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Sample records for quantum dots studied

  1. 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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    SciTech Connect

    Michael, Stephan; Chow, Weng; Schneider, Hans

    2016-05-01

    In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantum-dot material parameters, here, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  5. Optical Studies of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

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

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

  6. Single molecule study of silicon quantum dots

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  7. Luminescence studies of individual quantum dot photocatalysts.

    PubMed

    Amirav, Lilac; Alivisatos, A Paul

    2013-09-04

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

  8. Studies of electron spin in GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Craft, Daniel; Colton, John; Park, Tyler; White, Phil

    2013-03-01

    We have studied electron spins in GaAs quantum dots with a pump-probe technique that normally yields the T1 spin lifetime, the time required for initially polarized electrons to relax and randomize. Using a circularly polarized laser tuned to the wavelength response of the quantum dot we can ``pump'' the spins into alignment. After aligning the spins we can detect them using a second, linearly polarized ``probe'' laser. By changing the delay between the two lasers we can trace out the spin response over time. In contrast with other samples (bulk GaAs and a GaAs quantum well), where the spin response decayed exponentially with time, initial data on the quantum dots has shown an unexpected, oscillating behavior which dies out on the order of 700 ns, independent of both temperature and magnetic field.

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

    DOE PAGES

    Michael, Stephan; Chow, Weng; Schneider, Hans

    2016-05-01

    In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantum-dot material parameters, here, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.« less

  10. Electroluminescence Studies on Longwavelength Indium Arsenide Quantum Dot Microcavities Grown on Gallium Arsenide

    DTIC Science & Technology

    2011-12-01

    ELECTROLUMINESCENCE STUDIES ON LONG WAVELENGTH INDIUM ARSENIDE QUANTUM DOT MICROCAVITIES GROWN ON GALLIUM ARSENIDE THESIS John C...11-46 ELECTROLUMINESCENCE STUDIES ON LONGWAVELENGTH INDIUM ARSENIDE QUANTUM DOT MICROCAVITIES GROWN ON GALLIUM ARSENIDE THESIS...58 1 ELECTROLUMINESCENCE STUDIES ON LONGWAVELENGTH INDIUM ARSENIDE QUANTUM DOT MICROCAVITIES GROWN ON GALLIUM ARSENIDE I

  11. Quantum dots for biophotonics.

    PubMed

    Yong, Ken-Tye

    2012-01-01

    This theme issue provides an excellent collection of reviews and original research articles on the study of various bioconjugated quantum dot formulations for diagnostics and therapy applications using biophotonic imaging and sensing approaches.

  12. 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.

  13. Numerical renormalization group study of a dissipative quantum dot

    NASA Astrophysics Data System (ADS)

    Glossop, M. T.; Ingersent, K.

    2007-03-01

    We study the quantum phase transition (QPT) induced by dissipation in a quantum dot device at the degeneracy point. We employ a Bose-Fermi numerical renormalization group approach [1] to study the simplest case of a spinless resonant-level model that couples the charge density on the dot to a dissipative bosonic bath with density of states B(φ)ŝ. In anticipation of future experiments [2] and to assess further the validity of theoretical techniques in this rapidly developing area, we take the conduction-electron leads to have a pseudogap density of states: ρ(φ) |φ|^r, as considered in a very recent perturbative renormalization group study [3]. We establish the conditions on r and s such that a QPT arises with increasing dissipation strength --- from a delocalized phase, where resonant tunneling leads to large charge fluctuations on the dot, to a localized phase where such fluctuations are frozen. We present results for the single-particle spectrum and the response of the system to a local electric field, extracting critical exponents that depend in general on r and s and obey hyperscaling relations. We make full comparison with results of [3] where appropriate. Supported by NSF Grant DMR-0312939. [1] M. T. Glossop and K. Ingersent, PRL 95, 067202 (2005); PRB (2006). [2] L. G. G. V. Dias da Silva, N. P. Sandler, K. Ingersent, and S. E. Ulloa, PRL 97, 096603 (2006). [3] C.-H. Chung, M. Kir'can, L. Fritz, and M. Vojta (2006).

  14. Thermoelectric study of dissipative quantum-dot heat engines

    NASA Astrophysics Data System (ADS)

    De, Bitan; Muralidharan, Bhaskaran

    2016-10-01

    This paper examines the thermoelectric response of a dissipative quantum-dot heat engine based on the Anderson-Holstein model in two relevant operating limits, (i) when the dot phonon modes are out of equilibrium, and (ii) when the dot phonon modes are strongly coupled to a heat bath. In the first case, a detailed analysis of the physics related to the interplay between the quantum-dot level quantization, the on-site Coulomb interaction, and the electron-phonon coupling on the thermoelectric performance reveals that an n -type heat engine performs better than a p -type heat engine. In the second case, with the aid of the dot temperature estimated by incorporating a thermometer bath, it is shown that the dot temperature deviates from the bath temperature as electron-phonon interaction in the dot becomes stronger. Consequently, it is demonstrated that the dot temperature controls the direction of phonon heat currents, thereby influencing the thermoelectric performance. Finally, the conditions on the maximum efficiency with varying phonon couplings between the dot and all the other macroscopic bodies are analyzed in order to reveal the nature of the optimum junction.

  15. Study of stochastic resonance in a quantum dot network

    NASA Astrophysics Data System (ADS)

    Fujino, Hiroki; Oya, Takahide

    2012-10-01

    This paper reports a study of stochastic resonance in a huge quantum dot network for single-electron (SE) circuits. Such circuits, which are controlled by the Coulomb blockade, are one type of next-generation information-processing device. However, they are very sensitive to noises such as thermal noise and device mismatch noise. Thus, we introduce the stochastic resonance phenomenon into the circuit to improve its noise tolerance. Stochastic resonance is a phenomenon that was discovered in the brains of living things in noisy environments and was modeled for neural networks. When the phenomenon occurs, its harnessing of noise energy makes weak signals become clear. In current research, SE devices that operate with stochastic resonance have been reported. However, signals were attenuated in particularly noisy environments. In contrast, it was reported that a huge molecular network amplified weak signals by harnessing noise energy. The report said the current-voltage characteristics of the molecular network described the Coulomb blockade under a noisy environment. Thus, a huge quantum dot network that is partly similar to a molecular network is expected to amplify the weak signal harnessing noise, when the current-voltage characteristics of the network show the Coulomb blockade. To confirm this, in this study we use the Monte Carlo method to simulate the noisy-environment operation of a quantum dot network comprising quantum dots and tunneling junctions. We observe the current-voltage characteristics of the network, when changing the network size (5×5, 10×10, and 100×100) and the noise intensity (0 K, 2 K, 5 K, and 10 K for operating temperature, and 0%, 5%, 10%, and 30% for device mismatch). As a result, we are able to observe the Coulomb blockade under the appropriate noise strength, which in this study is 5 K or less with thermal noise, and 30% with device mismatch. From the results, we conclude the network operates correctly under appropriate noise strength

  16. Quantum control study of ultrafast optical responses in semiconductor quantum dot devices.

    PubMed

    Huang, Jung Y; Lin, Chien Y; Liu, Wei-Sheng; Chyi, Jen-Inn

    2014-12-15

    Two quantum control spectroscopic techniques were applied to study InAs quantum dot (QD) devices, which contain different strain-reducing layers. By adaptively control light matter interaction, a delayed resonant response from the InAs QDs was found to be encoded into the optimal phase profile of ultrafast optical pulse used. We verified the delayed resonant response to originate from excitons coupled to acoustic phonons of InAs QDs with two-dimensional coherent spectroscopy. Our study yields valuable dynamical information that can deepen our understanding of the coherent coupling process of exciton in the quantum-confined systems.

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

    PubMed

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

    2011-03-22

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

  18. Cellular uptake and photosensitizing properties of quantum dot-chlorin e6 complex: in vitro study.

    PubMed

    Steponkiene, Simona; Valanciunaite, Jurga; Skripka, Artiom; Rotomskis, Ricardas

    2014-04-01

    Recently it has been suggested that quantum dots could be used in the photodynamic therapy of cancer as resonant energy donors for conventional porphyrin type photosensitizers. Here we summarize our results obtained by studying a non-covalent complex formed between quantum dots and a second generation photosensitizer, chlorin e6, in aqueous medium and in live pancreatic MiaPaCa2 cancer cells. Spectral changes in the absorption and photoluminescence of quantum dots and chlorin e6, as well as changes in the photoluminescence lifetime of quantum dots, revealed the formation of quantum dot-chlorin e6 complex. Fluorescence confocal microscopy with spectral imaging unit showed uptake of quantum dot-chlorin e6 complex in live cancer cells: the complex localized in plasma membrane and endocytic vesicles. Fluorescence lifetime imaging revealed Forster resonance energy transfer from quantum dots to chlorin e6 within live cells. Finally, a light-induced damage to cancer cells by the quantum dot-chlorin e6 complex was achieved.

  19. The study of the formation of monolayers of quantum dots at different temperatures

    NASA Astrophysics Data System (ADS)

    Gorbachev, Ilya A.; Goryacheva, Irina Y.; Brezesinski, Gerald; Gluhovskoy, Evgeny G.

    2016-04-01

    The process of formation of Langmuir monolayers of quantum dots at the different subphase temperatures was studied by means of compression isotherm, Brewster angle microscopy and transmission electron microscopy. The increasing of the maximum surface pressure from 32 to 44 mN/m takes place with decreasing the temperature from 34 to 11°C. This is due to a decrease in the rate of dissolution of surfactant molecules in water. The increasing of a filling degree of monolayer by the quantum dots and increasing of it uniformity in thickness takes place in this temperature range. The area of bilayer and multilayer film of quantum dots decreasing and the area of quantum dots monolayer is increasing. This change explained by the difference in the phase condition of oleic acid molecules, which stabilized quantum dots.

  20. Quantum Monte Carlo Studies of Interaction-Induced Localization in Quantum Dots and Wires

    NASA Astrophysics Data System (ADS)

    Devrim Güçlü, A.

    2009-03-01

    We investigate interaction-induced localization of electrons in both quantum dots and inhomogeneous quantum wires using variational and diffusion quantum Monte Carlo methods. Quantum dots and wires are highly tunable systems that enable the study of the physics of strongly correlated electrons. With decreasing electronic density, interactions become stronger and electrons are expected to localize at their classical positions, as in Wigner crystallization in an infinite 2D system. (1) Dots: We show that the addition energy shows a clear progression from features associated with shell structure to those caused by commensurability of a Wigner crystal. This cross-over is, then, a signature of localization; it occurs near rs˜20. For higher values of rs, the configuration symmetry of the quantum dot becomes fully consistent with the classical ground state. (2) Wires: We study an inhomogeneous quasi-one-dimensional system -- a wire with two regions, one at low density and the other high. We find that strong localization occurs in the low density quantum point contact region as the gate potential is increased. The nature of the transition from high to low density depends on the density gradient -- if it is steep, a barrier develops between the two regions, causing Coulomb blockade effects. We find no evidence for ferromagnetic spin polarization for the range of parameters studied. The picture emerging here is in good agreement with the experimental measurements of tunneling between two wires. Collaborators: C. J. Umrigar (Cornell), Hong Jiang (Fritz Haber Institut), Amit Ghosal (IISER Calcutta), and H. U. Baranger (Duke).

  1. 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

  2. Colloidal Double Quantum Dots.

    PubMed

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

    2016-05-17

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

  3. 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.

  4. Computational studies of quantum dot sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Kolesov, Grigory

    This thesis presents a computational study of quantum dot (QD) sensitized solar cells. First part deals with the non-equilibrium many-body theory or non-equilibrium Green's function (NEGF) theory. In this approach I study electron dynamics in the quantum-dot sensitized solar cell subjected to time-dependent fields. NEGF theory, because it does not impose any conditions on a perturbation, is the fundamental one to describe ultrafast processes in small, strongly correlated systems and/or in strong fields. In this research I do not only perform analytical derivation, but also design and implement spectral numerical solution for the resulting complex system of partial integrodifferential equations. This numerical solution yielded an order of magnitude speedup over the methods used previously in the field. The forth chapter of this thesis deals with calculation of optical properties and the ground state configuration of Zn2SnO4 (ZTO). ZTO is used by experimentalists in UW to grow nanorods which are then sensitized by QDs. ZTO is a challenging material for computational analysis because of its inverse spinel structure; thus it has an immense number of configurations matching the X-ray diffraction experiments. I've applied a cluster expansion method and have found the ground state configuration and phase diagram for ZTO. Calculations of optical properties of ground state bulk ZTO were done with a recently developed DFT functional. The optical band gap obtained in these calculations matched the experimental value. The last chapter describes development of the general simulator for interdigitated array electrodes. The application of this simulation together with the experiments may lead to understanding of reaction parameters and mechanisms important for development of electrochemical solar cells.

  5. 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.

  6. 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.

  7. [Study of PbSe quantum dots for use in luminescence solar concentrators].

    PubMed

    Hu, Wen-Jia; Zhang, Yu; Jian, Xu; Wang, Jing-Kang

    2013-02-01

    With the study of the characteristic of luminescence solar concentrator, a simple and practicable Monte Carlo simulation system was invented based on ray tracing method. PbSe quantum dots were successfully introduced into this system, and the optical parameter and quantum dots concentration were simulated and optimized. The cost per unit of the solar cell base on luminescence solar concentrator was investigated, and it was found that the cost of traditional solar cells can be reduced by 49.2%.

  8. A study of energy absorption rate in a quantum dot and metallic nanosphere hybrid system

    NASA Astrophysics Data System (ADS)

    Schindel, Daniel; Singh, Mahi R.

    2015-09-01

    We have studied energy absorption rate in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. We applied a control field to induce dipole moments in the quantum dot and the metal nanosphere, and monitored the energy absorption using a probe field. These external fields induce dipole moments in the metal nanosphere and the quantum dot, and these two structures interact with one another via the dipole-dipole interaction. The density matrix method was used to evaluate the absorption, indicating that it can be shifted by moving the metal nanosphere close to the quantum dot. Also, absorption efficiency can either be quenched or enhanced by the addition of a metal nanosphere. This hybrid system can be used to create ultrafast switching and sensing nanodevices.

  9. Sized controlled synthesis, purification, and cell studies with silicon quantum dots

    NASA Astrophysics Data System (ADS)

    Shiohara, Amane; Prabakar, Sujay; Faramus, Angelique; Hsu, Chia-Yen; Lai, Ping-Shan; Northcote, Peter T.; Tilley, Richard D.

    2011-08-01

    This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using 1H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales.This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using 1H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales. Electronic supplementary information (ESI) available. See DOI: 10.1039/c1nr10458f

  10. 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.

  11. Electrochemical Study and Applications of Selective Electrodeposition of Silver on Quantum Dots.

    PubMed

    Martín-Yerga, Daniel; Rama, Estefanía Costa; Costa-García, Agustín

    2016-04-05

    In this work, selective electrodeposition of silver on quantum dots is described. The particular characteristics of the nanostructured silver thus obtained are studied by electrochemical and microscopic techniques. On one hand, quantum dots were found to catalyze the silver electrodeposition, and on the other hand, a strong adsorption between electrodeposited silver and quantum dots was observed, indicated by two silver stripping processes. Nucleation of silver nanoparticles followed different mechanisms depending on the surface (carbon or quantum dots). Voltammetric and confocal microscopy studies showed the great influence of electrodeposition time on surface coating, and high-resolution transmission electron microscopy (HRTEM) imaging confirmed the initial formation of Janus-like Ag@QD nanoparticles in this process. By use of moderate electrodeposition conditions such as 50 μM silver, -0.1 V, and 60 s, the silver was deposited only on quantum dots, allowing the generation of localized nanostructured electrode surfaces. This methodology can also be employed for sensing applications, showing a promising ultrasensitive electrochemical method for quantum dot detection.

  12. Quantum dot resonant tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Reed, Mark A.; Randall, John N.; Luscombe, James H.; Frensley, William R.; Aggarwal, Raj J.; Matyi, Richard J.; Moore, Tom M.; Wetsel, Anna E.

    The electronic transport through 3-dimensionally confined semiconductor quantum wells (quantum dots) is investigated and analyzed. The spectra corresponds to resonant tunneling from laterally-confined emitter contact subbands through the discrete 3-dimensionally confined quantum dot states. Momentum nonconservation is observed in these structures. Results on coupled quantum dot states (molccules) will be presented.

  13. Functional renormalization group study of parallel double quantum dots: Effects of asymmetric dot-lead couplings

    NASA Astrophysics Data System (ADS)

    Protsenko, V. S.; Katanin, A. A.

    2017-06-01

    We explore the effects of asymmetry of hopping parameters between double parallel quantum dots and the leads on the conductance and a possibility of local magnetic moment formation in this system using functional renormalization group approach with the counterterm. We demonstrate a possibility of a quantum phase transition to a local moment regime [so-called singular Fermi liquid (SFL) state] for various types of hopping asymmetries and discuss respective gate voltage dependencies of the conductance. We show that, depending on the type of the asymmetry, the system can demonstrate either a first-order quantum phase transition to an SFL state, accompanied by a discontinuous change of the conductance, similarly to the symmetric case, or the second-order quantum phase transition, in which the conductance is continuous and exhibits Fano-type asymmetric resonance near the transition point. A semianalytical explanation of these different types of conductance behavior is presented.

  14. Photostable epoxy polymerized carbon quantum dots luminescent thin films and the performance study

    NASA Astrophysics Data System (ADS)

    Zhang, Chang; Du, Lei; Liu, Cui; Li, Yunchuan; Yang, ZhenZhen; Cao, Yuan-Cheng

    High photostable epoxy polymerized carbon quantum dots (C-dots) luminescent thin films were prepared and their performances were compared with the CdTe quantum dots (QDs). First, water soluble C-dots (λem = 543.60 nm) were synthesized. Poly (ethylene glycol) diglycidyl ether (PEG) and diaminooctane were used as the polymer matrix to make the epoxy resin films. FT-IR spectra showed that there were vibration at 3448 cm-1 and 1644 cm-1 which contributed to -OH and -NH respectively. SEM observations showed that the polymerizations of the films were uniform and there were no structure defects. Mechanical tests showed the tensile modulus of C-dots composite films were 4.6, 4.9, 6.4 and 7.8 MPa respectively with corresponding 0%, 1%, 2% and 5% mass fraction of C-dots, while the tensile modulus of CdTe QDs films were 4.6 MPa under the same mass fraction of CdTe QDs. Compared with semiconductor QDs, the decay of quantum yield were 5% and 10% for the C-dots and CdTe QDs, respectively. The pictures in the continuous irradiation of 48 h showed that the C-dots film was more photostable. This study provides much helpful and profound towards the fluorescent enhancement films in the field of flexible displays.

  15. New quantum dot sensors

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  16. II-VI semiconductor quantum dot quantum wells: a tight-binding study

    NASA Astrophysics Data System (ADS)

    Pérez-Conde, J.; Bhattacharjee, A. K.

    2006-05-01

    We have studied the electronic structure, exciton states and optical spectra of spherical semiconductor quantum dot quantum wells (QDQW's) by means of a symmetry-adapted tight-binding (TB) method. We have investigated two classes of QDQW's: CdS/HgS/CdS, based on a CdS core which acts as a barrier, with a thin HgS well layer intercalated between the core and a clad layer of CdS. The second class of QDQW's is based on ZnS cores covered with CdS layers which act in this case as a well. The calculated values of the absorption onset show a good agreement with the experimental data. Large photoluminescence Stokes shifts are also predicted.

  17. Plasmonic fluorescent quantum dots.

    PubMed

    Jin, Yongdong; Gao, Xiaohu

    2009-09-01

    Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence. So far, the combination of quantum dot fluorescence with plasmonically active gold has only been demonstrated on flat surfaces. Here, we combine fluorescent and plasmonic activities in a single nanoparticle by controlling the spacing between a quantum dot core and an ultrathin gold shell with nanometre precision through layer-by-layer assembly. Our wet-chemistry approach provides a general route for the deposition of ultrathin gold layers onto virtually any discrete nanostructure or continuous surface, and should prove useful for multimodal bioimaging, interfacing with biological systems, reducing nanotoxicity, modulating electromagnetic fields and contacting nanostructures.

  18. Toward the in vivo study of captopril-conjugated quantum dots

    NASA Astrophysics Data System (ADS)

    Manabe, Noriyoshi; Hoshino, Akiyoshi; Liang, Yi-qiang; Goto, Tomomasa; Kato, Norihiro; Yamamoto, Kenji

    2005-04-01

    Photo-luminescent semiconductor quantum dots are nanometer-size probes that have the potential to be applied to the fields of the bio-imaging and the study of the cell mobility inside the body. At the same time, on the other hand, quantum dots are expected to carry some kind of molecules to the local organ inside of the animal body, which leads to the expectation that they can be used as a medicine-carrier. For this purpose, we conjugate (2S)-1-[(2s)-2-Methyl-3-sulfanylpropionyl]pyrrolidine-2-carboxylic acid (cap) with the quantum dot. Cap has the effect as an anti-hypertension drug, which inhibits angiotensin 1 converting enzyme. We conjugated the quantum dot with cap by the exchange reaction avoiding the regions which holds medicinal effect. Quantum dot conjugated with cap (QD-cap) were 3-times brighter than thioglycerol-coated quantum dots (QD-OH). The particle size of cap was 1.1nm and that of QD-cap was 12nm. QD-cap was permeated into the HeLa cells, while QD-MUA were taken into the HeLa cells by endocytosis. In addition, no apoptosis was detected against the cells that permeated QD-cap, because there was no damage to DNA. These results indicated that QD-conjugated medicines (QD-medicine) could be safe in the experiment on the level of the cell. More over, when QD-cap was intravenously injected into Stroke-prone Spontaneously Hypertensive Rats (SHRSP), they reduced blood pressure at systole. Therefore, the anti-hypertension effect of cap remained after conjugated with the quantum dot. These results suggested that QD-medicine were effective on the animal level.

  19. 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.

  20. Studies on ternary zinc blend based semiconducting quantum dots for hybrid solar cell applications

    NASA Astrophysics Data System (ADS)

    Sharma, Harit Kumar; Pandey, S. K.; Agrawal, S. L.

    2017-05-01

    A systematic study is presented in the present work on the fabrication of hybrid solar cell using doped zinc blend based semiconductor quantum dots (QDs) prepared by a simple wet chemical precipitation method. Formation of quantum dot has been ascertained by X-ray Diffraction (XRD), UV-visible Spectroscopy and Impedance Spectroscopy measurements. XRD studies established the zinc-blende phase in quantum dot regime. UV-visible studies reveal decrement in optical bandgap of the QDs with co-doping of Cd ion in ZnS lattice. Mott-Schottky analysis revealed n-type conductivity with increasein band bending from binary to ternary configuration respectively. Bulk heterojunction hybrid solar cells fabricated in 1cm X 1cm size in conjunction with p type Polypyrroleunder AM 1.5 illumination resulted in highest conversion efficiency of 1.6 %.

  1. Quantum optics in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Garrido, Mauricio

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

  2. Quantum dots: a new tool for studying quantum phase transitions (QPT)

    NASA Astrophysics Data System (ADS)

    Roch, N.; Florens, S.; Bouchiat, V.; Wernsdorfer, W.; Balestro, F.

    2009-03-01

    QPT were studied in many different systems: spin chains, strongly correlated materials, high Tc superconductors, etc. but all the properties (magnetism, superconductivity ...) of these materials can be difficult to control. On the other hand, thanks to microelectronic technologies, it is now possible to obtain taylor-made quantum dots in which all the interactions can be tuned finely. It was then proposed by several theoretic papers [1] to use them as model systems for probing QPT. In this experimental work, we observed a screening/non screening QPT transition in a single-molecule transistor. We will present a full study as a function of magnetic field, bias voltage and temperature [2].[3pt] [1] M.Vojta, Philosophical Magazine,86:13,1807 - 1846 (2006)[0pt] [2] N.Roch et al. , Nature 453, 633-637 (2008)

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

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

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

  5. Optical and impedance studies of pure and Ba-doped ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Firdous, Arfat; Baba, M. Aslam; Singh, D.; Bhat, Abdul Hamid

    2015-02-01

    Chemical precipitation method using a high-boiling solvent is used to synthesize ZnS and Ba-doped ZnS quantum dots. The presence of organic ligands in the prepared nanostructures is verified using Fourier transform infra-red spectroscopic studies. The samples have been analysed using X-ray diffraction analysis confirming nanocrystallinity of the as-prepared quantum dots (QD). The mean crystal size obtained by full width half maxima analysis is 3.2 nm for ZnS and 3.9, 4.2 nm for ZnS:Ba (2, 4 mM). TEM micrographs also reveal nanosized particles of ZnS and Ba-doped ZnS. An optical absorption study conducted in UV-Vis range 150-600 nm reveals the transparency of these quantum dots in entire visible range but not in ultraviolet range. The results based on optical analysis yield band gap values as 4.88 eV for ZnS and 4.69, 4.43 eV for ZnS:Ba (2, 4 mM) quantum dots. Impedance analysis of the samples was carried out to reveal the variation of impedance with frequency at room temperature. These results show the capacitive admittance associated with the quantum dots and hence nanostructure ZnS and Ba-doped ZnS can have potential applications in electronics as nano-tuned devices in which resonant frequency can be adjusted by controlling the size and shape of the quantum dots.

  6. Kondo effect in coupled quantum dots: a Non-crossing approximation study

    NASA Astrophysics Data System (ADS)

    Aguado, Ramon; Langreth, David

    2003-03-01

    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 inter-impurity hopping. The Hamiltonian, formulated in slave-boson language, is solved by means of a generalization of the non-crossing 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 inter-dot 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 non-monotonic, with a maximum at a temperature T characterizing quantum coherence between both Kondo states.

  7. Band-structure-corrected local density approximation study of semiconductor quantum dots and wires

    NASA Astrophysics Data System (ADS)

    Li, Jingbo; Wang, Lin-Wang

    2005-09-01

    This paper presents results of ab initio accuracy thousand atom calculations of colloidal quantum dots and wires using the charge patching method. We have used density functional theory under local density approximation (LDA), and we have corrected the LDA bulk band structures by modifying the nonlocal pseudopotentials, so that their effective masses agree with experimental values. We have systematically studied the electronic states of group III-V (GaAs, InAs, InP, GaN, AlN, and InN) and group II-VI (CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, and ZnO) systems. We have also calculated the electron-hole Coulomb interactions in these systems. We report the exciton energies as functions of the quantum dot sizes and quantum wire diameters for all the above materials. We found generally good agreements between our calculated results and experimental measurements. For CdSe and InP, the currently calculated results agree well with the previously calculated results using semiempirical pseudopotentials. The ratios of band-gap-increases between quantum wires and dots are material-dependent, but a majority of them are close to 0.586, as predicted by the simple effective-mass model. Finally, the size dependence of 1Se-1Pe transition energies of CdSe quantum dots agrees well with the experiment. Our results can be used as benchmarks for future experiments and calculations.

  8. 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

  9. Research on Self-Assembling Quantum Dots.

    DTIC Science & Technology

    1995-10-30

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

  10. Quantum dots as mineral- and matrix-specific strain gages for bone biomechanical studies

    NASA Astrophysics Data System (ADS)

    Zhu, Peizhi; Xu, Jiadi; Morris, Michael; Ramamoorthy, Ayyalusamy; Sahar, Nadder; Kohn, David

    2009-02-01

    We report the use of quantum dots (Qdots) as strain gages in the study of bone biomechanics using solid state nuclear magnetic resonance (NMR) spectroscopy. We have developed solid state NMR sample cells for investigation of deformations of bone tissue components at loads up to several Mega Pascal. The size constraints of the NMR instrumentation limit the bone specimen diameter and length to be no greater than 2-3 mm and 30 mm respectively. Further, magic angle spinning (MAS) solid state NMR experiments require the use of non-metallic apparatus that can be rotated at kilohertz rates. These experimental constraints preclude the use of standard biomechanical measurement systems. In this paper we explore the use of quantum dot center of gravity measurement as a strain gage technology consistent with the constraints of solid state NMR. We use Qdots that bind calcium (625 nm emission) and collagen (705 nm emission) for measurement of strain in these components. Compressive loads are applied to a specimen in a cell through a fine pitch screw turned with a mini-torque wrench. Displacement is measured as changes in the positions of arrays of quantum dots on the surface of a specimen. Arrays are created by spotting the specimen with dilute suspensions of Qdots. Mineral labeling is achieved with 705 nm carboxylated dots and matrix labeling with 565 nm quantum dots conjugated to collagen I antibodies. After each load increment the new positions of the quantum dots are measured by fluorescence microscopy. Changes in Qdot center of gravity as a function of applied load can be measured with submicron accuracy.

  11. Quantum Dot Sensitized Photoelectrodes

    PubMed Central

    Macdonald, Thomas J.; Nann, Thomas

    2011-01-01

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

  12. Quantum DOT IR Photodetectors

    DTIC Science & Technology

    2012-07-01

    4.1.3  ROIC Control and Readout Electronics ................................................................ 16  4.2  Device measurements...the voltage of the detector modifies its spectral response. In this effort a DWELL Quantum Dot device was fabricated and tested. The results...agility. Because of delays in the fabrication of the ROIC device by MOSIS, those results will not available for the final report until approximately

  13. 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.

  14. Comparison studies of infrared photodetectors with a quantum-dot and a quantum-wire base

    NASA Astrophysics Data System (ADS)

    El Tokhy, M. S.; Mahmoud, I. I.; Konber, H. A.

    2011-12-01

    This paper mainly presents a theoretical analysis for the characteristics of quantum dot infrared photodetectors (QDIPs) and quantum wire infrared photodetectors (QRIPs). The paper introduces a unique mathematical model of solving Poisson's equations with the usage of Lambert W functions for infrared detectors' structures based on quantum effects. Even though QRIPs and QDIPs have been the subject of extensive researches and development during the past decade, it is still essential to implement theoretical models allowing to estimate the ultimate performance of those detectors such as photocurrent and its figure-of-merit detectivity vs. various parameter conditions such as applied voltage, number of quantum wire layers, quantum dot layers, lateral characteristic size, doping density, operation temperature, and structural parameters of the quantum dots (QDs), and quantum wires (QRs). A comparison is made between the computed results of the implemented models and fine agreements are observed. It is concluded from the obtained results that the total detectivity of QDIPs can be significantly lower than that in the QRIPs and main features of the QRIPs such as large gap between the induced photocurrent and dark current of QRIP which allows for overcoming the problems in the QDIPs. This confirms what is evaluated before in the literature. It is evident that by increasing the QD/QR absorption volume in QDIPs/QRIPs as well as by separating the dark current and photocurrents, the specific detectivity can be improved and consequently the devices can operate at higher temperatures. It is an interesting result and it may be benefit to the development of QDIP and QRIP for infrared sensing applications.

  15. Plasmonic fluorescent quantum dots

    PubMed Central

    Jin, Yongdong

    2009-01-01

    Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem1,2. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence3,4. So far, the combination of quantum dot fluorescence with plasmonically active gold has only been demonstrated on flat surfaces5. Here, we combine fluorescent and plasmonic activities in a single nanoparticle by controlling the spacing between a quantum dot core and an ultrathin gold shell with nanometre precision through layer-by-layer assembly. Our wet-chemistry approach provides a general route for the deposition of ultrathin gold layers onto virtually any discrete nanostructure or continuous surface, and should prove useful for multimodal bioimaging6, interfacing with biological systems7, reducing nanotoxicity8, modulating electromagnetic fields5 and contacting nanostructures9,10. PMID:19734929

  16. (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.

  17. Optically active quantum-dot molecules.

    PubMed

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

    2017-02-20

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

  18. Quantum-dot supercrystals for future nanophotonics

    PubMed Central

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

    2013-01-01

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

  19. Quantum transport in ballistic quantum dots

    NASA Astrophysics Data System (ADS)

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

    1998-10-01

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

  20. In vivo study of immunogenicity and kinetic characteristics of a quantum dot-labelled baculovirus.

    PubMed

    Wang, Meng; Zheng, Zhenhua; Meng, Jin; Wang, Han; He, Man; Zhang, Fuxian; Liu, Yan; Hu, Bin; He, Zike; Hu, Qinxue; Wang, Hanzhong

    2015-09-01

    Nanomaterials conjugated with biomacromolecules, including viruses, have great potential for in vivo applications. Therefore, it is important to evaluate the safety of nanoparticle-conjugated macromolecule biomaterials (Nano-mbio). Although a number of studies have assessed the risks of nanoparticles and macromolecule biomaterials in living bodies, only a few of them investigated Nano-mbios. Here we evaluated the in vivo safety profile of a quantum dot-conjugated baculovirus (Bq), a promising new Nano-mbio, in mice. Each animal was injected twice intraperitoneally with 50 μg virus protein labelled with around 3*10(-5)nmol conjugated qds. Control animals were injected with PBS, quantum dots, baculovirus, or a mixture of quantum dots and baculovirus. Blood, tissues and body weight were analysed at a series of time points following both the first and the second injections. It turned out that the appearance and behaviour of the mice injected with Bq were similar to those injected with baculovirus alone. However, combination of baculovirus and quantum dot (conjugated or simply mixed) significantly induced stronger adaptive immune responses, and lead to a faster accumulation and longer existence of Cd in the kidneys. Thus, despite the fact that both quantum dot and baculovirus have been claimed to be safe in vivo, applications of Bq in vivo should be cautious. To our knowledge, this is the first study examining the interaction between a nanoparticle-conjugated virus and a living body from a safety perspective, providing a basis for in vivo application of other Nano-mbios. Copyright © 2015 Elsevier Ltd. All rights reserved.

  1. Optically active quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  2. 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. 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.

  4. Quantum Dot Spins and Photons

    NASA Astrophysics Data System (ADS)

    Atature, Mete

    2012-02-01

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

  5. Use of quantum dot-conjugated antibodies to study intracellular cancer biomarkers in living and fixed cells

    NASA Astrophysics Data System (ADS)

    Ling, Jian

    2008-02-01

    Quantum dots have unique properties for long-term immunofluorescence imaging of molecular activities inside living cells. The key is how to deliver the quantum dot-conjugated antibodies into cells and further allow the antibodies freely move inside cells to bind target molecules. This study investigated the feasibility of using Pep-1, a cell penetration protein, to facilitate the internalization of quantum dot-conjugated antibodies for the labeling of two intracellular cervical cancer biomarkers: p16 and Mcm5. Quantum dots were directly conjugated with the antibodies to p16 and Mcm5 and, they were able to stain fixed cells and to differentiate biomarker positive and negative cells. The non-covalent binding between the conjugates and Pep-1 peptides allows the quick internalization of the quantum dot-conjugated antibodies into living cells. The internalized conjugates were concentrated in the perinuclear regions of the biomarker-positive HeLa cells. In the biomarker negative Um-Uc-3 cells, however, the conjugates concentrated in juxtaneclear region. Cells bearing with quantum dots still go through the mitosis process. Although the study indicates many questions need to be answered and many problems need to be solved, the use of cell penetration peptide is a promising method for the intracellular labeling of living cell molecules using quantum dots.

