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Sample records for cdse quantum dot

  1. Amphoteric CdSe nanocrystalline quantum dots.

    Science.gov (United States)

    Islam, Mohammad A

    2008-06-25

    The nanocrystal quantum dot (NQD) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied a DC voltage across the pair, thin films of CdSe NQDs were deposited on both the positive and the negative electrodes. Extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: (1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, (2) there are equal numbers of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited dots is at least an order of magnitude higher than the number of initially charged dots, indicating regeneration. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of the CdSe NQDs.

  2. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum

    Directory of Open Access Journals (Sweden)

    Takaaki Yamaguchi

    2016-10-01

    Full Text Available CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were precipitated in the intracellular space, indicating that cadmium and selenium ions were incorporated into the cell and that the quantum dots were synthesized with intracellular metabolites. To reveal differences in F. oxysporum metabolism, cell extracts of F. oxysporum, before and after CdSe synthesis, were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE. The results suggested that the amount of superoxide dismutase (SOD decreased after CdSe synthesis. Fluorescence microscopy revealed that cytoplasmic superoxide increased significantly after CdSe synthesis. The accumulation of superoxide may increase the expression of various metabolites that play a role in reducing Se4+ to Se2− and inhibit the aggregation of CdSe to make nanoparticles.

  3. L-Cysteine Capped CdSe Quantum Dots Synthesized by Photochemical Route.

    Science.gov (United States)

    Singh, Avinash; Kunwar, Amit; Rath, M C

    2018-05-01

    L-cysteine capped CdSe quantum dots were synthesized via photochemical route in aqueous solution under UV photo-irradiation. The as grown CdSe quantum dots exhibit broad fluorescence at room temperature. The CdSe quantum dots were found to be formed only through the reactions of the precursors, i.e., Cd(NH3)2+4 and SeSO2-3 with the photochemically generated 1-hydroxy-2-propyl radicals, (CH3)2COH radicals, which are formed through the process of H atom abstraction by the photoexcited acetone from 2-propanol. L-Cysteine was found to act as a suitable capping agent for the CdSe quantum dots and increases their biocompatability. Cytotoxicty effects of these quantum dots were evaluated in Chinese Hamster Ovary (CHO) epithelial cells, indicated a significant lower level for the L-cysteine capped CdSe quantum dots as compare to the bare ones.

  4. Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

    International Nuclear Information System (INIS)

    Isnaeni,; Yulianto, Nursidik; Suliyanti, Maria Margaretha

    2016-01-01

    We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantum dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.

  5. Composition-controlled optical properties of colloidal CdSe quantum dots

    International Nuclear Information System (INIS)

    Ayele, Delele Worku; Su, Wei-Nien; Chou, Hung-Lung; Pan, Chun-Jern; Hwang, Bing-Joe

    2014-01-01

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties

  6. Composition-controlled optical properties of colloidal CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ayele, Delele Worku [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Department of Chemistry, Bahir Dar University, Bahir Dar (Ethiopia); Su, Wei-Nien, E-mail: wsu@mail.ntust.edu.tw [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Chou, Hung-Lung [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Pan, Chun-Jern [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Hwang, Bing-Joe, E-mail: bjh@mail.ntust.edu.tw [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China)

    2014-12-15

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.

  7. Fabrication of CdSe quantum dots/permutite luminescent materials

    Indian Academy of Sciences (India)

    Permutite incorporating CdSe in mesopores has been prepared with a simple route. Firstly, mercaptosuccinic acid-capped CdSe quantum dots (QDs) were prepared in aqueous solution by using SeO2 as selenium source and NaBH4 as reductant. Secondly, the commercial permutite was treated with acetic acid to induce a ...

  8. Thiolated graphene - a new platform for anchoring CdSe quantum dots for hybrid heterostructures

    Science.gov (United States)

    Debgupta, Joyashish; Pillai, Vijayamohanan K.

    2013-04-01

    Effective organization of small CdSe quantum dots on graphene sheets has been achieved by a simple solution exchange with thiol terminated graphene prepared by diazonium salt chemistry. This generic methodology of CdSe QD attachment to any graphene surface has remarkable implications in designing hybrid heterostructures.Effective organization of small CdSe quantum dots on graphene sheets has been achieved by a simple solution exchange with thiol terminated graphene prepared by diazonium salt chemistry. This generic methodology of CdSe QD attachment to any graphene surface has remarkable implications in designing hybrid heterostructures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00363a

  9. Switching CdSe quantum dot luminescence with a-Si:H.

    Science.gov (United States)

    Di Vece, M; van Duren, S N F; van den Heuvel, D J; Mitoraj, D; Kuang, Y; Gerritsen, H C; Schropp, R E I

    2013-08-09

    Dynamical control of the luminescence of quantum dots is highly important for technology in the field of telecommunication, displays, and photovoltaics. In this work we use an a-Si:H solar cell structure in which CdSe quantum dots are sandwiched. By applying a positive potential over the device, charge carriers generated in the quantum dots are transported to the a-Si:H layer and transformed into electrical energy, changing the luminescence intensity with a switching time lower than 60 ms. This is a promising new step towards using quantum dots in optical switching devices.

  10. Aqueous synthesis and characterization of TGA-capped CdSe quantum dots at freezing temperature.

    Science.gov (United States)

    Sun, Qizhuang; Fu, Shasha; Dong, Tingmei; Liu, Shuxian; Huang, Chaobiao

    2012-07-11

    CdSe quantum dots (QDs) have traditionally been synthesized in organic phase and then transferred to aqueous solution by functionalizing their surface with silica, polymers, short-chain thiol ligands, or phospholipid micelles. However, a drastic increase in the hydrodynamic size and biotoxicity of QDs may hinder their biomedical applications. In this paper, the TGA-capped CdSe QDs are directly synthesized in aqueous phase at freezing temperature, and they prove to possess high QY (up to 14%).

  11. Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots

    Science.gov (United States)

    Tohgha, Urice; Deol, Kirandeep K.; Porter, Ashlin G.; Bartko, Samuel G.; Choi, Jung Kyu; Leonard, Brian M.; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2014-01-01

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand. PMID:24200288

  12. Green wet chemical route to synthesize capped CdSe quantum dots

    Indian Academy of Sciences (India)

    cadmium selenide quantum dots (CdSe QDs) employing chemical bath deposition (CBD) method. The mechanism of capping using ... more, the process can be operated under open atmosphere. (Chang and Lee 2007). Here, we report ... kept in bath at 65. ◦. C for. 1 h. In order to control the pH further, appropriate amount of.

  13. Green wet chemical route to synthesize capped CdSe quantum dots

    Indian Academy of Sciences (India)

    In the present work, we report green synthesis of tartaric acid (TA) and triethanolamine (TEA) capped cadmium selenide quantum dots (CdSe QDs) employing chemical bath deposition (CBD) method. The mechanism of capping using non-toxic binary capping agents is also discussed. Stable QDs of various sizes were ...

  14. Application of CdSe quantum dots for the direct detection of TNT.

    Science.gov (United States)

    Yi, Kui-Yu

    2016-02-01

    CdSe quantum dots were synthesized through a simple, green organic-phase method. Paraffin was used as the reaction solvent and a reducing agent, oleic acid was the reaction ligand, and oleyl amine was the stabilizer. Based on the phenomenon of TNT quenched oil-soluble CdSe quantum dot fluorescence, a simple, fast, and direct method of TNT detection was established. Under optimum conditions, the degree of fluorescence quenching of oil-soluble CdSe quantum dots had a good linear correlation with TNT concentration in the 1.0×10(-7)-5.0×10(-5) mol/L range, and the correlation coefficient was 0.9990. TNT detection limit was 2.1×10(-8)mol/L. The method was successfully used to determine TNT-explosion dust samples, results were satisfactory. The fluorescence quenching mechanism of oil-soluble CdSe quantum dots by TNT was also discussed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  15. Green wet chemical route to synthesize capped CdSe quantum dots

    Indian Academy of Sciences (India)

    Green wet chemical route to synthesize capped CdSe quantum dots. A OUDHIA and P BICHPURIA. ∗. Department of Physics, Government VYT PG Autonomous College, Durg 491 001, India. MS received 25 November 2012; revised 13 February 2013. Abstract. In the present work, we report green synthesis of tartaric acid ...

  16. Fabrication of CdSe quantum dots/permutite luminescent materials

    Indian Academy of Sciences (India)

    Administrator

    tosuccinic acid-capped CdSe quantum dots (QDs) were prepared in aqueous solution by using SeO2 as selenium source and NaBH4 as reductant. Secondly, the commercial permutite was treated with acetic acid to induce a partial dealumnization, which can introduce a large number of intracrystal mesopores, and the.

  17. Cytotoxicity testing of bare CdSe quantum dots and their encapsulated structure

    Science.gov (United States)

    Kumari, Asha; Singh, Ragini Raj

    2017-07-01

    In this work we have synthesized CdSe quantum dots (QDs) and their polymer encapsulated structures by wet chemical method for cytotoxicity testing. These QDs were synthesized by using aqueous solvent to make them hydrophilic because we want to use these for bioimaging purpose. The cytotoxicity is major concern to use these quantum dots in bio application because these are made up of heavy metal ions so to make these QDs nontoxic and to improve their optical properties we encapsulated these QDs by polymers. Thereafter we have studied the cytotoxicity of CdSe QDs and their polymer encapsulated structure.MTT method (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method) was used to study toxicity of QDs toward MDCK epithelial cell line. Effect of encapsulation on optical properties was analyzed by Photoluminescence spectroscopy. QDs encapsulated with polymer possess improved optical properties with greater fluorescence intensity and lesser cytotoxicity as compare to bare CdSe.

  18. Sulforaphane Protects the Liver against CdSe Quantum Dot-Induced Cytotoxicity.

    Directory of Open Access Journals (Sweden)

    Wei Wang

    Full Text Available The potential cytotoxicity of cadmium selenide (CdSe quantum dots (QDs presents a barrier to their use in biomedical imaging or as diagnostic and therapeutic agents. Sulforaphane (SFN is a chemoprotective compound derived from cruciferous vegetables which can up-regulate antioxidant enzymes and induce apoptosis and autophagy. This study reports the effects of SFN on CdSe QD-induced cytotoxicity in immortalised human hepatocytes and in the livers of mice. CdSe QDs induced dose-dependent cell death in hepatocytes with an IC50 = 20.4 μM. Pre-treatment with SFN (5 μM increased cell viability in response to CdSe QDs (20 μM from 49.5 to 89.3%. SFN induced a pro-oxidant effect characterized by depletion of intracellular reduced glutathione during short term exposure (3-6 h, followed by up-regulation of antioxidant enzymes and glutathione levels at 24 h. SFN also caused Nrf2 translocation into the nucleus, up-regulation of antioxidant enzymes and autophagy. siRNA knockdown of Nrf2 suggests that the Nrf2 pathway plays a role in the protection against CdSe QD-induced cell death. Wortmannin inhibition of SFN-induced autophagy significantly suppressed the protective effect of SFN on CdSe QD-induced cell death. Moreover, the role of autophagy in SFN protection against CdSe QD-induced cell death was confirmed using mouse embryonic fibroblasts lacking ATG5. CdSe QDs caused significant liver damage in mice, and this was decreased by SFN treatment. In conclusion, SFN attenuated the cytotoxicity of CdSe QDs in both human hepatocytes and in the mouse liver, and this protection was associated with the induction of Nrf2 pathway and autophagy.

  19. Enhanced photoluminescence of corrugated Al2O3 film assisted by colloidal CdSe quantum dots.

    Science.gov (United States)

    Bai, Zhongchen; Hao, Licai; Zhang, Zhengping; Huang, Zhaoling; Qin, Shuijie

    2017-05-19

    We present the enhanced photoluminescence (PL) of a corrugated Al 2 O 3 film enabled by colloidal CdSe quantum dots. The colloidal CdSe quantum dots are fabricated directly on a corrugated Al 2 O 3 substrate using an electrochemical deposition (ECD) method in a microfluidic system. The photoluminescence is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the electron transfer from the conduction band of the CdSe quantum dots to that of Al 2 O 3 , the enhanced photoluminescence effect is observed, which results from the increase in the recombination rate of electrons and holes on the Al 2 O 3 surface and the reduction in the fluorescence of the CdSe quantum dots. A periodically-fluctuating fluorescent spectrum was exhibited because of the periodical wire-like corrugated Al 2 O 3 surface serving as an optical grating. The spectral topographic map around the fluorescence peak from the Al 2 O 3 areas covered with CdSe quantum dots was unique and attributed to the uniform deposition of CdSe QDs on the corrugated Al 2 O 3 surface. We believe that the microfluidic ECD system and the surface enhanced fluorescence method described in this paper have potential applications in forming uniform optoelectronic films of colloidal quantum dots with controllable QD spacing and in boosting the fluorescent efficiency of weak PL devices.

  20. Quantum Dots Sensitized Solar Cell: Effect of CdSe Nanoparticles Purification Procedure of QD Sensitized Photoanodes

    International Nuclear Information System (INIS)

    Yaacob, K A; Ishak, M N; Alias, N N

    2013-01-01

    In this research the effect of purification of CdSe nanoparticles for application in quantum dots sensitized solar cells (QDSSC) photoanodes are studied. The CdSe nanoparticles are attached to the titanium dioxide surface using a linker based approached (CdSe nanoparticles disperse in toluene) and direct mode attachment (CdSe re-disperse in dichloromethane (DCM)). Colloidal CdSe nanoparticles with estimated size of 3.0 nm were synthesized by hot injection method in trioctylphosphine oxide (TOPO) as stabilizing solvent. Prior to the sensitization, the CdSe nanoparticles were purified using a common purification step involving the alternate cycles of precipitation / redispersion in non-polar solvent and polar solvent. With increasing the number of purification, the concentrations of CdSe nanoparticles attached to the titanium dioxide were also increased; from 2.47 × 10 15 dots/cc for 3 × wash CdSe nanoparticles to 3.70 × 10 15 dots/cc for 4 × wash CdSe nanoparticles. Polysulfide electrolyte and Cu 2 S counterelectrodes were used to assemble a complete QDSSC. The highest efficiency of 0.05% was obtained from 4 × wash CdSe nanoparticles; V oc = 0.2V, J sc = 0.34 mA/cm 2 and FF = 0.07).

  1. Optical performance evolutions of reductive glutathione coated CdSe quantum dots in different environments

    International Nuclear Information System (INIS)

    Wang Lili; Jiang Jisen

    2011-01-01

    Optical performances of reductive glutathione coated CdSe quantum dots were studied under different ageing conditions. The enhancements of luminescence were obviously occurred for the samples ageing under illumination. The quantum yield of CdSe was enhanced continuously over 44 days at room temperature, and reached as high as 36.6%. O 2 was proved to make a certain contribute to the enhancement. The evolutions of the systems during the ageing time were deduced according to the variations of pH values with ageing time and the XRD results of the samples ageing in air with illumination. We conferred that the reduction of surface defects resulted from the photo-induced decomposition of CdSe quantum dots was the main reason for the enhancement of fluorescence. The production of CdO as a result of the surface reaction with O 2 made contributions to the enhancement for a certain extent. The curves of quantum yield versus ageing time were fitted with a stretched exponential function. It was found that the course of fluorescence enhancement accorded with the dynamics of system with strongly coupled hierarchical degrees of freedom.

  2. 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

  3. 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

  4. Multicolored silica coated CdSe core/shell quantum dots

    Science.gov (United States)

    Goftman, Valentina V.; Markin, Alexey V.; De Saeger, Sarah; Goryacheva, Irina Y.

    2016-04-01

    Silanization is a convenient route to provide water-solubility to the quantum dots (QDs) with different structure. Green, orange and red emitting CdSe-based QDs were synthesized by varying of number and material of wider-band gap shells and fluorescent properties of QDs were characterized before and after silanization. It was shown that structure of the QD influences on the quantum yield of the silanized QDs: the better CdSe core is protected with wider-band gap semiconductor shells, the more fluorescence properties remain after silica coated QD possess. Hence silica coated QDs have a great perspectives for the multiplex analysis.

  5. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Xingsheng, E-mail: xsxu@semi.ac.cn [State Key Laboratory of Integration Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China)

    2015-03-02

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

  6. Directed Energy Transfer in Films of CdSe Quantum Dots: Beyond the Point Dipole Approximation

    DEFF Research Database (Denmark)

    Zheng, Kaibo; Zídek, Karel; Abdellah, Mohamed

    2014-01-01

    Understanding of Förster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size...... of QDs, so that the simple point-dipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using...

  7. Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices

    Science.gov (United States)

    Bera, Susnata; Singh, Shashi B.; Ray, S. K.

    2012-05-01

    Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage (˜2.2 V) .The EL peak intensity was found to increase by increasing the operating current.

  8. Optical properties and the use of CdSe quantum dot for biolabeling applications

    International Nuclear Information System (INIS)

    Tran Hong Nhung; Nguyen Thi Van; Vu Xuan Hoa; Pham Minh Tan; Tong Kim Thuan; Tran Thi Thu Thuy; Jean Claude Brochon; Patrick Tauc

    2008-01-01

    The quantum dots CdSe type Qtracker 565 and 605 of Quantum Dot Company have been investigated by size, chemical structure and optical properties. The Qtracker 605 QDs were introduced into Lipomyces Starkeyi yeast cells. It was found that for the young cells (36 h of culture), the labeling QDs are mainly located in vacuoles, and the emission remains narrow with the maximum is clearly around 605 nm. For age cells (96 h of culture), the labeling QDs are concentrated in the cell cytoplasm, the emission is broaden with the maximum shifted to 580 nm. The live cell image was still observed after two months of introduction. The Qtracker 605 QDs were also successfully introduced into mouse blood cancerous cells. (author)

  9. Comparison of three empirical force fields for phonon calculations in CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Kelley, Anne Myers [Chemistry and Chemical Biology, University of California, Merced, 5200 North Lake Road, Merced, California 95343 (United States)

    2016-06-07

    Three empirical interatomic force fields are parametrized using structural, elastic, and phonon dispersion data for bulk CdSe and their predictions are then compared for the structures and phonons of CdSe quantum dots having average diameters of ~2.8 and ~5.2 nm (~410 and ~2630 atoms, respectively). The three force fields include one that contains only two-body interactions (Lennard-Jones plus Coulomb), a Tersoff-type force field that contains both two-body and three-body interactions but no Coulombic terms, and a Stillinger-Weber type force field that contains Coulombic interactions plus two-body and three-body terms. While all three force fields predict nearly identical peak frequencies for the strongly Raman-active “longitudinal optical” phonon in the quantum dots, the predictions for the width of the Raman peak, the peak frequency and width of the infrared absorption peak, and the degree of disorder in the structure are very different. The three force fields also give very different predictions for the variation in phonon frequency with radial position (core versus surface). The Stillinger-Weber plus Coulomb type force field gives the best overall agreement with available experimental data.

  10. Interaction of the CdSe quantum dots with plant cell walls.

    Science.gov (United States)

    Djikanović, Daniela; Kalauzi, Aleksandar; Jeremić, Milorad; Xu, Jianmin; Mićić, Miodrag; Whyte, Jeffrey D; Leblanc, Roger M; Radotić, Ksenija

    2012-03-01

    There is an increasing application of quantum dots (QDs) in plant science, as markers for the cells or their cell walls (CWs). In a plant cell the CW is a first target place for external agents. We studied interaction of CdSe QDs with CWs isolated from a conifer -Picea omorika (Panč) Purkynĕ branch. Binding of CdSe QDs was followed by using fluorescence microscopy, fluorescence and FT-IR spectroscopy. The aim of the study was to see whether the QDs induce structural changes in the CW, as well as to find out which kind of interactions between QDs and CWs occur and to which particular constituent polymers QDs preferably bind. The isolated CW is an appropriate object for study of the interactions with nanoparticles. The results show that in the CW, CdSe predominantly binds to cellulose, via OH groups and to lignin, via the conjugated CC/C-C chains. The differences in interaction of wet and dry CWs with QDs/chloroform were also studied. In the reaction of the dry CW sample with QDs/chloroform, hydrophobic interactions are dominant. When water was added after QDs/chloroform, hydrophilic interactions enable a partial reconstruction of the CC chains. The results have an implication on the use of the QDs in plant bio-imaging. Copyright © 2011 Elsevier B.V. All rights reserved.

  11. Synthesis and characterization of CdSe quantum dots dispersed in PVA matrix by chemical route

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Zubair M. S. H.; Ganaie, Mohsin; Husain, M.; Zulfequar, M., E-mail: mzulfe@rediffmail.com [Department of Physics, Jamia Millia Islamia, New Delhi-110025 (India); Khan, Shamshad A. [Department of Physics St. Andrews College, Gorakhpur-273001,U.P,-India (India)

    2016-05-23

    CdSe quantum dots using polyvinyl alcohol as a capping agent have been synthesized via a simple heat induced thermolysis technique. The structural analysis of CdSe/PVA thin film was studied by X-ray diffraction, which confirms crystalline nature of the prepared film. The surface morphology and particle size of the prepared sample was studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The SEM studies of CdSe/PVA thin film shows the average size of particles in the form of clusters of several quantum dots in the range of 10-20 nm. The morphology of CdSe/PVA thin film was further examined by TEM. The TEM image shows the fringes of tiny dots with average sizes of 4-7 nm. The optical properties of CdSe/PVA thin film were studied by UV-VIS absorption spectroscopy. The CdSe/PVA quantum dots follow the role of direct transition and the optical band gap is found to be 4.03 eV. From dc conductivity measurement, the observed value of activation energy was found to be 0.71 eV.

  12. Hyperbranched polyether hybrid nanospheres with CdSe quantum dots incorporated for selective detection of nitric oxide

    DEFF Research Database (Denmark)

    Liu, Shuiping; Jin, Lanming; Chronakis, Ioannis S.

    2014-01-01

    In this work, hybrid nanosphere vehicles consisting of cadmium selenide quantum dots (CdSe QDs) were synthesized for nitric oxide (NO) donating and real-time detecting. The nanospheres with QDs being encapsulation have spherical outline with dimension of ~127 nm. The fluorescence properties...

  13. A Suitable Polysulfide Electrolyte for CdSe Quantum Dot-Sensitized Solar Cells

    Directory of Open Access Journals (Sweden)

    H. K. Jun

    2013-01-01

    Full Text Available A polysulfide liquid electrolyte is developed for the application in CdSe quantum dot-sensitized solar cells (QDSSCs. A solvent consisting of ethanol and water in the ratio of 8 : 2 by volume has been found as the optimum solvent for preparing the liquid electrolytes. This solvent ratio appears to give higher cell efficiency compared to pure ethanol or water as a solvent. Na2S and S give rise to a good redox couple in the electrolyte for QDSSC operation, and the optimum concentrations required are 0.5 M and 0.1 M, respectively. Addition of guanidine thiocyanate (GuSCN to the electrolyte further enhances the performance. The QDSSC with CdSe sensitized electrode prepared using 7 cycles of successive ionic layer adsorption and reaction (SILAR produces an efficiency of 1.41% with a fill factor of 44% on using a polysulfide electrolyte of 0.5 M Na2S, 0.1 M S, and 0.05 M GuSCN in ethanol/water (8 : 2 by volume under the illumination of 100 mW/cm2 white light. Inclusion of small amount of TiO2 nanoparticles into the electrolyte helps to stabilize the polysulfide electrolyte and thereby improve the stability of the CdSe QDSSC. The CdSe QDs are also found to be stable in the optimized polysulfide liquid electrolyte.

  14. Intense Visible Luminescence in CdSe Quantum Dots by Efficiency Surface Passivation with H2O Molecules

    Directory of Open Access Journals (Sweden)

    Hyeoung Woo Park

    2012-01-01

    Full Text Available We have investigated the effect of water (H2O cooling and heat treatment on the luminescence efficiency of core CdSe quantum dots (QDs. The photoluminescence (PL quantum yield of the CdSe QDs was enhanced up to ~85%, and some periodic bright points were observed in wide color ranges during the heat treatment of QDs mixed with H2O. The PL enhancement of QDs could be attributed to the recovery of QDs surface traps by unreacted ligands confined within the hydrophilic H2O molecule containers.

  15. Spatially-resolved luminescence spectroscopy of CdSe quantum dots synthesized in ionic liquid crystal matrices

    International Nuclear Information System (INIS)

    Magaryan, K.A.; Mikhailov, M.A.; Karimullin, K.R.; Knyazev, M.V.; Eremchev, I.Y.; Naumov, A.V.; Vasilieva, I.A.; Klimusheva, G.V.

    2016-01-01

    The paper is devoted to investigation of luminescence properties of new quantum dot (QD)-doped materials. We studied CdSe QDs (1.8 nm and 2.3 nm) grown inside of a liquid crystalline cadmium alcanoate matrix. Temperature dependence of parameters of fluorescence spectra obtained in a wide temperature range using epi-luminescence microscopy technique was analyzed. Spatially-resolved luminescence images were measured for the areas of the samples of 150×150 µm 2 . Strong correlation between fluorescence spectra and sample structure was observed. - Highlights: • Glassy matrix with CdSe quantum dots inside fabricated in liquid crystalline mesophase. • Study of luminescence properties in a wide range of low temperatures. • Strong dependence of the luminescence spectra on spatial inhomogeneities. • Spatially-resolved luminescence imaging of quantum dots in liquid crystalline matrix.

  16. Interactions between water-soluble CdSe quantum dots and gold nanoparticles studied by UV-visible absorption spectroscopy.

    Science.gov (United States)

    Han, Heyou; Cai, Yawen; Liang, Jiangong; Sheng, Zonghai

    2007-06-01

    The interaction of water-soluble CdSe quantum dots (QDs) with gold (Au) nanoparticles was investigated by ultraviolet visible absorption spectroscopy. The results showed that the aggregation of Au nanoparticles was induced by CdSe QDs. The influences of factors such as the size of Au nanoparticles, acidity, buffer concentration and the concentration ratio of the CdSe QDs to Au nanoparticles were each investigated. The comparison of two different particle sizes (16 and 25 nm) of Au nanoparticles that interact with CdSe QDs in the solution showed that the aggregation of small Au nanoparticles (16 nm) is easier than that of big Au nanoparticles (25 nm). At pH 7.0 phosphate buffer solution (0.02 M), the optimal molar ratio of CdSe:Au is about 3100:1 according to calculations.

  17. Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

    DEFF Research Database (Denmark)

    Leistikow, M.D.; Johansen, Jeppe; Kettelarij, A.J.

    2009-01-01

    , allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. We manage to obtain the oscillator strength of the important class of CdSe quantum dots...

  18. Multiexciton Absorption and Multiple Exciton Generation in CdSe Quantum Dots

    Science.gov (United States)

    Franceschetti, Alberto; Zhang, Yong

    2008-04-01

    Efficient multiple-exciton generation (MEG) in semiconductor quantum dots has been recently reported. The MEG efficiency has so far been evaluated assuming that the change (bleaching) of the absorption spectrum due to MEG is linearly proportional to the number of excitons NX. Here, we critically examine this assumption using atomistic pseudopotential calculations for colloidal CdSe nanocrystals. We find that the bleaching of the first absorption peak depends nonlinearly on NX, due to carrier-carrier interactions. This nonlinearity mandates an upper bound of 1.5 to the value of the normalized bleaching that can be attributed to MEG, significantly smaller than the limit of 2.0 predicted by the linear scaling assumption. Thus, measured values of the normalized bleaching in excess of 1.5 cannot be due entirely to MEG, but must originate in part from other mechanisms.

  19. Surface defect assisted broad spectra emission from CdSe quantum dots for white LED application

    Science.gov (United States)

    Samuel, Boni; Mathew, S.; Anand, V. R.; Correya, Adrine Antony; Nampoori, V. P. N.; Mujeeb, A.

    2018-02-01

    This paper reports, broadband photoluminescence from CdSe quantum dots (QDs) under the excitation of 403 nm using fluorimeter and 403 nm CW laser excitation. The broad spectrum obtained from the colloidal quantum dots was ranges from 450 nm to 800 nm. The broadness of the spectra was attributed to the merging of band edge and defect driven emissions from the QDs. Six different sizes of particles were prepared via kinetic growth method by using CdO and elemental Se as sources of Cd and Se respectively. The particle sizes were measured from TEM images. The size dependent effect on broad emission was also studied and the defect state emission was found to be predominant in very small QDs. The defect driven emission was also observed to be redshifted, similar to the band edge emission, due to quantum confinement effect. The emission corresponding to different laser power was also studied and a linear relation was obtained. In order to study the colour characteristics of the emission, CIE chromaticity coordinate, CRI and CCT of the prepared samples were measured. It is observed that, these values were tunable by the addition of suitable intensity of blue light from the excitation source to yield white light of various colour temperatures. The broad photoluminescence spectrum of the QDs, were compared with that of a commercially available white LED. It was found that the prepared QDs are good alternatives for the phosphor in phosphor converted white LEDs, to provide good spectral tunability.

  20. Binding mechanism of CdSe quantum dots to carbon nanotubes/graphene

    Science.gov (United States)

    Jiang, Jie; Ismail-Beigi, Sohrab

    2013-03-01

    Decorating carbon nanotube or graphene with CdSe quantum dots (QDs) is one approach to creating next generation high efficiency photovoltaics. We have used first principles methods to calculate the binding mechanisms of oleic acid (OA) to CdSe QDs as well as how -COOH functional groups can link the QD to graphene. In both cases, the strongest binding involves the terminating double-bonded oxygen atom in the -COOH group covalently bonding to a surface Cd atom while the hydrogen (from the OH part of the -COOH) aligns to make a weak hydrogen-like bond to a neighboring surface Se. We find a strong defect enhanced binding of the QD to graphene via -COOH: when the -COOH links the QD to a defect site on the graphene, the binding energy of the complex is 0.5 eV larger than when a -COOH links the QD to a pristine graphene region. These results are consistent with available edge X-ray absorption fine structure (EXAFS) data and also rationalize the growth procedure by which ultrasonication of the OA functionalized QDs leads to the replacement of some QD-OA bonds by QD-COOH-graphene bonds, which strongly link the QDs to the graphene surface.

  1. Passivation of CdSe Quantum Dots by Graphene and MoS2 Monolayer Encapsulation

    Science.gov (United States)

    Zhang, Datong; Wang, Dennis Zi-Ren; Creswell, Richard C.; Lu, Chenguang; Herman, Irving P.

    The encapsulation of a monolayer of CdSe quantum dots (QDs) by one-to-three layer graphene and MoS2 sheets protects the QDs from oxidation. Photoluminescence (PL) from the QD cores shows a much slower decrease in core diameter over time due to slower oxidation in regions where the QDs are covered by van der Waals (vdW) layers than in those where they are not, for chips stored both in the dark and in the presence of light. PL mapping shows that the CdSe QDs under the central part of the vdW sheet age slower than those near its edges, because oxidation of the covered QDs is limited by transport of oxygen from the edges of the vdW sheets and not transport across the vdW layers. This encapsulation effect is also tested with other environments. Preliminary results show that vdW materials could be promising candidates for nano-coating materials for devices operating in extreme environments.

  2. Incorporation of Mn2+ into CdSe quantum dots by chemical bath co-deposition method for photovoltaic enhancement of quantum dot-sensitized solar cells.

    Science.gov (United States)

    Zhang, Chenguang; Liu, Shaowen; Liu, Xingwei; Deng, Fei; Xiong, Yan; Tsai, Fang-Chang

    2018-03-01

    A photoelectric conversion efficiency (PCE) of 4.9% was obtained under 100 mW cm -2 illumination by quantum-dot-sensitized solar cells (QDSSCs) using a CdS/Mn : CdSe sensitizer. CdS quantum dots (QDs) were deposited on a TiO 2 mesoporous oxide film by successive ionic layer absorption and reaction. Mn 2+ doping into CdSe QDs is an innovative and simple method-chemical bath co-deposition, that is, mixing the Mn ion source with CdSe precursor solution for Mn : CdSe QD deposition. Compared with the CdS/CdSe sensitizer without Mn 2+ incorporation, the PCE was increased from 3.4% to 4.9%. The effects of Mn 2+ doping on the chemical, physical and photovoltaic properties of the QDSSCs were investigated by energy dispersive spectrometry, absorption spectroscopy, photocurrent density-voltage characteristics and electrochemical impedance spectroscopy. Mn-doped CdSe QDs in QDSSCs can obtain superior light absorption, faster electron transport and slower charge recombination than CdSe QDs.

  3. Direct assembly of in situ templated CdSe quantum dots via crystalline lamellae structure of polyamide 66

    Science.gov (United States)

    Cheval, Nicolas; Brooks, Richard; Fahmi, Amir

    2012-03-01

    A simple concept is proposed for templating in situ synthesised CdSe quantum dots (QDs) into an organised nano-pattern using the crystalline lamellae structure of polyamide 66 (PA66). The morphology obtained for PA66 and the hybrid material on Si/SiO x solid substrate was characterised by means of atomic force microscope. Controlling the PA66 concentration in solution and the organic-inorganic interactions are found to be the keys factors to direct the assembly of CdSe QDs along the PA66 linear crystalline structure. This simple approach could be opened a new avenue for a large spectrum of innovative high-tech applications.

  4. Synthesis and characterization of optic properties of CdSe and CdSe/ZnS quantum dots

    Directory of Open Access Journals (Sweden)

    Brayan Stiven Gómez Piñeros

    2018-01-01

    Full Text Available CdSe and CdSe/ZnS (core/shell quantum dots with oleic acid as stabilizing agent in organic medium were prepared and their optical properties were examined. For CdSe synthesis, the influence of O2 in the growth kinetics of quantum dots was determined. In the first 90 s, the nanocrystals growth was 1.6 higher in presence of O2 than when reaction was carried out in N2 atmosphere. However, the growth rate with O2 is not favorable because the nanocrystal optical properties were affected: wider absorption band and lower fluorescence that those obtained in inert atmosphere. Properties of CdSe nanocrystals synthesized in inert atmosphere were intensified with 10% of monolayer. For a core with 2.5 nm diameter, the fluorescence quantum yield (ΦFl in the green region increased from 5.5% to 42.3%. In this work, a low Zn2+ (diethylzinc precursor concentration was used to produce a. The synthesis process of CdSe / ZnS nanocrystals developed with low concentration of Zn2+ and an excess of S2- can be used to obtain materials with excellent photoluminescent properties for applications such as biomarkers, sensors, catalysis, and solar cells.

  5. Bio-templated CdSe quantum dots green synthesis in the functional protein, lysozyme, and biological activity investigation

    International Nuclear Information System (INIS)

    Wang, Qisui; Li, Song; Liu, Peng; Min, Xinmin

    2012-01-01

    Bifunctional fluorescence (CdSe Quantum Dots) – protein (Lysozyme) nanocomposites were synthesized at room temperature by a protein-directed, solution-phase, green-synthetic method. Fluorescence (FL) and absorption spectra showed that CdSe QDs were prepared successfully with Lyz. The average particle size and crystalline structure of QDs were investigated by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively. With attenuated total reflection-fourier transform infrared (ATR-FTIR) spectra and thermogravimetric (TG) analysis, it was confirmed that there is interaction between QDs and amide I, amide II groups in Lyz. FL polarization was measured and FL imaging was done to monitor whether QDs could be responsible for possible changes in the conformation and activity of Lyz. Interestingly, the results showed Lyz still retain the biological activity after formation of QDs, but the secondary structure of the Lyz was changed. And the advantage of this synthesis method is producing excellent fluorescent QDs with specifically biological function. -- Highlights: ► Lysozyme-directed green synthesis of CdSe quantum dots. ► Lysozyme still retain the biological activity after formation of CdSe. ► The method is the production of fluorescent QDs with highly specific and functions.

  6. Electrochemiluminescent detection of Pb{sup 2+} by graphene/gold nanoparticles and CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Liping, E-mail: lipinglu@bjut.edu.cn; Guo, Linqing; Li, Jiao; Kang, Tianfang; Cheng, Shuiyuan

    2016-12-01

    Highlights: • An ECL sensor was fabricated based on the distance dependent between CdSe QDs and gold nanoparticles. • The ssDNA strands rich in G bases adopt the G4 conformation when Pb{sup 2+} is present in detection system. • AuNPs/RGO composite improved the performance of electron transfer of sensor. • The ECL sensor was used to detect Pb{sup 2+} concentration in an actual water sample with high sensitivity and selectivity. - Abstract: A highly sensitive electrochemiluminescent detection method for lead ions (Pb(II)) was fabricated based on the distance-dependent quenching of the electrochemiluminescence from CdSe quantum dots by nanocomposites of graphene and gold nanoparticles. Graphene/gold nanoparticles were electrochemically deposited onto a glassy carbon electrode through the constant potential method. Thiol-labeled DNA was then assembled on the surface of the electrode via gold−sulfur bonding, following which the amino-labeled terminal of the DNA was linked to carboxylated CdSe quantum dots by the formation of amide bonds. The 27-base aptamer was designed with two different domains: the immobilization and detection sequences. The immobilization sequence was paired with 12 complementary bases and immobilized on the gold electrode; the single-stranded detection sequence, rich in G bases, formed a G-quadruplex (G4) structure in the presence of Pb{sup 2+}. The formation of G4 shortens the distance between the CdSe quantum dots and the Au electrode, which decreases the electrochemiluminescent intensity in a linear fashion, proportional to the concentration of Pb(II). The linear range of the sensor was 10{sup −10} to 10{sup −8} mol/L (R = 0.9819) with a detection limit of 10{sup −10} mol/L. This sensor detected Pb(II) in real water samples with satisfactory results.

  7. Exciton diamagnetic shift and optical properties in CdSe nanocrystal quantum dots in magnetic fields

    Science.gov (United States)

    Wu, Shudong; Cheng, Liwen

    2018-04-01

    The magnetic field dependence of the optical properties of CdSe nanocrystal quantum dots (NQDs) is investigated theoretically using a perturbation method within the effective-mass approximation. The results show that the magnetic field lifts the degeneracy of the electron (hole) states. A blue-shift in the absorption spectra of m ≥ 0 exciton states is observed while the absorption peak of m magnetic field strength B. This is attributed to the interplay of the orbital Zeeman effect and the additive confinement induced by the magnetic field. The excitonic absorption coefficient is almost independent of B in the strong confinement regime. The applied magnetic field causes the splitting of degenerated exciton states, resulting in the new absorption peaks. Based on the first-order perturbation theory, we propose the analytical expressions for the exciton binding energy, exciton transition energy and exciton diamagnetic shift of 1s, 1p-1, 1p0, 1p1, 1d-2, 1d-1, 1d0, 1d1, 1d2 and 2s exciton states on the applied magnetic field in the strong confinement regime.

  8. Concentration-dependent binding of CdSe quantum dots on the SH3 domain.

    Science.gov (United States)

    Bell, David R; Kang, Seung-Gu; Huynh, Tien; Zhou, Ruhong

    2017-12-21

    Quantum dots (QDs) are being used increasingly in applications for solar panels, consumer electronics, and biomedical imaging. For biomedical applications, QDs are typically coated with a biocompatible molecule for the system of interest. Experiments have indicated a QD dose-dependent and surface coating-dependent toxicity, with a portion of the toxicity being ascribed to interference with biomolecules. In this work, the interaction of trioctylphosphine oxide (TOPO) coated (CdSe) 13 QDs with the SRC homology 3 domain (SH3) protein domain are explored using molecular dynamics simulations. The results of this research agree well with experiments that show that at the lowest concentration, the QDs have little affinity for the native proline-rich motif (PRM) binding site of SH3. At higher concentrations, the QDs aggregate and increasingly prefer the PRM binding site, indicating that the normal SH3 function is impeded. This binding dependence is attributed to changes in the local density of the surface coated TOPO molecules upon aggregation. These results present possible interesting QD toxicity patterns and reveal the interdependence between dose and surface coating effects in QD toxicity.

  9. Formation of a Colloidal CdSe and ZnSe Quantum Dots via a Gamma Radiolytic Technique

    Directory of Open Access Journals (Sweden)

    Aeshah Salem

    2016-09-01

    Full Text Available Colloidal cadmium selenide (CdSe and zinc selenide (ZnSe quantum dots with a hexagonal structure were synthesized by irradiating an aqueous solution containing metal precursors, poly (vinyl pyrrolidone, isopropyl alcohol, and organic solvents with 1.25-MeV gamma rays at a dose of 120 kGy. The radiolytic processes occurring in water result in the nucleation of particles, which leads to the growth of the quantum dots. The physical properties of the CdSe and ZnSe nanoparticles were measured by various characterization techniques. X-ray diffraction (XRD was used to confirm the nanocrystalline structure, energy-dispersive X-ray spectroscopy (EDX was used to estimate the material composition of the samples, transmission electron microscopy (TEM was used to determine the morphologies and average particle size distribution, and UV-visible spectroscopy was used to measure the optical absorption spectra, from which the band gap of the CdSe and ZnSe nanoparticles could be deduced.

  10. Synthesis, optical characterization, and size distribution determination by curve resolution methods of water-soluble CdSe quantum dots

    International Nuclear Information System (INIS)

    Santos, Calink Indiara do Livramento; Carvalho, Melissa Souza; Raphael, Ellen; Ferrari, Jefferson Luis; Schiavon, Marco Antonio; Dantas, Clecio

    2016-01-01

    In this work a colloidal approach to synthesize water-soluble CdSe quantum dots (QDs) bearing a surface ligand, such as thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), glutathione (GSH), or thioglycerol (TGH) was applied. The synthesized material was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-Vis), and fluorescence spectroscopy (PL). Additionally, a comparative study of the optical properties of different CdSe QDs was performed, demonstrating how the surface ligand affected crystal growth. The particles sizes were calculated from a polynomial function that correlates the particle size with the maximum fluorescence position. Curve resolution methods (EFA and MCR-ALS) were employed to decompose a series of fluorescence spectra to investigate the CdSe QDs size distribution and determine the number of fraction with different particle size. The results for the MPA-capped CdSe sample showed only two main fraction with different particle sizes with maximum emission at 642 and 686 nm. The calculated diameters from these maximum emission were, respectively, 2.74 and 3.05 nm. (author)

  11. Synthesis, optical characterization, and size distribution determination by curve resolution methods of water-soluble CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Calink Indiara do Livramento; Carvalho, Melissa Souza; Raphael, Ellen; Ferrari, Jefferson Luis; Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.br [Universidade Federal de Sao Joao del-Rei (UFSJ), MG (Brazil). Grupo de Pesquisa em Quimica de Materiais; Dantas, Clecio [Universidade Estadual do Maranhao (LQCINMETRIA/UEMA), Caxias, MA (Brazil). Lab. de Quimica Computacional Inorganica e Quimiometria

    2016-11-15

    In this work a colloidal approach to synthesize water-soluble CdSe quantum dots (QDs) bearing a surface ligand, such as thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), glutathione (GSH), or thioglycerol (TGH) was applied. The synthesized material was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-Vis), and fluorescence spectroscopy (PL). Additionally, a comparative study of the optical properties of different CdSe QDs was performed, demonstrating how the surface ligand affected crystal growth. The particles sizes were calculated from a polynomial function that correlates the particle size with the maximum fluorescence position. Curve resolution methods (EFA and MCR-ALS) were employed to decompose a series of fluorescence spectra to investigate the CdSe QDs size distribution and determine the number of fraction with different particle size. The results for the MPA-capped CdSe sample showed only two main fraction with different particle sizes with maximum emission at 642 and 686 nm. The calculated diameters from these maximum emission were, respectively, 2.74 and 3.05 nm. (author)

  12. Direct assembly of in situ templated CdSe quantum dots via crystalline lamellae structure of polyamide 66

    Energy Technology Data Exchange (ETDEWEB)

    Cheval, Nicolas; Brooks, Richard [University of Nottingham, Division of Materials, Mechanics and Structures, Faculty of Engineering (United Kingdom); Fahmi, Amir, E-mail: Amir.Fahmi@hochschule-Rhein-waal.de [Rhein-Waal University of Applied Sciences, Faculty of Technology and Bionics (Germany)

    2012-03-15

    A simple concept is proposed for templating in situ synthesised CdSe quantum dots (QDs) into an organised nano-pattern using the crystalline lamellae structure of polyamide 66 (PA66). The morphology obtained for PA66 and the hybrid material on Si/SiO{sub x} solid substrate was characterised by means of atomic force microscope. Controlling the PA66 concentration in solution and the organic-inorganic interactions are found to be the keys factors to direct the assembly of CdSe QDs along the PA66 linear crystalline structure. This simple approach could be opened a new avenue for a large spectrum of innovative high-tech applications.

  13. Assembly of CdSe nanoparticles on graphene for low-temperature fabrication of quantum dot sensitized solar cell

    Science.gov (United States)

    Sun, Shengrui; Gao, Lian; Liu, Yangqiao; Sun, Jing

    2011-02-01

    Quantum dot sensitized solar cell (QDSSC) was fabricated in a low-temperature process based on graphene-CdSe composite, which was prepared by the procedures of immobilizing CdSe on graphene oxide (GO) and reduction in GO. It was found that the charge separation between excited CdSe and graphene could be tapped to generate photocurrent from photocurrent measurements, which established the ability of graphene to collect and transport electrons. By optimizing the CdSe-to-GO ratio at 4.5:1, the obtained graphene-CdSe-based cells exhibited significantly higher short-circuit photocurrent and energy conversion efficiency (5.8 mA/cm2 and 0.72%, respectively) than the reported values of the C60 or carbon nanotube related QDSSC, demonstrating that the graphene-CdSe composite is an attractive candidate in energy conversion devices.

  14. Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots

    Science.gov (United States)

    Zhu, Huiguang; Prakash, Arjun; Benoit, Denise N.; Jones, Christopher J.; Colvin, Vicki L.

    2010-06-01

    Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core-shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 °C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on the solubility of the metal salts used to form shells; their inclusion in the precursor solutions, which use thiourea as a sulfur source, can lead to homogeneous and fully dissolved solutions. Upon addition to suspensions of quantum dot cores, these precursors deposit as uniform shells; the lowest temperature for shell growth (65 °C) yields the thinnest shells (d forms thicker shells (d ~ 1-2 nm). The growth of the shell structures, average particle size, size distribution, and shape were examined using optical spectroscopy, transmission electron microscopy, x-ray diffraction, and transmittance small angle x-ray scattering. The photoluminescence quantum yield (QY) of the as-prepared CdSe/ZnS quantum dots ranged from 26% to 46% as compared to 10% for the CdSe cores. This method was further generalized to CdZnS shells by mixing cadmium and zinc acetate precursors. The CdSe/CdZnS nanocrystals have a thicker shell and higher QY (40% versus 36%) as compared to the CdSe/ZnS prepared under similar conditions. These low temperature methods for shell growth are readily amenable to scale-up and can provide a route for economical and less energy intensive production of quantum dots.

  15. Quenching of coumarin emission by CdSe and CdSe/ZnS quantum dots: Implications for fluorescence reporting

    International Nuclear Information System (INIS)

    Baride, Aravind; Engebretson, Daniel; Berry, Mary T.; Stanley May, P.

    2013-01-01

    The photoinduced release of highly fluorescent 7-diethylamino coumarin (7DEAC) from CdSe quantum dots (QD) modified with a thiocinnamate ligand (11-mercapto undecyl-E-3-(4-(N,N-diethylamino)-2-hydroxy phenyl) propenoate, [4DEATC]) has been previously described. Coumarin fluorescence was used to ‘report’ the photochemical reaction. The current study quantifies the quenching effect of the QDs on the coumarin emission in this system. A systematic study is presented on the quenching of 7DEAC by CdSe and CdSe/ZnS quantum dots capped with 2-[2-(2-methoxyethoxy)ethoxy] ethanethiol (PEG-thiol). A new method for the functionalization of CdSe and CdSe/ZnS QDs with PEG-thiol was developed, which does not require isolation of the as-synthesized QDs. Stern–Volmer analysis was applied to quantify the effect of the PEG-CdSe and PEG-CdSe/ZnS on 7DEAC emission. The Stern–Volmer constant, K SV , was shown to be inversely proportional to temperature for quenching by PEG-CdSe, and the fluorescence lifetime of 7DEAC was shown to be independent of PEG-CdSe concentration. Room-temperature K SV values were similar for the PEG-CdSe and PEG-CdSe/ZnS quenchers. The large magnitude of K SV , the temperature dependence of K SV , the lifetime data, and the similarity of K SV values for the core and core–shell QD quenchers are all consistent with a static quenching mechanism. Assuming a static quenching mechanism, the temperature dependence of the coumarin-QD binding constant, K b , was used to estimate the ΔH and ΔS for the binding process. -- Highlights: • Quenching of a coumarin derivative by CdSe and CdSe/ZnS quantum dots is demonstrated • Stern–Volmer analysis is performed as a function of temperature • Fluorescence lifetime analysis was used to support Stern–Volmer analysis • Data overwhelmingly support quenching via a Static Mechanism • Quenching of coumarin by quantum dots is significant and must be considered in any release and report scheme

  16. Optical and Structural Investigation of CdSe Quantum Dots Dispersed in PVA Matrix and Photovoltaic Applications

    Directory of Open Access Journals (Sweden)

    Pallabi Phukan

    2013-01-01

    Full Text Available CdSe quantum dots (QDs dispersed in polyvinyl alcohol (PVA matrix with their sizes within the quantum dot regime have been synthesized via a simple heat induced thermolysis technique. The effect of the concentrations of the cadmium source on the optical properties of CdSe/PVA thin films was investigated through UV-Vis absorption spectroscopy. The structural analysis and particle size determination as well as morphological studies of the CdSe/PVA nanocomposite thin films were done with the help of X-ray diffraction (XRD and transmission electron microscopy (TEM. The XRD analysis reveals that CdSe/PVA nanocomposite thin film has a hexagonal (wurtzite structure. A prototype thin film solar cell of CdSe/CdTe has been synthesized and its photovoltaic parameters were measured.

  17. CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture

    International Nuclear Information System (INIS)

    Ung, Thi Dieu Thuy; Tran, Thi Kim Chi; Pham, Thu Nga; Nguyen, Quang Liem; Nguyen, Duc Nghia; Dinh, Duy Khang

    2012-01-01

    This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ∼500 and 700 nm with the luminescence quantum yield (LQY) of 30–85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml −1 . For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3–50 ng μl −1 with a detection limit of 3 ng μL −1 has been performed based on the antibody-antigen recognition. (review)

  18. CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture

    Science.gov (United States)

    Dieu Thuy Ung, Thi; Tran, Thi Kim Chi; Nga Pham, Thu; Nghia Nguyen, Duc; Khang Dinh, Duy; Liem Nguyen, Quang

    2012-12-01

    This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ˜500 and 700 nm with the luminescence quantum yield (LQY) of 30-85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml-1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3-50 ng μl-1 with a detection limit of 3 ng μL-1 has been performed based on the antibody-antigen recognition.

  19. Synthesis of CdSe colloidal quantum dots and quantum transitions under action of low power optical excitation

    International Nuclear Information System (INIS)

    Geru, I.I.; Mirzac, A.V.; Tarabukin, A.B.

    2013-01-01

    CdSe colloidal quantum dots were synthesized at low temperature (80-85 0C) on the basis of chemical reactions in colloidal solutions using trioctylphosphine (TOP), pure Se, oleic acid and cadmium acetate Cd(CH 3 COO) 2 . The average size of the synthesized nanocrystals is 2.04 nm, that is less then exciton Bohr radius in the bulk material, which is equal to 5.6 nm. Therefore in such QDs the electron with spin ? and the hole with total angular momentum 3/2 are in localized or slightly delocalized states. In absorption spectra in the UV-VIS range the lines corresponding to quantum transitions between hole state 1S 3/2 (h), 2S 3/2 (h), 1P 3/2 (h) and electron state 1S 1/2 (e), 1P 1/2 (1S 3/2 (h)→1S 1/2 (e), 2S 3/2 (h)→1S 1/2 (e) and 1P 3/2 (h) →1P 1/2 (e)) are detected. The location of photoluminescence maxima of QDs in hexane and in powder state coincide in the limits of experimental errors (570 and 568 nm, respectively). In photoluminescence spectra of powder QDs a broad long-wavelength band of low intensity with maximum at 570 nm was detected. (authors)

  20. Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

    Science.gov (United States)

    Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

    2016-06-15

    Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs.

  1. Poly(3-hexylthiophene) - CdSe quantum dot bulk heterojunction solar cells: Influence of the functional end-group of the polymer

    KAUST Repository

    Palaniappan, Kumaranand

    2009-06-23

    The synthesis of H/thiol terminated P3HT from Br/allyl-terminated P3HT precursor was analyzed. The photovoltaic response of blends were prepared of H/thiol terminated P3HT with spherical CdSe quantum dots(QD) and compares the results with regioregular H/Br and Br/aryl-terminated P3HT. Phase segregation was carried by mixing relatively polar pyridine treated CdSe QD with nonpolar P3HT. The experiment revealed that a high loading of CdSe is necessary for an efficient charge transport and different loading ratios of CdSe has been investigated to correlate the photovoltaic response as a function of ration between donor H/thiol-P3ht polymer and acceptor Cdse QD. The results show that H/Br-P3HT, H/thiol- and Br/allyl-terminated P3HT exhibits better performance and Cdse quantum dots were used to obtain results.

