2 demonstrated distinct transitional phases at the core-veneer interface. In the glassinfiltrated systems, intermixing of core (Ce, La) with veneer (Na, Si) elements occurred, whereas an abrupt drop of the core-veneer elemental concentration was documented at the interfaces of all densely sintered ceramics. The results of the study provided no evidence of elemental interdiffusion at the core-veneer interfaces in densely sintered ceramics, which implies lack of primary chemical bonding. For the glass-containing systems (glassceramics and glass-infiltrated ceramics) interdiffusion of the glass-phase seems to play a critical role in establishing a primary bonding condition between ceramic core and veneering porcelain.

  11. A Strategy to Enhance the Efficiency of Quantum Dot-Sensitized Solar Cells by Decreasing Electron Recombination with Polyoxometalate/TiO2 as the Electronic Interface Layer.

    Science.gov (United States)

    Chen, Li; Chen, Weilin; Li, Jianping; Wang, Jiabo; Wang, Enbo

    2017-07-21

    Electron recombination occurring at the TiO 2 /quantum dot sensitizer/electrolyte interface is the key reason for hindering further efficiency improvements to quantum dot sensitized solar cells (QDSCs). Polyoxometalate (POM) can act as an electron-transfer medium to decrease electron recombination in a photoelectric device owing to its excellent oxidation/reduction properties and thermostability. A POM/TiO 2 electronic interface layer prepared by a simple layer-by-layer self-assembly method was added between fluorine-doped tin oxide (FTO) and mesoporous TiO 2 in the photoanode of QDSCs, and the effect on the photovoltaic performance was systematically investigated. Photovoltaic experimental results and the electron transmission mechanism show that the POM/TiO 2 electronic interface layer in the QDSCs can clearly suppress electron recombination, increase the electron lifetime, and result in smoother electron transmission. In summary, the best conversion efficiency of QDSCs with POM/TiO 2 electronic interface layers increases to 8.02 %, which is an improvement of 25.1 % compared with QDSCs without POM/TiO 2 . This work first builds an electron-transfer bridge between FTO and the quantum dot sensitizer and paves the way for further improved efficiency of QDSCs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Photojunction Field-Effect Transistor Based on a Colloidal Quantum Dot Absorber Channel Layer

    KAUST Repository

    Adinolfi, Valerio

    2015-01-27

    © 2015 American Chemical Society. The performance of photodetectors is judged via high responsivity, fast speed of response, and low background current. Many previously reported photodetectors based on size-tuned colloidal quantum dots (CQDs) have relied either on photodiodes, which, since they are primary photocarrier devices, lack gain; or photoconductors, which provide gain but at the expense of slow response (due to delayed charge carrier escape from sensitizing centers) and an inherent dark current vs responsivity trade-off. Here we report a photojunction field-effect transistor (photoJFET), which provides gain while breaking prior photoconductors\\' response/speed/dark current trade-off. This is achieved by ensuring that, in the dark, the channel is fully depleted due to a rectifying junction between a deep-work-function transparent conductive top contact (MoO3) and a moderately n-type CQD film (iodine treated PbS CQDs). We characterize the rectifying behavior of the junction and the linearity of the channel characteristics under illumination, and we observe a 10 μs rise time, a record for a gain-providing, low-dark-current CQD photodetector. We prove, using an analytical model validated using experimental measurements, that for a given response time the device provides a two-orders-of-magnitude improvement in photocurrent-to-dark-current ratio compared to photoconductors. The photoJFET, which relies on a junction gate-effect, enriches the growing family of CQD photosensitive transistors.

  13. Lg = 100 nm In0.7Ga0.3As quantum well metal-oxide semiconductor field-effect transistors with atomic layer deposited beryllium oxide as interfacial layer

    International Nuclear Information System (INIS)

    Koh, D.; Kwon, H. M.; Kim, T.-W.; Veksler, D.; Gilmer, D.; Kirsch, P. D.; Kim, D.-H.; Hudnall, Todd W.; Bielawski, Christopher W.; Maszara, W.; Banerjee, S. K.

    2014-01-01

    In this study, we have fabricated nanometer-scale channel length quantum-well (QW) metal-oxide-semiconductor field effect transistors (MOSFETs) incorporating beryllium oxide (BeO) as an interfacial layer. BeO has high thermal stability, excellent electrical insulating characteristics, and a large band-gap, which make it an attractive candidate for use as a gate dielectric in making MOSFETs. BeO can also act as a good diffusion barrier to oxygen owing to its small atomic bonding length. In this work, we have fabricated In 0.53 Ga 0.47 As MOS capacitors with BeO and Al 2 O 3 and compared their electrical characteristics. As interface passivation layer, BeO/HfO 2 bilayer gate stack presented effective oxide thickness less 1 nm. Furthermore, we have demonstrated In 0.7 Ga 0.3 As QW MOSFETs with a BeO/HfO 2 dielectric, showing a sub-threshold slope of 100 mV/dec, and a transconductance (g m,max ) of 1.1 mS/μm, while displaying low values of gate leakage current. These results highlight the potential of atomic layer deposited BeO for use as a gate dielectric or interface passivation layer for III–V MOSFETs at the 7 nm technology node and/or beyond

  14. Thin-layer scanner with a dot printer recorder for radiolabelled compounds

    International Nuclear Information System (INIS)

    Kralova, M.; Kysela, F.; Hradil, Z.

    1982-01-01

    A scanner combined with a matrix printer is described for automatic evaluation of thin-layer radiochromatographs of soft beta emitters such as 3 H, 14 C, and 32 P. Details of the device including block schemes and electrical schemes are given

  15. Efficiency enhancement in a single emission layer yellow organic light emitting device: Contribution of CIS/ZnS quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Demir, Nuriye; Oner, Ilker; Varlikli, Canan, E-mail: canan.varlikli@ege.edu.tr; Ozsoy, Cihan; Zafer, Ceylan

    2015-08-31

    Electroluminescence (EL) efficiency from a single emission layer solution processed yellow emitting polymer, i.e. poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,10,3}-thiadiazole)] end-capped with dimethylphenyl (ADS233YE), is firstly enhanced by the optimization of stock polymer concentrations and the coating rates, and then with the addition of copper indium disulfide/zinc sulfide (CIS/ZnS) core/shell quantum dots (QDs). Using these bare core/shell QDs as the active layer in the studied device gave no EL at all. However, yellow EL with the maximum brightness of 56834 cd/m{sup 2}, maximum current efficiency of 4.7 cd/A and maximum power efficiency of 2.3 lm/W is obtained from the device structure of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/ADS233YE:0.4 wt.% CIS/ZnS QD/Ca/Al those of which correspond to approximately 4 and 2 folds of enhancements in the brightness and luminous and power efficiency values, respectively, compared to that of the device without CIS/ZnS. - Highlights: • Copper indium disulfide/zinc sulfide (CIS/ZnS) particles are synthesized. • Polymer light emitting diode performance of a yellow emitting polymer is enhanced. • The presence of CIS/ZnS in active layer enhanced the power efficiency two folds. • Optimum concentration of CIS/ZnS in polymer is 0.4 wt.%.

  16. Efficiency enhancement in a single emission layer yellow organic light emitting device: Contribution of CIS/ZnS quantum dot

    International Nuclear Information System (INIS)

    Demir, Nuriye; Oner, Ilker; Varlikli, Canan; Ozsoy, Cihan; Zafer, Ceylan

    2015-01-01

    Electroluminescence (EL) efficiency from a single emission layer solution processed yellow emitting polymer, i.e. poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,10,3}-thiadiazole)] end-capped with dimethylphenyl (ADS233YE), is firstly enhanced by the optimization of stock polymer concentrations and the coating rates, and then with the addition of copper indium disulfide/zinc sulfide (CIS/ZnS) core/shell quantum dots (QDs). Using these bare core/shell QDs as the active layer in the studied device gave no EL at all. However, yellow EL with the maximum brightness of 56834 cd/m 2 , maximum current efficiency of 4.7 cd/A and maximum power efficiency of 2.3 lm/W is obtained from the device structure of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/ADS233YE:0.4 wt.% CIS/ZnS QD/Ca/Al those of which correspond to approximately 4 and 2 folds of enhancements in the brightness and luminous and power efficiency values, respectively, compared to that of the device without CIS/ZnS. - Highlights: • Copper indium disulfide/zinc sulfide (CIS/ZnS) particles are synthesized. • Polymer light emitting diode performance of a yellow emitting polymer is enhanced. • The presence of CIS/ZnS in active layer enhanced the power efficiency two folds. • Optimum concentration of CIS/ZnS in polymer is 0.4 wt.%

  17. Multifunctional Organic-Semiconductor Interfacial Layers for Solution-Processed Oxide-Semiconductor Thin-Film Transistor.

    Science.gov (United States)

    Kwon, Guhyun; Kim, Keetae; Choi, Byung Doo; Roh, Jeongkyun; Lee, Changhee; Noh, Yong-Young; Seo, SungYong; Kim, Myung-Gil; Kim, Choongik

    2017-06-01

    The stabilization and control of the electrical properties in solution-processed amorphous-oxide semiconductors (AOSs) is crucial for the realization of cost-effective, high-performance, large-area electronics. In particular, impurity diffusion, electrical instability, and the lack of a general substitutional doping strategy for the active layer hinder the industrial implementation of copper electrodes and the fine tuning of the electrical parameters of AOS-based thin-film transistors (TFTs). In this study, the authors employ a multifunctional organic-semiconductor (OSC) interlayer as a solution-processed thin-film passivation layer and a charge-transfer dopant. As an electrically active impurity blocking layer, the OSC interlayer enhances the electrical stability of AOS TFTs by suppressing the adsorption of environmental gas species and copper-ion diffusion. Moreover, charge transfer between the organic interlayer and the AOS allows the fine tuning of the electrical properties and the passivation of the electrical defects in the AOS TFTs. The development of a multifunctional solution-processed organic interlayer enables the production of low-cost, high-performance oxide semiconductor-based circuits. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Analysis of photonic band gaps in two-dimensional photonic crystals with rods covered by a thin interfacial layer

    International Nuclear Information System (INIS)

    Trifonov, T.; Marsal, L.F.; Pallares, J.; Rodriguez, A.; Alcubilla, R.

    2004-01-01

    We investigate different aspects of the absolute photonic band gap (PBG) formation in two-dimensional photonic structures consisting of rods covered with a thin dielectric film. Specifically, triangular and honeycomb lattices in both complementary arrangements, i.e., air rods drilled in silicon matrix and silicon rods in air, are studied. We consider that the rods are formed of a dielectric core (silicon or air) surrounded by a cladding layer of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or germanium (Ge). Such photonic lattices present absolute photonic band gaps, and we study the evolution of these gaps as functions of the cladding material and thickness. Our results show that in the case of air rods in dielectric media the existence of dielectric cladding reduces the absolute gap width and may cause complete closure of the gap if thick layers are considered. For the case of dielectric rods in air, however, the existence of a cladding layer can be advantageous and larger absolute PBG's can be achieved

  19. Interfacial forces in aqueous media

    CERN Document Server

    van Oss, Carel J

    2006-01-01

    Thoroughly revised and reorganized, the second edition of Interfacial Forces in Aqueous Media examines the role of polar interfacial and noncovalent interactions among biological and nonbiological macromolecules as well as biopolymers, particles, surfaces, cells, and both polar and apolar polymers. The book encompasses Lifshitz-van der Waals and electrical double layer interactions, as well as Lewis acid-base interactions between colloidal entities in polar liquids such as water. New in this Edition: Four previously unpublished chapters comprising a new section on interfacial propertie

  20. Highest-order optical phonon-mediated relaxation in CdTe/ZnTe quantum dots

    International Nuclear Information System (INIS)

    Masumoto, Yasuaki; Nomura, Mitsuhiro; Okuno, Tsuyoshi; Terai, Yoshikazu; Kuroda, Shinji; Takita, K.

    2003-01-01

    The highest 19th-order longitudinal optical (LO) phonon-mediated relaxation was observed in photoluminescence excitation spectra of CdTe self-assembled quantum dots grown in ZnTe. Hot excitons photoexcited highly in the ZnTe barrier layer are relaxed into the wetting-layer state by emitting multiple LO phonons of the barrier layer successively. Below the wetting-layer state, the LO phonons involved in the relaxation are transformed to those of interfacial Zn x Cd 1-x Te surrounding CdTe quantum dots. The ZnTe-like and CdTe-like LO phonons of Zn x Cd 1-x Te and lastly acoustic phonons are emitted in the relaxation into the CdTe dots. The observed main relaxation is the fast relaxation directly into CdTe quantum dots and is not the relaxation through either the wetting-layer quantum well or the band bottom of the ZnTe barrier layer. This observation shows very efficient optical phonon-mediated relaxation of hot excitons excited highly in the ZnTe conduction band through not only the ZnTe extended state but also localized state in the CdTe quantum dots reflecting strong exciton-LO phonon interaction of telluride compounds

  1. Development of n-ZnO/p-Si single heterojunction solar cell with and without interfacial layer

    Science.gov (United States)

    Hussain, Babar

    The conversion efficiency of conventional silicon (Si) photovoltaic cells has not been improved significantly during last two decades but their cost decreased dramatically during this time. However, the higher price-per-watt of solar cells is still the main bottleneck in their widespread use for power generation. Therefore, new materials need to be explored for the fabrication of solar cells potentially with lower cost and higher efficiency. The n-type zinc oxide (n-ZnO) and p-type Si (p-Si) based single heterojunction solar cell (SHJSC) is one of the several attempts to replace conventional Si single homojunction solar cell technology. There are three inadequacies in the literature related to n-ZnO/p-Si SHJSC: (1) a detailed theoretical analysis to evaluate potential of the solar cell structure, (2) inconsistencies in the reported value of open circuit voltage (VOC) of the solar cell, and (3) lower value of experimentally achieved VOC as compared to theoretical prediction based on band-bending between n-ZnO and p-Si. Furthermore, the scientific community lacks consensus on the optimum growth parameters of ZnO. In this dissertation, I present simulation and experimental results related to n-ZnO/p-Si SHJSC to fill the gaps mentioned above. Modeling and simulation of the solar cell structure are performed using PC1D and AFORS-HET software taking practical constraints into account to explore the potential of the structure. Also, unnoticed benefits of ZnO in solar cells such as an additional antireflection (AR) effect and low temperature deposition are highlighted. The growth parameters of ZnO using metal organic chemical vapor deposition and sputtering are optimized. The structural, optical, and electrical characterization of ZnO thin films grown on sapphire and Si substrates is performed. Several n-ZnO/p-Si SHJSC devices are fabricated to confirm the repeatability of the VOC. Moreover, the AR effect of ZnO while working as an n-type layer is experimentally verified

  2. Exchange bias properties of 140 nm-sized dipolarly interacting circular dots with ultrafine IrMn and NiFe layers

    Energy Technology Data Exchange (ETDEWEB)

    Spizzo, F., E-mail: spizzo@fe.infn.it [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy); Tamisari, M. [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy); Dipartimento di Fisica e Geologia and CNISM, Università di Perugia, I-06123 Perugia (Italy); Chinni, F.; Bonfiglioli, E. [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy); Gerardino, A. [Istituto di Fotonica e Nanotecnologie, CNR, I-00156 Roma (Italy); Barucca, G. [Dipartimento SIMAU, Università Politecnica delle Marche, I-60131 Ancona (Italy); Bisero, D.; Fin, S.; Del Bianco, L. [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy)

    2016-02-15

    We studied the exchange bias effect in an array of IrMn(3 nm)/NiFe(3 nm) circular dots (size ~140 nm and center-to-center distance ~200 nm, as revealed by microscopy analyses), prepared on a large area (3×3 mm{sup 2}) by electron beam lithography and lift-off, using dc sputtering deposition. Hysteresis loops were measured by SQUID magnetometer at increasing values of temperature T (in the 5–300 K range) after cooling from 300 K down to 5 K in zero field (ZFC mode) and in a saturating magnetic field (FC mode). The exchange bias effect disappears above T~200 K and, at each temperature, the exchange field H{sub EX} measured in ZFC is substantially lower than the FC one. Micromagnetic calculations indicate that, at room temperature, each dot is in high-remanence ground state, but magnetic dipolar interactions establish a low-remanence configuration of the array as a whole. Hence, at low temperature, following the ZFC procedure, the exchange anisotropy in the dot array is averaged out, tending to zero. However, even the FC values of H{sub EX} and of the coercivity H{sub C} are definitely smaller compared to those measured in a reference continuous film with the same stack configuration (at T=5 K, H{sub EX}~90 Oe and H{sub C}~180 Oe in the dots and H{sub EX}~1270 Oe and H{sub C}~860 Oe in the film). Our explanation is based on the proven glassy magnetic nature of the ultrathin IrMn layer, implying the existence of magnetic correlations among the spins, culminating in a collective freezing below T~100 K. We propose, also by the light of micromagnetic simulations, that the small dot size imposes a spatial constraint on the magnetic correlation length among the IrMn spins so that, even at the lowest temperature, their thermal stability, especially at the dot border, is compromised. - Highlights: • Exchange bias in 140 nm-sized IrMn(3 nm)/NiFe(3 nm) dots much weaker than in a film. • Glassy magnetic nature of the IrMn phase and collective spin freezing at T<100 K

  3. Exchange bias properties of 140 nm-sized dipolarly interacting circular dots with ultrafine IrMn and NiFe layers

    International Nuclear Information System (INIS)

    Spizzo, F.; Tamisari, M.; Chinni, F.; Bonfiglioli, E.; Gerardino, A.; Barucca, G.; Bisero, D.; Fin, S.; Del Bianco, L.

    2016-01-01

    We studied the exchange bias effect in an array of IrMn(3 nm)/NiFe(3 nm) circular dots (size ~140 nm and center-to-center distance ~200 nm, as revealed by microscopy analyses), prepared on a large area (3×3 mm"2) by electron beam lithography and lift-off, using dc sputtering deposition. Hysteresis loops were measured by SQUID magnetometer at increasing values of temperature T (in the 5–300 K range) after cooling from 300 K down to 5 K in zero field (ZFC mode) and in a saturating magnetic field (FC mode). The exchange bias effect disappears above T~200 K and, at each temperature, the exchange field H_E_X measured in ZFC is substantially lower than the FC one. Micromagnetic calculations indicate that, at room temperature, each dot is in high-remanence ground state, but magnetic dipolar interactions establish a low-remanence configuration of the array as a whole. Hence, at low temperature, following the ZFC procedure, the exchange anisotropy in the dot array is averaged out, tending to zero. However, even the FC values of H_E_X and of the coercivity H_C are definitely smaller compared to those measured in a reference continuous film with the same stack configuration (at T=5 K, H_E_X~90 Oe and H_C~180 Oe in the dots and H_E_X~1270 Oe and H_C~860 Oe in the film). Our explanation is based on the proven glassy magnetic nature of the ultrathin IrMn layer, implying the existence of magnetic correlations among the spins, culminating in a collective freezing below T~100 K. We propose, also by the light of micromagnetic simulations, that the small dot size imposes a spatial constraint on the magnetic correlation length among the IrMn spins so that, even at the lowest temperature, their thermal stability, especially at the dot border, is compromised. - Highlights: • Exchange bias in 140 nm-sized IrMn(3 nm)/NiFe(3 nm) dots much weaker than in a film. • Glassy magnetic nature of the IrMn phase and collective spin freezing at T<100 K • Confinement of IrMn magnetic

  4. Interfacial Interactions in Monolayer and Few-Layer SnS/CH3 NH3 PbI3 Perovskite van der Waals Heterostructures and Their Effects on Electronic and Optical Properties.

    Science.gov (United States)

    Li, Jian-Cai; Wei, Zeng-Xi; Huang, Wei-Qing; Ma, Li-Li; Hu, Wangyu; Peng, Ping; Huang, Gui-Fang

    2018-02-05

    A high light-absorption coefficient and long-range hot-carrier transport of hybrid organic-inorganic perovskites give huge potential to their composites in solar energy conversion and environmental protection. Understanding interfacial interactions and their effects are paramount for designing perovskite-based heterostructures with desirable properties. Herein, we systematically investigated the interfacial interactions in monolayer and few-layer SnS/CH 3 NH 3 PbI 3 heterostructures and their effects on the electronic and optical properties of these structures by density functional theory. It was found that the interfacial interactions in SnS/CH 3 NH 3 PbI 3 heterostructures were van der Waals (vdW) interactions, and they were found to be insensitive to the layer number of 2D SnS sheets. Interestingly, although their band gap decreased upon increasing the layer number of SnS, the near-gap electronic states and optical absorption spectra of these heterostructures were found to be strikingly similar. This feature was determined to be critical for the design of 2D layered SnS-based heterostructures. Strong absorption in the ultraviolet and visible-light regions, type II staggered band alignment at the interface, and few-layer SnS as an active co-catalyst make 2D SnS/CH 3 NH 3 PbI 3 heterostructures promising candidates for photocatalysis, photodetectors, and solar energy harvesting and conversion. These results provide first insight into the nature of interfacial interactions and are useful for designing hybrid organic-inorganic perovskite-based devices with novel properties. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Efficient carbon dots/NiFe-layered double hydroxide/BiVO4 photoanodes for photoelectrochemical water splitting

    Science.gov (United States)

    Lv, Xiaowei; Xiao, Xin; Cao, Minglei; Bu, Yi; Wang, Chuanqing; Wang, Mingkui; Shen, Yan

    2018-05-01

    Modification of semiconductor photoanodes with oxygen evolution catalyst (OEC) is an effective approach for improving photoelectrochemical (PEC) water splitting efficiency. In the configuration, how to increase the activity of OEC is crucial to further improve PEC performance. Herein, a ternary photoanode system was designed to enhance PEC efficiency of photoelectrodes through introducing carbon dots (CDs), NiFe-layered double hydroxide (NiFe-LDH) nanosheets on BiVO4 particles. Systematic research shows that NiFe-LDH serves as an OEC which accelerates oxygen evolution kinetics, while the introduction of CDs can further reduce charge transfer resistance and overpotential for oxygen evolution. Under the synergistic effect of NiFe-LDH and CDs, the photocurrent and incident photon to current conversion efficiency (IPCE) of the resulting CDs/NiFe-LDH/BiVO4 photoanode is improved significantly than those of the NiFe-LDH/BiVO4 electrode. Consequently, such a ternary heterostructure could be an alternative way to further enhance PEC water splitting performance.

  6. Quantum dots transparent display (QDs-TPD) using a liquid QDs layer and N2 barrier discharge

    Science.gov (United States)

    Kim, Hong Tak; Lee, Sung-Youp; Sohn, Sang Ho

    2017-07-01

    Quantum dots transparent display (QDs-TPD) was realized using a liquid QDs layer and N2 barrier discharge panel. In the N2 discharge, the 2nd+ lines of N2 in the range of 300 - 400 nm (C3Πu - B3Πg), and the 1st- lines of N2+ at 391.4 and 427.8 nm (B2Σu+ - X2 Σg+) were mainly observed, while the visible emission lines were rarely observed. This implies the N2 discharge is suitable for the excitation source of the QDs, due to the strong ultra-violet radiations and the weak visible emissions. The emission centers for red, green, and blue color in QDs-TPD were positioned at 452, 540, and 638 nm, respectively, and the N2 emission peaks were seldom observed in the visible region. The transmittance of QDs-TPD was approximately 40% in the visible region and the luminescence was about 70 cd/m2. The CIE (x, y) coordinates of red, green, and blue colors were (0.670, 0.309), (0.378, 0.640), and (0.183, 0.118), respectively, and the color gamut was 71% of a NTSC standard. Thus, the QDs-TPD is expected as a way for realizing the TPD, due to its good transparency, excellent visibility, wide viewing-angle, aesthetical design, low cost production, and good scalability to large sizes.

  7. Deep levels in metamorphic InAs/InGaAs quantum dot structures with different composition of the embedding layers

    Science.gov (United States)

    Golovynskyi, S.; Datsenko, O.; Seravalli, L.; Kozak, O.; Trevisi, G.; Frigeri, P.; Babichuk, I. S.; Golovynska, I.; Qu, Junle

    2017-12-01

    Deep levels in metamorphic InAs/In x Ga1-x As quantum dot (QD) structures are studied with deep level thermally stimulated conductivity (TSC), photoconductivity (PC) and photoluminescence (PL) spectroscopy and compared with data from pseudomorphic InGaAs/GaAs QDs investigated previously by the same techniques. We have found that for a low content of indium (x = 0.15) the trap density in the plane of self-assembled QDs is comparable or less than the one for InGaAs/GaAs QDs. However, the trap density increases with x, resulting in a rise of the defect photoresponse in PC and TSC spectra as well as a reduction of the QD PL intensity. The activation energies of the deep levels and some traps correspond to known defect complexes EL2, EL6, EL7, EL9, and EL10 inherent in GaAs, and three traps are attributed to the extended defects, located in InGaAs embedding layers. The rest of them have been found as concentrated mainly close to QDs, as their density in the deeper InGaAs buffers is much lower. This an important result for the development of light-emitting and light-sensitive devices based on metamorphic InAs QDs, as it is a strong indication that the defect density is not higher than in pseudomorphic InAs QDs.

  8. Interfacial Energy-Level Alignment for High-Performance All-Inorganic Perovskite CsPbBr3 Quantum Dot-Based Inverted Light-Emitting Diodes.

    Science.gov (United States)

    Subramanian, Alagesan; Pan, Zhenghui; Zhang, Zhenbo; Ahmad, Imtiaz; Chen, Jing; Liu, Meinan; Cheng, Shuang; Xu, Yijun; Wu, Jun; Lei, Wei; Khan, Qasim; Zhang, Yuegang

    2018-04-18

    All-inorganic perovskite light-emitting diode (PeLED) has a high stability in ambient atmosphere, but it is a big challenge to achieve high performance of the device. Basically, device design, control of energy-level alignment, and reducing the energy barrier between adjacent layers in the architecture of PeLED are important factors to achieve high efficiency. In this study, we report a CsPbBr 3 -based PeLED with an inverted architecture using lithium-doped TiO 2 nanoparticles as the electron transport layer (ETL). The optimal lithium doping balances the charge carrier injection between the hole transport layer and ETL, leading to superior device performance. The device exhibits a current efficiency of 3 cd A -1 , a luminance efficiency of 2210 cd m -2 , and a low turn-on voltage of 2.3 V. The turn-on voltage is one of the lowest values among reported CsPbBr 3 -based PeLEDs. A 7-fold increase in device efficiencies has been obtained for lithium-doped TiO 2 compared to that for undoped TiO 2 -based devices.

  9. Ultrasensitive and Highly Stable Resistive Pressure Sensors with Biomaterial-Incorporated Interfacial Layers for Wearable Health-Monitoring and Human-Machine Interfaces.

    Science.gov (United States)

    Chang, Hochan; Kim, Sungwoong; Jin, Sumin; Lee, Seung-Woo; Yang, Gil-Tae; Lee, Ki-Young; Yi, Hyunjung

    2018-01-10

    Flexible piezoresistive sensors have huge potential for health monitoring, human-machine interfaces, prosthetic limbs, and intelligent robotics. A variety of nanomaterials and structural schemes have been proposed for realizing ultrasensitive flexible piezoresistive sensors. However, despite the success of recent efforts, high sensitivity within narrower pressure ranges and/or the challenging adhesion and stability issues still potentially limit their broad applications. Herein, we introduce a biomaterial-based scheme for the development of flexible pressure sensors that are ultrasensitive (resistance change by 5 orders) over a broad pressure range of 0.1-100 kPa, promptly responsive (20 ms), and yet highly stable. We show that employing biomaterial-incorporated conductive networks of single-walled carbon nanotubes as interfacial layers of contact-based resistive pressure sensors significantly enhances piezoresistive response via effective modulation of the interlayer resistance and provides stable interfaces for the pressure sensors. The developed flexible sensor is capable of real-time monitoring of wrist pulse waves under external medium pressure levels and providing pressure profiles applied by a thumb and a forefinger during object manipulation at a low voltage (1 V) and power consumption (<12 μW). This work provides a new insight into the material candidates and approaches for the development of wearable health-monitoring and human-machine interfaces.

  10. Comparison of MOVPE grown GaAs, InGaAs and GaAsSb covering layers for different InAs/GaAs quantum dot applications

    Czech Academy of Sciences Publication Activity Database

    Zíková, Markéta; Hospodková, Alice; Pangrác, Jiří; Oswald, Jiří; Hulicius, Eduard

    2017-01-01

    Roč. 464, Apr (2017), s. 59-63 ISSN 0022-0248 R&D Projects: GA MŠk LO1603 Institutional support: RVO:68378271 Keywords : MOVPE * quantum dot * strain reducing layer * InAs * GaAsSb * InGaAs Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

  11. MOVPE prepared InAs/GaAs quantum dots covered by GaAsSb layer with long wavelength emission at 1.8 µm

    Czech Academy of Sciences Publication Activity Database

    Zíková, Markéta; Hospodková, Alice; Pangrác, Jiří; Oswald, Jiří; Krčil, Pavel; Hulicius, Eduard; Komninou, Ph.; Kioseoglou, J.

    2015-01-01

    Roč. 414, Mar (2015), 167-171 ISSN 0022-0248 R&D Projects: GA ČR GA13-15286S; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : long emission wavelength * photocurrent * InAs quantum dots * MOVPE * GaAsSb layer Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.462, year: 2015

  12. Effect of Al 2 O 3 Recombination Barrier Layers Deposited by Atomic Layer Deposition in Solid-State CdS Quantum Dot-Sensitized Solar Cells

    KAUST Repository

    Roelofs, Katherine E.; Brennan, Thomas P.; Dominguez, Juan C.; Bailie, Colin D.; Margulis, George Y.; Hoke, Eric T.; McGehee, Michael D.; Bent, Stacey F.

    2013-01-01

    Despite the promise of quantum dots (QDs) as a light-absorbing material to replace the dye in dye-sensitized solar cells, quantum dot-sensitized solar cell (QDSSC) efficiencies remain low, due in part to high rates of recombination. In this article

  13. Thermal conductivity of InAs quantum dot stacks using AlAs strain compensating layers on InP substrate

    International Nuclear Information System (INIS)

    Salman, S.; Folliot, H.; Le Pouliquen, J.; Chevalier, N.; Rohel, T.; Paranthoën, C.; Bertru, N.; Labbé, C.; Letoublon, A.; Le Corre, A.

    2012-01-01

    Highlights: ► The thermal conductivity of InAs on InP (1 1 3)B quantum dots stacks is measured. ► The growth of a close stack of 100 layers of InAs using AlAs strain compensating layers is presented. ► New data on the thermal conductivity of InP n-doped susbtrate are given. - Abstract: The growth and thermal conductivity of InAs quantum dot (QD) stacks embedded in GaInAs matrix with AlAs compensating layers deposited on (1 1 3)B InP substrate are presented. The effect of the strain compensating AlAs layer is demonstrated through Atomic Force Microscopy (AFM) and X-ray diffraction structural analysis. The thermal conductivity (2.7 W/m K at 300 K) measured by the 3ω method reveals to be clearly reduced in comparison with a bulk InGaAs layer (5 W/m K). In addition, the thermal conductivity measurements of S doped InP substrates and the SiN insulating layer used in the 3ω method in the 20–200 °C range are also presented. An empirical law is proposed for the S doped InP substrate, which slightly differs from previously presented results.

  14. Type I - type II band alignment of GaAsSb/InAs/GaAs quantum dot heterostructure influenced by dot size and strain reducing layer composition

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Zíková, Markéta; Pangrác, Jiří; Oswald, Jiří; Kubištová, Jana; Kuldová, Karla; Hazdra, P.; Hulicius, Eduard

    2013-01-01

    Roč. 46, č. 9 (2013), "095103-1"-"095103-9" ISSN 0022-3727 R&D Projects: GA ČR GAP102/10/1201; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : quantum dot * band alignment * InAs/GaAs * GaAsSb * MOVPE Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.521, year: 2013 http://iopscience.iop.org/0022-3727/46/9/095103/

  15. Escaping the Ashby limit for mechanical damping/stiffness trade-off using a constrained high internal friction interfacial layer.

    Science.gov (United States)

    Unwin, A P; Hine, P J; Ward, I M; Fujita, M; Tanaka, E; Gusev, A A

    2018-02-06

    The development of new materials with reduced noise and vibration levels is an active area of research due to concerns in various aspects of environmental noise pollution and its effects on health. Excessive vibrations also reduce the service live of the structures and limit the fields of their utilization. In oscillations, the viscoelastic moduli of a material are complex and it is their loss part - the product of the stiffness part and loss tangent - that is commonly viewed as a figure of merit in noise and vibration damping applications. The stiffness modulus and loss tangent are usually mutually exclusive properties so it is a technological challenge to develop materials that simultaneously combine high stiffness and high loss. Here we achieve this rare balance of properties by filling a solid polymer matrix with rigid inorganic spheres coated by a sub-micron layer of a viscoelastic material with a high level of internal friction. We demonstrate that this combination can be experimentally realised and that the analytically predicted behaviour is closely reproduced, thereby escaping the often termed 'Ashby' limit for mechanical stiffness/damping trade-off and offering a new route for manufacturing advanced composite structures with markedly reduced noise and vibration levels.

  16. Large improvement of electron extraction from CdSe quantum dots into a TiO2 thin layer by N3 dye coabsorption

    International Nuclear Information System (INIS)

    Mora-Sero, Ivan; Dittrich, Thomas; Susha, Andrei S.; Rogach, Andrey L.; Bisquert, Juan

    2008-01-01

    Extraction of electrons and holes photogenerated in CdSe quantum dots (QD) of 2.3 nm diameter, is monitored by Surface Photovoltage Spectroscopy. The extraction of electrons into a thin TiO 2 layer increases five-fold by absorption of N3 dye molecules on top of the QD layer. This process is facilitated by efficient hole extraction from the valence band of the QDs to the ground state of the N3 dye. Our results represent a direct measurement of charge separation in the N3/QD/TiO 2 system

  17. Performance improvement of CdS quantum dots sensitized TiO{sub 2} solar cells by introducing a dense TiO{sub 2} blocking layer

    Energy Technology Data Exchange (ETDEWEB)

    Tachibana, Yasuhiro; Umekita, Kazuya; Otsuka, Yasuhide; Kuwabata, Susumu [Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871 (Japan)], E-mail: y.tachibana@chem.eng.osaka-u.ac.jp

    2008-05-21

    A dense TiO{sub 2} electron blocking layer was introduced on a conducting glass in CdS quantum dots sensitized solar cells to investigate electron leakage into the electrolyte. A ferricyanide/ferrocyanide redox couple was employed, as a model electrolyte, possessing a high standard rate constant. The analysis of the I-V characteristics, using a one-diode model, revealed that an increase in this layer, up to 50 nm, significantly suppresses the electron leakage, enhancing the shunt resistance by a factor of 200. An energy conversion efficiency of 1.0% was attained on account of the improved open circuit voltage and fill factor. (fast track communication)

  18. Quantum-dot-sensitized solar cells fabricated by the combined process of the direct attachment of colloidal CdSe quantum dots having a ZnS glue layer and spray pyrolysis deposition.

    Science.gov (United States)

    Im, Sang Hyuk; Lee, Yong Hui; Seok, Sang Il; Kim, Sung Woo; Kim, Sang-Wook

    2010-12-07

    We were able to attach CdSe quantum dots (QDs) having a ZnS inorganic glue layer directly to a mesoporous TiO(2) (mp-TiO(2)) surface by spray coating and thermal annealing. Quantum-dot-sensitized solar cells based on CdSe QDs having ZnS as the inorganic glue layer could easily transport generated charge carriers because of the intimate bonding between CdSe and mp-TiO(2). The application of spray pyrolysis deposition (SPD) to obtain additional CdSe layers improved the performance characteristics to V(oc) = 0.45 V, J(sc) = 10.7 mA/cm(2), fill factor = 35.8%, and power conversion efficiency = 1.7%. Furthermore, ZnS post-treatment improved the device performance to V(oc) = 0.57 V, J(sc) = 11.2 mA/cm(2), fill factor = 35.4%, and power conversion efficiency = 2.2%.

  19. Interfacial, Electrical, and Band Alignment Characteristics of HfO2/Ge Stacks with In Situ-Formed SiO2 Interlayer by Plasma-Enhanced Atomic Layer Deposition

    Science.gov (United States)

    Cao, Yan-Qiang; Wu, Bing; Wu, Di; Li, Ai-Dong

    2017-05-01

    In situ-formed SiO2 was introduced into HfO2 gate dielectrics on Ge substrate as interlayer by plasma-enhanced atomic layer deposition (PEALD). The interfacial, electrical, and band alignment characteristics of the HfO2/SiO2 high-k gate dielectric stacks on Ge have been well investigated. It has been demonstrated that Si-O-Ge interlayer is formed on Ge surface during the in situ PEALD SiO2 deposition process. This interlayer shows fantastic thermal stability during annealing without obvious Hf-silicates formation. In addition, it can also suppress the GeO2 degradation. The electrical measurements show that capacitance equivalent thickness of 1.53 nm and a leakage current density of 2.1 × 10-3 A/cm2 at gate bias of Vfb + 1 V was obtained for the annealed sample. The conduction (valence) band offsets at the HfO2/SiO2/Ge interface with and without PDA are found to be 2.24 (2.69) and 2.48 (2.45) eV, respectively. These results indicate that in situ PEALD SiO2 may be a promising interfacial control layer for the realization of high-quality Ge-based transistor devices. Moreover, it can be demonstrated that PEALD is a much more powerful technology for ultrathin interfacial control layer deposition than MOCVD.

  20. Photovoltaic performance of bithiazole-bridged dyes-sensitized solar cells employing semiconducting quantum dot CuInS2 as barrier layer material.

    Science.gov (United States)

    Guo, Fuling; He, Jinxiang; Li, Jing; Wu, Wenjun; Hang, Yandi; Hua, Jianli

    2013-10-15

    In this work, the quantum dot CuInS2 layer was deposited on TiO2 film using successive ionic layer absorption and reaction (SILAR) method, and then two bithiazole-bridged dyes (BTF and BTB) were sensitized on the CuInS2/TiO2 films to form dye/CuInS2/TiO2 photoanodes for DSSCs. It was found that the quantum dots CuInS2 as an energy barrier layer not only could effectively improve open-circuit voltage (Voc) of solar cell, but also increase short-circuit photocurrent (Jsc) compared to the large decrease in Jsc of ZnO as energy barrier layer. The electrochemical impedance spectroscopy (EIS) measurement showed that the CuInS2 formed a barrier layer to suppress the recombination from injection electron to the electrolyte and improve open-circuit voltage. Finally, the open-circuit voltage increased about 22 and 27mV for BTF and BTB-/CuInS2/TiO2-based cells, the overall conversion efficiencies also reached to 7.20% and 6.74%, respectively. Copyright © 2013 Elsevier Inc. All rights reserved.

