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.

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

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.

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

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.

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.

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.

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.

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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).

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)

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.

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

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.

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

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...

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.

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.

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....

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.

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.

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.

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.

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

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.

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...

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.

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.

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.

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

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

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...

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.

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.

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.

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.

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

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)

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.

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.

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.

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.

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

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.

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.

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.

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.

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)

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.

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.)

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

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.

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.

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.

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

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

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.

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)

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.

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...

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.

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.

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

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....

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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

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

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.

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.

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.

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)

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.

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.

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.

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.

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.

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.

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....

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.

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.

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.

Field dependent shape variation of magnetic fluid droplets on magnetic dots

International Nuclear Information System (INIS)

Lee, Chiun-Peng; Yang, Shu-Ting; Wei, Zung-Hang

2012-01-01

The morphology of magnetic fluid droplets on magnetic thin film dots is studied experimentally, including the aspect ratio and the contact angle variation of the droplets. Under a uniform external magnetic field, the droplet's aspect ratio increases with the external field and with the diameter of the magnetic dot due to the concentrated magnetic flux inside the magnetic fluid droplet. Similar to the electrical wetting phenomenon, the induced magnetic dipoles in the magnetic film and in the magnetic fluid near the solid–liquid interface change the solid–liquid interfacial tension, and in consequence reduce the apparent contact angle of the magnetic fluid droplet. - Highlights: ► Morphology of ferrofluid droplets on magnetic thin film dots was studied experimentally. ► Aspect ratio of ferrofluid droplets was found to increase with increasing of magnetic field. ► Liquid–solid contact angle of ferrofluid droplets was found to vary with magnetic field. ► Relationship between magnetic field and the liquid–solid interfacial tension was modeled.

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.

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

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

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

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.

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.

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

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

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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%.

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

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.

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.

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

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).

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.

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

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.

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

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.

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.

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)

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)

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.

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.

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.

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.

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

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.

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.

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.

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.

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.)

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.

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.

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.

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.

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.

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.

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.

Synthesis of reduced graphene oxide intercalated ZnO quantum dots nanoballs for selective biosensing detection

Energy Technology Data Exchange (ETDEWEB)

Chen, Jing; Zhao, Minggang, E-mail: zhaomg@ouc.edu.cn; Li, Yingchun; Fan, Sisi; Ding, Longjiang; Liang, Jingjing; Chen, Shougang, E-mail: sgchen@ouc.edu.cn

2016-07-15

Highlights: • A MWCNTs/rGO/ZnO quantum dots intercalation nanoballs decorated 3D hierarchical architecture is fabricated on Ni foam. • Large numbers of ZnO quantum dots are intercalated by rGO sheets to construct hierarchical nanoballs. • Improved mechanical, kinetic and electrochemical properties are found. • The strong interfacial effect makes the material can be used for selective detection of dopamine, ascorbic acid and uric acid. - Abstract: ZnO quantum dots (QDs), reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) are always used in sensors due to their excellent electrochemical characteristics. In this work, ZnO QDs were intercalated by rGO sheets with cross-linked MWCNTs to construct intercalation nanoballs. A MWCNTs/rGO/ZnO QDs 3D hierarchical architecture was fabricated on supporting Ni foam, which exhibited excellent mechanical, kinetic and electrochemical properties. The intercalation construction can introduce strong interfacial effects to improve the surface electronic state. The selectively determinate of uric acid, dopamine, and ascorbic acid by an electrode material using distinct applied potentials was realized.

Synthesis of reduced graphene oxide intercalated ZnO quantum dots nanoballs for selective biosensing detection

International Nuclear Information System (INIS)

Chen, Jing; Zhao, Minggang; Li, Yingchun; Fan, Sisi; Ding, Longjiang; Liang, Jingjing; Chen, Shougang

2016-01-01

Highlights: • A MWCNTs/rGO/ZnO quantum dots intercalation nanoballs decorated 3D hierarchical architecture is fabricated on Ni foam. • Large numbers of ZnO quantum dots are intercalated by rGO sheets to construct hierarchical nanoballs. • Improved mechanical, kinetic and electrochemical properties are found. • The strong interfacial effect makes the material can be used for selective detection of dopamine, ascorbic acid and uric acid. - Abstract: ZnO quantum dots (QDs), reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) are always used in sensors due to their excellent electrochemical characteristics. In this work, ZnO QDs were intercalated by rGO sheets with cross-linked MWCNTs to construct intercalation nanoballs. A MWCNTs/rGO/ZnO QDs 3D hierarchical architecture was fabricated on supporting Ni foam, which exhibited excellent mechanical, kinetic and electrochemical properties. The intercalation construction can introduce strong interfacial effects to improve the surface electronic state. The selectively determinate of uric acid, dopamine, and ascorbic acid by an electrode material using distinct applied potentials was realized.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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

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.

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.)

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.

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.

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.

The interfacial capacitance of an oxidised polycrystalline gold electrode in an aqueous HClO4 electrolyte

International Nuclear Information System (INIS)

Grdeń, M.

2013-01-01

The interfacial capacitance of a polycrystalline gold electrode electrochemically oxidised in an aqueous 0.1 M HClO 4 electrolyte has been investigated by means of the electrochemical impedance spectroscopy. From 1.3 to 3 monolayers of Au atoms were oxidised under constant potential conditions and for various oxidation times. The capacitance of the oxidised layers was analysed as a function of the electrode potential and the extent of the surface oxidation. It was found that the interfacial capacitance decreases upon surface oxidation. The components of the interfacial capacitance of the oxidised layer: the double layer capacitance and the capacitance of the oxidised layer; have been separated. The capacitance of the double layer of the oxidised surface was found to be comparable to the capacitance measured for the metallic surface. - Highlights: • The impedance spectra for thin layers of Au oxides/hydroxides were acquired. • Separate determination of the double layer and the oxide capacitances of oxidised Au • The double layer capacitances of oxidised and non-oxidised Au surfaces are comparable

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.

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)

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.

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.

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.

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.

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...

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).

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.

"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

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.

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

Effects of Interfacial Charge Depletion in Organic Thin-Film Transistors with Polymeric Dielectrics on Electrical Stability

Directory of Open Access Journals (Sweden)

Jaehoon Park

2010-06-01

Full Text Available We investigated the electrical stabilities of two types of pentacene-based organic thin-film transistors (OTFTs with two different polymeric dielectrics: polystyrene (PS and poly(4-vinyl phenol (PVP, in terms of the interfacial charge depletion. Under a short-term bias stress condition, the OTFT with the PVP layer showed a substantial increase in the drain current and a positive shift of the threshold voltage, while the PS layer case exhibited no change. Furthermore, a significant increase in the off-state current was observed in the OTFT with the PVP layer which has a hydroxyl group. In the presence of the interfacial hydroxyl group in PVP, the holes are not fully depleted during repetitive operation of the OTFT with the PVP layer and a large positive gate voltage in the off-state regime is needed to effectively refresh the electrical characteristics. It is suggested that the depletion-limited holes at the interface, i.e., interfacial charge depletion, between the PVP layer and the pentacene layer play a critical role on the electrical stability during operation of the OTFT.

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.

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.

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

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

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.

The sandwich InGaAs/GaAs quantum dot structure for IR photoelectric detectors

International Nuclear Information System (INIS)

Moldavskaya, L. D.; Vostokov, N. V.; Gaponova, D. M.; Danil'tsev, V. M.; Drozdov, M. N.; Drozdov, Yu. N.; Shashkin, V. I.

2008-01-01

A new possibility for growing InAs/GaAs quantum dot heterostructures for infrared photoelectric detectors by metal-organic vapor-phase epitaxy is discussed. The specific features of the technological process are the prolonged time of growth of quantum dots and the alternation of the low-and high-temperature modes of overgrowing the quantum dots with GaAs barrier layers. During overgrowth, large-sized quantum dots are partially dissolved, and the secondary InGaAs quantum well is formed of the material of the dissolved large islands. In this case, a sandwich structure is formed. In this structure, quantum dots are arranged between two thin layers with an increased content of indium, namely, between the wetting InAs layer and the secondary InGaAs layer. The height of the quantum dots depends on the thickness of the GaAs layer grown at a comparatively low temperature. The structures exhibit intraband photoconductivity at a wavelength around 4.5 μm at temperatures up to 200 K. At 90 K, the photosensitivity is 0.5 A/W, and the detectivity is 3 x 10 9 cm Hz 1/2 W -1

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.

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.

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

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.

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.

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.

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.

Layer-dependent surface potential of phosphorene and anisotropic/layer-dependent charge transfer in phosphorene-gold hybrid systems.

Science.gov (United States)

Xu, Renjing; Yang, Jiong; Zhu, Yi; Yan, Han; Pei, Jiajie; Myint, Ye Win; Zhang, Shuang; Lu, Yuerui

2016-01-07

The surface potential and the efficiency of interfacial charge transfer are extremely important for designing future semiconductor devices based on the emerging two-dimensional (2D) phosphorene. Here, we directly measured the strong layer-dependent surface potential of mono- and few-layered phosphorene on gold, which is consistent with the reported theoretical prediction. At the same time, we used an optical way photoluminescence (PL) spectroscopy to probe charge transfer in the phosphorene-gold hybrid system. We firstly observed highly anisotropic and layer-dependent PL quenching in the phosphorene-gold hybrid system, which is attributed to the highly anisotropic/layer-dependent interfacial charge transfer.

Spatially correlated two-dimensional arrays of semiconductor and metal quantum dots in GaAs-based heterostructures

International Nuclear Information System (INIS)

Nevedomskiy, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhernskiy, V. V.; Putyato, M. A.; Semyagin, B. R.

2015-01-01

A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix

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....

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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 �

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

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

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

Enhanced interfacial and electrical characteristics of 4H-SiC MOS capacitor with lanthanum silicate passivation interlayer

International Nuclear Information System (INIS)

Wang, Qian; Cheng, Xinhong; Zheng, Li; Ye, Peiyi; Li, Menglu; Shen, Lingyan; Li, Jingjie; Zhang, Dongliang; Gu, Ziyue; Yu, Yuehui

2017-01-01

Highlights: • The 4H-SiC MOS capacitor with an untra-thin LaSiO_x passivation layer and Al_2O_3 gate dielectric was fabricated. • The detrimental SiO_x interfacial layer could be effectively restrained by the LaSiO_x passivation layer. • The passivation mechanism of LaSiO_x was analyzed by HRTEM, XPS and electrical measurements. • The 4H-SiC MOS capacitor with a LaSiO_x passivation layer shows excellent device characteristics. • This technique provides an efficient path to improve dielectrics/4H-SiC interfaces for future high-power device applications. - Abstract: The detrimental sub-oxide (SiO_x) interfacial layer formed during the 4H-SiC metal-oxide-semiconductor (MOS) capacitor fabrication will drastically damage its device performance. In this work, an ultrathin lanthanum silicate (LaSiO_x) passivation layer was introduced to enhance the interfacial and electrical characteristics of 4H-SiC MOS capacitor with Al_2O_3 gate dielectric. The interfacial LaSiO_x formation was investigated by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The 4H-SiC MOS capacitor with ultrathin LaSiO_x passivation interlayer shows excellent interfacial and electrical characteristics, including lower leakage current density, higher dielectric breakdown electric field, smaller C–V hysteresis, and lower interface states density and border traps density. The involved mechanism implies that the LaSiO_x passivation interlayer can effectively restrain SiO_x formation and improve the Al_2O_3/4H-SiC interface quality. This technique provides an efficient path to improve dielectrics/4H-SiC interfaces for future high-power device applications.

