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Sample records for quantum dot nanostructures

  1. Quantum dot nanostructures

    Directory of Open Access Journals (Sweden)

    Mohamed Henini

    2002-06-01

    These sophisticated technologies for the growth of high quality epitaxial layers of compound semiconductor materials on single crystal semiconductor substrates are becoming increasingly important for the development of the semiconductor electronics industry. This article is intended to convey the flavor of the subject by focusing on the technology and applications of self-assembled quantum dots (QDs and to give an introduction to some of the essential characteristics.

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

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

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

  3. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2011-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...... is demonstrated and the influence of disorder is discussed. The findings have a strong bearing on future nanophotonic devices....

  4. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2010-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...... is demonstrated and the influence of disorder is discussed. The findings have a strong bearing on future nanophotonic devices....

  5. Quantum-dot emitters in photonic nanostructures

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2010-01-01

    The spontaneous emission from self-assembled semiconductor quantum dots is strongly influenced by the environment in which they are placed. This can be used to determine fundamental optical properties of the quantum dots as well as to manipulate and control the quantum-dot emission itself....

  6. Interfacing single photons and single quantum dots with photonic nanostructures

    CERN Document Server

    Lodahl, Peter; Stobbe, Søren

    2013-01-01

    Photonic nanostructures provide a way of tailoring the interaction between light and matter and the past decade has witnessed a tremendous experimental and theoretical progress on this subject. In particular, the combination with semiconductor quantum dots has proven very successful. This manuscript reviews quantum optics with excitons in single quantum dots embedded in photonic nanostructures. The ability to engineer the interaction strength in integrated photonic nanostructures enables a range of fundamental quantum-electrodynamics experiments on, e.g., spontaneous-emission control, modified Lamb shifts, and enhanced dipole-dipole interaction. Furthermore, highly efficient single-photon sources and giant photon nonlinearities may be constructed with immediate applications for photonic quantum-information processing. The review summarizes the general theoretical framework of photon emission including the role of dephasing processes, and applies it to photonic nanostructures of current interest, such as photo...

  7. Nanostructure assembly of indium sulphide quantum dots and their characterization.

    Science.gov (United States)

    Vigneashwari, B; Ravichandran, V; Parameswaran, P; Dash, S; Tyagi, A K

    2008-02-01

    Nanocrystals (approximately 5 nm) of the semiconducting wide band gap material beta-In2S3 obtained by chemical synthesis through a hydrothermal route were characterized for phase and compositional purity. These nanoparticles exhibited quantum confinement characteristics as revealed by a blue-shifted optical absorption. These quantum dots of beta-In2S3 were electrically driven from a monodisperse colloidal suspension on to conducting glass substrates by Electophoretic Deposition (EPD) technique and nanostructural thin films were obtained. The crystalline and morphological structures of these deposits were investigated by X-ray diffraction and nanoscopic techniques. We report here that certain interesting nanostructural morphologies were observed in the two-dimensional quantum dot assemblies of beta-In2S3. The effect of the controlling parameters on the cluster growth and deposit integrity was also systematically studied through a series of experiments and the results are reported here.

  8. Charge transport through a semiconductor quantum dot-ring nanostructure.

    Science.gov (United States)

    Kurpas, Marcin; Kędzierska, Barbara; Janus-Zygmunt, Iwona; Gorczyca-Goraj, Anna; Wach, Elżbieta; Zipper, Elżbieta; Maśka, Maciej M

    2015-07-08

    Transport properties of a gated nanostructure depend crucially on the coupling of its states to the states of electrodes. In the case of a single quantum dot the coupling, for a given quantum state, is constant or can be slightly modified by additional gating. In this paper we consider a concentric dot-ring nanostructure (DRN) and show that its transport properties can be drastically modified due to the unique geometry. We calculate the dc current through a DRN in the Coulomb blockade regime and show that it can efficiently work as a single-electron transistor (SET) or a current rectifier. In both cases the transport characteristics strongly depend on the details of the confinement potential. The calculations are carried out for low and high bias regime, the latter being especially interesting in the context of current rectification due to fast relaxation processes.

  9. Quantum dot behavior in transition metal dichalcogenides nanostructures

    Science.gov (United States)

    Luo, Gang; Zhang, Zhuo-Zhi; Li, Hai-Ou; Song, Xiang-Xiang; Deng, Guang-Wei; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

    2017-08-01

    Recently, transition metal dichalcogenides (TMDCs) semiconductors have been utilized for investigating quantum phenomena because of their unique band structures and novel electronic properties. In a quantum dot (QD), electrons are confined in all lateral dimensions, offering the possibility for detailed investigation and controlled manipulation of individual quantum systems. Beyond the definition of graphene QDs by opening an energy gap in nanoconstrictions, with the presence of a bandgap, gate-defined QDs can be achieved on TMDCs semiconductors. In this paper, we review the confinement and transport of QDs in TMDCs nanostructures. The fabrication techniques for demonstrating two-dimensional (2D) materials nanostructures such as field-effect transistors and QDs, mainly based on e-beam lithography and transfer assembly techniques are discussed. Subsequently, we focus on electron transport through TMDCs nanostructures and QDs. With steady improvement in nanoscale materials characterization and using graphene as a springboard, 2D materials offer a platform that allows creation of heterostructure QDs integrated with a variety of crystals, each of which has entirely unique physical properties.

  10. Coupling self-assembled quantum dots to nanostructures

    Science.gov (United States)

    Badolato, Antonio

    Self-assembled quantum dot (QD) grown by molecular beam epitaxy implements the ultimate quantum confined structure in the solid-state. Because electrons are confined in all three dimensions, QDs have shown delta-function-like energy dependence of the density of states. The identification of QDs as artificial atoms has been proven by the observation of fundamental exciton emission with perfect photon antibunching and with a linewidth limited by spontaneous emission. As artificial atoms that can be monolithically integrated with other functional devices in the setting of semiconductor technology, QDs have been the source of inspiration of several novel quantum devices. Nonetheless, QD self-assemble on random nucleation sites, whereas many proposals require precise positioning of a single QD. In this thesis, two new elements of design and control for coupling single QDs to single nanostructure will be presented: (i) a technique to control ab-initio the site nucleation of a single QD and (ii) a deterministic approach to the coupling of single QDs to single nanocavity modes. Chapter 1 is dedicated to a theoretical overview of the QD system, first, as a solid-state heterostructure that confines electrons and, second, as an artificial atom interacting with confined photons. Chapter 2 presents a technique to grow highly ordered QD arrays by engineering subsurface periodic strain templates. This technique achieved almost perfect registering of single QDs into a two-dimensional lattice. In Chapter 3 a deterministic approach to the realization of solid-state cavity quantum electrodynamics (QED) systems is demonstrated. Based on a precise spatial and spectral matching between a single QD and a PC microcavity, this approach yielded cavity QED effects (such as Purcell effect) in all fabricated nanostructures.

