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Sample records for ingaas quantum dot

  1. Uniform InGaAs quantum dot arrays fabricated using nanosphere lithography

    SciTech Connect

    Qian, X.; Li, J.; Wasserman, D.; Goodhue, W. D.

    2008-12-08

    We demonstrate the fabrication of optically active uniform InGaAs quantum dot arrays by combining nanosphere lithography and bromine ion-beam-assisted etching on a single InGaAs/GaAs quantum well. A wide range of lateral dot sizes was achieved from an oxygen plasma nanosphere resizing process. The increased lateral confinement of carriers in the dots results in low temperature photoluminescence blueshifts from 0.5 to 11 meV. Additional quantization was achieved using a selective wet-etch process. Our model suggests the presence of a 70 nm dead layer in the outer InGaAs radial edge, which we believe to be a result of defects and dislocations introduced during the dry-etch process.

  2. Cavity-enhanced single photon emission from site-controlled In(Ga)As quantum dots fabricated using nanoimprint lithography

    SciTech Connect

    Tommila, J.; Hakkarainen, T. V.; Schramm, A. Guina, M.; Belykh, V. V.; Sibeldin, N. N.; Heinonen, E.

    2014-05-26

    We report on the emission dynamics of single In(Ga)As quantum dots formed in etched GaAs pits and integrated into micropillar cavities. The site-controlled quantum dots were fabricated by molecular beam epitaxy on nanoimprint lithography patterned GaAs(001) surfaces. Triggered single photon emission confirmed by photon autocorrelation measurements is demonstrated. Time-resolved photoluminescence experiments clearly show an effect of the cavity on the spontaneous emission rate of the quantum dot.

  3. Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

    NASA Technical Reports Server (NTRS)

    Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

    2003-01-01

    NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

  4. InGaAs quantum dot molecules around self-assembled GaAs nanomound templates

    SciTech Connect

    Lee, J. H.; Wang, Zh. M.; Strom, N. W.; Mazur, Yu. I.; Salamo, G. J.

    2006-11-13

    Several distinctive self-assembled InGaAs quantum dot molecules (QDMs) are studied. The QDMs self-assemble around nanoscale-sized GaAs moundlike templates fabricated by droplet homoepitaxy. Depending on the specific InAs monolayer coverage, the number of QDs per GaAs mound ranges from two to six (bi-QDMs to hexa-QDMs). The Ga contribution from the mounds is analyzed in determining the morphologies of the QDMs, with respect to the InAs coverages ranging between 0.8 and 2.4 ML. Optical characterization shows that the resulting nanostructures are high-quality nanocrystals.

  5. Narrow optical line width from site-controlled InGaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Lily; Yakes, Michael; Sweeney, Timothy; Carter, Samuel; Kim, Chulsoo; Kim, Mijin; Bracker, Allan; Gammon, Daniel

    2013-03-01

    The incorporation of self-assembled quantum dots (QDs) in systematically scalable quantum devices requires a method of nucleating dots with nanometer-scale spatial accuracy while preserving their narrow optical line width. We have developed a technique combining e-beam lithography, wet etching, and molecular beam epitaxial (MBE) growth to deterministically position InGaAs QDs with spectrometer limited photoluminescence line widths. Our technique takes advantage of the anisotropy in GaAs growth to evolve an etched pattern of holes and lines into faceted structures in which dots nucleate. Using this technique, we were able to grow a buffer layer of pure GaAs up to 90 nm in thickness between the processed surface and the dot nucleation surface, effectively separating the QDs from unavoidable residual defects and impurities on the patterned surface that broaden their optical line widths. Additionally, we demonstrate control over the number of dots nucleating per site, from single to a chain of several, by varying the dimensions of the original pattern. Our dots are grown in a Schottky diode structure. Their PL spectrum shows discrete charging transitions, with narrow linewidths near the spectrometer's resolution limit of 20 micro eV.

  6. Imaging surface plasmon polaritons using proximal self-assembled InGaAs quantum dots

    SciTech Connect

    Bracher, Gregor; Schraml, Konrad; Blauth, Mäx; Wierzbowski, Jakob; López, Nicolás Coca; Bichler, Max; Müller, Kai; Finley, Jonathan J.; Kaniber, Michael

    2014-07-21

    We present optical investigations of hybrid plasmonic nanosystems consisting of lithographically defined plasmonic Au-waveguides or beamsplitters on GaAs substrates coupled to proximal self-assembled InGaAs quantum dots. We designed a sample structure that enabled us to precisely tune the distance between quantum dots and the sample surface during nano-fabrication and demonstrated that non-radiative processes do not play a major role for separations down to ∼10 nm. A polarized laser beam focused on one end of the plasmonic nanostructure generates propagating surface plasmon polaritons that, in turn, create electron-hole pairs in the GaAs substrate during propagation. These free carriers are subsequently captured by the quantum dots ∼25 nm below the surface, giving rise to luminescence. The intensity of the spectrally integrated quantum dot luminescence is used to image the propagating plasmon modes. As the waveguide width reduces from 5 μm to 1 μm, we clearly observe different plasmonic modes at the remote waveguide end, enabling their direct imaging in real space. This imaging technique is applied to a plasmonic beamsplitter facilitating the determination of the splitting ratio between the two beamsplitter output ports as the interaction length L{sub i} is varied. A splitting ratio of 50:50 is observed for L{sub i}∼9±1 μm and 1 μm wide waveguides for excitation energies close to the GaAs band edge. Our experimental findings are in good agreement with mode profile and finite difference time domain simulations for both waveguides and beamsplitters.

  7. Defect-Induced Photoluminescence Blinking of Single Epitaxial InGaAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Hu, Fengrui; Cao, Zengle; Zhang, Chunfeng; Wang, Xiaoyong; Xiao, Min

    2015-03-01

    Here we report two types of defect-induced photoluminescence (PL) blinking behaviors observed in single epitaxial InGaAs quantum dots (QDs). In the first type of PL blinking, the ``off'' period is caused by the trapping of hot electrons from the higher-lying excited state (absorption state) to the defect site so that its PL rise lifetime is shorter than that of the ``on'' period. For the ``off'' period in the second type of PL blinking, the electrons relax from the first excited state (emission state) into the defect site, leading to a shortened PL decay lifetime compared to that of the ``on'' period. This defect-induced exciton quenching in epitaxial QDs, previously demonstrated also in colloidal nanocrystals, confirms that these two important semiconductor nanostructures could share the same PL blinking mechanism.

  8. Development of a Quantum Dot, 0.6 eV InGaAs Thermophotovoltaic (TPV) Converter

    NASA Technical Reports Server (NTRS)

    Forbes, David; Sinharoy, Samar; Raffalle, Ryne; Weizer, Victor; Homann, Natalie; Valko, Thomas; Bartos,Nichole; Scheiman, David; Bailey, Sheila

    2007-01-01

    Thermophotovoltaic (TPV) power conversion has to date demonstrated conversion efficiencies exceeding 20% when coupled to a heat source. Current III-V semiconductor TPV technology makes use of planar devices with bandgaps tailored to the heat source. The efficiency can be improved further by increasing the collection efficiency through the incorporation of InAs quantum dots. The use of these dots can provide sub-gap absorption and thus improve the cell short circuit current without the normal increase in dark current associated with lowering the bandgap. We have developed self-assembled InAs quantum dots using the Stranski-Krastanov growth mode on 0.74 eV In0.53GaAs lattice-matched to InP and also on lattice-mismatched 0.6 eV In0.69GaAs grown on InP through the use of a compositionally graded InPAsx buffer structure, by metalorganic vapor phase epitaxy (MOVPE). Atomic force microscopy (AFM) measurements showed that the most reproducible dot pattern was obtained with 5 monolayers of InAs grown at 450 C. The lattice mismatch between InAs and In0.69GaAs is only 2.1%, compared to 3.2% between InAs and In0.53GaAs. The smaller mismatch results in lower strain, making dot formation somewhat more complicated, resulting in quantum dashes, rather than well defined quantum dots in the lattice-mismatched case. We have fabricated 0.6 eV InGaAs planer TPV cells with and without the quantum dashes

  9. Tunable lateral tunnel coupling between two self-assembled InGaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Beirne, Gareth J.; Hermannstädter, Claus; Wang, Lijuan; Rastelli, Armando; Müller, Elisabeth; Schmidt, Oliver G.; Michler, Peter

    2007-02-01

    We demonstrate direct control over the level of lateral quantum coupling between two self-assembled InGaAs/GaAs quantum dots. This coupled system, which we also refer to as a lateral quantum dot molecule, was produced using a unique technique which combines molecular beam epitaxy and in-situ atomic layer etching. Atomic force microscopy measurements show that each molecule consists of two structurally distinct dots, which are aligned along the [1-10] direction. Each molecule exhibits a characteristic photoluminescence spectrum primarily consisting of two neutral excitonic and two biexcitonic transitions. The various transitions have been investigated using micro-photoluminescence measurements as a function of excitation power density, time, and applied electric field. Photon statistics experiments between the excitonic emission lines display strong antibunching in the second-order cross-correlation function which confirms that the two dots are quantum coupled. Cascaded emission between corresponding biexcitonic and excitonic emission has also been observed. Using a parallel electric field we can control the quantum coupling between the dots. This control manifests itself as an ability to reversibly switch the relative intensities of the two neutral excitonic transitions. Furthermore, detailed studies of the emission energies of the two neutral excitonic transitions as a function of parallel lateral electric field show a clear anomalous Stark shift which further demonstrates the presence of quantum coupling between the dots. In addition, this shift allows for a reasonable estimate of the coupling energy. Finally, a simple one-dimensional model, which assumes that the coupling is due to electron tunneling, is used to qualitatively describe the observed effects.

  10. Long-wavelength emission InAs quantum dots grown on InGaAs metamorphic buffers.

    PubMed

    Wu, B P; Wu, D H; Xiong, Y H; Huang, S S; Ni, H Q; Xu, Y Q; Niu, Z C

    2009-02-01

    In this work, InAs quantum dots (QDs) grown on a linear graded InGaAs metamorphic buffer layer by molecular beam epitaxy have been investigated. The growth of the metamorphic buffer layers was carefully optimized, yielding a smooth surface with a minimum root mean square of roughness of less than 0.98 nm as measured by atomic force microscopy (AFM). InAs QDs were then grown on the buffer layers, and their emission wavelength at room-temperature is 1.49 microm as measured by photoluminescence (PL). The effects of post-growth rapid thermal annealing (RTA) on the optical properties of the InAs QDs were investigated. After the RTA, the PL peak of the QDs was blue-shifted and the full width at half maximum decreased.

  11. Controlling Planar and Vertical Ordering in Three-Dimensional (In,Ga)As Quantum Dot Lattices by GaAs Surface Orientation

    SciTech Connect

    Schmidbauer, M.; Seydmohamadi, Sh.; Wang, Zh.M.; Mazur, Yu.I.; Salamo, G.J.; Grigoriev, D.; Schaefer, P.; Koehler, R.; Hanke, M.

    2006-02-17

    Anisotropic surface diffusion and strain are used to explain the formation of three-dimensional (In,Ga)As quantum dot lattices. The diffusion characteristics of the surface, coupled with the elastic anisotropy of the matrix, provides an excellent opportunity to influence the dot positions. In particular, quantum dots that are laterally organized into long chains or chessboard two-dimensional arrays vertically organized with strict vertical ordering or vertical ordering that is inclined to the sample surface normal are accurately predicted and observed.

  12. All-optical tomography of electron spins in (In,Ga)As quantum dots

    NASA Astrophysics Data System (ADS)

    Varwig, S.; René, A.; Economou, Sophia E.; Greilich, A.; Yakovlev, D. R.; Reuter, D.; Wieck, A. D.; Reinecke, T. L.; Bayer, M.

    2014-02-01

    We demonstrate the basic features of an all-optical spin tomography on picosecond time scale. The magnetization vector associated with a mode-locked electron spin ensemble in singly charged quantum dots is traced by ellipticity measurements using picosecond laser pulses. After optical orientation the spins precess about a perpendicular magnetic field. By comparing the dynamics of two interacting ensembles with the dynamics of a single ensemble we find buildup of a spin component along the magnetic field in the two-ensemble case. This component arises from a Heisenberg-like spin-spin interaction.

  13. Spin noise of electrons and holes in (In,Ga)As quantum dots: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Glasenapp, Ph.; Smirnov, D. S.; Greilich, A.; Hackmann, J.; Glazov, M. M.; Anders, F. B.; Bayer, M.

    2016-05-01

    The spin fluctuations of electron and hole doped self-assembled quantum dot ensembles are measured optically in the low-intensity limit of a probe laser for absence and presence of longitudinal or transverse magnetic fields. The experimental results are modeled by two complementary approaches based either on a semiclassical or quantum mechanical description. This allows us to characterize the hyperfine interaction of electron and hole spins with the surrounding bath of nuclei on time scales covering several orders of magnitude. Our results demonstrate (i) the intrinsic precession of the electron spin fluctuations around the effective Overhauser field caused by the host lattice nuclear spins, (ii) the comparably long time scales for electron and hole spin decoherence, as well as (iii) the dramatic enhancement of the spin lifetimes induced by a longitudinal magnetic field due to the decoupling of nuclear and charge carrier spins.

  14. Size dependence of electron spin dephasing in InGaAs quantum dots

    SciTech Connect

    Huang, Y. Q.; Puttisong, Y.; Buyanova, I. A.; Chen, W. M.; Yang, X. J.; Subagyo, A.; Sueoka, K.; Murayama, A.

    2015-03-02

    We investigate ensemble electron spin dephasing in self-assembled InGaAs/GaAs quantum dots (QDs) of different lateral sizes by employing optical Hanle measurements. Using low excitation power, we are able to obtain a spin dephasing time T{sub 2}{sup *} (in the order of ns) of the resident electron after recombination of negative trions in the QDs. We show that T{sub 2}{sup *} is determined by the hyperfine field arising from the frozen fluctuation of nuclear spins, which scales with the size of QDs following the Merkulov-Efros-Rosen model. This scaling no longer holds in large QDs, most likely due to a breakdown in the lateral electron confinement.

  15. Ultrafast spin tunneling and injection in coupled nanostructures of InGaAs quantum dots and quantum well

    SciTech Connect

    Yang, Xiao-Jie Kiba, Takayuki; Yamamura, Takafumi; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro

    2014-01-06

    We investigate the electron-spin injection dynamics via tunneling from an In{sub 0.1}Ga{sub 0.9}As quantum well (QW) to In{sub 0.5}Ga{sub 0.5}As quantum dots (QDs) in coupled QW-QDs nanostructures. These coupled nanostructures demonstrate ultrafast (5 to 20 ps) spin injection into the QDs. The degree of spin polarization up to 45% is obtained in the QDs after the injection, essentially depending on the injection time. The spin injection and conservation are enhanced with thinner barriers due to the stronger electronic coupling between the QW and QDs.

  16. Carrier relaxation in (In,Ga)As quantum dots with magnetic field-induced anharmonic level structure

    NASA Astrophysics Data System (ADS)

    Kurtze, H.; Bayer, M.

    2016-07-01

    Sophisticated models have been worked out to explain the fast relaxation of carriers into quantum dot ground states after non-resonant excitation, overcoming the originally proposed phonon bottleneck. We apply a magnetic field along the quantum dot heterostructure growth direction to transform the confined level structure, which can be approximated by a Fock-Darwin spectrum, from a nearly equidistant level spacing at zero field to strong anharmonicity in finite fields. This changeover leaves the ground state carrier population rise time unchanged suggesting that fast relaxation is maintained upon considerable changes of the level spacing. This corroborates recent models explaining the relaxation by polaron formation in combination with quantum kinetic effects.

  17. Polarization fine structure and enhanced single-photon emission of self-assembled lateral InGaAs quantum dot molecules embedded in a planar microcavity

    NASA Astrophysics Data System (ADS)

    Hermannstädter, C.; Witzany, M.; Beirne, G. J.; Schulz, W.-M.; Eichfelder, M.; Rossbach, R.; Jetter, M.; Michler, P.; Wang, L.; Rastelli, A.; Schmidt, O. G.

    2009-06-01

    Single lateral InGaAs quantum dot molecules have been embedded in a planar microcavity in order to increase the luminescence extraction efficiency. Using a combination of metal-organic vapor phase and molecular beam epitaxy samples could be produced that exhibit a 30 times enhanced single-photon emission rate. We also show that the single-photon emission is fully switchable between two different molecular excitonic recombination energies by applying a lateral electric field. Furthermore, the presence of a polarization fine structure splitting of the molecular neutral excitonic states is reported which leads to two polarization split classically correlated biexciton-exciton cascades. The fine structure splitting is found to be on the order of 10 μeV.

  18. High net modal gain (>100 cm(-1)) in 19-stacked InGaAs quantum dot laser diodes at 1000 nm wavelength band.

    PubMed

    Tanoue, Fumihiko; Sugawara, Hiroharu; Akahane, Kouichi; Yamamoto, Naokatsu

    2013-07-01

    An InGaAs quantum dot (QD) laser diode with 19-stacked QDs separated by 20 nm-thick GaAs spacers was fabricated using an ultrahigh-rate molecular beam epitaxial growth technique, and the laser characteristics were evaluated. A 19-stacked simple broad area QD laser diode was lased at the 1000 nm waveband. A net modal gain of 103 cm(-1) was obtained at 2.25 kA/cm(2), and the saturated modal gain was 145.6 cm(-1); these are the highest values obtained to our knowledge. These results indicate that using this technique to highly stack QDs is effective for improving the net modal gain of QD lasers.

  19. Indistinguishable tunable single photons emitted by spin-flip Raman transitions in InGaAs quantum dots.

    PubMed

    He, Yu; He, Yu-Ming; Wei, Y-J; Jiang, X; Chen, M-C; Xiong, F-L; Zhao, Y; Schneider, Christian; Kamp, Martin; Höfling, Sven; Lu, Chao-Yang; Pan, Jian-Wei

    2013-12-01

    This Letter reports all-optically tunable and highly indistinguishable single Raman photons from a driven single quantum dot spin. The frequency, linewidth, and lifetime of the Raman photons are tunable by varying the driving field power and detuning. Under continuous-wave excitation, subnatural linewidth single photons from off-resonant Raman scattering show an indistinguishability of 0.98(3). Under π pulse excitation, spin- and time-tagged Raman fluorescence photons show an almost vanishing multiphoton emission probability of 0.01(2) and a two-photon quantum interference visibility of 0.95(3). Lastly, Hong-Ou-Mandel interference is demonstrated between two single photons emitted from remote, independent quantum dots with an unprecedented visibility of 0.87(4). PMID:24476302

  20. Hybrid InGaAs quantum well-dots nanostructures for light-emitting and photo-voltaic applications.

    PubMed

    Mintairov, S A; Kalyuzhnyy, N A; Lantratov, V M; Maximov, M V; Nadtochiy, A M; Rouvimov, Sergei; Zhukov, A E

    2015-09-25

    Hybrid quantum well-dots (QWD) nanostructures have been formed by deposition of 7-10 monolayers of In0.4Ga0.6As on a vicinal GaAs surface using metal-organic chemical vapor deposition. Transmission electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9-1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm(-2) for the terrestrial spectrum and by 4.1 mA cm(-2) for the space spectrum. Diode lasers based on QWD emitting around 1.1 μm revealed high saturated gain and low transparency current density of about 15 cm(-1) and 37 A cm(-2) per layer, respectively.

  1. Hybrid InGaAs quantum well-dots nanostructures for light-emitting and photo-voltaic applications

    NASA Astrophysics Data System (ADS)

    Mintairov, S. A.; Kalyuzhnyy, N. A.; Lantratov, V. M.; Maximov, M. V.; Nadtochiy, A. M.; Rouvimov, Sergei; Zhukov, A. E.

    2015-09-01

    Hybrid quantum well-dots (QWD) nanostructures have been formed by deposition of 7-10 monolayers of In0.4Ga0.6As on a vicinal GaAs surface using metal-organic chemical vapor deposition. Transmission electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9-1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm-2 for the terrestrial spectrum and by 4.1 mA cm-2 for the space spectrum. Diode lasers based on QWD emitting around 1.1 μm revealed high saturated gain and low transparency current density of about 15 cm-1 and 37 A cm-2 per layer, respectively.

  2. Growth-temperature dependence of optical spin-injection dynamics in self-assembled InGaAs quantum dots

    SciTech Connect

    Yamamura, Takafumi; Kiba, Takayuki; Yang, Xiaojie; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro

    2014-09-07

    The growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In{sub 0.5}Ga{sub 0.5}As was studied by increasing the sheet density of the dots from 2 × 10{sup 10} to 7 × 10{sup 10} cm{sup −2} and reducing their size through a decrease in growth temperature from 500 to 470 °C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases.

  3. Formation of quantum dots in the potential fluctuations of InGaAs heterostructures probed by scanning gate microscopy

    NASA Astrophysics Data System (ADS)

    Liu, P.; Martins, F.; Hackens, B.; Desplanque, L.; Wallart, X.; Pala, M. G.; Huant, S.; Bayot, V.; Sellier, H.

    2015-02-01

    The disordered potential landscape in an InGaAs/InAlAs two-dimensional electron gas patterned into narrow wires is investigated by means of scanning gate microscopy. It is found that scanning a negatively charged tip above particular sites of the wires produces conductance oscillations that are periodic in the tip voltage. These oscillations take the shape of concentric circles whose number and diameter increase for more negative tip voltages until full depletion occurs in the probed region. These observations cannot be explained by charging events in material traps, but are consistent with Coulomb blockade in quantum dots forming when the potential fluctuations are raised locally at the Fermi level by the gating action of the tip. This interpretation is supported by simple electrostatic simulations in the case of a disorder potential induced by ionized dopants. This work represents a local investigation of the mechanisms responsible for the disorder-induced metal-to-insulator transition observed in macroscopic two-dimensional electron systems at low enough density.

  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. Initial stages of chain formation in a single layer of (In,Ga)As quantum dots grown on GaAs (100)

    SciTech Connect

    Schmidbauer, M.; Wang, Zh. M.; Mazur, Yu. I.; Lytvyn, P. M.; Salamo, G. J.; Grigoriev, D.; Schaefer, P.; Koehler, R.; Hanke, M.

    2007-08-27

    The self-organized formation of In{sub 0.40}Ga{sub 0.60}As quantum dot chains was investigated using x-ray scattering. Two samples were compared grown on GaAs(100) by molecular beam epitaxy. The first sample with a single layer of In{sub 0.40}Ga{sub 0.60}As dots shows weak quantum dot alignment and a corresponding elongated shape along [011], while the top layer of a multilayered In{sub 0.40}Ga{sub 0.60}As/GaAs sample exhibits extended and highly regular quantum dot chains oriented along [011]. Numerical calculations of the three-dimensional strain fields are used to explain the initial stages of chain formation by anisotropic strain relaxation induced by the elongated dot shape.

  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. Impact of ex situ rapid thermal annealing on magneto-optical properties and oscillator strength of In(Ga)As quantum dots

    NASA Astrophysics Data System (ADS)

    Braun, T.; Betzold, S.; Lundt, N.; Kamp, M.; Höfling, S.; Schneider, C.

    2016-04-01

    We discuss the influence of a rapid thermal annealing step on the magneto-optical emission properties of In(Ga)As/GaAs quantum dots. We map out a strong influence of the growth and annealing parameters on the excitons' effective Landé g factors and in particular on their diamagnetic coefficients, which we directly correlate with the modification of the emitters' shape and material composition. In addition, we study the excitons' spontaneous emission lifetime as a function of the annealing temperature and the dot height and observe a strong increase of the emission rate with the quantum dot volume. The corresponding increase in oscillator strength yields fully consistent results with the analysis of the diamagnetic behavior. Specifically, we demonstrate that a rapid thermal annealing step of 850 ∘C can be employed to increase the oscillator strength of as-grown InAs/GaAs QDs by more than a factor of 2.

  8. 15 Gb/s index-coupled distributed-feedback lasers based on 1.3 μm InGaAs quantum dots

    SciTech Connect

    Stubenrauch, M. Stracke, G.; Arsenijević, D.; Bimberg, D.; Strittmatter, A.

    2014-07-07

    The static properties and large-signal modulation capabilities of directly modulated p-doped quantum-dot distributed-feedback lasers are presented. Based on pure index gratings the devices exhibit a side-mode-suppression ratio of 58 dB and optical output powers up to 34 mW. Assisted by a broad gain spectrum, which is typical for quantum-dot material, emission wavelengths from 1290 nm to 1310 nm are covered by the transversal and longitudinal single-mode lasers fabricated from the same single wafer. Thus, these lasers are ideal devices for on-chip wavelength division multiplexing within the original-band according to the IEEE802.3ba standard. 10 Gb/s data transmission across 30 km of single mode fiber is demonstrated. The maximum error-free data rate is found to be 15 Gb/s.

  9. Two-dimensional ordering of (In,Ga)As quantum dots in vertical multilayers grown on GaAs(100) and (n11)

    SciTech Connect

    Lytvyn, P. M.; Strelchuk, V. V.; Kolomys, O. F.; Prokopenko, I. V.; Valakh, M. Ya.; Mazur, Yu. I.; Wang, Zh. M.; Salamo, G. J.; Hanke, M.

    2007-10-22

    We have investigated lateral self-assembling in In{sub 0.4}Ga{sub 0.6}As/GaAs quantum dot (QD) multilayers, which were grown by molecular beam epitaxy on GaAs(100) and (n11)B substrates with n=9,8,7,5,4,3. The lateral self-assembling and the QD size distribution have been studied by atomic force microscopy depending on substrate orientation and the number of periods within the multilayers. The observed two-dimensional ordering can be described by a centered rectangular surface unit cell. Derived autocorrelation functions exhibit the most pronounced lateral QD assembling along the elastically soft directions [1n0]. This can be attributed to elastic interaction, the particular elastic anisotropy of the high index substrates, and the minimization of the strain energy.

  10. Screening nuclear field fluctuations to generate highly indistinguishable photons from negatively charged self-assembled InGaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Malein, Ralph; Santana, Ted; Zajac, Joanna; Petroff, Pierre; Gerardot, Brian

    2015-03-01

    Quantum dots (QDs) can generate highly coherent and indistinguishable single photons. However, a ground-state electron spin interacts with a QD's nuclear spins to create an effective Overhauser field (δBn) of ~30mT. We probe this interaction using resonance fluorescence. We observe the effect of δBn in high resolution (27 MHz) spectroscopy of the elastic and inelastic scattered photons, and characterize the effect of δBn on photon indistinguishability by monitoring the visibility of two-photon interference. With no external magnetic field (Bz = 0), δBn effectively splits the ground state, and at low Rabi frequencies we observe two broad (Γ = 200 MHz) peaks equally spaced by ~100MHz from the central elastic peak. The ratio of elastic to inelastic photons in the spectra gives a dephasing time T2 = 0 . 52T1 = 406 ps, far from the transform limit. With an external field Bz > δBn , we can successfully screen the fluctuating nuclear field. For Bz = 300 mT, nearly all photons in the spectrum are elastically scattered and we extract T2 = 1 . 94T1 = 1512 ps. This transform limited linewidth enables us to demonstrate very high visibility two-photon interference. These results point towards robust generation of indistinguishable photons.

  11. 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.

  12. Gallium arsenide-based long-wavelength quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Park, Gyoungwon

    2001-09-01

    GaAs-based long-wavelength quantum dot lasers have long been studied for applications to optical interconnects. The zero-dimensional confinement potential of quantum dots opens possibility of novel devices. Also, the quantum dot itself shows very interesting characteristics. This dissertation describes the development of GaAs-based 1.3 μm quantum dot lasers and the research on the unique characteristics of quantum dot ensemble. InGaAs quantum dots grown using molecular beam epitaxy in submonolayer deposition have extended wavelength around 1.3 μm and well resolved energy levels that can be described by three-dimensional harmonic oscillator model assuming parabolic confining potential. Lasing transitions from various InGaAs quantum dot energy levels are obtained from edge-emitting lasers. With optimized quantum dot active region and device structure, continuous-wave, room-temperature lasing operation around 1.3 μm is achieved with very low threshold current. Lateral confinement of carriers and photons in the cavity with AlxO y using wet-oxidation technique results in low waveguide loss, which lowers the threshold further. InGaAs quantum dot lasers have almost temperature- insensitive lasing threshold below ~200 K with very low threshold current density close to transparency current density. The rapid increase of threshold current along with temperature above ~200 K is due to thermal excitation of carriers into the higher energy levels and increase of non-radiative recombination. Quasi- equilibrium model for carrier dynamics shows that the optical gain of quantum dot ensemble is strongly temperature dependent, and that the separation between quantum dot energy levels plays an important role in the temperature dependence of the device characteristics. Several predictions of the model are compared with the experimental results. Lasing operation with less temperature-sensitivity is achieved from InAs quantum dot lasers with increased level separation.

  13. 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. PMID:27030886

  14. 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.

  15. 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.

  16. 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.

  17. Annealing-induced change in quantum dot chain formation mechanism

    NASA Astrophysics Data System (ADS)

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-01

    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.

  18. 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.

  19. Growing High-Quality InAs Quantum Dots for Infrared Lasers

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Uhl, David

    2004-01-01

    An improved method of growing high-quality InAs quantum dots embedded in lattice-matched InGaAs quantum wells on InP substrates has been developed. InAs/InGaAs/InP quantum dot semiconductor lasers fabricated by this method are capable of operating at room temperature at wavelengths greater than or equal to 1.8 mm. Previously, InAs quantum dot lasers based on InP substrates have been reported only at low temperature of 77 K at a wavelength of 1.9 micrometers. In the present method, as in the prior method, one utilizes metalorganic vapor phase epitaxy to grow the aforementioned semiconductor structures. The development of the present method was prompted in part by the observation that when InAs quantum dots are deposited on an InGaAs layer, some of the InAs in the InGaAs layer becomes segregated from the layer and contributes to the formation of the InAs quantum dots. As a result, the quantum dots become highly nonuniform; some even exceed a critical thickness, beyond which they relax. In the present method, one covers the InGaAs layer with a thin layer of GaAs before depositing the InAs quantum dots. The purpose and effect of this thin GaAs layer is to suppress the segregation of InAs from the InGaAs layer, thereby enabling the InAs quantum dots to become nearly uniform (see figure). Devices fabricated by this method have shown near-room-temperature performance.

  20. 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

  1. Photoconductivity of Er-doped InAs quantum dots embedded in strain-relaxed InGaAs layers with 1.5 µm cw and pulse excitation

    NASA Astrophysics Data System (ADS)

    Murakumo, Keisuke; Yamaoka, Yuya; Kumagai, Naoto; Kitada, Takahiro; Isu, Toshiro

    2016-04-01

    We fabricated a photoconductive antenna structure utilizing Er-doped InAs quantum dot layers embedded in strain-relaxed In0.35Ga0.65As layers on a GaAs substrate. Mesa-shaped electrodes for the antenna structure were formed by photolithography and wet etching in order to suppress its dark current. We measured the photocurrent with the excitation of ∼1.5 µm cw and femtosecond pulse lasers. Compared with the dark current, the photocurrent was clearly observed under both cw and pulse excitation conditions and almost linearly increased with increasing excitation power in a wide range of magnitudes from 10 W/cm2 to 10 MW/cm2 order.

  2. 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

  3. Self-assembling of In(Ga)As/GaAs quantum dots on (N11) substrates: the (311)A case

    PubMed

    Sanguinetti; Chiantoni; Miotto; Grilli; Guzzi; Henini; Polimeni; Patane; Eaves; Main

    2000-06-01

    We have investigated the In(Ga)As island formation, in the Stranski-Krastanov growth mode, on (311)A GaAs substrates. The surface topography of InAs and InGaAs strained epilayers was studied by contact microscopies. The different substrate affects the overgrown island shape. In(Ga)As grown on (311)A gives rise to quantum wire-like islands. Quantum dots (QDs), but with highly anisotropic shapes, are the outcomes of InAs deposition. QD samples were also characterized by photoluminescence (PL) measurements. Correlation between optical and morphological properties was observed.

  4. Quantum Dots as Cellular Probes

    SciTech Connect

    Alivisatos, A. Paul; Gu, Weiwei; Larabell, Carolyn

    2004-09-16

    Robust and bright light emitters, semiconductor nanocrystals[quantum dots (QDs)] have been adopted as a new class of fluorescent labels. Six years after the first experiments of their uses in biological applications, there have been dramatic improvements in understanding surface chemistry, biocompatibility, and targeting specificity. Many studies have shown the great potential of using quantum dots as new probes in vitro and in vivo. This review summarizes the recent advances of quantum dot usage at the cellular level, including immunolabeling, cell tracking, in situ hybridization, FRET, in vivo imaging, and other related technologies. Limitations and potential future uses of quantum dot probes are also discussed.

  5. Self-assembly drives quantum dot photoluminescence.

    PubMed

    Plain, J; Sonnefraud, Y; Viste, P; Lérondel, G; Huant, S; Royer, P

    2009-03-01

    Engineering the spectral properties of quantum dots can be achieved by a control of the quantum dots organization on a substrate. Indeed, many applications of quantum dots as LEDs are based on the realization of a 3D architecture of quantum dots. In this contribution, we present a systematic study of the quantum dot organization obtained on different chemically modified substrates. By varying the chemical affinity between the quantum dots and the substrate, the quantum dot organization is strongly modified from the 2D monolayer to the 3D aggregates. Then the photoluminescence of the different obtained samples has been systematically studied and correlated with the quantum dot film organization. We clearly show that the interaction between the substrate and the quantum dot must be stronger than the quantum dot-quantum dot interaction to avoid 3D aggregation and that these organization strongly modified the photoluminescence of the film rather than intrinsic changes of the quantum dot induced by pure surface chemistry.

  6. Quantum dot cascade laser

    PubMed Central

    2014-01-01

    We demonstrated an unambiguous quantum dot cascade laser based on InGaAs/GaAs/InAs/InAlAs heterostructure by making use of self-assembled quantum dots in the Stranski-Krastanow growth mode and two-step strain compensation active region design. The prototype generates stimulated emission at λ ~ 6.15 μm and a broad electroluminescence band with full width at half maximum over 3 μm. The characteristic temperature for the threshold current density within the temperature range of 82 to 162 K is up to 400 K. Moreover, our materials show the strong perpendicular mid-infrared response at about 1,900 cm-1. These results are very promising for extending the present laser concept to terahertz quantum cascade laser, which would lead to room temperature operation. PACS 42.55.Px; 78.55.Cr; 78.67.Hc PMID:24666965

  7. Quantum dots: Rethinking the electronics

    NASA Astrophysics Data System (ADS)

    Bishnoi, Dimple

    2016-05-01

    In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including "waste heat" from the sun's energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate band setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.

  8. Quantum light emission of two lateral tunnel-coupled (In,Ga)As/GaAs quantum dots controlled by a tunable static electric field.

    PubMed

    Beirne, G J; Hermannstädter, C; Wang, L; Rastelli, A; Schmidt, O G; Michler, P

    2006-04-01

    Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage. PMID:16712031

  9. Quantum Light Emission of Two Lateral Tunnel-Coupled (In,Ga)As/GaAs Quantum Dots Controlled by a Tunable Static Electric Field

    NASA Astrophysics Data System (ADS)

    Beirne, G. J.; Hermannstädter, C.; Wang, L.; Rastelli, A.; Schmidt, O. G.; Michler, P.

    2006-04-01

    Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage.

  10. Quantum Dots in Cell Biology

    PubMed Central

    Barroso, Margarida M.

    2011-01-01

    Quantum dots are semiconductor nanocrystals that have broad excitation spectra, narrow emission spectra, tunable emission peaks, long fluorescence lifetimes, negligible photobleaching, and ability to be conjugated to proteins, making them excellent probes for bioimaging applications. Here the author reviews the advantages and disadvantages of using quantum dots in bioimaging applications, such as single-particle tracking and fluorescence resonance energy transfer, to study receptor-mediated transport. PMID:21378278

  11. Lateral Quantum Dots for Quantum Information Processing

    NASA Astrophysics Data System (ADS)

    House, Matthew Gregory

    The possibility of building a computer that takes advantage of the most subtle nature of quantum physics has been driving a lot of research in atomic and solid state physics for some time. It is still not clear what physical system or systems can be used for this purpose. One possibility that has been attracting significant attention from researchers is to use the spin state of an electron confined in a semiconductor quantum dot. The electron spin is magnetic in nature, so it naturally is well isolated from electrical fluctuations that can a loss of quantum coherence. It can also be manipulated electrically, by taking advantage of the exchange interaction. In this work we describe several experiments we have done to study the electron spin properties of lateral quantum dots. We have developed lateral quantum dot devices based on the silicon metal-oxide-semiconductor transistor, and studied the physics of electrons confined in these quantum dots. We measured the electron spin excited state lifetime, which was found to be as long as 30 ms at the lowest magnetic fields that we could measure. We fabricated and characterized a silicon double quantum dot. Using this double quantum dot design, we fabricated devices which combined a silicon double quantum dot with a superconducting microwave resonator. The microwave resonator was found to be sensitive to two-dimensional electrons in the transistor channel, which we measured and characterized. We developed a new method for extracting information from random telegraph signals, which are produced when we observe thermal fluctuations of electrons in quantum dots. The new statistical method, based on the hidden Markov model, allows us to detect spin-dependent effects in such fluctuations even though we are not able to directly observe the electron spin. We use this analysis technique on data from two experiments involving gallium arsenide quantum dots and use it to measure spin-dependent tunneling rates. Our results advance the

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

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    stark shift, coherent coupling of electronic states in a quantum dot molecule etc.; (3) to assess the potential use of the quantum dots in real device implementation and to provide physical insight to the experimentalists. Full three dimensional strain and electronic structure simulations of quantum dot structures containing multi-million atoms are done using NEMO 3-D. Both single and vertically stacked quantum dot structures are analyzed in detail. The results show that the strain and the piezoelectricity significantly impact the electronic structure of these devices. This work shows that the InAs quantum dots when placed in the InGaAs quantum well red shifts the emission wavelength. Such InAs/GaAs-based optical devices can be used for optical-fiber based communication systems at longer wavelengths (1.3um -- 1.5um). Our atomistic simulations of InAs/InGaAs/GaAs quantum dots quantitatively match with the experiment and give the critical insight of the physics involved in these structures. A single quantum dot molecule is studied for coherent quantum coupling of electronic states under the influence of static electric field applied in the growth direction. Such nanostructures can be used in the implementation of quantum information technologies. A close quantitative match with the experimental optical measurements allowed us to get a physical insight into the complex physics of quantum tunnel couplings of electronic states as the device operation switches between atomic and molecular regimes. Another important aspect is to design the quantum dots for a desired isotropic polarization of the optical emissions. Both single and coupled quantum dots are studied for TE/TM ratio engineering. The atomistic study provides a detailed physical analysis of these computationally expensive large nanostructures and serves as a guide for the experimentalists for the design of the polarization independent devices for the optical communication systems.

  13. Mesoscopic cavity quantum electrodynamics with quantum dots

    SciTech Connect

    Childress, L.; Soerensen, A.S.; Lukin, M.D.