  2. Non-volatile resistive memory device fabricated from CdSe quantum dot embedded in thermally grown In2O3 nanostructure by oblique angle deposition

    Science.gov (United States)

    Kannan, V.; Kim, Hyun-Seok; Park, Hyun-Chang

    2016-11-01

    In this paper we report In2O3/CdSe quantum dot based non-volatile resistive memory device with ON/OFF ratio ∼1000. Indium nanostructures were grown by oblique angle deposition technique in a thermal evaporator. Indium oxide nanostructures had size ranging from 20 nm to 100 nm as observed from TEM and AFM methods. The facile device fabricated with a layer of CdSe quantum dot on indium oxide film exhibited excellent endurance characteristics over 100,000 switching cycles. Retention tests showed good stability for over 4000 s. Memory operating mechanism is proposed based on charge trapping/de-trapping in quantum dots with indium oxide acting as barrier leading to Coulomb blockade. The mechanism is supported by negative differential resistance (NDR) observed exclusively in the ON state.

  3. Morphologically controlled electrodeposition of CdSe on mesoporous TiO2 film for quantum dot-sensitized solar cells

    International Nuclear Information System (INIS)

    Song, Xiaohui; Wang, Minqiang; Zhang, Hao; Deng, Jianping; Yang, Zhi; Ran, Chenxin; Yao, Xi

    2013-01-01

    Highlights: • CdSe QDs were deposited onto mesoporous TiO 2 film via a one-step electrodeposition method. • The morphology and microstructure of TiO 2 /CdSe photoanodes can be controlled by electrodeposition current density. • A ZnS coating layer and thermal annealing could further enhance the performance of the TiO 2 /CdSe photoanodes. • A maximum power conversion efficiency of 2.72% was achieved with the optimum TiO 2 /CdSe/ZnS photoanodes. -- Abstract: CdSe quantum dots (QDs)-sensitized mesoporous TiO 2 (TiO 2 /CdSe) films were fabricated using a facile one-step electrodeposition method in an aqueous electrolyte. This technique has the advantage of being simple, low cost, and easily scalable to the sensitization of large-area panels. By adjusting the electrodeposition current density, the morphology and microstructure of the prepared TiO 2 /CdSe films can be precisely controlled, which influences the photovoltaic performances of quantum dot-sensitized solar cells based on the TiO 2 /CdSe films. At a moderate current density of 0.2 mA cm −2 , CdSe QDs can penetrate deep into the inner pores of the mesoporous TiO 2 film, thus leading to a dense and uniform distribution of QDs throughout the whole TiO 2 matrix, while higher current densities result in growth of larger, isolated CdSe nanoclusters. Furthermore, a ZnS passivation layer coated on TiO 2 /CdSe photoanodes and thermal annealing could significantly improve the photovoltaic performance. As a result, a quantum dot-sensitized solar cell based on a TiO 2 /CdSe/ZnS photoanode (350 °C, 30 min calcination), polysulfide electrolyte and Pt counter electrode achieves a power conversion efficiency of 2.72% under AM 1.5 G one sun illumination

  4. CdSe quantum dot in vertical ZnSe nanowire and photonic wire for efficient single-photon emission

    DEFF Research Database (Denmark)

    Cremel, Thibault; Bellet-Amalric, Edith; Cagnon, Laurent

    We’ve recently demonstrated that a CdSe quantum dot (QD) in a ZnSe nanowire (NW) can emit triggered single photons up to room temperature [1]. In this contribution, we present the possibilities of enhancing the photon emission and collection in such NW-QDs structures for a realistic application...... as a single photon source. We have grown vertically oriented ZnSe NWs (with typical diameter of 10 nm) by molecular beam epitaxy on a ZnSe(111)B buffer layer. The growth of a ZnMgSe passivating shell increases the (otherwise weak) ZnSe near-band-edge luminescence by two orders of magnitude. This has allowed...

  5. Comparative experiments of graphene covalently and physically binding CdSe quantum dots to enhance the electron transport in flexible photovoltaic devices

    Science.gov (United States)

    Jung, Mi-Hee; Chu, Moo-Jung

    2014-07-01

    In this research, we prepared composite films via covalent coupling of CdSe quantum dots (QDs) to graphene through the direct binding of aryl radicals to the graphene surface. To compare the carrier transport with the CdSe aryl binding graphene film, we prepared CdSe pyridine capping graphene films through the pi-pi interactions of noncovalent bonds between the graphene and pyridine molecules. The photovoltaic devices were fabricated from the two hybrid films using the electrophoretic deposition method on flexible substrates. Even though the two hybrid films have the same amount of QDs and graphene, time-resolved fluorescence emission decay results show that the emission lifetime of the CdSe aryl group binding graphene film is significantly shorter than that of the pyridine capping CdSe-graphene. The quantum efficiency and photocurrent density of the device fabricated from CdSe aryl binding graphene were also higher than those of the device fabricated from pyridine capping CdSe-graphene. These results indicated that the carrier transport of the QD-graphene system is not related to the additive effect from the CdSe and graphene components but rather is a result of the unique interactions between the graphene and QDs. We could expect that these results can be useful in designing QD-graphene composite materials, which are applied in photovoltaic devices.

  6. Comparative experiments of graphene covalently and physically binding CdSe quantum dots to enhance the electron transport in flexible photovoltaic devices.

    Science.gov (United States)

    Jung, Mi-Hee; Chu, Moo-Jung

    2014-08-07

    In this research, we prepared composite films via covalent coupling of CdSe quantum dots (QDs) to graphene through the direct binding of aryl radicals to the graphene surface. To compare the carrier transport with the CdSe aryl binding graphene film, we prepared CdSe pyridine capping graphene films through the pi-pi interactions of noncovalent bonds between the graphene and pyridine molecules. The photovoltaic devices were fabricated from the two hybrid films using the electrophoretic deposition method on flexible substrates. Even though the two hybrid films have the same amount of QDs and graphene, time-resolved fluorescence emission decay results show that the emission lifetime of the CdSe aryl group binding graphene film is significantly shorter than that of the pyridine capping CdSe-graphene. The quantum efficiency and photocurrent density of the device fabricated from CdSe aryl binding graphene were also higher than those of the device fabricated from pyridine capping CdSe-graphene. These results indicated that the carrier transport of the QD-graphene system is not related to the additive effect from the CdSe and graphene components but rather is a result of the unique interactions between the graphene and QDs. We could expect that these results can be useful in designing QD-graphene composite materials, which are applied in photovoltaic devices.

  7. Citrate-capped quantum dots of CdSe for the selective photometric detection of silver ions in aqueous solutions

    International Nuclear Information System (INIS)

    Ingole, Pravin P.; Abhyankar, Rajiv M.; Prasad, B.L.V.; Haram, Santosh K.

    2010-01-01

    A simple strategy for the synthesis of water soluble, luminescent, citrate-capped CdSe quantum dots (Q-CdSe) and their applications to selective detection of silver ions are described. The steady state photoluminescence (PL) spectra show single, narrow emission band at ca. 554 nm without any contribution from the trap states. The effect of various ions including physiologically important metal ions (viz. K + , Ca 2+ , Fe 3+ , Zn 2+ , Mg 2+ , Mn 2+ , Cu 2+ , Ag + , Pb 2+ and Cd 2+ ), on the PL intensity of citrate-capped Q-CdSe has been studied. Among these, selective luminescence quenching with Ag + ion was found to be predominant. Under the optimum conditions, the response was linear between 1.7 and 18 μM. The quenching constant K SV was found to be ca. 3.4 x 10 5 M -1 . The mechanism of photoluminescence quenching of Q-CdSe by metal ions (Ag + ) is also discussed. Based on these studies, the potential use of Q-CdSe as a luminescent probe for the selective detection of silver ion has been proposed. -- Graphical abstract: A simple strategy for the synthesis of water soluble, luminescent, citrate-capped quantum dots of CdSe (Q-CdSe) has been developed. The effect of various ions including physiologically important metal ions (viz. K + , Ca 2+ , Fe 3+ , Zn 2+ , Mg 2+ , Mn 2+ , Cu 2+ , Ag + , Pb 2+ and Cd 2+ ), on the luminescence intensity of citrate-capped Q-CdSe has been studied. Among these, a significant luminescence quenching only by Ag + ions was observed which suggests the potential use of Q-CdSe as a luminescent sensor for the selective optical detection of silver ions in a physiological condition.

  8. Formulating CdSe quantum dots for white light-emitting diodes with high color rendering index

    Energy Technology Data Exchange (ETDEWEB)

    Li, Fei [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); University of Chinese Academy of Sciences, Beijing 100190 (China); Li, Wan-Nan [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Fu, Shao-Yun, E-mail: syfu@mail.ipc.ac.cn [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Xiao, Hong-Mei [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-10-25

    Generation of white light using CdSe quantum dots (QDs) alone presents exciting possibilities for solid state lighting technology. In this work, Cd(Ac){sub 2}·2H{sub 2}O and Na{sub 2}SeSO{sub 3} are used as precursors to synthesize CdSe-QDs with an average diameter ranging from 2.77 to 4.65 nm at the low temperature from 60 to 180 °C. Smaller CdSe-QDs with an average diameter of 2.29 nm are got by an oxidation etching process using H{sub 2}O{sub 2} as oxidant. The structural and optical properties of these QDs are investigated and proper formulation of CdSe QDs with various sizes is carefully designed to achieve white light with a high color rendering index (CRI). It is observed for the first time that the as-prepared white light-emitting diodes from single CdSe-QDs show the Commission Inernationale del’Eclairage coordinate (CIE) of (0.30,0.34) very close to that (0.33,0.33) of pure white light and a high CRI of 84. Owing to these advantages, the as-prepared white light-emitting diodes from a single compound are promising for lighting applications. - Highlights: • CdSe-quantum dots (QDs) with a continuously changing size from 2.31 to 4.74 nm are prepared. • The obtained CdSe-QDs emit lights with tunable colors in the whole visible range. • The obtained mixture sample generates white light with a high color rendering index of 84. • The sample yields white light with the CIE coordinate (0.30, 0.34) very close to that of pure white light.

  9. Formulating CdSe quantum dots for white light-emitting diodes with high color rendering index

    International Nuclear Information System (INIS)

    Li, Fei; Li, Wan-Nan; Fu, Shao-Yun; Xiao, Hong-Mei

    2015-01-01

    Generation of white light using CdSe quantum dots (QDs) alone presents exciting possibilities for solid state lighting technology. In this work, Cd(Ac) 2 ·2H 2 O and Na 2 SeSO 3 are used as precursors to synthesize CdSe-QDs with an average diameter ranging from 2.77 to 4.65 nm at the low temperature from 60 to 180 °C. Smaller CdSe-QDs with an average diameter of 2.29 nm are got by an oxidation etching process using H 2 O 2 as oxidant. The structural and optical properties of these QDs are investigated and proper formulation of CdSe QDs with various sizes is carefully designed to achieve white light with a high color rendering index (CRI). It is observed for the first time that the as-prepared white light-emitting diodes from single CdSe-QDs show the Commission Inernationale del’Eclairage coordinate (CIE) of (0.30,0.34) very close to that (0.33,0.33) of pure white light and a high CRI of 84. Owing to these advantages, the as-prepared white light-emitting diodes from a single compound are promising for lighting applications. - Highlights: • CdSe-quantum dots (QDs) with a continuously changing size from 2.31 to 4.74 nm are prepared. • The obtained CdSe-QDs emit lights with tunable colors in the whole visible range. • The obtained mixture sample generates white light with a high color rendering index of 84. • The sample yields white light with the CIE coordinate (0.30, 0.34) very close to that of pure white light

  10. Linear and nonlinear optical properties of functionalized CdSe quantum dots prepared by plasma sputtering and wet chemistry.

    Science.gov (United States)

    Humbert, Christophe; Dahi, Abdellatif; Dalstein, Laetitia; Busson, Bertrand; Lismont, Marjorie; Colson, Pierre; Dreesen, Laurent

    2015-05-01

    We develop an innovative manufacturing process, based on radio-frequency magnetron sputtering (RFMS), to prepare neat CdSe quantum dots (QDs) on glass and silicon substrates and further chemically functionalize them. In order to validate the fabrication protocol, their optical properties are compared with those of QDs obtained from commercial solutions and deposited by wet chemistry on the substrates. Firstly, AFM measurements attest that nano-objects with a mean diameter around 13 nm are located on the substrate after RFMS treatment. Secondly, the UV-Vis absorption study of this deposited layer shows a specific optical absorption band, located at 550 nm, which is related to a discrete energy level of QDs. Thirdly, by using two-color sum-frequency generation (2C-SFG) nonlinear optical spectroscopy, we show experimentally the functionalization efficiency of the RFMS CdSe QDs layer with thiol derived molecules, which is not possible on the QDs layer prepared by wet chemistry due to the surfactant molecules from the native solution. Finally, 2C-SFG spectroscopy, performed at different visible wavelengths, highlights modifications of the vibration mode shape whatever the QDs deposition method, which is correlated to the discrete energy level of the QDs. Copyright © 2015 Elsevier Inc. All rights reserved.

  11. Au-assisted growth of anisotropic and epitaxial cdse colloidal nanocrystals via in situ dismantling of quantum dots

    KAUST Repository

    Fernàndez-Altable, Víctor

    2015-03-10

    Metallic nanocrystals have been revealed in the past years as valuable materials for the catalytic growth of semiconductor nanowires. Yet, only low melting point metals like Bi have been reported to successfully assist the growth of elongated CdX (X = S, Se, Te) systems in solution, and the possibility to use plasmonic noble metals has become a challenging task. In this work we show that the growth of anisotropic CdSe nanostructures in solution can also be efficiently catalyzed by colloidal Au nanoparticles, following a preferential crystallographic alignment between the metallic and semiconductor domains. Noteworthy, we report the heterodox use of semiconductor quantum dots as a homogeneous and tunable source of reactive monomer species to the solution. The mechanistic studies reveal that the in situ delivery of these cadmium and chalcogen monomer species and the formation of AuxCdy alloy seeds are both key factors for the epitaxial growth of elongated CdSe domains. The implementation of this method suggests an alternative synthetic approach for the assembly of different semiconductor domains into more complex heterostructures.

  12. Towards ion beam synthesis of single CdSe nanocrystal quantum dots in a SiO{sub 2} matrix

    Energy Technology Data Exchange (ETDEWEB)

    Mangold, Hans Moritz; Kinzel, Joerg B.; Krenner, Hubert J. [Emmy Noether Group at Lehrstuhl Experimentalphysik 1, Universitaet Augsburg (Germany); Karl, Helmut [Lehrstuhl Experimentalphysik IV, Universitaet Augsburg (Germany); Wixforth, Achim [Lehrstuhl Experimentalphysik I, Universitaet Augsburg (Germany)

    2013-07-01

    II-VI compound semiconductor quantum dots (QDs) are a promising class of materials for applications in optical devices in the visible spectral domain. Here we show that in addition to traditional fabrication techniques such as molecular beam epitaxy or chemical synthesis, high fluence ion-beam implantation followed by a rapid thermal annealing step, can be readily applied to synthesize CdSe nanocrystals with superior optical properties within the thermal oxide on a Si wafer. In order to confine the implantation volume we employ chromium masks with arrays of nanoscale aperture openings with diameters smaller than 250 nm. We analyzed the such implanted and annealed samples by scanning electron microscopy and micro-photoluminescence spectroscopy. We observe a pronounced broadening and blue shift of the nanocrystal emission when decreasing the aperture diameter to <1000 nm. We attribute this behavior to a reduction of the mean nanocrystal size but increase of its size distribution. For the smallest aperture sizes used we observe a pronounced shell-filling behavior characteristic for single quantum dot nanoemitters.

  13. The influence of sequential ligand exchange and elimination on the performance of P3HT: CdSe quantum dot hybrid solar cells.

    Science.gov (United States)

    Lee, Donggu; Lim, Jaehoon; Park, Myeongjin; Kim, Jun Young; Song, Jiyun; Kwak, Jeonghun; Lee, Seonghoon; Char, Kookheon; Lee, Changhee

    2015-11-20

    We report on a sequential ligand exchange and elimination process for the fast and easy surface modification of CdSe quantum dots (QDs) in order to improve the electronic interaction between poly(3-hexylthiophene) (P3HT) and CdSe QDs in P3HT:CdSe hybrid solar cells. We systematically investigated the influence of surface treatment on the insulating ligand shell of CdSe QDs using (1)H-NMR analysis, and correlated their influence on the photovoltaic properties of P3HT:CdSe hybrid solar cells. A decrease in the average thickness of the ligand shells directly improved carrier transport properties. Moreover, the presence of remnant 1-hexylamine ligands provided efficient surface trap passivation. As a result, overall solar cell performance (especially fill factor and power conversion efficiency) was enhanced and the recombination mechanism was dominated by monomolecular recombination due to enhanced carrier collection length (l(C0)).

  14. Facile and green synthesis of CdSe quantum dots in protein matrix: tuning of morphology and optical properties.

    Science.gov (United States)

    Ahmed, M; Guleria, A; Rath, M C; Singh, A K; Adhikari, S; Sarkar, S K

    2014-08-01

    Herein, we have demonstrated a facile and green approach for the synthesis of Cadmium selenide (CdSe) quantum dots (QDs). The process was mediated by bovine serum albumin (BSA) and it was found that BSA plays the dual role of reducing agent as well as a stabilizing agent. The QDs exhibited sharp excitonic absorption features at ~500 nm and subsequently showed reasonably good photoluminescence (PL) at room temperature. The PL is seen to be strongly dependent on the concentration of the precursors and hence, the luminescence of these QDs could be conveniently tuned across the visible spectrum simply by varying molar ratio of the precursors. It can be envisaged from the fact that a red-shift of about 100 nm in the PL peak position was observed when the molar ratio of the precursors ([Cd2+]:[Se2-], in mM) was varied from 10:5 to 10:40. Subsequently, the charge carrier relaxation dynamics associated with the different molar ratio of precursors has been investigated and very interesting information regarding the energy level structures of these QDs were revealed. Most importantly, in conjunction with the optical tuning, the nanomorphology of these nanoparticles was found to vary with the change in molar ratios of Se and Cd precursors. This aspect can provide a new direction of controlling the shape of CdSe nanoparticles. The possible mechanism of the formation as well as for the shape variation of these nanoparticles with the molar ratios of precursors has been proposed, taking into account the role of amino acid residues (present in BSA). Moreover, the QDs were water soluble and possessed fairly good colloidal stability therefore, can have potential applications in catalysis and bio-labeling. On the whole, the present methodology of protein assisted synthesis is relatively new especially for semiconducting nanomaterials and may provide some unique and interesting aspects to control and fine tune the morphology vis-à-vis, their optical properties.

  15. Pico-ampere current sensitivity and CdSe quantum dots assembly assisted charge transport in ferroelectric liquid crystal

    Science.gov (United States)

    Pratap Singh, Dharmendra; Boussoualem, Yahia; Duponchel, Benoit; Sahraoui, Abdelhak Hadj; Kumar, Sandeep; Manohar, Rajiv; Daoudi, Abdelylah

    2017-08-01

    Octadecylamine capped CdSe quantum dots (QDs) dispersed 4-(1-methyl-heptyloxy)-benzoic acid 4‧-octyloxy-biphenyl-4-yl ester ferroelectric liquid crystal (FLC) were deposited over gold coated quartz substrate using dip-coating. The topographical investigation discloses that the homogeneously dispersed QDs adopt face-on to edge-on assembly in FLC matrix owing to their concentration. Current-voltage (I-V) measurement was performed using conductive atomic force microscopy (CAFM) which yields ohmic to critical diode like I-V curves depending upon the concentration of QDs in FLC. The recorded pico-ampere (pA) current sensitivity in FLC-QDs composites is attributed to micro-second drift time of electron due to weak electronic coupling between the π-electrons on the FLC and s-electrons on the metal surface. The observed pico-ampere sensitivity is the least current sensitivity recorded so far. For FLC-QDs composites, almost 24% faster electro-optic response was observed in comparison to pure FLC. The pico-ampere current sensitivity can be utilized in touch screen displays whereas the change in polarization for low applied electric field ameliorates the increased electrical susceptibility counteracting the internal electric field and its use in electronic data storage and faster electro-optical devices.

  16. Mercaptoethanol capped CdSe quantum dots and CdSe/ZnS core/shell: synthesis, characterization and cytotoxicity evaluation.

    Science.gov (United States)

    Painuly, Diksha; Bhatt, Anugya; Krishnan, V Kalliyana

    2013-02-01

    CdSe Quantum dots (Q-dots) and CdSe/ZnS core/shell have been synthesized by wet chemical route using mercaptoethanol (ME) as cappant. The synthesized Q-dots and core/shell were characterized using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDS), Dynamic Light Scattering (DLS), Optical absorption and luminescence spectroscopy. The core/shell formation was confirmed by both XRD and TEM analysis. The luminescence was shown to be considerably enhanced in the core/shell sample. Effect of dialysis process on the optical properties of the Q-dots and core/shell has also been discussed. Cytotoxicity studies have been carried out for Q-dots and core/shell. CdSe/ZnS core/shell was found to be non-cytotoxic as compared to CdSe Q-dots up to a certain concentration range. Polyethylene glycol (PEG) coating enhances the non-cytotoxic nature of CdSe/ZnS core/shell when compared with bare core/shell.

  17. 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

  18. Synthesis of a CdSe-graphene hybrid composed of CdSe quantum dot arrays directly grown on CVD-graphene and its ultrafast carrier dynamics.

    Science.gov (United States)

    Kim, Yong-Tae; Shin, Hee-Won; Ko, Young-Seon; Ahn, Tae Kyu; Kwon, Young-Uk

    2013-02-21

    We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices.

  19. Investigation of biocompatible and protein sensitive highly luminescent quantum dots/nanocrystals of CdSe, CdSe/ZnS and CdSe/CdS

    Science.gov (United States)

    Ratnesh, R. K.; Mehata, Mohan Singh

    2017-05-01

    The size and shape dependent semiconductor quantum dots (0D nanoparticles) with color tunability demonstrating significant influence in a biological system and considered as ideal probes. Here, a non-coordinated colloidal approach was used for the synthesis of CdSe, CdSe/ZnS and CdSe/CdS core-shell quantum dots (QDs) of 3-4 nm. The synthesized nanocrystals show a high crystallinity, examined by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The core-shell semiconductor QDs exhibit stronger photoluminescence (PL) as compared to the core QDs. The strong PL with small full-width half maximum (FWHM) indicates that the prepared QDs have a nearly uniform size distribution and well dispersibility. The quantum yield (QY) of core-shell QDs increases due to the surface passivation. Further, the PL of BSA is quenched strongly by the presence of core-shell QDs and follows the well-known Stern-Volmer (S-V) relation, whereas the PL lifetime does not follow the S-V relation, demonstrating that the observed quenching is predominantly static in nature. Among CdSe core, CdSe/ZnS and CdSe/CdS core-shell QDs, the CdSe/ZnS QDs shows the least cytotoxicity and most biocompatibility. Thus, the prepared core-shell QDs are biocompatible and exhibit strong sensing ability.

  20. Controlling reabsorption effect of bi-color CdSe quantum dots-based white light-emitting diodes

    Science.gov (United States)

    Siao, Cyuan-Bin; Chung, Shu-Ru; Wang, Kuan-Wen

    2017-08-01

    The colloidal semiconductor quantum dots (QDs) have the potentials to be used in white light-emitting diode (WLED) as a down-converting component to replace incandescent lamps, because the traditional WLED composed of Y3Al5O12:Ce3+ (YAG:Ce) phosphor lack of red color emissions and shows low color quality. Among various QDs, CdSe has been extensively studied because it possesses attractive characteristics such as high quantum yields (QYs), narrow emission spectral bandwidth, as well as size-tunable optical characteristics. However, in order to enhance the color rendering index (CRI) of WLED, blending materials with different emission wavelengths has been used frequently. Unfortunately, these procedures are complex and time-consuming, and the emission energy of smaller QDs can be reabsorbed by larger QDs, resulting in decreasing the excitation intensity in yellowish-green region. Therefore, in this study, in order to decrease the reabsorption effect and to simplify the procedures, we have demonstrated a facile thermal pyrolyzed route to prepare bicolor CdSe QDs with dual-wavelengths. The emission wavelengths, particle sizes, and QYs of QDs can be tuned from 537/595 to 537/602 nm, 2.59/3.92 to 2.59/4.01 nm, and 27 to 40 %, for GR1 to 3 samples, respectively when the amount of Se precursor is decreased from 1.5 to 0.75 mmol. Meanwhile, the area ratio of green to red (Ag/Ar) in fluorescence spectra is gradually increased, due to the increase in growth rate, and decrease in nuclei formation in red emission. The GR1, GR2, and GR3 QDs are then encapsulated by convert types to form the LED, in which the QDs are deposited on the blue-emitting InGaN LED chip (λem = 450 nm). After encapsulation, the devices properties of Commission International d'Eclairage (CIE) chromaticity and Ag/Ar area ratio are (0.40, 0.24), 0.28/1, (0.40, 0.31), 0.52/1, and (0.40, 0.38), 1.02/1, respectively for GR1, GR2, and GR3. The results show that the green emission intensity are strongly

  1. White-light-emitting CdSe quantum dots with ''magic size'' via one-pot synthesis approach

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xinmei [School of Materials Science and Engineering, Hefei University of Technology, Hefei, Anhui 230009 (China); Department of Biological and Chemical Engineering, Guangxi University of Technology, Liuzhou, Guangxi 545006 (China); Jiang, Yang; Wang, Chun; Li, Shanying; Lan, Xinzheng; Chen, Yan [School of Materials Science and Engineering, Hefei University of Technology, Hefei, Anhui 230009 (China)

    2010-11-15

    Two stable magic-sized CdSe families were simply and reproducibly synthesized at different growth temperature via a one-pot approach, in which N-oleoylmorpholine was used as reaction medium, and cadmium acetate dehydrate and Se powder as precursors. The pure 392 family obtained by surface passivation with either lauric acid or stearic acid at 150 C exhibits strong white-light emission with a maximum quantum yield (QY) up to 27%. The broadband emission (370-680 nm), which is responsible for the white-light, is attributed to photoluminescence from both excitons and surface states. High-quality white-light emission can be stable for a long growth period (about 120 min) and at least a 2-month storage period. The high-resolution transmission electron microscopy (HRTEM) images verify the presence of the small size distribution and good crystallinity of the quantum dots (QDs) with a size range of 1.7-2.0 nm. X-ray diffraction (XRD) and selected area electron diffraction (SAED) confirm that the magic-sized CdSe QDs have a zincblende crystal structure. The energy-dispersed spectrometry (EDS) measurement indicates the as-prepared CdSe QDs have a cadmium-rich surface. The as-prepared CdSe QDs exhibit sharp and fixed absorption features and the white-light emitting from QDs can be retained for quite long reaction and storage periods. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Current matching using CdSe quantum dots to enhance the power conversion efficiency of InGaP/GaAs/Ge tandem solar cells.

    Science.gov (United States)

    Lee, Ya-Ju; Yao, Yung-Chi; Tsai, Meng-Tsan; Liu, An-Fan; Yang, Min-De; Lai, Jiun-Tsuen

    2013-11-04

    A III-V multi-junction tandem solar cell is the most efficient photovoltaic structure that offers an extremely high power conversion efficiency. Current mismatching between each subcell of the device, however, is a significant challenge that causes the experimental value of the power conversion efficiency to deviate from the theoretical value. In this work, we explore a promising strategy using CdSe quantum dots (QDs) to enhance the photocurrent of the limited subcell to match with those of the other subcells and to enhance the power conversion efficiency of InGaP/GaAs/Ge tandem solar cells. The underlying mechanism of the enhancement can be attributed to the QD's unique capacity for photon conversion that tailors the incident spectrum of solar light; the enhanced efficiency of the device is therefore strongly dependent on the QD's dimensions. As a result, by appropriately selecting and spreading 7 mg/mL of CdSe QDs with diameters of 4.2 nm upon the InGaP/GaAs/Ge solar cell, the power conversion efficiency shows an enhancement of 10.39% compared to the cell's counterpart without integrating CdSe QDs.

  3. High-performance solar cells with induced crystallization of perovskite by an evenly distributed CdSe quantum dots seed-mediated underlayer

    Science.gov (United States)

    Qi, Jiabin; Xiong, Hao; Wang, Gang; Xie, Huaqing; Jia, Wei; Zhang, Qinghong; Li, Yaogang; Wang, Hongzhi

    2018-02-01

    Crystallization and interface engineering of perovskite are the most important factors in achieving high-performance perovskite solar cells (PSCs). Herein, we construct an ultrathin CdSe quantum dots (QDs) underlayer via a solution-processable method, which acts as a seed-mediated layer for perfect perovskite film, with both uniform morphology and better absorption capacity. In addition, CdSe QDs and perovskites form a fully crystalline heterojunction, which is beneficial to minimizing the defect and trap densities. Then, an Ostwald ripening process is adopted to fabricate large-grain, pinhole-free perovskite thin film, by a simple methylammonium bromide treatment. Besides, the first principle is applied in calculating organic/inorganic hybrid perovskite, confirming that electrons can move even quicker and more effectively, as a result of our work. Due to these treatments, representing a very simple method to simultaneously control perovskite crystallization and optimize the interfaces in PSCs, a maximum power conversion efficiency of 15.68% is achieved, 35% higher than the PSC both without CdSe and MABr treatment (11.57%), indicating better performance.

  4. Single Enzyme Direct Biomineralization of CdSe and CdSe-CdS Core-Shell Quantum Dots.

    Science.gov (United States)

    Yang, Zhou; Lu, Li; Kiely, Christopher J; Berger, Bryan W; McIntosh, Steven

    2017-04-19

    Biomineralization is the process by which biological systems synthesize inorganic materials. Herein, we demonstrate an engineered cystathionine γ-lyase enzyme, smCSE that is active for the direct aqueous phase biomineralization of CdSe and CdSe-CdS core-shell nanocrystals. The nanocrystals are formed in an otherwise unreactive buffered solution of Cd acetate and selenocystine through enzymatic turnover of the selenocystine to form a reactive precursor, likely H 2 Se. The particle size of the CdSe core nanocrystals can be tuned by varying the incubation time to generated particle sizes between 2.74 ± 0.63 nm and 4.78 ± 1.16 nm formed after 20 min and 24 h of incubation, respectively. Subsequent purification and introduction of l-cysteine as a sulfur source facilitates the biomineralization of a CdS shell onto the CdSe cores. The quantum yield of the resulting CdSe-CdS core-shell particles is up to 12% in the aqueous phase; comparable to that reported for more traditional chemical synthesis routes for core-shell particles of similar size with similar shell coverage. This single-enzyme route to functional nanocrystals synthesis reveals the powerful potential of biomineralization processes.

  5. A Phosphine-Free Route to Size-Adjustable CdSe and CdSe/CdS Core-Shell Quantum Dots for White-Light-Emitting Diodes.

    Science.gov (United States)

    Zhang, Yugang; Li, Guopeng; Zhang, Ting; Song, Zihang; Wang, Hui; Zhang, Zhongping; Jiang, Yang

    2018-03-01

    The selenium dioxide was used as the precursor to synthesize wide-size-ranged CdSe quantum dots (2.4-5.7 nm) via hot-injection route. The CdSe quantum dots are featured with high crystalline, monodisperse, zinc blende structure and wide emission region (530-635 nm). In order to improve the stability and quantum yield, a phosphine-free single-molecular precursor approach is used to obtain CdSe/CdS core/shell quantum dots. The CdSe/CdS quantum dots are highly fluorescent with quantum yield up to 65%, and persist the good monodispersity and high crystallinity. Moreover, the quantum dots white light-emitting-diodes are fabricated by using the resultant red emission core/shell quantum dots and Y3Al5O12:Ce3+ yellow phosphors as color-conversion layers on a blue InGaN chip. The prepared light-emitting-diodes show good performance with CIE-1931 coordinated of (0.3583, 0.3349), an Ra of 92.9, and a Tc of 4410 K at 20 mA, which indicate that the combination of red-emission QDs and yellow phophors as a promising approach to obtain warm WLEDs with good color rendering.

  6. CdSe and ZnSe quantum dots capped with PEA for screening C-reactive protein in human serum.

    Science.gov (United States)

    Gomes, D; Algarra, M; Diez de los Rios, M J; Arrebola, M M; Herrera-Gutiérrez, M E; Seller-Pérez, G; Esteves da Silva, J C G

    2012-05-15

    A fluorescence chemical sensor for C-reactive protein (CRP) was developed based on the selective interaction with CdSe and ZnSe quantum dots (QDs) coated with O-phosphorylethanolamine (PEA). Synthesis procedure and analytical parameters such as pH and ionic strength were studied. The decrease in the fluorescence emission intensity was explained due to the specific interaction of the QDs-PEA with CRP, and a correlation was observed between the quenching of the fluorescence and the concentration of CRP. The accuracy of the proposed method was 0.37% as RSD. The proposed method was applied to screen serum samples, and showed to be sensible at the C-reactive protein concentrations of risks levels. Copyright © 2012 Elsevier B.V. All rights reserved.

  7. Synthesis of a CdSe-graphene hybrid composed of CdSe quantum dot arrays directly grown on CVD-graphene and its ultrafast carrier dynamics

    Science.gov (United States)

    Kim, Yong-Tae; Shin, Hee-Won; Ko, Young-Seon; Ahn, Tae Kyu; Kwon, Young-Uk

    2013-01-01

    We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices.We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices. Electronic supplementary information (ESI) available: TEM data of MSTF, AFM data of T-QD-G samples, PL decay fitting results to the multiexponential decay equation, photoconductivity data of T-QD-2LG with two different illumination wavelengths, photocurrent efficiencies of QD-G hybrids prepared in various ways, photoconductivity and photoresponse data of T-QD-2LG and T-QD-3LG, and the bending stress on a PET film. See DOI: 10.1039/c2nr33294a

  8. Uniform growth of high-quality oxide thin films on graphene using a CdSe quantum dot array seeding layer.

    Science.gov (United States)

    Kim, Yong-Tae; Lee, Seoung-Ki; Kim, Kwang-Seop; Kim, Yong Ho; Ahn, Jong-Hyun; Kwon, Young-Uk

    2014-08-13

    Graphene displays outstanding properties as an electrode and a semiconducting channel material for transistors; however, the weak interfacial bond between graphene and an inorganic oxide material-based insulator presents a major constraint on these applications. Here, we report a new approach to improving the interface between the two materials using a CdSe quantum dot (QD)-based seeding layer in an inorganic material-graphene junction. CdSe QDs were electrochemically grown on graphene without degrading the properties of the graphene layer. The graphene structure was then used as the electrode in an oxide semiconductor by depositing a zinc oxide thin film onto the graphene coated with a QD seed layer (QD/G). The zinc oxide film adhered strongly to the graphene layer and provided a low contact resistance. A high-k dielectric layer in the form of an HfO2 film, which is an essential element in the fabrication of high-performance graphene-based field effect transistors, was also uniformly formed on the QD/G sheet using atomic layer deposition. The resulting transistors provided a relatively good performance, yielding hole and electron mobilities of 2600 and 2000 cm(2)/V·s.

  9. Poly(glycidyl methacrylate) grafted CdSe quantum dots by surface-initiated atom transfer radical polymerization: Novel synthesis, characterization, properties, and cytotoxicity studies

    International Nuclear Information System (INIS)

    Bach, Long Giang; Islam, Md. Rafiqul; Lee, Doh Chang; Lim, Kwon Taek

    2013-01-01

    A novel approach for the synthesis of poly(glycidyl methacrylate) grafted CdSe quantum dot (QDs) (PGMA-g-CdSe) was developed. The PGMA-g-CdSe nanohybrids were synthesized by the surface-initiated atom transfer radical polymerization of glycidyl methacrylate from the surface of the strategic initiator, CdSe-BrIB QDs prepared by the interaction of 2-bromoisobutyryl bromide (BrIB) and CdSe-OH QDs. The structure, morphology, and optical property of the PGMA-g-CdSe nanohybrids were analyzed by FT-IR, XPS, TGA, XRD, TEM, and PL. The as-synthesized PGMA-g-CdSe nanohybrids having multi-epoxide groups were employed for the direct coupling of biotin via ring-opening reaction of the epoxide groups to afford the Biotin-f-PGMA-g-CdSe nanobioconjugate. The covalent immobilization of biotin onto PGMA-g-CdSe was confirmed by FT-IR, XPS, and EDX. Biocompatibility and imaging properties of the Biotin-f-PGMA-g-CdSe were investigated by MTT bioassay and PL analysis, respectively. The cell viability study suggested that the biocompatibility was significantly enhanced by the functionalization of CdSe QDs by biotin and PGMA.

  10. Hot electron and hole dynamics in thiol-capped CdSe quantum dots revealed by 2D electronic spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Lenngren, N.; Abdellah, M.A.; Zheng, K.; Al-Marri, M.J.; Zigmantas, D.; Žídek, Karel; Pullerits, T.

    2016-01-01

    Roč. 18, č. 37 (2016), s. 26199-26204 ISSN 1463-9076 Institutional support: RVO:61389021 Keywords : quantum dots (QDs) * two-dimesional coherent spectroscopy * carrier relaxation * carrier trapping Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.123, year: 2016

  11. Study of optically trapped living Trypanosoma cruzi/Trypanosoma rangeli - Rhodnius prolixus interactions by real time confocal images using CdSe quantum dots

    Science.gov (United States)

    de Thomaz, A. A.; Almeida, D. B.; Faustino, W. M.; Jacob, G. J.; Fontes, A.; Barbosa, L. C.; Cesar, C. L.; Stahl, C. V.; Santos-Mallet, J. R.; Gomes, S. A. O.; Feder, D.

    2008-08-01

    One of the fundamental goals in biology is to understand the interplay between biomolecules of different cells. This happen, for example, in the first moments of the infection of a vector by a parasite that results in the adherence to the cell walls. To observe this kind of event we used an integrated Optical Tweezers and Confocal Microscopy tool. This tool allow us to use the Optical Tweezers to trigger the adhesion of the Trypanosoma cruzi and Trypanosoma rangeli parasite to the intestine wall cells and salivary gland of the Rhodnius prolixus vector and to, subsequently observe the sequence of events by confocal fluorescence microscopy under optical forces stresses. We kept the microorganism and vector cells alive using CdSe quantum dot staining. Besides the fact that Quantum Dots are bright vital fluorescent markers, the absence of photobleaching allow us to follow the events in time for an extended period. By zooming to the region of interested we have been able to acquire confocal images at the 2 to 3 frames per second rate.

  12. Quantum dots

    International Nuclear Information System (INIS)

    Kouwenhoven, L.; Marcus, C.

    1998-01-01

    Quantum dots are man-made ''droplets'' of charge that can contain anything from a single electron to a collection of several thousand. Their typical dimensions range from nanometres to a few microns, and their size, shape and interactions can be precisely controlled through the use of advanced nanofabrication technology. The physics of quantum dots shows many parallels with the behaviour of naturally occurring quantum systems in atomic and nuclear physics. Indeed, quantum dots exemplify an important trend in condensed-matter physics in which researchers study man-made objects rather than real atoms or nuclei. As in an atom, the energy levels in a quantum dot become quantized due to the confinement of electrons. With quantum dots, however, an experimentalist can scan through the entire periodic table by simply changing a voltage. In this article the authors describe how quantum dots make it possible to explore new physics in regimes that cannot otherwise be accessed in the laboratory. (UK)

  13. 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

  14. Optics of colloidal quantum-confined CdSe nanoscrolls

    Energy Technology Data Exchange (ETDEWEB)

    Vasiliev, R B; Sokolikova, M S [M. V. Lomonosov Moscow State University, Moscow (Russian Federation); Vitukhnovskii, A G; Ambrozevich, S A; Selyukov, A S; Lebedev, V S [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2015-09-30

    Nanostructures in the form of 1.2-nm-thick colloidal CdSe nanoplatelets rolled into scrolls are investigated. The morphology of these scrolls is analysed and their basic geometric parameters are determined (diameter 29 nm, longitudinal size 100 – 150 nm) by TEM microscopy. Absorption and photoluminescence spectra of these objects are recorded, and the luminescence decay kinetics is studied. It is shown that the optical properties of CdSe nanoscrolls differ significantly from the properties of CdSe quantum dots and that these nanoscrolls are attractive for nanophotonic devices due to large oscillator strengths of the transition, small widths of excitonic peaks and short luminescence decay times. Nanoscrolls can be used to design hybrid organic–inorganic pure-color LEDs with a high luminescence quantum yield and low operating voltages. (optics and technology of nanostructures)

  15. Assessing potential harmful effects of CdSe quantum dots by using Drosophila melanogaster as in vivo model

    International Nuclear Information System (INIS)

    Alaraby, Mohamed; Demir, Esref; Hernández, Alba; Marcos, Ricard

    2015-01-01

    Since CdSe QDs are increasingly used in medical and pharmaceutical sciences careful and systematic studies to determine their biosafety are needed. Since in vivo studies produce relevant information complementing in vitro data, we promote the use of Drosophila melanogaster as a suitable in vivo model to detect toxic and genotoxic effects associated with CdSe QD exposure. Taking into account the potential release of cadmium ions, QD effects were compared with those obtained with CdCl 2 . Results showed that CdSe QDs penetrate the intestinal barrier of the larvae reaching the hemolymph, interacting with hemocytes, and inducing dose/time dependent significant genotoxic effects, as determined by the comet assay. Elevated ROS production, QD biodegradation, and significant disturbance in the conserved Hsps, antioxidant and p53 genes were also observed. Overall, QD effects were milder than those induced by CdCl 2 suggesting the role of Cd released ions in the observed harmful effects of Cd based QDs. To reduce the observed side-effects of Cd based QDs biocompatible coats would be required to avoid cadmium's undesirable effects. - Highlights: • CdSe QDs were able to cross the intestinal barrier of Drosophila. • Elevated ROS induction was detected in larval hemocytes. • Changes in the expression of Hsps and p53 genes were observed. • Primary DNA damage was induced by CdSe QDs in hemocytes. • Overall, CdSe QD effects were milder than those induced by CdCl 2

  16. Surface-modified CdSe quantum dots for the sensitive and selective determination of Cu(II) in aqueous solutions by luminescent measurements

    International Nuclear Information System (INIS)

    Fernandez-Argueelles, Maria Teresa; Jin, Wei Jun; Costa-Fernandez, Jose M.; Pereiro, Rosario; Sanz-Medel, Alfredo

    2005-01-01

    The use of water-soluble luminescent CdSe quantum dots (QDs), whose surface was modified either with 2-mercaptoethane sulphonic acid or with 2-mercaptoacetic acid, was investigated for the sensitive and selective determination of copper(II) ions in aqueous solutions. A pH 5.5 was selected for measurement. Also, the effect of the presence of different surfactant agents in the sample solution, in order to stabilize the fluorescent signals of the QDs in water, has been investigated. A 10 -3 M of dodecyltrimethylammonium chloride final concentration was selected. Fluorescence signals were found to be stable for at least several days in such conditions. Higher sensitivity was obtained for the sulphonic-modified CdSe QDs. Detection limits for Cu(II) of 0.2 μg l -1 , a dynamic range up to 30 μg l -1 , and a R.S.D. of ±2.8% for 10 replicates of a 2.5 μg l -1 Cu(II) solution were obtained as analytical performance characteristics. Besides, the influence on the fluorescence signal of foreign cations, including Na + , K + , Ca 2+ , Mg 2+ , Zn 2+ , Mn 2+ , Co 3+ , Ag + , Hg 2+ and Fe 3+ was studied (to avoid inner filter effect, the colourless complex FeF 6 3- was investigated instead of Fe 3+ ). Results showed a high selectivity of the sulphonic-modified QDs towards Cu(II) ions. The proposed method demonstrated improved sensitivity and selectivity characteristics for Cu(II) determinations as compared to other already described luminescence QDs-based analytical methods for metal ions determinations. Analytical applicability of the QDs has been demonstrated by tap and fountain water analysis. Results of Cu(II) determinations were in good agreement to those obtained by using an alternative analytical method

  17. SU-E-T-526: On the Linearity, Stability and Beam Energy Dependence of CdSe Quantum Dots as Scintillating Probes

    International Nuclear Information System (INIS)

    Delage, M-E; Lecavalier, M-E; Lariviere, D; Allen, C; Beaulieu, L

    2014-01-01

    Purpose: Structure and energy transfer mechanisms confer colloidal quantum dots (cQDs) interesting properties, among them their potential as scintillators. CdSe multi-shell cQDs in powder were investigated under photons irradiation. The purpose of this work is to characterize signal to dose linearity, stability with time and to quantify the dependence of their light output with beam energy. Methods: The cQDs are placed at the extremity of a non-scintillating plastic collecting fiber, with the other extremity connected to an Apogee U2000C CCD camera. The CCD camera collects the fluorescence light from irradiated cQDs from which the delivered dose is extracted. This signal is corrected for Cerenkov contamination at MV energies using the chromatic technique. The detector was irradiated with two devices: Xstrahl 200 orthovoltage unit for 120, 180 and 220 kVp and a Varian Clinac iX for 6 and 23 MV. Results: Linear output response with varying dose is observed for all beam energies with R2 factors > 0,999. Reproducibility measurements were performed at 120 kVp: the same set-up was irradiated at different time intervals (one week and three months). The results showed only a small relative decrease of light output of 3,2 % after a combine deposited dose of approximately 95 Gy. CdSe nanocrystals response has been studied as a function of beam energy. The output increases with decreasing energy from 120 kVp to 6 MV and increase again for 23 MV. This behavior could be explained in part by the cQDs high-Z composition. Conclusion: The fluorescence light output of CdSe cQDs was found to be linear as a function of dose. The results suggest stability of the scintillation output of cQDs over time. The specific composition of cQDs is the main cause of the observed energy dependence. We will further look into particle beam dependence of the cQDs. Bourse d'excellence aux etudes graduees du CRC (Centre de Recherche sur le Cancer, Universite Laval) Bourse d'excellence aux

  18. Use of Cdse/ZnS quantum dots for sensitive detection and quantification of paraquat in water samples

    Energy Technology Data Exchange (ETDEWEB)

    Durán, Gema M. [Department of Analytical Chemistry and Food Technology, University of Castilla – La Mancha, Avenida Camilo José Cela, 10, 13004 Ciudad Real (Spain); IRICA (Regional Institute of Applied Scientific Research), Avenida Camilo José Cela, s/n., 13071 Ciudad Real (Spain); Contento, Ana M. [Department of Analytical Chemistry and Food Technology, University of Castilla – La Mancha, Avenida Camilo José Cela, 10, 13004 Ciudad Real (Spain); Ríos, Ángel, E-mail: Angel.Rios@uclm.es [Department of Analytical Chemistry and Food Technology, University of Castilla – La Mancha, Avenida Camilo José Cela, 10, 13004 Ciudad Real (Spain)

    2013-11-01

    Graphical abstract: -- Highlights: •Analytical use of CdSe/ZnS quantum dots. •Methodology for water solubilization of CdSe/ZnS QDs. •Sensitive and selective reaction with paraquat herbicide. •Application to water samples. -- Abstract: Based on the highly sensitive fluorescence change of water-soluble CdSe/ZnS core-shell quantum dots (QD) by paraquat herbicide, a simple, rapid and reproducible methodology was developed to selectively determine paraquat (PQ) in water samples. The methodology enabled the use of simple pretreatment procedure based on the simple water solubilization of CdSe/ZnS QDs with hydrophilic heterobifunctional thiol ligands, such as 3-mercaptopropionic acid (3-MPA), using microwave irradiation. The resulting water-soluble QDs exhibit a strong fluorescence emission at 596 nm with a high and reproducible photostability. The proposed analytical method thus satisfies the need for a simple, sensible and rapid methodology to determine residues of paraquat in water samples, as required by the increasingly strict regulations for health protection introduced in recent years. The sensitivity of the method, expressed as detection limits, was as low as 3.0 ng L{sup −1}. The lineal range was between 10–5 × 10{sup 3} ng L{sup −1}. RSD values in the range of 71–102% were obtained. The analytical applicability of proposed method was demonstrated by analyzing water samples from different procedence.

  19. Use of Cdse/ZnS quantum dots for sensitive detection and quantification of paraquat in water samples

    International Nuclear Information System (INIS)

    Durán, Gema M.; Contento, Ana M.; Ríos, Ángel

    2013-01-01

    Graphical abstract: -- Highlights: •Analytical use of CdSe/ZnS quantum dots. •Methodology for water solubilization of CdSe/ZnS QDs. •Sensitive and selective reaction with paraquat herbicide. •Application to water samples. -- Abstract: Based on the highly sensitive fluorescence change of water-soluble CdSe/ZnS core-shell quantum dots (QD) by paraquat herbicide, a simple, rapid and reproducible methodology was developed to selectively determine paraquat (PQ) in water samples. The methodology enabled the use of simple pretreatment procedure based on the simple water solubilization of CdSe/ZnS QDs with hydrophilic heterobifunctional thiol ligands, such as 3-mercaptopropionic acid (3-MPA), using microwave irradiation. The resulting water-soluble QDs exhibit a strong fluorescence emission at 596 nm with a high and reproducible photostability. The proposed analytical method thus satisfies the need for a simple, sensible and rapid methodology to determine residues of paraquat in water samples, as required by the increasingly strict regulations for health protection introduced in recent years. The sensitivity of the method, expressed as detection limits, was as low as 3.0 ng L −1 . The lineal range was between 10–5 × 10 3 ng L −1 . RSD values in the range of 71–102% were obtained. The analytical applicability of proposed method was demonstrated by analyzing water samples from different procedence

  20. Assessing potential harmful effects of CdSe quantum dots by using Drosophila melanogaster as in vivo model

    Energy Technology Data Exchange (ETDEWEB)

    Alaraby, Mohamed [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); Sohag University, Faculty of Sciences, Zoology Department, 82524-Campus, Sohag (Egypt); Demir, Esref [Akdeniz University, Faculty of Sciences, Department of Biology, 07058-Campus, Antalya (Turkey); Hernández, Alba [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); CIBER Epidemiología y Salud Pública, ISCIII, Madrid (Spain); Marcos, Ricard, E-mail: ricard.marcos@uab.es [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); CIBER Epidemiología y Salud Pública, ISCIII, Madrid (Spain)

    2015-10-15

    Since CdSe QDs are increasingly used in medical and pharmaceutical sciences careful and systematic studies to determine their biosafety are needed. Since in vivo studies produce relevant information complementing in vitro data, we promote the use of Drosophila melanogaster as a suitable in vivo model to detect toxic and genotoxic effects associated with CdSe QD exposure. Taking into account the potential release of cadmium ions, QD effects were compared with those obtained with CdCl{sub 2}. Results showed that CdSe QDs penetrate the intestinal barrier of the larvae reaching the hemolymph, interacting with hemocytes, and inducing dose/time dependent significant genotoxic effects, as determined by the comet assay. Elevated ROS production, QD biodegradation, and significant disturbance in the conserved Hsps, antioxidant and p53 genes were also observed. Overall, QD effects were milder than those induced by CdCl{sub 2} suggesting the role of Cd released ions in the observed harmful effects of Cd based QDs. To reduce the observed side-effects of Cd based QDs biocompatible coats would be required to avoid cadmium's undesirable effects. - Highlights: • CdSe QDs were able to cross the intestinal barrier of Drosophila. • Elevated ROS induction was detected in larval hemocytes. • Changes in the expression of Hsps and p53 genes were observed. • Primary DNA damage was induced by CdSe QDs in hemocytes. • Overall, CdSe QD effects were milder than those induced by CdCl{sub 2}.

