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Sample records for active quantum dots

  1. Optically active quantum dots

    NASA Astrophysics Data System (ADS)

    Gerard, Valerie; Govan, Joseph; Loudon, Alexander; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii K.

    2015-10-01

    The main goal of our research is to develop new types of technologically important optically active quantum dot (QD) based materials, study their properties and explore their biological applications. For the first time chiral II-VI QDs have been prepared by us using microwave induced heating with the racemic (Rac), D- and L-enantiomeric forms of penicillamine as stabilisers. Circular dichroism (CD) studies of these QDs have shown that D- and L-penicillamine stabilised particles produced mirror image CD spectra, while the particles prepared with a Rac mixture showed only a weak signal. It was also demonstrated that these QDs show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. These QDs have demonstrated highly specific chiral recognition of various biological species including aminoacids. The utilisation of chiral stabilisers also allowed the preparation of new water soluble white emitting CdS nano-tetrapods, which demonstrated circular dichroism in the band-edge region of the spectrum. Biological testing of chiral CdS nanotetrapods displayed a chiral bias for an uptake of the D- penicillamine stabilised nano-tetrapods by cancer cells. It is expected that this research will open new horizons in the chemistry of chiral nanomaterials and their application in nanobiotechnology, medicine and optical chemo- and bio-sensing.

  2. Optically active quantum-dot molecules.

    PubMed

    Shlykov, Alexander I; Baimuratov, Anvar S; Baranov, Alexander V; Fedorov, Anatoly V; Rukhlenko, Ivan D

    2017-02-20

    Chiral molecules made of coupled achiral semiconductor nanocrystals, also known as quantum dots, show great promise for photonic applications owing to their prospective uses as configurable building blocks for optically active structures, materials, and devices. Here we present a simple model of optically active quantum-dot molecules, in which each of the quantum dots is assigned a dipole moment associated with the fundamental interband transition between the size-quantized states of its confined charge carriers. This model is used to analytically calculate the rotatory strengths of optical transitions occurring upon the excitation of chiral dimers, trimers, and tetramers of general configurations. The rotatory strengths of such quantum-dot molecules are found to exceed the typical rotatory strengths of chiral molecules by five to six orders of magnitude. We also study how the optical activity of quantum-dot molecules shows up in their circular dichroism spectra when the energy gap between the molecular states is much smaller than the states' lifetime, and maximize the strengths of the circular dichroism peaks by optimizing orientations of the quantum dots in the molecules. Our analytical results provide clear design guidelines for quantum-dot molecules and can prove useful in engineering optically active quantum-dot supercrystals and photonic devices.

  3. Quantum dots as active material for quantum cascade lasers: comparison to quantum wells

    NASA Astrophysics Data System (ADS)

    Michael, Stephan; Chow, Weng W.; Schneider, Hans Christian

    2016-03-01

    We review a microscopic laser theory for quantum dots as active material for quantum cascade lasers, in which carrier collisions are treated at the level of quantum kinetic equations. The computed characteristics of such a quantum-dot active material are compared to a state-of-the-art quantum-well quantum cascade laser. We find that the current requirement to achieve a comparable gain-length product is reduced compared to that of the quantum-well quantum cascade laser.

  4. Quantum Dots

    NASA Astrophysics Data System (ADS)

    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

  5. Reconfigurable Optical Elements Based on Single and Coupled Microdisk Resonators with Quantum Dot Active Media

    DTIC Science & Technology

    2009-08-31

    established above. One of the key components in this architecture is the integration of active waveguide consisting of colloidal quantum dots ( CdSe / ZnS ...microdisk resonators. In both configurations CdSe core-shell quantum dots were used as active gain media. Results of our theoretical efforts at understanding...microdisk resonators. In both configurations CdSe core-shell quantum dots (QDs) were used as active gain media. In Section 2, we discuss our

  6. Activation of molecular catalysts using semiconductor quantum dots

    DOEpatents

    Meyer, Thomas J [Chapel Hill, NC; Sykora, Milan [Los Alamos, NM; Klimov, Victor I [Los Alamos, NM

    2011-10-04

    Photocatalytic materials based on coupling of semiconductor nanocrystalline quantum dots (NQD) and molecular catalysts. These materials have capability to drive or catalyze non-spontaneous chemical reactions in the presence of visible radiation, ultraviolet radiation, or both. The NQD functions in these materials as a light absorber and charge generator. Following light absorption, the NQD activates a molecular catalyst adsorbed on the surface of the NQD via transfer of one or more charges (either electrons or electron-holes) from the NQD to the molecular catalyst. The activated molecular catalyst can then drive a chemical reaction. A photoelectrolytic device that includes such photocatalytic materials is also described.

  7. A self-assembled quantum dot probe for detecting {beta}-lactamase activity

    SciTech Connect

    Xu Chenjie; Xing Bengang; Rao Jianghong . E-mail: jrao@stanford.edu

    2006-06-09

    This communication describes a quantum dot probe that can be activated by a reporter enzyme, {beta}-lactamase. Our design is based on the principle of fluorescence resonance energy transfer (FRET). A biotinylated {beta}-lactamase substrate was labeled with a carbocyanine dye, Cy5, and immobilized on the surface of quantum dots through the binding of biotin to streptavidin pre-coated on the quantum dots. In assembling this nanoprobe, we have found that both the distance between substrates and the quantum dot surface, and the density of substrates are important for its function. The fluorescence emission from quantum dots can be efficiently quenched (up to 95%) by Cy5 due to FRET. Our final quantum dot probe, assembled with QD605 and 1:1 mixture of biotin and a Cy5-labeled lactam, can be activated by 32 {mu}g/mL of {beta}-lactamase with 4-fold increase in the fluorescence emission.

  8. Optically active quantum dots in monolayer WSe2

    NASA Astrophysics Data System (ADS)

    Srivastava, Ajit; Sidler, Meinrad; Allain, Adrien V.; Lembke, Dominik S.; Kis, Andras; Imamoğlu, A.

    2015-06-01

    Semiconductor quantum dots have emerged as promising candidates for the implementation of quantum information processing, because they allow for a quantum interface between stationary spin qubits and propagating single photons. In the meantime, transition-metal dichalcogenide monolayers have moved to the forefront of solid-state research due to their unique band structure featuring a large bandgap with degenerate valleys and non-zero Berry curvature. Here, we report the observation of zero-dimensional anharmonic quantum emitters, which we refer to as quantum dots, in monolayer tungsten diselenide, with an energy that is 20-100 meV lower than that of two-dimensional excitons. Photon antibunching in second-order photon correlations unequivocally demonstrates the zero-dimensional anharmonic nature of these quantum emitters. The strong anisotropic magnetic response of the spatially localized emission peaks strongly indicates that radiative recombination stems from localized excitons that inherit their electronic properties from the host transition-metal dichalcogenide. The large ˜1 meV zero-field splitting shows that the quantum dots have singlet ground states and an anisotropic confinement that is most probably induced by impurities or defects. The possibility of achieving electrical control in van der Waals heterostructures and to exploit the spin-valley degree of freedom renders transition-metal-dichalcogenide quantum dots interesting for quantum information processing.

  9. Quantum dot display enhances activity of a phosphotriesterase trimer.

    PubMed

    Breger, Joyce C; Walper, Scott A; Oh, Eunkeu; Susumu, Kimihiro; Stewart, Michael H; Deschamps, Jeffrey R; Medintz, Igor L

    2015-04-14

    Phosphotriesterase was engineered into a spontaneously forming trimer by appending it to a synthetic collagen-like triple-helix motif. Enzymatic hydrolysis of the insecticide and organophosphate nerve agent simulant paraoxon was then examined. Assembling the phosphotriesterase trimer onto semiconductor quantum dots increased the enzyme's catalytic rate and efficiency.

  10. Evaluation of biological activity of quantum dots in a microsystem.

    PubMed

    Grabowska-Jadach, Ilona; Haczyk, Maja; Drozd, Marcin; Fischer, Agnieszka; Pietrzak, Mariusz; Malinowska, Elżbieta; Brzózka, Zbigniew

    2016-02-01

    The presented work aimed at systematic investigation of biological activity of CdSex S1- x /ZnS and CdSe/ZnS quantum dots (QDs), whose surface was modified with different ligands. For these studies, we used a microfluidic system combined with fluorescence microscopy techniques, which enabled analysis of cells' morphology, viability, and QDs uptake. PDMS and glass-based microfluidic system enabled the precise control of the cell environment, allowed to examine five replications of each tested QDs concentrations (statistically significant number), monitor multiple cellular events, and avoid manual preparation of QDs dilutions. We investigated the influence of the core composition and the type of surface modifiers on QDs toxicity. We also determined whether the examined nanoparticles penetrate into the cells. For all tested nanoparticles, the decrease of cells' viability was observed when increasing nanoparticles concentration. The decrease of live cells' number in microchambers and the accumulation of the nanoparticles around cultured cells were observed. The effect of hydrocarbon chain length of surface modifiers and QDs core composition on the cell viability was confirmed in our tests.

  11. Quantum dot-NBD-liposome luminescent probes for monitoring phospholipase A2 activity.

    PubMed

    Kethineedi, Venkata R; Crivat, Georgeta; Tarr, Matthew A; Rosenzweig, Zeev

    2013-12-01

    In this paper we describe the fabrication and characterization of new liposome encapsulated quantum dot-fluorescence resonance energy transfer (FRET)-based probes for monitoring the enzymatic activity of phospholipase A2. To fabricate the probes, luminescent CdSe/ZnS quantum dots capped with trioctylphosphine oxide (TOPO) ligands were incorporated into the lipid bilayer of unilamellar liposomes with an average diameter of approximately 100 nm. Incorporating TOPO capped quantum dots in liposomes enabled their use in aqueous solution while maintaining their hydrophobicity and excellent photophysical properties. The phospholipid bilayer was labeled with the fluorophore NBD C6-HPC (2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl-1-hexa decanoyl-sn-glycero-3-phosphocholine). The luminescent quantum dots acted as FRET donors and the NBD dye molecules acted as FRET acceptors. The probe response was based on FRET interactions between the quantum dots and the NBD dye molecules. The NBD dye molecules were cleaved and released to the solution in the presence of the enzyme phospholipase A2. This led to an increase of the luminescence of the quantum dots and to a corresponding decrease in the fluorescence of the NBD molecules, because of a decrease in FRET efficiency between the quantum dots and the NBD dye molecules. Because the quantum dots were not attached covalently to the phospholipids, they did not hinder the enzyme activity as a result of steric effects. The probes were able to detect amounts of phospholipase A2 as low as 0.0075 U mL(-1) and to monitor enzyme activity in real time. The probes were also used to screen phospholipase A2 inhibitors. For example, we found that the inhibition efficiency of MJ33 (1-hexadecyl-3-(trifluoroethyl)-sn-glycero-2-phosphomethanol) was higher than that of OBAA (3-(4-octadecyl)benzoylacrylic acid).

  12. Evidence of thermally activated transfer of excited carriers between CdSe/ZnSe quantum dots

    NASA Astrophysics Data System (ADS)

    Zhang, X. B.; Ha, K. L.; Hark, S. K.

    2001-10-01

    Temperature dependent photoluminescence and cathodoluminescence of selfassembled CdSe/ZnSe quantum dots grown by metalorganic vapor phase deposition were investigated. We found an unusual large red shift and a narrowing of the photoluminescence peak with temperature increases. Cathodoluminescence studies of a small number of quantum dots showed that the broad peak observed in the photoluminescence spectra is, in fact, made up of a series of narrower peaks, coming from quantum dots of different sizes. While the intensity of luminescence from small dots drops monotonously with temperature rises, that from the large dots displays a peculiar behavior. It actually increases within the temperature range of 140 170 K, the same range in which the photoluminescence peak shows narrowing. The simultaneous increase of luminescence from some quantum dots and decrease from others are believed to be responsible for the red shift and narrowing of the observed photoluminescence peak. A simple analytically solvable rate equation model was used to understand the spectral data. We suggest that the unusual behaviors observed can be understood as resulting from a transfer of thermally activated carriers from small to large quantum dots.

  13. Quantum Dots: Theory

    SciTech Connect

    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.

  14. Optical activity of helical quantum-dot supercrystals

    NASA Astrophysics Data System (ADS)

    Baimuratov, A. S.; Tepliakov, N. V.; Gun'ko, Yu. K.; Baranov, A. V.; Federov, A. V.; Rukhlenko, I. D.

    2017-01-01

    The size of chiral nanoparticles is much smaller than the optical wavelength. As a result, the difference in interaction of enantiomers with circularly polarized light of different handedness is practically unobservable. Due to the large mismatch in scale, the problem of enhancement of enantioselectivity of optical properties of nanoparticles is particularly important for modern photonics. In this work, we show that ordering of achiral nanoparticles into a chiral supercrystal with dimensions comparable to the wavelength of light allows achieving nearly total dissymmetry of optical absorption and demonstrate this using a helical super-crystal made of semiconductor quantum dots as an example. The proposed approach may find numerous applications in various optical and analytical methods used in biomedicine, chemistry, and pharmacology.

  15. An integrated study on antimicrobial activity and ecotoxicity of quantum dots and quantum dots coated with the antimicrobial peptide indolicidin.

    PubMed

    Galdiero, Emilia; Siciliano, Antonietta; Maselli, Valeria; Gesuele, Renato; Guida, Marco; Fulgione, Domenico; Galdiero, Stefania; Lombardi, Lucia; Falanga, Annarita

    This study attempts to evaluate the antimicrobial activity and the ecotoxicity of quantum dots (QDs) alone and coated with indolicidin. To meet this objective, we tested the level of antimicrobial activity on Gram-positive and Gram-negative bacteria, and we designed an ecotoxicological battery of test systems and indicators able to detect different effects using a variety of end points. The antibacterial activity was analyzed against Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (ATCC 1025), Escherichia coli (ATCC 11229), and Klebsiella pneumoniae (ATCC 10031), and the results showed an improved germicidal action of QDs-Ind. Toxicity studies on Daphnia magna indicated a decrease in toxicity for QDs-Ind compared to QDs alone, lack of bioluminescence inhibition on Vibrio fisheri, and no mutations in Salmonella typhimurium TA 100. The comet assay and oxidative stress experiments performed on D. magna showed a genotoxic and an oxidative damage with a dose-response trend. Indolicidin retained its activity when bound to QDs. We observed an enhanced activity for QDs-Ind. The presence of indolicidin on the surface of QDs was able to decrease its QDs toxicity.

  16. An integrated study on antimicrobial activity and ecotoxicity of quantum dots and quantum dots coated with the antimicrobial peptide indolicidin

    PubMed Central

    Galdiero, Emilia; Siciliano, Antonietta; Maselli, Valeria; Gesuele, Renato; Guida, Marco; Fulgione, Domenico; Galdiero, Stefania; Lombardi, Lucia; Falanga, Annarita

    2016-01-01

    This study attempts to evaluate the antimicrobial activity and the ecotoxicity of quantum dots (QDs) alone and coated with indolicidin. To meet this objective, we tested the level of antimicrobial activity on Gram-positive and Gram-negative bacteria, and we designed an ecotoxicological battery of test systems and indicators able to detect different effects using a variety of end points. The antibacterial activity was analyzed against Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (ATCC 1025), Escherichia coli (ATCC 11229), and Klebsiella pneumoniae (ATCC 10031), and the results showed an improved germicidal action of QDs-Ind. Toxicity studies on Daphnia magna indicated a decrease in toxicity for QDs-Ind compared to QDs alone, lack of bioluminescence inhibition on Vibrio fisheri, and no mutations in Salmonella typhimurium TA 100. The comet assay and oxidative stress experiments performed on D. magna showed a genotoxic and an oxidative damage with a dose–response trend. Indolicidin retained its activity when bound to QDs. We observed an enhanced activity for QDs-Ind. The presence of indolicidin on the surface of QDs was able to decrease its QDs toxicity. PMID:27616887

  17. Quantum Dot Solar Cells

    NASA Technical Reports Server (NTRS)

    Raffaelle, Ryne P.; Castro, Stephanie L.; Hepp, Aloysius; Bailey, Sheila G.

    2002-01-01

    We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in the synthesis process. We will present XRD, TEM, SEM and EDS characterization of our initial attempts at fabricating these quantum dots. Investigation of the size distributions of these nanoparticles via laser light scattering and scanning electron microscopy will be presented. Theoretical estimates on appropriate quantum dot composition, size, and inter-dot spacing along with potential scenarios for solar cell fabrication will be discussed.

  18. Electron- and hole-related electrical activity of InAs/GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Kruszewski, P.; Dobaczewski, L.; Markevich, V. P.; Mitchell, C.; Missous, M.; Peaker, A. R.

    2007-12-01

    The electron- and hole-related electrical activity of the InAs/GaAs quantum dot system has been demonstrated with a use of the high-resolution Laplace and conventional DLTS methods combined with below GaAs bandgap illumination. Without the illumination, the DLTS signal refers to the emission process of electrons bound by the dot confining potential in the conduction band. In this experimental mode, single- and double-electron states of the dot could be observed. The resolution of the method allows both charge states of the dot to be observed in the same Laplace DLTS spectrum and thus the relative occupancy factor for both charge states can be determined. This gives the value of the Coulomb blockade energy (∼11 meV). When prior to the DLTS signal detection a short below-bandgap illumination resonant with the dot excitonic energy is applied, a non-equilibrium hole occupancy in the dot is created. This allows the same dots to be studied in order to establish the hole-referred electrical dot activity governed by the confining potential in the valence band.

  19. Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity.

    PubMed

    Kaur, Gurvir; Tripathi, S K

    2015-01-05

    The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent.

  20. Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity

    NASA Astrophysics Data System (ADS)

    Kaur, Gurvir; Tripathi, S. K.

    2015-01-01

    The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent.

  1. New quantum dot sensors

    NASA Astrophysics Data System (ADS)

    Gun'ko, Y. K.; Moloney, M. M.; Gallagher, S.; Govan, J.; Hanley, C.

    2010-04-01

    Quantum dots (QDs) are fluorescent semiconductor (e.g. II-VI) nanocrystals, which have a strong characteristic spectral emission. This emission is tunable to a desired energy by selecting variable particle size, size distribution and composition of the nanocrystals. QDs have recently attracted enormous interest due to their unique photophysical properties and range of potential applications in photonics and biochemistry. The main aim of our work is develop new chiral quantum dots (QDs) and establish fundamental principles influencing their structure, properties and biosensing behaviour. Here we present the synthesis and characterisation of chiral CdSe semiconductor nanoparticles and their utilisation as new chiral biosensors. Penicillamine stabilised CdSe nanoparticles have shown both very strong and very broad luminescence spectra. Circular dichroism (CD) spectroscopy studies have revealed that the D- and Lpenicillamine stabilised CdSe QDs demonstrate circular dichroism and possess almost identical mirror images of CD signals. Studies of photoluminescence and CD spectra have shown that there is a clear relationship between defect emission and CD activity. We have also demonstrated that these new QDs can serve as fluorescent nanosensors for various chiral biomolecules including nucleic acids. These novel nanosensors can be potentially utilized for detection of various chiral biological and chemical species with the broad range of potential applications.

  2. Specific detection of the cleavage activity of mycobacterial enzymes using a quantum dot based DNA nanosensor

    NASA Astrophysics Data System (ADS)

    Jepsen, Morten Leth; Harmsen, Charlotte; Godbole, Adwait Anand; Nagaraja, Valakunja; Knudsen, Birgitta R.; Ho, Yi-Ping

    2015-12-01

    We present a quantum dot based DNA nanosensor specifically targeting the cleavage step in the reaction cycle of the essential DNA-modifying enzyme, mycobacterial topoisomerase I. The design takes advantages of the unique photophysical properties of quantum dots to generate visible fluorescence recovery upon specific cleavage by mycobacterial topoisomerase I. This report, for the first time, demonstrates the possibility to quantify the cleavage activity of the mycobacterial enzyme without the pre-processing sample purification or post-processing signal amplification. The cleavage induced signal response has also proven reliable in biological matrices, such as whole cell extracts prepared from Escherichia coli and human Caco-2 cells. It is expected that the assay may contribute to the clinical diagnostics of bacterial diseases, as well as the evaluation of treatment outcomes.We present a quantum dot based DNA nanosensor specifically targeting the cleavage step in the reaction cycle of the essential DNA-modifying enzyme, mycobacterial topoisomerase I. The design takes advantages of the unique photophysical properties of quantum dots to generate visible fluorescence recovery upon specific cleavage by mycobacterial topoisomerase I. This report, for the first time, demonstrates the possibility to quantify the cleavage activity of the mycobacterial enzyme without the pre-processing sample purification or post-processing signal amplification. The cleavage induced signal response has also proven reliable in biological matrices, such as whole cell extracts prepared from Escherichia coli and human Caco-2 cells. It is expected that the assay may contribute to the clinical diagnostics of bacterial diseases, as well as the evaluation of treatment outcomes. Electronic supplementary information (ESI) available: Characterization of the QD-based DNA Nanosensor. See DOI: 10.1039/c5nr06326d

  3. Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor

    PubMed Central

    Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H. L.; Konstantatos, Gerasimos

    2016-01-01

    The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics. PMID:27311710

  4. Quantum optics in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Garrido, Mauricio

    Coupled quantum dots present an active field of study, both at the fundamental and applied level, due to their atomic and molecular-like energy structure and the ability to design and tune their parameters. Being single-photon emitters, they are systems that behave fully according to the laws of quantum mechanics. The work presented here involved the experimental study of the electro-optical properties of Indium Arsenide, coupled quantum dots. Initial experiments involved the use of spectroscopic methods such as photoluminescence and photoluminescence excitation (PLE). Through such techniques, the top dot's hole energy level structure was mapped and different types of resonant absorption were identified. The characterization of these excited states and the knowledge of how to resonantly excite into them is an integral part of the development of certain controlled spin gates in quantum computation. Additionally, a shift of the spectra in the electric field was observed with varying excitation wavelength through and above the wetting layer, which allowed for direct measurement of the optically-created electric field within the device. This extends the quantum dots' capabilities to using them as electric-field nano-probes and opens up the possibility of an all-optical, fast switching mechanism. In the course of these studies, a novel data visualization method for PLE in this type of system was developed. Finally, to study correlated photon effects, a Hanbury Brown - Twiss experiment was built which revealed bunching and antibunching signals typical of quantum statistics in biexciton cascade emissions. This is an important step towards the experimental investigation of entangled states in coupled quantum dots.

  5. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  6. Colloidal Double Quantum Dots.

    PubMed

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  7. PREFACE: Quantum Dot 2010

    NASA Astrophysics Data System (ADS)

    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

  8. Quantum Dot Sensitized Photoelectrodes

    PubMed Central

    Macdonald, Thomas J.; Nann, Thomas

    2011-01-01

    Quantum Dots (QDs) are promising alternatives to organic dyes as sensitisers for photocatalytic electrodes. This review article provides an overview of the current state of the art in this area. More specifically, different types of QDs with a special focus on heavy-metal free QDs and the methods for preparation and adsorption onto metal oxide electrodes (especially titania and zinc oxide) are discussed. Eventually, the key areas of necessary improvements are identified and assessed.

  9. Quantum transport in ballistic quantum dots

    NASA Astrophysics Data System (ADS)

    Ferry, D. K.; Akis, R. A.; Pivin, D. P., Jr.; Bird, J. P.; Holmberg, N.; Badrieh, F.; Vasileska, D.

    1998-10-01

    Carriers in small 3D quantum boxes take us from unintentional qquantum dots in MOSFETs (arising from the doping fluctuations) tto single-electron quantum dots in semiconductor hheterostructures. In between these two extremes are the realm of oopen, ballistic quantum dots, in which the transport can be quite regular. Several issues must be considered in treating the transport in these dots, among which are: (1) phase coherence within the dot; (2) the transition between semi-classical and fully quantum transport, (3) the role of the contacts, vis-à-vis the fabricated boundaries, and (4) the actual versus internal boundaries. In this paper, we discuss these issues, including the primary observables in experiment, the intrinsic nature of oscillatory behavior in magnetic field and dot size, and the connection to semi-classical transport emphasizing the importance of the filtering by the input (and output) quantum point contacts.

  10. Multiplex Detection of Protease Activity with Quantum Dot Nanosensors Prepared by Intein-Mediated Specific Bioconjugation

    PubMed Central

    Xia, Zuyong; Xing, Yun; So, Min-Kyung; Koh, Ai Leen; Sinclair, Robert; Rao, Jianghong

    2009-01-01

    We report here a protease sensing nanoplatform based on semiconductor nanocrystals or quantum dots (QDs) and bioluminescence resonance energy transfer (QD-BRET) to detect the protease activity in complex biological samples. These nanosensors consist of bioluminescent proteins as the BRET donor, quantum dots as the BRET acceptor, and protease substrates sandwiched between the two as a sensing group. An intein-mediated conjugation strategy was developed for site-specific conjugation of proteins to QDs in preparing these QD nanosensors. In this traceless ligation, the intein itself is spliced out and excluded from the final conjugation product. With this method, we have synthesized a series of QD nanosensors for highly sensitive detection of an important class of protease matrix metalloproteinase (MMP) activity. We demonstrated that these nanosensors can detect the MMP activity in buffers and in mouse serum with the sensitivity to a few ng/ml, and secreted proteases by tumor cells. The suitability of these nanosensors for a multiplex protease assay has also been shown. PMID:18922019

  11. Quantum Dot Spins and Photons

    NASA Astrophysics Data System (ADS)

    Atature, Mete

    2012-02-01

    Self-assembled semiconductor quantum dots are interesting and rich physical systems. Their inherently mesoscopic nature leads to a multitude of interesting interaction mechanisms of confined spins with the solid state environment of spins, charges and phonons. In parallel, the relatively clean spin-dependent optical transitions make quantum dots strong candidates for stationary and flying qubits within the context of spin-based quantum information science. The recently observed quantum dot resonance fluorescence has become a key enabler for further progress in this context. I will first discuss the real-time optical detection (or single-shot readout) of quantum dot spins, and then I will discuss how resonance fluorescence allows coherent generation of single photons suitable (and tailored) for linear-optics quantum computation and for establishing a high-efficiency spin-photon quantum interface within a distributed quantum network.

  12. Scanning Quantum Dot Microscopy

    NASA Astrophysics Data System (ADS)

    Wagner, Christian; Green, Matthew F. B.; Leinen, Philipp; Deilmann, Thorsten; Krüger, Peter; Rohlfing, Michael; Temirov, Ruslan; Tautz, F. Stefan

    2015-07-01

    We introduce a scanning probe technique that enables three-dimensional imaging of local electrostatic potential fields with subnanometer resolution. Registering single electron charging events of a molecular quantum dot attached to the tip of an atomic force microscope operated at 5 K, equipped with a qPlus tuning fork, we image the quadrupole field of a single molecule. To demonstrate quantitative measurements, we investigate the dipole field of a single metal adatom adsorbed on a metal surface. We show that because of its high sensitivity the technique can probe electrostatic potentials at large distances from their sources, which should allow for the imaging of samples with increased surface roughness.

  13. Single active-layer structured dual-function devices using hybrid polymer-quantum dots.

    PubMed

    Son, Dong-Ick; Park, Dong-Hee; Ie, Sang-Yub; Choi, Won-Kook; Choi, Ji-Won; Li, Fushan; Kim, Tae-Whan

    2008-10-01

    We demonstrate hybrid polymer-quantum dot dual-function devices with a single active-layer structure consisting of CdSe/ZnS semiconductor quantum dots dispersed with poly N-vinylcarbazole (PVK) and 1,3,5-tirs-(N-phenylbenzimidazol-2-yl) benzene (TPBi) fabricated on an indium-tin-oxide (ITO)/glass substrate by using a simple spin-coating technique. The dual-function devices are composed of light-emitting diodes (LED) on the top side and nonvolatile organic bistable memory devices (OBD) on the bottom side and can show electroluminescence (EL) along with electrical bistability concurrently. Both the functionality of LEDs and OBDs can be successfully achieved by adding an electron transport layer (ETL) TPBi to the OBD to attain an LED in which the lowest unoccupied molecular orbital (LUMO) level of TPBi is positioned at the energy level between the conduction band of CdSe/ZnS and the LiF/Al electrode. Through transmission electron microscopy (TEM) study, it is revealed that CdSe/ZnS QDs distributed on the interface of the hole transport layer (HTL) and ETL significantly take part in the electroluminescence process rather than those existing at the outer surface of the ETL.

  14. Interrogating the signaling dynamics of T cell activation with quantum dots

    NASA Astrophysics Data System (ADS)

    Warnement, Michael R.; Faley, Shannon L.; Wikswo, John P.; Rosenthal, Sandra J.

    2006-02-01

    We report the use of antibody-conjugated quantum dots (QDs) to monitor the expression dynamics of the membrane bound cytokine receptor interleukin-2 receptor-α (IL-2Rα) throughout the course of Jurkat T cell activation. Maximal receptor expression is observed 32-48 hours after activation, followed by a sharp decrease subsequent to 48 hours consistent with IL-2R internalization. Fluorescence microscopy, ELISA, and FACS analyses were used to verify controlled activation and specificity of QD labeling. Additionally, confocal microscopy demonstrated receptor internalization subsequent to expression and QD labeling. Antibody-conjugated QDs provide a convenient means to rapidly determine cell state and interrogate end products of cell signaling pathways. Interrogation of other signaling pathways can eventually be carried out in a similar manner upon identification of relevant membrane associated receptors. Ultimately, the multiplexing capabilities of QDs will allow the examination of several signaling pathways simultaneously and aid in toxin detection and discrimination.

  15. Zn(II)-Coordinated Quantum Dot-FRET Nanosensors for the Detection of Protein Kinase Activity

    PubMed Central

    Lim, Butaek; Park, Ji-In; Lee, Kyung Jin; Lee, Jin-Won; Kim, Tae-Wuk; Kim, Young-Pil

    2015-01-01

    We report a simple detection of protein kinase activity using Zn(II)-mediated fluorescent resonance energy transfer (FRET) between quantum dots (QDs) and dye-tethered peptides. With neither complex chemical ligands nor surface modification of QDs, Zn(II) was the only metal ion that enabled the phosphorylated peptides to be strongly attached on the carboxyl groups of the QD surface via metal coordination, thus leading to a significant FRET efficiency. As a result, protein kinase activity in intermixed solution was efficiently detected by QD-FRET via Zn(II) coordination, especially when the peptide substrate was combined with affinity-based purification. We also found that mono- and di-phosphorylation in the peptide substrate could be discriminated by the Zn(II)-mediated QD-FRET. Our approach is expected to find applications for studying physiological function and signal transduction with respect to protein kinase activity. PMID:26213934

  16. Sensitive fluorimetric assays for α-glucosidase activity and inhibitor screening based on β-cyclodextrin-coated quantum dots.

    PubMed

    Liu, Si-Yao; Wang, Huan; He, Tian; Qi, Liang; Zhang, Zhi-Qi

    2016-02-01

    A fluorescence method was established for a α-glucosidase activity assay and inhibitor screening based on β-cyclodextrin-coated quantum dots. p-Nitrophenol, the hydrolysis product of the α-glucosidase reaction, could quench the fluorescence of β-cyclodextrin-coated quantum dots via an electron transfer process, leading to fluorescence turn-off, whereas the fluorescence of the system turned on in the presence of α-glucosidase inhibitors. Taking advantage of the excellent properties of quantum dots, this method provided a very simple, rapid and sensitive screening method for α-glucosidase inhibitors. Two α-glucosidase inhibitors, 2,4,6-tribromophenol and acarbose, were used to evaluate the feasibility of this screening model, and IC50 values of 24 μM and 0.55 mM were obtained respectively, which were lower than those previously reported. The method may have potential application in screening α-glucosidase inhibitors.

  17. Efficient quantum dot-quantum dot and quantum dot-dye energy transfer in biotemplated assemblies.

    PubMed

    Achermann, Marc; Jeong, Sohee; Balet, Laurent; Montano, Gabriel A; Hollingsworth, Jennifer A

    2011-03-22

    CdSe semiconductor nanocrystal quantum dots are assembled into nanowire-like arrays employing microtubule fibers as nanoscale molecular "scaffolds." Spectrally and time-resolved energy-transfer analysis is used to assess the assembly of the nanoparticles into the hybrid inorganic biomolecular structure. Specifically, we demonstrate that a comprehensive study of energy transfer between quantum dot pairs on the biotemplate and, alternatively, between quantum dots and molecular dyes embedded in the microtubule scaffold comprises a powerful spectroscopic tool for evaluating the assembly process. In addition to revealing the extent to which assembly has occurred, the approach allows determination of particle-to-particle (and particle-to-dye) distances within the biomediated array. Significantly, the characterization is realized in situ, without need for further sample workup or risk of disturbing the solution-phase constructs. Furthermore, we find that the assemblies prepared in this way exhibit efficient quantum dot-quantum dot and quantum dot-dye energy transfer that affords faster energy-transfer rates compared to densely packed quantum dot arrays on planar substrates and to small-molecule-mediated quantum dot-dye couples, respectively.

  18. Enhanced Photocatalytic Activity of the Carbon Quantum Dot-Modified BiOI Microsphere

    NASA Astrophysics Data System (ADS)

    Chen, Yuan; Lu, Qiuju; Yan, Xuelian; Mo, Qionghua; Chen, Yun; Liu, Bitao; Teng, Liumei; Xiao, Wei; Ge, Liangsheng; Wang, Qinyi

    2016-02-01

    Novel carbon quantum dot (CQD)-modified BiOI photocatalysts were prepared via a facile hydrothermal process. The CQD-modified BiOI materials were characterized by multiple techniques. The CQD with an average size around several nanometers was distributed on the surface of BiOI microsphere. Its photocatalytic activity was investigated sufficiently by the photodegradation of methylene orange (MO). The results showed that the CQD/BiOI 1.5 wt.% sample exhibited the optimum photocatalytic activity, which was 2.5 times that of the pure BiOI. This improvement was attributed to the crucial role of CQDs, which could be acted as a photocenter for absorbing solar light, charge separation center for suppressing charge recombination.

  19. Low Threshold Quantum Dot Lasers.

    PubMed

    Iyer, Veena Hariharan; Mahadevu, Rekha; Pandey, Anshu

    2016-04-07

    Semiconductor quantum dots have replaced conventional inorganic phosphors in numerous applications. Despite their overall successes as emitters, their impact as laser materials has been severely limited. Eliciting stimulated emission from quantum dots requires excitation by intense short pulses of light typically generated using other lasers. In this Letter, we develop a new class of quantum dots that exhibit gain under conditions of extremely low levels of continuous wave illumination. We observe thresholds as low as 74 mW/cm(2) in lasers made from these materials. Due to their strong optical absorption as well as low lasing threshold, these materials could possibly convert light from diffuse, polychromatic sources into a laser beam.

  20. Ferredoxin:NADP+ oxidoreductase in junction with CdSe/ZnS quantum dots: characteristics of an enzymatically active nanohybrid.

    PubMed

    Szczepaniak, Krzysztof; Worch, Remigiusz; Grzyb, Joanna

    2013-05-15

    Ferredoxin:NADP(+) oxidoreductase (FNR) is a plant and cyanobacterial photosynthetic enzyme, also found in non-photosynthetic tissues, where it is involved in redox reactions of biosynthetic pathways. In vivo it transfers electrons to nicotinamide adenine dinucleotide phosphate (NADP(+)), forming its reduced version, NADPH, while in vitro it can also use NADPH to reduce several substrates, such as ferricyanide, various quinones and nitriles. As an oxidoreductase catalyzing reaction of a broad range of substrates, FNR may be used in biotechnological processes. Quantum dots are semiconductor nanocrystals of a few to several nanometers diameter, having very useful luminescent properties. We present the spectroscopic and functional characteristics of a covalent conjugation of FNR and CdSe/ZnS quantum dots. Two types of quantum dots, of different diameter and emission maximum (550 and 650 nm), were used for comparison. Steady-state fluorescence and gel electrophoresis confirmed efficient conjugation, while fluorescence correlation spectroscopy (FCS) allowed for determination of the conjugates' radii. The nanohybrids sustained enzymatic activity; however, changes in maximal reaction rates and Michaelis constant were found. Detailed analysis of the kinetic parameters showed that the changes in the enzyme activity depend on the substrate used for activity measurement but also on the size of the quantum dots. The presented nanohybrids, as the first example using plant and photosynthetic enzyme as a protein partner, may became a tool to study photosynthesis as well as other biosynthetic and biotechnological processes, involving enzymatically catalyzed electron transfer.

  1. Positioning of quantum dots on metallic nanostructures.

    PubMed

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

    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)(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.

  2. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    SciTech Connect

    Michael, Stephan; Chow, Weng; Schneider, Hans

    2016-05-01

    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. We study the influence of two important quantum-dot material parameters, here, 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. 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. Hydrophobin-Encapsulated Quantum Dots.

    PubMed

    Taniguchi, Shohei; Sandiford, Lydia; Cooper, Maggie; Rosca, Elena V; Ahmad Khanbeigi, Raha; Fairclough, Simon M; Thanou, Maya; Dailey, Lea Ann; Wohlleben, Wendel; von Vacano, Bernhard; de Rosales, Rafael T M; Dobson, Peter J; Owen, Dylan M; Green, Mark

    2016-02-01

    The phase transfer of quantum dots to water is an important aspect of preparing nanomaterials that are suitable for biological applications, and although numerous reports describe ligand exchange, very few describe efficient ligand encapsulation techniques. In this report, we not only report a new method of phase transferring quantum dots (QDs) using an amphiphilic protein (hydrophobin) but also describe the advantages of using a biological molecule with available functional groups and their use in imaging cancer cells in vivo and other imaging applications.

  4. Patterned semiconductor inverted quantum dot photonic devices

    NASA Astrophysics Data System (ADS)

    Coleman, J. J.

    2016-03-01

    A novel inverted quantum dot structure is presented, which consists of an InGaAs quantum well that has been periodically perforated and then filled with the higher bandgap GaAs barrier material. This structure exhibits a unique quantized energy structure something like a planar atomic bond structure and formation of allowed and forbidden energy bands instead of highly localized, fully discrete states. We describe the growth, processing and characteristics of inverted quantum dot structures and outline interesting and potentially important effects arising from the introduction of nanoscale features (<50 nm) in the active medium.

  5. Nanocrystal quantum dot-conjugated anti-myeloperoxidase antibody as the detector of activated neutrophils.

    PubMed

    Hoshino, Akiyoshi; Nagao, Tomokazu; Nakasuga, Akira; Ishida-Okawara, Akiko; Suzuki, Kazuo; Yasuhara, Masato; Yamamoto, Kenji

    2007-12-01

    Fluorescent nanocrystal quantum dots (QDs) have been applied to a wide range of biological studies by taking advantage of their fluorescence properties. Here we show that QDs conjugated with antibody against neutrophil peroxidase, myeloperoxidase (MPO). We designed a novel method to conjugate QDs to antibody without losing any antibody function including their antigen recognizing and Fc-receptor binding activities. When we applied anti-MPO antibody (Ab) with conventional organic probes in the case of immunostaining of living cells, the antibodies lost their fluorescence because of MPO enzymic activity to produce reactive oxygen species. Our QD-conjugated anti-MPO (alpha-MPO-QDs) can detect MPO on the surface of activated neutrophils. In addition, anti-MPO-QDs did not react to the inactivated neutrophils. In conclusion, we demonstrated that antibody visualized the expression of MPO on the neutrophil surface after stimulation with proinflammatory cytokines. Taken together, these techniques have the possibility that QDs can reveal the activation of neutrophils by immunostaining and flow cytometric analysis as a powerful tool for diagnosis of the neutrophil activation in vitro.

  6. Quantum dot based enzyme activity sensors present deviations from Michaelis-Menten kinetic model

    NASA Astrophysics Data System (ADS)

    Díaz, Sebastián. A.; Brown, Carl W.; Malanoski, Anthony P.; Oh, Eunkeu; Susumu, Kimihiro; Medintz, Igor L.

    2016-03-01

    Nanosensors employing quantum dots (QDs) and enzyme substrates with fluorescent moieties offer tremendous promise for disease surveillance/diagnostics and as high-throughput co-factor assays. Advantages of QDs over other nanoscaffolds include their small size and inherent photochemical properties such as size tunable fluorescence, ease in attaching functional moieties, and resistance to photobleaching. These properties make QDs excellent Förster Resonance Energy Transfer (FRET) donors; well-suited for rapid, optical measurement applications. We report enzyme sensors designed with a single FRET donor, the QD donor acting as a scaffold to multiple substrates or acceptors. The QD-sensor follows the concrete activity of the enzyme, as compared to the most common methodologies that quantify the enzyme amount or its mRNA precursor. As the sensor reports on the enzyme activity in real-time we can actively follow the kinetics of the enzyme. Though classic Michaelis-Menten (MM) parameters can be obtained to describe the activity. In the course of these experiments deviations, both decreasing and increasing the kinetics, from the common MM model were observed upon close examinations. From these observations additional experiments were undertaken to understand the varying mechanisms. Different enzymes can present different deviations depending on the chosen target, e.g. trypsin appears to present a positive hopping mechanism while collagenase demonstrates a QD caused reversible inhibition.

  7. Multifunctional Concentric FRET-Quantum Dot Probes for Tracking and Imaging of Proteolytic Activity.

    PubMed

    Massey, Melissa; Li, Jia Jun; Algar, W Russ

    2017-01-01

    Proteolysis has many important roles in physiological regulation. It is involved in numerous cell signaling processes and the pathogenesis of many diseases, including cancers. Methods of visualizing and assaying proteolytic activity are therefore in demand. Förster resonance energy transfer (FRET) probes offer several advantages in this respect. FRET supports end-point or real-time measurements, does not require washing or separation steps, and can be implemented in various assay or imaging formats. In this chapter, we describe methodology for preparing self-assembled concentric FRET (cFRET) probes for multiplexed tracking and imaging of proteolytic activity. The cFRET probe comprises a green-emitting semiconductor quantum dot (QD) conjugated with multiple copies of two different peptide substrates for two target proteases. The peptide substrates are labeled with different fluorescent dyes, Alexa Fluor 555 and Alexa Fluor 647, and FRET occurs between the QD and both dyes, as well as between the two dyes. This design enables a single QD probe to track the activity of two proteases simultaneously. Fundamental cFRET theory is presented, and procedures for using the cFRET probe for quantitative measurement of the activity of two model proteases are given, including calibration, fluorescence plate reader or microscope imaging assays, and data analysis. Sufficient detail is provided for other researchers to adapt this method to their specific requirements and proteolytic systems of interest.

  8. Near-infrared light controlled photocatalytic activity of carbon quantum dots for highly selective oxidation reaction

    NASA Astrophysics Data System (ADS)

    Li, Haitao; Liu, Ruihua; Lian, Suoyuan; Liu, Yang; Huang, Hui; Kang, Zhenhui

    2013-03-01

    Selective oxidation of alcohols is a fundamental and significant transformation for the large-scale production of fine chemicals, UV and visible light driven photocatalytic systems for alcohol oxidation have been developed, however, the long wavelength near infrared (NIR) and infrared (IR) light have not yet fully utilized by the present photocatalytic systems. Herein, we reported carbon quantum dots (CQDs) can function as an effective near infrared (NIR) light driven photocatalyst for the selective oxidation of benzyl alcohol to benzaldehyde. Based on the NIR light driven photo-induced electron transfer property and its photocatalytic activity for H2O2 decomposition, this metal-free catalyst could realize the transformation from benzyl alcohol to benzaldehyde with high selectivity (100%) and conversion (92%) under NIR light irradiation. HO&z.rad; is the main active oxygen specie in benzyl alcohol selective oxidative reaction confirmed by terephthalic acid photoluminescence probing assay (TA-PL), selecting toluene as the substrate. Such metal-free photocatalytic system also selectively converts other alcohol substrates to their corresponding aldehydes with high conversion, demonstrating a potential application of accessing traditional alcohol oxidation chemistry.Selective oxidation of alcohols is a fundamental and significant transformation for the large-scale production of fine chemicals, UV and visible light driven photocatalytic systems for alcohol oxidation have been developed, however, the long wavelength near infrared (NIR) and infrared (IR) light have not yet fully utilized by the present photocatalytic systems. Herein, we reported carbon quantum dots (CQDs) can function as an effective near infrared (NIR) light driven photocatalyst for the selective oxidation of benzyl alcohol to benzaldehyde. Based on the NIR light driven photo-induced electron transfer property and its photocatalytic activity for H2O2 decomposition, this metal-free catalyst could realize

  9. Extracellular biosynthesis of CdTe quantum dots by the fungus Fusarium oxysporum and their anti-bacterial activity

    NASA Astrophysics Data System (ADS)

    Syed, Asad; Ahmad, Absar

    2013-04-01

    The growing demand for semiconductor [quantum dots (Q-dots)] nanoparticles has fuelled significant research in developing strategies for their synthesis and characterization. They are extensively investigated by the chemical route; on the other hand, use of microbial sources for biosynthesis witnessed the highly stable, water dispersible nanoparticles formation. Here we report, for the first time, an efficient fungal-mediated synthesis of highly fluorescent CdTe quantum dots at ambient conditions by the fungus Fusarium oxysporum when reacted with a mixture of CdCl2 and TeCl4. Characterization of these biosynthesized nanoparticles was carried out by different techniques such as Ultraviolet-visible (UV-Vis) spectroscopy, Photoluminescence (PL), X-ray Diffraction (XRD), X-ray Photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and Fourier Transformed Infrared Spectroscopy (FTIR) analysis. CdTe nanoparticles shows antibacterial activity against Gram positive and Gram negative bacteria. The fungal based fabrication provides an economical, green chemistry approach for production of highly fluorescent CdTe quantum dots.

  10. Thermally activated tunneling in porous silicon nanowires with embedded Si quantum dots

    NASA Astrophysics Data System (ADS)

    Rezvani, S. J.; Pinto, N.; Enrico, E.; D'Ortenzi, L.; Chiodoni, A.; Boarino, L.

    2016-03-01

    Electronic transport properties of porous Si nanowires either with embedded Si quantum dots or with a percolative crystalline path are studied as a function of the temperature for the first time. We show that unlike bulk porous Si, the predesigned structure of the wires results in a single distinct conduction mechanism such as tunneling in the former case and variable range hopping in the latter case. We demonstrate that the geometry of the systems with a large internal surface area and high density of the Si quantum dots have a significant conduction enhancement compared to bulk porous silicon. These results can also improve the understanding of the basis of the different electronic transport mechanisms reported in bulk porous silicon.

  11. Proteolytic activity monitored by fluorescence resonance energy transfer through quantum-dot-peptide conjugates

    NASA Astrophysics Data System (ADS)

    Medintz, Igor L.; Clapp, Aaron R.; Brunel, Florence M.; Tiefenbrunn, Theresa; Tetsuo Uyeda, H.; Chang, Eddie L.; Deschamps, Jeffrey R.; Dawson, Philip E.; Mattoussi, Hedi

    2006-07-01

    Proteases are enzymes that catalyse the breaking of specific peptide bonds in proteins and polypeptides. They are heavily involved in many normal biological processes as well as in diseases, including cancer, stroke and infection. In fact, proteolytic activity is sometimes used as a marker for some cancer types. Here we present luminescent quantum dot (QD) bioconjugates designed to detect proteolytic activity by fluorescence resonance energy transfer. To achieve this, we developed a modular peptide structure which allowed us to attach dye-labelled substrates for the proteases caspase-1, thrombin, collagenase and chymotrypsin to the QD surface. The fluorescence resonance energy transfer efficiency within these nanoassemblies is easily controlled, and proteolytic assays were carried out under both excess enzyme and excess substrate conditions. These assays provide quantitative data including enzymatic velocity, Michaelis-Menten kinetic parameters, and mechanisms of enzymatic inhibition. We also screened a number of inhibitory compounds against the QD-thrombin conjugate. This technology is not limited to sensing proteases, but may be amenable to monitoring other enzymatic modifications.

  12. Alternative Patterning Process for Realization of Large-Area, Full-Color, Active Quantum Dot Display.

    PubMed

    Park, Joon-Suh; Kyhm, Jihoon; Kim, Hong Hee; Jeong, Shinyoung; Kang, JoonHyun; Lee, Song-Ee; Lee, Kyu-Tae; Park, Kisun; Barange, Nilesh; Han, JiYeong; Song, Jin Dong; Choi, Won Kook; Han, Il Ki

    2016-11-09

    Although various colloidal quantum dot (QD) coating and patterning techniques have been developed to meet the demands in optoelectronic applications over the past years, each of the previously demonstrated methods has one or more limitations and trade-offs in forming multicolor, high-resolution, or large-area patterns of QDs. In this study, we present an alternative QD patterning technique using conventional photolithography combined with charge-assisted layer-by-layer (LbL) assembly to solve the trade-offs of the traditional patterning processes. From our demonstrations, we show repeatable QD patterning process that allows multicolor QD patterns in both large-area and microscale. Also, we show that the QD patterns are robust against additional photolithography processes and that the thickness of the QD patterns can be controlled at each position. To validate that this process can be applied to actual device applications as an active material, we have fabricated inverted, differently colored, active QD light-emitting device (QD-LED) on a pixelated substrate, which achieved maximum electroluminescence intensity of 23 770 cd/m(2), and discussed the results. From our findings, we believe that our process provides a solution to achieving both high-resolution and large-scale QD pattern applicable to not only display, but also to practical photonic device research and development.