    2004-04-01

    We describe an electrodynamic mechanism for coherent, quantum-mechanical coupling between spatially separated quantum dots on a microchip. The technique is based on capacitive interactions between the electron charge and a superconducting transmission line resonator, and is closely related to atomic cavity quantum electrodynamics. We investigate several potential applications of this technique which have varying degrees of complexity. In particular, we demonstrate that this mechanism allows design and investigation of an on-chip double-dot microscopic maser. Moreover, the interaction may be extended to couple spatially separated electron-spin states while only virtually populating fast-decaying superpositions of charge states. This represents an effective, controllable long-range interaction, which may facilitate implementation of quantum information processing with electron-spin qubits and potentially allow coupling to other quantum systems such as atomic or superconducting qubits.

  14. 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

  15. Optically pumped semiconductor quantum dot disk laser operating at 1180 nm.

    PubMed

    Rautiainen, Jussi; Krestnikov, Igor; Butkus, Mantas; Rafailov, Edik U; Okhotnikov, Oleg G

    2010-03-01

    We demonstrate an optically pumped semiconductor disk laser using 39 layers of Stranski-Krastanov InGaAs quantum dots self-assembled during epitaxial growth on a monolithic GaAs/AlAs distributed Bragg reflector. The gain structure bonded to an intracavity diamond crystal heat spreader allows 1.75 W single-transverse-mode output (M(2)<1.2) with circular beam shape operating at 1180 nm in a disk laser geometry.

  16. Impact of nanomechanical resonances on lasing from electrically pumped quantum dot micropillars

    SciTech Connect

    Czerniuk, T. Tepper, J.; Akimov, A. V.; Unsleber, S.; Schneider, C.; Kamp, M.; Höfling, S.; Yakovlev, D. R.; Bayer, M.

    2015-01-26

    We use a picosecond acoustics technique to modulate the laser output of electrically pumped GaAs/AlAs micropillar lasers with InGaAs quantum dots. The modulation of the emission wavelength takes place on the frequencies of the nanomechanical extensional and breathing (radial) modes of the micropillars. The amplitude of the modulation for various nanomechanical modes is different for every micropillar which is explained by a various elastic contact between the micropillar walls and polymer environment.

  17. Nanoscale and Single-Dot Patterning of Colloidal Quantum Dots.

    PubMed

    Xie, Weiqiang; Gomes, Raquel; Aubert, Tangi; Bisschop, Suzanne; Zhu, Yunpeng; Hens, Zeger; Brainis, Edouard; Van Thourhout, Dries

    2015-11-11

    Using an optimized lift-off process we develop a technique for both nanoscale and single-dot patterning of colloidal quantum dot films, demonstrating feature sizes down to ~30 nm for uniform films and a yield of 40% for single-dot positioning, which is in good agreement with a newly developed theoretical model. While first of all presenting a unique tool for studying physics of single quantum dots, the process also provides a pathway toward practical quantum dot-based optoelectronic devices.

  18. Quantum Dots for Molecular Pathology

    PubMed Central

    True, Lawrence D.; Gao, Xiaohu

    2007-01-01

    Assessing malignant tumors for expression of multiple biomarkers provides data that are critical for patient management. Quantum dot-conjugated probes to specific biomarkers are powerful tools that can be applied in a multiplex manner to single tissue sections of biopsies to measure expression levels of multiple biomarkers. PMID:17251330

  19. Vertical asymmetric double quantum dots

    NASA Astrophysics Data System (ADS)

    Roßbach, R.; Reischle, M.; Beirne, G. J.; Schweizer, H.; Jetter, M.; Michler, P.

    2007-01-01

    Two layers of differently sized self-assembled InP-quantum dots (QDs) separated by a GaInP spacer layer with varying thickness were grown by metal organic vapor phase epitaxy (MOVPE). Photoluminescence measurements of the QD ensembles and of individual asymmetric double QDS show coupling due to the tunnelling of carriers.

  20. 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.

  1. 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

  2. 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

  3. Carrier capture dynamics of single InGaAs/GaAs quantum-dot layers

    SciTech Connect

    Chauhan, K. N.; Riffe, D. M.; Everett, E. A.; Kim, D. J.; Yang, H.; Shen, F. K.

    2013-05-28

    Using 800 nm, 25-fs pulses from a mode locked Ti:Al{sub 2}O{sub 3} laser, we have measured the ultrafast optical reflectivity of MBE-grown, single-layer In{sub 0.4}Ga{sub 0.6}As/GaAs quantum-dot (QD) samples. The QDs are formed via two-stage Stranski-Krastanov growth: following initial InGaAs deposition at a relatively low temperature, self assembly of the QDs occurs during a subsequent higher temperature anneal. The capture times for free carriers excited in the surrounding GaAs (barrier layer) are as short as 140 fs, indicating capture efficiencies for the InGaAs quantum layer approaching 1. The capture rates are positively correlated with initial InGaAs thickness and annealing temperature. With increasing excited carrier density, the capture rate decreases; this slowing of the dynamics is attributed to Pauli state blocking within the InGaAs quantum layer.

  4. Calculation of metamorphic two-dimensional quantum energy system: Application to wetting layer states in InAs/InGaAs metamorphic quantum dot nanostructures

    SciTech Connect

    Seravalli, L.; Trevisi, G.; Frigeri, P.

    2013-11-14

    In this work, we calculate the two-dimensional quantum energy system of the In(Ga)As wetting layer that arises in InAs/InGaAs/GaAs metamorphic quantum dot structures. Model calculations were carried on the basis of realistic material parameters taking in consideration their dependence on the strain relaxation of the metamorphic buffer; results of the calculations were validated against available literature data. Model results confirmed previous hypothesis on the extrinsic nature of the disappearance of wetting layer emission in metamorphic structures with high In composition. We also show how, by adjusting InGaAs metamorphic buffer parameters, it could be possible: (i) to spatially separate carriers confined in quantum dots from wetting layer carriers, (ii) to create an hybrid 0D-2D system, by tuning quantum dot and wetting layer levels. These results are interesting not only for the engineering of quantum dot structures but also for other applications of metamorphic structures, as the two design parameters of the metamorphic InGaAs buffer (thickness and composition) provide additional degrees of freedom to control properties of interest.

  5. Thermoelectric energy harvesting with quantum dots.

    PubMed

    Sothmann, Björn; Sánchez, Rafael; Jordan, Andrew N

    2015-01-21

    We review recent theoretical work on thermoelectric energy harvesting in multi-terminal quantum-dot setups. We first discuss several examples of nanoscale heat engines based on Coulomb-coupled conductors. In particular, we focus on quantum dots in the Coulomb-blockade regime, chaotic cavities and resonant tunneling through quantum dots and wells. We then turn toward quantum-dot heat engines that are driven by bosonic degrees of freedom such as phonons, magnons and microwave photons. These systems provide interesting connections to spin caloritronics and circuit quantum electrodynamics.

  6. Polariton condensation in a strain-compensated planar microcavity with InGaAs quantum wells

    SciTech Connect

    Cilibrizzi, Pasquale; Askitopoulos, Alexis Silva, Matteo; Lagoudakis, Pavlos G.; Bastiman, Faebian; Clarke, Edmund; Zajac, Joanna M.; Langbein, Wolfgang

    2014-11-10

    The investigation of intrinsic interactions in polariton condensates is currently limited by the photonic disorder of semiconductor microcavity structures. Here, we use a strain compensated planar GaAs/AlAs{sub 0.98}P{sub 0.02} microcavity with embedded InGaAs quantum wells having a reduced cross-hatch disorder to overcome this issue. Using real and reciprocal space spectroscopic imaging under non-resonant optical excitation, we observe polariton condensation and a second threshold marking the onset of photon lasing, i.e., the transition from the strong to the weak-coupling regime. Condensation in a structure with suppressed photonic disorder is a necessary step towards the implementation of periodic lattices of interacting condensates, providing a platform for on chip quantum simulations.

  7. Temperature dependent photoluminescence and micromapping of multiple stacks InAs quantum dots

    SciTech Connect

    Xu, Ming Jaffré, Alexandre Alvarez, José Kleider, Jean-Paul Boutchich, Mohamed; Jittrong, Apichat; Chokamnuai, Thitipong; Panyakeow, Somsak; Kanjanachuchai, Songphol

    2015-02-27

    We utilized temperature dependent photoluminescence (PL) techniques to investigate 1, 3 and 5 stack InGaAs quantum dots (QDs) grown on cross-hatch patterns. PL mapping can well reproduce the QDs distribution as AFM and position dependency of QD growth. It is possible to observe crystallographic dependent PL. The temperature dependent spectra exhibit the QDs energy distribution which reflects the size and shape. The inter-dot carrier coupling effect is observed and translated as a red shift of 120mV on the [1–10] direction peak is observed at 30K on 1 stack with regards to 3 stacks samples, which is assigned to lateral coupling.

  8. Quantum Dot Light Emitting Diode

    SciTech Connect

    Kahen, Keith

    2008-07-31

    The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, and environmental stability between that of LEDs and OLEDs. At the end of the project the Recipient shall gain an understanding of the device physics and properties of Quantum-Dot LEDs (QD-LEDs), have reliable and accurate nanocrystal synthesis routines, and have formed green-yellow emitting QD-LEDs with a device efficiency greater than 3 lumens/W, a brightness greater than 400 cd/m{sup 2}, and a device operational lifetime of more than 1000 hours. Thus the aim of the project is to break the current cost-efficiency paradigm by creating novel low cost inorganic LEDs composed of inorganic nanoparticles.

  9. Quantum Dot Light Emitting Diode

    SciTech Connect

    Keith Kahen

    2008-07-31

    The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, and environmental stability between that of LEDs and OLEDs. At the end of the project the Recipient shall gain an understanding of the device physics and properties of Quantum-Dot LEDs (QD-LEDs), have reliable and accurate nanocrystal synthesis routines, and have formed green-yellow emitting QD-LEDs with a device efficiency greater than 3 lumens/W, a brightness greater than 400 cd/m2, and a device operational lifetime of more than 1000 hours. Thus the aim of the project is to break the current cost-efficiency paradigm by creating novel low cost inorganic LEDs composed of inorganic nanoparticles.

  10. Detailed Study of the Influence of InGaAs Matrix on the Strain Reduction in the InAs Dot-In-Well Structure.

    PubMed

    Wang, Peng; Chen, Qimiao; Wu, Xiaoyan; Cao, Chunfang; Wang, Shumin; Gong, Qian

    2016-12-01

    InAs/InGaAs dot-in-well (DWELL) structures have been investigated with the systematically varied InGaAs thickness. Both the strained buffer layer (SBL) below the dot layer and the strain-reducing layer (SRL) above the dot layer were found to be responsible for the redshift in photoluminescence (PL) emission of the InAs/InGaAs DWELL structure. A linear followed by a saturation behavior of the emission redshift was observed as a function of the SBL and SRL thickness, respectively. The PL intensity is greatly enhanced by applying both of the SRL and SBL. Finite element analysis simulation and transmission electron microscopy (TEM) measurement were carried out to analyze the strain distribution in the InAs QD and the InGaAs SBL. The results clearly indicate the strain reduction in the QD induced by the SBL, which are likely the main cause for the emission redshift. PMID:26932758

  11. Detailed Study of the Influence of InGaAs Matrix on the Strain Reduction in the InAs Dot-In-Well Structure.

    PubMed

    Wang, Peng; Chen, Qimiao; Wu, Xiaoyan; Cao, Chunfang; Wang, Shumin; Gong, Qian

    2016-12-01

    InAs/InGaAs dot-in-well (DWELL) structures have been investigated with the systematically varied InGaAs thickness. Both the strained buffer layer (SBL) below the dot layer and the strain-reducing layer (SRL) above the dot layer were found to be responsible for the redshift in photoluminescence (PL) emission of the InAs/InGaAs DWELL structure. A linear followed by a saturation behavior of the emission redshift was observed as a function of the SBL and SRL thickness, respectively. The PL intensity is greatly enhanced by applying both of the SRL and SBL. Finite element analysis simulation and transmission electron microscopy (TEM) measurement were carried out to analyze the strain distribution in the InAs QD and the InGaAs SBL. The results clearly indicate the strain reduction in the QD induced by the SBL, which are likely the main cause for the emission redshift.

  12. Stability of quantum-dot excited-state laser emission under simultaneous ground-state perturbation

    SciTech Connect

    Kaptan, Y. Herzog, B.; Schöps, O.; Kolarczik, M.; Woggon, U.; Owschimikow, N.; Röhm, A.; Lingnau, B.; Lüdge, K.; Schmeckebier, H.; Arsenijević, D.; Bimberg, D.; Mikhelashvili, V.; Eisenstein, G.

    2014-11-10

    The impact of ground state amplification on the laser emission of In(Ga)As quantum dot excited state lasers is studied in time-resolved experiments. We find that a depopulation of the quantum dot ground state is followed by a drop in excited state lasing intensity. The magnitude of the drop is strongly dependent on the wavelength of the depletion pulse and the applied injection current. Numerical simulations based on laser rate equations reproduce the experimental results and explain the wavelength dependence by the different dynamics in lasing and non-lasing sub-ensembles within the inhomogeneously broadened quantum dots. At high injection levels, the observed response even upon perturbation of the lasing sub-ensemble is small and followed by a fast recovery, thus supporting the capacity of fast modulation in dual-state devices.

  13. Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors

    SciTech Connect

    Ameen, Tarek A.; El-Batawy, Yasser M.; Abouelsaood, A. A.

    2014-02-14

    A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.

  14. Quantum dot enabled high color gamut LCDs

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Kan, Shihai; Lee, Ernie; Gensler, Steve; Hartlove, Jason

    2015-03-01

    Quantum dots are a new generation of phosphor material that have high photon conversion efficiency, narrow spectral line-widths and can be continuously tuned in their emission wavelengths. Since 2013, quantum dots have been adopted by the consumer electronics industry into LCDs to significantly increase their color performance. Compared to the OLED solution, quantum dot LCDs have higher energy efficiency, larger color gamut, longer lifetime, and are offered at a fraction of the cost of OLED panels. In this paper, we demonstrate that quantum-dot based LCDs can achieve more than 90% coverage of the ultra-wide color gamut, Rec. 2020, which is the new color standard for UHDTV.

  15. 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.

  16. 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.

  17. Spin injection from Co2MnGa into an InGaAs quantum well

    NASA Astrophysics Data System (ADS)

    Hickey, M. C.; Damsgaard, C. D.; Holmes, S. N.; Farrer, I.; Jones, G. A. C.; Ritchie, D. A.; Jacobsen, C. S.; Hansen, J. B.; Pepper, M.

    2008-06-01

    We have demonstrated spin injection from a full Heusler alloy Co2MnGa thin film into a (100) InGaAs quantum well in a semiconductor light-emitting diode structure at a temperature of 5K. The detection is performed in the oblique Hanle geometry, allowing quantification of the effective spin lifetime and spin detection efficiency (22±4%). This work builds on existing studies on off-stoichiometric Heusler injectors into similar light-emitting-diode structures. The role of injector stoichiometry can therefore be quantitatively assessed with the result that the spin injection efficiency increases by a factor of approximately 2 as compared with an off-stoichiometric Co2.4Mn1.6Ga injector.

  18. Photoluminescence of a quantum-dot molecule

    SciTech Connect

    Kruchinin, Stanislav Yu.; Rukhlenko, Ivan D.; Baimuratov, Anvar S.; Leonov, Mikhail Yu.; Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii K.

    2015-01-07

    The coherent coupling of quantum dots is a sensitive indicator of the energy and phase relaxation processes taking place in the nanostructure components. We formulate a theory of low-temperature, stationary photoluminescence from a quantum-dot molecule composed of two spherical quantum dots whose electronic subsystems are resonantly coupled via the Coulomb interaction. We show that the coupling leads to the hybridization of the first excited states of the quantum dots, manifesting itself as a pair of photoluminescence peaks with intensities and spectral positions strongly dependent on the geometric, material, and relaxation parameters of the quantum-dot molecule. These parameters are explicitly contained in the analytical expression for the photoluminescence differential cross section derived in the paper. The developed theory and expression obtained are essential in interpreting and analyzing spectroscopic data on the secondary emission of coherently coupled quantum systems.

  19. 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.

  20. 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.

  1. STED nanoscopy with fluorescent quantum dots

    PubMed Central

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

    2015-01-01

    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. PMID:25980788

  2. 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.

  3. 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.

  4. STED nanoscopy with fluorescent quantum dots.

    PubMed

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

    2015-05-18

    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.

  5. Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers.

    PubMed

    Tiemeyer, S; Bombeck, M; Göhring, H; Paulus, M; Sternemann, C; Nase, J; Wirkert, F J; Möller, J; Büning, T; Seeck, O H; Reuter, D; Wieck, A D; Bayer, M; Tolan, M

    2016-10-21

    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots.

  6. Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers

    NASA Astrophysics Data System (ADS)

    Tiemeyer, S.; Bombeck, M.; Göhring, H.; Paulus, M.; Sternemann, C.; Nase, J.; Wirkert, F. J.; Möller, J.; Büning, T.; Seeck, O. H.; Reuter, D.; Wieck, A. D.; Bayer, M.; Tolan, M.

    2016-10-01

    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots.

  7. Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers.

    PubMed

    Tiemeyer, S; Bombeck, M; Göhring, H; Paulus, M; Sternemann, C; Nase, J; Wirkert, F J; Möller, J; Büning, T; Seeck, O H; Reuter, D; Wieck, A D; Bayer, M; Tolan, M

    2016-10-21

    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots. PMID:27622774

  8. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  10. Nanometer distance measurements between multicolor quantum dots.

    PubMed

    Antelman, Josh; Wilking-Chang, Connie; Weiss, Shimon; Michalet, Xavier

    2009-05-01

    Quantum dot dimers made of short double-stranded DNA molecules labeled with different color quantum dots at each end were imaged using multicolor stage-scanning confocal microscopy. This approach eliminates chromatic aberration and color registration issues usually encountered in other multicolor imaging techniques. We demonstrate nanometer accuracy in individual distance measurement by suppression of quantum dot blinking and thoroughly characterize the contribution of different effects to the variability observed between measurements. Our analysis opens the way to accurate structural studies of biomolecules and biomolecular complexes using multicolor quantum labeling.

  11. Substitutional impurity in the graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Sierański, K.; Szatkowski, J.

    2015-09-01

    The process of formation of the localized defect states due to substitutional impurity in sp2-bonded graphene quantum dot is considered using a simple tight-binding-type calculation. We took into account the interaction of the quantum dot atoms surrounding the substitutional impurity from the second row of elements. To saturate the external dangling sp2 orbitals of the carbon additionally 18 hydrogen atoms were introduced. The chemical formula of the quantum dot is H18C51X, where X is the symbol of substitutional atom. The position of the localized levels is determined relative to the host-atoms (C) εp energies. We focused on the effect of substitutional doping by the B, N and O on the eigenstate energies and on the total energy change of the graphene dots including for O the effect of lattice distorsion. We conclude that B, N, and O can form stable substitutional defects in graphene quantum dot.

  12. 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.

  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. Magnon-driven quantum dot refrigerators

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  15. Clocking an Array of Quantum Dots

    NASA Astrophysics Data System (ADS)

    Khatun, Mahfuza; Mandell, Eric

    2000-10-01

    Preferred Session: Condensed Matter Physics Clocking an Array of Quantum Dots* Eric Mandell and M. Khatun, Ball State University. We report a theoretical analysis of the time-dependent electric field due to a line of charged rods. The effects of both the real and image charge are taken into account. The rods are biased electrostatically to study the dynamical behavior of an array of quantum dots. The barrier heights between the quantum dots are controlled by the electric field. *Supported in part by the Indiana Academy of Science, Center for Energy Research/Education/Services(CERES) and the Office of Academic Research and Sponsored Programs, Ball State University.

  16. Instability-driven quantum dots

    NASA Astrophysics Data System (ADS)

    Aqua, Jean-Noël; Frisch, Thomas

    2015-10-01

    When a film is strained in two dimensions, it can relax by developing a corrugation in the third dimension. We review here the resulting morphological instability that occurs by surface diffusion, called the Asaro-Tiller-Grinfel'd instability (ATG), especially on the paradigmatic silicon/germanium system. The instability is dictated by the balance between the elastic relaxation induced by the morphological evolution, and its surface energy cost. We focus here on its development at the nanoscales in epitaxial systems when a crystal film is coherently deposited on a substrate with a different lattice parameter, thence inducing epitaxial stresses. It eventually leads to the self-organization of quantum dots whose localization is dictated by the instability long-time dynamics. In these systems, new effects, such as film/substrate wetting or crystalline anisotropy, come into play and lead to a variety of behaviors. xml:lang="fr"

  17. Quantum dots and prion proteins

    PubMed Central

    Sobrova, Pavlina; Blazkova, Iva; Chomoucka, Jana; Drbohlavova, Jana; Vaculovicova, Marketa; Kopel, Pavel; Hubalek, Jaromir; Kizek, Rene; Adam, Vojtech

    2013-01-01

    A diagnostics of infectious diseases can be done by the immunologic methods or by the amplification of nucleic acid specific to contagious agent using polymerase chain reaction. However, in transmissible spongiform encephalopathies, the infectious agent, prion protein (PrPSc), has the same sequence of nucleic acids as a naturally occurring protein. The other issue with the diagnosing based on the PrPSc detection is that the pathological form of prion protein is abundant only at late stages of the disease in a brain. Therefore, the diagnostics of prion protein caused diseases represent a sort of challenges as that hosts can incubate infectious prion proteins for many months or even years. Therefore, new in vivo assays for detection of prion proteins and for diagnosis of their relation to neurodegenerative diseases are summarized. Their applicability and future prospects in this field are discussed with particular aim at using quantum dots as fluorescent labels. PMID:24055838

  18. Understanding electronic systems in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Ciftja, Orion

    2013-11-01

    Systems of confined electrons are found everywhere in nature in the form of atoms where the orbiting electrons are confined by the Coulomb attraction of the nucleus. Advancement of nanotechnology has, however, provided us with an alternative way to confine electrons by using artificial confining potentials. A typical structure of this nature is the quantum dot, a nanoscale system which consists of few confined electrons. There are many types of quantum dots ranging from self-assembled to miniaturized semiconductor quantum dots. In this work we are interested in electrostatically confined semiconductor quantum dot systems where the electrostatic confining potential that traps the electrons is generated by external electrodes, doping, strain or other factors. A large number of semiconductor quantum dots of this type are fabricated by applying lithographically patterned gate electrodes or by etching on two-dimensional electron gases in semiconductor heterostructures. Because of this, the whole structure can be treated as a confined two-dimensional electron system. Quantum confinement profoundly affects the way in which electrons interact with each other, and external parameters such as a magnetic field. Since a magnetic field affects both the orbital and the spin motion of the electrons, the interplay between quantum confinement, electron-electron correlation effects and the magnetic field gives rise to very interesting physical phenomena. Thus, confined systems of electrons in a semiconductor quantum dot represent a unique opportunity to study fundamental quantum theories in a controllable atomic-like setup. In this work, we describe some common theoretical models which are used to study confined systems of electrons in a two-dimensional semiconductor quantum dot. The main emphasis of the work is to draw attention to important physical phenomena that arise in confined two-dimensional electron systems under various quantum regimes.

  19. Quantum repeaters using orbitals in quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Ohshima, Toshio

    2016-09-01

    We propose quantum repeaters using quantum dot molecules, in which matter-photon entanglement is generated by Raman scatterings in lambda systems composed of various coherent exciton levels formed in the ensembles of asymmetric coupled quantum dots. In our scheme, the wavelength of Stokes and anti-Stokes photons can be chosen to fulfill the requirements of optical fiber communication. Further, the relative superposition phase in the entangled states can be stabilized by the active feedback to the gate voltage in quantum dot system. These characteristics are favorable for implementing our scheme in practice.

  20. Persistent template effect in InAs/GaAs quantum dot bilayers

    SciTech Connect

    Clarke, E.; Howe, P.; Taylor, M.; Spencer, P.; Harbord, E.; Murray, R.; Kadkhodazadeh, S.; McComb, D. W.; Stevens, B. J.; Hogg, R. A.

    2010-06-15

    The dependence of the optical properties of InAs/GaAs quantum dot (QD) bilayers on seed layer growth temperature and second layer InAs coverage is investigated. As the seed layer growth temperature is increased, a low density of large QDs is obtained. This results in a concomitant increase in dot size in the second layer, which extends their emission wavelength, reaching a saturation value of around 1400 nm at room temperature for GaAs-capped bilayers. Capping the second dot layer with InGaAs results in a further extension of the emission wavelength, to 1515 nm at room temperature with a narrow linewidth of 22 meV. Addition of more InAs to high density bilayers does not result in a significant extension of emission wavelength as most additional material migrates to coalesced InAs islands but, in contrast to single layers, a substantial population of regular QDs remains.

  1. 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.

  2. 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

  3. 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.

  4. Indium segregation during III–V quantum wire and quantum dot formation on patterned substrates

    SciTech Connect

    Moroni, Stefano T.; Dimastrodonato, Valeria; Chung, Tung-Hsun; Juska, Gediminas; Gocalinska, Agnieszka; Pelucchi, Emanuele; Vvedensky, Dimitri D.

    2015-04-28

    We report a model for metalorganic vapor-phase epitaxy on non-planar substrates, specifically V-grooves and pyramidal recesses, which we apply to the growth of InGaAs nanostructures. This model—based on a set of coupled reaction-diffusion equations, one for each facet in the system—accounts for the facet-dependence of all kinetic processes (e.g., precursor decomposition, adatom diffusion, and adatom lifetimes) and has been previously applied to account for the temperature-, concentration-, and temporal-dependence of AlGaAs nanostructures on GaAs (111)B surfaces with V-grooves and pyramidal recesses. In the present study, the growth of In{sub 0.12}Ga{sub 0.88}As quantum wires at the bottom of V-grooves is used to determine a set of optimized kinetic parameters. Based on these parameters, we have modeled the growth of In{sub 0.25}Ga{sub 0.75}As nanostructures formed in pyramidal site-controlled quantum-dot systems, successfully producing a qualitative explanation for the temperature-dependence of their optical properties, which have been reported in previous studies. Finally, we present scanning electron and cross-sectional atomic force microscopy images which show previously unreported facetting at the bottom of the pyramidal recesses that allow quantum dot formation.

  5. Nanomaterials: Earthworms lit with quantum dots

    NASA Astrophysics Data System (ADS)

    Tilley, Richard D.; Cheong, Soshan

    2013-01-01

    Yeast, bacteria and fungi have been used to synthesize a variety of nanocrystals. Now, the metal detoxification process in the gut of an earthworm is exploited to produce biocompatible cadmium telluride quantum dots.

  6. Luminescence blinking of a reacting quantum dot.

    PubMed

    Routzahn, Aaron L; Jain, Prashant K

    2015-04-01

    Luminescence blinking is an inherent feature of optical emission from individual fluorescent molecules and quantum dots. There have been intense efforts, although not with complete resolution, toward the understanding of the mechanistic origin of blinking and also its mitigation in quantum dots. As an advance in our microscopic view of blinking, we show that the luminescence blinking of a quantum dot becomes unusually heavy in the temporal vicinity of a reactive transformation. This stage of heavy blinking is a result of defects/dopants formed within the quantum dot on its path to conversion. The evolution of blinking behavior along the reaction path allows us to measure the lifetime of the critical dopant-related intermediate in the reaction. This work establishes luminescence blinking as a single-nanocrystal level probe of catalytic, photocatalytic, and electrochemical events occurring in the solid-state or on semiconductor surfaces.

  7. Quantum dots: A charge for blinking

    NASA Astrophysics Data System (ADS)

    Krauss, Todd D.; Peterson, Jeffrey J.

    2012-01-01

    No accepted description of luminescent blinking in quantum dots is currently available. Now, experiments probing the connection between charge and fluorescence intensity fluctuations unveil an unexpected source of blinking, significantly advancing our fundamental understanding of this baffling phenomenon.

  8. 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.

  9. Electrical and Optical Gain Lever Effects in InGaAs Double Quantum Well Diode Lasers

    SciTech Connect

    Pocha, M D; Goddard, L L; Bond, T C; Nikolic, R J; Vernon, S P; Kallman, J S; Behymer, E M

    2007-01-03

    In multisection laser diodes, the amplitude or frequency modulation (AM or FM) efficiency can be improved using the gain lever effect. To study gain lever, InGaAs double quantum well (DQW) edge emitting lasers have been fabricated with integrated passive waveguides and dual sections providing a range of split ratios from 1:1 to 9:1. Both the electrical and the optical gain lever have been examined. An electrical gain lever with greater than 7 dB enhancement of AM efficiency was achieved within the range of appropriate DC biasing currents, but this gain dropped rapidly outside this range. We observed a 4 dB gain in the optical AM efficiency under non-ideal biasing conditions. This value agreed with the measured gain for the electrical AM efficiency under similar conditions. We also examined the gain lever effect under large signal modulation for digital logic switching applications. To get a useful gain lever for optical gain quenched logic, a long control section is needed to preserve the gain lever strength and a long interaction length between the input optical signal and the lasing field of the diode must be provided. The gain lever parameter space has been fully characterized and validated against numerical simulations of a semi-3D hybrid beam propagation method (BPM) model for the coupled electron-photon rate equation. We find that the optical gain lever can be treated using the electrical injection model, once the absorption in the sample is known.

  10. InGaAs quantum wells on wafer-bonded InP/GaAs substrates

    SciTech Connect

    Hayashi, S.; Sandhu, R.; Wojtowicz, M.; Chen, G.; Hicks, R.; Goorsky, M.S.

    2005-11-01

    Wafer bonding and hydrogen implantation exfoliation techniques have been used to fabricate a thin InP template layer on GaAs with intermediate silicon nitride bonding layers. This template layer was used to directly compare subsequent metal organic vapor phase epitaxial growth of InGaAs/InAlAs quantum-well structures on these wafer-bonded templates to growth on a standard InP substrate. Chemical mechanical polishing of the bonded structure and companion InP substrates was assessed. No effects from the coefficient of thermal mismatch are detected up to the growth temperature, and compositionally equivalent structures are grown on the wafer-bonded InP template and the bare InP substrate. However, after growth dislocation, loops can be identified in the InP template layer due to the ion implantation step. These defects incur a slight mosaic tilt but do not yield any crystalline defects in the epitaxial structure. Low-temperature photoluminescence measurements of the InGaAs grown on the template structure and the InP substrate exhibit near-band-edge luminescence on the same order; this indicates that ion implantation and exfoliation is a viable technique for the integration of III-V materials.

  11. 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.

  12. Renormalization in Periodically Driven Quantum Dots.

    PubMed

    Eissing, A K; Meden, V; Kennes, D M

    2016-01-15

    We report on strong renormalization encountered in periodically driven interacting quantum dots in the nonadiabatic regime. Correlations between lead and dot electrons enhance or suppress the amplitude of driving depending on the sign of the interaction. Employing a newly developed flexible renormalization-group-based approach for periodic driving to an interacting resonant level we show analytically that the magnitude of this effect follows a power law. Our setup can act as a non-Markovian, single-parameter quantum pump. PMID:26824557

  13. Electron Spin Dynamics in Semiconductor Quantum Dots

    SciTech Connect

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

    2011-07-15

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

  14. Fast electron spin resonance controlled manipulation of spin injection into quantum dots

    SciTech Connect

    Merz, Andreas Siller, Jan; Schittny, Robert; Krämmer, Christoph; Kalt, Heinz; Hetterich, Michael

    2014-06-23

    In our spin-injection light-emitting diodes, electrons are spin-polarized in a semimagnetic ZnMnSe spin aligner and then injected into InGaAs quantum dots. The resulting electron spin state can be read out by measuring the circular polarization state of the emitted light. Here, we resonantly excite the Mn 3d electron spin system with microwave pulses and perform time-resolved measurements of the spin dynamics. We find that we are able to control the spin polarization of the injected electrons on a microsecond timescale. This electron spin resonance induced spin control could be one of the ingredients required to utilize the quantum dot electrons or the Mn spins as qubits.

  15. Quantum Dots in Gated Nanowires and Nanotubes

    NASA Astrophysics Data System (ADS)

    Churchill, Hugh Olen Hill

    This thesis describes experiments on quantum dots made by locally gating one-dimensional quantum wires. The first experiment studies a double quantum dot device formed in a Ge/Si core/shell nanowire. In addition to measuring transport through the double dot, we detect changes in the charge occupancy of the double dot by capacitively coupling it to a third quantum dot on a separate nanowire using a floating gate. We demonstrate tunable tunnel coupling of the double dot and quantify the strength of the tunneling using the charge sensor. The second set of experiments concerns carbon nanotube double quantum dots. In the first nanotube experiment, spin-dependent transport through the double dot is compared in two sets of devices. The first set is made with carbon containing the natural abundance of 12C (99%) and 13C (1%), the second set with the 99% 13C and 1% 12C. In the devices with predominantly 13C, we find evidence in spin-dependent transport of the interaction between the electron spins and the 13C nuclear spins that was much stronger than expected and not present in the 12C devices. In the second nanotube experiment, pulsed gate experiments are used to measure the timescales of spin relaxation and dephasing in a two-electron double quantum dot. The relaxation time is longest at zero magnetic field and goes through a minimum at higher field, consistent with the spin-orbit-modified electronic spectrum of carbon nanotubes. We measure a short dephasing time consistent with the anomalously strong electron-nuclear interaction inferred from the first nanotube experiment.

  16. 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.

  17. Luminescent Quantum Dots as Ultrasensitive Biological Labels

    NASA Astrophysics Data System (ADS)

    Nie, Shuming

    2000-03-01

    Highly luminescent semiconductor quantum dots have been covalently coupled to biological molecules for use in ultrasensitive biological detection. This new class of luminescent labels is considerably brighter and more resistant againt photobleaching in comparison with organic dyes. Quantum dots labeled with the protein transferrin undergo receptor-mediated endocytosis (RME) in cultured HeLa cells, and those dots that were conjugated to immunomolecules recognize specific antibodies or antigens. In addition, we show that DNA functionalized quantum dots can be used to target specific genes by hybridization. We expect that quantum dot bioconjugates will have a broad range of biological applications, such as ligand-receptor interactions, real-time monitoring of molecular trafficking inside living cells, multicolor fluorescence in-situ hybridization (FISH), high-sensitivity detection in miniaturized devices (e.g., DNA chips), and fluorescent tagging of combinatorial chemical libraries. A potential clinical application is the use of quantum dots for ultrasensitive viral RNA detection, in which as low as 100 copies of hepatitis C and HIV viruses per ml blood should be detected.

  18. Spectroscopy characterization and quantum yield determination of quantum dots

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  19. (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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. Electronic Structure of Few-Electron Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Popsueva, V.; Hansen, J. P.; Caillat, J.

    2007-12-01

    We present a study of strongly correlated few-electron quantum dots, exploring the spectra of various few-electron quantum dot molecules: a double (diatomic) structure a quadruple two-electron quantum dot, and a three-electron double dot. Electron energy spectra are computed for different values of dot separation. All spectra show clear band structures and can be understood from asymptotical properties of the system.

  5. 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.

  6. 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.

  7. Electrical control of quantum dot spin qubits

    NASA Astrophysics Data System (ADS)

    Laird, Edward Alexander

    This thesis presents experiments exploring the interactions of electron spins with electric fields in devices of up to four quantum dots. These experiments are particularly motivated by the prospect of using electric fields to control spin qubits. A novel hyperfine effect on a single spin in a quantum dot is presented in Chapter 2. Fluctuations of the nuclear polarization allow single-spin resonance to be driven by an oscillating electric field. Spin resonance spectroscopy revealed a nuclear polarization built up inside the quantum dot device by driving the resonance. The evolution of two coupled spins is controlled by the combination of hyperfine interaction, which tends to cause spin dephasing, and exchange, which tends to prevent it. In Chapter 3, dephasing is studied in a device with tunable exchange, probing the crossover between exchange-dominated and hyperfine-dominated regimes. In agreement with theoretical predictions, oscillations of the spin conversion probability and saturation of dephasing are observed. Chapter 4 deals with a three-dot device, suggested as a potential qubit controlled entirely by exchange. Preparation and readout of the qubit state are demonstrated, together with one out of two coherent exchange operations needed for arbitrary manipulations. A new readout technique allowing rapid device measurement is described. In Chapter 5, an attempt to make a two-qubit gate using a four-dot device is presented. Although spin qubit operation has not yet been possible, the electrostatic interaction between pairs of dots was measured to be sufficient in principle for coherent qubit coupling.

  8. Quantum Dot-Based Cell Motility Assay

    SciTech Connect

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

    2005-06-06

    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.

  9. Isotopically enhanced triple-quantum-dot qubit.

    PubMed

    Eng, Kevin; Ladd, Thaddeus D; Smith, Aaron; Borselli, Matthew G; Kiselev, Andrey A; Fong, Bryan H; Holabird, Kevin S; Hazard, Thomas M; Huang, Biqin; Deelman, Peter W; Milosavljevic, Ivan; Schmitz, Adele E; Ross, Richard S; Gyure, Mark F; Hunter, Andrew T

    2015-05-01

    Like modern microprocessors today, future processors of quantum information may be implemented using all-electrical control of silicon-based devices. A semiconductor spin qubit may be controlled without the use of magnetic fields by using three electrons in three tunnel-coupled quantum dots. Triple dots have previously been implemented in GaAs, but this material suffers from intrinsic nuclear magnetic noise. Reduction of this noise is possible by fabricating devices using isotopically purified silicon. We demonstrate universal coherent control of a triple-quantum-dot qubit implemented in an isotopically enhanced Si/SiGe heterostructure. Composite pulses are used to implement spin-echo type sequences, and differential charge sensing enables single-shot state readout. These experiments demonstrate sufficient control with sufficiently low noise to enable the long pulse sequences required for exchange-only two-qubit logic and randomized benchmarking. PMID:26601186

  10. Three-terminal quantum-dot refrigerators

    NASA Astrophysics Data System (ADS)

    Zhang, Yanchao; Lin, Guoxing; Chen, Jincan

    2015-05-01

    Based on two capacitively coupled quantum dots in the Coulomb-blockade regime, a model of three-terminal quantum-dot refrigerators is proposed. With the help of the master equation, the transport properties of steady-state charge current and energy flow between two quantum dots and thermal reservoirs are revealed. It is expounded that such a structure can be used to construct a refrigerator by controlling the voltage bias and temperature ratio. The thermodynamic performance characteristics of the refrigerator are analyzed, including the cooling power, coefficient of performance (COP), maximum cooling power, and maximum COP. Moreover, the optimal regions of main performance parameters are determined. The influence of dissipative tunnel processes on the optimal performance is discussed in detail. Finally, the performance characteristics of the refrigerators operated in two different cases are compared.

  11. Isotopically enhanced triple-quantum-dot qubit

    PubMed Central

    Eng, Kevin; Ladd, Thaddeus D.; Smith, Aaron; Borselli, Matthew G.; Kiselev, Andrey A.; Fong, Bryan H.; Holabird, Kevin S.; Hazard, Thomas M.; Huang, Biqin; Deelman, Peter W.; Milosavljevic, Ivan; Schmitz, Adele E.; Ross, Richard S.; Gyure, Mark F.; Hunter, Andrew T.