  1. Purification non-aqueous solution of quantum dots CdSe- CdS-ZnS from excess organic substance-stabilizer by use PE- HD membrane

    International Nuclear Information System (INIS)

    Kosolapova, K; Al-Alwani, A; Gorbachev, I; Glukhovskoy, E

    2015-01-01

    Recently, a new simple method for the purification of CdSe-CdS-ZnS quantum dots by using membrane filtration, the filtration process, successfully separated the oleic acid from quantum dots through membranes purification after synthesis; purification of quantum dots is a very significant part of post synthetical treatment that determines the properties of the material. We explore the possibilities of the Langmuir-Blodgett technique to make such layers, using quantum dots as a model system. The Langmuir monolayer of quantum dots were then investigated the surface pressure-area isotherm. From isotherm, we found the surface pressure monolayer changed with time. (paper)

  2. Hole transport in organic field-effect transistors with active poly(3-hexylthiophene) layer containing CdSe quantum dots

    Czech Academy of Sciences Publication Activity Database

    Bielecka, Urszula; Lutsyk, P.; Nyk, M.; Janus, K.; Samoć, M.; Bartkowiak, W.; Nešpůrek, Stanislav

    2013-01-01

    Roč. 31, č. 2 (2013), s. 288-297 ISSN 2083-1331 EU Projects: European Commission(XE) 35859 - BIMORE Institutional research plan: CEZ:AV0Z40500505 Keywords : organic transistor * poly(3-hexylthiophene) * CdSe Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.327, year: 2013

  3. Simultaneous quantification of arginine, alanine, methionine and cysteine amino acids in supplements using a novel bioelectro-nanosensor based on CdSe quantum dot/modified carbon nanotube hollow fiber pencil graphite electrode via Taguchi method.

    Science.gov (United States)

    Hooshmand, Sara; Es'haghi, Zarrin

    2017-11-30

    A number of four amino acids have been simultaneously determined at CdSe quantum dot-modified/multi-walled carbon nanotube hollow fiber pencil graphite electrode in different bodybuilding supplements. CdSe quantum dots were synthesized and applied to construct a modified carbon nanotube hollow fiber pencil graphite electrode. FT-IR, TEM, XRD and EDAX methods were applied for characterization of the synthesized CdSe QDs. The electro-oxidation of arginine (Arg), alanine (Ala), methionine (Met) and cysteine (Cys) at the surface of the modified electrode was studied. Then the Taguchi's method was applied using MINITAB 17 software to find out the optimum conditions for the amino acids determination. Under the optimized conditions, the differential pulse (DP) voltammetric peak currents of Arg, Ala, Met and Cys increased linearly with their concentrations in the ranges of 0.287-33670μM and detection limits of 0.081, 0.158, 0.094 and 0.116μM were obtained for them, respectively. Satisfactory results were achieved for calibration and validation sets. The prepared modified electrode represents a very good resolution between the voltammetric peaks of the four amino acids which makes it suitable for the detection of each in presence of others in real samples. Copyright © 2017. Published by Elsevier B.V.

  4. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    International Nuclear Information System (INIS)

    Mahapatra, Suddhasatta

    2008-01-01

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at T G =300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at T G D =230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  5. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    Energy Technology Data Exchange (ETDEWEB)

    Mahapatra, Suddhasatta

    2008-01-16

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at T{sub G}=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at T{sub G}<{proportional_to}240 C. In the second variant technique, formation of large and distinct islands is demonstrated by deposition of amorphous selenium (a-Se) onto a 2D CdSe epilayer at room temperature and its subsequent desorption at a higher temperature (T{sub D}=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  6. Characterization of primary amine capped CdSe, ZnSe, and ZnS quantum dots by FT-IR: determination of surface bonding interaction and identification of selective desorption.

    Science.gov (United States)

    Cooper, Jason K; Franco, Alexandra M; Gul, Sheraz; Corrado, Carley; Zhang, Jin Z

    2011-07-05

    Surface ligands of semiconductor quantum dots (QDs) critically influence their properties and functionalities. It is of strong interest to understand the structural characteristics of surface ligands and how they interact with the QDs. Three quantum dot (QD) systems (CdSe, ZnSe, and ZnS) with primary aliphatic amine capping ligands were characterized primarily by FT-IR spectroscopy as well as NMR, UV-vis, and fluorescence spectroscopy, and by transmission electron microscopy (TEM). Representative primary amines ranging from 8 to 16 carbons were examined in the vapor phase, KBr pellet, and neat and were compared to the QD samples. The strongest hydrogen-bonding effects of the adsorbed ligands were observed in CdSe QDs with the weakest observed in ZnS QDs. There was an observed splitting of the N-H scissoring mode from 1610 cm(-1) in the neat sample to 1544 and 1635 cm(-1) when bound to CdSe QDs, which had the largest splitting of this type. The splitting is attributed to amine ligands bound to either Cd or Se surface sites, respectively. The effect of exposure of the QDs dispersed in nonpolar medium to methanol as a crashing agent was also examined. In the CdSe system, the Cd-bound scissoring mode disappeared, possibly due to methanol replacing surface cadmium sites. The opposite was observed for ZnSe QDs, in which the Se-bound scissoring mode disappeared. It was concluded that surface coverage and ligand bonding partners could be characterized by FT-IR and that selective removal of surface ligands could be achieved through introduction of competitive binding interactions at the surface. © 2011 American Chemical Society

  7. Ameliorating effects of extracellular polymeric substances excreted by Thalassiosira pseudonana on algal toxicity of CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Saijin, E-mail: zhangs@tamug.edu [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Jiang Yuelu, E-mail: jyuelu@gmail.com [Department of Marine Biology, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Chen, Chi-Shuo, E-mail: chen.chishuo@gmail.com [School of Engineering, University of California - Merced, Merced, CA 95344 (United States); Creeley, Danielle [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Schwehr, Kathleen A., E-mail: schwerhk@tamug.edu [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Quigg, Antonietta, E-mail: quigga@tamug.edu [Department of Marine Biology, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Department of Oceanography, Texas A and M University, College Station, TX 77843 (United States); Chin, Wei-Chun, E-mail: wchin2@ucmerced.edu [School of Engineering, University of California - Merced, Merced, CA 95344 (United States); Santschi, Peter H., E-mail: santschi@tamug.edu [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Department of Oceanography, Texas A and M University, College Station, TX 77843 (United States)

    2013-01-15

    Quantum dots (QDs) are engineered nanoparticles (ENs) that have found increasing applications and shown great potential in drug delivery, biological imaging and industrial products. Knowledge of their stability, fate and transport in the aquatic environment is still lacking, including details of how these nanomaterials interact with marine phytoplankton. Here, we examined the toxicity of functionalized CdSe/ZnS QDs (amine- and carboxyl-) by exposing them for five days to Thalassiosira pseudonana (marine diatom) grown under different nutrient-conditions (enriched versus nitrogen-limited media). The released polysaccharides and proteins, the major components of extracellular polymeric substances (EPS), were measured to assess their potential effects on the interactions between QDs and T. pseudonana. The partitioning of QDs was analyzed by monitoring the concentration of Cd in different size fractions of the cultures (i.e., filtrate, <0.22 {mu}m and permeate, <3 kDa). We found that the Cd release of QDs in the T. pseudonana culture was dependent on the nutrient conditions and nature of QDs' surface coating. Both amine- and carboxyl-functionalized QDs exhibited higher rates of Cd release in N-limited cultures than in nutrient enriched cultures. The results also showed that amine-functionalized QDs aggregate with minimal Cd release, independent of nutrient conditions. Laser scanning confocal microscopy images confirmed that aggregates are composed of QDs and the culture matrix (EPS). In addition, both types of QDs showed limited toxicity to T. pseudonana. The increasing production of proteins induced by QDs suggests that extracellular proteins might be involved in the detoxification of QDs to T. pseudonana via the Cd release of QDs. Our results here demonstrated that EPS can play an ameliorating role in QD toxicity, fate and transport in the aquatic environment.

  8. ATP synthesis in the energy metabolism pathway: a new perspective for manipulating CdSe quantum dots biosynthesized in Saccharomyces cerevisiae

    Directory of Open Access Journals (Sweden)

    Zhang R

    2017-05-01

    Full Text Available Rong Zhang,1–3 Ming Shao,1–3 Xu Han,1–3 Chuan Wang,3–4 Yong Li,3–4 Bin Hu,3–4 Daiwen Pang,3–4 Zhixiong Xie1–31Hubei Key Laboratory of Cell Homeostasis, 2College of Life Sciences, Wuhan University, 3Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education, 4College of Chemistry and Molecular Science, Wuhan University, Wuhan, People’s Republic of ChinaAbstract: Due to a growing trend in their biomedical application, biosynthesized nanomaterials are of great interest to researchers nowadays with their biocompatible, low-energy consumption, economic, and tunable characteristics. It is important to understand the mechanism of biosynthesis in order to achieve more efficient applications. Since there are only rare studies on the influences of cellular energy levels on biosynthesis, the influence of energy is often overlooked. Through determination of the intracellular ATP concentrations during the biosynthesis process, significant changes were observed. In addition, ATP synthesis deficiency caused great decreases in quantum dots (QDs biosynthesis in the Δatp1, Δatp2, Δatp14, and Δatp17 strains. With inductively coupled plasma-atomic emission spectrometry and atomic absorption spectroscopy analyses, it was found that ATP affected the accumulation of the seleno-precursor and helped with the uptake of Cd and the formation of QDs. We successfully enhanced the fluorescence intensity 1.5 or 2 times through genetic modification to increase ATP or SeAM (the seleno analog of S-adenosylmethionine, the product that would accumulate when ATP is accrued. This work explains the mechanism for the correlation of the cellular energy level and QDs biosynthesis in living cells, demonstrates control of the biosynthesis using this mechanism, and thus provides a new manipulation strategy for the biosynthesis of other nanomaterials to widen their applications. Keywords: ATP, biosynthesis, Saccharomyces cerevisiae, QDs, CdSe

  9. Chemical stability of CdSe quantum dots in seawater and their effects on a marine microalga.

    Science.gov (United States)

    Morelli, Elisabetta; Cioni, Patrizia; Posarelli, Mauro; Gabellieri, Edi

    2012-10-15

    With the increasing use of nanotechnologies, it is expected that nanomaterials end up in natural aquatic systems, from freshwater to the sea. In this work we studied the chemical behaviour of water-soluble CdSe QDs in seawater and their effects on the marine diatom Phaeodactylum tricornutum, as a model of a biological receptor in the marine environment. We evaluated QD toxicity in terms of growth rate inhibition, oxidative stress and ROS accumulation. In addition, we used the synthesis of phytochelatins (PCs) as a biomarker of the presence of free Cd(2+) ions released from QDs. The optical and chemical characterization demonstrated the propensity of QDs to aggregate after dispersion in raw seawater. In addition, bare CdSe QDs, lacking the ZnS shell, underwent a salinity-dependent degradation process. Short-term exposure experiments showed that the ease of degradation of QDs in seawater correlated with the synthesis of PCs in P. tricornutum cells. Long-term exposure experiments, carried out with the most stable CdSe/ZnS QDs, showed that algae accumulated Cd, but synthesized negligible amounts of PCs. Since the production of PCs is a specific signal of the presence of bioavailable metal ions, our findings suggest that QDs, associated to P. tricornutum cells, did not release PC-inducing metal species. Our data also showed a gradual decrease in algal growth rate at concentrations of QDs higher than 0.5nM. Measurements of the activity of the antioxidant enzymes showed that superoxide dismutase (SOD) and catalase (CAT) activities were increased by exposure to [QDs]≥0.5 nM, whereas ascorbate peroxidase (APX) and glutathione reductase (GR) activities were not significantly affected. The increase in SOD and CAT activity can be considered a symptom of oxidative stress induced by an enhanced production of ROS. This hypothesis was confirmed by the concomitant increase in the intracellular ROS concentration. Copyright © 2012 Elsevier B.V. All rights reserved.

  10. Chemical stability of CdSe quantum dots in seawater and their effects on a marine microalga

    International Nuclear Information System (INIS)

    Morelli, Elisabetta; Cioni, Patrizia; Posarelli, Mauro; Gabellieri, Edi

    2012-01-01

    With the increasing use of nanotechnologies, it is expected that nanomaterials end up in natural aquatic systems, from freshwater to the sea. In this work we studied the chemical behaviour of water-soluble CdSe QDs in seawater and their effects on the marine diatom Phaeodactylum tricornutum, as a model of a biological receptor in the marine environment. We evaluated QD toxicity in terms of growth rate inhibition, oxidative stress and ROS accumulation. In addition, we used the synthesis of phytochelatins (PCs) as a biomarker of the presence of free Cd 2+ ions released from QDs. The optical and chemical characterization demonstrated the propensity of QDs to aggregate after dispersion in raw seawater. In addition, bare CdSe QDs, lacking the ZnS shell, underwent a salinity-dependent degradation process. Short-term exposure experiments showed that the ease of degradation of QDs in seawater correlated with the synthesis of PCs in P. tricornutum cells. Long-term exposure experiments, carried out with the most stable CdSe/ZnS QDs, showed that algae accumulated Cd, but synthesized negligible amounts of PCs. Since the production of PCs is a specific signal of the presence of bioavailable metal ions, our findings suggest that QDs, associated to P. tricornutum cells, did not release PC-inducing metal species. Our data also showed a gradual decrease in algal growth rate at concentrations of QDs higher than 0.5 nM. Measurements of the activity of the antioxidant enzymes showed that superoxide dismutase (SOD) and catalase (CAT) activities were increased by exposure to [QDs] ≥ 0.5 nM, whereas ascorbate peroxidase (APX) and glutathione reductase (GR) activities were not significantly affected. The increase in SOD and CAT activity can be considered a symptom of oxidative stress induced by an enhanced production of ROS. This hypothesis was confirmed by the concomitant increase in the intracellular ROS concentration.

  11. Chemical stability of CdSe quantum dots in seawater and their effects on a marine microalga

    Energy Technology Data Exchange (ETDEWEB)

    Morelli, Elisabetta, E-mail: elisabetta.morelli@pi.ibf.cnr.it [National Research Council - Institute of Biophysics, Section of Pisa, Via Moruzzi, 1, 56124 Pisa (Italy); Cioni, Patrizia [National Research Council - Institute of Biophysics, Section of Pisa, Via Moruzzi, 1, 56124 Pisa (Italy); Posarelli, Mauro [Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Section of Pisa, Via Moruzzi, 1, 56124 Pisa (Italy); Gabellieri, Edi [National Research Council - Institute of Biophysics, Section of Pisa, Via Moruzzi, 1, 56124 Pisa (Italy)

    2012-10-15

    With the increasing use of nanotechnologies, it is expected that nanomaterials end up in natural aquatic systems, from freshwater to the sea. In this work we studied the chemical behaviour of water-soluble CdSe QDs in seawater and their effects on the marine diatom Phaeodactylum tricornutum, as a model of a biological receptor in the marine environment. We evaluated QD toxicity in terms of growth rate inhibition, oxidative stress and ROS accumulation. In addition, we used the synthesis of phytochelatins (PCs) as a biomarker of the presence of free Cd{sup 2+} ions released from QDs. The optical and chemical characterization demonstrated the propensity of QDs to aggregate after dispersion in raw seawater. In addition, bare CdSe QDs, lacking the ZnS shell, underwent a salinity-dependent degradation process. Short-term exposure experiments showed that the ease of degradation of QDs in seawater correlated with the synthesis of PCs in P. tricornutum cells. Long-term exposure experiments, carried out with the most stable CdSe/ZnS QDs, showed that algae accumulated Cd, but synthesized negligible amounts of PCs. Since the production of PCs is a specific signal of the presence of bioavailable metal ions, our findings suggest that QDs, associated to P. tricornutum cells, did not release PC-inducing metal species. Our data also showed a gradual decrease in algal growth rate at concentrations of QDs higher than 0.5 nM. Measurements of the activity of the antioxidant enzymes showed that superoxide dismutase (SOD) and catalase (CAT) activities were increased by exposure to [QDs] {>=} 0.5 nM, whereas ascorbate peroxidase (APX) and glutathione reductase (GR) activities were not significantly affected. The increase in SOD and CAT activity can be considered a symptom of oxidative stress induced by an enhanced production of ROS. This hypothesis was confirmed by the concomitant increase in the intracellular ROS concentration.

  12. Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence.

    Science.gov (United States)

    Nadtochenko, Victor; Denisov, Nikolay; Aybush, Arseniy; Gostev, Fedor; Shelaev, Ivan; Titov, Andrey; Umanskiy, Stanislav; Cherepanov, And Dmitry

    2017-11-04

    The main goal of the present work is to study the coherent phonon in strongly confined CdSe quantum dots (QDs) under varied pump fluences. The main characteristics of coherent phonons (amplitude, frequency, phase, spectrogram) of CdSe QDs under the red-edge pump of the excitonic band [1S(e)-1S 3/2 (h)] are reported. We demonstrate for the first time that the amplitude of the coherent optical longitudinal-optical (LO) phonon at 6.16 THz excited in CdSe nanoparticles by a femtosecond unchirped pulse shows a non-monotone dependence on the pump fluence. This dependence exhibits the maximum at pump fluence ~0.8 mJ/cm². At the same time, the amplitudes of the longitudinal acoustic (LA) phonon mode at 0.55 THz and of the coherent wave packet of toluene at 15.6, 23.6 THz show a monotonic rise with the increase of pump fluence. The time frequency representation of an oscillating signal corresponding to LO phonons revealed by continuous wavelet transform (CWT) shows a profound destructive quantum interference close to the origin of distinct (optical phonon) and continuum-like (exciton) quasiparticles. The CWT spectrogram demonstrates a nonlinear chirp at short time delays, where the chirp sign depends on the pump pulse fluence. The CWT spectrogram reveals an anharmonic coupling between optical and acoustic phonons.

  13. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jing [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Hu, Rui [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Jianwei [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Zhang, Butian; Wang, Yucheng [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Xin [Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Law, Wing-Cheung [Department of Industrial and System Engineering, The Hang Kong Polytechnic University, Hung Hom (Hong Kong); Liu, Liwei [School of Science, Changchun University of Science and Technology, Changchun 130022 (China); Ye, Ling, E-mail: lye_301@163.com [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Yong, Ken-Tye, E-mail: ktyong@ntu.edu.sg [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)

    2015-12-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  14. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

    International Nuclear Information System (INIS)

    Liu, Jing; Hu, Rui; Liu, Jianwei; Zhang, Butian; Wang, Yucheng; Liu, Xin; Law, Wing-Cheung; Liu, Liwei; Ye, Ling; Yong, Ken-Tye

    2015-01-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  15. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    Semiconductor quantum dots ("solid-state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution...... of quantum dots, however, results in a large inhomogeneous broadening of quantum dot spectra. Work on self-assembled InGaAs/GaAs quantum dots will be presented. Properties of atom-like single-dot states are investigated optically using high spatial and spectral resolution. Single-dot spectra can be used...

  16. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    1999-01-01

    Semiconductor quantum dots ("solid state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution...... of quantum dots, however, results in a large inhomogeneous broadening of quantum dot spectra.Work on self-assembled InGaAs/GaAs quantum dots will be presented. Properties of atom-like single-dots states are investigated optically using high spatial and spectral resolution. Single-dot spectra can be used...

  17. Structural and optical characterization of electrodeposited CdSe in mesoporous anatase TiO2 for regenerative quantum-dot-sensitized solar cells

    Science.gov (United States)

    Sauvage, Frédéric; Davoisne, Carine; Philippe, Laetitia; Elias, Jamil

    2012-10-01

    We investigated CdSe-sensitized TiO2 solar cells by means of electrodeposition under galvanostatic control. The electrodeposition of CdSe within the mesoporous film of TiO2 gives rise to a uniform, thickness controlled, conformal layer of nanostructured CdSe particles intimately wrapping the anatase TiO2 nanoparticles. This technique has the advantage of providing not only a fast method for sensitization ( panels. XRD together with SAED analysis highlight that the deposit of CdSe is exclusively constituted of the hexagonal polymorph. In addition, hierarchical growth has also been shown, starting from the formation of a TiO2-CdSe core-shell structure followed by the growth of an assembly of CdSe nanoparticles resembling cauliflowers. This assembly exhibits at its core a mosaic texture with crystallites of about 3 nm in size, in contrast to a shell composed of well-crystallized single crystals between 5 and 10 nm in size. Preliminary results on the photovoltaic performance of such a nanostructured composite of TiO2 and CdSe show 0.8% power conversion efficiency under A.M.1.5 G conditions—100 mW cm-2 in association with a new regenerative redox couple based on cobalt(+III/+II) polypyridil complex (Voc = 485 mV, Jsc = 4.26 mA cm -2, ff=0.37).

  18. Biodistribution and stability of CdSe core quantum dots in mouse digestive tract following per os administration: Advantages of double polymer/silica coated nanocrystals

    International Nuclear Information System (INIS)

    Loginova, Y.F.; Dezhurov, S.V.; Zherdeva, V.V.; Kazachkina, N.I.; Wakstein, M.S.; Savitsky, A.P.

    2012-01-01

    Highlights: ► New QDs coated with combination of polythiol ligands and silica shell were synthesized. ► We examine the QDs stability in digestive tract of mice after per os administration. ► The polymer/silica shell prevents QDs degradation and fluorescence quenching in vivo. -- Abstract: CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT–APS) to stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT–APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials – mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) – are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT–APS) are suitable for biological and biomedical applications in the gastrointestinal tract.

  19. Biodistribution and stability of CdSe core quantum dots in mouse digestive tract following per os administration: Advantages of double polymer/silica coated nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Loginova, Y.F. [Laboratory of Physical Biochemistry, A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow 119071 (Russian Federation); Dezhurov, S.V. [Trial Center For Science and Technology ' Nanotech-Dubna' , Dubna, Moscow Region 141983 (Russian Federation); Zherdeva, V.V.; Kazachkina, N.I. [Laboratory of Physical Biochemistry, A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow 119071 (Russian Federation); Wakstein, M.S. [Trial Center For Science and Technology ' Nanotech-Dubna' , Dubna, Moscow Region 141983 (Russian Federation); Savitsky, A.P., E-mail: apsavitsky@inbi.ras.ru [Laboratory of Physical Biochemistry, A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow 119071 (Russian Federation)

    2012-03-02

    Highlights: Black-Right-Pointing-Pointer New QDs coated with combination of polythiol ligands and silica shell were synthesized. Black-Right-Pointing-Pointer We examine the QDs stability in digestive tract of mice after per os administration. Black-Right-Pointing-Pointer The polymer/silica shell prevents QDs degradation and fluorescence quenching in vivo. -- Abstract: CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT-APS) to stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT-APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials - mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) - are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT-APS) are suitable for biological and biomedical applications in the gastrointestinal tract.

  20. Microfabricated disposable nanosensor based on CdSe quantum dot/ionic liquid-mediated hollow fiber-pencil graphite electrode for simultaneous electrochemical quantification of uric acid and creatinine in human samples

    Energy Technology Data Exchange (ETDEWEB)

    Hooshmand, Sara; Es' haghi, Zarrin, E-mail: eshaghi@pnu.ac.ir

    2017-06-15

    In this research, a novel sensitive electrochemical nanosensor based on the cadmium selenide quantum dots (QDs)/ionic liquid mediated hollow fiber-pencil graphite electrode (HF-PGE) was prepared and applied for simultaneous determination of uric acid (UA) and creatinine (Crn) in urine and serum samples. The electrocatalytic oxidation of the analytes was investigated via differential pulse (DPV) and cyclic voltammetry (CV). The experiments were designed, in two different steps, according to Taguchi's method; OA9 L9 (3{sup 3}) and OA9 L9 (3{sup 4}) orthogonal array to optimize experimental runs. The results revealed that the electrode response was initially influenced by the types of sensor and types of ionic liquids and their ratios. The amount of QD, buffer pH, equilibration time and scan rate also influenced electrode response efficiency. According to the results of Taguchi analysis, the amount of tetra phenyl phosphonium chloride (TPPC) and QD were the most influencing parameters on the yield response of the modified electrodes. Linear ranges were obtained between 0.297–2.970 × 10{sup 3} and 0.442–8.840 × 10{sup 3} μM, with the detection limits of 0.083 and 0.229 μM and relative standard deviations (RSD) of 2.4% and 1.8%, for UA and Crn, respectively. Finally, the proposed method was successfully examined for simultaneous determination of UA and Crn in human urine and serum samples. - Highlights: • Sensor based on modified CdSe quantum dot/ionic liquid mediated hollow fiber graphite electrode. • One-step simultaneous purification, pre-concentration, extraction, back-extraction and determination of electroactive analytes. • Target analyte uric acid (UA) and creatinine (Crn) in urine and serum samples. • Disposable nature of sensor reduced risk of carry-over.

  1. Uniform thin films of CdSe and CdSe(ZnS) core(shell) quantum dots by sol-gel assembly: enabling photoelectrochemical characterization and electronic applications.

    Science.gov (United States)

    Korala, Lasantha; Wang, Zhijie; Liu, Yi; Maldonado, Stephen; Brock, Stephanie L

    2013-02-26

    Optoelectronic properties of quantum dot (QD) films are limited by (1) poor interfacial chemistry and (2) nonradiative recombination due to surface traps. To address these performance issues, sol-gel methods are applied to fabricate thin films of CdSe and core(shell) CdSe(ZnS) QDs. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging with chemical analysis confirms that the surface of the QDs in the sol-gel thin films are chalcogen-rich, consistent with an oxidative-induced gelation mechanism in which connectivity is achieved by formation of dichalcogenide covalent linkages between particles. The ligand removal and assembly process is probed by thermogravimetric, spectroscopic, and microscopic studies. Further enhancement of interparticle coupling via mild thermal annealing, which removes residual ligands and reinforces QD connectivity, results in QD sol-gel thin films with superior charge transport properties, as shown by a dramatic enhancement of electrochemical photocurrent under white light illumination relative to thin films composed of ligand-capped QDs. A more than 2-fold enhancement in photocurrent, and a further increase in photovoltage can be achieved by passivation of surface defects via overcoating with a thin ZnS shell. The ability to tune interfacial and surface characteristics for the optimization of photophysical properties suggests that the sol-gel approach may enable formation of QD thin films suitable for a range of optoelectronic applications.

  2. Uniform Thin Films of CdSe and CdSe(ZnS) Core(shell) Quantum Dots by Sol-Gel Assembly: Enabling Photoelectrochemical Characterization and Electronic Applications

    Science.gov (United States)

    Korala, Lasantha; Wang, Zhijie; Liu, Yi; Maldonado, Stephen; Brock, Stephanie L.

    2013-01-01

    Optoelectronic properties of quantum dot (QD) films are limited by (1) poor interfacial chemistry and (2) non-radiative recombination due to surface traps. To address these performance issues, sol-gel methods are applied to fabricate thin films of CdSe and core(shell) CdSe(ZnS) QDs. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging with chemical analysis confirms that the surface of the QDs in the sol-gel thin films are chalcogen-rich, consistent with an oxidative-induced gelation mechanism in which connectivity is achieved by formation of dichalcogenide covalent linkages between particles. The ligand removal and assembly process is probed by thermogravimetric, spectroscopic and microscopic studies. Further enhancement of inter-particle coupling via mild thermal annealing, which removes residual ligands and reinforces QD connectivity, results in QD sol-gel thin films with superior charge transport properties, as shown by a dramatic enhancement of electrochemical photocurrent under white light illumination relative to thin films composed of ligand-capped QDs. A more than 2-fold enhancement in photocurrent, and a further increase in photovoltage can be achieved by passivation of surface defects via overcoating with a thin ZnS shell. The ability to tune interfacial and surface characteristics for the optimization of photophysical properties suggests that the sol-gel approach may enable formation of QD thin films suitable for a range of optoelectronic applications. PMID:23350924

  3. Intracellular Biosynthesis of Fluorescent CdSe Quantum Dots in Bacillus subtilis: A Strategy to Construct Signaling Bacterial Probes for Visually Detecting Interaction Between Bacillus subtilis and Staphylococcus aureus.

    Science.gov (United States)

    Yan, Zheng-Yu; Ai, Xiao-Xia; Su, Yi-Long; Liu, Xin-Ying; Shan, Xiao-Hui; Wu, Sheng-Mei

    2016-02-01

    In this work, fluorescent Bacillus subtilis (B. subtilis) cells were developed as probes for imaging applications and to explore behaviorial interaction between B. subtilis and Staphylococcus aureus (S. aureus). A novel biological strategy of coupling intracellular biochemical reactions for controllable biosynthesis of CdSe quantum dots by living B. subtilis cells was demonstrated, through which highly luminant and photostable fluorescent B. subtilis cells were achieved with good uniformity. With the help of the obtained fluorescent B. subtilis cells probes, S. aureus cells responded to co-cultured B. subtilis and to aggregate. The degree of aggregation was calculated and nonlinearly fitted to a polynomial model. Systematic investigations of their interactions implied that B. subtilis cells inhibit the growth of neighboring S. aureus cells, and this inhibition was affected by both the growth stage and the amount of surrounding B. subtilis cells. Compared to traditional methods of studying bacterial interaction between two species, such as solid culture medium colony observation and imaging mass spectrometry detection, the procedures were more simple, vivid, and photostable due to the efficient fluorescence intralabeling with less influence on the cells' surface, which might provide a new paradigm for future visualization of microbial behavior.

  4. Structural and optical characterization of electrodeposited CdSe in mesoporous anatase TiO2 for regenerative quantum-dot-sensitized solar cells

    International Nuclear Information System (INIS)

    Sauvage, Frédéric; Davoisne, Carine; Philippe, Laetitia; Elias, Jamil

    2012-01-01

    We investigated CdSe-sensitized TiO 2 solar cells by means of electrodeposition under galvanostatic control. The electrodeposition of CdSe within the mesoporous film of TiO 2 gives rise to a uniform, thickness controlled, conformal layer of nanostructured CdSe particles intimately wrapping the anatase TiO 2 nanoparticles. This technique has the advantage of providing not only a fast method for sensitization ( 2 –CdSe core–shell structure followed by the growth of an assembly of CdSe nanoparticles resembling cauliflowers. This assembly exhibits at its core a mosaic texture with crystallites of about 3 nm in size, in contrast to a shell composed of well-crystallized single crystals between 5 and 10 nm in size. Preliminary results on the photovoltaic performance of such a nanostructured composite of TiO 2 and CdSe show 0.8% power conversion efficiency under A.M.1.5 G conditions—100 mW cm −2 in association with a new regenerative redox couple based on cobalt(+III/+II) polypyridil complex (V oc = 485 mV, J sc = 4.26 mA cm −2 , ff=0.37). (paper)

  5. ATP synthesis in the energy metabolism pathway: a new perspective for manipulating CdSe quantum dots biosynthesized inSaccharomyces cerevisiae.

    Science.gov (United States)

    Zhang, Rong; Shao, Ming; Han, Xu; Wang, Chuan; Li, Yong; Hu, Bin; Pang, Daiwen; Xie, Zhixiong

    2017-01-01

    Due to a growing trend in their biomedical application, biosynthesized nanomaterials are of great interest to researchers nowadays with their biocompatible, low-energy consumption, economic, and tunable characteristics. It is important to understand the mechanism of biosynthesis in order to achieve more efficient applications. Since there are only rare studies on the influences of cellular energy levels on biosynthesis, the influence of energy is often overlooked. Through determination of the intracellular ATP concentrations during the biosynthesis process, significant changes were observed. In addition, ATP synthesis deficiency caused great decreases in quantum dots (QDs) biosynthesis in the Δ atp1 , Δ atp2 , Δ atp14 , and Δ atp17 strains. With inductively coupled plasma-atomic emission spectrometry and atomic absorption spectroscopy analyses, it was found that ATP affected the accumulation of the seleno-precursor and helped with the uptake of Cd and the formation of QDs. We successfully enhanced the fluorescence intensity 1.5 or 2 times through genetic modification to increase ATP or SeAM (the seleno analog of S -adenosylmethionine, the product that would accumulate when ATP is accrued). This work explains the mechanism for the correlation of the cellular energy level and QDs biosynthesis in living cells, demonstrates control of the biosynthesis using this mechanism, and thus provides a new manipulation strategy for the biosynthesis of other nanomaterials to widen their applications.

  6. Transmission electron microscopy investigations of the CdSe based quantum structures

    Energy Technology Data Exchange (ETDEWEB)

    Roventa, E.

    2006-09-22

    In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)

  7. Quantum Dots: Theory

    Energy Technology Data Exchange (ETDEWEB)

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    This review covers the description of the methodologies typically used for the calculation of the electronic structure of self-assembled and colloidal quantum dots. These are illustrated by the results of their application to a selected set of physical effects in quantum dots.

  8. Ultrasmall silicon quantum dots

    NARCIS (Netherlands)

    Zwanenburg, F.A.; Van Loon, A.A.; Steele, G.A.; Rijmenam, C.E.W.M.; Balder, T.; Fang, Y.; Lieber, C.M.; Kouwenhoven, L.P.

    2009-01-01

    We report the realization of extremely small single quantum dots in p-type silicon nanowires, defined by Schottky tunnel barriers with Ni and NiSi contacts. Despite their ultrasmall size the NiSi–Si–NiSi nanowire quantum dots readily allow spectroscopy of at least ten consecutive holes, and

  9. Synthesis of quantum dots

    Science.gov (United States)

    McDaniel, Hunter

    2017-10-17

    Common approaches to synthesizing alloyed quantum dots employ high-cost, air-sensitive phosphine complexes as the selenium precursor. Disclosed quantum dot synthesis embodiments avoid these hazardous and air-sensitive selenium precursors. Certain embodiments utilize a combination comprising a thiol and an amine that together reduce and complex the elemental selenium to form a highly reactive selenium precursor at room temperature. The same combination of thiol and amine acts as the reaction solvent, stabilizing ligand, and sulfur source in the synthesis of quantum dot cores. A non-injection approach may also be used. The optical properties of the quantum dots synthesized by this new approach can be finely tuned for a variety of applications by controlling size and/or composition of size and composition. Further, using the same approach, a shell can be grown around a quantum dot core that improves stability, luminescence efficiency, and may reduce toxicity.

  10. Anisotropy in CdSe quantum rods

    Energy Technology Data Exchange (ETDEWEB)

    Li, Liang-shi [Univ. of California, Berkeley, CA (United States)

    2003-01-01

    The size-dependent optical and electronic properties of semiconductor nanocrystals have drawn much attention in the past decade, and have been very well understood for spherical ones. The advent of the synthetic methods to make rod-like CdSe nanocrystals with wurtzite structure has offered us a new opportunity to study their properties as functions of their shape. This dissertation includes three main parts: synthesis of CdSe nanorods with tightly controlled widths and lengths, their optical and dielectric properties, and their large-scale assembly, all of which are either directly or indirectly caused by the uniaxial crystallographic structure of wurtzite CdSe. The hexagonal wurtzite structure is believed to be the primary reason for the growth of CdSe nanorods. It represents itself in the kinetic stabilization of the rod-like particles over the spherical ones in the presence of phosphonic acids. By varying the composition of the surfactant mixture used for synthesis we have achieved tight control of the widths and lengths of the nanorods. The synthesis of monodisperse CdSe nanorods enables us to systematically study their size-dependent properties. For example, room temperature single particle fluorescence spectroscopy has shown that nanorods emit linearly polarized photoluminescence. Theoretical calculations have shown that it is due to the crossing between the two highest occupied electronic levels with increasing aspect ratio. We also measured the permanent electric dipole moment of the nanorods with transient electric birefringence technique. Experimental results on nanorods with different sizes show that the dipole moment is linear to the particle volume, indicating that it originates from the non-centrosymmetric hexagonal lattice. The elongation of the nanocrystals also results in the anisotropic inter-particle interaction. One of the consequences is the formation of liquid crystalline phases when the nanorods are dispersed in solvent to a high enough

  11. Transport in quantum dots

    International Nuclear Information System (INIS)

    Deus, Fernanda; Continetino, Mucio

    2011-01-01

    Full text. In this work we study the time dependent transport in interacting quantum dot. This is a zero-dimensional nano structure system which has quantized electronic states. In our purpose, we are interested in studying such system in a Coulomb blockade regime where a mean-field treatment of the electronic correlations are appropriate. The quantum dot is described by an Anderson type of Hamiltonian where the hybridization term arises from the contact with the leads. We consider a time dependence of both the energy of the localized state in the quantum dot and of the hybridization-like term. These time dependent parameters, under certain conditions, induce a current in the quantum dot even in the absence of difference on the chemical potential of the leads. The approach to this non-equilibrium problem requires the use of a Keldysh formalism. We calculate the non- equilibrium Green's functions and obtain results for the average (equilibrium term) and the non-equilibrium values of the electronic occupation number in the dot. we consider the possibility of a magnetic solution, with different values for the average up and down spins in the quantum dot. Our results allow to obtain, for instance, the tunneling current through the dot. The magnetic nature of the dot, for a certain range of parameters should give rise also to an induced spin current through the dot

  12. Enhanced Photon Extraction from a Nanowire Quantum Dot Using a Bottom-Up Photonic Shell

    DEFF Research Database (Denmark)

    Jeannin, Mathieu; Cremel, Thibault; Häyrynen, Teppo

    2017-01-01

    Semiconductor nanowires offer the possibility to grow high-quality quantum-dot heterostructures, and, in particular, CdSe quantum dots inserted in ZnSe nanowires have demonstrated the ability to emit single photons up to room temperature. In this paper, we demonstrate a bottom-up approach...

  13. Quantum dot molecules

    CERN Document Server

    Wu, Jiang

    2014-01-01

    This book reviews recent advances in the exciting and rapidly growing field of quantum dot molecules (QDMs). It offers state-of-the-art coverage of novel techniques and connects fundamental physical properties with device design.

  14. Gate-induced carrier delocalization in quantum dot field effect transistors.

    Science.gov (United States)

    Turk, Michael E; Choi, Ji-Hyuk; Oh, Soong Ju; Fafarman, Aaron T; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R; Kikkawa, James M

    2014-10-08

    We study gate-controlled, low-temperature resistance and magnetotransport in indium-doped CdSe quantum dot field effect transistors. We show that using the gate to accumulate electrons in the quantum dot channel increases the "localization product" (localization length times dielectric constant) describing transport at the Fermi level, as expected for Fermi level changes near a mobility edge. Our measurements suggest that the localization length increases to significantly greater than the quantum dot diameter.

  15. Graphene quantum dots

    CERN Document Server

    Güçlü, Alev Devrim; Korkusinski, Marek; Hawrylak, Pawel

    2014-01-01

    This book reflects the current status of theoretical and experimental research of graphene based nanostructures, in particular quantum dots, at a level accessible to young researchers, graduate students, experimentalists and theorists. It presents the current state of research of graphene quantum dots, a single or few monolayer thick islands of graphene. It introduces the reader to the electronic and optical properties of graphite, intercalated graphite and graphene, including Dirac fermions, Berry's phase associated with sublattices and valley degeneracy, covers single particle properties of

  16. Quantum dot solar cells

    CERN Document Server

    Wu, Jiang

    2013-01-01

    The third generation of solar cells includes those based on semiconductor quantum dots. This sophisticated technology applies nanotechnology and quantum mechanics theory to enhance the performance of ordinary solar cells. Although a practical application of quantum dot solar cells has yet to be achieved, a large number of theoretical calculations and experimental studies have confirmed the potential for meeting the requirement for ultra-high conversion efficiency. In this book, high-profile scientists have contributed tutorial chapters that outline the methods used in and the results of variou

  17. Quantum optics with single quantum dot devices

    International Nuclear Information System (INIS)

    Zwiller, Valery; Aichele, Thomas; Benson, Oliver

    2004-01-01

    A single radiative transition in a single-quantum emitter results in the emission of a single photon. Single quantum dots are single-quantum emitters with all the requirements to generate single photons at visible and near-infrared wavelengths. It is also possible to generate more than single photons with single quantum dots. In this paper we show that single quantum dots can be used to generate non-classical states of light, from single photons to photon triplets. Advanced solid state structures can be fabricated with single quantum dots as their active region. We also show results obtained on devices based on single quantum dots

  18. Highly luminescent CdSe/ZnSe core-shell quantum dots of one-pot preparation in octadecene

    NARCIS (Netherlands)

    Zeng, Q.; Kong, X.; Zhang, Y.; Zhang, H.

    2008-01-01

    CdSe/ZnSe core-shell quantum dots were synthesized using a new one-pot procedure where the core was prepared in octadecene. A ZnSe shell around a CdSe nanoparticle was formed by the reaction of selenium-richness on the surfaces of CdSe nanoparticles with Zn2+ from the injected zinc stearate

  19. Auger-Limited Carrier Recombination and Relaxation in CdSe Colloidal Quantum Wells

    Energy Technology Data Exchange (ETDEWEB)

    Baghani, Erfan; O’Leary, Stephen K.; Fedin, Igor; Talapin, Dmitri V.; Pelton, Matthew

    2015-03-19

    Using time-resolved photoluminescence spectroscopy, we show that two-exciton Auger recombination dominates carrier recombination and cooling dynamics in CdSe nanoplatelets, or colloidal quantum wells. The electron-hole recombination rate depends only on the number of electron-hole pairs present in each nanoplatelet, and is consistent with a twoexciton recombination process over a wide range of exciton densities. The carrier relaxation rate within the conduction and valence bands also depends only on the number of electron-hole pairs present, apart from an initial rapid decay, and is consistent with the cooling rate being limited by reheating due to Auger recombination processes. These Auger-limited recombination and relaxation dynamics are qualitatively different from the carrier dynamics in either colloidal quantum dots or epitaxial quantum wells. TOC FIGURE:

  20. Quantum Dot Spectrometer (GSFC IRAD)

    Data.gov (United States)

    National Aeronautics and Space Administration — We are developing an ultra-compact, low mass, low-cost, yet high resolution, multispectral imager based on an innovative quantum dot array concept. The quantum dot...

  1. Hexagonal graphene quantum dots

    KAUST Repository

    Ghosh, Sumit

    2016-12-05

    We study hexagonal graphene quantum dots, using density functional theory, to obtain a quantitative description of the electronic properties and their size dependence, considering disk and ring geometries with both armchair and zigzag edges. We show that the electronic properties of quantum dots with armchair edges are more sensitive to structural details than those with zigzag edges. As functions of the inner and outer radii, we find in the case of armchair edges that the size of the band gap follows distinct branches, while in the case of zigzag edges it changes monotonically. This behaviour is further analyzed by studying the ground state wave function and explained in terms of its localisation.

  2. 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.

  3. Nanocrystal quantum dots

    CERN Document Server

    Klimov, Victor I

    2010-01-01

    ""Soft"" Chemical Synthesis and Manipulation of Semiconductor Nanocrystals, J.A. Hollingsworth and V.I. Klimov Electronic Structure in Semiconductor Nanocrystals: Optical Experiment, D.J. NorrisFine Structure and Polarization Properties of Band-Edge Excitons in Semiconductor Nanocrystals, A.L. EfrosIntraband Spectroscopy and Dynamics of Colloidal Semiconductor Quantum Dots, P. Guyot-Sionnest, M. Shim, and C. WangMultiexciton Phenomena in Semiconductor Nanocrystals, V.I. KlimovOptical Dynamics in Single Semiconductor Quantum Do

  4. Carbon nanotube quantum dots

    NARCIS (Netherlands)

    Sapmaz, S.

    2006-01-01

    Low temperature electron transport measurements on individual single wall carbon nanotubes are described in this thesis. Carbon nanotubes are small hollow cylinders made entirely out of carbon atoms. At low temperatures (below ~10 K) finite length nanotubes form quantum dots. Because of its small

  5. PREFACE: Quantum Dot 2010

    Science.gov (United States)

    Taylor, Robert A.

    2010-09-01

    These conference proceedings contain the written papers of the contributions presented at Quantum Dot 2010 (QD2010). The conference was held in Nottingham, UK, on 26-30 April 2010. The conference addressed topics in research on: 1. Epitaxial quantum dots (including self-assembled and interface structures, dots defined by electrostatic gates etc): optical properties and electron transport quantum coherence effects spin phenomena optics of dots in cavities interaction with surface plasmons in metal/semiconductor structures opto-electronics applications 2. Novel QD structures: fabrication and physics of graphene dots, dots in nano-wires etc 3. Colloidal quantum dots: growth (shape control and hybrid nanocrystals such as metal/semiconductor, magnetic/semiconductor) assembly and surface functionalisation optical properties and spin dynamics electrical and magnetic properties applications (light emitting devices and solar cells, biological and medical applications, data storage, assemblers) The Editors Acknowledgements Conference Organising Committee: Maurice Skolnick (Chair) Alexander Tartakovskii (Programme Chair) Pavlos Lagoudakis (Programme Chair) Max Migliorato (Conference Secretary) Paola Borri (Publicity) Robert Taylor (Proceedings) Manus Hayne (Treasurer) Ray Murray (Sponsorship) Mohamed Henini (Local Organiser) International Advisory Committee: Yasuhiko Arakawa (Tokyo University, Japan) Manfred Bayer (Dortmund University, Germany) Sergey Gaponenko (Stepanov Institute of Physics, Minsk, Belarus) Pawel Hawrylak (NRC, Ottawa, Canada) Fritz Henneberger (Institute for Physics, Berlin, Germany) Atac Imamoglu (ETH, Zurich, Switzerland) Paul Koenraad (TU Eindhoven, Nethehrlands) Guglielmo Lanzani (Politecnico di Milano, Italy) Jungil Lee (Korea Institute of Science and Technology, Korea) Henri Mariette (CNRS-CEA, Grenoble, France) Lu Jeu Sham (San Diego, USA) Andrew Shields (Toshiba Research Europe, Cambridge, UK) Yoshihisa Yamamoto (Stanford University, USA) Artur

  6. Silicon quantum dots: surface matters

    Czech Academy of Sciences Publication Activity Database

    Dohnalová, K.; Gregorkiewicz, T.; Kůsová, Kateřina

    2014-01-01

    Roč. 26, č. 17 (2014), 1-28 ISSN 0953-8984 R&D Projects: GA ČR GPP204/12/P235 Institutional support: RVO:68378271 Keywords : silicon quantum dots * quantum dot * surface chemistry * quantum confinement Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.346, year: 2014

  7. Quantum dots for quantum information technologies

    CERN Document Server

    2017-01-01

    This book highlights the most recent developments in quantum dot spin physics and the generation of deterministic superior non-classical light states with quantum dots. In particular, it addresses single quantum dot spin manipulation, spin-photon entanglement and the generation of single-photon and entangled photon pair states with nearly ideal properties. The role of semiconductor microcavities, nanophotonic interfaces as well as quantum photonic integrated circuits is emphasized. The latest theoretical and experimental studies of phonon-dressed light matter interaction, single-dot lasing and resonance fluorescence in QD cavity systems are also provided. The book is written by the leading experts in the field.

  8. Quantum Dots in Liquid Scintillator

    Science.gov (United States)

    Gooding, Diana

    2017-09-01

    Quantum dots are semiconducting crystals with dimensions on the order of nanometers. Due to quantum confinement, their size gives rise to optical properties that resemble those of single atoms, rather than bulk material. One of these is their absorption of light shorter than a characteristic wavelength and reemission in a narrow peak around that wavelength. This unique photoluminescence makes quantum dots ideal wavelength shifters. Moreover, their chemistry provides a straight-forward method to suspend heavy elements in organic scintillators. The NuDot collaboration has been pursuing a variety of new quantum dots, and a review of the current results will be presented.

  9. Characterization of graphene quantum dot hybrid structures

    Science.gov (United States)

    Chung, Ting-Fung; Hu, Jiuning; Jauregui, Luis A.; Chen, Liangliang; Zhao, Qing; Ruan, Xiulin; Chen, Yong P.

    2012-02-01

    We report electrical transport, photo-electric response and Raman spectroscopy measurements in macroscopic samples of graphene decorated with inorganic quantum dots (CdSe QDs). QDs are deposited on chemical vapor deposition (CVD) graphene by spin-coating. Raman measurements of graphene decorated with QDs on Si wafer show very similar spectra with clear G and 2D peaks that reveal no degradation of graphene during the QDs deposition process. Furthermore, two types of device architectures (QDs-graphene and graphene-QDs-graphene) are fabricated with graphene as a transparent electrode and QD as a light absorbent for electrical photoresponse characterization. Upon application of either a broadband light source or a 532-nm monochromatic laser source, graphene-QDs-graphene devices demonstrate photoconducting response, but not in the case of QDs-graphene devices.

  10. Quadra-Quantum Dots and Related Patterns of Quantum Dot Molecules: Basic Nanostructures for Quantum Dot Cellular Automata Application

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

    Full Text Available Laterally close-packed quantum dots (QDs called quantum dot molecules (QDMs are grown by modified molecular beam epitaxy (MBE. Quantum dots could be aligned and cross hatched. Quantum rings (QRs created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs and quantum dot rings (QDRs. Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA is laterally close-packed quantum dot molecules having four quantum dots at the corners of square configuration. These four quantum dot sets are called quadra-quantum dots (QQDs. Aligned quadra-quantum dots with two electron confinements work like a wire for digital information transmission by Coulomb repulsion force, which is fast and consumes little power. Combination of quadra-quantum dots in line and their cross-over works as logic gates and memory bits. Molecular Beam Epitaxial growth technique called 'Droplet Epitaxy' has been developed for several quantum nanostructures such as quantum rings and quantum dot rings. Quantum rings are prepared by using 20 ML In-Ga (15:85 droplets deposited on a GaAs substrate at 390'C with a droplet growth rate of 1ML/s. Arsenic flux (7'8'10-6Torr is then exposed for InGaAs crystallization at 200'C for 5 min. During droplet epitaxy at a high droplet thickness and high temperature, out-diffusion from the centre of droplets occurs under anisotropic strain. This leads to quantum ring structures having non-uniform ring stripes and deep square-shaped nanoholes. Using these peculiar quantum rings as templates, four quantum dots situated at the corners of a square shape are regrown. Two of these four quantum dots are aligned either or, which are preferable crystallographic directions of quantum dot alignment in general.

  11. Aggregation, sedimentation, dissolution and bioavailability of quantum dots in estuarine systems.

    Science.gov (United States)

    To understand their fate and transport in estuarine systems, the aggregation, sedimentation, and dissolution of CdSe quantum dots (QDs) in seawater were investigated. Hydrodynamic size increased from 40 to 60 nm to >1 mm within 1 h in seawater, and the aggregates were highly p...

  12. The use of bulk states to accelerate the band edge statecalculation of a semiconductor quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Vomel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques,Osni A.; Dongarra, Jack J.

    2006-05-10

    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations.

  13. Towards Ideal Quantum Dots

    Directory of Open Access Journals (Sweden)

    Vyacheslav A. Elyukhin

    2013-01-01

    Full Text Available Arrays of single photon emitters with the same energy of luminescence are necessary for the development of quantum imformation technology. The studied epitaxial quantum dots have an undresired inhomogeneity of luminescence. Here, AxB1-xCyD1-y alloys of AC, AD, BC and BD compounds are presented as semiconductors in which non-random distribution of cations and anions may result in self-assembling of identical tetrahedral clusters. It can be due to the preference of AC and BD bonding over AD and BC one, a decrease of the strain energy or both of them. The self-assembling conditions of 1P4Ga clusters in AlN-rich AlxGa1-xPyN1-y alloys with Ga and phosphorus contents in the dilute and ultra dilute limits, correspondingly, are represented. All phosphorus atoms should be in 1P4Ga clusters at ~1000 oC if the Ga content reaches several percents. AlN-rich AlxGa1-xPyN1-y alloys with 1P4Ga clusters are promising semiconductors for fabrication of arrays of identical single photon emitters with the same energy of luminescence

  14. Femtosecond Cooling of Hot Electrons in CdSe Quantum-Well Platelets

    NARCIS (Netherlands)

    Sippel, Philipp; Albrecht, Wiebke; van der Bok, Johanna C.; Moes, Relinde; Hannappel, Thomas; Eichberger, Rainer; Vanmaekelbergh, Daniel

    Semiconductor quantum wells are ubiquitous in high-performance optoelectronic devices such as solar cells and lasers. Understanding and controlling of the (hot) carrier dynamics is essential to optimize their performance. Here, we study hot electron cooling in colloidal CdSe quantum-well

  15. Quantum dots in photonic crystals for integrated quantum photonics

    Science.gov (United States)

    Kim, Je-Hyung; Richardson, Christopher J. K.; Leavitt, Richard P.; Waks, Edo

    2017-08-01

    Integrated quantum photonic technologies hold a great promise for application in quantum information processing. A major challenge is to integrate multiple single photon sources on a chip. Quantum dots are bright sources of high purity single photons, and photonic crystals can provide efficient photonic platforms for generating and manipulating single photons from integrated quantum dots. However, integrating multiple quantum dots with photonic crystal devices still remains as a challenging task due to the spectral randomness of the emitters. Here, we present the integration of multiple quantum dots with individual photonic crystal cavities and report quantum interference from chip-integrated multiple quantum dots. To solve the problem of spectral randomness, we introduce local engineering techniques for tuning multiple quantum dots and cavities. From integrated quantum dot devices we observe indistinguishable nature of single photons from individual quantum dots on the same chip. Therefore, our approach paves the way for large-scale quantum photonics with integrated quantum emitters.