  13. Chiral Graphene Quantum Dots.

    PubMed

    Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; Qu, Zhi-Bei; Kim, Kyoungwon; Jiang, Shuang; Baumeister, Elizabeth; Lee, Jaewook; Yeom, Bongjun; Bahng, Joong Hwan; Lee, Jaebeom; Violi, Angela; Kotov, Nicholas A

    2016-02-23

    Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

  14. Probing cytoskeletal modulation of passive and active intracellular dynamics using nanobody-functionalized quantum dots

    PubMed Central

    Katrukha, Eugene A.; Mikhaylova, Marina; van Brakel, Hugo X.; van Bergen en Henegouwen, Paul M.; Akhmanova, Anna; Hoogenraad, Casper C.; Kapitein, Lukas C.

    2017-01-01

    The cytoplasm is a highly complex and heterogeneous medium that is structured by the cytoskeleton. How local transport depends on the heterogeneous organization and dynamics of F-actin and microtubules is poorly understood. Here we use a novel delivery and functionalization strategy to utilize quantum dots (QDs) as probes for active and passive intracellular transport. Rapid imaging of non-functionalized QDs reveals two populations with a 100-fold difference in diffusion constant, with the faster fraction increasing upon actin depolymerization. When nanobody-functionalized QDs are targeted to different kinesin motor proteins, their trajectories do not display strong actin-induced transverse displacements, as suggested previously. Only kinesin-1 displays subtle directional fluctuations, because the subset of microtubules used by this motor undergoes prominent undulations. Using actin-targeting agents reveals that F-actin suppresses most microtubule shape remodelling, rather than promoting it. These results demonstrate how the spatial heterogeneity of the cytoskeleton imposes large variations in non-equilibrium intracellular dynamics. PMID:28322225

  15. Nanoengineered InAs quantum dot active medium for laser diodes

    NASA Astrophysics Data System (ADS)

    Tokranov, Vadim E.; Yakimov, Michael; Katsnelson, Alex; Lamberti, Matthew; Agnello, Gabriel; Oktyabrsky, Serge

    2004-05-01

    Nanoengineering approach was used to develop an efficient active medium based on self-assembled InAs/GaAs quantum dots (QDs) for laser diodes operating at elevated temperatures. Photoluminescence (PL), transmission electron microscopy, and electroluminescence were used to study the influence of an overgrowth procedure on the properties of multiple-layer QDs. Optical properties of QDs were optimized by the adjustment of a GaAs overlayer thickness prior to a heating step, responsible for the truncation of the pyramid-shaped QDs. Triple-layer QD edge-emitting lasers with 1220 nm emitting wavelength exhibited a maximum saturated modal gain of 16 cm-1. To use truncated QD active medium for vertical cavity surface emitting lasers, seven layers of QDs with 20 nm of short period superlattice barriers between layers was developed. A wavelength of 1190 nm edge-emitting lasers with 120 nm total thickness 7xQDs active medium showed almost two times higher maximum saturated gain, 31 cm-1. Unfortunately, these lasers with closer distance between QD layers in active medium demonstrated stronger temperature dependence (with To = 110 K) of threshold current density and lasing wavelength. A record high characteristic temperature for lasing threshold, To = 380 K up to 55 C, was measured for edge-emitting laser diodes, which contained triple-layer truncated QD active medium. We believe that AlAs capping in combination with truncation procedure result in significant suppression of carrier transport between QDs within the layer as well as between QD layers.

  16. Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

    SciTech Connect

    Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan J.; Atatüre, Mete

    2014-10-27

    We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191 Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.

  17. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

    Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.

  18. Nanoscale quantum-dot supercrystals

    NASA Astrophysics Data System (ADS)

    Baimuratov, Anvar S.; Turkov, Vadim K.; Rukhlenko, Ivan D.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-09-01

    We develop a theory allowing one to calculate the energy spectra and wave functions of collective excitations in twoand three-dimensional quantum-dot supercrystals. We derive analytical expressions for the energy spectra of twodimensional supercrystals with different Bravias lattices, and use them to analyze the possibility of engineering the supercrystals' band structure. We demonstrate that the variation of the supercrystal's parameters (such as the symmetry of the periodic lattice and the properties of the quantum dots or their environment) enables an unprecedented control over its optical properties, thus paving a way towards the development of new nanophotonics materials.

  19. Intermolecular and intramolecular quencher based quantum dot nanoprobes for multiplexed detection of endonuclease activity and inhibition.

    PubMed

    Huang, Yong; Zhao, Shulin; Shi, Ming; Chen, Jia; Chen, Zhen-Feng; Liang, Hong

    2011-12-01

    DNA cleavage by endonucleases plays an important role in many biological events such as DNA replication, recombination, and repair and is used as a powerful tool in medicinal chemistry. However, conventional methods for assaying endonuclease activity and inhibition by gel electrophoresis and chromatography techniques are time-consuming, laborious, not sensitive, or costly. Herein, we combine the high specificity of DNA cleavage reactions with the benefits of quantum dots (QDs) and ultrahigh quenching abilities of inter- and intramolecular quenchers to develop highly sensitive and specific nanoprobes for multiplexed detection of endonucleases. The nanoprobe was prepared by conjugating two sets of DNA substrates carrying quenchers onto the surface of aminated QDs through direct assembly and DNA hybridization. With this new design, the background fluorescence was significantly suppressed by introducing inter- and intramolecular quenchers. When these nanoprobes are exposed to the targeted endonucleases, specific DNA cleavages occur and pieces of DNA fragments are released from the QD surface along with the quenchers, resulting in fluorescence recovery. The endonuclease activity was quantified by monitoring the change in the fluorescence intensity. The detection was accomplished with a single excitation light. Multiplexed detection was demonstrated by simultaneously assaying EcoRI and BamHI (as model analytes) using two different emissions of QDs. The limits of detection were 4.0 × 10(-4) U/mL for EcoRI and 8.0 × 10(-4) U/mL for BamHI, which were at least 100 times more sensitive than traditional gel electrophoresis and chromatography assays. Moreover, the potential application of the proposed method for screening endonuclease inhibitors has also been demonstrated. The assay protocol presented here proved to be simple, sensitive, effective, and easy to carry out.

  20. On the pH-dependent quenching of quantum dot photoluminescence by redox active dopamine.

    PubMed

    Ji, Xin; Palui, Goutam; Avellini, Tommaso; Na, Hyon Bin; Yi, Chongyue; Knappenberger, Kenneth L; Mattoussi, Hedi

    2012-04-04

    We investigated the charge transfer interactions between luminescent quantum dots (QDs) and redox active dopamine. For this, we used pH-insensitive ZnS-overcoated CdSe QDs rendered water-compatible using poly (ethylene glycol)-appended dihydrolipoic acid (DHLA-PEG), where a fraction of the ligands was amine-terminated to allow for controlled coupling of dopamine-isothiocyanate onto the nanocrystal. Using this sample configuration, we probed the effects of changing the density of dopamine and the buffer pH on the fluorescence properties of these conjugates. Using steady-state and time-resolved fluorescence, we measured a pronounced pH-dependent photoluminescence (PL) quenching for all QD-dopamine assemblies. Several parameters affect the PL loss. First, the quenching efficiency strongly depends on the number of dopamines per QD-conjugate. Second, the quenching efficiency is substantially increased in alkaline buffers. Third, this pH-dependent PL loss can be completely eliminated when oxygen-depleted buffers are used, indicating that oxygen plays a crucial role in the redox activity of dopamine. We attribute these findings to charge transfer interactions between QDs and mainly two forms of dopamine: the reduced catechol and oxidized quinone. As the pH of the dispersions is changed from acidic to basic, oxygen-catalyzed transformation progressively reduces the dopamine potential for oxidation and shifts the equilibrium toward increased concentration of quinones. Thus, in a conjugate, a QD can simultaneously interact with quinones (electron acceptors) and catechols (electron donors), producing pH-dependent PL quenching combined with shortening of the exciton lifetime. This also alters the recombination kinetics of the electron and hole of photoexcited QDs. Transient absorption measurements that probed intraband transitions supported those findings where a simultaneous pronounced change in the electron and hole relaxation rates was measured when the pH was changed from

  1. Biosensing of matrix metalloproteinase activity with Cd-free quantum dots

    NASA Astrophysics Data System (ADS)

    Plumley, John Bryan

    Quantum dots (QDs) have become attractive in the biomedical field on account of their superior optical properties and stability, in comparison to traditional fluorophores. QDs also have properties which make them ideal for complex in vivo conditions. However, toxicity has been a chief concern in the eventual implementation of QDs for in vivo applications such as biosensing and tumor imaging. Commercially available QDs contain a notoriously noxious Cd component and therefore continuous research has gone into developing QDs without toxic heavy metals, generally Cd, that would still yield comparable performance in terms of their optical properties. Nonetheless, even in the case of Cd-free QDs, toxicity should be evaluated on a case by case basis, as other properties such as size, coating, stability, and charge can affect toxicity of nanomaterials as well, making it a very complex issue. With the high promise of QDs in the field of biomedical development as a motivation, this work strives to develop the efficient and repeatable synthesis of Cd-free QDs with high stability and luminescence, with proven low toxicity, and the ability to detect active matrix metalloproteinase (MMP) in a biosensing system, designed to identify direct biomarkers for pathological conditions, which in turn would enable early disease diagnosis and better treatment development. In this work, highly luminescent ZnSe:Mn/ZnS QDs have been synthesized, characterized, and modified with peptides with a bioconjugation procedure that utilized thiol-metal affinity. Experiments aiming at MMP detection were conducted using the peptide/QD conjugates. In addition, the ApoTox-Glo(TM) Triplex assay was utilized to evaluate cytotoxicity, and a safe concentration below 0.125 microM was identified for peptide-coated ZnSe:Mn/ZnS QDs in water. Finally, in contribution to developing an in vivo fiberoptic system for sensing MMP activity, the QDs were successfully tethered to silica and MMP detection was demonstrated

  2. Submonolayer Quantum Dot Infrared Photodetector

    NASA Technical Reports Server (NTRS)

    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.

  3. Optical Fiber Sensing Using Quantum Dots

    PubMed Central

    Jorge, Pedro; Martins, Manuel António; Trindade, Tito; Santos, José Luís; Farahi, Faramarz

    2007-01-01

    Recent advances in the application of semiconductor nanocrystals, or quantum dots, as biochemical sensors are reviewed. Quantum dots have unique optical properties that make them promising alternatives to traditional dyes in many luminescence based bioanalytical techniques. An overview of the more relevant progresses in the application of quantum dots as biochemical probes is addressed. Special focus will be given to configurations where the sensing dots are incorporated in solid membranes and immobilized in optical fibers or planar waveguide platforms.

  4. Quantum dot behavior in graphene nanoconstrictions.

    PubMed

    Todd, Kathryn; Chou, Hung-Tao; Amasha, Sami; Goldhaber-Gordon, David

    2009-01-01

    Graphene nanoribbons display an imperfectly understood transport gap. We measure transport through nanoribbon devices of several lengths. In long (>/=250 nm) nanoribbons we observe transport through multiple quantum dots in series, while shorter (quantum dots. New measurements indicate that dot size may scale with constriction width. We propose a model where transport occurs through quantum dots that are nucleated by background disorder potential in the presence of a confinement gap.

  5. New small quantum dots for neuroscience

    NASA Astrophysics Data System (ADS)

    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.

  6. Brightness-equalized quantum dots

    PubMed Central

    Lim, Sung Jun; Zahid, Mohammad U.; Le, Phuong; Ma, Liang; Entenberg, David; Harney, Allison S.; Condeelis, John; Smith, Andrew M.

    2015-01-01

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices. PMID:26437175

  7. Brightness-equalized quantum dots.

    PubMed

    Lim, Sung Jun; Zahid, Mohammad U; Le, Phuong; Ma, Liang; Entenberg, David; Harney, Allison S; Condeelis, John; Smith, Andrew M

    2015-10-05

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices.

  8. Visible-light driven photocatalytic activity of β-indium sulfide (In2S3) quantum dots embedded in Nafion matrix

    NASA Astrophysics Data System (ADS)

    Sumi, R.; Warrier, Anita R.; Vijayan, C.

    2014-03-01

    We report on the visible-light-driven photocatalytic activity of highly stable β-indium sulfide (In2S3) quantum dots embedded in Nafion matrix. β-indium sulfide (In2S3) quantum dots (6-10 nm) embedded in Nafion matrix with strong quantum confinement were synthesized by a simple chemical route. The UV-Vis absorption spectrum shows a large blue shift (˜1 eV) which can be controlled by the reaction temperature and time. Strong broadband photoluminescence is observed in the blue, green and red regions of the emission spectrum with variation in particle size and stoichiometry of the quantum dots. Photocatalytic activity measurements show that these hybrid membranes synthesized with equimolar precursors of In and S show paramount photocatalytic activity under visible-light irradiation, with the degradation of Rhodamine-6G dyes up to 95% within 90 min. The photocatalytic membranes are tested for reusable and stable operation.

  9. Designing quantum dots for solotronics

    PubMed Central

    Kobak, J.; Smoleński, T.; Goryca, M.; Papaj, M.; Gietka, K.; Bogucki, A.; Koperski, M.; Rousset, J.-G.; Suffczyński, J.; Janik, E.; Nawrocki, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

    2014-01-01

    Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory. PMID:24463946

  10. Acoustically regulated carrier injection into a single optically active quantum dot

    NASA Astrophysics Data System (ADS)

    Schülein, Florian J. R.; Müller, Kai; Bichler, Max; Koblmüller, Gregor; Finley, Jonathan J.; Wixforth, Achim; Krenner, Hubert J.

    2013-08-01

    We study the carrier injection into a single InGaAs/GaAs quantum dot regulated by a radio frequency surface acoustic wave. We find that the time of laser excitation during the acoustic cycle programs both the emission intensities and time of formation of neutral (X0) and negatively charged (X-) excitons. We identify underlying, characteristic formation pathways of both few-particle states in the time-domain experiments and show that both exciton species can be formed either with the optical pump or at later times by injection of single electrons and holes “surfing” the acoustic wave. All experimental observations are in excellent agreement with calculated electron and hole trajectories in the plane of the two-dimensional wetting layer which is dynamically modulated by the acoustically induced piezoelectric potentials. Taken together, our findings provide insight on both the onset of acoustoelectric transport of electrons and holes and their conversion into the optical domain after regulated injection into a single quantum dot emitter.

  11. Room-temperature lasing in microring cavities with an InAs/InGaAs quantum-dot active region

    SciTech Connect

    Kryzhanovskaya, N. V. Zhukov, A. E.; Nadtochy, A. M.; Maximov, M. V.; Moiseev, E. I.; Kulagina, M. M.; Savelev, A. V.; Arakcheeva, E. M.; Lipovskii, A. A.; Zubov, F. I.; Kapsalis, A.; Mesaritakis, C.; Syvridis, D.; Mintairov, A.; Livshits, D.

    2013-10-15

    Microring cavities (diameter D = 2.7-7 {mu}m) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 {mu}m. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 {mu}m.

  12. Mechanochemically synthesized sub-5 nm sized CuS quantum dots with high visible-light-driven photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Li, Shun; Ge, Zhen-Hua; Zhang, Bo-Ping; Yao, Yao; Wang, Huan-Chun; Yang, Jing; Li, Yan; Gao, Chao; Lin, Yuan-Hua

    2016-10-01

    We report a simple mechanochemical ball milling method for synthesizing monodisperse CuS quantum dots (QDs) with sizes as small as sub-5 nm. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy. The CuS QDs exhibited excellent visible-light-driven photocatalytic activity and stability for degradation of Rodanmine B aqueous solution as Fenton-like reagents. Our study opens the opportunity to low-cost and facile synthesis of QDs in large scale for future industrial applications.

  13. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

    SciTech Connect

    Patty, Kira; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Sadeghi, Seyed M.; Mao, Chuanbin

    2014-09-21

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

  14. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

    NASA Astrophysics Data System (ADS)

    Patty, Kira; Sadeghi, Seyed M.; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Mao, Chuanbin

    2014-09-01

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

  15. Quantitative multiplexed quantum dot immunohistochemistry

    SciTech Connect

    Sweeney, E.; Ward, T.H.; Gray, N.; Womack, C.; Jayson, G.; Hughes, A.; Dive, C.; Byers, R.

    2008-09-19

    Quantum dots are photostable fluorescent semiconductor nanocrystals possessing wide excitation and bright narrow, symmetrical, emission spectra. These characteristics have engendered considerable interest in their application in multiplex immunohistochemistry for biomarker quantification and co-localisation in clinical samples. Robust quantitation allows biomarker validation, and there is growing need for multiplex staining due to limited quantity of clinical samples. Most reported multiplexed quantum dot staining used sequential methods that are laborious and impractical in a high-throughput setting. Problems associated with sequential multiplex staining have been investigated and a method developed using QDs conjugated to biotinylated primary antibodies, enabling simultaneous multiplex staining with three antibodies. CD34, Cytokeratin 18 and cleaved Caspase 3 were triplexed in tonsillar tissue using an 8 h protocol, each localised to separate cellular compartments. This demonstrates utility of the method for biomarker measurement enabling rapid measurement of multiple co-localised biomarkers on single paraffin tissue sections, of importance for clinical trial studies.

  16. Monitoring Cellular Interactions during T Cell Activation at the Single Molecule Level Using Semiconductor Quantum-Dots

    DTIC Science & Technology

    2005-05-10

    correlation spectroscopy (FCS); (5) testing the lipid raft hypothesis by single molecule imaging of targeted peptide-coated quantum dots; and (6) molecular cloning and fusion of avidin to immunological synapse (IS) components.

  17. Fast gain and phase recovery of semiconductor optical amplifiers based on submonolayer quantum dots

    SciTech Connect

    Herzog, Bastian Owschimikow, Nina; Kaptan, Yücel; Kolarczik, Mirco; Switaiski, Thomas; Woggon, Ulrike; Schulze, Jan-Hindrik; Rosales, Ricardo; Strittmatter, André; Bimberg, Dieter; Pohl, Udo W.

    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.

  18. CdTe quantum dots induce activation of human platelets: implications for nanoparticle hemocompatibility.

    PubMed

    Samuel, Stephen P; Santos-Martinez, Maria J; Medina, Carlos; Jain, Namrata; Radomski, Marek W; Prina-Mello, Adriele; Volkov, Yuri

    2015-01-01

    New nanomaterials intended for systemic administration have raised concerns regarding their biocompatibility and hemocompatibility. Quantum dots (QD) nanoparticles have been used for diagnostics, and recent work suggests their use for in vivo molecular and cellular imaging. However, the hemocompatibility of QDs and their constituent components has not been fully elucidated. In the present study, comprehensive investigation of QD-platelet interactions is presented. These interactions were shown using transmission electron microscopy. The effects of QDs on platelet function were investigated using light aggregometry, quartz crystal microbalance with dissipation, flow cytometry, and gelatin zymography. Platelet morphology was also analyzed by phase-contrast, immunofluorescence, atomic-force and transmission electron microscopy. We show that the QDs bind to platelet plasma membrane with the resultant upregulation of glycoprotein IIb/IIIa and P-selectin receptors, and release of matrix metalloproteinase-2. These findings unravel for the first time the mechanism of functional response of platelets to ultrasmall QDs in vitro.

  19. Quantum Dot Detectors with Plasmonic Structures

    DTIC Science & Technology

    2015-05-15

    AFRL-RV-PS- AFRL-RV-PS- TR-2015-0102 TR-2015-0102 QUANTUM DOT DETECTORS WITH PLASMONIC STRUCTURES Sanjay Krishna University of...SUBTITLE Quantum Dot Detectors with Plasmonic Structures 5a. CONTRACT NUMBER FA9453-12-1-0131 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 63401F 6...characterization, of multi-spectral quantum dots-in-a-double well (DDWELL) infrared detectors, by the integration of a surface Plasmon (SP) assisted resonant

  20. Barrier Engineered Quantum Dot Infrared Photodetectors

    DTIC Science & Technology

    2015-06-01

    AFRL-RV-PS- AFRL-RV-PS- TR-2015-0111 TR-2015-0111 BARRIER ENGINEERED QUANTUM DOT INFRARED PHOTODETECTORS Sanjay Krishna Center for High Technology...2011 – 22 May 2012 4. TITLE AND SUBTITLE Barrier Engineered Quantum Dot Infrared Photodetectors 5a. CONTRACT NUMBER FA9453-12-1-0336 5b. GRANT...is Unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT To investigate barrier engineered designs to reduce the dark current in quantum dot infrared

  1. Synthetic Developments of Nontoxic Quantum Dots.

    PubMed

    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.

  2. Chiral quantum dot based materials

    NASA Astrophysics Data System (ADS)

    Govan, Joseph; Loudon, Alexander; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii

    2014-05-01

    Recently, the use of stereospecific chiral stabilising molecules has also opened another avenue of interest in the area of quantum dot (QD) research. The main goal of our research is to develop new types of technologically important quantum dot materials containing chiral defects, study their properties and explore their applications. The utilisation of chiral penicillamine stabilisers allowed the preparation of new water soluble white emitting CdS quantum nanostructures which demonstrated circular dichroism in the band-edge region of the spectrum. It was also demonstrated that all three types of QDs (D-, L-, and Rac penicillamine stabilised) show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. In this work the chiral CdS based quantum nanostructures have also been doped by copper metal ions and new chiral penicilamine stabilized CuS nanoparticles have been prepared and investigated. It was found that copper doping had a strong effect at low levels in the synthesis of chiral CdS nanostructures. We expect that this research will open new horizons in the chemistry of chiral nanomaterials and their application in biotechnology, sensing and asymmetric synthesis.

  3. The statistical theory of quantum dots

    NASA Astrophysics Data System (ADS)

    Alhassid, Y.

    2000-10-01

    A quantum dot is a sub-micron-scale conducting device containing up to several thousand electrons. Transport through a quantum dot at low temperatures is a quantum-coherent process. This review focuses on dots in which the electron's dynamics are chaotic or diffusive, giving rise to statistical properties that reflect the interplay between one-body chaos, quantum interference, and electron-electron interactions. The conductance through such dots displays mesoscopic fluctuations as a function of gate voltage, magnetic field, and shape deformation. The techniques used to describe these fluctuations include semiclassical methods, random-matrix theory, and the supersymmetric nonlinear σ model. In open dots, the approximation of noninteracting quasiparticles is justified, and electron-electron interactions contribute indirectly through their effect on the dephasing time at finite temperature. In almost-closed dots, where conductance occurs by tunneling, the charge on the dot is quantized, and electron-electron interactions play an important role. Transport is dominated by Coulomb blockade, leading to peaks in the conductance that at low temperatures provide information on the dot's ground-state properties. Several statistical signatures of electron-electron interactions have been identified, most notably in the dot's addition spectrum. The dot's spin, determined partly by exchange interactions, can also influence the fluctuation properties of the conductance. Other mesoscopic phenomena in quantum dots that are affected by the charging energy include the fluctuations of the cotunneling conductance and mesoscopic Coulomb blockade.

  4. Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots

    SciTech Connect

    Cundiff, Steven T.

    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.

  5. Photovoltaic Current in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Switkes, M.; Marcus, C. M.; Campman, K.; Gossard, A. C.

    1998-03-01

    We investigate the DC photovoltaic current, I_pv, due to coherent ``pumping'' in open ( g >= e^2/h ) quantum dots with radio-frequency modulation of the confining potential(B. Spivak, F. Zhou, and M. T. Beal Monod, Phys. Rev. B 51), p. 13226 (1995). I_pv is on the order of 20 pA≈ 10ef for a modulation frequency f = 15 MHz. The photovoltaic current exhibits mesoscopic fluctuations with magnetic field and with the static shape of the confining potential which do not appear to be correlated with fluctuations in the conductance of the dot. The photovoltaic current induced by pumping with two independent shape distortion gates depends on their relative phase; the relationship of this phase to time reversal symmetry is investigated with a view toward defining a generalized Landauer-Büttiker relation.

  6. On-chip generation and guiding of quantum light from a site-controlled quantum dot

    SciTech Connect

    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

    2014-03-10

    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. Charge state hysteresis in semiconductor quantum dots

    SciTech Connect

    Yang, C. H.; Rossi, A. Lai, N. S.; Leon, R.; Lim, W. H.; Dzurak, A. S.

    2014-11-03

    Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which accounts for the observed hysteretic behaviour by extending the established description for transport in double dots coupled to two reservoirs. We demonstrate that this type of device operates like a single-electron memory latch.

  8. A quantum dot in topological insulator nanofilm.

    PubMed

    Herath, Thakshila M; Hewageegana, Prabath; Apalkov, Vadym

    2014-03-19

    We introduce a quantum dot in topological insulator nanofilm as a bump at the surface of the nanofilm. Such a quantum dot can localize an electron if the size of the dot is large enough, ≳5 nm. The quantum dot in topological insulator nanofilm has states of two types, which belong to two ('conduction' and 'valence') bands of the topological insulator nanofilm. We study the energy spectra of such defined quantum dots. We also consider intraband and interband optical transitions within the dot. The optical transitions of the two types have the same selection rules. While the interband absorption spectra have multi-peak structure, each of the intraband spectra has one strong peak and a few weak high frequency satellites.

  9. Research on Self-Assembling Quantum Dots.

    DTIC Science & Technology

    1995-10-30

    0K. in a second phase of this contract we turned our efforts to the fabrication and studies of self assembled quantum dots . We first demonstrated a...method for producing InAs-GasAs self assembled quantum dots (SAD) using MBE. (AN)

  10. STED nanoscopy with fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Hanne, Janina; Falk, Henning J.; Görlitz, Frederik; Hoyer, Patrick; Engelhardt, Johann; Sahl, Steffen J.; Hell, Stefan W.

    2015-05-01

    The widely popular class of quantum-dot molecular labels could so far not be utilized as standard fluorescent probes in STED (stimulated emission depletion) nanoscopy. This is because broad quantum-dot excitation spectra extend deeply into the spectral bands used for STED, thus compromising the transient fluorescence silencing required for attaining super-resolution. Here we report the discovery that STED nanoscopy of several red-emitting commercially available quantum dots is in fact successfully realized by the increasingly popular 775 nm STED laser light. A resolution of presently ~50 nm is demonstrated for single quantum dots, and sub-diffraction resolution is further shown for imaging of quantum-dot-labelled vimentin filaments in fibroblasts. The high quantum-dot photostability enables repeated STED recordings with >1,000 frames. In addition, we have evidence that the tendency of quantum-dot labels to blink is largely suppressed by combined action of excitation and STED beams. Quantum-dot STED significantly expands the realm of application of STED nanoscopy, and, given the high stability of these probes, holds promise for extended time-lapse imaging.

  11. Thick-shell nanocrystal quantum dots

    DOEpatents

    Hollingsworth, Jennifer A.; Chen, Yongfen; Klimov, Victor I.; Htoon, Han; Vela, Javier

    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.

  12. Excitonic quantum interference in a quantum dot chain with rings.

    PubMed

    Hong, Suc-Kyoung; Nam, Seog Woo; Yeon, Kyu-Hwang

    2008-04-16

    We demonstrate excitonic quantum interference in a closely spaced quantum dot chain with nanorings. In the resonant dipole-dipole interaction model with direct diagonalization method, we have found a peculiar feature that the excitation of specified quantum dots in the chain is completely inhibited, depending on the orientational configuration of the transition dipole moments and specified initial preparation of the excitation. In practice, these excited states facilitating quantum interference can provide a conceptual basis for quantum interference devices of excitonic hopping.

  13. Biocompatible Quantum Dots for Biological Applications

    PubMed Central

    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

  14. Biocompatible Quantum Dots for Biological Applications

    SciTech Connect

    Rosenthal, Sandra; Chang, Jerry; Kovtun, Oleg; McBride, James; Tomlinson, Ian

    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, size-tunable, 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.

  15. Quantum-dot supercrystals for future nanophotonics

    PubMed Central

    Baimuratov, Anvar S.; Rukhlenko, Ivan D.; Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-01-01

    The study of supercrystals made of periodically arranged semiconductor quantum dots is essential for the advancement of emerging nanophotonics technologies. By combining the strong spatial confinement of elementary excitations inside quantum dots and exceptional design flexibility, quantum-dot supercrystals provide broad opportunities for engineering desired optical responses and developing superior light manipulation techniques on the nanoscale. Here we suggest tailoring the energy spectrum and wave functions of the supercrystals' collective excitations through the variation of different structural and material parameters. In particular, by calculating the excitonic spectra of quantum dots assembled in two-dimensional Bravais lattices we demonstrate a wide variety of spectrum transformation scenarios upon alterations in the quantum dot arrangement. This feature offers unprecedented control over the supercrystal's electromagnetic properties and enables the development of new nanophotonics materials and devices.

  16. Control of the Redox Activity of Quantum Dots through Introduction of Fluoroalkanethiolates into Their Ligand Shells.

    PubMed

    Weinberg, David J; He, Chen; Weiss, Emily A

    2016-02-24

    Increasing the fraction of 1H,1H,2H,2H-perfluorodecanethiol (PFDT) in the mixed-PFDT/oleate ligand shell of a PbS quantum dot (QD) dramatically reduces the permeability of the ligand shell to alkyl-substituted benzoquinones (s-BQs), as measured by a decrease in the efficiency of collisional photoinduced electron transfer. Replacing only 21% of the oleates on the QD surface with PFDT reduces the yield of photo-oxidation by tetramethyl BQ by 68%. Experiments with s-BQ quenchers of two different sizes reveal that the degree of protection provided by the PFDT-doped monolayer, relative to a decanethiolate (DT)-doped monolayer at similar coverage, is due to both size exclusion (PFDT is larger and more rigid than DT), and the oleophobicity of PFDT. This work demonstrates the usefulness of fluorinated ligands in designing molecule-selective and potentially corrosion-inhibiting surface coatings for QDs for applications as robust emitters or high fidelity sensing platforms.

  17. Enhancing cell nucleus accumulation and DNA cleavage activity of anti-cancer drug via graphene quantum dots.

    PubMed

    Wang, Chong; Wu, Congyu; Zhou, Xuejiao; Han, Ting; Xin, Xiaozhen; Wu, Jiaying; Zhang, Jingyan; Guo, Shouwu

    2013-10-04

    Graphene quantum dots (GQDs) maintain the intrinsic layered structural motif of graphene but with smaller lateral size and abundant periphery carboxylic groups, and are more compatible with biological system, thus are promising nanomaterials for therapeutic applications. Here we show that GQDs have a superb ability in drug delivery and anti-cancer activity boost without any pre-modification due to their unique structural properties. They could efficiently deliver doxorubicin (DOX) to the nucleus through DOX/GQD conjugates, because the conjugates assume different cellular and nuclear internalization pathways comparing to free DOX. Also, the conjugates could enhance DNA cleavage activity of DOX markedly. This enhancement combining with efficient nuclear delivery improved cytotoxicity of DOX dramatically. Furthermore, the DOX/GQD conjugates could also increase the nuclear uptake and cytotoxicity of DOX to drug-resistant cancer cells indicating that the conjugates may be capable to increase chemotherapy efficacy of anti-cancer drugs that are suboptimal due to the drug resistance.

  18. Tailoring Magnetism in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Zutic, Igor; Abolfath, Ramin; Hawrylak, Pawel

    2007-03-01

    We study magnetism in magnetically doped quantum dots as a function of particle numbers, temperature, confining potential, and the strength of Coulomb interaction screening. We show that magnetism can be tailored by controlling the electron-electron Coulomb interaction, even without changing the number of particles. The interplay of strong Coulomb interactions and quantum confinement leads to enhanced inhomogeneous magnetization which persists at substantially higher temperatures than in the non-interacting case or in the bulk-like dilute magnetic semiconductors. We predict a series of electronic spin transitions which arise from the competition between the many-body gap and magnetic thermal fluctuations. Cond-mat/0612489. [1] R. Abolfath, P. Hawrylak, I. Zuti'c, preprint.

  19. Optophononics with coupled quantum dots.

    PubMed

    Kerfoot, Mark L; Govorov, Alexander O; Czarnocki, Cyprian; Lu, Davis; Gad, Youstina N; Bracker, Allan S; Gammon, Daniel; Scheibner, Michael

    2014-01-01

    Modern technology is founded on the intimate understanding of how to utilize and control electrons. Next to electrons, nature uses phonons, quantized vibrations of an elastic structure, to carry energy, momentum and even information through solids. Phonons permeate the crystalline components of modern technology, yet in terms of technological utilization phonons are far from being on par with electrons. Here we demonstrate how phonons can be employed to render a single quantum dot pair optically transparent. This phonon-induced transparency is realized via the formation of a molecular polaron, the result of a Fano-type quantum interference, which proves that we have accomplished making typically incoherent and dissipative phonons behave in a coherent and non-dissipative manner. We find the transparency to be widely tunable by electronic and optical means. Thereby we show amplification of weakest coupling channels. We further outline the molecular polaron's potential as a control element in phononic circuitry architecture.

  20. Quantum dot spectroscopy using cavity quantum electrodynamics.

    PubMed

    Winger, Martin; Badolato, Antonio; Hennessy, Kevin J; Hu, Evelyn L; Imamoğlu, Ataç

    2008-11-28

    We show how cavity quantum electrodynamics using a tunable photonic crystal nanocavity in the strong-coupling regime can be used for single quantum dot spectroscopy. From the distinctive avoided crossings observed in the strongly coupled system we can identify the neutral and single positively charged exciton as well as the biexciton transitions. Moreover we are able to investigate the fine structure of those transitions and to identify a novel cavity mediated mixing of bright and dark exciton states, where the hyperfine interactions with lattice nuclei presumably play a key role. These results are enabled by a deterministic coupling scheme which allowed us to achieve unprecedented coupling strengths in excess of 150 microeV.

  1. Quantum dots in aperiodic order

    NASA Astrophysics Data System (ADS)

    Hörnquist, Michael; Ouchterlony, Thomas

    1998-12-01

    We study numerically with a Green-function technique one-dimensional arrays of quantum dots with two different models. The arrays are ordered according to the Fibonacci, the Thue-Morse, and the Rudin-Shapiro sequences. As a comparison, results from a periodically ordered chain and also from a random chain are included. The focus is on how the conductance (calculated within the Landauer-Büttiker formalism) depends on the Fermi level. In the first model, we find that in some cases rather small systems (≈60 dots) behave in the same manner as very large systems (>16,000 dots) and this makes it possible in these cases to interpret our results for the small systems in terms of the spectral properties of the infinite systems. In particular, we find that it is possible to see some consequences of the singular continuous spectra that some of the systems possess, at least for temperatures up to 100 mK. In the second model, we study the phenomenon ohmic addition, i.e. when the resistances of the constrictions add up to the total resistance. It results that of the systems studied, it is only the Rudin-Shapiro system that has this behaviour for large structures, while the resistances of the Fibonacci and the Thue-Morse systems might reach a limiting value (as a periodic system does).

  2. Biodetection using fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Speckman, Donna M.; Jennings, Travis L.; LaLumondiere, Steven D.; Klimcak, Charles M.; Moss, Steven C.; Loper, Gary L.; Beck, Steven M.

    2002-07-01

    Multi-pathogen biosensors that take advantage of sandwich immunoassay detection schemes and utilize conventional fluorescent dye reporter molecules are difficult to make into extremely compact and autonomous packages. The development of a multi-pathogen, immunoassay-based, fiber optic detector that utilizes varying sized fluorescent semiconductor quantum dots (QDs) as the reporter labels has the potential to overcome these problems. In order to develop such a quantum dot-based biosensor, it is essential to demonstrate that QDs can be attached to antibody proteins, such that the specificity of the antibody is maintained. We have been involved in efforts to develop a reproducible method for attaching QDs to antibodies for use in biodetection applications. We have synthesized CdSe/ZnS core-shell QDs of differing size, functionalized their surfaces with several types of organic groups for water solubility, and covalently attached these functionalized QDs to rabbit anti-ovalbumin antibody protein. We also demonstrated that these labeled antibodies exhibit selective binding to ovalbumin antigen. We characterized the QDs at each step in the overall synthesis by UV-VIS absorption spectroscopy and by picosecond (psec) transient photoluminescence (TPL) spectroscopy. TPL spectroscopy measurements indicate that QD lifetime depends on the size of the QD, the intensity of the optical excitation source, and whether or not they are functionalized and conjugated to antibodies. We describe details of these experiments and discuss the impact of our results on our biosensor development program.

  3. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    DOE PAGES

    Michael, Stephan; Chow, Weng; Schneider, Hans

    2016-05-01

    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. We study the influence of two important quantum-dot material parameters, here, 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 canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. 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.« less

  4. A novel sensitive colorimetric sensor for Cu(2+) based on in situ formation of fluorescent quantum dots with photocatalytic activity.

    PubMed

    Tang, Shurong; Wang, Meili; Li, Zhijun; Tong, Ping; Chen, Qiang; Li, Guangwen; Chen, Jinghua; Zhang, Lan

    2017-03-15

    This work demonstrates the use of quantum dots (QDs) with photocatalytic activity as a sensitive, inexpensive and rapid colorimetric platform for Cu(2+) sensing. Based on the simple thiol compound mediated QDs growing method, CdS QDs can be quickly formed in situ, which possess excellent photocatalytic ability for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce a colored product under light irradiation. Cu(2+) can catalyze the oxidation of sulfhydryl groups in glutathione (GSH) which act as a stabilizer for CdS QDs. In the presence of Cu(2+), GSH is oxidized and loss the stabilization ability for the growth of CdS QDs, thus resulting in the decrease of the absorbance. Under optimum conditions, as low as 5.3nM Cu(2+) can be detected. This sensing system is simple, reliable and holds great potential to provide a new general platform for ultrasensitive monitoring of a variety of analytes.

  5. Temperature-Dependent Energy Gap Shift and Thermally Activated Transition in Multilayer CdTe/ZnTe Quantum Dots.

    PubMed

    Man, Minh Tan; Lee, Hong Seok

    2015-10-01

    We investigated the influence of growth conditions on carrier dynamics in multilayer CdTe/ZnTe quantum dots (QDs) by monitoring the temperature dependence of the photoluminescence emission energy. The results were analyzed using the empirical Varshni and O'Donnell relations for temperature variation of the energy gap shift. Best fit values showed that the thermally activated transition between two different states occurs due to band low-temperature quenching with values separated by 5.0-6.5 meV. The addition of stack periods in multilayer CdTe/ZnTe QDs plays an important role in the energy gap shift, where the exciton binding energy is enhanced, and, conversely, the exciton-phonon coupling strength is suppressed with an average energy of 19.3-19.8 meV.

  6. Optical Spectroscopy of Hybrid Semiconductor Quantum Dots and Metal Nanoparticles

    DTIC Science & Technology

    2014-11-07

    SECURITY CLASSIFICATION OF: Optical studies of semiconductor quantum dots (SQDs), metal nanoparticles (MNPs), and their hybrid nanomaterials are...Distribution Unlimited Final Report: Optical Spectroscopy of Hybrid Semiconductor Quantum Dots and Metal Nanoparticles The views, opinions and/or findings...Semiconductor Quantum Dots and Metal Nanoparticles Report Title Optical studies of semiconductor quantum dots (SQDs), metal nanoparticles (MNPs), and their

  7. Heterovalent cation substitutional doping for quantum dot homojunction solar cells

    PubMed Central

    Stavrinadis, Alexandros; Rath, Arup K.; de Arquer, F. Pelayo García; Diedenhofen, Silke L.; Magén, César; Martinez, Luis; So, David; Konstantatos, Gerasimos

    2013-01-01

    Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%. PMID:24346430

  8. On-chip quantum optics with quantum dot microcavities.

    PubMed

    Stock, E; Albert, F; Hopfmann, C; Lermer, M; Schneider, C; Höfling, S; Forchel, A; Kamp, M; Reitzenstein, S

    2013-02-06

    A novel concept for on-chip quantum optics using an internal electrically pumped microlaser is presented. The microlaser resonantly excites a quantum dot microcavity system operating in the weak coupling regime of cavity quantum electrodynamics. This work presents the first on-chip application of quantum dot microlasers, and also opens up new avenues for the integration of individual microcavity structures into larger photonic networks.

  9. Organic molecules as tools to control the growth, surface structure, and redox activity of colloidal quantum dots.

    PubMed

    Weiss, Emily A

    2013-11-19

    In order to achieve efficient and reliable technology that can harness solar energy, the behavior of electrons and energy at interfaces between different types or phases of materials must be understood. Conversion of light to chemical or electrical potential in condensed phase systems requires gradients in free energy that allow the movement of energy or charge carriers and facilitate redox reactions and dissociation of photoexcited states (excitons) into free charge carriers. Such free energy gradients are present at interfaces between solid and liquid phases or between inorganic and organic materials. Nanostructured materials have a higher density of these interfaces than bulk materials. Nanostructured materials, however, have a structural and chemical complexity that does not exist in bulk materials, which presents a difficult challenge: to lower or eliminate energy barriers to electron and energy flux that inevitably result from forcing different materials to meet in a spatial region of atomic dimensions. Chemical functionalization of nanostructured materials is perhaps the most versatile and powerful strategy for controlling the potential energy landscape of their interfaces and for minimizing losses in energy conversion efficiency due to interfacial structural and electronic defects. Colloidal quantum dots are semiconductor nanocrystals synthesized with wet-chemical methods and coated in organic molecules. Chemists can use these model systems to study the effects of chemical functionalization of nanoscale organic/inorganic interfaces on the optical and electronic properties of a nanostructured material, and the behavior of electrons and energy at interfaces. The optical and electronic properties of colloidal quantum dots have an intense sensitivity to their surface chemistry, and their organic adlayers make them dispersible in solvent. This allows researchers to use high signal-to-noise solution-phase spectroscopy to study processes at interfaces. In this

  10. Quantum dots with single-atom precision.

    PubMed

    Fölsch, Stefan; Martínez-Blanco, Jesús; Yang, Jianshu; Kanisawa, Kiyoshi; Erwin, Steven C

    2014-07-01

    Quantum dots are often called artificial atoms because, like real atoms, they confine electrons to quantized states with discrete energies. However, although real atoms are identical, most quantum dots comprise hundreds or thousands of atoms, with inevitable variations in size and shape and, consequently, unavoidable variability in their wavefunctions and energies. Electrostatic gates can be used to mitigate these variations by adjusting the electron energy levels, but the more ambitious goal of creating quantum dots with intrinsically digital fidelity by eliminating statistical variations in their size, shape and arrangement remains elusive. We used a scanning tunnelling microscope to create quantum dots with identical, deterministic sizes. By using the lattice of a reconstructed semiconductor surface to fix the position of each atom, we controlled the shape and location of the dots with effectively zero error. This allowed us to construct quantum dot molecules whose coupling has no intrinsic variation but could nonetheless be tuned with arbitrary precision over a wide range. Digital fidelity opens the door to quantum dot architectures free of intrinsic broadening-an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies of confined electrons.

  11. Towards hybrid circuit quantum electrodynamics with quantum dots

    NASA Astrophysics Data System (ADS)

    Viennot, Jérémie J.; Delbecq, Matthieu R.; Bruhat, Laure E.; Dartiailh, Matthieu C.; Desjardins, Matthieu M.; Baillergeau, Matthieu; Cottet, Audrey; Kontos, Takis

    2016-08-01

    Cavity quantum electrodynamics allows one to study the interaction between light and matter at the most elementary level. The methods developed in this field have taught us how to probe and manipulate individual quantum systems like atoms and superconducting quantum bits with an exquisite accuracy. There is now a strong effort to extend further these methods to other quantum systems, and in particular hybrid quantum dot circuits. This could turn out to be instrumental for a noninvasive study of quantum dot circuits and a realization of scalable spin quantum bit architectures. It could also provide an interesting platform for quantum simulation of simple fermion-boson condensed matter systems. In this short review, we discuss the experimental state of the art for hybrid circuit quantum electrodynamics with quantum dots, and we present a simple theoretical modeling of experiments.

  12. Atomistic theory of excitonic fine structure in InAs/InP nanowire quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Świderski, M.; Zieliński, M.

    2017-03-01

    Nanowire quantum dots have peculiar electronic and optical properties. In this work we use atomistic tight binding to study excitonic spectra of artificial molecules formed by a double nanowire quantum dot. We demonstrate a key role of atomistic symmetry and nanowire substrate orientation rather than cylindrical shape symmetry of a nanowire and a molecule. In particular for [001 ] nanowire orientation we observe a nonvanishing bright exciton splitting for a quasimolecule formed by two cylindrical quantum dots of different heights. This effect is due to interdot coupling that effectively reduces the overall symmetry, whereas single uncoupled [001 ] quantum dots have zero fine structure splitting. We found that the same double quantum dot system grown on [111 ] nanowire reveals no excitonic fine structure for all considered quantum dot distances and individual quantum dot heights. Further we demonstrate a pronounced, by several orders of magnitude, increase of the dark exciton optical activity in a quantum dot molecule as compared to a single quantum dot. For [111 ] systems we also show spontaneous localization of single particle states in one of nominally identical quantum dots forming a molecule, which is mediated by strain and origins from the lack of the vertical inversion symmetry in [111 ] nanostructures of overall C3 v symmetry. Finally, we study lowering of symmetry due to alloy randomness that triggers nonzero excitonic fine structure and the dark exciton optical activity in realistic nanowire quantum dot molecules of intermixed composition.

  13. Fluorescent Quantum Dots for Biological Labeling

    NASA Technical Reports Server (NTRS)

    McDonald, Gene; Nadeau, Jay; Nealson, Kenneth; Storrie-Lomardi, Michael; Bhartia, Rohit

    2003-01-01

    Fluorescent semiconductor quantum dots that can serve as "on/off" labels for bacteria and other living cells are undergoing development. The "on/off" characterization of these quantum dots refers to the fact that, when properly designed and manufactured, they do not fluoresce until and unless they come into contact with viable cells of biological species that one seeks to detect. In comparison with prior fluorescence-based means of detecting biological species, fluorescent quantum dots show promise for greater speed, less complexity, greater sensitivity, and greater selectivity for species of interest. There are numerous potential applications in medicine, environmental monitoring, and detection of bioterrorism.

  14. Electronic properties of aperiodic quantum dot chains

    NASA Astrophysics Data System (ADS)

    Korotaev, P. Yu.; Vekilov, Yu. Kh.; Kaputkina, N. E.

    2012-04-01

    The electronic spectral and transport properties of aperiodic quantum dot chains are investigated. The systems with singular continuous energy spectrum are considered: Thue-Morse chain, double-periodic chain, Rudin-Shapiro chain. The influence of electronic energy in quantum dot on the spectral properties, band structure, density of states and spectral resistivity, is discussed. Low resistivity regions correspond to delocalized states and these states could be current states. Also we discuss the magnetic field application as the way to tune electronic energy in quantum dot and to obtain metallic or insulating conducting states of the systems.

  15. Quantum dot-based theranostics

    NASA Astrophysics Data System (ADS)

    Ho, Yi-Ping; Leong, Kam W.

    2010-01-01

    Luminescent semiconductor nanocrystals, also known as quantum dots (QDs), have advanced the fields of molecular diagnostics and nanotherapeutics. Much of the initial progress for QDs in biology and medicine has focused on developing new biosensing formats to push the limit of detection sensitivity. Nevertheless, QDs can be more than passive bio-probes or labels for biological imaging and cellular studies. The high surface-to-volume ratio of QDs enables the construction of a ``smart'' multifunctional nanoplatform, where the QDs serve not only as an imaging agent but also a nanoscaffold catering for therapeutic and diagnostic (theranostic) modalities. This mini review highlights the emerging applications of functionalized QDs as fluorescence contrast agents for imaging or as nanoscale vehicles for delivery of therapeutics, with special attention paid to the promise and challenges towards QD-based theranostics.

  16. Single to quadruple quantum dots with tunable tunnel couplings

    SciTech Connect

    Takakura, T.; Noiri, A.; Obata, T.; Yoneda, J.; Yoshida, K.; Otsuka, T.; Tarucha, S.

    2014-03-17

    We prepare a gate-defined quadruple quantum dot to study the gate-tunability of single to quadruple quantum dots with finite inter-dot tunnel couplings. The measured charging energies of various double dots suggest that the dot size is governed by the gate geometry. For the triple and quadruple dots, we study the gate-tunable inter-dot tunnel couplings. For the triple dot, we find that the effective tunnel coupling between side dots significantly depends on the alignment of the center dot potential. These results imply that the present quadruple dot has a gate performance relevant for implementing spin-based four-qubits with controllable exchange couplings.

  17. Quantum Dots Investigated for Solar Cells

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Castro, Stephanie L.; Raffaelle, Ryne P.; Hepp, Aloysius F.