    2015-01-01

    Like modern microprocessors today, future processors of quantum information may be implemented using all-electrical control of silicon-based devices. A semiconductor spin qubit may be controlled without the use of magnetic fields by using three electrons in three tunnel-coupled quantum dots. Triple dots have previously been implemented in GaAs, but this material suffers from intrinsic nuclear magnetic noise. Reduction of this noise is possible by fabricating devices using isotopically purified silicon. We demonstrate universal coherent control of a triple-quantum-dot qubit implemented in an isotopically enhanced Si/SiGe heterostructure. Composite pulses are used to implement spin-echo type sequences, and differential charge sensing enables single-shot state readout. These experiments demonstrate sufficient control with sufficiently low noise to enable the long pulse sequences required for exchange-only two-qubit logic and randomized benchmarking. PMID:26601186

  12. 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.

  13. Resonant tunneling in graphene pseudomagnetic quantum dots.

    PubMed

    Qi, Zenan; Bahamon, D A; Pereira, Vitor M; Park, Harold S; Campbell, D K; Neto, A H Castro

    2013-06-12

    Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction.

  14. Potential clinical applications of quantum dots

    PubMed Central

    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. PMID:18686776

  15. Bilayer graphene quantum dot defined by topgates

    SciTech Connect

    Müller, André; Kaestner, Bernd; Hohls, Frank; Weimann, Thomas; Pierz, Klaus; Schumacher, Hans W.

    2014-06-21

    We investigate the application of nanoscale topgates on exfoliated bilayer graphene to define quantum dot devices. At temperatures below 500 mK, the conductance underneath the grounded gates is suppressed, which we attribute to nearest neighbour hopping and strain-induced piezoelectric fields. The gate-layout can thus be used to define resistive regions by tuning into the corresponding temperature range. We use this method to define a quantum dot structure in bilayer graphene showing Coulomb blockade oscillations consistent with the gate layout.

  16. Ambipolar quantum dots in intrinsic silicon

    SciTech Connect

    Betz, A. C. Gonzalez-Zalba, M. F.; Podd, G.; Ferguson, A. J.

    2014-10-13

    We electrically measure intrinsic silicon quantum dots with electrostatically defined tunnel barriers. The presence of both p- and n-type ohmic contacts enables the accumulation of either electrons or holes. Thus, we are able to study both transport regimes within the same device. We investigate the effect of the tunnel barriers and the electrostatically defined quantum dots. There is greater localisation of charge states under the tunnel barriers in the case of hole conduction, leading to higher charge noise in the p-type regime.

  17. Light-trapping for room temperature Bose-Einstein condensation in InGaAs quantum wells.

    PubMed

    Vasudev, Pranai; Jiang, Jian-Hua; John, Sajeev

    2016-06-27

    We demonstrate the possibility of room-temperature, thermal equilibrium Bose-Einstein condensation (BEC) of exciton-polaritons in a multiple quantum well (QW) system composed of InGaAs quantum wells surrounded by InP barriers, allowing for the emission of light near telecommunication wavelengths. The QWs are embedded in a cavity consisting of double slanted pore (SP2) photonic crystals composed of InP. We consider exciton-polaritons that result from the strong coupling between the multiple quantum well excitons and photons in the lowest planar guided mode within the photonic band gap (PBG) of the photonic crystal cavity. The collective coupling of three QWs results in a vacuum Rabi splitting of 3% of the bare exciton recombination energy. Due to the full three-dimensional PBG exhibited by the SP2 photonic crystal (16% gap to mid-gap frequency ratio), the radiative decay of polaritons is eliminated in all directions. Due to the short exciton-phonon scattering time in InGaAs quantum wells of 0.5 ps and the exciton non-radiative decay time of 200 ps at room temperature, polaritons can achieve thermal equilibrium with the host lattice to form an equilibrium BEC. Using a SP2 photonic crystal with a lattice constant of a = 516 nm, a unit cell height of 2a=730nm and a pore radius of 0.305a = 157 nm, light in the lowest planar guided mode is strongly localized in the central slab layer. The central slab layer consists of 3 nm InGaAs quantum wells with 7 nm InP barriers, in which excitons have a recombination energy of 0.944 eV, a binding energy of 7 meV and a Bohr radius of aB = 10 nm. We take the exciton recombination energy to be detuned 35 meV above the lowest guided photonic mode so that an exciton-polariton has a photonic fraction of approximately 97% per QW. This increases the energy range of small-effective-mass photonlike states and increases the critical temperature for the onset of a Bose-Einstein condensate. With three quantum wells in the central slab layer

  18. Light-trapping for room temperature Bose-Einstein condensation in InGaAs quantum wells.

    PubMed

    Vasudev, Pranai; Jiang, Jian-Hua; John, Sajeev

    2016-06-27

    We demonstrate the possibility of room-temperature, thermal equilibrium Bose-Einstein condensation (BEC) of exciton-polaritons in a multiple quantum well (QW) system composed of InGaAs quantum wells surrounded by InP barriers, allowing for the emission of light near telecommunication wavelengths. The QWs are embedded in a cavity consisting of double slanted pore (SP2) photonic crystals composed of InP. We consider exciton-polaritons that result from the strong coupling between the multiple quantum well excitons and photons in the lowest planar guided mode within the photonic band gap (PBG) of the photonic crystal cavity. The collective coupling of three QWs results in a vacuum Rabi splitting of 3% of the bare exciton recombination energy. Due to the full three-dimensional PBG exhibited by the SP2 photonic crystal (16% gap to mid-gap frequency ratio), the radiative decay of polaritons is eliminated in all directions. Due to the short exciton-phonon scattering time in InGaAs quantum wells of 0.5 ps and the exciton non-radiative decay time of 200 ps at room temperature, polaritons can achieve thermal equilibrium with the host lattice to form an equilibrium BEC. Using a SP2 photonic crystal with a lattice constant of a = 516 nm, a unit cell height of 2a=730nm and a pore radius of 0.305a = 157 nm, light in the lowest planar guided mode is strongly localized in the central slab layer. The central slab layer consists of 3 nm InGaAs quantum wells with 7 nm InP barriers, in which excitons have a recombination energy of 0.944 eV, a binding energy of 7 meV and a Bohr radius of aB = 10 nm. We take the exciton recombination energy to be detuned 35 meV above the lowest guided photonic mode so that an exciton-polariton has a photonic fraction of approximately 97% per QW. This increases the energy range of small-effective-mass photonlike states and increases the critical temperature for the onset of a Bose-Einstein condensate. With three quantum wells in the central slab layer

  19. Metal-organic vapor-phase epitaxy-grown ultra-low density InGaAs/GaAs quantum dots exhibiting cascaded single-photon emission at 1.3 μm

    SciTech Connect

    Paul, Matthias Kettler, Jan; Zeuner, Katharina; Clausen, Caterina; Jetter, Michael; Michler, Peter

    2015-03-23

    By metal-organic vapor-phase epitaxy, we have fabricated InGaAs quantum dots on GaAs substrate with an ultra-low lateral density (<10{sup 7} cm{sup −2}). The photoluminescence emission from the quantum dots is shifted to the telecom O-band at 1.31 μm by an InGaAs strain reducing layer. In time-resolved measurements, we find fast decay times for exciton (∼600 ps) and biexciton (∼300 ps). We demonstrate triggered single-photon emission (g{sup (2)}(0)=0.08) as well as cascaded emission from the biexciton decay. Our results suggest that these quantum dots can compete with their counterparts grown by state-of-the-art molecular beam epitaxy.

  20. Cavity quantum electrodynamics with carbon nanotube quantum dots

    NASA Astrophysics Data System (ADS)

    Kontos, Takis

    Cavity quantum electrodynamics techniques have turned out to be instrumental to probe or manipulate the electronic states of nanoscale circuits. Recently, cavity QED architectures have been extended to quantum dot circuits. These circuits are appealing since other degrees of freedom than the traditional ones (e.g. those of superconducting circuits) can be investigated. I will show how one can use carbon nanotube based quantum dots in that context. In particular, I will focus on the coherent coupling of a single spin or non-local Cooper pairs to cavity photons. Quantum dots also exhibit a wide variety of many body phenomena. The cQED architecture could also be instrumental for understanding them. One of the most paradigmatic phenomenon is the Kondo effect which is at the heart of many electron correlation effects. I will show that a cQED architecture has allowed us to observe the decoupling of spin and charge excitations in a Kondo system.

  1. Demonstration of a two-color 320×256 quantum dots-in-a-well focal plane array

    NASA Astrophysics Data System (ADS)

    Varley, Eric S.; Ramirez, David A.; Brown, Jay S.; Lee, Sang Jun; Stintz, Andreas; Lenz, Michael; Krishna, Sanjay; Reisinger, Axel; Sundaram, Mani

    2007-09-01

    In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots embedded in InGaAs quantum wells. By adjusting the InGaAs well thickness, our structure allows for the manipulation of the operating wavelength and the nature of the transitions (bound-to-bound, bound-to-quasibound and bound-to-continuum) of the detector. Based on these principles, DWELL samples were grown using molecular beam epitaxy and fabricated into 320 x 256 focal plane arrays (FPAs) with Indium bumps using standard lithography at the University of New Mexico. The FPA evaluated was hybridized to an Indigo 9705 readout integrated circuit (ROIC) in collaboration with QmagiQ LLC and tested with a CamIRa TM system manufactured by SE-IR Corp. From this evaluation, we report the first two-color, co-located quantum dot based imaging system that can be used to take multicolor images using a single FPA. We demonstrated that we can operate the device at an intermediate bias (V b=-1.25 V) and obtain two color response from the FPA at 77K. Using filter lenses, both MWIR and LWIR responses were obtained from the array at the same bias voltage. The MWIR and LWIR responses are thought to be from bound states in the dot to higher and lower lying states in the quantum well respectively. Temporal NEDT for the DWELL FPA was measured to be 80mK at 77K.

  2. Deep level centers and their role in photoconductivity transients of InGaAs/GaAs quantum dot chains

    SciTech Connect

    Kondratenko, S. V. Vakulenko, O. V.; Mazur, Yu. I. Dorogan, V. G.; Marega, E.; Benamara, M.; Ware, M. E.; Salamo, G. J.

    2014-11-21

    The in-plane photoconductivity and photoluminescence are investigated in quantum dot-chain InGaAs/GaAs heterostructures. Different photoconductivity transients resulting from spectrally selecting photoexcitation of InGaAs QDs, GaAs spacers, or EL2 centers were observed. Persistent photoconductivity was observed at 80 K after excitation of electron-hole pairs due to interband transitions in both the InGaAs QDs and the GaAs matrix. Giant optically induced quenching of in-plane conductivity driven by recharging of EL2 centers is observed in the spectral range from 0.83 eV to 1.0 eV. Conductivity loss under photoexcitation is discussed in terms of carrier localization by analogy with carrier distribution in disordered media.

  3. Formation and ordering of epitaxial quantum dots

    NASA Astrophysics Data System (ADS)

    Atkinson, Paola; Schmidt, Oliver G.; Bremner, Stephen P.; Ritchie, David A.

    2008-10-01

    Single quantum dots (QDs) have great potential as building blocks for quantum information processing devices. However, one of the major difficulties in the fabrication of such devices is the placement of a single dot at a pre-determined position in the device structure, for example, in the centre of a photonic cavity. In this article we review some recent investigations in the site-controlled growth of InAs QDs on GaAs by molecular beam epitaxy. The method we use is ex-situ patterning of the GaAs substrate by electron beam lithography and conventional wet or dry etching techniques to form shallow pits in the surface which then determine the nucleation site of an InAs dot. This method is easily scalable and can be incorporated with marker structures to enable simple post-growth lithographic alignment of devices to each site-controlled dot. We demonstrate good site-control for arrays with up to 10 micron spacing between patterned sites, with no dots nucleating between the sites. We discuss the mechanism and the effect of pattern size, InAs deposition amount and growth conditions on this site-control method. Finally we discuss the photoluminescence from these dots and highlight the remaining challenges for this technique. To cite this article: P. Atkinson et al., C. R. Physique 9 (2008).

  4. 1.58 {mu}m InGaAs quantum well laser on GaAs

    SciTech Connect

    Taangring, I.; Ni, H. Q.; Wu, B. P.; Wu, D. H.; Xiong, Y. H.; Huang, S. S.; Niu, Z. C.; Wang, S. M.; Lai, Z. H.; Larsson, A.

    2007-11-26

    We demonstrate the 1.58 {mu}m emission at room temperature from a metamorphic In{sub 0.6}Ga{sub 0.4}As quantum well laser grown on GaAs by molecular beam epitaxy. The large lattice mismatch was accommodated through growth of a linearly graded buffer layer to create a high quality virtual In{sub 0.32}Ga{sub 0.68}As substrate. Careful growth optimization ensured good optical and structural qualities. For a 1250x50 {mu}m{sup 2} broad area laser, a minimum threshold current density of 490 A/cm{sup 2} was achieved under pulsed operation. This result indicates that metamorphic InGaAs quantum wells can be an alternative approach for 1.55 {mu}m GaAs-based lasers.

  5. 1.59 {mu}m room temperature emission from metamorphic InAs/InGaAs quantum dots grown on GaAs substrates

    SciTech Connect

    Seravalli, L.; Frigeri, P.; Trevisi, G.; Franchi, S.

    2008-05-26

    We present design, preparation by molecular beam epitaxy, and characterization by photoluminescence of long-wavelength emitting, strain-engineered quantum dot nanostructures grown on GaAs, with InGaAs confining layers and additional InAlAs barriers embedding InAs dots. Quantum dot strain induced by metamorphic lower confining layers is instrumental to redshift the emission, while a-few-nanometer thick InAlAs barriers allow to significantly increase the activation energy of carriers' thermal escape. This approach results in room temperature emission at 1.59 {mu}m and, therefore, is a viable method to achieve efficient emission in the 1.55 {mu}m window and beyond from quantum dots grown on GaAs substrates.

  6. Nonlocal quantum cloning via quantum dots trapped in distant cavities

    NASA Astrophysics Data System (ADS)

    Yu, Tao; Zhu, Ai-Dong; Zhang, Shou

    2012-05-01

    A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed. By modulating the parameters of the system, the optimal 1 → 2 universal quantum cloning machine, 1 → 2 phase-covariant cloning machine, and 1 → 3 economical phase-covariant cloning machine are constructed. The present scheme, which is attainable with current technology, saves two qubits compared with previous cloning machines.

  7. 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.

  8. Slow electron cooling in colloidal quantum dots.

    PubMed

    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 approximately 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.

  9. Applications of quantum dots in cell biology

    NASA Astrophysics Data System (ADS)

    Barroso, Margarida; Mehdibeigi, Roshanak; Brogan, Louise

    2006-02-01

    Quantum dots promise to revolutionize the way fluorescence imaging is used in the Cell Biology field. The unique fluorescent spectral characteristics, high photostability, low photobleaching and tight emission spectra of quantum dots, position them above traditional dyes. Here we will address the ability of EviTags, which are water stabilized quantum dot products from Evident Technologies, to behave as effective FRET donors in cells. EviTag-Hops Yellow (HY; Emission 566nm; Donor) conjugated to biotin were bound to stretapvidin-Alexa568 (Acceptor) conjugates. These HYbiotin-streptavidin-Alexa568 FRET EviTag conjugates were then internalized by fluid-phase into non-polarized MDCK cells. Confocal microscopy detects these FRET EviTag conjugates in endocytic compartments, suggesting that EviTags can be used to track fluid-phase internalization and trafficking. EviTags are shown here to be effective FRET donors when internalized into cells. Upon pairing with the appropriate acceptor dyes, quantum dots will reduce the laborious data processing that is required to compensate for bleed through contamination between organic dye donor and acceptor pair signals. The EviTag technology will simplify and expand the use of FRET in the analysis of cellular processes that may involve protein-protein interactions and other complex cellular processes.

  10. Nonequilibrium dephasing in Coulomb blockaded quantum dots.

    PubMed

    Altland, Alexander; Egger, Reinhold

    2009-01-16

    We present a theory of zero-bias anomalies and dephasing rates for a Coulomb-blockaded quantum dot, driven out of equilibrium by coupling to voltage biased source and drain leads. We interpret our results in terms of the statistics of voltage fluctuations in the system.

  11. Saturating optical resonances in quantum dots

    NASA Astrophysics Data System (ADS)

    Nair, Selvakumar V.; Rustagi, K. C.

    Optical bistability in quantum dots, recently proposed by Chemla and Miller, is studied in a two-resonance model. We show that for such classical electromagnetic resonances the applicability of a two-resonance model is far more restrictive than for those in atoms.

  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. 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

  15. Single-dot optical emission from ultralow density well-isolated InP quantum dots

    SciTech Connect

    Ugur, A.; Hatami, F.; Masselink, W. T.; Vamivakas, A. N.; Lombez, L.; Atatuere, M.

    2008-10-06

    We demonstrate a straightforward way to obtain single well-isolated quantum dots emitting in the visible part of the spectrum and characterize the optical emission from single quantum dots using this method. Self-assembled InP quantum dots are grown using gas-source molecular-beam epitaxy over a wide range of InP deposition rates, using an ultralow growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/{mu}m{sup 2} is realized. The resulting isolated InP quantum dots embedded in an InGaP matrix are individually characterized without the need for lithographical patterning and masks on the substrate. Such low-density quantum dots show excitonic emission at around 670 nm with a linewidth limited by instrument resolution. This system is applicable as a single-photon source for applications such as quantum cryptography.

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

    PubMed

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

    2015-03-10

    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.

  17. Quantum and classical thermoelectric transport in quantum dot nanocomposites

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Yang, Ronggui

    2011-10-01

    Quantum dot nanocomposites are potentially high-efficiency thermoelectric materials, which could outperform superlattices and random nanocomposites in terms of manufacturing cost-effectiveness and material properties because of the reduction of thermal conductivity due to the phonon-interface scattering, the enhancement of Seebeck coefficient due to the formation of minibands, and the enhancement of electrical conductivity due to the phonon-bottleneck effect in electron-phonon scattering for quantum-confined electrons. In this paper, we investigate the thermoelectric transport properties of quantum dot nanocomposites through a two-channel transport model that includes the transport of quantum-confined electrons through the hopping mechanism and the semiclassical transport of bulk-like electrons. For the quantum-confined electrons whose wave functions are confined in the quantum dots with overlapping tail extending to the matrix, we develop a tight-binding model together with the Kubo formula and the Green's function method to describe the transport processes of these electrons. The formation of minibands due to the quantum confinement and the phonon-bottleneck effect on carrier-phonon scattering are considered. For transport of bulk-like electrons, a Boltzmann-transport-equation-based semiclassical model is used to describe the multiband transport processes of carriers. The intrinsic carrier scatterings as well as the carrier-interface scattering of these bulk-like electrons are considered. We then apply the two-channel transport model to predict thermoelectric transport properties of n-type PbSe/PbTe quantum dot nanocomposites with PbSe quantum dots uniformly embedded in the PbTe matrix. The dependence of thermoelectric transport coefficients on the size of quantum dots, interdot distance, doping concentration, and temperature are studied in detail. Due to the formation of minibands and the phonon-bottleneck effect on carrier-phonon scattering, we show that

  18. Spatially correlated structural and optical characterization of a single InGaAs quantum well fin selectively grown on Si by microscopy and cathodoluminescence techniques

    NASA Astrophysics Data System (ADS)

    David, S.; Roque, J.; Rochat, N.; Bernier, N.; Piot, L.; Alcotte, R.; Cerba, T.; Martin, M.; Moeyaert, J.; Bogumilowizc, Y.; Arnaud, S.; Bertin, F.; Bassani, F.; Baron, T.

    2016-05-01

    Structural and optical properties of InGaAs quantum well fins (QWFs) selectively grown on Si using the aspect ratio trapping (ART) method in 200 nm deep SiO2 trenches are studied. A new method combining cathodoluminescence, transmission electron microscopy, and precession electron diffraction techniques is developed to spatially correlate the presence of defects and/or strain with the light emission properties of a single InGaAs QWF. Luminescence losses and energy shifts observed at the nanoscale along InGaAs QWF are correlated with structural defects. We show that strain distortions measured around threading dislocations delimit both high and low luminescent areas. We also show that trapped dislocations on SiO2 sidewalls can also result in additional distortions. Both behaviors affect optical properties of QWF at the nanoscale. Our study highlights the need to improve the ART growth method to allow integration of new efficient III-V optoelectronic components on Si.

  19. Entangling distant quantum dots using classical interference

    NASA Astrophysics Data System (ADS)

    Busch, Jonathan; Kyoseva, Elica S.; Trupke, Michael; Beige, Almut

    2008-10-01

    We show that it is possible to employ reservoir engineering to turn two distant and relatively bad cavities into one good cavity with a tunable spontaneous decay rate. As a result, quantum computing schemes, which would otherwise require the shuttling of atomic qubits in and out of an optical resonator, can now be applied to distant quantum dots. To illustrate this we transform a recent proposal to entangle two qubits via the observation of macroscopic fluorescence signals [J. Metz , Phys. Rev. Lett. 97, 040503 (2006)] to the electron-spin states of two semiconductor quantum dots. Our scheme requires neither the coherent control of qubit-qubit interactions nor the detection of single photons. Moreover, the scheme is relatively robust against spin-bath couplings, parameter fluctuations, and the spontaneous emission of photons.

  20. 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.

  1. Theory of the Quantum Dot Hybrid Qubit

    NASA Astrophysics Data System (ADS)

    Friesen, Mark

    2015-03-01

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

  2. Sensitivity and noise of micro-Hall magnetic sensors based on InGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Chenaud, B.; Segovia-Mera, A.; Delgard, A.; Feltin, N.; Hoffmann, A.; Pascal, F.; Zawadzki, W.; Mailly, D.; Chaubet, C.

    2016-01-01

    We study the room-temperature performance of micro-Hall magnetic sensors based on pseudomorphic InGaAs quantum wells. Active areas of our sensors range from 1 to 80 μm. We focus on the smallest detectable magnetic fields in small sensors and perform a systematic study of noise at room temperature in the frequency range between 1 Hz and 100 kHz. Our data are interpreted by the mobility fluctuation model. The Hooge parameter is determined for the applied technology. We show that, independently of the experimental frequency, the ratio of sensitivity to noise is proportional to characteristic length of the sensor. The resolution of 1 mG/√{Hz } is achievable in a 3 μm sensor at room temperature.

  3. Experimental demonstration of hot-carrier photo-current in an InGaAs quantum well solar cell

    SciTech Connect

    Hirst, L. C.; Walters, R. J.; Führer, M. F.; Ekins-Daukes, N. J.

    2014-06-09

    An unambiguous observation of hot-carrier photocurrent from an InGaAs single quantum well solar cell is reported. Simultaneous photo-current and photoluminescence measurements were performed for incident power density 0.04–3 kW cm{sup −2}, lattice temperature 10 K, and forward bias 1.2 V. An order of magnitude photocurrent increase was observed for non-equilibrium hot-carrier temperatures >35 K. This photocurrent activation temperature is consistent with that of equilibrium carriers in a lattice at elevated temperature. The observed hot-carrier photo-current is extracted from the well over an energy selective GaAs barrier, thus integrating two essential components of a hot-carrier solar cell: a hot-carrier absorber and an energy selective contact.

  4. Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression.

    PubMed

    Chen, Shaoqiang; Yoshita, Masahiro; Ito, Takashi; Mochizuki, Toshimitsu; Akiyama, Hidefumi; Yokoyama, Hiroyuki

    2013-03-25

    Gain-switched pulses of InGaAs double-quantum-well lasers fabricated from identical epitaxial laser wafers were measured under both current injection and optical pumping conditions. The shortest output pulse widths were nearly identical (about 40 ps) both for current injection and optical pumping; this result attributed the dominant pulse-width limitation factor to the intrinsic gain properties of the lasers. We quantitatively compared the experimental results with theoretical calculations based on rate equations incorporating gain nonlinearities. Close consistency between the experimental data and the calculations was obtained only when we assumed a dynamically suppressed gain value deviated from the steady-state gain value supported by standard microscopic theories.

  5. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  6. Demonstration of a bias tunable quantum dots-in-a-well focal plane array

    NASA Astrophysics Data System (ADS)

    Andrews, Jonathan; Jang, Woo-Yong; Pezoa, Jorge E.; Sharma, Yagya D.; Lee, Sang Jun; Noh, Sam Kyu; Hayat, Majeed M.; Restaino, Sergio; Teare, Scott W.; Krishna, Sanjay

    2009-11-01

    Infrared detectors based on quantum wells and quantum dots have attracted a lot of attention in the past few years. Our previous research has reported on the development of the first generation of quantum dots-in-a-well (DWELL) focal plane arrays, which are based on InAs quantum dots embedded in an InGaAs well having GaAs barriers. This focal plane array has successfully generated a two-color imagery in the mid-wave infrared (i.e. 3-5 μm) and the long-wave infrared (i.e. 8-12 μm) at a fixed bias voltage. Recently, the DWELL device has been further modified by embedding InAs quantum dots in InGaAs and GaAs double wells with AlGaAs barriers, leading to a less strained InAs/InGaAs/GaAs/AlGaAs heterostructure. This is expected to improve the operating temperature while maintaining a low dark current level. This paper examines 320 × 256 double DWELL based focal plane arrays that have been fabricated and hybridized with an Indigo 9705 read-out integrated circuit using Indium-bump (flip-chip) technology. The spectral tunability is quantified by examining images and determining the transmittance ratio (equivalent to the photocurrent ratio) between mid-wave and long-way infrared filter targets. Calculations were performed for a bias range from 0.3 to 1.0 V. The results demonstrate that the mid-wave transmittance dominates at these low bias voltages, and the transmittance ratio continuously varies over different applied biases. Additionally, radiometric characterization, including array uniformity and measured noise equivalent temperature difference for the double DWELL devices is computed and compared to the same results from the original first generation DWELL. Finally, higher temperature operation is explored. Overall, the double DWELL devices had lower noise equivalent temperature difference and higher uniformity, and worked at higher temperature (70 K and 80 K) than the first generation DWELL device.

  7. Small bright charged colloidal quantum dots.

    PubMed

    Qin, Wei; Liu, Heng; Guyot-Sionnest, Philippe

    2014-01-28

    Using electrochemical charge injection, the fluorescence lifetimes of negatively charged core/shell CdTe/CdSe QDs are measured as a function of core size and shell thickness. It is found that the ensemble negative trion lifetimes reach a maximum (∼4.5 ns) for an intermediate shell thickness. This leads to the smallest particles (∼4.5 nm) with the brightest trion to date. Single dot measurements show that the negative charge suppresses blinking and that the trion can be as bright as the exciton at room temperature. In contrast, the biexciton lifetimes remain short and exhibit only a monotonous increase with shell thickness, showing no correlation with the negative trion decays. The suppression of the Auger process in small negatively charged CdTe/CdSe quantum dots is unprecedented and a significant departure from prior results with ultrathick CdSe/CdS core/shell or dot-in-rod structures. The proposed reason for the optimum shell thickness is that the electron-hole overlap is restricted to the CdTe core while the electron is tuned to have zero kinetic energy in the core for that optimum shell thickness. The different trend of the biexciton lifetime is not explained but tentatively attributed to shorter-lived positive trions at smaller sizes. These results improve our understanding of multiexciton recombination in colloidal quantum dots and may lead to the design of bright charged QDs for more efficient light-emitting devices.

  8. Scanning photoluminescent spectroscopy of bioconjugated quantum dots

    NASA Astrophysics Data System (ADS)

    Chornokur, G.; Ostapenko, S.; Oleynik, E.; Phelan, C.; Korsunska, N.; Kryshtab, T.; Zhang, J.; Wolcott, A.; Sellers, T.

    2009-04-01

    We report on the application of the bio-conjugated quantum dots (QDs) for a "sandwich" enzyme-linked immunosorbent assay (ELISA) cancer testing technique. Quantum dot ELISA detection of the cancer PSA antigen at concentrations as low as 0.01 ng/ml which is ˜50 times lower than the classic "sandwich" ELISA was demonstrated. Scanning photoluminescence (PL) spectroscopy was performed on dried ELISA wells and the results compared with the same QD samples dried on a solid substrate. We confirmed a "blue" up to 37 nm PL spectral shift in a case of QDs conjugated to PSA antibodies. Increasing of the "blue" spectral shift was observed at lower PSA antigen concentrations. The results can be used to improve sensitivity of "sandwich" ELISA cancer antigen detection.

  9. Separability and dynamical symmetry of Quantum Dots

    SciTech Connect

    Zhang, P.-M.; Zou, L.-P.; Horvathy, P.A.; Gibbons, G.W.

    2014-02-15

    The separability and Runge–Lenz-type dynamical symmetry of the internal dynamics of certain two-electron Quantum Dots, found by Simonović et al. (2003), are traced back to that of the perturbed Kepler problem. A large class of axially symmetric perturbing potentials which allow for separation in parabolic coordinates can easily be found. Apart from the 2:1 anisotropic harmonic trapping potential considered in Simonović and Nazmitdinov (2013), they include a constant electric field parallel to the magnetic field (Stark effect), the ring-shaped Hartmann potential, etc. The harmonic case is studied in detail. -- Highlights: • The separability of Quantum Dots is derived from that of the perturbed Kepler problem. • Harmonic perturbation with 2:1 anisotropy is separable in parabolic coordinates. • The system has a conserved Runge–Lenz type quantity.

  10. Quantum dot molecular beacons for DNA detection.

    PubMed

    Cady, Nathaniel C

    2009-01-01

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

  11. TOPICAL REVIEW: Polar and nonpolar GaN quantum dots

    NASA Astrophysics Data System (ADS)

    Daudin, Bruno

    2008-11-01

    Growth, structural and optical properties of GaN quantum dots are reviewed, with a special emphasis on plasma-assisted molecular beam epitaxy. The versatility of this technique makes it particularly adapted to growth of quantum dots, either polar (c-plane) or nonpolar (a-plane and m-plane). After describing in detail the growth process and analyzing the morphology of the dots, we review the optical properties of these nanostructures and discuss the properties of single dots.

  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. Si quantum dots and different aspects of applications

    NASA Astrophysics Data System (ADS)

    Torchynska, Tetyana V.

    2011-09-01

    This paper presents briefly the history of the study of Si quantum dot (QDs) structures and the advances of different applications of Si quantum dots (QDs) in quantum electronics, such as: Si QD light emitting diodes, Si QD solar cells and memory structures, Si QD based one electron devices and double QD structures for spintronics [1].

  14. 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.

  15. Quantum-Dot Laser for Wavelengths of 1.8 to 2.3 micron

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming

    2006-01-01

    The figure depicts a proposed semiconductor laser, based on In(As)Sb quantum dots on a (001) InP substrate, that would operate in the wavelength range between 1.8 and 2.3 m. InSb and InAsSb are the smallest-bandgap conventional III-V semiconductor materials, and the present proposal is an attempt to exploit the small bandgaps by using InSb and InAsSb nanostructures as midinfrared emitters. The most closely related prior III-V semiconductor lasers are based, variously, on strained InGaAs quantum wells and InAs quantum dots on InP substrates. The emission wavelengths of these prior devices are limited to about 2.1 m because of critical quantum-well thickness limitations for these lattice mismatched material systems. The major obstacle to realizing the proposed laser is the difficulty of fabricating InSb quantum dots in sufficient density on an InP substrate. This difficulty arises partly because of the weakness of the bond between In and Sb and partly because of the high temperature needed to crack metalorganic precursor compounds during the vapor-phase epitaxy used to grow quantum dots: The mobility of the weakly bound In at the high growth temperature is so high that In adatoms migrate easily on the growth surface, resulting in the formation of large InSb islands at a density, usually less than 5 x 10(exp 9) cm(exp -2), that is too low for laser operation. The mobility of the In adatoms could be reduced by introducing As atoms to the growth surface because the In-As bond is about 30 percent stronger than is the In-Sb bond. The fabrication of the proposed laser would include a recently demonstrated process that involves the use of alternative supplies of precursors to separate group-III and group-V species to establish local non-equilibrium process conditions, so that In(As)Sb quantum dots assemble themselves on a (001) InP substrate at a density as high as 4 x 10(exp 10) cm(exp -2). Room-temperature photoluminescence spectra of quantum dots formed by this process

  16. Three-dimensional Si/Ge quantum dot crystals.

    PubMed

    Grützmacher, Detlev; Fromherz, Thomas; Dais, Christian; Stangl, Julian; Müller, Elisabeth; Ekinci, Yasin; Solak, Harun H; Sigg, Hans; Lechner, Rainer T; Wintersberger, Eugen; Birner, Stefan; Holý, Vaclav; Bauer, Günther

    2007-10-01

    Modern nanotechnology offers routes to create new artificial materials, widening the functionality of devices in physics, chemistry, and biology. Templated self-organization has been recognized as a possible route to achieve exact positioning of quantum dots to create quantum dot arrays, molecules, and crystals. Here we employ extreme ultraviolet interference lithography (EUV-IL) at a wavelength of lambda = 13.5 nm for fast, large-area exposure of templates with perfect periodicity. Si(001) substrates have been patterned with two-dimensional hole arrays using EUV-IL and reactive ion etching. On these substrates, three-dimensionally ordered SiGe quantum dot crystals with the so far smallest quantum dot sizes and periods both in lateral and vertical directions have been grown by molecular beam epitaxy. X-ray diffractometry from a sample volume corresponding to about 3.6 x 10(7) dots and atomic force microscopy (AFM) reveal an up to now unmatched structural perfection of the quantum dot crystal and a narrow quantum dot size distribution. Intense interband photoluminescence has been observed up to room temperature, indicating a low defect density in the three-dimensional (3D) SiGe quantum dot crystals. Using the Ge concentration and dot shapes determined by X-ray and AFM measurements as input parameters for 3D band structure calculations, an excellent quantitative agreement between measured and calculated PL energies is obtained. The calculations show that the band structure of the 3D ordered quantum dot crystal is significantly modified by the artificial periodicity. A calculation of the variation of the eigenenergies based on the statistical variation in the dot dimensions as determined experimentally (+/-10% in linear dimensions) shows that the calculated electronic coupling between neighboring dots is not destroyed due to the quantum dot size variations. Thus, not only from a structural point of view but also with respect to the band structure, the 3D ordered

  17. Blinking statistics of silicon quantum dots.

    PubMed

    Bruhn, Benjamin; Valenta, Jan; Sangghaleh, Fatemeh; Linnros, Jan

    2011-12-14

    The blinking statistics of numerous single silicon quantum dots fabricated by electron-beam lithography, plasma etching, and oxidation have been analyzed. Purely exponential on- and off-time distributions were found consistent with the absence of statistical aging. This is in contrast to blinking reports in the literature where power-law distributions prevail as well as observations of statistical aging in nanocrystal ensembles. A linear increase of the switching frequency with excitation power density indicates a domination of single-photon absorption processes, possibly through a direct transfer of charges to trap states without the need for a bimolecular Auger mechanism. Photoluminescence saturation with increasing excitation is not observed; however, there is a threshold in excitation (coinciding with a mean occupation of one exciton per nanocrystal) where a change from linear to square-root increase occurs. Finally, the statistics of blinking of single quantum dots in terms of average on-time, blinking frequency and blinking amplitude reveal large variations (several orders) without any significant correlation demonstrating the individual microscopic character of each quantum dot.

  18. Quantum dot spectroscopy using a single phosphorus donor

    NASA Astrophysics Data System (ADS)

    Büch, Holger; Fuechsle, Martin; Baker, William; House, Matthew G.; Simmons, Michelle Y.

    2015-12-01

    Using a deterministic single P donor placed with atomic precision accuracy next to a nanoscale silicon quantum dot, we present a way to analyze the energy spectrum of small quantum dots in silicon by tunnel-coupled transport measurements. The energy-level structure of the quantum dot is observed as resonance features within the transport bias triangles when the donor chemical potential is aligned with states within the quantum dot as confirmed by a numeric rate equation solver SIMON. This technique allows us to independently extract the quantum dot level structure irrespective of the density of states in the leads. Such a method is useful for the investigation of silicon quantum dots in the few-electron regime where the level structure is governed by an intricate interplay between the spin- and the valley-orbit degrees of freedom.

  19. The ground state properties of In(Ga)As/GaAs low strain quantum dots

    NASA Astrophysics Data System (ADS)

    Pieczarka, Maciej; Sęk, Grzegorz

    2016-08-01

    We present theoretical studies on the confined states in low-strain In(Ga)As quantum dots (QDs). The 8-band k·p model together with the continuum elasticity theory and piezoelectric fields were employed to calculate the potential and confined electron and hole eigenstates. We focused on low-indium-content QDs with distinct in-plane asymmetry, which are naturally formed in the low strain regime of the Stranski-Krastanow growth mode. It has been found that the naturally thick wetting layer together with piezoelectric potential affect the total confinement potential to such extent that the hole eigenstates can get the spatial in-plane orientation orthogonal to the main axis of the dot elongation. This can influence both, qualitatively and quantitatively, many of the electronic and optical properties, as e.g. the polarization selection rules for the optical transition or the transitions oscillator strength. Eventually, importance of the degree of the shape asymmetry or the dots' size, and differences between the low-strain (low-In-content) QDs and pure InAs dots formed in high strain conditions are discussed.

  20. 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.

  1. InAs quantum dot morphology after capping with In, N, Sb alloyed thin films

    SciTech Connect

    Keizer, J. G.; Koenraad, P. M.; Ulloa, J. M.; Utrilla, A. D.

    2014-02-03

    Using a thin capping layer to engineer the structural and optical properties of InAs/GaAs quantum dots (QDs) has become common practice in the last decade. Traditionally, the main parameter considered has been the strain in the QD/capping layer system. With the advent of more exotic alloys, it has become clear that other mechanisms significantly alter the QD size and shape as well. Larger bond strengths, surfactants, and phase separation are known to act on QD properties but are far from being fully understood. In this study, we investigate at the atomic scale the influence of these effects on the morphology of capped QDs with cross-sectional scanning tunneling microscopy. A broad range of capping materials (InGaAs, GaAsSb, GaAsN, InGaAsN, and GaAsSbN) are compared. The QD morphology is related to photoluminescence characteristics.

  2. Temperature-dependent modulated reflectance of InAs/InGaAs/GaAs quantum dots-in-a-well infrared photodetectors

    SciTech Connect

    Nedzinskas, R. Čechavičius, B.; Rimkus, A.; Pozingytė, E.; Kavaliauskas, J.; Valušis, G.; Li, L. H.; Linfield, E. H.

    2015-04-14

    We present a photoreflectance (PR) study of multi-layer InAs quantum dot (QD) photodetector structures, incorporating InGaAs overgrown layers and positioned asymmetrically within GaAs/AlAs quantum wells (QWs). The influence of the back-surface reflections on the QD PR spectra is explained and a temperature-dependent photomodulation mechanism is discussed. The optical interband transitions originating from the QD/QW ground- and excited-states are revealed and their temperature behaviour in the range of 3–300 K is established. In particular, we estimated the activation energy (∼320 meV) of exciton thermal escape from QD to QW bound-states at high temperatures. Furthermore, from the obtained Varshni parameters, a strain-driven partial decomposition of the InGaAs cap layer is determined.