  1. Observation of Dynamic Interfacial Layers in Li-Ion and Li-O_2 Batteries by Scanning Electrochemical Microscopy

    International Nuclear Information System (INIS)

    Bülter, Heinz; Schwager, Patrick; Fenske, Daniela; Wittstock, Gunther

    2016-01-01

    Highlights: • Imaging changes of solid electrolyte interphases on rinsed lithiated graphite. • Strongly non-uniform changes of SEI passivation properties. • In situ imaging of clogged gas diffusion electrodes of Li/O_2 batteries. - Abstract: The requirements of high energy density in modern batteries dictate the use of very high (oxidizing) or very low (reducing) potential for negative and positive electrode materials. These extreme potentials can cause molecular compounds to undergo electron transfer reactions at the interfaces. This is well documented for lithium-ion batteries, where a solid electrolyte interphase (SEI) between the lithiated graphite electrode and the electrolyte is formed by the decomposition of electrolyte components mainly during the first charging process. Characterization of the SEI is a challenge because of the variety of chemically similar components and enclosed electrolyte species. Furthermore, ex situ analysis of the SEI requires separation and isolation of the SEI, which may change the content and the structure of the SEI. Scanning electrochemical microscopy (SECM) provides in situ analysis of passivating layers formed at battery electrodes. Such approaches must deal with continuous changes of the studied interfaces. This is illustrated for the in situ investigation of the electron transport at SEI-covered lithiated graphite using 2,5-di-tert-butyl-1,4-dimethoxy benzene as SECM mediator in an inert atmosphere. With this setup, the influence of rinsing protocols on the passivating properties of the SEI was studied. An extensive rinsing compared to our previous studies [DOI 10.1002/anie.201403935] leads to much higher local variation of the SEI passivation properties which continue over the entire observation time of 54 h. The second example uses a SECM generation-collection experiment to detect gas permeation through a gas-diffusion electrode (GDE) of a Li-O_2 cell into a Li"+-containing organic electrolyte. The passivation of the

  2. Interfacial reactions of Ba 2YCu 3O 6+z with coated conductor buffer layer, LaMnO 3

    Science.gov (United States)

    Liu, G.; Wong-Ng, W.; Kaduk, J. A.; Cook, L. P.

    2010-03-01

    Chemical interactions between the Ba 2YCu 3O 6+x superconductor and the LaMnO 3 buffer layers employed in coated conductors have been investigated experimentally by determining the phases formed in the Ba 2YCu 3O 6+x-LaMnO 3 system. The Ba 2YCu 3O 6+x-LaMnO 3 join within the BaO-(Y 2O 3-La 2O 3)-MnO 2-CuO x multi-component system is non-binary. At 810 °C ( pO2 = 100 Pa) and at 950 °C in purified air, four phases are consistently present along the join, namely, Ba 2-x(La 1+x-yY y)Cu 3O 6+z, Ba(Y 2-xLa x)CuO 5, (La 1-xY x)MnO 3, (La,Y)Mn 2O 5. The crystal chemistry and crystallography of Ba(Y 2-xLa x)CuO 5 and (La 1-xY x)Mn 2O 5 were studied using the X-ray Rietveld refinement technique. The Y-rich and La-rich solid solution limits for Ba(Y 2-xLa x)CuO 5 are Ba(Y 1.8La 0.2)CuO 5 and Ba(Y 0.1La 1.9)CuO 5, respectively. The structure of Ba(Y 1.8La 0.2)CuO 5 is Pnma (No. 62), a = 12.2161(5) Å, b = 5.6690(2) Å, c = 7.1468(3) Å, V = 494.94(4) Å 3, and D x = 6.29 g cm -3. YMn 2O 5 and LaMn 2O 5 do not form solid solution at 810 °C ( pO2 = 100 Pa) or at 950 °C (in air). The structure of YMn 2O 5 was confirmed to be Pbam (No. 55), a = 7.27832(14) Å, b = 8.46707(14) Å, c = 5.66495(10) Å, and V = 349.108(14) Å 3. A reference X-ray pattern was prepared for YMn 2O 5.

  3. Oxide layer characteristics and interfacial analysis of porcelain fused to high-gold alloy using multitechnique analysis methods

    Directory of Open Access Journals (Sweden)

    Hao-Sheng Chang

    2017-12-01

    Full Text Available Background/purpose: In a previous fractural study, high-gold crowns possessed the second highest fracture force. The objective of this study is to analyze the interface of porcelain fused to high-gold alloy using different observation devices. Materials and methods: High-gold crowns specimens with the morphology of a maxillary second premolar were compressed vertically in the center of the occlusal surface until fracture using a universal testing machine. The fractured surfaces were examined using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM/EDX to determine the failure mode. The ceramic–metal interface of the crown was examined with electron probe microanalysis (EPMA. In addition, sheet specimens with dimensions of 10×9×4 mm3 were prepared to examine the surface morphology and composition of high-gold alloy after oxidation using X-ray photoelectron spectrometer (XPS. Results: The average fracture force was 1368±312 N. Photograph of fractured crown and SEM/EDX analyses reveal that the crown initially suffered from cohesive failure in the upper and middle regions, with the fracture occurring mostly within the ceramic. XPS results and both EPMA color photomicrographs of crown and sheet specimens show that indium was observed along the porcelain–metal interface with a 1- to 2-μm disrupted zone of oxide layer. Conclusion: In2O3 and Au were found along the interface from the multitechnique analysis methods; the presence of this oxide at the boundary promotes ceramic–metal adhesion. In2O3 is suggested to be beneficial for the second highest fracture resistance in a previous fractural study of implant-supported crowns. Keywords: electron probe microanalysis, gold–platinum alloy, scanning electron microscopy combined with energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy

  4. Improve the surface of silver nanowire transparent electrode using a double-layer structure for the quantum-dot light-emitting diodes

    Science.gov (United States)

    Cho, Seok Hyeon; Been Heo, Su; Kang, Seong Jun

    2018-03-01

    We developed a double-layer structured transparent electrode for use in flexible quantum-dot light-emitting diodes (QLEDs). Silver nanowires (AgNWs) and highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were coated on a transparent substrate to obtain a highly conductive and flexible transparent electrode. The highly conductive PEDOT:PSS improved the surface roughness of the AgNWs transparent electrode film as well as the surface coverage area of the film. The double-layer structured transparent electrode showed superior mechanical properties than conventional indium-tin oxide (ITO) and AgNWs transparent electrodes. QLEDs with the double-layer structured transparent electrode also showed good reliability under cyclic bending conditions. These results indicate that the double-layer structured AgNWs/PEDOT:PSS transparent electrode described here is a feasible alternative to ITO transparent electrodes for flexible QLEDs.

  5. Nonlinear optical rectification in a vertically coupled lens-shaped InAs/GaAs quantum dots with wetting layers under hydrostatic pressure and temperature

    Energy Technology Data Exchange (ETDEWEB)

    Ben Mahrsia, R.; Choubani, M., E-mail: mohsenchoubani3@yahoo.fr; Bouzaiene, L.; Maaref, H.

    2016-06-25

    In this paper we explore the structure parameters, hydrostatic pressure and temperature effects on Nonlinear optical rectification (NOR) in an asymmetric vertically coupled lens-shaped InAs/GaAs quantum dots. During epitaxial growth, lens-shaped quantum dots (QDs) are formed on the wetting layer (WL). Many theoretical works have neglected WL and its effect on nonlinear optical properties of QD-based systems for sake of simplicity. However, in this work the WL has been shown to be so influential in the intersubband energy and nonlinear optical rectification magnitude. Also, a detailed and comprehensive study of the nonlinear optical rectification is theoretical investigated within the framework of the compact density-matrix approach and finite difference method (FDM). It's found that nonlinear optical rectification coefficient is strongly affected not only by the WL, but also by the pressure, temperature and the coupled width between the QDs. Obtained results revealed that a red or a blue shift cane be observed. This behavior in the NOR gives a new degree of freedom in regions of interest for device applications. - Highlights: • Vertically coupled lens-shaped InAs/GaAs quantum dots is investigated. • Photon energy shifts towards the red with increasing pressure. • Photon energy shifts towards the blue with increasing temperature. • Intersubband energy decreases with increasing the wetting layer width. • Nonlinear optical rectification magnitude is controlled and adjusted.

  6. Fabrication, Characterization, and Optimization of CdS and CdSe Quantum Dot-Sensitized Solar Cells with Quantum Dots Prepared by Successive Ionic Layer Adsorption and Reaction

    Directory of Open Access Journals (Sweden)

    H. K. Jun

    2014-01-01

    Full Text Available CdS and CdSe quantum dot-sensitized solar cells (QDSSCs were used for the study of determining the optimum preparation parameters that could yield the best solar cell performance. The quantum dots (QDs were coated on the surface of mesoporous TiO2 layer deposited on FTO substrate using the successive ionic layer adsorption and reaction (SILAR method. In this method the QDs are allowed to grow on TiO2 by dipping the TiO2 electrode successively in two different solutions for predetermined times. This method allows the fabrication of QDs in a facile way. Three preparation parameters that control the QD fabrication were investigated: concentration of precursor solutions, number of dipping cycles (SILAR cycles, and dipping time in each solution. CdS based QDSSC showed optimum performance when the QDs were prepared from precursor solutions having the concentration of 0.10 M using 4 dipping cycles with the dipping time of 5 minutes in each solution. For CdSe QDSSC, the optimum performance was achieved with QDs prepared from 0.03 M precursor solutions using 7 dipping cycles with 30 s dipping time in each solution. The QDs deposited on TiO2 surface were characterized using UV-vis absorption spectroscopy, FESEM, and TEM imaging.

  7. Improving charge transport in PbS quantum Dot to Al:ZnO layer by changing the size of Quantum dots in hybrid solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Mehrabian, Masood [Maragheh Univ. (Iran, Islamic Republic of). Faculty of Basic Science; Abdollahian, Parinaz [Maragheh Univ. (Iran, Islamic Republic of). Dept. of Materials Engineering

    2016-07-01

    PbS Quantum dots and P3HT are promising materials for photovoltaic applications due to their absorption in the NIR and visible region, respectively. Our previous experimental work showed that doping Al to ZnO lattice (Al:ZnO) could efficiently improve the cell performance. In this article, hybrid solar cells containing of two active areas with ITO/Al:ZnO/PbS QDs/P3HT and PCBM/Ag structure were fabricated and the effect of PbS QD size on photovoltaic properties was investigated. Optimised solar cell showed maximum power conversion efficiency of 2.45 % with short-circuit current of 9.36 mA/cm{sup 2} and open-circuit voltage of 0.59 V under 1 sun illumination (AM1.5).

  8. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    Science.gov (United States)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  9. Ultrathin ZnO interfacial passivation layer for atomic layer deposited ZrO2 dielectric on the p-In0.2Ga0.8As substrate

    Science.gov (United States)

    Liu, Chen; Lü, Hongliang; Yang, Tong; Zhang, Yuming; Zhang, Yimen; Liu, Dong; Ma, Zhenqiang; Yu, Weijian; Guo, Lixin

    2018-06-01

    Interfacial and electrical properties were investigated on metal-oxidesemiconductor capacitors (MOSCAPs) fabricated with bilayer ZnO/ZrO2 films by atomic layer deposition (ALD) on p-In0.2Ga0.8As substrates. The ZnO passivated In0.2Ga0.8As MOSCAPs have exhibited significantly improved capacitance-voltage (C-V) characteristics with the suppressed "stretched out" effect, increased accumulation capacitance and reduced accumulation frequency dispersion as well as the lower gate leakage current. In addition, the interface trap density (Dit) estimated by the Terman method was decreased dramatically for ZnO passivated p-In0.2Ga0.8As. The inherent mechanism is attributed to the fact that an ultrathin ZnO IPL employed by ALD prior to ZrO2 dielectric deposition can effectively suppress the formation of defect-related low-k oxides and As-As dimers at the interface, thus effectively improving the interface quality by largely removing the border traps aligned near the valence band edge of the p-In0.2Ga0.8As substrate.

  10. Stochastic quantum confinement in nanocrystalline silicon layers: The role of quantum dots, quantum wires and localized states

    International Nuclear Information System (INIS)

    Ramírez-Porras, A.; García, O.; Vargas, C.; Corrales, A.; Solís, J.D.

    2015-01-01

    Highlights: • PL spectra of porous silicon samples have been studied using a stochastic model. • This model can deconvolute PL spectra into three components. • Quantum dots, quantum wires and localized states have been identified. • Nanostructure diameters are in the range from 2.2 nm to 4.0 nm. • Contributions from quantum wires are small compared to the others. - Abstract: Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models

  11. Stochastic quantum confinement in nanocrystalline silicon layers: The role of quantum dots, quantum wires and localized states

    Energy Technology Data Exchange (ETDEWEB)

    Ramírez-Porras, A., E-mail: aramirez@fisica.ucr.ac.cr [Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); García, O. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Vargas, C. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Corrales, A. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Solís, J.D. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica)

    2015-08-30

    Highlights: • PL spectra of porous silicon samples have been studied using a stochastic model. • This model can deconvolute PL spectra into three components. • Quantum dots, quantum wires and localized states have been identified. • Nanostructure diameters are in the range from 2.2 nm to 4.0 nm. • Contributions from quantum wires are small compared to the others. - Abstract: Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models.

  12. Interfacial pH-gradient induced micro-capillary filling with the aid of transverse electrodes arrays in presence of electrical double layer effects

    International Nuclear Information System (INIS)

    Jain, Avi; Chakraborty, Suman

    2010-01-01

    In the present work, we outline the design and analysis of a micro-capillary filling mechanism through the aid of interfacial pH gradients (and hence interfacial tension gradients) generated by employing arrays of transverse electrodes inducing step changes in voltages, in a natural buffer system that requires low power and no synthetic ampholytes. The capillary transport is modulated by a dynamic and non-trivial coupling between the interfacial tension and viscous resistances, as a consequence of the underlying intermolecular interactions. The competing effects of the driving and the retarding forces effectively determine the displacement, velocity and acceleration characteristics of the capillary front, in a dynamically evolving manner. A comprehensive theoretical model of capillary dynamics is developed here to address these issues in details, thereby revealing the combined influence of the interfacial electrochemistry and the applied transverse voltages, as guided by the pertinent fundamental thermodynamic principles governed by free energy considerations and the physico-chemical phenomena over interfacial scales. Non-trivial implications of the pH-gradient driven micro-capillary transport are aptly emphasized, so as to offer significant physical insights on the adopted strategy as a guiding principle for facilitating capillary filling processes by inducing a modulation in the effective interfacial energy. Particular implications on the capillary filling time are also pinpointed, revealing the effectiveness of the adopted design strategy. Finally, a universal scaling relationship of the capillary filling time as a function of the pertinent operating parameters is derived, so as to provide a generalized guideline for implementing the design scheme. A non-dimensional parameter, depending simultaneously on the inter-electrode pitch and the transverse voltage, is identified, which may be kept to a minimal limit within the other operating constraints of the chosen

  13. InAs/GaAs quantum dot lasers with InGaP cladding layer grown by solid-source molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Yeh, N.-T.; Liu, W.-S.; Chen, S.-H.; Chiu, P.-C.; Chyi, J.-I.

    2002-01-01

    This letter presents the lasing properties of InAs/GaAs quantum dot lasers with InGaP cladding layers grown by solid-source molecular-beam epitaxy. These Al-free lasers exhibit a threshold current density of 138 A/cm 2 , an internal loss of 1.35 cm -1 , and an internal quantum efficiency of 31% at room temperature. At a low temperature, a very high characteristic temperature of 425 K and very low threshold current density of 30 A/cm 2 are measured

  14. Luminous composite ultrathin films of CdTe quantum dots/silk fibroin co-assembled with layered doubled hydroxide: Enhanced photoluminescence and biosensor application

    Directory of Open Access Journals (Sweden)

    Muhammad Sohail Haroone

    2018-06-01

    Full Text Available Quantum dots (QDs luminescent films are extensively applied to optoelectronics and optical devices. However, QDs aggregation results in the quenching of their fluorescence property which limits their practical applications to a greater extent. In order to resolve this issue, 3-mercaptopropionic acid (3-MPA functionalized Cadmium Tellurium (CdTe QDs were stabilized by silk fibroin (SB and co-assembled with layered doubled hydroxide (LDH to form (QDs@SF/LDHn ultrathin films (UTFs via the layer-by-layer (LBL technique. UV–Vis absorption and fluorescence spectroscopy showed a stepwise and normal growth of the films upon increasing the number of deposition cycles. XRD and AFM studies confirmed the formation of a periodic layered structure and regular surface morphology of the thin films. As compared to (CdTe QDs/LDHnUTFs, the (CdTe QDs@SF/LDHnUTFs displayed fluorescence enhancement and longer fluorescent lifetime, both in solid states and aqueous solutions. Furthermore compared with the solution state, the fluorescence enhancement of SF-RC and SF-β are, respectively, 7 times and 17 times in the (CdTe QDs@SF/LDHn UTFs, indicating that the LDH nanosheets favor the fluorescence enhancement effect on the CdTe QDs@SF. The fabricated materials displayed fluorescence response to a biological molecule such as immune globulin, lgG. Thus, the (CdTe QDs@SF/LDHn UTFs has a potential to be used as biosensor. Keywords: CdTe quantum dots, Silk fibroin, Layered doubled hydroxide, Co-assembly, Fluorescence enhancement

  15. How Does a SILAR CdSe Film Grow? Tuning the Deposition Steps to Suppress Interfacial Charge Recombination in Solar Cells.

    Science.gov (United States)

    Becker, Matthew A; Radich, James G; Bunker, Bruce A; Kamat, Prashant V

    2014-05-01

    Successive ionic layer adsorption and reaction (SILAR) is a popular method of depositing the metal chalcogenide semiconductor layer on the mesoscopic metal oxide films for designing quantum-dot-sensitized solar cells (QDSSCs) or extremely thin absorber (ETA) solar cells. While this deposition method exhibits higher loading of the light-absorbing semiconductor layer than direct adsorption of presynthesized colloidal quantum dots, the chemical identity of these nanostructures and the evolution of interfacial structure are poorly understood. We have now analyzed step-by-step SILAR deposition of CdSe films on mesoscopic TiO2 nanoparticle films using X-ray absorption near-edge structure analysis and probed the interfacial structure of these films. The film characteristics interestingly show dependence on the order in which the Cd and Se are deposited, and the CdSe-TiO2 interface is affected only during the first few cycles of deposition. Development of a SeO2 passivation layer in the SILAR-prepared films to form a TiO2/SeO2/CdSe junction facilitates an increase in photocurrents and power conversion efficiencies of quantum dot solar cells when these films are integrated as photoanodes in a photoelectrochemical solar cell.

  16. Electrical characterization of InAs/InP self-assembled quantum dots with InGaAs strain-relief layers

    International Nuclear Information System (INIS)

    Kim, J. S.; Kim, E. K.; Hwang, H.; Park, K.; Yoon, E.; Park, I. W.; Park, Y. J.

    2004-01-01

    We have investigated the energy levels of InAs quantum dots (QDs) embedded in various barrier layers such as InP, InGaAs and GaAs by using deep level transient spectroscopy (DLTS) measurement. The apparent activation energy of 0.56 eV below the conduction band edge of barrier layers in the InAs/InP QD system was higher than 0.32 eV in the InAs/In 0.53 Ga 0.47 As QD system or 0.29 eV in the InAs/GaAs/In 0.53 Ga 0.47 As QD system, which was inserted in 10 mono-layers (MLs) GaAs between InAs QDs and the InGaAs barrier. The capture barrier heights of InAs QDs in the InAs/InP system was measured at more than about 0.18 eV, showing the existence of strain between QDs and barrier layers. The InAs/GaAs(10 MLs)/InGaAs system also showed about 0.12 eV capture barrier, but the InAs/InGaAs system has a very small barrier. This result might originate from the strain-relief effect due to InGaAs layers.

  17. Wetting layer states in low density InAs/InGaAs quantum dots from sub-critical InAs coverages

    International Nuclear Information System (INIS)

    Seravalli, L; Trevisi, G; Frigeri, P; Rossi, F; Buffagni, E; Ferrari, C

    2013-01-01

    In this work we study the properties of wetting layers in InAs/InGaAs/GaAs quantum dot (QD) structures suitable for single photon emission; the mandatory low density of QDs is obtained by an molecular beam epitaxy (MBE) approach based on the deposition of sub-critical InAs coverages followed by post-growth annealing. Such a growth regime is fundamentally different from the Stranski–Krastanow (SK) one commonly used for the deposition of QDs. By fitting x-ray diffraction (XRD) spectra, ten-steps composition profiles were derived and used as inputs of model calculations of the two-dimensional quantum energy system: model results were validated by comparison with photoluminescence spectra. A strong reduction of In molar fraction in wetting layers in comparison with SK structures was found, causing a larger wavefunction delocalization for carriers that populate the wetting layer energy levels. Moreover, by considering the limits for strain relaxation when In x Ga 1−x As capping layers are used, we grew structures with the highest possible values of x to study the modifications of the energy system. When x = 0.20 the electron–heavy hole overlap is almost halved and the carriers' probability of being in the first nanometre of the wetting layer is reduced by 60%. These results will be useful for advanced design of QD nanostructures for single photon sources. (paper)

  18. Time-resolved x-ray diffraction measurements of high-density InAs quantum dots on Sb/GaAs layers and the suppression of coalescence by Sb-irradiated growth interruption

    International Nuclear Information System (INIS)

    Kakuda, Naoki; Yamaguchi, Koichi; Kaizu, Toshiyuki; Takahasi, Masamitu; Fujikawa, Seiji

    2010-01-01

    Self-assembly of high-density InAs quantum dots (QDs) on Sb-irradiated GaAs buffer layers was observed in-situ by a time-resolved X-ray diffraction (XRD) technique using a combination of XRD and molecular beam epitaxy. Evolution of dot height and lattice constant was analyzed during InAs QD growth and subsequent growth interruption (GI), and as a result, dislocated giant dots due to coalescence and coherent dots were separately evaluated. An Sb-irradiated GI (Sb-GI) method to be applied after InAs growth was attempted for the suppression of coalescence. Using this method, the XRD intensity of giant dots decreased, and the photoluminescence intensity of InAs QDs was enhanced. High-density InAs QDs without giant dots were produced by using the combination of the QD growth on the Sb-irradiated GaAs buffer layers and the Sb-GI. (author)

  19. Nonvolatile memory thin film transistors using CdSe/ZnS quantum dot-poly(methyl methacrylate) composite layer formed by a two-step spin coating technique

    Science.gov (United States)

    Chen, Ying-Chih; Huang, Chun-Yuan; Yu, Hsin-Chieh; Su, Yan-Kuin

    2012-08-01

    The nonvolatile memory thin film transistors (TFTs) using a core/shell CdSe/ZnS quantum dot (QD)-poly(methyl methacrylate) (PMMA) composite layer as the floating gate have been demonstrated, with the device configuration of n+-Si gate/SiO2 insulator/QD-PMMA composite layer/pentacene channel/Au source-drain being proposed. To achieve the QD-PMMA composite layer, a two-step spin coating technique was used to successively deposit QD-PMMA composite and PMMA on the insulator. After the processes, the variation of crystal quality and surface morphology of the subsequent pentacene films characterized by x-ray diffraction spectra and atomic force microscopy was correlated to the two-step spin coating. The crystalline size of pentacene was improved from 147.9 to 165.2 Å, while the degree of structural disorder was decreased from 4.5% to 3.1% after the adoption of this technique. In pentacene-based TFTs, the improvement of the performance was also significant, besides the appearances of strong memory characteristics. The memory behaviors were attributed to the charge storage/discharge effect in QD-PMMA composite layer. Under the programming and erasing operations, programmable memory devices with the memory window (Δ Vth) = 23 V and long retention time were obtained.

  20. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    International Nuclear Information System (INIS)

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru; Suzuki, Hidetoshi; Sasaki, Takuo; Takahasi, Masamitu

    2015-01-01

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures

  1. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru, E-mail: kamiya@toyota-ti.ac.jp [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Suzuki, Hidetoshi [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192 (Japan); Sasaki, Takuo; Takahasi, Masamitu [Quantum Beam Science Center, Japan Atomic Energy Agency, Koto 1-1-1, Sayo-cho, Hyogo 679-5148 (Japan)

    2015-11-14

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

  2. Light-emitting diodes based on solution-processed nontoxic quantum dots: oxides as carrier-transport layers and introducing molybdenum oxide nanoparticles as a hole-inject layer.

    Science.gov (United States)

    Bhaumik, Saikat; Pal, Amlan J

    2014-07-23

    We report fabrication and characterization of solution-processed quantum dot light-emitting diodes (QDLEDs) based on a layer of nontoxic and Earth-abundant zinc-diffused silver indium disulfide (AIZS) nanoparticles as an emitting material. In the QDLEDs fabricated on indium tin oxide (ITO)-coated glass substrates, we use layers of oxides, such as graphene oxide (GO) and zinc oxide (ZnO) nanoparticles as a hole- and electron-transport layer, respectively. In addition, we introduce a layer of MoO3 nanoparticles as a hole-inject one. We report a comparison of the characteristics of different device architectures. We show that an inverted device architecture, ITO/ZnO/AIZS/GO/MoO3/Al, yields a higher electroluminescence (EL) emission, compared to direct ones, for three reasons: (1) the GO/MoO3 layers introduce barriers for electrons to reach the Al electrode, and, similarly, the ZnO layers acts as a barrier for holes to travel to the ITO electrode; (2) the introduction of a layer of MoO3 nanoparticles as a hole-inject layer reduces the barrier height for holes and thereby balances charge injection in the inverted structure; and (3) the wide-bandgap zinc oxide next to the ITO electrode does not absorb the EL emission during its exit from the device. In the QDLEDs with oxides as carrier inject and transport layers, the EL spectrum resembles the photoluminescence emission of the emitting material (AIZS), implying that excitons are formed in the quaternary nanocrystals and decay radiatively.

  3. High dielectric constant and energy density induced by the tunable TiO2 interfacial buffer layer in PVDF nanocomposite contained with core-shell structured TiO2@BaTiO3 nanoparticles

    Science.gov (United States)

    Hu, Penghao; Jia, Zhuye; Shen, Zhonghui; Wang, Peng; Liu, Xiaoru

    2018-05-01

    To realize application in high-capacity capacitors and portable electric devices, large energy density is eagerly desired for polymer-based nanocomposite. The core-shell structured nanofillers with inorganic buffer layer are recently supposed to be promising in improving the dielectric property of polymer nanocomposite. In this work, core-shell structured TO@BT nanoparticles with crystalline TiO2 buffer layer coated on BaTiO3 nanoparticle were fabricated via solution method and heat treatment. The thickness of the TO buffer layer can be tailored by modulating the additive amount of the titanate coupling agent in preparation process, and the apparent dielectric properties of nanocomposite are much related to the thickness of the TO layer. The relatively thin TO layer prefer to generate high polarization to increase dielectric constant while the relatively thick TO layer would rather to homogenize field to maintain breakdown strength. Simulation of electric field distribution in the interfacial region reveals the improving effect of the TO buffer layer on the dielectric properties of nanocomposite which accords with the experimental results well. The optimized nanoparticle TO@BT-2 with a mean thickness of 3-5 nm buffer layer of TO is effective in increasing both the ε and Eb in the PVDF composite film. The maximal discharged energy density of 8.78 J/cm3 with high energy efficiency above 0.6 is obtained in TO@BT-2/PVDF nanocomposite with 2.5 vol% loading close to the breakdown strength of 380 kV/mm. The present study demonstrates the approach to optimize the structure of core-shell nanoparticles by modulating buffer layer and provides a new way to further enlarge energy density in polymer nanocomposite.

  4. Synthesis and characterization of water-dispersed CdSe/CdS core-shell quantum dots prepared via Layer-by-layer Method capped with carboxylic-functionalized poly(vinyl alcohol)

    Energy Technology Data Exchange (ETDEWEB)

    Ramanery, Fabio Pereira; Mansur, Alexandra Ancelmo Piscitelli; Mansur, Herman Sander, E-mail: hmansur@demet.ufmg.br [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Metalurgia e Engenharia dos Materiais. Centro de Nanociencia, Nanotecnologia e Inovacao

    2014-08-15

    The main goal of this work was to synthesize CdSe/CdS (core-shell) nanoparticles stabilized by polymer ligand using entirely aqueous colloidal chemistry at room temperature. First, the CdSe core was prepared using precursors and acid-functionalized poly(vinyl alcohol) as the capping ligand. Next, a CdS shell was grown onto the CdSe core via the layer-by-layer technique. The CdS shell was formed by two consecutive monolayers, as estimated by empirical mathematical functions. The nucleation and growth of CdSe quantum dots followed by CdS shell deposition were characterized by UV-vis spectroscopy, photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). The results indicated a systematic red-shift of the absorption and emission spectra after the deposition of CdS, indicating the shell growth onto the CdSe core. TEM coupled with electron diffraction analysis revealed the presence of CdSe/CdS with an epitaxial shell growth. Therefore, it may be concluded that CdSe/CdS quantum dots with core-shell nanostructure were effectively synthesized.(author)

  5. Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

    International Nuclear Information System (INIS)

    McKerracher, Ian; Fu Lan; Hoe Tan, Hark; Jagadish, Chennupati

    2012-01-01

    Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiO x N y films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.

  6. Hot exciton relaxation in multiple layers CdSe/ZnSe self-assembled quantum dots separated by thick ZnSe barriers

    International Nuclear Information System (INIS)

    Eremenko, M; Budkin, G; Reznitsky, A

    2015-01-01

    We have studied PL and PLE spectra of two samples (A and B) of MBE grown CdSe/ZnSe asymmetric double quantum wells with different amount of deposited CdSe layers separated by 14 nm ZnSe barrier. It has been found that PLE spectra of the states forming short wavelength side of the PL spectra of both deep and shallow QWs of the sample A as well as that of deep QW of the sample B demonstrate oscillating structure in the spectral ranges corresponding to exciton states of self-assembled quantum dots only. Meanwhile PLE spectra of the short wavelength states of shallow QW the sample B revealed pronounced oscillating structure with energy period of ZnSe LO phonon under excitation with photons in a wide energy range both in the regions of quantum-dot states and in that of free states in the ZnSe barrier. In these spectra creating of excitons with kinetic energies more than 0.3 eV was observed which considerably exceed the exciton binding energy as well as LO phonon energy (both appr. 0.03 eV). It has been concluded that oscillating structure of the PLE spectra arises due to cascade relaxation of hot excitons. We discuss the model which explains these experimental findings. (paper)

  7. Hot exciton relaxation in multiple layers CdSe/ZnSe self-assembled quantum dots separated by thick ZnSe barriers

    Science.gov (United States)

    Eremenko, M.; Budkin, G.; Reznitsky, A.

    2015-11-01

    We have studied PL and PLE spectra of two samples (A and B) of MBE grown CdSe/ZnSe asymmetric double quantum wells with different amount of deposited CdSe layers separated by 14 nm ZnSe barrier. It has been found that PLE spectra of the states forming short wavelength side of the PL spectra of both deep and shallow QWs of the sample A as well as that of deep QW of the sample B demonstrate oscillating structure in the spectral ranges corresponding to exciton states of self-assembled quantum dots only. Meanwhile PLE spectra of the short wavelength states of shallow QW the sample B revealed pronounced oscillating structure with energy period of ZnSe LO phonon under excitation with photons in a wide energy range both in the regions of quantum-dot states and in that of free states in the ZnSe barrier. In these spectra creating of excitons with kinetic energies more than 0.3 eV was observed which considerably exceed the exciton binding energy as well as LO phonon energy (both appr. 0.03 eV). It has been concluded that oscillating structure of the PLE spectra arises due to cascade relaxation of hot excitons. We discuss the model which explains these experimental findings.

  8. Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot.

    Science.gov (United States)

    Song, Xiang-Xiang; Zhang, Zhuo-Zhi; You, Jie; Liu, Di; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

    2015-11-05

    Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs.

  9. InGaAs and GaAsSb strain reducing layers covering InAs/GaAs quantum dots

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Hulicius, Eduard; Pangrác, Jiří; Oswald, Jiří; Vyskočil, Jan; Kuldová, Karla; Šimeček, Tomislav; Hazdra, P.; Caha, O.

    2010-01-01

    Roč. 312, č. 8 (2010), 1383-1387 ISSN 0022-0248 R&D Projects: GA AV ČR IAA100100719; GA ČR GA202/09/0676; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : low dimensional structures * photoluminescence * low-pressure MOVPE * InAs/GaAs quantum dots * semiconducting III/V materials Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.737, year: 2010

  10. Interfacial phenomenon theory

    International Nuclear Information System (INIS)

    Kim, Jong Deuk

    2000-02-01

    This book is composed of 8 chapters. It tells what interfacial phenomenon is by showing interfacial energy, characteristic of interface and system of interface from chapter 1. It also introduces interfacial energy and structure theory, molecular structure and orientation theory, and interfacial electricity phenomenon theory in the following 3 chapters. It still goes on by introducing super molecule cluster, disequilibrium dispersion, and surface and film through 3 chapters. And the last chapter is about colloid and application of interface.

  11. Effect of wetting-layer density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers

    International Nuclear Information System (INIS)

    Kim, Jungho; Yu, Bong-Ahn

    2015-01-01

    We numerically investigate the effect of the wetting-layer (WL) density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers in both electrical and optical pumping schemes by solving 1088 coupled rate equations. The temporal variations of the ultrafast gain and phase recovery responses at the ground state (GS) are calculated as a function of the WL density of states. The ultrafast gain recovery responses do not significantly depend on the WL density of states in the electrical pumping scheme and the three optical pumping schemes such as the optical pumping to the WL, the optical pumping to the excited state ensemble, and the optical pumping to the GS ensemble. The ultrafast phase recovery responses are also not significantly affected by the WL density of states except the optical pumping to the WL, where the phase recovery component caused by the WL becomes slowed down as the WL density of states increases. (paper)

  12. In-situ confined formation of NiFe layered double hydroxide quantum dots in expanded graphite for active electrocatalytic oxygen evolution

    Science.gov (United States)

    Guo, Jinxue; Li, Xiaoyan; Sun, Yanfang; Liu, Qingyun; Quan, Zhenlan; Zhang, Xiao

    2018-06-01

    Development of noble-metal-free catalysts towards highly efficient electrochemical oxygen evolution reaction (OER) is critical but challenging in the renewable energy area. Herein, we firstly embed NiFe LDHs quantum dots (QDs) into expanded graphite (NiFe LDHs/EG) via in-situ confined formation process. The interlayer spacing of EG layers acts as nanoreactors for spatially confined formation of NiFe LDHs QDs. The QDs supply huge catalytic sites for OER. The in-situ decoration endows the strong affinity between QDs with EG, thus inducing fast charge transfer. Based on the aforementioned benefits, the designed catalyst exhibits outstanding OER properties, in terms of small overpotential (220 mV required to generate 10 mA cm-2), low Tafel slope, and good durable stability, making it a promising candidate for inexpensive OER catalyst.

  13. Formation of InAs/GaAs quantum dots from a subcritical InAs wetting layer: A reflection high-energy electron diffraction and theoretical study

    International Nuclear Information System (INIS)

    Song, H. Z.; Usuki, T.; Nakata, Y.; Yokoyama, N.; Sasakura, H.; Muto, S.

    2006-01-01

    InAs/GaAs quantum dots (QD's) are formed by postgrowth annealing of an InAs wetting layer thinner than the critical thickness for the transition from two- (2D) to three-dimensional (3D) growth mode. Reflection high energy electron diffraction is used to monitor the QD formation. Based on a mean-field theory [Phys. Rev. Lett. 79, 897 (1997)], the time evolution of total QD's volume, first increasing and finally saturating, is well explained by precursors forming during wetting layer growth and converting into nucleated QD's after growth stop. Both the saturation QD's volume and the QD nucleation rate depend exponentially on the InAs coverage. These behaviors and their temperature and InAs growth rate dependences are essentially understandable in the frame of the mean-field theory. Similar analysis to conventional QD growth suggests that the often observed significant mass transport from wetting layer to QD's can be ascribed to the precursors existing before 2D-3D growth mode transition

  14. Strain-engineering of GaInAsSb overgrown layers and its effects on the optical properties of InAs/GaAs quantum dots

    Science.gov (United States)

    Salhi, A.; Alshaibani, S.; Alaskar, Y.; Albrithen, H.; Albedri, A.; Alyamani, A.

    2018-05-01

    The effect of antimony incorporation in In0.11Ga0.89As overgrown layers on the optical properties of InAs/GaAs quantum dots grown by molecular beam epitaxy has been studied. The results of photoluminescence, high resolution X-ray diffraction, atomic force microscopy, power and temperature-dependent photoluminescence from 77 K to 300 K have been correlated to characterize the grown samples. The wavelength emission increases with Sb content, and it reaches ∼1367 nm and does not increase further because of Sb incorporation's saturation in the In0.11Ga0.89As layer. To redshift further the wavelength to 1432 nm, a reduction of the growth temperature of the In0.11Ga0.89As1-ySby layer from 500 °C to 440 °C was necessary. This achievement is accompanied by the transformation of the QDs distribution to 2 QDs families. The extracted activation energies suggest that the PL quenching is mainly attributed to the thermal transfer of carriers in the QDs to the higher energy levels in the defects located within the In0.11Ga0.89As1-ySby SRLs. The variation of PL FWHM with temperature was interpreted by carrier thermalization and capture among different QDs within the same QD family or between small and large QD families.

  15. Dentin-cement Interfacial Interaction

    Science.gov (United States)

    Atmeh, A.R.; Chong, E.Z.; Richard, G.; Festy, F.; Watson, T.F.

    2012-01-01

    The interfacial properties of a new calcium-silicate-based coronal restorative material (Biodentine™) and a glass-ionomer cement (GIC) with dentin have been studied by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), micro-Raman spectroscopy, and two-photon auto-fluorescence and second-harmonic-generation (SHG) imaging. Results indicate the formation of tag-like structures alongside an interfacial layer called the “mineral infiltration zone”, where the alkaline caustic effect of the calcium silicate cement’s hydration products degrades the collagenous component of the interfacial dentin. This degradation leads to the formation of a porous structure which facilitates the permeation of high concentrations of Ca2+, OH-, and CO32- ions, leading to increased mineralization in this region. Comparison of the dentin-restorative interfaces shows that there is a dentin-mineral infiltration with the Biodentine, whereas polyacrylic and tartaric acids and their salts characterize the penetration of the GIC. A new type of interfacial interaction, “the mineral infiltration zone”, is suggested for these calcium-silicate-based cements. PMID:22436906

  16. Atomic layer deposition in nanostructured photovoltaics: tuning optical, electronic and surface properties

    Science.gov (United States)

    Palmstrom, Axel F.; Santra, Pralay K.; Bent, Stacey F.

    2015-07-01

    Nanostructured materials offer key advantages for third-generation photovoltaics, such as the ability to achieve high optical absorption together with enhanced charge carrier collection using low cost components. However, the extensive interfacial areas in nanostructured photovoltaic devices can cause high recombination rates and a high density of surface electronic states. In this feature article, we provide a brief review of some nanostructured photovoltaic technologies including dye-sensitized, quantum dot sensitized and colloidal quantum dot solar cells. We then introduce the technique of atomic layer deposition (ALD), which is a vapor phase deposition method using a sequence of self-limiting surface reaction steps to grow thin, uniform and conformal films. We discuss how ALD has established itself as a promising tool for addressing different aspects of nanostructured photovoltaics. Examples include the use of ALD to synthesize absorber materials for both quantum dot and plasmonic solar cells, to grow barrier layers for dye and quantum dot sensitized solar cells, and to infiltrate coatings into colloidal quantum dot solar cell to improve charge carrier mobilities as well as stability. We also provide an example of monolayer surface modification in which adsorbed ligand molecules on quantum dots are used to tune the band structure of colloidal quantum dot solar cells for improved charge collection. Finally, we comment on the present challenges and future outlook of the use of ALD for nanostructured photovoltaics.