  6. Statistical study of stacked/coupled site-controlled pyramidal quantum dots and their excitonic properties

    NASA Astrophysics Data System (ADS)

    Moroni, S. T.; Chung, T. H.; Juska, G.; Gocalinska, A.; Pelucchi, E.

    2017-08-01

    We report on stacked multiple quantum dots (QDs) formed inside inverted pyramidal recesses, which allow for the precise positioning of the QDs themselves. Specifically, we fabricated double QDs with varying inter-dot distances and ensembles with more than two nominally highly symmetric QDs. For each, the effect of the interaction between QDs is studied by characterizing a large number of QDs through photoluminescence spectroscopy. A clear red-shift of the emission energy is observed together with a change in the orientation of its polarization, suggesting an increasing interaction between the QDs. Finally, we show how stacked QDs can help influencing the charging of the excitonic complexes.

  7. 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

  8. Scanning Quantum Dot Microscopy

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  9. The surface termination effect on the quantum confinement and electron affinities of 3C-SiC quantum dots: a first-principles study.

    PubMed

    Zhang, Zhenkui; Dai, Ying; Yu, Lin; Guo, Meng; Huang, Baibiao; Whangbo, Myung-Hwan

    2012-03-07

    In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C-H or Si-H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C-H termination and positive for the Si-H termination. The prediction of negative electron affinities in SiC quantum dots by simple C-H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems.

  10. Toxicological studies of semiconductor quantum dots on immune cells.

    SciTech Connect

    Ricken, James Bryce; Rios, Lynette; Poschet, Jens Fredrich; Bachand, Marlene; Bachand, George David; Greene, Adrienne Celeste; Carroll-Portillo, Amanda

    2008-11-01

    Nanoengineered materials hold a vast promise of enabling revolutionary technologies, but also pose an emerging and potentially serious threat to human and environmental health. While there is increasing knowledge concerning the risks posed by engineered nanomaterials, significant inconsistencies exist within the current data based on the high degree of variability in the materials (e.g., synthesis method, coatings, etc) and biological test systems (e.g., cell lines, whole organism, etc). In this project, we evaluated the uptake and response of two immune cell lines (RAW macrophage and RBL mast cells) to nanocrystal quantum dots (Qdots) with different sizes and surface chemistries, and at different concentrations. The basic experimental design followed a 2 x 2 x 3 factorial model: two Qdot sizes (Qdot 520 and 620), two surface chemistries (amine 'NH{sub 2}' and carboxylic acid 'COOH'), and three concentrations (0, 1 nM, and 1 {micro}M). Based on this design, the following Qdots from Evident Technologies were used for all experiments: Qdot 520-COOH, Qdot 520-NH{sub 2}, Qdot 620-COOH, and Qdot 620-NH{sub 2}. Fluorescence and confocal imaging demonstrated that Qdot 620-COOH and Qdot 620-NH{sub 2} nanoparticles had a greater level of internalization and cell membrane association in RAW and RBL cells, respectively. From these data, a two-way interaction between Qdot size and concentration was observed in relation to the level of cellular uptake in RAW cells, and association with RBL cell membranes. Toxicity of both RBL and RAW cells was also significantly dependent on the interaction of Qdot size and concentration; the 1 {micro}M concentrations of the larger, Qdot 620 nanoparticles induced a greater toxic effect on both cell lines. The RBL data also demonstrate that Qdot exposure can induce significant toxicity independent of cellular uptake. A significant increase in TNF-{alpha} and decrease in IL-10 release was observed in RAW cells, and suggested that Qdot exposure

  11. Plasmonic quantum dot solar concentrator

    NASA Astrophysics Data System (ADS)

    Chandra, S.; Ahmed, H.; Doran, J.; McCormack, S. J.

    2017-02-01

    The quantum dot solar concentrator optical efficiency is undermined by the parameters of re-absorption, scattering, and escape cone losses. These losses can be address through enhancing quantum dot (QDs) absorption and emission. This have been achieved through plasmonic coupling between QDs and gold nanoparticles (Au NPs). The plasmonic composite of various concertation of QDs and Au NPs were studied. The spacing between QDs and Au NPs is controlled through concentration distribution of both QD and Au NPs in the plasmonic composite, and it showed a significant increase in absorption and which is more pronounced for higher spectral overlap of QDs and surface plasmon resonance (SPR) frequency. The optimum plasmonic coupling showed a 17 % increase in the fluorescence emission for QDs in plasmonic composite. The results have shown significant enhancement in absorption, fluorescence emission for the p-QDSC.

  12. Quantitative multiplexed quantum dot immunohistochemistry

    SciTech Connect

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

    2008-09-19

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

  13. Quantum dots with single-atom precision.

    PubMed

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

    2014-07-01

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

  14. Grazing-incidence small-angle X-ray scattering: application to the study of quantum dot lattices.

    PubMed

    Buljan, Maja; Radić, Nikola; Bernstorff, Sigrid; Dražić, Goran; Bogdanović-Radović, Iva; Holý, Václav

    2012-01-01

    The ordering of quantum dots in three-dimensional quantum dot lattices is investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Theoretical models describing GISAXS intensity distributions for three general classes of lattices of quantum dots are proposed. The classes differ in the type of disorder of the positions of the quantum dots. The models enable full structure determination, including lattice type, lattice parameters, the type and degree of disorder in the quantum dot positions and the distributions of the quantum dot sizes. Applications of the developed models are demonstrated using experimentally measured data from several types of quantum dot lattices formed by a self-assembly process.

  15. A mirage study of CdSe colloidal quantum dot films, Urbach tail, and surface states.

    PubMed

    Guyot-Sionnest, Philippe; Lhuillier, Emmanuel; Liu, Heng

    2012-10-21

    Thermal deflection spectroscopy allows to measure very small absorption and uncovers absorption tails extending well below the bulk bandgap energy for CdSe quantum dots films after ligand exchange by sulfide. In this monodispersed system, the redshift, the broadening, and the absorption tails cannot be solely attributed to electronic coupling between the dots. Instead, mixing of hole states from the quantum dot and surface is proposed to dominate the changes of the interband spectra at the absorption edge.

  16. A mirage study of CdSe colloidal quantum dot films, Urbach tail, and surface states

    NASA Astrophysics Data System (ADS)

    Guyot-Sionnest, Philippe; Lhuillier, Emmanuel; Liu, Heng

    2012-10-01

    Thermal deflection spectroscopy allows to measure very small absorption and uncovers absorption tails extending well below the bulk bandgap energy for CdSe quantum dots films after ligand exchange by sulfide. In this monodispersed system, the redshift, the broadening, and the absorption tails cannot be solely attributed to electronic coupling between the dots. Instead, mixing of hole states from the quantum dot and surface is proposed to dominate the changes of the interband spectra at the absorption edge.

  17. 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.

  18. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    PubMed Central

    Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

  19. Ultrafast Optical Studies of Multiple Exciton Generation in Lead Chalcogenide Quantum Dots

    NASA Astrophysics Data System (ADS)

    Midgett, Aaron G.

    2011-12-01

    Providing affordable, clean energy is one of the major challenges facing society today, and one of the promising solutions is third generation solar energy conversion. Present day, first and second-generation solar cells can at most convert each absorbed photon into a single electron hole pair, thereby establishing a theoretical limit to the power conversion efficiency. The process of multiple exciton generation (MEG) in semiconductor quantum dots increases that theoretical efficiency from 33% to 42% by utilizing the excess energy of high energy photons that is otherwise wasted as heat to excite a second electron-hole pair, thereby boosting the potential photocurrent. This thesis explores the benefits of MEG in quantum confined systems and shows that quantum dots are more efficient at generating multiple excitons from a single photon than bulk semiconductors. The variations in optical measurements of MEG have raised skepticism and brought into question the validity of these experiments. The two important questions that this thesis attempts to address are (1) what are the enhanced QYs in isolated PbSe QDs and (2) does quantum confinement enhance MEG over bulk semiconductors. Experimental variations in the enhanced QYs are partially explained by the production of a long-lived photocharged state that increases the apparent photon-to-exciton QYs. A procedure is detailed that decreases the possibility of producing this charged state. By studying the production of these states, conditions are found that minimize their effect and produce less variation in the reported QYs. Variations in the MEG efficiency were studied in films of chemically treated PbSe quantum dots where a different mechanism was responsible for an apparent decrease of the measured QYs. Finally, for the first time, a quantum dot size-dependence in the MEG efficiency was found in colloidal PbSe, PbS, and PbSxSe1-x quantum dot solutions and is attributed to the increased Coulomb interaction in materials

  20. Quantum dot photodegradation due to CdSe-ZnO charge transfer: Transient absorption study

    NASA Astrophysics Data System (ADS)

    Žídek, K.; Zheng, K.; Chábera, P.; Abdellah, M.; Pullerits, T.

    2012-06-01

    We study changes in ultrafast transient absorption due to photodegradation of quantum dots attached to ZnO nanowire. The time-resolved measurements reveal impact of photodegradation on three distinct kinetic components present in transient absorption τ ˜ 7 ps, 80 ps, and 7.5 ns). In addition, we observe superlinear dependence of photodegradation rate on concentration of excited electrons. The data are used to evaluate the mean electron back-recombination time of ˜1 μs.

  1. Photon echo studies of biexcitons and coherences in colloidal CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Colonna, Anne E.; Yang, Xiujuan; Scholes, Gregory D.

    2005-04-01

    The cover picture shows the size-dependent photoluminescence from CdSe colloidal quantum dots that were investigated in the work [1]. Ultrafast photon echo experiments were undertaken in conjunction with simulations based on a realistic many-body theory, shown in the picture, to ascertain the significance of many-body contributions to the third-order nonlinear response.The first author Anne E. Colonna undertook this research during a summer internship in the Department of Chemistry, University of Toronto. She is currently pursuing graduate studies at École Polytechnique, Saclay, in the Laboratoire d'Optique et Biosciences.The author Gregory D. Scholes is an Assistant Professor in the Department of Chemistry, University of Toronto. His research interests include synthesis and shape control of quantum dots, as well as the application of ultrafast laser spectroscopy to investigate the electronic structure of inorganic and organic semiconductors.

  2. Optical study of electron-electron exchange interaction in CdTe/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Kazimierczuk, T.; Smoleński, T.; Kobak, J.; Goryca, M.; Pacuski, W.; Golnik, A.; Fronc, K.; Kłopotowski, Ł.; Wojnar, P.; Kossacki, P.

    2013-05-01

    We present an experimental study of electron-electron exchange interaction in self-assembled CdTe/ZnTe quantum dots based on the photoluminescence measurements. The character and strength of this interaction are obtained by simultaneous observation of various recombination channels of a doubly negatively charged exciton X2-, including previously unrecognized emission lines related to the electron-singlet configuration in the final state. A typical value of the electron singlet-triplet splitting, which corresponds to the exchange integral of electron-electron interaction, has been determined as 20.4 meV with a spread of 1.4 meV across the wide population of quantum dots. We also evidence an unexpected decrease of energy difference between the singlet and triplet states under a magnetic field in Faraday geometry.

  3. Studying nanotoxic effects of CdTe quantum dots in Trypanosoma cruzi

    NASA Astrophysics Data System (ADS)

    Stahl, C. V.; Almeida, D. B.; de Thomaz, A. A.; Fontes, A.; Menna-Barreto, R. F. S.; Santos-Mallet, J. R.; Cesar, C. L.; Gomes, S. A. O.; Feder, D.

    2010-02-01

    Many studies have been done in order to verify the possible nanotoxicity of quantum dots in some cellular types. Protozoan pathogens as Trypanosoma cruzi, etiologic agent of Chagas1 disease is transmitted to humans either by blood-sucking triatomine vectors, blood transfusion, organs transplantation or congenital transmission. The study of the life cycle, biochemical, genetics, morphology and others aspects of the T. cruzi is very important to better understand the interactions with its hosts and the disease evolution on humans. Quantum dot, nanocrystals, highly luminescent has been used as tool for experiments in in vitro and in vivo T. cruzi life cycle development in real time. We are now investigating the quantum dots toxicity on T. cruzi parasite cells using analytical methods. In vitro experiments were been done in order to test the interference of this nanoparticle on parasite development, morphology and viability (live-death). Ours previous results demonstrated that 72 hours after parasite incubation with 200 μM of CdTe altered the development of T. cruzi and induced cell death by necrosis in a rate of 34%. QDs labeling did not effect: (i) on parasite integrity, at least until 7 days; (ii) parasite cell dividing and (iii) parasite motility at a concentration of 2 μM CdTe. This fact confirms the low level of cytotoxicity of these QDs on this parasite cell. In summary our results is showing T. cruzi QDs labeling could be used for in vivo cellular studies in Chagas disease.

  4. The study of CdSe colloidal quantum dots synthesized in aqueous and organic media

    NASA Astrophysics Data System (ADS)

    Mikhailov, I. I.; Tarasov, S. A.; Solomonov, A. V.; Aleksandrova, O. A.; Matyushkin, L. B.; Mazing, D. S.

    2014-12-01

    The samples of CdSe colloidal quantum dots (CQDs) synthesized in aqueous and organic media are studied. The possibility of luminescence peak position control depending on nanoparticle growth process is demonstrated. The samples synthesized in organic medium revealed the luminescence color variation effect with nanoparticle growth. The relation of this effect with processes of nucleation and defect formation in nanoparticles is considered. The CQDs of CdSe coated with CdS shell are fabricated. The use of inorganic shell can provide a double increase of the luminescence quantum yield.

  5. Assessing clinical prospects of silicon quantum dots: studies in mice and monkeys.

    PubMed

    Liu, Jianwei; Erogbogbo, Folarin; Yong, Ken-Tye; Ye, Ling; Liu, Jing; Hu, Rui; Chen, Hongyan; Hu, Yazhuo; Yang, Yi; Yang, Jinghui; Roy, Indrajit; Karker, Nicholas A; Swihart, Mark T; Prasad, Paras N

    2013-08-27

    Silicon nanocrystals can provide the outstanding imaging capabilities of toxic heavy-metal-based quantum dots without employing heavy metals and have potential for rapid progression to the clinic. Understanding the toxicity of silicon quantum dots (SiQDs) is essential to realizing this potential. However, existing studies of SiQD biocompatibility are limited, with no systematic progression from small-animal to large-animal studies that are more clinically relevant. Here, we test the response of both mice and monkeys to high intravenous doses of a nanoconstruct created using only SiQDs and FDA-approved materials. We show that (1) neither mice nor monkeys show overt signs of toxicity reflected in their behavior, body mass, or blood chemistry, even at a dose of 200 mg/kg. (2) This formulation did not biodegrade as expected. Elevated levels of silicon were present in the liver and spleen of mice three months post-treatment. (3) Histopathology three months after treatment showed adverse effects of the nanoformulation in the livers of mice, but showed no such effects in monkeys. This investigation reveals that the systemic reactions of the two animal models may have some differences and there are no signs of toxicity clearly attributable to silicon quantum dots.

  6. Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study

    NASA Astrophysics Data System (ADS)

    Sindel, M.; Borda, L.; Martinek, J.; Bulla, R.; König, J.; Schön, G.; Maekawa, S.; von Delft, J.

    2007-07-01

    We systematically study the influence of ferromagnetic leads on the Kondo resonance in a quantum dot tuned to the local moment regime. We employ Wilson’s numerical renormalization group method, extended to handle leads with a spin asymmetric density of states, to identify the effects of (i) a finite spin polarization in the leads (at the Fermi surface), (ii) a Stoner splitting in the bands (governed by the band edges), and (iii) an arbitrary shape of the lead density of states. For a generic lead density of states, the quantum dot favors being occupied by a particular spin species due to exchange interaction with ferromagnetic leads, leading to suppression and splitting of the Kondo resonance. The application of a magnetic field can compensate this asymmetry, restoring the Kondo effect. We study both the gate voltage dependence (for a fixed band structure in the leads) and the spin polarization dependence (for fixed gate voltage) of this compensation field for various types of bands. Interestingly, we find that the full recovery of the Kondo resonance of a quantum dot in the presence of leads with an energy-dependent density of states is possible not only by an appropriately tuned external magnetic field but also via an appropriately tuned gate voltage. For flat bands, simple formulas for the splitting of the local level as a function of the spin polarization and gate voltage are given.

  7. Quantum dots: Rethinking the electronics

    SciTech Connect

    Bishnoi, Dimple

    2016-05-06

    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 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.

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

    NASA Astrophysics Data System (ADS)

    Hewageegana, Prabath; Apalkov, Vadym

    2009-03-01

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

  10. Synthesis of Luminescent Graphene Quantum Dots with High Quantum Yield and Their Toxicity Study

    PubMed Central

    Jiang, Dan; Chen, Yunping; Li, Na; Li, Wen; Wang, Zhenguo; Zhu, Jingli; Zhang, Hong; Liu, Bin; Xu, Shan

    2015-01-01

    High fluorescence quantum yield graphene quantum dots (GQDs) have showed up as a new generation for bioimaging. In this work, luminescent GQDs were prepared by an ameliorative photo-Fenton reaction and a subsequent hydrothermal process using graphene oxide sheets as the precursor. The as-prepared GQDs were nanomaterials with size ranging from 2.3 to 6.4 nm and emitted intense green luminescence in water. The fluorescence quantum yield was as high as 24.6% (excited at 340 nm) and the fluorescence was strongest at pH 7. Moreover, the influences of low-concentration (12.5, 25 μg/mL) GQDs on the morphology, viability, membrane integrity, internal cellular reactive oxygen species level and mortality of HeLa cells were relatively weak, and the in vitro imaging demonstrated GQDs were mainly in the cytoplasm region. More strikingly, zebrafish embryos were co-cultured with GQDs for in vivo imaging, and the results of heart rate test showed the intake of small amounts of GQDs brought little harm to the cardiovascular of zebrafish. GQDs with high quantum yield and strong photoluminescence show good biocompatibility, thus they show good promising for cell imaging, biolabeling and other biomedical applications. PMID:26709828

  11. Low Threshold Quantum Dot Lasers.

    PubMed

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

    2016-04-07

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

  12. Synthetic Developments of Nontoxic Quantum Dots.

    PubMed

    Das, Adita; Snee, Preston T

    2016-03-03

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

  13. Entangled exciton states in quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Bayer, Manfred

    2002-03-01

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

  14. 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.

  15. 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

  16. Theory of a double-quantum-dot spaser

    SciTech Connect

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

    2015-03-31

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

  17. Zinc sulfide quantum dots for photocatalytic and sensing applications

    NASA Astrophysics Data System (ADS)

    Sergeev, Alexander A.; Leonov, Andrei A.; Zhuikova, Elena I.; Postnova, Irina V.; Voznesenskiy, Sergey S.

    2017-09-01

    Herein, we report the photocatalytic and sensing applications of pure and Mn-doped ZnS quantum dots. The quantum dots were prepared by a chemical precipitation in an aqueous solution in the presence of glutathione as a stabilizing agent. The synthesized quantum dots were used as effective photocatalyst for the degradation of methylene blue dye. Interestingly, fully degradation of methylene blue dye was achieved in 5 min using pure ZnS quantum dots. Further, the synthesized quantum dots were used as efficient sensing element for methane fluorescent sensor. Interfering studies confirmed that the developed sensor possesses very good sensitivity and selectivity towards methane.

  18. Few-electron quantum dots

    NASA Astrophysics Data System (ADS)

    Kouwenhoven, L. P.; Austing, D. G.; Tarucha, S.

    2001-06-01

    We review some electron transport experiments on few-electron, vertical quantum dot devices. The measurement of current versus source-drain voltage and gate voltage is used as a spectroscopic tool to investigate the energy characteristics of interacting electrons confined to a small region in a semiconducting material. Three energy scales are distinguished: the single-particle states, which are discrete due to the confinement involved; the direct Coulomb interaction between electron charges on the dot; and the exchange interaction between electrons with parallel spins. To disentangle these energies, a magnetic field is used to reorganize the occupation of electrons over the single-particle states and to induce changes in the spin states. We discuss the interactions between small numbers of electrons (between 1 and 20) using the simplest possible models. Nevertheless, these models consistently describe a large set of experiments. Some of the observations resemble similar phenomena in atomic physics, such as shell structure and periodic table characteristics, Hund's rule, and spin singlet and triplet states. The experimental control, however, is much larger than for atoms: with one device all the artificial elements can be studied by adding electrons to the quantum dot when changing the gate voltage.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    PubMed

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

    2013-10-14

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

  1. 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

  2. Study of heterostructures with a combined In(Ga)As/GaAs quantum dot/quantum well layer and a Mn δ layer

    SciTech Connect

    Pavlova, E. D. Gorshkov, A. P.; Bobrov, A. I.; Malekhonova, N. V.; Zvonkov, B. N.

    2013-12-15

    Using high-resolution transmission electron microscopy and photoelectric spectroscopy methods, the effect of Mn δ layer embedding and GaAs coating layer growth techniques in structures with In(Ga)As/GaAs quantum dots and wells on their structural and optoelectronic characteristics is studied. It is shown that the low-temperature GaAs coating layer in a structure with a Mn δ layer is structurally inhomogeneous and can cause a decrease in the quantum-dot photosensitivity.

  3. Hydrophobin-Encapsulated Quantum Dots.

    PubMed

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

    2016-02-01

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

  4. Zeeman transitions in spherical quantum dot

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  5. Density functional theory studies of core-shell semiconductor nanoparticle quantum dots

    NASA Astrophysics Data System (ADS)

    Walker, Brent; Hendy, Shaun; Tilley, Richard

    2008-03-01

    In going from the macroscale to the nanoscale, quantum-mechanical effects become increasingly important and may mean that nanostructures of a material exhibit very different properties from the corresponding bulk. This is especially noticeable in the case of the optical properties of semiconductor nanoparticles (or quantum dots), which display a number of remarkable features (including very distinct peaks, and tunability across a broad range of wavelengths), due to quantum confinement. Our work involves modeling Si-Ge core-shell nanoparticles using large-scale computer simulations based on the density functional and time-dependent density functional theories. These simulations in particular provide us with predictions of the geometric structures and optical absorption spectra of nanoparticles in an accurate and computationally efficient way, and allow us to study the systematic trends in these properties as the composition and size of the nanoparticle change.

  6. Spatially highly resolved study of AFM scanning tip quantum dot local interaction

    NASA Astrophysics Data System (ADS)

    Kicin, S.; Pioda, A.; Ihn, T.; Sigrist, M.; Fuhrer, A.; Ensslin, K.; Reinwald, M.; Wegscheider, W.

    2005-08-01

    Scanning-gate imaging of semiconductor quantum dots (QDs) promises access to probability distributions of quantum states. It could therefore be a novel tool for designing and optimizing tailored quantum states in such systems. A detailed study of a lithographically defined semiconductor QD in the Coulomb-blockade regime is presented, making use of the scanning-gate technique at a base temperature of 300 mK. The method allows a one-by-one manipulation of electrons in the structure. The obtained images interpreted with a suitable QD model guide the way to a local investigation of the electronic interior of the QD. Future perspectives of scanning-gate experiments on QDs are discussed.

  7. 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.

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

    PubMed Central

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

    2015-01-01

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

  9. First-principle study of quantum confinement effect on small sized silicon quantum dots using density-functional theory

    SciTech Connect

    Anas, M. M.; Othman, A. P.; Gopir, G.

    2014-09-03

    Density functional theory (DFT), as a first-principle approach has successfully been implemented to study nanoscale material. Here, DFT by numerical basis-set was used to study the quantum confinement effect as well as electronic properties of silicon quantum dots (Si-QDs) in ground state condition. Selection of quantum dot models were studied intensively before choosing the right structure for simulation. Next, the computational result were used to examine and deduce the electronic properties and its density of state (DOS) for 14 spherical Si-QDs ranging in size up to ∼ 2 nm in diameter. The energy gap was also deduced from the HOMO-LUMO results. The atomistic model of each silicon QDs was constructed by repeating its crystal unit cell of face-centered cubic (FCC) structure, and reconstructed until the spherical shape obtained. The core structure shows tetrahedral (T{sub d}) symmetry structure. It was found that the model need to be passivated, and hence it was noticed that the confinement effect was more pronounced. The model was optimized using Quasi-Newton method for each size of Si-QDs to get relaxed structure before it was simulated. In this model the exchange-correlation potential (V{sub xc}) of the electrons was treated by Local Density Approximation (LDA) functional and Perdew-Zunger (PZ) functional.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Ahmad, SalmanOgli

    2016-10-01

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

  12. Theoretical and experimental studies of (In,Ga)As/GaP quantum dots

    PubMed Central

    2012-01-01

    (In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of k·p and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties are then studied in a low-In-content range through photoluminescence and time-resolved photoluminescence experiments. It suggests the proximity of two optical transitions of indirect and direct types. PMID:23176537

  13. Study of isolated cubic GaN quantum dots by low-temperature cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Garayt, J. P.; Gérard, J. M.; Enjalbert, F.; Ferlazzo, L.; Founta, S.; Martinez-Guerrero, E.; Rol, F.; Araujo, D.; Cox, R.; Daudin, B.; Gayral, B.; Si Dang, Le; Mariette, H.

    2005-02-01

    We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission.

  14. Quantum dots in aperiodic order

    NASA Astrophysics Data System (ADS)

    Hörnquist, Michael; Ouchterlony, Thomas

    1998-12-01

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

  15. Grazing-incidence small-angle X-ray scattering: application to the study of quantum dot lattices

    SciTech Connect

    Buljan, Maja Radić, Nikola; Bernstorff, Sigrid; Dražić, Goran; Bogdanović-Radović, Iva; Holý, Václav

    2012-01-01

    The modelling of grazing-incidence small-angle X-ray scattering (GISAXS) from three-dimensional quantum dot lattices is described. The ordering of quantum dots in three-dimensional quantum dot lattices is investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Theoretical models describing GISAXS intensity distributions for three general classes of lattices of quantum dots are proposed. The classes differ in the type of disorder of the positions of the quantum dots. The models enable full structure determination, including lattice type, lattice parameters, the type and degree of disorder in the quantum dot positions and the distributions of the quantum dot sizes. Applications of the developed models are demonstrated using experimentally measured data from several types of quantum dot lattices formed by a self-assembly process.

  16. 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.

  17. Tailoring Magnetism in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Zutic, Igor; Abolfath, Ramin; Hawrylak, Pawel

    2007-03-01

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

  18. Quantum Dots: Fundamentals, Applications, and Frontiers

    NASA Astrophysics Data System (ADS)

    Joyce, Bruce A.; Kelires, Pantelis C.; Naumovets, Anton G.; Vvedensky, Dimitri D.

    This volume contains papers delivered at a NATO Advanced Research Workshop and provides a broad introduction to all major aspects of quantum dot structures. Such structures have been produced for studies of basic physical phenomena, for device fabrication and, on a more speculative level, have been suggested as components of a solid-state realization of a quantum computer. The book is structured so that the reader is introduced to the methods used to produce and control quantum dots, followed by discussions of their structural, electronic, and optical properties.

  19. Quantum Entanglement of Quantum Dot Spin Using Flying Qubits

    DTIC Science & Technology

    2015-05-01

    QUANTUM ENTANGLEMENT OF QUANTUM DOT SPIN USING FLYING QUBITS UNIVERSITY OF MICHIGAN MAY 2015 FINAL TECHNICAL REPORT APPROVED FOR PUBLIC RELEASE...To) SEP 2012 – DEC 2014 4. TITLE AND SUBTITLE QUANTUM ENTANGLEMENT OF QUANTUM DOT SPIN USING FLYING QUBITS 5a. CONTRACT NUMBER FA8750-12-2-0333...semiconductor quantum dots doped with a single electron, made possible by the Coulomb blockade in this system. The quantum dots confine both electrons and

  20. Quantum dot heterojunction solar cells: The mechanism of device operation and impacts of quantum dot oxidation

    NASA Astrophysics Data System (ADS)

    Ihly, Rachelle

    This thesis explores the understanding of the chemistry and physics of colloidal quantum dots for practical solar energy photoconversion. Solar cell devices that make use of PbS quantum dots generally rely on constant and unchanged optical properties such that band gap energies remain tuned within the device. The design and development of unique experiments to ascertain mechanisms of optical band gap shifts occurring in PbS quantum dot thin-films exposed to air are discussed. The systematic study of the absorption properties of PbS quantum dot films exposed to air, heat, and UV illumination as a function of quantum dot size has been described. A method to improve the air-stability of films with atomic layer deposition of alumina is demonstrated. Encapsulation of quantum dot films using a protective layer of alumina results in quantum dot solids that maintain tuned absorption for 1000 hours. This thesis focuses on the use of atomic force microscopy and electrical variants thereof to study the physical and electrical characteristics of quantum dot arrays. These types of studies have broad implications in understanding charge transport mechanisms and solar cell device operation, with a particular emphasis on quantum dot transistors and solar cells. Imaging the channel potential of a PbSe quantum dot thin-film in a transistor showed a uniform distribution of charge coinciding with the transistor current voltage characteristics. In a second study, solar cell device operation of ZnO/PbS heterojunction solar cells was investigated by scanning active cross-sections with Kelvin probe microscopy as a function of applied bias, illumination and device architecture. This technique directly provides operating potential and electric field profiles to characterize drift and diffusion currents occurring in the device. SKPM established a field-free region occurring in the quantum dot layer, indicative of diffusion-limited transport. These results provide the path to optimization of

  1. The in vivo biodistribution and fate of CdSe quantum dots in the murine model: a laser ablation inductively coupled plasma mass spectrometry study.

    PubMed

    Wang, TsingHai; Hsieh, HuiAn; Hsieh, YiKong; Chiang, ChiShiun; Sun, YuhChang; Wang, ChuFang

    2012-12-01

    Understanding the cytotoxicity of quantum dots strongly relies upon the development of new analytical techniques to gather information about various aspects of the system. In this study, we demonstrate the in vivo biodistribution and fate of CdSe quantum dots in the murine model by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). By comparing the hot zones of each element acquired from LA-ICP-MS with those in fluorescence images, together with hematoxylin and eosin-stained images, we are able to perceive the fate and in vivo interactions between quantum dots and rat tissues. One hour after intravenous injection, we found that all of the quantum dots had been concentrated inside the spleen, liver and kidneys, while no quantum dots were found in other tissues (i.e., muscle, brain, lung, etc.). In the spleen, cadmium-114 signals always appeared in conjunction with iron signals, indicating that the quantum dots had been filtered from main vessels and then accumulated inside splenic red pulp. In the liver, the overlapped hot zones of quantum dots and those of phosphorus, copper, and zinc showed that these quantum dots have been retained inside hepatic cells. Importantly, it was noted that in the kidneys, quantum dots went into the cortical areas of adrenal glands. At the same time, hot zones of copper appeared in proximal tubules of the cortex. This could be a sign that the uptake of quantum dots initiates certain immune responses. Interestingly, the intensity of the selenium signals was not proportional to that of cadmium in all tissues. This could be the result of the decomposition of the quantum dots or matrix interference. In conclusion, the advantage in spatial resolution of LA-ICP-MS is one of the most powerful tools to probe the fate, interactions and biodistribution of quantum dots in vivo.

  2. Quantum dot quantum cascade infrared photodetector

    SciTech Connect

    Wang, Xue-Jiao; Zhai, Shen-Qiang; Zhuo, Ning; Liu, Jun-Qi E-mail: fqliu@semi.ac.cn; Liu, Feng-Qi E-mail: fqliu@semi.ac.cn; Liu, Shu-Man; Wang, Zhan-Guo

    2014-04-28

    We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3 μm. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski–Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64 × 10{sup 11} and 4.83 × 10{sup 6} Jones at zero bias were obtained at 80 K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging.

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

    NASA Astrophysics Data System (ADS)

    Song, Fayi; Chan, Warren C. W.

    2011-12-01

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

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

    PubMed

    Song, Fayi; Chan, Warren C W

    2011-12-09

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

  5. Comparative study of donor-induced quantum dots in Si nano-channels by single-electron transport characterization and Kelvin probe force microscopy

    SciTech Connect

    Tyszka, K.; Moraru, D.; Samanta, A.; Mizuno, T.; Tabe, M.; Jabłoński, R.

    2015-06-28

    We comparatively study donor-induced quantum dots in Si nanoscale-channel transistors for a wide range of doping concentration by analysis of single-electron tunneling transport and surface potential measured by Kelvin probe force microscopy (KPFM). By correlating KPFM observations of donor-induced potential landscapes with simulations based on Thomas-Fermi approximation, it is demonstrated that single-electron tunneling transport at lowest gate voltages (for smallest coverage of screening electrons) is governed most frequently by only one dominant quantum dot, regardless of doping concentration. Doping concentration, however, primarily affects the internal structure of the quantum dot. At low concentrations, individual donors form most of the quantum dots, i.e., “donor-atom” quantum dots. In contrast, at high concentrations above metal-insulator transition, closely placed donors instead of individual donors form more complex quantum dots, i.e., “donor-cluster” quantum dots. The potential depth of these “donor-cluster” quantum dots is significantly reduced by increasing gate voltage (increasing coverage of screening electrons), leading to the occurrence of multiple competing quantum dots.

  6. Comparative study of donor-induced quantum dots in Si nano-channels by single-electron transport characterization and Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Tyszka, K.; Moraru, D.; Samanta, A.; Mizuno, T.; Jabłoński, R.; Tabe, M.

    2015-06-01

    We comparatively study donor-induced quantum dots in Si nanoscale-channel transistors for a wide range of doping concentration by analysis of single-electron tunneling transport and surface potential measured by Kelvin probe force microscopy (KPFM). By correlating KPFM observations of donor-induced potential landscapes with simulations based on Thomas-Fermi approximation, it is demonstrated that single-electron tunneling transport at lowest gate voltages (for smallest coverage of screening electrons) is governed most frequently by only one dominant quantum dot, regardless of doping concentration. Doping concentration, however, primarily affects the internal structure of the quantum dot. At low concentrations, individual donors form most of the quantum dots, i.e., "donor-atom" quantum dots. In contrast, at high concentrations above metal-insulator transition, closely placed donors instead of individual donors form more complex quantum dots, i.e., "donor-cluster" quantum dots. The potential depth of these "donor-cluster" quantum dots is significantly reduced by increasing gate voltage (increasing coverage of screening electrons), leading to the occurrence of multiple competing quantum dots.