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

    PubMed

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

    2015-09-01

    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. Imaging ligand-gated ion channels with quantum dots

    NASA Astrophysics Data System (ADS)

    Tomlinson, I. D.; Orndorff, Rebecca L.; Gussin, Hélène; Mason, John N.; Blakely, Randy D.; Pepperberg, David R.; Rosenthal, Sandra J.

    2007-02-01

    In this paper we report two different methodologies for labeling ligand-gated receptors. The first of these builds upon our earlier work with serotonin conjugated quantum dots and our studies with pegilated quantum dots to reduce non specific binding. In this approach a pegilated derivative of muscimol was synthesized and attached via an amide linkage to quantum dots coated in an amphiphillic polymer derivative of poly acrylamide. These conjugates were used to image the GABA C receptor in oocytes. An alternative approach was used to image tissue sections to study nicotinic acetylcholine receptors in the neuro muscular junction with biotinylated Bungerotoxin and streptavidin coated quantum dots.

  5. Silver-enhanced fluorescence emission of single quantum dot nanocomposites.

    PubMed

    Fu, Yi; Zhang, Jian; Lakowicz, Joseph R

    2009-01-21

    A novel plasmon-coupled quantum dot (QD) nanocomposite via covalently interfacing the QD surfaces with silver nanoparticles was developed with greatly reduced blinking and enhanced emission fluorescence.

  6. 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.

  7. 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.

  8. 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

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

    PubMed

    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. Silicon quantum dots: fine-tuning to maturity

    NASA Astrophysics Data System (ADS)

    Morello, Andrea

    2015-12-01

    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.

  11. 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. PMID:26584678

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

    PubMed

    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

    2016-08-23

    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.

  13. 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.

  14. Self-Assembled Quantum Dots of Indium

    NASA Astrophysics Data System (ADS)

    Leonard, Devin Blaine

    1995-01-01

    The deposition of InAs or In_ xGa_{1-x}As upon GaAs substrates by molecular beam epitaxy (MBE) generally proceeds via the mode first described by Stranski and von Krastanow (SK). After the deposition of a certain thickness of this material, small islands of the deposited material nucleate on the surface. The island formation is attributed not to a large epitaxial surface energies, but to an elastic (dislocation free) relaxation of the mismatch strain (a _{InAs}=1.07cdot a_{GaAs}). I present a detailed study of the nucleation and growth of these InAs islands using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The islands are found to be lens-shaped, coherently-strained and remarkably uniform in their size. Embedding these 4 nm tall, 25 nm diameter InAs islands in GaAs confines injected carriers in three dimensions. The islands thus formed fulfill the requirements of a quantum dot (or box), which behave as "artificial atoms" whose allowed energy eigenstates are discrete. Quantum dots have been the "holy grail" for many scientists because of the advantages these discrete energy levels provide in electronic and optical devices, such as semiconductor lasers. Self-assembled quantum dots (SAQD), presented in this dissertation, surmount the fabrication difficulties typical for quantum dots, reducing efforts to more fundamental problems of size uniformity and control. SAQDs have distinct advantages over quantum dots formed with other methods. For instance, no processing is required before or after growth. In addition, layers of SAQDs can be easily integrated into GaAs/AlGaAs devices. Contrary to quantum dots formed with other techniques, a strong light emission is observed from the SAQD at ~1.2 eV. Further photoluminescence (PL) experiments reveal emission linewidths less than.5 meV from individual SAQD, but a ~50 meV linewidth from larger arrays due to small SAQD thickness fluctuations. PL excitation (PLE) spectra reveal a large shift between

  15. Reduced linewidth enhancement factor due to excited state transition of quantum dot lasers.

    PubMed

    Xu, Peng-Fei; Ji, Hai-Ming; Xiao, Jin-Long; Gu, Yong-Xian; Huang, Yong-Zhen; Yang, Tao

    2012-04-15

    The carrier induced refractive index change and linewidth enhancement factor α due to ground-state (GS) and excited-state (ES) transitions have been compared by measuring the optical gain spectra from an InAs/GaAs quantum dot (QD) laser structure. It is shown that the ES transition exhibits a reduced α-factor compared to the value due to the GS transition. This result can be explained by the α-factor due to the ES transition having a smaller increase from the non-resonant carriers in the combined state of the wetting layer and InGaAs strain reducing layer than the α-factor increase due to the GS transition, since the relaxation time for carriers from the combined state of the wetting layer and InGaAs strain reducing layer to the ES is shorter than to the GS. The result reported here shows another advantage of using ES QD lasers for optical communication, in addition to their higher modulation speed.

  16. Hybrid passivated colloidal quantum dot solids

    NASA Astrophysics Data System (ADS)

    Ip, Alexander H.; Thon, Susanna M.; Hoogland, Sjoerd; Voznyy, Oleksandr; Zhitomirsky, David; Debnath, Ratan; Levina, Larissa; Rollny, Lisa R.; Carey, Graham H.; Fischer, Armin; Kemp, Kyle W.; Kramer, Illan J.; Ning, Zhijun; Labelle, André J.; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H.

    2012-09-01

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

  17. Hybrid passivated colloidal quantum dot solids.

    PubMed

    Ip, Alexander H; Thon, Susanna M; Hoogland, Sjoerd; Voznyy, Oleksandr; Zhitomirsky, David; Debnath, Ratan; Levina, Larissa; Rollny, Lisa R; Carey, Graham H; Fischer, Armin; Kemp, Kyle W; Kramer, Illan J; Ning, Zhijun; Labelle, André J; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H

    2012-09-01

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

  18. 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.

  19. Passively Q-switched Yb3+:YCa4O(BO3)3 laser with InGaAs quantum wells as saturable absorbers

    NASA Astrophysics Data System (ADS)

    Liang, H. C.; Huang, J. Y.; Su, K. W.; Lai, H. C.; Chen, Y. F.; Huang, K. F.; Zhang, H. J.; Wang, J. Y.; Jiang, M. H.

    2007-04-01

    A diode-pumped Yb:YCOB laser at 1086 nm is passively Q switched by using InGaAs quantum wells as saturable absorbers and utilizing the Bragg mirror structure as an output coupler. With an absorbed pump power of 9.2 W the laser produces pulses of 100 ms duration with average pulse energy of as much as 165 μJ at a pulse repetition rate of 7 kHz.

  20. Passively Q-switched Yb3+:YCa4O(BO3)3 laser with InGaAs quantum wells as saturable absorbers.

    PubMed

    Liang, H C; Huang, J Y; Su, K W; Lai, H C; Chen, Y F; Huang, K F; Zhang, H J; Wang, J Y; Jiang, M H

    2007-04-20

    A diode-pumped Yb:YCOB laser at 1086 nm is passively Q switched by using InGaAs quantum wells as saturable absorbers and utilizing the Bragg mirror structure as an output coupler. With an absorbed pump power of 9.2 W the laser produces pulses of 100 ms duration with average pulse energy of as much as 165 microJ at a pulse repetition rate of 7 kHz.

  1. 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.

  2. Lifetime blinking in nonblinking nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Galland, Christophe; Ghosh, Yagnaseni; Steinbrück, Andrea; Hollingsworth, Jennifer A.; Htoon, Han; Klimov, Victor I.

    2012-06-01

    Nanocrystal quantum dots are attractive materials for applications as nanoscale light sources. One impediment to these applications is fluctuations of single-dot emission intensity, known as blinking. Recent progress in colloidal synthesis has produced nonblinking nanocrystals; however, the physics underlying blinking suppression remains unclear. Here we find that ultra-thick-shell CdSe/CdS nanocrystals can exhibit pronounced fluctuations in the emission lifetimes (lifetime blinking), despite stable nonblinking emission intensity. We demonstrate that lifetime variations are due to switching between the neutral and negatively charged state of the nanocrystal. Negative charging results in faster radiative decay but does not appreciably change the overall emission intensity because of suppressed nonradiative Auger recombination for negative trions. The Auger process involving excitation of a hole (positive trion pathway) remains efficient and is responsible for charging with excess electrons, which occurs via Auger-assisted ionization of biexcitons accompanied by ejection of holes.

  3. Lifetime blinking in nonblinking nanocrystal quantum dots.

    PubMed

    Galland, Christophe; Ghosh, Yagnaseni; Steinbrück, Andrea; Hollingsworth, Jennifer A; Htoon, Han; Klimov, Victor I

    2012-06-19

    Nanocrystal quantum dots are attractive materials for applications as nanoscale light sources. One impediment to these applications is fluctuations of single-dot emission intensity, known as blinking. Recent progress in colloidal synthesis has produced nonblinking nanocrystals; however, the physics underlying blinking suppression remains unclear. Here we find that ultra-thick-shell CdSe/CdS nanocrystals can exhibit pronounced fluctuations in the emission lifetimes (lifetime blinking), despite stable nonblinking emission intensity. We demonstrate that lifetime variations are due to switching between the neutral and negatively charged state of the nanocrystal. Negative charging results in faster radiative decay but does not appreciably change the overall emission intensity because of suppressed nonradiative Auger recombination for negative trions. The Auger process involving excitation of a hole (positive trion pathway) remains efficient and is responsible for charging with excess electrons, which occurs via Auger-assisted ionization of biexcitons accompanied by ejection of holes.

  4. 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.

  5. Photoluminescence Imaging of Focused Ion Beam Induced Individual Quantum Dots

    SciTech Connect

    Lee, Jieun; Saucer, Timothy W.; Martin, Andrew J.; Tien, Deborah; Millunchick, Joanna M.; Sih, Vanessa

    2011-02-08

    We report on scanning microphotoluminescence measurements that spectrally and spatially resolve emission from individual InAs quantum dots that were induced by focused ion beam patterning. Multilayers of quantum dots were spaced 2 μm apart, with a minimum single dot emission line width of 160 μeV, indicating good optical quality for dots patterned using this technique. Mapping 16 array sites, at least 65% were occupied by optically active dots and the spectral inhomogeneity was within 30 meV.

  6. 1.55 µm InAs/GaAs quantum dots and high repetition rate quantum dot SESAM mode-locked laser.

    PubMed

    Zhang, Z Y; Oehler, A E H; Resan, B; Kurmulis, S; Zhou, K J; Wang, Q; Mangold, M; Süedmeyer, T; Keller, U; Weingarten, K J; Hogg, R A

    2012-01-01

    High pulse repetition rate (≥ 10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

  7. 1.55 µm InAs/GaAs Quantum Dots and High Repetition Rate Quantum Dot SESAM Mode-locked Laser

    PubMed Central

    Zhang, Z. Y.; Oehler, A. E. H.; Resan, B.; Kurmulis, S.; Zhou, K. J.; Wang, Q.; Mangold, M.; Süedmeyer, T.; Keller, U.; Weingarten, K. J.; Hogg, R. A.

    2012-01-01

    High pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices. PMID:22745898

  8. 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.

  9. Quantum Adiabatic Pumping by Modulating Tunnel Phase in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Taguchi, Masahiko; Nakajima, Satoshi; Kubo, Toshihiro; Tokura, Yasuhiro

    2016-08-01

    In a mesoscopic system, under zero bias voltage, a finite charge is transferred by quantum adiabatic pumping by adiabatically and periodically changing two or more control parameters. We obtained expressions for the pumped charge for a ring of three quantum dots (QDs) by choosing the magnetic flux penetrating the ring as one of the control parameters. We found that the pumped charge shows a steplike behavior with respect to the variance of the flux. The value of the step heights is not universal but depends on the trajectory of the control parameters. We discuss the physical origin of this behavior on the basis of the Fano resonant condition of the ring.

  10. Power-law photoluminescence decay in quantum dots

    SciTech Connect

    Král, Karel; Menšík, Miroslav

    2014-05-15

    Some quantum dot samples show a long-time (power-law) behavior of their luminescence intensity decay. This effect has been recently explained as being due to a cooperation of many tunneling channels transferring electrons from small quantum dots with triplet exciton to quantum dots at which the electrons can recombine with the holes in the valence band states. In this work we show that the long-time character of the sample luminescence decay can also be caused by an intrinsic property of a single dot, namely, by a non-adiabatic effect of the electron occupation up-conversion caused by the electron-phonon multiple scattering mechanism.

  11. Terahertz hot electron bolometric detectors based on graphene quantum dots

    NASA Astrophysics Data System (ADS)

    El Fatimy, A.; Myers-Ward, R. L.; Boyd, A. K.; Daniels, K. M.; Gaskill, D. K.; Barbara, P.

    2015-03-01

    We study graphene quantum dots patterned from epitaxial graphene on SiC with a resistance strongly dependent on temperature. The combination of weak electron-phonon coupling and small electronic heat capacity in graphene makes these quantum dots ideal hot-electron bolometers. We measure and characterize the THz optical response of devices with different dot sizes, at operating temperatures from 2.5K to 80K. The high responsivity, the potential for operation above 80 K and the process scalability show great promise towards practical applications of graphene quantum dot THz detectors. This work was sponsored by the U.S. Office of Naval Research (Award Number N000141310865).

  12. Quantum dot loaded immunomicelles for tumor imaging

    PubMed Central

    2010-01-01

    Background Optical imaging is a promising method for the detection of tumors in animals, with speed and minimal invasiveness. We have previously developed a lipid coated quantum dot system that doubles the fluorescence of PEG-grafted quantum dots at half the dose. Here, we describe a tumor-targeted near infrared imaging agent composed of cancer-specific monoclonal anti-nucleosome antibody 2C5, coupled to quantum dot (QD)-containing polymeric micelles, prepared from a polyethylene glycol/phosphatidylethanolamine (PEG-PE) conjugate. Its production is simple and involves no special equipment. Its imaging potential is great since the fluorescence intensity in the tumor is twofold that of non-targeted QD-loaded PEG-PE micelles at one hour after injection. Methods Para-nitrophenol-containing (5%) PEG-PE quantum dot micelles were produced by the thin layer method. Following hydration, 2C5 antibody was attached to the PEG-PE micelles and the QD-micelles were purified using dialysis. 4T1 breast tumors were inoculated subcutaneously in the flank of the animals. A lung pseudometastatic B16F10 melanoma model was developed using tail vein injection. The contrast agents were injected via the tail vein and mice were depilated, anesthetized and imaged on a Kodak Image Station. Images were taken at one, two, and four hours and analyzed using a methodology that produces normalized signal-to-noise data. This allowed for the comparison between different subjects and time points. For the pseudometastatic model, lungs were removed and imaged ex vivo at one and twenty four hours. Results The contrast agent signal intensity at the tumor was double that of the passively targeted QD-micelles with equally fast and sharply contrasted images. With the side views of the animals only tumor is visible, while in the dorsal view internal organs including liver and kidney are visible. Ex vivo results demonstrated that the agent detects melanoma nodes in a lung pseudometastatic model after a 24 hours

  13. 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.

  14. Charge-separated state in strain-induced quantum dots

    SciTech Connect

    Gu, Y.; Sturge, M.D.; Kash, K.; Watkins, N.; Van der Gaag, B.P.; Gozdz, A.S.; Florez, L.T.; Harbison, J.P.

    1997-03-01

    We have measured the time-resolved photoluminescence of strain-induced quantum dots. We show that a long-lived intermediate state is involved in the excitation transfer from the interstitial quantum well to the dot. This intermediate state has the properties expected of the charge separated state predicted by theory. {copyright} {ital 1997 American Institute of Physics.}

  15. Thermoelectric transport in strongly correlated quantum dot nanocomposites

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Yang, Ronggui

    2010-08-01

    We investigate the thermoelectric transport properties (electrical conductivity, Seebeck coefficient, power factor, and thermoelectric figure of merit) in strongly correlated quantum dot nanocomposites at low temperature (77 K) by using the dynamical mean-field theory and the Kubo formula. The periodic Anderson model is applied to describe the strongly correlated quantum dot nanocomposites with tunable parameters such as the size of quantum dots and the electron occupation number. The electron occupation number can be controlled by the doping concentration in the both matrix and quantum dots, the size of quantum dots, and the interdot spacing. These parameters control the transition between n -type like behavior (with negative Seebeck coefficient) and p -type like behavior (with positive Seebeck coefficient) of strongly correlated quantum dot nanocomposites. Large Seebeck coefficient up to 260μV/K due to the asymmetry of the electron bands with sharp electron density of states can be obtained in the strongly correlated quantum dot nanocomposites, along with moderate electrical conductivity values in the order of 105/Ωm . This results in optimal power factor about 78μW/cmK2 and optimal figure of merit (ZT) over 0.55 which is much larger than the value of the state-of-the-art low-temperature thermoelectric materials. This study shows that high efficiency thermoelectric materials at low temperature can be obtained in strongly correlated quantum dot nanocomposites.

  16. 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.

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

    PubMed

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-04-11

    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.

  18. Polarization anisotropic luminescence of tunable single lateral quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Hermannstädter, C.; Witzany, M.; Heldmaier, M.; Hafenbrak, R.; Jöns, K. D.; Beirne, G. J.; Michler, P.

    2012-03-01

    We investigate the photoluminescence polarization anisotropy of self-assembled individual lateral InGaAs/GaAs quantum dot molecules. In contrast to similarly grown single quantum dots, the dot molecules exhibit a remarkable degree of linear polarization, which remains almost unchanged when a lateral electric field is applied to tune the exciton wave function and, thus, the luminescence spectral properties. We discuss the nature of this polarization anisotropy and suggest possible causes based on the system's symmetry and heterostructure alloy composition.

  19. Quantum dot blueing and blinking enables fluorescence nanoscopy.

    PubMed

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

    2011-01-12

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

  20. 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

  1. 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

  2. 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.

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

    PubMed

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

    2013-11-13

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

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

    PubMed

    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.

  5. Germanium based electrostatic quantum dots: design and characterization.

    NASA Astrophysics Data System (ADS)

    Mazzeo, Giovanni; Yablonovitch, Eli; Jiang, Hong-Wen

    2010-03-01

    While the less mature Germanium technology requires an extra effort for the realization of single electron quantum dots, unique properties of Germanium rich heterostructures together with spin coherence times comparable to Silicon, can justify the development of such new technology. We report our progresses on the formation of electrostatic quantum dots in Germanium. We employ an MOS-like structure with no modulation doping already successfully proven in Silicon devices. A two level gate stack is used: the top gate is positively biased to attract electrons while the lowers gates are negatively biased to form the quantum dot and attract holes in a transistor channel, used to detect the electrons in the adjacent quantum dot. Finite Element Method simulations are used to prove the concept of this hybrid holes-transistor/electron-QD device and estimate the sensitivity of the charge detection. Preliminary characterizations of quantum dot devices built with this structure are reported.

  6. 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.

  7. 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.

  8. 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.

  9. In Vivo Imaging of Quantum Dots

    NASA Astrophysics Data System (ADS)

    Texier, Isabelle; Josser, Véronique

    Noninvasive whole-body near-infrared fluorescence imaging is now acknowledged as a powerful method for the molecular mapping of biological events in live small animals such as mouse models. With outstanding optical properties such as high fluorescence quantum yields and low photobleaching rates, quantum dots (QDs) are labels of choice in the near-infrared domain. The main applications described in the literature for in vivo imaging of mice after injection of QDs encompass imaging of lymph nodes and tumors and cell tracking. Standard methods for the preparation, the purification, and the in vivo fluorescence whole-body imaging of QDs in the live mouse are described. Nanoparticles coated by PEG chains of different sizes and terminal groups are prepared using 705-nm-emitting commercial QDs. Their biodistribution after intravenous or intradermal injections in tumor-bearing mice is reported here.

  10. 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.

  11. Tunneling rate in double quantum dots

    NASA Astrophysics Data System (ADS)

    Filikhin, Igor; Matinyan, Sergei; Vlahovic, Branislav

    2014-03-01

    We study spectral properties of electron tunneling in double quantum dots (DQDs) (and double quantum wells (DQWs)) and their relation to the geometry. In particular we compare the tunneling in DQW with chaotic and regular geometry, taking into account recent evidence about regularization of the tunneling rate when the QW geometry is chaotic. Our calculations do not support this assumption. We confirm high influence of the QW geometry boundaries on the rate fluctuation along the spectrum. The factors of the effective mass anisotropy and violation of the symmetry of DQD and DQW are also considered. Generally, we found that the small violation of the symmetry drastically affects tunneling. This work is supported by the NSF (HRD-0833184) and NASA (NNX09AV07A).

  12. 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

  13. Quantum-dot optical temperature probes

    NASA Astrophysics Data System (ADS)

    Walker, Glen W.; Sundar, Vikram C.; Rudzinski, Christina M.; Wun, Aetna W.; Bawendi, Moungi G.; Nocera, Daniel G.

    2003-10-01

    The steady-state photoluminescence (PL) properties of cadmium selenide quantum dots (QDs) with a zinc sulfide overlayer [(CdSe)ZnS] can be strongly dependent on temperature in the range from 100 to 315 K. The PL intensity from 50 to 55 Å (CdSe)ZnS QDs in poly(lauryl methacrylate) matrices increases by a factor of ˜5 when the temperature is decreased from 315 to 100 K, and the peak of the emission band is blueshifted by 20 nm over the same range. The change in PL intensity is appreciable, linear, and reversible (-1.3% per °C) for temperatures close to ambient conditions. These properties of (CdSe)ZnS dots are retained in a variety of matrices including polymer and sol-gel films, and they are independent of excitation wavelength above the band gap. The significant temperature dependence of the luminescence combined with its insensitivity to oxygen quenching establishes (CdSe)ZnS dots as optical temperature indicators for temperature-sensitive coatings.

  14. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    PubMed

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs. PMID:27427737

  15. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    PubMed

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

  16. Spectroscopy of excitonic Zeeman levels in single quantum dots

    NASA Astrophysics Data System (ADS)

    Schaller, A.; Zrenner, A.; Abstreiter, G.; Böhm, G.

    1998-07-01

    Fully confined excitons are investigated in natural quantum dots, which are formed by well-width fluctuations in GaAs/AlAs coupled quantum-well structures. In magnetooptic experiments a population inversion of the Zeeman split levels in the quantum dots is found under the condition of charge injection from the AlAs X-point state. This new phenomenon is explained in terms of spin thermalization in the intermediate indirect exciton state and subsequent tunnelling into the direct quantum-dot state. Population inversion is thereby caused by the associated sign reversal of the effective exciton g-factor.

  17. Quantum Dot Enabled Molecular Sensing and Diagnostics

    PubMed Central

    Zhang, Yi; Wang, Tza-Huei

    2012-01-01

    Since its emergence, semiconductor nanoparticles known as quantum dots (QDs) have drawn considerable attention and have quickly extended their applicability to numerous fields within the life sciences. This is largely due to their unique optical properties such as high brightness and narrow emission band as well as other advantages over traditional organic fluorophores. New molecular sensing strategies based on QDs have been developed in pursuit of high sensitivity, high throughput, and multiplexing capabilities. For traditional biological applications, QDs have already begun to replace traditional organic fluorophores to serve as simple fluorescent reporters in immunoassays, microarrays, fluorescent imaging applications, and other assay platforms. In addition, smarter, more advanced QD probes such as quantum dot fluorescence resonance energy transfer (QD-FRET) sensors, quenching sensors, and barcoding systems are paving the way for highly-sensitive genetic and epigenetic detection of diseases, multiplexed identification of infectious pathogens, and tracking of intracellular drug and gene delivery. When combined with microfluidics and confocal fluorescence spectroscopy, the detection limit is further enhanced to single molecule level. Recently, investigations have revealed that QDs participate in series of new phenomena and exhibit interesting non-photoluminescent properties. Some of these new findings are now being incorporated into novel assays for gene copy number variation (CNV) studies and DNA methylation analysis with improved quantification resolution. Herein, we provide a comprehensive review on the latest developments of QD based molecular diagnostic platforms in which QD plays a versatile and essential role. PMID:22916072

  18. 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.

  19. Competing interactions in semiconductor quantum dots

    DOE PAGESBeta

    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 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

  20. Colloidal quantum dot light-emitting devices

    PubMed Central

    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. PMID:22110863

  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. Lifetime Blinking in Non Blinking Quantum Dots

    NASA Astrophysics Data System (ADS)

    Klimov, Victor; Ghosh, Yagnaseni; Steinbrueck, Andrea; Hollingsworth, Jennifer; Htoon, Han; Galland, Christophe

    2012-02-01

    Photoluminescence (PL) blinking is a common property of nanoscale light emitters. Nanocrystal quantum dots have often been used as model systems in studies of this intriguing phenomenon. Here, we use recently developed thick-shell CdSe/CdS NQDs to demonstrate a new regime of blinking where discrete fluctuations in the PL lifetime (``lifetime blinking'') occur without appreciable changes in the PL intensity. Single-dot measurements under controlled electrochemical charge injection [1] yield the PL lifetimes of neutral and charged excitons. We show that the observed ``lifetime blinking'' are due to random charging/discharging of the nanocrystal [2]. Indeed, the injection of electrons does not appreciably modify the PL quantum yield, which explains the coexistence of a nonblinking intensity with a ``blinking'' lifetime. At higher excitation power, charged excitons dominate the PL emission. We build a quantitative model showing that nanocrystal charging is caused by Auger-assisted ejection of a hole, producing negatively charged species. Importantly, Auger recombination that involves excitation of an electron is suppressed while hole-based processes remain efficient.[4pt] [1] Galland et al., Nature 479, 203-207 (2011)[0pt] [2] Galland et al., Submitted (2011)

  3. Fourier transform spectra of quantum dots

    NASA Astrophysics Data System (ADS)

    Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

    2010-05-01

    Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

  4. Fourier transform spectra of quantum dots

    NASA Astrophysics Data System (ADS)

    Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

    2009-09-01

    Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

  5. Study of metallothionein-quantum dots interactions.

    PubMed

    Tmejova, Katerina; Hynek, David; Kopel, Pavel; Krizkova, Sona; Blazkova, Iva; Trnkova, Libuse; Adam, Vojtech; Kizek, Rene

    2014-05-01

    Nanoparticles have gained increasing interest in medical and in vivo applications. Metallothionein (MT) is well known as a maintainer of metal ions balance in intracellular space. This is due to high affinity of this protein to any reactive species including metals and reactive oxygen species. The purpose of this study was to determine the metallothionein-quantum dots interactions that were investigated by spectral and electrochemical techniques. CuS, CdS, PbS, and CdTe quantum dots (QDs) were analysed. The highest intensity was shown for CdTe, than for CdS measured by fluorescence. These results were supported by statistical analysis and considered as significant. Further, these interactions were analysed using gel electrophoresis, where MT aggregates forming after interactions with QDs were detected. Using differential pulse voltammetry Brdicka reaction, QDs and MT were studied. This method allowed us to confirm spectral results and, moreover, to observe the changes in MT structure causing new voltammetric peaks called X and Y, which enhanced with the prolonged time of interaction up to 6 h.

  6. Growing InGaAs quasi-quantum wires inside semi-rhombic shaped planar InP nanowires on exact (001) silicon

    NASA Astrophysics Data System (ADS)

    Han, Yu; Li, Qiang; Chang, Shih-Pang; Hsu, Wen-Da; Lau, Kei May

    2016-06-01

    We report InGaAs quasi-quantum wires embedded in planar InP nanowires grown on (001) silicon emitting in the 1550 nm communication band. An array of highly ordered InP nanowire with semi-rhombic cross-section was obtained in pre-defined silicon V-grooves through selective-area hetero-epitaxy. The 8% lattice mismatch between InP and Si was accommodated by an ultra-thin stacking disordered InP/GaAs nucleation layer. X-ray diffraction and transmission electron microscope characterizations suggest excellent crystalline quality of the nanowires. By exploiting the morphological evolution of the InP and a self-limiting growth process in the V-grooves, we grew embedded InGaAs quantum-wells and quasi-quantum-wires with tunable shape and position. Room temperature analysis reveals substantially improved photoluminescence in the quasi-quantum wires as compared to the quantum-well reference, due to the reduced intrusion defects and enhanced quantum confinement. These results show great promise for integration of III-V based long wavelength nanowire lasers on the well-established (001) Si platform.

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

    PubMed

    Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal; Patriarche, Gilles; Harmand, Jean-Christophe; Akopian, Nika; Zwiller, Val

    2016-02-10

    We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width. We notice that the emission spectra consist often of two peaks close in energy, which we explain with a comprehensive theory showing that the symmetry of the system plays a crucial role for the hole levels forming hybridized orbitals. Our results state that crystal phase quantum dots have promising quantum optical properties for single photon application and quantum optics. PMID:26806321

  8. Charge-extraction strategies for colloidal quantum dot photovoltaics.

    PubMed

    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.

  9. Spectroscopy of the D1 transition of cesium by dressed-state resonance fluorescence from a single (In,Ga)As/GaAs quantum dot

    NASA Astrophysics Data System (ADS)

    Ulrich, S. M.; Weiler, S.; Oster, M.; Jetter, M.; Urvoy, A.; Löw, R.; Michler, P.

    2014-09-01

    We use a laser-driven single (In,Ga)As quantum dot (QD) in the dressed-state regime of resonance fluorescence (T =4K) to observe the four D1-transition lines of alkali atomic cesium (Cs) vapor at room temperature. We tune the frequency of the dressing continuous-wave laser in the vicinity of the bare QD resonance ˜335.116THz (˜894.592nm) at constant excitation power and thereby controllably tune the center and side channel frequencies of the probe light, i.e., the Mollow triplet. Resonances between individual QD Mollow triplet lines and the atomic hyperfine-split transitions are clearly identified in the Cs absorption spectrum. Our results show that narrow-band (In,Ga)As QD resonance fluorescence (RF) is suitable to optically address individual transitions of the D1 quadruplet without applying magnetic field or electric field tuning.

  10. 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.

  11. Spin transport measurements in gallium arsenide quantum dots

    NASA Astrophysics Data System (ADS)

    Folk, Joshua Alexander

    This thesis presents a series of measurements investigating the spin physics of lateral quantum dots, defined electrostatically in the 2-D electron gas at the interface of a GaAs/AlGaAs heterostructure. The experiments span a range from open dots, where the leads of the dot carry at least one fully transmitting mode, to closed dots, where the leads are set to be tunnel barriers. For open dots, spin physics is inferred from measurements of conductance fluctuations; the effects of spin degeneracy in the orbital levels as well as a spin-orbit interaction are observed. In the closed dot measurements, ground state spin transitions as electrons are added to the dot may be determined from the motion of Coulomb blockade peaks in an in-plane magnetic field. In addition, this thesis demonstrates for the first time a direct measurement of the spin polarization of current emitted from a quantum dot, or a quantum point contact, during transport. These experiments make use of a spin-sensitive focusing geometry in which a quantum point contact serves as a spin analyzer for the mesoscopic device under test. Measurements are presented both in the open dot regime, where good agreement with theory is found, as well as the closed dot regime, where the data defies a simple theoretical explanation.

  12. A dark-field microscope for background-free detection of resonance fluorescence from single semiconductor quantum dots operating in a set-and-forget mode.

    PubMed

    Kuhlmann, Andreas V; Houel, Julien; Brunner, Daniel; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D; Warburton, Richard J

    2013-07-01

    Optically active quantum dots, for instance self-assembled InGaAs quantum dots, are potentially excellent single photon sources. The fidelity of the single photons is much improved using resonant rather than non-resonant excitation. With resonant excitation, the challenge is to distinguish between resonance fluorescence and scattered laser light. We have met this challenge by creating a polarization-based dark-field microscope to measure the resonance fluorescence from a single quantum dot at low temperature. We achieve a suppression of the scattered laser exceeding a factor of 10(7) and background-free detection of resonance fluorescence. The same optical setup operates over the entire quantum dot emission range (920-980 nm) and also in high magnetic fields. The major development is the outstanding long-term stability: once the dark-field point has been established, the microscope operates for days without alignment. The mechanical and optical designs of the microscope are presented, as well as exemplary resonance fluorescence spectroscopy results on individual quantum dots to underline the microscope's excellent performance.

  13. A dark-field microscope for background-free detection of resonance fluorescence from single semiconductor quantum dots operating in a set-and-forget mode

    SciTech Connect

    Kuhlmann, Andreas V.; Houel, Julien; Warburton, Richard J.; Brunner, Daniel; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D.

    2013-07-15

    Optically active quantum dots, for instance self-assembled InGaAs quantum dots, are potentially excellent single photon sources. The fidelity of the single photons is much improved using resonant rather than non-resonant excitation. With resonant excitation, the challenge is to distinguish between resonance fluorescence and scattered laser light. We have met this challenge by creating a polarization-based dark-field microscope to measure the resonance fluorescence from a single quantum dot at low temperature. We achieve a suppression of the scattered laser exceeding a factor of 10{sup 7} and background-free detection of resonance fluorescence. The same optical setup operates over the entire quantum dot emission range (920–980 nm) and also in high magnetic fields. The major development is the outstanding long-term stability: once the dark-field point has been established, the microscope operates for days without alignment. The mechanical and optical designs of the microscope are presented, as well as exemplary resonance fluorescence spectroscopy results on individual quantum dots to underline the microscope's excellent performance.

  14. 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.

  15. 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

  16. 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.

  17. A Novel Particle Detector: Quantum Dot Doped Liquid Scintillator

    NASA Astrophysics Data System (ADS)

    Winslow, Lindley; Conrad, Janet; Jerry, Ruel

    2010-02-01

    Quantum dots are semiconducting nanocrystals. When excited by light shorter then their characteristic wavelength, they re-emit in a narrow band around this wavelength. The size of the quantum is proportional to the characteristic wavelength so they can be tuned for many applications. CdS quantum dots are made in wavelengths from 360nm to 460nm, a perfect range for the sensitivity of photo-multiplier tubes. The synthesis of quantum dots automatically leaves them in toluene, a good organic scintillator and Cd is a particularly interesting material as it has one of the highest thermal neutron cross sections and has several neutrinoless double beta decay and double electron capture isotopes. The performance of quantum dot loaded scintillator compared to standard scintillators is measured and some unique properties presented. )

  18. 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.

  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. Full counting statistics of quantum dot resonance fluorescence.

    PubMed

    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

  1. 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

  2. Nuclear spin physics in quantum dots: An optical investigation

    NASA Astrophysics Data System (ADS)

    Urbaszek, Bernhard; Marie, Xavier; Amand, Thierry; Krebs, Olivier; Voisin, Paul; Maletinsky, Patrick; Högele, Alexander; Imamoglu, Atac

    2013-01-01

    The mesoscopic spin system formed by the 104-106 nuclear spins in a semiconductor quantum dot offers a unique setting for the study of many-body spin physics in the condensed matter. The dynamics of this system and its coupling to electron spins is fundamentally different from its bulk counterpart or the case of individual atoms due to increased fluctuations that result from reduced dimensions. In recent years, the interest in studying quantum-dot nuclear spin systems and their coupling to confined electron spins has been further fueled by its importance for possible quantum information processing applications. The fascinating nonlinear (quantum) dynamics of the coupled electron-nuclear spin system is universal in quantum dot optics and transport. In this article, experimental work performed over the last decade in studying this mesoscopic, coupled electron-nuclear spin system is reviewed. Here a special focus is on how optical addressing of electron spins can be exploited to manipulate and read out the quantum-dot nuclei. Particularly exciting recent developments in applying optical techniques to efficiently establish nonzero mean nuclear spin polarizations and using them to reduce intrinsic nuclear spin fluctuations are discussed. Both results critically influence the preservation of electron-spin coherence in quantum dots. This overall recently gained understanding of the quantum-dot nuclear spin system could enable exciting new research avenues such as experimental observations of spontaneous spin ordering or nonclassical behavior of the nuclear spin bath.

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

    PubMed

    Tablero, C

    2005-02-01

    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. PMID:15740390

  4. Imaging a single quantum dot when it is dark.

    PubMed

    Kukura, P; Celebrano, M; Renn, A; Sandoghdar, V

    2009-03-01

    We have succeeded in recording extinction images of individual cadmium selenide quantum dots at ambient condition. This is achieved by optimizing the interference between the light that is coherently scattered from the quantum dot and the reflection of the incident laser beam. The ability to interrogate the dot in the absence of fluorescence has revealed that its extinction cross section diminishes in the photobleached state, but interestingly, it remains unchanged during fluorescence blinking off times. Our methodology makes optical imaging and spectroscopy accessible to the study of ultrasmall nanoscopic objects such as nonfluorescent macromolecules and single emitters with very low quantum efficiencies.

  5. 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.

  6. Kondo effects in triangular triple quantum dots

    NASA Astrophysics Data System (ADS)

    Oguri, Akira; Numata, Takahide; Nisikawa, Yunori; Hewson, A. C.

    2009-03-01

    We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. [4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496.

  7. Interaction matrix element fluctuations in quantum dots

    SciTech Connect

    Kaplan, L.; Alhassid, Y.

    2008-04-04

    In the Coulomb blockade regime of a ballistic quantum dot, the distribution of conductance peak spacings is well known to be incorrectly predicted by a single-particle picture; instead, matrix element fluctuations of the residual electronic interaction need to be taken into account. In the normalized random-wave model, valid in the semiclassical limit where the number of electrons in the dot becomes large, we obtain analytic expressions for the fluctuations of two-body and one-body matrix elements. However, these fluctuations may be too small to explain low-temperature experimental data. We have examined matrix element fluctuations in realistic chaotic geometries, and shown that at energies of experimental interest these fluctuations generically exceed by a factor of about 3-4 the predictions of the random wave model. Even larger fluctuations occur in geometries with a mixed chaotic-regular phase space. These results may allow for much better agreement between the Hartree-Fock picture and experiment. Among other findings, we show that the distribution of interaction matrix elements is strongly non-Gaussian in the parameter range of experimental interest, even in the random wave model. We also find that the enhanced fluctuations in realistic geometries cannot be computed using a leading-order semiclassical approach, but may be understood in terms of short-time dynamics.

  8. Wet electron microscopy with quantum dots.

    PubMed

    Timp, Winston; Watson, Nicki; Sabban, Alon; Zik, Ory; Matsudaira, Paul

    2006-09-01

    Wet electron microscopy (EM) is a new imaging method with the potential to allow higher spatial resolution of samples. In contrast to most EM methods, it requires little time to perform and does not require complicated equipment or difficult steps. We used this method on a common murine macrophage cell line, IC-21, in combination with various stains and preparations, to collect high resolution images of the actin cytoskeleton. Most importantly, we demonstrated the use of quantum dots in conjunction with this technique to perform light/electron correlation microscopy. We found that wet EM is a useful tool that fits into a niche between the simplicity of light microscopy and the high spatial resolution of EM. PMID:16989089

  9. 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.

  10. Spectral Properties of Multiply Charged Quantum Dots

    SciTech Connect

    Yalcin, Sibel Ebru; Labastide, Joelle A.; Sowle, Danielle L.; Barnes, Michael D.

    2011-10-12

    Spectrally resolved fluorescence imaging of single CdSe/ZnS quantum dots (QDs), charged by electrospray deposition under negative bias has revealed a surprising net blue shift (~60 meV peak-to-peak) in the distribution of center frequencies in QD band-edge luminescence. Electrostatic force microscopy (EFM) on the electrospray QD samples showed a subpopulation of charged QDs with 4.7 ± 0.7 excess electrons, as well as a significant fraction of uncharged QDs as evidenced by the distinct cantilever response under bias. We show that the blue-shifted peak recombination energy can be understood as a first-order electronic perturbation that affects the band-edge electron- and hole-states differently. These studies provide new insight into the role of electronic perturbations of QD luminescence by excess charges.