    2001-01-01

    The NASA Glenn Research Center has been investigating the synthesis of quantum dots of CdSe and CuInS2 for use in intermediate-bandgap solar cells. Using quantum dots in a solar cell to create an intermediate band will allow the harvesting of a much larger portion of the available solar spectrum. Theoretical studies predict a potential efficiency of 63.2 percent, which is approximately a factor of 2 better than any state-of-the-art devices available today. This technology is also applicable to thin-film devices--where it offers a potential four-fold increase in power-to-weight ratio over the state of the art. Intermediate-bandgap solar cells require that quantum dots be sandwiched in an intrinsic region between the photovoltaic solar cell's ordinary p- and n-type regions (see the preceding figure). The quantum dots form the intermediate band of discrete states that allow sub-bandgap energies to be absorbed. However, when the current is extracted, it is limited by the bandgap, not the individual photon energies. The energy states of the quantum dot can be controlled by controlling the size of the dot. Ironically, the ground-state energy levels are inversely proportional to the size of the quantum dots. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Ba Wendi et al., in the early 1990's. The most studied quantum dots prepared by this method have been of CdSe. To produce these dots, researchers inject a syringe of the desired organometallic precursors into heated triocytlphosphine oxide (TOPO) that has been vigorously stirred under an inert atmosphere (see the following figure). The solution immediately begins to change from colorless to yellow, then orange and red/brown, as the quantum dots increase in size. When the desired size is reached, the heat is removed from the flask. Quantum dots of different sizes can be identified by placing them under a "black light" and observing the various color differences in

  18. Spin Dynamics of Charged Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Stern, N. P.

    2005-03-01

    Colloidal semiconductor quantum dots are promising structures for controlling spin phenomena because of their highly size- tunable physical properties, ease of manufacture, and nanosecond-scale spin lifetimes at room temperature. Recent experiments have succeeded in controlling the charging of the lowest electronic state of colloidal quantum dots ootnotetextC. Wang, B. L. Wehrenberg, C. Y. Woo, and P. Guyot-Sionnest, J. Phys. Chem B 108, 9027 (2004).. Here we use time-resolved Faraday rotation measurements in the Voigt geometry to investigate the spin dynamics of colloidal CdSe quantum dot films in both a charged and uncharged state at room temperature. The charging of the film is controlled by applying a voltage in an electrochemical cell and is confirmed by absorbance measurements. Significant changes in the spin precession are observed upon charging, reflecting the voltage- controlled electron occupation of the quantum dot states and filling of surface states.

  19. Teleportation on a quantum dot array.

    PubMed

    de Pasquale, F; Giorgi, G; Paganelli, S

    2004-09-17

    We present a model of quantum teleportation protocol based on a double quantum dot array. The unknown qubit is encoded using a pair of quantum dots, with one excess electron, coupled by tunneling. It is shown how to create a maximally entangled state using an adiabatically increasing Coulomb repulsion between different dot pairs. This entangled state is exploited to perform teleportation again using an adiabatic coupling between itself and the incoming unknown state. Finally, a sudden separation of Bob's qubit allows a time evolution of Alice's, which amounts to a modified version of standard Bell measurement. A transmission over a long distance could be obtained by considering the entangled state of a chain of N coupled double quantum dots. The system is shown to be increasingly robust with N against decoherence due to phonons.

  20. First principle thousand atom quantum dot calculations

    SciTech Connect

    Wang, Lin-Wang; Li, Jingbo

    2004-03-30

    A charge patching method and an idealized surface passivation are used to calculate the single electronic states of IV-IV, III-V, II-VI semiconductor quantum dots up to a thousand atoms. This approach scales linearly and has a 1000 fold speed-up compared to direct first principle methods with a cost of eigen energy error of about 20 meV. The calculated quantum dot band gaps are parametrized for future references.

  1. Noninvasive detection of charge rearrangement in a quantum dot

    NASA Astrophysics Data System (ADS)

    Fricke, C.; Rogge, M. C.; Harke, B.; Reinwald, M.; Wegscheider, W.; Hohls, F.; Haug, R. J.

    2007-04-01

    We demonstrate new results on electron redistribution on a single quantum dot caused by magnetic field. A quantum point contact is used to detect changes in the quantum dot charge. We are able to measure both the change of the quantum dot charge and also changes of the electron configuration at constant number of electrons on the quantum dot. These features are used to exploit the quantum dot in a high magnetic field where transport through the quantum dot displays the effects of Landau shells and spin blockade.

  2. Intracellular delivery and activation of the genetically encoded photosensitizer Killer Red by quantum dots encapsulated in polymeric micelles.

    PubMed

    Muthiah, Muthunarayanan; Park, Seung-Hwan; Nurunnabi, Md; Lee, Jooyoung; Lee, Yong-Kyu; Park, Hansoo; Lee, Byeong-Il; Min, Jung-Joon; Park, In-Kyu

    2014-04-01

    We have prepared polymeric micelle-encapsulating quantum dots (QDots) for delivering the optically activatable protein Killer Red (KR) as a plasmid to cancer cells. QDots absorb light at a lower wavelength and emit light at a higher wavelength in the cell cytoplasm, activating the expressed KR. Once activated, KR triggers the generation of reactive oxygen species (ROS). We prepared cadmium selenide (CdSe)/zinc sulphide (ZnS) QDots and evaluated their optical properties. Subsequently, we performed morphology studies, elemental analysis, thermogravimetric analysis (TGA), and measurements of particle size and surface charge of prepared QDots encapsulated in PHEA-g-PEG-bPEI (PPP-QDot). Cellular uptake of PPP-QDot and PPP-QDot/KR nanoparticles was confirmed using confocal microscopy, and the cellular toxicity and transfection efficiency associated with uptake of PPP-QDot/KR nanoparticles were analyzed. KR expression in normal cells and cancer cells was confirmed using confocal microscopy and Western blotting. Cellular morphologies before and after intracellular activation of KR were observed using phase contrast, fluorescence, and confocal microscopy. Cell fate after exposure to blue light-emitting diode lighting was determined using apoptosis staining and a cell proliferation assay, confirming a suppression in proliferation and a reduction in metabolic activity. We determined that ROS generation contributed to cellular damage after treatment with PPP-QDot/KR nanoparticles and blue light exposure.

  3. Semiconductor Quantum Dots with Photoresponsive Ligands.

    PubMed

    Sansalone, Lorenzo; Tang, Sicheng; Zhang, Yang; Thapaliya, Ek Raj; Raymo, Françisco M; Garcia-Amorós, Jaume

    2016-10-01

    Photochromic or photocaged ligands can be anchored to the outer shell of semiconductor quantum dots in order to control the photophysical properties of these inorganic nanocrystals with optical stimulations. One of the two interconvertible states of the photoresponsive ligands can be designed to accept either an electron or energy from the excited quantum dots and quench their luminescence. Under these conditions, the reversible transformations of photochromic ligands or the irreversible cleavage of photocaged counterparts translates into the possibility to switch luminescence with external control. As an alternative to regulating the photophysics of a quantum dot via the photochemistry of its ligands, the photochemistry of the latter can be controlled by relying on the photophysics of the former. The transfer of excitation energy from a quantum dot to a photocaged ligand populates the excited state of the species adsorbed on the nanocrystal to induce a photochemical reaction. This mechanism, in conjunction with the large two-photon absorption cross section of quantum dots, can be exploited to release nitric oxide or to generate singlet oxygen under near-infrared irradiation. Thus, the combination of semiconductor quantum dots and photoresponsive ligands offers the opportunity to assemble nanostructured constructs with specific functions on the basis of electron or energy transfer processes. The photoswitchable luminescence and ability to photoinduce the release of reactive chemicals, associated with the resulting systems, can be particularly valuable in biomedical research and can, ultimately, lead to the realization of imaging probes for diagnostic applications as well as to therapeutic agents for the treatment of cancer.

  4. Delivering quantum dots to cells: bioconjugated quantum dots for targeted and nonspecific extracellular and intracellular imaging.

    PubMed

    Biju, Vasudevanpillai; Itoh, Tamitake; Ishikawa, Mitsuru

    2010-08-01

    Bioconjugated nanomaterials offer endless opportunities to advance both nanobiotechnology and biomedical technology. In this regard, semiconductor nanoparticles, also called quantum dots, are of particular interest for multimodal, multifunctional and multiplexed imaging of biomolecules, cells, tissues and animals. The unique optical properties, such as size-dependent tunable absorption and emission in the visible and NIR regions, narrow emission and broad absorption bands, high photoluminescence quantum yields, large one- and multi-photon absorption cross-sections, and exceptional photostability are the advantages of quantum dots. Multimodal imaging probes are developed by interfacing the unique optical properties of quantum dots with magnetic or radioactive materials. Besides, crystalline structure of quantum dots adds scope for high-contrast X-ray and TEM imaging. Yet another unique feature of a quantum dot is its spacious and flexible surface which is promising to integrate multiple ligands and antibodies and construct multi-functional probes for bioimaging. In this critical review, we will summarize recent advancements in the preparation of biocompatible quantum dots, bioconjugation of quantum dots, and applications of quantum dots and their bioconjugates for targeted and nonspecific imaging of extracellular and intracellular proteins, organelles and functions (181 references).

  5. Zeeman transitions in spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Yakar, Y.; ćakır, B.; Yılmazer, F.; Özmen, A.

    2017-02-01

    In this study, the effects of external magnetic field on the energy states of a spherical quantum dot with infinite potential barrier have been investigated by using Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method. Linear Zeeman states and Zeeman transition energies are calculated as a function of dot radius and magnetic field strength. We also carry out the effect of external magnetic field on the ground state binding energy. The results show that the impurity energy states, binding energy and Zeeman transition energies are strongly affected by magnetic field strength and dot radius.

  6. Metamorphic quantum dots: Quite different nanostructures

    SciTech Connect

    Seravalli, L.; Frigeri, P.; Nasi, L.; Trevisi, G.; Bocchi, C.

    2010-09-15

    In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantum dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.

  7. Advancements in the Field of Quantum Dots

    NASA Astrophysics Data System (ADS)

    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.

  8. Imaging Quantum Confinement in Multiple Graphene Quantum Dots

    NASA Astrophysics Data System (ADS)

    Wong, Dillon; Velasco, Jairo; Lee, Juwon; Rodriguez-Nieva, Joaquin; Kahn, Salman; Vo, Phong; Tsai, Hsinzon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid; Crommie, Michael

    Quantum dots provide a useful means for controlling the electronic and spin degrees of freedom of mesoscale and nanoscale materials. Here we demonstrate a new method for fabricating interacting graphene quantum dots that is compatible with electrostatic gating and visualization by way of scanning tunneling microscopy (STM). Using this new technique we have created and spatially characterized systems of two or more interacting quantum dots. Our results show that it is possible to engineer electronic wave functions in graphene with a high degree of spatial control.

  9. Quantum-dot-in-perovskite solids.

    PubMed

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H

    2015-07-16

    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.

  10. (In,Mn)As multilayer quantum dot structures

    SciTech Connect

    Bouravleuv, Alexei; Sapega, Victor; Nevedomskii, Vladimir; Khrebtov, Artem; Samsonenko, Yuriy; Cirlin, George

    2014-12-08

    (In,Mn)As multilayer quantum dots structures were grown by molecular beam epitaxy using a Mn selective doping of the central parts of quantum dots. The study of the structural and magneto-optical properties of the samples with three and five layers of (In,Mn)As quantum dots has shown that during the quantum dots assembly, the out-diffusion of Mn from the layers with (In,Mn)As quantum dots can occur resulting in the formation of the extended defects. To produce a high quality structures using the elaborated technique of selective doping, the number of (In,Mn)As quantum dot layers should not exceed three.

  11. Quantum Dot Detector Enhancement for Narrow Band Multispectral Applications

    DTIC Science & Technology

    2013-12-01

    AFRL-RY-WP-TR-2013-0168 QUANTUM DOT DETECTOR ENHANCEMENT FOR NARROW BAND MULTISPECTRAL APPLICATIONS John Derov and Neda Mojaverian... QUANTUM DOT DETECTOR ENHANCEMENT FOR NARROW BAND MULTISPECTRAL APPLICATIONS 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...enhancement of quantum dot photodetectors was also investigated. 15. SUBJECT TERMS quantum dot, quantum well, photodetectors, plasmonics 16

  12. Synthesis of water-dispersible zinc oxide quantum dots with antibacterial activity and low cytotoxicity for cell labeling

    NASA Astrophysics Data System (ADS)

    Hsu, Shan-hui; Lin, Ying Yi; Huang, Sherry; Lem, Kwok Wai; Huong Nguyen, Dinh; Lee, Dai Soo

    2013-11-01

    Typical photoluminescent semiconductor nanoparticles, called quantum dots (QDs), have potential applications in biological labeling. When used to label stem cells, QDs may impair the differentiation capacity of the stem cells. In this study, we synthesized zinc oxide (ZnO) QDs in methanol with an average size of ∼2 nm. We then employed two different types of polyethylene glycol (PEG) molecules (SH-PEG-NH2 and NH2-PEG-NH2) to conjugate ZnO QDs and made them water-dispersible. Fourier transform infrared spectroscopy spectra indicated the attachment of PEG molecules on ZnO QDs. No obvious size alteration was observed for ZnO QDs after PEG conjugation. The water-dispersible ZnO QDs still retained the antibacterial activity and fluorescence intensity. The cytotoxicity evaluation revealed that ZnO QDs at higher concentrations decreased cell viability but were generally safe at 30 ppm or below. Cell lines of hepatocytes (HepG2), osteoblasts (MC3T3-E1) and mesenchymal stem cells (MSCs) were successfully labeled by the water-dispersible ZnO QDs at 30 ppm. The ZnO QD-labeled MSCs maintained their stemness and differentiation capacity. Therefore, we conclude that the water-dispersible ZnO QDs developed in this study have antibacterial activity, low cytotoxicity, and proper labeling efficiency, and can be used to label a variety of cells including stem cells.

  13. Antimicrobial activity of CdS and Ag2S quantum dots immobilized on poly(amidoamine) grafted carbon nanotubes.

    PubMed

    Neelgund, Gururaj M; Oki, Aderemi; Luo, Zhiping

    2012-12-01

    Herein we report the design of antimicrobial nanohybrids, f-MWCNTs-CdS and f-MWCNTs-Ag(2)S developed by covalent grafting of cationic hyperbranched dendritic polyamidoamine (PAMAM) onto multiwalled carbon nanotubes (MWCNTs) and successive deposition of CdS and Ag(2)S quantum dots (QDs). The CdS and Ag(2)S QDs were in situ deposited on PAMAM grafted MWCNTs instead of anchoring the pre-synthesized QDs. The fourth generation, amine terminated hyperbranched PAMAM was grafted on MWCNTs, which was achieved through repetitive reactions of Michael addition of methylmethacrylate to the surface amino groups and amidation of terminal ester groups with ethylenediamine. The covalent grafting of PAMAM onto MWCNTs and the consecutive conjugation of CdS and Ag(2)S QDs were characterized using Fourier transform infrared spectroscopy, elemental analysis, powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy and energy dispersive spectroscopy. The antibacterial activity of f-MWCNTs-CdS and f-MWCNTs-Ag(2)S nanohybrids was evaluated against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus and the results were compared with the activity of carboxylated MWCNTs, PAMAM grafted MWCNTs, PAMAM dendrimer, and CdS and Ag(2)S QDs. It was found that the germicidal action of MWCNTs was enhanced by grafting of PAMAM, which was further improved with immobilization of CdS and Ag(2)S QDs.

  14. Aqueous synthesized near-infrared-emitting quantum dots for RGD-based in vivo active tumour targeting

    NASA Astrophysics Data System (ADS)

    Lu, Yimei; Zhong, Yiling; Wang, Jie; Su, Yuanyuan; Peng, Fei; Zhou, Yanfeng; Jiang, Xiangxu; He, Yao

    2013-04-01

    Over the past two decades, fluorescent quantum dots (QDs) have been highly attractive for a myriad of bioapplications due to their unique optical properties. For bioimaging applications, QD-based in vivo specific tumour targeting is vitally important in the biological and biomedical fields. Aqueous synthesized QDs (aqQDs) exhibit excellent aqueous dispersibility without requiring any post-treatment and have small hydrodynamic diameters (generally <5 nm), which are highly useful for bioimaging applications. We herein present the first example of in vivo active tumour targeting using water-dispersed near-infrared-emitting aqQDs modified with Arg-Gly-Asp (RGD) peptides. In vitro and in vivo studies (e.g., tumour cell labelling, histological analysis, and active tumour targeting) demonstrate that the prepared RGD-decorated aqQDs exhibit highly bio-specific properties, enabling sensitive and specific targeting of tumour sites in both cells and living animals. Our results suggest that the new class of RGD-decorated aqQDs are highly promising as fluorescent bioprobes for a wide range of biological applications.

  15. Silver nanoparticles in combination with acetic acid and zinc oxide quantum dots for antibacterial activities improvement-A comparative study

    NASA Astrophysics Data System (ADS)

    Sedira, Sofiane; Ayachi, Ahmed Abdelhakim; Lakehal, Sihem; Fateh, Merouane; Achour, Slimane

    2014-08-01

    Due to their remarkable antibacterial/antivirus properties, silver nanoparticles (Ag NPs) and zinc oxide quantum dots (ZnO Qds) have been widely used in the antimicrobial field. The mechanism of action of Ag NPs on bacteria was recently studied and it has been proven that Ag NPs exerts their antibacterial activities mainly by the released Ag+. In this work, Ag NPs and ZnO Qds were synthesized using polyol and hydrothermal method, respectively. It was demonstrated that Ag NPs can be oxidized easily in aqueous solution and the addition of acetic acid can increase the Ag+ release which improves the antibacterial activity of Ag NPs. A comparative study between bactericidal effect of Ag NPs/acetic acid and Ag NPs/ZnO Qds on Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia and Staphylococcus aureus was undertaken using agar diffusion method. The obtained colloids were characterized using UV-vis spectroscopy, Raman spectrometry, X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM).

  16. Chemical redox modulated fluorescence of nitrogen-doped graphene quantum dots for probing the activity of alkaline phosphatase.

    PubMed

    Liu, JingJing; Tang, Duosi; Chen, Zhitao; Yan, Xiaomei; Zhong, Zhou; Kang, Longtian; Yao, Jiannian

    2017-03-08

    Alkaline phosphatase (ALP) as an essential enzyme plays an important role in clinical diagnoses and biomedical researches. Hence, the development of convenient and sensitivity assay for monitoring ALP is extremely important. In this work, on the basis of chemical redox strategy to modulate the fluorescence of nitrogen-doped graphene quantum dots (NGQDs), a novel label-free fluorescent sensing system for the detection of alkaline phosphatase (ALP) activity has been developed. The fluorescence of NGQDs is firstly quenched by ultrathin cobalt oxyhydroxide (CoOOH) nanosheets, and then restored by ascorbic acid (AA), which can reduce CoOOH to Co(2+), thus the ALP can be monitored based on the enzymatic hydrolysis of L-ascorbic acid-2-phosphate (AAP) by ALP to generate AA. Quantitative evaluation of ALP activity in a range from 0.1 to 5U/L with the detection limit of 0.07U/L can be realized in this sensing system. Endowed with high sensitivity and selectivity, the proposed assay is capable of detecting ALP in biological system with satisfactory results. Meanwhile, this sensing system can be easily extended to the detection of various AA-involved analytes.

  17. Electromechanical transition in quantum dots

    NASA Astrophysics Data System (ADS)

    Micchi, G.; Avriller, R.; Pistolesi, F.

    2016-09-01

    The strong coupling between electronic transport in a single-level quantum dot and a capacitively coupled nanomechanical oscillator may lead to a transition towards a mechanically bistable and blocked-current state. Its observation is at reach in carbon-nanotube state-of-art experiments. In a recent publication [Phys. Rev. Lett. 115, 206802 (2015), 10.1103/PhysRevLett.115.206802] we have shown that this transition is characterized by pronounced signatures on the oscillator mechanical properties: the susceptibility, the displacement fluctuation spectrum, and the ring-down time. These properties are extracted from transport measurements, however the relation between the mechanical quantities and the electronic signal is not always straightforward. Moreover the dependence of the same quantities on temperature, bias or gate voltage, and external dissipation has not been studied. The purpose of this paper is to fill this gap and provide a detailed description of the transition. Specifically we find (i) the relation between the current-noise and the displacement spectrum; (ii) the peculiar behavior of the gate-voltage dependence of these spectra at the transition; (iii) the robustness of the transition towards the effect of external fluctuations and dissipation.

  18. Quantum analysis of plasmonic coupling between quantum dots and nanoparticles

    NASA Astrophysics Data System (ADS)

    Ahmad, SalmanOgli

    2016-10-01

    In this study, interaction between core-shells nanoparticles and quantum dots is discussed via the full-quantum-theory method. The electromagnetic field of the nanoparticles is derived by the quasistatic approximation method and the results for different regions of the nanoparticles are quantized from the time-harmonic to the wave equation. Utilizing the optical field quantization, the nanoparticles' and quantum dots' deriving amplitudes contributing to the excitation waves are determined. In the current model, two counterpropagating waves with two different frequencies are applied. We derived the Maxwell-Bloch equations from the Heisenberg-Langevin equations; thus the nanoparticles-quantum dots interaction is perused. Moreover, by full quantum analyzing of the analytical expression, the quantum-plasmonic coupling relation and the Purcell factor are achieved. We show that the spontaneous emission of quantum dots can be dramatically manipulated by engineering the plasmon-plasmon interaction in the core-shells nanoparticles. This issue is a very attractive point for designing a wide variety of quantum-plasmonic sensors. Through the investigation of the nanoparticle plasmonic interaction effects on absorbed power, the results show that the nanoparticles' and quantum dots' absorption saturation state can be switched to each other just by manipulation of their deriving amplitudes. In fact, we manage the interference between the two waves' deriving amplitudes just by the plasmonic interactions effect.

  19. Quantum dots for light emitting diodes.

    PubMed

    Qasim, Khan; Lei, Wei; Li, Qing

    2013-05-01

    In this article we discuss the development and key advantages of quantum dot based light emitting diode (QD-LED) and other applications based on their color purity, stability, and solution processibility. Analysis of quantum dot based LEDs and the main challenges faced in this field, such as the QD luminescence quenching, QD charging in thin films, and external quantum efficiency are discussed in detail. The description about how different optical down-conversion and structures enabled researchers to overcome these challenges and to commercialize the products. The recent developments about how to overcome these difficulties have also been discussed in this article.

  20. Origins and optimization of entanglement in plasmonically coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Otten, Matthew; Larson, Jeffrey; Min, Misun; Wild, Stefan M.; Pelton, Matthew; Gray, Stephen K.

    2016-08-01

    A system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines for maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.

  1. CdSe/ZnS quantum dots induce hepatocyte pyroptosis and liver inflammation via NLRP3 inflammasome activation.

    PubMed

    Lu, Yonghui; Xu, Shangcheng; Chen, Haiyan; He, Mindi; Deng, Youcai; Cao, Zhengwang; Pi, Huifeng; Chen, Chunhai; Li, Min; Ma, Qinlong; Gao, Peng; Ji, Yan; Zhang, Lei; Yu, Zhengping; Zhou, Zhou

    2016-06-01

    Increased biomedical applications of quantum dots (QDs) have raised considerable concern regarding their toxicological impact. However, the toxicity of QDs is largely unknown and the underlying mechanism is still undefined. This study was conducted to examine the hepatotoxicity of CdSe/ZnS core/shell QDs and the underlying mechanism. In hepatic L02 cells, the QDs caused cytotoxicity in a dose-dependent manner. The QDs were then shown to activate the NLR pyrin domain containing 3 (NLRP3) inflammasome in hepatocytes, leading to a novel pro-inflammatory form of cell death named pyroptosis. Further experiments demonstrated that the QDs induced mitochondrial reactive oxygen species (mtROS) production, and that both a mtROS and a total ROS scavenger attenuated QDs-induced NLRP3 activation and pyroptosis. In addition, QDs increased cytoplasmic calcium (Ca(2+)) levels, while a Ca(2+) release antagonist and chelator alleviated QDs-induced mtROS, NLRP3 activation and subsequent pyroptosis in hepatocytes. In vivo, QDs administration induced liver inflammation and dysfunction. Moreover, the QDs also resulted in NLRP3 activation in liver tissue. However, QDs-induced liver inflammation and dysfunction were abolished in NLRP3 knockout mice. Also, an elevation in mtROS was observed in liver after QDs administration, and the mtROS scavenger suppressed liver NLRP3 activation, inflammation and dysfunction induced by QDs. Our data suggest that QDs induced hepatocyte pyroptosis, liver inflammation and dysfunction via NLRP3 activation, which was caused by QDs-triggered mtROS production and Ca(2+) mobilization. Our results provide novel insights into QDs-induced hepatotoxicity and the underlying mechanism, facilitating control of the side effects of QDs.

  2. Dot-in-Well Quantum-Dot Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath; Bandara, Sumith; Ting, David; Hill, cory; Liu, John; Mumolo, Jason; Chang, Yia Chung

    2008-01-01

    Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material

  3. Photocatalytic activity of CdS and Ag(2)S quantum dots deposited on poly(amidoamine) functionalized carbon nanotubes.

    PubMed

    Neelgund, Gururaj M; Oki, Aderemi

    2011-10-02

    Two novel ternary nanocatalysts, f-MWCNTs-CdS and f-MWCNTs-Ag(2)S were successfully constructed by covalent grafting of fourth generation (G4) hyperbranched, crosslinked poly(amidoamine) (PAMAM) to carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and subsequent deposition of CdS or Ag(2)S quantum dots (QDs). The structural transformation, surface potential, and morphology of functionalized MWCNTs (f-MWCNTs) and nanocatalysts were characterized by UV-vis spectrophotometer, Fourier transform infrared spectroscopy, powder X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, scanning electron microscopy and energy dispersive spectroscopy. Transmission electron microscopy reveals the effective anchoring of QDs on f-MWCNTs. The catalytic activity of nanocatalysts was evaluated by photodegradation of methyl orange under illumination of UV light. The coupling of MWCNTs, PAMAM and CdS or Ag(2)S QDs significantly enhanced the catalytic efficiency of nanocatalysts. The rate constants for degradation of methyl orange in presence of nanocatalysts were calculated using the Langmuir-Hinshelwood model. Overall, the excellence in photodegradation was accomplished by hybridizing f-MWCNTs with CdS or Ag(2)S.

  4. Crossover between Anti- and Pro-oxidant Activities of Graphene Quantum Dots in the Absence or Presence of Light.

    PubMed

    Chong, Yu; Ge, Cuicui; Fang, Ge; Tian, Xin; Ma, Xiaochuan; Wen, Tao; Wamer, Wayne G; Chen, Chunying; Chai, Zhifang; Yin, Jun-Jie

    2016-09-27

    Graphene quantum dots (GQDs), zero-dimensional carbon materials displaying excellent luminescence properties, show great promise for medical applications such as imaging, drug delivery, biosensors, and novel therapeutics. A deeper understanding of how the properties of GQDs interact with biological systems is essential for these applications. Our work demonstrates that GQDs can efficiently scavenge a number of free radicals and thereby protect cells against oxidative damage. However, upon exposure to blue light, GQDs exhibit significant phototoxicity through increasing intracellular reactive oxygen species (ROS) levels and reducing cell viability, attributable to the generation of free radicals under light excitation. We confirm that light-induced formation of ROS originates from the electron-hole pair and, more importantly, reveal that singlet oxygen is generated by photoexcited GQDs via both energy-transfer and electron-transfer pathways. Moreover, upon light excitation, GQDs accelerate the oxidation of non-enzymic anti-oxidants and promote lipid peroxidation, contributing to the phototoxicity of GQDs. Our results reveal that GQDs can display both anti- and pro-oxidant activities, depending upon light exposure, which will be useful in guiding the safe application and development of potential anticancer/antibacterial applications for GQDs.

  5. Theoretical issues in silicon quantum dot qubits

    NASA Astrophysics Data System (ADS)

    Koh, Teck Seng

    Electrically-gated quantum dots in semiconductors is an excellent architecture on which to make qubits for quantum information processing. Silicon is attractive because of the potential for excellent manipulability, scalability, and for integration with classical electronics. This thesis describes several aspects of the theoretical issues related to quantum dot qubits in silicon. It may be broadly divided into three parts — (1) the hybrid qubit and quantum gates, (2) decoherence and (3) charge transport. In the first part, we present a novel architecture for a double quantum dot spin qubit, which we term the hybrid qubit, and demonstrate that implementing this qubit in silicon is feasible. Next, we consider both AC and DC quantum gating protocols and compare the optimal fidelities for these protocols that can be achieved for both the hybrid qubit and the more traditional singlet-triplet qubit. In the second part, we present evidence that silicon offers superior coherence properties by analyzing experimental data from which charge dephasing and spin relaxation times are extracted. We show that the internal degrees of freedom of the hybrid qubit enhance charge coherence, and demonstrate tunable spin loading of a quantum dot. In the last part, we explain three key features of spin-dependent transport — spin blockade, lifetime-enhanced transport and spin-flip cotunneling. We explain how these features arise in the conventional two-electron as well as the unconventional three-electron regimes, using a theoretical model that captures the key characteristics observed in the data.

  6. Quantum efficiency of a double quantum dot microwave photon detector

    NASA Astrophysics Data System (ADS)

    Wong, Clement; Vavilov, Maxim

    Motivated by recent interest in implementing circuit quantum electrodynamics with semiconducting quantum dots, we study charge transfer through a double quantum dot (DQD) capacitively coupled to a superconducting cavity subject to a microwave field. We analyze the DQD current response using input-output theory and determine the optimal parameter regime for complete absorption of radiation and efficient conversion of microwave photons to electric current. For experimentally available DQD systems, we show that the cavity-coupled DQD operates as a photon-to-charge converter with quantum efficiencies up to 80% C.W. acknowledges support by the Intelligence Community Postdoctoral Research Fellowship Program.

  7. Quantum Hall ferrimagnetism in lateral quantum dot molecules.

    PubMed

    Abolfath, Ramin M; Hawrylak, Pawel

    2006-11-03

    We demonstrate the existence of ferrimagnetic and ferromagnetic phases in a spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall regime. The spin phase diagram is determined from the Hartree-Fock configuration interaction method as a function of electron number N and magnetic field B. The quantum Hall ferrimagnetic phase corresponds to spatially imbalanced spin droplets resulting from strong interdot coupling of identical dots. The quantum Hall ferromagnetic phases correspond to ferromagnetic coupling of spin polarization at filling factors between nu=2 and nu=1.

  8. Surface treatment of nanocrystal quantum dots after film deposition

    DOEpatents

    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.

  9. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    DOEpatents

    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.

  10. Complex Förster energy transfer interactions between semiconductor quantum dots and a redox-active osmium assembly.

    PubMed

    Stewart, Michael H; Huston, Alan L; Scott, Amy M; Efros, Alexander L; Melinger, Joseph S; Gemmill, Kelly Boeneman; Trammell, Scott A; Blanco-Canosa, Juan B; Dawson, Philip E; Medintz, Igor L

    2012-06-26

    The ability of luminescent semiconductor quantum dots (QDs) to engage in diverse energy transfer processes with organic dyes, light-harvesting proteins, metal complexes, and redox-active labels continues to stimulate interest in developing them for biosensing and light-harvesting applications. Within biosensing configurations, changes in the rate of energy transfer between the QD and the proximal donor, or acceptor, based upon some external (biological) event form the principle basis for signal transduction. However, designing QD sensors to function optimally is predicated on a full understanding of all relevant energy transfer mechanisms. In this report, we examine energy transfer between a range of CdSe-ZnS core-shell QDs and a redox-active osmium(II) polypyridyl complex. To facilitate this, the Os complex was synthesized as a reactive isothiocyanate and used to label a hexahistidine-terminated peptide. The Os-labeled peptide was ratiometrically self-assembled to the QDs via metal affinity coordination, bringing the Os complex into close proximity of the nanocrystal surface. QDs displaying different emission maxima were assembled with increasing ratios of Os-peptide complex and subjected to detailed steady-state, ultrafast transient absorption, and luminescence lifetime decay analyses. Although the possibility exists for charge transfer quenching interactions, we find that the QD donors engage in relatively efficient Förster resonance energy transfer with the Os complex acceptor despite relatively low overall spectral overlap. These results are in contrast to other similar QD donor-redox-active acceptor systems with similar separation distances, but displaying far higher spectral overlap, where charge transfer processes were reported to be the dominant QD quenching mechanism.

  11. Quantum-dot-based cell motility assay.

    PubMed

    Gu, Weiwei; Pellegrino, Teresa; Parak, Wolfgang J; Boudreau, Rosanne; Le Gros, Mark A; Gerion, Daniele; Alivisatos, A Paul; Larabell, Carolyn A

    2005-06-28

    Because of their favorable physical and photochemical properties, colloidal CdSe/ZnS-semiconductor nanocrystals (commonly known as quantum dots) have enormous potential for use in biological imaging. In this report, we present an assay that uses quantum dots as markers to quantify cell motility. Cells that are seeded onto a homogeneous layer of quantum dots engulf and absorb the nanocrystals and, as a consequence, leave behind a fluorescence-free trail. By subsequently determining the ratio of cell area to fluorescence-free track area, we show that it is possible to differentiate between invasive and noninvasive cancer cells. Because this assay uses simple fluorescence detection, requires no significant data processing, and can be used in live-cell studies, it has the potential to be a powerful new tool for discriminating between invasive and noninvasive cancer cell lines or for studying cell signaling events involved in migration.

  12. Angiogenic Profiling of Synthesized Carbon Quantum Dots.

    PubMed

    Shereema, R M; Sruthi, T V; Kumar, V B Sameer; Rao, T P; Shankar, S Sharath

    2015-10-20

    A simple method was employed for the synthesis of green luminescent carbon quantum dots (CQDs) from styrene soot. The CQDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, and Raman spectroscopy. The prepared carbon quantum dots did not show cellular toxicity and could successfully be used for labeling cells. We also evaluated the effects of carbon quantum dots on the process of angiogenesis. Results of a chorioallantoic membrane (CAM) assay revealed the significant decrease in the density of branched vessels after their treatment with CQDs. Further application of CQDs significantly downregulated the expression levels of pro-angiogenic growth factors like VEGF and FGF. Expression of VEGFR2 and levels of hemoglobin were also significantly lower in CAMs treated with CQDs, indicating that the CQDs inhibit angiogenesis. Data presented here also show that CQDs can selectively target cancer cells and therefore hold potential in the field of cancer therapy.

  13. Fluorescence correlation spectroscopy using quantum dots: advances, challenges and opportunities.

    PubMed

    Heuff, Romey F; Swift, Jody L; Cramb, David T

    2007-04-28

    Semiconductor nanocrystals (quantum dots) have been increasingly employed in measuring the dynamic behavior of biomacromolecules using fluorescence correlation spectroscopy. This poses a challenge, because quantum dots display their own dynamic behavior in the form of intermittent photoluminescence, also known as blinking. In this review, the manifestation of blinking in correlation spectroscopy will be explored, preceded by an examination of quantum dot blinking in general.

  14. Potential clinical applications of quantum dots.

    PubMed

    Medintz, Igor L; Mattoussi, Hedi; Clapp, Aaron R

    2008-01-01

    The use of luminescent colloidal quantum dots in biological investigations has increased dramatically over the past several years due to their unique size-dependent optical properties and recent advances in biofunctionalization. In this review, we describe the methods for generating high-quality nanocrystals and report on current and potential uses of these versatile materials. Numerous examples are provided in several key areas including cell labeling, biosensing, in vivo imaging, bimodal magnetic-luminescent imaging, and diagnostics. We also explore toxicity issues surrounding these materials and speculate about the future uses of quantum dots in a clinical setting.

  15. Carcinogenic activity of PbS quantum dots screened using exosomal biomarkers secreted from HEK293 cells.

    PubMed

    Kim, Jung-Hee; Kim, Hye-Rim; Lee, Bo-Ram; Choi, Eun-Sook; In, Su-Il; Kim, Eunjoo

    2015-01-01

    Lead sulfide (PbS) quantum dots (QDs) have been applied in the biomedical area because they offer an excellent platform for theragnostic applications. In order to comprehensively evaluate the biocompatibility of PbS QDs in human cells, we analyzed the exosomes secreted from cells because exosomes are released during cellular stress to convey signals to other cells and serve as a reservoir of enriched biomarkers. PbS QDs were synthesized and coated with 3-mercaptopropionic acid (MPA) to allow the particles to disperse in water. Exosomes were isolated from HEK293 cells treated with PbS-MPA at concentrations of 0 µg/mL, 5 µg/mL, and 50 µg/mL, and the exosomal expression levels of miRNAs and proteins were analyzed. As a result, five miRNAs and two proteins were proposed as specific exosomal biomarkers for the exposure of HEK293 cells to PbS-MPA. Based on the pathway analysis, the molecular signature of the exosomes suggested that PbS-MPA QDs had carcinogenic activity. The comet assay and expression of molecular markers, such as p53, interleukin (IL)-8, and C-X-C motif chemokine 5, indicated that DNA damage occurred in HEK293 cells following PbS-MPA exposure, which supported the carcinogenic activity of the particles. In addition, there was obvious intensification of miRNA expression signals in the exosomes compared with that of the parent cells, which suggested that exosomal biomarkers could be detected more sensitively than those of whole cellular extracts.

  16. Carcinogenic activity of PbS quantum dots screened using exosomal biomarkers secreted from HEK293 cells

    PubMed Central

    Kim, Jung-Hee; Kim, Hye-Rim; Lee, Bo-Ram; Choi, Eun-Sook; In, Su-Il; Kim, Eunjoo

    2015-01-01

    Lead sulfide (PbS) quantum dots (QDs) have been applied in the biomedical area because they offer an excellent platform for theragnostic applications. In order to comprehensively evaluate the biocompatibility of PbS QDs in human cells, we analyzed the exosomes secreted from cells because exosomes are released during cellular stress to convey signals to other cells and serve as a reservoir of enriched biomarkers. PbS QDs were synthesized and coated with 3-mercaptopropionic acid (MPA) to allow the particles to disperse in water. Exosomes were isolated from HEK293 cells treated with PbS–MPA at concentrations of 0 µg/mL, 5 µg/mL, and 50 µg/mL, and the exosomal expression levels of miRNAs and proteins were analyzed. As a result, five miRNAs and two proteins were proposed as specific exosomal biomarkers for the exposure of HEK293 cells to PbS–MPA. Based on the pathway analysis, the molecular signature of the exosomes suggested that PbS–MPA QDs had carcinogenic activity. The comet assay and expression of molecular markers, such as p53, interleukin (IL)-8, and C-X-C motif chemokine 5, indicated that DNA damage occurred in HEK293 cells following PbS–MPA exposure, which supported the carcinogenic activity of the particles. In addition, there was obvious intensification of miRNA expression signals in the exosomes compared with that of the parent cells, which suggested that exosomal biomarkers could be detected more sensitively than those of whole cellular extracts. PMID:26355701

  17. Monolithic mode-locked quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Penty, R. V.; Thompson, M. G.; White, I. H.

    2008-02-01

    Monolithic mode-locked laser diodes based on QD active regions are regarded as potentially suitable for a large range of photonic applications due to their compactness, mechanical stability and robustness, high potential repetition rates and low potential jitter. Their inherent properties, such as high differential gain, low chirp and fast saturable absorption have led to demonstration of improved performance over their QW equivalents. Low background loss and the relatively long lengths of quantum dot laser devices also have encouraged studies of mode-locking at repetition rates previously not explored in monolithic devices. Applications include biomedicine, high-speed data transmission, clock signal generation and electro-optic sampling. This paper reviews some of the work at Cambridge on the realization of such devices.

  18. Quantum Entanglement of Quantum Dot Spin Using Flying Qubits

    DTIC Science & Technology

    2015-05-01

    ASSIGNED DISTRIBUTION STATEMENT. FOR THE DIRECTOR: / S / PAUL ALSING Work Unit Manager / S / MARK H. LINDERMAN Technical Advisor...been to advance the frontier of quantum entangled semiconductor electrons using ultrafast optical techniques . The approach is based on...15. SUBJECT TERMS Quantum Dots, ultrafast optical techniques , Coulomb blockade, two-photon (Raman) transitions 16. SECURITY CLASSIFICATION OF: 17

  19. Trapping of an electron in coupled quantum dots in graphene

    NASA Astrophysics Data System (ADS)

    Hewageegana, Prabath; Apalkov, Vadym

    2009-03-01

    Due to Klein’s tunneling the electronic states of a quantum dot in graphene have finite widths and an electron in quantum dot has a finite trapping time. This property introduces a special type of interdot coupling in a system of many quantum dots in graphene. The interdot coupling is realized not as a direct tunneling between quantum dots but as coupling through the continuum states of graphene. As a result the interdot coupling modifies both the positions and the widths of the energy levels of the quantum dot system. We study the system of quantum dots in graphene theoretically by analyzing the complex energy spectra of the quantum dot system. We show that in a double-dot system some energy levels become strongly localized with an infinite trapping time. Such strongly localized states are achieved only at one value of the interdot separation. We also study a periodic array of quantum dots in graphene within a tight-binding mode for a quantum dot system. The values of the hopping integrals in the tight-binding model are found from the expression for the energy spectra of the double quantum dot system. In the array of quantum dots the states with infinitely large trapping time are realized at all values of interdot separation smaller than some critical value. Such states have nonzero wave vectors.

  20. Probing silicon quantum dots by single-dot techniques

    NASA Astrophysics Data System (ADS)

    Sychugov, Ilya; Valenta, Jan; Linnros, Jan

    2017-02-01

    Silicon nanocrystals represent an important class of non-toxic, heavy-metal free quantum dots, where the high natural abundance of silicon is an additional advantage. Successful development in mass-fabrication, starting from porous silicon to recent advances in chemical and plasma synthesis, opens up new possibilities for applications in optoelectronics, bio-imaging, photovoltaics, and sensitizing areas. In this review basic physical properties of silicon nanocrystals revealed by photoluminescence spectroscopy, lifetime, intensity trace and electrical measurements on individual nanoparticles are summarized. The fabrication methods developed for accessing single Si nanocrystals are also reviewed. It is concluded that silicon nanocrystals share many of the properties of direct bandgap nanocrystals exhibiting sharp emission lines at low temperatures, on/off blinking, spectral diffusion etc. An analysis of reported results is provided in comparison with theory and with direct bandgap material quantum dots. In addition, the role of passivation and inherent interface/matrix defects is discussed.

  1. Quantum criticality in a double-quantum-dot system.

    PubMed

    Zaránd, Gergely; Chung, Chung-Hou; Simon, Pascal; Vojta, Matthias

    2006-10-20

    We discuss the realization of the quantum-critical non-Fermi-liquid state, originally discovered within the two-impurity Kondo model, in double-quantum-dot systems. Contrary to common belief, the corresponding fixed point is robust against particle-hole and various other asymmetries and is unstable only to charge transfer between the two dots. We propose an experimental setup where such charge transfer processes are suppressed, allowing a controlled approach to the quantum-critical state. We also discuss transport and scaling properties in the vicinity of the critical point.

  2. Quantum-confined Stark effects in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Wen, G. W.; Lin, J. Y.; Jiang, H. X.; Chen, Z.

    1995-08-01

    Quantum-confined Stark effects (QCSE) on excitons, i.e., the influence of a uniform electric field on the confined excitons in semiconductor quantum dots (QD's), have been studied by using a numerical matrix-diagonalization scheme. The energy levels and the wave functions of the ground and several excited states of excitons in CdS and CdS1-xSex quantum dots as functions of the size of the quantum dot and the applied electric field have been obtained. The electron and hole distributions and wave function overlap inside the QD's have also been calculated for different QD sizes and electric fields. It is found that the electron and hole wave function overlap decreases under an electric field, which implies an increased exciton recombination lifetime due to QCSE. The energy level redshift and the enhancement of the exciton recombination lifetime are due to the polarization of the electron-hole pair under the applied electric field.

  3. Application of zinc oxide quantum dots in food safety

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Zinc oxide quantum dots (ZnO QDs) are nanoparticles of purified powdered ZnO. The ZnO QDs were directly added into liquid foods or coated on the surface of glass jars using polylactic acid (PLA) as a carrier. The antimicrobial activities of ZnO QDs against Listeria monocytogenes, Salmonella Enteriti...

  4. Full-colour quantum dot displays fabricated by transfer printing

    NASA Astrophysics Data System (ADS)

    Kim, Tae-Ho; Cho, Kyung-Sang; Lee, Eun Kyung; Lee, Sang Jin; Chae, Jungseok; Kim, Jung Woo; Kim, Do Hwan; Kwon, Jang-Yeon; Amaratunga, Gehan; Lee, Sang Yoon; Choi, Byoung Lyong; Kuk, Young; Kim, Jong Min; Kim, Kinam

    2011-03-01

    Light-emitting diodes with quantum dot luminophores show promise in the development of next-generation displays, because quantum dot luminophores demonstrate high quantum yields, extremely narrow emission, spectral tunability and high stability, among other beneficial characteristics. However, the inability to achieve size-selective quantum dot patterning by conventional methods hinders the realization of full-colour quantum dot displays. Here, we report the first demonstration of a large-area, full-colour quantum dot display, including in flexible form, using optimized quantum dot films, and with control of the nano-interfaces and carrier behaviour. Printed quantum dot films exhibit excellent morphology, well-ordered quantum dot structure and clearly defined interfaces. These characteristics are achieved through the solvent-free transfer of quantum dot films and the compact structure of the quantum dot networks. Significant enhancements in charge transport/balance in the quantum dot layer improve electroluminescent performance. A method using plasmonic coupling is also suggested to further enhance luminous efficiency. The results suggest routes towards creating large-scale optoelectronic devices in displays, solid-state lighting and photovoltaics.

  5. Magnetic control of dipolaritons in quantum dots.

    PubMed

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

    2016-12-21

    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.

  6. Structural and optical characterization of pure and starch-capped ZnO quantum dots and their photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Vidhya, K.; Saravanan, M.; Bhoopathi, G.; Devarajan, V. P.; Subanya, S.

    2015-02-01

    Among the different types of metal oxides, zinc oxide (ZnO) is a most commonly used metal oxide in a broad variety of applications. In the present investigation, a modified green synthesis route was used to synthesize pure and starch-capped ZnO (ZnO/starch) quantum dots (QDs) and studied their structural and optical characteristics. In this study, hexagonal crystal structure was observed in both pure and ZnO/starch QDs using X-ray diffraction technique. A spherical-shaped surface morphology was found with the size of 5-10 nm using transmission electron microscope technique. The interaction between ZnO QDs and starch molecules was proved via Fourier infra-red spectrometer technique. On the other hand, their fluorescence behaviors were investigated using photoluminescence technique, in that the ZnO/starch QDs showed an enhanced emission behavior when compared to the pure ZnO QDs. Further, the solar photocatalytic activity of both the ZnO QDs was examined with the dye Rhodamine B (RhB) at the end of 30, 60, 90, and 120 min. In this, ZnO/starch QDs show a good and more decomposition of RhB than pure ZnO QDs. Collectively, in the present study, green synthesis route produced an efficient QDs (pure and ZnO/starch) and it will be very useful for many other QDs. The ZnO/starch QDs are suitable for decomposing the RhB and other toxic organic dyes.

  7. Theory of a double-quantum-dot spaser

    SciTech Connect

    Andrianov, E S; Pukhov, A A; Dorofeenko, A V; Vinogradov, A P; Lisyansky, A A

    2015-03-31

    We consider the influence of the number of quantum dots on spaser operation. It is shown that even in the presence of only two quantum dots, the spaser behaviour is qualitatively different from that of the previously studied spaser consisting of a nanoparticle and a single quantum dot. In particular, for nonzero detuning of resonant frequencies of a nanoparticle and quantum dots, an increase in the interaction constant between quantum dots first leads to a decrease in the spasing threshold and then to its growth and even the spasing breakdown. (nanostructures)

  8. PREFACE: Quantum dots as probes in biology

    NASA Astrophysics Data System (ADS)

    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

  9. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    SciTech Connect

    Singh, Neetu Kapoor, Avinashi; Kumar, Vinod; Mehra, R. M.

    2014-04-24

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5.

  10. Slow Electron Cooling in Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Pandey, Anshu; Guyot-Sionnest, Philippe

    2008-11-01

    Hot electrons in semiconductors lose their energy very quickly (within picoseconds) to lattice vibrations. Slowing this energy loss could prove useful for more efficient photovoltaic or infrared devices. With their well-separated electronic states, quantum dots should display slow relaxation, but other mechanisms have made it difficult to observe. We report slow intraband relaxation (>1 nanosecond) in colloidal quantum dots. The small cadmium selenide (CdSe) dots, with an intraband energy separation of ~0.25 electron volts, are capped by an epitaxial zinc selenide (ZnSe) shell. The shell is terminated by a CdSe passivating layer to remove electron traps and is covered by ligands of low infrared absorbance (alkane thiols) at the intraband energy. We found that relaxation is markedly slowed with increasing ZnSe shell thickness.

  11. Monolithically integrated single quantum dots coupled to bowtie nanoantennas

    NASA Astrophysics Data System (ADS)

    Lyamkina, A. A.; Schraml, K.; Regler, A.; Schalk, M.; Bakarov, A. K.; Toropov, A. I.; Moshchenko, S. P.; Kaniber, Michael

    2016-12-01

    Deterministically integrating semiconductor quantum emitters with plasmonic nano-devices paves the way towards chip-scale integrable, true nanoscale quantum photonics technologies. For this purpose, stable and bright semiconductor emitters are needed, which moreover allow for CMOS-compatibility and optical activity in the telecommunication band. Here, we demonstrate strongly enhanced light-matter coupling of single near-surface ($<10\\,nm$) InAs quantum dots monolithically integrated into electromagnetic hot-spots of sub-wavelength sized metal nanoantennas. The antenna strongly enhances the emission intensity of single quantum dots by up to $\\sim16\\times$, an effect accompanied by an up to $3.4\\times$ Purcell-enhanced spontaneous emission rate. Moreover, the emission is strongly polarised along the antenna axis with degrees of linear polarisation up to $\\sim85\\,\\%$. The results unambiguously demonstrate the efficient coupling of individual quantum dots to state-of-the-art nanoantennas. Our work provides new perspectives for the realisation of quantum plasmonic sensors, step-changing photovoltaic devices, bright and ultrafast quantum light sources and efficent nano-lasers.