  16. Microscale memory characteristics of virus-quantum dot hybrids

    Science.gov (United States)

    Portney, Nathaniel G.; Tseng, Ricky J.; Destito, Giuseppe; Strable, Erica; Yang, Yang; Manchester, Marianne; Finn, M. G.; Ozkan, Mihrimah

    2007-05-01

    An electrical multi stability effect was observed for a single layer device fabricated, comprising a hybrid virus-semiconducting quantum dot (CdSe /ZnS core/shell Qds) assembled onto icosahedral-mutant-virus template (CPMV-T184C). A substrate based bottom-up pathway was used to conjugate two different color emitting Qds for fluorescence visualization and to insert a charging/decharging factor. Pulsed wave measurements depicted distinct conductive states with repeatable and nonvolatile behavior as a functioning memory element.

  17. Photoluminescence intermittency of semiconductor quantum dots in dielectric environments

    Energy Technology Data Exchange (ETDEWEB)

    Isaac, A.

    2006-08-11

    The experimental studies presented in this thesis deal with the photoluminescence intermittency of semiconductor quantum dots in different dielectric environments. Detailed analysis of intermittency statistics from single capped CdSe/ZnS, uncapped CdSe and water dispersed CdSe/ZnS QDs in different matrices provide experimental evidence for the model of photoionization with a charge ejected into the surrounding matrix as the source of PL intermittency phenomenon. We propose a self-trapping model to explain the increase of dark state lifetimes with the dielectric constant of the matrix. (orig.)

  18. Room temperature excitation spectroscopy of single quantum dots

    Directory of Open Access Journals (Sweden)

    Christian Blum

    2011-08-01

    Full Text Available We report a single molecule detection scheme to investigate excitation spectra of single emitters at room temperature. We demonstrate the potential of single emitter photoluminescence excitation spectroscopy by recording excitation spectra of single CdSe nanocrystals over a wide spectral range of 100 nm. The spectra exhibit emission intermittency, characteristic of single emitters. We observe large variations in the spectra close to the band edge, which represent the individual heterogeneity of the observed quantum dots. We also find specific excitation wavelengths for which the single quantum dots analyzed show an increased propensity for a transition to a long-lived dark state. We expect that the additional capability of recording excitation spectra at room temperature from single emitters will enable insights into the photophysics of emitters that so far have remained inaccessible.

  19. From quantum dots to quantum circuits

    International Nuclear Information System (INIS)

    Ensslin, K.

    2008-01-01

    Full text: Quantum dots, or artificial atoms, confine charge carriers in three-dimensional islands in a semiconductor environment. Detailed understanding and exquisite control of the charge and spin state of the electrically tunable charge occupancy have been demonstrated over the years. Quantum dots with best quality for transport experiments are usually realized in n-type AlGaAs/GaAs heterostructures. Novel material systems, such as graphene, nanowires and p-type heterostructures offer unexplored parameter regimes in view of spin-orbit interactions, carrier-carrier interactions and hyperfine coupling between electron and nuclear spins, which might be relevant for future spin qubits realized in quantum dots. With more sophisticated nanotechnology it has become possible to fabricate coupled quantum systems where classical and quantum mechanical coupling and back action is experimentally investigated. A narrow constriction, or quantum point contact, in vicinity to a quantum dot has been shown to serve as a minimally invasive sensor of the charge state of the dot. If charge transport through the quantum dot is slow enough (kHz), the charge sensor allows the detection of time-resolved transport through quantum-confined structures. This has allowed us to measure extremely small currents not detectable with conventional electronics. In addition the full statistics of current fluctuations becomes experimentally accessible. This way correlations between electrons which influence the current flow can be analyzed by measuring the noise and higher moments of the distribution of current fluctuations. Mesoscopic conductors driven out of equilibrium can emit photons which may be detected by another nearby quantum system with suitably tuned energy levels. This way an on-chip microwave single photon detector has been realized. In a ring geometry containing a tunable double quantum dot it has been possible to measure the self-interference of individual electrons as they traverse

  20. Structure Optimization of Low-Dimensional Quantum Dots via Anisotropic Surface Energy

    Science.gov (United States)

    Yang, Lan-Hee; Hyun, Sangil; Koo, Eunhae; Ahn, Dong June

    2018-03-01

    Semiconductor quantum dots (QDs) exhibit remarkable photostability, large absorption spectra, tunable emission peaks, and high quantum yields. These features originate from their lowdimensionality. It is necessary to control the shape of QDs because their specific characteristics are normally determined by their particular shape and size. We employed first-principle calculations to identify the optimal structures of CdSe quantum dots and investigated the shape-determining mechanism governing the formation of low-dimensional nanomaterials. The anisotropy of surface energy is a key factor determining the shape of nanomaterials and we suggest how to control their geometry and characteristics by adjusting the surface energy.

  1. Quadra-quantum Dots and Related Patterns of Quantum Dot Molecules:

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

    Full Text Available Abstract Laterally close-packed quantum dots (QDs called quantum dot molecules (QDMs are grown by modified molecular beam epitaxy (MBE. Quantum dots could be aligned and cross hatched. Quantum rings (QRs created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs and quantum dot rings (QDRs. Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA is laterally close-packed quantum dot molecules having four quantum dots at the corners of square configuration. These four quantum dot sets are called quadra-quantum dots (QQDs. Aligned quadra-quantum dots with two electron confinements work like a wire for digital information transmission by Coulomb repulsion force, which is fast and consumes little power. Combination of quadra-quantum dots in line and their cross-over works as logic gates and memory bits. Molecular Beam Epitaxial growth technique called ‘‘Droplet Epitaxy” has been developed for several quantum nanostructures such as quantum rings and quantum dot rings. Quantum rings are prepared by using 20 ML In-Ga (15:85 droplets deposited on a GaAs substrate at 390°C with a droplet growth rate of 1ML/s. Arsenic flux (7–8×10-6Torr is then exposed for InGaAs crystallization at 200°C for 5 min. During droplet epitaxy at a high droplet thickness and high temperature, out-diffusion from the centre of droplets occurs under anisotropic strain. This leads to quantum ring structures having non-uniform ring stripes and deep square-shaped nanoholes. Using these peculiar quantum rings as templates, four quantum dots situated at the corners of a square shape are regrown. Two of these four quantum dots are aligned either or , which are preferable crystallographic directions of quantum dot alignment in general.

  2. High Efficiency Quantum Dot Sensitized Solar Cells Based on Direct Adsorption of Quantum Dots on Photoanodes.

    Science.gov (United States)

    Wang, Wenran; Jiang, Guocan; Yu, Juan; Wang, Wei; Pan, Zhenxiao; Nakazawa, Naoki; Shen, Qing; Zhong, Xinhua

    2017-07-12

    Unambiguously direct adsorption (DA) of initial oil-soluble quantum dots (QDs) on TiO 2 film electrode is a convenient and simple approach in the construction of quantum dot sensitized solar cells (QDSCs). Regrettably, low QD loading amount and poor reproducibility shadow the advantages of DA route and constrain its practical application. Herein, the influence of experimental variables in DA process on QD loading amount as well as on the photovoltaic performance of the resultant QDSCs was investigated and optimized systematically, including the choice of solvent, purification of QDs, and sensitization time, as well as QD concentration. Experimental results demonstrated that it is essential to choose appropriate solvent as well as control purification cycles of original QD suspensions so as to realize satisfactory QD loading amount and ensure the high reproducibility. In addition, DA mode renders efficient electron injection from QD to TiO 2 , yet low QD loading amount and adverse QD agglomeration in comparison with the well-developed capping ligand induced self-assembly (CLIS) deposition approach. Mg 2+ treatment on TiO 2 photoanodes can promote the QD loading amount in DA mode. The optimized QDSCs based on DA mode exhibited efficiencies of 6.90% and 9.02% for CdSe and Zn-Cu-In-Se QDSCs, respectively, which were comparable to the best results based on CLIS mode (6.88% and 9.56%, respectively).

  3. Large quantum dots with small oscillator strength

    DEFF Research Database (Denmark)

    Stobbe, Søren; Schlereth, T.W.; Höfling, S.

    2010-01-01

    We have measured the oscillator strength and quantum efficiency of excitons confined in large InGaAs quantum dots by recording the spontaneous emission decay rate while systematically varying the distance between the quantum dots and a semiconductor-air interface. The size of the quantum dots...... is measured by in-plane transmission electron microscopy and we find average in-plane diameters of 40 nm. We have calculated the oscillator strength of excitons of that size assuming a quantum-dot confinement given by a parabolic in-plane potential and a hard-wall vertical potential and predict a very large...... intermixing inside the quantum dots....

  4. Quantum kinetic exciton-LO-phonon interaction in CdSe

    DEFF Research Database (Denmark)

    Woggon, Ulrike; Gindele, Frank; Langbein, Wolfgang

    2000-01-01

    Oscillations with a period of similar to 150 fs are observed in the four-wave mixing (FWM) signal of bulk CdSe and interpreted in terms of non-Markovian exciton-LO-phonon scattering. The experiments show evidence of phonon quantum kinetics in semiconductors of strong polar coupling strength...

  5. Quantum-dot based photonic quantum networks

    Science.gov (United States)

    Lodahl, Peter

    2018-01-01

    Quantum dots (QDs) embedded in photonic nanostructures have in recent years proven to be a very powerful solid-state platform for quantum optics experiments. The combination of near-unity radiative coupling of a single QD to a photonic mode and the ability to eliminate decoherence processes imply that an unprecedent light-matter interface can be obtained. As a result, high-cooperativity photon-emitter quantum interfaces can be constructed opening a path-way to deterministic photonic quantum gates for quantum-information processing applications. In the present manuscript, I review current state-of-the-art on QD devices and their applications for quantum technology. The overarching long-term goal of the research field is to construct photonic quantum networks where remote entanglement can be distributed over long distances by photons.

  6. Electron correlations in quantum dots

    International Nuclear Information System (INIS)

    Tipton, Denver Leonard John

    2001-01-01

    Quantum dot structures confine electrons in a small region of space. Some properties of semiconductor quantum dots, such as the discrete energy levels and shell filling effects visible in addition spectra, have analogies to those of atoms and indeed dots are sometimes referred to as 'artificial atoms'. However, atoms and dots show some fundamental differences due to electron correlations. For real atoms, the kinetic energy of electrons dominates over their mutual Coulomb repulsion energy and for this reason the independent electron approximation works well. For quantum dots the confining potential may be shallower than that of real atoms leading to lower electron densities and a dominance of mutual Coulomb repulsion over kinetic energy. In this strongly correlated regime the independent electron picture leads to qualitatively incorrect results. This thesis concentrates on few-electron quantum dots in the strongly correlated regime both for quasi-one-dimensional and two-dimensional dots in a square confining potential. In this so-called 'Wigner' regime the ground-state electronic charge density is localised near positions of classical electrostatic minima and the interacting electronic spectrum consists of well separated spin multiplets. In the strongly correlated regime the structure of low-energy multiplets is explained by mapping onto lattice models with extended-Hubbard and Heisenberg effective Hamiltonians. The parameters for these effective models are calculated within a Hartree approximation and are shown to reproduce well the exact results obtained by numerical diagonalisation of the full interacting Hamiltonian. Comparison is made between square dots and quantum rings with full rotational symmetry. In the very low-density regime, direct diagonalisation becomes impractical due to excessive computer time for convergence. In this regime a numerical renormalisation group method is applied to one-dimensional dots, enabling effective spin-interactions to be

  7. Cell-permeable Ln(III) chelate-functionalized InP quantum dots as multimodal imaging agents

    NARCIS (Netherlands)

    Stasiuk, Graeme J.; Tamang, Sudarsan; Imbert, Daniel; Poillot, Cathy; Giardiello, Marco; Tisseyre, Céline; Barbier, Emmanuel L.; Fries, Pascal Henry; de Waard, Michel; Reiss, Peter; Mazzanti, Marinella

    2011-01-01

    Quantum dots (QDs) are ideal scaffolds for the development of multimodal imaging agents, but their application in clinical diagnostics is limited by the toxicity of classical CdSe QDs. A new bimodal MRI/optical nanosized contrast agent with high gadolinium payload has been prepared through direct

  8. The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot

    International Nuclear Information System (INIS)

    Voemel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques, Osni A.; Dongarra, Jack J.

    2007-01-01

    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations

  9. Microwave mediated synthesis of semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Afrasiabi, Roodabeh; Sugunan, Abhilash; Shahid, Robina; Toprak, Muhammet S.; Muhammed, Mamoun [Division of Functional Materials, Royal Institute of Technology (KTH), Stockholm (Sweden)

    2012-07-15

    Colloidal quantum dots (QD) have tuneable optoelectronic properties and can be easily handled by simple solution processing techniques, making them very attractive for a wide range of applications. Over the past decade synthesis of morphology controlled high quality (crystalline, monodisperse) colloidal QDs by thermal decomposition of organometallic precursors has matured and is well studied. Recently, synthesis of colloidal QDs by microwave irradiation as heating source is being studied due to the inherently different mechanisms of heat transfer, when compared to solvent convection based heating. Under microwave irradiation, polar precursor molecules directly absorb the microwave energy and heat up more efficiently. Here we report synthesis of colloidal II-VI semiconductor QDs (CdS, CdSe, CdTe) by microwave irradiation and compare it with conventional synthesis based on convection heating. Our findings show that QD synthesis by microwave heating is more efficient and the chalcogenide precursor strongly absorbs the microwave radiation shortening the reaction time and giving a high reaction yield (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Spin storage in quantum dot ensembles and single quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Heiss, Dominik

    2009-10-15

    This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T{sub 1}{proportional_to}T{sup -1}. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T{sub 1}{sup h

  11. Spin storage in quantum dot ensembles and single quantum dots

    International Nuclear Information System (INIS)

    Heiss, Dominik

    2009-01-01

    This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T 1 =20 ms at B=4 T and T=1 K. A strong magnetic field dependence T 1 ∝B -5 has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T 1 ∝T -1 . The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T 1 h in the microsecond range, therefore, comparable with

  12. Nuclear Spins in Quantum Dots

    NARCIS (Netherlands)

    Erlingsson, S.I.

    2003-01-01

    The main theme of this thesis is the hyperfine interaction between the many lattice nuclear spins and electron spins localized in GaAs quantum dots. This interaction is an intrinsic property of the material. Despite the fact that this interaction is rather weak, it can, as shown in this thesis,

  13. Polymer-coated quantum dots

    NARCIS (Netherlands)

    Tomczak, N.; Liu, Rongrong; Vancso, Gyula J.

    2013-01-01

    Quantum Dots (QDs) are semiconductor nanocrystals with distinct photophysical properties finding applications in biology, biosensing, and optoelectronics. Polymeric coatings of QDs are used primarily to provide long-term colloidal stability to QDs dispersed in solutions and also as a source of

  14. Performance Study of CdS/Co-Doped-CdSe Quantum Dot Sensitized Solar Cells

    Directory of Open Access Journals (Sweden)

    Xiaoping Zou

    2014-01-01

    Full Text Available In order to optimize the charge transfer path in quantum dot sensitized solar cells (QDSCs, we employed successive ionic layer adsorption and reaction method to dope CdSe with Co for fabricating CdS/Co-doped-CdSe QDSCs constructed with CdS/Co-doped-CdSe deposited on mesoscopic TiO2 film as photoanode, Pt counter electrode, and sulfide/polysulfide electrolyte. After Co doping, the bandgap of CdSe quantum dot decreases, and the conduction band and valence band all improve, forming a cascade energy level which is more conducive to charge transport inside the solar cell and reducing the recombination of electron-hole thus improving the photocurrent and ultimately improving the power conversion efficiency. This work has not been found in the literature.

  15. Coherent control of quantum dots

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Lodahl, Peter; Hvam, Jørn Märcher

    In recent years much effort has been devoted to the use of semiconductor quantum dotsystems as building blocks for solid-state-based quantum logic devices. One importantparameter for such devices is the coherence time, which determines the number ofpossible quantum operations. From earlier...... measurements the coherence time of the selfassembledquantum dots (QDs) has been reported to be limited by the spontaneousemission rate at cryogenic temperatures1.In this project we propose to alter the coherence time of QDs by taking advantage of arecent technique on modifying spontaneous emission rates...

  16. Colloidal-Quantum-Dot Ring Lasers with Active Color Control.

    Science.gov (United States)

    le Feber, Boris; Prins, Ferry; De Leo, Eva; Rabouw, Freddy T; Norris, David J

    2018-02-14

    To improve the photophysical performance of colloidal quantum dots for laser applications, sophisticated core/shell geometries have been developed. Typically, a wider bandgap semiconductor is added as a shell to enhance the gain from the quantum-dot core. This shell is designed to electronically isolate the core, funnel excitons to it, and reduce nonradiative Auger recombination. However, the shell could also potentially provide a secondary source of gain, leading to further versatility in these materials. Here we develop high-quality quantum-dot ring lasers that not only exhibit lasing from both the core and the shell but also the ability to switch between them. We fabricate ring resonators (with quality factors up to ∼2500) consisting only of CdSe/CdS/ZnS core/shell/shell quantum dots using a simple template-stripping process. We then examine lasing as a function of the optical excitation power and ring radius. In resonators with quality factors >1000, excitons in the CdSe cores lead to red lasing with thresholds at ∼25 μJ/cm 2 . With increasing power, green lasing from the CdS shell emerges (>100 μJ/cm 2 ) and then the red lasing begins to disappear (>250 μJ/cm 2 ). We present a rate-equation model that can explain this color switching as a competition between exciton localization into the core and stimulated emission from excitons in the shell. Moreover, by lowering the quality factor of the cavity we can engineer the device to exhibit only green lasing. The mechanism demonstrated here provides a potential route toward color-switchable quantum-dot lasers.

  17. Stark effect in finite-barrier quantum wells, wires, and dots

    International Nuclear Information System (INIS)

    Pedersen, Thomas Garm

    2017-01-01

    The properties of confined carriers in low-dimensional nanostructures can be controlled by external electric fields and an important manifestation is the Stark shift of quantized energy levels. Here, a unifying analytic theory for the Stark effect in arbitrary dimensional nanostructures is presented. The crucial role of finite potential barriers is stressed, in particular, for three-dimensional confinement. Applying the theory to CdSe quantum dots, finite barriers are shown to improve significantly the agreement with experiments. (paper)

  18. Lanthanide modification of CdSe/ZnS core/shell quantum dots

    DEFF Research Database (Denmark)

    Dethlefsen, Johannes Rytter; Mikhailovsky, Alexander A.; Burks, Peter T.

    2012-01-01

    Lanthanide-modified CdSe quantum dots (CdSe(Ln) QDs) have been prepared by heating a solution of Cd(oleate)(2), SeO2, and Ln(bipy)(S2CNEt2)(3) (bipy = 2,2'-bipyridine) to 180-190 degrees C for 10-15 min. The elemental compositions of the resulting CdSe(Ln) cores and CdSe(Ln)/ZnS core/shell QDs show...

  19. Ex Situ Formation of Metal Selenide Quantum Dots Using Bacterially Derived Selenide Precursors

    Energy Technology Data Exchange (ETDEWEB)

    Fellowes, Jonathan W.; Pattrick, Richard; Lloyd, Jon; Charnock, John M.; Coker, Victoria S.; Mosselmans, JFW; Weng, Tsu-Chien; Pearce, Carolyn I.

    2013-04-12

    Luminescent quantum dots were synthesized using bacterially derived selenide (SeII-) as the precursor. Biogenic SeII- was produced by the reduction of Se-IV by Veillonella atypica and compared directly against borohydride-reduced Se-IV for the production of glutathione-stabilized CdSe and beta-mercaptoethanol-stabilized ZnSe nanoparticles by aqueous synthesis. Biological SeII- formed smaller, narrower size distributed QDs under the same conditions. The growth kinetics of biologically sourced CdSe phases were slower. The proteins isolated from filter sterilized biogenic SeII- included a methylmalonyl-CoA decarboxylase previously characterized in the closely related Veillonella parvula. XAS analysis of the glutathione-capped CdSe at the S K-edge suggested that sulfur from the glutathione was structurally incorporated within the CdSe. A novel synchrotron based XAS technique was also developed to follow the nucleation of biological and inorganic selenide phases, and showed that biogenic SeII- is more stable and more resistant to beam-induced oxidative damage than its inorganic counterpart. The bacterial production of quantum dot precursors offers an alternative, 'green' synthesis technique that negates the requirement of expensive, toxic chemicals and suggests a possible link to the exploitation of selenium contaminated waste streams.

  20. Ex situ formation of metal selenide quantum dots using bacterially derived selenide precursors

    International Nuclear Information System (INIS)

    Fellowes, J W; Pattrick, R A D; Lloyd, J R; Charnock, J M; Coker, V S; Mosselmans, J F W; Weng, T-C; Pearce, C I

    2013-01-01

    Luminescent quantum dots were synthesized using bacterially derived selenide (Se II− ) as the precursor. Biogenic Se II− was produced by the reduction of Se IV by Veillonella atypica and compared directly against borohydride-reduced Se IV for the production of glutathione-stabilized CdSe and β-mercaptoethanol-stabilized ZnSe nanoparticles by aqueous synthesis. Biological Se II− formed smaller, narrower size distributed QDs under the same conditions. The growth kinetics of biologically sourced CdSe phases were slower. The proteins isolated from filter sterilized biogenic Se II− included a methylmalonyl-CoA decarboxylase previously characterized in the closely related Veillonella parvula. XAS analysis of the glutathione-capped CdSe at the S K-edge suggested that sulfur from the glutathione was structurally incorporated within the CdSe. A novel synchrotron based XAS technique was also developed to follow the nucleation of biological and inorganic selenide phases, and showed that biogenic Se II− is more stable and more resistant to beam-induced oxidative damage than its inorganic counterpart. The bacterial production of quantum dot precursors offers an alternative, ‘green’ synthesis technique that negates the requirement of expensive, toxic chemicals and suggests a possible link to the exploitation of selenium contaminated waste streams. (paper)

  1. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Borri, Paola; Ledentsov, N. N.

    2002-01-01

    -power surface emitting VCSELs. We investigated the ultrafast dynamics of quantum-dot semiconductor optical amplifiers. The dephasing time at room temperature of the ground-state transition in semiconductor quantum dots is around 250 fs in an unbiased amplifier, decreasing to below 50 fs when the amplifier...... is biased to positive net gain. We have further measured gain recovery times in quantum dot amplifiers that are significantly lower than in bulk and quantum-well semiconductor optical amplifiers. This is promising for future demonstration of quantum dot devices with high modulation bandwidth...

  2. Ultrasmall colloidal PbS quantum dots

    International Nuclear Information System (INIS)

    Reilly, Nick; Wehrung, Michael; O'Dell, Ryan Andrew; Sun, Liangfeng

    2014-01-01

    Ultrasmall colloidal lead sulfide quantum dots can increase the open circuit voltages of quantum-dot-based solar cells because of their large energy gap. Their small size and visible or near infrared light-emitting property make them attractive to the applications of biological fluorescence labeling. Through a modified organometallic route, we can synthesize lead sulfide quantum dots as small as 1.6 nm in diameter. The low reaction temperature and the addition of a chloroalkane cosolvent decrease the reaction rate, making it possible to obtain the ultrasmall quantum dots. - Highlights: • Ultrasmall colloidal PbS quantum dots as small as 1.6 nm in diameter are synthesized. • The quantum dots emit red light with photoluminescence peak at 760 nm. • The growth temperature is as low as 50 °C. • Addition of cosolvent 1,2-dichloroethane in the reaction decreases the reaction rate

  3. Quantum Logic Using Excitonic Quantum Dots in External Optical Microcavities

    National Research Council Canada - National Science Library

    Raymer, Michael

    2003-01-01

    An experimental project was undertaken to develop means to achieve quantum optical strong coupling between a single GaAs quantum dot and the optical mode of a microcavity for the purpose of quantum...

  4. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

    We will review recent studies performed on InAs quantum dots embedded in GaAs photonic wires, which highlight the strong interest of the photonic wire geometry for quantum optics experiments and quantum optoelectronic devices.......We will review recent studies performed on InAs quantum dots embedded in GaAs photonic wires, which highlight the strong interest of the photonic wire geometry for quantum optics experiments and quantum optoelectronic devices....

  5. 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...

  6. Optimization of conditions for cadmium selenide quantum dot biosynthesis in Saccharomyces cerevisiae.

    Science.gov (United States)

    Brooks, Jordan; Lefebvre, Daniel D

    2017-04-01

    The biosynthesis of quantum dots has been explored as an alternative to traditional physicochemical methods; however, relatively few studies have determined optimal synthesis parameters. Saccharomyces cerevisiae sequentially treated with sodium selenite and cadmium chloride synthesized CdSe quantum dots in the cytoplasm. These nanoparticles displayed a prominent yellow fluorescence, with an emission maximum of approximately 540 nm. The requirement for glutathione in the biosynthetic mechanism was explored by depleting its intracellular content through cellular treatments with 1-chloro-2,4-dinitrobenzene and buthionine sulfoximine. Synthesis was significantly inhibited by both of these reagents when they were applied after selenite treatment prior to the addition of cadmium, thereby indicating that glutathione contributes to the biosynthetic process. Determining the optimum conditions for biosynthesis revealed that quantum dots were produced most efficiently at entry into stationary phase followed by direct addition of 1 mM selenite for only 6 h and then immediately incubating these cells in fresh growth medium containing 3 mM Cd (II). Synthesis of quantum dots reached a maximum at 84 h of reaction time. Biosynthesis of 800-μg g -1 fresh weight cells was achieved. For the first time, significant efforts have been undertaken to optimize each aspect of the CdSe biosynthetic procedure in S. cerevisiae, resulting in a 70% increased production.

  7. Stark shifting two-electron quantum dot

    International Nuclear Information System (INIS)

    Dineykhan, M.; Zhaugasheva, S.A.; Duysebaeva, K.S.

    2003-01-01

    Advances in modern technology make it possible to create semiconducting nano-structures (quantum dot) in which a finite number of electrons are 'captured' in a bounded volume. A quantum dot is associated with a quantum well formed at the interface, between two finite-size semiconductors owing to different positions of the forbidden gaps on the energy scale in these semiconductors. The possibility of monitoring and controlling the properties of quantum dots attracts considerable attention to these objects, as a new elemental basis for future generations of computers. The quantum-mechanical effects and image potential play a significant role in the description of the formation mechanism quantum dot, and determined the confinement potential in a two-electron quantum dot only for the spherical symmetric case. In the present talk, we considered the formation dynamics of two-electron quantum dot with violation of spherical symmetry. So, we have standard Stark potential. The energy spectrum two-electron quantum dot were calculated. Usually Stark interactions determined the tunneling phenomena between quantum dots

  8. Hydrogenic impurity in double quantum dots

    International Nuclear Information System (INIS)

    Wang, X.F.

    2007-01-01

    The ground state binding energy and the average interparticle distances for a hydrogenic impurity in double quantum dots with Gaussian confinement potential are studied by the variational method. The probability density of the electron is calculated, too. The dependence of the binding energy on the impurity position is investigated for GaAs quantum dots. The result shows that the binding energy has a minimum as a function of the distance between the two quantum dots when the impurity is located at the center of one quantum dot or at the center of the edge of one quantum dot. When the impurity is located at the center of the two dots, the binding energy decreases monotonically

  9. Quantum Dot Devices for Optical Signal Processing

    DEFF Research Database (Denmark)

    Chen, Yaohui

    This thesis describes the physics and applications of quantum dot semiconductor optical ampliers through numerical simulations. As nano-structured materials with zero-dimensional quantum connement, semiconductor quantum dot material provides a number of unique physical properties compared...... with other semiconductor materials. The understanding of such properties is important in order to improve the performance of existing devices and to trigger the development of new semiconductor devices for dierent optical signal processing functionalities in the future. We present a detailed quantum dot...... semiconductor optical amplier model incorporating a carrier dynamics rate equation model for quantum dots with inhomogeneous broadening as well as equations describing propagation. A phenomenological description has been used to model the intradot electron scattering between discrete quantum dot states...

  10. Colloidal quantum dot photodetectors

    KAUST Repository

    Konstantatos, Gerasimos

    2011-05-01

    We review recent progress in light sensors based on solution-processed materials. Spin-coated semiconductors can readily be integrated with many substrates including as a post-process atop CMOS silicon and flexible electronics. We focus in particular on visible-, near-infrared, and short-wavelength infrared photodetectors based on size-effect-tuned semiconductor nanoparticles made using quantum-confined PbS, PbSe, Bi 2S3, and In2S3. These devices have in recent years achieved room-temperature D values above 1013 Jones, while fully-depleted photodiodes based on these same materials have achieved MHz response combined with 1012 Jones sensitivities. We discuss the nanoparticle synthesis, the materials processing, integrability, temperature stability, physical operation, and applied performance of this class of devices. © 2010 Elsevier Ltd. All rights reserved.

  11. Energy relaxation in CdSe nanocrystals: the effects of morphology and film preparation.

    Science.gov (United States)

    Spann, Bryan T; Chen, Liangliang; Ruan, Xiulin; Xu, Xianfan

    2013-01-14

    Ultrafast time-resolved absorption spectroscopy is used to investigate exciton dynamics in CdSe nanocrystal films. The effects of morphology, quantum-dot versus quantum-rod, and preparation of nanocrystals in a thin film form are investigated. The measurements revealed longer intraband exciton relaxation in quantum-rods than in quantum-dots. The slowed relaxation in quantum-rods is due to mitigation of the Auger-relaxation mechanism from elongating the nanocrystal. In addition, the nanocrystal thin film showed long-lived confined acoustic phonons corresponding to the ellipsoidal breathing mode, contrary to others work on colloidal systems of CdSe nanocrystals.

  12. Dynamic Trap Formation and Elimination in Colloidal Quantum Dots

    KAUST Repository

    Voznyy, O.

    2013-03-21

    Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers\\' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping. © 2013 American Chemical Society.

  13. Spin Switching via Quantum Dot Spin Valves

    Science.gov (United States)

    Gergs, N. M.; Bender, S. A.; Duine, R. A.; Schuricht, D.

    2018-01-01

    We develop a theory for spin transport and magnetization dynamics in a quantum dot spin valve, i.e., two magnetic reservoirs coupled to a quantum dot. Our theory is able to take into account effects of strong correlations. We demonstrate that, as a result of these strong correlations, the dot gate voltage enables control over the current-induced torques on the magnets and, in particular, enables voltage-controlled magnetic switching. The electrical resistance of the structure can be used to read out the magnetic state. Our model may be realized by a number of experimental systems, including magnetic scanning-tunneling microscope tips and artificial quantum dot systems.

  14. Thick-shell nanocrystal quantum dots

    Science.gov (United States)

    Hollingsworth, Jennifer A [Los Alamos, NM; Chen, Yongfen [Eugene, OR; Klimov, Victor I [Los Alamos, NM; Htoon, Han [Los Alamos, NM; Vela, Javier [Los Alamos, NM

    2011-05-03

    Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

  15. Many electron effects in semiconductor quantum dots

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 26; Issue 1. Many electron effects in ... Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as 'artificial atoms' by some, ... Our calculations have been performed in a three-dimensional quantum dot. We have carried out a study of ...

  16. PREFACE: Quantum dots as probes in biology

    Science.gov (United States)

    Cieplak, Marek

    2013-05-01

    The recent availability of nanostructured materials has resulted in an explosion of research focused on their unique optical, thermal, mechanical and magnetic properties. Optical imagining, magnetic enhancement of contrast and drug delivery capabilities make the nanoparticles of special interest in biomedical applications. These materials have been involved in the development of theranostics—a new field of medicine that is focused on personalized tests and treatment. It is likely that multimodal nanomaterials will be responsible for future diagnostic advances in medicine. Quantum dots (QD) are nanoparticles which exhibit luminescence either through the formation of three-dimensional excitons or excitations of the impurities. The excitonic luminescence can be tuned by changing the size (the smaller the size, the higher the frequency). QDs are usually made of semiconducting materials. Unlike fluorescent proteins and organic dyes, QDs resist photobleaching, allow for multi-wavelength excitations and have narrow emission spectra. The techniques to make QDs are cheap and surface modifications and functionalizations can be implemented. Importantly, QDs could be synthesized to exhibit useful optomagnetic properties and, upon functionalization with an appropriate biomolecule, directed towards a pre-selected target for diagnostic imaging and photodynamic therapy. This special issue on Quantum dots in Biology is focused on recent research in this area. It starts with a topical review by Sreenivasan et al on various physical mechanisms that lead to the QD luminescence and on using wavelength shifts for an improvement in imaging. The next paper by Szczepaniak et al discusses nanohybrids involving QDs made of CdSe coated by ZnS and combined covalently with a photosynthetic enzyme. These nanohybrids are shown to maintain the enzymatic activity, however the enzyme properties depend on the size of a QD. They are proposed as tools to study photosynthesis in isolated

  17. Solid-state cavity quantum electrodynamics using quantum dots

    International Nuclear Information System (INIS)

    Gerard, J.M.; Gayral, B.; Moreau, E.; Robert, I.; Abram, I.

    2001-01-01

    We review the recent development of solid-state cavity quantum electrodynamics using single self-assembled InAs quantum dots and three-dimensional semiconductor microcavities. We discuss first prospects for observing a strong coupling regime for single quantum dots. We then demonstrate that the strong Purcell effect observed for single quantum dots in the weak coupling regime allows us to prepare emitted photons in a given state (the same spatial mode, the same polarization). We present finally the first single-mode solid-state source of single photons, based on an isolated quantum dot in a pillar microcavity. This optoelectronic device, the first ever to rely on a cavity quantum electrodynamics effect, exploits both Coulomb interaction between trapped carriers in a single quantum dot and single mode photon tunneling in the microcavity. (author)

  18. Biocompatible Quantum Dots for Biological Applications

    Science.gov (United States)

    Rosenthal, Sandra J.; Chang, Jerry C.; Kovtun, Oleg; McBride, James R.; Tomlinson, Ian D.

    2011-01-01

    Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, sizetunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots. PMID:21276935

  19. Magnon-driven quantum dot refrigerators

    International Nuclear Information System (INIS)

    Wang, Yuan; Huang, Chuankun; Liao, Tianjun; Chen, Jincan

    2015-01-01

    Highlights: • A three-terminal quantum dot refrigerator is proposed. • The effects of magnetic field, applied voltage, and polarization are considered. • The region that the system can work as a refrigerator is determined. • Two different magnon-driven quantum dot refrigerators are compared. - Abstract: A new model of refrigerator consisting of a spin-splitting quantum dot coupled with two ferromagnetic reservoirs and a ferromagnetic insulator is proposed. The rate equation is used to calculate the occupation probabilities of the quantum dot. The expressions of the electron and magnon currents are obtained. The region that the system can work in as a refrigerator is determined. The cooling power and coefficient of performance (COP) of the refrigerator are derived. The influences of the magnetic field, applied voltage, and polarization of two leads on the performance are discussed. The performances of two different magnon-driven quantum dot refrigerators are compared.

  20. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

    -low threshold currents and amplifiers with record-high power levels. In this tutorial we will review the basic properties of quantum dots, emphasizing the properties which are important for laser and amplifier applications, as well as devices for all-optical signal processing. The high-speed properties....... The main property of semiconductor quantum dots compared to bulk material or even quantum well structures is the discrete nature of the allowed states, which means that inversion of the medium can be obtained for very low electron densities. This has led to the fabrication of quantum dot lasers with record...

  1. Coherent optoelectronics with single quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Zrenner, A; Ester, P; Michaelis de Vasconcellos, S; Huebner, M C; Lackmann, L; Stufler, S [Universitaet Paderborn, Department Physik, Warburger Strasse 100, D-33098 Paderborn (Germany); Bichler, M [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall, D-85748 Garching (Germany)], E-mail: zrenner@mail.upb.de

    2008-11-12

    The optical properties of semiconductor quantum dots are in many respects similar to those of atoms. Since quantum dots can be defined by state-of-the-art semiconductor technologies, they exhibit long-term stability and allow for well-controlled and efficient interactions with both optical and electrical fields. Resonant ps excitation of single quantum dot photodiodes leads to new classes of coherent optoelectronic functions and devices, which exhibit precise state preparation, phase-sensitive optical manipulations and the control of quantum states by electrical fields.

  2. Electron transport in quantum dots

    CERN Document Server

    2003-01-01

    When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the...

  3. Quantum dots: lasers and amplifiers

    CERN Document Server

    Bimberg, D

    2003-01-01

    Continuous wave room-temperature output power of approx 3 W for edge emitters and of 1.2 mW for vertical-cavity surface-emitting lasers is realized for GaAs-based devices using InAs quantum dots (QDs) operating at 1.3 mu m. Characteristic temperatures up to 170 K below 330 K are realized. Simultaneously, differential efficiency exceeds 80% for these devices. Lasers emitting up to 12 W at 1140-1160 nm are useful as pump sources for Tm sup 3 sup + -doped fibres for frequency up-conversion to 470 nm. Both types of lasers show transparency current densities of 6 A cm sup - sup 2 per dot layer, eta sub i sub n sub t = 98% and alpha sub i around 1.5 cm sup - sup 1. Long operation lifetimes (above 3000 h at 50 deg C heatsink temperature at 1.5 W CW) and improved radiation hardness as compared to quantum well (QW) devices are manifested. Cut-off frequencies of about 10 GHz at 1100 nm and 6 GHz at 1300 nm and low alpha factors resulting in reduced filamentation and improved M sup 2 values in single-mode operation are ...

  4. Temperature-dependent photoluminescence of water-soluble quantum dots for a bioprobe

    International Nuclear Information System (INIS)

    Liu Tiancai; Huang Zhenli; Wang Haiqiao; Wang Jianhao; Li Xiuqing; Zhao Yuandi; Luo Qingming

    2006-01-01

    The photoluminescence of water-soluble CdSe/ZnS core/shell quantum dots is found to be temperature-dependent: as temperature arising from 280 K to 351 K, the photoluminescence declines with emission peak shifting towards the red at a rate of ∼0.11 nm K -1 . And the studies show that the photoluminescence of water-soluble CdSe/ZnS quantum dots with core capped by a thinner ZnS shell is more sensitive to temperature than that of ones with core capped by a thicker one. That is, with 50% decrement of the quantum yield the temperature of the former need to arise from 280 K to 295 K, while the latter requires much higher temperature (315.6 K), which means that the integrality of shell coverage is a very important factor on temperature-sensitivity to for the photoluminescence of water-soluble CdSe/ZnS quantum dots. Moreover, it is found that the water-soluble CdSe quantum dots with different core sizes, whose cores are capped by thicker ZnS shells, possess almost the same sensitivity to the temperature. All of the studies about photoluminescence temperature-dependence of water-soluble CdSe/ZnS core/shell quantum dots show an indispensable proof for their applications in life science

  5. Thermoelectric transport through quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Merker, Lukas Heinrich

    2016-06-30

    In this thesis the thermoelectric properties (electrical conductance, Seebeck coefficient and thermal conductance)of quantum dots described by the Anderson impurity model have been investigated by using the numerical renormalization group (NRG) method. In order to make accurate calculations for thermoelectric properties of quantum impurity systems, a number of recent developments and refinements of the NRG have been implemented. These include the z-averaging and Campo discretization scheme, which enable the evaluation of physical quantities on an arbitrary temperature grid and at large discretization parameter Λ and the full density matrix (FDM) approach, which allows a more accurate calculation of spectral functions and transport coefficients. The implementation of the z-averaging and Campo discretization scheme has been tested within a new method for specific heats of quantum impurities. The accuracy of this new method was established by comparison with the numerical solution of the Bethe-ansatz equations for the Anderson model. The FDM approach was implemented and tested within a new approach to the calculation of impurity contributions to the uniform susceptibilities. Within this method a non-negligible contribution from the ''environmental'' degrees of freedom needs to be taken into account to recover the correct susceptibility, as shown by comparison with the Bethe-ansatz approach. An accurate method to calculate the conductance of a quantum dot is implemented, enabling the extraction of the Fermi liquid scaling coefficients c{sub T} and c{sub B} to high accuracy, being able to verify the results of the renormalized super perturbation theory approach (within its regime of validity). The method was generalized to higher order moments of the local level spectral function. This, as well as reduction of the SU(2) code to the U(1) symmetry, enabled the investigation of the effect of a magnetic field on the thermoelectric properties of quantum

  6. The electronic properties of semiconductor quantum dots

    International Nuclear Information System (INIS)

    Barker, J.A.

    2000-10-01

    This work is an investigation into the electronic behaviour of semiconductor quantum dots, particularly self-assembled quantum dot arrays. Processor-efficient models are developed to describe the electronic structure of dots, deriving analytic formulae for the strain tensor, piezoelectric distribution and diffusion- induced evolution of the confinement potential, for dots of arbitrary initial shape and composition profile. These models are then applied to experimental data. Transitions due to individual quantum dots have a narrow linewidth as a result of their discrete density of states. By contrast, quantum dot arrays exhibit inhomogeneous broadening which is generally attributed to size variations between the individual dots in the ensemble. Interpreting the results of double resonance spectroscopy, it is seen that variation in the indium composition of the nominally InAs dots is also present. This result also explains the otherwise confusing relationship between the spread in the ground-state and excited-state transition energies. Careful analysis shows that, in addition to the variations in size and composition, some other as yet unidentified broadening mechanism must also be present. The influence of rapid thermal annealing on dot electronic structure is also considered, finding that the experimentally observed blue-shift and narrowing of the photoluminescence linewidth may both be explained in terms of normal In/Ga interdiffusion. InAs/GaAs self-assembled quantum dots are commonly assumed to have a pyramidal geometry, so that we would expect the energy separation of the ground-state electron and hole levels in the dot to be largest at a positive applied field. This should also be the case for any dot of uniform composition whose shape tapers inwards from base to top, counter to the results of experimental Stark-shift spectroscopy which show a peak transition energy at a negative applied field. It is demonstrated that this inversion of the ground state

  7. Application of Quantum-Dot Conjugates for Detection and Subspecies Differentiation of Vibrio cholerae by Optical Methods

    Science.gov (United States)

    Erohin, P. S.; Utkin, D. V.; Kouklev, V. E.; Ossina, N. A.; Miheeva, E. A.; Alenkina, T. V.

    2016-03-01

    The application of bioconjugates of specific antibodies and CdSe quantum dots to identify two serovariants of Vibrio cholerae using fluorescence microscopy and optical spectroscopy is considered. It is found that a mixture of different bioconjugates with different emission maxima can be used without affecting the specificity of the method. Different V. cholerae serovariants are colored differently in fl uorescence microscopy (bright green and bright yellow), thereby allowing subspecies differentiation. The absorption spectrum of the bacterial suspension changed with homologous antigens in the sample and did not change with heterologous antigens. It is shown that the quantum-dot bioconjugates can serve as an alternative to the traditional fluorescence and agglutination diagnostics.

  8. Quantum walks in an array of quantum dots

    International Nuclear Information System (INIS)

    Manouchehri, K; Wang, J B

    2008-01-01

    Quantum random walks are shown to have non-intuitive dynamics, which makes them an attractive area of study for devising quantum algorithms for well-known classical problems as well as those arising in the field of quantum computing. In this work, we propose a novel scheme for the physical implementation of a discrete-time quantum random walk using laser excitations of the electronic states of an array of quantum dots. These dots represent the discrete nodes of the walk, while transitions between the energy levels inside each dot correspond to the required coin operation and stimulated Raman adiabatic passage (STIRAP) processes are employed to induce the steps of the walk. The quantum dot design is tailored in such a way as to enable selective coupling of the energy levels. Our simulation results show a close agreement with the ideal quantum walk distribution as well as modest robustness toward noise disturbance

  9. Electromagnetically induced transparency in quantum dot systems

    International Nuclear Information System (INIS)

    Jiang Yiwen; Zhu Kadi; Wu Zhuojie; Yuan Xiaozhong; Yao Ming

    2006-01-01

    Electromagnetically induced transparency (EIT) in quantum dot exciton systems in which the exciton behaves as a two-level system is investigated theoretically. It is shown that due to strong exciton-phonon coupling EIT can occur in such a quantum dot system and ultraslow light can propagate. The nonlinear optical absorption and Kerr coefficient based on EIT are also calculated. The numerical results show that giant nonlinear optical effects can be obtained while the frequency of the signal field differs only by an amount of LO phonon frequency from the exciton frequency in quantum dot systems

  10. Quantum Dots in Vertical Nanowire Devices

    NARCIS (Netherlands)

    Van Weert, M.

    2010-01-01

    The research described in this thesis is aimed at constructing a quantum interface between a single electron spin and a photon, using a nanowire quantum dot. Such a quantum interface enables information transfer from a local electron spin to the polarization of a photon for long distance readout.

  11. Synthesis of CdSe/ZnS and CdTe/ZnS Quantum Dots: Refined Digestive Ripening

    Directory of Open Access Journals (Sweden)

    Sreeram Cingarapu

    2012-01-01

    Full Text Available We report synthesis of CdSe and CdTe quantum dots (QDs from the bulk CdSe and CdTe material by evaporation/co-condensation using the solvated metal atom dispersion (SMAD technique and refined digestive ripening. The outcomes of this new process are (1 the reduction of digestive ripening time by employing ligands (trioctylphosphine oxide (TOPO and oleylamine (OA as capping agent as well as digestive ripening solvent, (2 ability to tune the photoluminescence (PL from 410 nm to 670 nm, (3 demonstrate the ability of SMAD synthesis technique for other semiconductors (CdTe, (4 direct comparison of CdSe QDs growth with CdTe QDs growth based on digestive ripening times, and (5 enhanced PL quantum yield (QY of CdSe QDs and CdTe QDs upon covering with a ZnS shell. Further, the merit of this synthesis is the use of bulk CdSe and CdTe as the starting materials, which avoids usage of toxic organometallic compounds, eliminates the hot injection procedure, and size selective precipitation processes. It also allows the possibility of scale up. These QDs were characterized by UV-vis, photoluminescence (PL, transmission electron microscopy (TEM, high-resolution transmission electron microscopy (HRTEM, X-ray photoelectron spectroscopy (XPS, and powder XRD.

  12. Excitons in semiconducting quantum filaments of CdS and CdSe with dielectric barriers

    CERN Document Server

    Dneprovskij, V S; Shalygina, O A; Lyaskovskij, V L; Mulyarov, E A; Gavrilov, S A; Masumoto, I

    2002-01-01

    The peculiarities of the luminescence spectra obtained by different polarization and intensity of the pumping excitation and luminescence kinetics of the CdS and CdSe nanocrystals are explained by the exciton transitions in the semiconducting quantum threads with dielectric barriers. The exciton transition energies correspond to the calculated ones with an account of both their dimensional quantization and the effect of the excitons dielectric intensification. It is shown that the excitons transition energies do not change by the change in the quantum threads diameter within the wide range, while the increase in the one-dimensional forbidden zone width of quantum thread by the decrease in its diameter is compensated through the decrease in the excitons binding energy

  13. Real-time in situ probing of high-temperature quantum dots solution synthesis.

    Science.gov (United States)

    Abécassis, Benjamin; Bouet, Cécile; Garnero, Cyril; Constantin, Doru; Lequeux, Nicolas; Ithurria, Sandrine; Dubertret, Benoit; Pauw, Brian Richard; Pontoni, Diego

    2015-04-08

    Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-angle X-ray scattering to experimentally monitor the formation of CdSe quantum dots synthesized in solution through the heating up of precursors in octadecene at 240 °C. Our experiment yields a complete movie of the structure of the solution from the self-assembly of the precursors to the formation of the quantum dots. We show that the initial cadmium precursor lamellar structure melts into small micelles at 100 °C and that the first CdSe nuclei appear at 218.7 °C. The size distributions and concentration in nanocrystals are measured in a quantitative fashion as a function of time. We show that a short nucleation burst lasting 30 s is followed by a slow decrease of nanoparticle concentration. The rate-limiting process of the quantum dot formation is found to be the thermal activation of selenium.

  14. Tunable Quantum Dot Solids: Impact of Interparticle Interactions on Bulk Properties

    Energy Technology Data Exchange (ETDEWEB)

    Sinclair, Michael B. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Fan, Hongyou [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Brener, Igal [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Liu, Sheng [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Luk, Ting S. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Li, Binsong [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    QD-solids comprising self-assembled semiconductor nanocrystals such as CdSe are currently under investigation for use in a wide array of applications including light emitting diodes, solar cells, field effect transistors, photodetectors, and biosensors. The goal of this LDRD project was develop a fundamental understanding of the relationship between nanoparticle interactions and the different regimes of charge and energy transport in semiconductor quantum dot (QD) solids. Interparticle spacing was tuned through the application of hydrostatic pressure in a diamond anvil cell, and the impact on interparticle interactions was probed using x-ray scattering and a variety of static and transient optical spectroscopies. During the course of this LDRD, we discovered a new, previously unknown, route to synthesize semiconductor quantum wires using high pressure sintering of self-assembled quantum dot crystals. We believe that this new, pressure driven synthesis approach holds great potential as a new tool for nanomaterials synthesis and engineering.

  15. Enhanced Photon Extraction from a Nanowire Quantum Dot Using a Bottom-Up Photonic Shell

    Science.gov (United States)

    Jeannin, Mathieu; Cremel, Thibault; Häyrynen, Teppo; Gregersen, Niels; Bellet-Amalric, Edith; Nogues, Gilles; Kheng, Kuntheak

    2017-11-01

    Semiconductor nanowires offer the possibility to grow high-quality quantum-dot heterostructures, and, in particular, CdSe quantum dots inserted in ZnSe nanowires have demonstrated the ability to emit single photons up to room temperature. In this paper, we demonstrate a bottom-up approach to fabricate a photonic fiberlike structure around such nanowire quantum dots by depositing an oxide shell using atomic-layer deposition. Simulations suggest that the intensity collected in our NA =0.6 microscope objective can be increased by a factor 7 with respect to the bare nanowire case. Combining microphotoluminescence, decay time measurements, and numerical simulations, we obtain a fourfold increase in the collected photoluminescence from the quantum dot. We show that this improvement is due to an increase of the quantum-dot emission rate and a redirection of the emitted light. Our ex situ fabrication technique allows a precise and reproducible fabrication on a large scale. Its improved extraction efficiency is compared to state-of-the-art top-down devices.

  16. Entangled exciton states in quantum dot molecules

    Science.gov (United States)

    Bayer, Manfred

    2002-03-01

    Currently there is strong interest in quantum information processing(See, for example, The Physics of Quantum Information, eds. D. Bouwmeester, A. Ekert and A. Zeilinger (Springer, Berlin, 2000).) in a solid state environment. Many approaches mimic atomic physics concepts in which semiconductor quantum dots are implemented as artificial atoms. An essential building block of a quantum processor is a gate which entangles the states of two quantum bits. Recently a pair of vertically aligned quantum dots has been suggested as optically driven quantum gate(P. Hawrylak, S. Fafard, and Z. R. Wasilewski, Cond. Matter News 7, 16 (1999).)(M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M. Korkusinski, Z.R. Wasilewski, O. Stern, and A. Forchel, Science 291, 451 (2001).): The quantum bits are individual carriers either on dot zero or dot one. The different dot indices play the same role as a "spin", therefore we call them "isospin". Quantum mechanical tunneling between the dots rotates the isospin and leads to superposition of these states. The quantum gate is built when two different particles, an electron and a hole, are created optically. The two particles form entangled isospin states. Here we present spectrocsopic studies of single self-assembled InAs/GaAs quantum dot molecules that support the feasibility of this proposal. The evolution of the excitonic recombination spectrum with varying separation between the dots allows us to demonstrate coherent tunneling of carriers across the separating barrier and the formation of entangled exciton states: Due to the coupling between the dots the exciton states show a splitting that increases with decreasing barrier width. For barrier widths below 5 nm it exceeds the thermal energy at room temperature. For a given barrier width, we find only small variations of the tunneling induced splitting demonstrating a good homogeneity within a molecule ensemble. The entanglement may be controlled by application of electromagnetic field. For

  17. Optical Fiber Sensing Using Quantum Dots

    Directory of Open Access Journals (Sweden)

    Faramarz Farahi

    2007-12-01

    Full Text Available Recent advances in the application of semiconductor nanocrystals, or quantumdots, as biochemical sensors are reviewed. Quantum dots have unique optical properties thatmake them promising alternatives to traditional dyes in many luminescence basedbioanalytical techniques. An overview of the more relevant progresses in the application ofquantum dots as biochemical probes is addressed. Special focus will be given toconfigurations where the sensing dots are incorporated in solid membranes and immobilizedin optical fibers or planar waveguide platforms.

  18. Electron Transport in Coupled Quantum Dots

    National Research Council Canada - National Science Library

    Antoniadis, D

    1998-01-01

    In the course of the investigation funded by this proposal we fabricated, modeled, and measured a variety of quantum dot structures in order to better understand how such nanostructures might be used for computation...

  19. Optical Studies of Single Quantum Dots

    National Research Council Canada - National Science Library

    Gammon, Daniel; Steel, Duncan G

    2002-01-01

    ...: the atomlike entities known as quantum dots (QDs). Measuring 1-100 nm across, QDs are semiconductor structures in which the electron wavefunction is confined in all three dimensions by the potential energy barriers that form the QD's boundaries...