  17. Amorphous-like interfacial layer between a high-Tc superconducting Tl-1223 film and a Ag substrate examined by high-voltage high-resolution transmission electron microscopy

    International Nuclear Information System (INIS)

    Kim, Bongjun; Kim, Hyuntak; Nagai, Takuro; Matsui, Yoshio; Horiuchi, Shigeo; Jeong, Daeyeong; Deinhofer, Christian; Gritzner, Gerhard; Kim, Youngmin; Kim, Younjoong

    2006-01-01

    The thin amorphous-like layer, formed at the interface between a high-T c superconducting (Tl 0.5 , Pb 0.5 )(Sr 0.8 , Ba 0.2 )Ca 2 Cu 3 O y (Tl-1223) film and a Ag substrate during heating at 910 .deg. C, has been examined by using high-voltage high-resolution transmission electron microscopy. The interfacial layer is less than 10 nm in thickness. It contacts the (001) plane of Tl-1223 and the (113) or (133) planes of Ag in most cases. Its composition is similar to that of Tl-1223, except for the inclusion of a substantial amount of Ag. Its formation proceeds by diffusion of Ag into Tl-1223, during which a structure change first occurs at the layer of CuO 2 + Ca planes. The Tl(Pb)O + the Sr(Ba)O layers are then destroyed to cause the total structure to become amorphous-like. Furthermore, we have found that it is formed under an irradiation of highly energetic electrons.

  18. Amorphous-like interfacial layer between a high-T{sub c} superconducting Tl-1223 film and a Ag substrate examined by high-voltage high-resolution transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Bongjun; Kim, Hyuntak [Electronics and Tele-Communications Research Institute, Daejeon (Korea, Republic of); Nagai, Takuro; Matsui, Yoshio [National Institute for Materials Science, Tsukuba, Ibaraki (Japan); Horiuchi, Shigeo; Jeong, Daeyeong [Electrotechnology Research Institute, Changwon (Korea, Republic of); Deinhofer, Christian; Gritzner, Gerhard [Johannes Kepler University, Linz (Austria); Kim, Youngmin; Kim, Younjoong [Electron Microscopy Team, Korea Basic Science Institute, Daejeon (Korea, Republic of)

    2006-05-15

    The thin amorphous-like layer, formed at the interface between a high-T{sub c} superconducting (Tl{sub 0.5}, Pb{sub 0.5})(Sr{sub 0.8}, Ba{sub 0.2})Ca{sub 2}Cu{sub 3}O{sub y} (Tl-1223) film and a Ag substrate during heating at 910 .deg. C, has been examined by using high-voltage high-resolution transmission electron microscopy. The interfacial layer is less than 10 nm in thickness. It contacts the (001) plane of Tl-1223 and the (113) or (133) planes of Ag in most cases. Its composition is similar to that of Tl-1223, except for the inclusion of a substantial amount of Ag. Its formation proceeds by diffusion of Ag into Tl-1223, during which a structure change first occurs at the layer of CuO{sub 2} + Ca planes. The Tl(Pb)O + the Sr(Ba)O layers are then destroyed to cause the total structure to become amorphous-like. Furthermore, we have found that it is formed under an irradiation of highly energetic electrons.

  19. Effects of InAlAs strain reducing layer on the photoluminescence properties of InAs quantum dots embedded in InGaAs/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Lingmin, E-mail: konglm@qq.com [School of Marine Science and Technology, Zhejiang Ocean University, Zhoushan 316000 (China); Sun, Wei [SEM School of Electromechanical Engineering, Weifang Engineering Vocational College, Qingzhou 262500 (China); Feng, Zhe Chuan, E-mail: zcfeng@nut.edu.tw [Institute of Photonics and Optoelectronics, Department of Electrical Engineering, and Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei 106-17, Taiwan (China); Xie, Sheng [School of Electronic and Information Engineering, Tianjin University, Tianjin 300072 (China); Zhou, Yunqing; Wang, Rui; Zhang, Cunxi; Zong, Zhaocun; Wang, Hongxia; Qiao, Qian [Department of Physics, Zhejiang Ocean University, Zhoushan 316000 (China); Wu, Zhengyun [Department of Physics, Xiamen University, Xiamen 361005 China (China)

    2014-07-01

    Two kinds of self-assembled quantum dots (QDs) embedded within InGaAs/GaAs quantum wells were grown by molecular beam epitaxy: one was capped with an InAlAs strain reducing (SR) layer, while the other was not. Their emission dynamics was investigated by time-resolved and temperature dependent (TD) photoluminescence (PL) measurements. A significant redshift can be observed in the emission peak position of InAs QDs with thin InAlAs SR cap layer, which results from SR effects. Different behaviors of the integrated PL intensity for the samples with or without InAlAs layer may be ascribed to the reduced carrier transition at higher temperature for the higher energy barrier of the InAlAs layer, and the TD mode of carrier migration. The PL decay time of quantum dots grown with InAlAs layer was much longer than that without the layer, which implies that the InAlAs layer with higher energy barrier may enhance the quantum restriction of carriers in InAs QDs. These observations are discussed from the viewpoint of strain compensation and potential barrier variation with SR layers. Our experiments also demonstrate that the main mode of carrier migration is quantum tunneling effect at lower temperature, while it is quantum transition at higher temperature. The results demonstrate the importance of InAlAs SR layer for the optical quality of InAs QDs. - Highlights: • InAs quantum dots (QDs) were grown on GaAs. • A thin InAlAs layer was grown on InAs QDs. • Temperature dependent photoluminescence (PL) and time-resolved PL were carried out. • Both a redshift and a double exponential decay of PL emission were generated by the InAlAs layer.

  20. Molecular Doping of the Hole-Transporting Layer for Efficient, Single-Step Deposited Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Kirmani, Ahmad R.; Garcia de Arquer, F. Pelayo; Fan, James Z.; Khan, Jafar Iqbal; Walters, Grant; Hoogland, Sjoerd; Wehbe, Nimer; Said, Marcel M.; Barlow, Stephen; Laquai, Fré dé ric; Marder, Seth R.; Sargent, Edward H.; Amassian, Aram

    2017-01-01

    solar cells. These promising architectures employ a QD hole-transporting layer (HTL) whose intrinsically shallow Fermi level (EF) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a

  1. Structural and optical properties of AlGaP confinement layers and InGaAs quantum dot light emitters onto GaP substrate: Towards photonics on silicon applications

    Energy Technology Data Exchange (ETDEWEB)

    Robert, C., E-mail: cedric.robert@insa.rennes.fr [Université Européenne de Bretagne, INSA Rennes (France); CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes 35708 Rennes (France); Thanh, T. Nguyen; Létoublon, A.; Perrin, M.; Cornet, C.; Levallois, C.; Jancu, J.M.; Even, J. [Université Européenne de Bretagne, INSA Rennes (France); CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes 35708 Rennes (France); Turban, P. [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Université de Rennes 1, F-35042 Rennes Cedex (France); Balocchi, A.; Marie, X. [Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 avenue de Rangueil, 31077 Toulouse (France); Durand, O.; Le Corre, A. [Université Européenne de Bretagne, INSA Rennes (France); CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes 35708 Rennes (France)

    2013-08-31

    AlGaP alloy and InGaAs/GaP quantum dots are studied toward possible solutions for the cladding layers and the active zone of a pseudomorphic laser structure on silicon. Coherent growth of AlGaP layers on GaP substrate is carefully analysed by X-ray reciprocal space mapping. The influence of Al content on refractive index is studied by spectroscopic ellipsometry. The structural and optical properties of InGaAs/GaP quantum dots are respectively studied by scanning tunnelling microscopy and time-resolved photoluminescence experiments. - Highlights: ► An active zone is proposed for a pseudomorphic laser structure on Si. ► Cladding layers are proposed for a pseudomorphic laser structure on Si. ► The AlGaP alloy is studied by X-ray diffraction and spectroscopic ellipsometry. ► InGaAs/GaP quantum dots are studied by scanning tunnelling microscopy. ► InGaAs/GaP quantum dots are studied by time-resolved photoluminescence.

  2. Thickness engineering of atomic layer deposited Al2O3 films to suppress interfacial reaction and diffusion of Ni/Au gate metal in AlGaN/GaN HEMTs up to 600 °C in air

    Science.gov (United States)

    Suria, Ateeq J.; Yalamarthy, Ananth Saran; Heuser, Thomas A.; Bruefach, Alexandra; Chapin, Caitlin A.; So, Hongyun; Senesky, Debbie G.

    2017-06-01

    In this paper, we describe the use of 50 nm atomic layer deposited (ALD) Al2O3 to suppress the interfacial reaction and inter-diffusion between the gate metal and semiconductor interface, to extend the operation limit up to 600 °C in air. Suppression of diffusion is verified through Auger electron spectroscopy (AES) depth profiling and X-ray diffraction (XRD) and is further supported with electrical characterization. An ALD Al2O3 thin film (10 nm and 50 nm), which functions as a dielectric layer, was inserted between the gate metal (Ni/Au) and heterostructure-based semiconductor material (AlGaN/GaN) to form a metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). This extended the 50 nm ALD Al2O3 MIS-HEMT (50-MIS) current-voltage (Ids-Vds) and gate leakage (Ig,leakage) characteristics up to 600 °C. Both, the 10 nm ALD Al2O3 MIS-HEMT (10-MIS) and HEMT, failed above 350 °C, as evidenced by a sudden increase of approximately 50 times and 5.3 × 106 times in Ig,leakage, respectively. AES on the HEMT revealed the formation of a Ni-Au alloy and Ni present in the active region. Additionally, XRD showed existence of metal gallides in the HEMT. The 50-MIS enables the operation of AlGaN/GaN based electronics in oxidizing high-temperature environments, by suppressing interfacial reaction and inter-diffusion of the gate metal with the semiconductor.

  3. Solution-Processed In2O3/ZnO Heterojunction Electron Transport Layers for Efficient Organic Bulk Heterojunction and Inorganic Colloidal Quantum-Dot Solar Cells

    KAUST Repository

    Eisner, Flurin

    2018-04-25

    We report the development of a solution‐processed In2O3/ZnO heterojunction electron transport layer (ETL) and its application in high efficiency organic bulk‐heterojunction (BHJ) and inorganic colloidal quantum dot (CQD) solar cells. Study of the electrical properties of this low‐dimensional oxide heterostructure via field‐effect measurements reveals that electron transport along the heterointerface is enhanced by more than a tenfold when compared to the individual single‐layer oxides. Use of the heterojunction as the ETL in organic BHJ photovoltaics is found to consistently improve the cell\\'s performance due to the smoothening of the ZnO surface, increased electron mobility and a noticeable reduction in the cathode\\'s work function, leading to a decrease in the cells’ series resistance and a higher fill factor (FF). Specifically, non‐fullerene based organic BHJ solar cells based on In2O3/ZnO ETLs exhibit very high power conversion efficiencies (PCE) of up to 12.8%, and high FFs of over 70%. The bilayer ETL concept is further extended to inorganic lead‐sulphide CQD solar cells. Resulting devices exhibit excellent performance with a maximum PCE of 8.2% and a FF of 56.8%. The present results highlight the potential of multilayer oxides as novel ETL systems and lay the foundation for future developments.

  4. Solution-Processed In2O3/ZnO Heterojunction Electron Transport Layers for Efficient Organic Bulk Heterojunction and Inorganic Colloidal Quantum-Dot Solar Cells

    KAUST Repository

    Eisner, Flurin; Seitkhan, Akmaral; Han, Yang; Khim, Dongyoon; Yengel, Emre; Kirmani, Ahmad R.; Xu, Jixian; Garcí a de Arquer, F. Pelayo; Sargent, Edward H.; Amassian, Aram; Fei, Zhuping; Heeney, Martin; Anthopoulos, Thomas D.

    2018-01-01

    We report the development of a solution‐processed In2O3/ZnO heterojunction electron transport layer (ETL) and its application in high efficiency organic bulk‐heterojunction (BHJ) and inorganic colloidal quantum dot (CQD) solar cells. Study of the electrical properties of this low‐dimensional oxide heterostructure via field‐effect measurements reveals that electron transport along the heterointerface is enhanced by more than a tenfold when compared to the individual single‐layer oxides. Use of the heterojunction as the ETL in organic BHJ photovoltaics is found to consistently improve the cell's performance due to the smoothening of the ZnO surface, increased electron mobility and a noticeable reduction in the cathode's work function, leading to a decrease in the cells’ series resistance and a higher fill factor (FF). Specifically, non‐fullerene based organic BHJ solar cells based on In2O3/ZnO ETLs exhibit very high power conversion efficiencies (PCE) of up to 12.8%, and high FFs of over 70%. The bilayer ETL concept is further extended to inorganic lead‐sulphide CQD solar cells. Resulting devices exhibit excellent performance with a maximum PCE of 8.2% and a FF of 56.8%. The present results highlight the potential of multilayer oxides as novel ETL systems and lay the foundation for future developments.

  5. Poly arginine-graphene quantum dots as a biocompatible and non-toxic nanocomposite: Layer-by-layer electrochemical preparation, characterization and non-invasive malondialdehyde sensory application in exhaled breath condensate

    Energy Technology Data Exchange (ETDEWEB)

    Hasanzadeh, Mohammad, E-mail: hasanzadehm@tbzmed.ac.ir [Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz 51664 (Iran, Islamic Republic of); Mokhtari, Fozieh [Pharmaceutical Analysis Research Center, Tabriz University of Medical Sciences, Tabriz (Iran, Islamic Republic of); Department of Biochemistry, Higher Education Institute of Rab-Rashid, Tabriz (Iran, Islamic Republic of); Shadjou, Nasrin [Department of Nanochemistry, Nano Technology Research Center, Urmia University, Urmia 57154 (Iran, Islamic Republic of); Department of Nano Technology, Faculty of Science, Urmia University, Urmia 57154 (Iran, Islamic Republic of); Eftekhari, Aziz [Department of Pharmacology and Toxicology, Faculty of Pharmacy, Tabriz University of Medical Sciences, 51664-14766 Tabriz (Iran, Islamic Republic of); Mokhtarzadeh, Ahad [Department of Biochemistry, Higher Education Institute of Rab-Rashid, Tabriz (Iran, Islamic Republic of); School of Medicine, Gonabad University of Medical Sciences, Gonabad (Iran, Islamic Republic of); Jouyban-Gharamaleki, Vahid [Department of Mechatronic Engineering, International Campus, University of Tabriz, Tabriz (Iran, Islamic Republic of); Mahboob, Soltanali [Department of Biochemistry, Higher Education Institute of Rab-Rashid, Tabriz (Iran, Islamic Republic of)

    2017-06-01

    This study reports on the electropolymerization of a low toxic and biocompatible polymer with entitle poly arginine-graphene quantum dots (PARG-GQDs) as a novel strategy for surface modification of glassy carbon (GC) surface and preparation a new interface for biomedical application. The fabrication of PARG-GQDs on GCE was performed using Layer-by-layer regime. Scanning electron microscopy (SEM) was confirmed dispersion of GQDs on the surface of PARG which lead to increase of surface coverage of PARG. The redox behavior of prepared sensor was then characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CHA), square wave voltammetry (SWV), linear sweep voltammetry (LSV). The electroactivity of PARG-GQDs coating towards detection and determination of malondialdehyde (MDA) as one of the most common biomarkers of oxidative stress, was then studied. Then, application of prepared sensor for the detection of MDA in exhaled breath condensate (EBC) is described. Electrochemical based sensor shows the lower limit of quantification (LLOQ) were 0.329 nanomolar. This work is the first report on the integration of GQDs to poly amino acids. Further development can lead to monitoring of MDA or other exhaled breath biomarkers by GQDs functionalized poly amino acids in EBC using electrochemical methods. - Highlights: • Simple and one pot electropolymerization was used to preparation of Poly arginine-graphene quantum dots. • PARG-GQDs-GCE shows an excellent electroactivity towards malondialdehyde. • High sensitivity and efficiency is achieved through a simple method of modification. • MDA electrochemical sensor for a direct evaluation of oxidative stress in EBC media is possible.

  6. Poly arginine-graphene quantum dots as a biocompatible and non-toxic nanocomposite: Layer-by-layer electrochemical preparation, characterization and non-invasive malondialdehyde sensory application in exhaled breath condensate

    International Nuclear Information System (INIS)

    Hasanzadeh, Mohammad; Mokhtari, Fozieh; Shadjou, Nasrin; Eftekhari, Aziz; Mokhtarzadeh, Ahad; Jouyban-Gharamaleki, Vahid; Mahboob, Soltanali

    2017-01-01

    This study reports on the electropolymerization of a low toxic and biocompatible polymer with entitle poly arginine-graphene quantum dots (PARG-GQDs) as a novel strategy for surface modification of glassy carbon (GC) surface and preparation a new interface for biomedical application. The fabrication of PARG-GQDs on GCE was performed using Layer-by-layer regime. Scanning electron microscopy (SEM) was confirmed dispersion of GQDs on the surface of PARG which lead to increase of surface coverage of PARG. The redox behavior of prepared sensor was then characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CHA), square wave voltammetry (SWV), linear sweep voltammetry (LSV). The electroactivity of PARG-GQDs coating towards detection and determination of malondialdehyde (MDA) as one of the most common biomarkers of oxidative stress, was then studied. Then, application of prepared sensor for the detection of MDA in exhaled breath condensate (EBC) is described. Electrochemical based sensor shows the lower limit of quantification (LLOQ) were 0.329 nanomolar. This work is the first report on the integration of GQDs to poly amino acids. Further development can lead to monitoring of MDA or other exhaled breath biomarkers by GQDs functionalized poly amino acids in EBC using electrochemical methods. - Highlights: • Simple and one pot electropolymerization was used to preparation of Poly arginine-graphene quantum dots. • PARG-GQDs-GCE shows an excellent electroactivity towards malondialdehyde. • High sensitivity and efficiency is achieved through a simple method of modification. • MDA electrochemical sensor for a direct evaluation of oxidative stress in EBC media is possible.

  7. Synthesis of GaAs quantum dots on Si-layers on AlGaAs films grown on GaAs(100) substrates

    International Nuclear Information System (INIS)

    Mendez-Garcia, V. H.; Zamora-Peredo, L.; Saucedo-Zeni, N.

    2002-01-01

    In this work we report a novel method for obtaining GaAs quantum dots by molecular beam epitaxy (MBE) on an AlGaAs underlying film. We propose to use a Si monolayer (ML) grown on AlGaAs, in order to induce a 3D nucleation during the GaAs overgrowth. The samples were prepared in a Riber 32P MBE system employing undoped Si-GaAs(100) substrates. First, a 500 nm thick layer of Al x Ga 1-x As was grown with a nominal concentration x=0.35. Several samples were grown in order to analyze the effects of changing the Si interlayer thickness, and the amount of GaAs overgrowth, on the final structures. Previous to the Si-exposure, the AlGaAs presented a (1x3) surface reconstruction which gradually turned to a (3x1) structure when the Si-thickness was 1 ML, as observed in the reflection high-energy electron diffraction (RHEED) patterns. When the GaAs overgrowth started on this surface, transmission RHEED spots appeared and showed a considerable increase in intensity until reaching a maximum. This behavior is typical from a 3D island growth. If the GaAs overgrowth continues, the initial streaky RHEED patterns recovered indicating a 2D-growth. Thus, we prepared a sample stopping the GaAs overgrowth at the time when the diffraction 3D spot reached the maximum intensity, equivalent to 2ML of GaAs. The sample surface was analyzed in air by atomic force microscopy (AFM). Islands of 1.5 nm-height and 20x20 nm of base were clearly observed, these dimensions are suitable for applications in quantum dots. (Authors)

  8. Improving the photovoltaic parameters in Quantum dot sensitized solar cells through employment of chemically deposited compact titania blocking layer

    Energy Technology Data Exchange (ETDEWEB)

    Rajendra Prasad, M.B., E-mail: rajendraprasadmb75@gmail.com [Advanced Physics Laboratory, Department of Physics, SavitibaiPhule Pune University, Pune, 411007 (India); National Defence Academy, Khadakwasla, Pune, 411023 (India); Kadam, Vishal [Advanced Physics Laboratory, Department of Physics, SavitibaiPhule Pune University, Pune, 411007 (India); Joo, Oh-Shim [Korea Institute of Science and Technology, PO Box No. 131, Chongryang, Seoul, 130-650 (Korea, Republic of); Pathan, Habib M. [Advanced Physics Laboratory, Department of Physics, SavitibaiPhule Pune University, Pune, 411007 (India)

    2017-06-15

    Incorporation of compact blocking layer at the Transparent Conducting Oxide (TCO)/Electrolyte interface is an effective method to improve the device performance in QDSSC through mitigation of electron recombinations at this interface. This paper reports the most facile and cost effective method of depositing a rutile titania Compact Layer (CL) over Fluorine doped Tin Oxide (FTO) substrate and its application in titania based CdS QD sensitized solar cells. The deposited compact layers are characterized to study their structural, optical, morphological and electrochemical properties using X-Ray Diffractometry, UV–Visible spectroscopy, Scanning electron microscopy, Cyclic Voltammetry and Contact Angle measurements. Sandwich solar cells are fabricated using these CL based electrodes and characterized using Electrochemical Impedance Spectroscopy, Open Circuit Voltage Decay and J-V characteristics. The CL incorporated CdS QDSSC showed more than 100% increase in the photoconversion efficiency (1.68%) as compared to its bare FTO counterpart (0.73%) proving the efficacy of employed strategy. - Highlights: • Deposited titania compact layer by a facile room temperature chemical bath method. • Employed this to mitigate back electron transfer at TCO/Electrolyte interface. • Compact layer incorporation has improved the solar cell performance by 130%.

  9. Millimeter Wave Modulators Using Quantum Dots

    National Research Council Canada - National Science Library

    Prather, Dennis W

    2008-01-01

    In this effort electro-optic modulators for millimeter wave sensing and imaging were developed and demonstrated via design, fabrication, and experimental characterization of multi layer quantum dot...

  10. Improving photoelectrochemical performance on quantum dots co-sensitized TiO{sub 2} nanotube arrays using ZnO energy barrier by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Min [Key Laboratory of Ministry of Education for Advanced Materials in Tropical Island Resources, College of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Zeng, Xi [College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming, 650500 (China); Peng, Xiange; Zhu, Zhuo; Liao, Jianjun; Liu, Kai; Wang, Guizhen [Key Laboratory of Ministry of Education for Advanced Materials in Tropical Island Resources, College of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Lin, Shiwei, E-mail: linsw@hainu.edu.cn [Key Laboratory of Ministry of Education for Advanced Materials in Tropical Island Resources, College of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China)

    2016-12-01

    Graphical abstract: - Highlights: • The length of TNTAs has a balance between the charge recombination and the QDs loading. • The introduction of ZnO interlayer by ALD could improve the QDs absorption. • The optimal thickness of ZnO interlayer is 1.5 nm prepared by 10 cycles ALD. - Abstract: PbS and CdS quantum dots (QDs) have been deposited onto TiO{sub 2} nanotube arrays (TNTAs) in turn via a sonication-assisted successive ionic layer adsorption and reaction method. This method could uniformly decorate TNTAs with QDs, avoiding QDs aggregation at the mouth of TiO{sub 2} nanotube. The loading amounts of QDs on TNTAs could be controlled by adjusting the TNTAs length. Under one sun illumination, the QDs co-sensitized TNTAs (TNTAs/QDs) with the length of about 2.4 μm displayed the highest photocurrent of 4.32 mA cm{sup −2}, which is 27 times higher than that of the bare TNTAs. Introduction of a thin ZnO energy barrier by atomic layer deposition (ALD) between the TNTAs and QDs can further improve the photocurrent of TNTAs/QDs. And the TNTAs/QDs with 10 ALD cycles of ZnO interlayer exhibits the highest photocurrent of 5.24 mA cm{sup −2} and best photoconversion efficiency of 4.9%, a more than 20% enhancement over the bare TNTAs/QDs. Such enhanced photoelectrochemical performance may be ascribed to the increased amounts of QDs on the TNTAs due to the introduction of ZnO interlayer. The benefits of ALD layers play a crucial role in development and optimization of high-performance photoelectrodes in the near future.

  11. Enhanced solar cell efficiency and stability using ZnS passivation layer for CdS quantum-dot sensitized actinomorphic hexagonal columnar ZnO

    International Nuclear Information System (INIS)

    Chen, Yanli; Tao, Qiang; Fu, Wuyou; Yang, Haibin; Zhou, Xiaoming; Zhang, Yanyan; Su, Shi; Wang, Peng; Li, Minghui

    2014-01-01

    Highlights: • The synthetic of ZnS/CdS QDs/AHC-ZnO photoanode with a simple method. • The power conversion efficiency of the ZnS/CdS QDs/AHC-ZnO is 1.81%. • The effects of photovoltaic performances caused by CdS and ZnS amounts were studied. • ZnS passivation layer enhanced electron lifetime significantly. - Abstract: We report the photoanodes consisting of CdS quantum-dots (QDs) sensitized actinomorphic hexagonal columnar ZnO (CdS QDs/AHC-ZnO) with ZnS passivation layer are applied for solar cells. Simple chemical solution synthesized AHC-ZnO films on transparent conducting glass substrates, and then, AHC-ZnO is functionalized with uniform CdS and ZnS QDs via successive ionic layer adsorption and reaction (SILAR) method. The as-prepared materials were characterized by XRD, SEM, TEM, UV–vis diffused reflectance absorption spectra and photovoltaic performances analysis. Photovoltaic performances results indicate the quantity of CdS QDs as well as the visible light absorption threshold can be effectively controlled by varying the coating cycles during the SILAR process, and the photocurrent density (Jsc) is greatly improved by increasing the amount of ZnS. By optimizing the AHC-ZnO with the amount of CdS and ZnS, the best efficiency of 1.81% was achieved for solar cell under AM 1.5 G illumination with Jsc = 7.44 mA/cm 2 , Voc = 0.57 V and FF = 43%

  12. Improving photoelectrochemical performance on quantum dots co-sensitized TiO_2 nanotube arrays using ZnO energy barrier by atomic layer deposition

    International Nuclear Information System (INIS)

    Zeng, Min; Zeng, Xi; Peng, Xiange; Zhu, Zhuo; Liao, Jianjun; Liu, Kai; Wang, Guizhen; Lin, Shiwei

    2016-01-01

    Graphical abstract: - Highlights: • The length of TNTAs has a balance between the charge recombination and the QDs loading. • The introduction of ZnO interlayer by ALD could improve the QDs absorption. • The optimal thickness of ZnO interlayer is 1.5 nm prepared by 10 cycles ALD. - Abstract: PbS and CdS quantum dots (QDs) have been deposited onto TiO_2 nanotube arrays (TNTAs) in turn via a sonication-assisted successive ionic layer adsorption and reaction method. This method could uniformly decorate TNTAs with QDs, avoiding QDs aggregation at the mouth of TiO_2 nanotube. The loading amounts of QDs on TNTAs could be controlled by adjusting the TNTAs length. Under one sun illumination, the QDs co-sensitized TNTAs (TNTAs/QDs) with the length of about 2.4 μm displayed the highest photocurrent of 4.32 mA cm"−"2, which is 27 times higher than that of the bare TNTAs. Introduction of a thin ZnO energy barrier by atomic layer deposition (ALD) between the TNTAs and QDs can further improve the photocurrent of TNTAs/QDs. And the TNTAs/QDs with 10 ALD cycles of ZnO interlayer exhibits the highest photocurrent of 5.24 mA cm"−"2 and best photoconversion efficiency of 4.9%, a more than 20% enhancement over the bare TNTAs/QDs. Such enhanced photoelectrochemical performance may be ascribed to the increased amounts of QDs on the TNTAs due to the introduction of ZnO interlayer. The benefits of ALD layers play a crucial role in development and optimization of high-performance photoelectrodes in the near future.

  13. High color rendering index of remote-type white LEDs with multi-layered quantum dot-phosphor films and short-wavelength pass dichroic filters

    Science.gov (United States)

    Yoon, Hee Chang; Oh, Ji Hye; Do, Young Rag

    2014-09-01

    This paper introduces high color rendering index (CRI) white light-emitting diodes (W-LEDs) coated with red emitting (Sr,Ca)AlSiN3:Eu phosphors and yellowish-green emitting AgIn5S8/ZnS (AIS/ZS) quantum dots (QDs) on glass or a short-wavelength pass dichroic filter (SPDF), which transmit blue wavelength regions and reflect yellow wavelength regions. The red emitting (Sr,Ca)AlSiN3:Eu phosphor film is coated on glass and a SPDF using a screen printing method, and then the yellowish-green emitting AIS/ZS QDs are coated on the red phosphor (Sr,Ca)AlSiN3:Eu film-coated glass and SPDF using the electrospray (e-spray) method.To fabricate the red phosphor film, the optimum amount of phosphor is dispersed in a silicon binder to form a red phosphor paste. The AIS/ZS QDs are mixed with dimethylformamide (DMF), toluene, and poly(methyl methacrylate) (PMMA) for the e-spray coating. The substrates are spin-coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to fabricate a conductive surface. The CRI of the white LEDs is improved through inserting the red phosphor film between the QD layer and the glass substrate. Furthermore, the light intensities of the multi-layered phosphor films are enhanced through changing the glass substrate to the SPDF. The correlated color temperatures (CCTs) vary as a function of the phosphor concentration in the phosphor paste. The optical properties of the yellowish-green AIS/ZS QDs and red (Sr,Ca)AlSiN3:Eu phosphors are characterized using photoluminescence (PL), and the multi-layered QD-phosphor films are measured using electroluminescence (EL) with an InGaN blue LED (λmax = 450 nm) at 60 mA.

  14. Rational design of a bi-layered reduced graphene oxide film on polystyrene foam for solar-driven interfacial water evaporation

    KAUST Repository

    Shi, Le; Wang, Yuchao; Zhang, Lianbin; Wang, Peng

    2016-01-01

    Solar-driven water evaporation has been emerging as a highly efficient way for utilizing solar energy for clean water production and wastewater treatment. Here we rationally designed and fabricated a bi-layered photothermal membrane with a porous

  15. Interfacial effects in multilayers

    International Nuclear Information System (INIS)

    Barbee, T.W. Jr.

    1998-01-01

    Interfacial structure and the atomic interactions between atoms at interfaces in multilayers or nano-laminates have significant impact on the physical properties of these materials. A technique for the experimental evaluation of interfacial structure and interfacial structure effects is presented and compared to experiment. In this paper the impact of interfacial structure on the performance of x-ray, soft x-ray and extreme ultra-violet multilayer optic structures is emphasized. The paper is concluded with summary of these results and an assessment of their implications relative to multilayer development and the study of buried interfaces in solids in general

  16. Anomalous Hall effect suppression in anatase Co:TiO2 by the insertion of an interfacial TiO2 buffer layer

    NARCIS (Netherlands)

    Lee, Y.J.; de Jong, Machiel Pieter; van der Wiel, Wilfred Gerard; Kim, Y.; Brock, J.D.

    2010-01-01

    We present the effect of introducing a TiO2 buffer layer at the SrTiO3 /Co:TiO2 interface on the magnetic and structural properties of anatase Co:TiO2 1.4 at. % Co. Inserting the buffer layer leads to suppression of the room-temperature anomalous Hall effect, accompanied by a reduced density of Co

  17. The effects of wetting layer on electronic and optical properties of intersubband P-to-S transitions in strained dome-shaped InAs/GaAs quantum dots

    Directory of Open Access Journals (Sweden)

    Mohammadreza Shahzadeh

    2014-06-01

    Full Text Available The authors report on the impact of wetting layer thickness and quantum dot size on the electronic and optical properties of dome-shaped InAs/GaAs quantum dots (QDs with strained potential. Two wetting layer thicknesses of 0.5 and 2.0 nm were compared. A strong size dependence of P-to-S transition energy, transition dipole moment, oscillator strength, and linear and third-order nonlinear susceptibilities were concluded. The P-to-S transition dipole moment was shown to be purely in-plane polarization. The linear and nonlinear absorption and dispersion showed a red shift when the wetting layer thickness was increased. Our results revealed that the nonlinear susceptibility is much more sensitive to QD size compared to the linear susceptibility. An interpretation of the results was presented based on the probability density of finding the electron inside the dot and wetting layer. The results are in good agreement with previously reported experimental data.

  18. Effects of Cr underlayer and Pt buffer layer on the interfacial structure and magnetic characteristics of sputtered FePt films

    International Nuclear Information System (INIS)

    Sun, A.-C.; Hsu, J.-H.; Huang, H.L.; Kuo, P.C.

    2006-01-01

    This work develops a new method for growing L1 0 FePt(0 0 1) thin film on a Pt/Cr bilayer using an amorphous glass substrate. Semi-coherent epitaxial growth was initiated from the Cr(0 0 2) underlayer, continued through the Pt(0 0 1) buffer layer, and extended into the L1 0 FePt(0 0 1) magnetic layer. The squareness of the L1 0 FePt film in the presence of both a Cr underlayer and a Pt buffer layer was close to unity as the magnetic field was applied perpendicular to the film plane. The single L1 0 FePt(1 1 1) orientation was observed in the absence of a Cr underlayer. When a Cr underlayer is inserted, the preferred orientation switched from L1 0 FePt(1 1 1) to L1 0 FePt(0 0 1) and the magnetic film exhibited perpendicular magnetic anisotropy. However, in the absence of an Pt intermediate layer, the Cr atoms diffused directly into the FePt magnetic layer and prevented the formation of the L1 0 FePt(0 0 1) preferred orientation. When a Pt buffer layer was introduced between the FePt and Cr underlayer, the L1 0 FePt(0 0 1) peak appeared. The thickness of the Pt buffer layer also substantially affected the magnetic properties and atomic arrangement at the FePt/Pt and Pt/Cr interfaces

  19. Impact of electrically formed interfacial layer and improved memory characteristics of IrOx/high-κx/W structures containing AlOx, GdOx, HfOx, and TaOx switching materials.

    Science.gov (United States)

    Prakash, Amit; Maikap, Siddheswar; Banerjee, Writam; Jana, Debanjan; Lai, Chao-Sung

    2013-09-06

    Improved switching characteristics were obtained from high-κ oxides AlOx, GdOx, HfOx, and TaOx in IrOx/high-κx/W structures because of a layer that formed at the IrOx/high-κx interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled 'SET/RESET' current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrOx/high-κx interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrOx/AlOx/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>105 cycles), and data retention of >104 s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications.

  20. Comparison of the Effect of Horizontal Vibrations on Interfacial Waves in a Two-Layer System of Inviscid Liquids to Effective Gravity Inversion

    Science.gov (United States)

    Pimenova, Anastasiya V.; Goldobin, Denis S.; Lyubimova, Tatyana P.

    2018-02-01

    We study the waves at the interface between two thin horizontal layers of immiscible liquids subject to high-frequency tangential vibrations. Nonlinear governing equations are derived for the cases of two- and three-dimensional flows and arbitrary ratio of layer thicknesses. The derivation is performed within the framework of the long-wavelength approximation, which is relevant as the linear instability of a thin-layers system is long-wavelength. The dynamics of equations is integrable and the equations themselves can be compared to the Boussinesq equation for the gravity waves in shallow water, which allows one to compare the action of the vibrational field to the action of the gravity and its possible effective inversion.

  1. Quantum Dots

    Science.gov (United States)

    Tartakovskii, Alexander

    2012-07-01

    Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by

  2. Competitive growth mechanisms of InAs quantum dots on InxGa1-xAs layer during post growth interruption

    International Nuclear Information System (INIS)

    Yang, Changjae; Kim, Jungsub; Sim, Uk; Lee, Jaeyel; Choi, Won Jun; Yoon, Euijoon

    2010-01-01

    We investigated the effect of the post growth interruption (GI) on InAs quantum dots (QDs) grown on In x Ga 1-x As strained buffer layers (SBL). When QDs were grown on the 5 and 10% In content SBLs by using post GI, the size of QDs increased as its density decreased. Based on the 50 meV red-shift of PL in these cases, the transport of materials between QDs leads to the increase of QD size with maintaining its composition during the post GI. On the other hand, when using SBLs with the 15 and 20% In contents, the size of QDs increased, but its density was a little reduced. In addition, PL results were observed blue-shifted by about 20 meV and 2 meV, respectively. Considering the interruption of source gases during the post GI, these observations are strong evidence of the Ga incorporation from 15 and 20% In content SBLs. Therefore, these results imply that the dominant mechanism which increases the size of QDs during the post GI depends on the growth condition of SBL.

  3. Narrow ridge waveguide high power single mode 1.3-μm InAs/InGaAs ten-layer quantum dot lasers

    Directory of Open Access Journals (Sweden)

    Cao Q

    2007-01-01

    Full Text Available AbstractTen-layer InAs/In0.15Ga0.85As quantum dot (QD laser structures have been grown using molecular beam epitaxy (MBE on GaAs (001 substrate. Using the pulsed anodic oxidation technique, narrow (2 μm ridge waveguide (RWG InAs QD lasers have been fabricated. Under continuous wave operation, the InAs QD laser (2 × 2,000 μm2 delivered total output power of up to 272.6 mW at 10 °C at 1.3 μm. Under pulsed operation, where the device heating is greatly minimized, the InAs QD laser (2 × 2,000 μm2 delivered extremely high output power (both facets of up to 1.22 W at 20 °C, at high external differential quantum efficiency of 96%. Far field pattern measurement of the 2-μm RWG InAs QD lasers showed single lateral mode operation.

  4. Effect of sodium acetate additive in successive ionic layer adsorption and reaction on the performance of CdS quantum-dot-sensitized solar cells

    Science.gov (United States)

    Liu, I.-Ping; Chen, Liang-Yih; Lee, Yuh-Lang

    2016-09-01

    Sodium acetate (NaAc) is utilized as an additive in cationic precursors of the successive ionic layer adsorption and reaction (SILAR) process to fabricate CdS quantum-dot (QD)-sensitized photoelectrodes. The effects of the NaAc concentration on the deposition rate and distribution of QDs in mesoporous TiO2 films, as well as on the performance of CdS-sensitized solar cells are studied. The experimental results show that the presence of NaAc can significantly accelerate the deposition of CdS, improve the QD distribution across photoelectrodes, and thereby, increase the performance of solar cells. These results are mainly attributed to the pH-elevation effect of NaAc to the cationic precursors which increases the electrostatic interaction of the TiO2 film to cadmium ions. The light-to-energy conversion efficiency of the CdS-sensitized solar cell increases with increasing concentration of the NaAc and approaches a maximum value (3.11%) at 0.05 M NaAc. Additionally, an ionic exchange is carried out on the photoelectrode to transform the deposited CdS into CdS1-xSex ternary QDs. The light-absorption range of the photoelectrode is extended and an exceptional power conversion efficiency of 4.51% is achieved due to this treatment.

  5. Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Room-Temperature-Processed Ga-Doped ZnO Nanoparticles as the Electron Transport Layer

    KAUST Repository

    Cao, Sheng

    2017-04-19

    Colloidal ZnO nanoparticle (NP) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QD-LEDs) with good stability and high efficiency. However, because of the inherently high work function of such films, spontaneous charge transfer occurs at the QD/ZnO interface in such a QD-LED, thus leading to reduced performance. Here, to improve the QD-LED performance, we prepared Ga-doped ZnO NPs with low work functions and tailored band structures via a room-temperature (RT) solution process without the use of bulky organic ligands. We found that the charge transfer at the interface between the CdSe/ZnS QDs and the doped ZnO NPs was significantly weakened because of the incorporated Ga dopants. Remarkably, the as-assembled QD-LEDs, with Ga-doped ZnO NPs as the ETLs, exhibited superior luminances of up to 44 000 cd/m2 and efficiencies of up to 15 cd/A, placing them among the most efficient red-light QD-LEDs ever reported. This discovery provides a new strategy for fabricating high-performance QD-LEDs by using RT-processed Ga-doped ZnO NPs as the ETLs, which could be generalized to improve the efficiency of other optoelectronic devices.