  7. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    SciTech Connect

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

    2016-05-16

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

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

    PubMed

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

    2011-01-01

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

  9. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

    PubMed Central

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

    2011-01-01

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

  10. Quantum-Dot Cellular Automata

    NASA Astrophysics Data System (ADS)

    Snider, Gregory

    2000-03-01

    Quantum-dot Cellular Automata (QCA) [1] is a promising architecture which employs quantum dots for digital computation. It is a revolutionary approach that holds the promise of high device density and low power dissipation. A basic QCA cell consists of four quantum dots coupled capacitively and by tunnel barriers. The cell is biased to contain two excess electrons within the four dots, which are forced to opposite "corners" of the four-dot cell by mutual Coulomb repulsion. These two possible polarization states of the cell will represent logic "0" and "1". Properly arranged, arrays of these basic cells can implement Boolean logic functions. Experimental results from functional QCA devices built of nanoscale metal dots defined by tunnel barriers will be presented. The experimental devices to be presented consist of Al islands, which we will call quantum dots, interconnected by tunnel junctions and lithographically defined capacitors. Aluminum/ aluminum-oxide/aluminum tunnel junctions were fabricated using a standard e-beam lithography and shadow evaporation technique. The experiments were performed in a dilution refrigerator at a temperature of 70 mK. The operation of a cell is evaluated by direct measurements of the charge state of dots within a cell as the input voltage is changed. The experimental demonstration of a functioning cell will be presented. A line of three cells demonstrates that there are no metastable switching states in a line of cells. A QCA majority gate will also be presented, which is a programmable AND/OR gate and represents the basic building block of QCA systems. The results of recent experiments will be presented. 1. C.S. Lent, P.D. Tougaw, W. Porod, and G.H. Bernstein, Nanotechnology, 4, 49 (1993).

  11. Chiral Graphene Quantum Dots.

    PubMed

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

    2016-02-23

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

  12. Strain-induced vertical self-organization of semiconductor quantum dots: A computational study

    SciTech Connect

    Shtinkov, N.

    2013-12-28

    Atomistic strain simulations based on the valence force field method are employed to study the vertical arrangements of semiconductor quantum dot (QD) multilayers. The effects of the QD shape, dimensions, and materials parameters are systematically investigated, varying independently the following parameters: spacer width H, QD lateral spacing D, base b, and height h, slope of the side facets, elastic properties of the dot and the substrate materials, and lattice mismatch between the dot and the substrate. The transition between vertically aligned and anti-aligned structures is found to be determined mainly by the ratios H/D and b/D, as well as by the strain anisotropy of the substrate and to a lesser extent of the QD. The dependence on the QD height h is significant only for steep side facets and large aspect ratios h/b, and the effects of the lattice mismatch strain and the bulk elastic moduli are found to be negligible. The comparison with experimental data shows an excellent agreement with the results from the simulations, demonstrating that the presented analysis results in precise theoretical predictions for the vertical self-organization regime in a wide range of QD materials systems.

  13. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

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

  14. Experimental study of the effect of addition of gold nanoparticles on CdSe quantum dots sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Indayani, Wahyu; Huda, Ichsanul; Herliansyah, Khuzaimah, Fasya; Musyaro'ah, Gunawan, Bodi; Endarko

    2017-01-01

    The effect of the gold nanoparticles on the quantum dots sensitized solar cells has been investigated. Gold nanoparticles were added in quantum dot CdSe before used as a sensitizer. The result showed that addition of colloidal gold nanoparticles could be enhanced the absorbance of quantum dot CdSe sensitizer. In this research, the QDSCs were arranged in the sandwich structure consecutively TiO2 as photoelectrode, gold nanoparticle, and quantum dot CdSe as a sensitizer, KI as electrolyte and black carbon as counter-electrode. The use of gold nanoparticles and quantum dot improved the average efficiency of the QDSC by about 104%.

  15. Nanoscale quantum-dot supercrystals

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  16. Double quantum dots defined in bilayer graphene

    NASA Astrophysics Data System (ADS)

    Żebrowski, D. P.; Peeters, F. M.; Szafran, B.

    2017-07-01

    Artificial molecular states of double quantum dots defined in bilayer graphene are studied with the atomistic tight-binding method and its low-energy continuum approximation. We indicate that the extended electron wave functions have opposite parities on sublattices of the layers and that the ground-state wave-function components change from bonding to antibonding with the interdot distance. In the weak-coupling limit, the one most relevant for quantum dots defined electrostatically, the signatures of the interdot coupling include, for the two-electron ground state, formation of states with symmetric or antisymmetric spatial wave functions split by the exchange energy. In the high-energy part of the spectrum the states with both electrons in the same dot are found with the splitting of energy levels corresponding to simultaneous tunneling of the electron pair from one dot to the other.

  17. Multiplexed and quantitative study of biomarker expression in tumor specimens using quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Aileen; True, Lawrence; Gao, Xiaohu

    2006-02-01

    When conjugated with targeting molecules, quantum dots (QD) can be used as powerful cancer diagnostic tools providing the molecular profiles of cancer cases based on common clinical biopsies. Such personalized analyses will enable doctors to treat and manage the patients' diseases more effectively. The unique optical properties (e.g., size-tunable emission, simultaneous excitation, high brightness and photostability) of these nanoparticles make them superior to conventionally popular organic fluorophores 1-2. Polymer-encapsulated, antibody-tagged QDs were prepared and used to successfully stain both fixed and live cells as well as clinical formalin-fixed paraffin-embedded (FFPE) tissue sections. In the tissue staining study, QD bioconjugates targeting mutated p53 and early growth response protein (egr-1) were used to examine prostate cancer tissues. The tissue slides were then analyzed with a wavelength-resolved spectrometer to accurately quantify the protein expression levels. In comparison to traditional qualitatively based diagnostic procedures, quantum dot nanotechnology allows for a more quantitative, rigorous and objective analysis of tissue specimens in question. In addition, new developments in imaging instrumentation could automate spectroscopy measurements and data analysis.

  18. Quantum-dot-based cell motility assay.

    PubMed

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

    2005-06-28

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

  19. Deposition of Quantum Dots in a Capillary Tube.

    PubMed

    Kong, Yong Lin; Boulogne, François; Kim, Hyoungsoo; Nunes, Janine; Feng, Jie; Stone, Howard A

    2015-11-17

    The ability to assemble nanomaterials, such as quantum dots, enables the creation of functional devices that present unique optical and electronic properties. For instance, light-emitting diodes with exceptional color purity can be printed via the evaporative-driven assembly of quantum dots. Nevertheless, current studies of the colloidal deposition of quantum dots have been limited to the surfaces of a planar substrate. Here, we investigate the evaporation-driven assembly of quantum dots inside a confined cylindrical geometry. Specifically, we observe distinct deposition patterns, such as banding structures along the length of a capillary tube. Such coating behavior can be influenced by the evaporation speed as well as the concentration of quantum dots. Understanding the factors governing the coating process can provide a means to control the assembly of quantum dots inside a capillary tube, ultimately enabling the creation of novel photonic devices.

  20. Linking computational and experimental studies of III-V quantum dots for optoelectronics and photovoltaics

    NASA Astrophysics Data System (ADS)

    Semichaevsky, A. V.; Goldman, R. S.; Johnson, H. T.

    2011-09-01

    Low-dimensional semiconductors (LDS) are semiconductor structures such as quantum dots, quantum wires, and quantum wells in which electron and hole wave functions are confined due to heterogeneous composition and often strongly affected by mismatch strain. Due to the quantum confinement, LDS exhibit unusual electronic and optical properties not found in bulk semiconductor materials. Quantum dots (QD) have found new applications in various semiconductor devices such as lasers, photodetectors, and solar cells. Precise design of QD structures requires understanding of their chemical composition and nanomechanical properties, and relies on both experimental and computational approaches. In this paper we provide an overview of computational and experimental methods for characterization of QD heterostructures. In particular, we review our own concerted efforts to bring together computation and experiment in order to better explain their optoelectronic and photovoltaic properties.

  1. Optical resonators and quantum dots: An excursion into quantum optics, quantum information and photonics

    NASA Astrophysics Data System (ADS)

    Bianucci, Pablo

    Modern communications technology has encouraged an intimate connection between Semiconductor Physics and Optics, and this connection shows best in the combination of electron-confining structures with light-confining structures. Semiconductor quantum dots are systems engineered to trap electrons in a mesoscopic scale (the are composed of ≈ 10000 atoms), resulting in a behavior resembling that of atoms, but much richer. Optical microresonators are engineered to confine light, increasing its intensity and enabling a much stronger interaction with matter. Their combination opens a myriad of new directions, both in fundamental Physics and in possible applications. This dissertation explores both semiconductor quantum dots and microresonators, through experimental work done with semiconductor quantum dots and microsphere resonators spanning the fields of Quantum Optics, Quantum Information and Photonics; from quantum algorithms to polarization converters. Quantum Optics leads the way, allowing us to understand how to manipulate and measure quantum dots with light and to elucidate the interactions between them and microresonators. In the Quantum Information area, we present a detailed study of the feasibility of excitons in quantum dots to perform quantum computations, including an experimental demonstration of the single-qubit Deutsch-Jozsa algorithm performedin a single semiconductor quantum dot. Our studies in Photonics involve applications of microsphere resonators, which we have learned to fabricate and characterize. We present an elaborate description of the experimental techniques needed to study microspheres, including studies and proof of concept experiments on both ultra-sensitive microsphere sensors and whispering gallery mode polarization converters.

  2. A study of specific features of the electronic spectrum of quantum dots in CdSe semiconductor

    NASA Astrophysics Data System (ADS)

    Mikhailov, A. I.; Kabanov, V. F.; Gorbachev, I. A.; Glukhovskoi, E. G.

    2016-08-01

    Monolayers of CdSe/CdS/ZnS quantum dots (QDs) formed on the aqueous subphase and transferred to solid substrates by the Langmuir-Blodgett method have been studied. The samples obtained were examined by transmission electron microscopy, atomic-force microscopy, and scanning tunnel microscopy. The structure of the QD monolayer obtained on the substrate was analyzed. Specific features of the electronic spectrum of the quantum objects formed in the samples under study were determined.

  3. Quantum dots-nanogap metamaterials fabrication by self-assembly lithography and photoluminescence studies.

    PubMed

    Tripathi, Laxmi Narayan; Kang, Taehee; Bahk, Young-Mi; Han, Sanghoon; Choi, Geunchang; Rhie, Jiyeah; Jeong, Jeeyoon; Kim, Dai-Sik

    2015-06-01

    We present a new and versatile technique of self-assembly lithography to fabricate a large scale Cadmium selenide quantum dots-silver nanogap metamaterials. After optical and electron microscopic characterizations of the metamaterials, we performed spatially resolved photoluminescence transmission measurements. We obtained highly quenched photoluminescence spectra compared to those from bare quantum dots film. We then quantified the quenching in terms of an average photoluminescence enhancement factor. A finite difference time domain simulation was performed to understand the role of an electric field enhancement in the nanogap over this quenching. Finally, we interpreted the mechanism of the photoluminescence quenching and proposed fabrication method of new metamaterials using our technique.

  4. Quantum-confined Stark effects in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

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

    1995-08-01

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

  5. 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.

  6. Quantum dot behavior in graphene nanoconstrictions.

    PubMed

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

    2009-01-01

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

  7. 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.

  8. Colloidal quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Sargent, Edward H.

    2012-03-01

    Solar cells based on solution-processed semiconductor nanoparticles -- colloidal quantum dots -- have seen rapid advances in recent years. By offering full-spectrum solar harvesting, these cells are poised to address the urgent need for low-cost, high-efficiency photovoltaics.

  9. Quantum dot-based theranostics

    NASA Astrophysics Data System (ADS)

    Ho, Yi-Ping; Leong, Kam W.

    2010-01-01

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

  10. 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.

  11. Study of the Spectral Properties of Nanocomposites with CdSe Quantum Dots in a Wide Range of Low Temperatures

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Luminescence spectra of the colloidal solution of CdSe quantum dots (in toluene) were studied in a wide range of low temperatures. Samples were synthesized in the liquid crystal matrix of cadmium octanoate (CdC8). A comparative analysis of the obtained data with previous results was performed.

  12. Study of optical nonlinearity of CdSe and CdSe@ZnO core-shell quantum dots in nanosecond regime

    NASA Astrophysics Data System (ADS)

    Deepika; Dhar, Rakesh; Mohan, Devendra

    2015-12-01

    Thioglycolic acid capped cadmium selenide (CdSe) and CdSe@ZnO core-shell quantum dots have been synthesized in aqueous phase. The sample was characterized by UV-vis spectrophotometer, TEM and Z-scan technique. The nonlinear optical parameters viz. nonlinear absorption coefficient (β), nonlinear refractive index (n2) and third-order nonlinear susceptibilities (χ3) of quantum dots have been estimated using second harmonic of Nd:YAG laser. The study predicts that CdSe@ZnO quantum dots exhibits strong nonlinearity as compared to core CdSe quantum dots. The nonlinearity in quantum dots is attributed to the presence of resonant excitation and free optical processes. The presence of RSA in these nanoparticles makes them a potential material for the development of optical limiter.

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

    PubMed Central

    Kobirumaki-Shimozawa, Fuyu; Oyama, Kotaro; Serizawa, Takahiro; Mizuno, Akari; Kagemoto, Tatsuya; Shimozawa, Togo; Ishiwata, Shin'ichi; Kurihara, Satoshi; Fukuda, Norio

    2012-01-01

    We here review the use of quantum dots (QDs) for the imaging of sarcomeric movements in cardiac muscle. QDs are fluorescence substances (CdSe) that absorb photons and reemit photons at a different wavelength (depending on the size of the particle); they are efficient in generating long-lasting, narrow symmetric emission profiles, and hence useful in various types of imaging studies. Recently, we developed a novel system in which the length of a particular, single sarcomere in cardiomyocytes can be measured at ~30 nm precision. Moreover, our system enables accurate measurement of sarcomere length in the isolated heart. We propose that QDs are the ideal tool for the study of sarcomere dynamics during excitation-contraction coupling in healthy and diseased cardiac muscle. PMID:22570526

  14. Semiconductor double quantum dot micromaser.

    PubMed

    Liu, Y-Y; Stehlik, J; Eichler, C; Gullans, M J; Taylor, J M; Petta, J R

    2015-01-16

    The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication. Here we demonstrate a maser that is driven by single-electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside a high-quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. Copyright © 2015, American Association for the Advancement of Science.

  15. 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

  16. Brightness-equalized quantum dots.

    PubMed

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

    2015-10-05

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

  17. A pilot study in non-human primates shows no adverse response to intravenous injection of quantum dots

    NASA Astrophysics Data System (ADS)

    Ye, Ling; Yong, Ken-Tye; Liu, Liwei; Roy, Indrajit; Hu, Rui; Zhu, Jing; Cai, Hongxing; Law, Wing-Cheung; Liu, Jianwei; Wang, Kai; Liu, Jing; Liu, Yaqian; Hu, Yazhuo; Zhang, Xihe; Swihart, Mark T.; Prasad, Paras N.

    2012-07-01

    Quantum dots have been used in biomedical research for imaging, diagnostics and sensing purposes. However, concerns over the cytotoxicity of their heavy metal constituents and conflicting results from in vitro and small animal toxicity studies have limited their translation towards clinical applications. Here, we show in a pilot study that rhesus macaques injected with phospholipid micelle-encapsulated CdSe/CdS/ZnS quantum dots do not exhibit evidence of toxicity. Blood and biochemical markers remained within normal ranges following treatment, and histology of major organs after 90 days showed no abnormalities. Our results show that acute toxicity of these quantum dots in vivo can be minimal. However, chemical analysis revealed that most of the initial dose of cadmium remained in the liver, spleen and kidneys after 90 days. This means that the breakdown and clearance of quantum dots is quite slow, suggesting that longer-term studies will be required to determine the ultimate fate of these heavy metals and the impact of their persistence in primates.

  18. Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

    ERIC Educational Resources Information Center

    Pan, Yi; Li, Yue Ru; Zhao, Yu; Akins, Daniel L.

    2015-01-01

    A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a…

  19. Study of the self-organization processes in lead sulfide quantum dots

    SciTech Connect

    Tarasov, S. A. Aleksandrova, O. A.; Maksimov, A. I.; Maraeva, E. V.; Matyushkin, L. B.; Men’kovich, E. A.; Moshnikov, V. A.; Musikhin, S. F.

    2014-12-15

    A procedure is described for the synthesis of nanoparticles based on lead chalcogenides. The procedure combines the synthesis of colloidal quantum dots (QDs) in aqueous solutions with simultaneous organization of the QDs into ordered arrays. The processes of the self-organization of QDs are analyzed at the nano- and microscopic levels by the photoluminescence method, atomic-force microscopy, and optical microscopy.

  20. Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

    ERIC Educational Resources Information Center

    Pan, Yi; Li, Yue Ru; Zhao, Yu; Akins, Daniel L.

    2015-01-01

    A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a…

  1. Ab initio study of phonon-induced dephasing of plasmon excitations in silver quantum dots

    NASA Astrophysics Data System (ADS)

    Guo, Zhenyu; Habenicht, Bradley F.; Liang, Wan-Zhen; Prezhdo, Oleg V.

    2010-03-01

    Phonon-induced pure dephasing of electronic excitations in silver quantum dots (QDs) is investigated with ab initio molecular dynamics at ambient and low temperatures. Three types of electronic states are studied corresponding to bulk, surface, and plasmon excitations. The electron-phonon coupling is strongest for bulk states and decreases for surface and plasmon states. The plasmon states dephase within 30-40 fs, which is consistent with the recent experiments [M. Z. Liu, M. Pelton, and P. Guyot-Sionnest, Phys. Rev. B 79, 035418 (2009)]. The dephasing time shows weak dependence on the QD size but changes significantly with temperature. The bulk, surface, and plasmon states couple primarily to low-frequency acoustic phonons.

  2. Magnetic control of dipolaritons in quantum dots.

    PubMed

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

    2016-12-21

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

  3. Quantum dot at a Luttinger liquid edge

    NASA Astrophysics Data System (ADS)

    Rylands, Colin; Andrei, Natan

    2017-09-01

    We study a system consisting of a Luttinger liquid coupled to a quantum dot on the boundary. The Luttinger liquid is expressed in terms of fermions interacting via density-density coupling, and the dot is modeled as an interacting resonant level onto which the bulk fermions can tunnel. We solve the Hamiltonian exactly and construct all eigenstates. We study both the zero- and finite-temperature properties of the system, in particular, we compute the exact dot occupation as a function of the dot energy in all parameter regimes. The system is seen to flow from weak to strong coupling for all values of the bulk interaction, with the flow characterized by a nonperturbative Kondo scale. We identify the critical exponents at the weak- and strong-coupling regimes.

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

    SciTech Connect

    Yakar, Y.; Özmen, A. Çakır, B.

    2016-03-25

    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.

  5. Electrostatically confined trilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; Vasilopoulos, P.; Peeters, F. M.

    2017-04-01

    Electrically gating of trilayer graphene (TLG) opens a band gap offering the possibility to electrically engineer TLG quantum dots. We study the energy levels of such quantum dots and investigate their dependence on a perpendicular magnetic field B and different types of stacking of the graphene layers. The dots are modeled as circular and confined by a truncated parabolic potential which can be realized by nanostructured gates or position-dependent doping. The energy spectra exhibit the intervalley symmetry EKe(m ) =-EK'h(m ) for the electron (e ) and hole (h ) states, where m is the angular momentum quantum number and K and K ' label the two valleys. The electron and hole spectra for B =0 are twofold degenerate due to the intervalley symmetry EK(m ) =EK'[-(m +1 ) ] . For both ABC [α =1.5 (1.2) for large (small) R ] and ABA (α =1 ) stackings, the lowest-energy levels show approximately a R-α dependence on the dot radius R in contrast with the 1 /R3 one for ABC-stacked dots with infinite-mass boundary. As functions of the field B , the oscillator strengths for dipole-allowed transitions differ drastically for the two types of stackings.

  6. 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.

  7. 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.

  8. Spin Wigner molecules in quantum dots

    NASA Astrophysics Data System (ADS)

    Zutic, Igor; Oszwaldowski, Rafal; Stano, Peter; Petukhov, A. G.

    2013-03-01

    The interplay of confinement and Coulomb interactions in quantum dots can lead to strongly correlated phases differing qualitatively from the Fermi liquid behavior. While in three dimensions the correlation-induced Wigner crystal is elusive and expected only in the limit of an extremely low carrier density, its nanoscale analog, the Wigner molecule, has been observed in quantum dots at much higher densities [1]. We explore how the presence of magnetic impurities in quantum dots can provide additional opportunities to study correlation effects and the resulting ordering in carrier and impurity spins[2]. By employing exact diagonalization we reveal that seemingly simple two-carrier quantum dots lead to a rich phase diagram [2,3]. We propose experiments to verify our predictions; in particular, we discuss interband optical transitions as a function of temperature and magnetic field. DOE-BES, meta-QUTE 259 ITMS NFP Grant No. 26240120022, CE SAS QUTE, EU 260 Project Q-essence, Grant No. APVV-0646-10, and SCIEX.

  9. Photo physical studies of PVP arrested ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Shahi, Ashutosh Kumar; Pandey, Bishnu Kumar; Singh, Bheeshma Pratap; Gupta, Bipin Kumar; Singh, Sukhvir; Gopal, Ram

    2017-03-01

    Monodispersed polyvinylpyrrolidone (PVP) arrested ZnS quantum dots (QDs) having diameter in range 2-5 nm are synthesized by a colloidal precipitation method using PVP as the stabilizing agent. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selective area electron diffraction (SAED) and Fourier transform infrared (FT-IR) spectroscopy are probed to investigate the structural information. The optical properties are studied using diffuse UV-visible reflectance and photoluminescence (PL) spectroscopy techniques. TEM images as well as XRD reflection peak broadening indicate the nanometer size particles formation with cubic (sphalerite) phase within the polymer matrix. Optical absorbance studies reveal an excitonic peak at around 310 nm dictates the effect of quantum confinement effect in the ZnS QDs. PL emission spectra for ZnS QDs in PVP exhibit four emission peaks at 382 nm, 414 nm, 480 nm and 527 nm are observed. These excitonic emissions from ZnS QDs are caused by the interstitial sulfur/Zn vacancies and surface states.

  10. Photo physical studies of PVP arrested ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Shahi, Ashutosh Kumar; Pandey, Bishnu Kumar; Singh, Bheeshma Pratap; Gupta, Bipin Kumar; Singh, Sukhvir; Gopal, Ram

    2016-12-01

    Monodispersed polyvinylpyrrolidone (PVP) arrested ZnS quantum dots (QDs) having diameter in range 2-5 nm are synthesized by a colloidal precipitation method using PVP as the stabilizing agent. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selective area electron diffraction (SAED) and Fourier transform infrared (FT-IR) spectroscopy are probed to investigate the structural information. The optical properties are studied using diffuse UV-visible reflectance and photoluminescence (PL) spectroscopy techniques. TEM images as well as XRD reflection peak broadening indicate the nanometer size particles formation with cubic (sphalerite) phase within the polymer matrix. Optical absorbance studies reveal an excitonic peak at around 310 nm dictates the effect of quantum confinement effect in the ZnS QDs. PL emission spectra for ZnS QDs in PVP exhibit four emission peaks at 382 nm, 414 nm, 480 nm and 527 nm are observed. These excitonic emissions from ZnS QDs are caused by the interstitial sulfur/Zn vacancies and surface states.

  11. 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)

  12. Surface photovoltage spectroscopy study of InAs quantum dot in quantum well multilayer structures for infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Donchev, V.; Ivanov, Ts.; Ivanova, Ts.; Mathews, S.; Kim, J. O.; Krishna, S.

    2015-12-01

    Inter-band optical transitions in InAs submonolayer and Stranski-Krastanov quantum dot (QD) in quantum well (QW) nanostructures are studied by means of room temperature surface photovoltage (SPV) spectroscopy taking advantage of its high sensitivity and contactless nature. The QD optical transitions are identified by the combined analysis of SPV amplitude and phase spectra and are in agreement with photoluminescence results. The SPV spectra have further revealed the optical transitions in all other relevant layers in the structures - wetting layer, QWs, and AlGaAs barriers. The analysis of the SPV phase spectra has revealed that the carrier separation and transport in the QD structure is determined by the energy band bending, resulting from the slight residual p-type doping. The complicated interaction between the SPV signals from the nanostructure and the semi-insulating GaAs substrate is discussed and clarified. The advantages of the SPV spectroscopy for characterizing complicated nanostructures at room temperature are highlighted.

  13. Optophononics with Coupled Quantum Dots

    DTIC Science & Technology

    2014-02-18

    the molecular polaron can be used as an efficient and tunable coherent coupler for quantum states in spatially separated low-dimensional structures...cold finger of a closed cycle microscopy cryostat and kept at a temperature of 20K. A tunable diode laser with a tuning range from about 900 to 1,000...et al. Tunable exciton relaxation in vertically coupled semiconductor InAs quantum dots. Phys. Rev. B 84, 081404(R) (2011). 10 100 1,000 0 5 A m pl ifi

  14. Size dependent magnetic and optical properties in diamond shaped graphene quantum dots: A DFT study

    NASA Astrophysics Data System (ADS)

    Das, Ritwika; Dhar, Namrata; Bandyopadhyay, Arka; Jana, Debnarayan

    2016-12-01

    The magnetic and optical properties of diamond shaped graphene quantum dots (DSGQDs) have been investigated by varying their sizes with the help of density functional theory (DFT). The study of density of states (DOS) has revealed that the Fermi energy decreases with increase in sizes (number of carbon atoms). The intermediate structure with 30 carbon atoms shows the highest magnetic moment (8 μB, μB being the Bohr magneton). The shifting of optical transitions to higher energy in smallest DSGQD (16 carbon atoms) bears the signature of stronger quantum confinement. However, for the largest structure (48 carbon atoms) multiple broad peaks appear in case of parallel polarization and in this case electron energy loss spectra (EELS) peak (in the energy range 0-5 eV) is sharp in nature (compared to high energy peak). This may be attributed to π plasmon and the broad peak (in the range 10-16 eV) corresponds to π + σ plasmon. A detail calculation of the Raman spectra has indicated some prominent mode of vibrations which can be used to characterize these structures (with hydrogen terminated dangling bonds). We think that these theoretical observations can be utilized for novel device designs involving DSGQDs.

  15. Ultralow Noise Monolithic Quantum Dot Photonic Oscillators

    DTIC Science & Technology

    2013-10-28

    laser, the dual-mode quantum dot laser, and the optically- injected quantum dot distributed feedback laser. The key milestones achieved were: 1.) the...distributed feedback device using optical injection to generate microwave, mm- wave and THz signals, and 5.) the generation of relaxation oscillations over...a continuous 5 octaves (below 1 GHz to 40 GHz) in an optically- injected quantum dot laser. UU N/A N/A N/A 100-200 words 15 Shannon Denetchiley (505

  16. 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.

  17. Solution-processed colloidal lead sulfide quantum dots for near-infrared quantum information processing applications

    NASA Astrophysics Data System (ADS)

    Bose, Ranojoy

    In this thesis, we study solution-processed lead sulfide quantum dots for near-infrared quantum information and communication applications. Quantum dots processed through synthetic routes and colloidally suspended in solution offer far-reaching device application possibilities that are unparalelled in traditional self-assembled quantum dots. Lead sulfide quantum dots are especially promising for near-infrared quantum optics due to their optical emission at the wavelengths of fiber-optic communications (1.3--1.5 microm). The broad absorption spectrum of these quantum dots can be used for solar light-harvesting applications, to which end the results of Chapter 2---where we study Forster resonance energy transfer in quantum dot solids---provide remarkable insights into photon emission from quantum-dot based solar cells. In subsequent chapters, we explore quantum-dot photonic crystal applications, where exciton-photon interactions in the cavity environment remarkably allow for the emission of indistinguishable single photons that are important for distribution of high-security quantum keys---being highly sensitive to 'eavesdropping'. Particularly, the suggestion of the solution-processed QED system is novel compared to traditional self-assembled systems, and as we will discuss, offer integration and processing capabilities that are unprecedented, and perform well at wavelength ranges where standard QED systems scale poorly. The results of chapters 3--6 are therefore significant in the general field of cavity quantum electrodynamics.

  18. Interaction of porphyrins with CdTe quantum dots.

    PubMed

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

    2011-05-13

    Porphyrins may be used as photosensitizers for photodynamic therapy, photocatalysts for organic pollutant dissociation, agents for medical imaging and diagnostics, applications in luminescence and electronics. The detection of porphyrins is significantly important and here the interaction of protoporphyrin-IX (PPIX) with CdTe quantum dots was studied. It was observed that the luminescence of CdTe quantum dots was quenched dramatically in the presence of PPIX. When CdTe quantum dots were embedded into silica layers, almost no quenching by PPIX was observed. This indicates that PPIX may interact and alter CdTe quantum dots and thus quench their luminescence. The oxidation of the stabilizers such as thioglycolic acid (TGA) as well as the nanoparticles by the singlet oxygen generated from PPIX is most likely responsible for the luminescence quenching. The quenching of quantum dot luminescence by porphyrins may provide a new method for photosensitizer detection.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  1. Study of alloy disorder in quantum dots through multi-million atom simulations

    NASA Technical Reports Server (NTRS)

    Kilmeck, Gerhard; Oyafuso, Fabiano; Boykin, T. B.; Bowen, R. C.; von Allmen, Paul A.

    2003-01-01

    A tight binding model which includes s, p, d, s orbitals is used to examine the electronic structures of an ensemble of dome-shaped In0.6 Ga0.4 As quantum dots. Given ensembles of identically sized quantum dots, variations in composition and configuration yield a linewidth broadening of less than 0.35 meV, much smaller than the total broadening determined from photoluminescence experiments. It is also found that the computed disorder-induced broadening is very sensitive to the applied boundary conditions, so that care must be taken to ensure proper convergence of the numerical results. Examination of local eigenenergies as functions of position shows similar convergence problems and indicates that an inaccurate resolution of the equilibrium atomic positions due to truncation of the simulation domain may be the source of the slow ground state convergence.

  2. Study of alloy disorder in quantum dots through multi-million atom simulations

    NASA Technical Reports Server (NTRS)

    Kilmeck, Gerhard; Oyafuso, Fabiano; Boykin, T. B.; Bowen, R. C.; von Allmen, Paul A.

    2003-01-01

    A tight binding model which includes s, p, d, s orbitals is used to examine the electronic structures of an ensemble of dome-shaped In0.6 Ga0.4 As quantum dots. Given ensembles of identically sized quantum dots, variations in composition and configuration yield a linewidth broadening of less than 0.35 meV, much smaller than the total broadening determined from photoluminescence experiments. It is also found that the computed disorder-induced broadening is very sensitive to the applied boundary conditions, so that care must be taken to ensure proper convergence of the numerical results. Examination of local eigenenergies as functions of position shows similar convergence problems and indicates that an inaccurate resolution of the equilibrium atomic positions due to truncation of the simulation domain may be the source of the slow ground state convergence.

  3. High excitation power photoluminescence studies of ultra-low density GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Sonnenberg, D.; Graf, A.; Paulava, V.; Heyn, Ch.; Hansen, W.

    2013-12-01

    We fabricate GaAs epitaxial quantum dots (QDs) by filling of self-organized nanoholes in AlGaAs. The QDs are fabricated under optimized process conditions and have ultra-low density in the 106 cm-2 regime. At low excitation power the optical emission of single QDs exhibit sharp excitonic lines, which are attributed to the recombination of excitonic and biexcitonic states. High excitation power measurements reveal surprisingly broad emission lines from at least six QD shell states.

  4. Colloidal quantum dots as optoelectronic elements

    NASA Astrophysics Data System (ADS)

    Vasudev, Milana; Yamanaka, Takayuki; Sun, Ke; Li, Yang; Yang, Jianyong; Ramadurai, Dinakar; Stroscio, Michael A.; Dutta, Mitra

    2007-02-01

    Novel optoelectronic systems based on ensembles of semiconductor nanocrystals are addressed in this paper. Colloidal semiconductor quantum dots and related quantum-wire structures have been characterized optically; these optical measurements include those made on self-assembled monolayers of DNA molecules terminated on one end with a common substrate and on the other end with TiO II quantum dots. The electronic properties of these structures are modeled and compared with experiment. The characterization and application of ensembles of colloidal quantum dots with molecular interconnects are considered. The chemically-directed assembly of ensembles of colloidal quantum dots with biomolecular interconnects is demonstrated with quantum dot densities in excess of 10 +17 cm -3. A number of novel photodetectors have been designed based on the combined use of double-barrier quantum-well injectors, colloidal quantum dots, and conductive polymers. Optoelectronic devices including photodetectors and solar cells based on threedimensional ensembles of quantum dots are considered along with underlying phenomena such as miniband formation and the robustness of minibands to displacements of quantum dots in the ensemble.

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

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  6. Andreev molecules in semiconductor nanowire double quantum dots.

    PubMed

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

    2017-09-19

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

  7. Electromechanical transition in quantum dots

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  8. 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.

  9. Photon echo in the ensemble of semiconductor quantum dots spread on a glass substrate

    NASA Astrophysics Data System (ADS)

    Karimullin, K. R.; Knyazev, M. V.; Arzhanov, A. I.; Nurtdinova, L. A.; Naumov, A. V.

    2017-06-01

    Simple procedure to prepare samples containing semiconductor quantum dots was developed. Test photon echo measurements in the ensemble of quantum dots spread on a glass substrate were performed to study optical dephasing processes.

  10. 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.

  11. The statistical theory of quantum dots

    NASA Astrophysics Data System (ADS)

    Alhassid, Y.

    2000-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  13. Photovoltaic Current in Quantum Dots

    NASA Astrophysics Data System (ADS)

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

    1998-03-01

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

  14. Optical and Surface Characterization Studies of CdSe Quantum Dots Undergoing Photooxidation

    NASA Astrophysics Data System (ADS)

    Powell, Lauren C. J.