  11. Wet electron microscopy with quantum dots.

    PubMed

    Timp, Winston; Watson, Nicki; Sabban, Alon; Zik, Ory; Matsudaira, Paul

    2006-09-01

    Wet electron microscopy (EM) is a new imaging method with the potential to allow higher spatial resolution of samples. In contrast to most EM methods, it requires little time to perform and does not require complicated equipment or difficult steps. We used this method on a common murine macrophage cell line, IC-21, in combination with various stains and preparations, to collect high resolution images of the actin cytoskeleton. Most importantly, we demonstrated the use of quantum dots in conjunction with this technique to perform light/electron correlation microscopy. We found that wet EM is a useful tool that fits into a niche between the simplicity of light microscopy and the high spatial resolution of EM.

  12. Building devices from colloidal quantum dots.

    PubMed

    Kagan, Cherie R; Lifshitz, Efrat; Sargent, Edward H; Talapin, Dmitri V

    2016-08-26

    The continued growth of mobile and interactive computing requires devices manufactured with low-cost processes, compatible with large-area and flexible form factors, and with additional functionality. We review recent advances in the design of electronic and optoelectronic devices that use colloidal semiconductor quantum dots (QDs). The properties of materials assembled of QDs may be tailored not only by the atomic composition but also by the size, shape, and surface functionalization of the individual QDs and by the communication among these QDs. The chemical and physical properties of QD surfaces and the interfaces in QD devices are of particular importance, and these enable the solution-based fabrication of low-cost, large-area, flexible, and functional devices. We discuss challenges that must be addressed in the move to solution-processed functional optoelectronic nanomaterials. PMID:27563099

  13. 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.

  14. Two-dimensional probe absorption in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Liu, Ningwu; Zhang, Yan; Kang, Chengxian; Wang, Zhiping; Yu, Benli

    2016-07-01

    We investigate the two-dimensional (2D) probe absorption in coupled quantum dots. It is found that, due to the position-dependent quantum interference effect, the 2D optical absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state quantum communication.

  15. Competitive hybridization in quantum dot-based nanodevices

    NASA Astrophysics Data System (ADS)

    Beltako, Katawoura; Cavassilas, Nicolas; Michelini, Fabienne

    2016-03-01

    By means of nonequilibrium Green's functions using the Born approximation to treat the light-matter coupling, we numerically investigate impacts of competitive hybridization on the photocurrent of a quantum dot based optoelectronic device. The model of device is an absorbing quantum dot connected to two semiconducting electrodes through energy filtering quantum dots. Hybridization occurs between the absorber and the filter, via the inter-dot coupling β, and between the filter and the electrode, via the dot-lead coupling Γ. At the tunnel resonance between the absorber and the filter, the investigation reveals the existence of two operating regimes in the nanodevice characterized by opposite variations of the photocurrent depending on ratio β/ Γ.

  16. Decoherence and Entanglement Simulation in a Model of Quantum Neural Network Based on Quantum Dots

    NASA Astrophysics Data System (ADS)

    Altaisky, Mikhail V.; Zolnikova, Nadezhda N.; Kaputkina, Natalia E.; Krylov, Victor A.; Lozovik, Yurii E.; Dattani, Nikesh S.

    2016-02-01

    We present the results of the simulation of a quantum neural network based on quantum dots using numerical method of path integral calculation. In the proposed implementation of the quantum neural network using an array of single-electron quantum dots with dipole-dipole interaction, the coherence is shown to survive up to 0.1 nanosecond in time and up to the liquid nitrogen temperature of 77K.We study the quantum correlations between the quantum dots by means of calculation of the entanglement of formation in a pair of quantum dots on the GaAs based substrate with dot size of 100 ÷ 101 nanometer and interdot distance of 101 ÷ 102 nanometers order.

  17. 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.

  18. Photoluminescence polarization of single InP quantum dots

    SciTech Connect

    Zwiller, Valery; Jarlskog, Linda; Pistol, Mats-Erik; Pryor, Craig; Castrillo, Pedro; Seifert, Werner; Samuelson, Lars

    2001-06-15

    The linear polarization dependence of photoluminescence emission was measured on single self-assembled InP quantum dots. The dots were obtained by Stranski-Krastanow growth on Ga{sub 0.5}In{sub 0.5}P. The highest-intensity emission occurred for light polarized parallel to the elongation of the dots in agreement with theoretical calculations. The excitation intensity was varied to obtain the polarization dependence of higher (state-filled) levels.

  19. Connecting trapped ions and quantum dots with photons

    NASA Astrophysics Data System (ADS)

    Koehl, Michael

    Coupling individual quantum systems lies at the heart of building scalable quantum networks. Here, we report the first direct photonic coupling between a semiconductor quantum dot and a trapped ion and we demonstrate that single photons generated by a quantum dot controllably change the internal state of an Yb+ ion. We ameliorate the effect of the sixty-fold mismatch of the radiative linewidths with coherent photon generation and a high-finesse fiber-based optical cavity enhancing the coupling between the single photon and the ion. The transfer of information presented here via the classical correlations between the σz projection of the quantum-dot spin and the internal state of the ion provides a promising step towards quantum state-transfer in a hybrid photonic network.

  20. 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).

  1. 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.

  2. Probing specific DNA sequences with luminescent semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Taylor, Jason R.; Nie, Shuming

    2001-06-01

    The development of new fluorescent probes has impacted many areas of research such as medical diagnostics, high-speed drug screening, and basic molecular biology. Main limitations to traditional organic fluorophores are their relatively weak intensities, short life times (eg., photobleaching), and broad emission spectra. The desire for more intense fluorescent probes with higher quality photostability and narrow emission wavelengths has led to the development and utilization of semiconductor quantum dots as a new label. In this work, we have modified semicondutor quantum dots (QD's) with synthetic oligonucleotides to probe a specific DNA target sequence both in solution as well as immobilized on a solid substrate. In the first approach, specific target sequences are detected in solution by using short oligonucleotide probes, which are covalently linked to semiconductor quantum dots. In the second approach, DNA target sequences are covalently attached to a glass substrate and detected using oligonucleotides linked to semiconductor quantum dots.

  3. 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

  4. 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.

  5. 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.

  6. Electro-absorption of silicene and bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Abdelsalam, Hazem; Talaat, Mohamed H.; Lukyanchuk, Igor; Portnoi, M. E.; Saroka, V. A.

    2016-07-01

    We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots.

  7. Nitrogen-Doped Carbon Dots for "green" Quantum Dot Solar Cells.

    PubMed

    Wang, Hao; Sun, Pengfei; Cong, Shan; Wu, Jiang; Gao, Lijun; Wang, Yun; Dai, Xiao; Yi, Qinghua; Zou, Guifu

    2016-12-01

    Considering the environment protection, "green" materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots' excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed "green" nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79 % under AM 1.5 G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells.

  8. 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.

  9. Coherent radiation by quantum dots and magnetic nanoclusters

    SciTech Connect

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

    2014-03-31

    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.

  10. 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.

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

    PubMed

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-01

    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).

  12. 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

  13. 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.

  14. 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)

  15. Controlled Photon Switch Assisted by Coupled Quantum Dots.

    PubMed

    Luo, Ming-Xing; Ma, Song-Ya; Chen, Xiu-Bo; Wang, Xiaojun

    2015-01-01

    Quantum switch is a primitive element in quantum network communication. In contrast to previous switch schemes on one degree of freedom (DOF) of quantum systems, we consider controlled switches of photon system with two DOFs. These controlled photon switches are constructed by exploring the optical selection rules derived from the quantum-dot spins in one-sided optical microcavities. Several double controlled-NOT gate on different joint systems are greatly simplified with an auxiliary DOF of the controlling photon. The photon switches show that two DOFs of photons can be independently transmitted in quantum networks. This result reduces the quantum resources for quantum network communication.

  16. Controlled Photon Switch Assisted by Coupled Quantum Dots.

    PubMed

    Luo, Ming-Xing; Ma, Song-Ya; Chen, Xiu-Bo; Wang, Xiaojun

    2015-01-01

    Quantum switch is a primitive element in quantum network communication. In contrast to previous switch schemes on one degree of freedom (DOF) of quantum systems, we consider controlled switches of photon system with two DOFs. These controlled photon switches are constructed by exploring the optical selection rules derived from the quantum-dot spins in one-sided optical microcavities. Several double controlled-NOT gate on different joint systems are greatly simplified with an auxiliary DOF of the controlling photon. The photon switches show that two DOFs of photons can be independently transmitted in quantum networks. This result reduces the quantum resources for quantum network communication. PMID:26095049

  17. 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.

  18. 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

  19. Si quantum dot structures and their applications

    NASA Astrophysics Data System (ADS)

    Shcherbyna, L.; Torchynska, T.

    2013-06-01

    This paper presents briefly the history of emission study in Si quantum dots (QDs) in the last two decades. Stable light emission of Si QDs and NCs was observed in the spectral ranges: blue, green, orange, red and infrared. These PL bands were attributed to the exciton recombination in Si QDs, to the carrier recombination through defects inside of Si NCs or via oxide related defects at the Si/SiOx interface. The analysis of recombination transitions and the different ways of the emission stimulation in Si QD structures, related to the element variation for the passivation of surface dangling bonds, as well as the plasmon induced emission and rare earth impurity activation, have been presented. The different applications of Si QD structures in quantum electronics, such as: Si QD light emitting diodes, Si QD single union and tandem solar cells, Si QD memory structures, Si QD based one electron devices and double QD structures for spintronics, have been discussed as well. Note the significant worldwide interest directed toward the silicon-based light emission for integrated optoelectronics is related to the complementary metal-oxide semiconductor compatibility and the possibility to be monolithically integrated with very large scale integrated (VLSI) circuits. The different features of poly-, micro- and nanocrystalline silicon for solar cells, that is a mixture of both amorphous and crystalline phases, such as the silicon NCs or QDs embedded in a α-Si:H matrix, as well as the thin film 2-cell or 3-cell tandem solar cells based on Si QD structures have been discussed as well. Silicon NC based structures for non-volatile memory purposes, the recent studies of Si QD base single electron devices and the single electron occupation of QDs as an important component to the measurement and manipulation of spins in quantum information processing have been analyzed as well.

  20. Effect of the nitrogen incorporation and fast carrier dynamics in (In,Ga)AsN/GaP self-assembled quantum dots

    SciTech Connect

    Gauthier, J.-P.; Almosni, S.; Léger, Y.; Perrin, M.; Even, J.; Cornet, C. Durand, O.; Robert, C.; Balocchi, A.; Carrère, H.; Marie, X.

    2014-12-15

    We report on the structural and optical properties of (In,Ga)AsN self-assembled quantum dots grown on GaP (001) substrate. A comparison with nitrogen free (In,Ga)As system is presented, showing a clear modification of growth mechanisms and a significant shift of the photoluminescence spectrum. Low temperature carrier recombination dynamics is studied by time-resolved photoluminescence, highlighting a drastic reduction of the characteristic decay-time when nitrogen is incorporated in the quantum dots. Room temperature photoluminescence is observed at 840 nm. These results reveal the potential of (In,Ga)AsN as an efficient active medium monolithically integrated on Si for laser applications.

  1. Effect of the nitrogen incorporation and fast carrier dynamics in (In,Ga)AsN/GaP self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Gauthier, J.-P.; Robert, C.; Almosni, S.; Léger, Y.; Perrin, M.; Even, J.; Balocchi, A.; Carrère, H.; Marie, X.; Cornet, C.; Durand, O.

    2014-12-01

    We report on the structural and optical properties of (In,Ga)AsN self-assembled quantum dots grown on GaP (001) substrate. A comparison with nitrogen free (In,Ga)As system is presented, showing a clear modification of growth mechanisms and a significant shift of the photoluminescence spectrum. Low temperature carrier recombination dynamics is studied by time-resolved photoluminescence, highlighting a drastic reduction of the characteristic decay-time when nitrogen is incorporated in the quantum dots. Room temperature photoluminescence is observed at 840 nm. These results reveal the potential of (In,Ga)AsN as an efficient active medium monolithically integrated on Si for laser applications.

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

    SciTech Connect

    Schindel, Daniel G.; Singh, Mahi R.

    2014-03-31

    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.

  3. 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.

  4. 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.

  5. Cavity -Quantum Dot interactions and mode coupling in a nanocavity

    NASA Astrophysics Data System (ADS)

    Kasisomayajula, Vijay; Russo, Onofrio

    2009-03-01

    We describe an approach for realizing effective manipulation of single electron state level transitions for quantum dots mediated by a nano-cavity. The two quantum dots interact with the cavity for the two dot system in the coulomb blockade energy region. Because of the zero dimensional structure of the quantum dots, the system can be implemented to be a characteristic entity for an efficient generator of single photons. This process is emphatically more selective in the coulomb/spin blockade region, where also, the system efficiency of the single photon event is most likely more probable. Whereas, it is clear that the photon efficiency is small, the cavity quantum electrodynamics (CQED) nature suggests an enhancement in the electron energy state being occupied by the second quantum dot. This is more likely with very strong coupling of the quantum dots to the cavity with cavity quality factors larger than perhaps 10^5. Quality factors in excess of 10^5 have been demonstrated experimentally^1. 1. K. Srinivasan, M. Borselli, T. J. Johnson, P. E. Barclay, O. Painter, A. Stintz, and S. Krishna, Appl. Phys. Lett. 86, 151106 (2005). [ISI

  6. Optical detection of brain tumors using quantum dots

    NASA Astrophysics Data System (ADS)

    Toms, Steven A.; Daneshvar, Hamid; Muhammad, Osman; Jackson, Heather; Vogelbaum, Michael A.; Bruchez, Marcel

    2005-11-01

    Introduction: Brain tumor margin detection remains a challenging problem in the operative resection of gliomas. A novel nanoparticle, a PEGylated quantum dot, has been shown to be phagocytized by macrophages in vivo. This feature may allow quantum dots to co-localize with brain tumors and serve as an optical aid in the surgical resection of brain tumors. Methods: Sprague-Daly rats were injected intracranially with C6 gliosarcoma cell lines to establish tumors. Two weeks after implantation of brain tumors, PEGylated quantum dots emitting at 705 nm (PEG-705 QD) were injected via the tail vein. Twenty-four hours post PEG-705 QD injection, the animals were sacrificed and their tissues examined. Results: PEGylated quantum dots are avidly phagocytized by macrophages and are taken up by liver, spleen and lymph nodes. Macrophages and microglia co-localize with glioma cells, carrying the optical nanoparticle, the quantum dot. Excitation of the PEG-705 quantum dots gives off a deep red fluorescence detectable with charge coupled device (CCD) cameras, optical spectroscopy units, and in dark field fluorescence microscopy. Conclusions: PEG-705QDs co-localize with brain tumors and may serve as an optical adjunct to aid in the operative resection of gliomas. The particles may be visualized in surgery with CCD cameras or detected by optical spectroscopy.

  7. Electron charging in epitaxial germanium quantum dots on silicon (100)

    NASA Astrophysics Data System (ADS)

    Ketharanathan, Sutharsan

    The electron charging behavior of self assembled epitaxial Ge quantum dots on Si(100) grown using molecular beam epitaxy has been studied. Ge quantum dots encapsulated in n-type Si matrix were incorporated into Schottky diodes to investigate their charging behavior using capacitance-voltage measurements. These experimental results were interpreted in the context of theoretical models to assess the degree of charge localization to the dot. Experiments involving Ge quantum dot growth, growth of Sb-doped Si and morphological evolution during encapsulation of the Ge dots during Si overgrowth were performed in order to optimize the conditions for obtaining distinct Ge quantum dot morphologies. This investigation included finding a suitable method to minimize Sb segregation while maintaining good dot epitaxy and overall crystal quality. Holes are confined to the Ge dots for which the valence band offsets are large (˜650 meV). Electrons are confined to the strained Si regions adjacent to the Ge quantum dots which have relatively smaller confinement potentials (˜100--150 meV). Experimentally, it was found that but and pyramid clusters in the range from 20--40 nm in diameter confine ˜1electron per dot while dome clusters in the range from 60--80 nm diameter confine ˜6--8 electrons per dot. Theoretical simulations predict that similar pyramid structures confine ˜0.4 electrons per dot and dome structures confine ˜2.2--3 electrons per dot. Even though the theory and the experimental results disagree due to various uncertainties and approximations, the ratio between theory and experiment agree remarkably well for both island types. We also investigated constructive three-dimensional nanolithography. Nanoscale Au rich dots and pure Ge dots were deposited on SiO2 and Si3N4 substrates by decomposing adsorbed precursors using a focused electron beam in an environmental transmission electron microscope. Dimethyl acetylacetonate gold was used for Au and digermane was used to

  8. Single-Photon Superradiance from a Quantum Dot.

    PubMed

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

    2016-04-22

    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. PMID:27152804

  9. Computation of energy states of hydrogenic quantum dot with two-electrons

    NASA Astrophysics Data System (ADS)

    Yakar, Y.; Özmen, A.; ćakır, B.

    2016-03-01

    In this study we have investigated the electronic structure of the hydrogenic quantum dot with two electrons inside an impenetrable potential surface. The energy eigenvalues and wavefunctions of the ground and excited states of spherical quantum dot have been calculated by using the Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method, and the energies are investigated as a function of dot radius. The results show that as dot radius increases, the energy of quantum dot decreases.

  10. Resonant intersubband plasmon induced current in InGaAs quantum wells on GaAs

    SciTech Connect

    Holzbauer, Martin Klang, Pavel; Detz, Hermann; Maxwell Andrews, Aaron; Strasser, Gottfried; Gornik, Erich; Bakshi, Pradip

    2014-03-24

    We present measurements of the current enhancement due to the coupling of two intersubband plasmons in In{sub 0.05}Ga{sub 0.95}As quantum wells. With changing bias, an emissive and an absorptive intersubband plasmon mode cross attractively and trapped electrons in the ground state gain enough energy from the plasma wave to be lifted up to the second subband, where they can contribute to the current. This effect can be directly observed as an increase of 33% in the current. A magnetic field applied parallel to the growth direction allows a control of the strength of the intersubband plasmon coupling up to a quenching.

  11. Shot noise at the quantum point contact in InGaAs heterostructure

    SciTech Connect

    Nishihara, Yoshitaka; Nakamura, Shuji; Ono, Teruo; Kobayashi, Kensuke; Kohda, Makoto; Nitta, Junsaku

    2013-12-04

    We study the shot noise at a quantum point contact (QPC) fabricated in an InGaAs/InGaAsP heterostructure, whose conductance can be electrically tuned by the gate voltages. Shot noise suppression is observed at the conductance plateau of N(2e{sup 2}/h) (N = 4,5,and 6), which indicates the coherent quantized channel formation in the QPC. The electron heating effect generated at the QPC explains the deviation of the observed Fano factor from the theory.

  12. State hybridization shapes the photocurrent in triple quantum dot nanojunctions

    NASA Astrophysics Data System (ADS)

    Beltako, Katawoura; Cavassilas, Nicolas; Michelini, Fabienne

    2016-08-01

    We investigated a prototype of a quantum dot based photodetector made of a dot absorber interconnected with two lateral dot filters in contact with semiconducting leads. Using the nonequilibrium Green's function technique, we found that there are two opposite evolutions of the photocurrent in the vicinity of the tunnel resonance for such a kind of nanodevice. This evolution depends on where the strongest hybridization of states happens, and hence still reveals a quantum effect. If the filter states hybridize more with the absorber states than the ones of the leads, the photocurrent shows a maximum at the tunnel resonance, while it is minimized in the opposite case.

  13. 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

  14. Impurity effects on coupled quantum dot spin qubits in semiconductors

    NASA Astrophysics Data System (ADS)

    Nguyen, Nga; Das Sarma, Sankar

    2011-03-01

    Localized electron spins confined in semiconductor quantum dots are being studied by many groups as possible elementary qubits for solid-state quantum computation. We theoretically consider the effects of having unintentional charged impurities in laterally coupled two-dimensional double (GaAs) quantum dot systems, where each dot contains one or two electrons and a single charged impurity in the presence of an external magnetic field. We calculate the effect of the impurity on the 2-electron energy spectrum of each individual dot as well as on the spectrum of the coupled-double-dot 2-electron system. We find that the singlet-triplet exchange splitting between the two lowest energy states, both for the individual dots and the coupled dot system, depends sensitively on the location of the impurity and its coupling strength (i.e. the effective charge). We comment on the impurity effect in spin qubit operations in the double dot system based on our numerical results. This work is supported by LPS-CMTC and CNAM.

  15. Spin qubits in quantum dots - beyond nearest-neighbour exchange

    NASA Astrophysics Data System (ADS)

    Vandersypen, Lieven

    The spin of a single electron is the canonical two-level quantum system. When isolated in a semiconductor quantum dot, a single electron spin provides a well-controlled and long-lived quantum bit. So far, two-qubit gates in this system have relied on the spin exchange interaction that arises when the wave functions of neighbouring electrons overlap. Furthermore, experimental demonstrations of controlled spin-exchange have been limited to 1D quantum dot arrays only. Here we explore several avenues for scaling beyond 1D arrays with nearest-neighbour coupling. First, we show that second-order tunnel processes allow for coherent spin-exchange between non-nearest neighbour quantum dots. The detuning of the intermediate quantum dot controls the frequency of the exchange-driven oscillations of the spins. Second, we demonstrate shuttling of electrons in quantum dot arrays preserving the spin projection for more than 500 hops. We use this technique to read out multiple spins in a way analogous to the operation of a CCD. Finally, we develop superconducting resonators that are resilient to magnetic field and with a predicted tenfold increase in vacuum electric field amplitudes. This makes coupling spin qubits via superconducting resonators in a circuit-QED approach a realistic possibility. Supported by ERC, FOM, NWO, IARPA, ARO, EU.

  16. Fabrication of Single-Photon Sources by Use of Pyramidal Quantum-Dot Microcavities

    NASA Astrophysics Data System (ADS)

    Rülke, Daniel; Reinheimer, C.; Schaadt, D. M.; Kalt, H.; Hetterich, M.

    In recent years the interest in single-photon emitters for quantum-optical applications is strongly increasing. For this purpose, we have investigated In(Ga)As quantum-dots (QDs) embedded in reversed pyramidal GaAs microcavities (Fig. 52.1a). Even though it has been shown recently, that such cavities can act as high-Q optical resonators [1], our focus has been on the directional radiation of the QD emission due to reflection at the facets of the reversed pyramids. With QDs embedded close to the vertex of the four facets and a base angle adaptable between 35° and 55° the pyramids can be perceived as a kind of retroreflector. Since the QD layer is inserted near the tip of the predicted reversed pyramid during molecular-beam epitaxial (MBE) growth, the average number of QDs inside the cavity can be reduced to one, depending on the size of the pyramid and density of QDs. The pyramidal cavities are shaped after MBE growth by a wet-chemical etching process with a solution of H3PO4, H2O2 and H2O [2, 3].

  17. Optically active quantum dots in monolayer WSe2.

    PubMed

    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.

  18. 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. PMID:27245962

  19. 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.

  20. Highly tuneable hole quantum dots in Ge-Si core-shell nanowires

    NASA Astrophysics Data System (ADS)

    Brauns, Matthias; Ridderbos, Joost; Li, Ang; van der Wiel, Wilfred G.; Bakkers, Erik P. A. M.; Zwanenburg, Floris A.

    2016-10-01

    We define single quantum dots of lengths varying from 60 nm up to nearly half a micron in Ge-Si core-shell nanowires. The charging energies scale inversely with the quantum dot length between 18 and 4 meV. Subsequently, we split up a long dot into a double quantum dot with a separate control over the tunnel couplings and the electrochemical potential of each dot. Both single and double quantum dot configurations prove to be very stable and show excellent control over the electrostatic environment of the dots, making this system a highly versatile platform for spin-based quantum computing.

  1. Characterization of spin-orbit fields in InGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Henn, T.; Czornomaz, L.; Salis, G.

    2016-10-01

    Coherent electron spin dynamics in 10-nm-wide InGaAs/InAlAs quantum wells is studied from 10 K to room temperature using time-resolved Kerr rotation. The spin lifetime exceeds 1 ns at 10 K and decreases with temperature. By varying the spatial overlap between pump and probe pulses, a diffusive velocity is imprinted on the measured electron spins and a spin precession in the spin-orbit field is measured. A Rashba symmetry of the spin-orbit interaction is determined. By comparing the spatial precession frequency gradient with the spin decay rate, an upper limit for the Rashba coefficients α of 2 × 10-12 eVm is estimated.

  2. Surface Induced Magnetism in Quantum Dots

    SciTech Connect

    Meulenberg, R W; Lee, J I

    2009-08-20

    The study of nanometer sized semiconductor crystallites, also known as quantum dots (QDs), has seen rapid advancements in recent years in scientific disciplines ranging from chemistry, physics, biology, materials science, and engineering. QD materials of CdSe, ZnSe, InP, as well as many others, can be prepared in the size range of 1-10 nm producing uniform, nearly monodisperse materials that are typically coated with organic molecules [1-3]. The strength of charge carrier confinement, which dictates the size-dependent properties, in these QDs depends on the nature of the material and can be correlated to the Bohr radius for the system of interest. For instance, the Bohr radius for CdSe is {approx} 5 nm, while in the more covalent structure of InP, the Bohr radius approaches {approx} 10 nm. The study of CdSe QDs has been particularly extensive during the last decade because they exhibit unique and tunable optical properties and are readily synthesized with high-crystallinity and narrow size dispersions. Although the core electronic properties of CdSe are explained in terms of the quantum confinement model, experimental efforts to elucidate the surface structure of these materials have been limited. Typically, colloidal CdSe QDs are coated with an organic surfactant, which typically consists of an organo-phosphine, -thiol, or -amine, that has the function of energetically relaxing defect states via coordination to partially coordinated surface atoms. The organic surfactant also acts to enhance carrier confinement and prevent agglomeration of the particles. Chemically, it has been shown that the bonding of the surfactant to the CdSe QD occurs through Cd atoms resulting cleavage of the Se atoms and formation of a Cd-rich (i.e. non-stoichiometric) particle [5].

  3. Origins of interlayer formation and misfit dislocation displacement in the vicinity of InAs/GaAs quantum dots

    SciTech Connect

    Huang, S.; Kim, S. J.; Pan, X. Q.; Goldman, R. S.

    2014-07-21

    We have examined the origins of interlayer formation and misfit dislocation (MD) displacement in the vicinity of InAs/GaAs quantum dots (QDs). For QDs formed by the Stranski-Krastanov mode, regularly spaced MDs nucleate at the interface between the QD and the GaAs buffer layer. In the droplet epitaxy case, both In island formation and In-induced “nano-drilling” of the GaAs buffer layer are observed during In deposition. Upon annealing under As flux, the In islands are converted to InAs QDs, with an InGaAs interlayer at the QD/buffer interface. Meanwhile, MDs nucleate at the QD/interlayer interface.

  4. 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.

  5. 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.

  6. Doping silicon nanocrystals and quantum dots.

    PubMed

    Oliva-Chatelain, Brittany L; Ticich, Thomas M; Barron, Andrew R

    2016-01-28

    The ability to incorporate a dopant element into silicon nanocrystals (NC) and quantum dots (QD) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications. Unlike doping of traditional bulk semiconductor materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping) or within the surrounding matrix (m-doping). A review of the various synthetic strategies for doping silicon NCs and QDs is presented, concentrating on the efficacy of the synthetic routes, both in situ and post synthesis, with regard to the structural location of the dopant and the doping level. Methods that have been applied to the characterization of doped NCs and QDs are summarized with regard to the information that is obtained, in particular to provide researchers with a guide to the suitable techniques for determining dopant concentration and location, as well as electronic and photonic effectiveness of the dopant.

  7. 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.

  8. 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

  9. 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.

  10. Counted Sb donors in Si quantum dots

    NASA Astrophysics Data System (ADS)

    Singh, Meenakshi; Pacheco, Jose; Bielejec, Edward; Perry, Daniel; Ten Eyck, Gregory; Bishop, Nathaniel; Wendt, Joel; Luhman, Dwight; Carroll, Malcolm; Lilly, Michael

    2015-03-01

    Deterministic control over the location and number of donors is critical for donor spin qubits in semiconductor based quantum computing. We have developed techniques using a focused ion beam and a diode detector integrated next to a silicon MOS single electron transistor to gain such control. With the diode detector operating in linear mode, the numbers of ions implanted have been counted and single ion implants have been detected. Poisson statistics in the number of ions implanted have been observed. Transport measurements performed on samples with counted number of implants have been performed and regular coulomb blockade and charge offsets observed. The capacitances to various gates are found to be in agreement with QCAD simulations for an electrostatically defined dot. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. The work was supported by Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.

  11. Doping silicon nanocrystals and quantum dots

    NASA Astrophysics Data System (ADS)

    Oliva-Chatelain, Brittany L.; Ticich, Thomas M.; Barron, Andrew R.

    2016-01-01

    The ability to incorporate a dopant element into silicon nanocrystals (NC) and quantum dots (QD) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications. Unlike doping of traditional bulk semiconductor materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping) or within the surrounding matrix (m-doping). A review of the various synthetic strategies for doping silicon NCs and QDs is presented, concentrating on the efficacy of the synthetic routes, both in situ and post synthesis, with regard to the structural location of the dopant and the doping level. Methods that have been applied to the characterization of doped NCs and QDs are summarized with regard to the information that is obtained, in particular to provide researchers with a guide to the suitable techniques for determining dopant concentration and location, as well as electronic and photonic effectiveness of the dopant.

  12. Quantum dot laser optimization: selectively doped layers

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  13. 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.

  14. Colloidal quantum dot photodetectors (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Adinolfi, Valerio; Sargent, Edward H.

    2015-08-01

    Colloidal quantum dots (CQDs) are emerging solution processed materials combining low cost, easy deposition on large and flexible substrates, and bandgap tunability. The latter feature, which allows spectral tuning of the absorption profile of the semiconductor, makes these materials particularly attractive for light detection applications. Lead sulfide (PbS) CQDs, in particular, have shown astonishing performance as a light sensitive material operating at visible and infrared (IR) wavelengths. Early studies of PbS CQDs used as a photosensitive resistor (photoconductor) showed an impressive responsivity - exceeding 1000 A/W - and a detectivity (D*) higher then 10^13 Jones. This impressive D* was preserved in the successive development of the first PbS CQD photodiode, showing the possibility to realize fast - f_3db > 1Mhz - and sensitive IR detectors. Currently, the field is moving toward the development of hybrid devices and phototransitors. PbS CQDs have been combined in field effect transistors (FETs) with graphene and MoS2 channels, showing ultra-high gain (exceeding 10^8 electrons/photons) and high D*. Recently a photo-junction FET (photo-JFET) has been reported that breaks the inherent dark current/gain/bandwidth compromise affecting photoconductive light detectors. With this presentation we offer a broad overview on CQD photodetection highlighting the past achievements, the benefits, the challenges and the prospects for the future research on this field.

  15. 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.

  16. 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)

  17. Computer-automated tuning of semiconductor double quantum dots into the single-electron regime

    NASA Astrophysics Data System (ADS)

    Baart, T. A.; Eendebak, P. T.; Reichl, C.; Wegscheider, W.; Vandersypen, L. M. K.

    2016-05-01

    We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.

  18. 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.

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

    DOE PAGESBeta

    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

  20. 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.

  1. 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.

  2. 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%.

  3. 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.

  4. 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.

  5. Signatures of single quantum dots in graphene nanoribbons within the quantum Hall regime.

    PubMed

    Tóvári, Endre; Makk, Péter; Rickhaus, Peter; Schönenberger, Christian; Csonka, Szabolcs

    2016-06-01

    We report on the observation of periodic conductance oscillations near quantum Hall plateaus in suspended graphene nanoribbons. They are attributed to single quantum dots that are formed in the narrowest part of the ribbon, in the valleys and hills of a disorder potential. In a wide flake with two gates, a double-dot system's signature has been observed. Electrostatic confinement is enabled in single-layer graphene due to the gaps that are formed between the Landau levels, suggesting a way to create gate-defined quantum dots that can be accessed with quantum Hall edge states. PMID:27198562

  6. Simulating electron spin entanglement in a double quantum dot

    NASA Astrophysics Data System (ADS)

    Rodriguez-Moreno, M. A.; Hernandez de La Luz, A. D.; Meza-Montes, Lilia

    2011-03-01

    One of the biggest advantages of having a working quantum-computing device when compared with a classical one, is the exponential speedup of calculations. This exponential increase is based on the ability of a quantum system to create and operate on entangled states. In order to study theoretically the entanglement between two electron spins, we simulate the dynamics of two electron spins in an electrostatically-defined double quantum dot with a finite barrier height between the dots. Electrons are initially confined to separated quantum dots. Barrier height is varied and the spin entanglement as a function of this variation is investigated. The evolution of the system is simulated by using a numerical approach for solving the time-dependent Schrödinger equation for two particles. Partially supported by VIEP-BUAP.

  7. Enlarged Symmetry and Coherence in Arrays of Quantum Dots

    NASA Astrophysics Data System (ADS)

    Onufriev, Alexey; Marston, Brad

    1997-03-01

    Advances in fabrication techniques have made nanostructures a promising arena for the study of many-body correlations(C.A. Stafford and S. Das Sarma Phys. Rev. Lett. 72), 3590 (1993). and the persistence of quantum coherence. We find conditions under which enhanced symmetry characterized by the group SU occurs in isolated semiconducting quantum dots. A Hubbard model then describes a pillar array of coupled dots and at half-filling it can be mapped onto a SU(4) spin chain. The physics of these new structures is rich as novel phases may be attainable. The chain spontaneously dimerizes which we confirm numerically by using the Density Matrix Renormalization Group (DMRG) technique. Our DMRG analysis also shows that this state is robust to perturbations which break SU(4) symmetry. We propose ways to experimentally verify the phases and comment on the possible application of quantum dot arrays to the problem of quantum computation(Seth Lloyd, Science, 23) 1073 (1996)..

  8. Theoretical studies of graphene nanoribbon quantum dot qubits

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Chieh; Chang, Yia-Chung

    2015-12-01

    Graphene nanoribbon quantum dot qubits have been proposed as promising candidates for quantum computing applications to overcome the spin-decoherence problems associated with typical semiconductor (e.g., GaAs) quantum dot qubits. We perform theoretical studies of the electronic structures of graphene nanoribbon quantum dots by solving the Dirac equation with appropriate boundary conditions. We then evaluate the exchange splitting based on an unrestricted Hartree-Fock method for the Dirac particles. The electronic wave function and long-range exchange coupling due to the Klein tunneling and the Coulomb interaction are calculated for various gate configurations. It is found that the exchange coupling between qubits can be significantly enhanced by the Klein tunneling effect. The implications of our results for practical qubit construction and operation are discussed.

  9. Theoretical studies of graphene nanoribbon quantum dot qubits

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Chieh; Chang, Yia-Chung

    Graphene nanoribbon quantum dot qubits have been proposed as promising candidates for quantum computing applications to overcome the spin-decoherence problems associated with typical semiconductor (e.g., GaAs) quantum dot qubits. We perform theoretical studies of the electronic structures of graphene nanoribbon quantum dots by solving the Dirac equation with appropriate boundary conditions. We then evaluate the exchange splitting based on an unrestricted Hartree-Fock method for the Dirac particles. The electronic wave function and long-range exchange coupling due to the Klein tunneling and the Coulomb interaction are calculated for various gate configurations. It is found that the exchange coupling between qubits can be significantly enhanced by the Klein tunneling effect. The implications of our results for practical qubit construction and operation are discussed. This work was supported in part by the Ministry of Science and Technology, Taiwan, under Contract No. MOST 104-2112-M-001-009-MY2.

  10. Properties of a polaron confined in a spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Melnikov, Dmitriy V.

    A Frohlich Hamiltonian describing the electron-phonon interaction in a spherical quantum dot embedded in another polar material is derived, taking into account interactions with both bulk longitudinal optical and surface optical phonons. The Hamiltonian is appropriate to the general case of a finite confining potential originating from a bandgap mismatch between the materials of the dot and the surrounding matrix. This Hamiltonian is then applied to treat the electron-phonon interaction in the adiabatic approximation for various quantum dot systems. It was found that, as the radius of the dot decreases, the magnitude of the electron-phonon interaction energy first increases, passes through a maximum, and then gradually decreases to the value appropriate to the situation where the electron is weakly localized inside the dot. For most dot radii the polaron properties are described well by a model assuming perfect electron confinement. Based on this result, the problem of the bound polaron confined perfectly in the quantum dot was investigated within the adiabatic and all-coupling variational approaches. The polaron properties have been studied performing both analytical and numerical calculations for various radii of the quantum dot and for different impurity positions inside the dot. Within the adiabatic approximation, it was found that the magnitude of the electron-phonon interaction increases as the radius decreases for any impurity position. It was also shown that the input from the electron-surface-phonon interaction to the total polaron energy is much larger than was found earlier for the free polaron confined in the dot. As a function of the impurity position, the electron-surface-phonon interaction energy increases as the impurity is shifted towards the surface, reaches its maximum when the impurity is positioned inside the dot and then decreases as the impurity moved close to surface. The all-coupling approach gave rise to the following results: for any

  11. Degradation processes in high power multi-mode InGaAs strained quantum well lasers

    NASA Astrophysics Data System (ADS)

    Sin, Yongkun; Presser, Nathan; Foran, Brendan; Moss, Steven C.

    2009-02-01

    Recently, broad-area InGaAs-AlGaAs strained quantum well (QW) lasers have attracted much attention because of their unparalleled high optical output power characteristics that narrow stripe lasers or tapered lasers can not achieve. However, broad-area lasers suffer from poor beam quality and their high reliability operation has not been proven for communications applications. This paper concerns reliability and degradation aspects of broad-area lasers. Good facet passivation techniques along with optimized structural designs have led to successful demonstration of reliable 980nm single-mode lasers, and the dominant failure mode of both single-mode and broadarea lasers is catastrophic optical mirror damage (COMD), which limits maximum output powers and also determines operating output powers. Although broad-area lasers have shown characteristics unseen from singlemode lasers including filamentation, their effects on long-term reliability and degradation processes have not been fully investigated. Filamentation can lead to instantaneous increase in optical power density and thus temperature rise at localized areas through spatial-hole burning and thermal lensing which significantly reduces filament sizes under high power operation, enhancing the COMD process. We investigated degradation processes in commercial MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers at ~975nm with and without passivation layers by performing accelerated lifetests of these devices followed by failure mode analyses with various micro-analytical techniques. Since instantaneous fluctuations of filaments can lead to faster wear-out of passivation layer thus leading to facet degradation, both passivated and unpassivated broad-area lasers were studied that yielded catastrophic failures at the front facet and also in the bulk. Electron beam induced current technique was employed to study dark line defects (DLDs) generated in degraded lasers stressed under different test conditions and focused

  12. Decoherence and adiabatic transport in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Switkes, Michael

    2000-10-01

    I present research on ballistic electron transport in lateral GaAs/AlGaAs quantum dots connected to the environment with leads supporting one or more fully transmitting quantum modes. The first part of this dissertation examines electron the phenomena which mediate the transition from quantum mechanical to classical behavior in these quantum dots. Measurements of electron phase coherence time based on the magnitude of weak localization correction are presented as a function both of temperature and of applied bias. The coherence time is found to depend on temperature approximately as a sum of two power laws, tauφ ≈ AT-1 + BT-2, in agreement with the prediction for diffusive two dimensional systems but not with predictions for closed quantum dots or ballistic 2D systems. The effects of a large applied bias can be described with an elevated effective electron temperature calculated from the balance of Joule heating and cooling by Wiedemann-Franz out diffusion of hot electrons. The limits this imposes for quantum dot based technologies are examined through the detailed analysis of a quantum dot magnetometer. The second part of the work presented here focuses on a novel form of electron transport, adiabatic quantum electron pumping, in which a current is driven by cyclic changes in the wave function of a mesoscopic system rather than by an externally imposed bias. After a brief review of other mechanisms which produce a dc current from an ac excitation, measurements of adiabatic pumping are presented. The pumped current (or voltage) is sinusoidal in the phase difference between the two ac voltages deforming the dot potential and fluctuates in both magnitude and direction with small changes in external parameters such as magnetic field. Dependencies of pumping on the strength of the deformations, temperature, and breaking of time-reversal symmetry are also investigated.