Enhanced interfacial and electrical characteristics of 4H-SiC MOS capacitor with lanthanum silicate passivation interlayer

Energy Technology Data Exchange (ETDEWEB)

Wang, Qian [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Cheng, Xinhong, E-mail: xh_cheng@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); Zheng, Li, E-mail: zhengli@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Ye, Peiyi; Li, Menglu [Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095 (United States); Shen, Lingyan; Li, Jingjie; Zhang, Dongliang; Gu, Ziyue [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Yu, Yuehui [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system & Information Technology, Chinese Academy of Sciences, Changning Road 865, Shanghai 200050 (China)

2017-07-15

Highlights: • The 4H-SiC MOS capacitor with an untra-thin LaSiO{sub x} passivation layer and Al{sub 2}O{sub 3} gate dielectric was fabricated. • The detrimental SiO{sub x} interfacial layer could be effectively restrained by the LaSiO{sub x} passivation layer. • The passivation mechanism of LaSiO{sub x} was analyzed by HRTEM, XPS and electrical measurements. • The 4H-SiC MOS capacitor with a LaSiO{sub x} passivation layer shows excellent device characteristics. • This technique provides an efficient path to improve dielectrics/4H-SiC interfaces for future high-power device applications. - Abstract: The detrimental sub-oxide (SiO{sub x}) interfacial layer formed during the 4H-SiC metal-oxide-semiconductor (MOS) capacitor fabrication will drastically damage its device performance. In this work, an ultrathin lanthanum silicate (LaSiO{sub x}) passivation layer was introduced to enhance the interfacial and electrical characteristics of 4H-SiC MOS capacitor with Al{sub 2}O{sub 3} gate dielectric. The interfacial LaSiO{sub x} formation was investigated by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The 4H-SiC MOS capacitor with ultrathin LaSiO{sub x} passivation interlayer shows excellent interfacial and electrical characteristics, including lower leakage current density, higher dielectric breakdown electric field, smaller C–V hysteresis, and lower interface states density and border traps density. The involved mechanism implies that the LaSiO{sub x} passivation interlayer can effectively restrain SiO{sub x} formation and improve the Al{sub 2}O{sub 3}/4H-SiC interface quality. This technique provides an efficient path to improve dielectrics/4H-SiC interfaces for future high-power device applications.

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

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

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.

Interfacial Phonon Transport Through Si/Ge Multilayer Film Using Monte Carlo Scheme With Spectral Transmissivity

Directory of Open Access Journals (Sweden)

Xin Ran

2018-05-01

Full Text Available The knowledge of interfacial phonon transport accounting for detailed phonon spectral properties is desired because of its importance for design of nanoscale energy systems. In this work, we investigate the interfacial phonon transport through Si/Ge multilayer films using an efficient Monte Carlo scheme with spectral transmissivity, which is validated for cross-plane phonon transport through both Si/Ge single-layer and Si/Ge bi-layer thin films by comparing with the discrete-ordinates solution. Different thermal boundary conductances between even the same material pair are declared at different interfaces within the multilayer system. Furthermore, the thermal boundary conductances at different interfaces show different trends with varying total system size, with the variation slope, very different as well. The results are much different from those in the bi-layer thin film or periodic superlattice. These unusual behaviors can be attributed to the combined interfacial local non-equilibrium effect and constraint effect from other interfaces.

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....

Nanostructured Quantum Dots or Dashes in Photovoltaic Devices and Methods Thereof

Science.gov (United States)

Raffaele, Ryne P. (Inventor); Wilt, David M. (Inventor)

2015-01-01

A photovoltaic device includes one or more structures, an array of at least one of quantum dots and quantum dashes, at least one groove, and at least one conductor. Each of the structures comprises an intrinsic layer on one of an n type layer and a p type layer and the other one of the n type layer and the p type layer on the intrinsic layer. The array of at least one of quantum dots and quantum dashes is located in the intrinsic layer in at least one of the structures. The groove extends into at least one of the structures and the conductor is located along at least a portion of the groove.

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

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

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).

Raman spectroscopy of in situ annealed InAs/GaAs quantum dots

International Nuclear Information System (INIS)

Luna, M.J.M. de; Somintac, A.; Estacio, E.; Salvador, A.

2004-01-01

Nonresonant Raman scattering measurements were performed on a three-layered sample of in situ annealed InAs/GaAs self-assembled quantum dots. The thermal annealing step was done during the growth of each GaAs spacer layer, where the substrate temperature was raised from 530 deg. C to 580 deg. C as measured by a pyrometer. Three Raman signals are clearly seen at 264 cm -1 , 268 cm -1 , and 271.5 cm -1 which can be attributed to the longitudinal optic (LO) phonons of the dots. These three different signals are attributed to different degrees of In/Ga alloying or intermixing in each dot layer as a consequence of the different thermal treatments that each layer was subjected to. The Raman signal of the wetting layer (WL) is remarkably weak and suggests erosion of the wetting layer. In contrast, Raman scattering measurements on an unannealed sample show two overlapping features at 259.5 cm -1 and 261.5 cm -1 , which are attributed to the LO phonons of the dots. The WL signal is clearly observed at 251.5 cm -1 . To support our Raman observations, the appearance of a strong higher-energy peak in photoluminescence measurements suggests that alloying did occur in the annealed sample

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.

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.

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.

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

Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-μm Quantum Dot Lasers.

Science.gov (United States)

Su, Xiang-Bin; Ding, Ying; Ma, Ben; Zhang, Ke-Lu; Chen, Ze-Sheng; Li, Jing-Lun; Cui, Xiao-Ran; Xu, Ying-Qiang; Ni, Hai-Qiao; Niu, Zhi-Chuan

2018-02-21

The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-μm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm 2 was demonstrated.

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.

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...

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.

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.

Influence of Quantum Dot Concentration on Carrier Transport in ZnO:TiO2 Nano-Hybrid Photoanodes for Quantum Dot-Sensitized Solar Cells

Directory of Open Access Journals (Sweden)

Francis S. Maloney

2016-10-01

Full Text Available Zinc oxide nanowire and titanium dioxide nanoparticle (ZnO:TiO2 NW/NP hybrid films were utilized as the photoanode layer in quantum dot-sensitized solar cells (QDSSCs. CdSe quantum dots (QDs with a ZnS passivation layer were deposited on the ZnO:TiO2 NW/NP layer as a photosensitizer by successive ion layer adsorption and reaction (SILAR. Cells were fabricated using a solid-state polymer electrolyte and intensity-modulated photovoltage and photocurrent spectroscopy (IMVS/PS was carried out to study the electron transport properties of the cell. Increasing the SILAR coating number enhanced the total charge collection efficiency of the cell. The electron transport time constant and diffusion length were found to decrease as more QD layers were added.

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.

Spatial carrier distribution in InP/GaAs type II quantum dots and quantum posts

Science.gov (United States)

Iikawa, F.; Donchev, V.; Ivanov, Ts; Dias, G. O.; Tizei, L. H. G.; Lang, R.; Heredia, E.; Gomes, P. F.; Brasil, M. J. S. P.; Cotta, M. A.; Ugarte, D.; Martinez Pastor, J. P.; de Lima, M. M., Jr.; Cantarero, A.

2011-02-01

We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for obtaining an effective spatial separation of electrons and holes in the case of single layer InP/GaAs quantum-dot samples. In the present case this effect seems to be less critical due to the particular carrier wavefunction distribution along the structures.

Spatial carrier distribution in InP/GaAs type II quantum dots and quantum posts

International Nuclear Information System (INIS)

Iikawa, F; Donchev, V; Dias, G O; Tizei, L H G; Lang, R; Gomes, P F; Brasil, M J S P; Cotta, M A; Ugarte, D; Ivanov, Ts; Heredia, E; Martinez Pastor, J P; De Lima, M M Jr; Cantarero, A

2011-01-01

We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for obtaining an effective spatial separation of electrons and holes in the case of single layer InP/GaAs quantum-dot samples. In the present case this effect seems to be less critical due to the particular carrier wavefunction distribution along the structures.

Spatial carrier distribution in InP/GaAs type II quantum dots and quantum posts

Energy Technology Data Exchange (ETDEWEB)

Iikawa, F; Donchev, V; Dias, G O; Tizei, L H G; Lang, R; Gomes, P F; Brasil, M J S P; Cotta, M A; Ugarte, D [Instituto de Fisica ' Gleb Wataghin' , Unicamp, CP-6165, 13083-970, Campinas-SP (Brazil); Ivanov, Ts [Faculty of Physics, Sofia University, 5, Boulevard J.Bourchier, Sofia-1164 (Bulgaria); Heredia, E [Laboratorio Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, CP 515, 12245-970, Sao Jose dos Campos-SP (Brazil); Martinez Pastor, J P; De Lima, M M Jr; Cantarero, A, E-mail: iikawa@ifi.unicamp.br [Materials Science Institute, University of Valencia, PO Box 22085, 46071 Valencia (Spain)

2011-02-11

We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for obtaining an effective spatial separation of electrons and holes in the case of single layer InP/GaAs quantum-dot samples. In the present case this effect seems to be less critical due to the particular carrier wavefunction distribution along the structures.

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.

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.

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

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

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.)

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.

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.

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.

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

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.

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.

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

Homogeneous CdTe quantum dots-carbon nanotubes heterostructures

Energy Technology Data Exchange (ETDEWEB)

Vieira, Kayo Oliveira [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Bettini, Jefferson [Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, CEP 13083-970, Campinas, SP (Brazil); Ferrari, Jefferson Luis [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.br [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil)

2015-01-15

The development of homogeneous CdTe quantum dots-carbon nanotubes heterostructures based on electrostatic interactions has been investigated. We report a simple and reproducible non-covalent functionalization route that can be accomplished at room temperature, to prepare colloidal composites consisting of CdTe nanocrystals deposited onto multi-walled carbon nanotubes (MWCNTs) functionalized with a thin layer of polyelectrolytes by layer-by-layer technique. Specifically, physical adsorption of polyelectrolytes such as poly (4-styrene sulfonate) and poly (diallyldimethylammonium chloride) was used to deagglomerate and disperse MWCNTs, onto which we deposited CdTe quantum dots coated with mercaptopropionic acid (MPA), as surface ligand, via electrostatic interactions. Confirmation of the CdTe quantum dots/carbon nanotubes heterostructures was done by transmission and scanning electron microscopies (TEM and SEM), dynamic-light scattering (DLS) together with absorption, emission, Raman and infrared spectroscopies (UV–vis, PL, Raman and FT-IR). Almost complete quenching of the PL band of the CdTe quantum dots was observed after adsorption on the MWCNTs, presumably through efficient energy transfer process from photoexcited CdTe to MWCNTs. - Highlights: • Highly homogeneous CdTe-carbon nanotubes heterostructures were prepared. • Simple and reproducible non-covalent functionalization route. • CdTe nanocrystals homogeneously deposited onto multi-walled carbon nanotubes. • Efficient energy transfer process from photoexcited CdTe to MWCNTs.

The synthesis of CdSe quantum dots with carboxyl group and study on their optical characteristics

International Nuclear Information System (INIS)

Ye, Chen; Park, Sangjoon; Kim, Jongsung

2009-01-01

Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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....

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

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.

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...

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

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.

Multiple evanescent white dot syndrome associated with retinal vasculitis

Directory of Open Access Journals (Sweden)

Takahashi A

2015-09-01

Full Text Available Akihiro Takahashi, Wataru Saito, Yuki Hashimoto, Susumu Ishida Department of Ophthalmology, Hokkaido University Graduate School of Medicine, Sapporo, Japan Purpose: A recent study revealed thickening of the inner retinal layers in acute stage of multiple evanescent white dot syndrome (MEWDS; however, the pathogenesis is still unknown. We report two cases with MEWDS whose funduscopy showed obvious retinal vasculitis. Methods: Case reports. Results: Healthy myopic 16- and 27-year-old women were the cases under study. In both cases, funduscopic examination revealed multiple, faint, small, subretinal white dots at the posterior pole to the midperiphery and macular granularity oculus dexter. Retinal vascular sheathing was also observed at midperiphery. Late-phase fluorescein angiography revealed leakages corresponding to the vascular sheathing. Enhanced depth imaging optical coherence tomography revealed the discontinuity of the ellipsoid zone corresponding to the white dots and increased macular choroidal thickness. One month later, these white dots and retinal sheathing spontaneously resolved in both cases. Three months later, impairments of the outer retinal morphology and the visual acuity were restored. Conclusion: These results suggest that retinal vasculitis possibly plays a role in the pathogenesis of thickened inner retinal layers in acute stage of MEWDS. Keywords: enhanced depth imaging optical coherence tomography, choroidal thickness, inner retinal layer, retinal vascular sheathing

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...