    Realization of the potential of Quantum Dots (QDs) for biological, energy-efficient lighting and energy harvesting applications requires that their long-term photostability be improved, especially with regards to protection from photooxidation. The overarching objective of this project was the determination of the chemical and physical mechanisms of photooxidation of CdSe QDs. Pittsburgh-based Crystalplex, Inc. provided CdSe QDs with different organic ligands for this research. Three integrated in situ and ex situ characterization techniques were used to observe changes in optical behavior, QD morphology, and surface chemistry during photooxidation conditions. Single-molecule fluorescence microscopy experiments were used to observe real-time changes in the photoluminescence (PL) behavior of single QDs with oleic and lauric acid ligands. The QDs are exposed to 1 atm of pure O2, dry Ar, Ar bubbled through DI water, or air in an environmental chamber and excited with a 488 nm light. Changes in PL intensities were analyzed with respect to the periods of exposure to controlled atmospheres and light. Samples illuminated continuously exhibited strong photoenhancement effects, while those kept in the dark showed atmospheric-dependent PL loss. Microstructural and chemical identification was performed with aberration-corrected transmission electron microscopy (TEM). Ex situ exposures of QD samples to air, dry O2, and dry Ar revealed changes in surface oxide growth with respect to exposure length, illumination, and column vacuum pressure. Samples exposed to air and light exhibited the most extensive photooxidation. Quantum dots with oleic acid ligands were treated with UV/ozone plasma, and extensive degradation of QDs was observed. X-ray photoemission spectroscopy (XPS) measurements at CMU were used to identify the chemical and bonding states of the surface species before and after photooxidation. Analysis of the acquired spectra showed that exposure to below-bandgap light

  15. Ferric oxide quantum dots in stable phosphate glass system and their magneto-optical study

    SciTech Connect

    Garaje, Sunil N.; Apte, Sanjay K.; Kumar, Ganpathy; Panmand, Rajendra P.; Naik, Sonali D.; Mahajan, Satish M.; Chand, Ramesh; Kale, Bharat B.

    2013-02-15

    Graphical abstract: We report synthesis of ferric oxide embedded low melting phosphate glass nanocomposite and also the effect of ferric oxide nanoparticles (NCs) content on the optical and magneto-optical properties of the glasses. Faraday rotation of the glass nanocomposites was measured and showed variation in Verdet constant with concentration of ferric oxide. Interestingly, the host glass itself showed fairly good Verdet constant (11.5°/T cm) and there is a threefold enhancement in the Verdet constant of ferric oxide quantum dot-glass nanocomposite. Highlights: ► We synthesize ferric oxide embedded low melting stable phosphate glass nanocomposite. ► Glasses doped with 0.25 and 2% ferric oxide show particle size in the range of 4–12 nm. ► The host phosphate glass itself shows fairly good Verdet constant (11.5°/T cm). ► Glasses doped with 0.25% ferric oxide show high Verdet constant (30.525°/T cm). ► The as synthesis glasses may have potential application in magneto optical devices. -- Abstract: Herein, we report the synthesis of ferric oxide embedded low melting phosphate glass nanocomposite and also the effect of ferric oxide nanoparticles content on the optical and magneto-optical properties of the glasses. The optical study clearly showed red shift in optical cut off with increasing ferric oxide concentration. The band gap of the host glass was observed to be 3.48 eV and it shifted to 3.14 eV after doping with ferric oxide. The glasses doped with 0.25 and 2% ferric oxide showed particle size of 4–6 nm and 8–12 nm, respectively. Faraday rotation of the glass nanocomposites was measured and showed variation in the Verdet constant as per increasing concentration of ferric oxide. Interestingly, the host glass itself showed fairly good Verdet constant (11.5°/T cm) and threefold enhancement was observed in the Verdet constant of ferric oxide quantum dot-glass nanocomposite.

  16. Electron Spin Qubits in Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eriksson, Mark

    2010-10-01

    It is intriguing that silicon, the central material of modern classical electronics, also has properties well suited to quantum electronics. Recent advances in Si/SiGe quantum devices have enabled the creation of high-quality silicon quantum dots, also known as artificial atoms. Motivated in part by the potential for very long spin coherence times in this material, we are pursuing the development of individual electron spin qubits in silicon quantum dots. I will discuss recent demonstrations of single-shot spin measurement in a Si/SiGe quantum dot spin qubit, and the demonstration of spin-relaxation times longer than one second in such a system. These and similar measurements depend on a knowledge of tunnel rates between quantum dots and nearby reservoirs or between pairs of quantum dots. Measurements of such rates provide an opportunity to revisit classic experiments in quantum mechanics. At the same time, the unique features of the silicon conduction band lead to novel and unexpected effects, demonstrating that Si/SiGe quantum dots provide a highly controlled experimental system in which to study ideas at the heart of quantum physics.

  17. First principles DFT study of dye-sensitized CdS quantum dots

    SciTech Connect

    Jain, Kalpna; Singh, Kh. S.; Kishor, Shyam; Josefesson, Ida; Odelius, Michael; Ramaniah, Lavanya M.

    2014-04-24

    Dye-sensitized quantum dots (QDs) are considered promising candidates for dye-sensitized solar cells. In order to maximize their efficiency, detailed theoretical studies are important. Here, we report a first principles density functional theory (DFT) investigation of experimentally realized dye - sensitized QD / ligand systems, viz., Cd{sub 16}S{sub 16}, capped with acetate molecules and a coumarin dye. The hybrid B3LYP functional and a 6−311+G(d,p)/LANL2dz basis set are used to study the geometric, energetic and electronic properties of these clusters. There is significant structural rearrangement in all the clusters studied - on the surface for the bare QD, and in the positions of the acetate / dye ligands for the ligated QDs. The density of states (DOS) of the bare QD shows states in the band gap, which disappear on surface passivation with the acetate molecules. Interestingly, in the dye-sensitised QD, the HOMO is found to be localized mainly on the dye molecule, while the LUMO is on the QD, as required for photo-induced electron injection from the dye to the QD.

  18. Computational study of dielectric function and optical properties of a graphane nano structure containing graphene quantum dot

    NASA Astrophysics Data System (ADS)

    Dhar Sharma, Jyoti; Sharma, Munish; Kumar, Naveen; Ahluwalia, P. K.

    2013-11-01

    Ab-Initio computational study of dielectric function and optical properties of a graphane nano structure containing graphene quantum dot has been undertaken within Density Functional Theory using SIESTA code. Band structure, PDOS, real and imaginary parts of dielectric function, reflectance and energy loss have been calculated and frequencies corresponding to peak positions have been tabulated for each case. A comparison has been made with the corresponding properties of pristine graphene.

  19. Nanoscale optimization of quantum dot solar sells

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  20. 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.

  1. Development of Quantum Dot Probes for Studies of Synergy Between Components of the Wood-Degrading Fungal Enzymes

    SciTech Connect

    Yang, Haw; Nixon, B. Tracy; Tien, Ming

    2011-09-01

    “Development of Quantum Dot Probes for Studies of Synergy Between Components of the Wood-Degrading Fungal Enzymes,” aims to develop quantum dot-based tagging and imaging technologies tailored for simultaneously monitoring, in real time and in the natural fungal / lignocellulose environment, the mode of action of several lignocellulosic enzymes at the single-molecule level. With a three-year research scope, it is designed to be the first project of a long-term research program for which the overarching goal is to bridge the aforementioned knowledge gap by a quantitative determination of the biochemical and biophysical properties of these fungal enzymes in realistic plant biomass-microbe milieus.

  2. Application of non-extensive entropy to study of decoherence of RbCl quantum dot qubit: Tsallis entropy

    NASA Astrophysics Data System (ADS)

    Khordad, R.; Rastegar Sedehi, H. R.

    2017-01-01

    In this work, an electron which is strongly coupled to the LO-phonon in triangular quantum dots with Coulomb impurity is considered. The eigenenergies and eigenfunctions of the ground and the first-excited states of the electron are obtained using the Pekar variational method. We have studied decoherence of RbCl quantum dot qubit using the non-extensive entropy (Tsallis entropy) for different values of Coulomb impurity parameter, polaronic radius and electron-LO phonon coupling strength. Numerical analysis shows that the entropy has the oscillatory periodic evolution as function of the time due to the triangular form of the confinement. It is found that entropy oscillates under a standing wave envelope with increasing the Coulomb impurity parameter, electron-LO phonon coupling strength and polaronic radius. With reducing the non-extensive parameter q, the entropy increases and thereby we can miss information about the system.

  3. Study of conduction mechanism and electroluminescence in CdSe/ZnS quantum dot composites

    NASA Astrophysics Data System (ADS)

    Hikmet, R. A. M.; Talapin, D. V.; Weller, H.

    2003-03-01

    Charge transport and electroluminesence properties of colloidally synthesized CdSe/ZnS core-shell nanocrystal quantum dots (QDs) were studied. Nanocrystals were prepared using the conventional technique of pyrolisis of organometallic reagents in a hot coordinating solvent medium. Thin film diodes were produced by depositing a layer of QDs on top of a layer of conducting polymer poly (3,4-ethylenedioxythiophene): polystyrenesulfonate followed by the deposition of a metal electrode. For all the metals used in this study only a small rectification could be observed upon reversing the bias. The efficiency of the light generation showed strong dependence on the work function and bias of the metal electrodes, indicating that light generation in these devices is a result of recombination of injected holes and electrons. Assuming that the charge transport is due mainly to electrons, the voltage dependence of the current in QD composites could be explained by space charge limited current (SCLC) in the presence of defects. At sufficiently high voltages the traps could be filled and a quadratic dependence of current on voltage, characteristic of trap free SCLC, could be observed. The mobility and the trap density were estimated to be μn=1.5×10-10 m2/V s and Nt=8×1023 m-3, respectively, and the characteristic trap depth was estimated to be around 0.15 eV.

  4. A fluorescence microscopy study of quantum dots as fluorescent probes for brain tumor diagnosis

    NASA Astrophysics Data System (ADS)

    Wang, Jingjing; Vernier, P. Thomas; Sun, Yinghua; Gundersen, Martin A.; Marcu, Laura

    2005-03-01

    In vivo fluorescent spectroscopy and imaging using endogenous and exogenous sources of contrast can provide new approaches for enhanced demarcation of brain tumor margins and infiltration. Quantum dots (QDs), nanometer-size fluorescent probes, represent excellent contrast agents for biomedical imaging due to their broader excitation spectrum, narrower emission spectra, and higher sensitivity and stability. The epidermal growth factor receptor (EGFR) is implicated in the development and progression of a number of human solid tumors including brain tumors and thus a potential target for brain tumor diagnosis. In this study, we investigate the up-take of ODs by brain tumor cells and the potential use of EGFR-targeted QDs for enhanced optical imaging of brain tumors. We conducted fluorescence microscopy studies of the up-take mechanism of the anti-EGFR-ODs complexes by Human U87, and SKMG-3 glioblastoma cells. Our preliminary results show that QDs can enter into glioma cells through anti-EGFR mediated endocytosis, suggesting that these nano-size particles can tag brain tumor cells.

  5. Studying nanotoxic effects of CdTe quantum dots in Trypanosoma cruzi.

    PubMed

    Vieira, Cecilia Stahl; Almeida, Diogo Burigo; de Thomaz, André Alexandre; Menna-Barreto, Rubem Figueredo Sadok; dos Santos-Mallet, Jacenir Reis; Cesar, Carlos Lenz; Gomes, Suzete Araujo Oliveira; Feder, Denise

    2011-03-01

    Semiconductor nanoparticles, such as quantum dots (QDs), were used to carry out experiments in vivo and ex vivo with Trypanosoma cruzi. However, questions have been raised regarding the nanotoxicity of QDs in living cells, microorganisms, tissues and whole animals. The objective of this paper was to conduct a QD nanotoxicity study on living T. cruzi protozoa using analytical methods. This was accomplished using in vitro experiments to test the interference of the QDs on parasite development, morphology and viability. Our results show that after 72 h, a 200 μM cadmium telluride (CdTe) QD solution induced important morphological alterations in T. cruzi, such as DNA damage, plasma membrane blebbing and mitochondrial swelling. Flow cytometry assays showed no damage to the plasma membrane when incubated with 200 μM CdTe QDs for up to 72 h (propidium iodide cells), giving no evidence of classical necrosis. Parasites incubated with 2 μM CdTe QDs still proliferated after seven days. In summary, a low concentration of CdTe QDs (2 μM) is optimal for bioimaging, whereas a high concentration (200 μM CdTe) could be toxic to cells. Taken together, our data indicate that 2 μM QD can be used for the successful long-term study of the parasite-vector interaction in real time.

  6. 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.

  7. Thick-shell nanocrystal quantum dots

    SciTech Connect

    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.

  8. 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.

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

    PubMed

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

    2008-04-16

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

  10. Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots

    NASA Astrophysics Data System (ADS)

    Unni, C.; Philip, Daizy; Gopchandran, K. G.

    2008-12-01

    Nanoparticles of CdS were prepared at 303 K by aqueous precipitation method using CdSO 4 and (NH 4) 2S in presence of the stabilizing agent thioglycerol. Adjustment of the thioglycerol (T) to ammonium sulphide (A) ratio (T:A) from 1:25 to 1:3.3 was done during synthesis and nanoparticles of different size were obtained. The prepared colloids were characterized by UV-vis and photoluminescence (PL) spectroscopic studies. Prominent first and second excitonic transitions are observed in the UV-vis spectrum of the colloid prepared with a T:A ratio of 1:3.3. Particle size analysis was done using XRD, high resolution TEM and dynamic light scattering and found to be ˜3 nm. UV-vis and PL spectral features also agree with this particle size in colloid with T:A of 1:3.3. The band gap of CdS quantum dots has increased from the bulk value 2.4-2.9 eV. PL spectra show quantum size effect and the peak is shifted from 628 to 556 nm when the ratio of T:A was changed from 1:25 to 1:3.3. Doping of CdS with Zn 2+ and Cu 2+ is found to enhance the PL intensity. PL band shows blue-shift and red-shift on doping with Zn 2+ and Cu 2+, respectively. UV and PL spectral features of the CdS/Au hybrid nanoparticles obtained by a physical mixing of CdS and Au nanoclusters in various volume ratios is also discussed. Au red-shifts and rapidly quenches the PL of CdS. An additional low energy band ˜650 nm is observed in the UV visible spectrum of the hybrid nanoparticles.

  11. Cytotoxicity and fluorescence studies of silica-coated CdSe quantum dots for bioimaging applications

    NASA Astrophysics Data System (ADS)

    Vibin, Muthunayagam; Vinayakan, Ramachandran; John, Annie; Raji, Vijayamma; Rejiya, Chellappan S.; Vinesh, Naresh S.; Abraham, Annie

    2011-06-01

    The toxicological effects of silica-coated CdSe quantum dots (QDs) were investigated systematically on human cervical cancer cell line. Trioctylphosphine oxide capped CdSe QDs were synthesized and rendered water soluble by overcoating with silica, using aminopropyl silane as silica precursor. The cytotoxicity studies were conducted by exposing cells to freshly synthesized QDs as a function of time (0-72 h) and concentration up to micromolar level by Lactate dehydrogenase assay, MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay, Neutral red cell viability assay, Trypan blue dye exclusion method and morphological examination of cells using phase contrast microscope. The in vitro analysis results showed that the silica-coated CdSe QDs were nontoxic even at higher loadings. Subsequently the in vivo fluorescence was also demonstrated by intravenous administration of the QDs in Swiss albino mice. The fluorescence images in the cryosections of tissues depicted strong luminescence property of silica-coated QDs under biological conditions. These results confirmed the role of these luminescent materials in biological labeling and imaging applications.

  12. Surface studies of gallium nitride quantum dots grown using droplet epitaxy on bulk, native substrates

    NASA Astrophysics Data System (ADS)

    Jones, Christina; Jeon, Sunyeol; Goldman, Rachel; Yacoby, Yizhak; Clarke, Roy

    Gallium nitride (GaN) and its applications in light-emitting diodes play an integral part in efficient, solid-state lighting, as evidenced by its recognition in the 2014 Nobel prize in physics. In order to push this technology towards higher efficiency and reliability and lower cost, we must understand device growth on bulk GaN substrates, which have lower defect densities and strain than template GaN substrates grown on sapphire. In this work, we present our findings on the surface properties of GaN quantum dots (QDs) grown on commercial bulk GaN. QDs are grown using the droplet epitaxy method and analyzed using a surface X-ray diffraction technique called Coherent Bragg Rod Analysis (COBRA), which uses phase retrieval to reconstruct atomic positions near the substrate surface. While several QD growth conditions in our study produce dense QDs, COBRA reveals that only low nitridation temperatures result in GaN QDs that are coherent with the bulk GaN substrate. Results are supported with atomic force microscopy and high-resolution transmission electron microscopy.

  13. Surface chemistry of InP quantum dots: a comprehensive study.

    PubMed

    Cros-Gagneux, Arnaud; Delpech, Fabien; Nayral, Céline; Cornejo, Alfonso; Coppel, Yannick; Chaudret, Bruno

    2010-12-29

    Advanced (1)H, (13)C, and (31)P solution and solid-state NMR studies combined with IR spectroscopy were used to probe, at the molecular scale, the composition and the surface chemistry of indium phosphide (InP) quantum dots (QDs) prepared via a non-coordinating solvent strategy. This nanomaterial can be described as a core-multishell object: an InP core, with a zinc blende bulk structure, is surrounded first by a partially oxidized surface shell, which is itself surrounded by an organic coating. This organic passivating layer is composed, in the first coordination sphere, of tightly bound palmitate ligands which display two different bonding modes. A second coordination sphere includes an unexpected dialkyl ketone and residual long-chain non-coordinating solvents (ODE and its isomers) which interact through weak intermolecular bonds with the alkyl chains of the carboxylate ligands. We show that this ketone is formed during the synthesis process via a decarboxylative coupling route and provides oxidative conditions which are responsible for the oxidation of the InP core surface. This phenomenon has a significant impact on the photoluminescence properties of the as-synthesized QDs and probably accounts for the failure of further growth of the InP core.

  14. Transport studies of quantum dots sensitized single Mn-ZnO nanowire field effect transistors

    NASA Astrophysics Data System (ADS)

    Sapkota, Keshab R.; Maloney, Francis Scott; Rimal, Gaurab; Poudyal, Uma; Tang, Jinke; Wang, Wenyong

    We present opto-electrical transport properties of Mn-CdSe quantum dots (QDs) sensitized single Mn-ZnO nanowire (NW) field effect transistors (FET). The ZnO NWs with 2 atomic % of Mn doping are grown by chemical vapor deposition. The NWs are ferromagnetic at low temperature. The as grown nanowires are transferred to clean SiO2/Si substrate and single nanowire field effect transistors (FET) are fabricated by standard e-beam lithography. Mobility and carrier concentration of Mn-ZnO NWs are estimated from FET device measurement which shows NWs are n-type semiconductors. Pulse laser deposition of Mn-CdSe QDs on the single NW FET significantly increases carrier concentration of the QD-NW system in dark where the QD monolayer conduction is negligibly small. The photoconductivity study of QD sensitized NW FET enlightens the conduction spectrum of QD-NW system and QD to NW carrier transfer mechanism. This work has been supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-10ER46728.

  15. Application of different entropies to study of bound magnetopolaron in an asymmetric quantum dot

    NASA Astrophysics Data System (ADS)

    Khordad, R.; Sedehi, H. R. Rastegar

    2017-02-01

    An electron strongly coupled to the LO-phonon in an asymmetric quantum dot has been considered. The system has a central impurity and it is under electric and magnetic fields. The eigenenergies and eigenfunctions of the ground and the first-excited states of the electron have been calculated using the Pekar variational method. Entropy of the system for different values of Coulomb impurity parameter, electron-LO phonon coupling strength, dispersion coefficient and electric field have been studied. Two entropies, Shannon and Gaussian entropy have been employed. It is found that the entropy has the oscillatory periodic evolution as function of the time due to the confinement form. It is deduced that the entropies increase with enhancing Coulomb impurity parameter, electron-LO phonon coupling strength and dispersion coefficient. With increasing electron-LO phonon coupling strength, the entropies decrease. The control of the coherence of the system can be done with the modulation of the electric field, the Coulomb bound potential, dispersion coefficient and electron-LO phonon coupling strength.

  16. Degradation products from consumer nanocomposites: a case study on quantum dot lighting.

    PubMed

    Liu, Jingyu; Katahara, John; Li, Guanglai; Coe-Sullivan, Seth; Hurt, Robert H

    2012-03-20

    Most nanomaterials enter the natural environment as nanoenabled products, which are typically composites with primary nanoparticles bound on substrates or embedded in liquid or solid matrices. The environmental risks associated with these products are expected to differ from those associated with the as-produced particles. This article presents a case study on the end-of-life emission of a commercial prototype polymer/quantum-dot (QD) composite used in solid-state lighting for homes. We report the extent of cadmium release upon exposure to a series of environmental and biological simulant fluids, and track the loss of QD-characteristic fluorescence as a marker for chemical damage to the CdSe/ZnS nanoparticles. Measured cadmium releases after 30-day exposure range from 0.007 to 1.2 mg/g of polymer, and the higher values arise for low-pH simulants containing nitric or gastric acid. Centrifugal ultrafiltration and ICP was used to distinguish soluble cadmium from particulate forms. The leachate is found to contain soluble metals with no evidence of free QDs or QD-containing polymeric debris. The absence of free nanoparticles suggests that this product does not raise nanotechnology-specific environmental issues associated with degradation and leaching, but is more usefully regarded as a conventional chemical product that is a potential source of small amounts of soluble cadmium.

  17. Degradation products from consumer nanocomposites - a case study on quantum dot lighting

    PubMed Central

    Liu, Jingyu; Katahara, John; Li, Guanglai; Coe-Sullivan, Seth; Hurt, Robert H.

    2012-01-01

    Most nanomaterials enter the natural environment as nano-enabled products, which are typically composites with primary nanoparticles bound on substrates or embedded in liquid or solid matrices. The environmental risks associated with these products are expected to differ from those associated with the as-produced particles. This article presents a case study on the end-of-life emission of a commercial prototype polymer/quantum-dot (QD) composite used in solid-state lighting for homes. We report the extent of cadmium release upon exposure to a series of environmental and biological simulant fluids, and track the loss of QD-characteristic fluorescence as a marker for chemical damage to the CdSe/ZnS nanoparticles. Measured cadmium releases after 30-day exposure range from 0.007-1.2 mg/g of polymer, and the higher values arise for low-pH simulants containing nitric or gastric acid. Centrifugal ultrafiltration and ICP was used to distinguish soluble cadmium from particulate forms. The leachate is found to contain soluble metals with no evidence of free QDs or QD-containing polymeric debris. The absence of free nanoparticles suggests that this product does not raise nanotechnology-specific environmental issues associated with degradation and leaching, but is more usefully regarded as a conventional chemical product that is a potential source of small amounts of soluble cadmium. PMID:22352378

  18. Application of different entropies to study of bound magnetopolaron in an asymmetric quantum dot

    NASA Astrophysics Data System (ADS)

    Khordad, R.; Sedehi, H. R. Rastegar

    2017-07-01

    An electron strongly coupled to the LO-phonon in an asymmetric quantum dot has been considered. The system has a central impurity and it is under electric and magnetic fields. The eigenenergies and eigenfunctions of the ground and the first-excited states of the electron have been calculated using the Pekar variational method. Entropy of the system for different values of Coulomb impurity parameter, electron-LO phonon coupling strength, dispersion coefficient and electric field have been studied. Two entropies, Shannon and Gaussian entropy have been employed. It is found that the entropy has the oscillatory periodic evolution as function of the time due to the confinement form. It is deduced that the entropies increase with enhancing Coulomb impurity parameter, electron-LO phonon coupling strength and dispersion coefficient. With increasing electron-LO phonon coupling strength, the entropies decrease. The control of the coherence of the system can be done with the modulation of the electric field, the Coulomb bound potential, dispersion coefficient and electron-LO phonon coupling strength.

  19. High Pressure Raman Spectroscopic Studies on CuInTe2 Quantum Dots

    NASA Astrophysics Data System (ADS)

    Yanxon, Howard; Kumar, Ravhi; HiPSEC-University of Nevada Las Vegas Team

    High pressure Raman spectroscopy studies were performed on CuInTe2 Quantum Dots (QD) up to 7.7 GPa. At ambient conditions, the Raman modes of the QD loaded into a high-pressure diamond anvil cell (DAC) were observed at 125.1 cm-1 (A1 mode) and 142.8 cm-1 (B2 or E mode). As the pressure increases, the A1 mode starts to split above 2 GPa and shifts to the left as indication of a structural change. A pressure-induced phase transition was observed around 2.9 GPa due to the collapse of the modes with the appearance of a new Raman peaks. The phase transition observed in our experiments compare well with the characteristics of bulk and larger nanoparticles. Further, it could be concluded that the phase transition pressure observed mainly depends on the particle size. H.Y. thanks McNair foundation for fellowship award. He also acknowledges Melanie White, Jason Baker and Phuc Tran for help in the experiments. He thanks Michael Pravica for using the Raman facility.

  20. A shotgun proteomic study of the protein corona associated with cholesterol and atheronal-B surface-modified quantum dots.

    PubMed

    Prapainop, Kanlaya; Wentworth, Paul

    2011-04-01

    As part of ongoing research in our group, we are keen to monitor the protein binding and movement of sterols and oxysterols in biological systems in real time. However, prior to performing these in vivo studies, we have herein studied how sterol and oxysterol surface modification of quantum dots affects their associated protein coronas. Thus, we have synthesized and analyzed cholesterol and atheronal-B surface-modified quantum dots (termed QD-chol and QD-ath-B, respectively). The fluorescence properties and aggregation propensities of QD-chol and QD-ath-B are unchanged relative to amino-functionalized quantum dots (QD-NH(2)) in aqueous buffers. Shotgun proteomic analyses of the protein coronas reveal that QD-ath-B and QD-chol are bound significantly higher to LDL, vLDL and HDL particles than QD-NH(2). Thus, almost all the component proteins of the HDL and LDL proteomes are elevated in the protein coronas around the QD-chol and QD-ath-B nanomaterials. In addition, the reduced positive surface charge of the QD-chol and QD-ath-B materials, relative to QD-NH(2), means that hydrophobic antibody light chain fragments and β-2-glycoprotein (apo H) bind them preferentially to QD-NH(2).

  1. Biocompatible Quantum Dots for Biological Applications

    PubMed Central

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

    2011-01-01

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

  2. 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.

  3. Quantum dot-based energy transfer: perspectives and potential for applications in photodynamic therapy.

    PubMed

    Samia, Anna C S; Dayal, Smita; Burda, Clemens

    2006-01-01

    Quantum dots have emerged as an important class of material that offers great promise to a diverse range of applications ranging from energy conversion to biomedicine. Here, we review the potential of using quantum dots and quantum dot conjugates as sensitizers for photodynamic therapy (PDT). The photophysics of singlet oxygen generation in relation to quantum dot-based energy transfer is discussed and the possibility of using quantum dots as photosensitizer in PDT is assessed, including their current limitations to applications in biological systems. The biggest advantage of quantum dots over molecular photosensitizers that comes into perspective is their tunable optical properties and surface chemistries. Recent developments in the preparation and photophysical characterization of quantum dot energy transfer processes are also presented in this review, to provide insights on the future direction of quantum dot-based photosensitization studies from the viewpoint of our ongoing research.

  4. Photoluminescence study of high density Si quantum dots with Ge core

    SciTech Connect

    Kondo, K. Makihara, K.; Ikeda, M.; Miyazaki, S.

    2016-01-21

    Si quantum dots (Si-QDs) with Ge core were self-assembled on thermally grown SiO{sub 2} from alternate thermal decomposition of pure SiH{sub 4} and GeH{sub 4} diluted with He. When the sample was excited by the 979 nm line of a semiconductor laser, fairly broad photoluminescence (PL) spectra in the region of 0.6–0.8 eV were observed at room temperature. The observed PL spectra suggested that radiative recombination of photo-generated carriers through quantized states of Ge core is the dominant pathway for the emission from the dots, reflecting the type II energy band discontinuity between the Si clad and Ge core. We also found that P-δ doping to Ge core plays an important role in recombination through the quantized states in the valence band of Ge core and P donor levels.

  5. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes

    NASA Astrophysics Data System (ADS)

    Gromova, Yulia A.; Orlova, Anna O.; Maslov, Vladimir G.; Fedorov, Anatoly V.; Baranov, Alexander V.

    2013-10-01

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

  6. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes.

    PubMed

    Gromova, Yulia A; Orlova, Anna O; Maslov, Vladimir G; Fedorov, Anatoly V; Baranov, Alexander V

    2013-10-31

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

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

    NASA Astrophysics Data System (ADS)

    Pathak, Smita

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

  8. Tuning the quantum critical crossover in quantum dots

    NASA Astrophysics Data System (ADS)

    Murthy, Ganpathy

    2005-03-01

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

  9. Optophononics with coupled quantum dots.

    PubMed

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

    2014-01-01

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

  10. Quantum dot spectroscopy using cavity quantum electrodynamics.

    PubMed

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

    2008-11-28

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

  11. 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.

  12. Optically injected quantum-dot lasers.

    PubMed

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

    2010-04-01

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

  13. Coherent optoelectronics with single quantum dots

    NASA Astrophysics Data System (ADS)

    Zrenner, A.; Ester, P.; Michaelis de Vasconcellos, S.; Hübner, M. C.; Lackmann, L.; Stufler, S.; Bichler, M.

    2008-11-01

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

  14. 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.

  15. 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.; hide

    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.

  16. 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.

  17. Quantum Dot Based Chemosensors: Selective Estimation of Cu2+ in Semi-aqueous Medium

    NASA Astrophysics Data System (ADS)

    Sheoran, Vandana; Saluja, Preeti; Singh, Narinder; Kaur, Navneet

    2011-12-01

    Quantum dots are the semiconducting nanocrystals whose exicitons are restricted in all the three dimensions within a range of 2-10 nm. Due to the phenomenon called quantum confinement they have unique optical and photo physical properties which makes them useful as chemosensors. Since quantum dots provide a useful framework for the surface confinement of the receptors thereby resulting in changes in the receptor binding affinity. Therefore capturing this feature of the quantum dots different ligands are synthesized and then attached to the quantum dots. Finally studying the surface modification of the quantum dots helps us to make chemosensorsors.

  18. Biodetection using fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

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

    2002-07-01

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

  19. Numerical Study of Complementary Nanostructures for Light Trapping in Colloidal Quantum Dot Solar Cells

    PubMed Central

    Wei, Jue; Xiong, Qiuyang; Mahpeykar, Seyed Milad; Wang, Xihua

    2016-01-01

    We have investigated two complementary nanostructures, nanocavity and nanopillar arrays, for light absorption enhancement in depleted heterojunction colloidal quantum dot (CQD) solar cells. A facile complementary fabrication process is demonstrated for patterning these nanostructures over the large area required for light trapping in photovoltaic devices. The simulation results show that both proposed periodic nanostructures can effectively increase the light absorption in CQD layer of the solar cell throughout the near-infrared region where CQD solar cells typically exhibit weak light absorption. The complementary fabrication process for implementation of these nanostructures can pave the way for large-area, inexpensive light trapping implementation in nanostructured solar cells. PMID:28335183

  20. Study of the nonlinear optical properties of CdS quantum dots in phosphate glass

    NASA Astrophysics Data System (ADS)

    De Souza, J. M.; Pilla, V.; Messias, D. N.; Silva, A. C. A.; Dantas, N. O.; Andrade, A. A.

    2017-02-01

    The aim of this work is the use of the Z-scan technique to determine the nonlinear refraction and nonlinear absorption of phosphate glass doped with CdS. This glass matrix, termed as PANK (P2O5-Al2O3-Na2O-K2O), was doped with 1, 2 and 3 % of CdS concentration. The quantum dots (QDs) are materials extensively investigated in the last years for their special physical properties associated to discrete energetic levels.

  1. Modeling on the size dependent properties of InP quantum dots: a hybrid functional study.

    PubMed

    Cho, Eunseog; Jang, Hyosook; Lee, Junho; Jang, Eunjoo

    2013-05-31

    Theoretical calculations based on density functional theory were performed to provide better understanding of the size dependent electronic properties of InP quantum dots (QDs). Using a hybrid functional approach, we suggest a reliable analytical equation to describe the change of energy band gap as a function of size. Synthesizing colloidal InP QDs with 2-4 nm diameter and measuring their optical properties was also carried out. It was found that the theoretical band gaps showed a linear dependence on the inverse size of QDs and gave energy band gaps almost identical to the experimental values.

  2. Nonequilibrium spin noise in a quantum dot ensemble

    NASA Astrophysics Data System (ADS)

    Smirnov, D. S.; Glasenapp, Ph.; Bergen, M.; Glazov, M. M.; Reuter, D.; Wieck, A. D.; Bayer, M.; Greilich, A.

    2017-06-01

    The spin noise in singly charged self-assembled quantum dots is studied theoretically and experimentally under the influence of a perturbation, provided by additional photoexcited charge carriers. The theoretical description takes into account generation and relaxation of charge carriers in the quantum dot system. The spin noise is measured under application of above barrier excitation for which the data are well reproduced by the developed model. Our analysis demonstrates a strong difference of the recharging dynamics for holes and electrons in quantum dots.

  3. Unraveling the Mesoscopic Character of Quantum Dots in Nanophotonics.

    PubMed

    Tighineanu, P; Sørensen, A S; Stobbe, S; Lodahl, P

    2015-06-19

    We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. The deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, where a strong variation of the multipolar moments across the emission spectrum of quantum dots is observed. Our work enriches the physical understanding of quantum dots and is of significance for the fields of nanophotonics, quantum photonics, and quantum-information science, where quantum dots are actively employed.

  4. Study on the Fabrication of Paint-Type Si Quantum Dot-Sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Seo, Hyunwoong; Son, Min-Kyu; Kim, Hee-Je; Wang, Yuting; Uchida, Giichiro; Kamataki, Kunihiro; Itagaki, Naho; Koga, Kazunori; Shiratani, Masaharu

    2013-10-01

    Quantum dots (QDs) have attracted much attention with their quantum characteristics in the research field of photochemical solar cells. Si QD was introduced as one of alternatives to conventional QD materials. However, their large particles could not penetrate inside TiO2 layer. Therefore, this work proposed the paint-type Si QD-sensitized solar cell. Its heat durability was suitable for the fabrication of paint-type solar cell. Si QDs were fabricated by multihollow discharge plasma chemical vapor deposition and characterized. The paste type, sintering temperature, and Si ratio were controlled and analyzed for better performance. Finally, its performance was enhanced by ZnS surface modification and the whole process was much simplified without sensitizing process.

  5. UV-VIS spectroscopic study of one pot synthesized strontium oxide quantum dots

    NASA Astrophysics Data System (ADS)

    Nemade, K. R.; Waghuley, S. A.