  13. Multiple Exciton Generation in PbSe Quantum Dots and Quantum Dot Solar Cells

    SciTech Connect

    Beard, M. C.; Semonin, O. E.; Nozik, A. J.; Midgett, A. G.; Luther, J. M.

    2012-01-01

    Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by channeling the excess photon energy (energy greater than the bandgap) to produce multiple electron-hole pairs. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron-phonon coupling that cools hot-excitons in bulk semiconductors. We have demonstrated that MEG in PbSe QDs is about two times as efficient at producing multiple electron-hole pairs than bulk PbSe. I will discuss our recent results investigating MEG in PbSe, PbS and PbSxSe1-x, which exhibits an interesting size-dependence of the MEG efficiency. Thin films of electronically coupled PbSe QDs have shown promise in simple photon-to-electron conversion architectures with power conversion efficiencies above 5%. We recently reported an enhancement in the photocurrent resulting from MEG in PbSe QD-based solar cells. We find that the external quantum efficiency (spectrally resolved ratio of collected charge carriers to incident photons) peaked at 114% in the best devices measured, with an internal quantum efficiency of 130%. These results demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells. We compare our results to transient absorption measurements and find reasonable agreement.

  14. 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.

  15. 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

  16. 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

  17. Detection of CdSe quantum dot photoluminescence for security label on paper

    NASA Astrophysics Data System (ADS)

    Isnaeni, Sugiarto, Iyon Titok; Bilqis, Ratu; Suseno, Jatmiko Endro

    2016-02-01

    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.

  18. 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.

  19. Low-temperature-grown InGaAs quantum wells for optical device applications

    NASA Astrophysics Data System (ADS)

    Juodawlkis, Paul William

    1999-11-01

    The large optical absorption and carrier-induced nonlinearities of semiconductor materials are useful for optical signal processing applications. For absorptive devices operating at ultrafast data rates (>100 Gb/s) or high optical intensities, it is necessary to reduce the intrinsic photo-excited carrier removal time. One method of achieving this reduction is to increase the nonradiative recombination rate through the controlled introduction of defects. In this thesis, we explore the use of low-temperature molecular-beam epitaxy (MBE) to introduce nonradiative recombination centers into InGaAs-based quantum-wells (QWs). The objectives of the thesis are: (i)to improve the understanding of the optoelectronic properties of low-temperature-grown (LTG) InGaAs/InAlAs QWs, and (ii)to assess the feasibility of using these materials for optical device applications in the 1.5-μm wavelength region. Time-resolved differential transmission measurements reveal that the nonlinear absorption recovery time in InGaAs/InAlAs QWs can be reduced from >100 ps to 0.6 ps through the combination of low-temperature growth (~250°C) and beryllium (Be) doping. The bandedge absorption slope and the nonlinear absorption cross- section are only diminished by factors of 2 to 3 relative to QWs grown at standard temperature (~500°C). The Be doping dependence of the recovery time and the residual electron density in the LTG-QWs can be mainly attributed to impurity-related compensation. Be doping also maintains the ultrafast recovery following thermal anneal. The recovery response results from fast electron- trapping followed by slow (>100 ps) trapped- electron/free-hole recombination. Detailed simulations of the nonlinear absorption saturation and recovery processes agree quantitatively with measured data and substantiate the importance of the photo-excitation wavelength on the observed recovery response. The absorption saturation model includes the competition between band-filling and band

  20. Towards deterministically controlled InGaAs/GaAs lateral quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Wang, L.; Rastelli, A.; Kiravittaya, S.; Atkinson, P.; Ding, F.; Bof Bufon, C. C.; Hermannstädter, C.; Witzany, M.; Beirne, G. J.; Michler, P.; Schmidt, O. G.

    2008-04-01

    We report on the fabrication, detailed characterization and modeling of lateral InGaAs quantum dot molecules (QDMs) embedded in a GaAs matrix and we discuss strategies to fully control their spatial configuration and electronic properties. The three-dimensional morphology of encapsulated QDMs was revealed by selective wet chemical etching of the GaAs top capping layer and subsequent imaging by atomic force microscopy (AFM). The AFM investigation showed that different overgrowth procedures have a profound consequence on the QDM height and shape. QDMs partially capped and annealed in situ for micro-photoluminescence spectroscopy consist of shallow but well-defined quantum dots (QDs) in contrast to misleading results usually provided by surface morphology measurements when they are buried by a thin GaAs layer. This uncapping approach is crucial for determining the QDM structural parameters, which are required for modeling the system. A single-band effective-mass approximation is employed to calculate the confined electron and heavy-hole energy levels, taking the geometry and structural information extracted from the uncapping experiments as inputs. The calculated transition energy of the single QDM shows good agreement with the experimentally observed values. By decreasing the edge-to-edge distance between the two QDs within a QDM, a splitting of the electron (hole) wavefunction into symmetric and antisymmetric states is observed, indicating the presence of lateral coupling. Site control of such lateral QDMs obtained by growth on a pre-patterned substrate, combined with a technology to fabricate gate structures at well-defined positions with respect to the QDMs, could lead to deterministically controlled devices based on QDMs.

  1. 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.

  2. Detection of viral infections using colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Bentzen, Elizabeth L.; House, Frances S.; Utley, Thomas J.; Crowe, James E., Jr.; Wright, David W.

    2006-02-01

    Fluorescence is a tool widely employed in biological assays. Fluorescent semiconducting nanocrystals, quantum dots (QDs), are beginning to find their way into the tool box of many biologist, chemist and biochemist. These quantum dots are an attractive alternative to the traditional organic dyes due to their broad excitation spectra, narrow emission spectra and photostability. Quantum dots were used to detect and monitor the progession of viral glycoproteins, F (fusion) and G (attachment), from Respiratory Syncytial Virus (RSV) in HEp-2 cells. Additionally, oligo-Qdot RNA probes have been developed for identification and detection of mRNA of the N(nucleocapsid) protein for RSV. The use of quantum dot-FISH probes provides another confirmatory route to diagnostics as well as a new class of probes for monitoring the flux and fate of viral RNA RSV is the most common cause of lower respiratory tract infection in children worldwide and the most common cause of hospitalization of infants in the US. Antiviral therapy is available for treatment of RSV but is only effective if given within the first 48 hours of infection. Existing test methods require a virus level of at least 1000-fold of the amount needed for infection of most children and require several days to weeks to obtain results. The use of quantum dots may provide an early, rapid method for detection and provide insight into the trafficking of viral proteins during the course of infection.

  3. 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.

  4. 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.

  5. Structural and emission properties of InGaAs/GaAs quantum dots emitting at 1.3 μm

    SciTech Connect

    Goldmann, Elias Jahnke, Frank; Paul, Matthias; Kettler, Jan; Jetter, Michael; Michler, Peter; Krause, Florian F.; Müller, Knut; Mehrtens, Thorsten; Rosenauer, Andreas

    2014-10-13

    A combined experimental and theoretical study of InGaAs/GaAs quantum dots (QDs) emitting at 1.3 μm under the influence of a strain-reducing InGaAs quantum well is presented. We demonstrate a red shift of 20–40 nm observed in photoluminescence spectra due to the quantum well. The InGaAs/GaAs QDs grown by metal organic vapor phase epitaxy show a bimodal height distribution (1 nm and 5 nm) and indium concentrations up to 90%. The emission properties are explained with combined tight-binding and configuration-interaction calculations of the emission wavelengths in conjunction with high-resolution scanning transmission electron microscopy investigations of QD geometry and indium concentrations in the QDs, which directly enter the calculations. QD geometries and concentration gradients representative for the ensemble are identified.

  6. 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.

  7. Biosensing with Quantum Dots: A Microfluidic Approach

    PubMed Central

    Vannoy, Charles H.; Tavares, Anthony J.; Noor, M. Omair; Uddayasankar, Uvaraj; Krull, Ulrich J.

    2011-01-01

    Semiconductor quantum dots (QDs) have served as the basis for signal development in a variety of biosensing technologies and in applications using bioprobes. The use of QDs as physical platforms to develop biosensors and bioprobes has attracted considerable interest. This is largely due to the unique optical properties of QDs that make them excellent choices as donors in fluorescence resonance energy transfer (FRET) and well suited for optical multiplexing. The large majority of QD-based bioprobe and biosensing technologies that have been described operate in bulk solution environments, where selective binding events at the surface of QDs are often associated with relatively long periods to reach a steady-state signal. An alternative approach to the design of biosensor architectures may be provided by a microfluidic system (MFS). A MFS is able to integrate chemical and biological processes into a single platform and allows for manipulation of flow conditions to achieve, by sample transport and mixing, reaction rates that are not entirely diffusion controlled. Integrating assays in a MFS provides numerous additional advantages, which include the use of very small amounts of reagents and samples, possible sample processing before detection, ultra-high sensitivity, high throughput, short analysis time, and in situ monitoring. Herein, a comprehensive review is provided that addresses the key concepts and applications of QD-based microfluidic biosensors with an added emphasis on how this combination of technologies provides for innovations in bioassay designs. Examples from the literature are used to highlight the many advantages of biosensing in a MFS and illustrate the versatility that such a platform offers in the design strategy. PMID:22163723

  8. 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). PMID:19441383

  9. Toxicity of Oxidatively Degraded Quantum Dots

    PubMed Central

    Wiecinski, Paige N.; Metz, Kevin M.; King Heiden, Tisha C.; Louis, Kacie M.; Mangham, Andrew N.; Hamers, Robert J.; Heideman, Warren; Peterson, Richard E.; Pedersen, Joel A.

    2014-01-01

    Once released into the environment, engineered nanoparticles (eNPs) are subjected to processes that may alter their physical or chemical properties, potentially altering their toxicity vis-à-vis the as-synthesized materials. We examined the toxicity to zebrafish embryos of CdSecore/ZnSshell quantum dots (QDs) before and after exposure to an in vitro chemical model designed to simulate oxidative weathering in soil environments based on a reductant-driven Fenton’s reaction. Exposure to these oxidative conditions resulted in severe degradation of the QDs: the Zn shell eroded, Cd2+ and selenium were released, and amorphous Se-containing aggregates were formed. Weathered QDs exhibited higher potency than did as-synthesized QDs. Morphological endpoints of toxicity included pericardial, ocular and yolk sac edema, non-depleted yolk, spinal curvature, tail malformations, and craniofacial malformations. To better understand the selenium-like toxicity observed in QD exposures, we examined the toxicity of selenite, selenate and amorphous selenium nanoparticles (SeNPs). Selenite exposures resulted in high mortality to embryos/larvae while selenate and SeNPs were non-toxic. Co-exposures to SeNPs + CdCl2 resulted in dramatic increase in mortality and recapitulated the morphological endpoints of toxicity observed with weathered QD exposures. Cadmium body burden was increased in larvae exposed to weathered QDs or SeNP + CdCl2 suggesting the increased potency of weathered QDs was due to selenium modulation of cadmium toxicity. Our findings highlight the need to examine the toxicity of eNPs after they have undergone environmental weathering processes. PMID:23815598

  10. 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).

  11. Correlation and current anomalies in helical quantum dots

    NASA Astrophysics Data System (ADS)

    De Beule, C.; Ziani, N. Traverso; Zarenia, M.; Partoens, B.; Trauzettel, B.

    2016-10-01

    We theoretically investigate the ground-state properties of a quantum dot defined on the surface of a strong three-dimensional time-reversal invariant topological insulator. Confinement is realized by ferromagnetic barriers and Coulomb interaction is treated numerically for up to seven electrons in the dot. Experimentally relevant intermediate interaction strengths are considered. The topological origin of the dot has several consequences: (i) spin polarization increases and the ground state exhibits quantum phase transitions at specific angular momenta as a function of interaction strength, (ii) the onset of Wigner correlations takes place mainly in one spin channel, and (iii) the ground state is characterized by a robust persistent current that changes sign as a function of the distance from the center of the dot.

  12. 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

  13. 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.

  14. 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.

  15. Charge transfer magnetoexciton formation at vertically coupled quantum dots.

    PubMed

    Gutiérrez, Willian; Marin, Jairo H; Mikhailov, Ilia D

    2012-01-01

    A theoretical investigation is presented on the properties of charge transfer excitons at vertically coupled semiconductor quantum dots in the presence of electric and magnetic fields directed along the growth axis. Such excitons should have two interesting characteristics: an extremely long lifetime and a permanent dipole moment. We show that wave functions and the low-lying energies of charge transfer exciton can be found exactly for a special morphology of quantum dots that provides a parabolic confinement inside the layers. To take into account a difference between confinement potentials of an actual structure and of our exactly solvable model, we use the Galerkin method. The density of energy states is calculated for different InAs/GaAs quantum dots' dimensions, the separation between layers, and the strength of the electric and magnetic fields. A possibility of a formation of a giant dipolar momentum under external electric field is predicted. PMID:23092373

  16. Colloidal Quantum Dot Photovoltaics Enhanced by Perovskite Shelling.

    PubMed

    Yang, Zhenyu; Janmohamed, Alyf; Lan, Xinzheng; García de Arquer, F Pelayo; Voznyy, Oleksandr; Yassitepe, Emre; Kim, Gi-Hwan; Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Sargent, Edward H

    2015-11-11

    Solution-processed quantum dots are a promising material for large-scale, low-cost solar cell applications. New device architectures and improved passivation have been instrumental in increasing the performance of quantum dot photovoltaic devices. Here we report photovoltaic devices based on inks of quantum dot on which we grow thin perovskite shells in solid-state films. Passivation using the perovskite was achieved using a facile solution ligand exchange followed by postannealing. The resulting hybrid nanostructure created a more intrinsic CQD film, which, when incorporated into a photovoltaic device with graded bandstructure, achieved a record solar cell performance for single-step-deposited CQD films, exhibiting an AM1.5 solar power conversion efficiency of 8.95%.

  17. 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.

  18. Peptide linkers for the assembly of semiconductor quantum dot bioconjugates

    NASA Astrophysics Data System (ADS)

    Boeneman, Kelly; Mei, Bing C.; Deschamps, Jeffrey R.; Delehanty, James B.; Mattoussi, Hedi; Medintz, Igor

    2009-02-01

    The use of semiconductor luminescent quantum dots for the labeling of biomolecules is rapidly expanding, however it still requires facile methods to attach functional globular proteins to biologically optimized quantum dots. Here we discuss the development of controlled variable length peptidyl linkers to attach biomolecules to poly(ethylene) glycol (PEG) coated quantum dots for both in vitro and in vivo applications. The peptides chosen, β-sheets and alpha helices are appended to polyhistidine sequences and this allows for control of the ratio of peptide bioconjugated to QD and the distance from QD to the biomolecule. Recombinant DNA engineering, bacterial peptide expression and Ni-NTA purification of histidine labeled peptides are utilized to create the linkers. Peptide length is confirmed by in vitro fluorescent resonance energy transfer (FRET).

  19. Single bump, two-color quantum dot camera

    NASA Astrophysics Data System (ADS)

    Varley, E.; Lenz, M.; Lee, S. J.; Brown, J. S.; Ramirez, D. A.; Stintz, A.; Krishna, S.; Reisinger, Axel; Sundaram, Mani

    2007-08-01

    The authors report a two-color, colocated quantum dot based imaging system used to take multicolor images using a single focal plane array (FPA). The dots-in-a-well (DWELL) detectors consist of an active region composed of InAs quantum dots embedded in In.15Ga.85As quantum wells. DWELL samples were grown using molecular beam epitaxy and fabricated into 320×256 focal plane arrays with indium bumps. The FPA was then hybridized to an Indigo ISC9705 readout circuit and tested. Calibrated blackbody measurements at a device temperature of 77K yield midwave infrared and long wave infrared noise equivalent difference in temperature of ˜55 and 70mK.

  20. 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.

  1. Kondo and Majorana doublet interactions in quantum dots

    NASA Astrophysics Data System (ADS)

    Kim, Younghyun; Liu, Dong E.; Gaidamauskas, Erikas; Paaske, Jens; Flensberg, Karsten; Lutchyn, Roman

    We study the properties of a quantum dot coupled to a normal lead and a time-reversal topological superconductor with Majorana Kramers pair at the end. We explore the phase diagram of the system as a function of Kondo and Majorana-induced coupling strengths using perturbative renormalization group study and slave-boson mean-field theory. We find that, in the presence of coupling between a quantum dot and a Majorana doublet, the system flows to a new fixed point controlled by the Majorana doublet, rather than the Kondo coupling, which is characterized by correlations between a localized spin and the fermion parity of each spin sector of the topological superconductor. We find that this fixed point is stable with respect to Gaussian fluctuations. We also investigate the effect of spin-spin interaction between a quantum dot and Majorana doublet and compare the result with a case where a normal lead is directly coupled to Majorana doublet.

  2. 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.

  3. Quantum Dots in H1 Photonic Crystal Microcavities for Quantum Information

    NASA Astrophysics Data System (ADS)

    Hagemeier, Jenna; Bonato, Cristian; Truong, Tuan-Anh; Kim, Hyochul; Bakker, Morten; Beirne, Gareth J.; van Exter, Martin P.; Petroff, Pierre; Bouwmeester, Dirk

    2013-03-01

    Coupling semiconductor quantum dots to optical microcavities is a promising technique for implementing quantum information processing protocols in the solid-state. By placing one or more emitters in a cavity, it is possible to create an efficient source of single photons or to explore collective interactions of few-emitter systems. Our devices consist of two layers of quantum dots, embedded in the cavity region of H1 photonic crystal microcavities. One of the quantum dot layers can be frequency-tuned deterministically, allowing two resonant quantum dots to be coupled to a single cavity mode. Because good mode-matching between the cavity mode and the input/output channel is necessary for many applications, we optimize the far-field profiles of our H1 cavities and demonstrate strong enhancement of the external mode matching properties. We will discuss our far-field optimization results as well as our ongoing work to study interactions of multiple emitters in a cavity.

  4. 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

  5. Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

    NASA Astrophysics Data System (ADS)

    Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

    1995-08-01

    One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

  6. Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

    NASA Technical Reports Server (NTRS)

    Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

    1995-01-01

    One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

  7. Quantum transport through the system of parallel quantum dots with Majorana bound states

    SciTech Connect

    Wang, Ning; Li, Yuxian; Lv, Shuhui

    2014-02-28

    We study the tunneling transport properties through a system of parallel quantum dots which are coupled to Majorana bound states (MBSs). The conductance and spectral function are computed using the retarded Green's function method based on the equation of motion. The conductance of the system is 2e{sup 2}/h at zero Fermi energy and is robust against the coupling between the MBSs and the quantum dots. The dependence of the Fermi energy on the spectral function is different for the first dot (dot1) than for the second dot (dot2) with fixed dot2-MBSs coupling. The influence of the Majorana bound states on the spectral function was studied for the series and parallel configurations of the system. It was found that when the configuration is in series, the Majorana bound states play an important role, resulting in a spectral function with three peaks. However, the spectral function shows two peaks when the system is in a parallel configuration. The zero Fermi energy spectral function is always 1/2 not only in series but also in the parallel configuration and robust against the coupling between the MBSs and the quantum dots. The phase diagram of the Fermi energy versus the quantum dot energy levels was also investigated.

  8. 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.

  9. Förster Resonance Energy Transfer between Quantum Dot Donors and Quantum Dot Acceptors

    PubMed Central

    Chou, Kenny F.; Dennis, Allison M.

    2015-01-01

    Förster (or fluorescence) resonance energy transfer amongst semiconductor quantum dots (QDs) is reviewed, with particular interest in biosensing applications. The unique optical properties of QDs provide certain advantages and also specific challenges with regards to sensor design, compared to other FRET systems. The brightness and photostability of QDs make them attractive for highly sensitive sensing and long-term, repetitive imaging applications, respectively, but the overlapping donor and acceptor excitation signals that arise when QDs serve as both the donor and acceptor lead to high background signals from direct excitation of the acceptor. The fundamentals of FRET within a nominally homogeneous QD population as well as energy transfer between two distinct colors of QDs are discussed. Examples of successful sensors are highlighted, as is cascading FRET, which can be used for solar harvesting. PMID:26057041

  10. 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;…

  11. 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.

  12. 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.

  13. Reentrant formation of magnetic polarons in quantum dots

    NASA Astrophysics Data System (ADS)

    Pientka, J. M.; Oszwałdowski, R.; Petukhov, A. G.; Han, J. E.; Žutić, Igor

    2012-10-01

    We propose a model of magnetic polaron formation in semiconductor quantum dots doped with magnetic ions. A wetting layer serves as a reservoir of photogenerated holes, which can be trapped by the adjacent quantum dots. For certain hole densities, the temperature dependence of the magnetization induced by the trapped holes is reentrant: it disappears for some temperature range and reappears at higher temperatures. We demonstrate that this peculiar effect is not an artifact of the mean-field approximation and persists after statistical spin fluctuations are accounted for. We predict fingerprints of reentrant magnetic polarons in photoluminescence spectra.

  14. Voltage-controlled slow light in asymmetry double quantum dots

    NASA Astrophysics Data System (ADS)

    Yuan, Chun-Hua; Zhu, Ka-Di

    2006-07-01

    The authors demonstrate theoretically that there exists electromagnetically induced transparency in an asymmetric double quantum dot system using tunneling instead of pump laser. The group velocity slowdown factor is theoretically analyzed as a function of electron tunneling at different broadened linewidths. With feasible parameters for applications to a 100Gbits/s optical network, numerical calculation infers group velocity as low as 300m/s. The scheme is expected to be useful in constructing a variable semiconductor optical buffer based on electromagnetically induced transparency in an asymmetric double quantum dot controlled by voltage.

  15. 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

  16. Entanglement dynamics of photon pairs emitted from quantum dots

    SciTech Connect

    Zou, Yang; Gong, Ming; Li, Chuan-Feng; Chen, Geng; Tang, Jian-Shun; Guo, Guang-Can

    2010-06-15

    We present a model that describes states of photon pairs, which have been generated by biexciton cascade decays of self-assembled quantum dots, the use of which yields a finding that agrees well with the experimental result. Furthermore, we calculate the concurrence and determine the temperature behavior associated with the so-called entanglement sudden death that prevents quantum dots emitting entangled photon pairs at raised temperatures. The relationship between the fine-structure splitting and the sudden death temperature is also provided.

  17. 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.

  18. Lateral photoconductivity in structures with Ge/Si quantum dots

    SciTech Connect

    Panevin, V. Yu. Sofronov, A. N.; Vorobjev, L. E.; Firsov, D. A.; Shalygin, V. A.; Vinnichenko, M. Ya.; Balagula, R. M.; Tonkikh, A. A.; Werner, P.; Fuhrman, B.; Schmidt, G.

    2013-12-15

    The spectra of lateral photoconductivity and optical absorption caused by the intraband optical transitions of holes in Ge/Si quantum dots are studied at different lattice temperatures. Polarization-dependent spectral features related to the transitions of holes from the quantum dot (QD) ground state are revealed in the optical spectra. Temperature photoconductivity quenching caused by the reverse trapping of nonequilibrium free holes by the QD bound state is observed. The obtained experimental data make it possible to determine the height of the surface band bending at the QD heterointerface.

  19. A high-efficiency double quantum dot heat engine

    NASA Astrophysics Data System (ADS)

    Liu, Y. S.; Yang, X. F.; Hong, X. K.; Si, M. S.; Chi, F.; Guo, Y.

    2013-08-01

    High-efficiency heat engine requires a large output power at the cost of less input heat energy as possible. Here we propose a heat engine composed of serially connected two quantum dots sandwiched between two metallic electrodes. The efficiency of the heat engine can approach the maximum allowable Carnot efficiency ηC. We also find that the strong intradot Coulomb interaction can induce additional work regions for the heat engine, whereas the interdot Coulomb interaction always suppresses the efficiency. Our results presented here indicate a way to fabricate high-efficiency quantum-dot thermoelectric devices.

  20. Tunable optical properties of colloidal quantum dots in electrolytic environments.

    PubMed

    Ramadurai, D; Kohanpour, B; Alexson, D; Shi, P; Sethuraman, A; Li, Y; Saini, V; Dutta, M; Stroscio, M A

    2004-12-01

    The absorption spectra of colloidal cadmium sulfide quantum dots in electrolytic solutions are found to manifest a shift in the absorption threshold as the concentration of the electrolyte is varied. These results are consistent with a shift in the absorption threshold that would be caused by electrolytic screening of the field caused by the intrinsic spontaneous polarisation of these würtzite structured quantum dots. These electrolyte-dependent absorption properties provide a potential means of gaining insights on the variable extracellular and intracellular electrolytic concentrations that are present in biological systems.

  1. Overview of Stabilizing Ligands for Biocompatible Quantum Dot Nanocrystals

    PubMed Central

    Zhang, Yanjie; Clapp, Aaron

    2011-01-01

    Luminescent colloidal quantum dots (QDs) possess numerous advantages as fluorophores in biological applications. However, a principal challenge is how to retain the desirable optical properties of quantum dots in aqueous media while maintaining biocompatibility. Because QD photophysical properties are directly related to surface states, it is critical to control the surface chemistry that renders QDs biocompatible while maintaining electronic passivation. For more than a decade, investigators have used diverse strategies for altering the QD surface. This review summarizes the most successful approaches for preparing biocompatible QDs using various chemical ligands. PMID:22247651

  2. 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.

  3. Si quantum dots in silicon nitride: Quantum confinement and defects

    SciTech Connect

    Goncharova, L. V. Karner, V. L.; D'Ortenzio, R.; Chaudhary, S.; Mokry, C. R.; Simpson, P. J.; Nguyen, P. H.

    2015-12-14

    Luminescence of amorphous Si quantum dots (Si QDs) in a hydrogenated silicon nitride (SiN{sub x}:H) matrix was examined over a broad range of stoichiometries from Si{sub 3}N{sub 2.08} to Si{sub 3}N{sub 4.14}, to optimize light emission. Plasma-enhanced chemical vapor deposition was used to deposit hydrogenated SiN{sub x} films with excess Si on Si (001) substrates, with stoichiometry controlled by variation of the gas flow rates of SiH{sub 4} and NH{sub 3} gases. The compositional and optical properties were analyzed by Rutherford backscattering spectroscopy, elastic recoil detection, spectroscopic ellipsometry, photoluminescence (PL), time-resolved PL, and energy-filtered transmission electron microscopy. Ultraviolet-laser-excited PL spectra show multiple emission bands from 400 nm (3.1 eV) to 850 nm (1.45 eV) for different Si{sub 3}N{sub x} compositions. There is a red-shift of the measured peaks from ∼2.3 eV to ∼1.45 eV as Si content increases, which provides evidence for quantum confinement. Higher N content samples show additional peaks in their PL spectra at higher energies, which we attribute to defects. We observed three different ranges of composition where Tauc band gaps, PL, and PL lifetimes change systematically. There is an interesting interplay of defect luminescence and, possibly, small Si QD luminescence observed in the intermediate range of compositions (∼Si{sub 3}N{sub 3.15}) in which the maximum of light emission is observed.

  4. Si quantum dots in silicon nitride: Quantum confinement and defects

    NASA Astrophysics Data System (ADS)

    Goncharova, L. V.; Nguyen, P. H.; Karner, V. L.; D'Ortenzio, R.; Chaudhary, S.; Mokry, C. R.; Simpson, P. J.

    2015-12-01

    Luminescence of amorphous Si quantum dots (Si QDs) in a hydrogenated silicon nitride (SiNx:H) matrix was examined over a broad range of stoichiometries from Si3N2.08 to Si3N4.14, to optimize light emission. Plasma-enhanced chemical vapor deposition was used to deposit hydrogenated SiNx films with excess Si on Si (001) substrates, with stoichiometry controlled by variation of the gas flow rates of SiH4 and NH3 gases. The compositional and optical properties were analyzed by Rutherford backscattering spectroscopy, elastic recoil detection, spectroscopic ellipsometry, photoluminescence (PL), time-resolved PL, and energy-filtered transmission electron microscopy. Ultraviolet-laser-excited PL spectra show multiple emission bands from 400 nm (3.1 eV) to 850 nm (1.45 eV) for different Si3Nx compositions. There is a red-shift of the measured peaks from ˜2.3 eV to ˜1.45 eV as Si content increases, which provides evidence for quantum confinement. Higher N content samples show additional peaks in their PL spectra at higher energies, which we attribute to defects. We observed three different ranges of composition where Tauc band gaps, PL, and PL lifetimes change systematically. There is an interesting interplay of defect luminescence and, possibly, small Si QD luminescence observed in the intermediate range of compositions (˜Si3N3.15) in which the maximum of light emission is observed.

  5. Quantum control and process tomography of a semiconductor quantum dot hybrid qubit.

    PubMed

    Kim, Dohun; Shi, Zhan; Simmons, C B; Ward, D R; Prance, J R; Koh, Teck Seng; Gamble, John King; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, Mark A

    2014-07-01

    The similarities between gated quantum dots and the transistors in modern microelectronics--in fabrication methods, physical structure and voltage scales for manipulation--have led to great interest in the development of quantum bits (qubits) in semiconductor quantum dots. Although quantum dot spin qubits have demonstrated long coherence times, their manipulation is often slower than desired for important future applications, such as factoring. Furthermore, scalability and manufacturability are enhanced when qubits are as simple as possible. Previous work has increased the speed of spin qubit rotations by making use of integrated micromagnets, dynamic pumping of nuclear spins or the addition of a third quantum dot. Here we demonstrate a qubit that is a hybrid of spin and charge. It is simple, requiring neither nuclear-state preparation nor micromagnets. Unlike previous double-dot qubits, the hybrid qubit enables fast rotations about two axes of the Bloch sphere. We demonstrate full control on the Bloch sphere with π-rotation times of less than 100 picoseconds in two orthogonal directions, which is more than an order of magnitude faster than any other double-dot qubit. The speed arises from the qubit's charge-like characteristics, and its spin-like features result in resistance to decoherence over a wide range of gate voltages. We achieve full process tomography in our electrically controlled semiconductor quantum dot qubit, extracting high fidelities of 85 per cent for X rotations (transitions between qubit states) and 94 per cent for Z rotations (phase accumulation between qubit states).

  6. Low Temperature Apertureless Near-field Scanning Optical Microscope for Optical Spectroscopy of Single Ge/Si Quantum Dots

    NASA Astrophysics Data System (ADS)

    Zhu, Henry; Patil, N. G.; Levy, Jeremy

    2001-03-01

    A low-temperature apertureless near-field scanning optical microscope has been designed and constructed for the purpose of investigating the optical properties of individual Ge/Si quantum dots. The microscope fits in the 37 mm bore of a Helium vapor magneto-optic cryostat, allowing operations down to liquid helium temperatures in magnetic fields up to 8 Tesla. An in situ microscope objective focuses light onto the sample, which is scanned in the three spatial directions using a compact modular stage. An AFM/STM tip resides on the top; feedback is achieved using a quartz tuning fork oscillator. Both tip and objective are attached to inertial sliding motors that can move in fine (10 nm) steps to achieve touchdown and focus. A femtosecond optical parametric oscillator is used to excite carriers in the quantum dots both resonantly and non-resonantly; scattered luminescence from the AFM/STM tip is collected and analyzed spectrally using a 1/2 meter imaging spectrometer and a LN_2-cooled InGaAs array. We gratefully acknowledge NSF (DMR-9701725, IMR-9802784) and DARPA (DAAD-16-99-C1036) for financial support of this work.

  7. Momentum Transfer Studies and Studies of Linear and Nonlinear Optical Properties of Metal Colloids and Semiconductor Quantum Dots

    NASA Technical Reports Server (NTRS)

    Collins, W. E.; Burger, A.; Dyer, K.; George, M.; Henderson, D.; Morgan, S.; Mu, R.; Shi, D.; Conner, D; Thompson, E.; Collins, L.; Curry, L.; Mattox, S.; Williams, G.

    1996-01-01

    Phase 1 of this work involved design work on a momentum transfer device. The progress on design and testing will be presented. Phase 2 involved the systematic study of the MPD thruster for dual uses. Though it was designed as a thruster for space vehicles, the characteristics of the plasma make it an excellent candidate for industrial applications. This project sought to characterize the system for use in materials processing and characterization. The surface modification on ZnCdTe, CdTe, and ZnTe will be presented. Phase 3 involved metal colloids and semiconductor quantum dots. One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantation for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga, and As. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb, and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. The results of some of this work will also be reported.

  8. Quantum chemistry of quantum dots: Effects of ligands and oxidation

    NASA Astrophysics Data System (ADS)

    Inerbaev, Talgat M.; Masunov, Artëm E.; Khondaker, Saiful I.; Dobrinescu, Alexandra; Plamadǎ, Andrei-Valentin; Kawazoe, Yoshiyuki

    2009-07-01

    We report Gaussian basis set density functional theory (DFT) calculations of the structure and spectra of several colloidal quantum dots (QDs) with a (CdSe)n core (n =6,15,17), that are either passivated by trimethylphosphine oxide ligands, or unpassivated and oxidized. From the ground state geometry optimization results we conclude that trimethylphosphine oxide ligands preserve the wurtzite structure of the QDs. Evaporation of the ligands may lead to surface reconstruction. We found that the number of two-coordinated atoms on the nanoparticle's surface is the critical parameter defining the optical absorption properties. For (CdSe)15 wurtzite-derived QD this number is maximal among all considered QDs and the optical absorption spectrum is strongly redshifted compared to QDs with threefold coordinated surface atoms. According to the time-dependent DFT results, surface reconstruction is accompanied by a significant decrease in the linear absorption. Oxidation of QDs destroys the perfection of the QD surface, increases the number of two-coordinated atoms and results in the appearance of an infrared absorption peak close to 700 nm. The vacant orbitals responsible for this near infrared transition have strong Se-O antibonding character. Conclusions of this study may be used in optimization of engineered nanoparticles for photodetectors and photovoltaic devices.

  9. Spin-valley physics in realistic silicon quantum dots

    NASA Astrophysics Data System (ADS)

    Ruskov, Rusko; Tahan, Charles

    2014-03-01

    Silicon quantum dots are leading approach for solid-state quantum bits. However, one must contend with new physics due to the multi-valley nature of silicon. At a Si heterostructure interface the valley degeneracy is lifted and the different valley subspaces of the confined electron spin configurations do not interact. When, however, the valley states are brought at resonance in the presence of a non-ideal interface, spin-valley mixing can occur via spin-orbit coupling. Within the same theoretical framework, we can successfully describe the spin relaxation processes in non-ideal quantum dots [e.g., relaxation ``hot spots'' in C. H. Yang, A. Rossi, R. Ruskov, N. S. Lai, F. A. Mohiyaddin, S. Lee, C. Tahan, G. Klimeck, A. Morello, and A. S. Dzurak, Nature Comm. 4, 2069, (2013)] and a new electron spin resonance (ESR) anticrossing splitting in a double quantum dot transport experiment [X. Hao, R. Ruskov, M. Xiao, C. Tahan, and H. W. Jiang, work in preparation]. Understanding the spin-valley physics of inelastic tunneling is critical to a proper understanding of the transport through double quantum dots, with or without an ESR drive field.

  10. 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

  11. Few-second-long correlation times in a quantum dot nuclear spin bath probed by frequency-comb nuclear magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Waeber, A. M.; Hopkinson, M.; Farrer, I.; Ritchie, D. A.; Nilsson, J.; Stevenson, R. M.; Bennett, A. J.; Shields, A. J.; Burkard, G.; Tartakovskii, A. I.; Skolnick, M. S.; Chekhovich, E. A.

    2016-07-01

    One of the key challenges in spectroscopy is the inhomogeneous broadening that masks the homogeneous spectral lineshape and the underlying coherent dynamics. Techniques such as four-wave mixing and spectral hole-burning are used in optical spectroscopy, and spin-echo in nuclear magnetic resonance (NMR). However, the high-power pulses used in spin-echo and other sequences often create spurious dynamics obscuring the subtle spin correlations important for quantum technologies. Here we develop NMR techniques to probe the correlation times of the fluctuations in a nuclear spin bath of individual quantum dots, using frequency-comb excitation, allowing for the homogeneous NMR lineshapes to be measured without high-power pulses. We find nuclear spin correlation times exceeding one second in self-assembled InGaAs quantum dots--four orders of magnitude longer than in strain-free III-V semiconductors. This observed freezing of the nuclear spin fluctuations suggests ways of designing quantum dot spin qubits with a well-understood, highly stable nuclear spin bath.

  12. Interface trap density and mobility extraction in InGaAs buried quantum well metal-oxide-semiconductor field-effect-transistors by gated Hall method

    SciTech Connect

    Chidambaram, Thenappan; Madisetti, Shailesh; Greene, Andrew; Yakimov, Michael; Tokranov, Vadim; Oktyabrsky, Serge; Veksler, Dmitry; Hill, Richard

    2014-03-31

    In this work, we are using a gated Hall method for measurement of free carrier density and electron mobility in buried InGaAs quantum well metal-oxide-semiconductor field-effect-transistor channels. At room temperature, mobility over 8000 cm{sup 2}/Vs is observed at ∼1.4 × 10{sup 12} cm{sup −2}. Temperature dependence of the electron mobility gives the evidence that remote Coulomb scattering dominates at electron density <2 × 10{sup 11} cm{sup −2}. Spectrum of the interface/border traps is quantified from comparison of Hall data with capacitance-voltage measurements or electrostatic modeling. Above the threshold voltage, gate control is strongly limited by fast traps that cannot be distinguished from free channel carriers just by capacitance-based methods and can be the reason for significant overestimation of channel density and underestimation of carrier mobility from transistor measurements.

  13. Persistent Inter-Excitonic Quantum Coherence in CdSe Quantum Dots

    PubMed Central

    Caram, Justin R.; Zheng, Haibin; Dahlberg, Peter D.; Rolczynski, Brian S.; Griffin, Graham B.; Fidler, Andrew F.; Dolzhnikov, Dmitriy S.; Talapin, Dmitri V.; Engel, Gregory S.