  6. Amphiphilic Quantum Dots with Asymmetric, Mixed Polymer Brush Layers: From Single Core-Shell Nanoparticles to Salt-Induced Vesicle Formation

    Directory of Open Access Journals (Sweden)

    Brian R. Coleman

    2018-03-01

    Full Text Available A mixed micelle approach is used to produce amphiphilic brush nanoparticles (ABNPs with cadmium sulfide quantum dot (QD cores and surface layers of densely grafted (σ = ~1 chain/nm2 and asymmetric (fPS = 0.9 mixed polymer brushes that contain hydrophobic polystyrene (PS and hydrophilic poly(methyl methacrylate (PMAA chains (PS/PMAA-CdS. In aqueous media, the mixed brushes undergo conformational rearrangements that depend strongly on prior salt addition, giving rise to one of two pathways to fluorescent and morphologically disparate QD-polymer colloids. (A In the absence of salt, centrosymmetric condensation of PS chains forms individual core-shell QD-polymer colloids. (B In the presence of salt, non-centrosymmetric condensation of PS chains forms Janus particles, which trigger anisotropic interactions and amphiphilic self-assembly into the QD-polymer vesicles. To our knowledge, this is the first example of an ABNP building block that can form either discrete core-shell colloids or self-assembled superstructures in water depending on simple changes to the chemical conditions (i.e., salt addition. Such dramatic and finely tuned morphological variation could inform numerous applications in sensing, biolabeling, photonics, and nanomedicine.

  7. Highly Enhanced Photoelectrochemical Water Oxidation Efficiency Based on Triadic Quantum Dot/Layered Double Hydroxide/BiVO 4 Photoanodes

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Yanqun; Wang, Ruirui; Yang, Ye; Yan, Dongpeng; Xiang, Xu

    2016-08-03

    The water oxidation half-reaction is considered to be a bottleneck for achieving highly efficient solar-driven water splitting due to its multiproton-coupled four-electron process and sluggish kinetics. Herein, a triadic photoanode consisting of dual-sized CdTe quantum dots (QDs), Co-based layered double hydroxide (LDH) nanosheets, and BiVO4 particles, that is, QD@LDH@BiVO4, was designed. Two sets of consecutive Type-II band alignments were constructed to improve photogenerated electron-hole separation in the triadic structure. The efficient charge separation resulted in a 2-fold enhancement of the photocurrent of the QD@LDH@BiVO4 photoanode. A significantly enhanced oxidation efficiency reaching above 90% in the low bias region (i.e., E < 0.8 V vs RHE) could be critical in determining the overall performance of a complete photoelectrochemical cell. The faradaic efficiency for water oxidation was almost 90%. The conduction band energy of QDs is -1.0 V more negative than that of LDH, favorable for the electron injection to LDH and enabling a more efficient hole separation. The enhanced photon-to-current conversion efficiency and improved water oxidation efficiency of the triadic structure may result from the non-negligible contribution of hot electrons or holes generated in QDs. Such a band-matching and multidimensional triadic architecture could be a promising strategy for achieving high-efficiency photoanodes by sufficiently utilizing and maximizing the functionalities of QDs.

  8. Interfacial engineering with ultrathin poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) layer for high efficient perovskite light-emitting diodes

    Science.gov (United States)

    Lin, Chunyan; Chen, Ping; Xiong, ZiYang; Liu, Debei; Wang, Gang; Meng, Yan; Song, Qunliang

    2018-02-01

    Organic-inorganic hybrid perovskites have attracted great attention in the field of lighting and display due to their very high color purity and low-cost solution-process. Researchers have done a lot of work in realizing high performance electroluminescent devices. However, the current efficiency (CE) of methyl-ammonium lead halide perovskite light-emitting diodes (PeLEDs) still needs to be improved. Herein, we demonstrate the enhanced performance of PeLEDs through introducing an ultrathin poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) buffer layer between poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and CH3NH3PbBr3 perovskite. Compared to the reference device without PFO, the optimal device luminous intensity, the maximum CE, and the maximum external quantum efficiency increases from 8139 cd m-2 to 30 150 cd m-2, from 7.20 cd A-1 (at 6.8 V) to 10.05 cd A-1 (at 6.6 V), and from 1.73% to 2.44%, respectively. The ultrathin PFO layer not only reduces the exciton quenching at the interface between the hole-transport layer and emission layer, but also passivates the shallow-trap ensure increasing hole injection, as well as increases the coverage of perovskite film.

  9. Quantum dots

    International Nuclear Information System (INIS)

    Kouwenhoven, L.; Marcus, C.

    1998-01-01

    Quantum dots are man-made ''droplets'' of charge that can contain anything from a single electron to a collection of several thousand. Their typical dimensions range from nanometres to a few microns, and their size, shape and interactions can be precisely controlled through the use of advanced nanofabrication technology. The physics of quantum dots shows many parallels with the behaviour of naturally occurring quantum systems in atomic and nuclear physics. Indeed, quantum dots exemplify an important trend in condensed-matter physics in which researchers study man-made objects rather than real atoms or nuclei. As in an atom, the energy levels in a quantum dot become quantized due to the confinement of electrons. With quantum dots, however, an experimentalist can scan through the entire periodic table by simply changing a voltage. In this article the authors describe how quantum dots make it possible to explore new physics in regimes that cannot otherwise be accessed in the laboratory. (UK)

  10. Al-oxynitride interfacial layer investigations for Pr{sub X}O{sub Y} on SiC and Si

    Energy Technology Data Exchange (ETDEWEB)

    Henkel, K; Karavaev, K; Torche, M; Schwiertz, C; Burkov, Y; Schmeisser, D [Brandenburgische Technische Universitaet Cottbus, Angewandte Physik-Sensorik, K-Wachsmann-Allee 17, 03046 Cottbus (Germany)], E-mail: henkel@tu-cottbus.de

    2008-01-15

    We investigate the dielectric properties of Praseodymium based oxides Pr{sub X}O{sub Y} by preparing MIS (metal insulator semiconductor) structures consisting of Pr{sub X}O{sub Y} as a high-k insulating layer and silicon (Si) or silicon carbide (SiC) as semiconductor substrates. The use of a buffer layer between Pr{sub X}O{sub Y} and the semiconductor is necessary as we found deleterious reactions between these materials such as silicate and graphite formation. Possessing a higher permittivity value ({epsilon}{sub r}) than silicon dioxide (SiO{sub 2}) and good lattice matching in conjunction with similar thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. In our spectroscopic investigations we found a decrease or indeed prevention of silicon diffusion into the oxide and an increased Pr{sub 2}O{sub 3} fraction after deposition. In electrical characterizations of Pr{sub X}O{sub Y}/AlON stacks we found considerable improvements in the leakage current by several orders on both substrates, especially on silicon where we obtain values down to 10{sup -7}A/cm{sup 2} at a CET (capacitance equivalent thickness) of 4nm. We observed interface state densities in the range of 5 x 10{sup 11}-1 x 10{sup 12}/eVcm{sup 2} and 1-5 x 10{sup 12}/eVcm{sup 2} on Si and SiC, respectively.

  11. Suppression of interfacial voids formation during silane (SiH4)-based silicon oxide bonding with a thin silicon nitride capping layer

    Science.gov (United States)

    Lee, Kwang Hong; Bao, Shuyu; Wang, Yue; Fitzgerald, Eugene A.; Seng Tan, Chuan

    2018-01-01

    The material properties and bonding behavior of silane-based silicon oxide layers deposited by plasma-enhanced chemical vapor deposition were investigated. Fourier transform infrared spectroscopy was employed to determine the chemical composition of the silicon oxide films. The incorporation of hydroxyl (-OH) groups and moisture absorption demonstrates a strong correlation with the storage duration for both as-deposited and annealed silicon oxide films. It is observed that moisture absorption is prevalent in the silane-based silicon oxide film due to its porous nature. The incorporation of -OH groups and moisture absorption in the silicon oxide films increase with the storage time (even in clean-room environments) for both as-deposited and annealed silicon oxide films. Due to silanol condensation and silicon oxidation reactions that take place at the bonding interface and in the bulk silicon, hydrogen (a byproduct of these reactions) is released and diffused towards the bonding interface. The trapped hydrogen forms voids over time. Additionally, the absorbed moisture could evaporate during the post-bond annealing of the bonded wafer pair. As a consequence, defects, such as voids, form at the bonding interface. To address the problem, a thin silicon nitride capping film was deposited on the silicon oxide layer before bonding to serve as a diffusion barrier to prevent moisture absorption and incorporation of -OH groups from the ambient. This process results in defect-free bonded wafers.

  12. Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density.

    Science.gov (United States)

    Zhou, Ling; Fu, Qiuyun; Xue, Fei; Tang, Xiahui; Zhou, Dongxiang; Tian, Yahui; Wang, Geng; Wang, Chaohong; Gou, Haibo; Xu, Lei

    2017-11-22

    Flexible nanocomposites composed of high dielectric constant fillers and polymer matrix have shown great potential for electrostatic capacitors and energy storage applications. To obtain the composited material with high dielectric constant and high breakdown strength, multi-interfacial composited particles, which composed of conductive cores and insulating shells and possessed the internal barrier layer capacitor (IBLC) effect, were adopted as fillers. Thus, Fe 3 O 4 @BaTiO 3 core-shell particles were prepared and loaded into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) polymer matrix. As the mass fraction of core-shell fillers increased from 2.5 wt % to 30 wt %, the dielectric constant of the films increased, while the loss tangent remained at a low level (capacitor model was also adopted to interpret the efficiency of IBLC effects on the suppressed loss tangent and the superior breakdown strength. This work explored an effective approach to prepare dielectric nanocomposites for energy storage applications experimentally and theoretically.

  13. Capping layer growth rate and the optical and structural properties of GaAsSbN-capped InAs/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ulloa, J. M., E-mail: jmulloa@isom.upm.es; Utrilla, A. D.; Guzman, A.; Hierro, A. [Institute for Systems based on Optoelectronics and Microtechnology (ISOM) and Dpto. Ingeniería Electrónica, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Reyes, D. F.; Ben, T.; González, D. [Departamento de Ciencia de los Materiales e IM y QI, Universidad de Cádiz, 11510 Puerto Real (Cádiz) (Spain)

    2014-10-07

    Changing the growth rate during the heteroepitaxial capping of InAs/GaAs quantum dots (QDs) with a 5 nm-thick GaAsSbN capping layer (CL) strongly modifies the QD structural and optical properties. A size and shape transition from taller pyramids to flatter lens-shaped QDs is observed when the CL growth rate is decreased from 1.5 to 0.5 ML/s. This indicates that the QD dissolution processes taking place during capping can be controlled to some extent by the GaAsSbN CL growth rate, with high growth rates allowing a complete preservation of the QDs. However, the dissolution processes are shown to have a leveling effect on the QD height, giving rise to a narrower size distribution for lower growth rates. Contrary to what could be expected, these effects are opposite to the strong blue-shift and improvement of the photoluminescence (PL) observed for higher growth rates. Nevertheless, the PL results can be understood in terms of the strong impact of the growth rate on the Sb and N incorporation into the CL, which results in lower Sb and N contents at higher growth rates. Besides the QD-CL band offsets and QD strain, the different CL composition alters the band alignment of the system, which can be transformed to type-II at low growth rates. These results show the key role of the alloyed CL growth parameters on the resulting QD properties and demonstrate an intricate correlation between the PL spectra and the sample morphology in complex QD-CL structures.

  14. Addition of Mn to Ge quantum dot surfaces—interaction with the Ge QD {105} facet and the Ge(001) wetting layer

    International Nuclear Information System (INIS)

    Nolph, C A; Kassim, J K; Floro, J A; Reinke, P

    2013-01-01

    The interaction of Mn with Ge quantum dots (QD), which are bounded by {105} facets, and the strained Ge wetting layer (WL), terminated by a (001) surface, is investigated with scanning tunneling microscopy (STM). These surfaces constitute the growth surfaces in the growth of Mn-doped QDs. Mn is deposited on the Ge QD and WL surface in sub-monolayer concentrations, and subsequently annealed up to a temperature of 400 ° C. The changes in bonding and surface topography are measured with STM during the annealing process. Mn forms flat islands on the Ge{105} facet, whose shape and position are guided by the rebonded step reconstruction of the facet. Voltage-dependent STM images reflect the Mn-island interaction with the empty and filled states of the Ge{105} reconstruction. Scanning tunneling spectra (STS) of the Ge{105} facet and as-deposited Mn-islands show a bandgap of 0.8 eV, and the Mn-island spectra are characterized by an additional empty state at about 1.4 eV. A statistical analysis of Mn-island shape and position on the QD yields a slight preference for edge positions, whereas the QD strain field does not impact Mn-island position. However, the formation of ultra-small Mn-clusters dominates on the Ge(001) WL, which is in contrast to Mn interaction with unstrained Ge(001) surfaces. Annealing to T 5 Ge 3 from a mass balance analysis. This reaction is accompanied by the disappearance of the original Mn-surface structures and de-wetting of Mn is complete. This study unravels the details of Mn–Ge interactions, and demonstrates the role of surface diffusion as a determinant in the growth of Mn-doped Ge materials. Surface doping of Ge-nanostructures at lower temperatures could provide a pathway to control magnetism in the Mn–Ge system. (paper)

  15. Surface and interfacial reaction study of half cycle atomic layer deposited HfO{sub 2} on chemically treated GaSb surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zhernokletov, D. M. [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Dong, H.; Brennan, B.; Kim, J. [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Yakimov, M.; Tokranov, V.; Oktyabrsky, S. [College of Nanoscale Science and Engineering, University at Albany - SUNY, Albany, New York 12203 (United States); Wallace, R. M. [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)

    2013-04-01

    An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO{sub 2} dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

  16. Effect of graphene layer thickness and mechanical compliance on interfacial heat flow and thermal conduction in solid-liquid phase change materials.

    Science.gov (United States)

    Warzoha, Ronald J; Fleischer, Amy S

    2014-08-13

    Solid-liquid phase change materials (PCMs) are attractive candidates for thermal energy storage and electronics cooling applications but have limited applicability in state-of-the-art technologies due to their low intrinsic thermal conductivities. Recent efforts to incorporate graphene and multilayer graphene into PCMs have led to the development of thermal energy storage materials with remarkable values of bulk thermal conductivity. However, the full potential of graphene as a filler material for the thermal enhancement of PCMs remains unrealized, largely due to an incomplete understanding of the physical mechanisms that govern thermal transport within graphene-based nanocomposites. In this work, we show that the number of graphene layers (n) within an individual graphene nanoparticle has a significant effect on the bulk thermal conductivity of an organic PCM. Results indicate that the bulk thermal conductivity of PCMs can be tuned by over an order of magnitude simply by adjusting the number of graphene layers (n) from n = 3 to 44. Using scanning electron microscopy in tandem with nanoscale analytical techniques, the physical mechanisms that govern heat flow within a graphene nanocomposite PCM are found to be nearly independent of the intrinsic thermal conductivity of the graphene nanoparticle itself and are instead found to be dependent on the mechanical compliance of the graphene nanoparticles. These findings are critical for the design and development of PCMs that are capable of cooling next-generation electronics and storing heat effectively in medium-to-large-scale energy systems, including solar-thermal power plants and building heating and cooling systems.

  17. Model of interfacial melting

    DEFF Research Database (Denmark)

    Mouritsen, Ole G.; Zuckermann, Martin J.

    1987-01-01

    A two-dimensional model is proposed to describe systems with phase transitions which take place in terms of crystalline as well as internal degrees of freedom. Computer simulation of the model shows that the interplay between the two sets of degrees of freedom permits observation of grain-boundar......-boundary formation and interfacial melting, a nonequilibrium process by which the system melts at the boundaries of a polycrystalline domain structure. Lipid membranes are candidates for systems with pronounced interfacial melting behavior....

  18. Influence of enzymatic reactions on the electrochemical behavior of EN X2CrNiMo17-11-2 (AISI 316L) stainless steel in bio-corrosion: role of interfacial processes on the modification of the passive layer

    International Nuclear Information System (INIS)

    Landoulsi, J.

    2008-01-01

    The outstanding corrosion behavior of stainless steels (SS) results from the presence of thin oxide layer (some nanometers). In non sterile aqueous media, stainless steels may exhibit a non stable behavior resulting from interactions between microbial species and passive film. In fact, microorganisms can be deeply involved in the corrosion processes usually reported as Microbial Influenced Corrosion (MIC). They can induce the initiation or the acceleration of this phenomenon and they do so when organized in bio-films. From the electrochemical point of view, stainless steels showed an increase of the free corrosion potential (Ecorr) attributed to the bio-film settlement. The Eco' ennoblement was broadly reported in seawater and seems to be confirmed in fresh water according to recent findings. A considerable progress in the comprehension of MIC processes was related to the role of extracellular species, essentially enzymes. Many enzymatic reactions occurring in bio-films consist on using oxygen as electron acceptor to generate hydrogen peroxide and related species. The aim of this work is to understand the mechanisms involved in the electrochemical behavior of stainless steel according to an enzymatic approach in medium simulating fresh water. To this end, glucose oxidase was chosen to globalize aerobic activities of bio-films. Electrochemical measurements in situ and surface analysis allow the comprehension of the role and the nature of interfacial processes. Surface characterization was performed with the help of a new quantitative utilization of XPS analysis and AFM. Results show a significant evolution in term of morphology (surface organization), (ii) chemical composition (passive layer, adsorbed organic species) and (iii) chemical reaction (oxidation, dissolution, effect of enzyme). Finally, a new enzymatic system is proposed to mimic specific physicochemical conditions at the SS / bio-film interface, in particular enzymatic generation of oxidant species in

  19. Impact of post-deposition annealing on interfacial chemical bonding states between AlGaN and ZrO2 grown by atomic layer deposition

    International Nuclear Information System (INIS)

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Ng, Serene Lay Geok; Ji, Rong; Liu, Zhi Hong

    2015-01-01

    The effect of post-deposition annealing on chemical bonding states at interface between Al 0.5 Ga 0.5 N and ZrO 2 grown by atomic layer deposition (ALD) is studied by angle-resolved x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that both of Al-O/Al 2p and Ga-O/Ga 3d area ratio decrease at annealing temperatures lower than 500 °C, which could be attributed to “clean up” effect of ALD-ZrO 2 on AlGaN. Compared to Ga spectra, a much larger decrease in Al-O/Al 2p ratio at a smaller take-off angle θ is observed, which indicates higher effectiveness of the passivation of Al-O bond than Ga-O bond through “clean up” effect near the interface. However, degradation of ZrO 2 /AlGaN interface quality due to re-oxidation at higher annealing temperature (>500 °C) is also found. The XPS spectra clearly reveal that Al atoms at ZrO 2 /AlGaN interface are easier to get oxidized as compared with Ga atoms

  20. Interfacial charge-induced polarization switching in Al{sub 2}O{sub 3}/Pb(Zr,Ti)O{sub 3} bi-layer

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yu Jin; Park, Min Hyuk; Jeon, Woojin; Kim, Han Joon; Moon, Taehwan; Lee, Young Hwan; Kim, Keum Do; Hyun, Seung Dam; Hwang, Cheol Seong, E-mail: cheolsh@snu.ac.kr [Department of Materials Science & Engineering and Inter-University Semiconductor Research Center, College of Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of)

    2015-12-14

    Detailed polarization switching behavior of an Al{sub 2}O{sub 3}/Pb(Zr,Ti)O{sub 3} (AO/PZT) structure is examined by comparing the phenomenological thermodynamic model to the experimental polarization–voltage (P-V) results. Amorphous AO films with various thicknesses (2–10 nm) were deposited on the polycrystalline 150-nm-thick PZT film. The thermodynamic calculation showed that the transition from the ferroelectric-like state to the paraelectric-like state with increasing AO thickness occurs at ∼3 nm thickness. This paraelectric-like state should have exhibited a negative capacitance effect without permanent polarization switching if no other adverse effects are involved. However, experiments showed typical ferroelectric-like hysteresis loops where the coercive voltage increased with the increasing AO thickness, which could be explained by the carrier injection through the thin AO layer and trapping of the carriers at the AO/PZT interface. The fitting of the experimental P-V loops using the thermodynamic model considering the depolarization energy effect showed that trapped charge density was ∼±0.1 Cm{sup −2} and critical electric field at the Pt electrode/AO interface, at which the carrier transport occurs, was ∼±10 MV/cm irrespective of the AO thickness. Energy band model at each electrostatic state along the P-V loop was provided to elucidate correlation between macroscopic polarization and internal charge state of the stacked films.

  1. Interfacial reactions of Ba{sub 2}YCu{sub 3}O{sub 6+z} with coated conductor buffer layer, LaMnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Liu, G. [Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Wong-Ng, W., E-mail: winnie.wong-ng@nist.go [Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Kaduk, J.A. [Poly Crystallography Inc., Naperville, IL 60540 (United States); Cook, L.P. [Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)

    2010-03-01

    Chemical interactions between the Ba{sub 2}YCu{sub 3}O{sub 6+x} superconductor and the LaMnO{sub 3} buffer layers employed in coated conductors have been investigated experimentally by determining the phases formed in the Ba{sub 2}YCu{sub 3}O{sub 6+x}-LaMnO{sub 3} system. The Ba{sub 2}YCu{sub 3}O{sub 6+x}-LaMnO{sub 3} join within the BaO-(Y{sub 2}O{sub 3}-La{sub 2}O{sub 3})-MnO{sub 2}-CuO{sub x} multi-component system is non-binary. At 810 deg. C (p{sub O2} = 100 Pa) and at 950 deg. C in purified air, four phases are consistently present along the join, namely, Ba{sub 2-x}(La{sub 1+x-y}Y{sub y})Cu{sub 3}O{sub 6+z}, Ba(Y{sub 2-x}La{sub x})CuO{sub 5}, (La{sub 1-x}Y{sub x})MnO{sub 3}, (La,Y)Mn{sub 2}O{sub 5}. The crystal chemistry and crystallography of Ba(Y{sub 2-x}La{sub x})CuO{sub 5} and (La{sub 1-x}Y{sub x})Mn{sub 2}O{sub 5} were studied using the X-ray Rietveld refinement technique. The Y-rich and La-rich solid solution limits for Ba(Y{sub 2-x}La{sub x})CuO{sub 5} are Ba(Y{sub 1.8}La{sub 0.2})CuO{sub 5} and Ba(Y{sub 0.1}La{sub 1.9})CuO{sub 5}, respectively. The structure of Ba(Y{sub 1.8}La{sub 0.2})CuO{sub 5} is Pnma (No. 62), a = 12.2161(5) A, b = 5.6690(2) A, c = 7.1468(3) A, V = 494.94(4) A{sup 3}, and D{sub x} = 6.29 g cm{sup -3}. YMn{sub 2}O{sub 5} and LaMn{sub 2}O{sub 5} do not form solid solution at 810 deg. C (p{sub O2} = 100 Pa) or at 950 deg. C (in air). The structure of YMn{sub 2}O{sub 5} was confirmed to be Pbam (No. 55), a = 7.27832(14) A, b = 8.46707(14) A, c = 5.66495(10) A, and V = 349.108(14) A{sup 3}. A reference X-ray pattern was prepared for YMn{sub 2}O{sub 5}.

  2. Role of interfacial rheological properties in oil field chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Lakatos-Szabo, J.; Lakatos, I.; Kosztin, B.

    1996-12-31

    Interfacial rheological properties of different Hungarian crude oil/water systems were determined in wide temperature and shear rate range and in presence of inorganic electrolytes, tensides, alkaline materials and polymers. The detailed laboratory study definitely proved that the interfacial rheological properties are extremely sensitive parameters towards the chemical composition of inmiscible formation liquids. Comparison and interpretation of the interfacial rheological properties may contribute significantly to extension of the weaponry of the reservoir characterization, better understanding of the displacement mechanism, development of the more profitable EOR/IOR methods, intensification of the surface technologies, optimization of the pipeline transportation and improvement of the refinery operations. It was evidenced that the interfacial rheology is an efficient and powerful detection technique, which may enhance the knowledge on formation, structure, properties and behaviour of interfacial layers. 17 refs., 18 figs., 2 tabs.

  3. Ordered quantum-ring chains grown on a quantum-dot superlattice template

    International Nuclear Information System (INIS)

    Wu Jiang; Wang, Zhiming M.; Holmes, Kyland; Marega, Euclydes; Mazur, Yuriy I.; Salamo, Gregory J.

    2012-01-01

    One-dimensional ordered quantum-ring chains are fabricated on a quantum-dot superlattice template by molecular beam epitaxy. The quantum-dot superlattice template is prepared by stacking multiple quantum-dot layers and quantum-ring chains are formed by partially capping quantum dots. Partially capping InAs quantum dots with a thin layer of GaAs introduces a morphological change from quantum dots to quantum rings. The lateral ordering is introduced by engineering the strain field of a multi-layer InGaAs quantum-dot superlattice.

  4. Interfacial effects of the Cu{sub 2}O nano-dots decorated Co{sub 3}O{sub 4} nanorods array and its photocatalytic activity for cleaving organic molecules

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, X.P. [Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018 (China); Yu, J.S. [Department of Chemistry and Chemical Engineering, University of New Haven, 300 Boston Post Road, West Haven, CT 06516 (United States); Xu, H.M.; Chen, W.X.; Hu, W. [Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018 (China); Chen, G.L., E-mail: glchen@zstu.edu.cn [Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018 (China)

    2016-09-30

    Highlights: • Co{sub 3}O{sub 4} rods were grown on plasma treated Ti foil. • Cu{sub 2}O QDs were uniformly distributed on the surface of nanorods. • Ti/Co{sub 3}O{sub 4}/Cu{sub 2}O exhibited visible light photocatalytic activity with KHSO{sub 5}. • Degradation mechanism was supported by ESR technique and radical scavenger tests. • The heterojunction was highly stable even after recycling many times. - Abstract: A heterogeneous nanocomposite catalyst constructed by the Co{sub 3}O{sub 4} nanorods decorated with the Cu{sub 2}O quantum dots (QDs) were successfully synthesized via a simple hydrothermal method followed by an oxidation-reduction processing. The fabricated Cu{sub 2}O/Co{sub 3}O{sub 4} nanocomposite was characterized by the SEM, TEM, XPS, XRD, UV–vis and PL, and the (2 2 0) and (3 1 1) facets of the Co{sub 3}O{sub 4} were exposed. Compared with the original Co{sub 3}O{sub 4} nanorods with an average diameter of 350 nm, a substantial decrease in the band gap was observed after doping the nanorods with the Cu{sub 2}O QDs (average diameter of 5 nm). Such a dramatic decrease in the band gap indicated a significant enhancement of the photocatalytic activities under visible light. The methylene blue (MB) dye and the phenol were used as model organic pollutants, and the Cu{sub 2}O/Co{sub 3}O{sub 4} nanocomposite catalyst exhibited both high catalytic activity and good recycling stability. The catalytic activities of the Cu{sub 2}O/Co{sub 3}O{sub 4}/potassium monopersulfate triple salt (PMS) system for cleaving the MB and the phenol were dependent on the dosages of the Cu{sub 2}O QDs, and the calculated degradation rates achieved by 7.0 wt% Cu{sub 2}O/Co{sub 3}O{sub 4} nanocomposite catalyst were about 11.3 and 1.8 times than that of the pristine Co{sub 3}O{sub 4} nanorod catalyst for the MB and the phenol, respectively. The reactive species of ·O{sub 2}{sup −} and the holes were determined to be the main active species for the phenol photocatalytic

  5. Effect of the ZnS shell layer on the charge storage capabilities of organic bistable memory devices fabricated utilizing CuInS2–ZnS core–shell quantum dots embedded in a poly(methylmethacrylate) layer

    International Nuclear Information System (INIS)

    Yun, Dong Yeol; Kim, Tae Whan; Kim, Sang Wook

    2013-01-01

    The electrical characteristics of organic bistable memory devices (OBDs) fabricated utilizing CuInS 2 (CIS) core or CIS–ZnS core–shell quantum dots (QDs) embedded in a poly(methylmethacrylate) (PMMA) layer on indium–tin-oxide (ITO) coated glass substrates were investigated. X-ray photoelectron spectroscopy spectra demonstrated that the stoichiometries of the QDs embedded in a PMMA layer were CIS or CIS–ZnS QDs. Current–voltage measurements on Al/CIS or CIS–ZnS QDs embedded in PMMA layer/ITO glass devices at 300 K showed current bistabilities. The maximum ON/OFF current ratios of the OBDs with CIS or CIS–ZnS QDs were approximately 1 × 10 3 and 1 × 10 5 , respectively. The retention number of ON and OFF states was measured by 1 × 10 5 . The memory mechanisms of the OBDs with CIS or CIS–ZnS QDs are described on the basis of the experimental results. - Highlights: • Organic bistable devices utilizing nanocomposites were fabricated. • Current–voltage results on organic bistable devices showed current bistabilities. • Maximum ON/OFF current ratio of the device with core–shell quantum dots was 1 × 10 5 . • Retention number of the device with core–shell quantum dots was 1 × 10 5

  6. Probing Interfacial Water on Nanodiamonds in Colloidal Dispersion.

    Science.gov (United States)

    Petit, Tristan; Yuzawa, Hayato; Nagasaka, Masanari; Yamanoi, Ryoko; Osawa, Eiji; Kosugi, Nobuhiro; Aziz, Emad F

    2015-08-06

    The structure of interfacial water layers around nanoparticles dispersed in an aqueous environment may have a significant impact on their reactivity and on their interaction with biological species. Using transmission soft X-ray absorption spectroscopy in liquid, we demonstrate that the unoccupied electronic states of oxygen atoms from water molecules in aqueous colloidal dispersions of nanodiamonds have a different signature than bulk water. X-ray absorption spectroscopy can thus probe interfacial water molecules in colloidal dispersions. The impacts of nanodiamond surface chemistry and concentration on interfacial water electronic signature are discussed.

  7. Interfacial functionalization and engineering of nanoparticles

    Science.gov (United States)

    Song, Yang

    also of the metal elements in the nanoparticle cores, in contrast to the bulk-exchange counterparts where these distributions were homogeneous within the nanoparticles, as manifested in contact angle, UV--vis, XPS, and TEM measurements. More interestingly, the electrocatalytic performance of the Janus nanoparticles was markedly better than the bulk-exchange ones, suggesting that the segregated distribution of the polar ligands from the apolar ones might further facilitate charge transfer from Ag to Au in the nanoparticle cores, leading to additional improvement of the adsorption and reduction of oxygen. This interfacial protocol was then adopted to prepare trimetallic Ag AuPt Neapolitan nanoparticles by two sequential galvanic exchange reactions of 1-hexanethiolate-capped silver nanoparticles with gold(I)-thiomalic acid and platinum(II)-hexanethiolate complexes. As both reactions were confined to an interface, the Au and Pt elements were situated on two opposite poles of the original Ag nanoparticles, which was clearly manifested in elemental mapping of the nanoparticles, and consistent with the damping and red-shift of the nanoparticle surface plasmon resonance. As nanoscale analogs to conventional amphiphilic molecules, the resulting Janus nanoparticles were found to form oil-in-water micelle-like or water-in-oil reverse micelle-like superparticulate structures depending on the solvent media. These unique characteristics were exploited for the effective transfer of diverse guest nanoparticles between organic and water phase. The transfer of hydrophobic nanoparticles from organic to water media or water-soluble nanoparticles to the organic phase was evidenced by TEM, DLS, UV-Vis, and PL measurements. In particular, line scans based on EDS analysis showed that the vesicle-like structures consisted of multiple layers of the Janus nanoparticles, which encapsulated the guest nanoparticles in the cores. The results highlight the unique effectiveness of using Janus

  8. Optical anisotropy in vertically coupled quantum dots

    DEFF Research Database (Denmark)

    Yu, Ping; Langbein, Wolfgang Werner; Leosson, Kristjan

    1999-01-01

    We have studied the polarization of surface and edge-emitted photoluminescence (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD's) grown by molecular beam epitaxy. The PL polarization is found to be strongly dependent on the number of stacked layers. While single...... number due to increasing dot size....

  9. Interfacial Shear Strength and Adhesive Behavior of Silk Ionomer Surfaces.

    Science.gov (United States)

    Kim, Sunghan; Geryak, Ren D; Zhang, Shuaidi; Ma, Ruilong; Calabrese, Rossella; Kaplan, David L; Tsukruk, Vladimir V

    2017-09-11

    The interfacial shear strength between different layers in multilayered structures of layer-by-layer (LbL) microcapsules is a crucial mechanical property to ensure their robustness. In this work, we investigated the interfacial shear strength of modified silk fibroin ionomers utilized in LbL shells, an ionic-cationic pair with complementary ionic pairing, (SF)-poly-l-glutamic acid (Glu) and SF-poly-l-lysine (Lys), and a complementary pair with partially screened Coulombic interactions due to the presence of poly(ethylene glycol) (PEG) segments and SF-Glu/SF-Lys[PEG] pair. Shearing and adhesive behavior between these silk ionomer surfaces in the swollen state were probed at different spatial scales and pressure ranges by using functionalized atomic force microscopy (AFM) tips as well as functionalized colloidal probes. The results show that both approaches were consistent in analyzing the interfacial shear strength of LbL silk ionomers at different spatial scales from a nanoscale to a fraction of a micron. Surprisingly, the interfacial shear strength between SF-Glu and SF-Lys[PEG] pair with partially screened ionic pairing was greater than the interfacial shear strength of the SF-Glu and SF-Lys pair with a high density of complementary ionic groups. The difference in interfacial shear strength and adhesive strength is suggested to be predominantly facilitated by the interlayer hydrogen bonding of complementary amino acids and overlap of highly swollen PEG segments.

  10. Nb and Ta layer doping effects on the interfacial energetics and electronic properties of LaAlO3/SrTiO3 heterostructure: first-principles analysis.

    Science.gov (United States)

    Nazir, Safdar; Behtash, Maziar; Cheng, Jianli; Luo, Jian; Yang, Kesong

    2016-01-28

    The two-dimensional electron gas (2DEG) formed at the n-type (LaO)(+1)/(TiO2)(0) interface in the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) has emerged as a prominent research area because of its great potential for nanoelectronic applications. Due to its practical implementation in devices, desired physical properties such as high charge carrier density and mobility are vital. In this respect, 4d and 5d transition metal doping near the interfacial region is expected to tailor electronic properties of the LAO/STO HS system effectively. Herein, we studied Nb and Ta-doping effects on the energetics, electronic structure, interfacial charge carrier density, magnetic moment, and the charge confinements of the 2DEG at the n-type (LaO)(+1)/(TiO2)(0) interface of LAO/STO HS using first-principles density functional theory calculations. We found that the substitutional doping of Nb(Ta) at Ti [Nb(Ta)@Ti] and Al [Nb(Ta)@Al] sites is energetically more favorable than that at La [Nb(Ta)@La] and Sr [Nb(Ta)@Sr] sites, and under appropriate thermodynamic conditions, the changes in the interfacial energy of HS systems upon Nb(Ta)@Ti and Nb(Ta)@Al doping are negative, implying that the formation of these structures is energetically favored. Our calculations also showed that Nb(Ta)@Ti and Nb(Ta)@Al doping significantly improve the interfacial charge carrier density with respect to that of the undoped system, which is because the Nb(Ta) dopant introduces excess free electrons into the system, and these free electrons reside mainly on the Nb(Ta) ions and interfacial Ti ions. Hence, along with the Ti 3d orbitals, the Nb 4d and Ta 5d orbitals also contribute to the interfacial metallic states; accordingly, the magnetic moments on the interfacial Ti ions increase significantly. As expected, the Nb@Al and Ta@Al doped LAO/STO HS systems show higher interfacial charge carrier density than the undoped and other doped systems. In contrast, Nb@Ti and Ta@Ti doped systems may

  11. Crystal orientation of monoclinic β-Ga2O3 thin films formed on cubic MgO substrates with a γ-Ga2O3 interfacial layer

    Science.gov (United States)

    Nakagomi, Shinji; Kokubun, Yoshihiro

    2017-12-01

    The crystal orientation relationship between β-Ga2O3 and MgO in β-Ga2O3 thin films prepared on (1 0 0), (1 1 1), and (1 1 0) MgO substrates was investigated by X-ray diffraction measurements and cross-sectional transmission electron microscopy images. The γ-Ga2O3 interfacial layer was present between β-Ga2O3 and MgO acted as a buffer to connect β-Ga2O3 on MgO. The following conditions were satisfied under each case: β-Ga2O3 (1 0 0)||MgO (1 0 0) and β-Ga2O3 [0 0 1]||MgO 〈0 1 1〉 for the formation of β-Ga2O3 on (1 0 0) MgO, and β-Ga2O3 (2 bar 0 1)||MgO (1 1 1) for the formation of β-Ga2O3 on (1 1 1) MgO, as well as each condition of β-Ga2O3 [0 1 0] (1 0 0)||MgO [ 1 bar 1 0 ] (0 0 1), β-Ga2O3 [0 1 0] (1 0 0)||MgO [ 0 1 bar 1 ] (1 0 0), and β-Ga2O3 [0 1 0] (1 0 0)||MgO [ 1 0 1 bar ] (0 1 0). β-Ga2O3 (1 bar 0 2)||MgO(1 1 0) and β-Ga2O3 [0 1 0] ⊥ MgO [0 0 1] for β-Ga2O3 formed on (1 1 0) MgO. The β-Ga2O3 formed on (1 1 1) MgO at 800 °C exhibited a threefold structure. The β-Ga2O3 formed on (1 1 0) MgO had a twofold structure but different by 90° from the result reported previously.

  12. Quantum Dot Sensitized Solar Cells Based on TiO2/AgInS2

    Science.gov (United States)

    Pawar, Sachin A.; Jeong, Jae Pil; Patil, Dipali S.; More, Vivek M.; Lee, Rochelle S.; Shin, Jae Cheol; Choi, Won Jun

    2018-05-01

    Quantum dot heterojunctions with type-II band alignment can efficiently separate photogenerated electron-hole pairs and, hence, are useful for solar cell studies. In this study, a quantum dot sensitized solar cell (QDSSC) made of TiO2/AgInS2 is achieved to boost the photoconversion efficiency for the TiO2-based system by varying the AgInS2 layer's thickness. The TiO2 nanorods array film is prepared by using a simple hydrothermal technique. The formation of a AgInS2 QD-sensitized TiO2-nanorod photoelectrode is carried out by successive ionic layer adsorption and reaction (SILAR) technique. The effect of the QD layer on the performance of the solar cell is studied by varying the SILAR cycles of the QD coating. The synthesized electrode materials are characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy and solar cell performances. The results indicate that the nanocrystals have effectively covered the outer surfaces of the TiO2 nanorods. The interfacial structure of quantum dots (QDs)/TiO2 is also investigated, and the growth interface is verified. A careful comparison between TiO2/AgInS2 sensitized cells reveals that the trasfer of electrons and hole proceeds efficiently, the recombination is suppressed for the optimum thickness of the QD layer and light from the entire visible spectrum is utilised. Under AM 1.5G illumination, a high photocurrent of 1.36 mAcm-2 with an improved power conversion efficiency of 0.48% is obtained. The solar cell properties of our photoanodes suggest that the TiO2 nanorod array films co-sensitized by AgInS2 nanoclusters have potential applications in solar cells.

  13. Quantum Dot Photonics

    Science.gov (United States)

    Kinnischtzke, Laura A.