    The properties of drastically change when matter makes transition from 1D, 2D, 3D, to 0D. The quantum dots (QDs) of strontium oxide (SrO) were synthesized by one pot chemical precipitation method using hexamethylenetetramine (HMT). The radius of SrO QDs was calculated from hyperbolic band model (HBM). The direct and indirect band gaps of SrO QDs were estimated from UV-VIS analysis. The particle size was found to be 2.48 nm. The quantum confinement effect in SrO QDs is discussed through exciton Bohr radius. The particle size from UV-VIS analysis is in excellent agreement with fluorescence and TEM.

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

    PubMed

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

    2013-02-06

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

  7. Charge Carrier Conduction Mechanism in PbS Quantum Dot Solar Cells: Electrochemical Impedance Spectroscopy Study.

    PubMed

    Wang, Haowei; Wang, Yishan; He, Bo; Li, Weile; Sulaman, Muhammad; Xu, Junfeng; Yang, Shengyi; Tang, Yi; Zou, Bingsuo

    2016-07-20

    With its properties of bandgap tunability, low cost, and substrate compatibility, colloidal quantum dots (CQDs) are becoming promising materials for optoelectronic applications. Additionally, solution-processed organic, inorganic, and hybrid ligand-exchange technologies have been widely used in PbS CQDs solar cells, and currently the maximum certified power conversion efficiency of 9.9% has been reported by passivation treatment of molecular iodine. Presently, there are still some challenges, and the basic physical mechanism of charge carriers in CQDs-based solar cells is not clear. Electrochemical impedance spectroscopy is a monitoring technology for current by changing the frequency of applied alternating current voltage, and it provides an insight into its electrical properties that cannot be measured by direct current testing facilities. In this work, we used EIS to analyze the recombination resistance, carrier lifetime, capacitance, and conductivity of two typical PbS CQD solar cells Au/PbS-TBAl/ZnO/ITO and Au/PbS-EDT/PbS-TBAl/ZnO/ITO, in this way, to better understand the charge carriers conduction mechanism behind in PbS CQD solar cells, and it provides a guide to design high-performance quantum-dots solar cells.

  8. Optimal excitation conditions for indistinguishable photons from quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  9. Blood group antigen studies using CdTe quantum dots and flow cytometry

    PubMed Central

    Cabral Filho, Paulo E; Pereira, Maria IA; Fernandes, Heloise P; de Thomaz, Andre A; Cesar, Carlos L; Santos, Beate S; Barjas-Castro, Maria L; Fontes, Adriana

    2015-01-01

    New methods of analysis involving semiconductor nanocrystals (quantum dots [QDs]) as fluorescent probes have been highlighted in life science. QDs present some advantages when compared to organic dyes, such as size-tunable emission spectra, broad absorption bands, and principally exceptional resistance to photobleaching. Methods applying QDs can be simple, not laborious, and can present high sensibility, allowing biomolecule identification and quantification with high specificity. In this context, the aim of this work was to apply dual-color CdTe QDs to quantify red blood cell (RBC) antigen expression on cell surface by flow cytometric analysis. QDs were conjugated to anti-A or anti-B monoclonal antibodies, as well as to the anti-H (Ulex europaeus I) lectin, to investigate RBCs of A1, B, A1B, O, A2, and Aweak donors. Bioconjugates were capable of distinguishing the different expressions of RBC antigens, both by labeling efficiency and by flow cytometry histogram profile. Furthermore, results showed that RBCs from Aweak donors present fewer amounts of A antigens and higher amounts of H, when compared to A1 RBCs. In the A group, the amount of A antigens decreased as A1 > A3 > AX = Ael, while H antigens were AX = Ael > A1. Bioconjugates presented stability and remained active for at least 6 months. In conclusion, this methodology with high sensibility and specificity can be applied to study a variety of RBC antigens, and, as a quantitative tool, can help in achieving a better comprehension of the antigen expression patterns on RBC membranes. PMID:26185442

  10. Metallomics Study of CdSe/ZnS Quantum Dots in HepG2 Cells.

    PubMed

    Peng, Lu; He, Man; Chen, Beibei; Qiao, Yu; Hu, Bin

    2015-10-27

    Toxicity of quantum dots (QDs) has been a hot research concern in the past decade, and there is a lot of challenge in this field. The physicochemical characteristics of QDs can affect their toxicity, while little is known about the specific chemical form of QDs in living cells after incubation so far. In this work, speciation of four CdSe/ZnS QDs in HepG2 cells was carried out from the metallomics' point of view for the first time by using size exclusion chromatography (SEC) coupled with inductively coupled plasma-mass spectrometry (ICP-MS). On the basis of the signal of Cd, two kinds of chemical forms, named as QD-1 and QD-2, were observed in HepG2 cells incubated with CdSe/ZnS QDs. QD-1 was demonstrated to be a kind of QD-like nanoparticles, confirmed by chromatographic retention time, transmission electron microscopy (TEM) characterization, and fluorescence detection. QD-2 was demonstrated to be cadmium-metallothioneins complex (Cd-MTs) by reversed phase liquid chromatography (RPLC) synchronously coupled with ICP-MS and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS) analysis. Meanwhile, speciation of QDs in HepG2 cells incubated with different conditions was analyzed. With the variation of QDs incubation concentration/time, and elimination time, the species of QD-1 and QD-2 were also observed without other obvious species, and both the amount of QD-1 and QD-2 increased with incubation concentration and time. The obtained results provide valuable information and a strategy for the study of existing chemical form of QDs, greatly benefiting the understanding of QDs toxicity in living cells.

  11. Study of binary and ternary organic hybrid CdSe quantum dot photodetector

    NASA Astrophysics Data System (ADS)

    Ramar, M.; Kajal, S.; Pal, Prabir; Srivastava, R.; Suman, C. K.

    2015-09-01

    The hybrid binary and ternary photodetectors (PDs) were fabricated from P3HT-PC71BM with CdSe quantum dot (QD) materials. The absorption spectra of P3HT:PC71BM (named as B1), P3HT:CdSe (B2) and P3HT:CdSe:PC71BM (T) active blended material were analyzed in the wavelength range from 350 to 800 nm. The current density-voltage characteristics of the device were measured in dark and under illumination for study of detector detectivities and the contact with electrode. The ratio at -0.5 V for PDs B1, B2 and T is 1.1 × 102, 1.9 × 102 and 1.8 × 103, respectively. The values of detectivity for B1, B2 and T are 1 × 1010, 2 × 1010 and 7 × 1011 Jones, respectively. The for PD T is ten times in comparison with B1 and B2 PDs. The linear dynamic range (LDR) value for ternary device is more than double to both binary PDs. The absorption by CdSe QD increases the photon efficiency in the ternary detector, and at the same time the ternary detectors have high detectivity in broad spectral range. The responsivity of current to the light intensity exponent θ for detector B1, B2 and T is ~0.55, 0.55 and 0.62, respectively, which represents a complex process of electron hole generation, recombination and trapping within active material.

  12. 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.

  13. Electronic properties of aperiodic quantum dot chains

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  14. Synthesis, characterization, Raman, and surface enhanced Raman studies of semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Pan, Yi

    The major contributions and discoveries of the dissertation include: (1) Homogeneous nucleation processes for the formation of nanocrystals can occur at low temperature and do not need to proceed at high temperature to overcome a high energy barrier. Monodisperse PbS quantum dots (QDs) obtained with nucleation and growth at 45°C support this finding. (2) Monodisperse single elemental Se QDs can be produced by simple solution crystallization from TDE (1-tetradecene) or ODE (1-octadecene). (3) TDE is a better non-coordinating solvent compare to ODE. STDE (S dissolved in TDE) and SeTDE (Se dissolved in TDE) are stable reagents with long storage time. They can be used as universal precursors for S-containing and Se-containing QDs. (4) QDs synthesis can be carried out at low temperature and relatively short reaction time using the simple, non-injection, one-pot synthetic method. (5) The one-pot method can be extended for the synthesis of QDs and graphene oxide nanocomposites and metal and graphene oxide nanocomposites. (6) PbCl2-OLA (oleylamine) is a universal system for the synthesis of Pb-chaclogenides QDs. (7) Surface enhanced Raman spectroscopy (SERS) is used to probe both size and wave length dependent quantum confinement effects (QCEs) of PbS QDs. (8) Raman spectroscopy is a powerful tool to elucidate crystal structure of Se nanoclusters with size of 1--2 nm. Semiconductor QDs have attracted considerable attention due to their potential for energy-efficient materials in optoelectronic and solar cell applications. When the radius of a QD is decreased to that of the exciton Bohr radius, the valence and conduction bands are known to split into narrower bands due to QCEs. QCEs are both size and wave length dependent. We have developed, synthesized and characterized a series of Pb-chaclogenide QDs, which all the sizes of the QDs are monodisperse and smaller than their respective exciton Bohr radius, to study the QCEs of these QDs. SERS is used as a crucial tool to

  15. 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

  16. 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.

  17. Deformation potentials of CdSe quantum dots

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2004-06-02

    The size dependent deformation potentials of CdSe quantum dots are studied by first principle and semi-empirical pseudopotentials calculations. They find that the amplitude of the quantum dot deformation potential is only slightly larger than the bulk value, and this increase is mostly caused by the off {Lambda} point deformation potentials in the bulk, which are larger in amplitude than the {Lambda} point deformation potential.

  18. On the density of states of circular graphene quantum dots

    NASA Astrophysics Data System (ADS)

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

    2017-10-01

    We suggest a simple approach to calculate the local density of states that effectively applies to any structure created by an axially symmetric potential on a continuous graphene sheet such as circular graphene quantum dots or rings. Calculations performed for the graphene quantum dot studied in a recent scanning tunneling microscopy measurement (Gutierrez et al 2016 Nat. Phys. 12 1069–75) show an excellent experimental-theoretical agreement.

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

    PubMed

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

    2017-05-17

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    SciTech Connect

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

    2016-07-07

    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.

  2. 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.

  3. 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.

  4. Optical properties of few layered graphene quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  5. 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.

  6. 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.

  7. GaSb/GaAs quantum dot formation and demolition studied with cross-sectional scanning tunneling microscopy

    SciTech Connect

    Smakman, E. P.; Garleff, J. K.; Rambabu, P.; Koenraad, P. M.; Young, R. J.; Hayne, M.

    2012-04-02

    We present a cross-sectional scanning tunneling microscopy study of GaSb/GaAs quantum dots grown by molecular beam epitaxy. Various nanostructures are observed as a function of the growth parameters. During growth, relaxation of the high local strain fields of the nanostructures plays an important role in their formation. Pyramidal dots with a high Sb content are often accompanied by threading dislocations above them. GaSb ring formation is favored by the use of a thin GaAs first cap layer and a high growth temperature of the second cap layer. At these capping conditions, strain-driven Sb diffusion combined with As/Sb exchange and Sb segregation remove the center of a nanostructure, creating a ring. Clusters of GaSb without a well defined morphology also appear regularly, often with a highly inhomogeneous structure which is sometimes divided up in fragments.

  8. 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.

  9. Scanning tunneling microscopy studies of charge transport in cadmium selenide/zinc sulfide quantum dots

    NASA Astrophysics Data System (ADS)

    Hummon, Marissa Rachel

    2009-12-01

    This thesis examines charge transport in individual colloidal nanocrystals (quantum dots) using a scanning tunneling microscope. We observe coulomb blockade (CB) at room temperature and extract the charging energy of the quantum dot (QD). We analyze time-dependent CB measurements to determine the lifetime and energy of the trapped charge on the QD. A model of the lifetime is presented, furthering our analysis of the charge detrapping mechanism. We observe a hysteresis in the current-voltage (IV) tunneling spectra as the substrate bias is swept from empty to filled states and then back to empty states. This hysteresis is consistent with trapped charge(s) presenting an additional potential barrier to tunneling, a measure of CB. Traditional CB experiments measure a coulomb repulsion due to charge build-up on the island between two electrodes. We observe CB, hysteresis in successive IV sweeps, due to charge trapping/detrapping in a state other than the transport level. This trap state may be related to the dark state in blinking experiments. Optical and electrical measurements of QD trap states are often related to a puzzling physical phenomena observed universally in QDs: blinking. Blinking is the stochastic photoluminescence behavior of quantum dots, where, under constant excitation by a laser, a QD does not emit a continuous stream of photons. In fact, the QD will blink "on" and "off" for completely unpredictable durations that are thought to be related to the QD being in either a neutral or charged state. We measure a lifetime for the charged state of 15 +/- 7 s when Vsub ≤ 1.5 V and 170 +/- 140 ms when Vsub ≥ 1.6 V. The abrupt transition in lifetime between 1.5 and 1.6 V implies that this is the voltage necessary to lower the Au Fermi level equal to the trap state energy, thus allowing the trapped charge to tunnel out of the trap state. The voltage drop between the QD and substrate, determined from a self-consistent calculation of the relative capacitance

  10. FeS2 quantum dots sensitized nanostructured TiO2 solar cell: photoelectrochemical and photoinduced absorption spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Bedja, I.

    2011-09-01

    Thin films of nanostructured TiO2 have been modified with FeS2 (pyrite) nano-particles by a low temperature chemical reaction of iron pentacarbonyl with sulfur in xylene. Quantum size effects are manifested by the observation of a blue shift in both absorption and photocurrent action spectra. PIA (Photoinduced absorption spectroscopy), where the excitation is provided by a square-wave modulated (on/off) monochromatic light emitting diode, is a multipurpose tool in the study of dye-sensitized solar cells. Here, PIA is used to study quantum-dot modified TiO2 nanostructured electrodes. The PIA spectra obtained give evidence for long-lived photoinduced charge separation: electrons are injected into the metal oxide and holes are left behind in the FeS2 quantum dot. Time-resolved PIA shows that recombination between electrons and holes occurs on a millisecond timescale. The Incident-Photon-to-Current Efficiency of about 23 % was obtained at 400 nm excitation. The performances of TiO2 electrodes modified with FeS2 are relatively low, which is explained by the presence of FeS2 phases other than the photoactive pyrite phase, as follows from the XRD spectrum.

  11. Coherent radiation by quantum dots and magnetic nanoclusters

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  12. 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.

  13. Spin Dynamics of Charged Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Stern, N. P.

    2005-03-01

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

  14. 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.

  15. 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.

  16. Adiabatic Spin Pumping with Quantum Dots

    NASA Astrophysics Data System (ADS)

    Mucciolo, Eduardo R.

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

  17. A validation study of quantum dot multispectral imaging to evaluate hormone receptor status in ductal carcinoma in situ of the breast.

    PubMed

    Yu, Jing; Monaco, Sara E; Onisko, Agnieszka; Bhargava, Rohit; Dabbs, David J; Cieply, Kathleen M; Fine, Jeffrey L

    2013-03-01

    The assessment of hormone receptors, including estrogen receptor and progesterone receptor, has become a standard practice in breast cancer management. However, the need for multiple sections to evaluate each receptor individually by conventional immunohistochemistry may preclude the analysis on some core biopsies with a limited amount of tumors. The aim of the study was to validate the quantitative analysis of nuclear markers estrogen receptor and progesterone receptor by quantum dot-based immunohistochemistry using a multispectral imaging system in ductal carcinoma in situ of the breast. Consecutive sections from a total of 17 cases of ductal carcinoma in situ with excisional biopsies or mastectomies were stained with conventional immunohistochemistry and quantum dot-based, single- and double-labeled immunohistochemistry for estrogen receptor and progesterone receptor. The semiquantitative results from double-labeled, quantum dot-based immunohistochemistry were compared with those from single-labeled, quantum dot-based immunohistochemistry as well as from conventional immunohistochemistry. There was good concordance between double- and single-labeled quantum dot-based immunohistochemistry, and quantum dot-based immunohistochemistry correlated well with conventional immunohistochemistry (Spearman correlation coefficient range from 0.884 to 0.958, P < .001). The findings proved the validity and accuracy of quantum dot-based multiplex, multispectral technique in detecting 2 tumor markers in the same cellular compartment simultaneously on a single slide. This technique may enhance our ability to assess multiple breast tumor markers in specimens with limited available tissue. However, several technical and logistic issues await significant improvement before this novel technique can be justified for routine clinical application. Copyright © 2013 Elsevier Inc. All rights reserved.

  18. 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.

  19. A triangular triple quantum dot with tunable tunnel couplings

    NASA Astrophysics Data System (ADS)

    Noiri, A.; Kawasaki, K.; Otsuka, T.; Nakajima, T.; Yoneda, J.; Amaha, S.; Delbecq, M. R.; Takeda, K.; Allison, G.; Ludwig, A.; Wieck, A. D.; Tarucha, S.

    2017-08-01

    A two-dimensional arrangement of quantum dots (QDs) with finite inter-dot tunnel coupling provides a promising platform for studying complicated spin correlations as well as for constructing large-scale quantum computers. Here, we fabricate a tunnel-coupled triangular triple QD with a novel gate geometry in which three dots are defined by positively biasing the surface gates. At the same time, the small area in the center of the triangle is depleted by negatively biasing the top gate placed above the surface gates. The size of the small center depleted area is estimated from the Aharonov-Bohm oscillation measured for the triangular channel but incorporating no gate-defined dots, with a value consistent with the design. With this approach, we can bring the neighboring gate-defined dots close enough to one another to maintain a finite inter-dot tunnel coupling. We finally confirm the presence of the inter-dot tunnel couplings in the triple QD from the measurement of tunneling current through the dots in the stability diagram. We also show that the charge occupancy of each dot and that the inter-dot tunnel couplings are tunable with gate voltages.

  20. Noninvasive detection of charge rearrangement in a quantum dot

    NASA Astrophysics Data System (ADS)

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

    2007-04-01

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

  1. Systematic study of the interaction of cobalt ions with different-sized CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Zhong, Wenying; Liang, Jiaran; Yu, Junsheng

    2009-10-01

    Five sizes of water-dispersed CdTe quantum dots (QDs) stabilized by thioglycolic acid (TGA) with a high photoluminescence (PL) quantum yield were synthesized and a size dependent quenching of the fluorescence by cobalt ions was also observed. No matter for smaller or larger particles, obvious quenching effect was observed, and the fluorescence quenching of CdTe nanoparticles depended on the concentration of cobalt ions solution. However, CdTe QDs with different size showed dramatically different quenching efficiency, sensitivity, linear range and selectivity. With the increase of size, the quenching efficiency reduced correspondingly. The smallest particle was the most sensitive with the limit of detection for cobalt ions is 7.3 × 10 -9 mol L -1 Co 2+. For larger particles, the sensitivity was much lower, but the linear range was relatively wide, under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of cobalt ions ranging from 3.32 × 10 -8 to 3.62 × 10 -6 mol L -1. Besides, the influence on the fluorescence signal of foreign cations, including Ca 2+, Mg 2+, Ni 2+, Ba 2+, Zn 2+, Cu 2+, Fe 3+ and Ag + were also studied, results showed a high selectivity of the smaller QDs towards cobalt ions. According to Stern-Volmer-type equation, quenching of quantum dot luminescence was most effective for the smallest particles with the highest Ksv.

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

    NASA Astrophysics Data System (ADS)

    Świderski, M.; Zieliński, M.

    2017-03-01

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

  3. 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.

  4. 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.

  5. 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.

  6. Quantum dots as biophotonics tools.

    PubMed

    Cesar, Carlos L

    2014-01-01

    This chapter provides a short review of quantum dots (QDs) physics, applications, and perspectives. The main advantage of QDs over bulk semiconductors is the fact that the size became a control parameter to tailor the optical properties of new materials. Size changes the confinement energy which alters the optical properties of the material, such as absorption, refractive index, and emission bands. Therefore, by using QDs one can make several kinds of optical devices. One of these devices transforms electrons into photons to apply them as active optical components in illumination and displays. Other devices enable the transformation of photons into electrons to produce QDs solar cells or photodetectors. At the biomedical interface, the application of QDs, which is the most important aspect in this book, is based on fluorescence, which essentially transforms photons into photons of different wavelengths. This chapter introduces important parameters for QDs' biophotonic applications such as photostability, excitation and emission profiles, and quantum efficiency. We also present the perspectives for the use of QDs in fluorescence lifetime imaging (FLIM) and Förster resonance energy transfer (FRET), so useful in modern microscopy, and how to take advantage of the usually unwanted blinking effect to perform super-resolution microscopy.

  7. Silicon Quantum Dots for Quantum Information Processing

    DTIC Science & Technology

    2013-11-01

    levels of the dot up and down. This pulse train modulates the sensor current via a cross- capacitance at a frequency fpulse and the resulting current...excited-state energy levels were detected using a SET charge sensor , with the aid of pulsed-voltage spectroscopy. The energy of the first orbital...were studied in detail. The electron occupancy and excited-state energy levels were detected using a SET charge sensor , with the aid of pulsed-voltage

  8. Magnetization studies of II-VI semiconductor columnar quantum dots with type-II band alignment

    NASA Astrophysics Data System (ADS)

    Eginligil, M.; Sellers, I. R.; McCombe, B. D.; Chou, W.-C.; Kuskovsky, I. L.

    2009-03-01

    We report SQUID magnetization measurements of MBE-grown type-II, II-VI semiconductor quantum dot (QD) samples, with and without Mn incorporation. In all samples, the easy axis is out-of-plane, possibly due to columnar QD formation that arises from strain interaction between adjacent thin dot-containing layers. In addition, both types of QDs display a non-zero spontaneous magnetic ordering at 300 K. One set of samples consists of five-layers of (Zn,Mn)Te/ZnSe with a nominal (Zn,Mn)Te thickness of 3 nm, and ZnSe spacer thickness of 5 nm and 20 nm. These magnetic QD samples show magnetization vs. temperature behavior that can be interpreted in terms of two independent FM phases characterized by transition temperatures TC1 < TC2. A sample containing no Mn consists of 130 ZnTe/ZnSe layers, which forms Zn(Se,Te) QD layers separated by ZnSe spacers. Evidence of ferromagnetism is also seen in this structure, but the spontaneous magnetization is much weaker. For this sample only one phase is seen with TC above 300 K. Results will be discussed in terms of magneto-polaronic effects and defect-level induced ferromagnetism.

  9. Linear and nonlinear optical studies of CdS1- x Se x quantum dots

    NASA Astrophysics Data System (ADS)

    Uhrig, A.; Banyai, L.; Gaponenko, S.; Wörner, A.; Neuroth, N.; Klingshirn, C.

    1991-03-01

    In this contribution we present and discuss our measurements on CdS1- x Se x quantum dots in a glass matrix. In linear absorption measurements we find the typical blue shift of the transitions with decreasing crystallite radius due to quantization. The luminescence shows a significant Stokes shift with respect to absorption, which is interpreted in terms of strong exciton-phonon coupling and allows to deduce the Huang-Rhys factor S. Under high excitation we find an additional emission band on the high energy side, which can be attributed to the recombination of an excited two electron-hole pair state to a one electron-hole pair state in agreement with theory. Pump and probe beam experiments give a bleaching but no hole burning. Finally we discuss some open questions especially concerning the high energy structures in the absorption spectrum.

  10. Trapping photon-dressed Dirac electrons in a quantum dot studied by coherent two dimensional photon echo spectroscopy

    PubMed Central

    Roslyak, O.; Gumbs, Godfrey; Mukamel, S.

    2012-01-01

    We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated. PMID:22612079

  11. Energy levels of bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  12. Heparin conjugated quantum dots for in vitro imaging applications.

    PubMed

    Maguire, Ciaran Manus; Mahfoud, Omar Kazem; Rakovich, Tatsiana; Gerard, Valerie Anne; Prina-Mello, Adriele; Gun'ko, Yurii; Volkov, Yuri

    2014-11-01

    In this work heparin-gelatine multi-layered cadmium telluride quantum dots (QDgel/hep) were synthesised using a novel 'one-pot' method. The QDs produced were characterised using various spectroscopic and physiochemical techniques. Suitable QDs were then selected and compared to thioglycolic acid stabilised quantum dots (QDTGA) and gelatine coated quantum dots (QDgel) for utilisation in in vitro imaging experiments on live and fixed permeabilised THP-1, A549 and Caco-2 cell lines. Exposure of live THP-1 cells to QDgel/hep resulted in localisation of the QDs to the nucleus of the cells. QDgel/hep show affinity for the nuclear compartment of fixed permeabilised THP-1 and A549 cells but remain confined to cytoplasm of fixed permeabilised Caco-2 cells. It is postulated that heparin binding to the CD11b receptor facilitates the internalisation of the QDs into the nucleus of THP-1 cells. In addition, the heparin layer may reduce the unfavourable thrombogenic nature of quantum dots observed in vivo. In this study, heparin conjugated quantum dots were found to have superior imaging properties compared to its native counterparts. The authors postulate that heparin binding to the CD11b receptor facilitates QD internalization to the nucleus, and the heparin layer may reduce the in vivo thrombogenic properties of quantum dots. Copyright © 2014 Elsevier Inc. All rights reserved.

  13. Positioning of quantum dots on metallic nanostructures.

    PubMed

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

    2010-04-09

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

  14. Positioning of quantum dots on metallic nanostructures

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  15. Semiconductor Quantum Dots with Photoresponsive Ligands.

    PubMed

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

    2016-10-01

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

  16. 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.

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

    PubMed

    Biju, Vasudevanpillai; Itoh, Tamitake; Ishikawa, Mitsuru

    2010-08-01

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

  18. Translocation of PEGylated quantum dots across rat alveolar epithelial cell monolayers

    PubMed Central

    Fazlollahi, Farnoosh; Sipos, Arnold; Kim, Yong Ho; Hamm-Alvarez, Sarah F; Borok, Zea; Kim, Kwang-Jin; Crandall, Edward D

    2011-01-01

    Background In this study, primary rat alveolar epithelial cell monolayers (RAECM) were used to investigate transalveolar epithelial quantum dot trafficking rates and underlying transport mechanisms. Methods Trafficking rates of quantum dots (PEGylated CdSe/ZnS, core size 5.3 nm, hydrodynamic size 25 nm) in the apical-to-basolateral direction across RAECM were determined. Changes in bioelectric properties (ie, transmonolayer resistance and equivalent active ion transport rate) of RAECM in the presence or absence of quantum dots were measured. Involvement of endocytic pathways in quantum dot trafficking across RAECM was assessed using specific inhibitors (eg, methyl-β-cyclodextrin, chlorpromazine, and dynasore for caveolin-, clathrin-, and dynamin-mediated endocytosis, respectively). The effects of lowering tight junctional resistance on quantum dot trafficking were determined by depleting Ca2+ in apical and basolateral bathing fluids of RAECM using 2 mM EGTA. Effects of temperature on quantum dot trafficking were studied by lowering temperature from 37°C to 4°C. Results Apical exposure of RAECM to quantum dots did not elicit changes in transmonolayer resistance or ion transport rate for up to 24 hours; quantum dot trafficking rates were not surface charge-dependent; methyl-β-cyclodextrin, chlorpromazine, and dynasore did not decrease quantum dot trafficking rates; lowering of temperature decreased transmonolayer resistance by approximately 90% with a concomitant increase in quantum dot trafficking by about 80%; and 24 hours of treatment of RAECM with EGTA decreased transmonolayer resistance by about 95%, with increased quantum dot trafficking of up to approximately 130%. Conclusion These data indicate that quantum dots do not injure RAECM and that quantum dot trafficking does not appear to take place via endocytic pathways involving caveolin, clathrin, or dynamin. We conclude that quantum dot translocation across RAECM takes place via both transcellular and

  19. Translocation of PEGylated quantum dots across rat alveolar epithelial cell monolayers.

    PubMed

    Fazlollahi, Farnoosh; Sipos, Arnold; Kim, Yong Ho; Hamm-Alvarez, Sarah F; Borok, Zea; Kim, Kwang-Jin; Crandall, Edward D

    2011-01-01

    In this study, primary rat alveolar epithelial cell monolayers (RAECM) were used to investigate transalveolar epithelial quantum dot trafficking rates and underlying transport mechanisms. Trafficking rates of quantum dots (PEGylated CdSe/ZnS, core size 5.3 nm, hydrodynamic size 25 nm) in the apical-to-basolateral direction across RAECM were determined. Changes in bioelectric properties (ie, transmonolayer resistance and equivalent active ion transport rate) of RAECM in the presence or absence of quantum dots were measured. Involvement of endocytic pathways in quantum dot trafficking across RAECM was assessed using specific inhibitors (eg, methyl-β-cyclodextrin, chlorpromazine, and dynasore for caveolin-, clathrin-, and dynamin-mediated endocytosis, respectively). The effects of lowering tight junctional resistance on quantum dot trafficking were determined by depleting Ca(2+) in apical and basolateral bathing fluids of RAECM using 2 mM EGTA. Effects of temperature on quantum dot trafficking were studied by lowering temperature from 37°C to 4°C. Apical exposure of RAECM to quantum dots did not elicit changes in transmonolayer resistance or ion transport rate for up to 24 hours; quantum dot trafficking rates were not surface charge-dependent; methyl-β-cyclodextrin, chlorpromazine, and dynasore did not decrease quantum dot trafficking rates; lowering of temperature decreased transmonolayer resistance by approximately 90% with a concomitant increase in quantum dot trafficking by about 80%; and 24 hours of treatment of RAECM with EGTA decreased transmonolayer resistance by about 95%, with increased quantum dot trafficking of up to approximately 130%. These data indicate that quantum dots do not injure RAECM and that quantum dot trafficking does not appear to take place via endocytic pathways involving caveolin, clathrin, or dynamin. We conclude that quantum dot translocation across RAECM takes place via both transcellular and paracellular pathways and, based on

  20. Controllable quantum scars in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Keski-Rahkonen, J.; Luukko, P. J. J.; Kaplan, L.; Heller, E. J.; Räsänen, E.

    2017-09-01

    Quantum scars are enhancements of quantum probability density along classical periodic orbits. We study the recently discovered phenomenon of strong perturbation-induced quantum scarring in the two-dimensional harmonic oscillator exposed to a homogeneous magnetic field. We demonstrate that both the geometry and the orientation of the scars are fully controllable with a magnetic field and a focused perturbative potential, respectively. These properties may open a path into an experimental scheme to manipulate electric currents in nanostructures fabricated in a two-dimensional electron gas.

  1. Performance analysis of quantum dots infrared photodetector

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  2. 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.

  3. 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.

  4. Imaging Quantum Confinement in Multiple Graphene Quantum Dots

    NASA Astrophysics Data System (ADS)

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

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

  5. Controlling quantum dot emission by plasmonic nanoarrays.

    PubMed

    Guo, R; Derom, S; Väkeväinen, A I; van Dijk-Moes, R J A; Liljeroth, P; Vanmaekelbergh, D; Törmä, P

    2015-11-02

    Metallic nanoparticle arrays support localized surface plasmon resonances (LSPRs) and propagating surface lattice resonances (SLRs). We study the control of quantum dot (QD) emission coupled to the optical modes of silver nanoparticle arrays, both experimentally and numerically. With a hybrid lithography-functionalization method, the QDs are deposited in the vicinity of the nanoparticles. Directionality and enhancement of the emission are observed in photoluminescence spectra and fluorescence lifetime measurements, respectively. Similar features are also demonstrated in the numerical simulations. The tunable emission of this type of hybrid structures could lead to potential applications in light sources.

  6. Protease sensing using nontoxic silicon quantum dots

    NASA Astrophysics Data System (ADS)

    Cheng, Xiaoyu; McVey, Benjamin F. P.; Robinson, Andrew B.; Longatte, Guillaume; O'Mara, Peter B.; Tan, Vincent T. G.; Thordarson, Pall; Tilley, Richard D.; Gaus, Katharina; Justin Gooding, John

    2017-08-01

    Herein is presented a proof-of-concept study of protease sensing that combines nontoxic silicon quantum dots (SiQDs) with Förster resonance energy transfer (FRET). The SiQDs serve as the donor and an organic dye as the acceptor. The dye is covalently attached to the SiQDs using a peptide linker. Enzymatic cleavage of the peptide leads to changes in FRET efficiency. The combination of interfacial design and optical imaging presented in this work opens opportunities for use of nontoxic SiQDs relevant to intracellular sensing and imaging.

  7. Purification processes of cadmium based quantum dots in aqueous medium: a comparative study

    NASA Astrophysics Data System (ADS)

    Petris, Dimitri; Freitas, Denilson V.; dos Santos, Rayany K. V.; Dias, Jéssica M. M.; Navarro, Marcelo

    2017-07-01

    Three different purification methods for CdTe-MPA quantum dot (QD) were performed in aqueous medium: acid titration (HCl, HClO4, H2SO4 and CH3COOH), non-selective precipitation by addition of acetone and co-precipitation of the QD in the presence of inorganic salts. The QD stock solutions were prepared by an electrochemical method of synthesis, in four different heating times (1 h, 4 h, 8 h and 12 h). After purifications, the QD solids were redispersed in distilled water and analyzed by absorption and emission spectra. The λ abs and λ em of the purified QDs showed similar data observed for QD stock solutions, and the recovery rate varied from 71% to 99%. Co-precipitation method showed some advantages: quantum yield maintenance of the QD redispersed solution, longer period of storage (over 6 months) in solution and in solid state (QD embedded into the KCl crystal lattice). CdSe-MPA and CdS-MPA solutions were also purified by co-precipitation method with KCl, showing good results as observed for CdTe-MPA.

  8. 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.

  9. 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.

  10. 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.

  11. Quantum-dot-in-perovskite solids.

    PubMed

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

    2015-07-16

    Heteroepitaxy-atomically aligned growth of a crystalline film atop a different crystalline substrate-is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned 'dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  12. Emission redistribution from a quantum dot-bowtie nanoantenna

    NASA Astrophysics Data System (ADS)

    Regler, Armin; Schraml, Konrad; Lyamkina, Anna A.; Spiegl, Matthias; Müller, Kai; Vuckovic, Jelena; Finley, Jonathan J.; Kaniber, Michael

    2016-07-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby (˜25 nm) plasmonic antenna. Microphotoluminescence spectroscopy shows a ˜2.4× increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of 2.5 μW for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell enhancement of the quantum dot coupled to the antenna as compared with an uncoupled dot, yielding comparable exciton lifetimes of τ˜0.5 ns. This observation is supported by numerical simulations, suggesting only minor Purcell-effects of <2× for emitter-antenna separations >25 nm. The observed increased emission from a coupled quantum dot-plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding of light-matter coupling in such semiconductor-plasmonic hybrid systems.

  13. Photoconductive gain and quantum efficiency of remotely doped Ge/Si quantum dot photodetectors

    NASA Astrophysics Data System (ADS)

    Yakimov, A. I.; Kirienko, V. V.; Armbrister, V. A.; Bloshkin, A. A.; Dvurechenskii, A. V.; Shklyaev, A. A.