  11. SILICON-GERMANIUM NANOSTRUCTURES WITH GERMANIUM QUANTUM DOTS FOR OPTOELECTRONIC APPLICATIONS

    Directory of Open Access Journals (Sweden)

    A. V. Mudryi

    2012-01-01

    Full Text Available Influence of technological parameters (temperature of substrate, number of Ge layers, ion treatment on optical properties of Si/Ge nanostructures with Ge quantum dots have been studied. The Raman scattering lines related to the Si-Si, Ge-Ge and Si-Ge vibration modes have been detected in the Raman spectra of Si/Ge nanostructures. A significant enhancement of intensity of luminescence band at 0.8 eV related with radiative recombination on Ge quantum dots is observed after hydrogen-plasma ion treatment of Si-Ge nanostructures. It is important for increasing of the luminescence quantum efficienty of devices on the base of Si nanolayer with Ge quantum dots.

  12. Templating growth of gold nanostructures with a CdSe quantum dot array.

    Science.gov (United States)

    Paul, Neelima; Metwalli, Ezzeldin; Yao, Yuan; Schwartzkopf, Matthias; Yu, Shun; Roth, Stephan V; Müller-Buschbaum, Peter; Paul, Amitesh

    2015-06-07

    In optoelectronic devices based on quantum dot arrays, thin nanolayers of gold are preferred as stable metal contacts and for connecting recombination centers. The optimal morphology requirements are uniform arrays with precisely controlled positions and sizes over a large area with long range ordering since this strongly affects device performance. To understand the development of gold layer nanomorphology, the detailed mechanism of structure formation are probed with time-resolved grazing incidence small-angle X-ray scattering (GISAXS) during gold sputter deposition. Gold is sputtered on a CdSe quantum dot array with a characteristic quantum dot spacing of ≈7 nm. In the initial stages of gold nanostructure growth, a preferential deposition of gold on top of quantum dots occurs. Thus, the quantum dots act as nucleation sites for gold growth. In later stages, the gold nanoparticles surrounding the quantum dots undergo a coarsening to form a complete layer comprised of gold-dot clusters. Next, growth proceeds dominantly via vertical growth of gold on these gold-dot clusters to form an gold capping layer. In this capping layer, a shift of the cluster boundaries due to ripening is found. Thus, a templating of gold on a CdSe quantum dot array is feasible at low gold coverage.

  13. Formation of strain-induced quantum dots in gated semiconductor nanostructures

    Directory of Open Access Journals (Sweden)

    Ted Thorbeck

    2015-08-01

    Full Text Available A long-standing mystery in the field of semiconductor quantum dots (QDs is: Why are there so many unintentional dots (also known as disorder dots which are neither expected nor controllable. It is typically assumed that these unintentional dots are due to charged defects, however the frequency and predictability of the location of the unintentional QDs suggests there might be additional mechanisms causing the unintentional QDs besides charged defects. We show that the typical strains in a semiconductor nanostructure from metal gates are large enough to create strain-induced quantum dots. We simulate a commonly used QD device architecture, metal gates on bulk silicon, and show the formation of strain-induced QDs. The strain-induced QD can be eliminated by replacing the metal gates with poly-silicon gates. Thus strain can be as important as electrostatics to QD device operation operation.

  14. Formation of strain-induced quantum dots in gated semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Thorbeck, Ted, E-mail: tcthorbeck@wisc.edu [Quantum Measurement Division, NIST, Gaithersburg, Maryland (United States); Joint Quantum Institute and Dept. of Physics, University of Maryland, College Park, Maryland (United States); Zimmerman, Neil M. [Quantum Measurement Division, NIST, Gaithersburg, Maryland (United States)

    2015-08-15

    A long-standing mystery in the field of semiconductor quantum dots (QDs) is: Why are there so many unintentional dots (also known as disorder dots) which are neither expected nor controllable. It is typically assumed that these unintentional dots are due to charged defects, however the frequency and predictability of the location of the unintentional QDs suggests there might be additional mechanisms causing the unintentional QDs besides charged defects. We show that the typical strains in a semiconductor nanostructure from metal gates are large enough to create strain-induced quantum dots. We simulate a commonly used QD device architecture, metal gates on bulk silicon, and show the formation of strain-induced QDs. The strain-induced QD can be eliminated by replacing the metal gates with poly-silicon gates. Thus strain can be as important as electrostatics to QD device operation operation.

  15. Transversal confined polar optical phonons in spherical quantum-dot/quantum-well nanostructures

    Science.gov (United States)

    Comas, F.; Trallero-Giner, C.; Prado, S. J.; Marques, G. E.; Roca, E.

    2006-02-01

    Confined polar optical phonons are studied in a spherical quantum-dot/quantum-well (QD/QW) nanostructure by using an approach that takes into account the coupling of electromechanical oscillations and is valid in the long-wave limit. This approach was developed a few years ago and provides results beyond the usually applied dielectric continuum approach (DCA), where just the electric aspect of the oscillations is considered. In the present paper we limit ourselves to the study of the so-called uncoupled modes, having a purely transversal character and not involving an electric potential. We display the dispersion curves for the frequencies considering three possible nanostructures, which show different bulk phonon curvatures near the Brillouin zone -point and have been actually grown: ZnS/CdSe, CdSe/CdS and CdS/HgS. A detailed discussion of the results obtained is made, emphasizing the novelties provided by our treatment and the relevance of infrared spectroscopy in the characterization of the geometrical features of the QD/QW nanostructure.