    2014-01-01

    The creation and manipulation of quantum superpositions is a fundamental goal for the development of materials with novel optoelectronic properties. In this letter, we report persistent (~80 fs lifetime) quantum coherence between the 1S and 1P excitonic states in zinc-blende colloidal CdSe quantum dots at room temperature, measured using Two-Dimensional Electronic Spectroscopy. We demonstrate that this quantum coherence manifests as an intradot phenomenon, the frequency of which depends on the size of the dot excited within the ensemble of QDs. We model the lifetime of the coherence and demonstrate that correlated interexcitonic fluctuations preserve relative phase between excitonic states. These observations suggest an avenue for engineering long-lived interexcitonic quantum coherence in colloidal quantum dots. PMID:24719679

  14. Interaction of Water-Soluble CdTe Quantum Dots with Bovine Serum Albumin

    PubMed Central

    2011-01-01

    Semiconductor nanoparticles (quantum dots) are promising fluorescent markers, but it is very little known about interaction of quantum dots with biological molecules. In this study, interaction of CdTe quantum dots coated with thioglycolic acid (TGA) with bovine serum albumin was investigated. Steady state spectroscopy, atomic force microscopy, electron microscopy and dynamic light scattering methods were used. It was explored how bovine serum albumin affects stability and spectral properties of quantum dots in aqueous media. CdTe–TGA quantum dots in aqueous solution appeared to be not stable and precipitated. Interaction with bovine serum albumin significantly enhanced stability and photoluminescence quantum yield of quantum dots and prevented quantum dots from aggregating. PMID:27502633

  15. Deterministic photonic cluster state generation from quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Economou, Sophia; Gimeno-Segovia, Mercedes; Rudolph, Terry

    2014-03-01

    Currently, the most promising approach for photon-based quantum information processing is measurement-based, or one-way, quantum computing. In this scheme, a large entangled state of photons is prepared upfront and the computation is implemented with single-qubit measurements alone. Available approaches to generating the cluster state are probabilistic, which makes scalability challenging. We propose to generate the cluster state using a quantum dot molecule with one electron spin per quantum dot. The two spins are coupled by exchange interaction and are periodically pulsed to produce photons. We show that the entanglement created by free evolution between the spins is transferred to the emitted photons, and thus a 2D photonic ladder can be created. Our scheme only utilizes single-spin gates and measurement, and is thus fully consistent with available technology.

  16. Effective Hamiltonian for the hybrid double quantum dot qubit

    NASA Astrophysics Data System (ADS)

    Ferraro, E.; De Michielis, M.; Mazzeo, G.; Fanciulli, M.; Prati, E.

    2014-05-01

    Quantum dot hybrid qubits formed from three electrons in double quantum dots represent a promising compromise between high speed and simple fabrication for solid state implementations of single-qubit and two-qubits quantum logic ports. We derive the Schrieffer-Wolff effective Hamiltonian that describes in a simple and intuitive way the qubit by combining a Hubbard-like model with a projector operator method. As a result, the Hubbard-like Hamiltonian is transformed in an equivalent expression in terms of the exchange coupling interactions between pairs of electrons. The effective Hamiltonian is exploited to derive the dynamical behavior of the system and its eigenstates on the Bloch sphere to generate qubits operation for quantum logic ports. A realistic implementation in silicon and the coupling of the qubit with a detector are discussed.

  17. Josephson ϕ0-junction in nanowire quantum dots

    NASA Astrophysics Data System (ADS)

    Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S. R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.

    2016-06-01

    The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models.

  19. Radiation Effects in Nanostructures: Comparison of Proton Irradiation Induced Changes on Quantum Dots and Quantum Wells

    NASA Technical Reports Server (NTRS)

    Leon, R.; Swift, G.; Magness, B.; Taylor, W.; Tang, Y.; Wang, K.; Dowd, P.; Zhang, Y.

    2000-01-01

    Successful implementation of technology using self-forming semiconductor Quantum Dots (QDs) has already demonstrated that temperature independent Dirac-delta density of states can be exploited in low current threshold QD lasers and QD infrared photodetectors.

  20. Electronic ground state properties of Coulomb blockaded quantum dots

    NASA Astrophysics Data System (ADS)

    Patel, Satyadev Rajesh

    Conductance through quantum dots at low temperature exhibits random but repeatable fluctuations arising from quantum interference of electrons. The observed fluctuations follow universal statistics arising from the underlying universality of quantum chaos. Random matrix theory (RMT) has provided an accurate description of the observed universal conductance fluctuations (UCF) in "open" quantum dots (device conductance ≥e 2/h). The focus of this thesis is to search for and decipher the underlying origin of similar universal properties in "closed" quantum dots (device conductance ≤e2/ h). A series of experiments is presented on electronic ground state properties measured via conductance measurements in Coulomb blockaded quantum dots. The statistics of Coulomb blockade (CB) peak heights with zero and non-zero magnetic field measured in various devices agree qualitatively with predictions from Random Matrix Theory (RMT). The standard deviation of the peak height fluctuations for non-zero magnetic field is lower than predicted by RMT; the temperature dependence of the standard deviation of the peak height for non-zero magnetic field is also measured. The second experiment summarizes the statistics of CB peak spacings. The peak spacing distribution width is observed to be on the order of the single particle level spacing, Delta, for both zero and non-zero magnetic field. The ratio of the zero field peak spacing distribution width to the non-zero field peak spacing distribution width is ˜1.2; this is good agreement with predictions from spin-resolved RMT predictions. The standard deviation of the non-zero magnetic field peak spacing distribution width shows a T-1/2 dependence in agreement with a thermal averaging model. The final experiment summarizes the measurement of the peak height correlation length versus temperature for various quantum dots. The peak height correlation length versus temperature saturates in small quantum dots, suggesting spectral scrambling

  1. Nonclassical correlation of cascaded photon pairs emitted from quantum dots

    SciTech Connect

    Li, Chuan-Feng; Zou, Yang; Xu, Jin-Shi; Ge, Rong-Chun; Guo, Guang-Can

    2011-11-15

    We studied the quantum correlation of the photon pairs generated by biexciton cascade decays of self-assembled quantum dots, and determined the correlation sudden-change temperature, which is shown to be independent of the background noise, far lower than the entanglement sudden-death temperature, and therefore, easier to be observed in experiments. The relationship between the fine-structure splitting and the sudden-change temperature is also provided.

  2. Optical levitation of a microdroplet containing a single quantum dot.

    PubMed

    Minowa, Yosuke; Kawai, Ryoichi; Ashida, Masaaki

    2015-03-15

    We demonstrate the optical levitation or trapping in helium gas of a single quantum dot (QD) within a liquid droplet. Bright single photon emission from the levitated QD in the droplet was observed for more than 200 s. The observed photon count rates are consistent with the value theoretically estimated from the two-photon-action cross section. This Letter presents the realization of an optically levitated solid-state quantum emitter. PMID:25768143

  3. The photosensitivity of carbon quantum dots/CuAlO2 films composites

    NASA Astrophysics Data System (ADS)

    Pan, Jiaqi; Sheng, Yingzhuo; Zhang, Jingxiang; Wei, Jumeng; Huang, Peng; Zhang, Xin; Feng, Boxue

    2015-07-01

    Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior.

  4. Recent Progress Towards Quantum Dot Solar Cells with Enhanced Optical Absorption

    NASA Astrophysics Data System (ADS)

    Zheng, Zerui; Ji, Haining; Yu, Peng; Wang, Zhiming

    2016-05-01

    Quantum dot solar cells, as a promising candidate for the next generation solar cell technology, have received tremendous attention in the last 10 years. Some recent developments in epitaxy growth and device structures have opened up new avenues for practical quantum dot solar cells. Unfortunately, the performance of quantum dot solar cells is often plagued by marginal photon absorption. In this review, we focus on the recent progress made in enhancing optical absorption in quantum dot solar cells, including optimization of quantum dot growth, improving the solar cells structure, and engineering light trapping techniques.

  5. Recent Progress Towards Quantum Dot Solar Cells with Enhanced Optical Absorption.

    PubMed

    Zheng, Zerui; Ji, Haining; Yu, Peng; Wang, Zhiming

    2016-12-01

    Quantum dot solar cells, as a promising candidate for the next generation solar cell technology, have received tremendous attention in the last 10 years. Some recent developments in epitaxy growth and device structures have opened up new avenues for practical quantum dot solar cells. Unfortunately, the performance of quantum dot solar cells is often plagued by marginal photon absorption. In this review, we focus on the recent progress made in enhancing optical absorption in quantum dot solar cells, including optimization of quantum dot growth, improving the solar cells structure, and engineering light trapping techniques.

  6. Molecular Spintronics: Wiring Spin Coherence between Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ouyang, Min

    2004-03-01

    Semiconductor quantum dots (QDs) are attractive candidates for scalable solid state implementations of quantum information processing based on electron spin states, where a crucial requirement for practical devices is to have efficient and tunable spin coupling between them. We focus on recent femtosecond time-resolved Faraday rotation studies of self-assembled multilayer spintronic devices based on colloidal quantum dots bridged by conjugated molecules (M. Ouyang et al., Science 301, 1074 (2003)). The data reveal the instantaneous transfer of spin coherence through conjugated molecular bridges spanning quantum dots of different size over a broad range of temperature. The room temperature spin transfer efficiency exceeds 20%, which approximately doubles the value measured at T=4.5K. A molecular π-orbital mediated spin coherence transfer mechanism is proposed to provide a qualitative insight into the experimental observations, suggesting a correlation between the stereochemistry of molecules and the transfer process. The results show that conjugated molecules can be used not only as physical links for the assembly of functional networks, but also as efficient channels for shuttling quantum information. This class of structures may be useful as two-spin quantum devices operating at ambient temperatures and may offer promising opportunities for future versatile molecule-based spintronic technologies.

  7. Externally mode-matched cavity quantum electrodynamics with charge-tunable quantum dots.

    PubMed

    Rakher, M T; Stoltz, N G; Coldren, L A; Petroff, P M; Bouwmeester, D

    2009-03-01

    We present coherent reflection spectroscopy on a charge and dc Stark tunable quantum dot embedded in a high-quality and externally mode-matched microcavity. The addition of an exciton to a single-electron-charged quantum dot forms a trion that interacts with the microcavity just below the strong-coupling regime of cavity quantum electrodynamics. Such an integrated, monolithic system is a crucial step towards the implementation of scalable hybrid quantum-information schemes that are based on an efficient interaction between a single photon and a confined electron spin.

  8. Giant fifth-order nonlinearity via tunneling induced quantum interference in triple quantum dots

    SciTech Connect

    Tian, Si-Cong Tong, Cun-Zhu Ning, Yong-Qiang; Wan, Ren-Gang

    2015-02-15

    Schemes for giant fifth-order nonlinearity via tunneling in both linear and triangular triple quantum dots are proposed. In both configurations, the real part of the fifth-order nonlinearity can be greatly enhanced, and simultaneously the absorption is suppressed. The analytical expression and the dressed states of the system show that the two tunnelings between the neighboring quantum dots can induce quantum interference, resulting in the giant higher-order nonlinearity. The scheme proposed here may have important applications in quantum information processing at low light level.

  9. Nonradiative recombination of excitons in semimagnetic quantum dots

    SciTech Connect

    Chernenko, A. V.

    2015-12-15

    The mechanisms of the nonradiative recombination of excitons in neutral and charged quantum dots based on II–VI semimagnetic semiconductors are investigated. It is shown that, along with the dipole–dipole and direct-exchange mechanisms, there is one more mechanism referred to as the indirect-exchange mechanism and related to sp–d mixing. The selection rules for nonradiative recombination by exchange mechanisms are subsequently derived. The dependence of the efficiency of all recombination mechanisms on the quantum-dot size is studied. The experimentally observed growth in the intracenter photoluminescence intensity with decreasing size of dots and nanocrystals is accounted for. Methods for experimental determination of the contributions of different mechanisms to nonradiative recombination are discussed.

  10. Probing charge fluctuator correlations using quantum dot pairs

    NASA Astrophysics Data System (ADS)

    Purohit, V.; Braunecker, B.; Lovett, B. W.

    2015-06-01

    We study a pair of quantum dot exciton qubits interacting with a number of fluctuating charges that can induce a Stark shift of both exciton transition energies. We do this by solving the optical master equation using a numerical transfer matrix method. We find that the collective influence of the charge environment on the dots can be detected by measuring the correlation between the photons emitted when each dot is driven independently. Qubits in a common charge environment display photon bunching, if both dots are driven on resonance or if the driving laser detunings have the same sense for both qubits, and antibunching if the laser detunings have opposite signs. We also show that it is possible to detect several charges fluctuating at different rates using this technique. Our findings expand the possibility of measuring qubit dynamics in order to investigate the fundamental physics of the environmental noise that causes decoherence.

  11. Microsecond-sustained lasing from colloidal quantum dot solids

    PubMed Central

    Adachi, Michael M.; Fan, Fengjia; Sellan, Daniel P.; Hoogland, Sjoerd; Voznyy, Oleksandr; Houtepen, Arjan J.; Parrish, Kevin D.; Kanjanaboos, Pongsakorn; Malen, Jonathan A.; Sargent, Edward H.

    2015-01-01

    Colloidal quantum dots have grown in interest as materials for light amplification and lasing in view of their bright photoluminescence, convenient solution processing and size-controlled spectral tunability. To date, lasing in colloidal quantum dot solids has been limited to the nanosecond temporal regime, curtailing their application in systems that require more sustained emission. Here we find that the chief cause of nanosecond-only operation has been thermal runaway: the combination of rapid heat injection from the pump source, poor heat removal and a highly temperature-dependent threshold. We show microsecond-sustained lasing, achieved by placing ultra-compact colloidal quantum dot films on a thermally conductive substrate, the combination of which minimizes heat accumulation. Specifically, we employ inorganic-halide-capped quantum dots that exhibit high modal gain (1,200 cm−1) and an ultralow amplified spontaneous emission threshold (average peak power of ∼50 kW cm−2) and rely on an optical structure that dissipates heat while offering minimal modal loss. PMID:26493282

  12. Self-action effects in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Dneprovskii, V. S.; Kanev, A. R.; Kozlova, M. V.; Smirnov, A. M.

    2014-05-01

    Two-dimensional (2D) dynamic photonic crystal regime has been utilized to investigate self-diffraction effect and nonlinear optical properties of excitons in CdSe/ZnS colloidal quantum dots (QDs). Self-diffraction at 2D photonic crystal arises for three intersecting beams of Nd+3:YAG laser second harmonic in the case of one-photon resonant excitation of the exciton (electron - hole) transition QDs. The relaxation time of excited excitons has been measured by pump and probe technique at induced one-dimensional transient diffraction grating. Two-exponential decay with initial fast and slow parts was discovered. Self-action effect has been discovered in the case of stationary resonant excitation of excitons in CdSe/ZnS QDs by the beam of second harmonic of powerful 12-nanosecond laser pulses. The bleaching of exciton absorption and the creation of transparency channel (this effect provokes self-diffraction of the second harmonic beam) was explained by the dominating coexisting and competing processes of state filling in stationary excited quantum dots and Stark-shift of exciton spectral band. The peculiarities of the influence of these processes at the change of exciton absorption in quantum dots in the case of different detuning from exciton resonance (quantum dots with different size have been used) was analyzed.

  13. Staircase Quantum Dots Configuration in Nanowires for Optimized Thermoelectric Power

    PubMed Central

    Li, Lijie; Jiang, Jian-Hua

    2016-01-01

    The performance of thermoelectric energy harvesters can be improved by nanostructures that exploit inelastic transport processes. One prototype is the three-terminal hopping thermoelectric device where electron hopping between quantum-dots are driven by hot phonons. Such three-terminal hopping thermoelectric devices have potential in achieving high efficiency or power via inelastic transport and without relying on heavy-elements or toxic compounds. We show in this work how output power of the device can be optimized via tuning the number and energy configuration of the quantum-dots embedded in parallel nanowires. We find that the staircase energy configuration with constant energy-step can improve the power factor over a serial connection of a single pair of quantum-dots. Moreover, for a fixed energy-step, there is an optimal length for the nanowire. Similarly for a fixed number of quantum-dots there is an optimal energy-step for the output power. Our results are important for future developments of high-performance nanostructured thermoelectric devices. PMID:27550093

  14. Electronic Structure of Helium Atom in a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Saha, Jayanta K.; Bhattacharyya, S.; Mukherjee, T. K.

    2016-03-01

    Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) (n = 1-6) states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns (n = 2-5) and 2pnp (n = 2-5) configurations of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential due to the quantum dot. It has been explicitly demonstrated that the electronic structural properties become sensitive functions of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within a quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the width of the quantum cavity is also discussed here. TKM Gratefully Acknowledges Financial Support under Grant No. 37(3)/14/27/2014-BRNS from the Department of Atomic Energy, BRNS, Government of India. SB Acknowledges Financial Support under Grant No. PSW-160/14-15(ERO) from University Grants Commission, Government of India

  15. Quantum Dots for Live Cell and In Vivo Imaging

    PubMed Central

    Walling, Maureen A; Novak, Jennifer A; Shepard, Jason R. E

    2009-01-01

    In the past few decades, technology has made immeasurable strides to enable visualization, identification, and quantitation in biological systems. Many of these technological advancements are occurring on the nanometer scale, where multiple scientific disciplines are combining to create new materials with enhanced properties. The integration of inorganic synthetic methods with a size reduction to the nano-scale has lead to the creation of a new class of optical reporters, called quantum dots. These semiconductor quantum dot nanocrystals have emerged as an alternative to organic dyes and fluorescent proteins, and are brighter and more stable against photobleaching than standard fluorescent indicators. Quantum dots have tunable optical properties that have proved useful in a wide range of applications from multiplexed analysis such as DNA detection and cell sorting and tracking, to most recently demonstrating promise for in vivo imaging and diagnostics. This review provides an in-depth discussion of past, present, and future trends in quantum dot use with an emphasis on in vivo imaging and its related applications. PMID:19333416

  16. 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...

  17. Quantum dots trace lymphatic drainage from the mouse eye

    NASA Astrophysics Data System (ADS)

    Tam, Alex L. C.; Gupta, Neeru; Zhang, Zhexue; Yücel, Yeni H.

    2011-10-01

    Glaucoma is a leading cause of blindness in the world, often associated with elevated eye pressure. Currently, all glaucoma treatments aim to lower eye pressure by improving fluid exit from the eye. We recently reported the presence of lymphatics in the human eye. The lymphatic circulation is known to drain fluid from organ tissues and, as such, lymphatics may also play a role in draining fluid from the eye. We investigated whether lymphatic drainage from the eye is present in mice by visualizing the trajectory of quantum dots once injected into the eye. Whole-body hyperspectral fluorescence imaging was performed in 17 live mice. In vivo imaging was conducted prior to injection, and 5, 20, 40 and 70 min, and 2, 6 and 24 h after injection. A quantum dot signal was observed in the left neck region at 6 h after tracer injection into the eye. Examination of immunofluorescence-labelled sections using confocal microscopy showed the presence of a quantum dot signal in the left submandibular lymph node. This is the first direct evidence of lymphatic drainage from the mouse eye. The use of quantum dots to image this lymphatic pathway in vivo is a novel tool to stimulate new treatments to reduce eye pressure and prevent blindness from glaucoma.

  18. High-fidelity gates in quantum dot spin qubits.

    PubMed

    Koh, Teck Seng; Coppersmith, S N; Friesen, Mark

    2013-12-01

    Several logical qubits and quantum gates have been proposed for semiconductor quantum dots controlled by voltages applied to top gates. The different schemes can be difficult to compare meaningfully. Here we develop a theoretical framework to evaluate disparate qubit-gating schemes on an equal footing. We apply the procedure to two types of double-dot qubits: the singlet-triplet and the semiconducting quantum dot hybrid qubit. We investigate three quantum gates that flip the qubit state: a DC pulsed gate, an AC gate based on logical qubit resonance, and a gate-like process known as stimulated Raman adiabatic passage. These gates are all mediated by an exchange interaction that is controlled experimentally using the interdot tunnel coupling g and the detuning [Symbol: see text], which sets the energy difference between the dots. Our procedure has two steps. First, we optimize the gate fidelity (f) for fixed g as a function of the other control parameters; this yields an f(opt)(g) that is universal for different types of gates. Next, we identify physical constraints on the control parameters; this yields an upper bound f(max) that is specific to the qubit-gate combination. We show that similar gate fidelities (~99:5%) should be attainable for singlet-triplet qubits in isotopically purified Si, and for hybrid qubits in natural Si. Considerably lower fidelities are obtained for GaAs devices, due to the fluctuating magnetic fields ΔB produced by nuclear spins.

  19. Microsecond-sustained lasing from colloidal quantum dot solids.

    PubMed

    Adachi, Michael M; Fan, Fengjia; Sellan, Daniel P; Hoogland, Sjoerd; Voznyy, Oleksandr; Houtepen, Arjan J; Parrish, Kevin D; Kanjanaboos, Pongsakorn; Malen, Jonathan A; Sargent, Edward H

    2015-01-01

    Colloidal quantum dots have grown in interest as materials for light amplification and lasing in view of their bright photoluminescence, convenient solution processing and size-controlled spectral tunability. To date, lasing in colloidal quantum dot solids has been limited to the nanosecond temporal regime, curtailing their application in systems that require more sustained emission. Here we find that the chief cause of nanosecond-only operation has been thermal runaway: the combination of rapid heat injection from the pump source, poor heat removal and a highly temperature-dependent threshold. We show microsecond-sustained lasing, achieved by placing ultra-compact colloidal quantum dot films on a thermally conductive substrate, the combination of which minimizes heat accumulation. Specifically, we employ inorganic-halide-capped quantum dots that exhibit high modal gain (1,200 cm(-1)) and an ultralow amplified spontaneous emission threshold (average peak power of ∼50 kW cm(-2)) and rely on an optical structure that dissipates heat while offering minimal modal loss. PMID:26493282

  20. Staircase Quantum Dots Configuration in Nanowires for Optimized Thermoelectric Power

    NASA Astrophysics Data System (ADS)

    Li, Lijie; Jiang, Jian-Hua

    2016-08-01

    The performance of thermoelectric energy harvesters can be improved by nanostructures that exploit inelastic transport processes. One prototype is the three-terminal hopping thermoelectric device where electron hopping between quantum-dots are driven by hot phonons. Such three-terminal hopping thermoelectric devices have potential in achieving high efficiency or power via inelastic transport and without relying on heavy-elements or toxic compounds. We show in this work how output power of the device can be optimized via tuning the number and energy configuration of the quantum-dots embedded in parallel nanowires. We find that the staircase energy configuration with constant energy-step can improve the power factor over a serial connection of a single pair of quantum-dots. Moreover, for a fixed energy-step, there is an optimal length for the nanowire. Similarly for a fixed number of quantum-dots there is an optimal energy-step for the output power. Our results are important for future developments of high-performance nanostructured thermoelectric devices.

  1. Staircase Quantum Dots Configuration in Nanowires for Optimized Thermoelectric Power.

    PubMed

    Li, Lijie; Jiang, Jian-Hua

    2016-01-01

    The performance of thermoelectric energy harvesters can be improved by nanostructures that exploit inelastic transport processes. One prototype is the three-terminal hopping thermoelectric device where electron hopping between quantum-dots are driven by hot phonons. Such three-terminal hopping thermoelectric devices have potential in achieving high efficiency or power via inelastic transport and without relying on heavy-elements or toxic compounds. We show in this work how output power of the device can be optimized via tuning the number and energy configuration of the quantum-dots embedded in parallel nanowires. We find that the staircase energy configuration with constant energy-step can improve the power factor over a serial connection of a single pair of quantum-dots. Moreover, for a fixed energy-step, there is an optimal length for the nanowire. Similarly for a fixed number of quantum-dots there is an optimal energy-step for the output power. Our results are important for future developments of high-performance nanostructured thermoelectric devices. PMID:27550093

  2. Kondo effect in coupled quantum dots: A noncrossing approximation study

    NASA Astrophysics Data System (ADS)

    Aguado, Ramón; Langreth, David C.

    2003-06-01

    The out-of-equilibrium transport properties of a double quantum dot system in the Kondo regime are studied theoretically by means of a two-impurity Anderson Hamiltonian with interimpurity hopping. The Hamiltonian, formulated in slave-boson language, is solved by means of a generalization of the noncrossing approximation (NCA) to the present problem. We provide benchmark calculations of the predictions of the NCA for the linear and nonlinear transport properties of coupled quantum dots in the Kondo regime. We give a series of predictions that can be observed experimentally in linear and nonlinear transport measurements through coupled quantum dots. Importantly, it is demonstrated that measurements of the differential conductance G=dI/dV, for the appropriate values of voltages and interdot tunneling couplings, can give a direct observation of the coherent superposition between the many-body Kondo states of each dot. This coherence can be also detected in the linear transport through the system: the curve linear conductance vs temperature is nonmonotonic, with a maximum at a temperature T* characterizing quantum coherence between both the Kondo states.

  3. Quantum-dot Carnot engine at maximum power.

    PubMed

    Esposito, Massimiliano; Kawai, Ryoichi; Lindenberg, Katja; Van den Broeck, Christian

    2010-04-01

    We evaluate the efficiency at maximum power of a quantum-dot Carnot heat engine. The universal values of the coefficients at the linear and quadratic order in the temperature gradient are reproduced. Curzon-Ahlborn efficiency is recovered in the limit of weak dissipation.

  4. Staircase Quantum Dots Configuration in Nanowires for Optimized Thermoelectric Power.

    PubMed

    Li, Lijie; Jiang, Jian-Hua

    2016-08-23

    The performance of thermoelectric energy harvesters can be improved by nanostructures that exploit inelastic transport processes. One prototype is the three-terminal hopping thermoelectric device where electron hopping between quantum-dots are driven by hot phonons. Such three-terminal hopping thermoelectric devices have potential in achieving high efficiency or power via inelastic transport and without relying on heavy-elements or toxic compounds. We show in this work how output power of the device can be optimized via tuning the number and energy configuration of the quantum-dots embedded in parallel nanowires. We find that the staircase energy configuration with constant energy-step can improve the power factor over a serial connection of a single pair of quantum-dots. Moreover, for a fixed energy-step, there is an optimal length for the nanowire. Similarly for a fixed number of quantum-dots there is an optimal energy-step for the output power. Our results are important for future developments of high-performance nanostructured thermoelectric devices.

  5. Robust hybrid quantum dot laser for integrated silicon photonics.

    PubMed

    Kurczveil, Géza; Liang, Di; Fiorentino, Marco; Beausoleil, Raymond G

    2016-07-11

    We demonstrate the first quantum dot (QD) laser on a silicon substrate with efficient coupling of light to a silicon waveguide under the QD gain region. Continuous wave operation up to 100 °C and multiwavelength operation are demonstrated, paving the way towards highly efficient CMOS-compatible, uncooled, WDM sources. PMID:27410883

  6. Making Ternary Quantum Dots From Single-Source Precursors

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila; Banger, Kulbinder; Castro, Stephanie; Hepp, Aloysius

    2007-01-01

    A process has been devised for making ternary (specifically, CuInS2) nanocrystals for use as quantum dots (QDs) in a contemplated next generation of high-efficiency solar photovoltaic cells. The process parameters can be chosen to tailor the sizes (and, thus, the absorption and emission spectra) of the QDs.

  7. Characterization of the Uptake of Quantum Dots by Algae

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Priyanka; Lin, Sijie; Sun, Xiaoqian; Brune, David; Ke, Pu-Chun

    2009-03-01

    The exposure of living systems to nanoparticles is inevitable due to a dramatic increase in their release into the environment, the most likely pathways being through inhalation, ingestion and skin uptake. The extremely small size of the nanoparticles may facilitate their tissue and cellular uptake by plants and animals, resulting in either positive (drug delivery, antioxidation) or negative (toxicity, cellular dysfunction) effects. Here we report the effects of quantum dots uptake by algae, the single-celled plant species and major food sources for aquatic organisms. In our studies, the presence of quantum dots in algal cells was detected using fluorescence microscopy and electron microscopy. Using spectrophotometry we found a supralinear increase of the uptake with the concentration of quantum dots, with a saturation of the uptake occurring beyond a concentration of 15 mg/mL. Using a bicarbonate indicator we further evaluated the effects of quantum dots uptake on algal photosynthesis and respiration. Such study facilitates our understanding of the environmental impact of nanomaterials.

  8. Scattering phase of quantum dots: emergence of universal behavior.

    PubMed

    Molina, Rafael A; Jalabert, Rodolfo A; Weinmann, Dietmar; Jacquod, Philippe

    2012-02-17

    We investigate scattering through chaotic ballistic quantum dots in the Coulomb-blockade regime. Focusing on the scattering phase, we show that large universal sequences emerge in the short wavelength limit, where phase lapses of π systematically occur between two consecutive resonances. Our results are corroborated by numerics and are in qualitative agreement with existing experiments. PMID:22401237

  9. Bit-Serial Adder Based on Quantum Dots

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Toomarian, Nikzad; Modarress, Katayoon; Spotnitz, Mathew

    2003-01-01

    A proposed integrated circuit based on quantum-dot cellular automata (QCA) would function as a bit-serial adder. This circuit would serve as a prototype building block for demonstrating the feasibility of quantum-dots computing and for the further development of increasingly complex and increasingly capable quantum-dots computing circuits. QCA-based bit-serial adders would be especially useful in that they would enable the development of highly parallel and systolic processors for implementing fast Fourier, cosine, Hartley, and wavelet transforms. The proposed circuit would complement the QCA-based circuits described in "Implementing Permutation Matrices by Use of Quantum Dots" (NPO-20801), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 42 and "Compact Interconnection Networks Based on Quantum Dots" (NPO-20855), which appears elsewhere in this issue. Those articles described the limitations of very-large-scale-integrated (VLSI) circuitry and the major potential advantage afforded by QCA. To recapitulate: In a VLSI circuit, signal paths that are required not to interact with each other must not cross in the same plane. In contrast, for reasons too complex to describe in the limited space available for this article, suitably designed and operated QCA-based signal paths that are required not to interact with each other can nevertheless 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. To enable a meaningful description of the proposed bit-serial adder, it is necessary to further recapitulate the description of a quantum-dot cellular automation from the first-mentioned prior article: A quantum-dot cellular automaton contains four quantum dots positioned at the corners of a square cell. The cell contains two extra mobile electrons that can tunnel (in the

  10. Investigation of the energy spectra and the electron-hole alignment of the InAs/GaAs quantum dots with an ultrathin cap layer

    NASA Astrophysics Data System (ADS)

    Gorshkov, Alexey P.; Volkova, Natalia S.; Istomin, Leonid A.; Zdoroveishev, Anton V.; Levichev, Sergey

    2016-08-01

    The effects of indium composition and the thickness of the combined InGaAs/GaAs thin cap layer on the energy spectra and relative electron-hole alignment of InAs quantum dots (QDs) grown by metal organic vapor phase epitaxy (MOVPE) are investigated by photoelectrical spectroscopy in a semiconductor/electrolyte system. In structures with InAs QDs and an InGaAs strain reducing layer, the shift of the hole's wave function to the QDs' top was revealed, which indicates In enrichment of the area near the top of QD'. In structures with an ultrathin GaAs cap layer a change of the sign of the built-in dipole moment was observed. This is explained by coupling effects of quantum-confined electrons with surface states.

  11. Towards Engineered Energy Flows in Quantum Dot Assemblies

    NASA Astrophysics Data System (ADS)

    Crooker, Scott A.

    2003-03-01

    Communication, coupling, and coherence between quantum dots are central themes in numerous scientific efforts of present physical and technological interest. In the limit of large numbers of coupled dots, colloidal semiconductor nanocrystal quantum dots (NQDs) are promising building blocks for the bottom-up assembly of macroscopic Â"artificial materialsÂ" having engineered functionality. Although NQDs offer size-tunable optical properties and ease of chemical manipulation into structures of varied complexity, strong inter-dot coupling (e.g., via electron tunneling) requires close proximity and a high degree of structural order, conditions which are difficult to achieve in practice. In this work [1] we investigate an alternative approach involving NQD coupling via long-range dipolar interactions, which allow inter-dot communication via resonant (Förster) energy transfer. We present studies of the dynamics of resonant energy transfer in monodisperse, mixed-size, and energy gradient (layered) assemblies of CdSe NQDs. Time- and spectrally-resolved photoluminescence data directly reveal the energy-dependent transfer rate of excitons from smaller to larger dots, showing sub-nanosecond energy transfer directly across a large tens-of-meV energy gap (i.e., between dots of disparate size). Results from layered NQD assemblies demonstrate unidirectional energy flows, a first step towards artificial light-harvesting structures. In comparison with some of Nature's most efficient energy transfer complexes -- chlorophylls -- the data suggest that inter-dot energy transfer can approach picosecond time scales in structurally optimized systems. [1] S. A. Crooker, J. A. Hollingsworth, S. Tretiak, and V. I. Klimov, Phys. Rev. Lett. v89, p186802 (2002).

  12. Double-layer-gate architecture for few-hole GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, D. Q.; Hamilton, A. R.; Farrer, I.; Ritchie, D. A.; Klochan, O.

    2016-08-01

    We report the fabrication of single and double hole quantum dots using a double-layer-gate design on an undoped accumulation mode {{Al}}x{{Ga}}1-x{As}/GaAs heterostructure. Electrical transport measurements of a single quantum dot show varying addition energies and clear excited states. In addition, the two-level-gate architecture can also be configured into a double quantum dot with tunable inter-dot coupling.

  13. Height control of self-assembled quantum dots by strain engineering during capping

    SciTech Connect

    Grossi, D. F. Koenraad, P. M.; Smereka, P.; Keizer, J. G.; Ulloa, J. M.

    2014-10-06

    Strain engineering during the capping of III-V quantum dots has been explored as a means to control the height of strained self-assembled quantum dots. Results of Kinetic Monte Carlo simulations are confronted with cross-sectional Scanning Tunnel Microscopy (STM) measurements performed on InAs quantum dots grown by molecular beam epitaxy. We studied InAs quantum dots that are capped by In{sub x}Ga{sub (1−x)}As layers of different indium compositions. Both from our realistic 3D kinetic Monte Carlo simulations and the X-STM measurements on real samples, a trend in the height of the capped quantum dot is found as a function of the lattice mismatch between the quantum dot material and the capping layer. Results obtained on additional material combinations show a generic role of the elastic energy in the control of the quantum dot morphology by strain engineering during capping.

  14. Numerical modeling of shape and size dependent intermediate band quantum dot solar cell

    NASA Astrophysics Data System (ADS)

    Sabeur, Abdelkader; Jiang, Jianliang; Imran, Ali

    2015-08-01

    The electronic structure of the self-assembled quantum dot is presented in this paper to explore the efficient design of quantum dot solar cell. The electronic states of InAs quantum dot embedded in a GaAs matrix have been studied in this article, in which it is assumed the effective mass is independent of level energy for simplification. The shape effect and the layer effect for single quantum dot are investigated, and a simple one-band model for array quantum dots is studied. In the array quantum dots the wave function interaction will be strong, when the space between quantum dots is very close, which will affect the level energy.

  15. Suppression of low-frequency charge noise in gates-defined GaAs quantum dots

    SciTech Connect

    You, Jie; Li, Hai-Ou E-mail: gpguo@ustc.edu.cn; Wang, Ke; Cao, Gang; Song, Xiang-Xiang; Xiao, Ming; Guo, Guo-Ping E-mail: gpguo@ustc.edu.cn

    2015-12-07

    To reduce the charge noise of a modulation-doped GaAs/AlGaAs quantum dot, we have fabricated shallow-etched GaAs/AlGaAs quantum dots using the wet-etching method to study the effects of two-dimensional electron gas (2DEG) underneath the metallic gates. The low-frequency 1/f noise in the Coulomb blockade region of the shallow-etched quantum dot is compared with a non-etched quantum dot on the same wafer. The average values of the gate noise are approximately 0.5 μeV in the shallow-etched quantum dot and 3 μeV in the regular quantum dot. Our results show the quantum dot low-frequency charge noise can be suppressed by the removal of the 2DEG underneath the metallic gates, which provides an architecture for noise reduction.

  16. Self-assembled quantum dots in a nanowire system for quantum photonics

    NASA Astrophysics Data System (ADS)

    Heiss, M.; Fontana, Y.; Gustafsson, A.; Wüst, G.; Magen, C.; O'Regan, D. D.; Luo, J. W.; Ketterer, B.; Conesa-Boj, S.; Kuhlmann, A. V.; Houel, J.; Russo-Averchi, E.; Morante, J. R.; Cantoni, M.; Marzari, N.; Arbiol, J.; Zunger, A.; Warburton, R. J.; Fontcuberta I Morral, A.

    2013-05-01

    Quantum dots embedded within nanowires represent one of the most promising technologies for applications in quantum photonics. Whereas the top-down fabrication of such structures remains a technological challenge, their bottom-up fabrication through self-assembly is a potentially more powerful strategy. However, present approaches often yield quantum dots with large optical linewidths, making reproducibility of their physical properties difficult. We present a versatile quantum-dot-in-nanowire system that reproducibly self-assembles in core-shell GaAs/AlGaAs nanowires. The quantum dots form at the apex of a GaAs/AlGaAs interface, are highly stable, and can be positioned with nanometre precision relative to the nanowire centre. Unusually, their emission is blue-shifted relative to the lowest energy continuum states of the GaAs core. Large-scale electronic structure calculations show that the origin of the optical transitions lies in quantum confinement due to Al-rich barriers. By emitting in the red and self-assembling on silicon substrates, these quantum dots could therefore become building blocks for solid-state lighting devices and third-generation solar cells.

  17. Self-assembled quantum dots in a nanowire system for quantum photonics.

    PubMed

    Heiss, M; Fontana, Y; Gustafsson, A; Wüst, G; Magen, C; O'Regan, D D; Luo, J W; Ketterer, B; Conesa-Boj, S; Kuhlmann, A V; Houel, J; Russo-Averchi, E; Morante, J R; Cantoni, M; Marzari, N; Arbiol, J; Zunger, A; Warburton, R J; Fontcuberta i Morral, A

    2013-05-01

    Quantum dots embedded within nanowires represent one of the most promising technologies for applications in quantum photonics. Whereas the top-down fabrication of such structures remains a technological challenge, their bottom-up fabrication through self-assembly is a potentially more powerful strategy. However, present approaches often yield quantum dots with large optical linewidths, making reproducibility of their physical properties difficult. We present a versatile quantum-dot-in-nanowire system that reproducibly self-assembles in core-shell GaAs/AlGaAs nanowires. The quantum dots form at the apex of a GaAs/AlGaAs interface, are highly stable, and can be positioned with nanometre precision relative to the nanowire centre. Unusually, their emission is blue-shifted relative to the lowest energy continuum states of the GaAs core. Large-scale electronic structure calculations show that the origin of the optical transitions lies in quantum confinement due to Al-rich barriers. By emitting in the red and self-assembling on silicon substrates, these quantum dots could therefore become building blocks for solid-state lighting devices and third-generation solar cells. PMID:23377293

  18. Graphene Quantum Dots: Molecularly Designed, Nitrogen-Functionalized Graphene Quantum Dots for Optoelectronic Devices (Adv. Mater. 23/2016).