  20. Ge Quantum Dot Infrared Imaging Camera Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Luna Innovations Incorporated proposes to develop a high performance Ge quantum dots-based infrared (IR) imaging camera on Si substrate. The high sensitivity, large...

  1. Synthetic Developments of Nontoxic Quantum Dots.

    Science.gov (United States)

    Das, Adita; Snee, Preston T

    2016-03-03

    Semiconductor nanocrystals, or quantum dots (QDs), are candidates for biological sensing, photovoltaics, and catalysis due to their unique photophysical properties. The most studied QDs are composed of heavy metals like cadmium and lead. However, this engenders concerns over heavy metal toxicity. To address this issue, numerous studies have explored the development of nontoxic (or more accurately less toxic) quantum dots. In this Review, we select three major classes of nontoxic quantum dots composed of carbon, silicon and Group I-III-VI elements and discuss the myriad of synthetic strategies and surface modification methods to synthesize quantum dots composed of these material systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. 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....

  3. Submonolayer Quantum Dot Infrared Photodetector

    Science.gov (United States)

    Ting, David Z.; Bandara, Sumith V.; Gunapala, Sarath D.; Chang, Yia-Chang

    2010-01-01

    A method has been developed for inserting submonolayer (SML) quantum dots (QDs) or SML QD stacks, instead of conventional Stranski-Krastanov (S-K) QDs, into the active region of intersubband photodetectors. A typical configuration would be InAs SML QDs embedded in thin layers of GaAs, surrounded by AlGaAs barriers. Here, the GaAs and the AlGaAs have nearly the same lattice constant, while InAs has a larger lattice constant. In QD infrared photodetector, the important quantization directions are in the plane perpendicular to the normal incidence radiation. In-plane quantization is what enables the absorption of normal incidence radiation. The height of the S-K QD controls the positions of the quantized energy levels, but is not critically important to the desired normal incidence absorption properties. The SML QD or SML QD stack configurations give more control of the structure grown, retains normal incidence absorption properties, and decreases the strain build-up to allow thicker active layers for higher quantum efficiency.

  4. Electron Spin Dynamics in Semiconductor Quantum Dots

    International Nuclear Information System (INIS)

    Marie, X.; Belhadj, T.; Urbaszek, B.; Amand, T.; Krebs, O.; Lemaitre, A.; Voisin, P.

    2011-01-01

    An electron spin confined to a semiconductor quantum dot is not subject to the classical spin relaxation mechanisms known for free carriers but it strongly interacts with the nuclear spin system via the hyperfine interaction. We show in time resolved photoluminescence spectroscopy experiments on ensembles of self assembled InAs quantum dots in GaAs that this interaction leads to strong electron spin dephasing.

  5. Positioning of quantum dots on metallic nanostructures

    Science.gov (United States)

    Kramer, R. K.; Pholchai, N.; Sorger, V. J.; Yim, T. J.; Oulton, R.; Zhang, X.

    2010-04-01

    The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has thus far been elusive. Placing an emission source within the influence of plasmonic structures now requires accuracy approaching molecular length scales. In this paper we report the ability to reliably position nanoscale functional objects, specifically quantum dots, with sub-100-nm accuracy, which is several times smaller than the diffraction limit of a quantum dot's emission light. Electron beam lithography-defined masks on metallic surfaces and a series of surface chemical functionalization processes allow the programmed assembly of DNA-linked colloidal quantum dots. The quantum dots are successfully functionalized to areas as small as (100 nm)2 using the specific binding of thiolated DNA to Au/Ag, and exploiting the streptavidin-biotin interaction. An analysis of the reproducibility of the process for various pattern sizes shows that this technique is potentially scalable to the single quantum dot level with 50 nm accuracy accompanied by a moderate reduction in yield.

  6. Positioning of quantum dots on metallic nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kramer, R K; Pholchai, N; Sorger, V J; Yim, T J; Oulton, R; Zhang, X, E-mail: xiang@berkeley.edu [NSF Nanoscale Science and Engineering Center, University of California, Berkeley, CA (United States)

    2010-04-09

    The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has thus far been elusive. Placing an emission source within the influence of plasmonic structures now requires accuracy approaching molecular length scales. In this paper we report the ability to reliably position nanoscale functional objects, specifically quantum dots, with sub-100-nm accuracy, which is several times smaller than the diffraction limit of a quantum dot's emission light. Electron beam lithography-defined masks on metallic surfaces and a series of surface chemical functionalization processes allow the programmed assembly of DNA-linked colloidal quantum dots. The quantum dots are successfully functionalized to areas as small as (100 nm){sup 2} using the specific binding of thiolated DNA to Au/Ag, and exploiting the streptavidin-biotin interaction. An analysis of the reproducibility of the process for various pattern sizes shows that this technique is potentially scalable to the single quantum dot level with 50 nm accuracy accompanied by a moderate reduction in yield.

  7. Universal quantum computing with nanowire double quantum dots

    International Nuclear Information System (INIS)

    Xue Peng

    2011-01-01

    We present a method for implementing universal quantum computing using a singlet and triplets of nanowire double quantum dots coupled to a one-dimensional transmission line resonator. This method is suitable and of interest for both quantum computing and quantum control with inhibition of spontaneous emission, enhanced spin qubit lifetime, strong coupling and quantum nondemolition measurements of spin qubits. We analyze the performance and stability of all the required operations and emphasize that all techniques are feasible with current experimental technology.

  8. Quantum Dot Chain Assembly Mediated by Nematic Liquid Crystals

    Science.gov (United States)

    Brereton, Peter; Basu, Rajratan; Finkenstadt, Daniel

    2015-03-01

    A small quantity of CdSe quantum dots (QDs) were dispersed in a nematic liquid crystal (LC) media and the QDs were found to exhibit self-assembled asymmetric structures, most likely QD-chains. In the nematic phase the ensemble LC +QD photoluminescence (PL) exhibits an anisotropic spectral line shape, as compared to the emission of QDs doped in the isotropic phase. This indicates a nematic mediated arrangement of the QDs. A simple model is proposed to explain the asymmetric behavior of the PL band as an effective chain of radiatively coupled emitters. The effect of the liquid crystals is to provide an entropic force that attracts dots to minimize the excluded volume. The dielectric reorientation dynamics immediately following the removal of an applied field appears as a one-step exponential decay for the LC and a two-step exponential decay with a slower process for the LC +QD system. The results suggest that anisotropic chain-like QD-assemblies are formed in the nematic platform. A related study has examined PL of ferroelectric LC doped with graphene QD [Kumar, Veeresh, et al., Liquid Crystals (2014)

  9. Spectroscopy characterization and quantum yield determination of quantum dots

    International Nuclear Information System (INIS)

    Ortiz, S N Contreras; Ospino, E Mejía; Cabanzo, R

    2016-01-01

    In this paper we show the characterization of two kinds of quantum dots: hydrophilic and hydrophobic, with core and core/shell respectively, using spectroscopy techniques such as UV-Vis, fluorescence and Raman. We determined the quantum yield in the quantum dots using the quinine sulphate as standard. This salt is commonly used because of its quantum yield (56%) and stability. For the CdTe excitation, we used a wavelength of 549nm and for the CdSe/ZnS excitation a wavelength of 527nm. The results show that CdSe/ZnS (49%) has better fluorescence, better quantum dots, and confirm the fluorescence result. The quantum dots have shown a good fluorescence performance, so this property will be used to replace dyes, with the advantage that quantum dots are less toxic than some dyes like the rhodamine. In addition, in this work we show different techniques to find the quantum dots emission: fluorescence spectrum, synchronous spectrum and Raman spectrum. (paper)

  10. Advancements in the Field of Quantum Dots

    Science.gov (United States)

    Mishra, Sambeet; Tripathy, Pratyasha; Sinha, Swami Prasad.

    2012-08-01

    Quantum dots are defined as very small semiconductor crystals of size varying from nanometer scale to a few micron i.e. so small that they are considered dimensionless and are capable of showing many chemical properties by virtue of which they tend to be lead at one minute and gold at the second minute.Quantum dots house the electrons just the way the electrons would have been present in an atom, by applying a voltage. And therefore they are very judiciously given the name of being called as the artificial atoms. This application of voltage may also lead to the modification of the chemical nature of the material anytime it is desired, resulting in lead at one minute to gold at the other minute. But this method is quite beyond our reach. A quantum dot is basically a semiconductor of very tiny size and this special phenomenon of quantum dot, causes the band of energies to change into discrete energy levels. Band gaps and the related energy depend on the relationship between the size of the crystal and the exciton radius. The height and energy between different energy levels varies inversely with the size of the quantum dot. The smaller the quantum dot, the higher is the energy possessed by it.There are many applications of the quantum dots e.g. they are very wisely applied to:Light emitting diodes: LEDs eg. White LEDs, Photovoltaic devices: solar cells, Memory elements, Biology : =biosensors, imaging, Lasers, Quantum computation, Flat-panel displays, Photodetectors, Life sciences and so on and so forth.The nanometer sized particles are able to display any chosen colour in the entire ultraviolet visible spectrum through a small change in their size or composition.

  11. 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.

  12. Electron Spins in Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Hanson, R.

    2005-01-01

    This thesis describes a series of experiments aimed at understanding and controlling the behavior of the spin degree of freedom of single electrons, confined in semiconductor quantum dots. This research work is motivated by the prospects of using the electron spin as a quantum bit (qubit), the basic

  13. Zeolite Y Films as Ideal Platform for Evaluation of Third-Order Nonlinear Optical Quantum Dots

    Directory of Open Access Journals (Sweden)

    Hyun Sung Kim

    2016-01-01

    Full Text Available Zeolites are ideal host material for generation and stabilization of regular ultrasmall quantum dots (QDs array with the size below 1.5 nm. Quantum dots (QDs with high density and extinction absorption coefficient have been expected to give high level of third-order nonlinear optical (3rd-NLO and to have great potential applications in optoelectronics. In this paper, we carried out a systematic elucidation of the third-order nonlinear optical response of various types of QDs including PbSe, PbS, CdSe, CdS, ZnSe, ZnS, Ag2Se, and Ag2S by manipulation of QDs into zeolites Y pores. In this respect, we could demonstrate that the zeolite offers an ideal platform for capability comparison 3rd-NLO response of various types of QDs with high sensitivities.

  14. Exploiting the optical and luminescence characteristic of quantum dots for optical device fabrication

    Science.gov (United States)

    Suriyaprakash, Jagadeesh; Qiao, Ting Ting

    2018-02-01

    One can design a robust optical device by engineering the optical band gap of the quantum dots (QDs) owing to their size-tunable quantum confinement effect. To do this, understanding the optical effects of QDs and composite materials is crucial. In this context, various sizes (2.8-4.2 nm) of CdSe QDs-PMMA nanocomposite are fabricated in a two-step process and their absorbance, luminescence and optical constants studied systematically. The ellipsometry spectroscopic analysis exhibits the heterogeneous medium feature of Ψ value and also the measured refractive index (1.51-1.59) values are increased with decreased band gap (2.24-2.10 eV). The observed red shift in the UV-Vis and photoluminescence spectra is indicative of early stage CdSe QD followed by a nucleation process of bigger size QD. In addition, the growth kinetics of the reaction and the band gap of the QDs are evaluated with respect to the time to testify the colloidal QDs formation. The thickness and QD composition of the nanocomposite thin films calculated by effective medium approximation are 100 nm and 8-12%, respectively. Morphology and structural feature transmission electron microscopy study of the fabricated nanocomposite demonstrated that spherical CdSe QDs are well dispersed in PMMA.

  15. Molecular beam epitaxy of CdSe epilayers and quantum wells on ZnTe substrate

    International Nuclear Information System (INIS)

    Park, Y.M.; Andre, R.; Kasprzak, J.; Dang, Le Si; Bellet-Amalric, E.

    2007-01-01

    We have grown zinc-blende cadmium selenide (CdSe) epilayers on ZnTe-(0 0 1) substrate by molecular beam epitaxy (MBE). By controlling the substrate temperature and beam-equivalent pressure (BEP) ratio, of Se to Cd, we determined the most suitable growth condition based on reflection high-energy electron diffraction (RHEED) pattern. At a substrate temperature of 280 deg. C and a BEP ratio of 3.6, the RHEED pattern showed a V-like feature, indicating a rough surface with facets. As the substrate temperature was increased to 360 deg. C at the same BEP ratio, a V-like RHEED pattern moved to a clear streaky pattern. Moreover when the BEP ratio was increased to 4.8 at 360 deg. C of substrate temperature, a clear (2 x 1) reconstruction of the CdSe layer was observed. A CdSe/CdMgSe single quantum well structure was also grown on ZnTe-(0 0 1) substrate by MBE. The RHEED pattern showed a clear (2 x 1) surface reconstruction during the growth. By photoluminescence measurement, a good optical property of the structure was obtained

  16. Quantum dot optoelectronic devices: lasers, photodetectors and solar cells

    International Nuclear Information System (INIS)

    Wu, Jiang; Chen, Siming; Seeds, Alwyn; Liu, Huiyun

    2015-01-01

    Nanometre-scale semiconductor devices have been envisioned as next-generation technologies with high integration and functionality. Quantum dots, or the so-called ‘artificial atoms’, exhibit unique properties due to their quantum confinement in all 3D. These unique properties have brought to light the great potential of quantum dots in optoelectronic applications. Numerous efforts worldwide have been devoted to these promising nanomaterials for next-generation optoelectronic devices, such as lasers, photodetectors, amplifiers, and solar cells, with the emphasis on improving performance and functionality. Through the development in optoelectronic devices based on quantum dots over the last two decades, quantum dot devices with exceptional performance surpassing previous devices are evidenced. This review describes recent developments in quantum dot optoelectronic devices over the last few years. The paper will highlight the major progress made in 1.3 μm quantum dot lasers, quantum dot infrared photodetectors, and quantum dot solar cells. (topical review)

  17. Acute toxicity of quantum dots on late pregnancy mice: Effects of nanoscale size and surface coating

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wanyi [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China); The Second Affiliated Hospital of Nanchang University, Nanchang 330000 (China); Yang, Lin; Kuang, Huijuan; Yang, Pengfei [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China); Aguilar, Zoraida P.; Wang, Andrew [Ocean NanoTech, LLC, Springdale, AR72764 (United States); Fu, Fen, E-mail: fu_fen@163.com [The Second Affiliated Hospital of Nanchang University, Nanchang 330000 (China); Xu, Hengyi, E-mail: kidyxu@163.com [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China)

    2016-11-15

    Graphical abstract: In spite of the immense benefits from quantum dots (QDs), there is scanty information regarding their toxicity mechanisms against late pregnancy. - Highlights: • QDs and CdCl{sub 2} were effectively blocked by the placental barrier. • CdSe QDs more effectively altered the expression levels of susceptive genes. • Nanoscale size of QDs is more important than free Cd in inducing toxicity. • Outer surface shell coating of QDs played a protective role. - Abstract: In this study, the effects of cadmium containing QDs (such as CdSe/ZnS and CdSe QDs) and bulk CdCl{sub 2} in pregnant mice, their fetuses, and the pregnancy outcomes were investigated. It was shown that although the QDs and bulk CdCl{sub 2} were effectively blocked by the placental barrier, the damage on the placenta caused by CdSe QDs still led to fetus malformation, while the mice in CdSe/ZnS QDs treatment group exhibited slightly hampered growth but showed no significant abnormalities. Moreover, the Cd contents in the placenta and the uterus of CdSe QDs and CdSe/ZnS QDs treatment groups showed significantly higher than the CdCl{sub 2} treated group which indicated that the nanoscale size of the QDs allowed relative ease of entry into the gestation tissues. In addition, the CdSe QDs more effectively altered the expression levels of susceptive genes related to cell apoptosis, dysplasia, metal transport, cryptorrhea, and oxidative stress, etc. These findings suggested that the nanoscale size of the QDs were probably more important than the free Cd in inducing toxicity. Furthermore, the results indicated that the outer surface shell coating played a protective role in the adverse effects of QDs on late pregnancy mice.

  18. Quantum computation with two-dimensional graphene quantum dots

    International Nuclear Information System (INIS)

    Li Jie-Sen; Li Zhi-Bing; Yao Dao-Xin

    2012-01-01

    We study an array of graphene nano sheets that form a two-dimensional S = 1/2 Kagome spin lattice used for quantum computation. The edge states of the graphene nano sheets are used to form quantum dots to confine electrons and perform the computation. We propose two schemes of bang-bang control to combat decoherence and realize gate operations on this array of quantum dots. It is shown that both schemes contain a great amount of information for quantum computation. The corresponding gate operations are also proposed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  19. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

    This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission into the...... quantum-dot-waveguide coupling. Such a structure is ideally suited for a number of applications in quantum information processing and among others we propose an on-chip spin-photon interface, a single photon transistor, and a deterministic cNOT gate.......This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission...... into the mode exceeding 98% for emitters spectrally close to the band-edge of the waveguide mode. In addition we illustrate the broadband nature of the underlying eects, by obtaining coupling eciencies above 90% for quantum dots detuned from the band edge by as far as 20nm. These values are in good agreement...

  20. 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)

  1. 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.

  2. Quantum Dot Systems: a versatile platform for quantum simulations

    International Nuclear Information System (INIS)

    Barthelemy, Pierre; Vandersypen, Lieven M.K.

    2013-01-01

    Quantum mechanics often results in extremely complex phenomena, especially when the quantum system under consideration is composed of many interacting particles. The states of these many-body systems live in a space so large that classical numerical calculations cannot compute them. Quantum simulations can be used to overcome this problem: complex quantum problems can be solved by studying experimentally an artificial quantum system operated to simulate the desired hamiltonian. Quantum dot systems have shown to be widely tunable quantum systems, that can be efficiently controlled electrically. This tunability and the versatility of their design makes them very promising quantum simulators. This paper reviews the progress towards digital quantum simulations with individually controlled quantum dots, as well as the analog quantum simulations that have been performed with these systems. The possibility to use large arrays of quantum dots to simulate the low-temperature Hubbard model is also discussed. The main issues along that path are presented and new ideas to overcome them are proposed. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Functionalization of Cadmium Selenide Quantum Dots with Poly(ethylene glycol): Ligand Exchange, Surface Coverage, and Dispersion Stability.

    Science.gov (United States)

    Wenger, Whitney Nowak; Bates, Frank S; Aydil, Eray S

    2017-08-22

    Semiconductor quantum dots synthesized using rapid mixing of precursors by injection into a hot solution of solvents and surfactants have surface ligands that sterically stabilize the dispersions in nonpolar solvents. Often, these ligands are exchanged to disperse the quantum dots in polar solvents, but quantitative studies of quantum dot surfaces before and after ligand exchange are scarce. We studied exchanging trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) ligands on as-synthesized CdSe quantum dots dispersed in hexane with a 2000 g/mol thiolated poly(ethylene glycol) (PEG) polymer. Using infrared spectroscopy we quantify the absolute surface concentration of TOP/TOPO and PEG ligands per unit area before and after ligand exchange. While 50-85% of the TOP/TOPO ligands are removed upon ligand exchange, only a few are replaced with PEG. Surprisingly, the remaining TOP/TOPO ligands outnumber the PEG ligands, but these few PEG ligands are sufficient to disperse the quantum dots in polar solvents such as chloroform, tetrahydrofuran, and water. Moreover, as-synthesized quantum dots once easily dispersed in hexane are no longer dispersible in nonpolar solvents after ligand exchange. A subtle coverage-dependent balance between attractive PEG-solvent interactions and repulsive TOP/TOPO-solvent interactions determines the dispersion stability.

  4. Inorganic passivation and doping control in colloidal quantum dot photovoltaics

    KAUST Repository

    Hoogland, Sjoerd H.

    2012-01-01

    We discuss strategies to reduce midgap trap state densities in colloidal quantum dot films and requirements to control doping type and magnitude. We demonstrate that these improvements result in colloidal quantum dot solar cells with certified 7.0% efficiency.

  5. Surface treatment of nanocrystal quantum dots after film deposition

    Science.gov (United States)

    Sykora, Milan; Koposov, Alexey; Fuke, Nobuhiro

    2015-02-03

    Provided are methods of surface treatment of nanocrystal quantum dots after film deposition so as to exchange the native ligands of the quantum dots for exchange ligands that result in improvement in charge extraction from the nanocrystals.

  6. Ultrafast light matter interaction in CdSe/ZnS core-shell quantum dots

    Science.gov (United States)

    Yadav, Rajesh Kumar; Sharma, Rituraj; Mondal, Anirban; Adarsh, K. V.

    2018-04-01

    Core-shell quantum dot are imperative for carrier (electron and holes) confinement in core/shell, which provides a stage to explore the linear and nonlinear optical phenomena at the nanoscalelimit. Here we present a comprehensive study of ultrafast excitation dynamics and nonlinear optical absorption of CdSe/ZnS core shell quantum dot with the help of ultrafast spectroscopy. Pump-probe and time-resolved measurements revealed the drop of trapping at CdSe surface due to the presence of the ZnS shell, which makes more efficient photoluminescence. We have carried out femtosecond transient absorption studies of the CdSe/ZnS core-shell quantum dot by irradiation with 400 nm laser light, monitoring the transients in the visible region. The optical nonlinearity of the core-shell quantum dot studied by using the Z-scan technique with 120 fs pulses at the wavelengths of 800 nm. The value of two photon absorption coefficients (β) of core-shell QDs extracted as80cm/GW, and it shows excellent benchmark for the optical limiting onset of 2.5GW/cm2 with the low limiting differential transmittance of 0.10, that is an order of magnitude better than graphene based materials.

  7. Coherent transport through interacting quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hiltscher, Bastian

    2012-10-05

    The present thesis is composed of four different works. All deal with coherent transport through interacting quantum dots, which are tunnel-coupled to external leads. There a two main motivations for the use of quantum dots. First, they are an ideal device to study the influence of strong Coulomb repulsion, and second, their discrete energy levels can easily be tuned by external gate electrodes to create different transport regimes. The expression of coherence includes a very wide range of physical correlations and, therefore, the four works are basically independent of each other. Before motivating and introducing the different works in more detail, we remark that in all works a diagrammatic real-time perturbation theory is used. The fermionic degrees of freedom of the leads are traced out and the elements of the resulting reduced density matrix can be treated explicitly by means of a generalized master equation. How this equation is solved, depends on the details of the problem under consideration. In the first of the four works adiabatic pumping through an Aharonov-Bohm interferometer with a quantum dot embedded in each of the two arms is studied. In adiabatic pumping transport is generated by varying two system parameters periodically in time. We consider the two dot levels to be these two pumping parameters. Since they are located in different arms of the interferometer, pumping is a quantum mechanical effect purely relying on coherent superpositions of the dot states. It is very challenging to identify a quantum pumping mechanism in experiments, because a capacitive coupling of the gate electrodes to the leads may yield an undesired AC bias voltage, which is rectified by a time dependent conductance. Therefore, distinguishing features of these two transport mechanisms are required. We find that the dependence on the magnetic field is the key feature. While the pumped charge is an odd function of the magnetic flux, the rectified current is even, at least in

  8. Coherent transport through interacting quantum dots

    International Nuclear Information System (INIS)

    Hiltscher, Bastian

    2012-01-01

    The present thesis is composed of four different works. All deal with coherent transport through interacting quantum dots, which are tunnel-coupled to external leads. There a two main motivations for the use of quantum dots. First, they are an ideal device to study the influence of strong Coulomb repulsion, and second, their discrete energy levels can easily be tuned by external gate electrodes to create different transport regimes. The expression of coherence includes a very wide range of physical correlations and, therefore, the four works are basically independent of each other. Before motivating and introducing the different works in more detail, we remark that in all works a diagrammatic real-time perturbation theory is used. The fermionic degrees of freedom of the leads are traced out and the elements of the resulting reduced density matrix can be treated explicitly by means of a generalized master equation. How this equation is solved, depends on the details of the problem under consideration. In the first of the four works adiabatic pumping through an Aharonov-Bohm interferometer with a quantum dot embedded in each of the two arms is studied. In adiabatic pumping transport is generated by varying two system parameters periodically in time. We consider the two dot levels to be these two pumping parameters. Since they are located in different arms of the interferometer, pumping is a quantum mechanical effect purely relying on coherent superpositions of the dot states. It is very challenging to identify a quantum pumping mechanism in experiments, because a capacitive coupling of the gate electrodes to the leads may yield an undesired AC bias voltage, which is rectified by a time dependent conductance. Therefore, distinguishing features of these two transport mechanisms are required. We find that the dependence on the magnetic field is the key feature. While the pumped charge is an odd function of the magnetic flux, the rectified current is even, at least in

  9. Coherence and dephasing in self-assembled quantum dots

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Leosson, K.; Birkedal, Dan

    2003-01-01

    We measured dephasing times in InGaAl/As self-assembled quantum dots at low temperature using degenerate four-wave mixing. At 0K, the coherence time of the quantum dots is lifetime limited, whereas at finite temperatures pure dephasing by exciton-phonon interactions governs the quantum dot...... coherence. The inferred homogeneous line widths are significantly smaller than the line widths usually observed in the photoluminescence from single quantum dots indicating an additional inhomogeneours broadening mechanism in the latter....

  10. Carbon quantum dots and a method of making the same

    Science.gov (United States)

    Zidan, Ragaiy; Teprovich, Joseph A.; Washington, Aaron L.

    2017-08-22

    The present invention is directed to a method of preparing a carbon quantum dot. The carbon quantum dot can be prepared from a carbon precursor, such as a fullerene, and a complex metal hydride. The present invention also discloses a carbon quantum dot made by reacting a carbon precursor with a complex metal hydride and a polymer containing a carbon quantum dot made by reacting a carbon precursor with a complex metal hydride.

  11. Quantum dot cosensitized solar cell based on PMOT@CdSe@ZnO core shell nanostructures with dual emission

    Energy Technology Data Exchange (ETDEWEB)

    Sehgal, Preeti; Narula, Anudeep Kumar, E-mail: researchchemlab58@gmail.com

    2016-01-15

    Quantum dot sensitized solar cell based on poly(3-methoxythiophene) (PMOT)@CdSe@ZnO core shell nanostructure were synthesized where PMOT serves as hole transport material, CdSe acts as a photosensitizer which enhances visible range absorption and also helps in injection of electrons from PMOT to ZnO where ZnO provides channel for efficient electron transport. The properties of the device were assessed with and without CdSe quantum dots and effect of annealing was also observed on the device. After the addition of CdSe QDs, the visible light absorption of PMOT@ZnO was enhanced due to increase in surface area. PMOT@CdSe@ZnO exhibited dual emission, where CdSe and ZnO exhibited visible and UV emission respectively. The interface formed between PMOT and CdSe improves the charge separation. The better photovoltaic measurement of PMOT@CdSe@ZnO over CdSe@ZnO indicates that PMOT efficiently dissociate excitons at interface and suppress the interfacial charge recombination. A power conversion efficiency of 0.989% was attained for the device PMOT@CdSe@ZnO with V{sub oc}=0.56 V and J{sub sc}=2.5 mA/cm{sup 2}. Upon annealing, the efficiency of the device was enhanced to 1.1609% with V{sub oc}=0.58, J{sub sc}=3.2 mA/cm{sup 2}. - Highlights: • Synthesized PMOT@CdSe@ZnO is biluminescent in nature. • A power conversion efficiency of 0.989% was achieved with PMOT@CdSe@ZnO device which is superior to CdSe@ZnO and PMOT@ZnO. • Upon annealing, an efficiency of 1.1609% was achieved for device PMOT@CdSe@ZnO.

  12. Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry

    Science.gov (United States)

    Lüker, S.; Kuhn, T.; Reiter, D. E.

    2017-12-01

    Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches, the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach, we show that, indeed, lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatiotemporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot, the phonon emission is strongly concentrated along the direction of the smallest axis of the dot, which is important for the use of phonons for the communication between different dots.

  13. Bright infrared LEDs based on colloidal quantum-dots

    KAUST Repository

    Sun, Liangfeng

    2013-01-01

    Record-brightness infrared LEDs based on colloidal quantum-dots have been achieved through control of the spacing between adjacent quantum-dots. By tuning the size of quantum-dots, the emission wavelengths can be tuned between 900nm and 1650nm. © 2013 Materials Research Society.

  14. Imaging vasculature and lymphatic flow in mice using quantum dots

    DEFF Research Database (Denmark)

    Ballou, Byron; Ernst, Lauren A.; Andreko, Susan

    2009-01-01

    Quantum dots are ideal probes for fluorescent imaging of vascular and lymphatic tissues. On injection into appropriate sites, red- and near-infrared-emitting quantum dots provide excellent definition of vasculature, lymphoid organs, and lymph nodes draining both normal tissues and tumors. We detail...... methods for use with commercially available quantum dots and discuss common difficulties....

  15. High resolution STEM of quantum dots and quantum wires

    DEFF Research Database (Denmark)

    Kadkhodazadeh, Shima

    2013-01-01

    This article reviews the application of high resolution scanning transmission electron microscopy (STEM) to semiconductor quantum dots (QDs) and quantum wires (QWRs). Different imaging and analytical techniques in STEM are introduced and key examples of their application to QDs and QWRs...

  16. THz quantum-confined Stark effect in semiconductor quantum dots

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Monozon, Boris S.; Livshits, Daniil A.

    2012-01-01

    We demonstrate an instantaneous all-optical manipulation of optical absorption at the ground state of InGaAs/GaAs quantum dots (QDs) via a quantum-confined Stark effect (QCSE) induced by the electric field of incident THz pulses with peak electric fields reaching 200 kV/cm in the free space...

  17. Some aspects of quantum dot toxicity.

    Science.gov (United States)

    Bottrill, Melanie; Green, Mark

    2011-07-07

    Quantum dot toxicity has become a hot topic in recent years due to the emergence of semiconductor nanoparticles as highly efficient biological imaging agents. The use of quantum dots in biology is arguably the most successful application of pure nanotechnology in recent times, although unfortunately, the most useful semiconductor particles contain elements that are often thought to be detrimental to health and the environment. In this article, we explore some key reports on this issue. This journal is © The Royal Society of Chemistry 2011

  18. Cadmium telluride quantum dots advances and applications

    CERN Document Server

    Donegan, John

    2013-01-01

    Optical Properties of Bulk and Nanocrystalline Cadmium Telluride, Núñez Fernández and M.I. VasilevskiyAqueous Synthesis of Colloidal CdTe Nanocrystals, V. Lesnyak, N. Gaponik, and A. EychmüllerAssemblies of Thiol-Capped CdTe Nanocrystals, N. GaponikFörster Resonant Energy Transfer in CdTe Nanocrystal Quantum Dot Structures, M. Lunz and A.L. BradleyEmission of CdTe Nanocrystals Coupled to Microcavities, Y.P. Rakovich and J.F. DoneganBiological Applications of Cadmium Telluride Semiconductor Quantum Dots, A. Le Cign

  19. Synthesis of Monodisperse CdSe QDs using Controlled Growth Temperatures

    International Nuclear Information System (INIS)

    Noor Razinah Rahmat; Akrajas Ali Umar; Muhammad Yahya; Muhamad Mat Salleh; Mohammad Hafizuddin Jumali

    2011-01-01

    The effect of growth temperatures on size of CdSe quantum dots (QDs) has been investigated. CdSe QDs were synthesized using thermolysis of organometallics precursor route using wet chemical method. The growth temperature was varied from 260-310 degree Celsius with growth period fixed at 60 s. As the growth temperature increased, the monodispersed CdSe QDs with diameter in the range 3-7 nm were obtained. Both absorption and PL spectra of the QDs revealed a strong red-shift supporting the increment size of QDs with the rise of growth temperature. (author)

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

    International Nuclear Information System (INIS)

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

    2013-01-01

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

  1. Dynamic localization in quantum dots: Analytical theory

    International Nuclear Information System (INIS)

    Basko, D.M.; Skvortsov, M.A.; Kravtsov, V.E.

    2003-02-01

    We analyze the response of a complex quantum-mechanical system (e.g., a quantum dot) to a time-dependent perturbation φ(t). Assuming the dot to be described by random matrix theory for GOE we find the quantum correction to the energy absorption rate as a function of the dephasing time t φ . If φ(t) is a sum of d harmonics with incommensurate frequencies, the correction behaves similarly to that to the conductivity δσ d (t φ ) in the d-dimensional Anderson model of the orthogonal symmetry class. For a generic periodic perturbation the leading quantum correction is absent as in the systems of the unitary symmetry class, unless φ(-t+τ)=φ(t+τ) for some τ, which falls into the quasi-1d orthogonal universality class. (author)

  2. Magnetic control of dipolaritons in quantum dots

    International Nuclear Information System (INIS)

    Rojas-Arias, J S; Vinck-Posada, H; Rodríguez, B A

    2016-01-01

    Dipolaritons are quasiparticles that arise in coupled quantum wells embedded in a microcavity, they are a superposition of a photon, a direct exciton and an indirect exciton. We propose the existence of dipolaritons in a system of two coupled quantum dots inside a microcavity in direct analogy with the quantum well case and find that, despite some similarities, dipolaritons in quantum dots have different properties and can lead to true dark polariton states. We use a finite system theory to study the effects of the magnetic field on the system, including the emission, and find that it can be used as a control parameter of the properties of excitons and dipolaritons, and the overall magnetic behaviour of the structure. (paper)

  3. Biosensing with Luminescent Semiconductor Quantum Dots

    OpenAIRE

    Sapsford, Kim E.; Pons, Thomas; Medintz, Igor L.; Mattoussi, Hedi

    2006-01-01

    Luminescent semiconductor nanocrystals or quantum dots (QDs) are a recently developed class of nanomaterial whose unique photophysical properties are helping to create a new generation of robust fluorescent biosensors. QD properties of interest for biosensing include high quantum yields, broad absorption spectra coupled to narrow size-tunable photoluminescent emissions and exceptional resistance to both photobleaching and chemical degradation. In this review, we examine the progress in adapti...

  4. Hybrid quantum-classical modeling of quantum dot devices

    Science.gov (United States)

    Kantner, Markus; Mittnenzweig, Markus; Koprucki, Thomas

    2017-11-01

    The design of electrically driven quantum dot devices for quantum optical applications asks for modeling approaches combining classical device physics with quantum mechanics. We connect the well-established fields of semiclassical semiconductor transport theory and the theory of open quantum systems to meet this requirement. By coupling the van Roosbroeck system with a quantum master equation in Lindblad form, we introduce a new hybrid quantum-classical modeling approach, which provides a comprehensive description of quantum dot devices on multiple scales: it enables the calculation of quantum optical figures of merit and the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way. We construct the interface between both theories in such a way, that the resulting hybrid system obeys the fundamental axioms of (non)equilibrium thermodynamics. We show that our approach guarantees the conservation of charge, consistency with the thermodynamic equilibrium and the second law of thermodynamics. The feasibility of the approach is demonstrated by numerical simulations of an electrically driven single-photon source based on a single quantum dot in the stationary and transient operation regime.

  5. Modeling high-efficiency quantum dot sensitized solar cells.

    Science.gov (United States)

    González-Pedro, Victoria; Xu, Xueqing; Mora-Seró, Iván; Bisquert, Juan

    2010-10-26

    With energy conversion efficiencies in continuous growth, quantum dot sensitized solar cells (QDSCs) are currently under an increasing interest, but there is an absence of a complete model for these devices. Here, we compile the latest developments in this kind of cells in order to attain high efficiency QDSCs, modeling the performance. CdSe QDs have been grown directly on a TiO(2) surface by successive ionic layer adsorption and reaction to ensure high QD loading. ZnS coating and previous growth of CdS were analyzed. Polysulfide electrolyte and Cu(2)S counterelectrodes were used to provide higher photocurrents and fill factors, FF. Incident photon-to-current efficiency peaks as high as 82%, under full 1 sun illumination, were obtained, which practically overcomes the photocurrent limitation commonly observed in QDSCs. High power conversion efficiency of up to 3.84% under full 1 sun illumination (V(oc) = 0.538 V, j(sc) = 13.9 mA/cm(2), FF = 0.51) and the characterization and modeling carried out indicate that recombination has to be overcome for further improvement of QDSC.

  6. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... to resolve luminescence lines from individual quantum dots, revealing an atomic-like spectrum of sharp transition lines. A parameter of fundamental importance is the intrinsic linewidth of these transitions. Using high-resolution spectroscopy we have determined the linewidth and investigated its dependence...... on temperature, which gives information about how the exciton confined to the quantum dot interacts with the surrounding lattice....

  7. Application of quantum dots as vectors in targeted survivin gene siRNA delivery

    Directory of Open Access Journals (Sweden)

    Zhao JJ

    2013-04-01

    Full Text Available Jianjiang Zhao, Xiaoling Qiu, Zhiping Wang, Jie Pan, Jun Chen, Jiusong Han Department of Surgery, Guangdong Provincial Stomatological Hospital, Southern Medical University, Guangzhou, People's Republic of China Abstract: Gene silencing using short interfering RNA (siRNA is becoming an attractive approach for probing gene function in mammalian cells. This study evaluated the specificity and efficiency of quantum dots (QDs as non-viral gene vectors for delivery of survivin siRNA and downregulation of survivin gene expression in oral squamous cell carcinoma Tca8113 cells. Water-dispersible cationically-modified QDs were electrostatically attached to anionic siRNA molecules and complexed with siRNA for downregulating expression of the survivin gene. Cellular uptake and allocation of QD–siRNA complexes in Tca8113 cells were monitored using confocal laser scanning microscopy. Real-time polymerase chain reaction (PCR was used to quantify survivin messenger RNA (mRNA levels. CdSe QDs were observed with high intensity fluorescence under confocal laser scanning microscopy. Tca8113 cells were successfully transfected by QDs with survivin siRNA, and the red fluorescence from CdSe QDs and green fluorescein amidite fluorescence from siRNA could both be easily observed after 6 hours of incubation. The release of siRNA into the cytoplasm was verified through real-time PCR quantification that showed reduced survivin mRNA levels. In this study, survivin siRNA successfully complexed with water-soluble CdSe QDs and exhibited excellent fluorescent properties and downregulated the expression of the survivin gene in oral squamous cell carcinoma Tca8113 cells. QDs are a novel non-viral gene delivery vector. Keywords: quantum dots, survivin, siRNA delivery, transfection, Tca8113, tongue cancer cells

  8. Imaging and Manipulating Energy Transfer Among Quantum Dots at Individual Dot Resolution.

    Science.gov (United States)

    Nguyen, Duc; Nguyen, Huy A; Lyding, Joseph W; Gruebele, Martin

    2017-06-27

    Many processes of interest in quantum dots involve charge or energy transfer from one dot to another. Energy transfer in films of quantum dots as well as between linked quantum dots has been demonstrated by luminescence shift, and the ultrafast time-dependence of energy transfer processes has been resolved. Bandgap variation among dots (energy disorder) and dot separation are known to play an important role in how energy diffuses. Thus, it would be very useful if energy transfer could be visualized directly on a dot-by-dot basis among small clusters or within films of quantum dots. To that effect, we report single molecule optical absorption detected by scanning tunneling microscopy (SMA-STM) to image energy pooling from donor into acceptor dots on a dot-by-dot basis. We show that we can manipulate groups of quantum dots by pruning away the dominant acceptor dot, and switching the energy transfer path to a different acceptor dot. Our experimental data agrees well with a simple Monte Carlo lattice model of energy transfer, similar to models in the literature, in which excitation energy is transferred preferentially from dots with a larger bandgap to dots with a smaller bandgap.

  9. System and method for making quantum dots

    KAUST Repository

    Bakr, Osman M.

    2015-05-28

    Embodiments of the present disclosure provide for methods of making quantum dots (QDs) (passivated or unpassivated) using a continuous flow process, systems for making QDs using a continuous flow process, and the like. In one or more embodiments, the QDs produced using embodiments of the present disclosure can be used in solar photovoltaic cells, bio-imaging, IR emitters, or LEDs.

  10. New small quantum dots for neuroscience

    Science.gov (United States)

    Selvin, Paul

    2014-03-01

    In "New Small Quantum Dots for Neuroscience," Paul Selvin (University of Illinois, Urbana-Champaign) notes how the details of synapsis activity in the brain involves chemical receptors that facilitate the creation of the electrical connection between two nerves. In order to understand the details of this neuroscience phenomenon you need to be able to "see" what is happening at the scale of these receptors, which is around 10 nanometers. This is smaller than the diffraction limit of normal microscopy and it takes place on a 3 dimensional structure. Selvin describes the development of small quantum dots (on the order of 6-9 microns) that are surface-sensitized to interact with the receptors. This allows the application of photo-activated localized microscopy (PALM), a superresolution microscopy that can be scanned through focus to develop a 3D map on a scale that is the same size as the emitter, which in this case are the small quantum dots. The quantum dots are stable in time and provide access to the receptors which allows the imaging of the interactions taking place at the synoptic level.

  11. Quantum Dot Detectors with Plasmonic Structures

    Science.gov (United States)

    2015-05-15

    high operating temperature quantum dots in a well photodetectors,” Appl. Phys. Lett. 97(6), 061105 (2010). 18. J. D. Jackson, Classical ... Electrodynamics (Wiley, New York, 3rd Edition, 1999). Approved for Public Release; Distribution is Unlimited. 10 19. J. O. Kim, S. Sengupta, A. V. Barve, Y. D

  12. Photoluminescence of hybrid quantum dot systems

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    2015-01-01

    Roč. 7, č. 4 (2015), 347-349 ISSN 2164-6627 R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

  13. Decoherence in Nearly-Isolated Quantum Dots

    DEFF Research Database (Denmark)

    Folk, J.; M. Marcus, C.; Harris jr, J.

    2000-01-01

    Decoherence in nearly-isolated GaAs quantum dots is investigated using the change in average Coulomb blockade peak height upon breaking time-reversal symmetry. The normalized change in average peak height approaches the predicted universal value of 1/4 at temperatures well below the single...

  14. Many electron effects in semiconductor quantum dots

    Indian Academy of Sciences (India)

    Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as 'artificial atoms' by some, they are much larger (1 100 nm) than real atoms. One can study a variety of manyelectron effects in them, which are otherwise difficult to observe in a real atom. We have treated these effects within the ...

  15. Effect of temperature on quantum dots

    Indian Academy of Sciences (India)

    MAHDI AHMADI BORJI

    2017-07-12

    Jul 12, 2017 ... Quantum dot semiconductor lasers, due to the discrete density of states, low threshold current and ... energy states, strain, and other physical features, and their change by varying some factors such as ... tion 2 explains the model and method of the numerical simulation. Our results and discussions on the ...

  16. Competing interactions in semiconductor quantum dots

    NARCIS (Netherlands)

    van den Berg, R.; Brandino, G.P.; El Araby, O.; Konik, R.M.; Gritsev, V.; Caux, J.S.

    2014-01-01

    We introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free-induction decay and spin-echo simulations

  17. Magnetic quantum dots for multimodal imaging

    NARCIS (Netherlands)

    Koole, Rolf; Mulder, Willem J. M.; van Schooneveld, Matti M.; Strijkers, Gustav J.; Meijerink, Andries; Nicolay, Klaas

    2009-01-01

    Multimodal contrast agents based on highly luminescent quantum dots (QDs) combined with magnetic nanoparticles (MNPs) or ions form an exciting class of new materials for bioimaging. With two functionalities integrated in a single nanoparticle, a sensitive contrast agent for two very powerful and

  18. Effect of temperature on quantum dots

    Indian Academy of Sciences (India)

    MAHDI AHMADI BORJI

    2017-07-12

    Jul 12, 2017 ... Abstract. In this paper, the strain, band-edge, and energy levels of pyramidal InxGa1−xAs/GaAs quantum dots are investigated by 1-band effective mass approach. It is shown that while temperature has no remarkable effect on the strain tensor, the band gap lowers and the radiation wavelength elongates ...

  19. Quantum Dots Coupled to a Superconductor

    DEFF Research Database (Denmark)

    Jellinggaard, Anders Robert

    are tuned electrostatically. This includes tuning the odd occupation of the dot through a quantum phase transition, where it forms a singlet with excitations in the superconductor. We detail the fabrication of these bottom gated devices, which additionally feature ancillary sensor dots connected......In this thesis, sub-gap states in bottom-gated InAs N–dot–S, N–double dot–S, and N–dot–S–dot–N devices are investigated, and several different theories are developed to model these states. Experimental results include tracking single levels of the dot in an N–dot–S device as the tunnel couplings...... with floating gates. A numerical technique is developed, which predicts the position of Yu-Shiba-Rusinov sub-gap states in the proximitized Anderson model as well as properties of these states. This theory is valid for all occupations of the dot and for weak to intermediate coupling. We compare...

  20. Synthesis and optical properties of core-multi-shell CdSe/CdS/ZnS quantum dots: Surface modifications

    Science.gov (United States)

    Ratnesh, R. K.; Mehata, Mohan Singh

    2017-02-01

    We report two port synthesis of CdSe/CdS/ZnS core-multi-shell quantum dots (Q-dots) and their structural properties. The multi-shell structures of Q-dots were developed by using successive ionic layer adsorption and reaction (SILAR) technique. The obtained Q-dots show high crystallinity with the step-wise adjustment of lattice parameters in the radial direction. The size of the core and core-shell Q-dots estimated by transmission electron microscopy images and absorption spectra is about 3.4 and 5.3 nm, respectively. The water soluble Q-dots (scheme-1) were prepared by using ligand exchange method, and the effect of pH was discussed regarding the variation of quantum yield (QY). The decrease of a lifetime of core-multi-shell Q-dots with respect to core CdSe indicates that the shell growth may be tuned by the lifetimes. Thus, the study clearly demonstrates that the core-shell approach can be used to substantially improve the optical properties of Q-dots desired for various applications.

  1. Efficient Luminescence from Perovskite Quantum Dot Solids

    KAUST Repository

    Kim, Younghoon

    2015-11-18

    © 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals\\' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

  2. Size effects in the quantum yield of Cd Te quantum dots for optimum fluorescence bioimaging

    International Nuclear Information System (INIS)

    Jacinto, C.; Rocha, U.S.; Maestro, L.M.; Garcia-Sole, J.; Jaque, D.

    2011-01-01

    Full text: Semiconductor nano-crystals, usually referred as Quantum Dots (QDs) are nowadays regarded as one of the building-blocks in modern photonics. They constitute bright and photostable fluorescence sources whose emission and absorption properties can be adequately tailored through their size. Recent advances on the controlled modification of their surface has made possible the development of water soluble QDs, without causing any deterioration in their fluorescence properties. This has made them excellent optical selective markers to be used in fluorescence bio-imaging experiments. The suitability of colloidal QDs for bio-imaging is pushed forward by their large two-photon absorption cross section so that their visible luminescence (associated to the recombination of electro-hole pairs) can be also efficiently excited under infrared excitation (two-photon excitation). This, in turns, allows for large penetration depths in tissues, minimization of auto-fluorescence and achievement of superior spatial imaging resolution. In addition, recent works have demonstrated the ability of QDs to act as nano-thermometers based on the thermal sensitivity of their fluorescence bands. Based on all these outstanding properties, QDs have been successfully used to mark individual receptors in cell membranes, to intracellular temperature measurements and to label living embryos at different stages. Most of the QD based bio-images reported up to now were obtained by using whether CdSe or CdTe QDs since both are currently commercial available with a high degree of quality. They show similar fluorescence properties and optical performance when used in bio-imaging. Nevertheless, CdTe-QDs have very recently attracted much attention since the hyper-thermal sensitivity of their fluorescence bands was discovered. Based on this, it has been postulated that intracellular thermal sensing with resolutions as large as 0.25 deg C can be achieved based on CdTe-QDs, three times better than

  3. Vertical quantum dot with a vertically coupled charge detector

    International Nuclear Information System (INIS)

    Zaitsu, Koichiro; Kitamura, Yosuke; Ono, Keiji; Tarucha, Seigo

    2008-01-01

    We fabricated a vertical quantum dot equipped with a charge detector. The dot current flows vertically between the top and bottom contacts. The charge detector is formed at the bottom contact layer with a current channel constricted to the region just under the dot. This channel current is reduced by addition of an extra electron onto the dot due to the electrostatic coupling to the dot. The charge state of the vertical dot was detected, starting from zero electrons. The sensitivity of the charge detector was comparable to that previously reported for lateral dots with nearby quantum point contacts

  4. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    Science.gov (United States)

    Pradhan, Prabhakar; Anantram, M. P.; Wang, K. L.; Roychowhury, V. P.; Saini, Subhash (Technical Monitor)

    1998-01-01

    A solid state model for quantum computation has potential advantages in terms of the ease of fabrication, characterization, and integration. The fundamental requirements for a quantum computer involve the realization of basic processing units (qubits), and a scheme for controlled switching and coupling among the qubits, which enables one to perform controlled operations on qubits. We propose a model for quantum computation based on optically coupled quantum dot arrays, which is computationally similar to the atomic model proposed by Cirac and Zoller. In this model, individual qubits are comprised of two coupled quantum dots, and an array of these basic units is placed in an optical cavity. Switching among the states of the individual units is done by controlled laser pulses via near field interaction using the NSOM technology. Controlled rotations involving two or more qubits are performed via common cavity mode photon. We have calculated critical times, including the spontaneous emission and switching times, and show that they are comparable to the best times projected for other proposed models of quantum computation. We have also shown the feasibility of accessing individual quantum dots using the NSOM technology by calculating the photon density at the tip, and estimating the power necessary to perform the basic controlled operations. We are currently in the process of estimating the decoherence times for this system; however, we have formulated initial arguments which seem to indicate that the decoherence times will be comparable, if not longer, than many other proposed models.

  5. High-resolution photoluminescence studies of single semiconductor quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis

    2000-01-01

    developed in the study of single quantum dots, characterized by sharp atomic-like transition lines revealing their zero-dimensional density of states. Substantial information about the fundamental properties of individual quantum dots, as well as their interactions with other dots and the host lattice, can...

  6. Microwave Synthesis of Nearly Monodisperse Core/Multishell Quantum Dots with Cell Imaging Applications

    Directory of Open Access Journals (Sweden)

    Xu Hengyi

    2010-01-01

    Full Text Available Abstract We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs overcoated with Cd0.5Zn0.5S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resulting CdSe/Cd0.5Zn0.5S/ZnS core/multishell QDs have been successfully applied to the labeling and imaging of breast cancer cells (SK-BR3.

  7. Enhancing Photocatalytic Degradation of Methyl Blue Using PVP-Capped and Uncapped CdSe Nanoparticles

    Directory of Open Access Journals (Sweden)

    Kgobudi Frans Chepape

    2017-01-01

    Full Text Available Quantum confinement of semiconductor nanoparticles is a potential feature which can be interesting for photocatalysis, and cadmium selenide is one simple type of quantum dot to use in the following photocatalytic degradation of organic dyes. CdSe nanoparticles capped with polyvinylpyrrolidone (PVP in various concentration ratios were synthesized by the chemical reduction method and characterized. The transmission electron microscopy (TEM analysis of the samples showed that 50% PVP-capped CdSe nanoparticles were uniformly distributed in size with an average of 2.7 nm and shape which was spherical-like. The photocatalytic degradation of methyl blue (MB in water showed efficiencies of 31% and 48% when using uncapped and 50% PVP-capped CdSe nanoparticles as photocatalysts, respectively. The efficiency of PVP-capped CdSe nanoparticles indicated that a complete green process can be utilized for photocatalytic treatment of water and waste water.

  8. Theory of the Quantum Dot Hybrid Qubit

    Science.gov (United States)

    Friesen, Mark

    2015-03-01

    The quantum dot hybrid qubit, formed from three electrons in two quantum dots, combines the desirable features of charge qubits (fast manipulation) and spin qubits (long coherence times). The hybridized spin and charge states yield a unique energy spectrum with several useful properties, including two different operating regimes that are relatively immune to charge noise due to the presence of optimal working points or ``sweet spots.'' In this talk, I will describe dc and ac-driven gate operations of the quantum dot hybrid qubit. I will analyze improvements in the dephasing that are enabled by the sweet spots, and I will discuss the outlook for quantum hybrid qubits in terms of scalability. This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), the USDOD, and the Intelligence Community Postdoctoral Research Fellowship Program. The views and conclusions contained in this presentation are those of the authors and should not be interpreted as representing the official policies or endorsements, either expressed or implied, of the US government.

  9. Single quantum dots fundamentals, applications, and new concepts

    CERN Document Server

    2003-01-01

    This book reviews recent advances in the exciting and rapid growing field of semiconductor quantum dots by contributions from some of the most prominent researchers in the field. Special focus is given to the optical and electronic properties of single quantum dots due to their potential applications in devices operating with single electrons and/or single photons. This includes quantum dots in electric and magnetic fields, cavity-quantum electrodynamics, nonclassical light generation, and coherent optical control of excitons. Single Quantum Dots also addresses various growth techniques as well as potential device applications such as quantum dot lasers, and new concepts like a single-photon source, and a single quantum dot laser.