  16. Time resolved single molecule spectroscopy of semiconductor quantum dot/conjugated organic hybrid nanostructures

    Science.gov (United States)

    Odoi, Michael Yemoh

    Single molecule studies on CdSe quantum dots functionalized with oligo-phenylene vinylene ligands (CdSe-OPV) provide evidence of strong electronic communication that facilitate charge and energy transport between the OPV ligands and the CdSe quantum dot core. This electronic interaction greatly modify, the photoluminescence properties of both bulk and single CdSe-OPV nanostructure thin film samples. Size-correlated wide-field fluorescence imaging show that blinking suppression in single CdSe-OPV is linked to the degree of OPV coverage (inferred from AFM height scans) on the quantum dot surface. The effect of the complex electronic environment presented by photoexcited OPV ligands on the excited state property of CdSe-OPV is measured with single photon counting and photon-pair correlation spectroscopy techniques. Time-tagged-time-resolved (TTTR) single photon counting measurements from individual CdSe-OPV nanostructures, show excited state lifetimes an order of magnitude shorter relative to conventional ZnS/CdSe quantum dots. Second-order intensity correlation measurements g(2)(tau) from individual CdSe-OPV nanostructures point to a weak multi-excitonic character with a strong wavelength dependent modulation depth. By tuning in and out of the absorption of the OPV ligands we observe changes in modulation depth from g(2) (0) ≈ 0.2 to 0.05 under 405 and 514 nm excitation respectively. Defocused images and polarization anisotropy measurements also reveal a well-defined linear dipole emission pattern in single CdSe-OPV nanostructures. These results provide new insights into to the mechanism behind the electronic interactions in composite quantum dot/conjugated organic composite systems at the single molecule level. The observed intensity flickering , blinking suppression and associated lifetime/count rate and antibunching behaviour is well explained by a Stark interaction model. Charge transfer from photo-excitation of the OPV ligands to the surface of the Cd

  17. Biomedical Applications of Quantum Dots, Nucleic Acid-Based Aptamers, and Nanostructures in Biosensors.

    Science.gov (United States)

    Meshik, Xenia; Farid, Sidra; Choi, Min; Lan, Yi; Mukherjee, Souvik; Datta, Debopam; Dutta, Mitra; Stroscio, Michael A

    2015-01-01

    This review is a survey of the biomedical applications of semiconductor quantum dots, nucleic acid-based aptamers, and nanosensors as molecular biosensors. It focuses on the detection of analytes in biomedical applications using (1) advances in molecular beacons incorporating semiconductor quantum dots and nanoscale quenching elements; (2) aptamer-based nanosensors on a variety of platforms, including graphene; (3) Raman scattering and surface-enhanced Raman scattering (SERS) using nanostructures for enhanced SERS spectra of biomolecules, including aptamers; and (4) the electrical and optical properties of nanostructures incorporated into molecular beacons and aptamer-based nanosensors. Research done at the University of Illinois at Chicago (UIC) is highlighted throughout since it emphasizes the specific approaches taken by the bioengineering department at UIC.

  18. Effect of confinement potential geometry on entanglement in quantum dot-based nanostructures

    CERN Document Server

    Abdullah, S; D'Amico, I

    2009-01-01

    We calculate the spatial entanglement between two electrons trapped in a nanostructure for a broad class of confinement potentials, including single and double quantum dots, and core-shell quantum dot structures. By using a parametrized confinement potential, we are able to switch from one structure to the others with continuity and to analyze how the entanglement is influenced by the changes in the confinement geometry. We calculate the many-body wave function by `exact' diagonalization of the time independent Schr\\"odinger equation. We discuss the relationship between the entanglement and specific cuts of the wave function, and show that the wave function at a single highly symmetric point could be a good indicator for the entanglement content of the system. We analyze the counterintuitive relationship between spatial entanglement and Coulomb interaction, which connects maxima (minima) of the first to minima (maxima) of the latter. We introduce a potential quantum phase transition which relates quantum stat...

  19. Quantum wells, wires and dots theoretical and computational physics of semiconductor nanostructures

    CERN Document Server

    Harrison, Paul

    2016-01-01

    Quantum Wells, Wires and Dots provides all the essential information, both theoretical and computational, to develop an understanding of the electronic, optical and transport properties of these semiconductor nanostructures. The book will lead the reader through comprehensive explanations and mathematical derivations to the point where they can design semiconductor nanostructures with the required electronic and optical properties for exploitation in these technologies. This fully revised and updated 4th edition features new sections that incorporate modern techniques and extensive new material including: - Properties of non-parabolic energy bands - Matrix solutions of the Poisson and Schrodinger equations - Critical thickness of strained materials - Carrier scattering by interface roughness, alloy disorder and impurities - Density matrix transport modelling -Thermal modelling Written by well-known authors in the field of semiconductor nanostructures and quantum optoelectronics, this user-friendly guide is pr...

  20. Radiation Anisotropy and Ordering Effects Inherent to Quantum Dots and Wires in (In,Ga)As/GaAs Nanostructures

    OpenAIRE

    V.V.Strelchuk,; Lytvyn, P. M.; A.F.Kolomys; M.P.Lysytsya; M.Ya.Valakh; Mazur, Yu. I.; Wang, Z. M.; Salamo, G. J.

    2005-01-01

    Atomic force microscopy and polarised luminescence is used for studying interrelations between the surface morphology and the optical properties of multilayer (In,Ga)As/GaAs(100) nanostructures grown with molecular-beam epitaxy technique, which possess self-organised quantum dots and quantum wires. With increasing number of periods in the structure, aligning of the quantum dots in rows parallel to the crystal direction is observed. The improvement of lateral ordering correlates with increas...