  12. Producing Quantum Dots by Spray Pyrolysis

    NASA Technical Reports Server (NTRS)

    Banger, Kulbinder; Jin, Michael H.; Hepp, Aloysius

    2006-01-01

    An improved process for making nanocrystallites, commonly denoted quantum dots (QDs), is based on spray pyrolysis. Unlike the process used heretofore, the improved process is amenable to mass production of either passivated or non-passivated QDs, with computer control to ensure near uniformity of size.

  13. Quantum-dot infrared photodetectors: a review

    NASA Astrophysics Data System (ADS)

    Stiff-Roberts, Adrienne D.

    2009-04-01

    Quantum-dot infrared photodetectors (QDIPs) are positioned to become an important technology in the field of infrared (IR) detection, particularly for high-temperature, low-cost, high-yield detector arrays required for military applications. High-operating temperature (>=150 K) photodetectors reduce the cost of IR imaging systems by enabling cryogenic dewars and Stirling cooling systems to be replaced by thermo-electric coolers. QDIPs are well-suited for detecting mid-IR light at elevated temperatures, an application that could prove to be the next commercial market for quantum dots. While quantum dot epitaxial growth and intraband absorption of IR radiation are well established, quantum dot non-uniformity remains as a significant challenge. Nonetheless, state-of-the-art mid-IR detection at 150 K has been demonstrated using 70-layer InAs/GaAs QDIPs, and QDIP focal plane arrays are approaching performance comparable to HgCdTe at 77 K. By addressing critical challenges inherent to epitaxial QD material systems (e.g., controlling dopant incorporation), exploring alternative QD systems (e.g., colloidal QDs), and using bandgap engineering to reduce dark current and enhance multi-spectral detection (e.g. resonant tunneling QDIPs), the performance and applicability of QDIPs will continue to improve.

  14. Nanocomposites of POC and quantum dots

    NASA Astrophysics Data System (ADS)

    Borriello, C.; Concilio, S.; Minarini, C.; Iannelli, P.; Di Luccio, T.

    2012-07-01

    New luminescent polymer nanocomposites were synthesized combining carbazole/oxadiazole copolymer (POC) and CdSe/ZnS quantum dots (QDs) surface passivated by ionic liquids. Ionic liquid ligands improve the photostability of QDs and their compatibility with polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites were characterized by UV and photoluminescence spectroscopy.

  15. Optical properties of quantum-dot-doped liquid scintillators

    PubMed Central

    Aberle, C.; Li, J.J.; Weiss, S.; Winslow, L.

    2014-01-01

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO. PMID:25392711

  16. Optical properties of quantum-dot-doped liquid scintillators

    NASA Astrophysics Data System (ADS)

    Aberle, C.; Li, J. J.; Weiss, S.; Winslow, L.

    2013-10-01

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.

  17. Optical properties of quantum-dot-doped liquid scintillators.

    PubMed

    Aberle, C; Li, J J; Weiss, S; Winslow, L

    2013-10-14

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.

  18. Nonlinear optical properties and supercontinuum spectrum of titania-modified carbon quantum dots

    NASA Astrophysics Data System (ADS)

    Kulchin, Yu N.; Mayor, A. Yu; Proschenko, D. Yu; Postnova, I. V.; Shchipunov, Yu A.

    2016-04-01

    We have studied the nonlinear optical properties and supercontinuum spectrum of solutions of carbon quantum dots prepared by a hydrothermal process from chitin and then coated with titania. The titania coating has been shown to have an activating effect on the carbon quantum dots, enhancing supercontinuum generation in the blue-violet spectral region and enabling their nonlinear optical characteristics to be varied.

  19. Non-Markovian full counting statistics in quantum dot molecules

    PubMed Central

    Xue, Hai-Bin; Jiao, Hu-Jun; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-01-01

    Full counting statistics of electron transport is a powerful diagnostic tool for probing the nature of quantum transport beyond what is obtainable from the average current or conductance measurement alone. In particular, the non-Markovian dynamics of quantum dot molecule plays an important role in the nonequilibrium electron tunneling processes. It is thus necessary to understand the non-Markovian full counting statistics in a quantum dot molecule. Here we study the non-Markovian full counting statistics in two typical quantum dot molecules, namely, serially coupled and side-coupled double quantum dots with high quantum coherence in a certain parameter regime. We demonstrate that the non-Markovian effect manifests itself through the quantum coherence of the quantum dot molecule system, and has a significant impact on the full counting statistics in the high quantum-coherent quantum dot molecule system, which depends on the coupling of the quantum dot molecule system with the source and drain electrodes. The results indicated that the influence of the non-Markovian effect on the full counting statistics of electron transport, which should be considered in a high quantum-coherent quantum dot molecule system, can provide a better understanding of electron transport through quantum dot molecules. PMID:25752245

  20. Innovative Ge Quantum Dot Functional Sensing/Metrology Devices

    DTIC Science & Technology

    2015-05-20

    QDs of desired size with high addressability In order to fully exert quantum mechanics effects arising from zero-dimensional quantum -dot structures...Final 3. DATES COVERED (From - To) 20140507 - 20150506 4. TITLE AND SUBTITLE Innovative Ge Quantum Dot Functional Sensing/Metrology...distinctive Coulomb blockade and quantum confinement effects onto nanometer-scaled QD structures, inducing size-tunable electronic structure

  1. Fabrication of 2D sheet-like BiOCl/carbon quantum dot hybrids via a template-free coprecipitation method and their tunable visible-light photocatalytic activities derived from different size distributions of carbon quantum dots

    NASA Astrophysics Data System (ADS)

    Deng, Fang; Lu, Xiaoying; Zhong, Fei; Pei, Xule; Luo, Xubiao; Luo, Shenglian; Dionysiou, Dionysios D.; Au, Chaktong

    2016-02-01

    A series of two-dimensional (2D) interlaced BiOCl/carbon quantum dot composites (denoted as BiOCl/CQD composites) were synthesized by a template-free coprecipitation method at room temperature, and the influence of different particle size distributions of the CQDs on the physiochemical properties and photocatalytic activities of the BiOCl/CQD composites was studied. CQDs can change the morphology and increase the specific surface area of the BiOCl/CQD composites. Moreover, the particle size distribution of the CQDs (CQD loading amount) has some effect on the light absorption, separation of photogenerated charge carriers, and photocatalytic performance of the BiOCl/CQD composites. The optimized size distribution of the CQDs is 50-150 nm. BiOCl/CQD (50-150 nm) composites showed the best improvement of light absorption and the highest photocurrent density of 0.44 μA cm-2, and exhibited the highest photocatalytic activity with almost 100% 2-nitrophenol removal under visible-light irradiation. The high efficacy of BiOCl/CQD (50-150 nm) composites could be attributed to their excellent light absorption and highly effective separation of photogenerated charge carriers.

  2. Efficient Luminescence from Perovskite Quantum Dot Solids.

    PubMed

    Kim, Younghoon; Yassitepe, Emre; Voznyy, Oleksandr; Comin, Riccardo; Walters, Grant; Gong, Xiwen; Kanjanaboos, Pongsakorn; Nogueira, Ana F; Sargent, Edward H

    2015-11-18

    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.

  3. Photoluminescence of individual doped GaAs /AlGaAs nanofabricated quantum dots

    NASA Astrophysics Data System (ADS)

    Kalliakos, Sokratis; García, César Pascual; Pellegrini, Vittorio; Zamfirescu, Marian; Cavigli, Lucia; Gurioli, Massimo; Vinattieri, Anna; Pinczuk, Aron; Dennis, Brian S.; Pfeiffer, Loren N.; West, Ken W.

    2007-04-01

    Dilute arrays of GaAs /AlGaAs modulation-doped quantum dots with same sizes fabricated by electron beam lithography and low impact reactive ion etching exhibit highly uniform luminescence lines. Single quantum dots display spectral emission with peak energies and linewidths linked largely to the geometrical diameter of the dot and to the built-in electron population. Multicharged excitonic and biexcitonic emission intensities have activation energy of about 2meV. These results highlight the potential of high quality nanofabricated quantum dots for applications in areas that require fine control of optical emission.

  4. Reconfigurable Optical Elements Based on Single and Coupled Microdisk Resonators with Quantum DOT Active Media

    DTIC Science & Technology

    2012-06-29

    successfully demonstrated (i) incorporation of CdSe QDs into polymer and dielectric host and realization of devices such as active waveguides , microdisk...14) These values are used as initial approximations for each of the two possible solutions. Results of numerical solution of Eq...between dielectric layers without having detrimental effect on the optical properties of the QDs. Characterization and Modeling By controlling

  5. Sensitivity of quantum-dot semiconductor lasers to optical feedback.

    PubMed

    O'Brien, D; Hegarty, S P; Huyet, G; Uskov, A V

    2004-05-15

    The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor.

  6. Giant Optical Activity of Quantum Dots, Rods, and Disks with Screw Dislocations

    PubMed Central

    Baimuratov, Anvar S.; Rukhlenko, Ivan D.; Noskov, Roman E.; Ginzburg, Pavel; Gun’ko, Yurii K.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2015-01-01

    For centuries mankind has been modifying the optical properties of materials: first, by elaborating the geometry and composition of structures made of materials found in nature, later by structuring the existing materials at a scale smaller than the operating wavelength. Here we suggest an original approach to introduce optical activity in nanostructured materials, by theoretically demonstrating that conventional achiral semiconducting nanocrystals become optically active in the presence of screw dislocations, which can naturally develop during the nanocrystal growth. We show the new properties to emerge due to the dislocation-induced distortion of the crystal lattice and the associated alteration of the nanocrystal’s electronic subsystem, which essentially modifies its interaction with external optical fields. The g-factors of intraband transitions in our nanocrystals are found comparable with dissymmetry factors of chiral plasmonic complexes, and exceeding the typical g-factors of chiral molecules by a factor of 1000. Optically active semiconducting nanocrystals—with chiral properties controllable by the nanocrystal dimensions, morphology, composition and blending ratio—will greatly benefit chemistry, biology and medicine by advancing enantiomeric recognition, sensing and resolution of chiral molecules. PMID:26424498

  7. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    NASA Technical Reports Server (NTRS)

    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.

  8. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

    PubMed Central

    Generalov, Roman; Kavaliauskiene, Simona; Westrøm, Sara; Chen, Wei; Kristensen, Solveig; Juzenas, Petras

    2011-01-01

    Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers. PMID:21931483

  9. Studies of silicon quantum dots prepared at different substrate temperatures

    NASA Astrophysics Data System (ADS)

    Al-Agel, Faisal A.; Suleiman, Jamal; Khan, Shamshad A.

    2017-03-01

    In this research work, we have synthesized silicon quantum dots at different substrate temperatures 193, 153 and 123 K at a fixed working pressure 5 Torr. of Argon gas. The structural studies of these silicon quantum dots have been undertaken using X-ray diffraction, Field Emission Scanning Electron Microscopy (FESEM) and High Resolution Transmission Electron Microscopy (HRTEM). The optical and electrical properties have been studied using UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Fluorescence spectroscopy and I-V measurement system. X-ray diffraction pattern of Si quantum dots prepared at different temperatures show the amorphous nature except for the quantum dots synthesized at 193 K which shows polycrystalline nature. FESEM images of samples suggest that the size of quantum dots varies from 2 to 8 nm. On the basis of UV-visible spectroscopy measurements, a direct band gap has been observed for Si quantum dots. FTIR spectra suggest that as-grown Si quantum dots are partially oxidized which is due exposure of as-prepared samples to air after taking out from the chamber. PL spectra of the synthesized silicon quantum dots show an intense peak at 444 nm, which may be attributed to the formation of Si quantum dots. Temperature dependence of dc conductivity suggests that the dc conductivity enhances exponentially by raising the temperature. On the basis above properties i.e. direct band gap, high absorption coefficient and high conductivity, these silicon quantum dots will be useful for the fabrication of solar cells.

  10. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots.

    PubMed

    Generalov, Roman; Kavaliauskiene, Simona; Westrøm, Sara; Chen, Wei; Kristensen, Solveig; Juzenas, Petras

    2011-01-01

    Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers.

  11. Principles of conjugating quantum dots to proteins via carbodiimide chemistry

    NASA Astrophysics Data System (ADS)

    Song, Fayi; Chan, Warren C. W.

    2011-12-01

    The covalent coupling of nanomaterials to bio-recognition molecules is a critical intermediate step in using nanomaterials for biology and medicine. Here we investigate the carbodiimide-mediated conjugation of fluorescent quantum dots to different proteins (e.g., immunoglobulin G, bovine serum albumin, and horseradish peroxidase). To enable these studies, we developed a simple method to isolate quantum dot bioconjugates from unconjugated quantum dots. The results show that the reactant concentrations and protein type will impact the overall number of proteins conjugated onto the surfaces of the quantum dots, homogeneity of the protein-quantum dot conjugate population, quantum efficiency, binding avidity, and enzymatic kinetics. We propose general principles that should be followed for the successful coupling of proteins to quantum dots.

  12. Principles of conjugating quantum dots to proteins via carbodiimide chemistry.

    PubMed

    Song, Fayi; Chan, Warren C W

    2011-12-09

    The covalent coupling of nanomaterials to bio-recognition molecules is a critical intermediate step in using nanomaterials for biology and medicine. Here we investigate the carbodiimide-mediated conjugation of fluorescent quantum dots to different proteins (e.g., immunoglobulin G, bovine serum albumin, and horseradish peroxidase). To enable these studies, we developed a simple method to isolate quantum dot bioconjugates from unconjugated quantum dots. The results show that the reactant concentrations and protein type will impact the overall number of proteins conjugated onto the surfaces of the quantum dots, homogeneity of the protein-quantum dot conjugate population, quantum efficiency, binding avidity, and enzymatic kinetics. We propose general principles that should be followed for the successful coupling of proteins to quantum dots.

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

    PubMed

    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.

  14. Silicon Quantum Dots for Quantum Information Processing

    DTIC Science & Technology

    2013-11-01

    Systems relaxes through SOC [40, 41, 42]. With the combination of SOC and the Zeeman effect , the typical dependency of a spin lifetime can be expressed as...diagram showing the effect of the 3-level pulse sequence on the electro-chemical potential of the dot. Energy levels in the QD are Zeeman split according...dependent on the valley splitting energy, with a dramatic rate enhancement (or hot-spot) when the Zeeman and valley splittings coincided, a process

  15. Nanoscale optimization of quantum dot solar sells

    NASA Astrophysics Data System (ADS)

    Li, Yanshu; Sergeev, Andrei; Vagidov, Nizami; Mitin, Vladimir; Sablon, Kimberly; State Univ of NY-Buffalo Team; Army Research Laboratory Team

    2015-03-01

    Quantum dots (QDs) offer possibilities for nanoscale control of photoelectron processes via engineering the band structure and potential profile. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AlGaAs atomically thin barriers) effectively suppress the photoelectron capture to QDs. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons that excited by high-energy photons. To study the effects of the band structure engineering and nanoscale potential barriers on the photovoltaic performance we fabricated 3- μm base GaAs devices with various InAs quantum dot media and selective doping. All quantum dot devices show improvement in conversion efficiency compared with the reference cell. Quantum efficiency measurements allow us to associate the spectral characteristics of photoresponse enhancement with nanoscale structure of QD media. The dark current analysis provides valuable information about recombination in QD solar cells. The two-diode model well fit the scope of data and recovers the measured open circuit voltage.

  16. Probing relaxation times in graphene quantum dots

    PubMed Central

    Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph

    2013-01-01

    Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100 ns. PMID:23612294

  17. Size-dependent active effect of cadmium telluride quantum dots on luminol-potassium periodate chemiluminescence system for levodopa detection.

    PubMed

    Wang, Jianbo; Cui, Lijuan; Han, Suqin; Hao, Fang

    2015-06-01

    It was found that cadmium telluride (CdTe) quantum dots (QDs) with different sizes can have a great sensitizing effect on chemiluminescence (CL) emission from luminol-potassium periodate (KIO4) system. Levodopa, a widely prescribed drug in the treatment of Parkinson's disease, could inhibit luminol-KIO4-CdTe QDs CL reaction in alkaline solution. The inhibited CL intensity was proportional to the concentration of levodopa in the range from 8.0 nM to 10.0 μM. The detection limit was 3.8 nM. This method has been successfully applied to determine levodopa in pharmaceutical preparation and human urine and plasma samples with recoveries of 94.1-105.4%. This was the first work for inhibition effect determination of levodopa using a QD-based CL method.

  18. Light-hole exciton in a nanowire quantum dot

    NASA Astrophysics Data System (ADS)

    Jeannin, Mathieu; Artioli, Alberto; Rueda-Fonseca, Pamela; Bellet-Amalric, Edith; Kheng, Kuntheak; André, Régis; Tatarenko, Serge; Cibert, Joël; Ferrand, David; Nogues, Gilles

    2017-01-01

    Quantum dots inserted inside semiconductor nanowires are extremely promising candidates as building blocks for solid-state-based quantum computation and communication. They provide very high crystalline and optical properties and offer a convenient geometry for electrical contacting. Having a complete determination and full control of their emission properties is one of the key goals of nanoscience researchers. Here we use strain as a tool to create in a single magnetic nanowire quantum dot a light-hole exciton, an optically active quasiparticle formed from a single electron bound to a single light hole. In this frame, we provide a general description of the mixing within the hole quadruplet induced by strain or confinement. A multi-instrumental combination of cathodoluminescence, polarization-resolved Fourier imaging, and magneto-optical spectroscopy, allows us to fully characterize the hole ground state, including its valence band mixing with heavy-hole states.

  19. Cadmium sulfide quantum dots induce oxidative stress and behavioral impairments in the marine clam Scrobicularia plana.

    PubMed

    Buffet, Pierre-Emmanuel; Zalouk-Vergnoux, Aurore; Poirier, Laurence; Lopes, Christelle; Risso-de-Faverney, Christine; Guibbolini, Marielle; Gilliland, Douglas; Perrein-Ettajani, Hanane; Valsami-Jones, Eugenia; Mouneyrac, Catherine

    2015-07-01

    Cadmium sulfide (CdS) quantum dots have a number of current applications in electronics and solar cells and significant future potential in medicine. The aim of the present study was to examine the toxic effects of CdS quantum dots on the marine clam Scrobicularia plana exposed for 14 d to these nanomaterials (10 µg Cd L(-1) ) in natural seawater and to compare them with soluble Cd. Measurement of labile Cd released from CdS quantum dots showed that 52% of CdS quantum dots remained in the nanoparticulate form. Clams accumulated the same levels of Cd regardless of the form in which it was delivered (soluble Cd vs CdS quantum dots). However, significant changes in biochemical responses were observed in clams exposed to CdS quantum dots compared with soluble Cd. Increased activities of catalase and glutathione-S-transferase were significantly higher in clams exposed in seawater to Cd as the nanoparticulate versus the soluble form, suggesting a specific nano effect. The behavior of S. plana in sediment showed impairments of foot movements only in the case of exposure to CdS quantum dots. The results show that oxidative stress and behavior biomarkers are sensitive predictors of CdS quantum dots toxicity in S. plana. Such responses, appearing well before changes might occur at the population level, demonstrate the usefulness of this model species and type of biomarker in the assessment of nanoparticle contamination in estuarine ecosystems.

  20. The impact of quantum dot filling on dual-band optical transitions via intermediate quantum states

    SciTech Connect

    Wu, Jiang; Passmore, Brandon; Manasreh, M. O.

    2015-08-28

    InAs/GaAs quantum dot infrared photodetectors with different doping levels were investigated to understand the effect of quantum dot filling on both intraband and interband optical transitions. The electron filling of self-assembled InAs quantum dots was varied by direct doping of quantum dots with different concentrations. Photoresponse in the near infrared and middle wavelength infrared spectral region was observed from samples with low quantum dot filling. Although undoped quantum dots were favored for interband transitions with the absence of a second optical excitation in the near infrared region, doped quantum dots were preferred to improve intraband transitions in the middle wavelength infrared region. As a result, partial filling of quantum dot was required, to the extent of maintaining a low dark current, to enhance the dual-band photoresponse through the confined electron states.

  1. Spin thermopower in interacting quantum dots

    NASA Astrophysics Data System (ADS)

    Rejec, Tomaž; Žitko, Rok; Mravlje, Jernej; Ramšak, Anton

    2012-02-01

    Using analytical arguments and the numerical renormalization group method, we investigate the spin thermopower of a quantum dot in a magnetic field. In the particle-hole-symmetric situation, the temperature difference applied across the dot drives a pure spin current without accompanying charge current. For temperatures and fields at or above the Kondo temperature, but of the same order of magnitude, the spin-Seebeck coefficient is large, of the order of kB/|e|. Via a mapping, we relate the spin-Seebeck coefficient to the charge-Seebeck coefficient of a negative-U quantum dot where the corresponding result was recently reported by Andergassen [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.241107 84, 241107 (2011)]. For several regimes, we provide simplified analytical expressions. In the Kondo regime, the dependence of the spin-Seebeck coefficient on the temperature and the magnetic field is explained in terms of the shift of the Kondo resonance due to the field and its broadening with the temperature and the field. We also consider the influence of breaking the particle-hole symmetry and show that a pure spin current can still be realized, provided a suitable electric voltage is applied across the dot. Then, except for large asymmetries, the behavior of the spin-Seebeck coefficient remains similar to that found in the particle-hole-symmetric point.

  2. Planar Dirac electrons in magnetic quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Ning; Zhu, Jia-Lin

    2012-05-01

    In this paper, we explore the size- and mass-dependent energy spectra and the electronic correlation of two- and three-electron graphene magnetic quantum dots. It is found that only the magnetic dots with large size can well confine the electrons. For large graphene magnetic dots with massless (ultra-relativity) electrons, the energy level structures of two Dirac electrons and even the ground state spin and angular momentum of three electrons are quite different from those of the usual semiconductor quantum dots. Also we reveal that such differences are not due to the magnetic confinement but originate from the character of the Coulomb interaction of two-component electronic wavefunctions in graphene. We reveal that the increase of the mass leads to both the crossover of the energy spectrum structures from the ultra-relativity to non-relativity ones and the increasing of the crystallization. The results are helpful for the understanding of the mass and size effects and may be useful in controlling the few-electron states in graphene-based nanodevices.

  3. Optically injected quantum-dot lasers.

    PubMed

    Erneux, T; Viktorov, E A; Kelleher, B; Goulding, D; Hegarty, S P; Huyet, G

    2010-04-01

    The response of an optically injected quantum-dot semiconductor laser (SL) is studied both experimentally and theoretically. In particular, the nature of the locking boundaries is investigated, revealing features more commonly associated with Class A lasers rather than conventional Class B SLs. Experimentally, two features stand out; the first is an absence of instabilities resulting from relaxation oscillations, and the second is the observation of a region of bistability between two locked solutions. Using rate equations appropriate for quantum-dot lasers, we analytically determine the stability diagram in terms of the injection rate and frequency detuning. Of particular interest are the Hopf and saddle-node locking boundaries that explain how the experimentally observed phenomena appear.

  4. Observing chaos for quantum-dot microlasers with external feedback.

    PubMed

    Albert, Ferdinand; Hopfmann, Caspar; Reitzenstein, Stephan; Schneider, Christian; Höfling, Sven; Worschech, Lukas; Kamp, Martin; Kinzel, Wolfgang; Forchel, Alfred; Kanter, Ido

    2011-06-21

    Chaos presents a striking and fascinating phenomenon of nonlinear systems. A common aspect of such systems is the presence of feedback that couples the output signal partially back to the input. Feedback coupling can be well controlled in optoelectronic devices such as conventional semiconductor lasers that provide bench-top platforms for the study of chaotic behaviour and high bit rate random number generation. Here we experimentally demonstrate that chaos can be observed for quantum-dot microlasers operating close to the quantum limit at nW output powers. Applying self-feedback to a quantum-dot microlaser results in a dramatic change in the photon statistics wherein strong, super-thermal photon bunching is indicative of random-intensity fluctuations associated with the spiked emission of light. Our experiments reveal that gain competition of few quantum dots in the active layer enhances the influence of self-feedback and will open up new avenues for the study of chaos in quantum systems.

  5. A fluorometric assay for alkaline phosphatase activity based on β-cyclodextrin-modified carbon quantum dots through host-guest recognition.

    PubMed

    Tang, Cong; Qian, Zhaosheng; Huang, Yuanyuan; Xu, Jiamin; Ao, Hang; Zhao, Meizhi; Zhou, Jin; Chen, Jianrong; Feng, Hui

    2016-09-15

    A convenient, reliable and highly sensitive assay for alkaline phosphatase (ALP) activity in the real-time manner is developed based on β-cyclodextrin-modified carbon quantum dots (β-CD-CQDs) nanoprobe through specific host-guest recognition. Carbon quantum dots were first functionalized with 3-aminophenyl boronic acid to produce boronic acid-functionalized CQDs, and then further modified with hydropropyl β-cyclodextrins (β-CD) through B-O bonds to form β-CD-CQDs nanoprobe. p-Nitrophenol phosphate disodium salt is used as the substrate of ALP, and can hydrolyze to p-nitrophenol under the catalysis of ALP. The resulting p-nitrophenol can enter the cavity of β-CD moiety in the nanoprobe due to their specific host-guest recognition, where photoinduced electron transfer process between p-nitrophenol and CQDs takes place to efficiently quench the fluorescence of the probe. The correlation between quenched fluorescence and ALP level can be used to establish quantitative evaluation of ALP activity in a broad range from 3.4 to 100.0U/L with the detection limit of 0.9U/L. This assay shows a high sensitivity to ALP even in the presence of a very high concentration of glucose. This study demonstrates a good electron donor/acceptor pair, which can be used to design general detection strategy through PET process, and also broadens the application of host-guest recognition for enzymes detection in clinical practice.

  6. Ultralow Noise Monolithic Quantum Dot Photonic Oscillators

    DTIC Science & Technology

    2013-10-28

    HBCU/MI) ULTRALOW NOISE MONOLITHIC QUANTUM DOT PHOTONIC OSCILLATORS LUKE LESTER UNIVERSITY OF NEW MEXICO 10/28/2013 Final Report DISTRIBUTION A...New Mexico , Albuquerque, NM 87131-0001 Air Force Office of Scientific Research 875 N. Randolph St., Rm 3112 Arlington, VA 22203-1954 patricia.bell...Report 06/01/2010 - 05/31/2013 Professor Luke F. Lester, PI, University of New Mexico Contact address: Center for High Technology Materials

  7. Carbon Nanotube Quantum Dots as THz Detectors

    DTIC Science & Technology

    2012-12-14

    devices that are viable for wafer -scale production. We recently started testing fabrication processes using epitaxial graphene on SiC in collaboration... laser sources at four different Fig. 4 Top: Drain current versus the gate voltage for different THz field intensities. Bottom: Temperature dependence...research. The first was the small coupling between the quantum dot and the powerful (10 mW) laser source. The second was the difficulty to reproduce the

  8. Nanoscale Imaging with a Single Quantum Dot

    DTIC Science & Technology

    2011-12-19

    not require the use of macroscopic manipulators. We use this technique to image the surface plasmon polariton (SPP) mode of a silver nanowire with...technique to image the surface plasmon polariton (SPP) mode of a silver nanowire with resolution as fine as 10 nm by monitoring the coupling...a single quantum dot (QD) by utilizing the enhanced electromagnetic interactions between the QD and the surface plasmon polariton (SPP) mode of a

  9. Multifunctional magnetic quantum dots for cancer theranostics.

    PubMed

    Singh, Surinder P

    2011-02-01

    The development of an innovative platform for cancer theranostics that will be capable of noninvasive imaging and treatment of cancerous tumors using biocompatible and multifunctional Fe3O4-ZnO core-shell magnetic quantum dots (M-QDs) is being explored. This multi-functional approach will facilitate deep tumor targeting using a combination of a specific cancer marker and an external magnetic field will simultaneously provide therapy that may evolve as a new paradigm in cancer theranostics.

  10. Intrinsic spin dynamics in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Valín-Rodríguez, Manuel

    2005-12-01

    We investigate the characteristic spin dynamics corresponding to semiconductor quantum dots within the multiband envelope function approximation (EFA). By numerically solving an 8 × 8 k·p Hamiltonian we treat systems based on different III-V semiconductor materials. It is shown that, even in the absence of an applied magnetic field, these systems show intrinsic spin dynamics governed by intraband and interband transitions leading to characteristic spin frequencies ranging from THz to optical frequencies.

  11. Single molecule study of silicon quantum dots

    NASA Astrophysics Data System (ADS)

    So, Woong Young; Li, Qi; Jin, Rongchao; Peteanu, Linda

    2016-09-01

    Recently, fluorescent Silicon (Si) Quantum Dots (QDs) have attracted much interest due to their high quantum yield, use of non-toxic and environmentally-benign chemicals, and water-solubility. However, more research is necessary to understand the energy level characteristics and single molecule behavior to enable their development for imaging applications. Therefore, single molecule time-resolved fluorescence spectroscopy of fluorescent Si QDs (cyan, green, and yellow) is needed. A rigorous analysis of time-resolved photon correlation spectroscopy and fluorescence lifetime data on single Si QDs at room temperature is presented.

  12. Relaxation dynamics in correlated quantum dots

    SciTech Connect

    Andergassen, S.; Schuricht, D.; Pletyukhov, M.; Schoeller, H.

    2014-12-04

    We study quantum many-body effects on the real-time evolution of the current through quantum dots. By using a non-equilibrium renormalization group approach, we provide analytic results for the relaxation dynamics into the stationary state and identify the microscopic cutoff scales that determine the transport rates. We find rich non-equilibrium physics induced by the interplay of the different energy scales. While the short-time limit is governed by universal dynamics, the long-time behavior features characteristic oscillations as well as an interplay of exponential and power-law decay.

  13. Near-field magnetoabsorption of quantum dots

    NASA Astrophysics Data System (ADS)

    Simserides, Constantinos; Zora, Anna; Triberis, Georgios

    2006-04-01

    We investigate the effect of an external magnetic field of variable orientation and magnitude (up to 20T ) on the linear near-field optical absorption spectra of single and coupled III-V semiconductor quantum dots. We focus on the spatial as well as on the magnetic confinement, varying the dimensions of the quantum dots and the magnetic field. We show that the ground-state exciton binding energy can be manipulated utilizing the spatial and magnetic confinement. The effect of the magnetic field on the absorption spectra, increasing the near-field illumination spot, is also investigated. The zero-magnetic-field “structural” symmetry can be destroyed varying the magnetic field orientation and this affects the near-field spectra. The asymmetry induced (except for specific orientations along symmetry axes) by the magnetic field can be revealed in the near-field but not in the far-field spectra. We predict that near-field magnetoabsorption experiments, of realistic spatial resolution, will be in the position to bring to light the quantum dot symmetry. This exceptional symmetry-resolving power of the near-field magnetoabsorption is lost in the far field. The influence of the Coulomb interactions on the absorption spectra is also discussed. Finally, we show that certain modifications of the magnetoexcitonic structure can be uncovered using a realistically acute near-field probe of ≈20nm .

  14. Si, Ge, and SiGe quantum wires and quantum dots

    NASA Astrophysics Data System (ADS)

    Pearsall, T. P.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses Si, Ge, and SiGe quantum wire and quantum dot structures, the synthesis of quantum wires and quantum dots, and applications of SiGe quantum-dot structures as photodetectors, light-emitting diodes, for optical amplification and as Si quantum-dot memories.

  15. UV Nano-Lights: Nonlinear Quantum Dot-Plasmon Coupling

    DTIC Science & Technology

    2014-08-01

    Final 3. DATES COVERED (From - To) 11-Mar-2013 to 10-Mar-2014 4. TITLE AND SUBTITLE UV Nano-Lights: Nonlinear Quantum Dot- Plasmon ...Nonlinear Quantum Dot- Plasmon Coupling 5a. CONTRACT NUMBER FA2386-13-1-4016 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Eric...nonlinear emission from Quantum Dots through Plasmon Coupling PERIOD OF PERFORMANCE 11 March 2013 - 11 March 2014 RECIPIENT PRINCIPAL

  16. Molecular Profiling of Prostate Cancer Specimens Using Multicolor Quantum Dots

    DTIC Science & Technology

    2009-02-01

    0117 TITLE: Molecular profiling of prostate cancer specimens using Multicolor Quantum Dots PRINCIPAL INVESTIGATOR: Xiaohu Gao...profiling of prostate cancer specimens using Multicolor Quantum Dots 5a. CONTRACT NUMBER W81XWH-07-1-0117 5b. GRANT NUMBER PC061345 5c...based on the biology of their tumors. We proposed to develop oligonucleotide tagged quantum dots and antibodies for multiplexed imaging of prostate

  17. Quantum transport through an array of quantum dots.

    PubMed

    Chen, Shuguang; Xie, Hang; Zhang, Yu; Cui, Xiaodong; Chen, Guanhua

    2013-01-07

    The transient current through an array of as many as 1000 quantum dots is simulated with two newly developed quantum mechanical methods. To our surprise, upon switching on the bias voltage, the current increases linearly with time before reaching its steady state value. And the time required for the current to reach its steady state value is proportional to the length of the array, and more interestingly, is exactly the time for a conducting electron to travel through the array at the Fermi velocity. These quantum phenomena can be understood by a simple analysis on the energetics of an equivalent classical circuit. An experimental design is proposed to confirm the numerical findings.

  18. Quantum interface between light and nuclear spins in quantum dots

    NASA Astrophysics Data System (ADS)

    Schwager, Heike; Cirac, J. Ignacio; Giedke, Géza

    2010-01-01

    The coherent coupling of flying photonic qubits to stationary matter-based qubits is an essential building block for quantum-communication networks. We show how such a quantum interface can be realized between a traveling-wave optical field and the polarized nuclear spins in a singly charged quantum dot strongly coupled to a high-finesse optical cavity. By adiabatically eliminating the electron a direct effective coupling is achieved. Depending on the laser field applied, interactions that enable either write-in or read-out are obtained.

  19. Quantum transport through an array of quantum dots

    NASA Astrophysics Data System (ADS)

    Chen, Shuguang; Xie, Hang; Zhang, Yu; Cui, Xiaodong; Chen, Guanhua

    2012-12-01

    The transient current through an array of as many as 1000 quantum dots is simulated with two newly developed quantum mechanical methods. To our surprise, upon switching on the bias voltage, the current increases linearly with time before reaching its steady state value. And the time required for the current to reach its steady state value is proportional to the length of the array, and more interestingly, is exactly the time for a conducting electron to travel through the array at the Fermi velocity. These quantum phenomena can be understood by a simple analysis on the energetics of an equivalent classical circuit. An experimental design is proposed to confirm the numerical findings.

  20. Tuning the quantum critical crossover in quantum dots

    NASA Astrophysics Data System (ADS)

    Murthy, Ganpathy

    2005-03-01

    Quantum dots with large Thouless number g embody a regime where both disorder and interactions can be treated nonperturbatively using large-N techniques (with N=g) and quantum phase transitions can be studied. Here we focus on dots where the noninteracting Hamiltonian is drawn from a crossover ensemble between two symmetry classes, where the crossover parameter introduces a new, tunable energy scale independent of and much smaller than the Thouless energy. We show that the quantum critical regime, dominated by collective critical fluctuations, can be accessed at the new energy scale. The nonperturbative physics of this regime can only be described by the large-N approach, as we illustrate with two experimentally relevant examples. G. Murthy, PRB 70, 153304 (2004). G. Murthy, R. Shankar, D. Herman, and H. Mathur, PRB 69, 075321 (2004)

  1. Tolerance of Intrinsic Defects in PbS Quantum Dots.

    PubMed

    Zherebetskyy, Danylo; Zhang, Yingjie; Salmeron, Miquel; Wang, Lin-Wang

    2015-12-03

    Colloidal quantum dots exhibit various defects and deviations from ideal structures due to kinetic processes, although their band gap frequently remains open and clean. In this Letter, we computationally investigate intrinsic defects in a real-size PbS quantum dot passivated with realistic Cl-ligands. We show that the colloidal intrinsic defects are ionic in nature. Unlike previous computational results, we find that even nonideal, atomically nonstoichiometric quantum dots have a clean band gap without in-gap-states provided that quantum dots satisfy electronic stoichiometry.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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.

  3. Realizing Rec. 2020 color gamut with quantum dot displays.

    PubMed

    Zhu, Ruidong; Luo, Zhenyue; Chen, Haiwei; Dong, Yajie; Wu, Shin-Tson

    2015-09-07

    We analyze how to realize Rec. 2020 wide color gamut with quantum dots. For photoluminescence, our simulation indicates that we are able to achieve over 97% of the Rec. 2020 standard with quantum dots by optimizing the emission spectra and redesigning the color filters. For electroluminescence, by optimizing the emission spectra of quantum dots is adequate to render over 97% of the Rec. 2020 standard. We also analyze the efficiency and angular performance of these devices, and then compare results with LCDs using green and red phosphors-based LED backlight. Our results indicate that quantum dot display is an outstanding candidate for achieving wide color gamut and high optical efficiency.

  4. Terahertz transmission through rings of quantum dots-nanogap

    NASA Astrophysics Data System (ADS)

    Tripathi, Laxmi-Narayan; Bahk, Young-Mi; Choi, Geunchang; Han, Sanghoon; Park, Namkyoo; Kim, Dai-Sik

    2016-03-01

    We report resonant funneling of terahertz (THz) waves through (9 ± 1) nm wide quantum dots-nanogap of cadmium selenide quantum dots silver nanogap metamaterials. We observed a giant THz intensity enhancement (∼104) through the quantum dots-nanogap at the resonant frequency. We, further report the experimentally measured effective mode indices for these metamaterials. A finite difference time domain simulation of the nanogap enabled by the quantum dots supports the experimentally measured THz intensity enhancement across the nanogap. We propose that these low effective mode index terahertz resonators will be useful as bio/chemical sensors, gain-enhanced antennas, and wave guides.

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

    SciTech Connect

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

    2015-08-03

    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.

  6. Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer.

    PubMed

    Zhao, Tianshuo; Goodwin, Earl D; Guo, Jiacen; Wang, Han; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2016-09-22

    Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI2-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency.

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

    PubMed

    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.

  8. Single-electron Spin Resonance in a Quadruple Quantum Dot

    NASA Astrophysics Data System (ADS)

    Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo

    2016-08-01

    Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible.

  9. Single-electron Spin Resonance in a Quadruple Quantum Dot

    PubMed Central

    Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo

    2016-01-01

    Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible. PMID:27550534

  10. Hybrid structures of polycationic aluminum phthalocyanines and quantum dots.

    PubMed

    Maksimov, E G; Gvozdev, D A; Strakhovskaya, M G; Paschenko, V Z

    2015-03-01

    Semiconductor nanocrystals (CdSe/ZnS quantum dots, QDs) were used as inorganic focusing antenna, allowing for the enhancement of fluorescence and photosensitizing activity of polycationic aluminum phthalocyanines (PCs). It was found that QDs form stable complexes with PCs in aqueous solutions due to electrostatic interactions. In such hybrid complexes, we observed highly efficient nonradiative energy transfer from QD to PC, leading to a sharp increase in the effective absorption cross section of PC in the absorption bands of the CdSe/ZnS quantum dots. When hybrid complexes are excited within these bands, the intensity of PC fluorescence and the rate of photosensitized singlet oxygen generation increases significantly (up to 500 and 350%, correspondingly) compared to free PC at the same concentration. The observed effect is of interest for modeling primary stages of photosynthesis and increasing photosensitizing activity of dyes used in photodynamic therapy.

  11. Nanoscale patterning of colloidal quantum dots for surface plasmon generation

    NASA Astrophysics Data System (ADS)

    Park, Yeonsang; Roh, Young-Geun; Kim, Un Jeong; Chung, Dae-Young; Suh, Hwansoo; Kim, Jineun; Cheon, Sangmo; Lee, Jaesoong; Kim, Tae-Ho; Cho, Kyung-Sang; Lee, Chang-Won

    2013-03-01

    The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing, and microcontact printing of quantum dots, have limits in fabrication resolution, positioning and the variation of structural shapes. Herein, we present an adaptation of a conventional liftoff method for patterning colloidal quantum dots. This simple method is easy and requires no complicated processes. Using this method, we formed straight lines, rings, and dot patterns of colloidal quantum dots on metallic substrates. Notably, patterned lines approximately 10 nm wide were fabricated. The patterned structures display high resolution, accurate positioning, and well-defined sidewall profiles. To demonstrate the applicability of our method, we present a surface plasmon generator elaborated from quantum dots.

  12. Nanopatterned Quantum Dot Lasers for High Speed, High Efficiency, Operation

    DTIC Science & Technology

    2015-04-27

    growth using metalorganic chemical vapor deposition (MOCVD). These methods allowed us to realize quantum dot active regions in which the injected carriers...on a higher energy (excited state) QD transition. Further improvements in QD growth and pre-etching are expected to lead to ground state emission...significantly better diffusion and chemical barrier than SiOx. Therefore, SiNx deposited by PECVD has been chosen as a dielectric mask. Also, in order to

  13. Optophononics with Coupled Quantum Dots

    DTIC Science & Technology

    2014-02-18

    the molecular polaron can be used as an efficient and tunable coherent coupler for quantum states in spatially separated low-dimensional structures...The molecular polaron’s power as a tunable coherent coupler can be seen as follows. In Fig. 4d–f we compare the two tunnel QDM Electric field 21 Ω Ω v...full sequence of layers deposited on top of the GaAs substrate was 500 nm nþ -GaAs buffer , 80 nm i-GaAs, 2.5 nm InAs QDs, 4 nm GaAs barrier, 2.5 nm

  14. Amphoteric CdSe nanocrystalline quantum dots.

    PubMed

    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.

  15. Thermoelectrics with Coulomb-coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Thierschmann, Holger; Sánchez, Rafael; Sothmann, Björn; Buhmann, Hartmut; Molenkamp, Laurens W.

    2016-12-01

    In this article we review the thermoelectric properties of three terminal devices with Coulomb-coupled quantum dots (QDs) as observed in recent experiments [1,2]. The system we consider consists of two Coulomb-blockade QDs, one of which can exchange electrons with only a single reservoir (heat reservoir), while the other dot is tunnel coupled with two reservoirs at a lower temperature (conductor). The heat reservoir and the conductor interact only via the Coulomb coupling of the quantum dots. It has been found that two regimes have to be considered. In the first one, the heat flow between the two systems is small. In this regime, thermally driven occupation fluctuations of the hot QD modify the transport properties of the conductor system. This leads to an effect called thermal gating. Experiments have shown how this can be used to control charge flow in the conductor by means of temperature in a remote reservoir. We further substantiate the observations with model calculations, and implications for the realisation of an all-thermal transistor are discussed. In the second regime, the heat flow between the two systems is relevant. Here the system works as a nanoscale heat engine, as proposed recently (Sánchez and Büttiker [3]). We review the conceptual idea, its experimental realisation and the novel features arising in this new kind of thermoelectric device such as decoupling of heat and charge flow. xml:lang="fr"

  16. Adiabatic Spin Pumping with Quantum Dots

    NASA Astrophysics Data System (ADS)

    Mucciolo, Eduardo R.

    Electronic transport in mesoscopic systems has been intensively studied for more the last three decades. While there is a substantial understanding of the stationary regime, much less is know about phase-coherent nonequilibrium transport when pulses or ac perturbations are used to drive electrons at low temperatures and at small length scales. However, about 20 years ago Thouless proposed to drive nondissipative currents in quantum systems by applying simultaneously two phase-locked external perturbations. The so-called adiabatic pumping mechanism has been revived in the last few years, both theoretically and experimentally, in part because of the development of lateral semiconductor quantum dots. Here we will explain how open dots can be used to create spin-polarized currents with little or no net charge transfer. The pure spin pump we propose is the analog of a charge battery in conventional electronics and may provide a needed circuit element for spin-based electronics. We will also discuss other relevant issues such as rectification and decoherence and point out possible extensions of the mechanism to closed dots.

  17. Nonrenewal statistics in transport through quantum dots

    NASA Astrophysics Data System (ADS)

    Ptaszyński, Krzysztof

    2017-01-01

    The distribution of waiting times between successive tunneling events is an already established method to characterize current fluctuations in mesoscopic systems. Here, I investigate mechanisms generating correlations between subsequent waiting times in two model systems, a pair of capacitively coupled quantum dots and a single-level dot attached to spin-polarized leads. Waiting time correlations are shown to give insight into the internal dynamics of the system; for example they allow distinction between different mechanisms of the noise enhancement. Moreover, the presence of correlations breaks the validity of the renewal theory. This increases the number of independent cumulants of current fluctuation statistics, thus providing additional sources of information about the transport mechanism. I also propose a method for inferring the presence of waiting time correlations based on low-order current correlation functions. This method gives a way to extend the analysis of nonrenewal current fluctuations to the systems for which single-electron counting is not experimentally feasible. The experimental relevance of the findings is also discussed; for example reanalysis of previous results concerning transport in quantum dots is suggested.

  18. Quantum Dots: An Experiment for Physical or Materials Chemistry

    ERIC Educational Resources Information Center

    Winkler, L. D.; Arceo, J. F.; Hughes, W. C.; DeGraff, B. A.; Augustine, B. H.

    2005-01-01

    An experiment is conducted for obtaining quantum dots for physical or materials chemistry. This experiment serves to both reinforce the basic concept of quantum confinement and providing a useful bridge between the molecular and solid-state world.

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

    SciTech Connect

    Singh, M. Luhman, D. R.; Lilly, M. P.; 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.

    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.

  20. Coral-Shaped MoS2 Decorated with Graphene Quantum Dots Performing as a Highly Active Electrocatalyst for Hydrogen Evolution Reaction.

    PubMed

    Guo, Bangjun; Yu, Ke; Li, Honglin; Qi, Ruijuan; Zhang, Yuanyuan; Song, Haili; Tang, Zheng; Zhu, Ziqiang; Chen, Mingwei

    2017-02-01

    We report a new CVD method to prepare coral-shaped monolayer MoS2 with a large amount of exposed edge sites for catalyzing hydrogen evolution reaction. The electrocatalytic activities of the coral-shaped MoS2 can be further enhanced by electronic band engineering via decorated with graphene quantum dot (GQD) decoration. Generally, GQDs improve the electrical conductivity of the MoS2 electrocatalyst. First-principles calculations suggest that the coral MoS2@GQD is a zero-gap material. The high electric conductivity and pronounced catalytically active sites give the hybrid catalyst outstanding electrocatalytic performance with a small onset overpotential of 95 mV and a low Tafel slope of 40 mV/dec as well as excellent long-term electrocatalytic stability. The present work provides a potential way to design two-dimensional hydrogen evolution reaction (HER) electrocatalysts through controlling the shape and modulating the electric conductivity.

  1. Energy levels of bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    da Costa, D. R.; Zarenia, M.; Chaves, Andrey; Farias, G. A.; Peeters, F. M.

    2015-09-01

    Within a tight binding approach we investigate the energy levels of hexagonal and triangular bilayer graphene (BLG) quantum dots (QDs) with zigzag and armchair edges. We study AA- and AB- (Bernal) stacked BLG QDs and obtain the energy levels in both the absence and the presence of a perpendicular electric field (i.e., biased BLG QDs). Our results show that the size dependence of the energy levels is different from that of monolayer graphene QDs. The energy spectrum of AB-stacked BLG QDs with zigzag edges exhibits edge states which spread out into the opened energy gap in the presence of a perpendicular electric field. We found that the behavior of these edges states is different for the hexagonal and triangular geometries. In the case of AA-stacked BLG QDs, the electron and hole energy levels cross each other in both cases of armchair and zigzag edges as the dot size or the applied bias increases.

  2. Nano-laser on silicon quantum dots

    NASA Astrophysics Data System (ADS)

    Huang, Wei-Qi; Liu, Shi-Rong; Qin, Chao-Jian; Lü, Quan; Xu, Li

    2011-04-01

    A new conception of nano-laser is proposed in which depending on the size of nano-clusters (silicon quantum dots (QD)), the pumping level of laser can be tuned by the quantum confinement (QC) effect, and the population inversion can be formed between the valence band and the localized states in gap produced from the surface bonds of nano-clusters. Here we report the experimental demonstration of nano-laser on silicon quantum dots fabricated by nanosecond pulse laser. The peaks of stimulated emission are observed at 605 nm and 693 nm. Through the micro-cavity of nano-laser, a full width at half maximum of the peak at 693 nm can reach to 0.5 nm. The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of QD (d < 3 nm) can make the localized states into band gap. The emission energy of nano-laser will be limited in the range of 1.7-2.3 eV generally due to the position of the localized states in gap, which is in good agreement between the experiments and the theory.

  3. Performance analysis of quantum dots infrared photodetector

    NASA Astrophysics Data System (ADS)

    Liu, Hongmei; Zhang, Fangfang; Zhang, Jianqi; He, Guojing

    2011-08-01

    Performance analysis of the quantum dots infrared photodetector(QDIP), which can provide device designers with theoretical guidance and experimental verification, arouses a wide interest and becomes a hot research topic in the recent years. In the paper, in comparison with quantum well infrared photodetector(QWIP) characteristic, the performance of QDIP is mainly discussed and summarized by analyzing the special properties of quantum dots material. To be specific, the dark current density and the detectivity in the normalized incident phenomenon are obtained from Phillip performance model, the carrier lifetime and the dark current of QDIP are studied by combing with the "photon bottleneck" effect, and the detectivity of QDIP is theoretically derived from considering photoconduction gain under the influence of the capture probability. From the experimental results, a conclusion is made that QDIP can not only receive the normal incidence light, but also has the advantages of the long carrier life, the big photoconductive gain, the low dark current and so on, and it further illustrates a anticipated superiority of QDIP in performance and a wide use of QDIP in many engineering fields in the future.