  10. Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots.

    Science.gov (United States)

    Sapkota, Bedanga; Benabbas, Abdelkrim; Lin, Hao-Yu Greg; Liang, Wentao; Champion, Paul; Wanunu, Meni

    2017-03-22

    We report here the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6500 Göppert-Mayer units). Furthermore, through noncovalent tailoring of the chemistry of these quantum dots, we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, but they do not enter the cell nucleus.

  11. Semiconductor nanocrystals or quantum dots

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 18; Issue 8. Various Quantum Mechanical Concepts for Confinements in Semiconductor Nanocrystals. Jayakrishna Khatei Karuna Kar Nanda. Classroom Volume 18 Issue 8 August 2013 pp 771-776 ...

  12. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    Energy Technology Data Exchange (ETDEWEB)

    Betz, A. C., E-mail: ab2106@cam.ac.uk; Broström, M.; Gonzalez-Zalba, M. F. [Hitachi Cambridge Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Tagliaferri, M. L. V. [Laboratorio MDM, CNR-IMM, Via C. Olivetti 2, 20864 Agrate Brianza (MB) (Italy); Dipartimento di Scienza dei Materiali, Universit di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy); Vinet, M. [CEA/LETI-MINATEC, CEA-Grenoble, 17 rue des martyrs, F-38054 Grenoble (France); Sanquer, M. [SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, 17 rue des Martyrs, 38054 Grenoble (France); Ferguson, A. J. [Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE (United Kingdom)

    2016-05-16

    We present a reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consists of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.

  13. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    International Nuclear Information System (INIS)

    Betz, A. C.; Broström, M.; Gonzalez-Zalba, M. F.; Tagliaferri, M. L. V.; Vinet, M.; Sanquer, M.; Ferguson, A. J.

    2016-01-01

    We present a reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consists of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.

  14. Biomagnification of cadmium selenide quantum dots in a simple experimental microbial food chain

    Science.gov (United States)

    Werlin, R.; Priester, J. H.; Mielke, R. E.; Krämer, S.; Jackson, S.; Stoimenov, P. K.; Stucky, G. D.; Cherr, G. N.; Orias, E.; Holden, P. A.

    2011-01-01

    Previous studies have shown that engineered nanomaterials can be transferred from prey to predator, but the ecological impacts of this are mostly unknown. In particular, it is not known if these materials can be biomagnified-a process in which higher concentrations of materials accumulate in organisms higher up in the food chain. Here, we show that bare CdSe quantum dots that have accumulated in Pseudomonas aeruginosa bacteria can be transferred to and biomagnified in the Tetrahymena thermophila protozoa that prey on the bacteria. Cadmium concentrations in the protozoa predator were approximately five times higher than their bacterial prey. Quantum-dot-treated bacteria were differentially toxic to the protozoa, in that they inhibited their own digestion in the protozoan food vacuoles. Because the protozoa did not lyse, largely intact quantum dots remain available to higher trophic levels. The observed biomagnification from bacterial prey is significant because bacteria are at the base of environmental food webs. Our findings illustrate the potential for biomagnification as an ecological impact of nanomaterials.

  15. Compact quantum dots for single-molecule imaging.

    Science.gov (United States)

    Smith, Andrew M; Nie, Shuming

    2012-10-09

    Single-molecule imaging is an important tool for understanding the mechanisms of biomolecular function and for visualizing the spatial and temporal heterogeneity of molecular behaviors that underlie cellular biology (1-4). To image an individual molecule of interest, it is typically conjugated to a fluorescent tag (dye, protein, bead, or quantum dot) and observed with epifluorescence or total internal reflection fluorescence (TIRF) microscopy. While dyes and fluorescent proteins have been the mainstay of fluorescence imaging for decades, their fluorescence is unstable under high photon fluxes necessary to observe individual molecules, yielding only a few seconds of observation before complete loss of signal. Latex beads and dye-labeled beads provide improved signal stability but at the expense of drastically larger hydrodynamic size, which can deleteriously alter the diffusion and behavior of the molecule under study. Quantum dots (QDs) offer a balance between these two problematic regimes. These nanoparticles are composed of semiconductor materials and can be engineered with a hydrodynamically compact size with exceptional resistance to photodegradation (5). Thus in recent years QDs have been instrumental in enabling long-term observation of complex macromolecular behavior on the single molecule level. However these particles have still been found to exhibit impaired diffusion in crowded molecular environments such as the cellular cytoplasm and the neuronal synaptic cleft, where their sizes are still too large (4,6,7). Recently we have engineered the cores and surface coatings of QDs for minimized hydrodynamic size, while balancing offsets to colloidal stability, photostability, brightness, and nonspecific binding that have hindered the utility of compact QDs in the past (8,9). The goal of this article is to demonstrate the synthesis, modification, and characterization of these optimized nanocrystals, composed of an alloyed HgxCd1-xSe core coated with an

  16. Quantum photonics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Kuhlmann, Andreas; Cadeddu, Davide

    2016-01-01

    We present results from the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter’s properties with the highest sensitivity. Weperform...

  17. Quantum optics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Cadeddu, Davide; Teissier, Jean

    2016-01-01

    We present an exploration of the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter's properties with the highest sensitivity, allowing...

  18. Facile labeling of lipoglycans with quantum dots

    International Nuclear Information System (INIS)

    Morales Betanzos, Carlos; Gonzalez-Moa, Maria; Johnston, Stephen Albert; Svarovsky, Sergei A.

    2009-01-01

    Bacterial endotoxins or lipopolysaccharides (LPS) are among the most potent activators of the innate immune system, yet mechanisms of their action and in particular the role of glycans remain elusive. Efficient non-invasive labeling strategies are necessary for studying interactions of LPS glycans with biological systems. Here we report a new method for labeling LPS and other lipoglycans with luminescent quantum dots. The labeling is achieved by partitioning of hydrophobic quantum dots into the core of various LPS aggregates without disturbing the native LPS structure. The biofunctionality of the LPS-Qdot conjugates is demonstrated by the labeling of mouse monocytes. This simple method should find broad applicability in studies concerned with visualization of LPS biodistribution and identification of LPS binding agents.

  19. Quantum Dot Molecular Beacons for DNA Detection

    Science.gov (United States)

    Cady, Nathaniel C.

    Molecular beacons have become an important fluorescent probe for sequence-specific DNA detection. To improve the sensitivity and robustness of molecular beacon assays, fluorescent semiconductor quantum dots (QDs) are now being used as the fluorescent moiety for molecular beacon synthesis. Multiple linkage strategies can be used for attaching molecular beacon DNA to QDs, and multiple quenchers, including gold particles, can be used for fluorescence quenching. Covalent attachment of QDs to DNA can be achieved through amide linkage, and affinity-based attachment can be achieved with streptavidin-biotin linkage. We have shown that these linkage strategies can be used to successfully create quantum dot molecular beacons that can be used in DNA detection assays with high specificity.

  20. Strain-tunable quantum dot devices

    International Nuclear Information System (INIS)

    Rastelli, A.; Trotta, R.; Zallo, E.; Atkinson, P.; Magerl, E.; Ding, F.; Plumhof, J.D.; Kumar, S.; Doerr, K.; Schmidt, O.G.

    2011-01-01

    We introduce a new class of quantum dot-based devices, in which the semiconductor structures are integrated on top of piezoelectric actuators. This combination allows on one hand to study in detail the effects produced by variable strains (up to about 0.2%) on the excitonic emission of single quantum dots and on the other to manipulate their electronic- and optical properties to achieve specific requirements. In fact, by combining strain with electric fields we are able to obtain (i) independent control of emission energy and charge-state of a QD, (II) wavelength-tunable single-QD light-emitting diodes and (III) frequency-stabilized sources of single photons at predefined wavelengths. Possible future extensions and applications of this technology will be discussed.

  1. Single Molecule Applications of Quantum Dots

    DEFF Research Database (Denmark)

    Rasmussen, Thomas Elmelund; Jauffred, Liselotte; Brewer, Jonathan R.

    2013-01-01

    Fluorescent nanocrystals composed of semiconductor materials were first introduced for biological applications in the late 1990s. The focus of this review is to give a brief survey of biological applications of quantum dots (QDs) at the single QD sensitivity level. These are described as follows:...... experiments held together with the prospects in localization microscopy and single molecule manipulation experiments gave QDs a promising future in single molecule research....

  2. Depleted Bulk Heterojunction Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Barkhouse, D. Aaron R.

    2011-05-26

    The first solution-processed depleted bulk heterojunction colloidal quantum dot solar cells are presented. The architecture allows for high absorption with full depletion, thereby breaking the photon absorption/carrier extraction compromise inherent in planar devices. A record power conversion of 5.5% under simulated AM 1.5 illumination conditions is reported. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. The Silicon:Colloidal Quantum Dot Heterojunction

    KAUST Repository

    Masala, Silvia

    2015-10-13

    A heterojunction between crystalline silicon and colloidal quantum dots (CQDs) is realized. A special interface modification is developed to overcome an inherent energetic band mismatch between the two semiconductors, and realize the efficient collection of infrared photocarriers generated in the CQD film. This junction is used to produce a sensitive near infrared photodetector. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. 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

  5. Size and ligand effects on the electrochemical and spectroelectrochemical responses of CdSe nanocrystals

    NARCIS (Netherlands)

    Querner, Claudia; Reiss, Peter; Sadki, Said; Zagorska, Malgorzata; Pron, Adam

    2005-01-01

    The electrochemical properties of CdSe quantum dots with electrochemically inactive surface ligands (TOPO) have been investigated in comparison with the analogous nanocrystals containing electrochemically active oligoaniline ligands. The TOPO-capped nanocrystals have been studied in a wide size

  6. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

    Claudon, Julien; Munsch, Matthieu; Bleuse, Joel

    2012-01-01

    Besides microcavities and photonic crystals, photonic nanowires have recently emerged as a novel resource for solidstate quantum optics. We will review recent studies which demonstrate an excellent control over the spontaneous emission of InAs quantum dots (QDs) embedded in single-mode Ga...... quantum optoelectronic devices. Quite amazingly, this approach has for instance permitted (unlike microcavity-based approaches) to combine for the first time a record-high efficiency (72%) and a negligible g(2) in a QD single photon source....

  7. Research Progress of Photoanodes for Quantum Dot Sensitized Solar Cells

    Directory of Open Access Journals (Sweden)

    LI Zhi-min

    2017-08-01

    Full Text Available This paper presents the development status and tendency of quantum dot sensitized solar cells. Photoanode research progress and its related technologies are analyzed in detail from the three ways of semiconductor thin films, quantum dot co-sensitization and quantum dot doping, deriving from the approach that the conversion efficiency can be improved by photoanode modification for quantum dot sensitized solar cells. According to the key factors which restrict the cell efficiency, the promising future development of quantum dot sensitized solar cells is proposed,for example,optimizing further the compositions and structures of semiconductor thin films for the photoanodes, exploring new quantum dots with broadband absorption and developing high efficient techniques of interface modification.

  8. Using of Quantum Dots in Biology and Medicine.

    Science.gov (United States)

    Pleskova, Svetlana; Mikheeva, Elza; Gornostaeva, Ekaterina

    2018-01-01

    Quantum dots are nanoparticles, which due to their unique physical and chemical (first of all optical) properties, are promising in biology and medicine. There are many ways for quantum dots synthesis, both in the form of nanoislands self-forming on the surfaces, which can be used as single-photon emitters in electronics for storing information, and in the form of colloidal quantum dots for diagnostic and therapeutic purposes in living systems. The paper describes the main methods of quantum dots synthesis and summarizes medical and biological ways of their use. The main emphasis is laid on the ways of quantum dots surface modification. Influence of the size and form of nanoparticles, charge on the surfaces of quantum dots, and cover type on the efficiency of internalization by cells and cell compartments is shown. The main mechanisms of penetration are considered.

  9. Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles.

    Science.gov (United States)

    Tvrdy, Kevin; Frantsuzov, Pavel A; Kamat, Prashant V

    2011-01-04

    Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO(2), TiO(2), and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO(2)) were not the same as those which showed the highest photocurrent (TiO(2)). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.

  10. Covalent Linking Greatly Enhances Photoinduced Electron Transfer in Fullerene-Quantum Dot Nanocomposites: Time-Domain Ab Initio Study

    DEFF Research Database (Denmark)

    Chaban, Vitaly V.; Prezhdo, Victor; Prezhdo, Oleg

    2013-01-01

    Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C-60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process......, it leads to a notably weaker QD-C-60 interaction than a lengthy molecular bridge. We show that the ET rate in a nonbonded mixture of QDs and C-60 can be enhanced by doping. The photoinduced ET is promoted primarily by mid- and low-frequency vibrations. The study establishes the basic design principles...

  11. Quantum dots-hyperbranched polyether hybrid nanospheres towards delivery and real-time detection of nitric oxide

    DEFF Research Database (Denmark)

    Liu, Shuiping; Gu, Tianxun; Fu, Jiajia

    2014-01-01

    In this work, novel hybrid nanosphere vehicles were synthesized for nitric oxide (NO) donating and real-time detection. The hybrid nanosphere vehicles consist of cadmium selenide quantum dots (CdSe QDs) as NO fluorescent probes, and the modified hyperbranched polyether (mHP)-based diazeniumdiolates...... as NO donors, respectively. The nanospheres have spherical outline with dimension of ~ 127 nm. The data of systematic characterization demonstrated that the mHP-based hybrid nanosphere vehicles (QDs-mHP-NO) can release and real-time detect NO with the low limit of 25 nM, based on fluorescence quenching...

  12. Electronic transport through a quantum dot chain with strong dot-lead coupling

    International Nuclear Information System (INIS)

    Liu, Yu; Zheng, Yisong; Gong, Weijiang; Gao, Wenzhu; Lue, Tianquan

    2007-01-01

    By means of the non-equilibrium Green function technique, the electronic transport through an N-quantum-dot chain is theoretically studied. By calculating the linear conductance spectrum and the local density of states in quantum dots, we find the resonant peaks in the spectra coincides with the eigen-energies of the N-quantum-dot chain when the dot-lead coupling is relatively weak. With the increase of the dot-lead coupling, such a correspondence becomes inaccurate. When the dot-lead coupling exceeds twice the interdot coupling, such a mapping collapses completely. The linear conductance turn to reflect the eigen-energies of the (N-2)- or (N-1)-quantum dot chain instead. The two peripheral quantum dots do not manifest themselves in the linear conductance spectrum. More interestingly, with the further increase of the dot-lead coupling, the system behaves just like an (N-2)- or (N-1)-quantum dot chain in weak dot-lead coupling limit, since the resonant peaks becomes narrower with the increase of dot-lead coupling

  13. Nonlinear optical response of planar and spherical CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Selyukov, A. S., E-mail: bachelor89@inbox.ru; Isaev, A. A.; Vitukhnovsky, A. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Litvak, V. L. [Moscow Institute of Physics and Technology (State University) (Russian Federation); Katsaba, A. V. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Korshunov, V. M. [Bauman Moscow State Technical University (Russian Federation); Vasiliev, R. B. [Moscow State University (Russian Federation)

    2016-07-15

    The nonlinear optical response of a colloidal solution of planar CdSe semiconductor nanocrystals (nanoplatelets) is studied for the first time. The nonlinear optical response of these nanoparticles is compared to that of spherical CdSe nanocrystals (quantum dots). The photoinduced nonlinearity is attributed to the optical generation of long-lived charge carriers in the nanoobjects under study. It is shown that, upon the exposure of a cell with the solution of nanoparticles to focused continuous-wave (cw) laser radiation with a wavelength of 473 nm, the nonlinear optical responses of CdSe nanoplatelets and quantum dots are somewhat different at identical optical densities at the above-indicated wavelength. The differences are supposedly associated with a higher diffusion rate of spherical nanoparticles in the solution because of their smaller size compared to that of nanoplatelets.

  14. Silicon quantum dots: fine-tuning to maturity.

    Science.gov (United States)

    Morello, Andrea

    2015-12-18

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science.

  15. Polarized quantum dot emission in electrohydrodynamic jet printed photonic crystals

    International Nuclear Information System (INIS)

    See, Gloria G.; Xu, Lu; Nuzzo, Ralph G.; Sutanto, Erick; Alleyne, Andrew G.; Cunningham, Brian T.

    2015-01-01

    Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure

  16. Correlation effects in side-coupled quantum dots

    International Nuclear Information System (INIS)

    Zitko, R; Bonca, J

    2007-01-01

    Using Wilson's numerical renormalization group (NRG) technique, we compute zero-bias conductance and various correlation functions of a double quantum dot (DQD) system. We present different regimes within a phase diagram of the DQD system. By introducing a negative Hubbard U on one of the quantum dots, we simulate the effect of electron-phonon coupling and explore the properties of the coexisting spin and charge Kondo state. In a triple quantum dot (TQD) system, a multi-stage Kondo effect appears where localized moments on quantum dots are screened successively at exponentially distinct Kondo temperatures

  17. Single-charge tunneling in ambipolar silicon quantum dots

    NARCIS (Netherlands)

    Müller, Filipp

    2015-01-01

    Spin qubits in coupled quantum dots (QDs) are promising for future quantum information processing (QIP). A quantum bit (qubit) is the quantum mechanical analogon of a classical bit. In general, each quantum mechanical two-level system can represent a qubit. For the spin of a single charge carrier

  18. Charge transfer modeling in monolayer circular graphene quantum dots-ZnO nanowires system for application in photovoltaic devices

    Science.gov (United States)

    Tamandani, Shahryar; Darvish, Ghafar

    2017-01-01

    We investigate electron transport between circular graphene quantum dots (CGQDs) and ZnO nanowires (ZnO NWs). This structure can be used as donor and acceptor in hybrid solar cells. We consider circular quantum dots (QDs) and use analytical calculation in order to estimate wavefunctions of GQD and ZnO NWs. After calculating the wavefunctions overlap, we use Marcus relation in order to calculate electron transfer rate. Also, we calculate this transfer rate for CdSe QDs-ZnO NWs system. Results from analytical calculation show that the transfer rate is limited to 1013 s-1. This result is in agreement with experimental results which are reported earlier. Such systems could be suitable for solar cells.

  19. Quantum size effect and thermal stability of carbon-nanotube-based quantum dot

    International Nuclear Information System (INIS)

    Huang, N.Y.; Peng, J.; Liang, S.D.; Li, Z.B.; Xu, N.S.

    2004-01-01

    Full text: Based on semi-experience quantum chemical calculation, we have investigated the quantum size effect and thermal stability of open-end carbon nanotube (5, 5) quantum dots of 20 to 400 atoms. It was found that there is a gap in the energy band of all carbon nanotube (5, 5) quantum dots although a (5, 5) carbon nanotube is metallic. The energy gap of quantum dots is much dependent of the number of atoms in a dot, as a result of the quantization rules imposed by the finite scales in both radial and axial directions of a carbon nanotube quantum dot. Also, the heat of formation of carbon nanotube quantum dots is dependent of the size of a quantum dot. (author)

  20. Hybrid passivated colloidal quantum dot solids

    KAUST Repository

    Ip, Alex

    2012-07-29

    Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electrong-"hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device. © 2012 Macmillan Publishers Limited. All rights reserved.

  1. Quantum Dot Spectrum Converters for Enhanced High Efficiency Photovoltaics, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This research proposes to enhance solar cell efficiency, radiation resistance and affordability. The Quantum Dot Spectrum Converter (QDSC) disperses quantum dots...

  2. Cytocompatibility of direct water synthesized cadmium selenide quantum dots in colo-205 cells

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Torres, Marcos R. [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States); Velez, Christian; Zayas, Beatriz [Universidad Metropolitana, ChemTox Laboratory, School of Environmental Affairs (United States); Rivera, Osvaldo [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States); Arslan, Zikri [Jackson State University, Department of Chemistry (United States); Gonzalez-Vega, Maxine N. [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States); Diaz-Diestra, Daysi; Beltran-Huarac, Juan; Morell, Gerardo [University of Puerto Rico, Molecular Science Research Center (United States); Primera-Pedrozo, Oliva M., E-mail: oprimera1@suagm.edu [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States)

    2015-06-15

    Cadmium selenide quantum dots (CdSe QDs), inorganic semiconducting nanocrystals, are alluring increased attraction due to their highly refined chemistry, availability, and super tunable optical properties suitable for many applications in different research areas, such as photovoltaics, light-emitting devices, environmental sciences, and nanomedicine. Specifically, they are being widely used in bio-imaging in contrast to organic dyes due to their high brightness and improved photo-stability, and their ability to tune their absorption and emission spectra upon changing the crystal size. The production of CdSe QDs is mostly assisted by trioctylphosphine oxide compound, which acts as solvent or solubilizing agent and renders the QDs soluble in organic compounds (such as toluene, chloroform, and hexane) that are highly toxic. To circumvent the toxicity-related factor in CdSe QDs, we report the synthesis of CdSe QDs capped with thioglycolic acid (TGA) in an aqueous medium, and their biocompatibility in colo-205 cancer cells. In this study, the [Cd{sup 2+}]/[TGA] ratio was adjusted to 11:1 and the Se concentration (10 and 15 mM) was monitored in order to evaluate its influence on the optical properties and cytocompatibility. QDs resulted to be quite stable in water (after purification) and RPMI cell medium and no precipitation was observed for long contact times, making them appealing for in vitro experiments. The spectroscopy analysis, advanced electron microscopy, and X-ray diffractometry studies indicate that the final products were successfully formed exhibiting an improved optical response. Colo-205 cells being exposed to different concentrations of TGA-capped CdSe QDs for 12, 24, and 48 h with doses ranging from 0.5 to 2.0 mM show high tolerance reaching cell viabilities as high as 93 %. No evidence of cellular apoptotic pathways was observed as pointed out by our Annexin V assays at higher concentrations. Moreover, confocal microscopy analysis conducted to

  3. Silicon Quantum Dots with Counted Antimony Donor Implants

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Meenakshi [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Pacheco, Jose L. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Perry, Daniel Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Garratt, E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Ten Eyck, Gregory A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Wendt, Joel R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Manginell, Ronald P. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Luhman, Dwight [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Bielejec, Edward S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Lilly, Michael [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies; Carroll, Malcolm S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies

    2015-10-01

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. A focused ion beam is used to implant close to quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of ions implanted can be counted to a precision of a single ion. Regular coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization, are observed in devices with counted implants.

  4. Electrostatically defined silicon quantum dots with counted antimony donor implants

    Energy Technology Data Exchange (ETDEWEB)

    Singh, M., E-mail: msingh@sandia.gov; Luhman, D. R.; Lilly, M. P. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87175 (United States); Pacheco, J. L.; Perry, D.; Garratt, E.; Ten Eyck, G.; Bishop, N. C.; Wendt, J. R.; Manginell, R. P.; Dominguez, J.; Pluym, T.; Bielejec, E.; Carroll, M. S. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

    2016-02-08

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

  5. Near-field strong coupling of single quantum dots.

    Science.gov (United States)

    Groß, Heiko; Hamm, Joachim M; Tufarelli, Tommaso; Hess, Ortwin; Hecht, Bert

    2018-03-01

    Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.

  6. Coherent Dynamics of Quantum Dots in Photonic-Crystal Cavities

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg

    In this thesis we have performed quantum-electrodynamics experiments on quantum dots embedded in photonic-crystal cavities. We perform a quantitative comparison of the decay dynamics and emission spectra of quantum dots embedded in a micropillar cavity and a photonic-crystal cavity. The light......-matter interaction in the micropiller caivty is so strong that we measure non-Markovian dynamics of the quantum dot, and we compare to the Jaynes-Cummings model with all parameters independently determined. We find an excellent agreement when comparing the dynamics, but the emission spectra show significant...... deviations. Similar measurements on a quantum dot in a photonic-crystal cavity sow a Rabi splitting on resonance, while time-resolved measurements prove that the system is in the weak coupling regime. Whle tuning the quantum dot through resonance of the high-Q mode we observe a strong and surprisingly...

  7. Studies on silicon quantum dots prepared at different working pressure

    Directory of Open Access Journals (Sweden)

    Faisal A. Al-Agel

    Full Text Available This research work describes the synthesis and characterization of Si quantum dots of thickness 20 nm prepared on glass/quartz substrate by Physical Vapour Condensation Technique at the working pressure of 5 and 10 Torr with fixed substrate temperature 77 K using liquid nitrogen. The synthesized quantum dots were studied by FESEM, HRTEM, X-ray diffraction, UV–visible spectroscopy, photoluminescence and FTIR spectroscopy. The X-ray diffraction pattern of synthesized quantum dots shows the amorphous nature. FESEM images of synthesized quantum dots suggest that the size of quantum dots varies from 4–6 nm which is further confirmed by HRTEM. On the basis of optical absorbance by UV–visible spectroscopy, a direct band gap has been detected. FTIR spectra suggest that the as-grown Si quantum dots are partially oxidized which is due exposure of samples to air after taking out the samples from the chamber. PL spectra show a broad peak at 444 nm, which may be attributed to the configuration of amorphous Si quantum dots. A slight shift in the peak position has been observed with increase in working pressure from 5 Torr to 10 Torr. The dc conductivity with temperature of Si quantum dots has also been studied from 303 to 454 K. It is evident that the dc conductivity (σdc enhances linearly with temperature, showing that conduction in Si quantum dots is due to an activated action which further verify the semiconductor deportment of these quantum dots. Keywords: Si quantum dots, Thin films, XRD, Optical properties, Electrical properties

  8. Highly Efficient Spontaneous Emission from Self-Assembled Quantum Dots

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Lund-Hansen, Toke; Hvam, Jørn Märcher

    2006-01-01

    We present time resolved measurements of spontaneous emission (SE) from InAs/GaAs quantum dots (QDs). The measurements are interpreted using Fermi's Golden Rule and from this analysis we establish the parameters for high quantum efficiency.......We present time resolved measurements of spontaneous emission (SE) from InAs/GaAs quantum dots (QDs). The measurements are interpreted using Fermi's Golden Rule and from this analysis we establish the parameters for high quantum efficiency....

  9. Systematic optimization of quantum junction colloidal quantum dot solar cells

    KAUST Repository

    Liu, Huan

    2012-01-01

    The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum junction solar cell that leverages an improved aluminum zinc oxide electrode for a stable contact to the n-side of the quantum junction and silver doping of the p-layer that greatly enhances the photocurrent by expanding the depletion region in the n-side of the device. These improvements result in greater stability and a power conversion efficiency of 6.1 under AM1.5 simulated solar illumination. © 2012 American Institute of Physics.

  10. Correlated Coulomb drag in capacitively coupled quantum-dot structures

    DEFF Research Database (Denmark)

    Kaasbjerg, Kristen; Jauho, Antti-Pekka

    2016-01-01

    We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs) -- a biasdriven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach which accounts for higher-order tunneling (cotunneling...

  11. Sarcomere Imaging by Quantum Dots for the Study of Cardiac Muscle Physiology

    Directory of Open Access Journals (Sweden)

    Fuyu Kobirumaki-Shimozawa

    2012-01-01

    Full Text Available We here review the use of quantum dots (QDs for the imaging of sarcomeric movements in cardiac muscle. QDs are fluorescence substances (CdSe that absorb photons and reemit photons at a different wavelength (depending on the size of the particle; they are efficient in generating long-lasting, narrow symmetric emission profiles, and hence useful in various types of imaging studies. Recently, we developed a novel system in which the length of a particular, single sarcomere in cardiomyocytes can be measured at ~30 nm precision. Moreover, our system enables accurate measurement of sarcomere length in the isolated heart. We propose that QDs are the ideal tool for the study of sarcomere dynamics during excitation-contraction coupling in healthy and diseased cardiac muscle.

  12. Quantum error prevention and leakage elimination for quantum dots

    Science.gov (United States)

    Pegahan, Saeed; Byrd, Mark S.; Reddy Chinni, Karthik

    2015-03-01

    Decoherence-free, or noiseless subsystems, are used to encode spin qubits in quantum dots in order to achieve universal quantum computing using only the exchange interaction. We investigate the use of dynamical decoupling controls for the purposes of eliminating leakage for a logical qubit encoded using three physical qubits. These leakage elimination operators (LEOs) can be used to eliminate all leakage errors using exchange interactions between the physical spin qubits. Depending on the encoding and the decoupling control, different types of errors can be eliminated. We show several different possible controls and the consequential noise reduction for different encodings as well as our general method for determining the effectiveness of these pulses.

  13. Colloidal Quantum Dot Photovoltaics: A Path Forward

    KAUST Repository

    Kramer, Illan J.

    2011-11-22

    Colloidal quantum dots (CQDs) offer a path toward high-efficiency photovoltaics based on low-cost materials and processes. Spectral tunability via the quantum size effect facilitates absorption of specific wavelengths from across the sun\\'s broad spectrum. CQD materials\\' ease of processing derives from their synthesis, storage, and processing in solution. Rapid advances have brought colloidal quantum dot photovoltaic solar power conversion efficiencies of 6% in the latest reports. These achievements represent important first steps toward commercially compelling performance. Here we review advances in device architecture and materials science. We diagnose the principal phenomenon-electronic states within the CQD film band gap that limit both current and voltage in devices-that must be cured for CQD PV devices to fulfill their promise. We close with a prescription, expressed as bounds on the density and energy of electronic states within the CQD film band gap, that should allow device efficiencies to rise to those required for the future of the solar energy field. © 2011 American Chemical Society.

  14. Dynamics of Energy Transfer in Quantum Dot Arrays

    Science.gov (United States)

    Al-Ahmadi, A. N.; Ulloa, S. E.

    2004-04-01

    Förster-type coupling is one of the most important mechanisms that influence the energy transport properties in a quantum dot array. We explore this mechanism by calculating the coupling strength V_F, and by studying the dynamics of the exciton state created in an array of quantum dots using the time evolution of the density matrix approach. We first estimate the coupling strength VF of Förster interaction based on microscopic descriptions of the exciton levels in the quantum dot. We study this parameter for different materials (CdS, CdSe,InP, and GaAs) as function of the dot size. The results show that the maximum value of VF depends on the specific sizes and that each material has optimal coupling for different pairs of quantum dot radii. Other key parameters that govern energy transport are determined for various materials and sizes of quantum dots. Second, we consider a model of coupled quantum dots with two exciton levels in each dot, one optically passive and another active. Analysis of the population of each level when the Förster channel is opened shows this is responsible for interesting physical behavior in different coupling regimes. Realistic parameters used to study the dynamics of the exciton state for dimer and trimer quantum dot clusters, allow us direct comparison with recent experiments by Klimov et al. Supported by US DOE, and Indiana 21^st Century Fund Research and Technology.

  15. Quantum computation with nuclear spins in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Christ, H.

    2008-01-24

    The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin

  16. Quantum computation with nuclear spins in quantum dots

    International Nuclear Information System (INIS)

    Christ, H.

    2008-01-01

    The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin

  17. Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot

    DEFF Research Database (Denmark)

    Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal

    2016-01-01

    We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offe...

  18. Fractional decay of quantum dots in photonic crystals

    DEFF Research Database (Denmark)

    Kristensen, Philip Trøst; Koenderink, Femius; Lodahl, Peter

    2008-01-01

    We define a practical measure for the degree of fractional decay and establish conditions for the effect to be observable for quantum dots in photonic crystals exhibiting absorptive losses.......We define a practical measure for the degree of fractional decay and establish conditions for the effect to be observable for quantum dots in photonic crystals exhibiting absorptive losses....

  19. Single-photon superradiance from a quantum dot

    DEFF Research Database (Denmark)

    Tighineanu, Petru; Daveau, Raphaël Sura; Lehmann, Tau Bernstorff

    2016-01-01

    We report on the observation of single-photon superradiance from an exciton in a semiconductor quantum dot. The confinement by the quantum dot is strong enough for it to mimic a two-level atom, yet sufficiently weak to ensure superradiance. The electrostatic interaction between the electron and t...

  20. Electronic properties of assemblies of zno quantum dots

    NARCIS (Netherlands)

    Roest, Aarnoud Laurens

    2003-01-01

    Electron transport in an assembly of ZnO quantum dots has been studied using an electrochemically gated transistor. The electron mobility shows a step-wise increase as a function of the electron occupation per quantum dot. When the occupation number is below two, transport occurs by tunnelling

  1. Stark effect and polarizability of graphene quantum dots

    DEFF Research Database (Denmark)

    Pedersen, Thomas Garm

    2017-01-01

    The properties of graphene quantum dots can be manipulated via lateral electric fields. Treating electrons in such structures as confined massless Dirac fermions, we derive an analytical expression for the quadratic Stark shift valid for arbitrary angular momentum and quantum dot size. Moreover, we...

  2. Electron transport and coherence in semiconductor quantum dots and rings

    NARCIS (Netherlands)

    Van der Wiel, W.G.

    2002-01-01

    A number of experiments on electron transport and coherence in semiconductor vertical and lateral quantum dots and semiconductor rings is described. Quantum dots are often referred to as "artificial atoms", because of their similarities with real atoms. Examples of such atom-like properties that

  3. Quantum dots for multimodal molecular imaging of angiogenesis

    NARCIS (Netherlands)

    Mulder, Willem J. M.; Strijkers, Gustav J.; Nicolay, Klaas; Griffioen, Arjan W.

    2010-01-01

    Quantum dots exhibit unique optical properties for bioimaging purposes. We have previously developed quantum dots with a paramagnetic and functionalized coating and have shown their potential for molecular imaging purposes. In the current mini-review we summarize the synthesis procedure, the in

  4. Fabrication of a graphene quantum dot device

    Science.gov (United States)

    Lee, Jeong Il; Kim, Eunseong

    2014-03-01

    Graphene, which exhibits a massless Dirac-like spectrum for its electrons, has shown impressive properties for nano-electronics applications including a high mobility and a width dependent bandgap. We will report the preliminary report on the transport property of the suspended graphene nano-ribbon(GNR) quantum dot device down to dilution refrigerator temperature. This GNR QD device was fabricated to realize an ideal probe to investigate Kondo physics--a characteristic phenomenon in the physics of strongly correlated electrons. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

  5. Quantum dot blueing and blinking enables fluorescence nanoscopy.

    Science.gov (United States)

    Hoyer, Patrick; Staudt, Thorsten; Engelhardt, Johann; Hell, Stefan W

    2011-01-12

    We demonstrate superresolution fluorescence imaging of cells using bioconjugated CdSe/ZnS quantum dot markers. Fluorescence blueing of quantum dot cores facilitates separation of blinking markers residing closer than the diffraction barrier. The high number of successively emitted photons enables ground state depletion microscopy followed by individual marker return with a resolving power of the size of a single dot (∼12 nm). Nanoscale imaging is feasible with a simple webcam.

  6. Interleukin-13 conjugated quantum dots for identification of glioma initiating cells and their extracellular vesicles.

    Science.gov (United States)

    Madhankumar, A B; Mrowczynski, Oliver D; Patel, Suhag R; Weston, Cody L; Zacharia, Brad E; Glantz, Michael J; Siedlecki, Christopher A; Xu, Li-Chong; Connor, James R

    2017-08-01

    Cadmium selenide (CdSe) based quantum dots modified with polyethylene glycol and chemically linked to interleukin-13 (IL13) were prepared with the aim of identifying the high affinity receptor (IL13Rα2) which is expressed in glioma stem cells and exosomes secreted by these cancer stem cells. IL13 conjugated quantum dots (IL13QD) were thoroughly characterized for their physicochemical properties including particle size and surface morphology. Furthermore, the specific binding of the IL13QD to glioma cells and to glioma stem cells (GSC) was verified using a competitive binding study. The exosomes were isolated from the GSC conditioned medium and the expression of IL13Rα2 in the GSC and exosomes was verified. The binding property of IL13QD to the tumor associated exosomes was initially confirmed by transmission electron microscopy. The force of attraction between the quantum dots and U251 glioma cells and the exosomes was investigated by atomic force microscopy, which indicated a higher force of binding interaction between the IL13QD and IL13Rα2 expressing glioma cells and exosomes secreted by glioma stem cells. Flow cytometry of the IL13QD and exosomes from the culture media and cerebrospinal fluid (CSF) of patients with glioma tumors indicated a distinctly populated complex pattern different from that of non-targeted quantum dots and bovine serum albumin (BSA) conjugated quantum dots confirming specific binding potential of the IL13QD to the tumor associated exosomes. The results of this study demonstrate that IL13QD can serve as an ex vivo marker for glioma stem cells and exosomes that can inform diagnosis and prognosis of patients harboring malignant disease. Functionalized quantum dots are flexible semiconductor nanomaterials which have an immense application in biomedical research. In particular, when they are functionalized with biomolecules like proteins or antibodies, they have the specialized ability to detect the expression of receptors and antigens in

  7. Direct synthesis of aqueous quantum dots through 4,4'-bipyridine-based twin ligand strategy.

    Science.gov (United States)

    Kalita, Mausam; Cingarapu, Sreeram; Roy, Santanu; Park, Seok Chan; Higgins, Daniel; Jankowiak, Ryszard; Chikan, Viktor; Klabunde, Kenneth J; Bossmann, Stefan H

    2012-04-16

    We report a new class of derivatized 4,4'-bipyridinium ligands for use in synthesizing highly fluorescent, extremely stable, water-soluble CdSe and CdTe quantum dots (QDs) for bioconjugation. We employed an evaporation-condensation technique, also known as solvated metal atom dispersion (SMAD), followed by a digestive ripening procedure. This method has been used to synthesize both metal nanoparticles and semiconductors in the gram scale with several stabilizing ligands in various solvents. The SMAD technique comprised evaporation condensation and stabilization of CdSe or CdTe in tetrahydrofuran. The as-prepared product was then digestively ripened in both water and dimethyl formamide, leading to narrowing of the particle size distributions. The ligands were synthesized by nucleophilic substitution (S(N)2) reactions using 4,4'-bipyridine as a nucleophile. Confocal microscopy images revealed the orange color of the nanocrystalline QDs with diameters of ~5 nm. The size has been confirmed by using transmission electron microscopy. As a part of our strategy, 85% of the 4,4'-bipyridinium salt was synthesized as propionic acid derivative and used to both stabilize the QDs in water and label basic amino acids and different biomarkers utilizing the carboxylic acid functional group. Fifteen percent of the 4,4'-bipyridinium salt was synthesized as N-propyl maleimide and used as a second ligand to label any protein containing the amino acid cysteine by means of a 1,4-Michael addition. © 2012 American Chemical Society

  8. Rapid determination of the toxicity of quantum dots with luminous bacteria

    International Nuclear Information System (INIS)

    Wang Lingling; Zheng Huzhi; Long Yijuan; Gao Mei; Hao Jianyu; Du Juan; Mao Xiaojiao; Zhou Dongbo

    2010-01-01

    In this paper, a novel method so-called bioluminescence inhibition assay with luminous bacteria (Photobacterium phosphoreum) was introduced to evaluate the toxicity of quantum dots. The bioassay was based on measuring the decrease of the light emitted by luminous bacteria. With obvious advantages of simplicity, rapidity and sensitivity, it can dramatically improve the efficiency of probing the toxicity of QDs. Based on this method, we systemically explored the effect of the composition and surface modification on QDs' toxicity. The experiment of composition effect was performed using three kinds of QDs, namely CdSe, CdTe and ZnS-AgInS 2 QDs with the same stabilizer - dihydrolipoic acid. As for the effect of different stabilizers, mercaptoacetic acid, L-cysteine and dihydrolipoic acid stabilized CdSe were researched, respectively. Our results demonstrated that both the composition and surface modification were the important factors affecting the toxicity of QDs. In addition, a concentration dependence of toxicity was also found.

  9. Optical properties of ZnO-nanowire/CdSe-colloidal-quantum-dot hybrid structures

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Dongchao; Richters, Jan-Peter; Dev, Apurba; Voss, Tobias [Semiconductor Optics, Institute of Solid State Physics, University of Bremen (Germany)

    2011-07-01

    One of the research interests in modern nanotechnology is the assembly and study of hybrid heterostructures composed of different materials that offer enhanced properties through the interactions between their different constituents. ZnO nanowires functionalized with colloidal semiconductor quantum dots (QDs) display tailored optical properties due to energy and electron transfer processes between these two components, and have a huge potential for applications in light-emitting and photovoltaic devices. Using a facile method, we synthesized water-soluble CdSe QDs with cadmium acetate and sodium selenosulfate as Cd and Se precursors, respectively. 3-mercaptopropionic acid (MPA) was used to cap the QDs, acting as the stabilizer, making the QDs water soluble and preventing them from agglomeration. TEM measurements demonstrated a narrow size distribution of the as-prepared QDs with the average diameter around 3 nm, consistent with UV-Vis absorption measurements. The carboxylic groups at the outer surface of the MPA-capped CdSe QDs render a tight and uniform attachment onto the surface of ZnO nanowires with high coverage efficiency possible. We studied the optical properties of the hybrid structures by photoluminescence spectroscopy under different temperatures to analyze the energy and electron transfer dynamics between the nanowires and the QDs.

  10. Emission variation in infrared (CdSeTe)/ZnS quantum dots conjugated to antibodies

    Science.gov (United States)

    Jaramillo Gómez, J. A.; Casas Espinola, J. L.; Douda, J.

    2014-11-01

    The paper presents the photoluminescence (PL) and Raman scattering investigations of infrared CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) in nonconjugated states and after the conjugation to the anti-papilloma virus antibodies (Ab). The Raman scattering study has shown that the CdSeTe core includes two layers with different material compositions such as: CdSe0.5Te0.5 and CdSe0.7Te0.3. PL spectra of nonconjugated CdSeTe/ZnS QDs are characterized by two Gaussian shape PL bands related to exciton emission in the CdSeTe core and in intermediate layer at the core/shell interface. PL spectra of bioconjugated QDs have changed essentially: the main PL band related to the core emission shifts into high energy and become asymmetric. The energy diagram of double core/shell CdSeTe/ZnS QDs has been analyzed to explain the PL spectrum of nonconjugated QDs and its transformation at the bioconjugation to the papiloma virus antibodies. It is shown that the PL spectrum transformation in bioconjugated QDs can be a powerful technique for biology and medicine.

  11. 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...... observe that second-harmonic images of the quantum-dot surface structure show wavelength-dependent spatial variations. Imaging at different wavelength is used to demonstrate second-harmonic generation from the semiconductor quantum dots. (C) 2000 American Institute of Physics....

  12. Interaction of porphyrins with CdTe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Xing; Liu Zhongxin; Ma Lun; Hossu, Marius; Chen Wei, E-mail: weichen@uta.edu [Department of Physics, University of Texas at Arlington, Box 19059 Arlington, TX 76019 (United States)

    2011-05-13

    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.

  13. Numerical simulation of optical feedback on a quantum dot lasers

    International Nuclear Information System (INIS)

    Al-Khursan, Amin H.; Ghalib, Basim Abdullattif; Al-Obaidi, Sabri J.

    2012-01-01

    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.

  14. 3D super-resolution imaging with blinking quantum dots

    Science.gov (United States)

    Wang, Yong; Fruhwirth, Gilbert; Cai, En; Ng, Tony; Selvin, Paul R.

    2013-01-01

    Quantum dots are promising candidates for single molecule imaging due to their exceptional photophysical properties, including their intense brightness and resistance to photobleaching. They are also notorious for their blinking. Here we report a novel way to take advantage of quantum dot blinking to develop an imaging technique in three-dimensions with nanometric resolution. We first applied this method to simulated images of quantum dots, and then to quantum dots immobilized on microspheres. We achieved imaging resolutions (FWHM) of 8–17 nm in the x-y plane and 58 nm (on coverslip) or 81 nm (deep in solution) in the z-direction, approximately 3–7 times better than what has been achieved previously with quantum dots. This approach was applied to resolve the 3D distribution of epidermal growth factor receptor (EGFR) molecules at, and inside of, the plasma membrane of resting basal breast cancer cells. PMID:24093439

  15. 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.

  16. Biosensing with Luminescent Semiconductor Quantum Dots

    Directory of Open Access Journals (Sweden)

    Hedi Mattoussi

    2006-08-01

    Full Text Available Luminescent semiconductor nanocrystals or quantum dots (QDs are a recentlydeveloped class of nanomaterial whose unique photophysical properties are helping tocreate a new generation of robust fluorescent biosensors. QD properties of interest forbiosensing include high quantum yields, broad absorption spectra coupled to narrow sizetunablephotoluminescent emissions and exceptional resistance to both photobleaching andchemical degradation. In this review, we examine the progress in adapting QDs for severalpredominantly in vitro biosensing applications including use in immunoassays, asgeneralized probes, in nucleic acid detection and fluorescence resonance energy transfer(FRET - based sensing. We also describe several important considerations when workingwith QDs mainly centered on the choice of material(s and appropriate strategies forattaching biomolecules to the QDs.

  17. Templated self-assembly of SiGe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Dais, Christian

    2009-08-19

    This PhD thesis reports on the fabrication and characterization of exact aligned SiGe quantum dot structures. In general, SiGe quantum dots which nucleate via the Stranski-Krastanov growth mode exhibit broad size dispersion and nucleate randomly on the surface. However, to tap the full potential of SiGe quantum dots it is necessary to control the positioning and size of the dots on a nanometer length, e.g. for electronically addressing of individual dots. This can be realized by so-called templated self-assembly, which combines top-down lithography with bottom-up selfassembly. In this process the lithographically defined pits serve as pre-defined nucleation points for the epitaxially grown quantum dots. In this thesis, extreme ultraviolet interference lithography at a wavelength of e=13.4 nm is employed for prepatterning of the Si substrates. This technique allows the precise and fast fabrication of high-resolution templates with a high degree of reproducibility. The subsequent epitaxial deposition is either performed by molecular beam epitaxy or low-pressure chemical vapour deposition. It is shown that the dot nucleation on pre-patterned substrates depends strongly on the lithography parameters, e.g. size and periodicity of the pits, as well as on the epitaxy parameters, e.g. growth temperature or material coverage. The interrelations are carefully analyzed by means of scanning force microscopy, transmission electron microscopy and X-ray diffraction measurements. Provided that correct template and overgrowth parameters are chosen, perfectly aligned and uniform SiGe quantum dot arrays of different period, size as well as symmetry are created. In particular, the quantum dot arrays with the so far smallest period (35 nm) and smallest size dispersion are fabricated in this thesis. Furthermore, the strain fields of the underlying quantum dots allow the fabrication of vertically aligned quantum dot stacks. Combining lateral and vertical dot alignment results in three

  18. Phonon-assisted decoherence and tunneling in quantum dot molecules

    DEFF Research Database (Denmark)

    Grodecka-Grad, Anna; Foerstner, Jens

    2011-01-01

    We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantum kinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual...... processes with relevant acoustic phonons. We show that the relaxation is dominated by phonon-assisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between...

  19. Enhancement of cell internalization and photostability of red and green emitter quantum dots upon entrapment in novel cationic nanoliposomes.

    Science.gov (United States)

    Samadikhah, Hamid Reza; Nikkhah, Maryam; Hosseinkhani, Saman

    2017-06-01

    Two quantum dots (QDs), a green emitter, CdSe and a red emitter, CdSe with ZnS shell are encapsulated into novel liposomes in two different formulations including cationic liposomes. Quantum dots have proven themselves as powerful inorganic fluorescent probes, especially for long-term, multiplexed imaging and detection. Upon delivery into a cell, in endocytic vesicles such as endosomes, their fluorescence is quenched. We have investigated the potential toxic effects, photophysical properties and cell internalization of QDs in new formulation of liposomes as an in vitro vesicle model. Entrapment of QDs into liposomes is brought about with a decrease in their intrinsic fluorescence and toxicities and an increase in their photostability and lifetime. The biomimetic lipid bilayer of liposomes provides high biocompatibility, thereby enhancing the effectiveness of fluorescent nanoparticles for biological recognition in vitro and in vivo. The prepared lipodots could effectively prevent QDs from photo-oxidation during storage and when exposed to ultraviolet (UV) light. Moreover, the flow cytometry of HEK 293 T cells showed that the cell internalization of encapsulated QDs in (DSPC/CHO/DOPE/DOAB) liposome is enhanced 10 times compared with non-encapsulated QD (bare QDs). Copyright © 2016 John Wiley & Sons, Ltd.

  20. Andreev molecules in semiconductor nanowire double quantum dots.

    Science.gov (United States)

    Su, Zhaoen; Tacla, Alexandre B; Hocevar, Moïra; Car, Diana; Plissard, Sébastien R; Bakkers, Erik P A M; Daley, Andrew J; Pekker, David; Frolov, Sergey M

    2017-09-19

    Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum dots are defined by gate voltages in indium antimonide nanowires. High transparency superconducting niobium titanium nitride contacts are made to each of the dots in order to induce superconductivity, as well as probe electron transport. Andreev bound states induced on each of dots hybridize to define Andreev molecular states. The evolution of these states is studied as a function of charge parity on the dots, and in magnetic field. The experiments are found in agreement with a numerical model.Quantum dots in a nanowire are one possible approach to creating a solid-state quantum simulator. Here, the authors demonstrate the coupling of electronic states in a double quantum dot to form Andreev molecule states; a potential building block for longer chains suitable for quantum simulation.

  1. Anisotropic morphology of nonpolar a-plane GaN quantum dots and quantum wells

    International Nuclear Information System (INIS)

    Founta, S.; Bougerol, C.; Mariette, H.; Daudin, B.; Vennegues, P.

    2007-01-01

    The growth of (11-20) or a-plane quantum dots and quantum wells by plasma-assisted molecular-beam epitaxy has been studied. It is shown that Ga-rich conditions lead to the formation of quantum dots, whereas quantum wells are obtained in N-rich conditions. Combining various experimental techniques, it is furthermore demonstrated that quantum dot nucleation along [1-100] and quantum well morphology in the (1-100) plane are influenced by anisotropic growth of AlN buffer layer. Moreover, it is established that peculiar morphological features of quantum dots and quantum wells, in particular the asymmetric shape of quantum dots, are related to the polar character of the [0001] direction in wurtzite nitride material

  2. Colloidal quantum dot light-emitting devices

    Directory of Open Access Journals (Sweden)

    Vanessa Wood

    2010-07-01

    Full Text Available Colloidal quantum dot light-emitting devices (QD-LEDs have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI. We review the key advantages of using quantum dots (QDs in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs – optical excitation, Förster energy transfer, and direct charge injection – that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt. We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs.

  3. Ferritin-Templated Quantum-Dots for Quantum Logic Gates

    Science.gov (United States)

    Choi, Sang H.; Kim, Jae-Woo; Chu, Sang-Hyon; Park, Yeonjoon; King, Glen C.; Lillehei, Peter T.; Kim, Seon-Jeong; Elliott, James R.

    2005-01-01

    Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The work presented here offers a new method to develop quantum-dots using a bio-template, called ferritin, that ensures QD production in uniform size of nano-scale proportion. The bio-template for uniform yield of QD is based on a ferritin protein that allows reconstitution of core material through the reduction and chelation processes. One of the biggest challenges for developing QLG is the requirement of ordered and uniform size of QD for arrays on a substrate with nanometer precision. The QD development by bio-template includes the electrochemical/chemical reconsitution of ferritins with different core materials, such as iron, cobalt, manganese, platinum, and nickel. The other bio-template method used in our laboratory is dendrimers, precisely defined chemical structures. With ferritin-templated QD, we fabricated the heptagonshaped patterned array via direct nano manipulation of the ferritin molecules with a tip of atomic force microscope (AFM). We also designed various nanofabrication methods of QD arrays using a wide range manipulation techniques. The precise control of the ferritin-templated QD for a patterned arrangement are offered by various methods, such as a site-specific immobilization of thiolated ferritins through local oxidation using the AFM tip, ferritin arrays induced by gold nanoparticle manipulation, thiolated ferritin positioning by shaving method, etc. In the signal measurements, the current-voltage curve is obtained by measuring the current through the ferritin, between the tip and the substrate for potential sweeping or at constant potential. The measured resistance near zero bias was 1.8 teraohm for single holoferritin and 5.7 teraohm for single apoferritin, respectively.

  4. 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.