  1. Element-free Galerkin method applied to quantum dot and quantum well nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sperotto, Lucas Kriesel [Instituto Tecnologico de Aeronautica (ITA/IEAv), Sao Jose dos Campos, SP (Brazil). Instituto de Estudos Avancados; Passaro, Angelo; Tanaka, Roberto Y. [Instituto de Estudos Avancados (IEAv), Sao Jose dos Campos, SP (Brazil); Marques, Gleber N. [Universidade do Estado de Mato Grosso (UNEMAT), MT (Brazil)

    2012-07-01

    Full text: The development of native technologies for the fabrication of infrared photodetectors based on quantum wells and quantum dots is the goal of a set of Brazilian Research Institutes and Universities gathered in a National Institute for Science and Technology. The research covers all phases of the production of such devices in Brazil, from the design to the growing of nanostructured semiconductors, processing and characterization of samples. In this context, a set of computer programs have been developed in the recent years in order to assist the design of such structures, some of them based on the Finite Element Methods (FEM). The Element-Free Galerkin Method (EFGM) is an attractive numerical alternative to the FEM. To perform an EFGM approximation it is required a set of nodal points and the shape functions associated to each node. In this sense its similar to FEM. In the EFGM, the Moving Least Squares (MLS) is used to build highly continuous shape functions, which also result in approximations (solutions) highly continuous. The assembling of the final linear system requires support for numerical integration, which in this work is the same triangular mesh generated for the FEM. One of the main drawbacks of the EFGM is the reproduction of the physical discontinuities inherent to each phenomenon, which means discontinuities of the state variable and/or of its spatial derivatives. If no additional numerical treatment is adopted, spurious oscillations arise in the approximation nearby the discontinuity lines. For instance, some aid techniques such as the domain truncation have been successfully applied for the treatment of material interfaces in the computation of electrostatic and electromagnetic fields. Although the EFGM has been successfully tested for one-dimensional quantum well structures, additional techniques are required for ensuring the Dirichlet boundary conditions, e.g. Lagrange multipliers, which spoil the symmetrical character of the final

  2. Self-organization of In2S3 quantum dots into fractal nanostructures by electrophoretic deposition.

    Science.gov (United States)

    Vigneashwari, B; Tyagi, A K; Dash, S; Shankar, P; Manna, I; Suthanthiraraj, S Austin

    2009-09-01

    This paper describes the assembly of In2S3 quantum dots by electrophoretic deposition (EPD) and their subsequent self-organization into fractal nanostructures over ITO substrates. The surface morphology and the organization of these dots into nanostructures were analyzed using SEM, HRSEM and AFM techniques. These analyses reveal the existence, under appropriate conditions, of very unique nanoscale structural motifs and scale invariance associated with the assembly. Formation of such a well correlated assembly, although seems to be electric field driven, appears to be dominated by self-organizing mechanism. Such self-organized nano-scale structures consisting of cavities are likely to have fascinating condensed phase transport properties. The paper reports microscopic study of such fractal assemblies using SEM, HTSEM and AFM.

  3. Equilibrium Distributions and the Nanostructure Diagram for Epitaxial Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Rudd, R E; Briggs, G D; Sutton, A P; Medeiros-Ribeiro, G; Williams, R S

    2006-05-01

    We present in detail a thermodynamic equilibrium model for the growth of nanostructures on semiconductor substrates in heteroepitaxy and its application to germanium deposition on silicon. Some results of this model have been published previously, but the details of the formulation of the model are given here for the first time. The model allows the computation of the shape and size distributions of the surface nanostructures, as well as other properties of the system. We discuss the results of the model, and their incorporation into a nanostructure diagram that summarizes the relative stability of domes and pyramids in the bimodal size distributions.

  4. Surface-plasmon-enhanced photoluminescence of quantum dots based on open-ring nanostructure array

    Science.gov (United States)

    Kannegulla, Akash; Liu, Ye; Cheng, Li-Jing

    2016-03-01

    Enhanced photoluminescence (PL) of quantum dots (QD) in visible range using plasmonic nanostructures has potential to advance several photonic applications. The enhancement effect is, however, limited by the light coupling efficiency to the nanostructures. Here we demonstrate experimentally a new open-ring nanostructure (ORN) array 100 nm engraved into a 200 nm thick silver thin film to maximize light absorption and, hence, PL enhancement at a broadband spectral range. The structure is different from the traditional isolated or through-hole split-ring structures. Theoretical calculations based on FDTD method show that the absorption peak wavelength can be adjusted by their period and dimension. A broadband absorption of about 60% was measured at the peak wavelength of 550 nm. The emission spectrum of CdSe/ZnS core-shell quantum dots was chosen to match the absorption band of the ORN array to enhance its PL. The engraved silver ORN array was fabricated on a silver thin film deposited on a silicon substrate using focus ion beam (FIB) patterning. The device was characterized by using a thin layer of QD water dispersion formed between the ORN substrate and a cover glass. The experimental results show the enhanced PL for the QD with emission spectrum overlapping the absorption band of ORN substrate and quantum efficiency increases from 50% to 70%. The ORN silver substrate with high absorption over a broadband spectrum enables the PL enhancement and will benefit applications in biosensing, wavelength tunable filters, and imaging.

  5. Resonance-induced absorption enhancement in colloidal quantum dot solar cells using nanostructured electrodes.

    Science.gov (United States)

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

    2014-10-20

    The application of nanostructured indium-doped tin oxide (ITO) electrodes as diffraction gratings for light absorption enhancement in colloidal quantum dot solar cells is numerically investigated using finite-difference time-domain (FDTD) simulation. Resonant coupling of the incident diffracted light with supported waveguide modes in light absorbing layer at particular wavelengths predicted by grating far-field projection analysis is shown to provide superior near-infrared light trapping for nanostructured devices as compared to the planar structure. Among various technologically feasible nanostructures, the two-dimensional nano-branch array is demonstrated as the most promising polarization-independent structure and proved to be able to maintain its performance despite structural imperfections common in fabrication.