  4. Spectroscopically characterized cadmium sulfide quantum dots lengthening the lag phase of Escherichia coli growth

    NASA Astrophysics Data System (ADS)

    Jaiganesh, T.; Daisy Vimala Rani, J.; Girigoswami, Agnishwar

    2012-06-01

    The present study reports the effect of cadmium sulfide (CdS) quantum dots on the life cycle of Escherichia coli. CdS quantum dots were synthesized by pH sensitive organochemical route using cadmium chloride and sodium sulfide as precursors and mercaptopropionic acid (MPA) as capping agent. It is observed that varying concentration of MPA leads to the production of different sized quantum dots with inverse proportionality and increment in the fluorescence quantum yield. The investigation also shows that CdS quantum dots have no antibacterial activity except it delays the log phase growth of bacteria in terms of size of the particles. The largest synthesized particles significantly elongate the lag phase growth.

  5. Nose-to-Brain Transport of Aerosolized Quantum Dots Following Acute Exposure

    PubMed Central

    Hopkins, Laurie E.; Patchin, Esther S.; Chiu, Po-Lin; Brandenberger, Christina; Smiley-Jewell, Suzette; Pinkerton, Kent E.

    2014-01-01

    Nanoparticles are of wide interest due to their potential use for diverse commercial applications. Quantum dots are semiconductor nanocrystals possessing unique optical and electrical properties. Although quantum dots are commonly made of cadmium, a metal known to have neurological effects, potential transport of quantum dots directly to the brain has not been assessed. This study evaluated whether quantum dots (CdSe/ZnS nanocrystals) could be transported from the olfactory tract to the brain via inhalation. Adult C57BL/6 mice were exposed to an aerosol of quantum dots for one hour via nasal inhalation, and nanoparticles were detected three hours post-exposure within the olfactory tract and olfactory bulb by a wide range of techniques, including visualization via fluorescent and transmission electron microscopy. We conclude that following short-term inhalation of solid quantum dot nanoparticles, there is rapid olfactory uptake and axonal transport to the brain/olfactory bulb with observed activation of microglial cells, indicating a pro-inflammatory response. To our knowledge, this is the first study to clearly demonstrate that quantum dots can be rapidly transported from the nose to the brain by olfactory uptake via axonal transport following inhalation. PMID:24040866

  6. Merging quantum dots, biomolecules, and polymers for record performance from solution-processed optoelectronics

    NASA Astrophysics Data System (ADS)

    Sargent, Edward H.

    2006-02-01

    We apply discoveries in nanoscience towards applications relevant to health, environment, security, and connectedness. A materials fundamental to our research is the quantum dot. Each quantum dot is a particle of semiconductor only a few nanometers in diameter. These semiconductor nanoparticles confine electrons to within their characteristic wavelength. Thus, just as changing the length of a guitar string changes the frequency of sound produced, so too does changing the size of a quantum dot alter the frequency - hence energy - the electron can adopt. As a result, quantum dots are tunable matter (Fig. 2). We work with colloidal quantum dots, nanoparticles produced in, and processed from, solution. They can be coated onto nearly anything - a semiconductor substrate, a window, a wall, fabric. Compared to epitaxially-grown semiconductors used to make optical detectors, lasers, and modulators, they are cheap, safe to work with, and easy to produce. Much of our work with quantum dots involves infrared light - its measurement, production, modulation, and harnessing. While there exists an abundance of work in colloidal quantum dots active in the visible, there are fewer results in the infrared. The wavelengths between 1000 and 2000 nm are nonetheless of great practical importance: half of the sun's power reaching the earth lies in this wavelength range; 'biological windows' in which tissue is relatively transparent and does not emit background light (autofluorescence) exist in the infrared; fiber-optic networks operate at 1.3 and 1.5 um.

  7. Implementing of Quantum Cloning with Spatially Separated Quantum Dot Spins

    NASA Astrophysics Data System (ADS)

    Wen, Jing-Ji; Yeon, Kyu-Hwang; Du, Xin; Lv, Jia; Wang, Ming; Wang, Hong-Fu; Zhang, Shou

    2016-07-01

    We propose some schemes for implementing optimal symmetric (asymmetric) 1 → 2 universal quantum cloning, optimal symmetric (asymmetric) 1 → 2 phase-covariant cloning, optimal symmetric 1 → 3 economical phase-covariant cloning and optimal symmetric 1 → 3 economical real state cloning with spatially separated quantum dot spins by choosing the single-qubit rotation angles appropriately. The decoherences of the spontaneous emission of QDs, cavity decay and fiber loss are suppressed since the effective long-distance off-resonant interaction between two distant QDs is mediated by the vacuum fields of the fiber and cavity, and during the whole process no system is excited.

  8. Energy transfer in hybrid systems quantum dot-plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Chaplik, A. V.

    2016-06-01

    Radiationless relaxation in hybrid systems quantum dot (QD)-plasmonic nanostructure is considered. For the system QD-2D plasma the relaxation rate extremely steeply depends on the radius of quantum dot while in the pair QD-cylindrical wire contacting each other this dependence is logarithmic weak.

  9. A Nanowire-Based Plasmonic Quantum Dot Laser.

    PubMed

    Ho, Jinfa; Tatebayashi, Jun; Sergent, Sylvain; Fong, Chee Fai; Ota, Yasutomo; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2016-04-13

    Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm(2) was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics.

  10. Fast synthesize ZnO quantum dots via ultrasonic method.

    PubMed

    Yang, Weimin; Zhang, Bing; Ding, Nan; Ding, Wenhao; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

    2016-05-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots.

  11. Quantum-dot cluster-state computing with encoded qubits

    SciTech Connect

    Weinstein, Yaakov S.; Hellberg, C. Stephen; Levy, Jeremy

    2005-08-15

    A class of architectures is advanced for cluster-state quantum computation using quantum dots. These architectures include using single and multiple dots as logical qubits. Special attention is given to supercoherent qubits introduced by Bacon et al. [Phys. Rev. Lett. 87, 247902 (2001)] for which we discuss the effects of various errors and present a means of error protection.

  12. Quantum model for mode locking in pulsed semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Beugeling, W.; Uhrig, Götz S.; Anders, Frithjof B.

    2016-12-01

    Quantum dots in GaAs/InGaAs structures have been proposed as a candidate system for realizing quantum computing. The short coherence time of the electronic quantum state that arises from coupling to the nuclei of the substrate is dramatically increased if the system is subjected to a magnetic field and to repeated optical pulsing. This enhancement is due to mode locking: oscillation frequencies resonant with the pulsing frequencies are enhanced, while off-resonant oscillations eventually die out. Because the resonant frequencies are determined by the pulsing frequency only, the system becomes immune to frequency shifts caused by the nuclear coupling and by slight variations between individual quantum dots. The effects remain even after the optical pulsing is terminated. In this work, we explore the phenomenon of mode locking from a quantum mechanical perspective. We treat the dynamics using the central-spin model, which includes coupling to 10-20 nuclei and incoherent decay of the excited electronic state, in a perturbative framework. Using scaling arguments, we extrapolate our results to realistic system parameters. We estimate that the synchronization to the pulsing frequency needs time scales in the order of 1 s .

  13. Mesoscopic admittance of a double quantum dot

    SciTech Connect

    Cottet, Audrey; Mora, Christophe; Kontos, Takis

    2011-03-15

    We calculate the mesoscopic admittance G({omega}) of a double quantum dot (DQD), which can be measured directly using microwave techniques. This quantity reveals spectroscopic information on the DQD and is also directly sensitive to a Pauli spin blockade effect. We then discuss the problem of a DQD coupled to a high quality photonic resonator. When the photon correlation functions can be developed along a random-phase-approximation-like scheme, the response of the resonator gives an access to G({omega}).

  14. Electron scattering in intrananotube quantum dots.

    PubMed

    Buchs, G; Bercioux, D; Ruffieux, P; Gröning, P; Grabert, H; Gröning, O

    2009-06-19

    Intratube quantum dots showing particle-in-a-box-like states with level spacings up to 200 meV are realized in metallic single-walled carbon nanotubes by means of low dose medium energy Ar(+) irradiation. Fourier-transform scanning tunneling spectroscopy compared to results of a Fabry-Perot electron resonator model yields clear signatures for inter- and intravalley scattering of electrons confined between consecutive irradiation-induced defects (interdefects distance

  15. Quantum dot intermixing using excimer laser irradiation

    SciTech Connect

    Djie, H. S.; Ooi, B. S; Gunawan, O.

    2006-08-21

    The authors report a spatial control of the band gap in InGaAs/GaAs quantum dots (QDs) using the combined effects of pulsed excimer laser irradiation and impurity-free dielectric cap induced intermixing technique. A large band gap shift of up to 180 meV has been obtained under laser irradiation of 480 mJ/cm{sup 2} and 150 pulses to the SiO{sub 2} capped shallow QD structure, while the nonirradiated SiO{sub 2} and Si{sub x}N{sub y} capped QDs only exhibit band gap shifts of 18 and 91 meV, respectively.

  16. Quantum Dots for Molecular Diagnostics of Tumors

    PubMed Central

    Zdobnova, T.A.; Lebedenko, E.N.; Deyev, S.М.

    2011-01-01

    Semiconductor quantum dots (QDs) are a new class of fluorophores with unique physical and chemical properties, which allow to appreciably expand the possibilities for the current methods of fluorescent imaging and optical diagnostics. Here we discuss the prospects of QD application for molecular diagnostics of tumors ranging from cancer-specific marker detection on microplates to non-invasive tumor imagingin vivo. We also point out the essential problems that require resolution in order to clinically promote QD, and we indicate innovative approaches to oncology which are implementable using QD. PMID:22649672

  17. Trion decay in colloidal quantum dots.

    PubMed

    Jha, Praket P; Guyot-Sionnest, Philippe

    2009-04-28

    Using charged films of colloidal CdSe/CdS core/shell quantum dots of approximately 3.5 to 4.5 nm core diameters and 0.6 to 1.2 nm thick CdS shells, the radiative and nonradiative decay of the negatively charged exciton, the trion T-, are measured. The T- radiative rate is faster than the exciton by a factor of 2.2 +/- 0.4 and estimated at approximately 10 ns. The T- lifetime is approximately 0.7-1.5 ns for the samples measured and is longer than the biexciton lifetime by a factor or 7.5 +/- 1.7.

  18. A hybrid silicon evanescent quantum dot laser

    NASA Astrophysics Data System (ADS)

    Jang, Bongyong; Tanabe, Katsuaki; Kako, Satoshi; Iwamoto, Satoshi; Tsuchizawa, Tai; Nishi, Hidetaka; Hatori, Nobuaki; Noguchi, Masataka; Nakamura, Takahiro; Takemasa, Keizo; Sugawara, Mitsuru; Arakawa, Yasuhiko

    2016-09-01

    We report the first demonstration of a hybrid silicon quantum dot (QD) laser, evanescently coupled to a silicon waveguide. InAs/GaAs QD laser structures with thin AlGaAs lower cladding layers were transferred by direct wafer bonding onto silicon waveguides defining cavities with adiabatic taper structures and distributed Bragg reflectors. The laser operates at temperatures up to 115 °C under pulsed current conditions, with a characteristic temperature T 0 of 303 K near room temperature. Furthermore, by reducing the width of the GaAs/AlGaAs mesa down to 8 µm, continuous-wave operation is realized at 25 °C.

  19. Luminescence studies of individual quantum dot photocatalysts.

    PubMed

    Amirav, Lilac; Alivisatos, A Paul

    2013-09-04

    Using far-field optical microscopy we report the first measurements of photoluminescence from single nanoparticle photocatalysts. Fluence-dependent luminescence is investigated from metal-semiconductor heterojunction quantum dot catalysts exposed to a variety of environments, ranging from gaseous argon to liquid water containing a selection of hole scavengers. The catalysts each exhibit characteristic nonlinear fluence dependence. From these structurally and environmentally sensitive trends, we disentangle the separate rate-determining steps in each particle across the very wide range of time scales, which follow the initial light absorption process. This information will significantly benefit the design of effective artificial photocatalytic systems for renewable direct solar-to-fuel energy conversion.

  20. Quantum dots confined in nanoporous alumina membranes

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Xia, Jianfeng; Wang, Jun; Shinar, Joseph; Lin, Zhiqun

    2006-09-01

    CdSe /ZnS core/shell quantum dots (QDs) were filled into porous alumina membranes (PAMs) by dip coating. The deposition of QDs induced changes in the refractive index of the PAMs. The amount of absorbed QDs was quantified by fitting the reflection and transmission spectra observed experimentally with one side open and freestanding (i.e., with two sides open) PAMs employed, respectively. The fluorescence of the QDs was found to be retained within the cylindrical nanopores of the PAMs.

  1. Spin-dependent shot noise enhancement in a quantum dot

    NASA Astrophysics Data System (ADS)

    Ubbelohde, Niels; Fricke, Christian; Hohls, Frank; Haug, Rolf J.

    2013-07-01

    The spin-dependent dynamical blockade was investigated in a lateral quantum dot in a magnetic field. Spin-polarized edge channels in the two-dimensional leads and the spatial distribution of Landau orbitals in the dot modulate the tunnel coupling of the quantum dot level spectrum. In a measurement of the electron shot noise we observe a pattern of super-Poissonian noise which is correlated to the spin-dependent competition between different transport channels.

  2. Hyper-parallel photonic quantum computation with coupled quantum dots

    PubMed Central

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-01-01

    It is well known that a parallel quantum computer is more powerful than a classical one. So far, there are some important works about the construction of universal quantum logic gates, the key elements in quantum computation. However, they are focused on operating on one degree of freedom (DOF) of quantum systems. Here, we investigate the possibility of achieving scalable hyper-parallel quantum computation based on two DOFs of photon systems. We construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on both the spatial-mode and the polarization DOFs of a two-photon system simultaneously, by exploiting the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics (QED). This hyper-CNOT gate is implemented by manipulating the four qubits in the two DOFs of a two-photon system without auxiliary spatial modes or polarization modes. It reduces the operation time and the resources consumed in quantum information processing, and it is more robust against the photonic dissipation noise, compared with the integration of several cascaded CNOT gates in one DOF. PMID:24721781

  3. Quantum Dots in Diagnostics and Detection: Principles and Paradigms

    PubMed Central

    Pisanic, T. R.; Zhang, Y.; Wang, T. H.

    2014-01-01

    Quantum dots are semiconductor nanocrystals that exhibit exceptional optical and electrical behaviors not found in their bulk counterparts. Following seminal work in the development of water-soluble quantum dots in the late 1990's, researchers have sought to develop interesting and novel ways of exploiting the extraordinary properties of quantum dots for biomedical applications. Since that time, over 10,000 articles have been published related to the use of quantum dots in biomedicine, many of which regard their use in detection and diagnostic bioassays. This review presents a didactic overview of fundamental physical phenomena associated with quantum dots and paradigm examples of how these phenomena can and have been readily exploited for manifold uses in nanobiotechnology with a specific focus on their implementation in in vitro diagnostic assays and biodetection. PMID:24770716

  4. Quantum dots in diagnostics and detection: principles and paradigms.

    PubMed

    Pisanic, T R; Zhang, Y; Wang, T H

    2014-06-21

    Quantum dots are semiconductor nanocrystals that exhibit exceptional optical and electrical behaviors not found in their bulk counterparts. Following seminal work in the development of water-soluble quantum dots in the late 1990's, researchers have sought to develop interesting and novel ways of exploiting the extraordinary properties of quantum dots for biomedical applications. Since that time, over 10,000 articles have been published related to the use of quantum dots in biomedicine, many of which regard their use in detection and diagnostic bioassays. This review presents a didactic overview of fundamental physical phenomena associated with quantum dots and paradigm examples of how these phenomena can and have been readily exploited for manifold uses in nanobiotechnology with a specific focus on their implementation in in vitro diagnostic assays and biodetection.

  5. Interaction of porphyrins with CdTe quantum dots.

    PubMed

    Zhang, Xing; Liu, Zhongxin; Ma, Lun; Hossu, Marius; Chen, Wei

    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.

  6. Combinatorial Approach to Studying Metal Enhanced Fluorescence from Quantum Dots

    NASA Astrophysics Data System (ADS)

    Le, Nguyet; Corrigan, Timothy; Norton, Michael; Neff, David

    2013-03-01

    Fluorescence is extensively used in biochemistry for determining the concentration or purity of molecules in a biological environment. In metal-enhanced fluorescence (MEF), the fluorescence molecules separated from a metal surface by several nanometers can be enhanced. The fluorescent enhancement is dependent on the size and spacing of the nanoparticles, as has been shown previously for a number of fluorophore molecules. Fluorescence from quantum dots is of particular interest because the quantum dots do not lose fluorescence ability when exposed to light and they have higher intensity of fluorescence. The purpose of this study is to determine the effect of size and spacing on fluorescence intensity when coupling gold nano-particles with quantum dots. We employ a combinatorial approach, depositing gold particles ranging in diameter from 30 nm to 130 nm with varied spacings onto the substrate, followed by a protein spacer-layer and quantum dots. The fluorescence signal from the metal enhanced quantum dots were determined by confocal microscopy.

  7. Quantum dots find their stride in single molecule tracking

    PubMed Central

    Bruchez, Marcel P.

    2011-01-01

    Thirteen years after the demonstration of quantum dots as biological imaging agents, and nine years after the initial commercial introduction of bioconjugated quantum dots, the brightness and photostability of the quantum dots has enabled a range of investigations using single molecule tracking. These materials are being routinely utilized by a number of groups to track the dynamics of single molecules in reconstituted biophysical systems and on living cells, and are especially powerful for investigations of single molecules over long timescales with short exposure times and high pointing accuracy. New approaches are emerging where the quantum dots are used as “hard-sphere” probes for intracellular compartments. Innovations in quantum dot surface modification are poised to substantially expand the utility of these materials. PMID:22055494

  8. Non-blinking quantum dot with a plasmonic nanoshell resonator

    NASA Astrophysics Data System (ADS)

    Ji, Botao; Giovanelli, Emerson; Habert, Benjamin; Spinicelli, Piernicola; Nasilowski, Michel; Xu, Xiangzhen; Lequeux, Nicolas; Hugonin, Jean-Paul; Marquier, Francois; Greffet, Jean-Jacques; Dubertret, Benoit

    2015-02-01

    Colloidal semiconductor quantum dots are fluorescent nanocrystals exhibiting exceptional optical properties, but their emission intensity strongly depends on their charging state and local environment. This leads to blinking at the single-particle level or even complete fluorescence quenching, and limits the applications of quantum dots as fluorescent particles. Here, we show that a single quantum dot encapsulated in a silica shell coated with a continuous gold nanoshell provides a system with a stable and Poissonian emission at room temperature that is preserved regardless of drastic changes in the local environment. This novel hybrid quantum dot/silica/gold structure behaves as a plasmonic resonator with a strong Purcell factor, in very good agreement with simulations. The gold nanoshell also acts as a shield that protects the quantum dot fluorescence and enhances its resistance to high-power photoexcitation or high-energy electron beams. This plasmonic fluorescent resonator opens the way to a new family of plasmonic nanoemitters with robust optical properties.

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

    SciTech Connect

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

    2012-02-15

    We use multi-population rate equations model to study feedback oscillations in the quantum dot laser. This model takes into account all peculiar characteristics in the quantum dots such as inhomogeneous broadening of the gain spectrum, the presence of the excited states on the quantum dot and the non-confined states due to the presence of wetting layer and the barrier. The contribution of quantum dot groups, which cannot follow by other models, is simulated. The results obtained from this model show the feedback oscillations, the periodic oscillations which evolves to chaos at higher injection current of higher feedback levels. The frequency fluctuation is attributed mainly to wetting layer with a considerable contribution from excited states. The simulation shows that is must be not using simple rate equation models to express quantum dots working at excited state transition.

  10. Ground-state lasing in high-power InAs/GaAs quantum dots-in-a-well laser using active multimode interference structure.

    PubMed

    Cheng, Yuanbing; Wu, Jian; Zhao, Lingjuan; Luo, Xianshu; Wang, Qi Jie

    2015-01-01

    We have designed and demonstrated InAs/GaAs quantum dots-in-a-well laser diodes for short cavities with transverse fundamental mode operation by using an active multimode interferometer (MMI) structure for the first time to the best of our knowledge. Room-temperature continuous-wave ground-state lasing at 1280 nm has been achieved with an output power of 116 mW per facet, which is 2.4 times higher than that of the conventional ridge laser diodes. By using the MMI structures, the excited-state (ES) lasing is effectively suppressed with no ES lasing, even at a high injection current of 400 mA. This device has great potential for high-power single-mode laser emission with low electric power consumption and simple fabrication processes.

  11. Fluorescent carbon nanomaterials: "quantum dots" or nanoclusters?

    PubMed

    Dekaliuk, Mariia O; Viagin, Oleg; Malyukin, Yuriy V; Demchenko, Alexander P

    2014-08-14

    Despite many efforts, the mechanisms of light absorption and emission of small fluorescent carbon nanoparticles (C-dots) are still unresolved and are a subject of active discussion. In this work we address the question as to whether the fluorescence is a collective property of these nanoparticles or they are composed of assembled individual emitters. Selecting three types of C-dots with "violet", "blue" and "green" emissions and performing a detailed study of fluorescence intensity, lifetime and time-resolved anisotropy as a function of excitation and emission wavelengths together with the effect of viscogen and dynamic fluorescence quencher, we demonstrate that the C-dots represent assemblies of surface-exposed fluorophores. They behave as individual emitters, display electronic anisotropy, do not exchange their excited-state energies via homo-FRET and possibly display sub-nanosecond intra-particle mobility.

  12. Reconfigurable quantum dot monolithic multisection passive mode-locked lasers.

    PubMed

    Xin, Y C; Li, Y; Kovanis, Vassilios; Gray, A L; Zhang, L; Lester, L F

    2007-06-11

    We investigate the dynamical response of a quantum dot photonic integrated circuit formed with a combination of eleven passive and active gain cells operating when these cells are appropriately biased as a multi-section quantum dot passively mode-locked laser. When the absorber section is judiciously positioned in the laser cavity then fundamental frequency and harmonic mode-locking at repetition rates from 7.2GHz to 51GHz are recorded. These carefully engineered multi-section configurations that include a passive wave-guide section significantly lower the pulse width up to 34% from 9.7 to 6.4 picoseconds, as well increase by 49% the peak pulsed power from 150 to 224 mW, in comparison to conventional two-section configurations that are formed on the identical device under the same average power. In addition an ultra broad operation range with pulse width below ten picoseconds is obtained with the 3rd-harmonic mode-locking configuration. A record peak power of 234 mW for quantum dot mode-locked lasers operating over 40 GHz is reported for the first time.

  13. A Surface Chemistry Approach to Enhancing Colloidal Quantum Dot Solids for Photovoltaics

    NASA Astrophysics Data System (ADS)

    Carey, Graham Hamilton

    Colloidal quantum dot (CQD) photovoltaic devices have improved rapidly over the past decade of research. By taking advantage of the quantum confinement effect, solar cells constructed using films of infrared-bandgap nanoparticles are able to capture previously untapped ranges of the solar energy spectrum. Additionally, films are fabricated using simple, cheap, reproducible solution processing techniques, enabling the creation of low-cost, flexible photovoltaic devices. A key factor limiting the creation of high efficiency CQD solar cells is the short charge carrier diffusion length in films. Driven by a combination of limited carrier mobility, poor nanoparticle surface passivation, and the presence of unexamined electrically active impurities throughout the film, the poor diffusion length limits the active layer thickness in CQD solar cells, leading to lower-than-desired light absorption, and curtailing the photocurrent generated by such devices. This thesis seeks to address poor diffusion length by addressing each of the limiting factors in turn. Electrical transport in quantum dot solids is examined in the context of improved quantum dot packing; methods are developed to improve packing by using actively densifying components, or by dramatically lowering the volume change required between quantum dots in solution and in solid state. Quantum dot surface passivation is improved by introducing a crucial secondary, small halide ligand source, and by surveying the impact of the processing environment on the final quality of the quantum dot surface. A heretofore unidentified impurity present in quantum dot solids is identified, characterized, and chemically eliminated. Finally, lessons learned through these experiments are combined into a single, novel materials system, leading to quantum dot devices with a significantly improved diffusion length (enhanced from 70 to 230 nm). This enabled thick, high current density (30 mA cm -2, compared to typical values in the 20

  14. Biosensing with Luminescent Semiconductor Quantum Dots

    PubMed Central

    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 adapting QDs for several predominantly in vitro biosensing applications including use in immunoassays, as generalized probes, in nucleic acid detection and fluorescence resonance energy transfer (FRET) - based sensing. We also describe several important considerations when working with QDs mainly centered on the choice of material(s) and appropriate strategies for attaching biomolecules to the QDs.

  15. Silicon quantum dots for biological applications.

    PubMed

    Chinnathambi, Shanmugavel; Chen, Song; Ganesan, Singaravelu; Hanagata, Nobutaka

    2014-01-01

    Semiconductor nanoparticles (or quantum dots, QDs) exhibit unique optical and electronic properties such as size-controlled fluorescence, high quantum yields, and stability against photobleaching. These properties allow QDs to be used as optical labels for multiplexed imaging and in drug delivery detection systems. Luminescent silicon QDs and surface-modified silicon QDs have also been developed as potential minimally toxic fluorescent probes for bioapplications. Silicon, a well-known power electronic semiconductor material, is considered an extremely biocompatible material, in particular with respect to blood. This review article summarizes existing knowledge related to and recent research progress made in the methods for synthesizing silicon QDs, as well as their optical properties and surface-modification processes. In addition, drug delivery systems and in vitro and in vivo imaging applications that use silicon QDs are also discussed.

  16. Semiconductor quantum dot-sensitized solar cells.

    PubMed

    Tian, Jianjun; Cao, Guozhong

    2013-10-31

    Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future.

  17. Semiconductor quantum dot-sensitized solar cells

    PubMed Central

    Tian, Jianjun; Cao, Guozhong

    2013-01-01

    Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future. PMID:24191178

  18. Electron states in semiconductor quantum dots

    SciTech Connect

    Dhayal, Suman S.; Ramaniah, Lavanya M.; Ruda, Harry E.; Nair, Selvakumar V.

    2014-11-28

    In this work, the electronic structures of quantum dots (QDs) of nine direct band gap semiconductor materials belonging to the group II-VI and III-V families are investigated, within the empirical tight-binding framework, in the effective bond orbital model. This methodology is shown to accurately describe these systems, yielding, at the same time, qualitative insights into their electronic properties. Various features of the bulk band structure such as band-gaps, band curvature, and band widths around symmetry points affect the quantum confinement of electrons and holes. These effects are identified and quantified. A comparison with experimental data yields good agreement with the calculations. These theoretical results would help quantify the optical response of QDs of these materials and provide useful input for applications.

  19. Facile synthetic method for pristine graphene quantum dots and graphene oxide quantum dots: origin of blue and green luminescence.

    PubMed

    Liu, Fei; Jang, Min-Ho; Ha, Hyun Dong; Kim, Je-Hyung; Cho, Yong-Hoon; Seo, Tae Seok

    2013-07-19

    Pristine graphene quantum dots and graphene oxide quantum dots are synthesized by chemical exfoliation from the graphite nanoparticles with high uniformity in terms of shape (circle), size (less than 4 nm), and thickness (monolayer). The origin of the blue and green photoluminescence of GQDs and GOQDs is attributed to intrinsic and extrinsic energy states, respectively.

  20. Impact of Nanostructure Configuration on the Photovoltaic Performance of Quantum-Dot Arrays

    NASA Astrophysics Data System (ADS)

    Berbezier, Aude; Aeberhard, Urs

    2015-10-01

    In this paper, a mesoscopic model based on the nonequilibrium Green's function formalism for a tight-binding-like effective Hamiltonian is used to investigate a selectively contacted quantum-dot array designed for operation as a single-junction quantum-dot solar cell. By establishing a direct relation between nanostructure configuration and optoelectronic properties, the investigation reveals the influence of interdot and dot-contact coupling strengths on the rates of charge-carrier photogeneration, radiative recombination, and extraction at contacts, and, consequently, on the ultimate performance of photovoltaic devices with finite quantum-dot arrays as the active medium. For long carrier lifetimes, the dominant configuration effects originate in the dependence of the joint density of states on the interdot coupling in terms of band width and effective band gap. In the low-carrier-lifetime regime, where recombination competes with carrier extraction, the extraction efficiency shows a critical dependence on the dot-contact coupling.

  1. Using quantum dot photoluminescence for load detection

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  2. Colloidal quantum dot light-emitting devices.

    PubMed

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

    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. Competing interactions in semiconductor quantum dots

    SciTech Connect

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

    2014-10-14

    In this study, 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 we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.

  4. Competing interactions in semiconductor quantum dots

    DOE PAGES

    van den Berg, R.; Brandino, G. P.; El Araby, O.; ...

    2014-10-14

    In this study, 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 we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions atmore » longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.« less

  5. Constant Capacitance-DLTS on InAs-Quantum Dots embedded in Schottkydiodes

    NASA Astrophysics Data System (ADS)

    Schramm, A.; Schaefer, J.; Schulz, S.; Hansen, W.

    2007-04-01

    Electron escape from self-assembled InAs quantum dots (QDs) in GaAs is studied. We apply constant capacitance deep level transient spectroscopy (CC-DLTS) to investigate the electric field dependence of the activation energies. As a major advantage for interpretation of the results in contrast to conventional DLTS the electric field of the quantum dot layer remains constant in CC-DLTS experiments. The results of conventional DLTS results are well reproduced.

  6. Charge-extraction strategies for colloidal quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Lan, Xinzheng; Masala, Silvia; Sargent, Edward H.

    2014-03-01

    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.

  7. Open quantum dots in graphene: Scaling relativistic pointer states

    NASA Astrophysics Data System (ADS)

    Ferry, D. K.; Huang, L.; Yang, R.; Lai, Y.-C.; Akis, R.

    2010-04-01

    Open quantum dots provide a window into the connection between quantum and classical physics, particularly through the decoherence theory, in which an important set of quantum states are not "washed out" through interaction with the environment-the pointer states provide connection to trapped classical orbits which remain stable in the dots. Graphene is a recently discovered material with highly unusual properties. This single layer, one atom thick, sheet of carbon has a unique bandstructure, governed by the Dirac equation, in which charge carriers imitate relativistic particles with zero rest mass. Here, an atomic orbital-based recursive Green's function method is used for studying the quantum transport. We study quantum fluctuations in graphene and bilayer graphene quantum dots with this recursive Green's function method. Finally, we examine the scaling of the domiant fluctuation frequency with dot size.

  8. Leveraging Crystal Anisotropy for Deterministic Growth of InAs Quantum Dots with Narrow Optical Linewidths

    DTIC Science & Technology

    2013-08-29

    spin qubit for quantum information. KEYWORDS: Quantum dot , InAs, molecular beam epitaxy, site...removes a major obstacle toward sophisticated quantum dot complexes such as a quantum network of spin qubits . Methods. Substrate Patterning. Lines and...controlled, quantum information, single photon source Epitaxial quantum dots (QDs) have atom-like electronicproperties, including long coherence

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Luminescent properties of cadmium selenide quantum dots in fluorophosphate glasses

    NASA Astrophysics Data System (ADS)

    Lipatova, Zh. O.; Kolobkova, E. V.; Babkina, A. N.

    2016-11-01

    The optical properties of fluorophosphate glasses with CdSe quantum dots are studied. Secondary heat treatment at a temperature exceeding the glass transition temperature resulted in the formation of quantum dots with sizes of 3.7-6.2 nm. The influence of the semiconductor component concentration on the spectral-luminescent characteristics of glasses is shown. It is experimentally demonstrated that glasses with a lower CdSe concentration have a higher absolute luminescence quantum yield.

  11. Size-dependent activation energy and carrier dynamics in Cd(x)Zn(1-x)Te/ZnTe quantum dots on Si substrates.

    PubMed

    Lee, Hong Seok

    2014-11-01

    We investigate the size-dependent activation energy and carrier dynamics in Cd(x)Zn(1-x)Te/ZnTe quantum dots (QDs) grown on Si substrates. The excitonic peak corresponding to transitions from the ground electronic subband to the ground heavy-hole band in Cd0.6Zn0.4Te/ZnTe QDs shifts to a lower energy with increasing Cd0.6Zn0.4Te thickness owing to an increase in the size of the QDs. The activation energy of the electrons confined in the Cd0.6Zn0.4Te/ZnTe QDs, as obtained from the temperature-dependent photoluminescence (PL) spectra, increases with increasing Cd0.6Zn0.4Te thickness owing to an enhancement of the quantum confinement effect resulting from an increase in the energy difference between the electronic state and the conduction band edge. The carrier dynamics of Cd0.6Zn0.4Te/ZnTe QDs is studied using time-resolved PL measurements, which shows a longer exciton lifetime for Cd0.6Zn0.4Te/ZnTe QDs with increasing Cd0.6Zn0.4Te thickness. This behavior is attributed to the reduction of the exciton oscillator strength resulting from a strong built-in electric field in the larger QDs.

  12. Thermal effects on photon-induced quantum transport in a single quantum dot.

    PubMed

    Assunção, M O; de Oliveira, E J R; Villas-Bôas, J M; Souza, F M

    2013-04-03

    We theoretically investigate laser induced quantum transport in a single quantum dot attached to electrical contacts. Our approach, based on a nonequilibrium Green function technique, allows us to include thermal effects on the photon-induced quantum transport and excitonic dynamics, enabling the study of non-Markovian effects. By solving a set of coupled integrodifferential equations, involving correlation and propagator functions, we obtain the photocurrent and the dot occupation as a function of time. Two distinct sources of decoherence, namely, incoherent tunneling and thermal fluctuations, are observed in the Rabi oscillations. As temperature increases, a thermally activated Pauli blockade results in a suppression of these oscillations. Additionally, the interplay between photon and thermally induced electron populations results in a switch of the current sign as time evolves and its stationary value can be maximized by tuning the laser intensity.

  13. Photon Antibunching from Few Quantum Dots in a Cavity

    SciTech Connect

    Gies, Christopher; Jahnke, Frank; Chow, Weng W.

    2015-06-25

    Single quantum dots (QDs) are frequently used as single-photon sources, taking advantage of the final exciton decay in a cascade that produces energetically detuned photons. We propose and analyze a new concept of single-photon source, namely, a few-QD microcavity system driven close to, but below the lasing threshold under strong excitation. Surprisingly, even for two or three QDs inside a cavity, antibunching is observed. To quantify the results, we find that a classification of single-photon emission in terms of antibunching in the autocorrelation function g(2)(0) is insufficient and more details of the photon statistics are required. Our investigations are based on a quantum-optical theory that we solve to obtain the density operator for the quantum-mechanical active medium and radiation field.

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

    NASA Astrophysics Data System (ADS)

    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.

  15. Photonic Enhancement of Colloidal Quantum Dot Photovoltaics

    NASA Astrophysics Data System (ADS)

    Labelle, Andre Jean-Romeo Richard

    Colloidal quantum dots, nanocrystal semiconductors that can be cross-linked and assembled into absorbing thin films, are an attractive material for third-generation photovoltaic applications due to low-cost fabrication and bandgap tunability. As a result of their limited charge transport, these solution-processed thin films suffer from a mismatch in absorption length and charge extraction length. Concepts based on the interdigitation of n- and p-doped layers, approaches that reduce the distance photogenerated carriers must travel before extraction, offer promise on overcoming this limitation. In this thesis, I explore and develop techniques to address the absorption-extraction compromise in CQD materials by implementing nano- and micro-structuring techniques to enhance light absorption in the active film. First, I focus on the development of nanomaterials for light guiding/scattering enhancement in CQD films. For this, I develop a nanostructured gold reflector that, when suitably designed, guides light and traps it within the active film. I show that this yields enhanced broadband absorption with more than 4-fold improvement at the most improved wavelength, which translated into a 34% improvement in photocurrent in a working solar cell. I also show that periodic nanostructures employed for absorption enhancement can lead to improvements in solar cell performance. Limitations in device architecture and film formation, however, prevented significant performance advances for these nano-scale approaches. Regardless, these early results pointed me to a new and more impactful strategy. I focus in on realizing micron-scale structured electrodes to enhance absorption, which I show to be considerably more useful in view of the need to extract charge carriers with high efficiency. I discover that conformal film formation atop these structured electrodes is an absolute prerequisite to enhancing performance. These devices, which I term micro-pyramid CQD cells, provide a 24

  16. Quantum Monte Carlo finite temperature electronic structure of quantum dots

    NASA Astrophysics Data System (ADS)

    Leino, Markku; Rantala, Tapio T.

    2002-08-01

    Quantum Monte Carlo methods allow a straightforward procedure for evaluation of electronic structures with a proper treatment of electronic correlations. This can be done even at finite temperatures [1]. We test the Path Integral Monte Carlo (PIMC) simulation method [2] for one and two electrons in one and three dimensional harmonic oscillator potentials and apply it in evaluation of finite temperature effects of single and coupled quantum dots. Our simulations show the correct finite temperature excited state populations including degeneracy in cases of one and three dimensional harmonic oscillators. The simulated one and two electron distributions of a single and coupled quantum dots are compared to those from experiments and other theoretical (0 K) methods [3]. Distributions are shown to agree and the finite temperature effects are discussed. Computational capacity is found to become the limiting factor in simulations with increasing accuracy. Other essential aspects of PIMC and its capability in this type of calculations are also discussed. [1] R.P. Feynman: Statistical Mechanics, Addison Wesley, 1972. [2] D.M. Ceperley, Rev.Mod.Phys. 67, 279 (1995). [3] M. Pi, A. Emperador and M. Barranco, Phys.Rev.B 63, 115316 (2001).

  17. Laser synthesis and size tailor of carbon quantum dots

    NASA Astrophysics Data System (ADS)

    Hu, Shengliang; Liu, Jun; Yang, Jinlong; Wang, Yanzhong; Cao, Shirui

    2011-12-01

    Carbon quantum dots (C-dots) with average sizes of about 3, 8, and 13 nm were synthesized by laser irradiation of graphite flakes in polymer solution. The obtained C-dots display size and excitation wavelength dependent photoluminescence behavior. The size control of C-dots can be realized by tuning laser pulse width. The original reason could be the effects of laser pulse width on the conditions of nucleation and growth of C-dots. Compared with short-pulse-width laser, the long-pulse-width laser would be better fitted to the size and morphology control of nanostructures in the different material systems.

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

    NASA Astrophysics Data System (ADS)

    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

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

    SciTech Connect

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

    2015-09-14

    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.

  20. The transfer matrix approach to circular graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Chau Nguyen, H.; Nguyen, Nhung T. T.; Nguyen, V. Lien

    2016-07-01

    We adapt the transfer matrix (T-matrix) method originally designed for one-dimensional quantum mechanical problems to solve the circularly symmetric two-dimensional problem of graphene quantum dots. Similar to one-dimensional problems, we show that the generalized T-matrix contains rich information about the physical properties of these quantum dots. In particular, it is shown that the spectral equations for bound states as well as quasi-bound states of a circular graphene quantum dot and related quantities such as the local density of states and the scattering coefficients are all expressed exactly in terms of the T-matrix for the radial confinement potential. As an example, we use the developed formalism to analyse physical aspects of a graphene quantum dot induced by a trapezoidal radial potential. Among the obtained results, it is in particular suggested that the thermal fluctuations and electrostatic disorders may appear as an obstacle to controlling the valley polarization of Dirac electrons.

  1. Gate-controlled electromechanical backaction induced by a quantum dot.

    PubMed

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-04-11

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter.

  2. Gate-controlled electromechanical backaction induced by a quantum dot

    PubMed Central

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-01-01

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter. PMID:27063939

  3. Full counting statistics of quantum dot resonance fluorescence

    PubMed Central

    Matthiesen, Clemens; Stanley, Megan J.; Hugues, Maxime; Clarke, Edmund; Atatüre, Mete

    2014-01-01

    The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding. PMID:24810097

  4. White light emitting diodes realized by using an active packaging method with CdSe/ZnS quantum dots dispersed in photosensitive epoxy resins

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Lee, Kyu-Seung; Ryu, Jae-Hyoung; Hong, Chang-Hee; Cho, Yong-Hoon

    2008-04-01

    White light emitting diodes (LEDs) have been realized using the active packaging (AP) method. The starting materials were bare InGaN LED chips and CdSe/ZnS core-shell quantum dots (QDs) dispersed in photosensitive epoxy resins. Such hybrid LED devices were fabricated using QD mixtures with one ('single'), two ('dual') or four ('multi') emission wavelengths. The AP method allows for convenient adjustment of multiple parameters such as the CIE-1931 coordinate (x, y), color temperature, and color rending index (CRI). All samples show good white balance, and under a 20 mA working current the luminous efficacies of the single, dual, and multi hybrid devices were 8.1 lm W-1, 5.1 lm W-1, and 6.4 lm W-1, respectively. The corresponding quantum efficiencies were 4.1%, 3.1%, and 3.1%; the CRIs were 21.46, 43.76, and 66.20; and the color temperatures were 12 000, 8190, and 7740 K. This shows that the CRI of the samples can be enhanced by broadening the QD emission band, as is exemplified by the 21.46 CRI of the single hybrid LED compared to the 66.20 value for the multi hybrid LED. In addition, we were able to increase the CRI of the single hybrid LED from 15.31 to 32.50 by increasing the working currents from 1 to 50 mA.

  5. Hybrid Circuit QED with Double Quantum Dots

    NASA Astrophysics Data System (ADS)

    Petta, Jason

    2014-03-01

    Cavity quantum electrodynamics explores quantum optics at the most basic level of a single photon interacting with a single atom. We have been able to explore cavity QED in a condensed matter system by placing a double quantum dot (DQD) inside of a high quality factor microwave cavity. Our results show that measurements of the cavity field are sensitive to charge and spin dynamics in the DQD.[2,3] We can explore non-equilibrium physics by applying a finite source-drain bias across the DQD, which results in sequential tunneling. Remarkably, we observe a gain as large as 15 in the cavity transmission when the DQD energy level detuning is matched to the cavity frequency. These results will be discussed in the context of single atom lasing.[4] I will also describe recent progress towards reaching the strong-coupling limit in cavity-coupled Si DQDs. In collaboration with Manas Kulkarni, Yinyu Liu, Karl Petersson, George Stehlik, Jacob Taylor, and Hakan Tureci. We acknowledge support from the Sloan and Packard Foundations, ARO, DARPA, and NSF.

  6. Silver Embedded Nanomesas as Enhanced Single Quantum Dot Emitters in the Telecommunication C Band

    NASA Astrophysics Data System (ADS)

    Huh, Jae-Hoon; Hermannstädter, Claus; Akahane, Kouichi; Jahan, Nahid A.; Sasaki, Masahide; Suemune, Ikuo

    2012-06-01

    We use high-density InAs quantum dots, which were grown by molecular beam epitaxy on InP(311)B substrates, as photon sources in the telecommunication C band at approximately 1.55 µm. To select a small numbers of dots, we fabricate sub-micrometer sized mesas by electron beam lithography and reactive ion etching. The benefit of using high-density quantum dot samples is that at least one optically active quantum dot can be expected in every single mesa. We show that the etching rate and resulting mesa shape of the In0.53Al0.22Ga0.25As epitaxial layer can be varied with the chamber pressure during the etching process. Furthermore, under constant pressure and with increasing etching time, the sequential etching of the epitaxial layer and the underneath substrate leads to a significant modification in the mesa shape, too. We demonstrate that the isolation of a small number of quantum dots within one mesa results in the appearance of single quantum dot emission with a narrow line width and minimal spectral overlap between different emission lines. We moreover present significant enhancement of the luminescence collected from single dots in silver-embedded nanomesas when compared with as-etched mesas.

  7. Energy levels in self-assembled quantum arbitrarily shaped dots.

    PubMed

    Tablero, C

    2005-02-08

    A model to determine the electronic structure of self-assembled quantum arbitrarily shaped dots is applied. This model is based principally on constant effective mass and constant potentials of the barrier and quantum dot material. An analysis of the different parameters of this model is done and compared with those which take into account the variation of confining potentials, bands, and effective masses due to strain. The results are compared with several spectra reported in literature. By considering the symmetry, the computational cost is reduced with respect to other methods in literature. In addition, this model is not limited by the geometry of the quantum dot.

  8. Graphene mediated Stark shifting of quantum dot energy levels

    NASA Astrophysics Data System (ADS)

    Kinnischtzke, Laura; Goodfellow, Kenneth M.; Chakraborty, Chitraleema; Lai, Yi-Ming; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Vamivakas, A. Nick

    2016-05-01

    We demonstrate an optoelectronic device comprised of single InAs quantum dots in an n-i-Schottky diode where graphene has been used as the Schottky contact. Deterministic electric field tuning is shown using Stark-shifted micro-photoluminescence from single quantum dots. The extracted dipole moments from the Stark shifts are comparable to conventional devices where the Schottky contact is a semi-transparent metal. Neutral and singly charged excitons are also observed in the well-known Coulomb-blockade plateaus. Our results indicate that graphene is a suitable replacement for metal contacts in quantum dot devices which require electric field control.

  9. Plasmonic quantum dot solar cells for enhanced infrared response

    NASA Astrophysics Data System (ADS)

    Feng Lu, Hao; Mokkapati, Sudha; Fu, Lan; Jolley, Greg; Hoe Tan, Hark; Jagadish, Chennupati

    2012-03-01

    Enhanced near infrared photoresponse in plasmonic InGaAs/GaAs quantum dot solar cells (QDSC) is demonstrated. Long wavelength light absorption in the wetting-layer and quantum-dot region of the quantum dot solar cell is enhanced through scattering of light by silver nanoparticles deposited on the solar cell surface. Plasmonic light trapping results in simultaneous increase in short-circuit current density by 5.3% and open circuit voltage by 0.9% in the QDSC, leading to an overall efficiency enhancement of 7.6%.

  10. Semiconductor Quantum Dots in Chemical Sensors and Biosensors

    PubMed Central

    Frasco, Manuela F.; Chaniotakis, Nikos

    2009-01-01

    Quantum dots are nanometre-scale semiconductor crystals with unique optical properties that are advantageous for the development of novel chemical sensors and biosensors. The surface chemistry of luminescent quantum dots has encouraged the development of multiple probes based on linked recognition molecules such as peptides, nucleic acids or small-molecule ligands. This review overviews the design of sensitive and selective nanoprobes, ranging from the type of target molecules to the optical transduction scheme. Representative examples of quantum dot-based optical sensors from this fast-moving field have been selected and are discussed towards the most promising directions for future research. PMID:22423206

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

    NASA Technical Reports Server (NTRS)

    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.

  12. Quantum dots microstructured optical fiber for x-ray detection

    NASA Astrophysics Data System (ADS)

    DeHaven, S. L.; Williams, P. A.; Burke, E. R.

    2016-02-01

    A novel concept for the detection of x-rays with microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide is 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 dots application technique are discussed.

  13. What Quantum Dots Can Do for You

    NASA Astrophysics Data System (ADS)

    Salamo, Gregory

    2008-03-01

    Recent clever techniques for fabricating nanosize materials, one-atomic-layer-at-a-time, have simultaneously opened a door to a fantastic adventure at the frontier of physics, chemistry, biology, and engineering. Nanosize materials simply do not behave as the bulk. Indeed, the rules that govern the growth and behavior of these tiny structures are unexplored. In this talk we will discuss our recent efforts to be the architect of their shape, size, density, and position of nanostructures and along the way, the interactions between them that lead to their optical and electrical behavior. While self-assembly is providing exciting quantum dot (QD) structures to explore, like the QD molecules shown here, it is equally exciting to try to use the rules we uncover to encourage QD formation to take a desired path. Can we understand the formation of faceted nanostructures? Can we encourage or seed dot structures to form specific arrays? Is it possible to engineer greater homogeneity of dot shape and size? Can we design both the optical and electrical behavior of either individual or arrays of nanostructures to mimic those we find in nature? In this talk we will review our progress to answer these questions and discuss the possibilities and challenges ahead. For example, we will discuss the formation of individual faceted nanostructures as well as the fabrication of a vertically and laterally ordered QD stacks forming three-dimensional QD arrays. As another example, we will discuss the importance of surfaces with high Miller indices, as a template to the formation of nanostructures as well as their potential role in determining the shape and increased size uniformity of the confined structures. Importantly, these observations lead to an even more basic question of when and why high index surfaces are stable. Indeed, we have found that in order to understand the origin of high index surfaces that bound nanostructures we have to study them directly.