    2016-10-01

    We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

  14. Cooper pair splitting in parallel quantum dot Josephson junctions

    PubMed Central

    Deacon, R. S.; Oiwa, A.; Sailer, J.; Baba, S.; Kanai, Y.; Shibata, K.; Hirakawa, K.; Tarucha, S.

    2015-01-01

    Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172

  15. Cooper pair splitting in parallel quantum dot Josephson junctions.

    PubMed

    Deacon, R S; Oiwa, A; Sailer, J; Baba, S; Kanai, Y; Shibata, K; Hirakawa, K; Tarucha, S

    2015-07-01

    Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair.

  16. Tailoring the physical properties of thiol-capped PbS quantum dots by thermal annealing.

    PubMed

    Turyanska, L; Elfurawi, U; Li, M; Fay, M W; Thomas, N R; Mann, S; Blokland, J H; Christianen, P C M; Patanè, A

    2009-08-05

    We show that the thermal annealing of thiol-capped PbS colloidal quantum dots provides a means of narrowing the nanoparticle size distribution, increasing the size of the quantum dots and facilitating their coalescence preferentially along the 100 crystallographic axes. We exploit these phenomena to tune the photoluminescence emission of an ensemble of dots and to narrow the optical linewidth to values that compare with those reported at room temperature for single PbS quantum dots. We probe the influence of annealing on the electronic properties of the quantum dots by temperature dependent studies of the photoluminescence and magneto-photoluminescence.

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

    SciTech Connect

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

    2016-08-11

    In this paper, 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.

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

    DOE PAGES

    Otten, Matthew; Larson, Jeffrey; Min, Misun; ...

    2016-08-11

    In this paper, 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 formore » 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.« less

  19. 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.

  20. Quantum dots for light emitting diodes.

    PubMed

    Qasim, Khan; Lei, Wei; Li, Qing

    2013-05-01

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

  1. Patterned semiconductor inverted quantum dot photonic devices

    NASA Astrophysics Data System (ADS)

    Coleman, J. J.

    2016-03-01

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

  2. Study of gold nanostar@SiO2@CdTeS quantum dots@SiO2 with enhanced-fluorescence and photothermal therapy multifunctional cell nanoprobe

    NASA Astrophysics Data System (ADS)

    Yin, Naiqiang; Jiang, Tongtong; Yu, Jing; He, Jiawei; Li, Xu; Huang, Qianpeng; Liu, Ling; Xu, Xiaoliang; Zhu, Lixin

    2014-03-01

    A novel class of cell probe structured as gold nanostar@SiO2@CdTeS quantum dots@SiO2 nanoprobes with multifunctional (MFNPs) fluorescent and photothermal properties were demonstrated. The MFNPs with good homogeneity (129 ± 10 nm) and dispersity were synthesized by a liquid phase method. The fluorescence signal of quantum dots was enhanced in the MFNPs, compared with the pure quantum dots. The vitro study showed that the MFNPs can realize the targeted labeling after functionalized with anti-body. Furthermore, the nanoprobe displays strong surface plasmonic resonance absorbance in the near-infrared region, thus exhibiting an NIR (808 nm)-induced temperature elevation. When cancer cells were cultured with the anti-body linked MFNPs and irradiated by laser, the MFNPs were demonstrated as good candidates for curing cancer cells. Therefore, such a multifunctional probe can be developed as a promising nanosystem that integrates multiple capabilities for effective cancer diagnosis and therapy.

  3. Excitation spectra of circular, few-electron quantum dots

    PubMed

    Kouwenhoven; Oosterkamp; Danoesastro; Eto; Austing; Honda; Tarucha

    1997-12-05

    Studies of the ground and excited states in semiconductor quantum dots containing 1 to 12 electrons showed that the quantum numbers of the states in the excitation spectra can be identified and compared with exact calculations. A magnetic field induces transitions between the ground and excited states. These transitions were analyzed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. These impurity-free quantum dots allow "atomic physics" experiments to be performed in magnetic field regimes not accessible for atoms.

  4. Are quantum dots toxic? Exploring the discrepancy between cell culture and animal studies.

    PubMed

    Tsoi, Kim M; Dai, Qin; Alman, Benjamin A; Chan, Warren C W

    2013-03-19

    Despite significant interest in developing quantum dots (QDs) for biomedical applications, many researchers are convinced that QDs will never be used for treating patients because of their potential toxicity. The perception that QDs are toxic is rooted in two assumptions. Cadmium-containing QDs can kill cells in culture. Many researchers then assume that because QDs are toxic to cells, they must be toxic to humans. In addition, many researchers classify QDs as a homogeneous group of materials. Therefore, if CdSe QDs are harmful, they extrapolate this result to all QDs. Though unsubstantiated, these assumptions continue to drive QD research. When dosing is physiologically appropriate, QD toxicity has not been demonstrated in animal models. In addition, QDs are not uniform: each design is a unique combination of physicochemical properties that influence biological activity and toxicity. In this Account, we summarize key findings from in vitro and in vivo studies, explore the causes of the discrepancy in QD toxicological data, and provide our view of the future direction of the field. In vitro and in vivo QD studies have advanced our knowledge of cellular transport kinetics, mechanisms of QD toxicity, and biodistribution following animal injection. Cell culture experiments have shown that QDs undergo design-dependent intracellular localization and they can cause cytotoxicity by releasing free cadmium into solution and by generating free radical species. In animal experiments, QDs preferentially enter the liver and spleen following intravascular injection, undergo minimal excretion if larger than 6 nm, and appear to be safe to the animal. In vitro and in vivo studies show an apparent discrepancy with regard to toxicity. Dosing provides one explanation for these findings. Under culture conditions, a cell experiences a constant QD dose, but the in vivo QD concentration can vary, and the organ-specific dose may not be high enough to induce detectable toxicity. Because QDs

  5. 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

  6. Theoretical issues in silicon quantum dot qubits

    NASA Astrophysics Data System (ADS)

    Koh, Teck Seng

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

  7. Quantum Hall ferrimagnetism in lateral quantum dot molecules.

    PubMed

    Abolfath, Ramin M; Hawrylak, Pawel

    2006-11-03

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

  8. Competing interactions in semiconductor quantum dots

    DOE PAGES

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

    2014-10-14

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

  9. 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.

  10. Quantum dot lasers and integrated guided wave devices on Si

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Mi, Zetian; Bhattacharya, Pallab

    2007-02-01

    We have studied the growth and characteristics of self-organized InGaAs/GaAs quantum dot lasers and their monolithic integration with waveguides and quantum well electroabsorption modulators on Si. Utilizing multiple layers of InAs quantum dots as effective dislocation filters near the GaAs-Si interface, we have demonstrated high performance quantum dot lasers grown directly on Si that exhibit, for the first time, relatively low threshold current (J th = 900 A/cm2), large characteristic temperature (T 0 = 278 K), and output slope efficiency ( >=0.3 W/A). Focused-ion-beam milling has been used to form high-quality facets for the cavity mirror and coupling groove of an integrated laser/waveguide system on Si. We have also achieved a groove-coupled laser/modulator system on Si that exhibits a coupling coefficient greater than 20% and a modulation depth of ~ 100% at 5 V reverse bias.

  11. 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.

  12. Cathodic stripping synthesis and cytotoxity studies of glutathione-capped CdTe quantum dots.

    PubMed

    Ge, Cunwang; Zhao, Yu; Hui, Jie; Zhang, Tianyi; Miao, Wujian; Yu, Wei

    2011-08-01

    A cathodic stripping of Te precursor in the presence of Cd2+ and biocompatible glutathione (GSH) was reported for facile synthesis of lowly cytotoxic and highly luminescent CdTe quantum dots (QDs) in aqueous solution. The photoluminescence, electrogenerated chemiluminescence (ECL), toxicity, and cyto-osmosis of the QDs were evaluated to reveal their potential bio-applications. The morphology and composition of as-prepared QDs were investigated by HRTEM and powder XRD spectroscopy, which indicated that the QDs consisted of a CdTe core coated with a CdS shell. The obtained CdTe/CdS core/shell QDs possessed good crystallinity, narrow monodispersity and long-term stability. These QDs showed high fluorescence quantum yields of 49% to 63% over a broad spectral range of 540-650 nm. Efficient and stable ECL of QDs was observed on the anodic potential region upon the electrode potential cycled between 1.5 and -2.0 V versus Ag/AgCl. Furthermore, human liver cancer HepG2 cells were chosen as model cells for toxicity assay of QDs. Effects of the concentration, size, and incubation time of CdTe QDs capped with GSH or mercaptoacetic acid (MAA) on the cell metabolic viability and cyto-osmosis were evaluated. GSH-capped CdTe QDs could infiltrate cytomembrane and karyothecas, and were less cytotoxic than MAA-capped ones under the same experimental conditions. The reported CdTe QDs could be good candidates of fluorescent and ECL probes for biosensing and cell imaging.

  13. 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.

  14. 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.

  15. 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.

  16. Magneto-optical studies of (Zn,Mn)Se/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, B.; Tsai, Y.; Scrace, T.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W. C.; Tsou, M. H.; Yang, C. S.; Sellers, I. R.; Oszwaldowski, R.; Petukhov, A. G.

    2014-03-01

    We have recorded the circular polarization P of photoluminescence from (Zn,Mn)Se/ZnTe quantum dots (QDs) as function of magnetic field B. The polarization at a fixed temperature increases monotonically with B and saturates for B >3 tesla at Psat. The value of Psat depends strongly on the laser photon energy. When we excite above (below) the ZnMnSe gap with photons of energy of 3.81 eV (2.54 eV), we measure Psat = 55 %(Psat = 20 %) . We interpret these results as due to the difference in the Zeeman band splitting between the magnetic (Zn,Mn)Se matrix and the non-magnetic ZnTe QDs. For 3.81 eV excitation, electron-hole pairs are generated mainly in the (Zn,Mn)Se matrix. The majority of the holes relax to the +3/2 state before capture by the ZnTe QDs. With 2.54 eV excitation, all electron-hole pairs are excited in the QDs where the Zeeman splitting is negligible. Thus, Psat is determined in this case by the relatively small Zeeman splitting of ZnMnSe conduction band. We relate these findings to our previous results for magnetic type-II QDs, where Psat does not depend on the exciting photon energy. The work at SUNY Buffalo is supported by NSF, DOE-BES, and ONR.

  17. Photoconductivity of Si/Ge multilayer structures with Ge quantum dots pseudomorphic to the Si matrix

    SciTech Connect

    Talochkin, A. B. Chistokhin, I. B.

    2011-07-15

    Longitudinal photoconductivity spectra of Si/Ge multilayer structures with Ge quantum dots grown pseudomorphically to the Si matrix are studied. Lines of optical transitions between hole levels of quantum dots and Si electronic states are observed. This allowed us to construct a detailed energy-level diagram of electron-hole levels of the structure. It is shown that hole levels of pseudomorphic Ge quantum dots are well described by the simplest 'quantum box' model using actual sizes of Ge islands. The possibility of controlling the position of the long-wavelength photosensitivity edge by varying the growth parameters of Si/Ge structures with Ge quantum dots is determined.

  18. Synthesis and Characterization of Mercaptoacetic Acid Capped Cadmium Sulphide Quantum Dots.

    PubMed

    Wageh, S; Maize, Mai; Donia, A M; Al-Ghamdi, Ahmed A; Umar, Ahmad

    2015-12-01

    This paper reports the facile synthesis and detailed characterization of mercaptoacetic acid capped cadmium sulphide (CdS) quantum dots using various cadmium precursors. The mercaptoacetic acid capped CdS quantum dots were prepared by facile and simple wet chemical method and characterized by several techniques such as energy dispersive spectroscopy (EDS), X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, UV-vis. spectroscopy, photoluminescence spectroscopy, high-resolution transmission microscopy (HRTEM) and thremogravimetric analysis. The EDS studies revealed that the prepared quantum dots possess higher atomic percentage of sulfur compared to cadmium due to the coordination of thiolate to the quantum dots surfaces. The X-ray and absorption analyses exhibited that the size of quantum dots prepared by cadmium acetate is larger than the quantum dots prepared by cadmium chloride and cadmium nitrate. The increase in size can be attributed to the low stability constant of cadmium acetate in comparison with cadmium chloride and cadmium nitrate. The FTIR and thermogravimetric analysis showed that the nature of capping molecule on the surface of quantum dots are different depending on the cadmium precursors which affect the emission from CdS quantum dots. Photoemission spectroscopy revealed that the emission of quantum dots prepared by cadmium acetate has high intensity band edge emission along with low intensity trapping state emission. However the CdS quantum dots prepared by cadmium chloride and cadmium nitrate produced only trapping state emissions.

  19. 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

  20. Innovative Ge Quantum Dot Functional Sensing/Metrology Devices

    DTIC Science & Technology

    2015-05-20

    Final 3. DATES COVERED (From - To) 20140507 - 20150506 4. TITLE AND SUBTITLE Innovative Ge Quantum Dot Functional Sensing/Metrology...15. SUBJECT TERMS Quantum Dots , Germanium (Ge) quantum dot 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER...07-05-2014 to 06-05-2015 4. TITLE AND SUBTITLE Innovative Ge Quantum Dot Functional Sensing/Metrology Devices 5a. CONTRACT NUMBER FA2386-14-1

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

    DOEpatents

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

    2017-08-22

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

  2. [Effect of quantum dots CdSe/ZnS's concentration on its fluorescence].

    PubMed

    Jin, Min; Huang, Yu-hua; Luo, Ji-xiang

    2015-02-01

    The authors measured the absorption and the fluorescence spectra of the quantum dots CdSe/ZnS with 4 nm in size at different concentration with the use of the UV-Vis absorption spectroscopy and fluorescence spectrometer. The effect of quantum dots CdSe/ZnS's concentration on its fluorescence was especially studied and its physical mechanism was analyzed. It was observed that the optimal concentration of the quantum dots CdSe/ZnS for fluorescence is 2 micromole x L(-1). When the quantum dot's concentration is over 2 micromol x L(-1), the fluorescence is decreased with the increase in the concentration. While the quantum dot's concentration is less than 2 micromol x L(-1), the fluorescence is decreased with the decrease in the concentration. There are two main reasons: (1) fluorescence quenching and 2) the competition between absorption and fluorescence. When the quantum dot's concentration is over 2 micromol x L(-1), the distance between quantum dots is so close that the fluorescence quenching is induced. The closer the distance between quantum dots is, the more serious the fluorescence quenching is induced. Also, in this case, the absorption is so large that some of the quantum dots can not be excited because the incident light can not pass through the whole sample. As a result, the fluorescence is decreased with the increase in the quantum dot's concentration. As the quantum dot's concentration is below 2 micromol x L(-1), the distance between quantum dots is far enough that no more fluorescence quenching is induced. In this case, the fluorescence is determined by the particle number per unit volume. More particle number per unit volume produces more fluorescence. Therefore, the fluorescence is decreased with the decrease in the quantum dot's concentration.

  3. Multiple Exciton Generation in Semiconductor Quantum Dots.

    PubMed

    Beard, Matthew C

    2011-06-02

    Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by utilizing the excess energy in the absorbed photons. 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. However, variations in the reported enhanced quantum yields (QYs) have led to disagreements over the role that quantum confinement plays. The enhanced yield of excitons per absorbed photon is deduced from a dynamical signature in the transient absorption or transient photoluminescence and is ascribed to the creation of biexcitons. Extraneous effects such as photocharging are partially responsible for the observed variations. When these extraneous effects are reduced, the MEG efficiency, defined in terms of the number of additional electron-hole pairs produced per additional band gap of photon excitation, is about two times better in PbSe QDs than that in bulk PbSe. Thin films of electronically coupled QDs have shown promise in simple photon-to-electron conversion architectures. If the MEG efficiency can be further enhanced and charge separation and transport can be optimized within QD films, then QD solar cells can lead to third-generation solar energy conversion technologies.

  4. Coherent coupling of two quantum dots embedded in an Aharonov-Bohm interferometer.

    PubMed

    Holleitner, A W; Decker, C R; Qin, H; Eberl, K; Blick, R H

    2001-12-17

    We define two laterally gated small quantum dots with less than 15 electrons in an Aharonov-Bohm geometry in which the coupling between the two dots can be changed. We measure Aharonov-Bohm oscillations for weakly coupled quantum dots. In an intermediate coupling regime we study molecular states of the double dot and extract the magnetic field dependence of the coherently coupled states.

  5. A case study: Te in ZnSe and Mn-doped ZnSe quantum dots.

    PubMed

    Sonawane, Kiran G; Rajesh, Ch; Temgire, Mayur; Mahamuni, Shailaja

    2011-07-29

    Photoluminescence (PL) behavior of ZnSe(1-y)Te(y) quantum dots is investigated by varying Te concentration as well as size. The striking effect of quantum confinement is the observation of isoelectronic center-related emission at room temperature in lieu of near-band-edge emission that dominates the optical scenario. ZnSe(0.99)Te(0.01) quantum dots were also doped by Mn(2+) ions. The Mn(2+) ion-related d-d transition is drastically suppressed by Te isoelectronic centers. Incorporation of Mn(2+) at substitutional sites in ZnSe(0.99)Te(0.01) quantum dots is also confirmed by the electron paramagnetic resonance measurements. Effect of Te isoelectronic impurity on the emission behavior is more pronounced than that of Mn(2+) ions. A subtle blueshift in the orange d-d transition is a sign of a decrease in crystal field strength. PL and photoluminescence excitation measurements on Zn(1-x)Se(0.99)Te(0.01)Mn(x) quantum dots indicate that the transition probability from the lowest unoccupied molecular orbital to Te levels is substantially larger than that to Mn(2+) d-d levels.

  6. 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.

  7. Angiogenic Profiling of Synthesized Carbon Quantum Dots.

    PubMed

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

    2015-10-20

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

  8. Exciton binding energy in semiconductor quantum dots

    SciTech Connect

    Pokutnii, S. I.

    2010-04-15

    In the adiabatic approximation in the context of the modified effective mass approach, in which the reduced exciton effective mass {mu} = {mu}(a) is a function of the radius a of the semiconductor quantum dot, an expression for the exciton binding energy E{sub ex}(a) in the quantum dot is derived. It is found that, in the CdSe and CdS quantum dots with the radii a comparable to the Bohr exciton radii a{sub ex}, the exciton binding energy E{sub ex}(a) is substantially (respectively, 7.4 and 4.5 times) higher than the exciton binding energy in the CdSe and CdS single crystals.

  9. Vertically stacked quantum dot pairs fabricated by nanohole filling

    NASA Astrophysics Data System (ADS)

    Sonnenberg, D.; Küster, A.; Graf, A.; Heyn, Ch; Hansen, W.

    2014-05-01

    Strain-free, vertically coupled GaAs quantum dots (QDs) with an ultra-low density below 1\\times {{10}^{7}} \\text{c}{{\\text{m}}^{-2}} are fabricated by filling of self-assembled nanoholes with a GaAs/AlGaAs/GaAs layer sequence. The sizes of the two QDs, forming a QD pair (QDP), as well as the AlGaAs tunnel-barrier between the dots are tuned independently. We present atomic force microscopy studies of the QDP formation steps. We have performed photoluminescence studies of single QDPs with varied dot size and tunnel-barrier thickness. The data indicate non-resonant tunnelling between the dots. Furthermore, we apply the quantum confined Stark effect to tune the photoluminescence energy by up to 25 meV.

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

    DTIC Science & Technology

    2015-04-27

    SECURITY CLASSIFICATION OF: Quantum dot (QD) active regions hold potential for realizing extremely high performance semiconductor diode lasers...2009 31-Dec-2014 Approved for Public Release; Distribution Unlimited Final Report: Nanopatterned Quantum Dot Lasers for High Speed, High Efficiency...Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 quantum dots , nanopatterning, MOCVD, laser REPORT DOCUMENTATION PAGE 11

  11. 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.

  12. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum.

    PubMed

    Yamaguchi, Takaaki; Tsuruda, Yoshijiro; Furukawa, Tomohiro; Negishi, Lumi; Imura, Yuki; Sakuda, Shohei; Yoshimura, Etsuro; Suzuki, Michio

    2016-10-20

    CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum) were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were precipitated in the intracellular space, indicating that cadmium and selenium ions were incorporated into the cell and that the quantum dots were synthesized with intracellular metabolites. To reveal differences in F. oxysporum metabolism, cell extracts of F. oxysporum, before and after CdSe synthesis, were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results suggested that the amount of superoxide dismutase (SOD) decreased after CdSe synthesis. Fluorescence microscopy revealed that cytoplasmic superoxide increased significantly after CdSe synthesis. The accumulation of superoxide may increase the expression of various metabolites that play a role in reducing Se(4+) to Se(2-) and inhibit the aggregation of CdSe to make nanoparticles.

  13. Temperature-dependent electron transport in quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Padilla, Derek J.

    Quantum dot photovoltaics have attracted much interest from researchers in recent years. They have the potential to address both costs and efficiencies of solar cells while simultaneously demonstrating novel physics. Thin-film devices inherently require less material than bulk crystalline silicon, and solution deposition removes the high energy used in fabrication processes. The ease of bandgap tunability in quantum dots through size control allows for simple graded bandgap structures, which is one method of breaking beyond the Shockley-Queisser limit. Power output can also be increased through the process of multiple exciton generation, whereby more than one electron participates in conduction after the absorption of a single photon. In this dissertation work, quantum dot photovoltaics are examined through a range of temperatures. Exploring the current-voltage-temperature parameter space provides insight into the dominant conduction mechanisms within these materials, which is largely not agreed upon. Beginning with PbS quantum dots, changes in device structure are examined by varying the capping ligand and nanoparticle size. This leads similar studies of new, germanium quantum dot devices. Through this understanding, further optimization of device structure can lead to enhanced device performance.

  14. Density functional calculation of the structural and electronic properties of germanium quantum dots

    NASA Astrophysics Data System (ADS)

    Anas, M. M.; Gopir, G.

    2015-04-01

    We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.

  15. Density functional calculation of the structural and electronic properties of germanium quantum dots

    SciTech Connect

    Anas, M. M.; Gopir, G.

    2015-04-24

    We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.

  16. Imaging characteristics of zinc sulfide shell, cadmium telluride core quantum dots.

    PubMed

    Daneshvar, Hamid; Nelms, Jennifer; Muhammad, Osman; Jackson, Heather; Tkach, Jean; Davros, William; Peterson, Todd; Vogelbaum, Michael A; Bruchez, Marcel P; Toms, Steven A

    2008-02-01

    Quantum dots are optical nanocrystals whose in vitro and in vivo use in molecular imaging is expanding rapidly. In comparison with organic fluorophores, quantum dots exhibit desirable properties, such as multiwavelength fluorescence emission, excellent brightness and resistance to photobleaching. Their electron-dense, metallic cores suggest utility in other clinical imaging modalities. Core-shell zinc sulfide-cadmium telluride quantum dots were studied by magnetic resonance and computed tomography phantoms. Quantum dots were also injected into rat brain, as well as intravenously, using convection-enhanced delivery, prior to animal imaging. Computed tomography studies suggest that current formulations of quantum dots might be imaged in vivo in animals. Used in conjunction with optical imaging techniques, quantum dots have the potential to function as multimodal imaging platforms in vivo. The ability to detect an optical nanoparticle preoperatively with clinical imaging modality offers a distinct advantage to clinicians engaged in image-guided surgical applications.

  17. 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.

  18. Potential clinical applications of quantum dots.

    PubMed

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

    2008-01-01

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

  19. Single quantum dots as local temperature markers.

    PubMed

    Li, Sha; Zhang, Kai; Yang, Jui-Ming; Lin, Liwei; Yang, Haw

    2007-10-01

    This work describes noncontact, local temperature measurements using wavelength shifts of CdSe quantum dots (QDs). Individual QDs are demonstrated to be capable of sensing temperature variations and reporting temperature changes remotely through optical readout. Temperature profiles of a microheater under different input voltages are evaluated based on the spectral shift of QDs on the heater, and results are consistent with a one-dimensional electrothermal model. The theoretical resolution of this technique could go down to the size of a single quantum dot using far-field optics for temperature characterizations of micro/nanostructures.

  20. Zitterbewegung and quantum revivals in monolayer graphene quantum dots in magnetic fields

    NASA Astrophysics Data System (ADS)

    García, Trinidad; Cordero, Nicolás A.; Romera, Elvira

    2014-02-01

    The wave-packet evolution in graphene quantum dots in magnetic fields has been theoretically studied. By analyzing an effective Hamiltonian model we show the wave-packet dynamics exhibits three types of periodicities (Zitterbewegung, classical, and revival times). The influence of the size of the quantum dot and the strength of the external magnetic field in these periodicities has been considered. In addition, we have found that valley degeneracy breaking is shown by both classical and revival times.

  1. Photon-assisted tunneling in an asymmetrically coupled triple quantum dot

    SciTech Connect

    Wang, Bao-Chuan; Cao, Gang Chen, Bao-Bao; Yu, Guo-Dong; Li, Hai-Ou; Xiao, Ming; Guo, Guo-Ping

    2016-08-14

    The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-central dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems.

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

    PubMed

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

    2006-10-20

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

  3. Electron nuclear spin transfer in quantum-dot networks

    NASA Astrophysics Data System (ADS)

    Prada, M.; Toonen, R. C.; Blick, R. H.; Harrison, P.

    2005-05-01

    We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of different geometries of a two-dimensional network of quantum dots and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalized to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in the presence of nuclear spin relaxation. We find that the gradual depolarization of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.

  4. Relaxation of hot excitons in CdZnSe/ZnSe quantum wells and quantum dots

    NASA Astrophysics Data System (ADS)

    Spiegel, R.; Bacher, G.; Breitwieser, O.; Forchel, A.; Jobst, B.; Hommel, D.; Landwehr, G.

    1998-05-01

    The relaxation dynamics of hot excitons was studied in (Zn,Cd)Se/ZnSe quantum wells and quantum dots. A fast population of the radiative excitonic ground state occurs for an excitation excess energy corresponding to an integer number of optical phonon energies. This is indicated by a spectrally narrow photoluminescence peak observed immediately after the exciting laser pulse. Spatial diffusion of excitons, controlled by the interaction between excitons and acoustic phonons, causes a distinct linewidth broadening with increasing delay time in quantum wells. In contrast, this process is found to be strongly suppressed in quantum dots.

  5. Towards a feasible implementation of quantum neural networks using 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.

    2016-03-01

    We propose an implementation of quantum neural networks using an array of quantum dots with dipole-dipole interactions. We demonstrate that this implementation is both feasible and versatile by studying it within the framework of GaAs based quantum dot qubits coupled to a reservoir of acoustic phonons. Using numerically exact Feynman integral calculations, we have found that the quantum coherence in our neural networks survive for over a hundred ps even at liquid nitrogen temperatures (77 K), which is three orders of magnitude higher than current implementations, which are based on SQUID-based systems operating at temperatures in the mK range.

  6. Towards a feasible implementation of quantum neural networks using quantum dots

    SciTech Connect

    Altaisky, Mikhail V. E-mail: nzolnik@iki.rssi.ru; Zolnikova, Nadezhda N. E-mail: nzolnik@iki.rssi.ru; Krylov, Victor A.; Lozovik, Yurii E.; Dattani, Nikesh S.

    2016-03-07

    We propose an implementation of quantum neural networks using an array of quantum dots with dipole-dipole interactions. We demonstrate that this implementation is both feasible and versatile by studying it within the framework of GaAs based quantum dot qubits coupled to a reservoir of acoustic phonons. Using numerically exact Feynman integral calculations, we have found that the quantum coherence in our neural networks survive for over a hundred ps even at liquid nitrogen temperatures (77 K), which is three orders of magnitude higher than current implementations, which are based on SQUID-based systems operating at temperatures in the mK range.

  7. Radiative coupling of quantum dots in photonic crystal structures

    NASA Astrophysics Data System (ADS)

    Minkov, Momchil; Savona, Vincenzo

    2013-03-01

    We derive a general formalism to model the polariton states resulting from the radiation-matter interaction between an arbitrary number of excitonic transitions in semiconductor quantum dots and photon modes in a photonic crystal structure in which the quantum dots are embedded. The Maxwell equations, including the linear nonlocal susceptibility of the exciton transitions in the quantum dots, are cast into an eigenvalue problem, which can be applied to any structure whose photon modes can be computed with reliable accuracy, and in addition naturally allows for disorder effects to be taken into account. We compute realistic photon modes using Bloch-mode expansion. As example systems, we study typical InGaAs quantum dots in a GaAs photonic crystal structures—an Ln cavity or a W1 waveguide. For a single dot, we reproduce known analytical results, while for the two-dot case we study the radiative excitation transfer mechanism and characterize its strength, the dependence on the detuning between quantum dot and photon modes, and the dependence on interdot distance. We find in particular that the interdot radiative coupling strength can reach 100μeV in a short cavity, and its decay with distance in longer cavities and waveguides is determined by the group velocity of the exchanged photons and their radiative lifetime. We also show that, for an Ln cavity of increasing length, the radiative excitation transfer mechanism is subject to a crossover from a regime where a single photon mode is dominating, to a multimode regime—occurring around n = 150 for the system under study.

  8. Probing silicon quantum dots by single-dot techniques

    NASA Astrophysics Data System (ADS)

    Sychugov, Ilya; Valenta, Jan; Linnros, Jan

    2017-02-01

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

  9. Optical fiber temperature sensor utilizing alloyed Zn(x)Cd(1-x)S quantum dots.

    PubMed

    Zhao, Fei; Kim, Jongsung

    2014-08-01

    In this paper, optical fiber temperature sensors have been prepared by using alloyed Zn(x)Cd(1-x)S quantum dots as sensing media. The surface of the optical fiber was silanized to enhance covalent bond between quantum dots and optical fiber. The quantum dots were bonded to the surface of optical fiber and further encapsulated via sol-gel coating using 3-glycidoxypropyl trimethoxysilane (GPTMS) and 3-aminopropyl trimethoxysilane (APTMS) in ethyl alcohol in acidic condition. Quantum dots with green, yellow, and red fluorescence were used. The dependence of photoluminescence (PL) intensity from quantum dots on ambient temperature has been studied. Linear relation between the fluorescent intensity and temperature was obtained from alloyed quantum dots immobilized on the surface of optical fiber. The PL intensity, sensitivity, and thermal stability were increased by the silica encapsulation.

  10. Gain without inversion in hybrid quantum dot-metallic nanoparticle systems

    NASA Astrophysics Data System (ADS)

    Sadeghi, S. M.

    2010-11-01

    We study the generation of tunable gain without inversion in semiconductor quantum dots using plasmonic effects. For this we investigate the impact of localized surface plasmons on coherent nonlinear exciton effects in a quantum dot when it is located in the vicinity of a metallic nanoparticle. It is shown that when such a system is exposed to a laser field and the distance between the quantum dot and the metallic nanoparticle is reduced the initial impact of plasmons is enhancement of the ac-Stark shift in the quantum dot. When this distance is reduced beyond a critical value, the results show abrupt formation of a significant of amount of gain without inversion in the quantum dot. We show that such a 'molecular' gain is associated with the plasmonic metaresonance (PMR) formed via combined effects of laser-induced coherence in the quantum dot and plasmons.

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

    PubMed

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

    2014-10-08

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

  12. Magnetic quantum dot in two-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Li, Guo; Zhu, Jia-Lin; Yang, Ning

    2017-03-01

    Magnetic quantum dots in two-dimensional band and topological insulators are studied by solving the modified Dirac model under nonuniform magnetic fields. The Landau levels split into discrete states with certain angular momentum. The states splitting from the zero Landau levels lie in the energy gap for topological insulators but are out of the gap for band insulators. It is found that the ground states oscillate between the spin-up and spin-down states when the magnetic field or the dot size changes. The oscillation manifests itself as changes of sign and strength of charge currents near the dot's edge.

  13. Magneto-optical studies of ensembles of semimagnetic self-organized Cd(Mn)Se/Zn(Mn)Se Quantum Dots

    SciTech Connect

    Reshina, I. I.; Ivanov, S. V.; Toropov, A. A.

    2013-12-04

    Ensembles of Cd(Mn)Se/ZnSe and CdSe/Zn(Mn)Se semimagnetic self-organized quantum dots with different Mn content have been studied by photoluminescence and resonant Raman scattering under strong magnetic fields in Faraday and Voigt geometries and with spectral and polarization selective excitation. Electron spin-flip Raman scattering has been observed in Voigt geometry in the structures with large Mn content. Narrow exciton peaks completely σ{sup −}σ{sup +} polarized have been observed under selective excitation in Faraday geometry in the structures with medium and small Mn content. A number of specific effects manifested themselves in the structures with a smallest Mn content where no Zeeman shift of the photoluminescence bands was observed.

  14. Uptake of silica covered Quantum Dots into living cells: Long term vitality and morphology study on hyaluronic acid biomaterials.

    PubMed

    D'Amico, Michele; Fiorica, Calogero; Palumbo, Fabio Salvatore; Militello, Valeria; Leone, Maurizio; Dubertret, Benoit; Pitarresi, Giovanna; Giammona, Gaetano

    2016-10-01

    Quantum Dots (QDs) are promising very bright and stable fluorescent probes for optical studies in the biological field but water solubility and possible metal bio-contamination need to be addressed. In this work, a simple silica-QD hybrid system is prepared and the uptake in bovine chondrocytes living cells without any functionalization of the external protective silica shield is demonstrated. Moreover, long term treated cells vitality (up to 14days) and the transfer of silica-QDs to the next cell generations are here reported. Confocal fluorescence microscopy was also used to determine the morphology of the so labelled cells and the relative silica-QDs distribution. Finally, we employ silica-QD stained chondrocytes to characterize, as proof of concept, hydrogels obtained from an amphiphilic derivative of hyaluronic acid (HA-EDA-C18) functionalized with different amounts of the RGD peptide.