  6. Atomic Force Microscopy-based Cell Nanostructure for Ligand-conjugated Quantum Dot Endocytosis

    Institute of Scientific and Technical Information of China (English)

    Yun-Long PAN; Ji-Ye CAI; Li QIN; Hao WANG

    2006-01-01

    While it has been well demonstrated that quantum dots (QDs) play an important role in biological labeling both in vitro and in vivo,there is no report describing the cellular nanostructure basis of receptor-mediated endocytosis. Here, nanostructure evolution responses to the endocytosis of transferrin force microscopy (AFM). AFM-based nanostructure analysis demonstrated that the Tf-conjugated QDs were specifically and tightly bound to the cell receptors rrelated with the cell membrane receptor-mediated transduction.Consistently, confocal microscopic and flow cytometry results have demonstrated the specificity and the internalization of Tf-QD is linearly related to time. Moreover, while the nanoparticles on the cell membrane increased, the endocytosis was still nanoparticles did not interfere sterically with the binding and function of receptors. Therefore, ligand-conjugated QDs are potentially useful in biological labeling of cells at a nanometer scale.

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

    Science.gov (United States)

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

    2000-01-01

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

  8. Recent advances in exciton-based quantum information processing in quantum dot nanostructures

    Science.gov (United States)

    Krenner, Hubert J.; Stufler, Stefan; Sabathil, Matthias; Clark, Emily C.; Ester, Patrick; Bichler, Max; Abstreiter, Gerhard; Finley, Jonathan J.; Zrenner, Artur

    2005-08-01

    Recent experimental developments in the field of semiconductor quantum dot (QD) spectroscopy are discussed. Firstly, we report about single QD exciton two-level systems and their coherent properties in terms of single-qubit manipulations. In the second part, we report on coherent quantum coupling in a prototype 'two-qubit' system consisting of a vertically stacked pair of QDs. The interaction can be tuned in such QD molecule devices using an applied voltage as external parameter.

  9. Recent advances in exciton-based quantum information processing in quantum dot nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Krenner, Hubert J [Physik Department and Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Stufler, Stefan [Universitaet Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany); Sabathil, Matthias [Physik Department and Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Clark, Emily C [Physik Department and Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Ester, Patrick [Universitaet Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany); Bichler, Max [Physik Department and Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Abstreiter, Gerhard [Physik Department and Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Finley, Jonathan J [Physik Department and Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Zrenner, Artur [Universitaet Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany)

    2005-08-01

    Recent experimental developments in the field of semiconductor quantum dot (QD) spectroscopy are discussed. Firstly, we report about single QD exciton two-level systems and their coherent properties in terms of single-qubit manipulations. In the second part, we report on coherent quantum coupling in a prototype 'two-qubit' system consisting of a vertically stacked pair of QDs. The interaction can be tuned in such QD molecule devices using an applied voltage as external parameter.

  10. Enhanced Cross-Phase Modulation via Phase Control in a Quantum dot Nanostructure

    Institute of Scientific and Technical Information of China (English)

    郝向英; 郑安寿; 王英; 李小刚

    2012-01-01

    A four-level quantum dot (QD) nanostructure interacting with four fields (two weak near-infrared (NIR) pulses and two control fields) forms the well-known double-cascade configuration.We investigate the cross-phase modulation (XPM) between the two NIR pulses.The results show,in such a closed-loop scheme,that the XPM can be greatly enhanced,while the linear absorption and two-photon absorption (gain) can be efficiently depressed by tuning the relative phase among the applied fields.This protocol may have potential applications in NIR all-optical switch design and quantum information processing with the solid-state materials.

  11. Graphene quantum dots

    CERN Document Server

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

    2014-01-01

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

  12. Quantum optics with semiconductor nanostructures

    CERN Document Server

    Jahnke, Frank

    2012-01-01

    A guide to the theory, application and potential of semiconductor nanostructures in the exploration of quantum optics. It offers an overview of resonance fluorescence emission.$bAn understanding of the interaction between light and matter on a quantum level is of fundamental interest and has many applications in optical technologies. The quantum nature of the interaction has recently attracted great attention for applications of semiconductor nanostructures in quantum information processing. Quantum optics with semiconductor nanostructures is a key guide to the theory, experimental realisation, and future potential of semiconductor nanostructures in the exploration of quantum optics. Part one provides a comprehensive overview of single quantum dot systems, beginning with a look at resonance fluorescence emission. Quantum optics with single quantum dots in photonic crystal and micro cavities are explored in detail, before part two goes on to review nanolasers with quantum dot emitters. Light-matter interaction...

  13. Manipulating transmission and reflection properties of a photonic crystal doped with quantum dot nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Solookinejad, G.; Panahi, M.; Sangachin, E. A.; Asadpour, S. H., E-mail: s.hosein.asadpour@gmail.com, E-mail: S.Hosein.Asadpour@miau.ac.ir [Islamic Azad University, Department of Physics, Marvdasht Branch (Iran, Islamic Republic of)

    2016-12-15

    The transmission and reflection properties of incident light in a defect dielectric structure is studied theoretically. The defect structure consists of donor and acceptor quantum dot nanostructures embedded in a photonic crystal. It is shown that the transmission and reflection properties of incident light can be controlled by adjusting the corresponding parameters of the system. The role of dipole–dipole interaction is considered as a new parameter in our calculations. It is noted that the features of transmission and reflection curves can be adjusted in the presence of dipole–dipole interaction. It is found that the absorption of weak probe light can be converted to the probe amplification in the presence of dipole–dipole interaction. Moreover, the group velocity of transmitted and reflected probe light is discussed in detail in the absence and presence of dipole–dipole interaction. Our proposed model can be used as a new all-optical devices based on photonic materials doped with nanoparticles.

  14. The role of nanostructures and quantum dots in detectors and solar cells for radiation hardened space applications

    Science.gov (United States)

    Taylor, Edward W.

    2006-08-01

    Highly efficient IR detectors and photo-voltaic solar cells that incorporate nanotechnology composed of nanostructures and nanoparticles (including quantum dots) will play an important role in advanced photonic space applications. While the development of Si-based solar cells has successfully evolved into an efficient and economical technology these devices are predicted to soon reach their theoretical 29% limit efficiency. Alternative organic/polymer solar cells and IR detectors incorporating quantum dots and various nanoparticle or nanostructure materials are emerging which are expected to eventually outperform current state-of-the-art detectors and solar cell devices. By tailoring the QD design wavelength-optimized detectors and detector arrays operating over the UV-IR range can be realized. Specific examples for achieving near-IR photovoltaic and photoconductive detectors with high quantum efficiencies are presented along with brief examples of empirical data reported for assessing the radiation resistance of QD nanocrystalline devices for application in space environments.