Synthesis of WO{sub n}-WX{sub 2} (n=2.7, 2.9; X=S, Se) heterostructures for highly efficient green quantum dot light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Han, Shikui; Tan, Chaoliang; Zhang, Xiao; Chen, Junze; Huang, Ying; Chen, Bo; Luo, Zhimin; Ma, Qinglang; Sindoro, Melinda; Zhang, Hua [Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, Singapore (Singapore); Yang, Xuyong [Luminous. Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore (Singapore); Zhu, Yihan; Han, Yu [Advanced Membranes and Porous Materials Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal (Saudi Arabia); Zhang, Hao; Li, Hai; Huang, Xiao; Huang, Wei [Institute of Advanced Materials (IAM), Nanjing Tech University (NanjingTech) (China); Qi, Xiaoying [Singapore Institute of Manufacturing Technology, Singapore (Singapore); Sun, Xiao Wei [Luminous. Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore (Singapore); Dept. of Electrical and Electronic Engineering, College of Engineering, Southern Univ. of Science and Technology, Nanshan, Shenzhen, Guangdong (China)

2017-08-21

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 WO{sub n}-WX{sub 2} (n=2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WO{sub n} nanomaterials. The WO{sub n}-WX{sub 2} heterostructures are composed of WO{sub 2.9} nanoparticles (NPs) or WO{sub 2.7} nanowires (NWs) grown together with single- or few-layer WX{sub 2} nanosheets (NSs). As a proof-of-concept application, the WO{sub n}-WX{sub 2} heterostructures are used as the anode interfacial buffer layer for green quantum dot light-emitting diodes (QLEDs). The QLED prepared with WO{sub 2.9} NP-WSe{sub 2} 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. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

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.

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

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...

Phase diagrams of magnetic state transformations in multiferroic composites controlled by size, shape and interfacial coupling strain

Directory of Open Access Journals (Sweden)

Qiang Sheng

2017-10-01

Full Text Available This work aims to give a comprehensive view of magnetic state stability and transformations in PZT-film/FeGa-dot multiferroic composite systems due to the combining effects of size, shape and interfacial coupling strain. It is found that the stable magnetic state of the FeGa nanodots is not only a function of the size and shape of the nanodot but also strongly sensitive to the interfacial coupling strain modified by the polarization state of PZT film. In particular, due to the large magnetostriction of FeGa, the phase boundaries between different magnetic states (i.e., in-plane/out-of-plane polar states, and single-/multi-vortex states of FeGa nanodots can be effectively tuned by the polarization-mediated strain. Fruitful strain-mediated transformation paths of magnetic states including those between states with different orderings (i.e., one is polar and the other is vortex, as well as those between states with the same ordering (i.e., both are polar or both are vortex have been revealed in a comprehensive view. Our result sheds light on the potential of utilizing electric field to induce fruitful magnetic state transformation paths in multiferroic film-dot systems towards a development of novel magnetic random access memories.

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

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.

Nanoparticle packing within block copolymer micelles prepared by the interfacial instability method.

Science.gov (United States)

Nabar, Gauri M; Winter, Jessica O; Wyslouzil, Barbara E

2018-05-02

The interfacial instability method has emerged as a viable approach for encapsulating high concentrations of nanoparticles (NPs) within morphologically diverse micelles. In this method, transient interfacial instabilities at the surface of an emulsion droplet guide self-assembly of block co-polymers and NP encapsulants. Although used by many groups, there are no systematic investigations exploring the relationship between NP properties and micelle morphology. Here, the effect of quantum dot (QD) and superparamagnetic iron oxide NP (SPION) concentration on the shape, size, and surface deformation of initially spherical poly(styrene-b-ethylene oxide) (PS-b-PEO) micelles was examined. Multi-NP encapsulation and uniform dispersion within micelles was obtained even at low NP concentrations. Increasing NP concentration initially resulted in larger numbers of elongated micelles and cylinders with tightly-controlled diameters smaller than those of spherical micelles. Beyond a critical NP concentration, micelle formation was suppressed; the dominant morphology became densely-loaded NP structures that were coated with polymer and exhibited increased polydispersity. Transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) revealed that NPs in densely-loaded structures can be well-ordered, with packing volume fractions of up to 24%. These effects were enhanced in magnetic composites, possibly by dipole interactions. Mechanisms governing phase transitions triggered by NP loading in the interfacial instability process were proposed. The current study helps establish and elucidate the active role played by NPs in directing block copolymer assembly in the interfacial instability process, and provides important guiding principles for the use of this approach in generating NP-loaded block copolymer composites.

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.

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.

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

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.

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...

Improved interfacial adhesion in carbon fiber/polyether sulfone composites through an organic solvent-free polyamic acid sizing

Energy Technology Data Exchange (ETDEWEB)

Yuan, Haojie [National Engineering Laboratory for carbon fiber technology, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhang, Shouchun, E-mail: zschun@sxicc.ac.cn [National Engineering Laboratory for carbon fiber technology, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001 (China); Lu, Chunxiang, E-mail: chunxl@sxicc.ac.cn [National Engineering Laboratory for carbon fiber technology, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001 (China); He, Shuqing [National Engineering Laboratory for carbon fiber technology, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); An, Feng [National Engineering Laboratory for carbon fiber technology, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001 (China)

2013-08-15

An organic solvent-free polyamic acid (PAA) nanoemulsion was obtained by direct ionization of the solid PAA in deionized water, with the average particle size of 261 nm and Zeta potential of −55.1 mV, and used as a carbon fiber sizing to improve the interfacial adhesion between the carbon fiber and polyether sulfone (PES). The surface characteristics of PAA coated carbon fibers were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and dynamic contact angle measurement. The results demonstrated that a continuous and uniform PAA sizing layer was formed on the surface of carbon fibers, and the surface energy of carbon fibers increased from 42.91 to 54.55 mN/m after sizing treatment. The single fiber pull-out testing was also performed, which showed the increased interfacial shear strength (IFSS) of carbon fiber/PES composites from 33.6 to 49.7 MPa by 47.9%. The major reasons for the improved interfacial adhesion were the increased van der Waals forces between the PES matrix and sizing layer as well as the chemical bonding between the sizing layer and carbon fiber surface. Furthermore, the PAA sizing also presented a positive effect on the interfacial adhesion of carbon fiber/PES composites under hydrothermal condition.

Improved interfacial adhesion in carbon fiber/polyether sulfone composites through an organic solvent-free polyamic acid sizing

International Nuclear Information System (INIS)

Yuan, Haojie; Zhang, Shouchun; Lu, Chunxiang; He, Shuqing; An, Feng

2013-01-01

An organic solvent-free polyamic acid (PAA) nanoemulsion was obtained by direct ionization of the solid PAA in deionized water, with the average particle size of 261 nm and Zeta potential of −55.1 mV, and used as a carbon fiber sizing to improve the interfacial adhesion between the carbon fiber and polyether sulfone (PES). The surface characteristics of PAA coated carbon fibers were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and dynamic contact angle measurement. The results demonstrated that a continuous and uniform PAA sizing layer was formed on the surface of carbon fibers, and the surface energy of carbon fibers increased from 42.91 to 54.55 mN/m after sizing treatment. The single fiber pull-out testing was also performed, which showed the increased interfacial shear strength (IFSS) of carbon fiber/PES composites from 33.6 to 49.7 MPa by 47.9%. The major reasons for the improved interfacial adhesion were the increased van der Waals forces between the PES matrix and sizing layer as well as the chemical bonding between the sizing layer and carbon fiber surface. Furthermore, the PAA sizing also presented a positive effect on the interfacial adhesion of carbon fiber/PES composites under hydrothermal condition.

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.

Wavelength characteristics of chirped quantum dot superluminescent diodes for broad spectrum

Energy Technology Data Exchange (ETDEWEB)

Bae, Hyung-Chul; Park, Hong-Lee [Yonsei University, Seoul (Korea, Republic of); You, Young-Chae [Sungkyunkwan University, Suwon (Korea, Republic of); Han, Il-Ki [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

2006-04-15

A chirped InAs quantum dot superluminescent diode both with and without a In{sub 0.15}Ga{sub 0.85}As cap layer was fabricated for a broad-band spectrum. This study shows that the cap layer reduces strain and operates as a carrier capturer and that carriers excited by lattice heating also affect the radiative recombination in the quantum dots (QDs) as well as the cap layer through the characteristic temperature (T{sub 0}). In addition, by surveying peaks of each QD layers, the characteristics of carriers in QDs, such as band-filling effect and the thermal effect, were analyzed, in QDs, and a more effective method for creating a wider spectrum is proposed.

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.

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.

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%.

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%.

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...

MBE-grown Si and Si1−xGex quantum dots embedded within epitaxial Gd2O3 on Si(111) substrate for floating gate memory device

International Nuclear Information System (INIS)

Manna, S; Aluguri, R; Katiyar, A; Ray, S K; Das, S; Laha, A; Osten, H J

2013-01-01

Si and Si 1−x Ge x quantum dots embedded within epitaxial Gd 2 O 3 grown by molecular beam epitaxy have been studied for application in floating gate memory devices. The effect of interface traps and the role of quantum dots on the memory properties have been studied using frequency-dependent capacitance–voltage and conductance–voltage measurements. Multilayer quantum dot memory comprising four and five layers of Si quantum dots exhibits a superior memory window to that of single-layer quantum dot memory devices. It has also been observed that single-layer Si 1−x Ge x quantum dots show better memory characteristics than single-layer Si quantum dots. (paper)

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.

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.

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.

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.

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.

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.

Zinc Cadmium Selenide Cladded Quantum Dot Based Electroluminescent and Nonvolatile Memory Devices

Science.gov (United States)

Al-Amody, Fuad H.

This dissertation presents electroluminescent (EL) and nonvolatile memory devices fabricated using pseudomorphic ZnCdSe-based cladded quantum dots (QDs). These dots were grown using our own in-school built novel reactor. The EL device was fabricated on a substrate of ITO (indium tin oxide) coated glass with the quantum dots sandwiched between anode and cathode contacts with a small barrier layer on top of the QDs. The importance of these cladded dots is to increase the quantum yield of device. This device is unique as they utilize quantum dots that are pseudomorphic (nearly lattice-matched core and the shell of the dot). In the case of floating quantum dot gate nonvolatile memory, cladded ZnCdSe quantum dots are deposited on single crystalline gate insulator (ZnMgS/ZnMgSe), which is grown using metal-organic chemical vapor deposition (MOCVD). The control gate dielectric layer of the nonvolatile memory is Si3N4 or SiO2 and is grown using plasma enhanced chemical vapor deposition (PECVD). The cladded dots are grown using an improved methodology of photo-assisted microwave plasma metal-organic chemical vapor deposition (PMP-MOCVD) enhanced reactor. The cladding composition of the core and shell of the dots was engineered by the help of ultraviolet light which changed the incorporation of zinc (and hence composition of ZnCdSe). This makes ZnxCd1--xSe-ZnyCd1--y Se QDs to have a low composition of zinc in the core than the cladding (x

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.

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.

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.

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.

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.

Modeling and simulation of InGaN/GaN quantum dots solar cell

Energy Technology Data Exchange (ETDEWEB)

Aissat, A., E-mail: sakre23@yahoo.fr [LATSI Laboratory, Faculty of Technology, University of Blida 1 (Algeria); LASICOMLaboratory, Faculty of Sciences, University of Blida 1 (Algeria); Benyettou, F. [LASICOMLaboratory, Faculty of Sciences, University of Blida 1 (Algeria); Vilcot, J. P. [Institute of Electronics, Micro-Electronics and Nanotechnologies,UMR CNRS 8520, Université des Sciences et Technologies de Lille1, Avenue Poincaré, CS 60069, 59652 Villeneuve d’Ascq (France)

2016-07-25

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{sub 0.25}Ga{sub 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{sub 0.25}Ga{sub 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%.

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

Stranski-Krastanov InN/InGaN quantum dots grown directly on Si(111)

Energy Technology Data Exchange (ETDEWEB)

Soto Rodriguez, Paul E. D., E-mail: p.soto@isom.upm.es; Aseev, Pavel; Gómez, Victor J.; Kumar, Praveen; Ul Hassan Alvi, Naveed; Calleja, Enrique [Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM), Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Mánuel, José M.; Jiménez, Juan J.; García, Rafael [Dep. Ciencia de los Materiales e IM y QI., F. Ciencias, Universidad de Cádiz, 11510-Puerto Real, Cádiz (Spain); Morales, Francisco M. [Dep. Ciencia de los Materiales e IM y QI., F. Ciencias, Universidad de Cádiz, 11510-Puerto Real, Cádiz (Spain); IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz, Cádiz (Spain); Senichev, Alexander [Max Planck Institute of Microstructure Physics, Weinberg 2, Halle 06120 (Germany); Lienau, Christoph [Institut für Physik, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg (Germany); Nötzel, Richard, E-mail: noetzel500@gmail.com [L-NESS and Dipartimento di Scienza dei Materiali, Universitá di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy)

2015-01-12

The authors discuss and demonstrate the growth of InN surface quantum dots on a high-In-content In{sub 0.73}Ga{sub 0.27}N layer, directly on a Si(111) substrate by plasma-assisted molecular beam epitaxy. Atomic force microscopy and transmission electron microscopy reveal uniformly distributed quantum dots with diameters of 10–40 nm, heights of 2–4 nm, and a relatively low density of ∼7 × 10{sup 9} cm{sup −2}. A thin InN wetting layer below the quantum dots proves the Stranski-Krastanov growth mode. Near-field scanning optical microscopy shows distinct and spatially well localized near-infrared emission from single surface quantum dots. This holds promise for future telecommunication and sensing devices.