  14. Quantum dots as FRET acceptors for highly sensitive multiplexing immunoassays

    NASA Astrophysics Data System (ADS)

    Geissler, Daniel; Hildebrandt, Niko; Charbonnière, Loïc J.; Ziessel, Raymond F.; Löhmannsröben, Hans-Gerd

    2009-02-01

    Homogeneous immunoassays have the benefit that they do not require any time-consuming separation steps. FRET is one of the most sensitive homogeneous methods used for immunoassays. Due to their extremely strong absorption over a broad wavelength range the use of quantum dots as FRET acceptors allows for large Foerster radii, an important advantage for assays in the 5 to 10 nm distance range. Moreover, because of their size-tunable emission, quantum dots of different sizes can be used with a single donor for the detection of different analytes (multiplexing). As the use of organic dyes with short fluorescence decay times as donors is known to be inefficient with quantum dot acceptors, lanthanide complexes with long luminescence decays are very efficient alternatives. In this contribution we present the application of commercially available biocompatible CdSe/ZnS core/shell quantum dots as multiplexing FRET acceptors together with a single terbium complex as donor in a homogeneous immunoassay system. Foerster radii of 10 nm and FRET efficiencies of 75 % are demonstrated. The high sensitivity of the terbium-toquantum dot FRET assay is shown by sub-100-femtomolar detection limits for two different quantum dots (emitting at 605 and 655 nm) within the same biotin-streptavidin assay. Direct comparison to the FRET immunoassay "gold standard" (FRET from Eu-TBP to APC) yields a three orders of magnitude sensitivity improvement, demonstrating the big advantages of quantum dots not only for multiplexing but also for highly sensitive nanoscale analysis.

  15. Quantum dots: synthesis, bioapplications, and toxicity

    PubMed Central

    2012-01-01

    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. PMID:22929008

  16. Highly Fluorescent Noble Metal Quantum Dots

    PubMed Central

    Zheng, Jie; Nicovich, Philip R.; Dickson, Robert M.

    2009-01-01

    Highly fluorescent, water-soluble, few-atom noble metal quantum dots have been created that behave as multi-electron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near IR. These “molecular metals” exhibit highly polarizable transitions and scale in size according to the simple relation, Efermi/N1/3, predicted by the free electron model of metallic behavior. This simple scaling indicates that fluorescence arises from intraband transitions of free electrons and that these conduction electron transitions are the low number limit of the plasmon – the collective dipole oscillations occurring when a continuous density of states is reached. Providing the “missing link” between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy transfer pairs, and light emitting sources in nanoscale optoelectronics. PMID:17105412

  17. Phonon Overlaps in Molecular Quantum Dot Systems

    NASA Astrophysics Data System (ADS)

    Chang, Connie; Sethna, James

    2004-03-01

    We model the amplitudes and frequencies of the vibrational sidebands for the new molecular quantum dot systems. We calculate the Franck-Condon phonon overlaps in the 3N-dimensional configuration sapce. We solve the general case where the vibrational frequencies and eigenmodes change during the transition. We perform PM3 and DFT calculations for the case of the dumb bell-shaped C140 molecule. We find that the strongest amplitudes are associated with the 11 meV stretch mode, in agreement with experiment. The experimental amplitudes vary from molecule to molecule; indicating that the molecular overlaps are environment dependent. We explore overlaps in the presence of external electric fields from image charges and counter ions.

  18. Andreev Conductance of a Chaotic Quantum Dot

    NASA Astrophysics Data System (ADS)

    Clerk, A. A.; Brouwer, P. W.; Ambegaokar, V.

    2000-03-01

    Using random matrix theory, we study the full magnetic field (B) and voltage (V) dependence of the Andreev conductance of a chaotic quantum dot coupled via point contacts to both a normal metal and a superconductor. We recover previous results in the zero and large B,V limits, but also observe interesting non-monotonic behaviour in the crossover regime. Our results demonstrate that the induced superconductivity effect previously seen in calculations of the density of states (J.A. Melsen, P.W. Brouwer, K.M. Frahm and C.W.J. Beenakker, Europhys. Lett., 35), 7 (1996). can also have a pronounced signature in the conductance; this may explain certain anomalous features observed in recent experiments on metallic normal-superconducting point contacts (P. Chalsani, S.K. Uphadyay, R.A. Buhrman, unpublished.).

  19. Correlation energy of anisotropic quantum dots

    SciTech Connect

    Zhao Yan; Loos, Pierre-Francois; Gill, Peter M. W.

    2011-09-15

    We study the D-dimensional high-density correlation energy E{sub c} of the singlet ground state of two electrons confined by a harmonic potential with Coulombic repulsion. We allow the harmonic potential to be anisotropic and examine the behavior of E{sub c} as a function of the anisotropy {alpha}{sup -1}. In particular, we are interested in the limit where the anisotropy goes to infinity ({alpha}{yields}0) and the electrons are restricted to a lower-dimensional space. We show that tuning the value of {alpha} from 0 to 1 allows a smooth dimensional interpolation and we demonstrate that the usual model, in which a quantum dot is treated as a two-dimensional system, is inappropriate. Finally, we provide a simple function which reproduces the behavior of E{sub c} over the entire range of {alpha}.

  20. Quantum Dots Confined in Nanoporous Alumina Membranes

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Xia, Jianfeng; Wang, Jun; Shinar, Joseph; Lin, Zhiqun

    2007-03-01

    Precise control over the dispersion and lateral distribution of quantum dots (QDs) within nanoscopic porous media provides a unique route to manipulate the optical and/or electronic properties of QDs in a very simple and controllable manner for applications related to light emitting, optoelectronic, and sensor devices. Here we filled nanoporous alumina membranes (PAMs) with CdSe/ZnS core/shell QDs by dip coating. The deposition of QDs induced changes in the refractive index of PAMs. The amount of absorbed QDs was quantified by fitting the reflection and transmission spectra observed experimentally with one side open and freestanding (i.e., with two sides open) PAMs employed, respectively. The fluorescence of the QDs was found to be retained within the cylindrical nanopores of PAMs.

  1. Quantum dots as a possible oxygen sensor

    NASA Astrophysics Data System (ADS)

    Ziółczyk, Paulina; Kur-Kowalska, Katarzyna; Przybyt, Małgorzata; Miller, Ewa

    Results of studies on optical properties of low toxicity quantum dots (QDs) obtained from copper doped zinc sulfate are discussed in the paper. The effect of copper admixture concentration and solution pH on the fluorescence emission intensity of QDs was investigated. Quenching of QDs fluorescence by oxygen was reported and removal of the oxygen from the environment by two methods was described. In the chemical method oxygen was eliminated by adding sodium sulfite, in the other method oxygen was removed from the solution using nitrogen gas. For elimination of oxygen by purging the solution with nitrogen the increase of fluorescence intensity with decreasing oxygen concentration obeyed Stern-Volmer equation indicating quenching. For the chemical method Stern-Volmer equation was not fulfilled. The fluorescence decays lifetimes were determined and the increase of mean lifetimes at the absence of oxygen support hypothesis that QDs fluorescence is quenched by oxygen.

  2. Nanosecond colloidal quantum dot lasers for sensing.

    PubMed

    Guilhabert, B; Foucher, C; Haughey, A-M; Mutlugun, E; Gao, Y; Herrnsdorf, J; Sun, H D; Demir, H V; Dawson, M D; Laurand, N

    2014-03-24

    Low-threshold, gain switched colloidal quantum dot (CQD) distributed-feedback lasers operating in the nanosecond regime are reported and proposed for sensing applications for the first time to the authors' knowledge. The lasers are based on a mechanically-flexible polymeric, second order grating structure overcoated with a thin-film of CQD/PMMA composite. The threshold fluence of the resulting lasers is as low as 0.5 mJ/cm² for a 610 nm emission and the typical linewidth is below 0.3 nm. The emission wavelength of the lasers can be set at the design stage and laser operation between 605 nm and 616 nm, while using the exact same CQD gain material, is shown. In addition, the potential of such CQD lasers for refractive index sensing in solution is demonstrated by immersion in water.

  3. Selenium quantum dots: Preparation, structure, and properties

    NASA Astrophysics Data System (ADS)

    Qian, Fuli; Li, Xueming; Tang, Libin; Lai, Sin Ki; Lu, Chaoyu; Lau, Shu Ping

    2017-01-01

    An interesting class of low-dimensional nanomaterials, namely, selenium quantum dots (SeQDs), which are composed of nano-sized selenium particles, is reported in this study. The SeQDs possess a hexagonal crystal structure. They can be synthesized in large quantity by ultrasound liquid-phase exfoliation using NbSe2 powders as the source material and N-Methyl-2-pyrrolidone (NMP) as the dispersant. During sonication, the Nb-Se bonds dissociate; the SeQDs are formed, while niobium is separated by centrifugation. The SeQDs have a narrow diameter distribution from 1.9 to 4.6 nm and can be dispersed with high stability in NMP without the need for passivating agents. They exhibit photoluminescence properties that are expected to find useful applications in bioimaging, optoelectronics, as well as nanocomposites.

  4. Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids.

    PubMed

    Talgorn, Elise; Gao, Yunan; Aerts, Michiel; Kunneman, Lucas T; Schins, Juleon M; Savenije, T J; van Huis, Marijn A; van der Zant, Herre S J; Houtepen, Arjan J; Siebbeles, Laurens D A

    2011-09-25

    Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots.

  5. Chemically Triggered Formation of Two-Dimensional Epitaxial Quantum Dot Superlattices.

    PubMed

    Walravens, Willem; De Roo, Jonathan; Drijvers, Emile; Ten Brinck, Stephanie; Solano, Eduardo; Dendooven, Jolien; Detavernier, Christophe; Infante, Ivan; Hens, Zeger

    2016-07-26

    Two dimensional superlattices of epitaxially connected quantum dots enable size-quantization effects to be combined with high charge carrier mobilities, an essential prerequisite for highly performing QD devices based on charge transport. Here, we demonstrate that surface active additives known to restore nanocrystal stoichiometry can trigger the formation of epitaxial superlattices of PbSe and PbS quantum dots. More specifically, we show that both chalcogen-adding (sodium sulfide) and lead oleate displacing (amines) additives induce small area epitaxial superlattices of PbSe quantum dots. In the latter case, the amine basicity is a sensitive handle to tune the superlattice symmetry, with strong and weak bases yielding pseudohexagonal or quasi-square lattices, respectively. Through density functional theory calculations and in situ titrations monitored by nuclear magnetic resonance spectroscopy, we link this observation to the concomitantly different coordination enthalpy and ligand displacement potency of the amine. Next to that, an initial ∼10% reduction of the initial ligand density prior to monolayer formation and addition of a mild, lead oleate displacing chemical trigger such as aniline proved key to induce square superlattices with long-range, square micrometer order; an effect that is the more pronounced the larger the quantum dots. Because the approach applies to PbS quantum dots as well, we conclude that it offers a reproducible and rational method for the formation of highly ordered epitaxial quantum dot superlattices.

  6. 1310 nm quantum dot DFB lasers with high dot density and ultra-low linewidth-power product

    NASA Technical Reports Server (NTRS)

    Qiu, Y.; Lester, L. F.; Gray, A. L.; Newell, T. C.; Hains, C.; Gogna, P.; Muller, R.; Maker, P.; Su, H.; Stintz, A.

    2002-01-01

    Laterally coupled distributed feedback lasers using high-density InAs quantum dots-in-a-well (DWELL) active region demonstrate a nominal wavelength of 1310 nm, a linewidth as small as 68 kHz, and a linewidth-power product of 100 kHz-mW.

  7. Strongly nonlinear thermovoltage and heat dissipation in interacting quantum dots

    NASA Astrophysics Data System (ADS)

    Sierra, Miguel A.; Sánchez, David

    2014-09-01

    We investigate the nonlinear regime of charge and energy transport through Coulomb-blockaded quantum dots. We discuss crossed effects that arise when electrons move in response to thermal gradients (Seebeck effect) or energy flows in reaction to voltage differences (Peltier effect). We find that the differential thermoelectric conductance shows a characteristic Coulomb butterfly structure due to charging effects. Importantly, we show that experimentally observed thermovoltage zeros are caused by the activation of Coulomb resonances at large thermal shifts. Furthermore, the power dissipation asymmetry between the two attached electrodes can be manipulated with the applied voltage, which has implications for the efficient design of nanoscale coolers.

  8. Multi-million atom electronic structure calculations for quantum dots

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined

  9. Long-distance coherent coupling in a quantum dot array.

    PubMed

    Braakman, F R; Barthelemy, P; Reichl, C; Wegscheider, W; Vandersypen, L M K

    2013-06-01

    Controlling long-distance quantum correlations is central to quantum computation and simulation. In quantum dot arrays, experiments so far rely on nearest-neighbour couplings only, and inducing long-distance correlations requires sequential local operations. Here, we show that two distant sites can be tunnel-coupled directly. The coupling is mediated by virtual occupation of an intermediate site, with a strength that is controlled via the energy detuning of this site. It permits a single charge to oscillate coherently between the outer sites of a triple dot array without passing through the middle, as demonstrated through the observation of Landau-Zener-Stückelberg interference. The long-distance coupling significantly improves the prospects of fault-tolerant quantum computation using quantum dot arrays, and opens up new avenues for performing quantum simulations in nanoscale devices.

  10. Ultrafast optical spin echo in a single quantum dot

    NASA Astrophysics Data System (ADS)

    Press, David; de Greve, Kristiaan; McMahon, Peter L.; Ladd, Thaddeus D.; Friess, Benedikt; Schneider, Christian; Kamp, Martin; Höfling, Sven; Forchel, Alfred; Yamamoto, Yoshihisa

    2010-06-01

    Many proposed photonic quantum networks rely on matter qubits to serve as memory elements. The spin of a single electron confined in a semiconductor quantum dot forms a promising matter qubit that may be interfaced with a photonic network. Ultrafast optical spin control allows gate operations to be performed on the spin within a picosecond timescale, orders of magnitude faster than microwave or electrical control. One obstacle to storing quantum information in a single quantum dot spin is the apparent nanosecond-timescale dephasing due to slow variations in the background nuclear magnetic field. Here we use an ultrafast, all-optical spin echo technique to increase the decoherence time of a single quantum dot electron spin from nanoseconds to several microseconds. The ratio of decoherence time to gate time exceeds 105, suggesting strong promise for future photonic quantum information processors and repeater networks.

  11. Improved activity and thermo-stability of the horse radish peroxidase with graphene quantum dots and its application in fluorometric detection of hydrogen peroxide

    NASA Astrophysics Data System (ADS)

    Xiaoyan, Zhou; Yuanyuan, Jiang; Zaijun, Li; Zhiguo, Gu; Guangli, Wang

    2016-08-01

    Graphene quantum dots (GQDs) have received extensive concern in many fields such as optical probe, bioimaging and biosensor. However, few reports refer on the influence of GQDs on enzyme performance. The paper reports two kinds of graphene quantum dots (termed as GO-GQDs and N,S-GQDs) that were prepared by cutting of graphene oxide and pyrolysis of citric acid and L-cysteine, and their use for the horse radish peroxidase (HRP) modification. The study reveals that GO-GQDs and N,S-GQDs exhibit an opposite effect on the HRP performance. Only HRP modified with GO-GQDs offers an enhanced activity (more than 1.9 times of pristine enzyme) and thermo-stability. This is because GO-GQDs offer a larger conjugate rigid plane and fewer hydrophilic groups compared to N,S-GQDs. The characteristics can make GO-GQDs induce a proper conformational change in the HRP for the catalytic performance, improving the enzyme activity and thermo-stability. The HRP modified with green luminescent GO-GQDs was also employed as a biocatalyst for sensing of H2O2 by a fluorometric sensor. The colorless tetramethylbenzidine (TMB) is oxidized into blue oxidized TMB in the presence of H2O2 by the assistance of HRP/GO-GQDs, leading to an obvious fluorescence quenching. The fluorescence intensity linearly decreases with the increase of H2O2 concentration in the range from 2 × 10 - 9 to 2 × 10 - 4 M with the detection limit of 6.8 × 10 - 10 M. The analytical method provides the advantage of sensitivity, stability and accuracy compared with present H2O2 sensors based on the pristine HRP. It has been successfully applied in the determination of H2O2 in real water samples. The study also opens a new avenue for modification of enzyme activity and stability that offers great promise in applications such as biological catalysis, biosensing and enzyme engineering.

  12. Improved activity and thermo-stability of the horse radish peroxidase with graphene quantum dots and its application in fluorometric detection of hydrogen peroxide.

    PubMed

    Xiaoyan, Zhou; Yuanyuan, Jiang; Zaijun, Li; Zhiguo, Gu; Guangli, Wang

    2016-08-05

    Graphene quantum dots (GQDs) have received extensive concern in many fields such as optical probe, bioimaging and biosensor. However, few reports refer on the influence of GQDs on enzyme performance. The paper reports two kinds of graphene quantum dots (termed as GO-GQDs and N,S-GQDs) that were prepared by cutting of graphene oxide and pyrolysis of citric acid and l-cysteine, and their use for the horse radish peroxidase (HRP) modification. The study reveals that GO-GQDs and N,S-GQDs exhibit an opposite effect on the HRP performance. Only HRP modified with GO-GQDs offers an enhanced activity (more than 1.9 times of pristine enzyme) and thermo-stability. This is because GO-GQDs offer a larger conjugate rigid plane and fewer hydrophilic groups compared to N,S-GQDs. The characteristics can make GO-GQDs induce a proper conformational change in the HRP for the catalytic performance, improving the enzyme activity and thermo-stability. The HRP modified with green luminescent GO-GQDs was also employed as a biocatalyst for sensing of H2O2 by a fluorometric sensor. The colorless tetramethylbenzidine (TMB) is oxidized into blue oxidized TMB in the presence of H2O2 by the assistance of HRP/GO-GQDs, leading to an obvious fluorescence quenching. The fluorescence intensity linearly decreases with the increase of H2O2 concentration in the range from 2×10-9 to 2×10-4M with the detection limit of 6.8×10-10M. The analytical method provides the advantage of sensitivity, stability and accuracy compared with present H2O2 sensors based on the pristine HRP. It has been successfully applied in the determination of H2O2 in real water samples. The study also opens a new avenue for modification of enzyme activity and stability that offers great promise in applications such as biological catalysis, biosensing and enzyme engineering.

  13. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Yoon, Yeung-Pil; Kim, Jae-Hong; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook; Ahn, Kwang-Soon

    2014-08-01

    Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO2 (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of Sn2- + 2e- (CE) → Sn-12- + S2- at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, Sn2- + 2e- (TiO2 in the photoanode) → Sn-12- + S2-, and significantly improved overall energy conversion efficiency.

  14. Increase of third-order nonlinear optical activity of PbS quantum dots in zeolite Y by increasing cation size.

    PubMed

    Kim, Hyun Sung; Yoon, Kyung Byung

    2012-02-08

    The third-order nonlinear optical (3NLO) activity of PbS quantum dots (QDs) encapsulated in zeolite Y has been expected to depend sensitively on the countercation of the zeolite host. However, ion exchange of the pristine countercation, H(+), with other cations has not been possible because the framework decomposes and the QDs aggregate immediately when the PbS QD-incorporating zeolite Y with H(+) as the countercation is exposed to the atmosphere. We now report that when H(+) is transformed to NH(4)(+), the framework of PbS QD-containing zeolite Y does not undergo decomposition and the PbS QDs do not undergo aggregation to form larger QDs during the aqueous ion exchange of NH(4)(+) with alkali-metal ions (M(A)(+) = Li, Na(+), K(+), Rb(+)). The 3NLO activity of the M(A)(+)-exchanged PbS QD-incorporating zeolite Y film increases with increasing size of M(A)(+). The stabilization of the surface-bound exciton by the electron-rich framework oxide and electron-poor cation is proposed to be responsible for the increase. This is the first example of a method for systematically increasing the 3NLO activity of QDs dispersed in a dielectric matrix by systematically changing its properties. These results will serve as a guideline for future research and also promote applications of QD-incorporating zeolites in various fields.

  15. Optical properties of few layered graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Pratap Choudhary, Raghvendra; Shukla, Shobha; Vaibhav, Kumar; Bhagwan Pawar, Pranav; Saxena, Sumit

    2015-09-01

    Quantum dots provide a unique opportunity to study the confinement effects of electronic wave function on the properties of materials. We have investigated the optical properties of graphene quantum dots synthesized using ultra-fast light-matter interactions followed by one step reduction process. Atomic-scale morphological information suggests the presence of both zigzag and armchair edges in these quantum dots. Optical characterizations were performed using absorption, photoluminescence, and infrared spectroscopy. A shift in the emission spectrum and disappearance of n → π* transition in the absorption spectrum on reduction of the ablated samples confirmed the formation of graphene quantum dots. First principles calculations are in good agreement with the experimentally reported infrared data.

  16. Majorana dc Josephson current mediated by a quantum dot.

    PubMed

    Xu, Luting; Li, Xin-Qi; Sun, Qing-Feng

    2017-05-17

    The Josephson supercurrent through a hybrid Majorana-quantum dot-Majorana junction is investigated. We particularly analyze the effect of spin-selective coupling between the Majorana and quantum dot states, which only emerges in the topological phase and will influence the current through bent junctions and/or in the presence of magnetic fields in the quantum dot. We find that the characteristic behavior of the supercurrent through this system is quite counterintuitive, differing remarkably from the resonant tunneling, e.g. through the similar (normal phase) superconductor-quantum dot-superconductor junction. Our analysis is carried out under the influence of the full set-up parameters and for both the [Formula: see text] and [Formula: see text] periodic currents. The present study is expected to be relevant to the future exploration of applications of Majorana-nanowire circuits.

  17. Energy levels of hybrid monolayer-bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; Ketabi, S. A.; da Costa, D. R.; Peeters, F. M.

    2016-04-01

    Often real samples of graphene consist of islands of both monolayer and bilayer graphene. Bound states in such hybrid quantum dots are investigated for (i) a circular single-layer graphene quantum dot surrounded by an infinite bilayer graphene sheet and (ii) a circular bilayer graphene quantum dot surrounded by an infinite single-layer graphene. Using the continuum model and applying zigzag boundary conditions at the single-layer-bilayer graphene interface, we obtain analytical results for the energy levels and the corresponding wave spinors. Their dependence on perpendicular magnetic and electric fields are studied for both types of quantum dots. The energy levels exhibit characteristics of interface states, and we find anticrossings and closing of the energy gap in the presence of a bias potential.

  18. Engineering multifunctional magnetic-quantum dot barcodes by flow focusing.

    PubMed

    Giri, Supratim; Li, Dawei; Chan, Warren C W

    2011-04-14

    A simple one-step flow focusing method was used to embed both magnetic nanoparticles and quantum dots in microbeads in controlled ratios to generate a large library of molecular barcodes for biological applications.

  19. Probing of Unembedded Metallic Quantum Dots with Positrons

    SciTech Connect

    Fischer, C G; Denison, A B; Weber, M H; Wilcoxon, J P; Woessner, S; Lynn, K G

    2003-08-01

    We employed the two detector coincident Doppler Broadening Technique (coPAS) to investigate Ag, Au and Ag/Au alloy quantum dots of varying sizes which were deposited in thin layers on glass slides. The Ag quantum dots range from 2 to 3 nm in diameter, while the Ag/Au alloy quantum dots exhibit Ag cores of 2 nm and 3 nm and Au shells of varying thickness. We investigate the possibility of positron confinement in the Ag core due to positron affinity differences between Ag and Au. We describe the results and their significance to resolving the issue of whether positrons annihilate within the quantum dot itself or whether surface and positron escape effects play an important role.

  20. Quantum dot conjugates in a sub-micrometer fluidic channel

    DOEpatents

    Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.

    2008-07-29

    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.

  1. Quantum dot conjugates in a sub-micrometer fluidic channel

    DOEpatents

    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.

  2. Fundamental and applied aspects of luminescence of colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Razumov, V. F.

    2017-03-01

    The spectral luminescent characteristics of colloidal quantum dots as a new class of luminophores are discussed and state-of-the-art investigations, problems, and prospects for their applications are considered.

  3. Berry phase jumps and giant nonreciprocity in Dirac quantum dots

    NASA Astrophysics Data System (ADS)

    Rodriguez-Nieva, Joaquin F.; Levitov, Leonid S.

    2016-12-01

    We predict that a strong nonreciprocity in the resonance spectra of Dirac quantum dots can be induced by the Berry phase. The nonreciprocity arises in relatively weak magnetic fields and is manifest in anomalously large field-induced splittings of quantum dot resonances which are degenerate at B =0 due to time-reversal symmetry. This exotic behavior, which is governed by field-induced jumps in the Berry phase of confined electronic states, is unique to quantum dots in Dirac materials and is absent in conventional quantum dots. The effect is strong for gapless Dirac particles and can overwhelm the B -induced orbital and Zeeman splittings. A finite Dirac mass suppresses the effect. The nonreciprocity, predicted for generic two-dimensional Dirac materials, is accessible through Faraday and Kerr optical rotation measurements and scanning tunneling spectroscopy.

  4. Laterally Coupled Quantum-Dot Distributed-Feedback Lasers

    NASA Technical Reports Server (NTRS)

    Qui, Yueming; Gogna, Pawan; Muller, Richard; Maker, paul; Wilson, Daniel; Stintz, Andreas; Lester, Luke

    2003-01-01

    InAs quantum-dot lasers that feature distributed feedback and lateral evanescent- wave coupling have been demonstrated in operation at a wavelength of 1.3 m. These lasers are prototypes of optical-communication oscillators that are required to be capable of stable single-frequency, single-spatial-mode operation. A laser of this type (see figure) includes an active layer that comprises multiple stacks of InAs quantum dots embedded within InGaAs quantum wells. Distributed feedback is provided by gratings formed on both sides of a ridge by electron lithography and reactive-ion etching on the surfaces of an AlGaAs/GaAs waveguide. The lateral evanescent-wave coupling between the gratings and the wave propagating in the waveguide is strong enough to ensure operation at a single frequency, and the waveguide is thick enough to sustain a stable single spatial mode. In tests, the lasers were found to emit continuous-wave radiation at temperatures up to about 90 C. Side modes were found to be suppressed by more than 30 dB.

  5. Colloidal quantum dot solar cells exploiting hierarchical structuring.

    PubMed

    Labelle, André J; Thon, Susanna M; Masala, Silvia; Adachi, Michael M; Dong, Haopeng; Farahani, Maryam; Ip, Alexander H; Fratalocchi, Andrea; Sargent, Edward H

    2015-02-11

    Extremely thin-absorber solar cells offer low materials utilization and simplified manufacture but require improved means to enhance photon absorption in the active layer. Here, we report enhanced-absorption colloidal quantum dot (CQD) solar cells that feature transfer-stamped solution-processed pyramid-shaped electrodes employed in a hierarchically structured device. The pyramids increase, by up to a factor of 2, the external quantum efficiency of the device at absorption-limited wavelengths near the absorber band edge. We show that absorption enhancement can be optimized with increased pyramid angle with an appreciable net improvement in power conversion efficiency, that is, with the gain in current associated with improved absorption and extraction overcoming the smaller fractional decrease in open-circuit voltage associated with increased junction area. We show that the hierarchical combination of micron-scale structured electrodes with nanoscale films provides for an optimized enhancement at absorption-limited wavelengths. We fabricate 54.7° pyramid-patterned electrodes, conformally apply the quantum dot films, and report pyramid CQD solar cells that exhibit a 24% improvement in overall short-circuit current density with champion devices providing a power conversion efficiency of 9.2%.

  6. Improved dot size uniformity and luminescense of InAs quantum dots on InP substrate

    NASA Technical Reports Server (NTRS)

    Qiu, Y.; Uhl, D.

    2002-01-01

    InAs self-organized quantum dots have been grown in InGaAs quantum well on InP substrates by metalorganic vapor phase epitaxy. Atomic Force Microscopy confirmed of quantum dot formation with dot density of 3X10(sup 10) cm(sup -2). Improved dot size uniformity and strong room temperature photoluminescence up to 2 micron were observed after modifying the InGaAs well.

  7. Coherent radiation by quantum dots and magnetic nanoclusters

    NASA Astrophysics Data System (ADS)

    Yukalov, V. I.; Yukalova, E. P.

    2014-03-01

    The assemblies of either quantum dots or magnetic nanoclusters are studied. It is shown that such assemblies can produce coherent radiation. A method is developed for solving the systems of nonlinear equations describing the dynamics of such assemblies. The method is shown to be general and applicable to systems of different physical nature. Despite mathematical similarities of dynamical equations, the physics of the processes for quantum dots and magnetic nanoclusters is rather different. In a quantum dot assembly, coherence develops due to the Dicke effect of dot interactions through the common radiation field. For a system of magnetic clusters, coherence in the spin motion appears due to the Purcell effect caused by the feedback action of a resonator. Self-organized coherent spin radiation cannot arise without a resonator. This principal difference is connected with the different physical nature of dipole forces between the objects. Effective dipole interactions between the radiating quantum dots, appearing due to photon exchange, collectivize the dot radiation. While the dipolar spin interactions exist from the beginning, yet before radiation, and on the contrary, they dephase spin motion, thus destroying the coherence of moving spins. In addition, quantum dot radiation exhibits turbulent photon filamentation that is absent for radiating spins.

  8. Colloidal quantum dot materials for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Arinze, Ebuka S.; Nyirjesy, Gabrielle; Cheng, Yan; Palmquist, Nathan; Thon, Susanna M.

    2015-09-01

    Colloidal quantum dots (CQDs) are an attractive material for optoelectronic applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Specifically, the bandgap of films composed of arrays of CQDs can be tuned via the quantum confinement effect for tailored spectral utilization. PbS-based CQDs can be tuned throughout the near and mid-infrared wavelengths and are a promising materials system for photovoltaic devices that harvest non-visible solar radiation. The performance of CQD solar cells is currently limited by an absorption-extraction compromise, whereby photon absorption lengths in the near infrared spectral regime exceed minority carrier diffusion lengths in the bulk films. Several light trapping strategies for overcoming this compromise and increasing the efficiency of infrared energy harvesting will be reviewed. A thin-film interference technique for creating multi-colored and transparent solar cells will be presented, and a discussion of designing plasmonic nanomaterials based on earth-abundant materials for integration into CQD solar cells is developed. The results indicate that it should be possible to achieve high absorption and color-tunability in a scalable nanomaterials system.

  9. Optical Studies of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Yükselici, H.; Allahverdi, Ç.; Aşıkoğlu, A.; Ünlü, H.; Baysal, A.; Çulha, M.; İnce, R.; İnce, A.; Feeney, M.; Athalin, H.

    Optical absorption (ABS), steady-state photoluminescence (PL), resonant Raman, and photoabsorption (PA) spectroscopies are employed to study quantum-size effects in II-VI semiconductor quantum dots (QDs) grown in glass samples. We observe a size-dependent shift in the energetic position of the first exciton peak and have examined the photoinduced evolution of the differential absorption spectra. The Raman shifts of the phonon modes are employed to monitor stoichiometric changes in the composition of the QDs during growth. Two sets of glass samples were prepared from color filters doped with CdS x Se1 - x and Zn x Cd1 - x Te. We analyze the optical properties of QDs through the ABS, PL, resonant Raman, and PA spectroscopies. The glass samples were prepared from commercially available semiconductor doped filters by a two-step thermal treatment. The average size of QDs is estimated from the energetic position of the first exciton peak in the ABS spectrum. A calculation based on a quantized-state effective mass model in the strong confinement regime predicts that the average radius of QDs in the glass samples ranges from 2.9 to 4.9 nm for CdTe and from 2.2 to 9.3 nm for CdS0. 08Se0. 92. We have also studied the nonlinear optical properties of QDs by reviewing the results of size-dependent photoinduced modulations in the first exciton band of CdTe QDs studied by PA spectroscopy.

  10. Optical nuclear spin polarization in quantum dots

    NASA Astrophysics Data System (ADS)

    Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei

    2016-10-01

    Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot (QD) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip-flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time. Project partially supported by the National Natural Science Foundations of China (Grant Nos. 11374039 and 11174042) and the National Basic Research Program of China (Grant Nos. 2011CB922204 and 2013CB632805).

  11. Los Alamos Quantum Dots for Solar, Display Technology

    SciTech Connect

    Klimov, Victor

    2015-04-13

    Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.

  12. Quantized charge pumping through a carbon nanotube double quantum dot

    NASA Astrophysics Data System (ADS)

    Chorley, S. J.; Frake, J.; Smith, C. G.; Jones, G. A. C.; Buitelaar, M. R.

    2012-04-01

    We demonstrate single-electron pumping in a gate-defined carbon nanotube double quantum dot. By periodic modulation of the potentials of the two quantum dots, we move the system around charge triple points and transport exactly one electron or hole per cycle. We investigate the pumping as a function of the modulation frequency and amplitude and observe good current quantization up to frequencies of 18 MHz where rectification effects cause the mechanism to break down.

  13. Ultrafast optical properties of lithographically defined quantum dot amplifiers

    SciTech Connect

    Miaja-Avila, L.; Verma, V. B.; Mirin, R. P.; Silverman, K. L.; Coleman, J. J.

    2014-02-10

    We measure the ultrafast optical response of lithographically defined quantum dot amplifiers at 40 K. Recovery of the gain mostly occurs in less than 1 picosecond, with some longer-term transients attributable to carrier heating. Recovery of the absorption proceeds on a much longer timescale, representative of relaxation between quantum dot levels and carrier recombination. We also measure transparency current-density in these devices.

  14. Resonant Scattering of Surface Plasmon Polaritons by Dressed Quantum Dots

    DTIC Science & Technology

    2014-06-23

    Resonant scattering of surface plasmon polaritons by dressed quantum dots Danhong Huang,1 Michelle Easter,2 Godfrey Gumbs,3 A. A. Maradudin,4 Shawn... polariton waves (SPP) by embedded semiconductor quantum dots above the dielectric/metal interface is explored in the strong-coupling regime. In con- trast to...induced polarization field, treated as a source term9 arising from photo-excited electrons, allows for a resonant scattering of surface plasmon- polariton

  15. Programmable Periodicity of Quantum Dot Arrays with DNA Origami Nanotubes

    PubMed Central

    2010-01-01

    To fabricate quantum dot arrays with programmable periodicity, functionalized DNA origami nanotubes were developed. Selected DNA staple strands were biotin-labeled to form periodic binding sites for streptavidin-conjugated quantum dots. Successful formation of arrays with periods of 43 and 71 nm demonstrates precise, programmable, large-scale nanoparticle patterning; however, limitations in array periodicity were also observed. Statistical analysis of AFM images revealed evidence for steric hindrance or site bridging that limited the minimum array periodicity. PMID:20681601

  16. Stability and Tolerance to Optical Feedback of Quantum Dot Lasers

    DTIC Science & Technology

    2012-01-01

    Analytical approach to modulation properties of quantum dot lasers, K. Lüdge, E. Schöll, E. Viktorov, and T. Erneux, J. Appl. Physics , 109, 103112...Huyet, Optics Letters 35, 937- 939 (2010) 2. Analytical approach to modulation properties of quantum dot lasers, K. Lüdge, E. Schöll, E. Viktorov, and T...Erneux, J. Appl. Physics , 109, 103112 (2011) 3. Dimensional signature on noise-induced excitable statistics in an op- tically injected semiconductor

  17. Los Alamos Quantum Dots for Solar, Display Technology

    ScienceCinema

    Klimov, Victor

    2016-07-12

    Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.

  18. Dynamical symmetries in Kondo tunneling through complex quantum dots.

    PubMed

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-07

    Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4).

  19. Whispering-gallery mode microcavity quantum-dot lasers

    SciTech Connect

    Kryzhanovskaya, N V; Maximov, M V; Zhukov, A E

    2014-03-28

    This review examines axisymmetric-cavity quantum-dot microlasers whose emission spectrum is determined by whisperinggallery modes. We describe the possible designs, fabrication processes and basic characteristics of the microlasers and demonstrate the possibility of lasing at temperatures above 100 °C. The feasibility of creating multichannel optical sources based on a combination of a broadband quantum-dot laser and silicon microring modulators is discussed. (review)

  20. Optimal excitation conditions for indistinguishable photons from quantum dots

    NASA Astrophysics Data System (ADS)

    Huber, Tobias; Predojević, Ana; Föger, Daniel; Solomon, Glenn; Weihs, Gregor

    2015-12-01

    In this paper, we present a detailed, all optical study of the influence of different excitation schemes on the indistinguishability of single photons from a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel interference of consecutive photons from the spontaneous emission of an InAs quantum dot state under various excitation schemes and different excitation conditions and give a comparison.

  1. Coupling capacitance between double quantum dots tunable by the number of electrons in Si quantum dots

    SciTech Connect

    Uchida, Takafumi Arita, Masashi; Takahashi, Yasuo; Fujiwara, Akira

    2015-02-28

    Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD.

  2. Microscopic model for intersubband gain from electrically pumped quantum-dot structures

    NASA Astrophysics Data System (ADS)

    Michael, Stephan; Chow, Weng W.; Schneider, Hans Christian

    2014-10-01

    We study theoretically the performance of electrically pumped self-organized quantum dots as a gain material in the mid-IR range at room temperature. We analyze an AlGaAs/InGaAs based structure composed of dots-in-a-well sandwiched between two quantum wells. We numerically analyze a comprehensive model by combining a many-particle approach for electronic dynamics with a realistic modeling of the electronic states in the whole structure. We investigate the gain both for quasiequilibrium conditions and current injection. Comparing different structures, we find that steady-state gain can only be realized by an efficient extraction process, which prevents an accumulation of electrons in continuum states, that make the available scattering pathways through the quantum dot active region too fast to sustain inversion. The tradeoff between different extraction/injection pathways is discussed. Comparing the modal gain to a standard quantum-well structure as used in quantum cascade lasers, our calculations predict reduced threshold current densities of the quantum dot structure for comparable modal gain. Such a comparable modal gain can, however, only be achieved for an inhomogeneous broadening of a quantum-dot ensemble that is close to the lower limit achievable today using self-organized growth.

  3. Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

    SciTech Connect

    Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep

    2013-01-28

    We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

  4. Interaction of solitons with a string of coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Kumar, Vijendra; Swami, O. P.; Taneja, S.; Nagar, A. K.

    2016-05-01

    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.

  5. Direct Imaging of Electron States in Open Quantum Dots

    NASA Astrophysics Data System (ADS)

    Aoki, N.; Brunner, R.; Burke, A. M.; Akis, R.; Meisels, R.; Ferry, D. K.; Ochiai, Y.

    2012-03-01

    We use scanning gate microscopy to probe the ballistic motion of electrons within an open GaAs/AlGaAs quantum dot. Conductance maps are recorded by scanning a biased tip over the open quantum dot while a magnetic field is applied. We show that, for specific magnetic fields, the measured conductance images resemble the classical transmitted and backscattered trajectories and their quantum mechanical analogue. In addition, we prove experimentally, with this direct measurement technique, the existence of pointer states. The demonstrated direct imaging technique is essential for the fundamental understanding of wave function scarring and quantum decoherence theory.

  6. Silicon/silicon-germanium quantum dot spin qubits

    NASA Astrophysics Data System (ADS)

    Simmons, Christine B.

    Gate-defined quantum dots are tunable devices that are capable of trapping individual electrons. This thesis presents measurements of gate-defined quantum dots formed in Si/SiGe semiconductor heterostuctures. The motivation for this work is the development of a solid state electron spin qubit for quantum information processing. The fundamental properties of silicon make it an attractive option for spin qubit development, because electron spins are weakly coupled to the material. In particular, the coherence time for electron spins in silicon is expected to be long because of relatively weak spin-orbit coupling and the natural abundance of 28Si, a spin-zero nuclear isotope. The results presented in this thesis demonstrate significant advances in the manipulation and measurement of electrons in Si/SiGe quantum dots, including the first demonstration of a single electron quantum dot. An integrated quantum point contact is utilized as a local sensor to detect charge transitions on the neighboring quantum dot and to determine the absolute number of electrons on the dot. Gated control of the dot tunnel barriers enables tuning of the tunnel coupling to the leads and to other dots. Careful tuning of the tunnel rate to the leads in combination with fast, pulsed-gate manipulation of individual electrons enables a spectroscopy technique to identify electronic excited states. Using this technique, the Zeeman split spin qubit levels were observed. A 3-level voltage pulse sequence was utilized to perform single-shot readout of the spin state of individual electrons, to demonstrate tunable spin-selective loading, and to measure the spin relaxation time T1 . Double quantum dots are important for achieving two-qubit operations. Here, charge sensing measurements on a double dot are demonstrated. Analysis of the interdot transfer of a single electron is used to measure the tunnel coupling between the dots, and control of a single gate voltage is used to tune this coupling by over an

  7. Quantum computation: algorithms and implementation in quantum dot devices

    NASA Astrophysics Data System (ADS)

    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

  8. Fluorescence from a quantum dot and metallic nanosphere hybrid system

    NASA Astrophysics Data System (ADS)

    Schindel, Daniel G.; Singh, Mahi R.

    2014-03-01

    We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

  9. Long-Term Retention of Fluorescent Quantum Dots In Vivo

    NASA Astrophysics Data System (ADS)

    Ballou, Byron; Ernst, Lauren A.; Andreko, Susan; Eructiez, Marcel P.; Lagerholm, B. Christoffer; Waggoner, Alan S.

    Quantum dots that emit in the near-infrared can be used in vivo to follow circulation, to target the reticuloendothelial system, and to map lymphatic drainage from normal tissues and tumors. We have explored the role of surface charge and passivation by polyethylene glycol in determining circulating lifetimes and sites of deposition. Use of long polyethylene glycol polymers increases circulating lifetime. Changing surface charge can partially direct quantum dots to the liver and spleen, or the lymph nodes. Quantum dots are cleared in the order liver > spleen > bone marrow > lymph nodes. Quantum dots retained by lymph nodes maintained fluorescence for two years, suggesting either that the coating is extremely stable or that some endosomes preserve quantum dot function. We also explored migration from tumors to sentinel lymph nodes using tumor models in mice; surface charge and size make little difference to transport from tumors. Antibody and Fab-conjugates of polymer-coated quantum dots failed to target tumors in vivo, probably because of size.

  10. Rhizopus stolonifer mediated biosynthesis of biocompatible cadmium chalcogenide quantum dots.

    PubMed

    Mareeswari, P; Brijitta, J; Harikrishna Etti, S; Meganathan, C; Kaliaraj, Gobi Saravanan

    2016-12-01

    We report an efficient method to biosynthesize biocompatible cadmium telluride and cadmium sulphide quantum dots from the fungus Rhizopus stolonifer. The suspension of the quantum dots exhibited purple and greenish-blue luminescence respectively upon UV light illumination. Photoluminescence spectroscopy, X-ray diffraction, and transmission electron microscopy confirms the formation of the quantum dots. From the photoluminescence spectrum the emission maxima is found to be 424 and 476nm respectively. The X-ray diffraction of the quantum dots matches with results reported in literature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability evaluation carried out on 3-days transfer, inoculum 3×10(5) cells, embryonic fibroblast cells lines shows that more than 80% of the cells are viable even after 48h, indicating the biocompatible nature of the quantum dots. A good contrast in imaging has been obtained upon incorporating the quantum dots in human breast adenocarcinoma Michigan Cancer Foundation-7 cell lines.

  11. Synergistically enhanced activity of graphene quantum dots/graphene hydrogel composites: a novel all-carbon hybrid electrocatalyst for metal/air batteries

    NASA Astrophysics Data System (ADS)

    Wang, Mengran; Fang, Zhao; Zhang, Kai; Fang, Jing; Qin, Furong; Zhang, Zhian; Li, Jie; Liu, Yexiang; Lai, Yanqing

    2016-06-01

    Primary zinc/air batteries could be the next generation of energy storage devices because of their high power density and high safety. Graphene quantum dots nested in the graphene hydrogel have been proposed as excellent all-carbon hybrid oxygen reduction reaction (ORR) catalysts, indicative of their great potential in primary zinc/air batteries.Primary zinc/air batteries could be the next generation of energy storage devices because of their high power density and high safety. Graphene quantum dots nested in the graphene hydrogel have been proposed as excellent all-carbon hybrid oxygen reduction reaction (ORR) catalysts, indicative of their great potential in primary zinc/air batteries. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02622b

  12. Enhanced electrocatalytic activity of electrodeposited F-doped SnO2/Cu2S electrodes for quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Vinh Quy, Vu Hong; Kim, Jae-Hong; Kang, Soon-Hyung; Choi, Cheol-Jong; Rajesh, John Anthuvan; Ahn, Kwang-Soon

    2016-06-01

    Copper sulfide (Cu2S) films were deposited on F-doped SnO2 (FTO) substrates via the electrodeposition (ED) of copper (Cu) nanoparticles followed by sulfurization. The Cu nanoparticles were deposited on FTO substrates for various ED times ranging from 10 to 30 min at a constant -0.4 V. The FTO/Cu films consisted of flower-like nanoparticles comprised of randomly-clustering nanoflakes. The Cu nanoparticles electrodeposited for 10 min (FTO/Cu (10 min)) were dispersed sparsely over the FTO substrate, whereas the FTO/Cu (20 and 30 min) provided increased coverage. Unlike FTO/Cu2S (10 min), the FTO/Cu2S (20 and 30 min) consisted of vertically-standing large Cu2S nanosheets with numerous small nanosheets in between. This was attributed to the sufficient number of Cu seed nanoflakes, which not only facilitate ion transport of the redox couple but also increased the surface area, leading to significantly enhanced electrocatalytic activity. The quantum dot-sensitized solar cell (QD-SSC) with FTO/Cu2S (20 min) exhibited a significantly improved cell efficiency of 4.58%, compared to those with Pt and FTO/Cu2S (10 min). The QD-SSC with the FTO/Cu2S (30 min) showed similar cell efficiency to that with the FTO/Cu2S (20 min), despite the larger surface area because of its amorphous crystallographic structure offsetting the electrocatalytic activity.

  13. Growth and Characterization of III-V Nitride Quantum Dots and Quantum Wires

    DTIC Science & Technology

    2010-03-26

    REPORT Growth and Characterization of III - V Nitride Quantum Dots and Quantum Wires 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: Our research program...ANSI Std. Z39.18 - 14-Sep-2009 Final report Growth and Characterization of III - V Nitride Quantum Dots and Quantum Wires Statement of the...has two interrelated components: the growth of GaN nanowires and the fabrication of electronic devices, including gas sensors, on these nanowires . A

  14. Influence of surface states of CuInS2 quantum dots in quantum dots sensitized photo-electrodes

    NASA Astrophysics Data System (ADS)

    Peng, Zhuoyin; Liu, Yueli; Wu, Lei; Zhao, Yinghan; Chen, Keqiang; Chen, Wen

    2016-12-01

    Surface states are significant factor for the enhancement of electrochemical performance in CuInS2 quantum dot sensitized photo-electrodes. DDT, OLA, MPA, and S2- ligand capped CuInS2 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 S2- 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 S2- ligand for the interfacial region of quantum dots may improve the electron transfer rate. These S2--capped CuInS2 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.

  15. Quantum dots coupled to chip-based dielectric resonators via DNA origami mediated assembly (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Mitskovets, Anya; Gopinath, Ashwin; Rothemund, Paul; Atwater, Harry A.

    2016-09-01

    Interfacing of single photon emitters, such as quantum dots, with photonic nanocavities enables study of fundamental quantum electrodynamic phenomena. In such experiments, the inability to precisely position quantum emitters at the nanoscale usually limits the ability to control spontaneous emission, despite sophisticated control of optical density of states by cavity design. Thus, effective light-matter interactions in photonic nanostructures strongly depend on deterministic positioning of quantum emitters. In this work by using directed self-assembly of DNA origami we demonstrate deterministic coupling of quantum dots with gallium phosphide (GaP) dielectric whispering gallery mode resonators design to enhance CdSe quantum dot emission at 600nm-650nm. GaP microdisk and microring resonators are dry-etched through 200nm layer of gallium phosphide on silicon dioxide/silicon substrates. Our simulations show that such GaP resonators may have quality factors up to 10^5, which ensures strong light-matter interaction. On the top surface of microresonators, we write binding sites in the shape of DNA origami using electron beam lithography, and use oxygen plasma exposure to chemically activate these binding sites. DNA origami self-assembly is accomplished by placing DNA origami - quantum dot complexes into these binding sites. This approach allows us to achieve deterministic placement of the quantum dots with a few nm precision in position relative to the resonator. We will report photoluminescence spectroscopy and lifetime measurements of quantum dot - resonator deterministic coupling to probe the cavity-enhanced spontaneous emission rate. Overall, this approach offers precise control of emitter positioning in nanophotonic structures, which is a critical step for scalable quantum information processing.

  16. Distinctive signature of indium gallium nitride quantum dot lasing in microdisk cavities.

    PubMed

    Woolf, Alexander; Puchtler, Tim; Aharonovich, Igor; Zhu, Tongtong; Niu, Nan; Wang, Danqing; Oliver, Rachel; Hu, Evelyn L

    2014-09-30

    Low-threshold lasers realized within compact, high-quality optical cavities enable a variety of nanophotonics applications. Gallium nitride materials containing indium gallium nitride (InGaN) quantum dots and quantum wells offer an outstanding platform to study light-matter interactions and realize practical devices such as efficient light-emitting diodes and nanolasers. Despite progress in the growth and characterization of InGaN quantum dots, their advantages as the gain medium in low-threshold lasers have not been clearly demonstrated. This work seeks to better understand the reasons for these limitations by focusing on the simpler, limited-mode microdisk cavities, and by carrying out comparisons of lasing dynamics in those cavities using varying gain media including InGaN quantum wells, fragmented quantum wells, and a combination of fragmented quantum wells with quantum dots. For each gain medium, we use the distinctive, high-quality (Q ∼ 5,500) modes of the cavities, and the change in the highest-intensity mode as a function of pump power to better understand the dominant radiative processes. The variations of threshold power and lasing wavelength as a function of gain medium help us identify the possible limitations to lower-threshold lasing with quantum dot active medium. In addition, we have identified a distinctive lasing signature for quantum dot materials, which consistently lase at wavelengths shorter than the peak of the room temperature gain emission. These findings not only provide better understanding of lasing in nitride-based quantum dot cavity systems but also shed insight into the more fundamental issues of light-matter coupling in such systems.