    We report on several experiments using single excitons confined to single semiconductor quantum dots (QDs). Electric and magnetic fields have previously been used as experimental knobs to understand and control individual excitons in single quantum dots. We realize new ways of electric field control by changing materials and device geometry in the first two experiments with strain-based InAs QDs. A standard Schottky diode heterostructure is demonstrated with graphene as the Schottky gate material, and its performance is bench-marked against a diode with a standard gate material, semi-transparent nickel-chromium (NiCr). This change of materials increases the photon collection rate by eliminating absorption in the metallic NiCr layer. A second set of experiments investigates the electric field response of QDs as a possible metrology source. A linear voltage potential drop in a plane near the QDs is used to describe how the spatially varying voltage profile is also imparted on the QDs. We demonstrate a procedure to map this voltage profile as a preliminary route towards a full quantum sensor array. Lastly, InAs QDs are explored as potential spin-photon interfaces. We describe how a magnetic field is used to realize a reversible exchange of information between light and matter, including a discussion of the polarization-dependence of the photoluminesence, and how that can be linked to the spin of a resident electron or hole. We present evidence of this in two wavelength regimes for InAs quantum dots, and discuss how an external magnetic field informs the spin physics of these 2-level systems. This thesis concludes with the discovery of a new class of quantum dots. As-yet unidentified defect states in single layer tungsten diselenide (WSe 2 ) are shown to host quantum light emission. We explore the spatial extent of electron confinement and tentatively identify a radiative lifetime of 1 ns for these single photon emitters.

  14. Light emitting diodes with InAs/GaAsSb self-assembled quantum dot layer embedded in GaAs

    Czech Academy of Sciences Publication Activity Database

    Hazdra, P.; Oswald, Jiří; Hospodková, Alice; Hulicius, Eduard; Pangrác, Jiří

    2013-01-01

    Roč. 543, Sept (2013), 83-87 ISSN 0040-6090 R&D Projects: GA ČR GAP102/10/1201; GA ČR GA202/09/0676 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * electroluminescence * metalorganic vapor phase epitaxy * InAs * GaAsSb * light emitting diodes Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.867, year: 2013

  15. Exciton in type-II quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Sierra-Ortega, J; Escorcia, R A [Universidad del Magdalena, A. A. 731, Santa Marta (Colombia); Mikhailov, I D, E-mail: jsierraortega@gmail.co [Universidad Industrial de Santander, A. A. 678, Bucaramanga (Colombia)

    2009-05-01

    We study the quantum-size effect and the influence of the external magnetic field on the exciton ground state energy in the type-II InP quantum disk, lens and pyramid deposited on a wetting layer and embedded in a GaInP matrix. We show that the charge distribution over and below quantum dot and wetting layer induced by trapped exciton strongly depends on the quantum dot morphology and the strength of the magnetic field.

  16. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    Science.gov (United States)

    Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

    2014-08-26

    A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

  17. Quantum-dot-in-perovskite solids

    KAUST Repository

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H.

    2015-01-01

    © 2015 Macmillan Publishers Limited. All rights reserved. Heteroepitaxy - atomically aligned growth of a crystalline film atop a different crystalline substrate - is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned 'dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  18. Quantum-dot-in-perovskite solids

    KAUST Repository

    Ning, Zhijun

    2015-07-15

    © 2015 Macmillan Publishers Limited. All rights reserved. Heteroepitaxy - atomically aligned growth of a crystalline film atop a different crystalline substrate - is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned \\'dots-in-a-matrix\\' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  19. Graphene based quantum dots.

    Science.gov (United States)

    Zhang, H G; Hu, H; Pan, Y; Mao, J H; Gao, M; Guo, H M; Du, S X; Greber, T; Gao, H-J

    2010-08-04

    Laterally localized electronic states are identified on a single layer of graphene on ruthenium by low temperature scanning tunneling spectroscopy (STS). The individual states are separated by 3 nm and comprise regions of about 90 carbon atoms. This constitutes a highly regular quantum dot-array with molecular precision. It is evidenced by quantum well resonances (QWRs) with energies that relate to the corrugation of the graphene layer. The dI/dV conductance spectra are modeled by a layer height dependent potential-well with a delta-function potential that describes the barrier for electron penetration into graphene. The resulting QWRs are strongest and lowest in energy on the isolated 'hill' regions with a diameter of 2 nm, where the graphene is decoupled from the surface.

  20. Synthesis of Won-WX2 (n=2.7, 2.9; X=S, Se) Heterostructures for Highly Efficient Green Quantum Dot Light-Emitting Diodes

    KAUST Repository

    Han, Shikui

    2017-07-04

    Preparation of two-dimensional (2D) heterostructures is important not only fundamentally, but also technologically for applications in electronics and optoelectronics. Herein, we report a facile colloidal method for the synthesis of WOn -WX2 (n=2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WOn nanomaterials. The WOn -WX2 heterostructures are composed of WO2.9 nanoparticles (NPs) or WO2.7 nanowires (NWs) grown together with single- or few-layer WX2 nanosheets (NSs). As a proof-of-concept application, the WOn -WX2 heterostructures are used as the anode interfacial buffer layer for green quantum dot light-emitting diodes (QLEDs). The QLED prepared with WO2.9 NP-WSe2 NS heterostructures achieves external quantum efficiency (EQE) of 8.53 %. To our knowledge, this is the highest efficiency in the reported green QLEDs using inorganic materials as the hole injection layer.

  1. Interfacial solvation thermodynamics

    International Nuclear Information System (INIS)

    Ben-Amotz, Dor

    2016-01-01

    Previous studies have reached conflicting conclusions regarding the interplay of cavity formation, polarizability, desolvation, and surface capillary waves in driving the interfacial adsorptions of ions and molecules at air–water interfaces. Here we revisit these questions by combining exact potential distribution results with linear response theory and other physically motivated approximations. The results highlight both exact and approximate compensation relations pertaining to direct (solute–solvent) and indirect (solvent–solvent) contributions to adsorption thermodynamics, of relevance to solvation at air–water interfaces, as well as a broader class of processes linked to the mean force potential between ions, molecules, nanoparticles, proteins, and biological assemblies. (paper)

  2. DOT's CAFE rulemaking analysis.

    Science.gov (United States)

    2013-02-13

    Presentation discusses what DOT needs to consider in setting CAFE standards. How DOT's use of the CAFE Compliance and Effects Modeling System helps to analyze potential CAFE Standards. How DOT might approach the next round of CAFE standards for model...

  3. Temperature and compositional dependence of solid-liquid interfacial energy: application of the Cahn-Hilliard theory

    International Nuclear Information System (INIS)

    Shimizu, I.; Takei, Y.

    2005-01-01

    A simple thermodynamic method to estimate the solid-liquid interfacial energy (or interfacial tension) is proposed, based on the Cahn-Hilliard theory. In the model, the liquid is treated as a regular solution, and the interfacial layers are assumed to have liquid-like thermodynamic properties. In eutectic systems, interfacial adsorption occurs within a few atomic layers, and interfacial energy monotonously increases with decreasing concentration of the solid species in the liquid phase. If non-ideal atomic interaction is strong and the liquid immiscibility region appears in the phase diagrams (this is the case of monotectic systems), the interfacial thickness drastically increases and the interfacial energy is reduced around the immiscibility gap

  4. ‘Green’-synthesized near-infrared PbS quantum dots with silica-PEG dual-layer coating: ultrastable and biocompatible optical probes for in vivo animal imaging

    Science.gov (United States)

    Wang, D.; Qian, J.; Cai, F.; He, S.; Han, S.; Mu, Y.

    2012-06-01

    In this paper, PbS semiconductor quantum dots (QDs) with near-infrared (NIR) photoluminescence were synthesized in oleic acid and paraffin liquid mixture by using an easily handled and ‘green’ approach. Surface functionalization of the QDs was accomplished with a silica and polyethylene glycol (PEG) phospholipid dual-layer coating and the excellent chemical stability of the nanoparticles is demonstrated. We then successfully applied the ultrastable PbS QDs to in vivo sentinel lymph node (SLN) mapping of mice. Histological analyses were also carried out to ensure that the intravenously injected nanoparticles did not produce any toxicity to the organism of mice. These experimental results suggested that our ultrastable NIR PbS QDs can serve as biocompatible and efficient probes for in vivo optical bioimaging and has great potentials for disease diagnosis and clinical therapies in the future.

  5. Virtual-bound, filamentary and layered states in a box-shaped quantum dot of square potential form the exact numerical solution of the effective mass Schrödinger equation

    Energy Technology Data Exchange (ETDEWEB)

    Luque, A., E-mail: a.luque@upm.es [Instituto de Energía Solar, Universidad Politécnica de Madrid (Spain); Mellor, A.; Tobías, I.; Antolín, E.; Linares, P.G.; Ramiro, I.; Martí, A. [Instituto de Energía Solar, Universidad Politécnica de Madrid (Spain)

    2013-03-15

    The effective mass Schrödinger equation of a QD of parallelepipedic shape with a square potential well is solved by diagonalizing the exact Hamiltonian matrix developed in a basis of separation-of-variables wavefunctions. The expected below bandgap bound states are found not to differ very much from the former approximate calculations. In addition, the presence of bound states within the conduction band is confirmed. Furthermore, filamentary states bounded in two dimensions and extended in one dimension and layered states with only one dimension bounded, all within the conduction band—which are similar to those originated in quantum wires and quantum wells—coexist with the ordinary continuum spectrum of plane waves. All these subtleties are absent in spherically shaped quantum dots, often used for modeling.

  6. ‘Green’-synthesized near-infrared PbS quantum dots with silica–PEG dual-layer coating: ultrastable and biocompatible optical probes for in vivo animal imaging

    International Nuclear Information System (INIS)

    Wang, D; Qian, J; Cai, F; He, S; Han, S; Mu, Y

    2012-01-01

    In this paper, PbS semiconductor quantum dots (QDs) with near-infrared (NIR) photoluminescence were synthesized in oleic acid and paraffin liquid mixture by using an easily handled and ‘green’ approach. Surface functionalization of the QDs was accomplished with a silica and polyethylene glycol (PEG) phospholipid dual-layer coating and the excellent chemical stability of the nanoparticles is demonstrated. We then successfully applied the ultrastable PbS QDs to in vivo sentinel lymph node (SLN) mapping of mice. Histological analyses were also carried out to ensure that the intravenously injected nanoparticles did not produce any toxicity to the organism of mice. These experimental results suggested that our ultrastable NIR PbS QDs can serve as biocompatible and efficient probes for in vivo optical bioimaging and has great potentials for disease diagnosis and clinical therapies in the future. (paper)

  7. Highly Efficient Flexible Quantum Dot Solar Cells with Improved Electron Extraction Using MgZnO Nanocrystals.

    Science.gov (United States)

    Zhang, Xiaoliang; Santra, Pralay Kanti; Tian, Lei; Johansson, Malin B; Rensmo, Håkan; Johansson, Erik M J

    2017-08-22

    Colloidal quantum dot (CQD) solar cells have high potential for realizing an efficient and lightweight energy supply for flexible or wearable electronic devices. To achieve highly efficient and flexible CQD solar cells, the electron transport layer (ETL), extracting electrons from the CQD solid layer, needs to be processed at a low-temperature and should also suppress interfacial recombination. Herein, a highly stable MgZnO nanocrystal (MZO-NC) layer is reported for efficient flexible PbS CQD solar cells. Solar cells fabricated with MZO-NC ETL give a high power conversion efficiency (PCE) of 10.4% and 9.4%, on glass and flexible plastic substrates, respectively. The reported flexible CQD solar cell has the record efficiency to date of flexible CQD solar cells. Detailed theoretical simulations and extensive characterizations reveal that the MZO-NCs significantly enhance charge extraction from CQD solids and diminish the charge accumulation at the ETL/CQD interface, suppressing charge interfacial recombination. These important results suggest that the low-temperature processed MZO-NCs are very promising for use in efficient flexible solar cells or other flexible optoelectronic devices.

  8. Interfacial characterization of CVI-SiC/SiC composites

    International Nuclear Information System (INIS)

    Yang, W.; Kohyama, A.; Noda, T.; Katoh, Y.; Hinoki, T.; Araki, H.; Yu, J.

    2002-01-01

    The mechanical properties of the interfaces of two families of chemical vapor infiltration SiC/SiC composites, advanced Tyranno-SA and Hi-Nicalon fibers reinforced SiC/SiC composites with various carbon and SiC/C interlayers, were investigated by single fiber push-out/push-back tests. Interfacial debonding and fibers sliding mainly occurred adjacent to the first carbon layer on the fibers. The interfacial debonding strengths and frictional stresses for both Tyranno-SA/SiC and Hi-Nicalon/SiC composites were correlated with the first carbon layer thickness. Tyranno-SA/SiC composites exhibited much larger interfacial frictional stresses compared to Hi-Nicalon/SiC composites. This was assumed to be mainly contributed by the rather rough surface of the Tyranno-SA fiber

  9. A direct investigation of photocharge transfer across monomolecular layer between C{sub 60} and CdS quantum dots by photoassisted conductive atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xiaohong; Liu, He; Zhang, Xingtang; Cheng, Gang; Wang, Shujie; Du, Zuliang, E-mail: zld@henu.edu.cn [Key Laboratory for Special Functional Materials, Collaborative Innovation Center of Nano Functional Materials and Applications, Henan University, Kaifeng, 475004, PR. China (China)

    2016-04-15

    The composite assembly of C{sub 60} and CdS Quantum Dots (QDs) on ITO substrate was prepared by Langmuir-Blodgett (LB) technique using arachic acid (AA), stearic acid (SA) and octadecanyl amine (OA) as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V) measurements on both the CdS QDs and the composite assembly of C{sub 60}/CdS. The result make it clear that the CdS, C{sub 60}/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

  10. A direct investigation of photocharge transfer across monomolecular layer between C60 and CdS quantum dots by photoassisted conductive atomic force microscopy

    Directory of Open Access Journals (Sweden)

    Xiaohong Jiang

    2016-04-01

    Full Text Available The composite assembly of C60 and CdS Quantum Dots (QDs on ITO substrate was prepared by Langmuir-Blodgett (LB technique using arachic acid (AA, stearic acid (SA and octadecanyl amine (OA as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V measurements on both the CdS QDs and the composite assembly of C60/CdS. The result make it clear that the CdS, C60/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

  11. Specific interface area in a thin layer system of two immiscible liquids with vapour generation at the contact interface

    Science.gov (United States)

    Pimenova, Anastasiya V.; Gazdaliev, Ilias M.; Goldobin, Denis S.

    2017-06-01

    For well-stirred multiphase fluid systems the mean interface area per unit volume, or “specific interface area” SV, is a significant characteristic of the system state. In particular, it is important for the dynamics of systems of immiscible liquids experiencing interfacial boiling. We estimate the value of parameter SV as a function of the heat influx {\\dot{Q}}V to the system or the average system overheat above the interfacial boiling point. The derived results can be reformulated for the case of an endothermic chemical reaction between two liquid reagents with the gaseous form of one of the reaction products. The final results are restricted to the case of thin layers, where the potential gravitational energy of bubbles leaving the contact interface is small compared to their surface tension energy.

  12. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    Directory of Open Access Journals (Sweden)

    Wei-Ting eLai

    2016-02-01

    Full Text Available We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5−90 nm, the SiO2 thickness (3−4 nm, and as well the SiGe-shell thickness (2−15 nm has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5 in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge MOS nanoelectronic and nanophotonic applications.

  13. Molecular dynamics study on interfacial thermal conductance of unirradiated and irradiated SiC/C

    International Nuclear Information System (INIS)

    Wang, Qingyu; Wang, Chenglong; Zhang, Yue; Li, Taosheng

    2014-01-01

    SiC f /SiC composite materials have been considered as candidate structural materials for several types of advanced nuclear reactors. Both experimental and computer simulations studies have revealed the degradation of thermal conductivity for this material after irradiation. The objective of this study is to investigate the effect of SiC/graphite interface structure and irradiation on the interfacial thermal conductance by using molecular dynamics simulation. Five SiC/graphite composite models were created with different interface structures, and irradiation was introduced near the interfaces. Thermal conductance was calculated by means of reverse-NEMD method. Results show that there is a positive correlation between the interfacial energy and interfacial C–Si bond quantity, and irradiated models showed higher interfacial energy compared with their unirradiated counterparts. Except the model with graphite atom plane parallel to the interface, the interfacial thermal conductance of unirradiated and irradiated (1000 eV) models, increases as the increase of interfacial energy, respectively. For all irradiated models, lattice defects are of importance in impacting the interfacial thermal conductance depending on the interface structure. For the model with graphite layer parallel to the interface, the interfacial thermal conductance increased after irradiation, for the other models the interfacial thermal conductance decreased. The vibrational density of states of atoms in the interfacial region was calculated to analyze the phonon mismatch at the interface

  14. Interfacial density of states in magnetic tunnel junctions

    NARCIS (Netherlands)

    LeClair, P.R.; Kohlhepp, J.T.; Swagten, H.J.M.; Jonge, de W.J.M.

    2001-01-01

    Large zero-bias resistance anomalies as well as a collapse of magnetoresistance were observed in Co/Al2O3/Co magnetic tunnel junctions with thin Cr interfacial layers. The tunnel magnetoresistance decays exponentially with nominal Cr interlayer thickness with a length scale of ~1 Å more than twice

  15. Impact of capping layer type on emission of InAs quantum dots embedded in InGaAs/In{sub x}Al{sub y}Ga{sub z}As/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Torchynska, T. V., E-mail: ttorch@esfm.ipn.mx; Casas Espinola, J. L. [ESFM–Instituto Politécnico Nacional, México D. F. 07738, México (Mexico); Stintz, A. [Center of High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87106 (United States)

    2014-01-07

    The optical and structural properties of In{sub 0.15}Ga{sub 0.85}As/In{sub x}Al{sub y}Ga{sub z}As/GaAs quantum wells with embedded InAs quantum dots (QDs) were investigated by the photoluminescence (PL), its temperature dependence, X-ray diffraction (XRD), and high resolution (HR-XRD) methods in dependence on the composition of capping In{sub x}Al{sub y}Ga{sub z}As layers. Three types of capping layers (Al{sub 0.3}Ga{sub 0.7}As, Al{sub 0.10}Ga{sub 0.75}In{sub 0.15}As, and Al{sub 0.40}Ga{sub 0.45}In{sub 0.15}As) have been used and their impact on PL parameters has been compared. Temperature dependences of PL peak positions in QDs have been analyzed in the range of 10–500 K and to compare with the temperature shrinkage of band gap in the bulk InAs crystal. This permits to investigate the QD material composition and the efficiency of Ga(Al)/In inter diffusion in dependence on the type of In{sub x}Al{sub y}Ga{sub z}As capping layers. XRD and HR-XRD used to control the composition of quantum well layers. It is shown that QD material composition is closer to InAs in the structure with the Al{sub 0.40}Ga{sub 0.45}In{sub 0.15}As capping layer and for this structure the emission 1.3 μm is detected at 300 K. The thermal decay of the integrated PL intensity has been studied as well. It is revealed the fast 10{sup 2}-fold thermal decay of the integrated PL intensity in the structure with the Al{sub 0.10}Ga{sub 0.75}In{sub 0.15}As capping layer in comparison with 10-fold decay in other structures. Finally, the reasons of PL spectrum transformation and the mechanism of PL thermal decay for different capping layers have been analyzed and discussed.

  16. Cold welding of organic light emitting diode: Interfacial and contact models

    Directory of Open Access Journals (Sweden)

    J. Asare

    2016-06-01

    Full Text Available This paper presents the results of an analytical and computational study of the contacts and interfacial fracture associated with the cold welding of Organic Light Emitting diodes (OLEDs. The effects of impurities (within the possible interfaces are explored for contacts and interfacial fracture between layers that are relevant to model OLEDs. The models are used to study the effects of adhesion, pressure, thin film layer thickness and dust particle modulus (between the contacting surfaces on contact profiles around impurities between cold-welded thin films. The lift-off stage of thin films (during cold welding is then modeled as an interfacial fracture process. A combination of adhesion and interfacial fracture theories is used to provide new insights for the design of improved contact and interfacial separation during cold welding. The implications of the results are discussed for the design and fabrication of cold welded OLED structures.

  17. Interfacial effects in organic semiconductor heterojunctions

    International Nuclear Information System (INIS)

    Stadler, P.

    2011-01-01

    The field of organic electronics has systematically gained interest in recent years, technologically and scientifically advances have been made leading to practical applications such as organic light emitting diodes, organic field-effect transistors and organic photo-voltaic cells. In this thesis a fundamental study on organic molecules is presented targeting on interfacial effects at organic heterojunctions. Generally in organic electronic devices interfaces are considered as key parameters for achieving high performance applications. Therefore in this work the emphasis is to investigate layer-by-layer heterojunctions of organic molecules. Defined heterojunctions at inorganic III-V semiconductors form superlattices and quantum-wells, which lead to interfacial effects summarized as quantum confinement and two-dimensional electron gases. Although organic molecules differ in many aspects from their inorganic counterparts, similar effects can be theoretically expected at organic heterojunctions as well. Organic molecules form van-der-Waals type crystals and domains which are macroscopically anisotropic and polycrystalline or amorphous. Organic molecules are intrinsic semiconductors and at interfaces dipoles are formed, which control the energy level alignment. In order to characterize such structures and compare them to inorganic superlattices and quantum-wells it is necessary to induce charge carriers. In this work this is established either by interfacial doping using high-performance dielectrics in a field-effect transistor structure or by photo-doping by exciting a donor-acceptor bilayer. In both cases C 60 was chosen as organic semiconductor exhibiting good acceptor properties and an electron mobility in the range of 0.5 cm 2 V -1 s -1 . The fabrication of well-defined few-molecular layers allows probing directly at the interface. Spectroscopic methods and transport measurements are applied for characterization: Photoemission spectroscopy, absorption and photo

  18. Interfacial Instabilities in Evaporating Drops

    Science.gov (United States)

    Moffat, Ross; Sefiane, Khellil; Matar, Omar

    2007-11-01

    We study the effect of substrate thermal properties on the evaporation of sessile drops of various liquids. An infra-red imaging technique was used to record the interfacial temperature. This technique illustrates the non-uniformity in interfacial temperature distribution that characterises the evaporation process. Our results also demonstrate that the evaporation of methanol droplets is accompanied by the formation of wave-trains in the interfacial temperature field; similar patterns, however, were not observed in the case of water droplets. More complex patterns are observed for FC-72 refrigerant drops. The effect of substrate thermal conductivity on the structure of the complex pattern formation is also elucidated.

  19. Mode-locking of an InAs Quantum Dot Based Vertical External Cavity Surface Emitting Laser Using Atomic Layer Graphene

    Science.gov (United States)

    2015-07-16

    catalyzed on either a copper foil or on nickel coated substrates. The graphene must be transferred off of these substrates and then on to the DBR/spacer to...properties of graphene in both the exfoliated single layer graphene (SLG) and few layer graphene (FLG) flakes . Sun et al. make use of bile salts to...semiconductors and dielectrics is the transfer of CVD graphene grown on copper foils. The graphene is grown on thin Cu-foils by CVD using methane and

  20. Charge-extraction strategies for colloidal quantum dot photovoltaics

    KAUST Repository

    Lan, Xinzheng

    2014-02-20

    The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p-and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction. © 2014 Macmillan Publishers Limited.

  1. Effects of Hydroxylation on PbS Quantum Dot Sensitized TiO2 Nanotube Array Photoelectrodes

    International Nuclear Information System (INIS)

    Liu, Zhongqing; Wang, Bin; Wu, Jianchun; Dong, Qiang; Zhang, Xiaoming; Xu, He

    2016-01-01

    ABSTRACT: The contact state at the heterojunction interfaces greatly influences the interfacial kinetics of the photoinduced charge carriers. In this study, we used a facile NaOH pretreatment to replenish the hydroxyl groups lost during the heat treatment for crystallization of TiO 2 nanotube arrays (TNAs) prepared via anodic oxidization. By reacting the carboxylic acid groups of thioglycolic acid (TGA) with the TiO 2 surface hydroxyl groups, TGA molecules were covalently linked to the TiO 2 surface and then PbS quantum dots (QDs) were anchored onto the TNAs via the successive ionic layer adsorption and reaction (SILAR) method. The sample microstructure and photoelectrochemical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM),current–voltage characteristics (J–V), electrochemical impedance spectroscopy (EIS), transient photovoltage plots and Mott-Schottky curves. The contact state and electrostatic potential distribution between TiO 2 {1 0 1} and PbS {1 1 1} planes were estimated by using first principle simulation. It was found that the NaOH pretreatment could enhance the crystallization degree of PbS QDs, decrease the crystal face mismatch, dangling bond density and the interfacial resistance between PbS QDs and TiO 2 , and accelerate the interfacial separation and transfer of photoinduced charge carriers. The first principle calculations demonstrated that the PbS QDs and TiO 2 interfacial contact was strengthened, and the built-in electric field was induced from TiO 2 {1 0 1} towards PbS {1 1 1}. These combined effects apparently improved the device photoelectrochemical performance. Compared to the sample without pretreatment, the specimen pretreated with NaOH demonstrated 19.96% and 29.93% increases in peak photoconversion efficiency after five and ten cycles of SILAR deposition, respectively.

  2. Ultrasensitive electrochemical detection of tumor cells based on multiple layer CdS quantum dots-functionalized polystyrene microspheres and graphene oxide - polyaniline composite.

    Science.gov (United States)

    Wang, Jidong; Wang, Xiaoyu; Tang, Hengshan; Gao, Zehua; He, Shengquan; Li, Jian; Han, Shumin

    2018-02-15

    In this work, a novel ultrasensitive electrochemical biosensor was developed for the detection of K562 cell by a signal amplification strategy based on multiple layer CdS QDs functionalized polystyrene microspheres(PS) as bioprobe and graphene oxide(GO) -polyaniline(PANI) composite as modified materials of capture electrode. Due to electrostatic force of different charge, CdS QDs were decorated on the surface of PS by PDDA (poly(diallyldimethyl-ammonium chloride)) through a layer-by-layer(LBL) assemble technology, in which the structure of multiple layer CdS QDs increased the detection signal intensity. Moreover, GO-PANI composite not only enhanced the electron transfer rate, but also increased tumor cells load ratio. The resulting electrochemical biosensor was used to detect K562 cells with a lower detection limit of 3 cellsmL -1 (S/N = 3) and a wider linear range from 10 to 1.0 × 10 7 cellsmL -1 . This sensor was also used for mannosyl groups on HeLa cells and Hct116 cells, which showed high specificity and sensitivity. This signal amplification strategy would provide a novel approach for detection, diagnosis and treatment for tumor cells. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. A modified gradient approach for the growth of low-density InAs quantum dot molecules by molecular beam epitaxy

    Science.gov (United States)

    Sharma, Nandlal; Reuter, Dirk

    2017-11-01

    Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

  4. Solid/liquid interfacial free energies in binary systems

    Science.gov (United States)

    Nason, D.; Tiller, W. A.

    1973-01-01

    Description of a semiquantitative technique for predicting the segregation characteristics of smooth interfaces between binary solid and liquid solutions in terms of readily available thermodynamic parameters of the bulk solutions. A lattice-liquid interfacial model and a pair-bonded regular solution model are employed in the treatment with an accommodation for liquid interfacial entropy. The method is used to calculate the interfacial segregation and the free energy of segregation for solid-liquid interfaces between binary solutions for the (111) boundary of fcc crystals. The zone of compositional transition across the interface is shown to be on the order of a few atomic layers in width, being moderately narrower for ideal solutions. The free energy of the segregated interface depends primarily upon the solid composition and the heats of fusion of the component atoms, the composition difference of the solutions, and the difference of the heats of mixing of the solutions.

  5. Effects of QD surface coverage in solid-state PbS quantum dot-sensitized solar cells

    KAUST Repository

    Roelofs, Katherine E.; Brennan, Thomas P.; Trejo, Orlando; Xu, John; Prinz, Fritz B.; Bent, Stacey F.

    2013-01-01

    Lead sulfide quantum dots (QDs) were grown in situ on nanoporous TiO 2 by successive ion layer adsorption and reaction (SILAR) and by atomic layer deposition (ALD), to fabricate solid-state quantum-dot sensitized solar cells (QDSSCs). With the ultimate goal of increasing QD surface coverage, this work compares the impact of these two synthetic routes on the light absorption and electrical properties of devices. A higher current density was observed in the SILAR-grown QD devices under reverse bias, as compared to ALD-grown QD devices, attributed to injection problems of the lower-band-gap QDs present in the SILAR-grown QD device. To understand the effects of QD surface coverage on device performance, particularly interfacial recombination, electron lifetimes were measured for varying QD deposition cycles. Electron lifetimes were found to decrease with increasing SILAR cycles, indicating that the expected decrease in recombination between electrons in the TiO2 and holes in the hole-transport material, due to increased QD surface coverage, is not the dominant effect of increased deposition cycles. © 2013 IEEE.

  6. Effects of QD surface coverage in solid-state PbS quantum dot-sensitized solar cells

    KAUST Repository

    Roelofs, Katherine E.

    2013-06-01

    Lead sulfide quantum dots (QDs) were grown in situ on nanoporous TiO 2 by successive ion layer adsorption and reaction (SILAR) and by atomic layer deposition (ALD), to fabricate solid-state quantum-dot sensitized solar cells (QDSSCs). With the ultimate goal of increasing QD surface coverage, this work compares the impact of these two synthetic routes on the light absorption and electrical properties of devices. A higher current density was observed in the SILAR-grown QD devices under reverse bias, as compared to ALD-grown QD devices, attributed to injection problems of the lower-band-gap QDs present in the SILAR-grown QD device. To understand the effects of QD surface coverage on device performance, particularly interfacial recombination, electron lifetimes were measured for varying QD deposition cycles. Electron lifetimes were found to decrease with increasing SILAR cycles, indicating that the expected decrease in recombination between electrons in the TiO2 and holes in the hole-transport material, due to increased QD surface coverage, is not the dominant effect of increased deposition cycles. © 2013 IEEE.

  7. Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules.

    Science.gov (United States)

    Usman, Muhammad

    2015-10-21

    Strongly-coupled quantum dot molecules (QDMs) are widely employed in the design of a variety of optoelectronic, photovoltaic, and quantum information devices. An efficient and optimized performance of these devices demands engineering of the electronic and optical properties of the underlying QDMs. The application of electric fields offers a way to realise such a control over the QDM characteristics for a desired device operation. We performed multi-million-atom atomistic tight-binding calculations to study the influence of electric fields on the electron and hole wave function confinements and symmetries, the ground-state transition energies, the band-gap wavelengths, and the optical transition modes. Electrical fields parallel (Ep) and anti-parallel (Ea) to the growth direction were investigated to provide a comprehensive guide for understanding the electric field effects. The strain-induced asymmetry of the hybridized electron states is found to be weak and can be balanced by applying a small Ea electric field, of the order of 1 kV cm(-1). The strong interdot couplings completely break down at large electric fields, leading to single QD states confined at the opposite edges of the QDM. This mimics a transformation from a type-I band structure to a type-II band structure for the QDMs, which is a critical requirement for the design of intermediate-band solar cells (IBSCs). The analysis of the field-dependent ground-state transition energies reveals that the QDM can be operated both as a high dipole moment device by applying large electric fields and as a high polarizability device under the application of small electric field magnitudes. The quantum confined Stark effect (QCSE) red shifts the band-gap wavelength to 1.3 μm at the 15 kV cm(-1) electric field; however the reduced electron-hole wave function overlaps lead to a decrease in the interband optical transition strengths by roughly three orders of magnitude. The study of the polarisation-resolved optical

  8. Metamorphic quantum dots: Quite different nanostructures

    International Nuclear Information System (INIS)

    Seravalli, L.; Frigeri, P.; Nasi, L.; Trevisi, G.; Bocchi, C.

    2010-01-01

    In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantum dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.

  9. The enhancement of photoresponse of an ordered inorganic-organic hybrid architecture by increasing interfacial contacts

    International Nuclear Information System (INIS)

    Zhang Bin; Chen Xudong; Ma Shaohua; Yang Jin; Zhang Mingqiu; Chen Yujie

    2010-01-01

    A modified ZnO quantum dot/polythiophene (ZnO/PTh) inorganic-organic hybrid architecture was fabricated by using ordered mesoporous silica (SBA-15) as the retaining template. First, a two-step strategy was developed to synthesize an ordered organic conducting polymer composite (PTh/SBA-15). Then, ZnO quantum dots were in situ formed on the pore walls of the ordered PTh/SBA-15 composite. Photoresponse of the inorganic-organic hybrid was studied with respect to its incident photon to collected electron conversion efficiency (IPCE) and morphology. The presence of SBA-15 proved to be critical for controlling the interfacial morphology and hence enlarging the interfacial area of the inorganic-organic heterojunction. The proposed approach may act as a key method to open up potential applications in photovoltaic devices.

  10. The enhancement of photoresponse of an ordered inorganic-organic hybrid architecture by increasing interfacial contacts.

    Science.gov (United States)

    Zhang, Bin; Chen, Xudong; Ma, Shaohua; Chen, Yujie; Yang, Jin; Zhang, Mingqiu

    2010-02-10

    A modified ZnO quantum dot/polythiophene (ZnO/PTh) inorganic-organic hybrid architecture was fabricated by using ordered mesoporous silica (SBA-15) as the retaining template. First, a two-step strategy was developed to synthesize an ordered organic conducting polymer composite (PTh/SBA-15). Then, ZnO quantum dots were in situ formed on the pore walls of the ordered PTh/SBA-15 composite. Photoresponse of the inorganic-organic hybrid was studied with respect to its incident photon to collected electron conversion efficiency (IPCE) and morphology. The presence of SBA-15 proved to be critical for controlling the interfacial morphology and hence enlarging the interfacial area of the inorganic-organic heterojunction. The proposed approach may act as a key method to open up potential applications in photovoltaic devices.

  11. Electroluminescence spectra of an STM-tip-induced quantum dot

    NARCIS (Netherlands)

    Croitoru, M.D.; Gladilin, V.N.; Fomin, V.; Devreese, J.T.; Kemerink, M.; Koenraad, P.M.; Sauthoff, K.; Wolter, J.H.; Long, A.R.; Davies, J.H.

    2003-01-01

    We analyse the electroluminescence measurements performed on a STM-tipImduced quantum dot in a GaAs layer. Positions of electroluminescence peaks, attributed to the electron-hole recombination in the quantum dot, are very sensitive to the electron tunnelling current even in the case when the current

  12. Dynamic modeling of interfacial structures via interfacial area transport equation

    International Nuclear Information System (INIS)

    Seungjin, Kim; Mamoru, Ishii

    2004-01-01

    Full text of publication follows:In the current thermal-hydraulic system analysis codes using the two-fluid model, the empirical correlations that are based on the two-phase flow regimes and regime transition criteria are being employed as closure relations for the interfacial transfer terms. Due to its inherent shortcomings, however, such static correlations are inaccurate and present serious problems in the numerical analysis. In view of this, a new dynamic approach employing the interfacial area transport equation has been studied. The interfacial area transport equation dynamically models the two-phase flow regime transitions and predicts continuous change of the interfacial area concentration along the flow field. Hence, when employed in the thermal-hydraulic system analysis codes, it eliminates artificial bifurcations stemming from the use of the static flow regime transition criteria. Therefore, the interfacial area transport equation can make a leapfrog improvement in the current capability of the two-fluid model from both scientific and practical point of view. Accounting for the substantial differences in the transport phenomena of various sizes of bubbles, the two-group interfacial area transport equations have been developed. The group 1 equation describes the transport of small-dispersed bubbles that are either distorted or spherical in shapes, and the group 2 equation describes the transport of large cap, slug or churn-turbulent bubbles. The source and sink terms in the right hand-side of the transport equations have been established by mechanistically modeling the creation and destruction of bubbles due to major bubble interaction mechanisms. The coalescence mechanisms include the random collision driven by turbulence, and the entrainment of trailing bubbles in the wake region of the preceding bubble. The disintegration mechanisms include the break-up by turbulence impact, shearing-off at the rim of large cap bubbles and the break-up of large cap

  13. Room-temperature dephasing in InAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang; Hvam, Jørn Märcher

    1999-01-01

    Summary form only given. Semiconductor quantum dots (QDs) are receiving increasing attention for fundamental studies on zero-dimensional confinement and for device applications. Quantum-dot lasers are expected to show superior performances, like high material gain, low and temperature...... stacked layers of InAs-InGaAs-GaAs quantum dots....

  14. Recent advances in interfacial engineering of perovskite solar cells

    Science.gov (United States)

    Ye, Meidan; He, Chunfeng; Iocozzia, James; Liu, Xueqin; Cui, Xun; Meng, Xiangtong; Rager, Matthew; Hong, Xiaodan; Liu, Xiangyang; Lin, Zhiqun

    2017-09-01

    Due to recent developments, organometallic halide perovskite solar cells (PSCs) have attracted even greater interest owing to their impressive photovoltaic properties and simple device manufacturing processes with the potential for commercial applications. The power conversion efficiencies (PCEs) of PSCs have surged from 3.8% for methyl ammonium lead halide-sensitized liquid solar cells, CH3NH3PbX3 (X  =  Cl, Br, I), in 2009, to more than 22% for all-solid-state solar cells in 2016. Over the past few years, significant effort has been dedicated to realizing PSCs with even higher performance. In this review, recent advances in the interfacial engineering of PSCs are addressed. The specific strategies for the interfacial engineering of PSCs fall into two categories: (1) solvent treatment and additives to improve the light-harvesting capabilities of perovskite films, and (2) the incorporation of various functional materials at the interfaces between the active layers (e.g. electron transporting layer, perovskite layer, and hole transporting layer). This review aims to provide a comprehensive overview of strategies for the interfacial engineering of PSCs with potential benefits including enhanced light harvesting, improved charge separation and transport, improved device stability, and elimination of photocurrent hysteresis.

  15. Scaling of interfacial jump conditions

    International Nuclear Information System (INIS)

    Quezada G, S.; Vazquez R, A.; Espinosa P, G.

    2015-09-01

    To model the behavior of a nuclear reactor accurately is needed to have balance models that take into account the different phenomena occurring in the reactor. These balances have to be coupled together through boundary conditions. The boundary conditions have been studied and different treatments have been given to the interface. In this paper is a brief description of some of the interfacial jump conditions that have been proposed in recent years. Also, the scaling of an interfacial jump condition is proposed, for coupling the different materials that are in contact within a nuclear reactor. (Author)

  16. Dynamic modeling of interfacial structures via interfacial area transport equation

    International Nuclear Information System (INIS)

    Seungjin, Kim; Mamoru, Ishii

    2005-01-01

    The interfacial area transport equation dynamically models the two-phase flow regime transitions and predicts continuous change of the interfacial area concentration along the flow field. Hence, when employed in the numerical thermal-hydraulic system analysis codes, it eliminates artificial bifurcations stemming from the use of the static flow regime transition criteria. Accounting for the substantial differences in the transport phenomena of various sizes of bubbles, the two-group interfacial area transport equations have been developed. The group 1 equation describes the transport of small-dispersed bubbles that are either distorted or spherical in shapes, and the group 2 equation describes the transport of large cap, slug or churn-turbulent bubbles. The source and sink terms in the right-hand-side of the transport equations have been established by mechanistically modeling the creation and destruction of bubbles due to major bubble interaction mechanisms. In the present paper, the interfacial area transport equations currently available are reviewed to address the feasibility and reliability of the model along with extensive experimental results. These include the data from adiabatic upward air-water two-phase flow in round tubes of various sizes, from a rectangular duct, and from adiabatic co-current downward air-water two-phase flow in round pipes of two sizes. (authors)

  17. All-Quantum-Dot Infrared Light-Emitting Diodes

    KAUST Repository

    Yang, Zhenyu; Voznyy, Oleksandr; Liu, Mengxia; Yuan, Mingjian; Ip, Alexander H.; Ahmed, Osman S.; Levina, Larissa; Kinge, Sachin; Hoogland, Sjoerd; Sargent, Edward H.