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.

Energy spectrums of bilayer triangular phosphorene quantum dots and antidots

Directory of Open Access Journals (Sweden)

Z. T. Jiang

2017-04-01

Full Text Available We theoretically investigate the confined states of the bilayer triangular phosphorene dots and antidots by means of the tight-binding approach. The dependence of the energy levels on the size, the type of the boundary edges, and the orientation of the dots and antidots, and the influences of the electric and magnetic fields on the energy levels, are all completely analyzed. It is found that the energy level numbers of the bilayer dots and antidots are determined by the energy levels in two layers. The external electric field can effectively tune the energy levels of the edge states in both layers to move in opposite directions. With the increase of the magnetic field, the magnetic energy levels can approach the Landau levels of the phosphorene monolayer, the phosphorene bilayer, or both, depending on the specific geometry of the monolayer-bilayer hybrid phosphorene quantum dots. This research should be helpful for the overall understanding of the electronic properties of the multilayer hybrid phosphorene nanostructures and designing the corresponding phosphorene devices.

Densification rate and interfacial adhesion of bilayer cemented tungsten carbide and steel

Energy Technology Data Exchange (ETDEWEB)

Ojo-kupoluyi, Oluwatosin Job; Tahir, Suraya Mohd; Ariff, Azmah Hanim Mohamed; Baharudin, B.T. Hang Tuah [Univ. Putra Malaysia, Selangor (Malaysia). Dept. of Mechanical and Manufacturing Engineering; Matori, Khamirul Amin [Univ. Putra Malaysia, Selangor (Malaysia). Dept. of Physics; Univ. Putra Malaysia, Selangor (Malaysia). Inst. of Advanced Technology (ITMA); Shamsul Anuar, Mohd [Univ. Putra Malaysia, Selangor (Malaysia). Dept. of Process and Food Engineering

2017-12-15

Manufacturing tailored materials is commonly faced with the challenge of shrinkage mismatch between layers resulting in delamination. The effects of sintering temperature and carbon variation on the densification and interfacial bond strength of bilayer cemented tungsten carbide and steel processed through powder metallurgy are analyzed. It is revealed through field-emission scanning electron microscopy images that inter-layer diffusion induced by liquid-phase sintering plays a major role in the densification and bonding of layers. Through dimensional analysis of sintered bilayer specimens, the strain rate of cemented tungsten carbide is observed to surpass that of steel. An enhanced densification rate of 6.1 % and M{sub 6}C (eta carbide) reduction with increased carbon level results in strong interfacial bonding in specimens sintered at 1 280 C. At 1 295 C, diffusion accelerates and the axial and radial shrinkage increase by 14.05 % and 13.35 %, respectively, in 93.8 wt.% WC - 6 wt.% Fe - 0.2 wt.% C and 93.2 wt.% Fe - 6 wt.% WC - 0.8 wt.% C, thereby increasing the tendency for complete delamination.

Densification rate and interfacial adhesion of bilayer cemented tungsten carbide and steel

International Nuclear Information System (INIS)

Ojo-kupoluyi, Oluwatosin Job; Tahir, Suraya Mohd; Ariff, Azmah Hanim Mohamed; Baharudin, B.T. Hang Tuah; Shamsul Anuar, Mohd

2017-01-01

Manufacturing tailored materials is commonly faced with the challenge of shrinkage mismatch between layers resulting in delamination. The effects of sintering temperature and carbon variation on the densification and interfacial bond strength of bilayer cemented tungsten carbide and steel processed through powder metallurgy are analyzed. It is revealed through field-emission scanning electron microscopy images that inter-layer diffusion induced by liquid-phase sintering plays a major role in the densification and bonding of layers. Through dimensional analysis of sintered bilayer specimens, the strain rate of cemented tungsten carbide is observed to surpass that of steel. An enhanced densification rate of 6.1 % and M 6 C (eta carbide) reduction with increased carbon level results in strong interfacial bonding in specimens sintered at 1 280 C. At 1 295 C, diffusion accelerates and the axial and radial shrinkage increase by 14.05 % and 13.35 %, respectively, in 93.8 wt.% WC - 6 wt.% Fe - 0.2 wt.% C and 93.2 wt.% Fe - 6 wt.% WC - 0.8 wt.% C, thereby increasing the tendency for complete delamination.

Control of spontaneous emission of quantum dots using correlated effects of metal oxides and dielectric materials.

Science.gov (United States)

Sadeghi, S M; Wing, W J; Gutha, R R; Capps, L

2017-03-03

We study the emission dynamics of semiconductor quantum dots in the presence of the correlated impact of metal oxides and dielectric materials. For this we used layered material structures consisting of a base substrate, a dielectric layer, and an ultrathin layer of a metal oxide. After depositing colloidal CdSe/ZnS quantum dots on the top of the metal oxide, we used spectral and time-resolved techniques to show that, depending on the type and thickness of the dielectric material, the metal oxide can characteristically change the interplay between intrinsic excitons, defect states, and the environment, offering new material properties. Our results show that aluminum oxide, in particular, can strongly change the impact of amorphous silicon on the emission dynamics of quantum dots by balancing the intrinsic near band emission and fast trapping of carriers. In such a system the silicon/aluminum oxide charge barrier can lead to large variation of the radiative lifetime of quantum dots and control of the photo-ejection rate of electrons in quantum dots. The results provide unique techniques to investigate and modify physical properties of dielectrics and manage optical and electrical properties of quantum dots.

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.

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.

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

Atmospheric pressure-MOVPE growth of GaSb/GaAs quantum dots

Science.gov (United States)

Tile, Ngcali; Ahia, Chinedu C.; Olivier, Jaco; Botha, Johannes Reinhardt

2018-04-01

This study focuses on the growth of GaSb/GaAs quantum dots (QD) using an atmospheric pressure MOVPE system. For the best uncapped dots, the average dot height, base diameter and density are 5 nm, 45 nm and 4.5×1010 cm-2, respectively. Capping of GaSb QDs at high temperatures caused flattening and formation of thin inhomogeneous GaSb layer inside GaAs resulting in no obvious QD PL peak. Capping at low temperatures lead to the formation of dot-like features and a wetting layer (WL) with distinct PL peaks for QD and WL at 1097 nm and 983 nm respectively. Some of the dot-like features had voids. An increase in excitation power caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending leading to triangular potential wells, typical of type-II alignment between GaAs and strained GaSb. Variable temperature PL measurements of the QD sample showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the temperature increased.

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.

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)

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.

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

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

Novel Quantum Dot Gate FETs and Nonvolatile Memories Using Lattice-Matched II-VI Gate Insulators

Science.gov (United States)

Jain, F. C.; Suarez, E.; Gogna, M.; Alamoody, F.; Butkiewicus, D.; Hohner, R.; Liaskas, T.; Karmakar, S.; Chan, P.-Y.; Miller, B.; Chandy, J.; Heller, E.

2009-08-01

This paper presents the successful use of ZnS/ZnMgS and other II-VI layers (lattice-matched or pseudomorphic) as high- k gate dielectrics in the fabrication of quantum dot (QD) gate Si field-effect transistors (FETs) and nonvolatile memory structures. Quantum dot gate FETs and nonvolatile memories have been fabricated in two basic configurations: (1) monodispersed cladded Ge nanocrystals (e.g., GeO x -cladded-Ge quantum dots) site-specifically self-assembled over the lattice-matched ZnMgS gate insulator in the channel region, and (2) ZnTe-ZnMgTe quantum dots formed by self-organization, using metalorganic chemical vapor-phase deposition (MOCVD), on ZnS-ZnMgS gate insulator layers grown epitaxially on Si substrates. Self-assembled GeO x -cladded Ge QD gate FETs, exhibiting three-state behavior, are also described. Preliminary results on InGaAs-on-InP FETs, using ZnMgSeTe/ZnSe gate insulator layers, are presented.

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

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

Tunable anomalous hall effect induced by interfacial catalyst in perpendicular multilayers

Science.gov (United States)

Zhang, J. Y.; Peng, W. L.; Sun, Q. Y.; Liu, Y. W.; Dong, B. W.; Zheng, X. Q.; Yu, G. H.; Wang, C.; Zhao, Y. C.; Wang, S. G.

2018-04-01

The interfacial structures, playing a critical role on the transport properties and the perpendicular magnetic anisotropy in thin films and multilayers, can be modified by inserting an ultrathin functional layer at the various interfaces. The anomalous Hall effect (AHE) in the multilayers with core structure of Ta/CoFeB/X/MgO/Ta (X: Hf or Pt) is tuned by interfacial catalytic engineering. The saturation anomalous Hall resistance (RAH) is increased by 16.5% with 0.1 nm Hf insertion compared with the reference sample without insertion. However, the RAH value is decreased by 9.0% with 0.1 nm Pt insertion. The interfacial states were characterized by the X-ray photoelectron spectroscopy (XPS). The XPS results indicate that a strong bonding between Hf and O for Hf insertion, but no bonding between Pt and O for Pt insertion. The bonding between metal and oxygen leads to various oxygen migration behavior at the interfaces. Therefore, the opposite behavior about the RAH originates from the different oxygen behavior due to various interfacial insertion. This work provides a new approach to manipulate spin transport property for the potential applications.

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

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.

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)

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.

Four-wave mixing in InAlGaAs quantum dots

DEFF Research Database (Denmark)

Leosson, Kristjan; Birkedal, Dan; Hvam, Jørn Märcher

2001-01-01

broadening strongly reduce the interaction with the electromagnetic field. Until now, four-wave mixing (FWM) in III-V quantum dots has only been reported in optical amplifiers at room temperature, where the interaction length is increased by waveguiding in the quantum dot plane. We have carried out...... degenerate FWM experiments in a slab geometry on a sample containing 10 layers of MBE-grown In0.5Al0.04Ga0.46As quantum dots (QDs) with 50-nm Al0.08Ga0.92As barriers. Ground state photoluminescence emission was measured....

Photoemission Studies of Si Quantum Dots with Ge Core: Dots formation, Intermixing at Si-clad/Ge-core interface and Quantum Confinement Effect

Directory of Open Access Journals (Sweden)

Yudi Darma

2008-03-01

Full Text Available Spherical Si nanocrystallites with Ge core (~20nm in average dot diameter have been prepared by controlling selective growth conditions of low-pressure chemical vapor deposition (LPCVD on ultrathin SiO2 using alternately pure SiH4 and 5% GeH4 diluted with He. XPS results confirm the highly selective growth of Ge on the pregrown Si dots and subsequently complete coverage by Si selective growth on Ge/Si dots. Compositional mixing and the crystallinity of Si dots with Ge core as a function of annealing temperature in the range of 550-800oC has been evaluated by XPS analysis and confirms the diffusion of Ge atoms from Ge core towards the Si clad accompanied by formation of GeOx at the Si clad surface. The first subband energy at the valence band of Si dot with Ge core has been measured as an energy shift at the top of the valence band density of state using XPS. The systematic shift of the valence band maximum towards higher binding energy with progressive deposition in the dot formation indicate the charging effect of dots and SiO2 layer by photoemission during measurements.

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.

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.

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.

Effects of annealing on electrical and optical properties of a multilayer InAs/GaAs quantum dots system

Directory of Open Access Journals (Sweden)

Adenilson José Chiquito

2004-09-01

Full Text Available A systematic investigation of the properties of the InAs/GaAs self-assembled quantum dots (SAQDs system subjected to a post-growth annealing using capacitance-voltage, Raman scattering and photoluminescence measurements is presented. The application of both electrical and optical methods allowed us to obtain reliable information on the microscopic structural evolution of this system. The single layer and the multilayer quantum dots were found to respond differently to the annealing process, due to the differences in strain that occur in both systems. The diffusion activated by strain provoked the appearance of an InGaAs alloy layer in substitution to the quantum dots layers; this change occurred at the annealing temperature T = 600 ºC in the multilayer system. A single dot layer, however, was observed even after the annealing at T = 700 ºC. Moreover, the low temperature annealing was found to improve the homogeneity of the multilayer system and to decrease the electrical interlayer coupling.