    PubMed

    Tetsuka, Hiroyuki; Nagoya, Akihiro; Fukusumi, Takanori; Matsui, Takayuki

    2016-06-01

    H. Tetsuka and co-workers develop a versatile technique to tune the energy levels and energy gaps of nitrogen-functionalized graphene quantum dots (NGQDs) continuously through molecular structure design, as described on page 4632. The incorporation of layers of NGQDs into the structures markedly improves the performance of optoelectronic devices. PMID:27281048

  19. Fano-Andreev effect in Quantum Dots in Kondo regime

    NASA Astrophysics Data System (ADS)

    Orellana, Pedro; Calle, Ana Maria; Pacheco, Monica; Apel, Victor

    In the present work, we investigate the transport through a T-shaped double quantum dot system coupled to two normal leads and to a superconducting lead. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot and by means of a slave boson mean field approximation at low temperature regime. We inquire into the influence of intradot interactions in the electronic properties of the system as well. Our results show that Fano resonances due to Andreev bound states are exhibited in the transmission from normal to normal lead as a consequence of quantum interference and proximity effect. This Fano effect produced by Andreev bound states in a side quantum dot was called Fano-Andreev effect, which remains valid even if the electron-electron interaction are taken into account, that is, the Fano-Andreev effect is robust against e-e interactions even in Kondo regime. We acknowledge the financial support from FONDECYT program Grants No. 3140053 and 11400571.

  20. Fluorescence and Bonding of Quantum Dots on DNA Origami Constructs

    NASA Astrophysics Data System (ADS)

    Kessinger, Matthew; Corrigan, Timothy; Neff, David; Norton, Michael; Concord University Collaboration; Marshall University Collaboration

    2015-03-01

    Semiconductor quantum dots (QDots) have historically been of interest to the scientific community since their creation for various applications ranging from solar energy to optical labeling. In this study, bioconjugated CdSe/ZnS core/shell QDots were synthesized and functionalized with 3-mercaptopropionic acid using both traditional ligand exchange as well as newly developed in situ functionalization techniques used to increase the quantum yield of the QDots. Their fluorescence and bonding to both gold as well as DNA origami were investigated for use in self assembled DNA constructs. It is believed that controlling the attachment and spacing of these nanoparticles on DNA origami could be used in a variety of optical labeling and sensing applications. Commercially available biotin and streptavidin functionalized quantum dots were also examined, and subject to the same experiments with gold nanoparticles as the MPA functionalized QDots.

  1. Synthesis, Characterization and Application Of PbS Quantum Dots

    SciTech Connect

    Sarma, Sweety; Datta, Pranayee; Barua, Kishore Kr.; Karmakar, Sanjib

    2009-06-29

    Lead Chalcogenides (PbS, PbSe, PbTe) quantum dots (QDs) are ideal for fundamental studies of strongly quantum confined systems with possible technological applications. Tunable electronic transitions at near--infrared wavelengths can be obtained with these QDs. Applications of lead chalcogenides encompass quite a good number of important field viz. the fields of telecommunications, medical electronics, optoelectronics etc. Very recently, it has been proposed that 'memristor'(Memory resistor) can be realized in nanoscale systems with coupled ionic and electronic transports. The hystersis characteristics of 'memristor' are observed in many nanoscale electronic devices including semiconductor quantum dot devices. This paper reports synthesis of PbS QDs by chemical route. The fabricated samples are characterized by UV-Vis, XRD, SEM, TEM, EDS, etc. Observed characteristics confirm nano formation. I-V characteristics of the sample are studied for investigating their applications as 'memristor'.

  2. Deterministic teleportation of electrons in a quantum dot nanostructure.

    PubMed

    de Visser, R L; Blaauboer, M

    2006-06-23

    We present a proposal for deterministic quantum teleportation of electrons in a semiconductor nanostructure consisting of a single and a double quantum dot. The central issue addressed in this Letter is how to design and implement the most efficient--in terms of the required number of single and two-qubit operations--deterministic teleportation protocol for this system. Using a group-theoretical analysis, we show that deterministic teleportation requires a minimum of three single-qubit rotations and two entangling (square root SWAP) operations. These can be implemented for spin qubits in quantum dots using electron-spin resonance (for single-spin rotations) and exchange interaction (for square root SWAP operations).

  3. Photoluminescence of patterned arrays of vertically stacked InAs/GaAs quantum dots

    SciTech Connect

    Saucer, Timothy W.; Lee, J. E.; Martin, Andrew J.; Tien, Deborah; Millunchick, Joanna M.; Sih, Vanessa

    2010-12-22

    We report on photoluminescence measurements of vertically stacked InAs/GaAs quantum dots grown by molecular beam epitaxy on focused ion beam patterned hole arrays with varying array spacing. Quantum dot emission at 1.24 eV was observed only on patterned regions, demonstrating preferential nucleation of optically active dots at desired locations and below the critical thickness for dot formation at these growth conditions. Photoluminescence measurements as a function of varying focused ion beam irradiated hole spacing showed that the quantum dot emission intensity increased with decreasing array periodicity, consistent with increasing dot density.

  4. Confinement and inhomogeneous broadening effects in the quantum oscillatory magnetization of quantum dot ensembles

    NASA Astrophysics Data System (ADS)

    Herzog, F.; Heedt, S.; Goerke, S.; Ibrahim, A.; Rupprecht, B.; Heyn, Ch; Hardtdegen, H.; Schäpers, Th; Wilde, M. A.; Grundler, D.

    2016-02-01

    We report on the magnetization of ensembles of etched quantum dots with a lateral diameter of 460 nm, which we prepared from InGaAs/InP heterostructures. The quantum dots exhibit 1/B-periodic de-Haas-van-Alphen-type oscillations in the magnetization M(B) for external magnetic fields B  >  2 T, measured by torque magnetometry at 0.3 K. We compare the experimental data to model calculations assuming different confinement potentials and including ensemble broadening effects. The comparison shows that a hard wall potential with an edge depletion width of 100 nm explains the magnetic behavior. Beating patterns induced by Rashba spin-orbit interaction (SOI) as measured in unpatterned and nanopatterned InGaAs/InP heterostructures are not observed for the quantum dots. From our model we predict that signatures of SOI in the magnetization could be observed in larger dots in tilted magnetic fields.

  5. The structural and optical properties of GaSb/InGaAs type-II quantum dots grown on InP (100) substrate

    PubMed Central

    2012-01-01

    We have investigated the structural and optical properties of type-II GaSb/InGaAs quantum dots [QDs] grown on InP (100) substrate by molecular beam epitaxy. Rectangular-shaped GaSb QDs were well developed and no nanodash-like structures which could be easily found in the InAs/InP QD system were formed. Low-temperature photoluminescence spectra show there are two peaks centered at 0.75eV and 0.76ev. The low-energy peak blueshifted with increasing excitation power is identified as the indirect transition from the InGaAs conduction band to the GaSb hole level (type-II), and the high-energy peak is identified as the direct transition (type-I) of GaSb QDs. This material system shows a promising application on quantum-dot infrared detectors and quantum-dot field-effect transistor. PMID:22277096

  6. Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

    SciTech Connect

    Barettin, Daniele Auf der Maur, Matthias; De Angelis, Roberta; Prosposito, Paolo; Casalboni, Mauro; Pecchia, Alessandro

    2015-03-07

    We report on numerical simulations of InP surface lateral quantum-dot molecules on In{sub 0.48}Ga{sub 0.52 }P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k{sup →}·p{sup →} bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.

  7. Fabrication and characterization of an undoped GaAs/AlGaAs quantum dot device

    SciTech Connect

    Li, Hai-Ou; Cao, Gang; Xiao, Ming You, Jie; Wei, Da; Tu, Tao; Guo, Guang-Can; Guo, Guo-Ping; Jiang, Hong-Wen

    2014-11-07

    We demonstrate the development of a double quantum dot with an integrated charge sensor fabricated in undoped GaAs/AlGaAs heterostructures using a double top-gated design. Based on the evaluation of the integrated charge sensor, the double quantum dot can be tuned to a few-electron region. Additionally, the inter-dot coupling of the double quantum dot can be tuned to a large extent according to the voltage on the middle gate. The quantum dot is shown to be tunable from a single dot to a well-isolated double dot. To assess the stability of such design, the potential fluctuation induced by 1/f noise was measured. Based on the findings herein, the quantum dot design developed in the undoped GaAs/AlGaAs semiconductor shows potential for the future exploitation of nano-devices.

  8. Evaporation-Induced Assembly of Quantum Dots into Nanorings

    PubMed Central

    Chen, Jixin; Liao, Wei-Ssu; Chen, Xin; Yang, Tinglu; Wark, Stacey E.; Son, Dong Hee; Batteas, James D.; Cremer, Paul S.

    2011-01-01

    Herein, we demonstrate the controlled formation of two-dimensional periodic arrays of ring-shaped nanostructures assembled from CdSe semiconductor quantum dots (QDs). The patterns were fabricated by using an evaporative templating method. This involves the introduction of an aqueous solution containing both quantum dots and polystyrene microspheres onto the surface of a planar hydrophilic glass substrate. The quantum dots became confined to the meniscus of the microspheres during evaporation, which drove ring assembly via capillary forces at the polystyrene sphere/glass substrate interface. The geometric parameters for nanoring formation could be controlled by tuning the size of the microspheres and the concentration of the QDs employed. This allowed hexagonal arrays of nanorings to be formed with thicknesses ranging from single dot necklaces to thick multilayer structures over surface areas of many square millimeters. Moreover, the diameter of the ring structures could be simultaneously controlled. A simple model was employed to explain the forces involved in the formation of nanoparticle nanorings. PMID:19206264

  9. Quantum dot-sized organic fluorescent dots for long-term cell tracing

    NASA Astrophysics Data System (ADS)

    Li, Kai; Tang, Ben Zhong; Liu, Bin

    2014-03-01

    Fluorescence techniques have been extensively employed to develop non-invasive methodologies for tracking and understanding complex biological processes both in vitro and in vivo, which is of high importance in modern life science research. Among a variety of fluorescent probes, inorganic semiconductor quantum dots (QDs) have shown advantages in terms of better photostability, larger Stokes shift and more feasible surface functionalization. However, their intrinsic toxic heavy metal components and unstable fluorescence at low pH greatly impede the applications of QDs in in vivo studies. In this work, we developed novel fluorescent probes that can outperform currently available QD based probes in practice. Using conjugated oligomer with aggregation-induced emission characteristics as the fluorescent domain and biocompatible lipid-PEG derivatives as the encapsulation matrix, the obtained organic dots have shown higher brightness, better stability in biological medium and comparable size and photostability as compared to their counterparts of inorganic QDs. More importantly, unlike QD-based probes, the organic fluorescent dots do not blink, and also do not contain heavy metal ions that could be potentially toxic when applied for living biosubstrates. Upon surface functionalization with a cell-penetrating peptide, the organic dots greatly outperform inorganic quantum dots in both in vitro and in vivo long-term cell tracing studies, which will be beneficial to answer crucial questions in stem cell/immune cell therapies. Considering the customized fluorescent properties and surface functionalities of the organic dots, a series of biocompatible organic dots will be developed to serve as a promising platform for multifarious bioimaging tasks in future.

  10. Carbon "Quantum" Dots for Fluorescence Labeling of Cells.

    PubMed

    Liu, Jia-Hui; Cao, Li; LeCroy, Gregory E; Wang, Ping; Meziani, Mohammed J; Dong, Yiyang; Liu, Yuanfang; Luo, Pengju G; Sun, Ya-Ping

    2015-09-01

    The specifically synthesized and selected carbon dots of relatively high fluorescence quantum yields were evaluated in their fluorescence labeling of cells. For the cancer cell lines, the cellular uptake of the carbon dots was generally efficient, resulting in the labeling of the cells with bright fluorescence emissions for both one- and two-photon excitations from predominantly the cell membrane and cytoplasm. In the exploration on labeling the live stem cells, the cellular uptake of the carbon dots was relatively less efficient, though fluorescence emissions could still be adequately detected in the labeled cells, with the emissions again predominantly from the cell membrane and cytoplasm. This combined with the observed more efficient internalization of the same carbon dots by the fixed stem cells might suggest some significant selectivity of the stem cells toward surface functionalities of the carbon dots. The needs and possible strategies for more systematic and comparative studies on the fluorescence labeling of different cells, including especially live stem cells, by carbon dots as a new class of brightly fluorescent probes are discussed.

  11. Approaches to Future Generation Photovoltaics and Solar Fuels: Quantum Dots, Arrays, and Quantum Dot Solar Cells

    SciTech Connect

    Semonin, O.; Luther, J.; Beard, M.; Johnson, J.; Gao, J.; Nozik, A.

    2012-01-01

    One potential, long-term approach to more efficient and lower cost future generation solar cells for solar electricity and solar fuels is to utilize the unique properties of quantum dots (QDs) to control the relaxation pathways of excited states to enhance multiple exciton generation (MEG). We have studied MEG in close-packed PbSe QD arrays where the QDs are electronically coupled in the films and thus exhibit good transport while still maintaining quantization and MEG. We have developed simple, all-inorganic solution-processable QD solar cells that produce large short-circuit photocurrents and power conversion efficiencies above 5% via nanocrystalline p-n junctions. These solar cells show QYs for photocurrent that exceed 100% in the photon energy regions where MEG is possible; the photocurrent MEG QYs as a function of photon energy match those determined via time-resolved spectroscopy Recent analyses of the major effect of MEG combined with solar concentration on the conversion efficiency of solar cells will also be discussed.

  12. Increased in vivo skin penetration of quantum dots with UVR and in vitro quantum dot cytotoxicity

    NASA Astrophysics Data System (ADS)

    Mortensen, Luke; Zheng, Hong; Faulknor, Renea; De Benedetto, Anna; Beck, Lisa; DeLouise, Lisa A.

    2009-02-01

    The growing presence of quantum dots (QD) in a variety of biological, medical, and electronics applications means an increased risk of human exposure in manufacturing, research, and consumer use. However, very few studies have investigated the susceptibility of skin to penetration of QD - the most common exposure route- and the results of those that exist are conflicting. This suggests that a technique allowing determination of skin barrier status and prediction of skin permeability to QD would be of crucial interest as recent findings have provided evidence of in vitro cytotoxicity and long-term in vivo retention in the body for most QD surface chemistries. Our research focuses on barrier status of the skin (intact and with ultraviolet radiation induced barrier defect) and its impact on QD skin penetration. These model studies are particularly relevant to the common application condition of NP containing sunscreen and SPF cosmetics to UV exposed skin. Herein we present our initial efforts to develop an in vivo model of nanoparticle skin penetration using the SKH-1 hairless mouse with transepidermal water loss (TEWL) to evaluate skin barrier status and determine its ability to predict QD penetration. Our results show that ultraviolet radiation increases both TEWL and skin penetration of QD. Additionally, we demonstrate cytotoxic potential of QD to skin cells using a metastatic melanoma cell line. Our research suggests future work in specific targeting of nanoparticles, to prevent or enhance penetration. This knowledge will be used to develop powerful therapeutic agents, decreased penetration cosmetic nanoparticles, and precise skin cancer imaging modalities.

  13. The emission wavelength dependent photoluminescence lifetime of the N-doped graphene quantum dots

    SciTech Connect

    Deng, Xingxia; Sun, Jing; Yang, Siwei; Ding, Guqiao; Shen, Hao; Zhou, Wei; Lu, Jian; Wang, Zhongyang

    2015-12-14

    Aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques. The PL lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum, which is different from most semiconductor quantum dots and fluorescent dyes. This result shows the synergy and competition between the quantum confinement effect and edge functional groups, which may have the potential to guide the synthesis and expand the applications of graphene quantum dots.

  14. Miniband formulation in Ge/Si quantum dot array

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    In this work, we estimate the coupling effect of miniband structure and density of states (DoS) resulting from different qunatum-dot physical parameters in a well-aligned Ge/Si quantum dot (QD) array fabricated by neutral beam etching technology. The density of QDs dominates the coupling effect and miniband’s bandwidth, the radius of QDs affects the magnitude of energy levels and miniband bandwidth, and the thickness of QDs has a great impact on the magnitude of energy levels. Among the different shapes of Ge/Si QDs, discoid QDs exhibit the most band crossing and broadest bandwith under the same physical parameters.

  15. Fractional boundary charges in quantum dot arrays with density modulation

    NASA Astrophysics Data System (ADS)

    Park, Jin-Hong; Yang, Guang; Klinovaja, Jelena; Stano, Peter; Loss, Daniel

    2016-08-01

    We show that fractional charges can be realized at the boundaries of a linear array of tunnel-coupled quantum dots in the presence of a periodically modulated onsite potential. While the charge fractionalization mechanism is similar to the one in polyacetylene, here the values of fractional charges can be tuned to arbitrary values by varying the phase of the onsite potential or the total number of dots in the array. We also find that the fractional boundary charges, unlike the in-gap bound states, are stable against static random disorder. We discuss the minimum array size where fractional boundary charges can be observed.

  16. Quantum interference and control of the optical response in quantum dot molecules

    SciTech Connect

    Borges, H. S.; Sanz, L.; Villas-Boas, J. M.; Alcalde, A. M.

    2013-11-25

    We discuss the optical response of a quantum molecule under the action of two lasers fields. Using a realistic model and parameters, we map the physical conditions to find three different phenomena reported in the literature: the tunneling induced transparency, the formation of Autler-Townes doublets, and the creation of a Mollow-like triplet. We found that the electron tunneling between quantum dots is responsible for the different optical regime. Our results not only explain the experimental results in the literature but also give insights for future experiments and applications in optics using quantum dots molecules.

  17. Quantum Well and Quantum Dot Modeling for Advanced Infrared Detectors and Focal Plane Arrays

    NASA Technical Reports Server (NTRS)

    Ting, David; Gunapala, S. D.; Bandara, S. V.; Hill, C. J.

    2006-01-01

    This viewgraph presentation reviews the modeling of Quantum Well Infrared Detectors (QWIP) and Quantum Dot Infrared Detectors (QDIP) in the development of Focal Plane Arrays (FPA). The QWIP Detector being developed is a dual band detector. It is capable of running on two bands Long-Wave Infrared (LWIR) and Medium Wavelength Infrared (MWIR). The same large-format dual-band FPA technology can be applied to Quantum Dot Infrared Photodetector (QDIP) with no modification, once QDIP exceeds QWIP in single device performance. Details of the devices are reviewed.

  18. Investigation of quantum confinement behavior of zinc sulphide quantum dots synthesized via various chemical methods

    SciTech Connect

    Jose, Meera Sakthivel, T. Chandran, Hrisheekesh T. Nivea, R. Gunasekaran, V.

    2014-10-15

    In this work, undoped and Ag-doped ZnS quantum dots were synthesized using various chemical methods. The products were characterized using X-ray diffraction (XRD), UV-visible spectroscopy and Photoluminescence spectroscopy. Our results revealed that the size of the as-prepared samples range from 1–6 nm in diameter and have a cubic zinc-blende structure. Also, we observed the emission of different wavelength of light from different sized quantum dots of the same material due to quantum confinement effect. The results will be presented in detail and ZnS can be a potential candidate for optical device development and applications.

  19. Dynamic light-matter coupling across multiple spatial dimensions in a quantum dots-in-a-well heterostructure

    SciTech Connect

    Prasankumar, Rohit P; Taylor, Antoinette J

    2009-01-01

    Ultrafast density-dependent optical spectroscopic measurements on a quantum dots-in-a-well heterostructure reveal several distinctive phenomena, most notably a strong coupling between the quantum well population and light absorption at the quantum dot excited state.

  20. Biexciton induced refractive index changes in a semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Shojaei, S.

    2015-06-01

    We present a detailed theoretical study of linear and third order nonlinear refractive index changes in a optically driven disk-like GaN quantum dot. In our numerical calculations, we consider the three level system containing biexciton, exciton, and ground states and use the compact density matrix formalism and iterative method to obtain refractive index changes. Variational method through effective mass approximation are employed to calculate the ground state energy of biexciton and exciton states. The evolution of refractive index changes around one, two and three photon resonance is investigated and discussed for different quantum dot sizes and light intensities. Size-dependent three-photon nonlinear refractive index change versus incident photon energy compared to that of two-photon is obtained and analyzed. As main result, we found that around resonance frequency at exciton-biexciton transition the quantum confinement has great influence on the linear change in refractive index so that for very large quantum dots, it decreases. Moreover, it was found that third order refractive index changes for three photon process is strongly dependent on QD size and light intensity. Our study reveals that considering our simple model leads to results which are in good agreement with other rare numerical results. Comparison with experimental results has been done.

  1. Two-Photon Photochemistry of CdSe Quantum Dots.

    PubMed

    Zeng, Youhong; Kelley, David F

    2015-10-27

    The two-photon photochemistry of CdSe quantum dots (QDs) has been systematically studied. We find that upon intense irradiation CdSe quantum dots that absorb two or more visible photons undergo photodarkening. The quantum yield for this process is on the order of 6% in chloroform and much smaller in nonpolar solvents, such as octane. An analysis of the energetics indicates that, following two-photon excitation, the biexciton undergoes an Auger process producing a hot hole. This hot hole is ejected to a surface-bound TOP ligand, forming a QD(-)/TOP(+) contact ion pair that separates in chloroform, but not in octane. The charged and deligated QD is dark, resulting in the overall photodarkening. This photodarkening reaction may or may not be reversible, depending on what other chemical components are in the irradiated solution. The quantum dot concentration dependence and PL decay kinetics indicate that charge recombination occurs rapidly, followed by ligand reattachment and reorganization on a longer (tens of minutes) time scale. The relation of this mechanism to one-photon photochemistry is also discussed.

  2. Spectroscopic Characterization of Streptavidin Functionalized Quantum dots1

    PubMed Central

    Wu, Yang; Lopez, Gabriel P.; Sklar, Larry A.; Buranda, Tione

    2007-01-01

    The spectroscopic properties of quantum dots can be strongly influenced by the conditions of their synthesis. In this work we have characterized several spectroscopic properties of commercial, streptavidin functionalized quantum dots (QD525, lot#1005-0045 and QD585, Lot#0905-0031 from Invitrogen). This is the first step in the development of calibration beads, to be used in a generalizable quantification scheme of multiple fluorescent tags in flow cytometry or microscopy applications. We used light absorption, photoexcitation, and emission spectra, together with excited-state lifetime measurements to characterize their spectroscopic behavior, concentrating on the 400-500nm wavelength ranges that are important in biological applications. Our data show an anomalous dependence of emission spectrum, lifetimes, and quantum yield (QY) on excitation wavelength that is particularly pronounced in the QD525. For QD525, QY values ranged from 0.2 at 480nm excitation up to 0.4 at 450nm and down again to 0.15 at 350nm. For QD585, QY values were constant at 0.2 between 500nm and 400nm, but dropped to 0.1 at 350nm. We attribute the wavelength dependences to heterogeneity in size and surface defects in the QD525, consistent with characteristics previously described in the chemistry literature. The results are discussed in the context of bridging the gap between what is currently known in the physical chemistry literature of quantum dots, and the quantitative needs of assay development in biological applications. PMID:17368555

  3. Quantum Dot Platform for Single-Cell Molecular Profiling

    NASA Astrophysics Data System (ADS)

    Zrazhevskiy, Pavel S.

    In-depth understanding of the nature of cell physiology and ability to diagnose and control the progression of pathological processes heavily rely on untangling the complexity of intracellular molecular mechanisms and pathways. Therefore, comprehensive molecular profiling of individual cells within the context of their natural tissue or cell culture microenvironment is essential. In principle, this goal can be achieved by tagging each molecular target with a unique reporter probe and detecting its localization with high sensitivity at sub-cellular resolution, primarily via microscopy-based imaging. Yet, neither widely used conventional methods nor more advanced nanoparticle-based techniques have been able to address this task up to date. High multiplexing potential of fluorescent probes is heavily restrained by the inability to uniquely match probes with corresponding molecular targets. This issue is especially relevant for quantum dot probes---while simultaneous spectral imaging of up to 10 different probes is possible, only few can be used concurrently for staining with existing methods. To fully utilize multiplexing potential of quantum dots, it is necessary to design a new staining platform featuring unique assignment of each target to a corresponding quantum dot probe. This dissertation presents two complementary versatile approaches towards achieving comprehensive single-cell molecular profiling and describes engineering of quantum dot probes specifically tailored for each staining method. Analysis of expanded molecular profiles is achieved through augmenting parallel multiplexing capacity with performing several staining cycles on the same specimen in sequential manner. In contrast to other methods utilizing quantum dots or other nanoparticles, which often involve sophisticated probe synthesis, the platform technology presented here takes advantage of simple covalent bioconjugation and non-covalent self-assembly mechanisms for straightforward probe

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

    NASA Astrophysics Data System (ADS)

    Isnaeni, Yulianto, Nursidik; Suliyanti, Maria Margaretha

    2016-03-01

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

  5. Aptamer-conjugated dendrimer-modified quantum dots for glioblastoma cells imaging

    NASA Astrophysics Data System (ADS)

    Li, Zhiming; Huang, Peng; He, Rong; Zhang, Xiaomin; Bao, Chenchen; Ren, Qiushi; Cui, Daxiang

    2009-09-01

    Targeted quantum dots have shown potential as a platform for development of cancer imaging. Aptamers have recently been demonstrated as ideal candidates for molecular targeting applications. In present work, polyamidoamine dendrimers were used to modify surface of quantum dots and improve their solubility in water solution. Then, dendrimer-modified quantum dots were conjugated with DNA aptamer, GBI-10, can recognize the extracellular matrix protein tenascin-C on the surface of human glioblastoma cells. The dendrimer-modified quantum dots exhibit water-soluble, high quantum yield, and good biocompatibility. Aptamer-conjugated quantum dots can specifically target U251 human glioblastoma cells. High-performance aptamer-conjugated dendrimers modified quantum dot-based nanoprobes have great potential in application such as cancer imaging.

  6. Templated self-assembly of quantum dots from aqueous solution using protein scaffolds

    NASA Astrophysics Data System (ADS)

    Szuchmacher Blum, Amy; Soto, Carissa M.; Wilson, Charmaine D.; Whitley, Jessica L.; Moore, Martin H.; Sapsford, Kim E.; Lin, Tianwei; Chatterji, Anju; Johnson, John E.; Ratna, Banahalli R.

    2006-10-01

    Short, histidine-containing peptides can be conjugated to lysine-containing protein scaffolds to controllably attach quantum dots (QDs) to the scaffold, allowing for generic attachment of quantum dots to any protein without the use of specially engineered domains. This technique was used to bind quantum dots from aqueous solution to both chicken IgG and cowpea mosaic virus (CPMV), a 30 nm viral particle. These quantum dot protein assemblies were studied in detail. The IgG QD complexes were shown to retain binding specificity to their antigen after modification. The CPMV QD complexes have a local concentration of quantum dots greater than 3000 nmol ml-1, and show a 15% increase in fluorescence quantum yield over free quantum dots in solution.

  7. Quasi-periodic quantum dot arrays produced by electrochemical synthesis

    SciTech Connect

    Bandyopadhyay, S.; Miller, A.E.; Yue, D.F.; Banerjee, G.; Ricker, R.E.; Jones, S.; Eastman, J.A.; Baugher, E.; Chandrasekhar, M.

    1994-06-01

    We discuss a ``gentle`` electrochemical technique for fabricating quasi-periodic quantum dot arrays. The technique exploits a self-organizing phenomenon to produce quasi-periodic arrangement of dots and provides excellent control over dot size and interdot spacing. Unlike conventional nanolithography, it does not cause radiation damage to the structures during exposure to pattern delineating beams (e-beam, ion-beam or x-ray). Moreover, it does not require harsh processing steps like reactive ion etching, offers a minimum feature size of {approximately}40 {angstrom}, allows the fabrication of structures on nonplanar surfaces (e.g. spherical or cylindrical substrates), is amenable to mass production (millions of wafers can be processed simultaneously) and is potentially orders of magnitude cheaper than conventional nanofabrication. In this paper, we describe our initial results and show the promise of this technique for low-cost and high-yield nanosynthesis.

  8. InN Quantum Dot Based Infra-Red Photodetectors.

    PubMed

    Shetty, Arjun; Kumar, Mahesh; Roull, Basanta; Vinoy, K J; Krupanidhj, S B

    2016-01-01

    Self-assembled InN quantum dots (QDs) were grown on Si(111) substrate using plasma assisted molecular beam epitaxy (PA-MBE). Single-crystalline wurtzite structure of InN QDs was confirmed by X-ray diffraction. The dot densities were varied by varying the indium flux. Variation of dot density was confirmed by FESEM images. Interdigitated electrodes were fabricated using standard lithog- raphy steps to form metal-semiconductor-metal (MSM) photodetector devices. The devices show strong infrared response. It was found that the samples with higher density of InN QDs showed lower dark current and higher photo current. An explanation was provided for the observations and the experimental results were validated using Silvaco Atlas device simulator. PMID:27398511

  9. Correlated Coulomb Drag in Capacitively Coupled Quantum-Dot Structures.

    PubMed

    Kaasbjerg, Kristen; Jauho, Antti-Pekka

    2016-05-13

    We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs)-a bias-driven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach that accounts for higher-order tunneling (cotunneling) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multielectron cotunneling processes. Our theory establishes the conditions for a nonzero drag as well as the direction of the drag current in terms of microscopic system parameters. Interestingly, the direction of the drag current is not determined by the drive current, but by an interplay between the energy-dependent lead couplings. Studying the drag mechanism in a graphene-based CQD heterostructure, we show that the predictions of our theory are consistent with recent experiments on Coulomb drag in CQD systems.

  10. Improvement of plasmonic enhancement of quantum dot emission via an intermediate silicon-aluminum oxide interface

    SciTech Connect

    Wing, Waylin J.; Sadeghi, Seyed M. Campbell, Quinn

    2015-01-05

    We studied the emission of quantum dots in the presence of plasmon-metal oxide substrates, which consist of arrays of metallic nanorods embedded in amorphous silicon coated with a nanometer-thin layer of aluminum oxide on the top. We showed that the combined effects of plasmons and the silicon-aluminum oxide interface can lead to significant enhancement of the quantum efficiency of quantum dots. Our results show that such an interface can significantly enhance plasmonic effects of the nanorods via quantum dot-induced exciton-plasmon coupling, leading to partial polarization of the quantum dots' emission.

  11. Charging dynamics of a floating gate transistor with site-controlled quantum dots

    SciTech Connect

    Maier, P. Hartmann, F.; Emmerling, M.; Schneider, C.; Höfling, S.; Kamp, M.; Worschech, L.

    2014-08-04

    A quantum dot memory based on a GaAs/AlGaAs quantum wire with site-controlled InAs quantum dots was realized by means of molecular beam epitaxy and etching techniques. By sampling of different gate voltage sweeps for the determination of charging and discharging thresholds, it was found that discharging takes place at short time scales of μs, whereas several seconds of waiting times within a distinct negative gate voltage range were needed to charge the quantum dots. Such quantum dot structures have thus the potential to implement logic functions comprising charge and time dependent ingredients such as counting of signals or learning rules.

  12. Direct observation of long-distance coherent superexchange spin coupling in a quantum dot arraySpin Exchange oscillations between distant quantum dots

    NASA Astrophysics Data System (ADS)

    Fujita, Takafumi; Baart, Tim; Reichl, Christian; Wegscheider, Werner; Vandersypen, Lieven

    Interactions mediated by long-range quantum coherence lie at the heart of important phenomena in many different fields. Charge transfer during oxidative stress in DNA, reactions in photosynthetic molecules, and behaviour of cuprate superconductors are all described by tunnelling via virtual hopping. Such mechanism may also provide new ways of using quantum dots for fault tolerant quantum information processing. In the presence of long-range tunnel coupling mediated by virtual occupation of intermediate levels, superexchange interactions can induce coherent oscillations between two distant electron spins. We implement this scheme in a linear array of three quantum dots with one electron on each of the outer dots. We observe coherent exchange oscillations between the two spins, and the oscillation frequency is controlled by the detuning of the electrochemical potential of the dot in between. Spin exchange at a distance may provide a new route for scaling up electron spin qubits using quantum dots.

  13. Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

    SciTech Connect

    Hendra, P. I. B. Rahayu, F. Darma, Y.

    2014-03-24

    Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

  14. Induced spin-accumulation and spin-polarization in a quantum-dot ring by using magnetic quantum dots and Rashba spin-orbit effect

    SciTech Connect

    Eslami, L. Faizabadi, E.

    2014-05-28

    The effect of magnetic contacts on spin-dependent electron transport and spin-accumulation in a quantum ring, which is threaded by a magnetic flux, is studied. The quantum ring is made up of four quantum dots, where two of them possess magnetic structure and other ones are subjected to the Rashba spin-orbit coupling. The magnetic quantum dots, referred to as magnetic quantum contacts, are connected to two external leads. Two different configurations of magnetic moments of the quantum contacts are considered; the parallel and the anti-parallel ones. When the magnetic moments are parallel, the degeneracy between the transmission coefficients of spin-up and spin-down electrons is lifted and the system can be adjusted to operate as a spin-filter. In addition, the accumulation of spin-up and spin-down electrons in non-magnetic quantum dots are different in the case of parallel magnetic moments. When the intra-dot Coulomb interaction is taken into account, we find that the electron interactions participate in separation between the accumulations of electrons with different spin directions in non-magnetic quantum dots. Furthermore, the spin-accumulation in non-magnetic quantum dots can be tuned in the both parallel and anti-parallel magnetic moments by adjusting the Rashba spin-orbit strength and the magnetic flux. Thus, the quantum ring with magnetic quantum contacts could be utilized to create tunable local magnetic moments which can be used in designing optimized nanodevices.

  15. Numerical subgap spectroscopy of double quantum dots coupled to superconductors

    NASA Astrophysics Data System (ADS)

    Žitko, Rok

    2015-04-01

    Double quantum dot nanostructures embedded between two superconducting leads or in a superconducting ring have complex excitation spectra inside the gap which reveal the competition between different many-body phenomena. We study the corresponding two-impurity Anderson model using the nonperturbative numerical renormalization group (NRG) technique and identify the characteristic features in the spectral function in various parameter regimes. At half-filling, the system always has a singlet ground state. For large hybridization, we observe an inversion of excited interdot triplet and singlet states due to the level repulsion between two subgap singlet states. The Shiba doublet states split in two cases: (a) at nonzero superconducting phase difference and (b) away from half-filling. The most complex structure of subgap states is found when one or both dots are in the valence fluctuation regime. Doublet splitting can lead to a parity-changing quantum phase transition to a doublet ground state in some circumstances. In such cases, we observe very different spectral weights for the transitions to singlet or triplet excited Shiba states: the triplet state is best visible on the valence-fluctuating dot, while the singlets are more pronounced on the half-filled dot.

  16. Optical injection enables coherence resonance in quantum-dot lasers

    NASA Astrophysics Data System (ADS)

    Ziemann, D.; Aust, R.; Lingnau, B.; Schöll, E.; Lüdge, K.

    2013-07-01

    We demonstrate that optically injected semiconductor quantum-dot lasers operated in the frequency-locked regime exhibit the counterintuitive effect of coherence resonance, i.e., the regularity of noise-induced spiking is a non-monotonic function of the spontaneous emission noise, and it is optimally correlated at a non-zero value of the noise intensity. We uncover the mechanism of coherence resonance from a microscopically based model of the quantum-dot laser structure, and show that it is related to excitability under optical injection and to a saddle-node infinite period (SNIPER) bifurcation occurring for small injection strength at the border of the frequency locking regime. By a model reduction we argue that the phenomenon of coherence resonance is generic for a wide class of optically injected lasers.

  17. Titanium-based silicide quantum dot superlattices for thermoelectrics applications.

    PubMed

    Savelli, Guillaume; Stein, Sergio Silveira; Bernard-Granger, Guillaume; Faucherand, Pascal; Montès, Laurent; Dilhaire, Stefan; Pernot, Gilles

    2015-07-10

    Ti-based silicide quantum dot superlattices (QDSLs) are grown by reduced-pressure chemical vapor deposition. They are made of titanium-based silicide nanodots scattered in an n-doped SiGe matrix. This is the first time that such nanostructured materials have been grown in both monocrystalline and polycrystalline QDSLs. We studied their crystallographic structures and chemical properties, as well as the size and the density of the quantum dots. The thermoelectric properties of the QDSLs are measured and compared to equivalent SiGe thin films to evaluate the influence of the nanodots. Our studies revealed an increase in their thermoelectric properties-specifically, up to a trifold increase in the power factor, with a decrease in the thermal conductivity-making them very good candidates for further thermoelectric applications in cooling or energy-harvesting fields. PMID:26086207

  18. Quantum Dots — Characterization, Preparation and Usage in Biological Systems

    PubMed Central

    Drbohlavova, Jana; Adam, Vojtech; Kizek, Rene; Hubalek, Jaromir

    2009-01-01

    The use of fluorescent nanoparticles as probes for bioanalytical applications is a highly promising technique because fluorescence-based techniques are very sensitive. Quantum dots (QDs) seem to show the greatest promise as labels for tagging and imaging in biological systems owing to their impressive photostability, which allow long-term observations of biomolecules. The usage of QDs in practical applications has started only recently, therefore, the research on QDs is extremely important in order to provide safe and effective biosensing materials for medicine. This review reports on the recent methods for the preparation of quantum dots, their physical and chemical properties, surface modification as well as on some interesting examples of their experimental use. PMID:19333427

  19. Interfacial Engineering for Quantum-Dot-Sensitized Solar Cells.

    PubMed

    Shen, Chao; Fichou, Denis; Wang, Qing

    2016-04-20

    Quantum-dot-sensitized solar cells (QDSCs) are promising solar-energy-conversion devices, as low-cost alternatives to the prevailing photovoltaic technologies. Compared with molecular dyes, nanocrystalline quantum dot (QD) light absorbers exhibit higher molar extinction coefficients and a tunable photoresponse. However, the power-conversion efficiencies (PCEs) of QDSCs are generally below 9.5 %, far behind their molecular sensitizer counterparts (up to 13 %). These low PCEs have been attributed to a large free-energy loss during sensitizer regeneration, energy loss during the charge-carrier transport and transfer processes, and inefficient charge separation at the QD/electrolyte interfaces, and various interfacial engineering strategies for enhancing the PCE and cell stability have been reported. Herein, we review recent progress in the interfacial engineering of QDSCs and discuss future prospects for the development of highly efficient and stable QDSCs. PMID:26879244

  20. Real-Time Nanoscopy by Using Blinking Enhanced Quantum Dots

    PubMed Central

    Watanabe, Tomonobu M.; Fukui, Shingo; Jin, Takashi; Fujii, Fumihiko; Yanagida, Toshio

    2010-01-01

    Superresolution optical microscopy (nanoscopy) is of current interest in many biological fields. Superresolution optical fluctuation imaging, which utilizes higher-order cumulant of fluorescence temporal fluctuations, is an excellent method for nanoscopy, as it requires neither complicated optics nor illuminations. However, it does need an impractical number of images for real-time observation. Here, we achieved real-time nanoscopy by modifying superresolution optical fluctuation imaging and enhancing the fluctuation of quantum dots. Our developed quantum dots have higher blinking than commercially available ones. The fluctuation of the blinking improved the resolution when using a variance calculation for each pixel instead of a cumulant calculation. This enabled us to obtain microscopic images with 90-nm and 80-ms spatial-temporal resolution by using a conventional fluorescence microscope without any optics or devices. PMID:20923631