  15. Optical properties and effect of carrier tunnelling in CdSe colloidal quantum dots: A comparative study with different ligands

    NASA Astrophysics Data System (ADS)

    Goswami, Syamanta Kumar; Kim, Tae Soo; Oh, Eunsoon; Challa, Kiran Kumar; Kim, Eui-Tae

    2012-09-01

    We studied both cw and time-resolved photoluminescence of colloidal CdSe/ZnS core-shell quantum dots capped with chemical ligands. For the trioctylphosphine oxide capped CdSe/ZnS QDs, both the luminescence intensity and lifetime were found to be increased with increasing temperatures, which can be explained by the thermal activation of the carriers trapped at shallow trapping centers. After the ligand exchange into 3-mercaptopropionic acid, the non-radiative recombination rate was increased and the luminescence efficiency was decreased at room temperature. When the QDs were employed in photovoltaic devices, photocurrent was found to be increased after the ligand exchange. The improved photocurrents observed in photovoltaic devices can be explained by the improved tunnelling probability between the neighbouring QDs.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

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

    PubMed

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

    2017-06-27

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

  18. Nuclear spin effects in semiconductor quantum dots.

    PubMed

    Chekhovich, E A; Makhonin, M N; Tartakovskii, A I; Yacoby, A; Bluhm, H; Nowack, K C; Vandersypen, L M K

    2013-06-01

    The interaction of an electronic spin with its nuclear environment, an issue known as the central spin problem, has been the subject of considerable attention due to its relevance for spin-based quantum computation using semiconductor quantum dots. Independent control of the nuclear spin bath using nuclear magnetic resonance techniques and dynamic nuclear polarization using the central spin itself offer unique possibilities for manipulating the nuclear bath with significant consequences for the coherence and controlled manipulation of the central spin. Here we review some of the recent optical and transport experiments that have explored this central spin problem using semiconductor quantum dots. We focus on the interaction between 10(4)-10(6) nuclear spins and a spin of a single electron or valence-band hole. We also review the experimental techniques as well as the key theoretical ideas and the implications for quantum information science.

  19. Probing lectin and sperm with carbohydrate-modified quantum dots.

    PubMed

    Robinson, Anandakathir; Fang, Jim-Min; Chou, Pi-Tai; Liao, Kuang-Wen; Chu, Rea-Min; Lee, Shyh-Jye

    2005-10-01

    We report the encapsulation of quantum dots with biologically important beta-N-acetylglucosamine (GlcNAc) in different ratios, together with studies of their specific/sensitive multivalent interactions with lectins and sperm by fluorimetry, transmission electron microscopy, dynamic light scattering microscopy, confocal imaging techniques, and flow cytometry. These GlcNAc-encapsulated quantum dots (QDGLNs) specifically bind to wheat germ agglutinin, and cause fluorescence quenching and aggregation. Further studies of QDGLNs and the mannose-encapsulated QDs (QDMANs) with sperm revealed site-specific interactions, in which QDGLNs bind to the head of the sperm, while QDMANs spread over the whole sperm body.

  20. 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.

  1. Emerging application of quantum dots for drug delivery and therapy.

    PubMed

    Qi, Lifeng; Gao, Xiaohu

    2008-03-01

    Quantum dots have proven themselves as powerful fluorescent probes, especially for long-term, multiplexed, and quantitative imaging and detection. Newly engineered quantum dots with integrated targeting, imaging and therapeutic functionalities have become excellent material to study drug delivery in cells and small animals. This fluorescent 'prototype' will provide important information in the rational design of biocompatible drug carriers and will serve as a superior alternative to magnetic and radioactive imaging contrast agents in preclinical drug screening, validation and delivery research. This Editorial article is not intended to offer a comprehensive review on drug delivery, but to highlight the breakthroughs in the emerging applications of quantum dots in this field and to provide our perspective on future research.

  2. 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.

  3. 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.

  4. Modeling interfacial charge transport of quantum dots using cyclic voltammetry

    NASA Astrophysics Data System (ADS)

    Tobias, Andrew K.; Jones, Marcus

    2011-10-01

    Quantum dot applications are numerous and range from photovoltaic devices and lasers, to bio labeling. Complexities in the electronic band structure of quantum dots create the necessity for analysis techniques that can accurately and reproducibly provide their absolute band energies. Cyclic voltammetry (CV) is a novel candidate for these studies and has the potential to become a useful tool in engineering new nanocrystal technology, by providing information necessary for predicting and modeling interfacial charge transfer to and from quantum dots. Advancing from previous reports of nanocrystal CV, a carbon paste electrode was utilized in an attempt to increase measured current by ensuring intimate contact between nanocrystals and the electrode. Our goal was to investigate band energies and model nanocrystal-molecule electron transfer systems.

  5. Electro-optical properties of phosphorene quantum dots

    NASA Astrophysics Data System (ADS)

    Saroka, V. A.; Lukyanchuk, I.; Portnoi, M. E.; Abdelsalam, H.

    2017-08-01

    We study the electronic and optical properties of single-layer phosphorene quantum dots with various shapes, sizes, and edge types (including disordered edges) subjected to an external electric field normal to the structure plane. Compared to graphene quantum dots, in phosphorene clusters of similar shape and size there is a set of edge states with energies dispersed at around the Fermi level. These states make the majority of phosphorene quantum dots metallic and enrich the phosphorene absorption gap with low-energy absorption peaks tunable by the electric field. The presence of the edge states dispersed around the Fermi level is a characteristic feature that is independent of the edge morphology and roughness.

  6. Probing electric and magnetic vacuum fluctuations with quantum dots.

    PubMed

    Tighineanu, P; Andersen, M L; Sørensen, A S; Stobbe, S; Lodahl, P

    2014-07-25

    The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this Letter we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level.

  7. Germanium quantum dots: Optical properties and synthesis

    NASA Astrophysics Data System (ADS)

    Heath, James R.; Shiang, J. J.; Alivisatos, A. P.

    1994-07-01

    Three different size distributions of Ge quantum dots (≳200, 110, and 60 Å) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray photoemission, infrared spectroscopy, and Raman spectroscopy. Colloidal suspensions of these quantum dots were prepared and their extinction spectra are measured with ultraviolet/visible (UV/Vis) and near infrared (IR) spectroscopy, in the regime from 0.6 to 5 eV. The optical spectra are correlated with a Mie theory extinction calculation utilizing bulk optical constants. This leads to an assignment of three optical features to the E(1), E(0'), and E(2) direct band gap transitions. The E(0') transitions exhibit a strong size dependence. The near IR spectra of the largest dots is dominated by E(0) direct gap absorptions. For the smallest dots the near IR spectrum is dominated by the Γ25→L indirect transitions.

  8. Semiconductor quantum dot-inorganic nanotube hybrids.

    PubMed

    Kreizman, Ronen; Schwartz, Osip; Deutsch, Zvicka; Itzhakov, Stella; Zak, Alla; Cohen, Sidney R; Tenne, Reshef; Oron, Dan

    2012-03-28

    A synthetic route for preparation of inorganic WS(2) nanotube (INT)-colloidal semiconductor quantum dot (QD) hybrid structures is developed, and transient carrier dynamics on these hybrids are studied via transient photoluminescence spectroscopy utilizing several different types of QDs. Measurements reveal efficient resonant energy transfer from the QDs to the INT upon photoexcitation, provided that the QD emission is at a higher energy than the INT direct gap. Charge transfer in the hybrid system, characterized using QDs with band gaps below the INT direct gap, is found to be absent. This is attributed to the presence of an organic barrier layer due to the relatively long-chain organic ligands of the QDs under study. This system, analogous to carbon nanotube-QD hybrids, holds potential for a variety of applications, including photovoltaics, luminescence tagging and optoelectronics.

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

    SciTech Connect

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

    2014-04-24

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

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

    SciTech Connect

    Xu, Xingsheng

    2015-03-02

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

  11. Slow Electron Cooling in Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Pandey, Anshu; Guyot-Sionnest, Philippe

    2008-11-01

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

  12. Electronic properties of zigzag, armchair and their hybrid quantum dots of graphene and boron-nitride with and without substitution: A DFT study

    NASA Astrophysics Data System (ADS)

    Yamijala, Sharma S. R. K. C.; Bandyopadhyay, Arkamita; Pati, Swapan K.

    2014-05-01

    Spin-polarized density functional theory calculations have been performed on armchair graphene quantum dots and boron-nitride quantum dots (AG/BNQDs) and the effect of carbon/boron-nitride substitution on the electronic properties of these AG/BNQDs has been investigated. As a first step to consider more realistic quantum dots, quantum dots which are a combination of zigzag QDs and armchair QDs have been considered. Effect of substitution on these hybrid quantum dots has been explored for both GQDs and BNQDs and such results have been compared and contrasted with the results of substituted AG/BNQDs and their zigzag analogs. Our work suggests that the edge substitution can play an important tool while tuning the electronic properties of quantum dots.

  13. Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes

    PubMed Central

    2013-01-01

    Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed. PMID:24172215

  14. Size and spatial homogeneity of SiGe quantum dots in amorphous silica matrix

    SciTech Connect

    Buljan, Maja; Pinto, Sara R. C.; Rolo, Anabela G.; Levichev, Sergey; Gomes, Maria J. M.; Kashtiban, Reza J.; Bangert, Ursel; Chahboun, Adil; Holy, Vaclav

    2009-10-15

    In this paper, we present a study of structural properties of SiGe quantum dots formed in amorphous silica matrix by magnetron sputtering technique. We investigate deposition conditions leading to the formation of dense and uniformly sized quantum dots, distributed homogeneously in the matrix. X-ray and Raman spectroscopy were used to estimate the Si content. A detailed analysis based on grazing incidence small angle x-ray scattering revealed the influence of the deposition conditions on quantum dot sizes, size distributions, spatial arrangement, and concentration of quantum dots in the matrix, as well as the Si:Ge content.

  15. Cytotoxicity studies of CdSeS/ZnS quantum dots on cell culture in microfluidic system

    NASA Astrophysics Data System (ADS)

    Haczyk, Maja; Grabowska-Jadach, Ilona; Drozd, Marcin; Pietrzak, Mariusz; Malinowska, ElŻbieta; Brzózka, Zbigniew

    2014-08-01

    Quantum dots (QDs) semi-conducting nanocrystals have found numerous applications in many fields of science. Nowadays one can observe a growing perspective to use them in biomedicine. Thanks to QDs unique fluorescence properties (narrow emission spectra, high extinction coefficients, high quantum yields, photostability) and possibility to form conjugates with bioactive molecules, they can become a chance for better cancer cells imaging in cancer therapy. Therefore there is a need for better understanding of biological interactions between QDs and cancer cells in vitro. For this purpose we performed cytotoxicity tests of CdSeS/ZnS quantum dots stabilized with mercaptopropionic acid (MPA) ligand, on human lung cancer cell line (A549) in vitro in macro- (96-well plate) and micro-scale (a specially designed and fabricated microfluidic device). The results obtained demonstrated a little extent of cytotoxic effect of selected solutions of QDs to A549 cells.

  16. Study of valence-band intersublevel transitions in InAs/GaAs quantum dots-in-well infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Lao, Yan-Feng; Wolde, Seyoum; Unil Perera, A. G.; Zhang, Y. H.; Wang, T. M.; Kim, J. O.; Schuler-Sandy, Ted; Tian, Zhao-Bing; Krishna, S. S.

    2014-04-01

    The n-type quantum dot (QD) and dots-in-well (DWELL) infrared photodetectors, in general, display bias-dependent multiple-band response as a result of optical transitions between different quantum levels. Here, we present a unique characteristic of the p-type hole response, a well-preserved spectral profile, due to the much reduced tunneling probability of holes compared to electrons. This feature remains in a DWELL detector, with the dominant transition contributing to the response occurring between the QD ground state and the quantum-well states. The bias-independent response will benefit applications where single-color detection is desired and also allows achieving optimum performance by optimizing the bias.

  17. Study of valence-band intersublevel transitions in InAs/GaAs quantum dots-in-well infrared photodetectors

    SciTech Connect

    Lao, Yan-Feng; Wolde, Seyoum; Unil Perera, A. G.; Zhang, Y. H.; Wang, T. M.; Kim, J. O.; Schuler-Sandy, Ted; Tian, Zhao-Bing; Krishna, S. S.

    2014-04-28

    The n-type quantum dot (QD) and dots-in-well (DWELL) infrared photodetectors, in general, display bias-dependent multiple-band response as a result of optical transitions between different quantum levels. Here, we present a unique characteristic of the p-type hole response, a well-preserved spectral profile, due to the much reduced tunneling probability of holes compared to electrons. This feature remains in a DWELL detector, with the dominant transition contributing to the response occurring between the QD ground state and the quantum-well states. The bias-independent response will benefit applications where single-color detection is desired and also allows achieving optimum performance by optimizing the bias.

  18. Spin qubit relaxation in a moving quantum dot

    NASA Astrophysics Data System (ADS)

    Huang, Peihao; Hu, Xuedong

    2013-08-01

    Long-range quantum communication for spin qubits is an important open problem. Here we study decoherence of an electron spin qubit that is being transported in a moving quantum dot. We focus on spin decoherence due to spin-orbit interaction and a random electric potential. We find that at the lowest order, the motion induces longitudinal spin relaxation, with a rate linear in the dot velocity. Our calculated spin relaxation time ranges from sub μs in GaAs to above ms in Si, making this relaxation a significant decoherence channel. Our results also give clear indications on how to reduce the decoherence effect of electron motion.

  19. Stark effect and polarizability of graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Pedersen, Thomas Garm

    2017-09-01

    The properties of graphene quantum dots can be manipulated via lateral electric fields. Treating electrons in such structures as confined massless Dirac fermions, we derive an analytical expression for the quadratic Stark shift valid for arbitrary angular momentum and quantum dot size. Moreover, we determine the perturbative regime, beyond which higher-order field effects are observed. The Dirac approach is validated by comparison with atomistic tight-binding simulations. Finally, we study the influence on the Stark effect of band gaps produced by, e.g., interaction with the substrate.

  20. Bayesian based fluorescence coded imaging using quantum dots

    NASA Astrophysics Data System (ADS)

    Nishimura, Takahiro; Kimura, Hitoshi; Ogura, Yusuke; Tanida, Jun

    2017-04-01

    Single-molecule localization techniques are effective to resolve fluorescence images with higher resolution. To increase the frame rate, high-density positions of individual fluorescence emitters should be measured. We are studying a Bayesian-based localization method for measuring high density molecular positions with fluorescence coded images. In this paper, a scheme of several color quantum dots aligned with DNA nanostructures are considered. We confirmed that the proposed method could be applied to fluorescence images of quantum dots experimentally and that the positions of the aligned fluorescence emitters at intervals of 80 nm could be measured with little errors in numerical simulations.

  1. Nonlinear optical susceptibilities of semiconductor quantum dot - metal nanoparticle hybrids

    NASA Astrophysics Data System (ADS)

    Terzis, A. F.; Kosionis, S. G.; Boviatsis, J.; Paspalakis, E.

    2016-03-01

    We theoretically study nonlinear optical effects of a semiconductor quantum dot and a spherical metal nanoparticle coupled via long-range Coulomb interaction. We solve the relevant density matrix equations in steady state and use proper perturbation theory to obtain closed-form analytical expressions for the nonlinear susceptibilities of the quantum dot, the metal nanoparticle, and the entire coupled system, up to fifth order. We also investigate the influence of the material of the semiconductor and the impact of the interparticle distance on the form of the spectra of the nonlinear susceptibilities.

  2. Interactions of quantum dots with donor blood erythrocytes in vitro.

    PubMed

    Pleskova, S N; Pudovkina, E E; Mikheeva, E R; Gorshkova, E N

    2014-01-01

    The effects of quantum dots CdSe/ZnS-mercaptopropionic acid, (CdSe/CdZnS)ZnS-polyT, and CdSeCdSZnS/polyT/SiO2-NH2 on human erythrocytes were studied. The nanomaterials reduced signifi cantly the erythrocyte sedimentation rate and modified the erythrocyte membrane resistance to induced (acid and hypo-osmotic) hemolysis. Evaluation of the erythrocyte morphology by atomic force microscopy in the control and after exposure to quantum dots showed significant differences in erythrocyte size and changes in their morphology as a result of exposure to the nanomaterials.

  3. New small quantum dots for neuroscience

    NASA Astrophysics Data System (ADS)

    Selvin, Paul

    2014-03-01

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

  4. 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.

  5. Nanocomposites of POC and quantum dots

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  6. 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.

  7. Photonic crystal nanocavity laser with a single quantum dot gain.

    PubMed

    Nomura, Masahiro; Kumagai, Naoto; Iwamoto, Satoshi; Ota, Yasutomo; Arakawa, Yasuhiko

    2009-08-31

    We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain. The investigated nanocavities contain only 0.4 quantum dots on an average; an ultra-low density quantum dot sample (1.5 x 10(8) cm(-2)) is used so that a single quantum dot can be isolated from the surrounding quantum dots. Laser oscillation begins at a pump power of 42 nW under resonant condition, while the far-detuning conditions require ~145 nW for lasing. This spectral detuning dependence of laser threshold indicates substantial contribution of the single quantum dot to the total gain. Moreover, photon correlation measurements show a distinct transition from anti-bunching to Poissonian via bunching with the increase of the excitation power, which is also an evidence of laser oscillation using the single quantum dot gain.

  8. Quantum Dot Cellular Automata: Computing with Coupled Quantum-Dot Molecules

    NASA Astrophysics Data System (ADS)

    Porod, Wolfgang

    1998-05-01

    We have recently proposed a scheme of using coupled quantum dots to realize digital computing elements.(C. S. Lent, P. D. Tougaw, W. Porod, and G. H. Bernstein, Nanotechnology 4, 49 (1993); C. S. Lent, P. D. Tougaw, and W. Porod, Applied Physics Letters 62, 714 (1993).) Our scheme was inspired by recent work on nanometer-scale lithography in semiconductors which has permitted the construction of quantum dots which may be viewed as artificial atoms; furthermore, the principle of dot-dot coupling has also been demonstrated, thus realizing artificial semiconductor molecules. This talk will review the work of the Notre Dame group on the theory and modeling of cellular arrays of coupled quantum-dot molecules, which we refer to as quantum-dot cellular automata (QCA). We consider inhomogeneous arrays of quantum-dot molecules, where each molecule forms the basic unit in a cellular automaton-type array architecture. These cells (molecules) consists of four or five quantum dots in close enough proximity to enable electron tunneling between dots. Coulomb repulsion between electrons in the cell results in a bistable ground state whose configuration is determined by the configuration of neighboring cells. The electrons tend to occupy antipodal sites in one of two ground-state configurations which may be used to encode binary information. We have demonstrated that Boolean logic gates can be constructed, and simple design rules permit the fabrication of any logic function. The basic principle of QCA operation was demonstrated in recent experiments.(A. O. Orlov, I. Amlani, G. H. Bernstein, C. S. Lent, and G. L. Snider, Science 277, 928, (1997).)

  9. 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.

  10. Optoelectronic Applications of Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Zhang, Nanzhu; Brenneman, Kimber; Wu, Tsai Chin; Jung, Hyeson; Biswas, Sushmita; Sen, Banani; Reinhardt, Kitt; Liao, Sicheng; Stroscio, Michael A.; Dutta, Mitra

    This chapter highlights recent optoelectronic applications of colloidal quantum dots (QDs). In recent years, many colloidal QD-based optoelectronic devices, and device concepts have been proposed and studied. Many of these device concepts build on traditional optoelectronic device concepts. Increasingly, many new optoelectronic device concepts have been based on the use of biomolecule QD complexes. In this chapter, both types of structures are discussed. Special emphasis is placed on new optoelectronic device concepts that incorporate DNA-based aptamers in biomolecule QD complexes. Not only are the extensions of traditional devices and concepts realizable, such as QD-based photo detectors, displays, photoluminescent and photovoltaic devices, light-emitting diodes (LEDs), photovoltaic devices, and solar cells, but new devices concepts such a biomolecule-based molecular sensors possible. This chapter highlights a number of such novel QD-based devices and device concepts.

  11. 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.

  12. Correlation energy of anisotropic quantum dots

    SciTech Connect

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

    2011-09-15

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

  13. Andreev Conductance of a Chaotic Quantum Dot

    NASA Astrophysics Data System (ADS)

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

    2000-03-01

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

  14. Quantum dots: synthesis, bioapplications, and toxicity

    PubMed Central

    2012-01-01

    This review introduces quantum dots (QDs) and explores their properties, synthesis, applications, delivery systems in biology, and their toxicity. QDs are one of the first nanotechnologies to be integrated with the biological sciences and are widely anticipated to eventually find application in a number of commercial consumer and clinical products. They exhibit unique luminescence characteristics and electronic properties such as wide and continuous absorption spectra, narrow emission spectra, and high light stability. The application of QDs, as a new technology for biosystems, has been typically studied on mammalian cells. Due to the small structures of QDs, some physical properties such as optical and electron transport characteristics are quite different from those of the bulk materials. PMID:22929008

  15. Monolithic mode-locked quantum dot lasers

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  17. Tellurium quantum dots: Preparation and optical properties

    NASA Astrophysics Data System (ADS)

    Lu, Chaoyu; Li, Xueming; Tang, Libin; Lai, Sin Ki; Rogée, Lukas; Teng, Kar Seng; Qian, Fuli; Zhou, Liangliang; Lau, Shu Ping

    2017-08-01

    Herein, we report an effective and simple method for producing Tellurium Quantum dots (TeQDs), zero-dimensional nanomaterials with great prospects for biomedical applications. Their preparation is based on the ultrasonic exfoliation of Te powder dispersed in 1-methyl-2-pyrrolidone. Sonication causes the van der Waals forces between the structural hexagons of Te to break so that the relatively coarse powder breaks down into nanoscale particles. The TeQDs have an average size of about 4 nm. UV-Vis absorption spectra of the TeQDs showed an absorption peak at 288 nm. Photoluminescence excitation (PLE) and photoluminescence (PL) are used to study the optical properties of TeQDs. Both the PLE and PL peaks revealed a linear relationship against the emission and excitation energies, respectively. TeQDs have important potential applications in biological imaging and catalysis as well as optoelectronics.

  18. Light-emitting quantum dot transistors: emission at high charge carrier densities.

    PubMed

    Schornbaum, Julia; Zakharko, Yuriy; Held, Martin; Thiemann, Stefan; Gannott, Florentina; Zaumseil, Jana

    2015-03-11

    For the application of colloidal semiconductor quantum dots in optoelectronic devices, for example, solar cells and light-emitting diodes, it is crucial to understand and control their charge transport and recombination dynamics at high carrier densities. Both can be studied in ambipolar, light-emitting field-effect transistors (LEFETs). Here, we report the first quantum dot light-emitting transistor. Electrolyte-gated PbS quantum dot LEFETs exhibit near-infrared electroluminescence from a confined region within the channel, which proves true ambipolar transport in ligand-exchanged quantum dot solids. Unexpectedly, the external quantum efficiencies improve significantly with current density. This effect correlates with the unusual increase of photoluminescence quantum yield and longer average lifetimes at higher electron and hole concentrations in PbS quantum dot thin films. We attribute the initially low emission efficiencies to nonradiative losses through trap states. At higher carrier densities, these trap states are deactivated and emission is dominated by trions.

  19. Effects of Shape and Strain Distribution of Quantum Dots on Optical Transition in the Quantum Dot Infrared Photodetectors

    PubMed Central

    2008-01-01

    We present a systemic theoretical study of the electronic properties of the quantum dots inserted in quantum dot infrared photodetectors (QDIPs). The strain distribution of three different shaped quantum dots (QDs) with a same ratio of the base to the vertical aspect is calculated by using the short-range valence-force-field (VFF) approach. The calculated results show that the hydrostatic strain ɛHvaries little with change of the shape, while the biaxial strain ɛBchanges a lot for different shapes of QDs. The recursion method is used to calculate the energy levels of the bound states in QDs. Compared with the strain, the shape plays a key role in the difference of electronic bound energy levels. The numerical results show that the deference of bound energy levels of lenslike InAs QD matches well with the experimental results. Moreover, the pyramid-shaped QD has the greatest difference from the measured experimental data. PMID:20596318

  20. What Quantum Dots Can Do for You

    NASA Astrophysics Data System (ADS)

    Salamo, Gregory

    2008-03-01

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

  1. 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.

  2. Experimental study of nanomagnets for magnetic quantum-dot cellular automata (MQCA) logic applications

    NASA Astrophysics Data System (ADS)

    Imre, Alexandra

    Nanomagnets that exhibit only two stable states of magnetization can represent digital bits. Magnetic random access memories store binary information in such nanomagnets, and currently, fabrication of dense arrays of nanomagnets is also under development for application in hard disk drives. The latter faces the challenge of avoiding magnetic dipole interactions between the individual elements in the arrays, which limits data storage density. On the contrary, these interactions are utilized in the magnetic quantum-dot cellular automata (MQCA) system, which is a network of closely-spaced, dipole-coupled, single-domain nanomagnets designed for digital computation. MQCA offers very low power dissipation together with high integration density of functional devices, as QCA implementations do in general. In addition, MQCA can operate over a wide temperature range from sub-Kelvin to the Curie temperature. Information propagation and inversion have previously been demonstrated in MQCA. In this dissertation, room temperature operation of the basic MQCA logic gate, i.e. the three-input majority gate, is demonstrated for the first time. The samples were fabricated on silicon wafers by using electron-beam lithography for patterning thermally evaporated ferromagnetic metals. The networks of nanomagnets were imaged by magnetic force microscopy (MFM), with which individual magnetization states were distinguished and mapped. Magnetic dipole-ordering in the networks was investigated in different samples. Average ordering lengths were calculated by statistical analysis of the MFM images taken after several independent demagnetization processes. The average ordering length was found to be dependent on the shape and size of the nanomagnets and limited by defects introduced during fabrication. Defect tolerant shape-design was investigated in samples of many different ring-shaped and elongated nanomagnets. The shape-effects were explained by means of micromagnetic simulations. The

  3. Andreev and Majorana bound states in single and double quantum dot structures.

    PubMed

    Silva, Joelson F; Vernek, E

    2016-11-02

    We present a numerical study of the emergence of Majorana and Andreev bound states in a system composed of two quantum dots, one of which is coupled to a conventional superconductor, SC1, and the other connects to a topological superconductor, SC2. By controlling the interdot coupling we can drive the system from two single (uncoupled) quantum dots to double (coupled) dot system configurations. We employ a recursive Green's function technique that provides us with numerically exact results for the local density of states of the system. We first show that in the uncoupled dot configuration (single dot behavior) the Majorana and the Andreev bound states appear in an individual dot in two completely distinct regimes. Therefore, they cannot coexist in the single quantum dot system. We then study the coexistence of these states in the coupled double dot configuration. In this situation we show that in the trivial phase of SC2, the Andreev states are bound to an individual quantum dot in the atomic regime (weak interdot coupling) or extended over the entire molecule in the molecular regime (strong interdot coupling). More interesting features are actually seen in the topological phase of SC2. In this case, in the atomic limit, the Andreev states appear bound to one of the quantum dots while a Majorana zero mode appears in the other one. In the molecular regime, on the other hand, the Andreev bound states take over the entire molecule while the Majorana state remains always bound to one of the quantum dots.

  4. 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

  5. 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

  6. Intracellular distribution of nontargeted quantum dots after natural uptake and microinjection

    PubMed Central

    Damalakiene, Leona; Karabanovas, Vitalijus; Bagdonas, Saulius; Valius, Mindaugas; Rotomskis, Ricardas

    2013-01-01

    Background: The purpose of this study was to elucidate the mechanism of natural uptake of nonfunctionalized quantum dots in comparison with microinjected quantum dots by focusing on their time-dependent accumulation and intracellular localization in different cell lines. Methods: The accumulation dynamics of nontargeted CdSe/ZnS carboxyl-coated quantum dots (emission peak 625 nm) was analyzed in NIH3T3, MCF-7, and HepG2 cells by applying the methods of confocal and steady-state fluorescence spectroscopy. Intracellular colocalization of the quantum dots was investigated by staining with Lysotracker®. Results: The uptake of quantum dots into cells was dramatically reduced at a low temperature (4°C), indicating that the process is energy-dependent. The uptake kinetics and imaging of intracellular localization of quantum dots revealed three accumulation stages of carboxyl-coated quantum dots at 37°C, ie, a plateau stage, growth stage, and a saturation stage, which comprised four morphological phases: adherence to the cell membrane; formation of granulated clusters spread throughout the cytoplasm; localization of granulated clusters in the perinuclear region; and formation of multivesicular body-like structures and their redistribution in the cytoplasm. Diverse quantum dots containing intracellular vesicles in the range of approximately 0.5–8 μm in diameter were observed in the cytoplasm, but none were found in the nucleus. Vesicles containing quantum dots formed multivesicular body-like structures in NIH3T3 cells after 24 hours of incubation, which were Lysotracker-negative in serum-free medium and Lysotracker-positive in complete medium. The microinjected quantum dots remained uniformly distributed in the cytosol for at least 24 hours. Conclusion: Natural uptake of quantum dots in cells occurs through three accumulation stages via a mechanism requiring energy. The sharp contrast of the intracellular distribution after microinjection of quantum dots in comparison

  7. Quantum Dots and Their Multimodal Applications: A Review

    PubMed Central

    Bera, Debasis; Qian, Lei; Tseng, Teng-Kuan; Holloway, Paul H.

    2010-01-01

    Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

  8. 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

  9. Carrier dynamics in InAs/AlAs quantum dots: lack in carrier transfer from wetting layer to quantum dots.

    PubMed

    Shamirzaev, T S; Abramkin, D S; Nenashev, A V; Zhuravlev, K S; Trojánek, F; Dzurnák, B; Malý, P

    2010-04-16

    Structures with self-assembled InAs quantum dots (QDs) embedded in an AlAs matrix have been studied by steady-state and transient photoluminescence. It has been shown that in contrast to InAs/GaAs QD systems carriers are mainly captured by quantum dots directly from the AlAs matrix, while transfer of carriers captured by the wetting layer far away from QDs to the QDs is suppressed. At low temperatures the carriers captured by the wetting layer are localized by potential fluctuations at the wetting layer interface, while at high temperatures the carriers are delocalized but captured by nonradiative centers located in the wetting layer.

  10. A real-time spectrum acquisition system design based on quantum dots-quantum well detector

    NASA Astrophysics Data System (ADS)

    Zhang, S. H.; Guo, F. M.

    2016-01-01

    In this paper, we studied the structure characteristics of quantum dots-quantum well photodetector with response wavelength range from 400 nm to 1000 nm. It has the characteristics of high sensitivity, low dark current and the high conductance gain. According to the properties of the quantum dots-quantum well photodetectors, we designed a new type of capacitive transimpedence amplifier (CTIA) readout circuit structure with the advantages of adjustable gain, wide bandwidth and high driving ability. We have implemented the chip packaging between CTIA-CDS structure readout circuit and quantum dots detector and tested the readout response characteristics. According to the timing signals requirements of our readout circuit, we designed a real-time spectral data acquisition system based on FPGA and ARM. Parallel processing mode of programmable devices makes the system has high sensitivity and high transmission rate. In addition, we realized blind pixel compensation and smoothing filter algorithm processing to the real time spectrum data by using C++. Through the fluorescence spectrum measurement of carbon quantum dots and the signal acquisition system and computer software system to realize the collection of the spectrum signal processing and analysis, we verified the excellent characteristics of detector. It meets the design requirements of quantum dot spectrum acquisition system with the characteristics of short integration time, real-time and portability.

  11. Laterally-biased quantum dot infrared photodetector

    NASA Astrophysics Data System (ADS)

    Cardimona, D. A.; Morath, C. P.; Guidry, D. H.; Cowan, V. M.

    2013-07-01

    At the Air Force Research Laboratory, Space Vehicles Directorate, we are interested in improving the performance of or modifying the capabilities of infrared detectors in order to locate and identify dim and/or distant objects in space. One characteristic we are very interested in is multicolor detection. To this end, we have turned to a novel detector design that we have come to call a Lateral Quantum Dot Infrared Photodetector (LQDIP). In this design, InAs quantum dots are buried in a GaAs quantum well, which in turn is tunnel-coupled to another GaAs quantum well. Photoexcited electrons from the quantum dots tunnel over to the second well and are then swept out via a lateral (perpendicular to the growth direction) bias voltage. This architecture should exhibit the ability to tune to select infrared frequencies with reduced dark current and unity gain. The lateral photocurrent is directed by a vertical (parallel to the growth direction) gate voltage. We will discuss this detector architecture and the LQDIP operating principles and conditions, and we will present some preliminary results of current-voltage, photocurrent, differential conductance, and spectral measurements.

  12. Efficient Luminescence from Perovskite Quantum Dot Solids.

    PubMed

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

    2015-11-18

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

  13. Quantum state measurement in double quantum dots with a radio-frequency quantum point contact

    NASA Astrophysics Data System (ADS)

    Yan, Lei; Wang, Hai-Xia; Yin, Wen; Wang, Fang-Wei

    2014-02-01

    We study the dynamics of two electron spins in coupled quantum dots (CQDs) monitored by a quantum point contact (QPC) detector. Their quantum state can be measured by embedding the QPC in an LC circuit. We derive the Bloch-type rate equations of the reduced density matrix for CQDs. Special attention is paid to the numerical results for the weak measurement condintion under a strong Coulomb interaction. It is shown that the evolution of QPC current always follows that of electron occupation in the right dot. In addition, we find that the output voltage of the circuit can reflect the evolution of QPC current when the circuit and QPC are approximately equal in frequency. In particular, the wave shape of the output voltage can be improved by adjusting the circuit resonance frequency and bandwidth.

  14. Ultrafast Laser Studies of Two-Photon Excited Fluorescence Intermittency in Single CdSe/ZnS Quantum Dots.

    PubMed

    Early, Kevin T; Nesbitt, David J

    2015-12-09

    Two-photon fluorescence microscopy of single quantum dots conditions has been reported by several groups, with contrasting observations regarding the kinetics and dynamics of fluorescence intermittency or "blinking". Here, we investigate the power dependence, kinetics, and statistics of two photon-excited fluorescence intermittency from single CdSe/ZnS quantum dots in a solid PMMA film as a function of sub-bandgap laser intensity at 800 nm. Fluorescence intermittency is observed at all excitation powers and a quadratic (n = 1.97(3)) dependence of the shot noise-limited fluorescence intensity on the incident laser power is verified, confirming essentially zero background contribution from one-photon excitation processes. Such analyses permit two photon absorption cross sections for single quantum dots to be extracted quantitatively from the data, which reveal good agreement with those obtained from previous two-photon FCS measurements. Strictly inverse power law-distributed off-state dwell times are observed for all excitation powers, with a mean power law exponent ⟨m(off)⟩ = 1.65(4) in excellent agreement with the behavior observed under one-photon excitation conditions. Finally, a superquadratic (n = 2.3(2)) rather than quartic (n = 4) power dependence is observed for the on-state blinking dwell times, which we kinetically analyze and interpret in terms of a novel 2 + 1 "hot" exciton ionization/blinking mechanism due to partially saturated 1-photon sub-bandgap excitation out of the two-photon single exciton state. The kinetic results are consistent with quantum dot photoionization quantum yields from "hot" exciton states (4(1) × 10(-6)) comparable with experimental estimates (10(-6)-10(-5)) of Auger ionization efficiencies out of the biexcitonic state.