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.

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.

Using quantum dot photoluminescence for load detection

Science.gov (United States)

Moebius, M.; Martin, J.; Hartwig, M.; Baumann, R. R.; Otto, T.; Gessner, T.

2016-08-01

We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N',N'-Tetrakis(3-methylphenyl)-3,3'-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

Using quantum dot photoluminescence for load detection

Directory of Open Access Journals (Sweden)

M. Moebius

2016-08-01

Full Text Available We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N′,N′-Tetrakis(3-methylphenyl-3,3′-dimethylbenzidine (HMTPD and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

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.

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.

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)

Improvement in interfacial characteristics of low-voltage carbon nanotube thin-film transistors with solution-processed boron nitride thin films

Energy Technology Data Exchange (ETDEWEB)

Jeon, Jun-Young; Ha, Tae-Jun, E-mail: taejunha0604@gmail.com

2017-08-15

Highlights: • We demonstrate the potential of solution-processed boron nitride (BN) thin films for nanoelectronics. • Improved interfacial characteristics reduced the leakage current by three orders of magnitude. • The BN encapsulation improves all the device key metrics of low-voltage SWCNT-TFTs. • Such improvements were achieved by reduced interaction of interfacial localized states. - Abstract: In this article, we demonstrate the potential of solution-processed boron nitride (BN) thin films for high performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with low-voltage operation. The use of BN thin films between solution-processed high-k dielectric layers improved the interfacial characteristics of metal-insulator-metal devices, thereby reducing the current density by three orders of magnitude. We also investigated the origin of improved device performance in SWCNT-TFTs by employing solution-processed BN thin films as an encapsulation layer. The BN encapsulation layer improves the electrical characteristics of SWCNT-TFTs, which includes the device key metrics of linear field-effect mobility, sub-threshold swing, and threshold voltage as well as the long-term stability against the aging effect in air. Such improvements can be achieved by reduced interaction of interfacial localized states with charge carriers. We believe that this work can open up a promising route to demonstrate the potential of solution-processed BN thin films on nanoelectronics.

Quantum Dots in Two-Dimensional Perovskite Matrices for Efficient Near-Infrared Light Emission

KAUST Repository

Yang, Zhenyu

2017-03-13

Quantum-dot-in-perovskite solids are excellent candidates for infrared light-emitting applications. The first generation of dot-in-perovskite light-emitting diodes (LEDs) has shown bright infrared electroluminescence with tunable emission wavelength; however, their performance has been limited by degradation of the active layer at practical operating voltages. This arises from the instability of the three-dimensional (3D) organolead halide perovskite matrix. Herein we report the first dot-in-perovskite solids that employ two-dimensional (2D) perovskites as the matrix. 2D perovskite passivation is achieved via an in situ alkylammonium/alkylamine substitution carried out during the quantum dot (QD) ligand exchange process. This single-step film preparation process enables deposition of the QD/perovskite active layers with thicknesses of 40 nm, over seven times thinner than the first-generation dot-in-perovskite thin films that relied on a multistep synthesis. The dot-in-perovskite film roughness improved from 31 nm for the first-generation films to 3 nm for films as a result of this new approach. The best devices exhibit external quantum efficiency peaks exceeding 2% and radiances of ∼1 W sr–1 m–2, with an improved breakdown voltage up to 7.5 V. Compared to first-generation dot-in-perovskites, this new process reduces materials consumptions 10-fold and represents a promising step toward manufacturable devices.

Quantum Dots in Two-Dimensional Perovskite Matrices for Efficient Near-Infrared Light Emission

KAUST Repository

Yang, Zhenyu; Voznyy, Oleksandr; Walters, Grant; Fan, James Z.; Liu, Min; Kinge, Sachin; Hoogland, Sjoerd; Sargent, Edward H.

2017-01-01

Quantum-dot-in-perovskite solids are excellent candidates for infrared light-emitting applications. The first generation of dot-in-perovskite light-emitting diodes (LEDs) has shown bright infrared electroluminescence with tunable emission wavelength; however, their performance has been limited by degradation of the active layer at practical operating voltages. This arises from the instability of the three-dimensional (3D) organolead halide perovskite matrix. Herein we report the first dot-in-perovskite solids that employ two-dimensional (2D) perovskites as the matrix. 2D perovskite passivation is achieved via an in situ alkylammonium/alkylamine substitution carried out during the quantum dot (QD) ligand exchange process. This single-step film preparation process enables deposition of the QD/perovskite active layers with thicknesses of 40 nm, over seven times thinner than the first-generation dot-in-perovskite thin films that relied on a multistep synthesis. The dot-in-perovskite film roughness improved from 31 nm for the first-generation films to 3 nm for films as a result of this new approach. The best devices exhibit external quantum efficiency peaks exceeding 2% and radiances of ∼1 W sr–1 m–2, with an improved breakdown voltage up to 7.5 V. Compared to first-generation dot-in-perovskites, this new process reduces materials consumptions 10-fold and represents a promising step toward manufacturable devices.

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

Proposal for a magnetic field induced graphene dot

International Nuclear Information System (INIS)

Maksym, P A; Roy, M; Craciun, M F; Russo, S; Yamamoto, M; Tarucha, S; Aoki, H

2010-01-01

Quantum dots induced by a strong magnetic field applied to a single layer of graphene in the perpendicular direction are investigated. The dot is defined by a model potential which consists of a well of depth ΔV relative to a flat asymptotic part and quantum states formed from the zeroth Landau level are considered. The energy of the dot states cannot be lower than -ΔV relative to the asymptotic potential. Consequently, when ΔV is chosen to be about half of the gap between the zeroth and first Landau levels, the dot states are isolated energetically in the gap between Landau level 0 and Landau level -1. This is confirmed with numerical calculations of the magnetic field dependent energy spectrum and the quantum states. Remarkably, an antidot formed by reversing the sign of ΔV also confines electrons but in the energy region between Landau level 0 and Landau level +1. This unusual behaviour gives an unambiguous signal of the novel physics of graphene quantum dots.

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.

Monte Carlo studies on the interfacial properties and interfacial structures of ternary symmetric blends with gradient copolymers.

Science.gov (United States)

Sun, Dachuan; Guo, Hongxia

2012-08-09

Using Monte Carlo simulation methods, the effects of the comonomer sequence distribution on the interfacial properties (including interfacial tension, interfacial thickness, saturated interfacial area per copolymer, and bending modulus) and interfacial structures (including chain conformations and comonomer distributions of the simulated copolymers at the interfaces) of a ternary symmetric blend containing two immiscible homopolymers and one gradient copolymer are investigated. We find that copolymers with a larger composition gradient width have a broader comonomer distribution along the interface normal, and hence more pronouncedly enlarge the interfacial thickness and reduce the interfacial tension. Furthermore, the counteraction effect, which arises from the tendency of heterogeneous segments in gradient copolymers to phase separate and enter their miscible phases to reduce the local enthalpy, decreases the stretching of copolymers along the interface normal direction. As a result, copolymers with a larger width of gradient composition can occupy a larger interfacial area and form softer monolayers at saturation and are more efficient in facilitating the formation of bicontinuous microemulsions. Additionally, chain length ratio, segregation strength, and interactions between homopolymers and copolymers can alter the interfacial character of gradient copolymers. There exists a strong coupling between the comonomer sequence distribution, chain conformation, and interfacial properties. Especially, bending modulus is mainly determined by the complicated interplay of interfacial copolymer density and interfacial chain conformation.

Assembly of CdS Quantum Dots onto Hierarchical TiO2 Structure for Quantum Dots Sensitized Solar Cell Applications

Directory of Open Access Journals (Sweden)

Syed Mansoor Ali

2015-05-01

Full Text Available Quantum dot (QD sensitized solar cells based on Hierarchical TiO2 structure (HTS consisting of spherical nano-urchins on transparent conductive fluorine doped tin oxide glass substrate is fabricated. The hierarchical TiO2 structure consisting of spherical nano-urchins on transparent conductive fluorine doped tin oxide glass substrate synthesized by hydrothermal route. The CdS quantum dots were grown by the successive ionic layer adsorption and reaction deposition method. The quantum dot sensitized solar cell based on the hierarchical TiO2 structure shows a current density JSC = 1.44 mA, VOC = 0.46 V, FF = 0.42 and η = 0.27%. The QD provide a high surface area and nano-urchins offer a highway for fast charge collection and multiple scattering centers within the photoelectrode.

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

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

Pressure dependence of the interfacial structure of potassium chloride films on iron

International Nuclear Information System (INIS)

Olson, Dustin; Gao, Hongyu; Tang, Chun; Tysoe, Wilfred T.; Martini, Ashlie

2015-01-01

Potassium chloride films on a clean iron surface are used as a model system to explore the interfacial structure of the films and the dependence of that structure on film thickness and pressure. The interfacial structure of one-, two-, three- and four-layer films is measured experimentally using low-energy electron diffraction. Those findings are then complemented by molecular dynamics simulations in which the atomic interaction between the film and substrate is tuned to match film thickness-dependent sublimation activation energy obtained from temperature-programmed desorption measurements. The resultant simulation reliably predicts the structure of thicker films and is then used to study the effect of pressure on the distribution of the lattice constant within and between each layer of the potassium chloride films. Findings indicate that both film thickness and pressure affect the structure within the films as well as the degree of registry between the film and adjacent substrate. - Highlights: • KCl films on an Fe surface are used as a model system to explore interfacial structure • Thin film structure is measured using low-energy electron diffraction • An empirical potential is tuned to match sublimation activation energy • Simulations reveal the effect of pressure on the lattice constant within the KCl films • Pressure affects the film structure and registry between film and substrate

Pressure dependence of the interfacial structure of potassium chloride films on iron

Energy Technology Data Exchange (ETDEWEB)

Olson, Dustin [Department of Chemistry and Laboratory for Surface Studies, University of Wisconsin—Milwaukee, Milwaukee, WI 53211 (United States); Gao, Hongyu; Tang, Chun [School of Engineering, University of California Merced, Merced CA 95343 (United States); Tysoe, Wilfred T. [Department of Chemistry and Laboratory for Surface Studies, University of Wisconsin—Milwaukee, Milwaukee, WI 53211 (United States); Martini, Ashlie [School of Engineering, University of California Merced, Merced CA 95343 (United States)

2015-10-30

Potassium chloride films on a clean iron surface are used as a model system to explore the interfacial structure of the films and the dependence of that structure on film thickness and pressure. The interfacial structure of one-, two-, three- and four-layer films is measured experimentally using low-energy electron diffraction. Those findings are then complemented by molecular dynamics simulations in which the atomic interaction between the film and substrate is tuned to match film thickness-dependent sublimation activation energy obtained from temperature-programmed desorption measurements. The resultant simulation reliably predicts the structure of thicker films and is then used to study the effect of pressure on the distribution of the lattice constant within and between each layer of the potassium chloride films. Findings indicate that both film thickness and pressure affect the structure within the films as well as the degree of registry between the film and adjacent substrate. - Highlights: • KCl films on an Fe surface are used as a model system to explore interfacial structure • Thin film structure is measured using low-energy electron diffraction • An empirical potential is tuned to match sublimation activation energy • Simulations reveal the effect of pressure on the lattice constant within the KCl films • Pressure affects the film structure and registry between film and substrate.

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.

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

Interfacial pattern changes of imprinted multilayered material in milli- and microscales

Science.gov (United States)

Yonekura, Kazuhiro; Tokumaru, Kazuki; Tsumori, Fujio

2018-06-01

Nanoimprint lithography (NIL) is a technique that transfers a mold pattern of nanometer order to the surface of a resist material by heating and pressing. NIL is an excellent technology in terms of high productivity, accuracy, and resolution. Recently, NIL has been applied to the processing of different multilayered materials, in which it is possible to process multiple materials simultaneously. In this processing of multilayered materials, it is possible to form an interfacial pattern between the upper layer and the lower layer simultaneously with patterning on the mold surface. This interface pattern can be controlled by the deformation characteristics, initial thickness, and so forth. In this research, we compared the interfacial pattern changes of imprinted multilayered materials in milli- and microscales. For multilayered imprint using multiple materials, it is important to know the flow of the resist and its dependence on the scale. If there is similarity in the relationship produced by the scale on the imprinted samples, a process design with a number of feedbacks could be realized. It also becomes easier to treat structures in the millimeter scale for the experiment. In this study, we employed micropowder imprint (µPI) for multilayered material imprint. A compound sheet of alumina powder and polymer binder was used for imprint. Two similar experiments in different scales, micro- and millimeter scales, were carried out. Results indicate that the interfacial patterns of micro- and millimeter-scale-imprinted samples are similar.