  17. Negative differential gain in quantum dot systems: Interplay of structural properties and many-body effects

    SciTech Connect

    Goldmann, E. Jahnke, F.; Lorke, M.; Frauenheim, T.

    2014-06-16

    The saturation behaviour of optical gain with increasing excitation density is an important factor for laser device performance. For active materials based on self-organized InGaAs/GaAs quantum dots, we study the interplay between structural properties of the quantum dots and many-body effects of excited carriers in the optical properties via a combination of tight-binding and quantum-kinetic calculations. We identify regimes where either phase-space filling or excitation-induced dephasing dominates the saturation behavior of the optical gain. The latter can lead to the emergence of a negative differential material gain.

  18. Quantum dot spin coherence governed by a strained nuclear environment

    NASA Astrophysics Data System (ADS)

    Stockill, R.; Le Gall, C.; Matthiesen, C.; Huthmacher, L.; Clarke, E.; Hugues, M.; Atatüre, M.

    2016-09-01

    The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin-photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity.

  19. Quantum dot spin coherence governed by a strained nuclear environment

    PubMed Central

    Stockill, R.; Le Gall, C.; Matthiesen, C.; Huthmacher, L.; Clarke, E.; Hugues, M.; Atatüre, M.

    2016-01-01

    The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin–photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity. PMID:27615704

  20. Single-Photon Superradiance from a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Tighineanu, Petru; Daveau, Raphaël S.; Lehmann, Tau B.; Beere, Harvey E.; Ritchie, David A.; Lodahl, Peter; Stobbe, Søren

    2016-04-01

    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 the hole comprising the exciton gives rise to an anharmonic spectrum, which we exploit to prepare the superradiant quantum state deterministically with a laser pulse. We observe a fivefold enhancement of the oscillator strength compared to conventional quantum dots. The enhancement is limited by the base temperature of our cryostat and may lead to oscillator strengths above 1000 from a single quantum emitter at optical frequencies.

  1. Hole-Nuclear Spin Interaction in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eble, B.; Testelin, C.; Desfonds, P.; Bernardot, F.; Balocchi, A.; Amand, T.; Miard, A.; Lemaître, A.; Marie, X.; Chamarro, M.

    2009-04-01

    We have measured the carrier spin dynamics in p-doped InAs/GaAs quantum dots by pump-probe and time-resolved photoluminescence experiments. We obtained experimental evidence of the hyperfine interaction between hole and nuclear spins. In the absence of an external magnetic field, our calculations based on dipole-dipole coupling between the hole and the quantum dot nuclei lead to a hole-spin dephasing time for an ensemble of dots of 14 ns, in close agreement with experiments.

  2. Coupled Landau-Zener-Stückelberg quantum dot interferometers

    NASA Astrophysics Data System (ADS)

    Gallego-Marcos, Fernando; Sánchez, Rafael; Platero, Gloria

    2016-02-01

    We investigate the interplay between long-range and direct photon-assisted transport in a triple quantum dot chain where local ac voltages are applied to the outer dots. We propose the phase difference between the two ac voltages as an external parameter, which can be easily tuned to manipulate the current characteristics. For gate voltages in phase opposition we find quantum destructive interferences analogous to the interferences in closed-loop undriven triple dots. As the voltages oscillate in phase, interferences between multiple paths give rise to dark states. Those totally cancel the current, and could be experimentally resolved.

  3. Annealing-induced change in quantum dot chain formation mechanism

    SciTech Connect

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-15

    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.

  4. High quantum yield ZnO quantum dots synthesizing via an ultrasonication microreactor method.

    PubMed

    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.

  5. Theory of spin blockade in a triple quantum dots

    NASA Astrophysics Data System (ADS)

    Hsieh, Chang-Yu; Shim, Yun-Pil; Hawrylak, Pawel

    2011-03-01

    We present a theory of electronic properties and spin blockade in a linear triple quantum dots. We use micoroscopic LCHO-CI and double-band Hubbard model to analyze the electronic and spin properties of a triple quantum dots near a symmetrical quadruple point involving the (1,1,1) configuration which is essential for implementing quantum information processing with electron spin. We calculate spectral functions and relate them via the rate equation, including coupling with a phonon bath, to current as a function of applied bias. We show that the spin blockade in a triple quantum dots can serve as a spectroscopic tool to distinguish spin polarized states from spin depolarized states. We also show that a spin blockade is developed only at high bias when an onsite triplet state on the edge quantum dot connected to the source lead becomes accessible in the transport window. In contradiction to the case of double quantum dot molecule, the onsite triplet is not only essential for lifting spin blockade but also important for building up spin polarisation and spin blockade in the system. The authors would like to acknowledge financial support from NSERC, OGS, and QuantumWorks.

  6. Toward quantitatively fluorescent carbon-based "quantum" dots.

    PubMed

    Anilkumar, Parambath; Wang, Xin; Cao, Li; Sahu, Sushant; Liu, Jia-Hui; Wang, Ping; Korch, Katerina; Tackett, Kenneth N; Parenzan, Alexander; Sun, Ya-Ping

    2011-05-01

    Carbon-based "quantum" dots (or "carbon dots") are generally defined as surface-passivated small carbon nanoparticles that are brightly fluorescent. Apparently, the carbon particle surface passivation in carbon dots is critical to their fluorescence performance. An effective way to improve the surface passivation is to dope the surface of the precursor carbon nanoparticles with an inorganic salt, followed by the typical functionalization with organic molecules. In this work we passivated small carbon nanoparticles by a combination of the surface-doping with nanoscale semiconductors and the organic functionalization, coupled with gel column fractionation to harvest the most fluorescent carbon dots, which exhibited fluorescence emission quantum yields of up to 78%. Experimental and mechanistic issues relevant to potentially further improve the performance of carbon dots toward their being quantitatively fluorescent are discussed.

  7. Thermoelectric study of dissipative quantum-dot heat engines

    NASA Astrophysics Data System (ADS)

    De, Bitan; Muralidharan, Bhaskaran

    2016-10-01

    This paper examines the thermoelectric response of a dissipative quantum-dot heat engine based on the Anderson-Holstein model in two relevant operating limits, (i) when the dot phonon modes are out of equilibrium, and (ii) when the dot phonon modes are strongly coupled to a heat bath. In the first case, a detailed analysis of the physics related to the interplay between the quantum-dot level quantization, the on-site Coulomb interaction, and the electron-phonon coupling on the thermoelectric performance reveals that an n -type heat engine performs better than a p -type heat engine. In the second case, with the aid of the dot temperature estimated by incorporating a thermometer bath, it is shown that the dot temperature deviates from the bath temperature as electron-phonon interaction in the dot becomes stronger. Consequently, it is demonstrated that the dot temperature controls the direction of phonon heat currents, thereby influencing the thermoelectric performance. Finally, the conditions on the maximum efficiency with varying phonon couplings between the dot and all the other macroscopic bodies are analyzed in order to reveal the nature of the optimum junction.

  8. Compact Interconnection Networks Based on Quantum Dots

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Toomarian, Nikzad; Modarress, Katayoon; Spotnitz, Matthew

    2003-01-01

    Architectures that would exploit the distinct characteristics of quantum-dot cellular automata (QCA) have been proposed for digital communication networks that connect advanced digital computing circuits. In comparison with networks of wires in conventional very-large-scale integrated (VLSI) circuitry, the networks according to the proposed architectures would be more compact. The proposed architectures would make it possible to implement complex interconnection schemes that are required for some advanced parallel-computing algorithms and that are difficult (and in many cases impractical) to implement in VLSI circuitry. The difficulty of implementation in VLSI and the major potential advantage afforded by QCA were described previously in Implementing Permutation Matrices by Use of Quantum Dots (NPO-20801), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 42. To recapitulate: Wherever two wires in a conventional VLSI circuit cross each other and are required not to be in electrical contact with each other, there must be a layer of electrical insulation between them. This, in turn, makes it necessary to resort to a noncoplanar and possibly a multilayer design, which can be complex, expensive, and even impractical. As a result, much of the cost of designing VLSI circuits is associated with minimization of data routing and assignment of layers to minimize crossing of wires. Heretofore, these considerations have impeded the development of VLSI circuitry to implement complex, advanced interconnection schemes. On the other hand, with suitable design and under suitable operating conditions, QCA-based signal paths can be allowed to cross each other in the same plane without adverse effect. In principle, this characteristic could be exploited to design compact, coplanar, simple (relative to VLSI) QCA-based networks to implement complex, advanced interconnection schemes. The proposed architectures require two advances in QCA-based circuitry beyond basic QCA-based binary

  9. White light emitting diodes realized by using an active packaging method with CdSe/ZnS quantum dots dispersed in photosensitive epoxy resins.

    PubMed

    Wang, Hao; Lee, Kyu-Seung; Ryu, Jae-Hyoung; Hong, Chang-Hee; Cho, Yong-Hoon

    2008-04-09

    White light emitting diodes (LEDs) have been realized using the active packaging (AP) method. The starting materials were bare InGaN LED chips and CdSe/ZnS core-shell quantum dots (QDs) dispersed in photosensitive epoxy resins. Such hybrid LED devices were fabricated using QD mixtures with one ('single'), two ('dual') or four ('multi') emission wavelengths. The AP method allows for convenient adjustment of multiple parameters such as the CIE-1931 coordinate (x, y), color temperature, and color rending index (CRI). All samples show good white balance, and under a 20 mA working current the luminous efficacies of the single, dual, and multi hybrid devices were 8.1 lm W(-1), 5.1 lm W(-1), and 6.4 lm W(-1), respectively. The corresponding quantum efficiencies were 4.1%, 3.1%, and 3.1%; the CRIs were 21.46, 43.76, and 66.20; and the color temperatures were 12 000, 8190, and 7740 K. This shows that the CRI of the samples can be enhanced by broadening the QD emission band, as is exemplified by the 21.46 CRI of the single hybrid LED compared to the 66.20 value for the multi hybrid LED. In addition, we were able to increase the CRI of the single hybrid LED from 15.31 to 32.50 by increasing the working currents from 1 to 50 mA.

  10. Highly sensitive detection of caspase-3 activities via a nonconjugated gold nanoparticle-quantum dot pair mediated by an inner-filter effect.

    PubMed

    Li, Jingwen; Li, Xinming; Shi, Xiujuan; He, Xuewen; Wei, Wei; Ma, Nan; Chen, Hong

    2013-10-09

    We describe here a simple fluorometric assay for the highly sensitive detection of caspase-3 activities on the basis of the inner-filter effect of gold nanoparticles (AuNPs) on CdTe quantum dots (QDs). The method takes advantage of the high molar absorptivity of the plasmon band of gold nanoparticles as well as the large absorption band shift from 520 to 680 nm upon nanoparticle aggregation. When labeled with a peptide possessing the caspase-3 cleavage sequence (DEVD), the monodispersed Au-Ps (peptide-modified AuNPs) exhibited a tendency to aggregate when exposed to caspase-3, which induced the absorption band transition from 520 to 680 nm and turned on the fluorescence of the CdTe QDs for caspase-3 sensing. Under optimum conditions, a high sensitivity towards caspase-3 was achieved with a detection limit as low as 18 pM, which was much lower than the corresponding assays based on absorbance or other approaches. Overall, we demonstrated a facile and sensitive approach for caspase-3 detection, and we expected that this method could be potentially generalized to design more fluorescent assays for sensing other bioactive entities.

  11. Carbon nanotube quantum dots as highly sensitive THz spectrometers

    NASA Astrophysics Data System (ADS)

    Rinzan, Mohamed; Jenkins, Greg; Drew, Dennis; Shafranjuk, Serhii; Barbara, Paola

    2012-02-01

    We show that carbon nanotube quantum dots (CNT-Dots) coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors. Their response is due to photon-assisted single-electron tunneling (PASET)[1], but cannot be fully understood with orthodox PASET models[2]. We consider intra-dot excitations and non-equilibrium cooling to explain the anomalous response. REFERENCES: [1] Y. Kawano, S. Toyokawa, T. Uchida and K. Ishibashi, THz photon assisted tunneling in carbon-nanotube quantum dots, Journal of Applied Physics 103, 034307 (2008). [2] P. K. Tien and J. P. Gordon, Multiphoton Process Observed in the Interaction of Microwave Fields with the Tunneling between Superconductor Films, Phys. Rev. 129, 647 (1963).

  12. Cooper pair splitting in parallel quantum dot Josephson junctions

    PubMed Central

    Deacon, R. S.; Oiwa, A.; Sailer, J.; Baba, S.; Kanai, Y.; Shibata, K.; Hirakawa, K.; Tarucha, S.

    2015-01-01

    Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172

  13. Emission redistribution from a quantum dot-bowtie nanoantenna

    NASA Astrophysics Data System (ADS)

    Regler, Armin; Schraml, Konrad; Lyamkina, Anna A.; Spiegl, Matthias; Müller, Kai; Vuckovic, Jelena; Finley, Jonathan J.; Kaniber, Michael

    2016-07-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby (˜25 nm) plasmonic antenna. Microphotoluminescence spectroscopy shows a ˜2.4× increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of 2.5 μW for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell enhancement of the quantum dot coupled to the antenna as compared with an uncoupled dot, yielding comparable exciton lifetimes of τ˜0.5 ns. This observation is supported by numerical simulations, suggesting only minor Purcell-effects of <2× for emitter-antenna separations >25 nm. The observed increased emission from a coupled quantum dot-plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding of light-matter coupling in such semiconductor-plasmonic hybrid systems.

  14. Extraction of inhomogeneous broadening and nonradiative losses in InAs quantum-dot lasers

    SciTech Connect

    Chow, Weng W.; Liu, Alan Y.; Gossard, Arthur C.; Bowers, John E.

    2015-10-26

    We present a method to quantify inhomogeneous broadening and nonradiative losses in quantum dot lasers by comparing the gain and spontaneous emission results of a microscopic laser theory with measurements made on 1.3 μm InAs quantum-dot lasers. Calculated spontaneous-emission spectra are first matched to those measured experimentally to determine the inhomogeneous broadening in the experimental samples. This is possible because treatment of carrier scattering at the level of quantum kinetic equations provides the homogeneously broadened spectra without use of free parameters, such as the dephasing rate. We then extract the nonradiative recombination current associated with the quantum-dot active region from a comparison of measured and calculated gain versus current relations.

  15. Multiplexed tracking of protease activity using a single color of quantum dot vector and a time-gated Förster resonance energy transfer relay.

    PubMed

    Algar, W Russ; Malanoski, Anthony P; Susumu, Kimihiro; Stewart, Michael H; Hildebrandt, Niko; Medintz, Igor L

    2012-11-20

    Semiconductor quantum dots (QDs) are attractive probes for optical sensing and imaging due to their unique photophysical attributes and nanoscale size. In particular, the development of assays and biosensors based on QDs and Förster resonance energy transfer (FRET) continues to be a prominent focus of research. Here, we demonstrate the application of QDs as simultaneous donors and acceptors in a time-gated FRET relay for the multiplexed detection of protease activity. In contrast to the current state-of-the-art, which uses multiple colors of QDs, multiplexing was achieved using only a single color of QD. The other constituents of the FRET relay, a luminescent terbium complex and fluorescent dye, were assembled to QDs via peptides that were selected as substrates for the model proteases trypsin and chymotrypsin. Loss of prompt FRET between the QD and dye signaled the activity of chymotrypsin; loss of time-gated FRET between the terbium and QD signaled the activity of trypsin. We applied the FRET relay in a series of quantitative, real-time kinetic assays of increasing biochemical complexity, including multiplexed sensing, measuring inhibition in a multiplexed format, and tracking the proteolytic activation of an inactive pro-protease to its active form in a coupled, multienzyme system. These capabilities were derived from a ratiometric analysis of the two FRET pathways in the relay and permitted extraction of initial reaction rates, enzyme specificity constants, and apparent inhibition constants. This work adds to the growing body of research on multifunctional nanoparticles and introduces multiplexed sensing as a novel capability for a single nanoparticle vector. Furthermore, the ability to track both enzymes within a coupled biological system using one vector represents a significant advancement for nanoparticle-based biosensing. Prospective applications in biochemical research, applied diagnostics, and drug discovery are discussed.

  16. Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers

    SciTech Connect

    Korenev, V. V. Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V.

    2013-10-15

    It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.

  17. Analysis of the efficiency of intermediate band solar cells based on quantum dot supercrystals

    SciTech Connect

    Heshmati, S; Golmohammadi, S; Abedi, K; Taleb, H

    2014-03-28

    We have studied the influence of the quantum-dot (QD) width and the quantum-dot conduction band (QD-CB) offset on the efficiency of quantum-dot intermediate band solar cells (QD-IBSCs). Simulation results demonstrate that with increasing QD-CB offset and decreasing QD width, the maximum efficiency is achieved. (laser applications and other topics in quantum electronics)

  18. Quantum Hall effect in semiconductor systems with quantum dots and antidots

    SciTech Connect

    Beltukov, Ya. M.; Greshnov, A. A.

    2015-04-15

    The integer quantum Hall effect in systems of semiconductor quantum dots and antidots is studied theoretically as a factor of temperature. It is established that the conditions for carrier localization in quantum-dot systems favor the observation of the quantum Hall effect at higher temperatures than in quantum-well systems. The obtained numerical results show that the fundamental plateau corresponding to the transition between the ground and first excited Landau levels can be retained up to a temperature of T ∼ 50 K, which is an order of magnitude higher than in the case of quantum wells. Implementation of the quantum Hall effect at such temperatures requires quantum-dot systems with controllable characteristics, including the optimal size and concentration and moderate geometrical and composition fluctuations. In addition, ordered arrangement is desirable, hence quantum antidots are preferable.

  19. Deep level transient capacitance measurements of GaSb self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Magno, R.; Bennett, Brian R.; Glaser, E. R.

    2000-11-01

    Deep level transient spectroscopy (DLTS) measurements have been made on GaAs n+p diodes containing GaSb self-assembled quantum dots and control junctions without dots. The self-assembled dots were formed by molecular beam epitaxy using the Stranski-Krastanov growth mode. The dots are located in the depletion region on the p side of the junction where they act as a potential well that may capture and emit holes. Spectra recorded for temperatures between 77 and 440 K reveal several peaks in diodes containing dots. A control sample with a GaSb wetting layer was found to contain a single broad high temperature peak that is similar to a line found in the GaSb quantum dot samples. No lines were found in the spectra of a control sample prepared without GaSb. DLTS profiling procedures indicate that one of the peaks is due to a quantum-confined energy level associated with the GaSb dots while the others are due to defects in the GaAs around the dots. The peak identified as a quantum-confined energy level shifts to higher temperatures and its intensity decreases on increasing the reverse bias. The activation energy for the quantum-confined level increases from 400 meV when measured at a low reverse bias to 550 meV for a large reverse bias. Lines with activation energies of 400, 640, and 840 meV are associated with defects in the GaAs based on the bias dependence of their peak positions and amplitudes.

  20. Electrical control of single hole spins in nanowire quantum dots.

    PubMed

    Pribiag, V S; Nadj-Perge, S; Frolov, S M; van den Berg, J W G; van Weperen, I; Plissard, S R; Bakkers, E P A M; Kouwenhoven, L P

    2013-03-01

    The development of viable quantum computation devices will require the ability to preserve the coherence of quantum bits (qubits). Single electron spins in semiconductor quantum dots are a versatile platform for quantum information processing, but controlling decoherence remains a considerable challenge. Hole spins in III-V semiconductors have unique properties, such as a strong spin-orbit interaction and weak coupling to nuclear spins, and therefore, have the potential for enhanced spin control and longer coherence times. A weaker hyperfine interaction has previously been reported in self-assembled quantum dots using quantum optics techniques, but the development of hole-spin-based electronic devices in conventional III-V heterostructures has been limited by fabrication challenges. Here, we show that gate-tunable hole quantum dots can be formed in InSb nanowires and used to demonstrate Pauli spin blockade and electrical control of single hole spins. The devices are fully tunable between hole and electron quantum dots, which allows the hyperfine interaction strengths, g-factors and spin blockade anisotropies to be compared directly in the two regimes.

  1. 2 Micrometers InAsSb Quantum-dot Lasers

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Uhl, David; Keo, Sam

    2004-01-01

    InAsSb quantum-dot lasers near 2 micrometers were demonstrated in cw operation at room temperature with a threshold current density of 733 A,/cm(sup 2), output power of 3 mW/facet and a differential quantum efficiency of 13%.

  2. Quantum dots: Time to get the nukes out

    NASA Astrophysics Data System (ADS)

    Schroer, Michael D.; Petta, Jason R.

    2008-07-01

    The ability to electrically control spin dynamics in quantum dots makes them one of the most promising platforms for solid-state quantum-information processing. Minimizing the influence of the nuclear spin environment is an important step towards realizing such promise.

  3. Size-Minimized Quantum Dots for Molecular and Cellular Imaging

    NASA Astrophysics Data System (ADS)

    Smith, Andrew M.; Wen, Mary M.; Wang, May D.; Nie, Shuming

    Semiconductor quantum dots, tiny light-emitting particles on thenanometer scale, are emerging as a new class of fluorescent labels for a broad range of molecular and cellular applications. In comparison with organic dyes and fluorescent proteins, they have unique optical and electronic properties such as size-tunable light emission, intense signal brightness, resistance to photobleaching, and broadband absorption for simultaneous excitation of multiple fluorescence colors. Here we report new advances in minimizing the hydrodynamic sizes of quantum dots using multidentate and multifunctional polymer coatings. A key finding is that a linear polymer containing grafted amine and thiol coordinating groups can coat nanocrystals and lead to a highly compact size, exceptional colloidal stability, strong resistance to photobleaching, and high fluorescence quantum yields. This has allowed a new generation of bright and stable quantum dots with small hydrodynamic diameters between 5.6 and 9.7 nm with tunable fluorescence emission from the visible (515 nm) to the near infrared (720 nm). These quantum dots are well suited for molecular and cellular imaging applications in which the nanoparticle hydrodynamic size needs to be minimized. Together with the novel properties of new strain-tunable quantum dots, these findings will be especially useful for multicolor and super-resolution imaging at the single-molecule level.

  4. Sunlight assisted photodegradation by tin oxide quantum dots

    NASA Astrophysics Data System (ADS)

    Shajira, P. S.; Prabhu, V. Ganeshchandra; Bushiri, M. Junaid

    2015-12-01

    Rutile phase of SnO2 quantum dots of average size of 2.5 nm were synthesized at a growth temperature of 70 °C and characterized with XRD, TEM, FTIR and Raman analysis. The effective strain within the lattice of SnO2 quantum dots was calculated by Williamson-Hall method. The broad peaks in XRD as well as Raman spectra and the presence of Raman bands at 569 and 432 cm-1 are due to lower crystallinity of nanoparticles. The optical band gap of SnO2 quantum dots was increased to 3.75 eV attributed to the quantum size effect. SnO2 quantum dots were annealed in air atmosphere and the crystallite size of the particles increased with annealing temperature. Sunlight assisted photodegration property of SnO2 quantum dots was investigated with vanillin as a model system and it shows the photodegradation efficiency of 87%. The photoluminescence and photodegradation efficiency of nanocrystallite SnO2 decreases with increase of crystallite size contributed to the reduction in population of defects and surface area.

  5. Advancing colloidal quantum dot photovoltaic technology

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

    2016-06-01

    Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.

  6. Quantum dot mediated imaging of atherosclerosis

    NASA Astrophysics Data System (ADS)

    Jayagopal, Ashwath; Su, Yan Ru; Blakemore, John L.; Linton, MacRae F.; Fazio, Sergio; Haselton, Frederick R.

    2009-04-01

    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-/- 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.

  7. Single-quantum-dot-based DNA nanosensor

    NASA Astrophysics Data System (ADS)

    Zhang, Chun-Yang; Yeh, Hsin-Chih; Kuroki, Marcos T.; Wang, Tza-Huei

    2005-11-01

    Rapid and highly sensitive detection of DNA is critical in diagnosing genetic diseases. Conventional approaches often rely on cumbersome, semi-quantitative amplification of target DNA to improve detection sensitivity. In addition, most DNA detection systems (microarrays, for example), regardless of their need for target amplification, require separation of unhybridized DNA strands from hybridized stands immobilized on a solid substrate, and are thereby complicated by solution-surface binding kinetics. Here, we report an ultrasensitive nanosensor based on fluorescence resonance energy transfer (FRET) capable of detecting low concentrations of DNA in a separation-free format. This system uses quantum dots (QDs) linked to DNA probes to capture DNA targets. The target strand binds to a dye-labelled reporter strand thus forming a FRET donor-acceptor ensemble. The QD also functions as a concentrator that amplifies the target signal by confining several targets in a nanoscale domain. Unbound nanosensors produce near-zero background fluorescence, but on binding to even a small amount of target DNA (~50 copies or less) they generate a very distinct FRET signal. A nanosensor-based oligonucleotide ligation assay has been demonstrated to successfully detect a point mutation typical of some ovarian tumours in clinical samples.

  8. Carbon Quantum Dots for Zebrafish Fluorescence Imaging

    NASA Astrophysics Data System (ADS)

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-07-01

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. Herein, we describe fluorescence bioimaging of zebrafish using C-QDs as probe in terms of the preparation of C-QDs, zebrafish husbandry, embryo harvesting, and introduction of C-QDs into embryos and larvae by soaking and microinjection. The multicolor of C-QDs was validated with their imaging for zebrafish embryo. The distribution of C-QDs in zebrafish embryos and larvae were successfully observed from their fluorescence emission. the bio-toxicity of C-QDs was tested with zebrafish as model and C-QDs do not interfere to the development of zebrafish embryo. All of the results confirmed the high biocompatibility and low toxicity of C-QDs as imaging probe. The absorption, distribution, metabolism and excretion route (ADME) of C-QDs in zebrafish was revealed by their distribution. Our work provides the useful information for the researchers interested in studying with zebrafish as a model and the applications of C-QDs. The operations related zebrafish are suitable for the study of the toxicity, adverse effects, transport, and biocompatibility of nanomaterials as well as for drug screening with zebrafish as model.

  9. Graphene quantum dots derived from carbon fibers.

    PubMed

    Peng, Juan; Gao, Wei; Gupta, Bipin Kumar; Liu, Zheng; Romero-Aburto, Rebeca; Ge, Liehui; Song, Li; Alemany, Lawrence B; Zhan, Xiaobo; Gao, Guanhui; Vithayathil, Sajna Antony; Kaipparettu, Benny Abraham; Marti, Angel A; Hayashi, Takuya; Zhu, Jun-Jie; Ajayan, Pulickel M

    2012-02-08

    Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating optical and electronic properties. These have been synthesized either by nanolithography or from starting materials such as graphene oxide (GO) by the chemical breakdown of their extended planar structure, both of which are multistep tedious processes. Here, we report that during the acid treatment and chemical exfoliation of traditional pitch-based carbon fibers, that are both cheap and commercially available, the stacked graphitic submicrometer domains of the fibers are easily broken down, leading to the creation of GQDs with different size distribution in scalable amounts. The as-produced GQDs, in the size range of 1-4 nm, show two-dimensional morphology, most of which present zigzag edge structure, and are 1-3 atomic layers thick. The photoluminescence of the GQDs can be tailored through varying the size of the GQDs by changing process parameters. Due to the luminescence stability, nanosecond lifetime, biocompatibility, low toxicity, and high water solubility, these GQDs are demonstrated to be excellent probes for high contrast bioimaging and biosensing applications.

  10. Photodynamic antibacterial effect of graphene quantum dots.

    PubMed

    Ristic, Biljana Z; Milenkovic, Marina M; Dakic, Ivana R; Todorovic-Markovic, Biljana M; Milosavljevic, Momir S; Budimir, Milica D; Paunovic, Verica G; Dramicanin, Miroslav D; Markovic, Zoran M; Trajkovic, Vladimir S

    2014-05-01

    Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD.

  11. Carbon Quantum Dots for Zebrafish Fluorescence Imaging

    PubMed Central

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-01-01

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. Herein, we describe fluorescence bioimaging of zebrafish using C-QDs as probe in terms of the preparation of C-QDs, zebrafish husbandry, embryo harvesting, and introduction of C-QDs into embryos and larvae by soaking and microinjection. The multicolor of C-QDs was validated with their imaging for zebrafish embryo. The distribution of C-QDs in zebrafish embryos and larvae were successfully observed from their fluorescence emission. the bio-toxicity of C-QDs was tested with zebrafish as model and C-QDs do not interfere to the development of zebrafish embryo. All of the results confirmed the high biocompatibility and low toxicity of C-QDs as imaging probe. The absorption, distribution, metabolism and excretion route (ADME) of C-QDs in zebrafish was revealed by their distribution. Our work provides the useful information for the researchers interested in studying with zebrafish as a model and the applications of C-QDs. The operations related zebrafish are suitable for the study of the toxicity, adverse effects, transport, and biocompatibility of nanomaterials as well as for drug screening with zebrafish as model. PMID:26135470

  12. Toxicity of carbon group quantum dots

    NASA Astrophysics Data System (ADS)

    Hanada, Sanshiro; Fujioka, Kouki; Hoshino, Akiyoshi; Manabe, Noriyoshi; Hirakuri, Kenji; Yamamoto, Kenji

    2009-02-01

    Carbon group quantum dots (QDs) such as carbon, silicon and germanium, have potential for biomedical applications such as bio-imaging markers and drug delivery systems and are expected to demonstrate several advantages over conventional fluorescent QDs such as CdSe, especially in biocompatibility. We assessed biocompatibility of newly manufactured silicon QDs (Si-QDs), by means of both MTT assay and LDH assay for HeLa cells in culture and thereby detected the cellular toxicity by administration of high concentration of Si-QD (>1000 μg/mL), while we detected the high toxicity by administration of over 100 μg/mL of CdSe-QDs. As a hypothesis for the cause of the cellular toxicity, we measured oxy-radical generation from the QDs by means of luminol reaction method. We detected generation of oxy-radicals from the Si-QDs and those were decreased by radical scavenger such as superoxide dismutase (SOD) and N-acetyl cysteine (NAC). We concluded that the Si-QD application to cultured cells in high concentration led cell membrane damage by oxy-radicals and combination usage with radical scavenger is one of the answers.

  13. Hole transfer from single quantum dots.

    PubMed

    Song, Nianhui; Zhu, Haiming; Jin, Shengye; Lian, Tianquan

    2011-11-22

    Photoinduced hole transfer dynamics from single CdSe/CdS(3ML)/CdZnS(2ML)/ZnS(2ML) core/multishell quantum dots (QDs) to phenothiazine (PTZ) molecules were studied by single QD fluorescence spectroscopy to investigate the static and dynamic heterogeneities of the hole transfer process as well as its effect on the blinking dynamics of QDs. Ensemble-averaged transient absorption and fluorescence decay measurements show that excitons in QDs dissociate by transferring the valence band hole to PTZ with a time constant of 50 ns for the 1:1 PTZ-QD complex, and the subsequent charge recombination process (i.e., electron transfer from the conduction band of the reduced QD to oxidized PTZ to regenerate the complex in the ground state) occurs mainly on the 100 to 1000 ns time scale. Single QD-PTZ complexes show pronounced correlated fluctuations of fluorescence intensity and lifetime with time. In addition to the dynamic fluctuation, there are considerable heterogeneities of average hole transfer rate among different QD-PTZ complexes. The hole transfer process has little effect on the statistics of the off-states, which is often believed to be positively charged QDs with a valence band hole. Instead, it increases the probability of weakly emissive or "gray" states.

  14. Immune cells tracing using quantum dots

    NASA Astrophysics Data System (ADS)

    Hoshino, Akiyoshi; Fujioka, Kouki; Kawamura, Yuki I.; Toyama-Sorimachi, Noriko; Yasuhara, Masato; Dohi, Taeko; Yamamoto, Kenji

    2006-02-01

    Fluorescent nanoparticles, such as nanocrystal quantum dots (QDs), have potential to be applied to molecular biology and bioimaging, since some nanocrystals emit higher and longer lasting fluorescence than conventional organic probes do. Here we report an example of labeling immune cells by QDs. We collected splenic CD4 + T-lymphocyte and peritoneal macrophages from mice. Then cells were labeled with QDs. QDs are incorporated into the T-lymphocyte and macrophages immediately after addition and located in the cytoplasm via endocytosis pathway. The fluorescence of QDs held in the endosomes was easily detected for more than a week. In addition, T-lymphocytes labeled with QDs were stable and cell proliferation or cytokine production including IL-2 and IFN-γ was not affected. When QD-labeled T-lymphocytes were adoptively transferred intravenously to mice, they remained in the peripheral blood and spleen up to a week. Using QD-labeled peritoneal macrophages, we studied cell traffic during inflammation on viscera in peritoneum cavity. QD-labeled macrophages were transplanted into the peritoneum of the mouse, and colitis was induced by intracolonic injection of a hapten, trinitrobenzensulfonic acid. With the aid of stong signals of QDs, we found that macrophage accumuled on the inflammation site of the colon. These results suggested that fluorescent probes of QDs might be useful as bioimaging tools for tracing target cells in vivo.

  15. Asymmetric shape transitions of epitaxial quantum dots

    NASA Astrophysics Data System (ADS)

    Wei, Chaozhen; Spencer, Brian J.

    2016-06-01

    We construct a two-dimensional continuum model to describe the energetics of shape transitions in fully faceted epitaxial quantum dots (strained islands) via minimization of elastic energy and surface energy at fixed volume. The elastic energy of the island is based on a third-order approximation, enabling us to consider shape transitions between pyramids, domes, multifaceted domes and asymmetric intermediate states. The energetics of the shape transitions are determined by numerically calculating the facet lengths that minimize the energy of a given island type of prescribed island volume. By comparing the energy of different island types with the same volume and analysing the energy surface as a function of the island shape parameters, we determine the bifurcation diagram of equilibrium solutions and their stability, as well as the lowest barrier transition pathway for the island shape as a function of increasing volume. The main result is that the shape transition from pyramid to dome to multifaceted dome occurs through sequential nucleation of facets and involves asymmetric metastable transition shapes. We also explicitly determine the effect of corner energy (facet edge energy) on shape transitions and interpret the results in terms of the relative stability of asymmetric island shapes as observed in experiment.

  16. Colloidal quantum dot solar cells on curved and flexible substrates

    SciTech Connect

    Kramer, Illan J.; Moreno-Bautista, Gabriel; Minor, James C.; Kopilovic, Damir; Sargent, Edward H.

    2014-10-20

    Colloidal quantum dots (CQDs) are semiconductor nanocrystals synthesized with, processed in, and deposited from the solution phase, potentially enabling low-cost, facile manufacture of solar cells. Unfortunately, CQD solar cell reports, until now, have only explored batch-processing methods—such as spin-coating—that offer limited capacity for scaling. Spray-coating could offer a means of producing uniform colloidal quantum dot films that yield high-quality devices. Here, we explore the versatility of the spray-coating method by producing CQD solar cells in a variety of previously unexplored substrate arrangements. The potential transferability of the spray-coating method to a roll-to-roll manufacturing process was tested by spray-coating the CQD active layer onto six substrates mounted on a rapidly rotating drum, yielding devices with an average power conversion efficiency of 6.7%. We further tested the manufacturability of the process by endeavoring to spray onto flexible substrates, only to find that spraying while the substrate was flexed was crucial to achieving champion performance of 7.2% without compromise to open-circuit voltage. Having deposited onto a substrate with one axis of curvature, we then built our CQD solar cells onto a spherical lens substrate having two axes of curvature resulting in a 5% efficient device. These results show that CQDs deposited using our spraying method can be integrated to large-area manufacturing processes and can be used to make solar cells on unconventional shapes.

  17. Qubit protection in nuclear-spin quantum dot memories.

    PubMed

    Kurucz, Z; Sørensen, M W; Taylor, J M; Lukin, M D; Fleischhauer, M

    2009-07-03

    We present a mechanism to protect quantum information stored in an ensemble of nuclear spins in a semiconductor quantum dot. When the dot is charged the nuclei interact with the spin of the excess electron through the hyperfine coupling. If this coupling is made off-resonant, it leads to an energy gap between the collective storage states and all other states. We show that the energy gap protects the quantum memory from local spin-flip and spin-dephasing noise. Effects of nonperfect initial spin polarization and inhomogeneous hyperfine coupling are discussed.

  18. Excitation spectra of circular, few-electron quantum dots

    PubMed

    Kouwenhoven; Oosterkamp; Danoesastro; Eto; Austing; Honda; Tarucha

    1997-12-05

    Studies of the ground and excited states in semiconductor quantum dots containing 1 to 12 electrons showed that the quantum numbers of the states in the excitation spectra can be identified and compared with exact calculations. A magnetic field induces transitions between the ground and excited states. These transitions were analyzed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. These impurity-free quantum dots allow "atomic physics" experiments to be performed in magnetic field regimes not accessible for atoms.

  19. Studies of electron spin in GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Craft, Daniel; Colton, John; Park, Tyler; White, Phil

    2013-03-01

    We have studied electron spins in GaAs quantum dots with a pump-probe technique that normally yields the T1 spin lifetime, the time required for initially polarized electrons to relax and randomize. Using a circularly polarized laser tuned to the wavelength response of the quantum dot we can ``pump'' the spins into alignment. After aligning the spins we can detect them using a second, linearly polarized ``probe'' laser. By changing the delay between the two lasers we can trace out the spin response over time. In contrast with other samples (bulk GaAs and a GaAs quantum well), where the spin response decayed exponentially with time, initial data on the quantum dots has shown an unexpected, oscillating behavior which dies out on the order of 700 ns, independent of both temperature and magnetic field.

  20. Detection of CdSe quantum dot photoluminescence for security label on paper

    SciTech Connect

    Isnaeni, Sugiarto, Iyon Titok; Bilqis, Ratu; Suseno, Jatmiko Endro

    2016-02-08

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word ’RAHASIA’. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.

  1. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    SciTech Connect

    Yoon, Yeung-Pil; Kim, Jae-Hong; Ahn, Kwang-Soon; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook

    2014-08-25

    Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO{sub 2} (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of S{sub n}{sup 2− }+ 2e{sup −} (CE) → S{sub n−1}{sup 2−} + S{sup 2−} at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, S{sub n}{sup 2− }+ 2e{sup −} (TiO{sub 2} in the photoanode) → S{sub n-1}{sup 2−} + S{sup 2−}, and significantly improved overall energy conversion efficiency.

  2. Encapsulation of zinc-rifampicin complex into transferrin-conjugated silver quantum-dots improves its antimycobacterial activity and stability and facilitates drug delivery into macrophages

    PubMed Central

    Pati, Rashmirekha; Sahu, Rojalin; Panda, Jagannath; Sonawane, Avinash

    2016-01-01

    In order to improve the chemotherapy of tuberculosis, there is an urgent need to enhance the efficacy of existing agents and also to develop more efficient drug delivery systems. Here, we synthesized a novel anti-TB drug complex consisting of zinc and rifampicin (Zn-RIF), and encapsulated it into transferrin-conjugated silver quantum-dots (Zn-RIF-Tf-QD) to improve delivery in macrophages. Successful synthesis of Zn-RIF and Zn-RIF-Tf-QD was confirmed by UV/Vis-spectroscopy, TEM, FTIR, photoluminescence, XRD, XPS, and NMR. The sizes of silver QDs and transferrin-conjugated QDs were found to be in the range of 5–20 nm. Activity assays showed that Zn-RIF-Tf-QD exhibited 10-fold higher antibacterial activity against Mycobacterium smegmatis and Mycobacterium bovis-BCG as compared to Zn-RIF, RIF and Zn. Immunofluorescence studies showed that Zn-RIF-Tf-QD-conjugates were actively endocytosed by macrophages and dendritic cells, but not by lung epithelial cells. Treatment with Zn-RIF-Tf-QD efficiently killed mycobacteria residing inside macrophages without exhibiting cytotoxicity and genotoxicity. Moreover, the conjugates remained stable for upto 48 h, were taken up into the late endosomal compartment of macrophages, and released the drug in a sustainable manner. Our data demonstrate that Zn-RIF-Tf-QDs have a great potential as anti-TB drugs. In addition, transferrin-conjugated QDs may constitute an effective drug delivery system for tuberculosis therapy. PMID:27113139

  3. InAsP quantum dot lasers grown by MOVPE.

    PubMed

    Karomi, Ivan; Smowton, Peter M; Shutts, Samuel; Krysa, Andrey B; Beanland, Richard

    2015-10-19

    We report on InAsP quantum dot lasers grown by MOVPE for 730-780 nm wavelength emission and compare performance with InP dot samples grown under similar conditions and with similar structures. 1-4 mm long, uncoated facet InAsP dot lasers emit between 760 and 775 nm and 2 mm long lasers with uncoated facets have threshold current density of 260 Acm(-2), compared with 150 Acm(-2) for InP quantum dot samples, which emit at shorter wavelengths, 715-725 nm. Pulsed lasing is demonstrated for InAsP dots up to 380 K with up to 200 mW output power. Measured absorption spectra indicate the addition of Arsenic to the dots has shifted the available transitions to longer wavelengths but also results in a much larger degree of spectral broadening. These spectra and transmission electron microscopy images indicate that the InAsP dots have a much larger degree of inhomogeneous broadening due to dot size variation, both from layer to layer and within a layer.

  4. Ultrafast optical control of individual quantum dot spin qubits.

    PubMed

    De Greve, Kristiaan; Press, David; McMahon, Peter L; Yamamoto, Yoshihisa

    2013-09-01

    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 entangled

  5. Ultrafast optical control of individual quantum dot spin qubits

    NASA Astrophysics Data System (ADS)

    De Greve, Kristiaan; Press, David; McMahon, Peter L.; Yamamoto, Yoshihisa

    2013-09-01

    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

  6. Physical optimization of quantum error correction circuits with spatially separated quantum dot spins.

    PubMed

    Wang, Hong-Fu; Zhu, Ai-Dong; Zhang, Shou

    2013-05-20

    We propose an efficient protocol for optimizing the physical implementation of three-qubit quantum error correction with spatially separated quantum dot spins via virtual-photon-induced process. In the protocol, each quantum dot is trapped in an individual cavity and each two cavities are connected by an optical fiber. We propose the optimal quantum circuits and describe the physical implementation for correcting both the bit flip and phase flip errors by applying a series of one-bit unitary rotation gates and two-bit quantum iSWAP gates that are produced by the long-range interaction between two distributed quantum dot spins mediated by the vacuum fields of the fiber and cavity. The protocol opens promising perspectives for long distance quantum communication and distributed quantum computation networks.

  7. Hard chaos, quantum billiards, and quantum dot computers

    SciTech Connect

    Mainieri, R.; Cvitanovic, P.; Hasslacher, B.

    1996-07-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Research was performed in analytic and computational techniques for dealing with hard chaos, especially the powerful tool of cycle expansions. This work has direct application to the understanding of electrons in nanodevices, such as junctions of quantum wires, or in arrays of dots or antidots. We developed a series of techniques for computing the properties of quantum systems with hard chaos, in particular the flow of electrons through nanodevices. These techniques are providing the insight and tools to design computers with nanoscale components. Recent efforts concentrated on understanding the effects of noise and orbit pruning in chaotic dynamical systems. We showed that most complicated chaotic systems (not just those equivalent to a finite shift) will develop branch points in their cycle expansion. Once the singularity is known to exist, it can be removed with a dramatic increase in the speed of convergence of quantities of physical interest.

  8. Imaging electrostatically confined Dirac fermions in graphene quantum dots

    NASA Astrophysics Data System (ADS)

    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.

  9. Periodic scarred States in open quantum dots as evidence of quantum Darwinism.

    PubMed

    Burke, A M; Akis, R; Day, T E; Speyer, Gil; Ferry, D K; Bennett, B R

    2010-04-30

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  10. Periodic Scarred States in Open Quantum Dots as Evidence of Quantum Darwinism

    NASA Astrophysics Data System (ADS)

    Burke, A. M.; Akis, R.; Day, T. E.; Speyer, Gil; Ferry, D. K.; Bennett, B. R.

    2010-04-01

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  11. Intermediate-band photosensitive device with quantum dots having tunneling barrier embedded in organic matrix

    DOEpatents

    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.

  12. Photoconductive gain and quantum efficiency of remotely doped Ge/Si quantum dot photodetectors

    NASA Astrophysics Data System (ADS)

    Yakimov, A. I.; Kirienko, V. V.; Armbrister, V. A.; Bloshkin, A. A.; Dvurechenskii, A. V.; Shklyaev, A. A.

    2016-10-01

    We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

  13. Double Quantum Dots in Carbon Nanotubes

    DTIC Science & Technology

    2010-06-02

    occupation of one dot is favored by increasing the detuning between the dots, the Coulomb interaction causes strong correlation effects realized by...of an additional val- ley degree of freedom, the two-electron eigenstates can be separated in an orbital part and a spin-valley part that are, to a...detuning, each dot is populated by a single electron and tunneling is sup- pressed because of Coulomb interactions. Thus, interdot coupling only occurs

  14. Data detection algorithms for multiplexed quantum dot encoding.

    PubMed

    Goss, Kelly C; Messier, Geoff G; Potter, Mike E

    2012-02-27

    A group of quantum dots can be designed to have a unique spectral emission by varying the size of the quantum dots (wavelength) and number of quantum dots (intensity). This technique has been previously proposed for biological tags and object identification. The potential of this system lies in the ability to have a large number of distinguishable wavelengths and intensity levels. This paper presents a communications system model for MxQDs including the interference between neighbouring QD colours and detector noise. An analytical model of the signal-to-noise ratio of a Charge-Coupled Device (CCD) spectrometer is presented and confirmed with experimental results. We then apply a communications system perspective and propose data detection algorithms that increase the readability of the quantum dots tags. It is demonstrated that multiplexed quantum dot barcodes can be read with 99.7% accuracy using the proposed data detection algorithms in a system with 6 colours and 6 intensity values resulting in 46,655 unique spectral codes.

  15. Temperature-dependent electron transport in quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Padilla, Derek J.

    Quantum dot photovoltaics have attracted much interest from researchers in recent years. They have the potential to address both costs and efficiencies of solar cells while simultaneously demonstrating novel physics. Thin-film devices inherently require less material than bulk crystalline silicon, and solution deposition removes the high energy used in fabrication processes. The ease of bandgap tunability in quantum dots through size control allows for simple graded bandgap structures, which is one method of breaking beyond the Shockley-Queisser limit. Power output can also be increased through the process of multiple exciton generation, whereby more than one electron participates in conduction after the absorption of a single photon. In this dissertation work, quantum dot photovoltaics are examined through a range of temperatures. Exploring the current-voltage-temperature parameter space provides insight into the dominant conduction mechanisms within these materials, which is largely not agreed upon. Beginning with PbS quantum dots, changes in device structure are examined by varying the capping ligand and nanoparticle size. This leads similar studies of new, germanium quantum dot devices. Through this understanding, further optimization of device structure can lead to enhanced device performance.

  16. Three Quantum Dots Embedded in Aharonov-Bohm Rings

    NASA Astrophysics Data System (ADS)

    Toonen, Ryan; Hãttel, Andreas; Goswami, Srijit; Eberl, Karl; Eriksson, Mark; van der Weide, Daniel; Blick, Robert

    2004-03-01

    Coherent coupling of two quantum dots embedded in a ring-geometry has been demonstrated by Holleitner et al.(A.W. Holleitner, H. Qin, C.R. Decker, K. Eberl, and R.H. Blick, phCoherent Coupling of Two Quantum Dots Embedded in an Aharonov-Bohm Ring), Phys. Rev. Lett. 87, 256802 (2001) Recording of the Aharonov-Bohm oscillations in such a circuit has proven that the phases of electron wave functions can be manipulated directly. We have since enhanced the complexity of this system by embedding three quantum dots in such a ring-geometry. As before, our quantum dots are formed by laterally constricting a two-dimensional electron gas (2DEG) in an Al_xGa_1-xAs/GaAs heterostructure. The new, essential ingredient of this experiment is an additional third port--added to the ring for individually addressing the third quantum dot. This circuit allows us to investigate phenomena associated with phase-switching between separate ports. We will discuss first results and give a simple model of circuit operation.

  17. Photons and (artificial) atoms: an overview of optical spectroscopy techniques on quantum dots

    NASA Astrophysics Data System (ADS)

    Vamivakas, A. N.; Atatüre, M.

    2010-01-01

    In most branches within experimental physics technical prowess lies at the heart of many seminal works. From the observation of the photoelectric effect and the ultraviolet catastrophe that led to the development of quantum mechanics to the first transistor that shaped the modern age of electronics, significant physical insight has been achieved on the shoulders of technical advances and progress. Research on self-assembled quantum dots may be a drop in the sea of physics, but it still is no exception to this trend, and more physical insight continues to be revealed as the tools of the trade get increasingly more complex and advanced. This article is written primarily for senior undergraduate students and first year graduate students of experimental physics involving optically active quantum dots. More often than not, we have seen students shuffling through journal articles trying to relate the reported physics to the used experimental techniques. What we want to cover here is not in any way the history or the recent progress in quantum dot research - there are an ample number of topical books and review articles for that - but rather to highlight a selection of optics-based measurement techniques that have led to significant progress in our understanding of quantum dot physics as well as their applications in the last two decades. We hope a basic survey of the relevant optical spectroscopy techniques will help the newcomers in connecting the dots between measurements and physics.