    2015-01-01

    © 2015 American Chemical Society. Colloidal quantum dots (CQDs) are promising candidates for infrared electroluminescent devices. To date, CQD-based light-emitting diodes (LEDs) have employed a CQD emission layer sandwiched between carrier transport

  18. Systematic optimization of quantum junction colloidal quantum dot solar cells

    KAUST Repository

    Liu, Huan; Zhitomirsky, David; Hoogland, Sjoerd; Tang, Jiang; Kramer, Illan J.; Ning, Zhijun; Sargent, Edward H.

    2012-01-01

    The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum

  19. Colloidal quantum dot solar cells exploiting hierarchical structuring

    KAUST Repository

    Labelle, André J.; Thon, Susanna; Masala, Silvia; Adachi, Michael M.; Dong, Haopeng; Farahani, Maryam; Ip, Alexander H.; Fratalocchi, Andrea; Sargent, E. H.

    2015-01-01

    Extremely thin-absorber solar cells offer low materials utilization and simplified manufacture but require improved means to enhance photon absorption in the active layer. Here, we report enhanced-absorption colloidal quantum dot (CQD) solar cells

  20. Interfacial crystalline structures in injection over-molded polypropylene and bond strength.

    Science.gov (United States)

    Yan, Bowen; Wu, Hong; Jiang, Genjie; Guo, Shaoyun; Huang, Jian

    2010-11-01

    This paper describes interfacial crystalline structures found in injection overmolded polypropylene components and the relationship of these structures to bond strength between the components. The combined effects of the development of hierarchical gradient structures and the particular thermomechanical environment near the interface on the interfacial crystalline structures were investigated in detail by PLM, SEM, DSC, WAXD, and infrared dichroism spectroscopy. The experimental results showed that during molding there was competitive formation of interfacial crystalline structures consisted of "shish-kebab" layer (SKL) and a transcrystalline layers (TCL). Variation in shear stress (controlled by injection pressure and injection speed) plays an important role in the formation of the SKL. The formation of TCL is influenced by the thermal environment, namely melt temperature and mold temperature. Increasing within certain limits, interfacial temperature and the thermal gradient near the interface promotes β-iPP growth. The relationship between interfacial crystalline structures and interfacial bond strength was established by lap shear measurement. The interfacial bond strength is improved by enhancing the formation of TCL, but reduced if SKL predominates.

  1. Nonlinear Dot Plots.

    Science.gov (United States)

    Rodrigues, Nils; Weiskopf, Daniel

    2018-01-01

    Conventional dot plots use a constant dot size and are typically applied to show the frequency distribution of small data sets. Unfortunately, they are not designed for a high dynamic range of frequencies. We address this problem by introducing nonlinear dot plots. Adopting the idea of nonlinear scaling from logarithmic bar charts, our plots allow for dots of varying size so that columns with a large number of samples are reduced in height. For the construction of these diagrams, we introduce an efficient two-way sweep algorithm that leads to a dense and symmetrical layout. We compensate aliasing artifacts at high dot densities by a specifically designed low-pass filtering method. Examples of nonlinear dot plots are compared to conventional dot plots as well as linear and logarithmic histograms. Finally, we include feedback from an expert review.

  2. Diffuse x-ray scattering study of interfacial structure of self-assembled conjugated polymers

    International Nuclear Information System (INIS)

    Wang Jun; Park, Y.J.; Lee, K.-B.; Hong, H.; Davidov, D.

    2002-01-01

    The interfacial structures of self-assembled heterostructures through alternate deposition of conjugated and nonconjugated polymers were studied by x-ray reflectivity and nonspecular scattering. We found that the interfacial width including the effects of both interdiffusion and interfacial roughness (correlated) was mainly contributed by the latter one. The self-assembled deposition induced very small interdiffusion between layers. The lateral correlation length ξ parallel grew as a function of deposition time (or film thickness) described by a power law ξ parallel ∝t β/H and was also observed from the off-specular scattering

  3. Interfacial structure of V2AlC thin films deposited on (112-bar 0)-sapphire

    International Nuclear Information System (INIS)

    Sigumonrong, Darwin P.; Zhang, Jie; Zhou, Yanchun; Music, Denis; Emmerlich, Jens; Mayer, Joachim; Schneider, Jochen M.

    2011-01-01

    Local epitaxy between V 2 AlC and sapphire without intentionally or spontaneously formed seed layers was observed by transmission electron microscopy. Our ab initio calculations suggest that the most stable interfacial structure is characterized by the stacking sequence ...C-V-Al-V//O-Al..., exhibiting the largest work of separation for the configurations studied and hence strong interfacial bonding. It is proposed that a small misfit accompanied by strong interfacial bonding enable the local epitaxial growth of V 2 AlC on (112-bar 0)-sapphire.

  4. Noise and saturation properties of semiconductor quantum dot optical amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper

    2002-01-01

    We present a detailed theoretical analysis of quantum dot optical amplifiers. Due to the presence of a reservoir of wetting layer states, the saturation and noise properties differ markedly from bulk or QW amplifiers and may be significantly improved.......We present a detailed theoretical analysis of quantum dot optical amplifiers. Due to the presence of a reservoir of wetting layer states, the saturation and noise properties differ markedly from bulk or QW amplifiers and may be significantly improved....

  5. Numerical simulation of optical feedback on a quantum dot lasers

    Energy Technology Data Exchange (ETDEWEB)

    Al-Khursan, Amin H., E-mail: ameen_2all@yahoo.com [Thi-Qar University, Nassiriya Nanotechnology Research Laboratory (NNRL), Science College (Iraq); Ghalib, Basim Abdullattif [Babylon University, Laser Physics Department, Science College for Women (Iraq); Al-Obaidi, Sabri J. [Al-Mustansiriyah University, Physics Department, Science College (Iraq)

    2012-02-15

    We use multi-population rate equations model to study feedback oscillations in the quantum dot laser. This model takes into account all peculiar characteristics in the quantum dots such as inhomogeneous broadening of the gain spectrum, the presence of the excited states on the quantum dot and the non-confined states due to the presence of wetting layer and the barrier. The contribution of quantum dot groups, which cannot follow by other models, is simulated. The results obtained from this model show the feedback oscillations, the periodic oscillations which evolves to chaos at higher injection current of higher feedback levels. The frequency fluctuation is attributed mainly to wetting layer with a considerable contribution from excited states. The simulation shows that is must be not using simple rate equation models to express quantum dots working at excited state transition.

  6. On the stabilization of viscoelastic laminated beams with interfacial slip

    Science.gov (United States)

    Mustafa, Muhammad I.

    2018-04-01

    In this paper, we consider a viscoelastic laminated beam model. This structure is given by two identical uniform layers on top of each other, taking into account that an adhesive of small thickness is bonding the two surfaces and produces an interfacial slip. We use viscoelastic damping with general assumptions on the relaxation function and establish explicit energy decay result from which we can recover the optimal exponential and polynomial rates. Our result generalizes the earlier related results in the literature.

  7. Organic molecules as tools to control the growth, surface structure, and redox activity of colloidal quantum dots.

    Science.gov (United States)

    Weiss, Emily A

    2013-11-19

    In order to achieve efficient and reliable technology that can harness solar energy, the behavior of electrons and energy at interfaces between different types or phases of materials must be understood. Conversion of light to chemical or electrical potential in condensed phase systems requires gradients in free energy that allow the movement of energy or charge carriers and facilitate redox reactions and dissociation of photoexcited states (excitons) into free charge carriers. Such free energy gradients are present at interfaces between solid and liquid phases or between inorganic and organic materials. Nanostructured materials have a higher density of these interfaces than bulk materials. Nanostructured materials, however, have a structural and chemical complexity that does not exist in bulk materials, which presents a difficult challenge: to lower or eliminate energy barriers to electron and energy flux that inevitably result from forcing different materials to meet in a spatial region of atomic dimensions. Chemical functionalization of nanostructured materials is perhaps the most versatile and powerful strategy for controlling the potential energy landscape of their interfaces and for minimizing losses in energy conversion efficiency due to interfacial structural and electronic defects. Colloidal quantum dots are semiconductor nanocrystals synthesized with wet-chemical methods and coated in organic molecules. Chemists can use these model systems to study the effects of chemical functionalization of nanoscale organic/inorganic interfaces on the optical and electronic properties of a nanostructured material, and the behavior of electrons and energy at interfaces. The optical and electronic properties of colloidal quantum dots have an intense sensitivity to their surface chemistry, and their organic adlayers make them dispersible in solvent. This allows researchers to use high signal-to-noise solution-phase spectroscopy to study processes at interfaces. In this

  8. Interfacial and Surface Science | Materials Science | NREL

    Science.gov (United States)

    Science group within the Material Science Center. He oversees research studies of surfaces and interfaces Interfacial and Surface Science Interfacial and Surface Science Image of irregular-outlined, light address a broad range of fundamental and applied issues in surface and interfacial science that are

  9. The effect of interfacial intermixing on magnetization and anomalous Hall effect in Co/Pd multilayers

    KAUST Repository

    Guo, Zaibing

    2015-05-01

    The effect of interfacial intermixing on magnetization and anomalous Hall effect (AHE) in Co/Pd multilayers is studied by using rapid thermal annealing to enhance the interfacial diffusion. The dependence of saturation magnetization and coercivity on the temperature of rapid thermal annealing at 5 K is discussed. It is found that AHE is closely related to the relative thickness of the Co and Pd layers. Localized paramagnetism has been observed which destroys AHE, while AHE can be enhanced by annealing.

  10. Interfacial behaviour of biopolymer multilayers

    NARCIS (Netherlands)

    Corstens, Meinou N.; Osorio Caltenco, Lilia A.; Vries, de Renko; Schroën, Karin; Berton-Carabin, Claire C.

    2017-01-01

    Although multilayered emulsions have been related to reduced lipolysis, the involved interfacial phenomena have never been studied directly. In this work, we systematically built multilayers of whey protein and pectin, which we further subjected to digestive conditions, using two different

  11. Enhanced H2/CH4 and H2/CO2 Separation by Carbon Molecular Sieve Membrane Coated on Titania Modified Alumina Support: Effects of TiO2 Intermediate Layer Preparation Variables on Interfacial Adhesion.

    Czech Academy of Sciences Publication Activity Database

    Tseng, H.-H.; Wang, Ch.-T.; Zhuang, G.-L.; Uchytil, Petr; Řezníčková Čermáková, Jiřina; Setničková, Kateřina

    2016-01-01

    Roč. 510, JUL 15 (2016), s. 391-404 ISSN 0376-7388 Grant - others:NSC(TW) NSC100-2221-E- 040-004-MY3 Institutional support: RVO:67985858 Keywords : carbon membrane * intermediate layer * adhesion Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 6.035, year: 2016

  12. Photo-stability and time-resolved photoluminescence study of colloidal CdSe/ZnS quantum dots passivated in Al{sub 2}O{sub 3} using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Chih-Yi [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan (China); Mao, Ming-Hua, E-mail: mhmao@ntu.edu.tw [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan (China); Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2016-08-28

    We report photo-stability enhancement of colloidal CdSe/ZnS quantum dots (QDs) passivated in Al{sub 2}O{sub 3} thin film using the atomic layer deposition (ALD) technique. 62% of the original peak photoluminescence (PL) intensity remained after ALD. The photo-oxidation and photo-induced fluorescence enhancement effects of both the unpassivated and passivated QDs were studied under various conditions, including different excitation sources, power densities, and environment. The unpassivated QDs showed rapid PL degradation under high excitation due to strong photo-oxidation in air while the PL intensity of Al{sub 2}O{sub 3} passivated QDs was found to remain stable. Furthermore, recombination dynamics of the unpassivated and passivated QDs were investigated by time-resolved measurements. The average lifetime of the unpassivated QDs decreases with laser irradiation time due to photo-oxidation. Photo-oxidation creates surface defects which reduces the QD emission intensity and enhances the non-radiative recombination rate. From the comparison of PL decay profiles of the unpassivated and passivated QDs, photo-oxidation-induced surface defects unexpectedly also reduce the radiative recombination rate. The ALD passivation of Al{sub 2}O{sub 3} protects QDs from photo-oxidation and therefore avoids the reduction of radiative recombination rate. Our experimental results demonstrated that passivation of colloidal QDs by ALD is a promising method to well encapsulate QDs to prevent gas permeation and to enhance photo-stability, including the PL intensity and carrier lifetime in air. This is essential for the applications of colloidal QDs in light-emitting devices.

  13. Wafer scale integration of catalyst dots into nonplanar microsystems

    DEFF Research Database (Denmark)

    Gjerde, Kjetil; Kjelstrup-Hansen, Jakob; Gammelgaard, Lauge

    2007-01-01

    In order to successfully integrate bottom-up fabricated nanostructures such as carbon nanotubes or silicon, germanium, or III-V nanowires into microelectromechanical systems on a wafer scale, reliable ways of integrating catalyst dots are needed. Here, four methods for integrating sub-100-nm...... diameter nickel catalyst dots on a wafer scale are presented and compared. Three of the methods are based on a p-Si layer utilized as an in situ mask, an encapsulating layer, and a sacrificial window mask, respectively. All methods enable precise positioning of nickel catalyst dots at the end...

  14. Optimization of charge transfer and transport processes at the CdSe quantum dots/TiO2 nanorod interface by TiO2 interlayer passivation

    International Nuclear Information System (INIS)

    Jaramillo-Quintero, O A; Rincon, M E; Triana, M A

    2017-01-01

    Surface trap states hinder charge transfer and transport properties in TiO 2 nanorods (NRs), limiting its application on optoelectronic devices. Here, we study the interfacial processes between rutile TiO 2 NR and CdSe quantum dots (QDs) using TiO 2 interlayer passivation treatments. Anatase or rutile TiO 2 thin layers were deposited on an NR surface by two wet-chemical deposition treatments. Reduced interfacial charge recombination between NRs and CdSe QDs was observed by electrochemical impedance spectroscopy with the introduction of TiO 2 thin film interlayers compared to bare TiO 2 NRs. These results can be ascribed to in-gap trap state passivation of the TiO 2 NR surface, which led to an increase in open circuit voltage. Moreover, the rutile thin layer was more efficient than anatase to promote a higher photo-excited electron transfer from CdSe QDs to TiO 2 NRs due to a large driving force for charge injection, as confirmed by surface photovoltage spectroscopy. (paper)

  15. Intermediate-band photosensitive device with quantum dots embedded in energy fence barrier

    Science.gov (United States)

    Forrest, Stephen R.; Wei, Guodan

    2010-07-06

    A plurality of layers of a first semiconductor material and a plurality of dots-in-a-fence barriers disposed in a stack between a first electrode and a second electrode. Each dots-in-a-fence barrier consists essentially of a plurality of quantum dots of a second semiconductor material embedded between and in direct contact with two layers of a third semiconductor material. Wave functions of the quantum dots overlap as at least one intermediate band. The layers of the third semiconductor material are arranged as tunneling barriers to require a first electron and/or a first hole in a layer of the first material to perform quantum mechanical tunneling to reach the second material within a respective quantum dot, and to require a second electron and/or a second hole in a layer of the first semiconductor material to perform quantum mechanical tunneling to reach another layer of the first semiconductor material.

  16. Liquid metal actuation by electrical control of interfacial tension

    Energy Technology Data Exchange (ETDEWEB)

    Eaker, Collin B.; Dickey, Michael D., E-mail: michael-dickey@ncsu.edu [Department of Chemical and Biomolecular Engineering, North Carolina State University, 911 Partners Way, Raleigh, North Carolina 27695 (United States)

    2016-09-15

    By combining metallic electrical conductivity with low viscosity, liquid metals and liquid metal alloys offer new and exciting opportunities to serve as reconfigurable components of electronic, microfluidic, and electromagnetic devices. Here, we review the physics and applications of techniques that utilize voltage to manipulate the interfacial tension of liquid metals; such techniques include electrocapillarity, continuous electrowetting, electrowetting-on-dielectric, and electrochemistry. These techniques lower the interfacial tension between liquid metals and a surrounding electrolyte by driving charged species (or in the case of electrochemistry, chemical species) to the interface. The techniques are useful for manipulating and actuating liquid metals at sub-mm length scales where interfacial forces dominate. We focus on metals and alloys that are liquid near or below room temperature (mercury, gallium, and gallium-based alloys). The review includes discussion of mercury—despite its toxicity—because it has been utilized in numerous applications and it offers a way of introducing several phenomena without the complications associated with the oxide layer that forms on gallium and its alloys. The review focuses on the advantages, applications, opportunities, challenges, and limitations of utilizing voltage to control interfacial tension as a method to manipulate liquid metals.

  17. Iridium Interfacial Stack - IrIS

    Science.gov (United States)

    Spry, David

    2012-01-01

    Iridium Interfacial Stack (IrIS) is the sputter deposition of high-purity tantalum silicide (TaSi2-400 nm)/platinum (Pt-200 nm)/iridium (Ir-200 nm)/platinum (Pt-200 nm) in an ultra-high vacuum system followed by a 600 C anneal in nitrogen for 30 minutes. IrIS simultaneously acts as both a bond metal and a diffusion barrier. This bondable metallization that also acts as a diffusion barrier can prevent oxygen from air and gold from the wire-bond from infiltrating silicon carbide (SiC) monolithically integrated circuits (ICs) operating above 500 C in air for over 1,000 hours. This TaSi2/Pt/Ir/Pt metallization is easily bonded for electrical connection to off-chip circuitry and does not require extra anneals or masking steps. There are two ways that IrIS can be used in SiC ICs for applications above 500 C: it can be put directly on a SiC ohmic contact metal, such as Ti, or be used as a bond metal residing on top of an interconnect metal. For simplicity, only the use as a bond metal is discussed. The layer thickness ratio of TaSi2 to the first Pt layer deposited thereon should be 2:1. This will allow Si from the TaSi2 to react with the Pt to form Pt2Si during the 600 C anneal carried out after all layers have been deposited. The Ir layer does not readily form a silicide at 600 C, and thereby prevents the Si from migrating into the top-most Pt layer during future anneals and high-temperature IC operation. The second (i.e., top-most) deposited Pt layer needs to be about 200 nm to enable easy wire bonding. The thickness of 200 nm for Ir was chosen for initial experiments; further optimization of the Ir layer thickness may be possible via further experimentation. Ir itself is not easily wire-bonded because of its hardness and much higher melting point than Pt. Below the iridium layer, the TaSi2 and Pt react and form desired Pt2Si during the post-deposition anneal while above the iridium layer remains pure Pt as desired to facilitate easy and strong wire-bonding to the Si

  18. Structural and interfacial defects in c-axis oriented LiNbO{sub 3} thin films grown by pulsed laser deposition on Si using Al : ZnO conducting layer

    Energy Technology Data Exchange (ETDEWEB)

    Shandilya, Swati; Sreenivas, K; Gupta, Vinay [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India); Tomar, Monika [Miranda House, University of Delhi, Delhi 110007 (India)

    2009-05-07

    Highly c-axis oriented LiNbO{sub 3} films are deposited using pulsed laser deposition on a silicon substrate using a transparent conducting Al doped ZnO layer. X-ray diffraction and Raman spectroscopic analysis show the fabrication of single phase and oriented LiNbO{sub 3} films under the optimized deposition condition. An extra peak at 905 cm{sup -1} was observed in the Raman spectra of LiNbO{sub 3} film deposited at higher substrate temperature and higher oxygen pressure, and attributed to the presence of niobium antisite defects in the lattice. Dielectric constant and ac conductivity of oriented LiNbO{sub 3} films deposited under the static and rotating substrate modes have been studied. Films deposited under the rotating substrate mode exhibit dielectric properties close to the LiNbO{sub 3} single crystal. The cause of deviation in the dielectric properties of the film deposited under the static substrate mode, in comparison with the bulk, are discussed in the light of the possible formation of an interdiffusion layer at the interface of the LiNbO{sub 3} film and the Al : ZnO layer.

  19. Structural and interfacial defects in c-axis oriented LiNbO3 thin films grown by pulsed laser deposition on Si using Al : ZnO conducting layer

    International Nuclear Information System (INIS)

    Shandilya, Swati; Sreenivas, K; Gupta, Vinay; Tomar, Monika

    2009-01-01

    Highly c-axis oriented LiNbO 3 films are deposited using pulsed laser deposition on a silicon substrate using a transparent conducting Al doped ZnO layer. X-ray diffraction and Raman spectroscopic analysis show the fabrication of single phase and oriented LiNbO 3 films under the optimized deposition condition. An extra peak at 905 cm -1 was observed in the Raman spectra of LiNbO 3 film deposited at higher substrate temperature and higher oxygen pressure, and attributed to the presence of niobium antisite defects in the lattice. Dielectric constant and ac conductivity of oriented LiNbO 3 films deposited under the static and rotating substrate modes have been studied. Films deposited under the rotating substrate mode exhibit dielectric properties close to the LiNbO 3 single crystal. The cause of deviation in the dielectric properties of the film deposited under the static substrate mode, in comparison with the bulk, are discussed in the light of the possible formation of an interdiffusion layer at the interface of the LiNbO 3 film and the Al : ZnO layer.

  20. Structural and interfacial defects in c-axis oriented LiNbO3 thin films grown by pulsed laser deposition on Si using Al : ZnO conducting layer

    Science.gov (United States)

    Shandilya, Swati; Tomar, Monika; Sreenivas, K.; Gupta, Vinay

    2009-05-01

    Highly c-axis oriented LiNbO3 films are deposited using pulsed laser deposition on a silicon substrate using a transparent conducting Al doped ZnO layer. X-ray diffraction and Raman spectroscopic analysis show the fabrication of single phase and oriented LiNbO3 films under the optimized deposition condition. An extra peak at 905 cm-1 was observed in the Raman spectra of LiNbO3 film deposited at higher substrate temperature and higher oxygen pressure, and attributed to the presence of niobium antisite defects in the lattice. Dielectric constant and ac conductivity of oriented LiNbO3 films deposited under the static and rotating substrate modes have been studied. Films deposited under the rotating substrate mode exhibit dielectric properties close to the LiNbO3 single crystal. The cause of deviation in the dielectric properties of the film deposited under the static substrate mode, in comparison with the bulk, are discussed in the light of the possible formation of an interdiffusion layer at the interface of the LiNbO3 film and the Al : ZnO layer.

  1. From DOT to Dotty

    CERN Multimedia

    CERN. Geneva

    2017-01-01

    - Module types are interfaces, which can be abstracted. In this talk Martin will present DOT, a particularly simple calculus that can express systems following these principles. DOT has been developed as the foundation of the next version of Scala. He will also report on dotty, a new Scala compiler that implements the constructs of DOT in its core data structures and that uses the lessons learned to drive Scala’s evolution.

  2. Transport in quantum dots

    International Nuclear Information System (INIS)

    Deus, Fernanda; Continetino, Mucio

    2011-01-01

    Full text. In this work we study the time dependent transport in interacting quantum dot. This is a zero-dimensional nano structure system which has quantized electronic states. In our purpose, we are interested in studying such system in a Coulomb blockade regime where a mean-field treatment of the electronic correlations are appropriate. The quantum dot is described by an Anderson type of Hamiltonian where the hybridization term arises from the contact with the leads. We consider a time dependence of both the energy of the localized state in the quantum dot and of the hybridization-like term. These time dependent parameters, under certain conditions, induce a current in the quantum dot even in the absence of difference on the chemical potential of the leads. The approach to this non-equilibrium problem requires the use of a Keldysh formalism. We calculate the non- equilibrium Green's functions and obtain results for the average (equilibrium term) and the non-equilibrium values of the electronic occupation number in the dot. we consider the possibility of a magnetic solution, with different values for the average up and down spins in the quantum dot. Our results allow to obtain, for instance, the tunneling current through the dot. The magnetic nature of the dot, for a certain range of parameters should give rise also to an induced spin current through the dot

  3. Photovoltaic Performance of Inverted Polymer Solar Cells Using Hybrid Carbon Quantum Dots and Absorption Polymer Materials

    Science.gov (United States)

    Lim, Hwain; Lee, Kyu Seung; Liu, Yang; Kim, Hak Yong; Son, Dong Ick

    2018-05-01

    We report the synthesis and characterization of the carbon quantum dots (C-dots) easily obtained from citric acid and ethanediamine, and also investigated structural, optical and electrical properties. The C-dots have extraordinary optical and electrical features such as absorption of ultraviolet range and effective interface for charge separation and transport in active layer, which make them attractive materials for applications in photovoltaic devices (PV). The C-dots play important roles in charge extraction in the PV structures, they can be synthesized by a simple method and used to insert in active layer of polymer solar cells. In this study, we demonstrate that improve charge transport properties of inverted polymer solar cells (iPSCs) with C-dots and structural, optical and electrical properties of C-dots. As a result, iPSCs with C-dots showed enhancement of more than 30% compared with that of the contrast device in power conversion efficiency.

  4. Interfacial transport processes and rheology

    CERN Document Server

    Brenner, Howard

    1991-01-01

    This textbook is designed to provide the theory, methods of measurement, and principal applications of the expanding field of interfacial hydrodynamics. It is intended to serve the research needs of both academic and industrial scientists, including chemical or mechanical engineers, material and surface scientists, physical chemists, chemical and biophysicists, rheologists, physiochemical hydrodynamicists, and applied mathematicians (especially those with interests in viscous fluid mechanics and continuum mechanics).As a textbook it provides materials for a one- or two-semester graduate-level

  5. Molecular beam deposition of Al2O3 on p-Ge(001)/Ge0.95Sn0.05 heterostructure and impact of a Ge-cap interfacial layer

    International Nuclear Information System (INIS)

    Merckling, C.; Franquet, A.; Vincent, B.; Vandervorst, W.; Loo, R.; Caymax, M.; Sun, X.; Shimura, Y.; Takeuchi, S.; Nakatsuka, O.; Zaima, S.

    2011-01-01

    We investigated the molecular beam deposition of Al 2 O 3 on Ge 0.95 Sn 0.05 surface with and without an ultra thin Ge cap layer in between. We first studied the atomic configuration of both Ge 1-x Sn x and Ge/Ge 1-x Sn x surfaces after deoxidation by reflection high-energy electron diffraction and resulted, respectively, in a c(4x2) and (2x1) surface reconstructions. After in situ deposition of an Al 2 O 3 high-κ gate dielectric we evidenced using time-of-flight secondary ion mass spectroscopy analyses that Sn diffusion was at the origin of high leakage current densities in the Ge 1-x Sn x /Al 2 O 3 gate stack. This damage could be avoided by inserting a thin 5-nm-thick Ge cap between the oxide and the Ge 1-x Sn x layer. Finally, metal-oxide-semiconductor capacitors on the Ge capped sample showed well-behaved capacitance-voltage (C-V) characteristics with interface trap density (D it ) in the range of 10 12 eV -1 cm -2 in mid gap and higher close to the valence band edge.

  6. Photovoltaic Performance of a Nanowire/Quantum Dot Hybrid Nanostructure Array Solar Cell.

    Science.gov (United States)

    Wu, Yao; Yan, Xin; Zhang, Xia; Ren, Xiaomin

    2018-02-23

    An innovative solar cell based on a nanowire/quantum dot hybrid nanostructure array is designed and analyzed. By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires, not only the absorption spectrum of GaAs nanowires is extended by quantum dots but also the light absorption of quantum dots is dramatically enhanced due to the light-trapping effect of the nanowire array. By incorporating five layers of InAs quantum dots into a 500-nm high-GaAs nanowire array, the power conversion efficiency enhancement induced by the quantum dots is six times higher than the power conversion efficiency enhancement in thin-film solar cells which contain the same amount of quantum dots, indicating that the nanowire array structure can benefit the photovoltaic performance of quantum dot solar cells.

  7. The analysis of interfacial waves

    International Nuclear Information System (INIS)

    Galimov, Azat Yu.; Drew, Donald A.; Lahey, Richard T.; Moraga, Francisco J.

    2005-01-01

    We present analytical results for stable stratified wavy two-phase flow and functional forms for the various interfacial force densities in a two-fluid model. In particular, we have derived analytically the components of the non-drag interfacial force density [Drew, D.A., Passman, S.L., 1998. Theory of Multicomponent Fluids. Springer-Verlag, New York; Nigmatulin, T.R., Drew, D.A., Lahey, R.T., Jr., 2000. An analysis of wavy annular flow. In: International Conference on Multiphase Systems, ICMS'2000, Ufa, Russia, June 15-17], Reynolds stress tensor, and the term, (p-bar cl i -p-bar cl )-bar α cl , where p-bar cl i is interfacial average pressure, p-bar cl the average pressure, and α cl is the volume fraction of the continuous liquid phase. These functional forms should be useful for assessing two-fluid closure relations and Computational Multiphase Fluid Dynamics (CMFD) numerical models for stratified wavy flows. Moreover, it appears that this approach can be generalized to other flow regimes (e.g., annular flows)

  8. Probing Interfacial Processes on Graphene Surface by Mass Detection

    Science.gov (United States)

    Kakenov, Nurbek; Kocabas, Coskun

    2013-03-01

    In this work we studied the mass density of graphene, probed interfacial processes on graphene surface and examined the formation of graphene oxide by mass detection. The graphene layers were synthesized by chemical vapor deposition method on copper foils and transfer-printed on a quartz crystal microbalance (QCM). The mass density of single layer graphene was measured by investigating the mechanical resonance of the QCM. Moreover, we extended the developed technique to probe the binding dynamics of proteins on the surface of graphene, were able to obtain nonspecific binding constant of BSA protein of graphene surface in aqueous solution. The time trace of resonance signal showed that the BSA molecules rapidly saturated by filling the available binding sites on graphene surface. Furthermore, we monitored oxidation of graphene surface under oxygen plasma by tracing the changes of interfacial mass of the graphene controlled by the shifts in Raman spectra. Three regimes were observed the formation of graphene oxide which increases the interfacial mass, the release of carbon dioxide and the removal of small graphene/graphene oxide flakes. Scientific and Technological Research Council of Turkey (TUBITAK) grant no. 110T304, 109T209, Marie Curie International Reintegration Grant (IRG) grant no 256458, Turkish Academy of Science (TUBA-Gebip).

  9. Morphological Instability in InAs/GaSb Superlattices due to Interfacial Bonds

    International Nuclear Information System (INIS)

    Li, J.H.; Moss, S.C.; Stokes, D.W.; Caha, O.; Bassler, K.E.; Ammu, S.L.; Bai, J.

    2005-01-01

    Synchrotron x-ray diffraction is used to compare the misfit strain and composition in a self-organized nanowire array in an InAs/GaSb superlattice with InSb interfacial bonds to a planar InAs/GaSb superlattice with GaAs interfacial bonds. It is found that the morphological instability that occurs in the nanowire array results from the large misfit strain that the InSb interfacial bonds have in the nanowire array. Based on this result, we propose that tailoring the type of interfacial bonds during the epitaxial growth of III-V semiconductor films provides a novel approach for producing the technologically important morphological instability in anomalously thin layers

  10. A biomimetic approach to enhancing interfacial interactions: polydopamine-coated clay as reinforcement for epoxy resin.

    Science.gov (United States)

    Yang, Liping; Phua, Si Lei; Teo, Jun Kai Herman; Toh, Cher Ling; Lau, Soo Khim; Ma, Jan; Lu, Xuehong

    2011-08-01

    A facile biomimetic method was developed to enhance the interfacial interaction in polymer-layered silicate nanocomposites. By mimicking mussel adhesive proteins, a monolayer of polydopamine was constructed on clay surface by a controllable coating method. The modified clay (D-clay) was incorporated into an epoxy resin, it is found that the strong interfacial interactions brought by the polydopamine benefits not only the dispersion of the D-clay in the epoxy but also the effective interfacial stress transfer, leading to greatly improved thermomechanical properties at very low inorganic loadings. Rheological and infrared spectroscopic studies show that the interfacial interactions between the D-clay and epoxy are dominated by the hydrogen bonds between the catechol-enriched polydopamine and the epoxy.

  11. Structural and electrooptical characteristics of quantum dots emitting at 1.3 μm on gallium arsenide

    DEFF Research Database (Denmark)

    Fiore, A.; Oesterle, U.; Stanley, R.P.

    2001-01-01

    We present a comprehensive study of the structural and emission properties of self-assembled InAs quantum dots emitting at 1.3 mum. The dots are grown by molecular beam epitaxy on gallium arsenide substrates. Room-temperature emission at 1.3 mum is obtained by embedding the dots in an InGaAs layer...

  12. Quantum Dots: Theory

    Energy Technology Data Exchange (ETDEWEB)

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    This review covers the description of the methodologies typically used for the calculation of the electronic structure of self-assembled and colloidal quantum dots. These are illustrated by the results of their application to a selected set of physical effects in quantum dots.

  13. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    1999-01-01

    Semiconductor quantum dots ("solid state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution of...

  14. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    Semiconductor quantum dots ("solid-state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution of...

  15. Synthesis of quantum dots

    Science.gov (United States)

    McDaniel, Hunter

    2017-10-17

    Common approaches to synthesizing alloyed quantum dots employ high-cost, air-sensitive phosphine complexes as the selenium precursor. Disclosed quantum dot synthesis embodiments avoid these hazardous and air-sensitive selenium precursors. Certain embodiments utilize a combination comprising a thiol and an amine that together reduce and complex the elemental selenium to form a highly reactive selenium precursor at room temperature. The same combination of thiol and amine acts as the reaction solvent, stabilizing ligand, and sulfur source in the synthesis of quantum dot cores. A non-injection approach may also be used. The optical properties of the quantum dots synthesized by this new approach can be finely tuned for a variety of applications by controlling size and/or composition of size and composition. Further, using the same approach, a shell can be grown around a quantum dot core that improves stability, luminescence efficiency, and may reduce toxicity.

  16. Interaction of porphyrins with CdTe quantum dots

    International Nuclear Information System (INIS)

    Zhang Xing; Liu Zhongxin; Ma Lun; Hossu, Marius; Chen Wei

    2011-01-01

    Porphyrins may be used as photosensitizers for photodynamic therapy, photocatalysts for organic pollutant dissociation, agents for medical imaging and diagnostics, applications in luminescence and electronics. The detection of porphyrins is significantly important and here the interaction of protoporphyrin-IX (PPIX) with CdTe quantum dots was studied. It was observed that the luminescence of CdTe quantum dots was quenched dramatically in the presence of PPIX. When CdTe quantum dots were embedded into silica layers, almost no quenching by PPIX was observed. This indicates that PPIX may interact and alter CdTe quantum dots and thus quench their luminescence. The oxidation of the stabilizers such as thioglycolic acid (TGA) as well as the nanoparticles by the singlet oxygen generated from PPIX is most likely responsible for the luminescence quenching. The quenching of quantum dot luminescence by porphyrins may provide a new method for photosensitizer detection.

  17. Gunn's dots in retinal images of 2,286 adolescents

    DEFF Research Database (Denmark)

    Boberg-Ans, Lars C.; Munch, Inger C.; Larsen, Michael

    2017-01-01

    a 6 mm grid centered on the optic disc. Results: One or more Gunn's dots were seen in at least one eye in 82.6% of children. The median number of Gunn's dots per eye was 46 (range 0-482). Most Gunn's dots were found inferior and superior of the optic disc (49.3% and 45.8%, respectively, of the total...... number of Gunn's dots in the population). The odds for having 1 or more Gunn's dots were 3-fold greater in children with dark brown irides compared with children with blue irides (odds ratio 2.99, 95% CI 1.81 to 4.94, P, 0.0001 adjusted for age, sex, retinal nerve fiber layer thickness, refraction...

  18. Single-crystal micromachining using multiple fusion-bonded layers

    Science.gov (United States)

    Brown, Alan; O'Neill, Garry; Blackstone, Scott C.

    2000-08-01

    Multi-layer structures have been fabricated using Fusion bonding. The paper shows void free layers of between 2 and 100 microns that have been bonded to form multi-layer structures. Silicon layers have been bonded both with and without interfacial oxide layers.

  19. Physical properties of metal–insulator–semiconductor structures based on n-GaAs with InAs quantum dots deposited onto the surface of an n-GaAs layer

    Energy Technology Data Exchange (ETDEWEB)

    Tikhov, S. V.; Gorshkov, O. N.; Koryazhkina, M. N., E-mail: mahavenok@mail.ru; Kasatkin, A. P.; Antonov, I. N.; Vihrova, O. V.; Morozov, A. I. [Lobachevsky State University of Nizhny Novgorod (NNSU) (Russian Federation)

    2016-12-15

    The properties of metal–insulator–semiconductor (MIS) structures based on n-GaAs in which silicon oxide and yttria-stabilized zirconia and hafnia are used as the insulator containing InAs quantum dots, which are embedded at the insulator/n-GaAs interface, are investigated. The structures manifest the resistive switching and synaptic behavior.

  20. Dielectrophoretic Manipulation and Separation of Microparticles Using Microarray Dot Electrodes

    Directory of Open Access Journals (Sweden)

    Bashar Yafouz

    2014-04-01

    Full Text Available This paper introduces a dielectrophoretic system for the manipulation and separation of microparticles. The system is composed of five layers and utilizes microarray dot electrodes. We validated our system by conducting size-dependent manipulation and separation experiments on 1, 5 and 15 μm polystyrene particles. Our findings confirm the capability of the proposed device to rapidly and efficiently manipulate and separate microparticles of various dimensions, utilizing positive and negative dielectrophoresis (DEP effects. Larger size particles were repelled and concentrated in the center of the dot by negative DEP, while the smaller sizes were attracted and collected by the edge of the dot by positive DEP.

  1. Second-harmonic imaging of semiconductor quantum dots

    DEFF Research Database (Denmark)

    Østergaard, John Erland; Bozhevolnyi, Sergey I.; Pedersen, Kjeld

    2000-01-01

    Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of similar to 885 nm corresponding to the quantum-dot photoluminescence maximum....... In addition, the second-harmonic spectrum exhibits another smaller but well-pronounced peak at 765 nm not found in the linear experiments. We attribute this peak to the generation of second-harmonic radiation in the AlGaAs spacer layer enhanced by the local symmetry at the quantum-dot interface. We further...

  2. Solution-Processed Nanocrystal Quantum Dot Tandem Solar Cells

    KAUST Repository

    Choi, Joshua J.; Wenger, Whitney N.; Hoffman, Rachel S.; Lim, Yee-Fun; Luria, Justin; Jasieniak, Jacek; Marohn, John A.; Hanrath, Tobias

    2011-01-01

    Solution-processed tandem solar cells created from nanocrystal quantum dots with size-tuned energy levels are demonstrated. Prototype devices featuring interconnected quantum dot layers of cascaded energy gaps exhibit IR sensitivity and an open circuit voltage, V oc, approaching 1 V. The tandem solar cell performance depends critically on the optical and electrical properties of the interlayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Gain recovery dynamics and limitations in quantum dot amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Bischoff, Svend; Magnúsdóttir, Ingibjörg

    2001-01-01

    gain recovery in a quantum dot amplifier, and it is thus not yet clear what the limiting processes for the device response are. We present the results of a comprehensive theoretical model, which agrees well with the experimental results, and indicates the importance of slow recovery of higher energy...... levels. The model used is of the rate-equation type with three energy levels: ground state (GS) and excited state (ES) dot levels and a wetting layer...

  4. Solution-Processed Nanocrystal Quantum Dot Tandem Solar Cells

    KAUST Repository

    Choi, Joshua J.

    2011-06-03

    Solution-processed tandem solar cells created from nanocrystal quantum dots with size-tuned energy levels are demonstrated. Prototype devices featuring interconnected quantum dot layers of cascaded energy gaps exhibit IR sensitivity and an open circuit voltage, V oc, approaching 1 V. The tandem solar cell performance depends critically on the optical and electrical properties of the interlayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Protein interfacial structure and nanotoxicology

    International Nuclear Information System (INIS)

    White, John W.; Perriman, Adam W.; McGillivray, Duncan J.; Lin, J.-M.