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.

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)

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...

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...

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.

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.

Preferential orientation of magnetization and interfacial disorder in Co/Au multilayers

Energy Technology Data Exchange (ETDEWEB)

Quispe-Marcatoma, J., E-mail: justinianoqm@gmail.com [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil); Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, P.O. Box 14–0149, Lima 14, Perú (Peru); Pandey, B. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil); Alayo, W. [Departamento de Física, Universidade Federal de Pelotas, Campus Universitário, 96010-900 Pelotas, RS (Brazil); Sousa, M.A. de; Pelegrini, F. [Instituto de Física, Universidade Federal de Goiás, Goiânia 74001-970 (Brazil); Saitovitch, E. Baggio [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil)

2013-10-15

Two families of Co/Au multilayer films with different interlayer magnetostatic coupling were grown by the DC magnetron sputtering technique. The structure of these films was analyzed by X-ray diffraction (XRD), and the magnetic properties by vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) spectroscopy. All these techniques give complementary information about the structure of the multilayers and the magnetization direction as a function of thickness of the Co layers. The structural analysis shows a decrease of the interfacial disorder for increasing Co layer thickness in both groups of samples. This behavior has been correlated with a transition of the magnetization direction from perpendicular to parallel to the films plane. Thin Co layer samples gave high remnant magnetization with very low saturation field while thick Co layer samples showed low remnant magnetization with high value of saturation field. In the FMR study, the spectra showed two resonance modes, which were associated to the internal and interfacial Co atoms. Volume (K{sub v}) and surface (K{sub s}) anisotropy constants were deduced from the FMR experiments and are in good agreement with the reported values for Co/Au multilayers. - Highlights: • We find a competition between the magnetostatic coupling and magnetic anisotropy. • We find two resonant modes associated to different environments of Co atoms. • The main mode shows perpendicular magnetic anisotropy for samples with t{sub Co}<10 Å. • The secondary mode shows in-plane anisotropy for samples with t{sub Co}<10 Å.

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.

Preparation of 1-pyrenebutyric acid and pyrene submicron dots by laser-induced molecular micro-jet implantation

International Nuclear Information System (INIS)

Pihosh, Y.; Goto, M.; Kasahara, A.; Tosa, M.

2009-01-01

Pyrene and 1-pyrenebuturic acid molecules were deposited on glass and copper substrates with the formation of submicron dots by laser-induced molecular micro-jet implantation through polar and non-polar liquid layers. The size of the smallest 1-pyrenebuturic acid molecules dots prepared on a glass substrate by implantation through water and diiodomethane was estimated to be about 400 nm and 300 nm at laser fluences of 235 J/cm 2 and 326 J/cm 2 , respectively. The fluorescence and the Raman spectra showed that the implanted 1-pyrenebutyric acid molecules did not decompose during the implantation process. The smallest size of a pyrene dot was 700 nm at the laser fluence of 378 J/cm 2 . However, the pyrene dots could be formed only by implantation through a water layer.

Mixed layers of sodium caseinate + dextran sulfate: influence of order of addition to oil-water interface.

Science.gov (United States)

Jourdain, Laureline S; Schmitt, Christophe; Leser, Martin E; Murray, Brent S; Dickinson, Eric

2009-09-01

We report on the interfacial properties of electrostatic complexes of protein (sodium caseinate) with a highly sulfated polysaccharide (dextran sulfate). Two routes were investigated for preparation of adsorbed layers at the n-tetradecane-water interface at pH = 6. Bilayers were made by the layer-by-layer deposition technique whereby polysaccharide was added to a previously established protein-stabilized interface. Mixed layers were made by the conventional one-step method in which soluble protein-polysaccharide complexes were adsorbed directly at the interface. Protein + polysaccharide systems gave a slower decay of interfacial tension and stronger dilatational viscoelastic properties than the protein alone, but there was no significant difference in dilatational properties between mixed layers and bilayers. Conversely, shear rheology experiments exhibited significant differences between the two kinds of interfacial layers, with the mixed system giving much stronger interfacial films than the bilayer system, i.e., shear viscosities and moduli at least an order of magnitude higher. The film shear viscoelasticity was further enhanced by acidification of the biopolymer mixture to pH = 2 prior to interface formation. Taken together, these measurements provide insight into the origin of previously reported differences in stability properties of oil-in-water emulsions made by the bilayer and mixed layer approaches. Addition of a proteolytic enzyme (trypsin) to both types of interfaces led to a significant increase in the elastic modulus of the film, suggesting that the enzyme was adsorbed at the interface via complexation with dextran sulfate. Overall, this study has confirmed the potential of shear rheology as a highly sensitive probe of associative electrostatic interactions and interfacial structure in mixed biopolymer layers.

Combination of short-length TiO_2 nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantum-dot-sensitized solar cells

International Nuclear Information System (INIS)

Zhang, Zhengguo; Shi, Chengwu; Chen, Junjun; Xiao, Guannan; Li, Long

2017-01-01

Graphical abstract: The TiO_2 nanorod array with the length of 600 nm, the diameter of 20 nm, the areal density of 500 μm"−"2 was successfully prepared. The compact PbS quantum-dot thin film was firstly obtained on the TiO_2 nanorod array by spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol. The photoelectric conversion efficiency (PCE) of the compact PbS quantum-dot thin film sensitized solar cells achieved 4.10% using spiro-OMeTAD as a hole transporting layer, while the PCE of the PbS quantum-dot sensitized solar cells was only 0.54%. - Highlights: • Preparation of TiO_2 nanorod arrays with the length of 600 nm, diameter of 20 nm. • The compact PbS QD thin film and short-length TiO_2 nanorod array were combined. • EDT addition improved PbS nanoparticle coverage and photovoltaic performance. • The compact PbS QD thin film sensitized solar cell achieved the PCE of 4.10%. - Abstract: Considering the balance of the hole diffusion length and the loading quantity of quantum-dots, the rutile TiO_2 nanorod array with the length of 600 nm, the diameter of 20 nm, and the areal density of 500 μm"−"2 is successfully prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 105 min. The compact PbS quantum-dot thin film on the TiO_2 nanorod array is firstly obtained by the spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol (EDT). The result reveals that the strong interaction between lead and EDT is very important to control the crystallite size of PbS quantum-dots and obtain the compact PbS quantum-dot thin film on the TiO_2 nanorod array. The all solid-state sensitized solar cell with the combination of the short-length, high-density TiO_2 nanorod array and the compact PbS quantum-dot thin film achieves the photoelectric conversion efficiency of 4.10%, along with an open

Hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer

International Nuclear Information System (INIS)

Kim, Taehee; Choi, Jin Young; Jeon, Jun Hong; Kim, Youn-Su; Kim, Bong-Soo; Lee, Doh-Kwon; Kim, Honggon; Han, Seunghee; Kim, Kyungkon

2012-01-01

Highlights: ► This work enhanced power conversion efficiency of the hybrid tandem solar cell from 1.0% to 2.6%. ► The interfacial series resistance of the tandem solar cell was eliminated by inserting ITO layer. ► This work shows the feasibility of the highly efficient hybrid tandem solar cells. -- Abstract: We demonstrate hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer. The series-connected hybrid tandem photovoltaic devices were developed by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). In order to enhance the interfacial connection between the subcells, we employed highly transparent and conductive indium tin oxide (ITO) thin layer. By using the ITO interconnecting layer, the power conversion efficiency of the hybrid tandem solar cell was enhanced from 1.0% (V OC = 1.041 V, J SC = 2.97 mA/cm 2 , FF = 32.3%) to 2.6% (V OC = 1.336 V, J SC = 4.65 mA/cm 2 , FF = 41.98%) due to the eliminated interfacial series resistance.

Nonequilibrium carrier dynamics in self-assembled InGaAs quantum dots

International Nuclear Information System (INIS)

Wesseli, M.; Ruppert, C.; Trumm, S.; Betz, M.; Krenner, H.J.; Finley, J.J.

2006-01-01

Carrier dynamics in InGaAs/GaAs quantum dots is analyzed with highly sensitive femtosecond transmission spectroscopy. In a first step, measurements on a large ensemble of nanoislands reveal the dynamical electronic filling of quantum dots from the surrounding wetting layer. Most interestingly, we find a spin-preserving phonon mediated scattering into fully localized states within a few picoseconds. Then, individual artificial atoms are isolated with metallic shadow masks. For the first time, a single self-assembled quantum dot is addressed in an ultrafast transmission experiment. We find bleaching signals in the order of 10 -5 that arise from individual interband transitions of one quantum dot. As a result, we have developed an ultrafast optical tool for both manipulation and read-out of a single self-assembled quantum dot. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Angular dependence of dose sensitivity of nanoDot optically stimulated luminescent dosimeters in different radiation geometries

Energy Technology Data Exchange (ETDEWEB)

Jursinic, Paul A., E-mail: pjursinic@wmcc.org [West Michigan Cancer Center, 200 North Park Street, Kalamazoo, Michigan 49007 (United States)

2015-10-15

Purpose: A type of in vivo dosimeter, an optically stimulated luminescent dosimeter, OSLD, may have dose sensitivity that depends on the angle of incidence of radiation. This work measures how angular dependence of a nanoDot changes with the geometry of the phantom in which irradiation occurs and with the intrinsic structure of the nanoDot. Methods: The OSLDs used in this work were nanoDot dosimeters (Landauer, Inc., Glenwood, IL), which were read with a MicroStar reader (Landauer, Inc., Glenwood, IL). Dose to the OSLDs was delivered by 6 MV x-rays. NanoDots with various intrinsic sensitivities were irradiated in numerous phantoms that had geometric shapes of cylinders, rectangles, and a cube. Results: No angular dependence was seen in cylindrical phantoms, cubic phantoms, or rectangular phantoms with a thickness to width ratio of 0.3 or 1.5. An angular dependence of 1% was observed in rectangular phantoms with a thickness to width of 0.433–0.633. A group of nanoDots had sensitive layers with mass density of 2.42–2.58 g/cm{sup 3} and relative sensitivity of 0.92–1.09 and no difference in their angular dependence. Within experimental uncertainty, nanoDot measurements agree with a parallel-plate ion chamber at a depth of maximum dose. Conclusions: When irradiated in cylindrical, rectangular, and cubic phantoms, nanoDots show a maximum angular dependence of 1% or less at an incidence angle of 90°. For a sample of 78 new nanoDots, the range of their relative intrinsic sensitivity is 0.92–1.09. For a sample of ten nanoDots, on average, the mass in the sensitive layer is 73.1% Al{sub 2}O{sub 3}:C and 26.9% polyester. The mass density of the sensitive layer of a nanoDot disc is between 2.42 and 2.58 g/cm{sup 3}. The angular dependence is not related to Al{sub 2}O{sub 3}:C loading of the nanoDot disc. The nanoDot at the depth of maximum dose has no more angular dependence than a parallel-plate ion chamber.

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

Interfacial bonding and electronic structure of GaN/GaAs interface: A first-principles study

International Nuclear Information System (INIS)

Cao, Ruyue; Zhang, Zhaofu; Wang, Changhong; Li, Haobo; Dong, Hong; Liu, Hui; Wang, Weichao; Xie, Xinjian

2015-01-01

Understanding of GaN interfacing with GaAs is crucial for GaN to be an effective interfacial layer between high-k oxides and III-V materials with the application in high-mobility metal-oxide-semiconductor field effect transistor (MOSFET) devices. Utilizing first principles calculations, here, we investigate the structural and electronic properties of the GaN/GaAs interface with respect to the interfacial nitrogen contents. The decrease of interfacial N contents leads to more Ga dangling bonds and As-As dimers. At the N-rich limit, the interface with N concentration of 87.5% shows the most stability. Furthermore, a strong band offsets dependence on the interfacial N concentration is also observed. The valance band offset of N7 with hybrid functional calculation is 0.51 eV. The electronic structure analysis shows that significant interface states exist in all the GaN/GaAs models with various N contents, which originate from the interfacial dangling bonds and some unsaturated Ga and N atoms. These large amounts of gap states result in Fermi level pinning and essentially degrade the device performance

Polarization-dependent interfacial coupling modulation of ferroelectric photovoltaic effect in PZT-ZnO heterostructures.