  15. Optical absorption and refraction index change of a confined exciton in a spherical quantum dot nanostructure

    Science.gov (United States)

    Mathan Kumar, K.; John Peter, A.; Lee, C. W.

    2011-12-01

    Electronic energies of an exciton confined in a strained Zn1- x Cd x Se/ZnSe quantum dot have been computed as a function of dot radius with various Cd content. Calculations have been performed using Bessel function as an orthonormal basis for different confinement potentials of barrier height considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption coefficients and the refractive index changes between the ground state ( L = 0) and the first excited state ( L = 1) are investigated. It is found that the optical properties in the strained ZnCdSe/ZnSe quantum dot are strongly affected by the confinement potentials and the dot radii. The intensity of the total absorption spectra increases for the transition between higher levels. The obtained optical nonlinearity brings out the fact that it should be considered in calculating the optical properties in low dimensional semiconductors especially in quantum dots.

  16. Bandgap Engineering of 1300 nm Quantum Dots/Quantum Well Nanostructures Based Devices

    KAUST Repository

    Alhashim, Hala H.

    2016-05-29

    The main objectives of this thesis are to develop viable process and/or device technologies for bandgap tuning of 1300-nm InGaAs/GaAs quantum-dot (QD) laser structures, and broad linewidth 1300-nm InGaAsP/InP quantum well (QW) superluminescent diode structures. The high performance bandgap-engineered QD laser structures were achieved by employing quantum-dot intermixing (QDI) based on impurity free vacancy diffusion (IFVD) technique for eventual seamless active-passive integration, and bandgap-tuned lasers. QDI using various dielectric-capping materials, such as HfO2, SrTiO3, TiO2, Al2O3 and ZnO, etc, were experimented in which the resultant emission wavelength can be blueshifted to ∼ 1100 nm ─ 1200 nm range depending on process conditions. The significant results extracted from the PL characterization were used to perform an extensive laser characterization. The InAs/GaAs quantum-dot lasers with QDs transition energies were blueshifted by ~185 nm, and lasing around ~1070 – 1190 nm was achieved. Furthermore, from the spectral analysis, a simultaneous five-state lasing in the InAs/InGaAs intermixed QD laser was experimentally demonstrated for the first time in the very important wavelength range from 1030 to 1125 nm. The QDI methodology enabled the facile formation of a plethora of devices with various emission wavelengths suitable for a wide range of applications in the infrared. In addition, the wavelength range achieved is also applicable for coherent light generation in the green – yellow – orange visible wavelength band via frequency doubling, which is a cost-effective way of producing compact devices for pico-projectors, semiconductor laser based solid state lighting, etc. [1, 2] In QW-based superluminescent diode, the problem statement lies on achieving a flat-top and ultra-wide emission bandwidth. The approach was to design an inhomogeneous active region with a comparable simultaneous emission from different transition states in the QW stacks, in

  17. A brilliant sandwich type fluorescent nanostructure incorporating a compact quantum dot layer and versatile silica substrates.

    Science.gov (United States)

    Huang, Liang; Wu, Qiong; Wang, Jing; Foda, Mohamed; Liu, Jiawei; Cai, Kai; Han, Heyou

    2014-03-18

    A "hydrophobic layer in silica" structure was designed to integrate a compact quantum dot (QD) layer with high quantum yield into scalable silica hosts containing desired functionality. This was based on metal affinity driven assembly of hydrophobic QDs with versatile silica substrates and homogeneous encapsulation of organosilica/silica layers.

  18. Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Bastos-Arrieta, Julio, E-mail: julio.bastos@upc.edu [Department of Chemical Engineering, Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028 Barcelona (Spain); Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Barcelona (Spain); Muñoz, Jose, E-mail: josemaria.munoz@uab.cat [Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Barcelona (Spain); Stenbock-Fermor, Anja, E-mail: stenbock@dwi.rwth-aachen.de [DWI – Leibniz-Institut für Interaktive Materialien, Aachen 52056 (Germany); Muñoz, Maria, E-mail: Maria.Munoz@uab.cat [Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Barcelona (Spain); Muraviev, Dmitri N., E-mail: Dimitri.Muraviev@uab.es [Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Barcelona (Spain); Céspedes, Francisco, E-mail: francisco.cespedes@uab.cat [Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Barcelona (Spain); Tsarkova, Larisa A., E-mail: tsarkova@dwi.rwth-aachen.de [DWI – Leibniz-Institut für Interaktive Materialien, Aachen 52056 (Germany); Baeza, Mireia, E-mail: MariaDelMar.Baeza@uab.cat [Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Barcelona (Spain)

    2016-04-15

    Graphical abstract: - Highlights: • Nanodiamond functionalization with CdS quantum dots. • Approach for carbon nanotube detection in water samples. • Simple functionalization of thin polymeric nanolayers with quantum dots. - Abstract: Intermatrix Synthesis (IMS) technique has proven to be a valid methodology for the in situ incorporation of quantum dots (QDs) in a wide range of nanostructured surfaces for the preparation of advanced hybrid-nanomaterials. In this sense, this communication reports the recent advances in the application of IMS for the synthesis of CdS-QDs with favourable distribution on sulfonated polyetherether ketone (SPEEK) membrane thin films (TFs), multiwall carbon nanotubes (MWCNTs) and nanodiamonds (NDs). The synthetic route takes advantage of the ion exchange functionality of the reactive surfaces for the loading of the QDs precursor and consequent QDs appearance by precipitation. The benefits of such modified nanomaterials were studied using CdS-QDs@MWCNTs hybrid-nanomaterials. CdS-QDs@MWCNTs has been used as conducting filler for the preparation of electrochemical nanocomposite sensors, which present electrocatalytic properties. Finally, the optical properties of the QDs contained on MWCNTs could allow a new procedure for the analytical detection of nanostructured carbon allotropes in water.

  19. Switching from optical bistability to multistability via terahertz signal radiation in a InGaN/GaN quantum dot nanostructure

    Science.gov (United States)

    Asadpour, Seyyed Hossein; Rahimpour Soleimani, H.