  18. Apoptosis induced by cadmium selenide quantum dots in JB6 cells.

    PubMed

    Kong, Lu; Zhang, Ting; Tang, Meng; Pu, Yuepu

    2012-11-01

    Quantum dots are being widely used in physics and in the biomedical industry in recent years due to their excellent optical characteristics. However, studies have shown that cadmium selenide core-shell quantum dots exhibit cytotoxicity. The present study investigates the induction of apoptosis and the signal pathways involved in this process by cadmium selenide-core quantum dots in JB6 cells. We found that cadmium selenide-core quantum dots exhibited high cytotoxicity and caused apoptosis and necrosis of JB6 cells. Cell cycle detection showed an increase in the percentage of G1 phase cells but a decrease in the percentage of S and G2 phase cells after JB6 cells treated with various concentrations of cadmium selenide core-shell quantum dots for 24 h. At the same time, western-blot analysis showed an activation of pro-apoptotic factors including FAS, BAX and BID. Apoptosis-inducing factor (AIF), full length and cleaved caspase-6 and -8 were up-regulated. The current study provides a guide for the safe use of QDs as a new kind of biological fluorescence material for biological and medical applications.

  19. Self-assembly of nanosized 0D clusters: CdS quantum dot-polyoxotungstate nanohybrids with strongly coupled electronic structures and visible-light-active photofunctions.

    PubMed

    Kim, Hyo Na; Kim, Tae Woo; Choi, Kyong-Hoon; Kim, In Young; Kim, Yong-Rok; Hwang, Seong-Ju

    2011-08-22

    Nanohybrids of CdS-polyoxotungstate with strongly coupled electronic structures and visible-light-active photofunctions can be synthesized by electrostatically derived self-assembly of very small CdS quantum dots, or QDs, (particle size ≈ 2.5 nm) and polyoxotungstate nanoclusters (cluster size ≈1 nm). The formation of CdS-polyoxotungstate nanohybrids is confirmed by high-resolution transmission electron microscopy, elemental mapping, and powder X-ray diffraction analysis. Due to the strong electronic coupling between two semiconductors, the CdS-polyoxotungstate nanohybrids show a narrow bandgap energy of around 1.9-2.7 eV, thus reflecting their ability to harvest visible light. Time-resolved photoluminescence experiments indicate that the self-assembly between nanosized CdS and polyoxotungstate is very effective in increasing the lifetime of holes and electrons, thus indicating an efficient electron transfer between two-component semiconductors. The hybridization results not only in a significant improvement in the photostability of CdS QD but also in the creation of visible-light-induced photochromism. Of particular importance is that the present nanohybrids show visible-light-driven photocatalytic activity to produce H(2) and O(2) , which is superior to those of the unhybridized CdS and polyoxotungstate. The self-assembly of nanometer-level semiconductor clusters can provide a powerful way of optimizing the photoinduced functionalities of each component (i.e., visible-induced photochromism and photocatalysis) by means of strong electronic coupling.

  20. Quantum dot-based energy transfer: perspectives and potential for applications in photodynamic therapy.

    PubMed

    Samia, Anna C S; Dayal, Smita; Burda, Clemens

    2006-01-01

    Quantum dots have emerged as an important class of material that offers great promise to a diverse range of applications ranging from energy conversion to biomedicine. Here, we review the potential of using quantum dots and quantum dot conjugates as sensitizers for photodynamic therapy (PDT). The photophysics of singlet oxygen generation in relation to quantum dot-based energy transfer is discussed and the possibility of using quantum dots as photosensitizer in PDT is assessed, including their current limitations to applications in biological systems. The biggest advantage of quantum dots over molecular photosensitizers that comes into perspective is their tunable optical properties and surface chemistries. Recent developments in the preparation and photophysical characterization of quantum dot energy transfer processes are also presented in this review, to provide insights on the future direction of quantum dot-based photosensitization studies from the viewpoint of our ongoing research.

  1. A Quantum Dot with Spin-Orbit Interaction--Analytical Solution

    ERIC Educational Resources Information Center

    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.

  2. Quantum-dot-tagged photonic crystal beads for multiplex detection of tumor markers.

    PubMed

    Li, Juan; Wang, Huan; Dong, Shujun; Zhu, Peizhi; Diao, Guowang; Yang, Zhanjun

    2014-12-04

    Novel quantum-dot-tagged photonic crystal beads were fabricated for multiplex detection of tumor markers via self-assembly of quantum dot-embedded polystyrene nanospheres into photonic crystal beads through a microfluidic device.

  3. Generation of heralded entanglement between distant quantum dot hole spins

    NASA Astrophysics Data System (ADS)

    Delteil, Aymeric

    Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of

  4. Diamond LED substrate and novel quantum dots.

    PubMed

    Sung, James C; Sung, Michael

    2009-02-01

    Nitride LED (e.g., GaN) has become the mainstream of blue light source. The blue light can be converted to white light by exciting a phosphor (e.g., Nichia's YAG or Osram's TAG) with the complementary yellow emission. However, GaN is typically deposited on sapphire (Al2O3) substrates formed by crystal pulling or hexagonal (e.g., 4 H or 6 H) SiC wafers condensed from SiC vapor. In either case, the nitride lattice is ridden (e.g., 10(9)/cm2) with dislocations. The high dislocation density with sapphire is due to the large (>13%) lattice mismatch; and with hexagonal SiC, because of intrinsic defects. Cubic (beta) SiC may be deposited epitaxially using a CVD reactor onto silicon wafer by diffusing the interface and by chemical gradation. A reactive echant (e.g., hydrogen or fluorine) can be introduced periodically to gasify mis-aligned atoms. In this case, large single crystal wafers would be available for the manufacture of high bright LED with superb electro-optical efficiency. The SiC wafer may be coated with diamond film that can eliminate heat in real time. As a result of lower temperature, the nitride LED can be brighter and it will last longer. The blue light of GaN LED formed on SiC on Diamond (SiCON) LED may also be scattered by using novel quantum dots (e.g., 33 atom pairs of CdSe) to form a broad yellow light that blend in with the original blue light to form sunlight-like white light. This would be the ideal source for general illumination (e.g., for indoor) or backlighting (e.g., for LCD).

  5. Biosensing with quantum dots: a microfluidic approach.

    PubMed

    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.

  6. Silicon quantum dots for optical applications

    NASA Astrophysics Data System (ADS)

    Wu, Jeslin J.

    Luminescent silicon quantum dots (SiQDs) are emerging as attractive materials for optoelectronic devices, third generation photovoltaics, and bioimaging. Their applicability in the real world is contingent on their optical properties and long-term environmental stability; and in biological applications, factors such as water solubility and toxicity must also be taken into consideration. The aforementioned properties are highly dependent on the QDs' surface chemistry. In this work, SiQDs were engineered for the respective applications using liquid-phase and gas-phase functionalization techniques. Preliminary work in luminescent downshifting for photovoltaic systems are also reported. Highly luminescent SiQDs were fabricated by grafting unsaturated hydrocarbons onto the surface of hydrogen-terminated SiQDs via thermal and photochemical hydrosilylation. An industrially attractive, all gas-phase, nonthermal plasma synthesis, passivation (aided by photochemical reactions), and deposition process was also developed to reduce solvent waste. With photoluminescence quantum yields (PLQYs) nearing 60 %, the alkyl-terminated QDs are attractive materials for optical applications. The functionalized SiQDs also exhibited enhanced thermal stability as compared to their unfunctionalized counterparts, and the photochemically-hydrosilylated QDs further displayed photostability under UV irradiation. These environmentally-stable SiQDs were used as luminescent downshifting layers in photovoltaic systems, which led to enhancements in the blue photoresponse of heterojunction solar cells. Furthermore, the QD films demonstrated antireflective properties, improving the coupling efficiency of sunlight into the cell. For biological applications, oxide, amine, or hydroxyl groups were grafted onto the surface to create water-soluble SiQDs. Luminescent, water-soluble SiQDs were produced in by microplasma treating the QDs in water. Stable QYs exceeding 50 % were obtained. Radical-based and

  7. InGaN/GaN self-organized quantum dot lasers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Banerjee, Animesh; Frost, Thomas; Jahangir, Shafat; Stark, Ethan; Bhattacharya, Pallab

    2013-09-01

    Blue-and green-emitting quantum dots have been characterized and ridge waveguide lasers incorporating such quantum dots into the active region have been realized. The laser heteroscturctures were grown by plasma assisted molecular beam epitaxy. Injected carrier lifetimes in the quantum dots have also been measured by temperature dependent and time resolved photoluminescence. A threshold current density of 930 A/cm2 in the blue-emitting lasers was measured under pulsed bias. A tunnel injection scheme to inject holes has been incorporated in the design of the green quantum dot lasers, and a threshold current density of 945 A/cm2 in the green-emitting lasers has been measured under pulsed bias. Slope efficiencies of 0.41 W/A and 0.25 W/A have been measured, corresponding to differential quantum efficiencies of 13.9% and 11.3%, in the blue and green lasers, respectively.

  8. Multicolor 3D super-resolution imaging by quantum dot stochastic optical reconstruction microscopy.

    PubMed

    Xu, Jianquan; Tehrani, Kayvan F; Kner, Peter

    2015-03-24

    We demonstrate multicolor three-dimensional super-resolution imaging with quantum dots (QSTORM). By combining quantum dot asynchronous spectral blueing with stochastic optical reconstruction microscopy and adaptive optics, we achieve three-dimensional imaging with 24 nm lateral and 37 nm axial resolution. By pairing two short-pass filters with two appropriate quantum dots, we are able to image single blueing quantum dots on two channels simultaneously, enabling multicolor imaging with high photon counts.

  9. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes

    NASA Astrophysics Data System (ADS)

    Gromova, Yulia A.; Orlova, Anna O.; Maslov, Vladimir G.; Fedorov, Anatoly V.; Baranov, Alexander V.

    2013-10-01

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

  10. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes.

    PubMed

    Gromova, Yulia A; Orlova, Anna O; Maslov, Vladimir G; Fedorov, Anatoly V; Baranov, Alexander V

    2013-10-31

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

  11. Capping biological quantum dots with the peptide CLPFFD to increase stability and to reduce effects on cell viability

    NASA Astrophysics Data System (ADS)

    Riveros, A. L.; Astudillo, J.; Vásquez, C. C.; Jara, Danilo H.; Guerrero, Ariel R.; Guzman, F.; Osorio-Roman, I. O.; Kogan, M. J.

    2016-08-01

    Highly fluorescent nanoparticles, or quantum dots, have multiple applications in biology and biomedicine; however, in most cases, it is necessary to functionalize them to enhance their biocompatibility and selectivity. Generally, functionalization is performed after nanoparticle synthesis and involves the use of molecules or macromolecules having two important traits: specific biological activity and functional groups that facilitate nanoparticle capping (i.e. atom-atom interaction). For this reason, we carried out a simple protocol for the chemical synthesis of cadmium telluride quantum dots capped with glutathione, and we then functionalized these nanoparticles with the amphipathic peptide CLPFFD. This peptide attaches selectively to β-Amyloid fibres, which are involved in Alzheimer's disease. Our results show that the optical properties of the quantum dots are not affected by functionalization with this peptide. Infrared spectra showed that cadmium telluride quantum dots were functionalized with the peptide CLPFFD. In addition, no significant differences were observed between the surface charge of the quantum dots with or without CLPFFD and the nanocrystal size calculated for HR-TEM was 4.2 nm. Finally, our results show that quantum dots with CLPFFD are stable and that they resulted in a significantly reduced cytotoxicity with respect to that induced by quantum dots not conjugated with the peptide. Moreover, the results show that the CLPFFD-functionalized nanoparticles bind to β-Amyloid fibres.

  12. Use of quantum dot-conjugated antibodies to study intracellular cancer biomarkers in living and fixed cells

    NASA Astrophysics Data System (ADS)

    Ling, Jian

    2008-02-01

    Quantum dots have unique properties for long-term immunofluorescence imaging of molecular activities inside living cells. The key is how to deliver the quantum dot-conjugated antibodies into cells and further allow the antibodies freely move inside cells to bind target molecules. This study investigated the feasibility of using Pep-1, a cell penetration protein, to facilitate the internalization of quantum dot-conjugated antibodies for the labeling of two intracellular cervical cancer biomarkers: p16 and Mcm5. Quantum dots were directly conjugated with the antibodies to p16 and Mcm5 and, they were able to stain fixed cells and to differentiate biomarker positive and negative cells. The non-covalent binding between the conjugates and Pep-1 peptides allows the quick internalization of the quantum dot-conjugated antibodies into living cells. The internalized conjugates were concentrated in the perinuclear regions of the biomarker-positive HeLa cells. In the biomarker negative Um-Uc-3 cells, however, the conjugates concentrated in juxtaneclear region. Cells bearing with quantum dots still go through the mitosis process. Although the study indicates many questions need to be answered and many problems need to be solved, the use of cell penetration peptide is a promising method for the intracellular labeling of living cell molecules using quantum dots.

  13. Quantum strain sensor with a topological insulator HgTe quantum dot

    PubMed Central

    Korkusinski, Marek; Hawrylak, Pawel

    2014-01-01

    We present a theory of electronic properties of HgTe quantum dot and propose a strain sensor based on a strain-driven transition from a HgTe quantum dot with inverted bandstructure and robust topologically protected quantum edge states to a normal state without edge states in the energy gap. The presence or absence of edge states leads to large on/off ratio of conductivity across the quantum dot, tunable by adjusting the number of conduction channels in the source-drain voltage window. The electronic properties of a HgTe quantum dot as a function of size and applied strain are described using eight-band Luttinger and Bir-Pikus Hamiltonians, with surface states identified with chirality of Luttinger spinors and obtained through extensive numerical diagonalization of the Hamiltonian. PMID:24811674

  14. Quantum strain sensor with a topological insulator HgTe quantum dot.

    PubMed

    Korkusinski, Marek; Hawrylak, Pawel

    2014-05-09

    We present a theory of electronic properties of HgTe quantum dot and propose a strain sensor based on a strain-driven transition from a HgTe quantum dot with inverted bandstructure and robust topologically protected quantum edge states to a normal state without edge states in the energy gap. The presence or absence of edge states leads to large on/off ratio of conductivity across the quantum dot, tunable by adjusting the number of conduction channels in the source-drain voltage window. The electronic properties of a HgTe quantum dot as a function of size and applied strain are described using eight-band k · p Luttinger and Bir-Pikus Hamiltonians, with surface states identified with chirality of Luttinger spinors and obtained through extensive numerical diagonalization of the Hamiltonian.

  15. Magnetic quantum dot in two-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Li, Guo; Zhu, Jia-Lin; Yang, Ning

    2017-03-01

    Magnetic quantum dots in two-dimensional band and topological insulators are studied by solving the modified Dirac model under nonuniform magnetic fields. The Landau levels split into discrete states with certain angular momentum. The states splitting from the zero Landau levels lie in the energy gap for topological insulators but are out of the gap for band insulators. It is found that the ground states oscillate between the spin-up and spin-down states when the magnetic field or the dot size changes. The oscillation manifests itself as changes of sign and strength of charge currents near the dot's edge.

  16. Fluorescent carbon 'quantum' dots from thermochemical functionalization of carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Rednic, Monica I.; Lu, Zhuomin; Wang, Ping; LeCroy, Gregory E.; Yang, Fan; Liu, Yun; Qian, Haijun; Terec, Anamaria; Veca, L. Monica; Lu, Fushen; Sun, Ya-Ping

    2015-10-01

    Fluorescent carbon 'quantum' dots are generally obtained by deliberate chemical functionalization of carbon nanoparticles or by 'one-pot' carbonization processing. For brightly fluorescent carbon dots with optoelectronic polymers, a hybrid approach was developed to use pre-processed and selected carbon nanoparticles as precursor for surface passivation by poly(9-vinylcarbazole) (PVK) in one-pot thermochemical processing, thus taking advantage of the more controllable feature from the deliberate functionalization and also the versatility associated with the one-pot synthesis. The PVK-carbon dots were characterized by optical spectroscopy, microscopy, and other techniques. The broad applicability of the hybrid approach is discussed.

  17. Spin degeneracy and conductance fluctuations in open quantum dots.

    PubMed

    Folk, J A; Patel, S R; Birnbaum, K M; Marcus, C M; Duruöz, C I; Harris, J S

    2001-03-05

    The dependence of conductance fluctuations on parallel magnetic field is used as a probe of spin degeneracy in open GaAs quantum dots. The variance of fluctuations at high parallel field is reduced from the low-field variance (with broken time-reversal symmetry) by factors ranging from roughly 2 in a 1 microm (2) dot to greater than 4 in 8 microm (2) dots. The factor of 2 is expected for Zeeman splitting of spin-degenerate channels. A possible explanation for the larger suppression based on field-dependent spin-orbit scattering is proposed.

  18. Dual-channel spontaneous emission of quantum dots in magnetic metamaterials

    NASA Astrophysics Data System (ADS)

    Decker, Manuel; Staude, Isabelle; Shishkin, Ivan I.; Samusev, Kirill B.; Parkinson, Patrick; Sreenivasan, Varun K. A.; Minovich, Alexander; Miroshnichenko, Andrey E.; Zvyagin, Andrei; Jagadish, Chennupati; Neshev, Dragomir N.; Kivshar, Yuri S.

    2013-12-01

    Metamaterials, artificial electromagnetic media realized by subwavelength nano-structuring, have become a paradigm for engineering electromagnetic space, allowing for independent control of both electric and magnetic responses of the material. Whereas most metamaterials studied so far are limited to passive structures, the need for active metamaterials is rapidly growing. However, the fundamental question on how the energy of emitters is distributed between both (electric and magnetic) interaction channels of the metamaterial still remains open. Here we study simultaneous spontaneous emission of quantum dots into both of these channels and define the control parameters for tailoring the quantum-dot coupling to metamaterials. By superimposing two orthogonal modes of equal strength at the wavelength of quantum-dot photoluminescence, we demonstrate a sharp difference in their interaction with the magnetic and electric metamaterial modes. Our observations reveal the importance of mode engineering for spontaneous emission control in metamaterials, paving a way towards loss-compensated metamaterials and metamaterial nanolasers.

  19. Microscopic model for intersubband gain from electrically pumped quantum-dot structures

    SciTech Connect

    Michael, Stephan; Chow, Weng Wah; Schneider, Han Christian

    2014-10-03

    We study theoretically the performance of electrically pumped self-organized quantum dots as a gain material in the mid-infrared range at room temperature. We analyze an AlGaAs/InGaAs based structure composed of dots-in-a-well sandwiched between two quantum wells. We numerically analyze a comprehensive model by combining a many-particle approach for electronic dynamics with a realistic modeling of the electronic states in the whole structure. We investigate the gain both for quasi-equilibrium conditions and current injection. We find, comparing different structures, that steady-state gain can only be realized by an efficient extraction process, which prevents an accumulation of electrons in continuum states, that make the available scattering pathways through the quantum-dot active region too fast to sustain inversion.

  20. Microscopic model for intersubband gain from electrically pumped quantum-dot structures

    DOE PAGES

    Michael, Stephan; Chow, Weng Wah; Schneider, Han Christian

    2014-10-03

    We study theoretically the performance of electrically pumped self-organized quantum dots as a gain material in the mid-infrared range at room temperature. We analyze an AlGaAs/InGaAs based structure composed of dots-in-a-well sandwiched between two quantum wells. We numerically analyze a comprehensive model by combining a many-particle approach for electronic dynamics with a realistic modeling of the electronic states in the whole structure. We investigate the gain both for quasi-equilibrium conditions and current injection. We find, comparing different structures, that steady-state gain can only be realized by an efficient extraction process, which prevents an accumulation of electrons in continuum states, thatmore » make the available scattering pathways through the quantum-dot active region too fast to sustain inversion.« less

  1. Broadband external cavity tunable quantum dot lasers with low injection current density.

    PubMed

    Lv, X Q; Jin, P; Wang, W Y; Wang, Z G

    2010-04-26

    Broadband grating-coupled external cavity laser, based on InAs/GaAs quantum dots, is achieved. The device has a wavelength tuning range from 1141.6 nm to 1251.7 nm under a low continuous-wave injection current density (458 A/cm(2)). The tunable bandwidth covers consecutively the light emissions from both the ground state and the 1st excited state of quantum dots. The effects of cavity length and antireflection facet coating on device performance are studied. It is shown that antireflection facet coating expands the tuning bandwidth up to ~150 nm, accompanied by an evident increase in threshold current density, which is attributed to the reduced interaction between the light field and the quantum dots in the active region of the device.

  2. Chirped InGaAs quantum dot molecules for broadband applications

    PubMed Central

    2012-01-01

    Lateral InGaAs quantum dot molecules (QDMs) formed by partial-cap and regrowth technique exhibit two ground-state (GS) peaks controllable via the thicknesses of InAs seed quantum dots (x), GaAs cap (y), and InAs regrowth (z). By adjusting x/y/z in a stacked QDM bilayer, the GS peaks from the two layers can be offset to straddle, stagger, or join up with each other, resulting in multi-GS or broadband spectra. A non-optimized QDM bilayer with a 170-meV full-width at half-maximum is demonstrated. The temperature dependencies of the emission peak energies and intensities from the chirped QDM bilayers are well explained by Varshni's equation and thermal activation of carriers out of constituent quantum dots. PMID:22480323

  3. Noninvasive detection of charge rearrangement in a quantum dot in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Fricke, C.; Rogge, M. C.; Harke, B.; Reinwald, M.; Wegscheider, W.; Hohls, F.; Haug, R. J.

    2005-11-01

    We demonstrate electron redistribution caused by magnetic field on a single quantum dot measured by means of a quantum point contact as noninvasive detector. Our device, which is fabricated by local anodic oxidation, allows us to control independently the quantum point contact and all tunneling barriers of the quantum dot. Thus we are able to measure both the change of the quantum dot charge and also changes of the electron configuration at constant number of electrons on the quantum dot. We use these features to exploit the quantum dot in a high magnetic field where transport through the quantum dot displays the effects of Landau shells and spin blockade. We confirm the internal rearrangement of electrons as function of the magnetic field for a fixed number of electrons on the quantum dot.

  4. Highly sensitive humidity sensing properties of carbon quantum dots films

    SciTech Connect

    Zhang, Xing; Ming, Hai; Liu, Ruihua; Han, Xiao; Kang, Zhenhui; Liu, Yang; Zhang, Yonglai

    2013-02-15

    Graphical abstract: Display Omitted Highlights: ► A humidity sensing device was fabricated based on carbon quantum dots (CQDs) films. ► The conductivity of the CQDs films shows a linear and rapid response to atmosphere humidity. ► The humidity sensing property was due to the hydrogen bonds between the functional groups on CQDs. -- Abstract: We reported the fabrication of a humidity sensing device based on carbon quantum dots (CQDs) film. The conductivity of the CQDs film has a linear and rapid response to relative humidity, providing the opportunity for the fabrication of humidity sensing devices. The mechanism of our humidity sensor was proposed to be the formation of hydrogen bonds between carbon quantum dots and water molecules in the humidity environment, which significantly promote the electrons migration. In a control experiment, this hypothesis was confirmed by comparing the humidity sensitivity of candle soot (i.e. carbon nanoparticles) with and without oxygen containing groups on the surfaces.

  5. Gradient-Doped Thermophotovoltaic Devices based on Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Fayaz Movahed, Hamidreza

    Electromagnetic radiation emitted from hot objects represents a sizeable supply of energy; however, even for relatively hot bodies, its flux peaks in the short-wavelength infrared between 1 and 3 mum, standing in the way of its photovoltaic harvest using the most widely-available optoelectronic materials such as Si and CdTe. Colloidal quantum dots combine low-cost solution-processing with bandgap tunability in this spectral region, thereby offering a route to harnessing thermal power photovoltaically. Here we report thermophotovoltaic devices constructed using colloidal quantum dots that harvest infrared radiation from an 800°C blackbody source. Only by constructing a gradient-doped colloidal quantum dot thermophotovoltaic device were we able to achieve thermophotovoltaic power generation with a power conversion efficiency of 0.39%. The device showed stable operation at ambient temperatures above 100°C.

  6. Dynamical cooling of nuclear spins in double quantum dots.

    PubMed

    Rudner, M S; Levitov, L S

    2010-07-09

    Electrons trapped in quantum dots can exhibit quantum-coherent spin dynamics over long timescales. These timescales are limited by the coupling of electron spins to the disordered nuclear spin background, which is a major source of noise and dephasing in such systems. We propose a scheme for controlling and suppressing fluctuations of nuclear spin polarization in double quantum dots, which uses nuclear spin pumping in the spin-blockade regime. We show that nuclear spin polarization fluctuations can be suppressed when electronic levels in the two dots are properly positioned near resonance. The proposed mechanism is analogous to that of optical Doppler cooling. The Overhauser shift due to fluctuations of nuclear polarization brings electron levels in and out of resonance, creating internal feedback to suppress fluctuations. Estimates indicate that a better than 10-fold reduction of fluctuations is possible.

  7. Modeling interfacial charge transport of quantum dots using cyclic voltammetry

    NASA Astrophysics Data System (ADS)

    Tobias, Andrew K.; Jones, Marcus

    2011-10-01

    Quantum dot applications are numerous and range from photovoltaic devices and lasers, to bio labeling. Complexities in the electronic band structure of quantum dots create the necessity for analysis techniques that can accurately and reproducibly provide their absolute band energies. Cyclic voltammetry (CV) is a novel candidate for these studies and has the potential to become a useful tool in engineering new nanocrystal technology, by providing information necessary for predicting and modeling interfacial charge transfer to and from quantum dots. Advancing from previous reports of nanocrystal CV, a carbon paste electrode was utilized in an attempt to increase measured current by ensuring intimate contact between nanocrystals and the electrode. Our goal was to investigate band energies and model nanocrystal-molecule electron transfer systems.

  8. Gate-controlled electron spins in quantum dots

    SciTech Connect

    Prabhakar, Sanjay; Melnik, Roderick; Bonilla, Luis L.

    2013-12-16

    In this paper we study the properties of anisotropic semiconductor quantum dots (QDs) formed in the conduction band in the presence of the magnetic field. The Kane-type model is formulated and is analyzed by using both analytical and finite element techniques. Among other things, we demonstrate that in such quantum dots, the electron spin states in the phonon-induced spin-flip rate can be manipulated with the application of externally applied anisotropic gate potentials. More precisely, such potentials enhance the spin flip rates and reduce the level crossing points to lower quantum dot radii. This happens due to the suppression of the g-factor towards bulk crystal. We conclude that the phonon induced spin-flip rate can be controlled through the application of spin-orbit coupling. Numerical examples are shown to demonstrate these findings.

  9. Electron nuclear spin transfer in quantum-dot networks

    NASA Astrophysics Data System (ADS)

    Prada, M.; Toonen, R. C.; Blick, R. H.; Harrison, P.

    2005-05-01

    We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of different geometries of a two-dimensional network of quantum dots and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalized to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in the presence of nuclear spin relaxation. We find that the gradual depolarization of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.

  10. Emerging application of quantum dots for drug delivery and therapy.

    PubMed

    Qi, Lifeng; Gao, Xiaohu

    2008-03-01

    Quantum dots have proven themselves as powerful fluorescent probes, especially for long-term, multiplexed, and quantitative imaging and detection. Newly engineered quantum dots with integrated targeting, imaging and therapeutic functionalities have become excellent material to study drug delivery in cells and small animals. This fluorescent 'prototype' will provide important information in the rational design of biocompatible drug carriers and will serve as a superior alternative to magnetic and radioactive imaging contrast agents in preclinical drug screening, validation and delivery research. This Editorial article is not intended to offer a comprehensive review on drug delivery, but to highlight the breakthroughs in the emerging applications of quantum dots in this field and to provide our perspective on future research.

  11. Colloidal quantum dot solids for solution-processed solar cells

    NASA Astrophysics Data System (ADS)

    Yuan, Mingjian; Liu, Mengxia; Sargent, Edward H.

    2016-03-01

    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.

  12. Bioconjugate recognition molecules to quantum dots as tumor probes.

    PubMed

    Liu, Tian-Cai; Wang, Jian-Hao; Wang, Hai-Qiao; Zhang, Hai-Li; Zhang, Zhi-Hong; Hua, Xiao-Feng; Cao, Yuan-Cheng; Zhao, Yuan-Di; Luo, Qing-Ming

    2007-12-15

    Transferrin and mouse anti-human CD71 monoclonal antibody were respectively conjugated covalently to the core/shell CdSe/ZnS quantum dots with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydrocylsulfo-succinimide (Sulfo-NHS). The conjugation worked well and the bioactivities of these macromolecules still remained, which was verified by column filtration, sodium dodecyl sulfate polyacrylamide gel electrophoresis, absorption spectra, fluorescence spectra, and circular dichroism spectrometry. Thus, these two kinds of quantum dot conjugates were used to recognize the tumor cells involved. In case of pseudo positivity, FITC-labeling secondary antibody IgG was used, and the results showed that as-prepared fluorescent quantum dot bioprobes were highly specific to tumor cells.

  13. Charge transport and localization in atomically coherent quantum dot solids

    NASA Astrophysics Data System (ADS)

    Whitham, Kevin; Yang, Jun; Savitzky, Benjamin H.; Kourkoutis, Lena F.; Wise, Frank; Hanrath, Tobias

    2016-05-01

    Epitaxial attachment of quantum dots into ordered superlattices enables the synthesis of quasi-two-dimensional materials that theoretically exhibit features such as Dirac cones and topological states, and have major potential for unprecedented optoelectronic devices. Initial studies found that disorder in these structures causes localization of electrons within a few lattice constants, and highlight the critical need for precise structural characterization and systematic assessment of the effects of disorder on transport. Here we fabricated superlattices with the quantum dots registered to within a single atomic bond length (limited by the polydispersity of the quantum dot building blocks), but missing a fraction (20%) of the epitaxial connections. Calculations of the electronic structure including the measured disorder account for the electron localization inferred from transport measurements. The calculations also show that improvement of the epitaxial connections will lead to completely delocalized electrons and may enable the observation of the remarkable properties predicted for these materials.

  14. Pauli spin blockade in CMOS double quantum dot devices

    NASA Astrophysics Data System (ADS)

    Kotekar-Patil, D.; Corna, A.; Maurand, R.; Crippa, A.; Orlov, A.; Barraud, S.; Hutin, L.; Vinet, M.; Jehl, X.; De Franceschi, S.; Sanquer, M.

    2017-03-01

    Silicon quantum dots are attractive candidates for the development of scalable, spin-based qubits. Pauli spin blockade in double quantum dots provides an efficient, temperature independent mechanism for qubit readout. Here we report on transport experiments in double gate nanowire transistors issued from a CMOS process on 300 mm silicon-on-insulator wafers. At low temperature the devices behave as two few-electron quantum dots in series. We observe signatures of Pauli spin blockade with a singlet-triplet splitting ranging from 0.3 to 1.3 meV. Magneto-transport measurements show that transitions which conserve spin are shown to be magnetic-field independent up to B = 6 T.

  15. Probing electric and magnetic vacuum fluctuations with quantum dots.

    PubMed

    Tighineanu, P; Andersen, M L; Sørensen, A S; Stobbe, S; Lodahl, P

    2014-07-25

    The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this Letter we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level.

  16. Preparation of carbon quantum dots based high photostability luminescent membranes.

    PubMed

    Zhao, Jinxing; Liu, Cui; Li, Yunchuan; Liang, Jiyuan; Liu, Jiyan; Qian, Tonghui; Ding, Jianjun; Cao, Yuan-Cheng

    2016-11-21

    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.

  17. Quantum state measurement in double quantum dots with a radio-frequency quantum point contact

    NASA Astrophysics Data System (ADS)

    Yan, Lei; Wang, Hai-Xia; Yin, Wen; Wang, Fang-Wei

    2014-02-01

    We study the dynamics of two electron spins in coupled quantum dots (CQDs) monitored by a quantum point contact (QPC) detector. Their quantum state can be measured by embedding the QPC in an LC circuit. We derive the Bloch-type rate equations of the reduced density matrix for CQDs. Special attention is paid to the numerical results for the weak measurement condintion under a strong Coulomb interaction. It is shown that the evolution of QPC current always follows that of electron occupation in the right dot. In addition, we find that the output voltage of the circuit can reflect the evolution of QPC current when the circuit and QPC are approximately equal in frequency. In particular, the wave shape of the output voltage can be improved by adjusting the circuit resonance frequency and bandwidth.

  18. Spatial mode dynamics in wide-aperture quantum-dot lasers

    SciTech Connect

    Mukherjee, Jayanta; McInerney, John G.

    2009-05-15

    We present a systematic theoretical study of spatial mode dynamics in wide-aperture semiconductor quantum-dot lasers within the Maxwell-Bloch formalism. Our opto-electro-thermal model self-consistently captures the essential dynamical coupling between field, polarization, and carrier density in both thermal and nonthermal regimes, providing detailed description of the complex spatiotemporal modal intensity structure and spectra in these novel devices and broad area edge-emitting lasers in general. Using linear stability analysis and high resolution adaptive-grid finite element numerical simulation, we show that in the nonthermal regime, the presence of inhomogeneous broadening in quantum-dot active media leads to suppressed filamentation and enhanced spatial coherence compared to conventional quantum well devices with comparable phase-amplitude coupling (alpha parameter). Increasing the degree of inhomogeneous broadening in the active medium leads to further improvement in spatial coherence. In the thermal regime, there is further suppression of filamentation in the inhomogeneously broadened quantum-dot active medium; however, the spatial coherence aided by inhomogeneous broadening is partly lost due to the effect of temperature on cavity detuning. We propose that device designs based on optimized inhomogeneous broadening of quantum-dot gain medium could ultimately lead to diffraction-limited outputs in the quasi-cw regime which are still very difficult to achieve in conventional wide-aperture designs.

  19. Electroluminescence Studies on Longwavelength Indium Arsenide Quantum Dot Microcavities Grown on Gallium Arsenide

    DTIC Science & Technology

    2011-12-01

    ELECTROLUMINESCENCE STUDIES ON LONG WAVELENGTH INDIUM ARSENIDE QUANTUM DOT MICROCAVITIES GROWN ON GALLIUM ARSENIDE THESIS John C...11-46 ELECTROLUMINESCENCE STUDIES ON LONGWAVELENGTH INDIUM ARSENIDE QUANTUM DOT MICROCAVITIES GROWN ON GALLIUM ARSENIDE THESIS...58 1 ELECTROLUMINESCENCE STUDIES ON LONGWAVELENGTH INDIUM ARSENIDE QUANTUM DOT MICROCAVITIES GROWN ON GALLIUM ARSENIDE I

  20. Quantum Dots in a Polymer Composite: A Convenient Particle-in-a-Box Laboratory Experiment

    ERIC Educational Resources Information Center

    Rice, Charles V.; Giffin, Guinevere A.

    2008-01-01

    Semiconductor quantum dots are at the forefront of materials science chemistry with applications in biological imaging and photovoltaic technologies. We have developed a simple laboratory experiment to measure the quantum-dot size from fluorescence spectra. A major roadblock of quantum-dot based exercises is the particle synthesis and handling;…

  1. Self-organized formation of quantum dots of a material on a substrate

    DOEpatents

    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.

  2. A comparative analysis of electronic and molecular quantum dot cellular automata

    SciTech Connect

    Umamahesvari, H. E-mail: ajithavijay1@gmail.com; Ajitha, D. E-mail: ajithavijay1@gmail.com

    2015-06-24

    This paper presents a comparative analysis of electronic quantum-dot cellular automata (EQCA) and Magnetic quantum dot Cellular Automata (MQCA). QCA is a computing paradigm that encodes and processes information by the position of individual electrons. To enhance the high dense and ultra-low power devices, various researches have been actively carried out to find an alternative way to continue and follow Moore’s law, so called “beyond CMOS technology”. There have been several proposals for physically implementing QCA, EQCA and MQCA are the two important QCAs reported so far. This paper provides a comparative study on these two QCAs.

  3. QCAD simulation and optimization of semiconductor double quantum dots

    SciTech Connect

    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

  4. Optical and electronic properties of quantum dots with magnetic impurities

    NASA Astrophysics Data System (ADS)

    Govorov, Alexander O.

    2008-10-01

    The article discusses some of the recent results on semiconductor quantum dots with magnetic impurities. A single Mn impurity incorporated in a quantum dot strongly changes the optical response of a quantum-dot system. A character of Mn-carrier interaction is very different for II-VI and III-V quantum dots (QDs). In the II-VI QDs, a Mn impurity influences mostly the spin-structure of an exciton. In the III-V dots, a spatial localization of hole by a Mn impurity can be very important, and ultimately yields a totally different spin structure. A Mn-doped QD with a variable number of mobile carriers represents an artificial magnetic atom. Due to the Mn-carrier interaction, the order of filling of electronic shells in the magnetic QDs can be very different to the case of the real atoms. The "periodic" table of the artificial magnetic atoms can be realized in voltage-tunable transistor structures. For the electron numbers corresponding to the regime of Hund's rule, the magnetic Mn-carrier coupling is especially strong and the magnetic-polaron states are very robust. Magnetic QD molecules are also very different to the real molecules. QD molecules can demonstrate spontaneous breaking of symmetry and phase transitions. Single QDs and QD molecules can be viewed as voltage-tunable nanoscale memory cells where information is stored in the form of robust magnetic-polaron states. To cite this article: A.O. Govorov, C. R. Physique 9 (2008).

  5. Are quantum dots in unexpected locations due to strain?

    NASA Astrophysics Data System (ADS)

    Zimmerman, Neil; Thorbeck, Ted

    It is a fairly common occurrence that, in top-gated Si quantum dots, the dots appear in reproducible but unexpected positions. For instance, sometimes a group will make gates in order to electrostatically generate tunnel barriers, but discover that the quantum dot is formed underneath the gate rather than between two barrier gates. We will discuss the possibility that such quantum dots arise from the mechanical strain induced by the gate. The model is simple: i) We simulate metal or polysilicon gates on top of a Si/SiO2 wafer, and calculate the stress and strain from differential thermal contraction of the materials; ii) Using the fact that the energy of the Si conduction band depends on strain through the deformation potential, we then convert the strain modulation to a potential energy modulation. As an example, we find that, for a single Al gate, there is a potential well directly underneath the gate with the size of a few meV, in agreement with recent experimental results. We also show that polysilicon gates will not produce such strain-induced quantum dots.

  6. Static gain saturation in quantum dot semiconductor optical amplifiers.

    PubMed

    Meuer, Christian; Kim, Jungho; Laemmlin, Matthias; Liebich, Sven; Capua, Amir; Eisenstein, Gadi; Kovsh, Alexey R; Mikhrin, Sergey S; Krestnikov, Igor L; Bimberg, Dieter

    2008-05-26

    Measurements of saturated amplified spontaneous emission-spectra of quantum dot semiconductor optical amplifiers demonstrate efficient replenishment of the quantum-dot ground state population from excited states. This saturation behavior is perfectly modeled by a rate equation model. We examined experimentally the dependence of saturation on the drive current and the saturating optical pump power as well as on the pump wavelength. A coherent noise spectral hole is observed with which we assess dynamical properties and propose optimization of the SOA operating parameters for high speed applications.

  7. Photoluminescence limiting of colloidal PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Ullrich, B.; Xi, H.; Wang, J. S.

    2016-02-01

    The exposure of colloidal 2 nm PbS quantum dots to growing continuous wave laser excitation at 532 nm increases the photoluminescence intensity with the square root of the optical stimulus. The results herein in conjunction with previous findings [B. Ullrich and H. Xi, Opt. Lett. 38, 4698 (2013)] advocate the square root trend to be the general limiting function for photo-carrier transport and emission of optically excited nano-sized materials. We further show that the excitation of one electron-hole pair per quantum dot defines the saturation threshold for photoluminescence intensity and dynamic band filling.

  8. Time scales and relaxation dynamics in quantum-dot lasers

    SciTech Connect

    Erneux, Thomas; Viktorov, Evgeny A.; Mandel, Paul

    2007-08-15

    We analyze a three-variable rate equation model that takes into account carrier capture and Pauli blocking in quantum dot semiconductor lasers. The exponential decay of the relaxation oscillations is analyzed from the linearized equations in terms of three key parameters that control the time scales of the laser. Depending on their relative values, we determine two distinct two-variable reductions of the rate equations in the limit of large capture rates. The first case leads to the rate equations for quantum well lasers, exhibiting relaxation oscillations dynamics. The second case corresponds to dots nearly saturated by the carriers and is characterized by the absence of relaxation oscillations.

  9. Quantum dot lasers with controllable spectral and modal characteristics

    NASA Astrophysics Data System (ADS)

    Zhukov, A. E.; Maximov, M. V.; Gordeev, N. Yu; Savelyev, A. V.; Livshits, D. A.; Kovsh, A. R.

    2011-01-01

    Simple analytical expressions for the shape and width of the multi-frequency lasing spectra of quantum dot lasers are derived by using a parabolic approximation of the gain spectrum. A giant nonlinear gain coefficient of 2.5 × 10-15 cm3 was estimated from the experimental dependence of the lasing spectrum width on the output power. A monolithic diffraction optical filter was used to suppress lasing of higher-order transverse modes in a quantum dot laser with a relatively broad ridge waveguide. Stable lasing on a fundamental transverse mode is observed with the maximum continuous wave (CW) single-spatial-mode power of 700 mW.

  10. Nonlinear optical susceptibilities of semiconductor quantum dot - metal nanoparticle hybrids

    NASA Astrophysics Data System (ADS)

    Terzis, A. F.; Kosionis, S. G.; Boviatsis, J.; Paspalakis, E.

    2016-03-01

    We theoretically study nonlinear optical effects of a semiconductor quantum dot and a spherical metal nanoparticle coupled via long-range Coulomb interaction. We solve the relevant density matrix equations in steady state and use proper perturbation theory to obtain closed-form analytical expressions for the nonlinear susceptibilities of the quantum dot, the metal nanoparticle, and the entire coupled system, up to fifth order. We also investigate the influence of the material of the semiconductor and the impact of the interparticle distance on the form of the spectra of the nonlinear susceptibilities.

  11. Quantum-dot based nanothermometry in optical plasmonic recording media

    SciTech Connect

    Maestro, Laura Martinez; Zhang, Qiming; Li, Xiangping; Gu, Min; Jaque, Daniel

    2014-11-03

    We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media.

  12. Quantum dot-embedded microspheres for remote refractive index sensing

    PubMed Central

    Pang, Shuo; Beckham, Richard E.; Meissner, Kenith E.

    2008-01-01

    We present a refractometric sensor based on quantum dot-embedded polystyrene microspheres. Optical resonances within a microsphere, known as whispering-gallery modes (WGMs), produce narrow spectral peaks. For sensing applications, spectral shifts of these peaks are sensitive to changes in the local refractive index. In this work, two-photon excited luminescence from the quantum dots couples into several WGMs within the microresonator. By optimizing the detection area, the spectral visibility of the WGMs is improved. The spectral shifts are measured as the surrounding index of the refraction changes. The experimental sensitivity is about five times greater than that predicted by the Mie theory. PMID:19488403

  13. Engineering band structure in nanoscale quantum-dot supercrystals.

    PubMed

    Baimuratov, Anvar S; Rukhlenko, Ivan D; Fedorov, Anatoly V

    2013-07-01

    Supercrystals made of periodically arranged semiconductor quantum dots (QDs) are promising structures for nanophotonics applications due to almost unlimited degrees of freedom enabling fine tuning of their optical responses. Here we demonstrate broad engineering opportunities associated with the possibility of tailoring the energy bands of excitons in two-dimensional quantum-dot supercrystals through the alteration in the QD arrangement. These opportunities offer an unprecedented control over the optical properties of the supercrystals, which may be used as a versatile material base for advanced photonics devices on the nanoscale.

  14. Proposal for fast optical spin rotations in quantum dots

    NASA Astrophysics Data System (ADS)

    Economou, Sophia E.; Reinecke, T. L.

    2008-04-01

    A proposal for fast optical rotation of the spin of an electron in a quantum dot is presented. Hyperbolic secant pulses of appropriate polarization are employed to induce a relative phase between two spin basis states. This phase is the angle of spin rotation, and the polarization determines the direction of the spin. Varying both allows for the construction of arbitrary rotations. Simulations with typical parameters for InAs self-assembled quantum dots-including dissipative dynamics-show that the fidelity of the operations is at least 99%. The effect of deviation from the ideal pulse shape is also examined.

  15. Polaritons in a nonideal array of ultracold quantum dots

    NASA Astrophysics Data System (ADS)

    Rumyantsev, V. V.; Fedorov, S. A.; Gumennyk, K. V.

    2016-05-01

    We develop a numerical model for a defect-containing square lattice of microcavities with embedded ultracold atomic clusters (quantum dots). It is assumed that certain fractions of quantum dots and cavities are absent, which leads to transformation of polariton spectrum of the overall structure. The dispersion relations for polaritonic modes are derived as functions of defect concentrations and on this basis the band gap, the effective masses of lower and upper dispersion branch polaritons as well as their densities of states are evaluated.

  16. Interactions of quantum dots with donor blood erythrocytes in vitro.

    PubMed

    Pleskova, S N; Pudovkina, E E; Mikheeva, E R; Gorshkova, E N

    2014-01-01

    The effects of quantum dots CdSe/ZnS-mercaptopropionic acid, (CdSe/CdZnS)ZnS-polyT, and CdSeCdSZnS/polyT/SiO2-NH2 on human erythrocytes were studied. The nanomaterials reduced signifi cantly the erythrocyte sedimentation rate and modified the erythrocyte membrane resistance to induced (acid and hypo-osmotic) hemolysis. Evaluation of the erythrocyte morphology by atomic force microscopy in the control and after exposure to quantum dots showed significant differences in erythrocyte size and changes in their morphology as a result of exposure to the nanomaterials.

  17. Ultrafast electron trapping in ligand-exchanged quantum dot assemblies.

    PubMed

    Turk, Michael E; Vora, Patrick M; Fafarman, Aaron T; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R; Kikkawa, James M

    2015-02-24

    We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature optical properties of CdSe quantum dot solids after exchanging native aliphatic ligands for thiocyanate and subsequent thermal annealing. In contrast to trends established at room temperature, our data show that at low temperature the band-edge absorptive bleach is dominated by 1S3/2h hole occupation in the quantum dot interior. We find that our ligand treatments, which bring enhanced interparticle coupling, lead to faster surface state electron trapping, a greater proportion of surface-related photoluminescence, and decreased band-edge photoluminescence lifetimes.

  18. Spin qubit relaxation in a moving quantum dot

    NASA Astrophysics Data System (ADS)

    Huang, Peihao; Hu, Xuedong

    2013-08-01

    Long-range quantum communication for spin qubits is an important open problem. Here we study decoherence of an electron spin qubit that is being transported in a moving quantum dot. We focus on spin decoherence due to spin-orbit interaction and a random electric potential. We find that at the lowest order, the motion induces longitudinal spin relaxation, with a rate linear in the dot velocity. Our calculated spin relaxation time ranges from sub μs in GaAs to above ms in Si, making this relaxation a significant decoherence channel. Our results also give clear indications on how to reduce the decoherence effect of electron motion.

  19. Quantum Dots: Proteomics characterization of the impact on biological systems

    NASA Astrophysics Data System (ADS)

    Pozzi-Mucelli, Stefano; Boschi, F.; Calderan, L.; Sbarbati, A.; Osculati, F.

    2009-05-01

    Over the past few years, Quantum Dots have been tested in most biotechnological applications that use fluorescence, including DNA array technology, immunofluorescence assays, cell and animal biology. Quantum Dots tend to be brighter than conventional dyes, because of the compounded effects of extinction coefficients that are an order of magnitude larger than those of most dyes. Their main advantage resides in their resistance to bleaching over long periods of time (minutes to hours), allowing the acquisition of images that are crisp and well contrasted. This increased photostability is especially useful for three-dimensional (3D) optical sectioning, where a major issue is bleaching of fluorophores during acquisition of successive z-sections, which compromises the correct reconstruction of 3D structures. The long-term stability and brightness of Quantum Dots make them ideal candidates also for live animal targeting and imaging. The vast majority of the papers published to date have shown no relevant effects on cells viability at the concentration used for imaging applications; higher concentrations, however, caused some issues on embryonic development. Adverse effects are due to be caused by the release of cadmium, as surface PEGylation of the Quantum Dots reduces these issues. A recently published paper shows evidences of an epigenetic effect of Quantum Dots treatment, with general histones hypoacetylation, and a translocation to the nucleus of p53. In this study, mice treated with Quantum Dots for imaging purposes were analyzed to investigate the impact on protein expression and networking. Differential mono-and bidimensional electrophoresis assays were performed, with the individuation of differentially expressed proteins after intravenous injection and imaging analysis; further, as several authors indicate an increase in reactive oxygen species as a possible mean of damage due to the Quantum Dots treatment, we investigated the signalling pathway of APE1/Ref1, a

  20. Optical control of the emission direction of a quantum dot

    SciTech Connect

    Luxmoore, I. J.; Wasley, N. A.; Fox, A. M.; Skolnick, M. S.; Ramsay, A. J.; Thijssen, A. C. T.; Oulton, R.; Hugues, M.

    2013-12-09

    Using the helicity of a non-resonant excitation laser, control over the emission direction of an InAs/GaAs quantum dot is demonstrated. The quantum dot is located off-center in a crossed-waveguide structure, such that photons of opposite circular polarization are emitted into opposite waveguide directions. By preferentially exciting spin-polarized excitons, the direction of emission can therefore be controlled. The directional control is quantified by using the ratio of the intensity of the light coupled into the two waveguides, which reaches a maximum of ±35%.