Science.gov (United States)

Pan, Dan-Feng; Bi, Gui-Feng; Chen, Guang-Yi; Zhang, Hao; Liu, Jun-Ming; Wang, Guang-Hou; Wan, Jian-Guo

2016-03-08

Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices.

In situ study of the formation kinetics of InSb quantum dots grown in an InAs(Sb) matrix

International Nuclear Information System (INIS)

Semenov, A. N.; Lyublinskaya, O. G.; Solov’ev, V. A.; Mel’tser, B. Ya.; Ivanov, S. V.

2008-01-01

Formation of InSb quantum dots grown in an InAs matrix by molecular-beam epitaxy that does not involve forced deposition of InSb is studied. Detection of intensity oscillations in the reflection of high-energy electron diffraction patterns was used to study in situ the kinetics of the formation of InSb quantum dots and an InAsSb wetting layer. The effects of the substrate temperature, the shutter operation sequence, and the introduction of growth interruptions on the properties of the array of InSb quantum dots are examined. Introduction of a growth interruption immediately after completing the exposure of the InAs surface to the antimony flux leads to a reduction in the nominal thickness of InSb and to an enhancement in the uniformity of the quantum-dot array. It is shown that, in the case of deposition of submonolayer-thickness InSb/InAs quantum dots, the segregation layer of InAsSb plays the role of the wetting layer. The Sb segregation length and segregation ratio, as well as their temperature dependences, are determined.

An orientation analysis method for protein immobilized on quantum dot particles

Energy Technology Data Exchange (ETDEWEB)

Aoyagi, Satoka, E-mail: aoyagi@life.shimane-u.ac.jp [Faculty of Life and Environmental Science, Shimane University, 1060 Matsue-shi, Shimane 690-8504 (Japan); Inoue, Masae [Toyota Central R and D Labs., Inc., Nagakute, Aichi 480-1192 (Japan)

2009-11-30

The evaluation of orientation of biomolecules immobilized on nanodevices is crucial for the development of high performance devices. Such analysis requires ultra high sensitivity so as to be able to detect less than one molecular layer on a device. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has sufficient sensitivity to evaluate the uppermost surface structure of a single molecular layer. The objective of this study is to develop an orientation analysis method for proteins immobilized on nanomaterials such as quantum dot particles, and to evaluate the orientation of streptavidin immobilized on quantum dot particles by means of TOF-SIMS. In order to detect fragment ions specific to the protein surface, a monoatomic primary ion source (Ga{sup +}) and a cluster ion source (Au{sub 3}{sup +}) were employed. Streptavidin-immobilized quantum dot particles were immobilized on aminosilanized ITO glass plates at amino groups by covalent bonding. The reference samples streptavidin directly immobilized on ITO plates were also prepared. All samples were dried with a freeze dryer before TOF-SIMS measurement. The positive secondary ion spectra of each sample were obtained using TOF-SIMS with Ga{sup +} and Au{sub 3}{sup +}, respectively, and then they were compared so as to characterize each sample and detect the surface structure of the streptavidin immobilized with the biotin-immobilized quantum dots. The chemical structures of the upper surface of the streptavidin molecules immobilized on the quantum dot particles were evaluated with TOF-SIMS spectra analysis. The indicated surface side of the streptavidin molecules immobilized on the quantum dots includes the biotin binding site.

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.

Growth and photovoltaic performance of SnS quantum dots

Energy Technology Data Exchange (ETDEWEB)

Deepa, K.G., E-mail: deepachaithanya@gmail.com [Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore (India); Nagaraju, J. [Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore (India)

2012-08-01

Highlights: Black-Right-Pointing-Pointer Orthorhombic SnS quantum dots are synthesized by chemical method. Black-Right-Pointing-Pointer HOMO-LUMO level alignments confirmed the electron transport from SnS to TiO{sub 2}. Black-Right-Pointing-Pointer Cell characteristics are analyzed with different size quantum dots. Black-Right-Pointing-Pointer FF increased drastically from 15 to 51% on adding a buffer layer to the structure. Black-Right-Pointing-Pointer The SnS QDSSC showed highest V{sub oc} of 504 mV and 2.3 mA/cm{sup 2}. - Abstract: Tin sulphide (SnS) quantum dots of size ranging from 2.4 to 14.4 nm are prepared by chemical precipitation method in aqueous media. Growth of the SnS particles is monitored by controlling the deposition time. Both XRD and SAED patterns confirm that the particles possess orthorhombic structure. The uncapped SnS particles showed secondary phases like Sn{sub 2}S{sub 3} and SnS{sub 2} which is visible in the SAED pattern. From the electrochemical characterization, HOMO-LUMO levels of both TiO{sub 2} and SnS are determined and the band alignment is found to be favorable for electron transfer from SnS to TiO{sub 2}. Moreover, the HOMO-LUMO levels varied for different particle sizes. Solar cell is fabricated by sensitizing porous TiO{sub 2} thin film with SnS QDs. Cell structure is characterized with and without buffer layer between FTO and TiO{sub 2}. Without the buffer layer, cell showed an open circuit voltage (V{sub oc}) of 504 mV and short circuit current density (J{sub sc}) of 2.3 mA/cm{sup 2} under AM1.5 condition. The low fill factor of this structure (15%) is seen to be increased drastically to 51%, on the incorporation of the buffer layer. The cell characteristics are analyzed using two different size quantum dots.

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.

Double capping of molecular beam epitaxy grown InAs/InP quantum dots studied by cross-sectional scanning tunneling microscopy

International Nuclear Information System (INIS)

Ulloa, J. M.; Koenraad, P. M.; Gapihan, E.; Letoublon, A.; Bertru, N.

2007-01-01

Cross-sectional scanning tunneling microscopy was used to study at the atomic scale the double capping process of self-assembled InAs/InP quantum dots (QDs) grown by molecular beam epitaxy on a (311)B substrate. The thickness of the first capping layer is found to play a mayor role in determining the final results of the process. For first capping layers up to 3.5 nm, the height of the QDs correspond to the thickness of the first capping layer. Nevertheless, for thicknesses higher than 3.5 nm, a reduction in the dot height compared to the thickness of the first capping layer is observed. These results are interpreted in terms of a transition from a double capping to a classical capping process when the first capping layer is thick enough to completely cover the dots

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics

KAUST Repository

Mora-Sero, Ivan; Bertoluzzi, Luca; Gonzalez-Pedro, Victoria; Gimenez, Sixto; Fabregat-Santiago, Francisco; Kemp, Kyle W.; Sargent, Edward H.; Bisquert, Juan

2013-01-01

Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells. © 2013 Macmillan Publishers Limited. All rights reserved.

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics

KAUST Repository

Mora-Sero, Ivan

2013-08-12

Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells. © 2013 Macmillan Publishers Limited. All rights reserved.

Optoelectronic devices, low temperature preparation methods, and improved electron transport layers

KAUST Repository

Eita, Mohamed S.

2016-08-04

An optoelectronic device such as a photovoltaic device which has at least one layer, such as an electron transport layer, which comprises a plurality of alternating, oppositely charged layers including metal oxide layers. The metal oxide can be zinc oxide. The plurality of layers can be prepared by layer-by-layer processing in which alternating layers are built up step-by-step due to electrostatic attraction. The efficiency of the device can be increased by this processing method compared to a comparable method like sputtering. The number of layers can be controlled to improve device efficiency. Aqueous solutions can be used which is environmentally friendly. Annealing can be avoided. A quantum dot layer can be used next to the metal oxide layer to form a quantum dot heterojunction solar device.

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

Resonant photoionization absorption spectra of spherical quantum dots

CERN Document Server

Bondarenko, V

2003-01-01

We study theoretically the mid-infrared photon absorption spectra due to bound-free transitions of electrons in individual spherical quantum dots. It is established that change of the dot size in one or two atomic layers or/and number of electrons by one or two can change the peak value of the absorption spectra in orders of magnitude and energy of absorbed photons by tens of millielectronvolts. The reason for this is the formation of specific free states, called resonance states. Numerical calculations are performed for quantum dots (QDs) with radius varying up to 200 A, and one to eight electrons occupying the two lowest bound states. It is supposed that realistic QD systems with resonance states would be of much advantage to design novel infrared QD photo-detectors.

Combination of short-length TiO{sub 2} nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantum-dot-sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zhengguo [School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 (China); School of Chemistry and Chemical Engineering, Beifang University of Nationalities, Yinchuan 750021 (China); Shi, Chengwu, E-mail: shicw506@foxmail.com [School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 (China); Chen, Junjun; Xiao, Guannan; Li, Long [School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 (China)

2017-07-15

Graphical abstract: The TiO{sub 2} nanorod array with the length of 600 nm, the diameter of 20 nm, the areal density of 500 μm{sup −2} was successfully prepared. The compact PbS quantum-dot thin film was firstly obtained on the TiO{sub 2} nanorod array by spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol. The photoelectric conversion efficiency (PCE) of the compact PbS quantum-dot thin film sensitized solar cells achieved 4.10% using spiro-OMeTAD as a hole transporting layer, while the PCE of the PbS quantum-dot sensitized solar cells was only 0.54%. - Highlights: • Preparation of TiO{sub 2} nanorod arrays with the length of 600 nm, diameter of 20 nm. • The compact PbS QD thin film and short-length TiO{sub 2} nanorod array were combined. • EDT addition improved PbS nanoparticle coverage and photovoltaic performance. • The compact PbS QD thin film sensitized solar cell achieved the PCE of 4.10%. - Abstract: Considering the balance of the hole diffusion length and the loading quantity of quantum-dots, the rutile TiO{sub 2} nanorod array with the length of 600 nm, the diameter of 20 nm, and the areal density of 500 μm{sup −2} is successfully prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 105 min. The compact PbS quantum-dot thin film on the TiO{sub 2} nanorod array is firstly obtained by the spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol (EDT). The result reveals that the strong interaction between lead and EDT is very important to control the crystallite size of PbS quantum-dots and obtain the compact PbS quantum-dot thin film on the TiO{sub 2} nanorod array. The all solid-state sensitized solar cell with the combination of the short-length, high-density TiO{sub 2} nanorod array and the compact PbS quantum-dot thin film achieves the photoelectric conversion

Layer-by-Layer technique employed to construct multitask interfaces in polymer composites

Directory of Open Access Journals (Sweden)

Luísa Sá Vitorino

Full Text Available Abstract The properties of glass fiber-reinforced polymer composites are closely related to the fiber-matrix interface. Interfacial treatments to improve mechanical properties are usually limited to enhance interfacial adhesion. In this work, Layer-by-Layer (LbL technique was introduced to build a novel interface in polymer composites. Different numbers of bilayers of poly(diallyldimethylammonium chloride and poly(sodium 4-styrenesulfonate with carbon nanotubes were deposited through LbL on the surface of woven glass fibers (GFs. Polypropylene composites containing the modified GFs were prepared by compression molding. Thermogravimetric analysis, scanning electron microscopy and Raman spectroscopy proved that multilayers of polymers with carbon nanotubes could be deposited on GFs surface. Mechanical tests on composites with modified GFs revealed an increase in Flexural Modulus and toughness. The overall results attested that the LbL technique can be used to design interfaces with different compositions to perform diverse tasks, such as to improve the stiffness of composites and to encapsulate active nanocomponents.

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

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

Optical properties of hybrid quantum-well–dots nanostructures grown by MOCVD

Energy Technology Data Exchange (ETDEWEB)

Mintairov, S. A., E-mail: mintairov@scell.ioffe.ru; Kalyuzhnyy, N. A.; Nadtochiy, A. M.; Maximov, M. V. [St. Petersburg Academic University (Russian Federation); Rouvimov, S. S. [University of Notre Dame (United States); Zhukov, A. E. [St. Petersburg Academic University (Russian Federation)

2017-03-15

The deposition of In{sub x}Ga{sub 1–x}As with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In{sub x}Ga{sub 1–x}As thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined.

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.

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.

Interfacial microstructure of partial transient liquid phase bonded Si3N4-to-Inconel 718 joints

International Nuclear Information System (INIS)

Kim, Jae Joong; Park, Jin-Woo; Eagar, Thomas W.