    2009-01-01

    Here we briefly recapitulate the use of X-ray and neutron reflectometry at the air-water interface to find protein structures and thermodynamics at interfaces and test a possibility for understanding those interactions between nanoparticles and proteins which lead to nanoparticle toxicology through entry into living cells. Stable monomolecular protein films have been made at the air-water interface and, with a specially designed vessel, the substrate changed from that which the air-water interfacial film was deposited. This procedure allows interactions, both chemical and physical, between introduced species and the monomolecular film to be studied by reflectometry. The method is briefly illustrated here with some new results on protein-protein interaction between β-casein and κ-casein at the air-water interface using X-rays. These two proteins are an essential component of the structure of milk. In the experiments reported, specific and directional interactions appear to cause different interfacial structures if first, a β-casein monolayer is attacked by a κ-casein solution compared to the reverse. The additional contrast associated with neutrons will be an advantage here. We then show the first results of experiments on the interaction of a β-casein monolayer with a nanoparticle titanium oxide sol, foreshadowing the study of the nanoparticle 'corona' thought to be important for nanoparticle-cell wall penetration.

  6. Protein interfacial structure and nanotoxicology

    Energy Technology Data Exchange (ETDEWEB)

    White, John W. [Research School of Chemistry, Australian National University, Canberra (Australia)], E-mail: jww@rsc.anu.edu.au; Perriman, Adam W.; McGillivray, Duncan J.; Lin, J.-M. [Research School of Chemistry, Australian National University, Canberra (Australia)

    2009-02-21

    Here we briefly recapitulate the use of X-ray and neutron reflectometry at the air-water interface to find protein structures and thermodynamics at interfaces and test a possibility for understanding those interactions between nanoparticles and proteins which lead to nanoparticle toxicology through entry into living cells. Stable monomolecular protein films have been made at the air-water interface and, with a specially designed vessel, the substrate changed from that which the air-water interfacial film was deposited. This procedure allows interactions, both chemical and physical, between introduced species and the monomolecular film to be studied by reflectometry. The method is briefly illustrated here with some new results on protein-protein interaction between {beta}-casein and {kappa}-casein at the air-water interface using X-rays. These two proteins are an essential component of the structure of milk. In the experiments reported, specific and directional interactions appear to cause different interfacial structures if first, a {beta}-casein monolayer is attacked by a {kappa}-casein solution compared to the reverse. The additional contrast associated with neutrons will be an advantage here. We then show the first results of experiments on the interaction of a {beta}-casein monolayer with a nanoparticle titanium oxide sol, foreshadowing the study of the nanoparticle 'corona' thought to be important for nanoparticle-cell wall penetration.

  7. Influence of surface states of CuInS{sub 2} quantum dots in quantum dots sensitized photo-electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Zhuoyin; Liu, Yueli [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China); Wu, Lei [School of Electronic and Electrical, Wuhan Railway Vocational College of Technology, Wuhan 430205 (China); Zhao, Yinghan; Chen, Keqiang [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China); Chen, Wen, E-mail: chenw@whut.edu.cn [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China)

    2016-12-01

    Graphical abstract: J–V curves of different ligands capped CuInS{sub 2} QDs sensitized TiO{sub 2} photo-electrodes. - Highlights: • DDT, OLA, MPA, and S{sup 2−} ligand capped CuInS{sub 2} quantum dot sensitized photo-electrodes are prepared. • Surface states of quantum dots greatly influence the electrochemical performance of CuInS{sub 2} quantum dot sensitized photo-electrodes. • S{sup 2−} ligand enhances the UV–vis absorption and electron–hole separation property as well as the excellent charge transfer performance of the photo-electrodes. - Abstract: Surface states are significant factor for the enhancement of electrochemical performance in CuInS{sub 2} quantum dot sensitized photo-electrodes. DDT, OLA, MPA, and S{sup 2−} ligand capped CuInS{sub 2} quantum dot sensitized photo-electrodes are prepared by thermolysis, solvethermal and ligand-exchange processes, respectively, and their optical properties and photoelectrochemical properties are investigated. The S{sup 2−} ligand enhances the UV–vis absorption and electron–hole separation property as well as the excellent charge transfer performance of the photo-electrodes, which is attributed to the fact that the atomic S{sup 2−} ligand for the interfacial region of quantum dots may improve the electron transfer rate. These S{sup 2−}-capped CuInS{sub 2} quantum dot sensitized photo-electrodes exhibit the excellent photoelectrochemical efficiency and IPCE peak value, which is higher than that of the samples with DDT, OLA and MPA ligands.

  8. Optical manipulation of electron spin in quantum dot systems

    Science.gov (United States)

    Villas-Boas, Jose; Ulloa, Sergio; Govorov, Alexander

    2006-03-01

    Self-assembled quantum dots (QDs) are of particular interest for fundamental physics because of their similarity with atoms. Coupling two of such dots and addressing them with polarized laser light pulses is perhaps even more interesting. In this paper we use a multi-exciton density matrix formalism to model the spin dynamics of a system with single or double layers of QDs. Our model includes the anisotropic electron-hole exchange in the dots, the presence of wetting layer states, and interdot tunneling [1]. Our results show that it is possible to switch the spin polarization of a single self-assembled quantum dot under elliptically polarized light by increasing the laser intensity. In the nonlinear mechanism described here, intense elliptically polarized light creates an effective exchange channel between the exciton spin states through biexciton states, as we demonstrate by numerical and analytical methods. We further show that the effect persists in realistic ensembles of dots, and we propose alternative ways to detect it. We also extend our study to a double layer of quantum dots, where we find a competition between Rabi frequency and tunneling oscillations. [1] J. M. Villas-Boas, S. E. Ulloa, and A. O. Govorov, Phys. Rev. Lett. 94, 057404 (2005); Phys. Rev. B 69, 125342 (2004).

  9. Heparin conjugated quantum dots for in vitro imaging applications.

    Science.gov (United States)

    Maguire, Ciaran Manus; Mahfoud, Omar Kazem; Rakovich, Tatsiana; Gerard, Valerie Anne; Prina-Mello, Adriele; Gun'ko, Yurii; Volkov, Yuri

    2014-11-01

    In this work heparin-gelatine multi-layered cadmium telluride quantum dots (QDgel/hep) were synthesised using a novel 'one-pot' method. The QDs produced were characterised using various spectroscopic and physiochemical techniques. Suitable QDs were then selected and compared to thioglycolic acid stabilised quantum dots (QDTGA) and gelatine coated quantum dots (QDgel) for utilisation in in vitro imaging experiments on live and fixed permeabilised THP-1, A549 and Caco-2 cell lines. Exposure of live THP-1 cells to QDgel/hep resulted in localisation of the QDs to the nucleus of the cells. QDgel/hep show affinity for the nuclear compartment of fixed permeabilised THP-1 and A549 cells but remain confined to cytoplasm of fixed permeabilised Caco-2 cells. It is postulated that heparin binding to the CD11b receptor facilitates the internalisation of the QDs into the nucleus of THP-1 cells. In addition, the heparin layer may reduce the unfavourable thrombogenic nature of quantum dots observed in vivo. In this study, heparin conjugated quantum dots were found to have superior imaging properties compared to its native counterparts. The authors postulate that heparin binding to the CD11b receptor facilitates QD internalization to the nucleus, and the heparin layer may reduce the in vivo thrombogenic properties of quantum dots. Copyright © 2014 Elsevier Inc. All rights reserved.

  10. Quantum dot molecules

    CERN Document Server

    Wu, Jiang

    2014-01-01

    This book reviews recent advances in the exciting and rapidly growing field of quantum dot molecules (QDMs). It offers state-of-the-art coverage of novel techniques and connects fundamental physical properties with device design.

  11. Effect of Concentration on the Interfacial and Bulk Structure of Ionic Liquids in Aqueous Solution.

    Science.gov (United States)

    Cheng, H-W; Weiss, H; Stock, P; Chen, Y-J; Reinecke, C R; Dienemann, J-N; Mezger, M; Valtiner, M

    2018-02-27

    Bio and aqueous applications of ionic liquids (IL) such as catalysis in micelles formed in aqueous IL solutions or extraction of chemicals from biologic materials rely on surface-active and self-assembly properties of ILs. Here, we discuss qualitative relations of the interfacial and bulk structuring of a water-soluble surface-active IL ([C 8 MIm][Cl]) on chemically controlled surfaces over a wide range of water concentrations using both force probe and X-ray scattering experiments. Our data indicate that IL structuring evolves from surfactant-like surface adsorption at low IL concentrations, to micellar bulk structure adsorption above the critical micelle concentration, to planar bilayer formation in ILs with Interfacial structuring is controlled by mesoscopic bulk structuring at high water concentrations. Surface chemistry and surface charges decisively steer interfacial ordering of ions if the water concentration is low and/or the surface charge is high. We also demonstrate that controlling the interfacial forces by using self-assembled monolayer chemistry allows tuning of interfacial structures. Both the ratio of the head group size to the hydrophobic tail volume as well as the surface charging trigger the bulk structure and offer a tool for predicting interfacial structures. Based on the applied techniques and analyses, a qualitative prediction of molecular layering of ILs in aqueous systems is possible.

  12. Interfacial heat transfer - State of the art

    International Nuclear Information System (INIS)

    Yadigaroglu, G.

    1987-01-01

    Interfacial heat exchanges control the interfacial mass exchange rate, depend on the interfacial area, and are tied to the prediction of thermal nonequilibrium. The nature of the problem usually requires the formulation of mechanistic laws and precludes the general use of universal correlations. This is partly due to the fact that the length scale controlling the interfacial exchanges varies widely from one situation to another and has a strong influence on the exchange coefficients. Within the framework of the ''two-fluid models'', the exchanges occurring at the interfaces are explicitly taken into consideration by the jump condition linking the volumetric mass exchange (evaporation) rate between the phases, to the interfacial energy transfer rates

  13. Manipulating interfacial polymer structures through mixed surfactant adsorption and complexation.

    Science.gov (United States)

    Cattoz, Beatrice; de Vos, Wiebe M; Cosgrove, Terence; Crossman, Martin; Prescott, Stuart W

    2012-04-17

    The effects of a nonionic alcohol ethoxylate surfactant, C(13)E(7), on the interactions between PVP and SDS both in the bulk and at the silica nanoparticle interface are studied by photon correlation spectroscopy, solvent relaxation NMR, SANS, and optical reflectometry. Our results confirmed that, in the absence of SDS, C(13)E(7) and PVP are noninteracting, while SDS interacts strongly both with PVP and C(13)E(7) . Studying interfacial interactions showed that the interfacial interactions of PVP with silica can be manipulated by varying the amounts of SDS and C(13)E(7) present. Upon SDS addition, the adsorbed layer thickness of PVP on silica increases due to Coulombic repulsion between micelles in the polymer layer. When C(13)E(7) is progressively added to the system, it forms mixed micelles with the complexed SDS, reducing the total charge per micelle and thus reducing the repulsion between micelle and the silica surface that would otherwise cause the PVP to desorb. This causes the amount of adsorbed polymer to increase with C(13)E(7) addition for the systems containing SDS, demonstrating that addition of C(13)E(7) hinders the SDS-mediated desorption of an adsorbed PVP layer. © 2012 American Chemical Society

  14. Graphene quantum dots

    CERN Document Server

    Güçlü, Alev Devrim; Korkusinski, Marek; Hawrylak, Pawel

    2014-01-01

    This book reflects the current status of theoretical and experimental research of graphene based nanostructures, in particular quantum dots, at a level accessible to young researchers, graduate students, experimentalists and theorists. It presents the current state of research of graphene quantum dots, a single or few monolayer thick islands of graphene. It introduces the reader to the electronic and optical properties of graphite, intercalated graphite and graphene, including Dirac fermions, Berry's phase associated with sublattices and valley degeneracy, covers single particle properties of

  15. Interfacial instabilities in vibrated fluids

    Science.gov (United States)

    Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier

    2016-07-01

    Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced

  16. A nanoscale study of charge extraction in organic solar cells: the impact of interfacial molecular configurations.

    Science.gov (United States)

    Tang, Fu-Ching; Wu, Fu-Chiao; Yen, Chia-Te; Chang, Jay; Chou, Wei-Yang; Gilbert Chang, Shih-Hui; Cheng, Horng-Long

    2015-01-07

    In the optimization of organic solar cells (OSCs), a key problem lies in the maximization of charge carriers from the active layer to the electrodes. Hence, this study focused on the interfacial molecular configurations in efficient OSC charge extraction by theoretical investigations and experiments, including small molecule-based bilayer-heterojunction (sm-BLHJ) and polymer-based bulk-heterojunction (p-BHJ) OSCs. We first examined a well-defined sm-BLHJ model system of OSC composed of p-type pentacene, an n-type perylene derivative, and a nanogroove-structured poly(3,4-ethylenedioxythiophene) (NS-PEDOT) hole extraction layer. The OSC with NS-PEDOT shows a 230% increment in the short circuit current density compared with that of the conventional planar PEDOT layer. Our theoretical calculations indicated that small variations in the microscopic intermolecular interaction among these interfacial configurations could induce significant differences in charge extraction efficiency. Experimentally, different interfacial configurations were generated between the photo-active layer and the nanostructured charge extraction layer with periodic nanogroove structures. In addition to pentacene, poly(3-hexylthiophene), the most commonly used electron-donor material system in p-BHJ OSCs was also explored in terms of its possible use as a photo-active layer. Local conductive atomic force microscopy was used to measure the nanoscale charge extraction efficiency at different locations within the nanogroove, thus highlighting the importance of interfacial molecular configurations in efficient charge extraction. This study enriches understanding regarding the optimization of the photovoltaic properties of several types of OSCs by conducting appropriate interfacial engineering based on organic/polymer molecular orientations. The ultimate power conversion efficiency beyond at least 15% is highly expected when the best state-of-the-art p-BHJ OSCs are combined with present arguments.

  17. An experimental investigation of the interfacial condensation heat transfer in steam/water countercurrent stratified flow in a horizontal pipe

    Energy Technology Data Exchange (ETDEWEB)

    Chu, In Cheol; Yu, Seon Oh; Chun, Moon Hyun [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of); Kim, Byong Sup; Kim, Yang Seok; Kim, In Hwan; Lee, Sang Won [Korea Electric Power Research Institute, Taejon (Korea, Republic of)

    1998-12-31

    An interfacial condensation heat transfer phenomenon in a steam/water countercurrent stratified flow in a nearly horizontal pipe has been experimentally investigated. The present study has been focused on the measurement of the temperature and velocity distributions within the water layer. In particular, the water layer thickness used in the present work is large enough so that the turbulent mixing is limited and the thermal stratification is established. As a result, the thermal resistance of the water layer to the condensation heat transfer is increased significantly. An empirical correlation of the interfacial condensation heat transfer has been developed. The present correlation agrees with the data within {+-} 15%. 5 refs., 6 figs. (Author)

  18. Hyperbolic metamaterials based on quantum-dot plasmon-resonator nanocomposites

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Ozel, T.; Mutlugun, E.

    2014-01-01

    We theoretically demonstrate that nanocomposites made of colloidal semiconductor quantum dot monolayers placed between metal nanoparticle monolayers can function as multilayer hyperbolic metamaterials. Depending on the thickness of the spacer between the quantum dot and nanoparticle layers......, the effective permittivity tensor of the nanocomposite is shown to become indefinite, resulting in increased photonic density of states and strong enhancement of quantum dot luminescence. This explains the results of recent experiments [T. Ozel et al., ACS Nano 5, 1328 (2011)] and confirms that hyperbolic...

  19. Influence of nitrogen on the growth and the properties of InAs quantum dots

    International Nuclear Information System (INIS)

    Schumann, O.

    2004-01-01

    This work investigates the influence of nitrogen incorporation on the growth and the optical properties of InAs quantum dots on GaAs(001) substrates. On the basis of systematic growth interruptions it was shown that the large quantum dots nucleate at dislocations, which are already formed during the growth of the wetting layer. After solving the growth problems, the influence of different combinations of matrix layers on the structural and optical properties of the quantum dots was investigated in the second part of this work. The strain and bandgap of these layers were varied systematically. (orig.)

  20. Effect of organic materials used in the synthesis on the emission from CdSe quantum dots

    Science.gov (United States)

    Lee, Jae-Won; Yang, Ho-Soon; Hong, K. S.; Kim, S. M.

    2013-12-01

    Quantum-dot nanocrystals have particular optical properties due to the quantum confinement effect and the surface effect. This study focuses on the effect of surface conditions on the emission from quantum dots. The quantum dots prepared with 1-hexadecylamine (HDA) in the synthesis show strong emission while the quantum dots prepared without HDA show weak emission, as well as emission from surface energy traps. The comparison of the X-ray patterns of these two sets of quantum dots reveals that HDA forms a layer on the surface of quantum dot during the synthesis. This surface passivation with a layer of HDA reduces surface energy traps, therefore the emission from surface trap levels is suppressed in the quantum dots synthesized with HDA.

  1. Interfacial Structure and Double Layer Capacitance of Ionic Liquids

    NARCIS (Netherlands)

    Jitvisate, Monchai

    2018-01-01

    Ionic liquids are organic salts that are in liquid phase at room temperature. Their wide liquidus range, particularly at room temperature, results from the liquids’ large and asymmetric molecular geometry. This leads to a collection of unique properties, such as, high ionic strength, extremely low

  2. Integrated photonics using colloidal quantum dots

    Science.gov (United States)

    Menon, Vinod M.; Husaini, Saima; Okoye, Nicky; Valappil, Nikesh V.

    2009-11-01

    Integrated photonic devices were realized using colloidal quantum dot composites such as flexible microcavity laser, microdisk emitters and integrated active-passive waveguides. The microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. Planar photonic devices consisting of vertically coupled microring resonators, microdisk emitters, active-passive integrated waveguide structures and coupled active microdisk resonators were realized using soft lithography, photo-lithography, and electron beam lithography, respectively. The gain medium in all these devices was a composite consisting of quantum dots embedded in SU8 matrix. Finally, the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements was determined. In addition to their specific functionalities, these novel device demonstrations and their development present a low-cost alternative to the traditional photonic device fabrication techniques.

  3. Control of interfacial intermetallic compounds in Fe–Al joining by Zn addition

    Energy Technology Data Exchange (ETDEWEB)

    Yang, J. [Key Laboratory of Robot and Welding Automation of Jiangxi Province, School of Mechanical and Electrical Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China); Center for Advanced Materials Joining, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Li, Y.L., E-mail: liyulong1112ster@gmail.com [Key Laboratory of Robot and Welding Automation of Jiangxi Province, School of Mechanical and Electrical Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China); Zhang, H. [Key Laboratory of Robot and Welding Automation of Jiangxi Province, School of Mechanical and Electrical Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China); Guo, W. [Center for Advanced Materials Joining, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); School of Mechanical Engineering and Automation, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Zhou, Y. [Center for Advanced Materials Joining, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada)

    2015-10-01

    By Zn addition to the fusion zone, the interfacial intermetallic compounds (IMCs) of laser Al/steel joint changed from layered Fe{sub 2}Al{sub 5} and needle-like FeAl{sub 3} to layered Fe{sub 2}Al{sub 5−x}Zn{sub x} and dispersed FeZn{sub 10} with minor Al-rich amorphous phase. This resulted in an improvement in the joint strength and the change of failure mode.

  4. Incorporating interfacial phenomena in solidification models

    Science.gov (United States)

    Beckermann, Christoph; Wang, Chao Yang

    1994-01-01

    A general methodology is available for the incorporation of microscopic interfacial phenomena in macroscopic solidification models that include diffusion and convection. The method is derived from a formal averaging procedure and a multiphase approach, and relies on the presence of interfacial integrals in the macroscopic transport equations. In a wider engineering context, these techniques are not new, but their application in the analysis and modeling of solidification processes has largely been overlooked. This article describes the techniques and demonstrates their utility in two examples in which microscopic interfacial phenomena are of great importance.

  5. Gain dynamics and saturation in semiconductor quantum dot amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper; Hvam, Jørn Märcher

    2004-01-01

    Quantum dot (QD)-based semiconductor optical amplifiers offer unique properties compared with conventional devices based on bulk or quantum well material. Due to the bandfilling properties of QDs and the existence of a nearby reservoir of carriers in the form of a wetting layer, QD semiconductor...... optical amplifiers may be operated in regimes of high linearity, i.e. with a high saturation power, but can also show strong and fast nonlinearities by breaking the equilibrium between discrete dot states and the continuum of wetting layer states. In this paper, we analyse the interplay of these two...

  6. GaAs structures with InAs and As quantum dots produced in a single molecular beam epitaxy process

    International Nuclear Information System (INIS)

    Nevedomskii, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2009-01-01

    Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults.

  7. Molecular Level Manipulation of Interfacial Charge Transport

    Science.gov (United States)

    Song, Charles Kiseok

    The bulk-heterojunction organic (BHJ) photovoltaics (OPVs) and lithium ion battery (LiB) have been extensively studied. Power conversion efficiency (PCE) of an OPV greater than 10% and utilizing group 4 elements as the anode to accommodate high capacity for LiBs are the goals of many studies. However, the currently ubiquitous hole-collecting layer of OPVs limit device performance and durability, and group 4 elements are unstable and brittle to be commercially produced. Thus, my thesis has focused on developing functional and durable interfacial layers (IFLs) for OPVs and characterizing flexible artificial solid-electrolyte interphase (SEI) for LiBs. In Chapter 2, a series of robust organosilane-based dipolar self-assembled monolayer (SAM) IFLs on the tin-doped indium oxide (ITO) anodes of OPVs are developed. These hydrophobic and amorphous IFLs modify anode work functions from 4.66 to 5.27 eV. Two series of Glass/ITO/SAM IFL/Active Layer/LiF/Al BHJ OPVs are fabricated, and a strong positive correlation between the electrochemically-derived heterogeneous electron transport rate constants (ks) and OPV PCEs are observed due to enhanced anode carrier extraction. In Chapter 3, a series of unusually denser organosilane-based SAM IFLs on ITO anodes of OPVs are developed. Precursor mixtures having short and long tail groups were simultaneously deposited to minimize sterical encumbrance and denser SAM IFLs are achieved. These heterogeneous supersaturated SAMs (SHSAMs), with PCE (7.62%) exceeding that of PEDOT:PSS IFL, are found to be 17% denser and enhances PCE by 54% versus comparable devices with homogeneous SAM IFLs due to enhanced charge selectivity and collection. In Chapter 4, libraries of electron affinities (EAs) of widely used conductive polymers are constructed by cyclic voltammetry (CV) in conventional and LiB media. The EAs of the conductive polymer films measured via CV in conventional (EAC) and Li+ battery (EAB) media could be linearly correlated by EAB = (1

  8. Interfacial spectroscopic characterization of organic/ferromagnet hetero-junction of 3,4,9,10-perylene-teracarboxylic dianhydride-based organic spin valves

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Jhen-Yong; Ou Yang, Kui-Hon; Li, Kai-Shin [Department of Physics, National Taiwan University, 10617 Taipei, Taiwan (China); Wang, Bo-Yao [Department of Physics, National Taiwan University, 10617 Taipei, Taiwan (China); Department of Physics, National Changhua University of Education, Changhua 500, Taiwan (China); Shiu, Hung-Wei; Chen, Chia-Hao; Chan, Yuet-Loy; Wei, Der-Hsin; Chang, Fan-Hsiu; Lin, Hong-Ji [National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan (China); Chiang, Wen-Chung, E-mail: wchiang@faculty.pccu.edu.tw [Department of Physics, Chinese Culture University, 11114 Taipei, Taiwan (China); Lin, Minn-Tsong, E-mail: mtlin@phys.ntu.edu.tw [Department of Physics, National Taiwan University, 10617 Taipei, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, 10617 Taipei, Taiwan (China)

    2014-02-24

    We report interfacial characterization of 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA)-based organic spin valves (OSV) dusted with a thin layer of partially oxidized alumina at the organic semiconductor (OSC)/ferromagnet (FM) interfaces. Up to 13.5% magnetoresistance is achieved at room temperature. X-ray photoelectron spectroscopy measurements reveal interfacial electronic interaction between PTCDA and FM while the application of a thin alumina layer at the PTCDA/FM interfaces prevents the electronic hybridization and effectively preserves the spin injection into the OSC spacer. This finding demonstrates the critical effect of interfacial structure on magnetotransport behavior in OSV.

  9. Miscibility–dispersion, interfacial strength and nanoclay mobility relationships in polymer nanocomposites

    KAUST Repository

    Carretero-Gonzá lez, Javier; Retsos, Haris; Giannelis, Emmanuel P.; Ezquerra, Tiberio A.; Herná ndez, Marianella; Ló pez-Manchado, Miguel A.

    2009-01-01

    Fully dispersed layered silicate nanoparticles (nanoclay) in a polymer matrix have provided a new class of multi-functional materials exhibiting several performance improvements over conventional composites. Yet the challenges of miscibility and interfacial strength might prevent nanocomposites from realizing their full potential. In this paper we demonstrate the effect of the chemical characteristics of the nanoclay on the miscibility and dispersion in the polymer matrix as well as on the interfacial strength of the bound polymer and the nanoclay mobility, all of which determine the macroscopic properties of the nanocomposite. © 2009 The Royal Society of Chemistry.

  10. Realization of electrically tunable single quantum dot nanocavities

    Energy Technology Data Exchange (ETDEWEB)

    Hofbauer, Felix Florian Georg

    2009-03-15

    We investigated the design, fabrication and optical investigation of electrically tunable single quantum dot-photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light matter interaction. We demonstrate that the quantum confined Stark effect can be employed to quickly and reversibly switch the dot-cavity coupling, simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by up to {proportional_to}4 meV relative to the nanocavity mode, before the emission quenches due to carrier tunneling escape from the dots. We directly probe spontaneous emission, irreversible polariton decay and the statistics of the emitted photons from a single-dot nanocavity in the weak and strong coupling regimes. New information is obtained on the nature of the dot-cavity coupling in the weak coupling regime and electrical control of zero dimensional polaritons is demonstrated for the first time. The structures investigated are p-i-n photodiodes consisting of an 180nm thick free-standing GaAs membrane into which a two dimensional photonic crystal is formed by etching a triangular lattice of air holes. Low mode volume nanocavities (V{sub mode}<1.6 ({lambda}/n){sup 3}) are realized by omitting 3 holes in a line to form L3 cavities and a single layer of InGaAs self-assembled quantum dots is embedded into the midpoint of the membrane. The nanocavities are electrically contacted via 35 nm thick p- and n-doped contact layers in the GaAs membrane. In the weak coupling regime, time resolved spectroscopy reveals a {proportional_to}7 x shortening of the spontaneous emission lifetime as the dot is tuned through the nanocavity mode, due to the Purcell effect. Upon strongly detuning the same quantum dot transition from the nanocavity mode we observe an additional {proportional_to}8 x lengthening of the spontaneous emission lifetime. These observations unequivocally highlight two regimes of dot

  11. Fabrication of quantum-dot devices in graphene

    Directory of Open Access Journals (Sweden)

    Satoshi Moriyama, Yoshifumi Morita, Eiichiro Watanabe, Daiju Tsuya, Shinya Uji, Maki Shimizu and Koji Ishibashi

    2010-01-01

    Full Text Available We describe our recent experimental results on the fabrication of quantum-dot devices in a graphene-based two-dimensional system. Graphene samples were prepared by micromechanical cleavage of graphite crystals on a SiO2/Si substrate. We performed micro-Raman spectroscopy measurements to determine the number of layers of graphene flakes during the device fabrication process. By applying a nanofabrication process to the identified graphene flakes, we prepared a double-quantum-dot device structure comprising two lateral quantum dots coupled in series. Measurements of low-temperature electrical transport show the device to be a series-coupled double-dot system with varied interdot tunnel coupling, the strength of which changes continuously and non-monotonically as a function of gate voltage.

  12. A fabrication guide for planar silicon quantum dot heterostructures

    Science.gov (United States)

    Spruijtenburg, Paul C.; Amitonov, Sergey V.; van der Wiel, Wilfred G.; Zwanenburg, Floris A.

    2018-04-01

    We describe important considerations to create top-down fabricated planar quantum dots in silicon, often not discussed in detail in literature. The subtle interplay between intrinsic material properties, interfaces and fabrication processes plays a crucial role in the formation of electrostatically defined quantum dots. Processes such as oxidation, physical vapor deposition and atomic-layer deposition must be tailored in order to prevent unwanted side effects such as defects, disorder and dewetting. In two directly related manuscripts written in parallel we use techniques described in this work to create depletion-mode quantum dots in intrinsic silicon, and low-disorder silicon quantum dots defined with palladium gates. While we discuss three different planar gate structures, the general principles also apply to 0D and 1D systems, such as self-assembled islands and nanowires.

  13. Novel strip-cast Mg/Al clad sheets with excellent tensile and interfacial bonding properties.

    Science.gov (United States)

    Kim, Jung-Su; Lee, Dong Ho; Jung, Seung-Pill; Lee, Kwang Seok; Kim, Ki Jong; Kim, Hyoung Seop; Lee, Byeong-Joo; Chang, Young Won; Yuh, Junhan; Lee, Sunghak

    2016-06-01

    In order to broaden industrial applications of Mg alloys, as lightest-weight metal alloys in practical uses, many efforts have been dedicated to manufacture various clad sheets which can complement inherent shortcomings of Mg alloys. Here, we present a new fabrication method of Mg/Al clad sheets by bonding thin Al alloy sheet on to Mg alloy melt during strip casting. In the as-strip-cast Mg/Al clad sheet, homogeneously distributed equi-axed dendrites existed in the Mg alloy side, and two types of thin reaction layers, i.e., γ (Mg17Al12) and β (Mg2Al3) phases, were formed along the Mg/Al interface. After post-treatments (homogenization, warm rolling, and annealing), the interfacial layers were deformed in a sawtooth shape by forming deformation bands in the Mg alloy and interfacial layers, which favorably led to dramatic improvement in tensile and interfacial bonding properties. This work presents new applications to multi-functional lightweight alloy sheets requiring excellent formability, surface quality, and corrosion resistance as well as tensile and interfacial bonding properties.

  14. Interfacial structures - Thermodynamical and experimental studies of the interfacial mass transfer

    International Nuclear Information System (INIS)

    Morel, Jean-Emile

    1972-01-01

    In the first section, we put forward hypotheses concerning the structure of the interfacial regions between two immiscible liquid phases. It appears that the longitudinal structure is comparable with that of a crystallized solid and that the transversal structure is nearest of that of a liquid. In the second section, we present a thermodynamical treatment of the irreversible phenomena in the interfacial region. The equation of evolution of a system consisting of two immiscible liquid phases are deduced. The third part allows an experimental verification of the theoretical relations. We also make clear, in certain cases, the appearance of a great 'interfacial resistance' which slows down the interfacial mass transfer. (author) [fr

  15. Electron and hole spectrum in InAs quantum dot renormalized by InAs/GaAs heterostructure deformation

    International Nuclear Information System (INIS)

    Dan'kiv, O.O.; Peleshchak, R.M.

    2005-01-01

    Analytical expressions describing the energy spectrum of electrons and holes are obtained for a quantum dot occurring in a self-consistent strain field created by an array of coherently stressed quantum dots. A method of taking into account the lattice mismatch at the quantum dot-matrix interface is proposed that allows for the dependence of the mismatch parameter on the quantum dot size and the matrix layer thickness. It is shown that the internal elastic strain arising at the quantum dot-matrix interface influences the energy spectrum of electrons more significantly than the spectrum of holes [ru

  16. Electron microscopy of GaAs-based structures with InAs and As quantum dots separated by an AlAs barrier

    International Nuclear Information System (INIS)

    Nevedomskiy, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskiy, V. V.; Putyato, M. A.; Semyagin, B. R.

    2013-01-01

    Electron microscopy studies of GaAs-based structures grown by molecular beam epitaxy and containing arrays of semiconductor InAs quantum dots and metal As quantum dots are performed. The array of InAs quantum dots is formed by the Stranski-Krastanov mechanism and consists of vertically coupled pairs of quantum dots separated by a GaAs spacer 10 nm thick. To separate the arrays of semiconductor and metal quantum dots and to prevent diffusion-induced mixing, the array of InAs quantum dots is overgrown with an AlAs barrier layer 5 or 10 nm thick, after which a GaAs layer is grown at a comparatively low temperature (180°C). The array of As quantum dots is formed in an As-enriched layer of the low-temperature GaAs by means of post-growth annealing at 400–760°C for 15 min. It is established that the AlAs barrier layer has a surface profile corresponding to that of a subbarrier layer with InAs quantum dots. The presence of such a profile causes the formation of V-shaped structural defects upon subsequent overgrowth with the GaAs layer. Besides, it was obtained that AlAs layer is thinned over the InAs quantum dots tops. It is shown that the AlAs barrier layer in the regions between the InAs quantum dots effectively prevents the starting diffusion of excess As at annealing temperatures up to 600°C. However, the concentration of mechanical stresses and the reduced thickness of the AlAs barrier layer near the tops of the InAs quantum dots lead to local barrier breakthroughs and the diffusion of As quantum dots into the region of coupled pairs of InAs quantum dots at higher annealing temperatures

  17. Computing optimal interfacial structure of modulated phases

    OpenAIRE

    Xu, Jie; Wang, Chu; Shi, An-Chang; Zhang, Pingwen

    2016-01-01

    We propose a general framework of computing interfacial structures between two modulated phases. Specifically we propose to use a computational box consisting of two half spaces, each occupied by a modulated phase with given position and orientation. The boundary conditions and basis functions are chosen to be commensurate with the bulk structures. It is observed that the ordered nature of modulated structures stabilizes the interface, which enables us to obtain optimal interfacial structures...

  18. Design of quaternary logic circuit using quantum dot gate-quantum dot channel FET (QDG-QDCFET)

    Science.gov (United States)

    Karmakar, Supriya

    2014-10-01

    This paper presents the implementation of quaternary logic circuits based on quantum dot gate-quantum dot channel field effect transistor (QDG-QDCFET). The super lattice structure in the quantum dot channel region of QDG-QDCFET and the electron tunnelling from inversion channel to the quantum dot layer in the gate region of a QDG-QDCFET change the threshold voltage of this device which produces two intermediate states between its ON and OFF states. This property of QDG-QDCFET is used to implement multi-valued logic for future multi-valued logic circuit. This paper presents the design of basic quaternary logic operation such as inverter, AND and OR operation based on QDG-QDCFET.

  19. Hexagonal graphene quantum dots

    KAUST Repository

    Ghosh, Sumit; Schwingenschlö gl, Udo

    2016-01-01

    We study hexagonal graphene quantum dots, using density functional theory, to obtain a quantitative description of the electronic properties and their size dependence, considering disk and ring geometries with both armchair and zigzag edges. We show that the electronic properties of quantum dots with armchair edges are more sensitive to structural details than those with zigzag edges. As functions of the inner and outer radii, we find in the case of armchair edges that the size of the band gap follows distinct branches, while in the case of zigzag edges it changes monotonically. This behaviour is further analyzed by studying the ground state wave function and explained in terms of its localisation.

  20. Quantum dot solar cells

    CERN Document Server

    Wu, Jiang

    2013-01-01

    The third generation of solar cells includes those based on semiconductor quantum dots. This sophisticated technology applies nanotechnology and quantum mechanics theory to enhance the performance of ordinary solar cells. Although a practical application of quantum dot solar cells has yet to be achieved, a large number of theoretical calculations and experimental studies have confirmed the potential for meeting the requirement for ultra-high conversion efficiency. In this book, high-profile scientists have contributed tutorial chapters that outline the methods used in and the results of variou

  1. Hexagonal graphene quantum dots

    KAUST Repository

    Ghosh, Sumit

    2016-12-05

    We study hexagonal graphene quantum dots, using density functional theory, to obtain a quantitative description of the electronic properties and their size dependence, considering disk and ring geometries with both armchair and zigzag edges. We show that the electronic properties of quantum dots with armchair edges are more sensitive to structural details than those with zigzag edges. As functions of the inner and outer radii, we find in the case of armchair edges that the size of the band gap follows distinct branches, while in the case of zigzag edges it changes monotonically. This behaviour is further analyzed by studying the ground state wave function and explained in terms of its localisation.

  2. Modeling interfacial fracture in Sierra.

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Arthur A.; Ohashi, Yuki; Lu, Wei-Yang; Nelson, Stacy A. C.; Foulk, James W.,; Reedy, Earl David,; Austin, Kevin N.; Margolis, Stephen B.

    2013-09-01

    This report summarizes computational efforts to model interfacial fracture using cohesive zone models in the SIERRA/SolidMechanics (SIERRA/SM) finite element code. Cohesive surface elements were used to model crack initiation and propagation along predefined paths. Mesh convergence was observed with SIERRA/SM for numerous geometries. As the funding for this project came from the Advanced Simulation and Computing Verification and Validation (ASC V&V) focus area, considerable effort was spent performing verification and validation. Code verification was performed to compare code predictions to analytical solutions for simple three-element simulations as well as a higher-fidelity simulation of a double-cantilever beam. Parameter identification was conducted with Dakota using experimental results on asymmetric double-cantilever beam (ADCB) and end-notched-flexure (ENF) experiments conducted under Campaign-6 funding. Discretization convergence studies were also performed with respect to mesh size and time step and an optimization study was completed for mode II delamination using the ENF geometry. Throughout this verification process, numerous SIERRA/SM bugs were found and reported, all of which have been fixed, leading to over a 10-fold increase in convergence rates. Finally, mixed-mode flexure experiments were performed for validation. One of the unexplained issues encountered was material property variability for ostensibly the same composite material. Since the variability is not fully understood, it is difficult to accurately assess uncertainty when performing predictions.

  3. Effect of Atmospheric Ions on Interfacial Water

    Directory of Open Access Journals (Sweden)

    Chien-Chang Kurt Kung

    2014-11-01

    Full Text Available The effect of atmospheric positivity on the electrical properties of interfacial water was explored. Interfacial, or exclusion zone (EZ water was created in the standard way, next to a sheet of Nafion placed horizontally at the bottom of a water-filled chamber. Positive atmospheric ions were created from a high voltage source placed above the chamber. Electrical potential distribution in the interfacial water was measured using microelectrodes. We found that beyond a threshold, the positive ions diminished the magnitude of the negative electrical potential in the interfacial water, sometimes even turning it to positive. Additionally, positive ions produced by an air conditioner were observed to generate similar effects; i.e., the electrical potential shifted in the positive direction but returned to negative when the air conditioner stopped blowing. Sometimes, the effect of the positive ions from the air conditioner was strong enough to destroy the structure of interfacial water by turning the potential decidedly positive. Thus, positive air ions can compromise interfacial water negativity and may explain the known negative impact of positive ions on health.

  4. Chemical sensitive interfacial free volume studies of nanophase Al-rich alloys

    International Nuclear Information System (INIS)

    Lechner, W.; Puff, W.; Wuerschum, R.; Wilde, G.