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

    PubMed

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

    2004-05-15

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

  16. UV Nano-Lights - Nonlinear Quantum Dot-Plasmon Coupling

    DTIC Science & Technology

    2016-06-20

    grant, with results communicated by thesis and journal papers throughout Morgana’s PhD. This study expanded quantum mechanical model previously...SUBJECT TERMS Quantum Dots, Energy Conversion, Up-conversion, Modeling 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES...confirmed a prediction for crystallisation promotion predicted by hard-sphere modelling of seeded crystal growth. By controlling gold seed-size, our

  17. Spontaneous emission and optical control of spins in quantum dots

    NASA Astrophysics Data System (ADS)

    Economou, Sophia E.

    Quantum dots are attractive due to their potential technological applications and the opportunity they provide for study of fundamental physics in the mesoscopic scale. This dissertation studies optically controlled spins in quantum dots in connection to quantum information processing. The physical realization of the quantum bit (qubit) consists of the two spin states of an extra electron confined in a quantum dot. Spin rotations are performed optically, by use of an intermediate charged exciton (trion) state. The two spin states and the trion form a Λ-type system. The merits of this system for quantum information processing include integrability into a solid-state device, long spin coherence time, and fast and focused optical control. In this dissertation, we study the optical decay mechanisms of the trion state in the quantum dot. Using a master-equation approach, we derive microscopically the optical decay of the three-level system and find a novel term, the so-called spontaneously generated coherence (SGC). The latter, though predicted more than a decade ago for atomic Λ-systems satisfying certain conditions, had not been detected yet in any system. We found that in quantum dots, these conditions can be satisfied. We present the experiment which, in collaboration with our theory, constituted the first measurement of SGC. We establish the unification of SGC, polarization entanglement, and two-pathway decay. By keeping track of the spontaneously emitted photon dynamics, we find the conditions on the couplings that determine which effect will take place. We have thus placed SGC in a more quantum informational framework, characterizing it as lack of entanglement between the emitted photon and the three-level system. We develop a theory of ultrafast optical single-qubit rotations by use of 2pi pulses, which have the two-fold advantage of minimal trion excitation and negligible spin precession. The analytically solvable hyperbolic secant pulses of Rosen and Zener

  18. Energy transfer in monodisperse quantum dot solids in the presence of self-organized array of metallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Sadeghi, S. M.; West, R. G.

    2013-03-01

    We examined the interdot energy transfer between monodisperse quantum dots under different degrees of plasmonic effects (plasmonic field enhancement and Forster energy transfer from quantum dots to metallic nanoparticles). For this we studied emission of CdSe/ZnS quantum dots deposited on substrates containing self-organized arrays of gold nanoislands with radially distributed sizes gradually reduced from the centers of the substrates to their sides. The results suggest how metallic nanoparticles can be used to enhance interdot energy transfer in monodisperse quantum dots and how this process can explain some of the spectral changes seen in the emission of quantum dots when they are close to the metallic nanoparticles.

  19. GaAs structures with InAs and As quantum dots produced in a single molecular beam epitaxy process

    SciTech Connect

    Nevedomskii, V. N. Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2009-12-15

    Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults.

  20. Coherent and incoherent charge transport in linear triple quantum dots.

    PubMed

    Contreras-Pulido, L Debora; Bruderer, Martin

    2017-03-15

    One of the fundamental questions in quantum transport is how charge transfer through complex nanostructures is influenced by quantum coherence. We address this issue for linear triple quantum dots by comparing a Lindblad density matrix description with a Pauli rate equation approach and analyze the corresponding zero-frequency counting statistics of charge transfer. The impact of decaying coherences of the density matrix due to dephasing is also studied. Our findings reveal that the sensitivity to coherence shown by shot noise and skewness, in particular in the limit of large coupling to the drain reservoir, can be used to unambiguously evidence coherent processes involved in charge transport across triple quantum dots. Our analytical results are obtained by using the characteristic polynomial approach to full counting statistics.

  1. Mitigation of Quantum Dot Cytotoxicity by Microencapsulation

    PubMed Central

    Romoser, Amelia; Ritter, Dustin; Majitha, Ravish; Meissner, Kenith E.; McShane, Michael; Sayes, Christie M.

    2011-01-01

    When CdSe/ZnS-polyethyleneimine (PEI) quantum dots (QDs) are microencapsulated in polymeric microcapsules, human fibroblasts are protected from acute cytotoxic effects. Differences in cellular morphology, uptake, and viability were assessed after treatment with either microencapsulated or unencapsulated dots. Specifically, QDs contained in microcapsules terminated with polyethylene glycol (PEG) mitigate contact with and uptake by cells, thus providing a tool to retain particle luminescence for applications such as extracellular sensing and imaging. The microcapsule serves as the “first line of defense” for containing the QDs. This enables the individual QD coating to be designed primarily to enhance the function of the biosensor. PMID:21814567

  2. 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.

  3. 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.

  4. Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot

    NASA Astrophysics Data System (ADS)

    M, Tiotsop; A, J. Fotue; S, C. Kenfack; N, Issofa; H, Fotsin; L, C. Fai

    2016-04-01

    In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electric-LO-phonon strong-coupling and polar angle in RbCl triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a two-level quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbCl triangular quantum dot are also studied.

  5. Car-Parrinello molecular dynamics study of the melting behaviors of n-atom (n = 6, 10) graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Shekaari, Ashkan; Abolhassani, Mohammad Reza

    2017-06-01

    First-principles molecular dynamics has been applied to inquire into the melting behaviors of n-atom (n = 6, 10) graphene quantum dots (GQD6 and zigzag GQD10) within the temperature range of T = 0-500 K. The temperature dependence of the geometry of each quantum dot is thoroughly evaluated via calculating the related shape deformation parameters and the eigenvalues of the quadrupole tensors. Examining the variations of some phase-transition indicators such as root-mean-square bond length fluctuations and mean square displacements broadly proposes the value of Tm = 70 K for the melting point of GQD6 while a continuous, two-stage phase transition has been concluded for zigzag GQD10.

  6. Elementary excitations in charge-tunable InGaAs quantum dots studied by resonant Raman and resonant photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Köppen, Tim; Franz, Dennis; Schramm, Andreas; Heyn, Christian; Gutjahr, Johann; Pfannkuche, Daniela; Heitmann, Detlef; Kipp, Tobias

    2011-04-01

    We report on resonant optical spectroscopy of self-assembled InGaAs quantum dots in which the number of electrons can accurately be tuned to N=0,1,2 by an external gate voltage. Polarization, wave vector, and magnetic field dependent measurements enable us to clearly distinguish between resonant Raman and resonant photoluminescence processes. The Raman spectra for N=1 and 2 electrons considerably differ from each other. In particular, for N=2, the quantum-dot He, the spectra exhibit both singlet and triplet transitions reflecting the elementary many-particle interaction. Also the resonant photoluminescence spectra are significantly changed by varying the number of electrons in the QDs. For N=1 we observe complex spectra possibly induced by strong polaronic effects that are suppressed for N=2.

  7. SU(4) Kondo entanglement in double quantum dot devices

    NASA Astrophysics Data System (ADS)

    Bonazzola, Rodrigo; Andrade, J. A.; Facio, Jorge I.; García, D. J.; Cornaglia, Pablo S.

    2017-08-01

    We analyze, from a quantum information theory perspective, the possibility of realizing an SU(4) entangled Kondo regime in semiconductor double quantum dot devices. We focus our analysis on the ground-state properties and consider the general experimental situation where the coupling parameters of the two quantum dots differ. We model each quantum dot with an Anderson-type Hamiltonian including an interdot Coulomb repulsion and tunnel couplings for each quantum dot to independent fermionic baths. We find that the spin and pseudospin entanglements can be made equal, and the SU(4) symmetry recovered, if the gate voltages are chosen in such a way that the average charge occupancies of the two quantum dots are equal, and the double occupancy on the double quantum dot is suppressed. We present density matrix renormalization group numerical results for the spin and pseudospin entanglement entropies, and analytical results for a simplified model that captures the main physics of the problem.

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

    PubMed

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

    2017-03-22

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

  9. Comparison of three cell fixation methods for high content analysis assays utilizing quantum dots.

    PubMed

    Williams, Y; Byrne, S; Bashir, M; Davies, A; Whelan, A; Gun'ko, Y; Kelleher, D; Volkov, Y

    2008-10-01

    Semiconductor nanoparticles or quantum dots are being increasingly utilized as fluorescent probes in cell biology both in live and fixed cell assays. Quantum dots possess an immense potential for use in multiplexing assays that can be run on high content screening analysers. Depending on the nature of the biological target under investigation, experiments are frequently required on cells retaining an intact cell membrane or also on those that have been fixed and permeabilized to expose intracellular antigens. Fixation of cell lines before or after the addition of quantum dots may affect their localization, emission properties and stability. Using a high content analysis platform we perform a quantitative comparative analysis of three common fixation techniques in two different cell lines exposed to carboxylic acid stabilized CdTe quantum dots. Our study demonstrates that in prefixed and permeabilized cells, quantum dots are readily internalized regardless of cell type, and their intracellular location is primarily determined by the properties of the quantum dots themselves. However, if the fixation procedures are preformed on live cells previously incubated with quantum dots, other important factors have to be considered. The choice of the fixative significantly influences the fluorescent characteristics of the quantum dots. Fixatives, regardless of their chemical nature, negatively affected quantum dots fluorescence intensity. Comparative analysis of gluteraldehyde, methanol and paraformaldehyde demonstrated that 2% paraformaldehyde was the fixative of choice. The presence of protein in the media did not significantly alter the quantum dot fluorescence. This study indicates that multiplexing assays utilizing quantum dots, despite being a cutting edge tool for high content cell imaging, still require careful consideration of the basic steps in biological sample processing.

  10. Probing relaxation times in graphene quantum dots

    PubMed Central

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

    2013-01-01

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

  11. 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.

  12. Bismides: 2D structures and quantum dots

    NASA Astrophysics Data System (ADS)

    Pačebutas, Vaidas; Butkutė, Renata; Čechavičius, Bronislovas; Stanionytė, Sandra; Pozingytė, Evelina; Skapas, Martynas; Selskis, Algirdas; Geižutis, Andrejus; Krotkus, Arūnas

    2017-09-01

    The growth and characterization of ternary GaAsBi and quaternary GaInAsBi compound quantum wells (QWs) on GaAs substrates is presented in this study. The influence of technological parameters, such as different growth modes, substrate temperatures, beam equivalent pressure ratios and thermal treating on structural and luminescent properties of QWs is discussed. The complex structural investigations using x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy revealed high crystal structure, smooth surfaces and abrupt interfaces of both GaAsBi and GaInAsBi QWs. The temperature dependent photoluminescence measurements demonstrated emission wavelengths up to 1.43 µm in room temperature PL spectra measured for GaAsBi/GaAs QWs containing 12% Bi, whereas GaInAsBi QWs with 4.2% of bismuth inserted between GaAs barriers has reached 1.25 µm. Moreover, the annealing at high temperatures of GaAsBi/AlAs QWs stimulated agglomeration of bismuth to quantum dots in the well layers, emitting at 1.5 µm. The achieved wavelengths are the longest ones declared for the GaAsBi and GaInAsBi QW structures grown on the GaAs substrate, therefore bismide-based QWs are the promising structures for applications in infrared devices.

  13. Quantum Optical Signature of Plasmonically Coupled Nanocrystal Quantum Dots.

    PubMed

    Wang, Feng; Karan, Niladri S; Nguyen, Hue Minh; Mangum, Benjamin D; Ghosh, Yagnaseni; Sheehan, Chris J; Hollingsworth, Jennifer A; Htoon, Han

    2015-10-01

    Small clusters of two to three silica-coated nanocrystals coupled to plasmonic gap-bar antennas can exhibit photon antibunching, a characteristic of single quantum emitters. Through a detailed analysis of their photoluminescence emissions characteristics, it is shown that the observed photon antibunching is the evidence of coupled quantum dot formation resulting from the plasmonic enhancement of dipole-dipole interaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. 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.

  15. Spectral response of the intrinsic region of a GaAs-InAs quantum dot solar cell considering the absorption spectra of ideal cubic dots

    NASA Astrophysics Data System (ADS)

    Biswas, Sayantan; Chatterjee, Avigyan; Biswas, Ashim Kumar; Sinha, Amitabha

    2016-10-01

    Recently, attempts have been made by some researchers to improve the efficiency of quantum dot solar cells by incorporating different types of quantum dots. In this paper, the photocurrent density has been obtained considering the absorption spectra of ideal cubic dots. The effects of quantum dot size dispersion on the spectral response of the intrinsic region of a GaAs-InAs quantum dot solar cell have been studied. The dependence of the spectral response of this region on the size of quantum dots of such solar cell has also been investigated. The investigation shows that for smaller quantum dot size dispersion, the spectral response of the intrinsic region of the cell increases significantly. It is further observed that by enlarging the quantum dot size it is possible to enhance the spectral response of such solar cells as it causes better match between absorption spectra of the quantum dots and the solar spectrum. These facts indicate the significant role of quantum dot size and size dispersion on the performance of such devices. Also, the power conversion efficiency of such solar cell has been studied under 1 sun, AM 1.5 condition.

  16. Thermopower and thermal conductance for a Kondo correlated quantum dot

    NASA Astrophysics Data System (ADS)

    Franco, R.; Silva-Valencia, J.; Figueira, M. S.

    We study the thermopower and thermal conductivity of a gate-defined quantum dot, with a very strong Coulomb repulsion inside the dot, employing the X-boson approach for the impurity Anderson model. Our results show a change in the sign of the thermopower as function of the energy level of the quantum dot (gate voltage), which is associated with an oscillatory behavior and a suppression of the thermopower magnitude at low temperatures. We identify two relevant energy scales: a low temperature scale dominated by the Kondo effect and a T˜Δ temperature scale characterized by charge fluctuations. We also discuss the Wiedemann-Franz relation and the thermoelectric figure of merit. Our results are in qualitative agreement with recent experimental reports and other theoretical treatments.

  17. 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.

  18. Operator-sum models of quantum decoherence in molecular quantum-dot cellular automata

    NASA Astrophysics Data System (ADS)

    Ramsey, Jackson S.; Blair, Enrique P.

    2017-08-01

    Quantum-dot cellular automata is a paradigm for classical computing which departs from the transistor paradigm and provides a system in which quantum phenomena may be studied. Here, the elementary computing device is a cell, a structure having multiple quantum dots and a few mobile charges. A specific operator-sum representation is developed for an exactly modeled double-dot, molecular cell within an environment of N similar neighboring molecules. While an operator-sum representation is not unique, a specific model can be determined by selecting a particular environmental basis. We select the environment's computational basis and calculate the specific and full set of 2N Kraus operators, which match exactly previous models of quantum decoherence in this system. Finally, the timescale for environmental interaction is characterized, enabling the reduction of the large set of Kraus operators to an approximate pair of Kraus operators, exact in the limit of large N.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  1. Suppressed blinking in single quantum dots (QDs) immobilized near silver island films (SIFs)

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

    In this report, we use single-molecule spectroscopic method to study emission behaviors of streptavidin-conjugated quantum dots immobilized on a biotinylated BSA (bovine serum albumin) monolayer near non-continuous rough silver nanostructures. We observed greatly reduced blinking and enhanced emission fluorescence of quantum dots next to silver island films.

  2. Reprint of : Thermodynamic properties of a quantum Hall anti-dot interferometer

    NASA Astrophysics Data System (ADS)

    Levy Schreier, Sarah; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.

    2016-08-01

    We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov-Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.

  3. 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.

  4. Interdependence of ICD rates in paired quantum dots on geometry.

    PubMed

    Weber, Fabian; Aziz, Emad F; Bande, Annika

    2017-09-30

    Using state-of-the-art antisymmetrized multiconfiguration time-dependent Hartree (MCTDH) electron dynamics calculations we study the interdependence of the intermolecular Coulombic decay (ICD) process on the geometric parameters of a doubly-charged paired quantum dot (PQD) model system in the framework of the effective mass approximation (EMA). We find that ICD displays a maximum rate for a certain geometry of the electron-emitting quantum dot, which is simultaneously dependent on both the distance between the quantum dots as well as the photon-absorbing quantum dot's geometry. The rate maximum is shown to be caused by the competing effects of polarization of electron density and Coulomb repulsion. The ICD rate-maximized PQD geometry in GaAs QDs yields a decay time of 102.39 ps. It is given by two vertically-aligned cylindrical QDs with radii of 14.42 nm separated by 86.62 nm. The photon absorbing QD then has a height of 46.59 nm and the electron emitting QD a height of 16.33 nm. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  5. High-fidelity quantum memory utilizing inhomogeneous nuclear polarization in a quantum dot

    NASA Astrophysics Data System (ADS)

    Ding, Wenkui; Shi, Anqi; You, J. Q.; Zhang, Wenxian

    2014-12-01

    We numerically investigate the encoding and retrieval processes for quantum memory realized in a semiconductor quantum dot by focusing on the effect of inhomogeneously polarized nuclear spins whose polarization depends on the local hyperfine coupling strength. We find that the performance of quantum memory is significantly improved by inhomogeneous nuclear polarization, as compared with homogeneous nuclear polarization. Moreover, the narrower the nuclear polarization distribution is, the better is the performance of the quantum memory. We ascribe the improvement in performance to the full harnessing of the highly polarized and strongly coupled nuclear spins by carefully studying the entropy change of individual nuclear spins during the encoding process. Our results shed light on the implementation of quantum memory in a quantum dot.

  6. Self-consistent magnetization dynamics of a ferromagnetic quantum dot driven by a spin bias

    NASA Astrophysics Data System (ADS)

    Siu, Z. B.; Jalil, M. B. A.; Tan, S. G.

    2012-04-01

    We present an iterative scheme which combines the non-equilibrium Green's function (NEGF) for evaluating the quantum spin transport in a ferromagnetic quantum dot device and the Landau-Lifshitz (LL) equation for modeling the magnetization dynamics of the dot. For a given initial magnetization, the spin polarization of current and the resulting spin torque in the dot are calculated using the NEGF formalism. The torque acts on the magnetic moment of the dot, and the resultant magnetization dynamics is obtained from the LL equation. The new value of the dot's magnetization is then used as an input for the next round of NEGF calculation, and the whole process is repeated iteratively. The spin torque is thus calculated self-consistently with the dynamics of the magnetic moment of the dot. We apply this self-consistent iterative scheme to study the magnetization dynamics in an exemplary quantum dot system with an induced spin bias in the leads under varying damping conditions.

  7. Decoherence dynamics of two charge qubits in vertically coupled quantum dots

    SciTech Connect

    Ben Chouikha, W.; Bennaceur, R.; Jaziri, S.

    2007-12-15

    The decoherence dynamics of two charge qubits in a double quantum dot is investigated theoretically. We consider the quantum dynamics of two interacting electrons in a vertically coupled quantum dot driven by an external electric field. We derive the equations of motion for the density matrix, in which the presence of an electron confined in the double dot represents one qubit. A Markovian approach to the dynamical evolution of the reduced density matrix is adopted. We evaluate the concurrence of two qubits in order to study the effect of acoustic phonons on the entanglement. We also show that the disentanglement effect depends on the double dot parameters and increases with the temperature.

  8. Spin thermopower in interacting quantum dots

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  9. Planar Dirac electrons in magnetic quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Ning; Zhu, Jia-Lin

    2012-05-01

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

  10. Quantum Dot Detector Enhancement for Narrow Band Multispectral Applications

    DTIC Science & Technology

    2013-12-01

    Report contains color. 14. ABSTRACT The underlying principle of a photodetector is converting the optical signal into electrical signal. Under...enhancement of quantum dot photodetectors was also investigated. 15. SUBJECT TERMS quantum dot, quantum well, photodetectors , plasmonics 16...1.0 Introduction – Photodetectors .............................................................................................. 1 1.1 Types of

  11. Synthesis of Cesium Lead Halide Perovskite Quantum Dots

    ERIC Educational Resources Information Center

    Shekhirev, Mikhail; Goza, John; Teeter, Jacob D.; Lipatov, Alexey; Sinitskii, Alexander

    Synthesis of quantum dots is a valuable experiment for demonstration and discussion of quantum phenomena in undergraduate chemistry curricula. Recently, a new class of all-inorganic perovskite quantum dots (QDs) with a formula of CsPbX[subscript 3] (X = Cl, Br, I) was presented and attracted tremendous attention. Here we adapt the synthesis of…

  12. Barrier Engineered Quantum Dot Infrared Photodetectors

    DTIC Science & Technology

    2015-06-01

    REPORT Kirtland AFB, NM 87117-5776 NUMBER(S) AFRL -RV-PS-TR-2015-0111 12. DISTRIBUTION / AVAILABILITY STATEMENT Approved for Public Release; Distribution... Kirtland AFB, NM 87117-5776 2 cys Official Record Copy AFRL /RVSS/David Cardimona 1 cy ... AFRL -RV-PS- AFRL -RV-PS- TR-2015-0111 TR-2015-0111 BARRIER ENGINEERED QUANTUM DOT INFRARED PHOTODETECTORS Sanjay Krishna Center for High Technology

  13. Multifunctional magnetic quantum dots for cancer theranostics.

    PubMed

    Singh, Surinder P

    2011-02-01

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

  14. Intrinsic spin dynamics in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Valín-Rodríguez, Manuel

    2005-12-01

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

  15. Carbon Nanotube Quantum Dots as THz Detectors

    DTIC Science & Technology

    2012-12-14

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

  16. Solar cell with charged quantum dots: optimization for high efficiency

    NASA Astrophysics Data System (ADS)

    Sablon, K.; Mitin, V.; Vagidov, N.; Sergeev, A.

    2013-05-01

    Most of investigations of quantum dot photovoltaic devices are aimed at the development of the intermediate band solar cell. To form the intermediate band by quantum dot electron levels, the dots should be placed close to one to another. This leads to strain accumulation and defects, which increase the photocarrier recombination, and recombination losses. To avoid the nanostructuring-induced recombination, we proposed and studied an alternative approach, which is based on the separation of quantum dots (QDs) or QD clusters from the conducting channels by potential barriers created by quantum dots with built-in charge (Q-BIC). Charging of QDs improves the performance of QD solar cells due to the following factors: Negative dot charging increases electron coupling to sub-bandgap photons and provides effective harvesting of IR energy. Because of the strong difference in effective masses of electrons and holes, an electron level spacing in QDs substantially exceeds a level spacing for holes. Therefore, QDs act as deep traps for electrons, but they are shallow traps for holes. Thus, the holes trapped in QDs may be excited by thermal phonons, while excitation of localized QDs electrons requires IR radiation or the interaction with hot electrons. Therefore, n-doping of QD structures is strongly preferable for photovoltaic applications. Charging of QDs is also an effective tool for managing the potential profile at micro- and nanoscales. Filling QDs predominantly from dopants in the QD medium allows one to maintain the macroscale profile analogous to that in the best conventional single-junction solar cells.

  17. Introducing single Mn2+ ions into spontaneously coupled quantum dot pairs

    NASA Astrophysics Data System (ADS)

    Koperski, M.; Goryca, M.; Kazimierczuk, T.; Smoleński, T.; Golnik, A.; Wojnar, P.; Kossacki, P.

    2014-02-01

    We present the photoluminescence excitation study of the self-assembled CdTe/ZnTe quantum dots doped with manganese ions. We demonstrate the identification method of spontaneously coupled quantum dots pairs containing single Mn2+ ions. As the result of the coupling, the resonant absorption of the photon in one quantum dot is followed by the exciton transfer into a neighboring dot. It is shown that the Mn2+ ion might be present in the absorbing, emitting, or both quantum dots. The magnetic properties of the Mn2+ spin are revealed by a characteristic sixfold splitting of the excitonic line. The statistics of the value of this splitting is analyzed for the large number of the dots and gives the information on the maximum density of the neutral exciton wave function.

  18. 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.

  19. Near-field magnetoabsorption of quantum dots

    NASA Astrophysics Data System (ADS)

    Simserides, Constantinos; Zora, Anna; Triberis, Georgios

    2006-04-01

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

  20. First principle study on interfacial energetic alignment and charge transfer in quantum dots functionalized via metal-organic dye

    NASA Astrophysics Data System (ADS)

    Cui, Peng

    Quantum dots (QDs) are promising materials for applications in solar energy conversion because of tunable band gap, multi-exciton generation, photon-upconversion, etc. One of the main challenges of increasing solar energy conversion is to extend the lifetime of photoexcited charge-carriers in conduction band, and one of the strategies is to functionalize QD with mediator molecules. Functionalizing QD with metal-organic dye serves as the additional channel of manipulating charge transfer - the key process increasing solar energy conversion. When metal-organic dye is attached to QD, the interfacial charge transfer direction as well as the rates are determined by a balance between the energetic alignment, QD-dye interaction as well as charge-carrier relaxation dynamics. In this dissertation, we explore the effect of dye functionalization on these elements. We change the metal ion, organic ligands as well as binding geometry of dye, size of QD, polarity of solvent, and use density functional theory to study their effects on energetic alignment. Embedding density functional calculation is used to study the dipole interaction between QD and dye providing additional controllability on charge transfer excitation. At last, we apply Tully surface hopping scheme in combining with density functional theory in time domain to study the charge-carrier relaxation dynamics and charge transfer across the heterogeneous interface in QD/dye nanocrystal composite.

  1. 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.

  2. Semiconductor quantum dot scintillation under gamma-ray irradiation.

    PubMed

    Létant, S E; Wang, T-F

    2006-12-01

    We recently demonstrated the ability of semiconductor quantum dots to convert alpha radiation into visible photons. In this letter, we report on the scintillation of quantum dots under gamma irradiation and compare the energy resolution of the 59 keV line of americium-241 obtained with our quantum dot-glass nanocomposite to that of a standard sodium iodide scintillator. A factor 2 improvement is demonstrated experimentally and interpreted theoretically using a combination of energy-loss and photon-transport models.

  3. Nanocarbons and quantum dots formation in new hybrid materials

    NASA Astrophysics Data System (ADS)

    Bogdanov, Kirill V.; Gromova, Yulia A.; Ermakov, Victor A.; Alaferdov, Andrei V.; Orlova, Anna O.; Moshkalev, Stanislav A.; Fedorov, Anatoly V.; Baranov, Alexander V.

    2014-05-01

    We present technique of obtaining complex hybrid structures combining the multi-walled carbon nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a spatial correlation between the luminescence and Raman signals is found.

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

    DTIC Science & Technology

    2014-08-01

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

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

    DTIC Science & Technology

    2009-02-01

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

  6. Four-wave mixing analysis of quantum dot and quantum well lasers

    NASA Astrophysics Data System (ADS)

    Lin, Hung-Hsin; Lin, Chih-Hao; Lin, Fan-Yi

    2011-02-01

    In this paper, we characterize and compare a quantum dot and a quantum well lasers using the four-wave mixing analysis. The optical and power spectra of the four-wave mixing state in the quantum dot laser are studied both numerically and experimentally. The tendency of the amplitude versus detuning in the quantum dot laser is very similar to those seen in the quantum well laser. The four-wave mixing signals and the power spectra from both lasers are symmetric, while asymmetry in the regenerated signal is found. Compared to the quantum well lasers, the higher resonance peak of the regenerated signal of the quantum dot lasers appears on the opposite side of the detuning in the optical spectra. The intrinsic parameters of the lasers are also obtained by fitting the optical spectra and power spectra obtained experimentally with those derived directly from the rate equations. The measured value of the linewidth enhancement factor has a good agreement with that obtained by the injection locking method.

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

  8. Quantum transport through an array of quantum dots.

    PubMed

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

    2013-01-07

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

  9. Quantum transport through an array of quantum dots

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  10. Quantum dot-linked immunosorbent assay (QLISA) using orientation-directed antibodies.

    PubMed

    Suzuki, Miho; Udaka, Hikari; Fukuda, Takeshi

    2017-09-05

    An approach similar to the enzyme-linked immunosorbent assay (ELISA), with the advantage of saving time and effort but exhibiting high performance, was developed using orientation-directed half-part antibodies immobilized on CdSe/ZnS quantum dots. ELISA is a widely accepted assay used to detect the presence of a target substance. However, it takes time to quantify the target with specificity and sensitivity owing to signal amplification. In this study, CdSe/ZnS quantum dots are introduced as bright and photobleaching-tolerant fluorescent materials. Since hydrophilic surface coating of quantum dots rendered biocompatibility and functional groups for chemical reactions, the quantum dots were modified with half-sized antibodies after partial reduction. The half-sized antibody could be bound to a quantum dot through a unique thiol site to properly display the recognition domain for the core process of ELISA, which is an antigen-antibody interaction. The reducing conditions were investigated to generate efficient conjugates of quantum dots and half-sized antibodies. This was applied to IL-6 detection, as the quantification of IL-6 is significant owing to its close relationships with various biomedical phenomena that cause different diseases. An ELISA-like assay with CdSe/ZnS quantum dot institution (QLISA; Quantum dot-linked immunosorbent assay) was developed to detect 0.05ng/mL IL-6, which makes it sufficiently sensitive as an immunosorbent assay. Copyright © 2017 Elsevier B.V. All rights reserved.

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

    PubMed

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

    2015-07-01

    Cadmium sulfide (CdS) quantum dots have a number of current applications in electronics and solar cells and significant future potential in medicine. The aim of the present study was to examine the toxic effects of CdS quantum dots on the marine clam Scrobicularia plana exposed for 14 d to these nanomaterials (10 µg Cd L(-1) ) in natural seawater and to compare them with soluble Cd. Measurement of labile Cd released from CdS quantum dots showed that 52% of CdS quantum dots remained in the nanoparticulate form. Clams accumulated the same levels of Cd regardless of the form in which it was delivered (soluble Cd vs CdS quantum dots). However, significant changes in biochemical responses were observed in clams exposed to CdS quantum dots compared with soluble Cd. Increased activities of catalase and glutathione-S-transferase were significantly higher in clams exposed in seawater to Cd as the nanoparticulate versus the soluble form, suggesting a specific nano effect. The behavior of S. plana in sediment showed impairments of foot movements only in the case of exposure to CdS quantum dots. The results show that oxidative stress and behavior biomarkers are sensitive predictors of CdS quantum dots toxicity in S. plana. Such responses, appearing well before changes might occur at the population level, demonstrate the usefulness of this model species and type of biomarker in the assessment of nanoparticle contamination in estuarine ecosystems. © 2015 SETAC.

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

    PubMed

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

    2011-06-21

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

  13. Study of Dislocation-Ordered In(x)Ga(1-x)As/GaAs Quantum Dots

    NASA Technical Reports Server (NTRS)

    Leon, Rose

    2003-01-01

    A report describes an experimental study of dislocation-induced spatial ordering of quantum dots (QDs) comprising nanometer-sized In(x)Ga(1-x)As islands surrounded by GaAs. Metastable heteroepitaxial structures were grown by molecular-beam epitaxy of In(x)Ga(1-x)As onto n+ GaAs and semi-insulating GaAs substrates. Then the structures were relaxed during a post-growth annealing/self-organizing process leading to the formation of surface undulations that acted as preferential sites for the nucleation of QDs. Structural effects of annealing times and temperatures on the strain-relaxed In(x)Ga(1-x)As/GaAs and the subsequent spatial ordering of the QDs were analyzed by atomic-force microscopy and transmission electron microscopy. Continuous-wave spectral and time-resolved photoluminescence (PL) measurements were performed to study the effects, upon optical properties, of increased QD positional ordering, increased QD uniformity, and proximity of QDs to arrays of dislocations. PL spectral peaks of ordered QD structures formed on strain-relaxed In(x)Ga(1-x)As/GaAs layers were found to be narrower than those of structures not so formed and ordered. Rise and decay times of time-resolved PL were found to be lower at lower temperatures -- apparently as a consequence of decreased carrier-transport times within the barriers surrounding the QDs.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  15. Plasmon Enhancement of Electronic Energy Transfer Between Quantum Dots on the Surface of Nanoporous Silica

    NASA Astrophysics Data System (ADS)

    Tikhomirova, N. S.; Myslitskaya, N. A.; Samusev, I. G.; Bryukhanov, V. V.

    2016-01-01

    We use spectral kinetic methods to study electronic energy transfer processes between semiconductor quantum dots on the surface of wide-pore silica in the absence of and in the presence of silver nanoparticles, obtained by laser ablation methods. We have determined the efficiencies of dipole-dipole energy transfer between two-shell (CdSe/CdS/ZnS) and one-shell (CdSe/ZnS) quantum dots on the surface, the luminescence lifetimes and quantum yields, transfer distances and transfer rate constants. We have studied enhancement of photoprocesses in individual quantum dots and in a pair under the influence of resonant localized plasmons of ablative silver nanoparticles.

  16. Tuning the dynamic properties of electrons between a quantum well and quantum dots

    NASA Astrophysics Data System (ADS)

    Cerulo, G.; Nevou, L.; Liverini, V.; Castellano, F.; Faist, J.

    2012-08-01

    We present a study of the dynamic properties of electrons tunneling from an InGaAs quantum well to self assembled InAs quantum dots. The experiments were conducted on three highly asymmetric quantum dot infrared photodetectors, where the quantum well and quantum dots were separated by a composite GaAs/AlGaAs/GaAs barrier, which varied from 3.5 nm to 7.0 nm. We performed interband (photoluminescence) and intraband (photocurrent) measurements to characterize the spectral properties of the well and the dots. The photoluminescence measurements revealed that the two nanostructures are decoupled when the device is at zero bias. By intraband pump-probe experiments and photocurrent saturation experiments, we were able to extrapolate a refilling time τ from the well to the dots, which varied from a few μs for the thinnest barrier and hundreds of μs for the thickest one. The extracted values are in good agreement with characteristic tunneling times computed by using a model based on the theoretically predicted transmission coefficient of the electrons through the composite barrier.

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  20. Correlated electrons in coupled quantum dots and related phenomena

    NASA Astrophysics Data System (ADS)

    Ugajin, Ryuichi

    1998-01-01

    Three topics related to correlated electrons in coupled quantum dots are discussed. The first is quasi-resonance between multi-electron states, which causes hitherto unremarked types of resonant absorption in coupled quantum dots. The second is electron tunneling through a Hubbard gap, which is induced by an increase in the density of electrons in a quantum-dot chain under an overall confining potential. The third is Mott transition in a two-dimensional quantum-dot array induced by an external electric field. In this system, the metal-insulator transition goes through a heavy electron phase in which the density of correlated electrons fluctuates.