2003-01-01

This work presents transmission electron microscopy (TEM) analysis of the interfacial microstructure in Si 3 N 4 -to-Inconel 718 joints with Ni interlayers produced by partial transient liquid phase bonding (PTLPB). Ti and Cu microfoils have been inserted between Si 3 N 4 and the Ni interlayer and joining has been performed at lower temperatures than previous PTLPBs of Si 3 N 4 with the same insert metals. The TEM work is focused on phase identification of the reaction layers between the Si 3 N 4 and the Ni interlayer. According to the TEM analysis, most of the Cu precipitates without reacting with Ti and Ni. Si diffused in the filler metal and thin reaction layer formed at the interface between Si 3 N 4 and the filler metal producing good bond-formation and hence, high interfacial strength. No interfacial fractures occurred after cooling from the bonding temperature of 900 deg. C, which supports the results observed in the TEM analysis. This work confirms that this joining process can produce a more heat resistant Si 3 N 4 -to-Inconel 718 joint than active brazing using Ag-Cu-Ti alloys

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

Phase diagram of interfacial growth modes by vapor deposition and its application for ZnO nanostructures

Science.gov (United States)

Shu, Da-Jun; Xiong, Xiang; Liu, Ming; Wang, Mu

2017-09-01

Interfacial growth from vapor has been extensively studied. However, a straightforward picture of the growth mode under different growth conditions is still lacking. In this paper, we develop a comprehensive interfacial growth theory based on the stochastic approach. Using a critical interisland separation, we construct a general phase diagram of the growth modes. It has been revealed that if the Ehrlich-Schwoebel barrier EES is smaller than a critical value, the interfacial growth proceeds in a layer-by-layer (LBL) mode at any deposition rate. However, if EES is larger than the critical value, LBL growth occurs only at very small or very large deposition rates relative to the intralayer hopping rate, and multilayer (ML) growth occurs at a moderate deposition rate. Experiments with zinc oxide growth by chemical vapor deposition have been designed to qualitatively demonstrate the theoretical model. By changing the flux of the carrier gas (nitrogen gas) in chemical vapor deposition, we realize LBL, ML, and then reentrance of LBL homoepitaxial growth of ZnO successively. Moreover, we find that surface kinetics of ZnO is suppressed by decreasing oxygen partial pressure by comparing the experimental observations and theoretical models, which is supported by our recent first-principles calculations. Since the influence of the substrate and the growth species on growth can approximately be represented by binding energy and surface kinetics, we suggest that the phase diagram is essential for interfacial growth of different materials by vapor deposition.

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.

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.

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.

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)

Quantifying Interfacial pH Variation at Molecular Length Scales Using a Concurrent Non-Faradaic Reaction.

Science.gov (United States)

Ryu, Jaeyune; Wuttig, Anna; Surendranath, Yogesh

2018-05-15

We quantify changes in the interfacial pH local to the electrochemical double layer during electrocatalysis, using a concurrent non-faradaic probe reaction. In the absence of electrocatalysis, nanostructured Pt/C surfaces mediate the reaction of H2 with cis-2-butene-1,4-diol to form a mixture of 1,4-butanediol and n-butanol with a selectivity that is linearly dependent on the bulk solution pH. We show that kinetic branching occurs from a common surface-bound intermediate, ensuring that this probe reaction is uniquely sensitive to the interfacial pH within molecular length scales of the surface. We use the pH-dependent selectivity of this reaction to track changes in interfacial pH during concurrent hydrogen oxidation electrocatalysis and find that the local pH can vary dramatically, > 3 units, relative to the bulk value even at modest current densities in well-buffered electrolytes. This work highlights the key role that interfacial pH variation plays in modulating inner-sphere electrocatalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

From structure to spectra. Tight-binding theory of InGaAs quantum dots

International Nuclear Information System (INIS)

Goldmann, Elias

2014-01-01

Self-assembled semiconductor quantum dots have raised considerable interest in the last decades due to a multitude of possible applications ranging from carrier storage to light emitters, lasers and future quantum communication devices. Quantum dots offer unique electronic and photonic properties due to the three-dimensional confinement of charge carriers and the coupling to a quasi-continuum of wetting layer and barrier states. In this work we investigate the electronic structure of In x Ga 1-x As quantum dots embedded in GaAs, considering realistic quantum dot geometries and Indium concentrations. We utilize a next-neighbour sp 3 s * tight-binding model for the calculation of electronic single-particle energies and wave functions bound in the nanostructure and account for strain arising from lattice mismatch of the constituent materials atomistically. With the calculated single-particle wave functions we derive Coulomb matrix elements and include them into a configuration interaction treatment, yielding many-particle states and energies of the interacting many-carrier system. Also from the tight-binding single-particle wave functions we derive dipole transition strengths to obtain optical quantum dot emission and absorption spectra with Fermi's golden rule. Excitonic fine-structure splittings are obtained, which play an important role for future quantum cryptography and quantum communication devices for entanglement swapping or quantum repeating. For light emission suited for long-range quantum-crypted fiber communication InAs quantum dots are embedded in an In x Ga 1-x As strain-reducing layer, shifting the emission wavelength into telecom low-absorption windows. We investigate the influence of the strain-reducing layer Indium concentration on the excitonic finestructure splitting. The fine-structure splitting is found to saturate and, in some cases, even reduce with strain-reducing layer Indium concentration, a result being counterintuitively. Our result

From structure to spectra. Tight-binding theory of InGaAs quantum dots

Energy Technology Data Exchange (ETDEWEB)

Goldmann, Elias

2014-07-23

Self-assembled semiconductor quantum dots have raised considerable interest in the last decades due to a multitude of possible applications ranging from carrier storage to light emitters, lasers and future quantum communication devices. Quantum dots offer unique electronic and photonic properties due to the three-dimensional confinement of charge carriers and the coupling to a quasi-continuum of wetting layer and barrier states. In this work we investigate the electronic structure of In{sub x}Ga{sub 1-x}As quantum dots embedded in GaAs, considering realistic quantum dot geometries and Indium concentrations. We utilize a next-neighbour sp{sup 3}s{sup *} tight-binding model for the calculation of electronic single-particle energies and wave functions bound in the nanostructure and account for strain arising from lattice mismatch of the constituent materials atomistically. With the calculated single-particle wave functions we derive Coulomb matrix elements and include them into a configuration interaction treatment, yielding many-particle states and energies of the interacting many-carrier system. Also from the tight-binding single-particle wave functions we derive dipole transition strengths to obtain optical quantum dot emission and absorption spectra with Fermi's golden rule. Excitonic fine-structure splittings are obtained, which play an important role for future quantum cryptography and quantum communication devices for entanglement swapping or quantum repeating. For light emission suited for long-range quantum-crypted fiber communication InAs quantum dots are embedded in an In{sub x}Ga{sub 1-x}As strain-reducing layer, shifting the emission wavelength into telecom low-absorption windows. We investigate the influence of the strain-reducing layer Indium concentration on the excitonic finestructure splitting. The fine-structure splitting is found to saturate and, in some cases, even reduce with strain-reducing layer Indium concentration, a result being

A Method for Promoting Assembly of Metallic and Nonmetallic Nanoparticles into Interfacial Monolayer Films.

Science.gov (United States)

Xu, Yikai; Konrad, Magdalena P; Lee, Wendy W Y; Ye, Ziwei; Bell, Steven E J

2016-08-10

Two-dimensional metal nanoparticle arrays are normally constructed at liquid-oil interfaces by modifying the surfaces of the constituent nanoparticles so that they self-assemble. Here we present a general and facile new approach for promoting such interfacial assembly without any surface modification. The method use salts that have hydrophobic ions of opposite charge to the nanoparticles, which sit in the oil layer and thus reduce the Coulombic repulsion between the particles in the organic phase, allowing the particles to sit in close proximity to each other at the interface. The advantage of this method is that because it does not require the surface of the particles to be modified it allows nonmetallic particles including TiO2 and SiO2 to be assembled into dense interfacial layers using the same procedure as is used for metallic particles. This opens up a route to a new family of nanostructured functional materials.

Valley-orbit hybrid states in Si quantum dots

Science.gov (United States)

Gamble, John; Friesen, Mark; Coppersmith, S. N.

2013-03-01

The conduction band for electrons in layered Si nanostructures oriented along (001) has two low-lying valleys. Most theoretical treatments assume that these valleys are decoupled from the long-wavelength physics of electron confinement. In this work, we show that even a minimal amount of disorder (a single atomic step at the quantum well interface) is sufficient to mix valley states and electron orbitals, causing a significant distortion of the long-wavelength electron envelope. For physically realistic electric fields and dot sizes, this valley-orbit coupling impacts all electronic states in Si quantum dots, implying that one must always consider valley-orbit hybrid states, rather than distinct valley and orbital degrees of freedom. We discuss the ramifications of our results on silicon quantum dot qubits. This work was supported in part by ARO (W911NF-08-1-0482) and NSF (DMR-0805045).

Factors influencing epitaxial growth of three-dimensional Ge quantum dot crystals on pit-patterned Si substrate

International Nuclear Information System (INIS)

Ma, Y J; Zhong, Z; Yang, X J; Fan, Y L; Jiang, Z M

2013-01-01

We investigated the molecular beam epitaxy growth of three-dimensional (3D) Ge quantum dot crystals (QDCs) on periodically pit-patterned Si substrates. A series of factors influencing the growth of QDCs were investigated in detail and the optimized growth conditions were found. The growth of the Si buffer layer and the first quantum dot (QD) layer play a key role in the growth of QDCs. The pit facet inclination angle decreased with increasing buffer layer thickness, and its optimized value was found to be around 21°, ensuring that all the QDs in the first layer nucleate within the pits. A large Ge deposition amount in the first QD layer favors strain build-up by QDs, size uniformity of QDs and hence periodicity of the strain distribution; a thin Si spacer layer favors strain correlation along the growth direction; both effects contribute to the vertical ordering of the QDCs. Results obtained by atomic force microscopy and cross-sectional transmission electron microscopy showed that 3D ordering was achieved in the Ge QDCs with the highest ever areal dot density of 1.2 × 10 10 cm −2 , and that the lateral and the vertical interdot spacing were ∼10 and ∼2.5 nm, respectively. (paper)

Factors influencing epitaxial growth of three-dimensional Ge quantum dot crystals on pit-patterned Si substrate.

Science.gov (United States)

Ma, Y J; Zhong, Z; Yang, X J; Fan, Y L; Jiang, Z M

2013-01-11

We investigated the molecular beam epitaxy growth of three-dimensional (3D) Ge quantum dot crystals (QDCs) on periodically pit-patterned Si substrates. A series of factors influencing the growth of QDCs were investigated in detail and the optimized growth conditions were found. The growth of the Si buffer layer and the first quantum dot (QD) layer play a key role in the growth of QDCs. The pit facet inclination angle decreased with increasing buffer layer thickness, and its optimized value was found to be around 21°, ensuring that all the QDs in the first layer nucleate within the pits. A large Ge deposition amount in the first QD layer favors strain build-up by QDs, size uniformity of QDs and hence periodicity of the strain distribution; a thin Si spacer layer favors strain correlation along the growth direction; both effects contribute to the vertical ordering of the QDCs. Results obtained by atomic force microscopy and cross-sectional transmission electron microscopy showed that 3D ordering was achieved in the Ge QDCs with the highest ever areal dot density of 1.2 × 10(10) cm(-2), and that the lateral and the vertical interdot spacing were ~10 and ~2.5 nm, respectively.

High efficiency of the spin-orbit torques induced domain wall motion in asymmetric interfacial multilayered Tb/Co wires

International Nuclear Information System (INIS)

Bang, Do; Awano, Hiroyuki

2015-01-01

We investigated current-induced DW motion in asymmetric interfacial multilayered Tb/Co wires for various thicknesses of magnetic and Pt-capping layers. It is found that the driving mechanism for the DW motion changes from interfacial to bulk effects at much thick magnetic layer (up to 19.8 nm). In thin wires, linearly depinning field dependence of critical current density and in-plane field dependence of DW velocity suggest that the extrinsic pinning governs field-induced DW motion and injecting current can be regarded as an effective field. It is expected that the high efficiency of spin-orbit torques in thick magnetic multilayers would have important implication for future spintronic devices based on in-plane current induced-DW motion or switching

High efficiency of the spin-orbit torques induced domain wall motion in asymmetric interfacial multilayered Tb/Co wires