    2014-06-01

    In this paper, the effect of terahertz signal field on optical bistability and multistability in InGaN/GaN quantum dot nanostructure inside a unidirectional ring cavity is investigated. Quantum dot nanostructure is designed numerically by Schrödinger and Poisson equations which solve self consistently. By size control of quantum dot and external voltage, one can design a four level quantum dot with appropriate energy levels which can be suitable for controlling the optical bistability and multistability by terahertz signal field. It is found that the frequency detuning and intensity control of terahertz signal radiation as well as the dephasing decay rates can influence the optical bistability and multistability behaviors.

  20. Controlling of group velocity via terahertz signal radiation in a defect medium doped by four-level InGaN/GaN quantum dot nanostructure

    Science.gov (United States)

    Jafarzadeh, Hossein; Sangachin, Elnaz Ahmadi; Asadpour, Seyyed Hossein

    2015-07-01

    In this paper, we propose a novel scheme for controlling the group velocity of transmitted and reflected pulse from defect medium doped with four-level InGaN/GaN quantum dot nanostructure. Quantum dot nanostructure is designed numerically by Schrödinger and Poisson equations which solve self consistently. By size control of quantum dot and external voltage, one can design a four-level quantum dot with appropriate energy levels which can be suitable for controlling the group velocity of pulse transmission and reflection from defect slab with terahertz signal field. It is found that in the presence and absence of terahertz signal field the behaviors of transmission and reflection pulses are completely different. Moreover, it is shown that for strong terahertz signal field, by changing the thickness of the slab, simultaneous peak and dip for transmission and reflection pulse are obtained.

  1. Three-dimensional nanostructures on Ge/Si(100) wetting layers: Hillocks and pre-quantum dots

    Science.gov (United States)

    Ramalingam, Gopalakrishnan; Floro, Jerrold A.; Reinke, Petra

    2016-05-01

    The annealing of sub-critical Ge wetting layers (WL cake-type structure where the step edges run parallel to the ⟨110⟩ direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy controls the type of structure. The crossover thickness between the hillock and p-QDs regime is between 1.6 and 2.1 ML. The hillocks have larger lateral dimensions and volumes than p-QDs, and the p-QDs are exceptionally small quantum dots with a lower limit of 10 nm in width. Our work opens a new pathway to the control of nanostructure morphology and size in the elastically strained Ge/Si system.

  2. Quantum-Dot-Sensitized Solar Cells: Effect of Nanostructured TiO2 Morphologies on Photovoltaic Properties.

    Science.gov (United States)

    Toyoda, Taro; Shen, Qing

    2012-07-19

    There is a great deal of interest in dye-sensitized solar cells (DSCs) fabricated with nanostructured TiO2 electrodes. Many different dye molecules have been designed and synthesized to achieve high photovoltaic conversion efficiency. Recently, as an alternative to organic dyes, semiconductor quantum dots (QDs) have been studied for their light-harvesting capability compared with other sensitizers. Accordingly, an attractive configuration to exploit these fascinating properties of semiconductor QDs is the quantum-dot-sensitized solar cell (QDSC) due to their high photoactivity, process realization, and low cost of production. The morphology of TiO2 electrodes included with surface orientation is important for satisfactory assembly of QDSCs in order to improve the efficiency. Breakthroughs allowing an increase in efficiency will advance on two areas of electrode morphology control, namely, (A) TiO2 nanotube electrodes and (B) inverse opal TiO2 electrodes.

  3. Beyond the heteroepitaxial quantum dot : self-assembling complex nanostructures controlled by strain and growth kinetics.

    Energy Technology Data Exchange (ETDEWEB)

    Sutter, Peter (Brookhaven National Laboratory, Upton, NY); Lam, Chi-Hang (Hong Kong Polytechnic University, Hong Kong); Gray, Jennifer Lynn (University of Virginia, Charlottesville, VA); Means, Joel L. (Texas A& M University, College Station, TX); Floro, Jerrold Anthony; Hull, Robert (University of Virginia, Charlottesville, VA)

    2005-06-01

    Heteroepitaxial growth of GeSi alloys on Si (001) under deposition conditions that partially limit surface mobility leads to an unusual form of strain-induced surface morphological evolution. We discuss a kinetic growth regime wherein pits form in a thick metastable wetting layer and, with additional deposition, evolve to a quantum dot molecule - a symmetric assembly of four quantum dots bound by the central pit. We discuss the size selection and scaling of quantum dot molecules. We then examine the key mechanism - preferred pit formation - in detail, using ex situ atomic force microscopy, in situ scanning tunneling microscopy, and kinetic Monte Carlo simulations. A picture emerges wherein localized pits appear to arise from a damped instability. When pits are annealed, they extend into an array of highly anisotropic surface grooves via a one-dimensional growth instability. Subsequent deposition on this grooved film results in a fascinating structure where compact quantum dots and molecules, as well as highly ramified quantum wires, are all simultaneously self-assembled.

  4. Nanostructured Quantum Dots or Dashes in Photovoltaic Devices and Methods Thereof

    Science.gov (United States)

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

    2015-01-01

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

  5. Influence of incoherent pumping field on spatial evolution of gain without inversion in a four-level quantum dot nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Karimi, R.; Asadpour, S.H.; Batebi, S., E-mail: S_Batebi@guilan.ac.ir; Rahimpour Soleimani, H.

    2015-09-15

    We investigated the propagation effect on gain without inversion (GWI) phenomena in an open four level quantum dot nanostructure in the presence and absence of incoherent pumping field. The simulation results show that, the ratio of the injection rates and strength of incoherent pumping field has remarkable effect on spatial evolution of GWI and output. We can obtain the optimal GWI and output by choosing appropriate values of parameters. The theoretical results show that, in the open system the value of gain (output) in the absence of incoherent pumping field is much larger than that in the presence of incoherent pumping field.

  6. Quantum Pumping and Adiabatic Transport in Nanostructures

    NARCIS (Netherlands)

    Wakker, G.M.M.