  5. Uncovering the role of the ZnS treatment in the performance of quantum dot sensitized solar cells.

    Science.gov (United States)

    Guijarro, Néstor; Campiña, José M; Shen, Qing; Toyoda, Taro; Lana-Villarreal, Teresa; Gómez, Roberto

    2011-07-07

    Among the third-generation photovoltaic devices, much attention is being paid to the so-called Quantum Dot sensitized Solar Cells (QDSCs). The currently poor performance of QDSCs seems to be efficiently patched by the ZnS treatment, increasing the output parameters of the devices, albeit its function remains rather unclear. Here new insights into the role of the ZnS layer on the QDSC performance are provided, revealing simultaneously the most active recombination pathways. Optical and AFM characterization confirms that the ZnS deposit covers, at least partially, both the TiO(2) nanoparticles and the QDs (CdSe). Photoanodes submitted to the ZnS treatment before and/or after the introduction of colloidal CdSe QDs were studied by electrochemical impedance spectroscopy, cyclic voltammetry and photocurrent experiments. The corresponding results prove that the passivation of the CdSe QDs rather than the blockage of the TiO(2) surface is the main factor leading to the efficiency improvement. In addition, a study of the ultrafast carrier dynamics by means of the Lens-Free Heterodyne Detection Transient Grating technique indicates that the ZnS shell also increases the rate of electron transfer. The dual role of the ZnS layer should be kept in mind in the quest for new modifiers for enhancing the performance of QDSCs. This journal is © the Owner Societies 2011

  6. Atomically precise, coupled quantum dots fabricated by cleaved edge overgrowth

    Science.gov (United States)

    Wegscheider, W.; Schedelbeck, G.; Bichler, M.; Abstreiter, G.

    Recent progress in the fabrication of quantum dots by molecular beam epitaxy along three directions in space is reviewed. The optical properties of different sample structures consisting of individual quantum dots, pairs of coupled dots as well as of linear arrays of dots are studied by microscopic photoluminescence spectroscopy. The high degree of control over shape, composition and position of the 7×7×7 nm3 size GaAs quantum dots, which form at the intesection of three orthogonal quantum wells, allows a detailed investigation of the influence of coupling between almost identical zero-dimensional objects. In contrast to the inhomogeneously broadened quantum well and quantum wire signals originating from the complex twofold cleaved edge overgrowth structure, the photoluminescence spetrum of an individual quantum dot exhibits a single sharp line (full width at half maximum denomination "artificial atoms" for the quantum dots. It is further demonstrated that an "artifical molecule", characterized by the existence of bonding and antibonding states can be assembled from two of such "artificial atoms". The coupling strength between the "artificial atoms" is adjusted by the "interatomic" distance and is reflected in the energetic separation of the bonding and antibonding levels and the linewidths of the corresponding interband transitions.

  7. Spin-based all-optical quantum computation with quantum dots: Understanding and suppressing decoherence

    International Nuclear Information System (INIS)

    Calarco, T.; Datta, A.; Fedichev, P.; Zoller, P.; Pazy, E.

    2003-01-01

    We present an all-optical implementation of quantum computation using semiconductor quantum dots. Quantum memory is represented by the spin of an excess electron stored in each dot. Two-qubit gates are realized by switching on trion-trion interactions between different dots. State selectivity is achieved via conditional laser excitation exploiting Pauli exclusion principle. Read out is performed via a quantum-jump technique. We analyze the effect on our scheme's performance of the main imperfections present in real quantum dots: exciton decay, hole mixing, and phonon decoherence. We introduce an adiabatic gate procedure that allows one to circumvent these effects and evaluate quantitatively its fidelity

  8. Chemical substitution of Cd ions by Hg in CdSe nanorods and nanodots: Spectroscopic and structural examination

    International Nuclear Information System (INIS)

    Prudnikau, Anatol; Artemyev, Mikhail; Molinari, Michael; Troyon, Michel; Sukhanova, Alyona; Nabiev, Igor; Baranov, Alexandr V.; Cherevkov, Sergey A.; Fedorov, Anatoly V.

    2012-01-01

    Highlights: ► We studied cadmium-by-mercury chemical substitution in CdSe nanocrystals. ► Zinc blende CdSe quantum dots can be easily converted to isostructural Cd x Hg 1−x Se. ► Wurtzite CdSe QDs require longer time to convert to a zinc blende Cd x Hg 1−x Se. ► Wurtzite CdSe nanorods transform to nanoheterogeneous luminescent Cd x Hg 1−x Se rods. - Abstract: The chemical substitution of cadmium by mercury in colloidal CdSe quantum dots (QDs) and nanorods has been examined by absorption, photoluminescence and Raman spectroscopy. The crystalline structure of original CdSe QDs used for Cd/Hg substitution (zinc blende versus wurtzite) shows a strong impact on the optical and structural properties of resultant Cd x Hg 1−x Se nanocrystals. Substitution of Cd by Hg in isostructural zinc blende CdSe QDs converts them to ternary Cd x Hg 1−x Se zinc blende nanocrystals with significant NIR emission. Whereas, the wurtzite CdSe QDs transformed first to ternary nanocrystals with almost no emission followed by slow structural reorganization to a NIR-emitting zinc blende Cd x Hg 1−x Se QDs. CdSe nanorods with intrinsic wurtzite structure show unexpectedly intense NIR emission even at early Cd/Hg substitution stage with PL active zinc blende Cd x Hg 1−x Se regions.

  9. Gate-defined quantum dots in intrinsic silicon.

    Science.gov (United States)

    Angus, Susan J; Ferguson, Andrew J; Dzurak, Andrew S; Clark, Robert G

    2007-07-01

    We report the fabrication and measurement of silicon quantum dots with tunable tunnel barriers in a narrow-channel field-effect transistor. Low-temperature transport spectroscopy is performed in both the many-electron ( approximately 100 electrons) regime and the few-electron ( approximately 10 electrons) regime. Excited states in the bias spectroscopy provide evidence of quantum confinement. These results demonstrate that depletion gates are an effective technique for defining quantum dots in silicon.

  10. Pulse train amplification and regeneration based on semiconductor quantum dots waveguide

    DEFF Research Database (Denmark)

    Chen, Yaohui; Öhman, Filip; Mørk, Jesper

    2008-01-01

    We numerical analyze pulse train amplification up to 200 Gbit/s in quantum dot amplifiers and present regeneration properties with saturable absorber based on semiconductor quantum dot waveguides.......We numerical analyze pulse train amplification up to 200 Gbit/s in quantum dot amplifiers and present regeneration properties with saturable absorber based on semiconductor quantum dot waveguides....

  11. Exciton dephasing in single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis

    2000-01-01

    The homogeneous linewidth of excitonic transitions is a parameter of fundamental physical importance. In self-assembled quantum dot systems, a strong inhomogeneous broadening due to dot size fluctuations masks the homogeneous linewidth associated with transitions between individual states....... The homogeneous and inhomogeneous broadening of InGaAs quantum dot luminescence is of central importance for the potential application of this material system in optoelectronic devices. Recent measurements of MOCVD-grown InAs/InGaAs quantum dots indicate a large homogeneous broadening at room temperature due...... to fast dephasing. We present an investigation of the low-temperature homogeneous linewidth of individual PL lines from MBE-grown In0.5Ga0.5As/GaAs quantum dots....

  12. Spin current through quantum-dot spin valves

    International Nuclear Information System (INIS)

    Wang, J; Xing, D Y

    2006-01-01

    We report a theoretical study of the influence of the Coulomb interaction on the equilibrium spin current in a quantum-dot spin valve, in which the quantum dot described by the Anderson impurity model is coupled to two ferromagnetic leads with noncollinear magnetizations. In the Kondo regime, electrons transmit through the quantum dot via higher-order virtual processes, in which the spin of either lead electrons or a localized electron on the quantum dot may reverse. It is found that the magnitude of the spin current decreases with increasing Coulomb interactions due to spin flip effects on the dot. However, the spatial direction of the spin current remains unchanged; it is determined only by the exchange coupling between two noncollinear magnetizations

  13. On-chip quantum optics with quantum dots and superconducting resonators

    Science.gov (United States)

    Deng, Guang-Wei; Guo, Guo-Ping; Guo, Guang-Can

    2016-11-01

    Benefit from the recent nanotechnology process, people can integrate different nanostructures on a single chip. Particularly, quantum dots (QD), which behave as artificial atoms, have been shown to couple with a superconducting resonator, indicating that quantum-dot based quantum chip has a highly scalable possibility. Here we show a quantum chip architecture by combining graphene quantum dots and superconducting resonators together. A double quantum dot (DQD) and a microwave hybrid system can be described by the Jaynes-Cummings model, while a multi-quantum-dots system is conformed to the Tavis-Cummings model. These simple quantum optics models are experimentally realized in our device, providing a compelling platform for both graphene study and potential applications.

  14. Enhancing Photocatalytic Degradation of Methyl Blue Using PVP-Capped and Uncapped CdSe Nanoparticles

    OpenAIRE

    Chepape, Kgobudi Frans; Mofokeng, Thapelo Prince; Nyamukamba, Pardon; Mubiayi, Kalenga Pierre; Moloto, Makwena Justice

    2017-01-01

    Quantum confinement of semiconductor nanoparticles is a potential feature which can be interesting for photocatalysis, and cadmium selenide is one simple type of quantum dot to use in the following photocatalytic degradation of organic dyes. CdSe nanoparticles capped with polyvinylpyrrolidone (PVP) in various concentration ratios were synthesized by the chemical reduction method and characterized. The transmission electron microscopy (TEM) analysis of the samples showed that 50% PVP-capped Cd...

  15. Quantum efficiency and oscillator strength of site-controlled InAs quantum dots

    DEFF Research Database (Denmark)

    Albert, F.; Stobbe, Søren; Schneider, C.

    2010-01-01

    We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled InAs quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

  16. Quantum efficiency and oscillator strength of site-controlled InGaAs quantum dots

    DEFF Research Database (Denmark)

    Albert, F.; Schneider, C.; Stobbe, Søren

    2010-01-01

    We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled In(Ga)As quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

  17. Quantum phase transition of light as a control of the entanglement between interacting quantum dots

    NARCIS (Netherlands)

    Barragan, Angela; Vera-Ciro, Carlos; Mondragon-Shem, Ian

    We study coupled quantum dots arranged in a photonic crystal, interacting with light which undergoes a quantum phase transition. At the mean-field level for the infinite lattice, we compute the concurrence of the quantum dots as a measure of their entanglement. We find that this quantity smoothly

  18. Comparative study of polymer and liquid electrolytes in quantum dot sensitized solar cells

    Science.gov (United States)

    Poudyal, Uma; Wang, Wenyong

    We present the study of CdS/CdSe quantum dot sensitized solar cells (QDSSCs) in which Zn2SnO4\\ nanowires on the conductive glass are used as photoanode. The CdS/CdSe quantum dots (QDs) are deposited in the Zn2SnO4 photoanode by the Successive Ionic Layer Adsorption and Reaction (SILAR) method. CdS is first deposited on the nanowires after which it is further coated with 5 cycles of CdSe QDs. Finally, ZnS is coated on the QDs as a passivation layer. The QD sensitized photoanode are then used to assemble a solar device with the polymer and liquid electrolytes. The Incident Photon to Current Efficiency (IPCE) spectra are obtained for the CdS/CdSe coated nanowires. Further, a stability test of these devices is performed, using the polymer and liquid electrolytes, which provides insight to determine the better working electrolyte in the CdS/CdSe QDSSCs. Department of Energy.

  19. Quantum dot nanoparticle conjugation, characterization, and applications in neuroscience

    Science.gov (United States)

    Pathak, Smita

    Quantum dot are semiconducting nanoparticles that have been used for decades in a variety of applications such as solar cells, LEDs and medical imaging. Their use in the last area, however, has been extremely limited despite their potential as revolutionary new biological labeling tools. Quantum dots are much brighter and more stable than conventional fluorophores, making them optimal for high resolution imaging and long term studies. Prior work in this area involves synthesizing and chemically conjugating quantum dots to molecules of interest in-house. However this method is both time consuming and prone to human error. Additionally, non-specific binding and nanoparticle aggregation currently prevent researchers from utilizing this system to its fullest capacity. Another critical issue that has not been addressed is determining the number of ligands bound to nanoparticles, which is crucial for proper interpretation of results. In this work, methods to label fixed cells using two types of chemically modified quantum dots are studied. Reproducible non-specific artifact labeling is consistently demonstrated if antibody-quantum dot conditions are less than optimal. In order to explain this, antibodies bound to quantum dots were characterized and quantified. While other groups have qualitatively characterized antibody functionalized quantum dots using TEM, AFM, UV spectroscopy and gel electrophoresis, and in some cases have reported calculated estimates of the putative number of total antibodies bound to quantum dots, no quantitative experimental results had been reported prior to this work. The chemical functionalization and characterization of quantum dot nanocrystals achieved in this work elucidates binding mechanisms of ligands to nanoparticles and allows researchers to not only translate our tools to studies in their own areas of interest but also derive quantitative results from these studies. This research brings ease of use and increased reliability to

  20. A triple quantum dot based nano-electromechanical memory device

    International Nuclear Information System (INIS)

    Pozner, R.; Lifshitz, E.; Peskin, U.

    2015-01-01

    Colloidal quantum dots (CQDs) are free-standing nano-structures with chemically tunable electronic properties. This tunability offers intriguing possibilities for nano-electromechanical devices. In this work, we consider a nano-electromechanical nonvolatile memory (NVM) device incorporating a triple quantum dot (TQD) cluster. The device operation is based on a bias induced motion of a floating quantum dot (FQD) located between two bound quantum dots (BQDs). The mechanical motion is used for switching between two stable states, “ON” and “OFF” states, where ligand-mediated effective interdot forces between the BQDs and the FQD serve to hold the FQD in each stable position under zero bias. Considering realistic microscopic parameters, our quantum-classical theoretical treatment of the TQD reveals the characteristics of the NVM

  1. Rabi oscillations a quantum dot exposed to quantum light

    International Nuclear Information System (INIS)

    Magyarov, A.; Slepyan, G.Ya.; Maksimenko, S.A.; Hoffmann, A.

    2007-01-01

    The influence of the local field on the excitonic Rabi oscillations in an isolated quantum dot driven by the coherent state of light has been theoretically investigated. Local field is predicted to entail the appearance of two oscillatory regimes in the Rabi effect separated by the bifurcation. In the first regime Rabi oscillations are periodic and do not reveal collapse-revivals phenomenon, while in the second one collapse and revivals appear, showing significant difference as compared to those predicted by the standard Jaynes-Cummings model

  2. Imaging GABAc Receptors with Ligand-Conjugated Quantum Dots

    Directory of Open Access Journals (Sweden)

    Ian D. Tomlinson

    2007-01-01

    Full Text Available We report a methodology for labeling the GABAc receptor on the surface membrane of intact cells. This work builds upon our earlier work with serotonin-conjugated quantum dots and our studies with PEGylated quantum dots to reduce nonspecific binding. In the current approach, a PEGylated derivative of muscimol was synthesized and attached via an amide linkage to quantum dots coated in an amphiphilic polymer derivative of a modified polyacrylamide. These conjugates were used to image GABAC receptors heterologously expressed in Xenopus laevis oocytes.

  3. Study of a Quantum Dot in an Excited State

    Science.gov (United States)

    Slamet, Marlina; Sahni, Viraht

    We have studied the first excited singlet state of a quantum dot via quantal density functional theory (QDFT). The quantum dot is represented by a 2D Hooke's atom in an external magnetostatic field. The QDFT mapping is from an excited singlet state of this interacting system to one of noninteracting fermions in a singlet ground state. The results of the study will be compared to (a) the corresponding mapping from a ground state of the quantum dot and (b) to the similar mapping from an excited singlet state of the 3D Hooke's atom.

  4. Quantum Dots Microstructured Optical Fiber for X-Ray Detection

    Science.gov (United States)

    DeHaven, Stan; Williams, Phillip; Burke, Eric

    2015-01-01

    Microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide are presented. These quantum dots are applied inside the microstructured optical fibers using capillary action. The x-ray photon counts of these fibers are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The results of the fiber light output and associated effects of an acrylate coating and the quantum dot application technique are discussed.

  5. Highly Luminescent Phase-Stable CsPbI3 Perovskite Quantum Dots Achieving Near 100% Absolute Photoluminescence Quantum Yield.

    Science.gov (United States)

    Liu, Feng; Zhang, Yaohong; Ding, Chao; Kobayashi, Syuusuke; Izuishi, Takuya; Nakazawa, Naoki; Toyoda, Taro; Ohta, Tsuyoshi; Hayase, Shuzi; Minemoto, Takashi; Yoshino, Kenji; Dai, Songyuan; Shen, Qing

    2017-10-24

    Perovskite quantum dots (QDs) as a new type of colloidal nanocrystals have gained significant attention for both fundamental research and commercial applications owing to their appealing optoelectronic properties and excellent chemical processability. For their wide range of potential applications, synthesizing colloidal QDs with high crystal quality is of crucial importance. However, like most common QD systems such as CdSe and PbS, those reported perovskite QDs still suffer from a certain density of trapping defects, giving rise to detrimental nonradiative recombination centers and thus quenching luminescence. In this paper, we show that a high room-temperature photoluminescence quantum yield of up to 100% can be obtained in CsPbI 3 perovskite QDs, signifying the achievement of almost complete elimination of the trapping defects. This is realized with our improved synthetic protocol that involves introducing organolead compound trioctylphosphine-PbI 2 (TOP-PbI 2 ) as the reactive precursor, which also leads to a significantly improved stability for the resulting CsPbI 3 QD solutions. Ultrafast kinetic analysis with time-resolved transient absorption spectroscopy evidence the negligible electron or hole-trapping pathways in our QDs, which explains such a high quantum efficiency. We expect the successful synthesis of the "ideal" perovskite QDs will exert profound influence on their applications to both QD-based light-harvesting and -emitting devices.

  6. Tellurium quantum dots: Preparation and optical properties

    Science.gov (United States)

    Lu, Chaoyu; Li, Xueming; Tang, Libin; Lai, Sin Ki; Rogée, Lukas; Teng, Kar Seng; Qian, Fuli; Zhou, Liangliang; Lau, Shu Ping

    2017-08-01

    Herein, we report an effective and simple method for producing Tellurium Quantum dots (TeQDs), zero-dimensional nanomaterials with great prospects for biomedical applications. Their preparation is based on the ultrasonic exfoliation of Te powder dispersed in 1-methyl-2-pyrrolidone. Sonication causes the van der Waals forces between the structural hexagons of Te to break so that the relatively coarse powder breaks down into nanoscale particles. The TeQDs have an average size of about 4 nm. UV-Vis absorption spectra of the TeQDs showed an absorption peak at 288 nm. Photoluminescence excitation (PLE) and photoluminescence (PL) are used to study the optical properties of TeQDs. Both the PLE and PL peaks revealed a linear relationship against the emission and excitation energies, respectively. TeQDs have important potential applications in biological imaging and catalysis as well as optoelectronics.

  7. Quantum dots: synthesis, bioapplications, and toxicity

    Science.gov (United States)

    Valizadeh, Alireza; Mikaeili, Haleh; Samiei, Mohammad; Farkhani, Samad Mussa; Zarghami, Nosratalah; kouhi, Mohammad; Akbarzadeh, Abolfazl; Davaran, Soodabeh

    2012-08-01

    This review introduces quantum dots (QDs) and explores their properties, synthesis, applications, delivery systems in biology, and their toxicity. QDs are one of the first nanotechnologies to be integrated with the biological sciences and are widely anticipated to eventually find application in a number of commercial consumer and clinical products. They exhibit unique luminescence characteristics and electronic properties such as wide and continuous absorption spectra, narrow emission spectra, and high light stability. The application of QDs, as a new technology for biosystems, has been typically studied on mammalian cells. Due to the small structures of QDs, some physical properties such as optical and electron transport characteristics are quite different from those of the bulk materials.

  8. Recent advances in quantum dot surface chemistry.

    Science.gov (United States)

    Hines, Douglas A; Kamat, Prashant V

    2014-03-12

    Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, this review addresses three main issues: (i) how surface chemistry affects the optical properties of QDs, (ii) how it influences the excited state dynamics, and (iii) how one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles, and in self-assembled QD monolayers.

  9. Electronic levels of cubic quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Aristone, Flavio [Federal De Mato Grosso Do Sul Univ., Campo Grande (Brazil); Sanchez-Dehesa, Jose [Autonoma De Madrid Univ., Madrid (Spain); Marques, Gilmar E. [Federal De Sao Carlos Univ., Sao Carlos (Brazil)

    2003-09-01

    We introduce an efficient variational method to solve the three-dimensional Schroedinger equation for any arbitrary potential V(x,y,z). The method uses a basis set of localized functions which are build up as products of one-dimensional cubic {beta}-splines. We calculated the energy levels of GaAs/AlGaAs cubic quantum dots and make a comparison with the results from two well-known simplification schemes based on a decomposition of the full potential problem into three separate one-dimensional problems. We show that the scheme making a sequential decomposition gives eigenvalues in better agreement with the ones obtained variationally, but an exact solution is necessary when looking for highly precise values.

  10. Protease-activated quantum dot probes

    International Nuclear Information System (INIS)

    Chang, Emmanuel; Miller, Jordan S.; Sun, Jiantang; Yu, William W.; Colvin, Vicki L.; Drezek, Rebekah; West, Jennifer L.

    2005-01-01

    We have developed a novel nanoparticulate luminescent probe with inherent signal amplification upon interaction with a targeted proteolytic enzyme. This construct may be useful for imaging in cancer detection and diagnosis. In this system, quantum dots (QDs) are bound to gold nanoparticles (AuNPs) via a proteolytically degradable peptide sequence to non-radiatively suppress luminescence. A 71% reduction in luminescence was achieved with conjugation of AuNPs to QDs. Release of AuNPs by peptide cleavage restores radiative QD photoluminescence. Initial studies observed a 52% rise in luminescence over 47 h of exposure to 0.2 mg/mL collagenase. These probes can be customized for targeted degradation simply by changing the sequence of the peptide linker

  11. Decoherence and Entanglement Simulation in a Model of Quantum Neural Network Based on Quantum Dots

    Directory of Open Access Journals (Sweden)

    Altaisky Mikhail V.

    2016-01-01

    Full Text Available We present the results of the simulation of a quantum neural network based on quantum dots using numerical method of path integral calculation. In the proposed implementation of the quantum neural network using an array of single-electron quantum dots with dipole-dipole interaction, the coherence is shown to survive up to 0.1 nanosecond in time and up to the liquid nitrogen temperature of 77K.We study the quantum correlations between the quantum dots by means of calculation of the entanglement of formation in a pair of quantum dots on the GaAs based substrate with dot size of 100 ÷ 101 nanometer and interdot distance of 101 ÷ 102 nanometers order.

  12. Visible Light Responsive Catalysts Using Quantum Dot-Modified Ti02 for Air and Water Purification

    Science.gov (United States)

    Coutts, Janelle L.; Levine, Lanfang H.; Richards, Jeffrey T.; Hintze, paul; Clausen, Christian

    2012-01-01

    The method of photocatalysis utilizing titanium dioxide, TiO2, as the catalyst has been widely studied for trace contaminant control for both air and water applications because of its low energy consumption and use of a regenerable catalyst. Titanium dioxide requires ultraviolet light for activation due to its band gap energy of 3.2 eV. Traditionally, Hg-vapor fluorescent light sources are used in PCO reactors and are a setback for the technology for space application due to the possibility of Hg contamination. The development of a visible light responsive (VLR) TiO2-based catalyst could lead to the use of solar energy in the visible region (approx.45% of the solar spectrum lies in the visible region; > 400 nm) or highly efficient LEDs (with wavelengths > 400 nm) to make PCO approaches more efficient, economical, and safe. Though VLR catalyst development has been an active area of research for the past two decades, there are few commercially available VLR catalysts; those that are available still have poor activity in the visible region compared to that in the UV region. Thus, this study was aimed at the further development of VLR catalysts by a new method - coupling of quantum dots (QD) of a narrow band gap semiconductor (e.g., CdS, CdSe, PbS, ZnSe, etc.) to the TiO2 by two preparation methods: 1) photodeposition and 2) mechanical alloying using a high-speed ball mill. A library of catalysts was developed and screened for gas and aqueous phase applications, using ethanol and 4-chlorophenol as the target contaminants, respectively. Both target compounds are well studied in photocatalytic systems serve as model contaminants for this research. Synthesized catalysts were compared in terms of preparation method, type of quantum dots, and dosage of quantum dots.

  13. Spectral and Dynamical Properties of Single Excitons, Biexcitons, and Trions in Cesium-Lead-Halide Perovskite Quantum Dots.

    Science.gov (United States)

    Makarov, Nikolay S; Guo, Shaojun; Isaienko, Oleksandr; Liu, Wenyong; Robel, István; Klimov, Victor I

    2016-04-13

    Organic-inorganic lead-halide perovskites have been the subject of recent intense interest due to their unusually strong photovoltaic performance. A new addition to the perovskite family is all-inorganic Cs-Pb-halide perovskite nanocrystals, or quantum dots, fabricated via a moderate-temperature colloidal synthesis. While being only recently introduced to the research community, these nanomaterials have already shown promise for a range of applications from color-converting phosphors and light-emitting diodes to lasers, and even room-temperature single-photon sources. Knowledge of the optical properties of perovskite quantum dots still remains vastly incomplete. Here we apply various time-resolved spectroscopic techniques to conduct a comprehensive study of spectral and dynamical characteristics of single- and multiexciton states in CsPbX3 nanocrystals with X being either Br, I, or their mixture. Specifically, we measure exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton-exciton coupling. The overall conclusion of this work is that spectroscopic properties of Cs-Pb-halide quantum dots are largely similar to those of quantum dots of more traditional semiconductors such as CdSe and PbSe. At the same time, we observe some distinctions including, for example, an appreciable effect of the halide identity on radiative lifetimes, considerably shorter biexciton Auger lifetimes, and apparent deviation of their size dependence from the "universal volume scaling" previously observed for many traditional nanocrystal systems. The high efficiency of Auger decay in perovskite quantum dots is detrimental to their prospective applications in light-emitting devices and lasers. This points toward the need for the development of approaches for effective suppression of Auger

  14. Optimal tunneling enhances the quantum photovoltaic effect in double quantum dots

    International Nuclear Information System (INIS)

    Wang, Chen; Cao, Jianshu; Ren, Jie

    2014-01-01

    We investigate the quantum photovoltaic effect in double quantum dots by applying the nonequilibrium quantum master equation. A drastic suppression of the photovoltaic current is observed near the open circuit voltage, which leads to a large filling factor. We find that there always exists an optimal inter-dot tunneling that significantly enhances the photovoltaic current. Maximal output power will also be obtained around the optimal inter-dot tunneling. Moreover, the open circuit voltage behaves approximately as the product of the eigen-level gap and the Carnot efficiency. These results suggest a great potential for double quantum dots as efficient photovoltaic devices

  15. Application of Quantum Dots in Biological Imaging

    Directory of Open Access Journals (Sweden)

    Shan Jin

    2011-01-01

    Full Text Available Quantum dots (QDs are a group of semiconducting nanomaterials with unique optical and electronic properties. They have distinct advantages over traditional fluorescent organic dyes in chemical and biological studies in terms of tunable emission spectra, signal brightness, photostability, and so forth. Currently, the major type of QDs is the heavy metal-containing II-IV, IV-VI, or III-V QDs. Silicon QDs and conjugated polymer dots have also been developed in order to lower the potential toxicity of the fluorescent probes for biological applications. Aqueous solubility is the common problem for all types of QDs when they are employed in the biological researches, such as in vitro and in vivo imaging. To circumvent this problem, ligand exchange and polymer coating are proven to be effective, besides synthesizing QDs in aqueous solutions directly. However, toxicity is another big concern especially for in vivo studies. Ligand protection and core/shell structure can partly solve this problem. With the rapid development of QDs research, new elements and new morphologies have been introduced to this area to fabricate more safe and efficient QDs for biological applications.

  16. First principles study of edge carboxylated graphene quantum dots

    Science.gov (United States)

    Abdelsalam, Hazem; Elhaes, Hanan; Ibrahim, Medhat A.

    2018-05-01

    The structure stability and electronic properties of edge carboxylated hexagonal and triangular graphene quantum dots are investigated using density functional theory. The calculated binding energies show that the hexagonal clusters with armchair edges have the highest stability among all the quantum dots. The binding energy of carboxylated graphene quantum dots increases by increasing the number of carboxyl groups. Our study shows that the total dipole moment significantly increases by adding COOH with the highest value observed in triangular clusters. The edge states in triangular graphene quantum dots with zigzag edges produce completely different energy spectrum from other dots: (a) the energy gap in triangular zigzag is very small as compared to other clusters and (b) the highest occupied molecular orbital is localized at the edges which is in contrast to other clusters where it is distributed over the cluster surface. The enhanced reactivity and the controllable energy gap by shape and edge termination make graphene quantum dots ideal for various nanodevice applications such as sensors. The infrared spectra are presented to confirm the stability of the quantum dots.

  17. Quantum dot cadmium selenide as a saturable absorber for Q-switched and mode-locked double-clad ytterbium-doped fiber lasers

    Science.gov (United States)

    Mahyuddin, M. B. H.; Latiff, A. A.; Rusdi, M. F. M.; Irawati, N.; Harun, S. W.

    2017-08-01

    This paper demonstrates the integration of quantum dot (QD) cadmium selenide (CdSe) nanoparticles, which is embedded into polymethyl methacrylate (PMMA) film into an ytterbium-doped fiber laser (YDFL) cavity to produce Q-switched and mode-locked fiber lasers. The QD CdSe based film functions as a saturable absorber (SA). For Q-switching operation, stable pulse is generated within 970-1200 mW pump power, with tunable repetition rate and pulse width of 24.5-40.5 kHz and 6.8-3.7 μs, respectively. Maximum pulse energy and peak power are obtained about 1.1 μJ and 0.28 W, respectively. As we tune the polarization state of the laser cavity and use a single QD CdSe film, the mode-locking operation could also be generated within 310-468 mW pump power with repetition rate of 14.5 MHz and pulse width of 3.5 ps. Maximum pulse energy and peak power are obtained about 2 nJ and 0.11 W, respectively. These results may contribute to continuous research work on laser pulse generation, providing new opportunities of CdSe material in photonics applications.

  18. Collective Rabi dynamics of electromagnetically coupled quantum-dot ensembles

    Science.gov (United States)

    Glosser, Connor; Shanker, B.; Piermarocchi, Carlo

    2017-09-01

    Rabi oscillations typify the inherent nonlinearity of optical excitations in quantum dots. Using an integral kernel formulation to solve the three-dimensional Maxwell-Bloch equations in ensembles of up to 104 quantum dots, we observe features in Rabi oscillations due to the interplay of nonlinearity, nonequilibrium excitation, and electromagnetic coupling between the dots. This approach allows us to observe the dynamics of each dot in the ensemble without resorting to spatial averages. Our simulations predict synchronized multiplets of dots that exchange energy, dots that dynamically couple to screen the effect of incident external radiation, localization of the polarization due to randomness and interactions, as well as wavelength-scale regions of enhanced and suppressed polarization.

  19. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications

    Directory of Open Access Journals (Sweden)

    Lin Wen

    2017-07-01

    Full Text Available Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

  20. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications.

    Science.gov (United States)

    Wen, Lin; Qiu, Liping; Wu, Yongxiang; Hu, Xiaoxiao; Zhang, Xiaobing

    2017-07-28

    Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

  1. 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)

  2. Nodal ground states and orbital textures in semiconductor quantum dots

    Czech Academy of Sciences Publication Activity Database

    Lee, J.; Výborný, Karel; Han, J.E.; Žutič, I.

    2014-01-01

    Roč. 89, č. 4 (2014), "045315-1"-"045315-17" ISSN 1098-0121 Institutional support: RVO:68378271 Keywords : quantum dots * electronic structure Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  3. Nonequilibrium electron transport through quantum dots in the Kondo regime

    DEFF Research Database (Denmark)

    Wölfle, Peter; Paaske, Jens; Rosch, Achim

    2005-01-01

    Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how the ...

  4. Light Scattering Spectroscopies of Semiconductor Nanocrystals (Quantum Dots)

    International Nuclear Information System (INIS)

    Yu, Peter Y; Gardner, Grat; Nozaki, Shinji; Berbezier, Isabelle

    2006-01-01

    We review the study of nanocrystals or quantum dots using inelastic light scattering spectroscopies. In particular recent calculations of the phonon density of states and low frequency Raman spectra in Ge nanocrystals are presented for comparison with experimental results

  5. 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.

  6. Coal as an abundant source of graphene quantum dots

    Science.gov (United States)

    Ye, Ruquan; Xiang, Changsheng; Lin, Jian; Peng, Zhiwei; Huang, Kewei; Yan, Zheng; Cook, Nathan P.; Samuel, Errol L. G.; Hwang, Chih-Chau; Ruan, Gedeng; Ceriotti, Gabriel; Raji, Abdul-Rahman O.; Martí, Angel A.; Tour, James M.

    2013-12-01

    Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

  7. Ge Quantum Dot Infrared Imaging Camera, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Luna Innovations Incorporated proposes to develop a high performance Ge quantum dots-based infrared (IR) imaging camera on Si substrate. The high sensitivity, large...

  8. Non-Markovian spontaneous emission from a single quantum dot

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg; Ates, Serkan; Lund-Hansen, Toke

    2011-01-01

    We observe non-Markovian dynamics of a single quantum dot when tuned into resonance with a cavity mode. Excellent agreement between experiment and theory is observed providing the first quantitative description of such a system....

  9. Quantum dot conjugates in a sub-micrometer fluidic channel

    Science.gov (United States)

    Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.

    2010-04-13

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  10. The impact of doped silicon quantum dots on human osteoblasts

    Czech Academy of Sciences Publication Activity Database

    Ostrovská, L.; Brož, Antonín; Fučíková, A.; Bělinová, T.; Sugimoto, H.; Kanno, T.; Fujii, M.; Valenta, J.; Kalbáčová, M.H.

    2016-01-01

    Roč. 6, č. 68 (2016), s. 63403-63413 ISSN 2046-2069 Institutional support: RVO:67985823 Keywords : silicon quantum dots * osteoblasts * cytotoxicity * photoluminiscence bioimaging Subject RIV: EI - Biotechnology ; Bionics Impact factor: 3.108, year: 2016

  11. CdS/CdSSe quantum dots in glass matrix

    Indian Academy of Sciences (India)

    Wintec

    –5 nm are uniformly distributed into the glass matrix. Keywords. CdS; CdSSe; nanocrystals; glasses; optical filters. 1. Introduction. Today nanostructured materials and quantum dots have immense importance in the field of optoelectronics and.

  12. Quantum Dots in the Therapy: Current Trends and Perspectives.

    Science.gov (United States)

    Pohanka, Miroslav

    2017-01-01

    Quantum dots are an emerging nanomaterial with broad use in technical disciplines; however, their application in the field of biomedicine becomes also relevant and significant possibilities have appeared since the discovery in 1980s. The current review is focused on the therapeutic applications of quantum dots which become an emerging use of the particles. They are introduced as potent carriers of drugs and as a material well suited for the diagnosis of disparate pathologies like visualization of cancer cells or pathogenic microorganisms. Quantum dots toxicity and modifications for the toxicity reduction are discussed here as well. Survey of actual papers and patents in the field of quantum dots use in the biomedicine is provided. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  13. Multiple Wavelength Quantum Dot Lasers (MW-QDL)

    Data.gov (United States)

    National Aeronautics and Space Administration — An innovative method to achieve optical gain over a wide spectral range using new laser materials is being investigated.  Multiple wavelength quantum dot lasers...

  14. Electron Energy Level Statistics in Graphene Quantum Dots

    NARCIS (Netherlands)

    De Raedt, H.; Katsnellson, M. I.; Katsnelson, M.I.

    2008-01-01

    Motivated by recent experimental observations of size quantization of electron energy levels in graphene quantum dots [7] we investigate the level statistics in the simplest tight-binding model for different dot shapes by computer simulation. The results are in a reasonable agreement with the

  15. Ultrafast gain and index dynamics in quantum dot amplifiers

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang; Mørk, Jesper

    1999-01-01

    The ultrafast dynamics of gain and refractive index in an InAs/GaAs quantum dot amplifier are investigated at room temperature. The gain is observed to recover with a 90 fs time constant, ruling out problems of slow carrier capture into the dots, and making this component promising for high...

  16. On dephasing and spin decay in open quantum dots

    NARCIS (Netherlands)

    Michaelis, Björn Dieter

    2006-01-01

    The thesis contains three topics on transport in nanostructres. Chpt. 2 explains the loss of entanglement in electronic pairs that enter chaotic quantum dots. The quantitiy that is affected are timedependent and spaceresolving current measurements. Looking at statisticcs dots, it is discovered

  17. Quantum computation: algorithms and implementation in quantum dot devices

    Science.gov (United States)

    Gamble, John King

    In this thesis, we explore several aspects of both the software and hardware of quantum computation. First, we examine the computational power of multi-particle quantum random walks in terms of distinguishing mathematical graphs. We study both interacting and non-interacting multi-particle walks on strongly regular graphs, proving some limitations on distinguishing powers and presenting extensive numerical evidence indicative of interactions providing more distinguishing power. We then study the recently proposed adiabatic quantum algorithm for Google PageRank, and show that it exhibits power-law scaling for realistic WWW-like graphs. Turning to hardware, we next analyze the thermal physics of two nearby 2D electron gas (2DEG), and show that an analogue of the Coulomb drag effect exists for heat transfer. In some distance and temperature, this heat transfer is more significant than phonon dissipation channels. After that, we study the dephasing of two-electron states in a single silicon quantum dot. Specifically, we consider dephasing due to the electron-phonon coupling and charge noise, separately treating orbital and valley excitations. In an ideal system, dephasing due to charge noise is strongly suppressed due to a vanishing dipole moment. However, introduction of disorder or anharmonicity leads to large effective dipole moments, and hence possibly strong dephasing. Building on this work, we next consider more realistic systems, including structural disorder systems. We present experiment and theory, which demonstrate energy levels that vary with quantum dot translation, implying a structurally disordered system. Finally, we turn to the issues of valley mixing and valley-orbit hybridization, which occurs due to atomic-scale disorder at quantum well interfaces. We develop a new theoretical approach to study these effects, which we name the disorder-expansion technique. We demonstrate that this method successfully reproduces atomistic tight-binding techniques

  18. Controlling the quantum dot nucleation site

    International Nuclear Information System (INIS)

    Motta, Nunzio; Sgarlata, Anna; Rosei, Federico; Szkutnik, P.D.; Nufris, S.; Scarselli, M.; Balzarotti, A.

    2003-01-01

    Quantum dots (QDs) are actually easily produced by self-assembling during heteroepitaxial growth of semiconductors. In order to exploit the unique electronic properties of semiconductor QDs in novel quantum effect devices, the lateral dimensions of these structures have to be reduced to the order of tens of nanometers, which is the range of the De Broglie wavelength of electrons inside these materials. Moreover, millions of QDs must be arranged in dense ordered arrays to achieve the necessary active volume for optoelectronic applications. Nowadays it is possible to control size and shape of the nanocrystals, but it is still difficult to decide their nucleation site. Many approaches have been undertaken to overcome this problem, like using regular dislocation networks, lithographically and Atomic Force Microscopy (AFM) patterned substrates, naturally patterned surfaces. We present results obtained by some of these methods, visualized by Scanning Tunnelling Microscopy (STM) or AFM microscopy. STM measurements at high temperature during the epitaxial growth are of great help in these studies. Images and movies of the growth of Ge on Si help to identify the real nucleation sites of the islands and to follow their evolution. The influence of the 'step bunching' on the self-organization of Ge islands on Si(111) surfaces will be analysed, as an example of growth on self-nanostructured surfaces

  19. Bismides: 2D structures and quantum dots

    Science.gov (United States)

    Pačebutas, Vaidas; Butkutė, Renata; Čechavičius, Bronislovas; Stanionytė, Sandra; Pozingytė, Evelina; Skapas, Martynas; Selskis, Algirdas; Geižutis, Andrejus; Krotkus, Arūnas

    2017-09-01

    The growth and characterization of ternary GaAsBi and quaternary GaInAsBi compound quantum wells (QWs) on GaAs substrates is presented in this study. The influence of technological parameters, such as different growth modes, substrate temperatures, beam equivalent pressure ratios and thermal treating on structural and luminescent properties of QWs is discussed. The complex structural investigations using x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy revealed high crystal structure, smooth surfaces and abrupt interfaces of both GaAsBi and GaInAsBi QWs. The temperature dependent photoluminescence measurements demonstrated emission wavelengths up to 1.43 µm in room temperature PL spectra measured for GaAsBi/GaAs QWs containing 12% Bi, whereas GaInAsBi QWs with 4.2% of bismuth inserted between GaAs barriers has reached 1.25 µm. Moreover, the annealing at high temperatures of GaAsBi/AlAs QWs stimulated agglomeration of bismuth to quantum dots in the well layers, emitting at 1.5 µm. The achieved wavelengths are the longest ones declared for the GaAsBi and GaInAsBi QW structures grown on the GaAs substrate, therefore bismide-based QWs are the promising structures for applications in infrared devices.

  20. Cyto-molecular Tuning of Quantum Dots

    Science.gov (United States)

    Lee, Bong; Suresh, Sindhuja; Ekpenyong, Andrew

    Quantum dots (QDs) are semiconductor nanoparticles composed of groups II-VI or III-V elements, with physical dimensions smaller than the exciton Bohr radius, and between 1-10 nm. Their applications and promising myriad applications in photovoltaic cells, biomedical imaging, targeted drug delivery, quantum computing, etc, have led to much research on their interactions with other systems. For biological systems, research has focused on biocompatibility and cytotoxicity of QDs in the context of imaging/therapy. However, there is a paucity of work on how biological systems might be used to tune QDs. Here, we hypothesize that the photo-electronic properties of QDs can be tuned by biological macromolecules following controlled changes in cellular activities. Using CdSe/ZnS core-shell QDs, we perform spectroscopic analysis of optically excited colloidal QDs with and without promyelocytic HL60 cells. Preliminary results show shifts in the emission spectra of the colloidal dispersions with and without cells. We will present results for activated HL60-derived cells where specific macromolecules produced by these cells perturb the electric dipole moments of the excited QDs and the associated electric fields, in ways that constitute what we describe as cyto-molecular tuning. Startup funds from the College of Arts and Sciences, Creighton University (to AEE).

  1. Interaction of solitons with a string of coupled quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Vijendra, E-mail: vsmedphysics@gmail.com; Swami, O. P., E-mail: omg1789@gmail.com; Nagar, A. K., E-mail: ajaya.nagar@gmail.com [Department of Physics, Govt. Dungar College, Bikaner, Rajasthan 334001 (India); Taneja, S., E-mail: sachintaneja9@gmail.com [Department of Radiotherapy, CHAF Bangalore, Karnataka 560007 (India)

    2016-05-06

    In this paper, we develop a theory for discrete solitons interaction with a string of coupled quantum dots in view of the local field effects. Discrete nonlinear Schrodinger (DNLS) equations are used to describe the dynamics of the string. Numerical calculations are carried out and results are analyzed with the help of matlab software. With the help of numerical solutions we demonstrate that in the quantum dots string, Rabi oscillations (RO) are self trapped into stable bright Rabi solitons. The Rabi oscillations in different types of nanostructures have potential applications to the elements of quantum logic and quantum memory.

  2. Spin and edge channel dependent transport through quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ridder, T; Rogge, M C; Haug, R J [Institut fuer Festkoerperphysik, Gottfried Wilhelm Leibniz Universitaet Hannover, Appelstrasse 2, D-30167 Hannover (Germany)], E-mail: ridder@nano.uni-hannover.de

    2008-11-12

    We investigate the influence of spin polarized currents and non-equilibrated edge channels on the transport properties of a single quantum dot. Polarized currents are realized by the manual depletion of edge channels in high magnetic fields via a metallic top gate covering the source contact in the system. We observe a suppression and enhancement in the conductance of the quantum dot dependent on the edge channel configuration in the leads.

  3. Spin-orbit-enhanced Wigner localization in quantum dots

    DEFF Research Database (Denmark)

    Cavalli, Andrea; Malet, F.; Cremon, J. C.

    2011-01-01

    We investigate quantum dots with Rashba spin-orbit coupling in the strongly-correlated regime. We show that the presence of the Rashba interaction enhances the Wigner localization in these systems, making it achievable for higher densities than those at which it is observed in Rashba-free quantum...... dots. Recurring shapes in the pair distribution functions of the yrast spectrum, which might be associated with rotational and vibrational modes, are also reported....

  4. Solution-Processed Nanocrystal Quantum Dot Tandem Solar Cells

    KAUST Repository

    Choi, Joshua J.

    2011-06-03

    Solution-processed tandem solar cells created from nanocrystal quantum dots with size-tuned energy levels are demonstrated. Prototype devices featuring interconnected quantum dot layers of cascaded energy gaps exhibit IR sensitivity and an open circuit voltage, V oc, approaching 1 V. The tandem solar cell performance depends critically on the optical and electrical properties of the interlayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Self-Sustaining Dynamical Nuclear Polarization Oscillations in Quantum Dots

    DEFF Research Database (Denmark)

    Rudner, Mark Spencer; Levitov, Leonid

    2013-01-01

    Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear polarization, the mechanism has remained a mystery. Here we introduce......) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The proposed framework naturally explains the differences in phenomenology between vertical and lateral quantum dot structures as well as the extremely long oscillation periods....

  6. On-chip generation and guiding of quantum light from a site-controlled quantum dot

    International Nuclear Information System (INIS)

    Jamil, Ayesha; Farrer, Ian; Griffiths, Jonathan P.; Jones, Geb A. C.; Ritchie, David A.; Skiba-Szymanska, Joanna; Kalliakos, Sokratis; Ward, Martin B.; Ellis, David J. P.; Shields, Andrew J.; Schwagmann, Andre; Brody, Yarden

    2014-01-01

    We demonstrate the emission and routing of single photons along a semiconductor chip originating from carrier recombination in an actively positioned InAs quantum dot. Device–scale arrays of quantum dots are formed by a two–step regrowth process. We precisely locate the propagating region of a unidirectional photonic crystal waveguide with respect to the quantum dot nucleation site. Under pulsed optical excitation, the multiphoton emission probability from the waveguide's exit is 12% ± 5% before any background correction. Our results are a major step towards the deterministic integration of a quantum emitter with the waveguiding components of photonic quantum circuits

  7. Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Cundiff, Steven T. [Univ. of Colorado, Boulder, CO (United States)

    2016-05-03

    This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.

  8. Si quantum dot structures and their applications

    Science.gov (United States)

    Shcherbyna, L.; Torchynska, T.

    2013-06-01

    This paper presents briefly the history of emission study in Si quantum dots (QDs) in the last two decades. Stable light emission of Si QDs and NCs was observed in the spectral ranges: blue, green, orange, red and infrared. These PL bands were attributed to the exciton recombination in Si QDs, to the carrier recombination through defects inside of Si NCs or via oxide related defects at the Si/SiOx interface. The analysis of recombination transitions and the different ways of the emission stimulation in Si QD structures, related to the element variation for the passivation of surface dangling bonds, as well as the plasmon induced emission and rare earth impurity activation, have been presented. The different applications of Si QD structures in quantum electronics, such as: Si QD light emitting diodes, Si QD single union and tandem solar cells, Si QD memory structures, Si QD based one electron devices and double QD structures for spintronics, have been discussed as well. Note the significant worldwide interest directed toward the silicon-based light emission for integrated optoelectronics is related to the complementary metal-oxide semiconductor compatibility and the possibility to be monolithically integrated with very large scale integrated (VLSI) circuits. The different features of poly-, micro- and nanocrystalline silicon for solar cells, that is a mixture of both amorphous and crystalline phases, such as the silicon NCs or QDs embedded in a α-Si:H matrix, as well as the thin film 2-cell or 3-cell tandem solar cells based on Si QD structures have been discussed as well. Silicon NC based structures for non-volatile memory purposes, the recent studies of Si QD base single electron devices and the single electron occupation of QDs as an important component to the measurement and manipulation of spins in quantum information processing have been analyzed as well.

  9. Enhanced thermoelectric properties in boron nitride quantum-dot

    Science.gov (United States)

    Pan, Changning; Long, Mengqiu; He, Jun

    We have investigated the ballistic thermoelectric properties in boron nitride quantum dots by using the nonequilibrium Green's function approach and the Landauer transport theory. The result shows that the phonon transport is substantially suppressed by the interface in the quantum dots. The resonant tunneling effect of electron leads to the fluctuations of the electronic conductance. It enhances significantly the Seebeck coefficient. Combined with the low thermal conductance of phonon, the high thermoelectric figure of merit ZT ∼0.78 can be obtained at room temperature T = 300 K and ZT ∼0.95 at low temperature T = 100 K. It is much higher than that of graphene quantum dots with the same geometry parameters, which is ZT ∼0.29 at room temperature T = 300 K and ZT ∼0.48 at low temperature T = 100 K. The underlying mechanism is that the boron nitride quantum dots possess higher thermopower and lower phonon thermal conductance than the graphene quantum dots. Thus the results indicate that the thermoelectric properties of boron nitride can be significantly enhanced by the quantum dot and are better than those of graphene.

  10. Graphene quantum dots probed by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Morgenstern, Markus; Freitag, Nils; Nent, Alexander; Nemes-Incze, Peter; Liebmann, Marcus [II. Institute of Physics B and JARA-FIT, RWTH Aachen University, Aachen (Germany)

    2017-11-15

    Scanning tunneling spectroscopy results probing the electronic properties of graphene quantum dots are reviewed. After a short summary of the study of squared wave functions of graphene quantum dots on metal substrates, we firstly present data where the Landau level gaps caused by a perpendicular magnetic field are used to electrostatically confine electrons in monolayer graphene, which are probed by the Coulomb staircase revealing the consecutive charging of a quantum dot. It turns out that these quantum dots exhibit much more regular charging sequences than lithographically confined ones. Namely, the consistent grouping of charging peaks into quadruplets, both, in the electron and hole branch, portrays a regular orbital splitting of about 10meV. At low hole occupation numbers, the charging peaks are, partly, additionally grouped into doublets. The spatially varying energy separation of the doublets indicates a modulation of the valley splitting by the underlying BN substrate. We outline that this property might be used to eventually tune the valley splitting coherently. Afterwards, we describe graphene quantum dots with multiple contacts produced without lithographic resist, namely by local anodic oxidation. Such quantum dots target the goal to probe magnetotransport properties during the imaging of the corresponding wave functions by scanning tunneling spectroscopy. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Colloidal quantum dot photovoltaics: The effect of polydispersity

    KAUST Repository

    Zhitomirsky, David

    2012-02-08

    The size-effect tunability of colloidal quantum dots enables facile engineering of the bandgap at the time of nanoparticle synthesis. The dependence of effective bandgap on nanoparticle size also presents a challenge if the size dispersion, hence bandgap variability, is not well-controlled within a given quantum dot solid. The impact of this polydispersity is well-studied in luminescent devices as well as in unipolar electronic transport; however, the requirements on monodispersity have yet to be quantified in photovoltaics. Here we carry out a series of combined experimental and model-based studies aimed at clarifying, and quantifying, the importance of quantum dot monodispersity in photovoltaics. We successfully predict, using a simple model, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using this same experimentally tested model the implications of a broadened quantum dot population on device performance. We report that present-day colloidal quantum dot photovoltaic devices with typical inhomogeneous linewidths of 100-150 meV are dominated by surface traps, and it is for this reason that they see marginal benefit from reduction in polydispersity. Upon eliminating surface traps, achieving inhomogeneous broadening of 50 meV or less will lead to device performance that sees very little deleterious impact from polydispersity. © 2012 American Chemical Society.

  12. 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.

  13. Synthesis, solubilization, and surface functionalization of highly fluorescent quantum dots for cellular targeting through a small molecule

    Science.gov (United States)

    Galloway, Justin F.

    To achieve long-term fluorescence imaging with quantum dots (QDs), a CdSe core/shell must first be synthesized. The synthesis of bright CdSe QDs is not trivial and as a consequence, the role of surfactant in nucleation and growth was investigated. It was found that the type of surfactant used, either phosphonic or fatty acid, played a pivotal role in the size of the CdSe core. The study of surfactant on CdSe synthesis, ultimately led to an electrical passivation method that utilized a short-chained phosphonic acid and highly reactive organometallic precursors to achieve high quantum yield (QY) as has been previously described. The synthesis of QDs using organometallic precursors and a phosphonic acid for passivation resulted in 4 out of 9 batches of QDs achieving QYs greater than 50% and 8 out of 9 batches with QYs greater than 35%. The synthesis of CdSe QDs was done in organic solutions rendering the surface of the particle hydrophobic. To perform cell-targeting experiments, QDs must be transferred to water. The transfer of QDs to water was successfully accomplished by using single acyl chain lipids. A systematic study of different lipid combinations and coatings demonstrated that 20-40 mol% single acyl chained lipids were able to transfer QDs to water resulting in monodispersed, stable QDs without adversely affecting the QY. The advantage to water solubilization using single acyl chain lipids is that the QD have a hydrodynamic radius less than 15 nm, QYs that can exceed 50% and additional surface functionalization can be down using the reactive sites incorporated into the lipid bilayer. QDs that are bright and stable in water were studied for the purpose of targeting G protein-coupled Receptors (GPCR). GPCRs are transmembrane receptors that internalize extracellular cues, and thus mediate signal transduction. The cyclic Adenosine Monophosphate Receptor 1 of the model organism Dictyostelium disodium was the receptor of interest. The Halo protein, a genetically

  14. 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.