    2006-01-01

    Full text: Al-based nanocrystalline alloys have attracted substantial interest due to their outstanding mechanical properties. These alloys can be obtained by crystallization of melt-spun amorphous precursors or by grain refinement upon repeated cold-rolling of elemental layers. For both synthesis routes, the nanocrystallization process is sensitively affected by interfacial chemistry and free volumes. In order to contribute to an atomistic understanding of the interfacial structure and processes during nanocrystallization, the present work deals with studies of interfacial free volumes by means of positron-annihilation-spectroscopy. In addition to positron lifetime spectroscopy which yields information on the size of free volumes, coincident Doppler broadening of the positron-electron annihilation photons is applied as novel technique for studying the chemistry of interfaces in nanophase materials on an atomistic scale. Al-rich alloys of the above mentioned synthesis routes were studied in this work. (author)

  5. Color-selective photodetection from intermediate colloidal quantum dots buried in amorphous-oxide semiconductors.

    Science.gov (United States)

    Cho, Kyung-Sang; Heo, Keun; Baik, Chan-Wook; Choi, Jun Young; Jeong, Heejeong; Hwang, Sungwoo; Lee, Sang Yeol

    2017-10-10

    We report color-selective photodetection from intermediate, monolayered, quantum dots buried in between amorphous-oxide semiconductors. The proposed active channel in phototransistors is a hybrid configuration of oxide-quantum dot-oxide layers, where the gate-tunable electrical property of silicon-doped, indium-zinc-oxide layers is incorporated with the color-selective properties of quantum dots. A remarkably high detectivity (8.1 × 10 13 Jones) is obtained, along with three major findings: fast charge separation in monolayered quantum dots; efficient charge transport through high-mobility oxide layers (20 cm 2  V -1  s -1 ); and gate-tunable drain-current modulation. Particularly, the fast charge separation rate of 3.3 ns -1 measured with time-resolved photoluminescence is attributed to the intermediate quantum dots buried in oxide layers. These results facilitate the realization of efficient color-selective detection exhibiting a photoconductive gain of 10 7 , obtained using a room-temperature deposition of oxide layers and a solution process of quantum dots. This work offers promising opportunities in emerging applications for color detection with sensitivity, transparency, and flexibility.The development of highly sensitive photodetectors is important for image sensing and optical communication applications. Cho et al., report ultra-sensitive photodetectors based on monolayered quantum dots buried in between amorphous-oxide semiconductors and demonstrate color-detecting logic gates.

  6. Interfacial Structures of Trihexyltetradecylphosphonium-bis(mandelato)borate Ionic Liquid Confined between Gold Electrodes.

    Science.gov (United States)

    Wang, Yong-Lei; Golets, Mikhail; Li, Bin; Sarman, Sten; Laaksonen, Aatto

    2017-02-08

    Atomistic molecular dynamics simulations have been performed to study microscopic the interfacial ionic structures, molecular arrangements, and orientational preferences of trihexyltetradecylphosphonium-bis(mandelato)borate ([P 6,6,6,14 ][BMB]) ionic liquid confined between neutral and charged gold electrodes. It was found that both [P 6,6,6,14 ] cations and [BMB] anions are coabsorbed onto neutral electrodes at different temperatures. The hexyl and tetradecyl chains in [P 6,6,6,14 ] cations lie preferentially flat on neutral electrodes. The oxalato and phenyl rings in [BMB] anions are characterized by alternative parallel-perpendicular orientations in the mixed innermost ionic layer adjacent to neutral electrodes. An increase in temperature has a marginal effect on the interfacial ionic structures and molecular orientations of [P 6,6,6,14 ][BMB] ionic species in a confined environment. Electrifying gold electrodes leads to peculiar changes in the interfacial ionic structures and molecular orientational arrangements of [P 6,6,6,14 ] cations and [BMB] anions in negatively and positively charged gold electrodes, respectively. As surface charge density increases (but lower than 20 μC/cm 2 ), the layer thickness of the mixed innermost interfacial layer gradually increases due to a consecutive accumulation of [P 6,6,6,14 ] cations and [BMB] anions at negatively and positively charged electrodes, respectively, before the formation of distinct cationic and anionic innermost layers. Meanwhile, the molecular orientations of two oxalato rings in the same [BMB] anions change gradually from a parallel-perpendicular feature to being partially characterized by a tilted arrangement at an angle of 45° from the electrodes and finally to a dominant parallel coordination pattern along positively charged electrodes. Distinctive interfacial distribution patterns are also observed accordingly for phenyl rings that are directly connected to neighboring oxalato rings in [BMB] anions.

  7. Surface and interfacial chemistry of high-k dielectric and interconnect materials on silicon

    Science.gov (United States)

    Kirsch, Paul Daniel

    Surfaces and interfaces play a critical role in the manufacture and function of silicon based integrated circuits. It is therefore reasonable to study the chemistries at these surfaces and interfaces to improve existing processes and to develop new ones. Model barium strontium titanate high-k dielectric systems have been deposited on ultrathin silicon oxynitride in ultrahigh vacuum. The resulting nanostructures are characterized with secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). An interfacial reaction between Ba and Sr atoms and SiOxNy was found to create silicates, BaSixOy or SrSi xOy. Inclusion of N in the interfacial oxide decreased silicate formation in both Ba and Sr systems. Furthermore, inclusion of N in the interfacial oxide decreased the penetration of Ba and Sr containing species, such as silicides and silicates. Sputter deposited HfO2 was studied on nitrided and unnitrided Si(100) surfaces. XPS and SIMS were used to verify the presence of interfacial HfSixOy and estimate its relative amount on both nitrided and unnitrided samples. More HfSixOy formed without the SiNx interfacial layer. These interfacial chemistry results are then used to explain the electrical measurements obtained from metal oxide semiconductor (MOS) capacitors. MOS capacitors with interfacial SiNx exhibit reduced leakage current and increased capacitance. Lastly, surface science techniques were used to develop a processing technique for reducing thin films of copper (II) and copper (I) oxide to copper. Deuterium atoms (D*) and methyl radicals (CH3*) were shown to reduce Cu 2+ and/or Cu1+ to Cu0 within 30 min at a surface temperature of 400 K under a flux of 1 x 1015 atoms/cm2s. Temperature programmed desorption experiments suggest that oxygen leaves the surface as D2O and CO2 for the D* and CH3* treated surfaces, respectively.

  8. Interfacial microstructure and mechanical property of Ti6Al4V/A6061 dissimilar joint by direct laser brazing without filler metal and groove

    International Nuclear Information System (INIS)

    Song, Zhihua; Nakata, Kazuhiro; Wu, Aiping; Liao, Jinsun

    2013-01-01

    Laser brazing of Ti6Al4V and A6061-T6 alloys with 2 mm thickness was conducted by focusing laser beam on aluminum alloy side, and the effect of laser offset distance on microstructure and mechanical properties of the dissimilar butt joint was investigated. Laser offset has a great influence on the thickness of interfacial intermetallic compound (IMC) layer and the mechanical property of joint. The thickness of interfacial IMC layer is less than 500 nm, and the average tensile strength of the joint reaches 64% of aluminum base material strength, when suitable welding conditions are used. The interfacial IMC is TiAl 3 . The formation of interfacial IMC layer and its effect on mechanical property of the joint are discussed in the present study.

  9. Wide emission spectrum from superluminescent diodes with chirped quantum dot multilayers

    NARCIS (Netherlands)

    Li, L.H.; Rossetti, M.; Fiore, A.; Occhi, L.; Velez, C.

    2005-01-01

    A superluminescent diode (SLED) using chirped multiple InAs quantum dot (QD) layers as the active region is demonstrated. The fabricated QD SLEDs exhibit a large spectral width up to 121 nm, covering the range 1165-1286 nm.

  10. Patterning effects in quantum dot amplifiers characterized through pump probe spectroscopy using two pump pulses

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Poel, Mike van der; Laemmlin, M.

    2004-01-01

    Patterning effects at ultrahigh bitrates in quantum dot amplifiers are investigated by a novel experimental technique. Slow carrier dynamics in the excited states and wetting layer are found to limit the potential for ultrahigh-speed signal processing....

  11. Linear electro-optic coefficient in multilayer self-organized InAs quantum dot structures

    NARCIS (Netherlands)

    Akca, I.B.; Dana, A.; Aydinli, A.; Rossetti, M.; Li, L.; Dagli, N.; Fiore, A.

    2007-01-01

    The electro-optic coefficients of self-organized InAs quantum dot layers in molecular beam epitaxy grown laser structures in reverse bias have been investigated. Enhanced electrooptic coefficients compared to bulk GaAs were observed.

  12. Interfacial exchange coupling and magnetization reversal in perpendicular [Co/Ni]N/TbCo composite structures.

    Science.gov (United States)

    Tang, M H; Zhang, Zongzhi; Tian, S Y; Wang, J; Ma, B; Jin, Q Y

    2015-06-15

    Interfacial exchange coupling and magnetization reversal characteristics in the perpendicular heterostructures consisting of an amorphous ferrimagnetic (FI) TbxCo(100-x) alloy layer exchange-coupled with a ferromagnetic (FM) [Co/Ni]N multilayer have been investigated. As compared with pure TbxCo(100-x) alloy, the magnetization compensation composition of the heterostructures shift to a higher Tb content, implying Co/Ni also serves to compensate the Tb moment in TbCo layer. The net magnetization switching field Hc⊥ and interlayer interfacial coupling field Hex, are not only sensitive to the magnetization and thickness of the switched TbxCo(100-x) or [Co/Ni]N layer, but also to the perpendicular magnetic anisotropy strength of the pinning layer. By tuning the layer structure we achieve simultaneously both large Hc⊥ = 1.31 T and Hex = 2.19 T. These results, in addition to the fundamental interest, are important to understanding of the interfacial coupling interaction in the FM/FI heterostructures, which could offer the guiding of potential applications in heat-assisted magnetic recording or all-optical switching recording technique.

  13. Direct observation of interfacial Au atoms on TiO₂ in three dimensions.

    Science.gov (United States)

    Gao, Wenpei; Sivaramakrishnan, Shankar; Wen, Jianguo; Zuo, Jian-Min

    2015-04-08

    Interfacial atoms, which result from interactions between the metal nanoparticles and support, have a large impact on the physical and chemical properties of nanoparticles. However, they are difficult to observe; the lack of knowledge has been a major obstacle toward unraveling their role in chemical transformations. Here we report conclusive evidence of interfacial Au atoms formed on the rutile (TiO2) (110) surfaces by activation using high-temperature (∼500 °C) annealing in air. Three-dimensional imaging was performed using depth-sectioning enabled by aberration-corrected scanning transmission electron microscopy. Results show that the interface between Au nanocrystals and TiO2 (110) surfaces consists of a single atomic layer with Au atoms embedded inside Ti-O. The number of interfacial Au atoms is estimated from ∼1-8 in an interfacial atomic column. Direct impact of interfacial Au atoms is observed on an enhanced Au-TiO2 interaction and the reduction of surface TiO2; both are critical to Au catalysis.

  14. Ionic Liquids as the MOFs/Polymer Interfacial Binder for Efficient Membrane Separation.

    Science.gov (United States)

    Lin, Rijia; Ge, Lei; Diao, Hui; Rudolph, Victor; Zhu, Zhonghua

    2016-11-23

    Obtaining strong interfacial affinity between filler and polymer is critical to the preparation of mixed matrix membranes (MMMs) with high separation efficiency. However, it is still a challenge for micron-sized metal organic frameworks (MOFs) to achieve excellent compatibility and defect-free interface with polymer matrix. Thin layer of ionic liquid (IL) was immobilized on micron-sized HKUST-1 to eliminate the interfacial nonselective voids in MMMs with minimized free ionic liquid (IL) in polymer matrix, and then the obtained IL decorated HKUST-1 was incorporated into 4,4'-(hexafluoroisopropylidene)diphthalic anhydride-2,3,5,6-tetramethyl-1,3-phenyldiamine (6FDA-Durene) to fabricate MMMs. Acting as a filler/polymer interfacial binder, the favorable MOF/IL and IL/polymer interaction can facilitate the enhancement of MOF/polymer affinity. Compared to MMM with only HKUST-1 incorporation, MMM with IL decorated HKUST-1 succeeded in restricting the formation of nonselective interfacial voids, leading to an increment in CO 2 selectivity. The IL decoration method can be an effective approach to eliminate interfacial voids in MMMs, extending the filler selection to a wide range of large-sized fillers.

  15. Bioinspired design and interfacial failure of biomedical systems

    Science.gov (United States)

    Rahbar, Nima

    The deformation mechanism of nacre as a model biological material is studied in this project. A numerical model is presented which consists of tensile pillars, shear pillars, asperities and aragonite platelets. It has been shown that the tensile pillars are the main elements that control the global stiffness of the nacre structure. Meanwhile, ultimate strength of the nacre structure is controlled by asperities and their behavior and the ratio of L/2D which is itself a function of the geometry of the platelets. Protein/shear pillars provide the glue which holds the assembly of entire system together, particularly in the direction normal to the platelets main axis. This dissertation also presents the results of a combined theoretical/computational and experimental effort to develop crack resistant dental multilayers that are inspired by the functionally graded dento-enamel junction (DEJ) structure that occurs between dentin and enamel in natural teeth. The complex structures of natural teeth and ceramic crowns are idealized using at layered configurations. The potential effects of occlusal contact are then modeled using finite element simulations of Hertzian contact. The resulting stress distributions are compared for a range of possible bioinspired, functionally graded architecture. The computed stress distributions show that the highest stress concentrations in the top ceramic layer of crown structures are reduced significantly by the use of bioinspired functionally graded architectures. The reduced stresses are shown to be associated with significant improvements (30%) in the pop-in loads over a wide range of clinically-relevant loading rates. The implications of the results are discussed for the design of bioinspired dental ceramic crown structures. The results of a combined experimental and computational study of mixed mode fracture in glass/cement and zirconia/cement interfaces that are relevant to dental restorations is also presented. The interfacial fracture

  16. Quantum dots and nanocomposites.

    Science.gov (United States)

    Mansur, Herman Sander

    2010-01-01

    Quantum dots (QDs), also known as semiconducting nanoparticles, are promising zero-dimensional advanced materials because of their nanoscale size and because they can be engineered to suit particular applications such as nonlinear optical devices (NLO), electro-optical devices, and computing applications. QDs can be joined to polymers in order to produce nanocomposites which can be considered a scientific revolution of the 21st century. One of the fastest moving and most exciting interfaces of nanotechnology is the use of QDs in medicine, cell and molecular biology. Recent advances in nanomaterials have produced a new class of markers and probes by conjugating semiconductor QDs with biomolecules that have affinities for binding with selected biological structures. The nanoscale of QDs ensures that they do not scatter light at visible or longer wavelengths, which is important in order to minimize optical losses in practical applications. Moreover, at this scale, quantum confinement and surface effects become very important and therefore manipulation of the dot diameter or modification of its surface allows the properties of the dot to be controlled. Quantum confinement affects the absorption and emission of photons from the dot. Thus, the absorption edge of a material can be tuned by control of the particle size. This paper reviews developments in the myriad of possibilities for the use of semiconductor QDs associated with molecules producing novel hybrid nanocomposite systems for nanomedicine and bioengineering applications.

  17. Polarization-insensitive quantum-dot coupled quantum-well semiconductor optical amplifier

    International Nuclear Information System (INIS)

    Huang Lirong; Yu Yi; Tian Peng; Huang Dexiu

    2009-01-01

    The optical gain of a quantum-dot semiconductor optical amplifier is usually seriously dependent on polarization; we propose a quantum-dot coupled tensile-strained quantum-well structure to obtain polarization insensitivity. The tensile-strained quantum well not only serves as a carrier injection layer of quantum dots but also offers gain to the transverse-magnetic mode. Based on the polarization-dependent coupled carrier rate-equation model, we study carrier competition among quantum well and quantum dots, and study the polarization dependence of the quantum-dot coupled quantum-well semiconductor optical amplifier. We also analyze polarization-dependent photon-mediated carrier distribution among quantum well and quantum dots. It is shown that polarization-insensitive gain can be realized by optimal design

  18. Submonolayer Quantum Dot Infrared Photodetector

    Science.gov (United States)

    Ting, David Z.; Bandara, Sumith V.; Gunapala, Sarath D.; Chang, Yia-Chang

    2010-01-01

    A method has been developed for inserting submonolayer (SML) quantum dots (QDs) or SML QD stacks, instead of conventional Stranski-Krastanov (S-K) QDs, into the active region of intersubband photodetectors. A typical configuration would be InAs SML QDs embedded in thin layers of GaAs, surrounded by AlGaAs barriers. Here, the GaAs and the AlGaAs have nearly the same lattice constant, while InAs has a larger lattice constant. In QD infrared photodetector, the important quantization directions are in the plane perpendicular to the normal incidence radiation. In-plane quantization is what enables the absorption of normal incidence radiation. The height of the S-K QD controls the positions of the quantized energy levels, but is not critically important to the desired normal incidence absorption properties. The SML QD or SML QD stack configurations give more control of the structure grown, retains normal incidence absorption properties, and decreases the strain build-up to allow thicker active layers for higher quantum efficiency.

  19. Interfacial reactions in thermoelectric modules

    KAUST Repository

    Wu, Hsin-jay

    2018-02-21

    Engineering transport properties of thermoelectric (TE) materials leads to incessantly breakthroughs in the zT values. Nevertheless, modular design holds a key factor to advance the TE technology. Herein, we discuss the structures of TE module and illustrate the inter-diffusions across the interface of constituent layers. For Bi2Te3-based module, soldering is the primary bonding method, giving rise to the investigations on the selections of solder, diffusion barrier layer and electrode. For mid-temperature PbTe-based TE module, hot-pressing or spark plasma sintering are alternative bonding approaches; the inter-diffusions between the diffusion barrier layer, electrode and TE substrate are addressed as well.

  20. PREFACE: Quantum Dot 2010

    Science.gov (United States)

    Taylor, Robert A.

    2010-09-01

    These conference proceedings contain the written papers of the contributions presented at Quantum Dot 2010 (QD2010). The conference was held in Nottingham, UK, on 26-30 April 2010. The conference addressed topics in research on: 1. Epitaxial quantum dots (including self-assembled and interface structures, dots defined by electrostatic gates etc): optical properties and electron transport quantum coherence effects spin phenomena optics of dots in cavities interaction with surface plasmons in metal/semiconductor structures opto-electronics applications 2. Novel QD structures: fabrication and physics of graphene dots, dots in nano-wires etc 3. Colloidal quantum dots: growth (shape control and hybrid nanocrystals such as metal/semiconductor, magnetic/semiconductor) assembly and surface functionalisation optical properties and spin dynamics electrical and magnetic properties applications (light emitting devices and solar cells, biological and medical applications, data storage, assemblers) The Editors Acknowledgements Conference Organising Committee: Maurice Skolnick (Chair) Alexander Tartakovskii (Programme Chair) Pavlos Lagoudakis (Programme Chair) Max Migliorato (Conference Secretary) Paola Borri (Publicity) Robert Taylor (Proceedings) Manus Hayne (Treasurer) Ray Murray (Sponsorship) Mohamed Henini (Local Organiser) International Advisory Committee: Yasuhiko Arakawa (Tokyo University, Japan) Manfred Bayer (Dortmund University, Germany) Sergey Gaponenko (Stepanov Institute of Physics, Minsk, Belarus) Pawel Hawrylak (NRC, Ottawa, Canada) Fritz Henneberger (Institute for Physics, Berlin, Germany) Atac Imamoglu (ETH, Zurich, Switzerland) Paul Koenraad (TU Eindhoven, Nethehrlands) Guglielmo Lanzani (Politecnico di Milano, Italy) Jungil Lee (Korea Institute of Science and Technology, Korea) Henri Mariette (CNRS-CEA, Grenoble, France) Lu Jeu Sham (San Diego, USA) Andrew Shields (Toshiba Research Europe, Cambridge, UK) Yoshihisa Yamamoto (Stanford University, USA) Artur

  1. Modeling and simulation of InGaN/GaN quantum dots solar cell

    International Nuclear Information System (INIS)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-01-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In 0.25 Ga 0.75 N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In 0.25 Ga 0.75 N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  2. Modeling and simulation of InGaN/GaN quantum dots solar cell

    Science.gov (United States)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-07-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In0.25Ga0.75N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In0.25Ga0.75N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  3. Improved photovoltaic performance and stability of quantum dot sensitized solar cells using Mn-ZnSe shell structure with enhanced light absorption and recombination control.

    Science.gov (United States)

    Gopi, Chandu V V M; Venkata-Haritha, M; Kim, Soo-Kyoung; Kim, Hee-Je

    2015-08-07

    To make quantum-dot-sensitized solar cells (QDSSCs) competitive, photovoltaic parameters comparable to those of other emerging solar cell technologies are necessary. In the present study, ZnSe was used as an alternative to ZnS, one of the most widely used passivation materials in QDSSCs. ZnSe was deposited on a TiO2-CdS-CdSe photoanode to form a core-shell structure, which was more efficient in terms of reducing the electron recombination in QDSSCs. The development of an efficient passivation layer is a requirement for preventing recombination processes in order to attain high-performance and stable QDSSCs. A layer of inorganic Mn-ZnSe was applied to a QD-sensitized photoanode to enhance the adsorption and strongly inhibit interfacial recombination processes in QDSSCs, which greatly improved the power conversion efficiency. Impedance spectroscopy revealed that the combined Mn doping with ZnSe treatment reduces interfacial recombination and increases charge collection efficiency compared with Mn-ZnS, ZnS, and ZnSe. A solar cell based on the CdS-CdSe-Mn-ZnSe photoanode yielded excellent performance with a solar power conversion efficiency of 5.67%, Voc of 0.584 V, and Jsc of 17.59 mA cm(-2). Enhanced electron transport and reduced electron recombination are responsible for the improved Jsc and Voc of the QDSSCs. The effective electron lifetime of the device with Mn-ZnSe was higher than those with Mn-ZnS, ZnSe, and ZnS, leading to more efficient electron-hole separation and slower electron recombination.

  4. Interfacial area and interfacial transfer in two-phase systems. DOE final report

    Energy Technology Data Exchange (ETDEWEB)

    Ishii, Mamoru; Hibiki, T.; Revankar, S.T.; Kim, S.; Le Corre, J.M.

    2002-07-01

    In the two-fluid model, the field equations are expressed by the six conservation equations consisting of mass, momentum and energy equations for each phase. The existence of the interfacial transfer terms is one of the most important characteristics of the two-fluid model formulation. The interfacial transfer terms are strongly related to the interfacial area concentration and to the local transfer mechanisms such as the degree of turbulence near interfaces. This study focuses on the development of a closure relation for the interfacial area concentration. A brief summary of several problems of the current closure relation for the interfacial area concentration and a new concept to overcome the problem are given.

  5. Growth and temperature dependent photoluminescence of InGaAs quantum dot chains

    International Nuclear Information System (INIS)

    Yang, Haeyeon; Kim, Dong-Jun; Colton, John S.; Park, Tyler; Meyer, David; Jones, Aaron M.; Thalman, Scott; Smith, Dallas; Clark, Ken; Brown, Steve

    2014-01-01

    Highlights: • We examine the optical properties of novel quantum dot chains. • Study shows that platelets evolve into quantum dots during heating of the InGaAs platelets encapsulated with GaAs. • Single stack of quantum dots emits light at room temperature. • Quantum dots are of high quality, confirmed by cross-section TEM images and photoluminescence. • Light emission at room temperature weakens beyond the detection limit when the quantum dots form above the critical annealing temperature. - Abstract: We report a study of growth and photoluminescence from a single stack of MBE-grown In 0.4 Ga 0.6 As quantum dot chains. The InGaAs epilayers were grown at a low temperature so that the resulting surfaces remain flat with platelets even though their thicknesses exceed the critical thickness of the conventional Stranski–Krastanov growth mode. The flat InGaAs layers were then annealed at elevated temperatures to induce the formation of quantum dot chains. A reflection high energy electron diffraction study suggests that, when the annealing temperature is at or below 480 °C, the surface of growth front remains flat during the periods of annealing and growth of a 10 nm thick GaAs capping layer. Surprisingly, transmission electron microscopy images do indicate the formation of quantum dot chains, however, so the dot-chains in those samples may form from precursory platelets during the period of temperature ramping and subsequent capping with GaAs due to intermixing of group III elements. The optical emission from the quantum dot layer demonstrates that there is a critical annealing temperature of 480–500 °C above which the properties of the low temperature growth approach are lost, as the optical properties begin to resemble those of quantum dots produced by the conventional Stranski–Krastanov technique

  6. Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films

    International Nuclear Information System (INIS)

    Qu, Ge; Zhao, Xikang; Newbloom, Gregory M.; Zhang, Fengjiao; Mohammadi, Erfan

    2017-01-01

    Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor–acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiopheneco- thieno[3,2-b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π–π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacial morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. As a result, we further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front.

  7. Magnetically pinned ring dots for spin valve or magnetic tunnel junction memory cells

    International Nuclear Information System (INIS)

    Nakatani, Ryoichi; Yoshida, Tetsuo; Endo, Yasushi; Kawamura, Yoshio; Yamamoto, Masahiko; Takenaga, Takashi; Aya, Sunao; Kuroiwa, Takeharu; Beysen, Sadeh; Kobayashi, Hiroshi

    2005-01-01

    Ni-Fe/Mn-Ir asymmetric ring dots with partially planed outer sides are investigated in order to confirm a method for obtaining pinned layers in magnetic memories with asymmetric ring shapes. Magnetic force microscopy revealed that the direction of vortical magnetization is pinned in Ni-Fe/Mn-Ir asymmetric ring dots despite the direction of the magnetic fields. This investigation shows that the Ni-Fe/Mn-Ir asymmetric ring dots can be applied to pinned layers in magnetic memories with asymmetric ring shapes

  8. Formation of self assembled PbTe quantum dots in CdTe on Si(111)

    Science.gov (United States)

    Felder, F.; Fognini, A.; Rahim, M.; Fill, M.; Müller, E.; Zogg, H.

    2010-01-01

    We describe the growth and formation of self assembled PbTe quantum dots in a CdTe host on a silicon (111) substrate. Annealing yields different photoluminescence spectra depending on initial PbTe layer thickness, thickness of the CdTe cap layer and annealing temperature. Generally two distinct emission peaks at ˜0.3 eV and ˜0.45 eV are visible. Model calculations explaining their temperature dependence are performed. The dot size corresponds well with the estimated sizes from electron microscopy images. The quantum dots may be used as absorber within a mid-infrared detector.

  9. Characteristics of chirped quantum dot superluminescent diodes

    Energy Technology Data Exchange (ETDEWEB)

    Bae, H.C.; Park, H.L. [Department of Physics, Yonsei University, Seoul 120-749 (Korea); You, Y.C. [Department of Information and Communication Engineering, Sungkyunkwan University, Seoul 440-746 (Korea); Han, I.K. [Nano Device Research Center, Korea Institute of Science and Technology, Seoul 130-650 (Korea); Kim, J.S. [Department of Image System Science and Engineering, Pukyong National University, Pusan Department of Image System Science and Engineering, Pukyong National University, Pusan 608-739 (Korea)

    2009-04-15

    We compared the superluminescent diodes (SLDs) of two types in order to see the effect of embedding another quantum dots (QDs) layer. The insertion of another QDs layer showed a new possibility for a wider spectrum. In addition, through comparing two kinds of SLD structures, the peak positions of the ground state and excited state were observed to be affected differently by band-filling, thermal effect, and the overlap of tails of excited state (ES) gain, according to the wafer structure, and the effect of the cap layer is superior to the carrier non-uniformity. We also revealed the temperature sensitivity of carriers in QDs through measuring characteristic temperature. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. FAST TRACK COMMUNICATION: Graphene based quantum dots

    Science.gov (United States)

    Zhang, H. G.; Hu, H.; Pan, Y.; Mao, J. H.; Gao, M.; Guo, H. M.; Du, S. X.; Greber, T.; Gao, H.-J.

    2010-08-01

    Laterally localized electronic states are identified on a single layer of graphene on ruthenium by low temperature scanning tunneling spectroscopy (STS). The individual states are separated by 3 nm and comprise regions of about 90 carbon atoms. This constitutes a highly regular quantum dot-array with molecular precision. It is evidenced by quantum well resonances (QWRs) with energies that relate to the corrugation of the graphene layer. The dI/dV conductance spectra are modeled by a layer height dependent potential-well with a delta-function potential that describes the barrier for electron penetration into graphene. The resulting QWRs are strongest and lowest in energy on the isolated 'hill' regions with a diameter of 2 nm, where the graphene is decoupled from the surface.

  11. Measurements of the weak bonding interfacial stiffness by using air-coupled ultrasound

    Directory of Open Access Journals (Sweden)

    Wen-Lin Wu

    2017-12-01

    Full Text Available An air-coupled ultrasonic method, focusing on the problem that weak bonding interface is difficult to accurately measure using conventional nondestructive testing technique, is proposed to evaluate the bond integrity. Based on the spring model and the potential function theory, a theoretical model is established to predict the through-transmission spectrum in double-layer adhesive structure. The result of a theoretical algorithm shows that all the resonant transmission peaks move towards higher frequency with the increase of the interfacial stiffness. The reason for these movements is related to either the normal stiffness (KN or the transverse stiffness (KT. A method to optimize the measurement parameters (i.e. the incident angle and testing frequency is put forward through analyzing the relationship between the resonant transmission peaks and the interfacial spring stiffness at the frequency below 1MHz. The air-coupled ultrasonic testing experiments at the normal and oblique incident angle respectively are carried out to verify the theoretical analysis and to accurately measure the interfacial stiffness of double-layer adhesive composite plate. The experimental results are good agreement with the results from the theoretical algorithm, and the relationship between bonding time and interfacial stiffness is presented at the end of this paper.

  12. Cell characteristics of a multiple alloy nano-dots memory structure

    International Nuclear Information System (INIS)

    Bea, Ji Chel; Lee, Kang-Wook; Tanaka, Tetsu; Koyanagi, Mitsumasa; Song, Yun Heub; Lee, Gae-Hun

    2009-01-01

    A multiple alloy metal nano-dots memory using FN tunneling was investigated in order to confirm its structural possibility for future flash memory. In this work, a multiple FePt nano-dots device with a high work function (∼5.2 eV) and extremely high dot density (∼1.2 × 10 13 cm −2 ) was fabricated. Its structural effect for multiple layers was evaluated and compared to the one with a single layer in terms of the cell characteristics and reliability. We confirm that MOS capacitor structures with two to four multiple FePt nano-dot layers provide a larger threshold voltage window and better retention characteristics. Furthermore, it was also revealed that several process parameters for block oxide and inter-tunnel oxide between the nano-dot layers are very important to improve the efficiency of electron injection into multiple nano-dots. From these results, it is expected that a multiple FePt nano-dots memory using Fowler–Nordheim (FN) tunneling could be a candidate structure for future flash memory

  13. Comparison of crude oil interfacial behavior

    Energy Technology Data Exchange (ETDEWEB)

    Beetge, J.H.; Panchev, N. [Champion Technologies Inc., Fresno, TX (United States)

    2008-07-01

    The bulk properties of crude oil are used to predict its behaviour with regards to treatment, transport and processing. Surface active components, such as asphaltenes, are often used to study or explain critical interfacial behaviour of crude oil. This study investigated the differences and similarities in the interfacial behaviour of the collective surface active component in various crude oils from different sources. The properties of interfaces between crude oil and water were compared using a Teclis drop shape tensiometer. A portion of a crude oil sample was diluted in toluene and contacted with water in a rising drop configuration. Dynamic surface tension and interfacial rheology was examined as a function of time from the early stages of interface formation. Sinusoidal oscillation of the drop volume allowed for the evaluation of visco-elastic behaviour of the crude oil/water interface as it developed with time. The Gibbs elastic modulus, as well as its elastic and viscose components were calculated from the drop shape. The interfacial behaviour was expressed in terms of concentration, oscillation frequency and interface age. It was concluded that knowledge of crude oil interfacial character could be of value in the treatment, transport and processing of crude oils because the its behaviour may play a significant role in crude oil production and processing.

  14. Band-structure tailoring and surface passivation for highly efficient near-infrared responsive PbS quantum dot photovoltaics

    Science.gov (United States)

    Zhou, Ru; Niu, Haihong; Ji, Fengwei; Wan, Lei; Mao, Xiaoli; Guo, Huier; Xu, Jinzhang; Cao, Guozhong

    2016-11-01

    PbS is a promising light harvester for near-infrared (NIR) responsive quantum dot (QD) photovoltaics due to its narrow bulk band gap (0.41 eV) and large exciton Bohr radius (18 nm). However, the relatively low conduction band (CB) and high-density surface defects of PbS as two major drawbacks for its use in solar cells severely hamper the photovoltaic performance enhancement. In this work, a modified solution-based successive ionic layer adsorption and reaction (SILAR) utilizing mixed cationic precursors of Pb2+ and Cd2+ is explored, and such a scheme offers two benefits, band-structure tailoring and surface passivation. In-situ deposited CdS suppresses the excessive growth of PbS in the mesopores, thereby facilitating the favorable electron injection from PbS to TiO2 in view of the up-shifted CB level of QDs; the intimate interpenetration of two sulfides with each other leads to superior passivation of trap state defects on PbS, which suppresses the interfacial charge recombination. With the construction of photovoltaics based on such a hybrid (Pb,Cd)S/CdS configuration, impressive power conversion efficiency up to 4.08% has been reached, outperforming that of the conventional PbS/CdS pattern (2.95%). This work highlights the great importance of band-structure tailoring and surface passivation for constructing highly efficient PbS QD photovoltaics.

  15. Theoretical Determination of Optimal Material Parameters for ZnCdTe/ZnCdSe Quantum Dot Intermediate Band Solar Cells

    Science.gov (United States)

    Imperato, C. M.; Ranepura, G. A.; Deych, L. I.; Kuskovsky, I. L.

    2018-03-01

    Intermediate band solar cells (IBSCs) are designed to enhance the photovoltaic efficiency significantly over that of a single-junction solar cell as determined by the Shockley-Queisser limit. In this work we present calculations to determine parameters of type-II Zn1-xCdxTe/Zn1-yCdySe quantum dots (QDs) grown on the InP substrate suitable for IBSCs. The calculations are done via the self-consistent variational method, accounting for the disk form of the QDs, presence of the strained ZnSe interfacial layer, and under conditions of a strain-free device structure. We show that to achieve the required parameters relatively thick QDs are required. Barriers must contain Cd concentration in the range of 35-44%, while Cd concentration in QD can vary widely from 0% to 70%, depending on their thickness to achieve the intermediate band energies in the range of 0.50-0.73 eV. It is also shown that the results are weakly dependent on the barrier thickness.

  16. Tuning band alignment by CdS layers using a SILAR method to enhance TiO2/CdS/CdSe quantum-dot solar-cell performance.

    Science.gov (United States)

    Zhang, Bingkai; Zheng, Jiaxin; Li, Xiaoning; Fang, Yanyan; Wang, Lin-Wang; Lin, Yuan; Pan, Feng

    2016-04-28

    We report tuning band alignment by optimized CdS layers using a SILAR method to achieve the recorded best performance with about 6% PCE in TiO2/CdS/CdSe QDSSCs. Combining experimental and theoretical studies, we find that a better lattices match between CdS and TiO2 assists the growth of CdSe, and the combined effect of charge transfer and surface dipole moment at the TiO2/CdS/CdSe interface shifts the energy levels of TiO2 upward and increases Voc of the solar cells. More importantly, the band gap of CdS buffer layers is sensitive to the distortion induced by lattice mismatch and numbers of CdS layers. For example, the barrier for charge transfer disappears when there are more than 4 layers of CdS, facilitating the charge injection from CdSe to TiO2.

  17. Phase Transitions in Layered Diguanidinium Hexachlorostannate(IV)

    DEFF Research Database (Denmark)

    Szafranski, Marek; Ståhl, Kenny

    2016-01-01

    is different. The transitions involve also transformations in the networks of N-H center dot center dot center dot Cl hydrogen bonds. The large volume (similar to 3%) and entropy (similar to R ln 3) change at the transition between phases II and III, and the giant pressure coefficient of -755 K GPa(-1......Five crystalline phases of diguanidinium hexachlorostannate(IV), [C(NH2)(3)](2)SnCl6, have been identified and characterized by calorimetric and dielectric measurements, single crystal X-ray diffraction at atmospheric and high pressure, and synchrotron X-ray powder diffraction. The crystal...... structures of all phases are built of similar layers in which the tin hexachloride anions are connected to the guanidinium cations by N-H center dot center dot center dot Cl hydrogen bonds, forming a interact primarily by Coulombic forces between the ions from ap. double H-bonded sheets. The layers, neutral...

  18. Solar-Pumping Upconversion of Interfacial Coordination Nanoparticles.

    Science.gov (United States)

    Ishii, Ayumi; Hasegawa, Miki

    2017-01-30

    An interfacial coordination nanoparticle successfully exhibited an upconversion blue emission excited by very low-power light irradiation, such as sunlight. The interfacial complex was composed of Yb ions and indigo dye, which formed a nano-ordered thin shell layer on a Tm 2 O 3 nanoparticle. At the surface of the Tm 2 O 3 particle, the indigo dye can be excited by non-laser excitation at 640 nm, following the intramolecular energy transfer from the indigo dye to the Yb ions. Additionally, the excitation energy of the Yb ion was upconverted to the blue emission of the Tm ion at 475 nm. This upconversion blue emission was achieved by excitation with a CW Xe lamp at an excitation power of 0.14 mW/cm 2 , which is significantly lower than the solar irradiation power of 1.4 mW/cm 2 at 640 ± 5 nm.

  19. Interfacial Shear Strength of Multilayer Graphene Oxide Films.

    Science.gov (United States)

    Daly, Matthew; Cao, Changhong; Sun, Hao; Sun, Yu; Filleter, Tobin; Singh, Chandra Veer

    2016-02-23

    Graphene oxide (GO) is considered as one of the most promising layered materials with tunable physical properties and applicability in many important engineering applications. In this work, the interfacial behavior of multilayer GO films was directly investigated via GO-to-GO friction force microscopy, and the interfacial shear strength (ISS) was measured to be 5.3 ± 3.2 MPa. Based on high resolution atomic force microscopy images and the available chemical data, targeted molecular dynamics simulations were performed to evaluate the influence of functional structure, topological defects, and interlayer registry on the shear response of the GO films. Theoretical values for shear strength ranging from 17 to 132 MPa were predicted for the different structures studied, providing upper bounds for the ISS. Computational results also revealed the atomic origins of the stochastic nature of friction measurements. Specifically, the wide scatter in experimental measurements was attributed to variations in functional structure and topological defects within the sliding volume. The findings of this study provide important insight for understanding the significant differences in strength between monolayer and bulk graphene oxide materials and can be useful for engineering topological structures with tunable mechanical properties.

  20. Interfacial Reaction and IMC Growth of an Ultrasonically Soldered Cu/SAC305/Cu Structure during Isothermal Aging

    Directory of Open Access Journals (Sweden)

    Yulong Li

    2018-01-01

    Full Text Available In order to accelerate the growth of interfacial intermetallic compound (IMC layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic soldering. The isothermal aging was conducted at 150 °C for 0, 120, 240, and 360 h. The evolution of microstructure, the IMC layer growth mechanism during aging, and the shear strength of the joints after aging were systemically investigated. Results showed the following. (i Formation of intermetallic compounds was accelerated by ultrasonic cavitation and streaming effects, the thickness of the interfacial Cu6Sn5 layer increased with aging time, and a thin Cu3Sn layer was identified after aging for 360 h. (ii The growth of the interfacial IMC layer of the ultrasonically soldered Cu/SAC305/Cu joints followed a linear function of the square root of the aging time, revealing a diffusion-controlled mechanism. (iii The tensile shear strength of the joint decreased to a small extent with increasing aging time, owing to the combined effects of IMC grain coarsening and the increase of the interfacial IMC. (iv Finally, although the fracture surfaces and failure locations of the joint soldered with 400 ms and 800 ms vibration times show similar characteristics, they are influenced by the aging time.