  15. High quantum yield ZnO quantum dots synthesizing via an ultrasonication microreactor method.

    Science.gov (United States)

    Yang, Weimin; Yang, Huafang; Ding, Wenhao; Zhang, Bing; Zhang, Le; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

    2016-11-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. Rainbow Emission from an Atomic Transition in Doped Quantum Dots.

    Science.gov (United States)

    Hazarika, Abhijit; Pandey, Anshu; Sarma, D D

    2014-07-03

    Although semiconductor quantum dots are promising materials for displays and lighting due to their tunable emissions, these materials also suffer from the serious disadvantage of self-absorption of emitted light. The reabsorption of emitted light is a serious loss mechanism in practical situations because most phosphors exhibit subunity quantum yields. Manganese-based phosphors that also exhibit high stability and quantum efficiency do not suffer from this problem but in turn lack emission tunability, seriously affecting their practical utility. Here, we present a class of manganese-doped quantum dot materials, where strain is used to tune the wavelength of the dopant emission, extending the otherwise limited emission tunability over the yellow-orange range for manganese ions to almost the entire visible spectrum covering all colors from blue to red. These new materials thus combine the advantages of both quantum dots and conventional doped phosphors, thereby opening new possibilities for a wide range of applications in the future.

  17. Universal parametric correlations of conductance peaks in quantum dots

    International Nuclear Information System (INIS)

    Alhassid, Y.; Attias, H.

    1996-01-01

    We compute the parametric correlation function of the conductance peaks in chaotic and weakly disordered quantum dots in the Coulomb blockade regime and demonstrate its universality upon an appropriate scaling of the parameter. For a symmetric dot we show that this correlation function is affected by breaking time-reversal symmetry but is independent of the details of the channels in the external leads. We derive a new scaling which depends on the eigenfunctions alone and can be extracted directly from the conductance peak heights. Our results are in excellent agreement with model simulations of a disordered quantum dot. copyright 1996 The American Physical Society

  18. Electronic transient processes and optical spectra in quantum dots for quantum computing

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Zdeněk, Petr; Khás, Zdeněk

    2004-01-01

    Roč. 3, č. 1 (2004), s. 17-25 ISSN 1536-125X R&D Projects: GA AV ČR IAA1010113 Institutional research plan: CEZ:AV0Z1010914 Keywords : depopulation * electronic relaxation * optical spectra * quantum dots * self-assembled quantum dots * upconversion Subject RIV: BE - Theoretical Physics Impact factor: 3.176, year: 2004

  19. Quantitative analysis of quantum dot dynamics and emission spectra in cavity quantum electrodynamics

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg; Lodahl, Peter

    2013-01-01

    -resolved measurements reveal that the actual coupling strength is significantly smaller than anticipated from the spectral measurements and that the quantum dot is rather weakly coupled to the cavity. We suggest that the observed Rabi splitting is due to cavity feeding by other quantum dots and/or multi...

  20. Annealing-induced change in quantum dot chain formation mechanism

    Directory of Open Access Journals (Sweden)

    Tyler D. Park

    2014-12-01

    Full Text Available Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

  1. Transport properties of a Kondo dot with a larger side-coupled noninteracting quantum dot

    International Nuclear Information System (INIS)

    Liu, Y S; Fan, X H; Xia, Y J; Yang, X F

    2008-01-01

    We investigate theoretically linear and nonlinear quantum transport through a smaller quantum dot in a Kondo regime connected to two leads in the presence of a larger side-coupled noninteracting quantum dot, without tunneling coupling to the leads. To do this we employ the slave boson mean field theory with the help of the Keldysh Green's function at zero temperature. The numerical results show that the Kondo conductance peak may develop multiple resonance peaks and multiple zero points in the conductance spectrum owing to constructive and destructive quantum interference effects when the energy levels of the large side-coupled noninteracting dot are located in the vicinity of the Fermi level in the leads. As the coupling strength between two quantum dots increases, the tunneling current through the quantum device as a function of gate voltage applied across the two leads is suppressed. The spin-dependent transport properties of two parallel coupled quantum dots connected to two ferromagnetic leads are also investigated. The numerical results show that, for the parallel configuration, the spin current or linear spin differential conductance are enhanced when the polarization strength in the two leads is increased

  2. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    Directory of Open Access Journals (Sweden)

    Stephan Michael

    2016-05-01

    Full Text Available In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. Here, we study the influence of two important quantum-dot material parameters, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. However, by minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.

  3. A theoretical study of exciton energy levels in laterally coupled quantum dots

    International Nuclear Information System (INIS)

    Barticevic, Z; Pacheco, M; Duque, C A; Oliveira, L E

    2009-01-01

    A theoretical study of the electronic and optical properties of laterally coupled quantum dots, under applied magnetic fields perpendicular to the plane of the dots, is presented. The exciton energy levels of such laterally coupled quantum-dot systems, together with the corresponding wavefunctions and eigenvalues, are obtained in the effective-mass approximation by using an extended variational approach in which the magnetoexciton states are simultaneously obtained. One achieves the expected limits of one single quantum dot, when the distance between the dots is zero, and of two uncoupled quantum dots, when the distance between the dots is large enough. Moreover, present calculations-with appropriate structural dimensions of the two-dot system-are shown to be in agreement with measurements in self-assembled laterally aligned GaAs quantum-dot pairs and naturally/accidentally occurring coupled quantum dots in GaAs/GaAlAs quantum wells.

  4. Quantum description of nuclear spin cooling in a quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Giedke, Geza; Christ, H.; Cirac, I. [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany)

    2007-07-01

    We study theoretically the cooling of an ensemble of nuclear spins coupled to the spin of a localized electron in a quantum dot. We obtain a master equation for the state of the nuclear spins interacting with a sequence of polarized electrons that allows to study quantitatively the cooling process including the effect of nuclear spin coherences, which can lead to 'dark states' of the nuclear system in which further cooling is inhibited. We show that the inhomogeneous Knight field mitigates this effect strongly and that the remaining dark state limitations can be overcome by very few shifts of the electron wave function, allowing for cooling far beyond the dark state limit. Numerical integration of the master equation indicates that polarizations larger than 90% can be achieved within a millisecond timescale.

  5. 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.

  6. Computer-automated tuning of semiconductor double quantum dots into the single-electron regime

    Energy Technology Data Exchange (ETDEWEB)

    Baart, T. A.; Vandersypen, L. M. K. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Eendebak, P. T. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Netherlands Organisation for Applied Scientific Research (TNO), P.O. Box 155, 2600 AD Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)

    2016-05-23

    We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.

  7. Suppression of LO phonon scattering in Landau quantized quantum dots

    NARCIS (Netherlands)

    Murdin, B. N.; Hollingworth, A. R.; Kamal-Saadi, M.; Kotitschke, R. T.; Ciesla, C. M.; Pidgeon, C. R.; Findlay, P. C.; Pellemans, H. P. M.; Langerak, Cjgm; Rowe, A. C.; Stradling, R. A.; Gornik, E.

    1999-01-01

    Picosecond time-resolved far-infrared measurements are presented of the scattering between conduction-band states in a doped quasi quantum dot. These states are created by the application of a magnetic field along the growth direction of an InAs/AlSb quantum well. A clear suppression of the cooling

  8. Counted Sb donors in Si quantum dots

    Science.gov (United States)

    Singh, Meenakshi; Pacheco, Jose; Bielejec, Edward; Perry, Daniel; Ten Eyck, Gregory; Bishop, Nathaniel; Wendt, Joel; Luhman, Dwight; Carroll, Malcolm; Lilly, Michael

    2015-03-01

    Deterministic control over the location and number of donors is critical for donor spin qubits in semiconductor based quantum computing. We have developed techniques using a focused ion beam and a diode detector integrated next to a silicon MOS single electron transistor to gain such control. With the diode detector operating in linear mode, the numbers of ions implanted have been counted and single ion implants have been detected. Poisson statistics in the number of ions implanted have been observed. Transport measurements performed on samples with counted number of implants have been performed and regular coulomb blockade and charge offsets observed. The capacitances to various gates are found to be in agreement with QCAD simulations for an electrostatically defined dot. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. The work was supported by Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.

  9. Selective targeting of microglia by quantum dots

    Directory of Open Access Journals (Sweden)

    Minami S Sakura

    2012-01-01

    Full Text Available Abstract Background Microglia, the resident immune cells of the brain, have been implicated in brain injury and various neurological disorders. However, their precise roles in different pathophysiological situations remain enigmatic and may range from detrimental to protective. Targeting the delivery of biologically active compounds to microglia could help elucidate these roles and facilitate the therapeutic modulation of microglial functions in neurological diseases. Methods Here we employ primary cell cultures and stereotaxic injections into mouse brain to investigate the cell type specific localization of semiconductor quantum dots (QDs in vitro and in vivo. Two potential receptors for QDs are identified using pharmacological inhibitors and neutralizing antibodies. Results In mixed primary cortical cultures, QDs were selectively taken up by microglia; this uptake was decreased by inhibitors of clathrin-dependent endocytosis, implicating the endosomal pathway as the major route of entry for QDs into microglia. Furthermore, inhibiting mannose receptors and macrophage scavenger receptors blocked the uptake of QDs by microglia, indicating that QD uptake occurs through microglia-specific receptor endocytosis. When injected into the brain, QDs were taken up primarily by microglia and with high efficiency. In primary cortical cultures, QDs conjugated to the toxin saporin depleted microglia in mixed primary cortical cultures, protecting neurons in these cultures against amyloid beta-induced neurotoxicity. Conclusions These findings demonstrate that QDs can be used to specifically label and modulate microglia in primary cortical cultures and in brain and may allow for the selective delivery of therapeutic agents to these cells.

  10. Quantum dot mediated imaging of atherosclerosis

    Energy Technology Data Exchange (ETDEWEB)

    Jayagopal, Ashwath; Haselton, Frederick R [Department of Biomedical Engineering, Vanderbilt University School of Medicine, Nashville, TN 37232 (United States); Su Yanru; Blakemore, John L; Linton, MacRae F; Fazio, Sergio [Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232 (United States)], E-mail: rick.haselton@vanderbilt.edu

    2009-04-22

    The progression of atherosclerosis is associated with leukocyte infiltration within lesions. We describe a technique for the ex vivo imaging of cellular recruitment in atherogenesis which utilizes quantum dots (QD) to color-code different cell types within lesion areas. Spectrally distinct QD were coated with the cell-penetrating peptide maurocalcine to fluorescently-label immunomagnetically isolated monocyte/macrophages and T lymphocytes. QD-maurocalcine bioconjugates labeled both cell types with a high efficiency, preserved cell viability, and did not perturb native leukocyte function in cytokine release and endothelial adhesion assays. QD-labeled monocyte/macrophages and T lymphocytes were reinfused in an ApoE{sup -/-} mouse model of atherosclerosis and age-matched controls and tracked for up to four weeks to investigate the incorporation of cells within aortic lesion areas, as determined by oil red O (ORO) and immunofluorescence ex vivo staining. QD-labeled cells were visible in atherosclerotic plaques within two days of injection, and the two cell types colocalized within areas of subsequent ORO staining. Our method for tracking leukocytes in lesions enables high signal-to-noise ratio imaging of multiple cell types and biomarkers simultaneously within the same specimen. It also has great utility in studies aimed at investigating the role of distinct circulating leukocyte subsets in plaque development and progression.

  11. Exciton coherence in semiconductor quantum dots

    International Nuclear Information System (INIS)

    Ishi-Hayase, Junko; Akahane, Kouichi; Yamamoto, Naokatsu; Sasaki, Masahide; Kujiraoka, Mamiko; Ema, Kazuhiro

    2009-01-01

    The coherent dynamics of excitons in InAs quantum dots (QDs) was investigated in the telecommunication wavelength range using a transient four-wave mixing technique. The sample was fabricated on an InP(311)B substrate using strain compensation to control the emission wavelength. This technique also enabled us to fabricate a 150-layer stacked QD structure for obtaining a high S/N in the four-wave mixing measurements, although no high-sensitive heterodyne detection was carried out. The dephasing time and transition dipole moment were precisely estimated from the polarization dependence of signals, taking into account their anisotropic properties. The population lifetimes of the excitons were also measured by using a polarization-dependent pumpprobe technique. A quantitative comparison of these anisotropies demonstrates that in our QDs, non-radiative population relaxation, polarization relaxation and pure dephasing are considerably smaller than the radiative relaxation. A comparison of the results of the four-wave mixing and pump-probe measurements revealed that the pure dephasing could be directly estimated with an accuracy of greater than 0.1 meV by comparing the results of four-wave mixing and pump-probe measurements. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Quantum dot lasers: From promise to high-performance devices

    Science.gov (United States)

    Bhattacharya, P.; Mi, Z.; Yang, J.; Basu, D.; Saha, D.

    2009-03-01

    Ever since self-organized In(Ga)As/Ga(AI)As quantum dots were realized by molecular beam epitaxy, it became evident that these coherently strained nanostructures could be used as the active media in devices. While the expected advantages stemming from three-dimensional quantum confinement were clearly outlined, these were not borne out by the early experiments. It took a very detailed understanding of the unique carrier dynamics in the quantum dots to exploit their full potential. As a result, we now have lasers with emission wavelengths ranging from 0.7 to 1.54 μm, on GaAs, which demonstrate ultra-low threshold currents, near-zero chip and α-factor and large modulation bandwidth. State-of-the-art performance characteristics of these lasers are briefly reviewed. The growth, fabrication and characteristics of quantum dot lasers on silicon substrates are also described. With the incorporation of multiple quantum dot layers as a dislocation filter, we demonstrate lasers with Jth=900 A/cm 2. The monolithic integration of the lasers with guided wave modulators on silicon is also described. Finally, the properties of spin-polarized lasers with quantum dot active regions are described. Spin injection of electrons is done with a MnAs/GaAs tunnel barrier. Laser operation at 200 K is demonstrated, with the possibility of room temperature operation in the near future.

  13. Quantum computation in semiconductor quantum dots of electron-spin asymmetric anisotropic exchange

    International Nuclear Information System (INIS)

    Hao Xiang; Zhu Shiqun

    2007-01-01

    The universal quantum computation is obtained when there exists asymmetric anisotropic exchange between electron spins in coupled semiconductor quantum dots. The asymmetric Heisenberg model can be transformed into the isotropic model through the control of two local unitary rotations for the realization of essential quantum gates. The rotations on each qubit are symmetrical and depend on the strength and orientation of asymmetric exchange. The implementation of the axially symmetric local magnetic fields can assist the construction of quantum logic gates in anisotropic coupled quantum dots. This proposal can efficiently use each physical electron spin as a logical qubit in the universal quantum computation

  14. Folded-light-path colloidal quantum dot solar cells.

    KAUST Repository

    Koleilat, Ghada I

    2013-01-01

    Colloidal quantum dot photovoltaics combine low-cost solution processing with quantum size-effect tuning to match absorption to the solar spectrum. Rapid advances have led to certified solar power conversion efficiencies of over 7%. Nevertheless, these devices remain held back by a compromise in the choice of quantum dot film thickness, balancing on the one hand the need to maximize photon absorption, mandating a thicker film, and, on the other, the need for efficient carrier extraction, a consideration that limits film thickness. Here we report an architecture that breaks this compromise by folding the path of light propagating in the colloidal quantum dot solid. Using this method, we achieve a substantial increase in short-circuit current, ultimately leading to improved power conversion efficiency.

  15. Simulating electron spin entanglement in a double quantum dot

    Science.gov (United States)

    Rodriguez-Moreno, M. A.; Hernandez de La Luz, A. D.; Meza-Montes, Lilia

    2011-03-01

    One of the biggest advantages of having a working quantum-computing device when compared with a classical one, is the exponential speedup of calculations. This exponential increase is based on the ability of a quantum system to create and operate on entangled states. In order to study theoretically the entanglement between two electron spins, we simulate the dynamics of two electron spins in an electrostatically-defined double quantum dot with a finite barrier height between the dots. Electrons are initially confined to separated quantum dots. Barrier height is varied and the spin entanglement as a function of this variation is investigated. The evolution of the system is simulated by using a numerical approach for solving the time-dependent Schrödinger equation for two particles. Partially supported by VIEP-BUAP.

  16. Bound state properties of ABC -stacked trilayer graphene quantum dots

    International Nuclear Information System (INIS)

    Xiong, Haonan; Jiang, Wentao; Song, Yipu; Duan, Luming

    2017-01-01

    The few-layer graphene quantum dot provides a promising platform for quantum computing with both spin and valley degrees of freedom. Gate-defined quantum dots in particular can avoid noise from edge disorders. In connection with the recent experimental efforts (Song et al 2016 Nano Lett . 16 6245), we investigate the bound state properties of trilayer graphene (TLG) quantum dots (QDs) through numerical simulations. We show that the valley degeneracy can be lifted by breaking the time reversal symmetry through the application of a perpendicular magnetic field. The spectrum under such a potential exhibits a transition from one group of Landau levels to another group, which can be understood analytically through perturbation theory. Our results provide insight into the transport property of TLG QDs, with possible applications to study of spin qubits and valleytronics in TLG QDs. (paper)

  17. Carbon quantum dots and applications in photocatalytic energy conversion.

    Science.gov (United States)

    Fernando, K A Shiral; Sahu, Sushant; Liu, Yamin; Lewis, William K; Guliants, Elena A; Jafariyan, Amirhossein; Wang, Ping; Bunker, Christopher E; Sun, Ya-Ping

    2015-04-29

    Quantum dots (QDs) generally refer to nanoscale particles of conventional semiconductors that are subject to the quantum-confinement effect, though other nanomaterials of similar optical and redox properties are also named as QDs even in the absence of strictly defined quantum confinement. Among such nanomaterials that have attracted tremendous recent interest are carbon dots, which are small carbon nanoparticles with some form of surface passivation, and graphene quantum dots in various configurations. In this article, we highlight these carbon-based QDs by focusing on their syntheses, on their photoexcited state properties and redox processes, and on their applications as photocatalysts in visible-light carbon dioxide reduction and in water-splitting, as well as on their mechanistic similarities and differences.

  18. Fast gain and phase recovery of semiconductor optical amplifiers based on submonolayer quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Herzog, Bastian, E-mail: BHerzog@physik.tu-berlin.de; Owschimikow, Nina; Kaptan, Yücel; Kolarczik, Mirco; Switaiski, Thomas; Woggon, Ulrike [Institut für Optik und Atomare Physik, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany); Schulze, Jan-Hindrik; Rosales, Ricardo; Strittmatter, André; Bimberg, Dieter; Pohl, Udo W. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

    2015-11-16

    Submonolayer quantum dots as active medium in opto-electronic devices promise to combine the high density of states of quantum wells with the fast recovery dynamics of self-assembled quantum dots. We investigate the gain and phase recovery dynamics of a semiconductor optical amplifier based on InAs submonolayer quantum dots in the regime of linear operation by one- and two-color heterodyne pump-probe spectroscopy. We find an as fast recovery dynamics as for quantum dot-in-a-well structures, reaching 2 ps at moderate injection currents. The effective quantum well embedding the submonolayer quantum dots acts as a fast and efficient carrier reservoir.

  19. Ultrafast optical control of individual quantum dot spin qubits

    International Nuclear Information System (INIS)

    De Greve, Kristiaan; Press, David; McMahon, Peter L; Yamamoto, Yoshihisa

    2013-01-01

    Single spins in semiconductor quantum dots form a promising platform for solid-state quantum information processing. The spin-up and spin-down states of a single electron or hole, trapped inside a quantum dot, can represent a single qubit with a reasonably long decoherence time. The spin qubit can be optically coupled to excited (charged exciton) states that are also trapped in the quantum dot, which provides a mechanism to quickly initialize, manipulate and measure the spin state with optical pulses, and to interface between a stationary matter qubit and a ‘flying’ photonic qubit for quantum communication and distributed quantum information processing. The interaction of the spin qubit with light may be enhanced by placing the quantum dot inside a monolithic microcavity. An entire system, consisting of a two-dimensional array of quantum dots and a planar microcavity, may plausibly be constructed by modern semiconductor nano-fabrication technology and could offer a path toward chip-sized scalable quantum repeaters and quantum computers. This article reviews the recent experimental developments in optical control of single quantum dot spins for quantum information processing. We highlight demonstrations of a complete set of all-optical single-qubit operations on a single quantum dot spin: initialization, an arbitrary SU(2) gate, and measurement. We review the decoherence and dephasing mechanisms due to hyperfine interaction with the nuclear-spin bath, and show how the single-qubit operations can be combined to perform spin echo sequences that extend the qubit decoherence from a few nanoseconds to several microseconds, more than 5 orders of magnitude longer than the single-qubit gate time. Two-qubit coupling is discussed, both within a single chip by means of exchange coupling of nearby spins and optically induced geometric phases, as well as over longer-distances. Long-distance spin–spin entanglement can be generated if each spin can emit a photon that is

  20. Effect of nanostructured electrode architecture and semiconductor deposition strategy on the photovoltaic performance of quantum dot sensitized solar cells

    International Nuclear Information System (INIS)

    Samadpour, Mahmoud; Giménez, Sixto; Boix, Pablo P.; Shen, Qing; Calvo, Mauricio E.; Taghavinia, Nima; Azam Iraji zad; Toyoda, Taro; Míguez, Hernán

    2012-01-01

    Highlights: ► Electrode nanostructure and quantum dot growth method have a clear influence in the final quantum dot solar cell performance. ► Higher V oc values are systematically obtained for TiO 2 morphologies with decreasing surface area. ► Higher V oc values are systematically obtained for cells using CBD growth method in comparison with SILAR method. - Abstract: Here we analyze the effect of two relevant aspects related to cell preparation on quantum dot sensitized solar cells (QDSCs) performance: the architecture of the TiO 2 nanostructured electrode and the growth method of quantum dots (QD). Particular attention is given to the effect on the photovoltage, V oc , since this parameter conveys the main current limitation of QDSCs. We have analyzed electrodes directly sensitized with CdSe QDs grown by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). We have carried out a systematic study comprising structural, optical, photophysical and photoelectrochemical characterization in order to correlate the material properties of the photoanodes with the functional performance of the manufactured QDSCs. The results show that the correspondence between photovoltaic conversion efficiency and the surface area of TiO 2 depends on the QDs deposition method. Higher V oc values are systematically obtained for TiO 2 morphologies with decreasing surface area and for cells using CBD growth method. This is systematically correlated to a higher recombination resistance of CBD sensitized electrodes. Electron injection kinetics from QDs into TiO 2 also depends on both the TiO 2 structure and the QDs deposition method, being systematically faster for CBD. Only for electrodes prepared with small TiO 2 nanoparticles SILAR method presents better performance than CBD, indicating that the small pore size disturb the CBD growth method. These results have important implications for the optimization of QDSCs.

  1. Tuning Single Quantum Dot Emission with a Micromirror.

    Science.gov (United States)

    Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul

    2018-02-14

    The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

  2. Imaging electrostatically confined Dirac fermions in graphene quantum dots

    Science.gov (United States)

    Lee, Juwon; Wong, Dillon; Velasco, Jairo, Jr.; Rodriguez-Nieva, Joaquin F.; Kahn, Salman; Tsai, Hsin-Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid S.; Crommie, Michael F.

    2016-11-01

    Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries. Reflection and transmission at these boundaries affect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions.

  3. 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.

  4. Intermediate-band photosensitive device with quantum dots having tunneling barrier embedded in organic matrix

    Science.gov (United States)

    Forrest, Stephen R.

    2008-08-19

    A plurality of quantum dots each have a shell. The quantum dots are embedded in an organic matrix. At least the quantum dots and the organic matrix are photoconductive semiconductors. The shell of each quantum dot is arranged as a tunneling barrier to require a charge carrier (an electron or a hole) at a base of the tunneling barrier in the organic matrix to perform quantum mechanical tunneling to reach the respective quantum dot. A first quantum state in each quantum dot is between a lowest unoccupied molecular orbital (LUMO) and a highest occupied molecular orbital (HOMO) of the organic matrix. Wave functions of the first quantum state of the plurality of quantum dots may overlap to form an intermediate band.

  5. SELF-ORGANIZATION OF LEAD SULFIDE QUANTUM DOTS INTO SUPERSTRUCTURES

    Directory of Open Access Journals (Sweden)

    Elena V. Ushakova

    2014-11-01

    Full Text Available The method of X-ray structural analysis (X-ray scattering at small angles is used to show that the structures obtained by self-organization on a substrate of lead sulfide (PbS quantum dots are ordered arrays. Self-organization of quantum dots occurs at slow evaporation of solvent from a cuvette. The cuvette is a thin layer of mica with teflon ring on it. The positions of peaks in SAXS pattern are used to calculate crystal lattice of obtained ordered structures. Such structures have a primitive orthorhombic crystal lattice. Calculated lattice parameters are: a = 21,1 (nm; b = 36,2 (nm; c = 62,5 (nm. Dimensions of structures are tens of micrometers. The spectral properties of PbS QDs superstructures and kinetic parameters of their luminescence are investigated. Absorption band of superstructures is broadened as compared to the absorption band of the quantum dots in solution; the luminescence band is slightly shifted to the red region of the spectrum, while its bandwidth is not changed much. Luminescence lifetime of obtained structures has been significantly decreased in comparison with the isolated quantum dots in solution, but remained the same for the lead sulfide quantum dots close-packed ensembles. Such superstructures can be used to produce solar cells with improved characteristics.

  6. Electroluminescence of colloidal ZnSe quantum dots

    International Nuclear Information System (INIS)

    Dey, S.C.; Nath, S.S.

    2011-01-01

    The article reports a green chemical synthesis of colloidal ZnSe quantum dots at a moderate temperature. The prepared colloid sample is characterised by UV-vis absorption spectroscopy and transmission electron microscopy. UV-vis spectroscopy reveals as-expected blue-shift with strong absorption edge at 400 nm and micrographs show a non-uniform size distribution of ZnSe quantum dots in the range 1-4 nm. Further, photoluminescence and electroluminescence spectroscopies are carried out to study optical emission. Each of the spectroscopies reveals two emission peaks, indicating band-to-band transition and defect related transition. From the luminescence studies, it can be inferred that the recombination of electrons and holes resulting from interband transition causes violet emission and the recombination of a photon generated hole with a charged state of Zn-vacancy gives blue emission. Meanwhile electroluminescence study suggests the application of ZnSe quantum dots as an efficient light emitting device with the advantage of colour tuning (violet-blue-violet). - Highlights: → Synthesis of ZnSe quantum dots by a green chemical route. → Characterisation: UV-vis absorption spectroscopy and transmission electron microscopy. → Analysis of UV-vis absorption spectrum and transmission electron micrographs. → Study of electro-optical properties by photoluminescence and electroluminescence. → Conclusion: ZnSe quantum dots can be used as LED with dual colour emission.

  7. Carrier-phonon interaction in semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Seebeck, Jan

    2009-03-10

    In recent years semiconductor quantum dots have been studied extensively due to their wide range of possible applications, predominantly for light sources. For successful applications, efficient carrier scattering processes as well as a detailed understanding of the optical properties are of central importance. The aims of this thesis are theoretical investigations of carrier scattering processes in InGaAs/GaAs quantum dots on a quantum-kinetic basis. A consistent treatment of quasi-particle renormalizations and carrier kinetics for non-equilibrium conditions is presented, using the framework of non-equilibrium Green's functions. The focus of our investigations is the interaction of carriers with LO phonons. Important for the understanding of the scattering mechanism are the corresponding quasi-particle properties. Starting from a detailed study of quantum-dot polarons, scattering and dephasing processes are discussed for different temperature regimes. The inclusion of polaron and memory effects turns out to be essential for the description of the carrier kinetics in quantum-dot systems. They give rise to efficient scattering channels and the obtained results are in agreement with recent experiments. Furthermore, a consistent treatment of the carrier-LO-phonon and the carrier-carrier interaction is presented for the optical response of semiconductor quantum dots, both giving rise to equally important contributions to the dephasing. Beside the conventional GaAs material system, currently GaN based light sources are of high topical interest due to their wide range of possible emission frequencies. In this material additionally intrinsic properties like piezoelectric fields and strong band-mixing effects have to be considered. For the description of the optical properties of InN/GaN quantum dots a procedure is presented, where the material properties obtained from an atomistic tight-binding approach are combined with a many-body theory for non

  8. A Quantum Dot with Spin-Orbit Interaction--Analytical Solution

    Science.gov (United States)

    Basu, B.; Roy, B.

    2009-01-01

    The practical applicability of a semiconductor quantum dot with spin-orbit interaction gives an impetus to study analytical solutions to one- and two-electron quantum dots with or without a magnetic field.

  9. 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.

  10. Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots

    NARCIS (Netherlands)

    de Weerd, C.; Shin, Y.; Marino, E.; Kim, J.; Lee, H.; Saeed, S.; Gregorkiewicz, T.

    2017-01-01

    Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other

  11. Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control

    KAUST Repository

    Sun, Liangfeng

    2012-05-06

    Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr \\'1 m \\'2) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH 2 groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.© 2012 Macmillan Publishers Limited.

  12. Quantum dots based electrochemiluminescent immunosensor by coupling enzymatic amplification for ultrasensitive detection of clenbuterol

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Xun; Yan, Panpan; Tang, Qinghui [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); The Key Lab of Health Chemistry and Molecular Diagnosis of Suzhou, Suzhou 215123 (China); Deng, Anping, E-mail: denganping@suda.edu.cn [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); The Key Lab of Health Chemistry and Molecular Diagnosis of Suzhou, Suzhou 215123 (China); Li, Jianguo, E-mail: lijgsd@suda.edu.cn [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); The Key Lab of Health Chemistry and Molecular Diagnosis of Suzhou, Suzhou 215123 (China)

    2013-10-10

    Graphical abstract: -- Highlights: •An ultrasensitive ECL immunosensor of CdSe QDs for clenbuterol determination is developed. •The CdSe QDs showed great biocompatibility and could be easier to make direct use of such QDs in the region of biological system. •Enzymatic amplification strategy was proposed by combining the coreactant and pAb/GaRIgG-HRP. •Enzymatic amplification increased ECL emission and extended the analyte in presence of substrate. •It provided a method for detecting clenbuterol and enlarged the usage of QDs in ECL biosensing. -- Abstract: An ultrasensitive electrochemiluminescence (ECL) immunosensor based on CdSe quantum dots (QDs) has been designed for the detection of clenbuterol. The immunosensor was fabricated by layer by layer and characterized with atomic force microscopic images (AFM) and electrochemical impedance spectra (EIS). In oxygen-saturated pH = 9.0 Tris-HCl buffer, a strong ECL emission of QDs could be observed during the cathodic process due to the H{sub 2}O{sub 2} product from electrochemical reduction of dissolved oxygen. Upon the formation of immunocomplex, the second antibody labeled with horseradish peroxidase was simply immobilized on the electrode surface. The ECL emission decreased since steric hindrance of the immunocomplex slowed down the electron-transfer speed of dissolved oxygen, and also could be greatly amplified by an enzymatic cycle to consume the self-produced coreactant. Using clenbuterol as model analyte, the ECL intensity was determined by the concentration of competitive immunoassay of clenbuterol with a wide calibration in the range of 0.05 ng mL{sup −1} to 1000 ng mL{sup −1}, and a low detection limit was 0.02 ng mL{sup −1}. The immunosensor shows good stability and fabrication reproducibility. It was applied to detecting practical samples with the satisfactory results. This immunosensing strategy opens a new avenue for detection of residue and application of QDs in ECL biosensing.

  13. Fluorometric immunoassay for human serum albumin based on its inhibitory effect on the immunoaggregation of quantum dots with silver nanoparticles

    Science.gov (United States)

    Marukhyan, Seda S.; Gasparyan, Vardan K.

    2017-02-01

    Quantitative determination of HSA was conducted by competitive immunoassay. Inhibition of aggregation of antibody conjugated quantum dots (QD) with albumin conjugated silver nanoparticles (AgNPs) in the presence of HSA was conducted. If antibody-loaded CdSe QDs aggregate with HSA-coated silver nanoparticles the distance between the two kinds of nanoparticles will be reduced enough to cause fluorescence resonance energy transfer (FRET). In this case the yellow fluorescence of the Ab-QDs is quenched. However if HSA (antigen) is added to the Ab-QDs their surface will be blocked and they cannot aggregate any longer with the HSA-AgNPs. Hence, fluorescence will not be quenched. The drop of the intensity of fluorescence (peaking at 570 nm) is inversely correlated with the concentration of HSA in the sample. The method allows to determine HSA in the 30-600 ng·mL-1 concentration range.

  14. Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

    Science.gov (United States)

    Pham, Chuyen V.; Krueger, Michael; Eck, Michael; Weber, Stefan; Erdem, Emre

    2014-03-01

    Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

  15. A quantum dot conjugated sugar ball and its cellular uptake. On the size effects of endocytosis in the subviral region.

    Science.gov (United States)

    Osaki, Fumio; Kanamori, Takuya; Sando, Shinsuke; Sera, Takashi; Aoyama, Yasuhiro

    2004-06-02

    The lipophilic CdSe quantum dot (QD) coated with trioctylphosphine oxide (TOPOQD) can be extracted from chloroform into water upon interaction with macrocyclic glycocluster amphiphile 1. The QD-conjugated and highly fluorescent sugar ball of a size of 15 nm (TOPOQD1) thus solubilized in water readily invades Hela cells via endocytosis. The endocytic activity of TOPOQD1 (15 nm), in light of those of the micellar homoaggregate of 1 (5 nm) and the virus-like 1-DNA conjugate (50 nm) as references, reveals a dramatic size effect (50 > 15 > 5) in the subviral size region. The optimal size at approximately 50 nm indicates that size complementarity which governs molecular recognition in small host-guest systems also plays key roles in the encapsulation of nanometric guest particles by the endocytic vesicles (probe, etc.) delivery machines.

  16. Effect of quantum lattice fluctuations on quantum coherent oscillations in a coherently driven quantum dot-cavity system

    International Nuclear Information System (INIS)

    Zhu, Ka-Di; Li, Wai-Sang

    2003-01-01

    The quantum coherent oscillations in a coherently driven quantum dot-cavity system with the presence of strong exciton-phonon interactions are investigated theoretically in a fully quantum treatment. It is shown that even at zero temperature, the strong exciton-phonon interactions still affect the quantum coherent oscillations significantly

  17. Biosensing with Quantum Dots: A Microfluidic Approach

    Science.gov (United States)

    Vannoy, Charles H.; Tavares, Anthony J.; Noor, M. Omair; Uddayasankar, Uvaraj; Krull, Ulrich J.

    2011-01-01

    Semiconductor quantum dots (QDs) have served as the basis for signal development in a variety of biosensing technologies and in applications using bioprobes. The use of QDs as physical platforms to develop biosensors and bioprobes has attracted considerable interest. This is largely due to the unique optical properties of QDs that make them excellent choices as donors in fluorescence resonance energy transfer (FRET) and well suited for optical multiplexing. The large majority of QD-based bioprobe and biosensing technologies that have been described operate in bulk solution environments, where selective binding events at the surface of QDs are often associated with relatively long periods to reach a steady-state signal. An alternative approach to the design of biosensor architectures may be provided by a microfluidic system (MFS). A MFS is able to integrate chemical and biological processes into a single platform and allows for manipulation of flow conditions to achieve, by sample transport and mixing, reaction rates that are not entirely diffusion controlled. Integrating assays in a MFS provides numerous additional advantages, which include the use of very small amounts of reagents and samples, possible sample processing before detection, ultra-high sensitivity, high throughput, short analysis time, and in situ monitoring. Herein, a comprehensive review is provided that addresses the key concepts and applications of QD-based microfluidic biosensors with an added emphasis on how this combination of technologies provides for innovations in bioassay designs. Examples from the literature are used to highlight the many advantages of biosensing in a MFS and illustrate the versatility that such a platform offers in the design strategy. PMID:22163723

  18. Progress and prospect of quantum dot lasers

    Science.gov (United States)

    Arakawa, Yasuhiko

    2001-10-01

    Optical properties and growth of self-assembled quantum dots (SAQDs) for optoelectronic device applications are discussed. After briefly reviewing the history of research on QD lasers, we discuss growth of InAs SQDs including the light emission at the wavelength of 1.52)mum with a narrow linewidth (22 meV) and the area-controlled growth which demonstrates formation of SAQDs in selected local areas on a growth plane using a SiO)-2) mask with MOCVD growth. Then properties of the InGaAs AQDs are investigated by the near- field photoluminescence excitation spectroscopy which reveals gradually increasing continuum absorption connected with the two-dimensional-like (2D-like) wetting layer, resulting in faster relaxation of electrons due to a crossover between OD and 2D character in the density of states. Moreover, we have investigated InGaN self-assembled QDs on a GaN layer achieving the average diameter as small as 8.4nm and a strong light at room temperature. A laser structure with the stacked InGAN QDs embedded in the active layer was fabricated and room temperature operation of blue InGaN QD lasers was achieved under optical excitation. Carrier confinement in QDs was examined using near-field $DAL- photoluminescence measurement: A very sharp spectral line emitted from excitons in individual InGaN QDs was observed. Establishing AlGaN/GaN DBR of high quality, we succeeded in lasing action in InGaN blue light emitting VCSELs. Enhancement of spontaneous emission is demonstrated. Finally, perspective of QD lasers.

  19. A quantum walk in phase space with resonator-assisted double quantum dots

    International Nuclear Information System (INIS)

    Bian Zhi-Hao; Qin Hao; Zhan Xiang; Li Jian; Xue Peng

    2016-01-01

    We implement a quantum walk in phase space with a new mechanism based on the superconducting resonator-assisted double quantum dots. By analyzing the hybrid system, we obtain the necessary factors implementing a quantum walk in phase space: the walker, coin, coin flipping and conditional phase shift. The coin flipping is implemented by adding a driving field to the resonator. The interaction between the quantum dots and resonator is used to implement conditional phase shift. Furthermore, we show that with different driving fields the quantum walk in phase space exhibits a ballistic behavior over 25 steps and numerically analyze the factors influencing the spreading of the walker in phase space. (paper)

  20. Multiple Exciton Generation in Quantum Dot Solar Cells

    Science.gov (United States)

    Semonin, O. E.

    Photovoltaics are limited in their power conversion efficiency (PCE) by very rapid relaxation of energetic carriers to the band edge. Therefore, photons from the visible and ultraviolet parts of the spectrum typically are not efficiently converted into electrical energy. One approach that can address this is multiple exciton generation (MEG), where a single photon of sufficient energy can generate multiple excited electron-hole pairs. This process has been shown to be more efficient in quantum dots than bulk semiconductors, but it has never been demonstrated in the photocurrent of a solar cell. In order to demonstrate that multiple exciton generation can address fundamental limits for conventional photovoltaics, I have developed prototype devices from colloidal PbS and PbSe quantum dot inks. I have characterized both the colloidal suspensions and films of quantum dots with the goal of understanding what properties determine the efficiency of the solar cell and of the MEG process. I have found surface chemistry effects on solar cells, photoluminescence, and MEG, and I have found some chemical treatments that lead to solar cells showing MEG. These devices show external quantum efficiency (EQE) greater than 100% for certain parts of the solar spectrum, and I extract internal quantum efficiency (IQE) consistent with previous measurements of colloidal suspensions of quantum dots. These findings are a small first step toward breaking the single junction Shockley-Queisser limit of present-day first and second generation solar cells, thus moving photovoltaic cells toward a new regime of efficiency.

  1. Dynamically broken symmetry in periodically gated quantum dots: charge accumulation and DC-current

    International Nuclear Information System (INIS)

    Kwapinski, T.; Kohler, S.; Hanggi, P.

    2010-01-01

    Time-dependent electron transport through a quantum dot and double quantum dot systems in the presence of polychromatic external periodic quantum dot energy-level modulations is studied within the time evolution operator method for a tight-binding Hamiltonian. Analytical relations for the dc-current flowing through the system and the charge accumulated on a quantum dot are obtained for the zero-temperature limit.

  2. Double Rashba Quantum Dots Ring as a Spin Filter

    Directory of Open Access Journals (Sweden)

    Chi Feng

    2008-01-01

    Full Text Available AbstractWe theoretically propose a double quantum dots (QDs ring to filter the electron spin that works due to the Rashba spin–orbit interaction (RSOI existing inside the QDs, the spin-dependent inter-dot tunneling coupling and the magnetic flux penetrating through the ring. By varying the RSOI-induced phase factor, the magnetic flux and the strength of the spin-dependent inter-dot tunneling coupling, which arises from a constant magnetic field applied on the tunneling junction between the QDs, a 100% spin-polarized conductance can be obtained. We show that both the spin orientations and the magnitude of it can be controlled by adjusting the above-mentioned parameters. The spin filtering effect is robust even in the presence of strong intra-dot Coulomb interactions and arbitrary dot-lead coupling configurations.

  3. Charge pumping in strongly coupled molecular quantum dots

    Science.gov (United States)

    Haughian, Patrick; Yap, Han Hoe; Gong, Jiangbin; Schmidt, Thomas L.

    2017-11-01

    The interaction between electrons and the vibrational degrees of freedom of a molecular quantum dot can lead to an exponential suppression of the conductance, an effect which is commonly termed Franck-Condon blockade. Here, we investigate this effect in a quantum dot driven by time-periodic gate voltages and tunneling amplitudes using nonequilibrium Green's functions and a Floquet expansion. Building on previous results showing that driving can lift the Franck-Condon blockade, we investigate driving protocols which can be used to pump charge across the quantum dot. In particular, we show that due to the strongly coupled nature of the system, the pump current at resonance is an exponential function of the drive strength.

  4. Electro-optical properties of phosphorene quantum dots

    Science.gov (United States)

    Saroka, V. A.; Lukyanchuk, I.; Portnoi, M. E.; Abdelsalam, H.

    2017-08-01

    We study the electronic and optical properties of single-layer phosphorene quantum dots with various shapes, sizes, and edge types (including disordered edges) subjected to an external electric field normal to the structure plane. Compared to graphene quantum dots, in phosphorene clusters of similar shape and size there is a set of edge states with energies dispersed at around the Fermi level. These states make the majority of phosphorene quantum dots metallic and enrich the phosphorene absorption gap with low-energy absorption peaks tunable by the electric field. The presence of the edge states dispersed around the Fermi level is a characteristic feature that is independent of the edge morphology and roughness.

  5. A tunable colloidal quantum dot photo field-effect transistor

    KAUST Repository

    Ghosh, Subir

    2011-01-01

    We fabricate and investigate field-effect transistors in which a light-absorbing photogate modulates the flow of current along the channel. The photogate consists of colloidal quantum dots that efficiently transfer photoelectrons to the channel across a charge-separating (type-II) heterointerface, producing a primary and sustained secondary flow that is terminated via electron back-recombination across the interface. We explore colloidal quantum dot sizes corresponding to bandgaps ranging from 730 to 1475 nm and also investigate various stoichiometries of aluminum-doped ZnO (AZO) channel materials. We investigate the role of trap state energies in both the colloidal quantum dot energy film and the AZO channel. © 2011 American Institute of Physics.

  6. Broadband room temperature strong coupling between quantum dots and metamaterials.

    Science.gov (United States)

    Indukuri, Chaitanya; Yadav, Ravindra Kumar; Basu, J K

    2017-08-17

    Herein, we report the first demonstration of room temperature enhanced light-matter coupling in the visible regime for metamaterials using cooperative coupled quasi two dimensional quantum dot assemblies located at precise distances from the hyperbolic metamaterial (HMM) templates. The non-monotonic variation of the magnitude of strong coupling, manifested in terms of strong splitting of the photoluminescence of quantum dots, can be explained in terms of enhanced LDOS near the surface of such metamaterials as well as the plasmon mediated super-radiance of closely spaced quantum dots (QDs). Our methodology of enhancing broadband, room temperature, light-matter coupling in the visible regime for metamaterials opens up new possibilities of utilising these materials for a wide range of applications including QD based thresholdless nanolasers and novel metamaterial based integrated photonic devices.

  7. 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).

  8. Colloidal quantum dot solids for solution-processed solar cells

    KAUST Repository

    Yuan, Mingjian

    2016-02-29

    Solution-processed photovoltaic technologies represent a promising way to reduce the cost and increase the efficiency of solar energy harvesting. Among these, colloidal semiconductor quantum dot photovoltaics have the advantage of a spectrally tuneable infrared bandgap, which enables use in multi-junction cells, as well as the benefit of generating and harvesting multiple charge carrier pairs per absorbed photon. Here we review recent progress in colloidal quantum dot photovoltaics, focusing on three fronts. First, we examine strategies to manage the abundant surfaces of quantum dots, strategies that have led to progress in the removal of electronic trap states. Second, we consider new device architectures that have improved device performance to certified efficiencies of 10.6%. Third, we focus on progress in solution-phase chemical processing, such as spray-coating and centrifugal casting, which has led to the demonstration of manufacturing-ready process technologies.

  9. QCAD simulation and optimization of semiconductor double quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Nielsen, Erik; Gao, Xujiao; Kalashnikova, Irina; Muller, Richard Partain; Salinger, Andrew Gerhard; Young, Ralph Watson

    2013-12-01

    We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling quantum devices, particularly silicon double quantum dots (DQDs) developed for quantum qubits. The simulator has three di erentiating features: (i) its core contains nonlinear Poisson, e ective mass Schrodinger, and Con guration Interaction solvers that have massively parallel capability for high simulation throughput, and can be run individually or combined self-consistently for 1D/2D/3D quantum devices; (ii) the core solvers show superior convergence even at near-zero-Kelvin temperatures, which is critical for modeling quantum computing devices; (iii) it couples with an optimization engine Dakota that enables optimization of gate voltages in DQDs for multiple desired targets. The Poisson solver includes Maxwell- Boltzmann and Fermi-Dirac statistics, supports Dirichlet, Neumann, interface charge, and Robin boundary conditions, and includes the e ect of dopant incomplete ionization. The solver has shown robust nonlinear convergence even in the milli-Kelvin temperature range, and has been extensively used to quickly obtain the semiclassical electrostatic potential in DQD devices. The self-consistent Schrodinger-Poisson solver has achieved robust and monotonic convergence behavior for 1D/2D/3D quantum devices at very low temperatures by using a predictor-correct iteration scheme. The QCAD simulator enables the calculation of dot-to-gate capacitances, and comparison with experiment and between solvers. It is observed that computed capacitances are in the right ballpark when compared to experiment, and quantum con nement increases capacitance when the number of electrons is xed in a quantum dot. In addition, the coupling of QCAD with Dakota allows to rapidly identify which device layouts are more likely leading to few-electron quantum dots. Very efficient QCAD simulations on a large number of fabricated and proposed Si DQDs have made it possible to provide fast feedback for design

  10. Long lived coherence in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    2001-01-01

    We report measurements of ultralong coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mu eV, which is significantly smaller than the linewidth observed in single-dot...... luminescence. Time-resolved luminescence measurements show a lifetime of the dot ground state of 800 ps, demonstrating the presence of pure dephasing at finite temperature. The homogeneous width is lifetime limited only at temperatures approaching 0 K....

  11. 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

  12. Long coherence times in self-assembled semiconductor quantum dots

    DEFF Research Database (Denmark)

    Birkedal, Dan; Leosson, K.; Hvam, Jørn Märcher

    2002-01-01

    We report measurements of ultra-long coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mueV, which is significantly smaller than the linewidth observed in single-dot...... luminescence. Time-resolved luminescence measurements show a lifetime of the dot ground state of 800 ps demonstrating the presence of pure dephasing at finite temperature. The homogeneous width is lifetime limited only at temperatures approaching 0 K....

  13. Preparation of carbon quantum dots based high photostability luminescent membranes.

    Science.gov (United States)

    Zhao, Jinxing; Liu, Cui; Li, Yunchuan; Liang, Jiyuan; Liu, Jiyan; Qian, Tonghui; Ding, Jianjun; Cao, Yuan-Cheng

    2017-06-01

    Urethane acrylate (UA) was used to prepare carbon quantum dots (C-dots) luminescent membranes and the resultants were examined with FT-IR, mechanical strength, scanning electron microscope (SEM) and quantum yields (QYs). FT-IR results showed the polyurethane acrylate (PUA) prepolymer -C = C-vibration at 1101 cm -1 disappeared but there was strong vibration at1687cm -1 which was contributed from the-C = O groups in cross-linking PUA. Mechanical strength results showed that the different quantity of C-dots loadings and UV-curing time affect the strength. SEM observations on the cross-sections of the membranes are uniform and have no structural defects, which prove that the C-dots are compatible with the water-soluble PUA resin. The C-dot loading was increased from 0 to 1 g, the maximum tensile stress was nearly 2.67 MPa, but the tensile strain was decreased from 23.4% to 15.1% and 7.2% respectively. QYs results showed that the C-dots in the membrane were stable after 120 h continuous irradiation. Therefore, the C-dots photoluminescent film is the promising material for the flexible devices in the future applications. Copyright © 2016 John Wiley & Sons, Ltd.

  14. 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....

  15. Incorporation of graphene in quantum dot sensitized solar cells based on ZnO nanorods.

    Science.gov (United States)

    Chen, Jing; Li, Chu; Eda, Goki; Zhang, Yan; Lei, Wei; Chhowalla, Manish; Milne, William I; Deng, Wei-Qiao

    2011-06-07

    We demonstrate a novel architecture of solar cell by incorporating graphene thin film in a quantum dot sensitized solar cell. Quantum dot sensitized nanorods with a graphene layer exhibited a 54.7% improvement comparing a quantum dot sensitized ZnO nanorods without graphene layer. A fill factor as high as ∼62% was also obtained.

  16. A triple quantum dot in a single-wall carbon nanotube

    DEFF Research Database (Denmark)

    Grove-Rasmussen, Kasper; Jørgensen, Henrik Ingerslev; Hayashi, T.

    2008-01-01

    A top-gated single-wall carbon nanotube is used to define three coupled quantum dots in series between two electrodes. The additional electron number on each quantum dot is controlled by top-gate voltages allowing for current measurements of single, double, and triple quantum dot stability diagrams...

  17. Sub-diffraction positioning of a two-photon excited and optically trapped quantum dot

    DEFF Research Database (Denmark)

    Pedersen, Liselotte Jauffred; Kyrsting, Anders Højbo; Christensen, Eva Arnspang

    2014-01-01

    to blueshift. A quantum dot is much smaller than a diffraction limited laser focus and by mapping out the intensity of the focal volume and overlaying this with the positions visited by a quantum dot, a quantum dot is shown often to explore regions of the focal volume where the intensity is too low to render...

  18. Self-organized formation of quantum dots of a material on a substrate

    Science.gov (United States)

    Zhang, Zhenyu; Wendelken, John F.; Chang, Ming-Che; Pai, Woei Wu

    2001-01-01

    Systems and methods are described for fabricating arrays of quantum dots. A method for making a quantum dot device, includes: forming clusters of atoms on a substrate; and charging the clusters of atoms such that the clusters of atoms repel one another. The systems and methods provide advantages because the quantum dots can be ordered with regard to spacing and/or size.

  19. Computer-automated tuning of semiconductor double quantum dots into the single-electron regime

    NARCIS (Netherlands)

    Baart, T.A.; Eendebak, P.T.; Reichl, C.; Wegscheider, W.; Vandersypen, L.M.K.

    2016-01-01

    We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the

  20. Analysis of MBE-grown II-VI hetero-interfaces and quantum-dots by Raman spectroscopy

    International Nuclear Information System (INIS)

    Bass, Utz

    2012-01-01

    The material system of interest in this thesis are II-VI-semiconductors. The first part of this thesis focuses on the formation of self-assembled CdSe-based quantum dots (QD) on ZnSe. The lattice constants of ZnSe and CdSe differ as much as about 7% and therefore a CdSe layer grown on top of ZnSe experiences a huge strain. The aspired strain relief constitutes in the self-assembly of QDs (i.e. a roughened layer structure). Additionally, this QD layer is intermixed with Zn as this is also a possibility to decrease the strain in the layer. For CdSe on ZnSe, in Molecular Beam Epitaxy (MBE), various QD growth procedures were analysed with respect to the resulting Cd-content of the non-stoichiometric ternary (Zn,Cd)Se. The evaluation was performed by Raman Spectroscopy as the phonon frequency depends on the Cd-content. The second part of the thesis emphasis on the interface properties of n-ZnSe on n-GaAs. Different growth start procedures of the ZnSe epilayer may lead to different interface configurations with characteristic band-offsets and carrier depletion layer widths. The analysis is mainly focused on the individual depletion layer widths in the GaAs and ZnSe. This non-destructive analysis is performed by evaluating the Raman signal which comprises of phonon scattering from the depleted regions and coupled plasmon-phonon scattering from regions with free carriers.