    2011-01-01

    This thesis consists of a theoretical exploration of quantum transport phenomena and quantum dynamics in nanostructures. Specifically, we investigate adiabatic quantum pumping of charge in several novel types of nanostructures involving open quantum dots or graphene. For a bilayer of graphene we fin

  7. Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

    Science.gov (United States)

    Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

    2016-06-01

    The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters (including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring the underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. This study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen-vacancy centres that use these freestanding hybrid nanostructures as building blocks.

  8. Single semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Michler, Peter (ed.) [Stuttgart Univ. (Germany). Inst. fuer Halbleiteroptik und Funktionelle Grenzflaechen

    2009-07-01

    This book reviews recent advances in the exciting and rapidly growing field of semiconductor quantum dots via contributions from some of the most prominent researchers in the scientific community. Special focus is given to optical, quantum optical, and spin properties of single quantum dots due to their potential applications in devices operating with single electron spins and/or single photons. This includes single and coupled quantum dots in external fields, cavity-quantum electrodynamics, and single and entangled photon pair generation. Single Semiconductor Quantum Dots also addresses growth techniques to allow for a positioned nucleation of dots as well as applications of quantum dots in quantum information technologies. (orig.)

  9. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

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

  10. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    1999-01-01

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

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

    Science.gov (United States)

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

    2015-09-01

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

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

    Science.gov (United States)

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

    2015-09-25

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

  13. Quantum Wells, Wires and Dots Theoretical and Computational Physics of Semiconductor Nanostructures

    CERN Document Server

    Harrison, Paul

    2011-01-01

    Quantum Wells, Wires and Dots, 3rd Edition is aimed at providing all the essential information, both theoretical and computational, in order that the reader can, starting from essentially nothing, understand how the electronic, optical and transport properties of semiconductor heterostructures are calculated. Completely revised and updated, this text is designed to lead the reader through a series of simple theoretical and computational implementations, and slowly build from solid foundations, to a level where the reader can begin to initiate theoretical investigations or explanations of their

  14. Characterization and Monte Carlo simulation of single ion Geiger mode avalanche diodes integrated with a quantum dot nanostructure

    Science.gov (United States)

    Sharma, Peter; Abraham, J. B. S.; Ten Eyck, G.; Childs, K. D.; Bielejec, E.; Carroll, M. S.

    Detection of single ion implantation within a nanostructure is necessary for the high yield fabrication of implanted donor-based quantum computing architectures. Single ion Geiger mode avalanche (SIGMA) diodes with a laterally integrated nanostructure capable of forming a quantum dot were fabricated and characterized using photon pulses. The detection efficiency of this design was measured as a function of wavelength, lateral position, and for varying delay times between the photon pulse and the overbias detection window. Monte Carlo simulations based only on the random diffusion of photo-generated carriers and the geometrical placement of the avalanche region agrees qualitatively with device characterization. Based on these results, SIGMA detection efficiency appears to be determined solely by the diffusion of photo-generated electron-hole pairs into a buried avalanche region. Device performance is then highly dependent on the uniformity of the underlying silicon substrate and the proximity of photo-generated carriers to the silicon-silicon dioxide interface, which are the most important limiting factors for reaching the single ion detection limit with SIGMA detectors. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  15. Temperature-dependent spontaneous emission of PbS quantum dots inside photonic nanostructures at telecommunication wavelength

    Science.gov (United States)

    Birowosuto, Muhammad Danang; Takiguchi, Masato; Olivier, Aurelien; Tobing, Landobasa Y.; Kuramochi, Eiichi; Yokoo, Atsushi; Hong, Wang; Notomi, Masaya

    2017-01-01

    Spontaneous emission of PbS quantum dots (QDs) in different photonic nanostructures has been studied. We use the temperature-dependent exciton photoluminescence and the classic dipole near interface models to understand the spontaneous emission control at various temperatures. Then, we demonstrate that the enhancement and the inhibition of PbS QDs due to the local density of states (LDOS) inside nanostructures are more efficient at temperature as low as 77 K than the inhibition at 300 K. Largest emission rate enhancement at 77 K of 1.67 ± 0.10 and inhibition factors at 100 K of 2.27 ± 0.15 are reported for the gold (Au) planar mirror and silicon (Si) two-dimensional photonic crystal bandgap, respectively. We attribute those enhancement and inhibition to the large quantum yields Qe at low temperatures, which is much larger than that at 300 K. These results are relevant for application and optimization of PbS QDs in nanophotonics at telecommunication wavelength.

  16. Colloidal Double Quantum Dots.

    Science.gov (United States)

    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

  17. Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots

    Science.gov (United States)

    Bastos-Arrieta, Julio; Muñoz, Jose; Stenbock-Fermor, Anja; Muñoz, Maria; Muraviev, Dmitri N.; Céspedes, Francisco; Tsarkova, Larisa A.; Baeza, Mireia

    2016-04-01

    Intermatrix Synthesis (IMS) technique has proven to be a valid methodology for the in situ incorporation of quantum dots (QDs) in a wide range of nanostructured surfaces for the preparation of advanced hybrid-nanomaterials. In this sense, this communication reports the recent advances in the application of IMS for the synthesis of CdS-QDs with favourable distribution on sulfonated polyetherether ketone (SPEEK) membrane thin films (TFs), multiwall carbon nanotubes (MWCNTs) and nanodiamonds (NDs). The synthetic route takes advantage of the ion exchange functionality of the reactive surfaces for the loading of the QDs precursor and consequent QDs appearance by precipitation. The benefits of such modified nanomaterials were studied using CdS-QDs@MWCNTs hybrid-nanomaterials. CdS-QDs@MWCNTs has been used as conducting filler for the preparation of electrochemical nanocomposite sensors, which present electrocatalytic properties. Finally, the optical properties of the QDs contained on MWCNTs could allow a new procedure for the analytical detection of nanostructured carbon allotropes in water.

  18. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    1999-01-01

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

  19. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

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

  20. Fabrication of ZnO nanostructures sensitized with CdS quantum dots for photovoltaic application using a convenient solution method

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Huan [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); Zhang, Gengmin, E-mail: zgmin@pku.edu.cn [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); SIP-UCLA Institute for Technology Advancement, Suzhou 215123, Jiangsu Province (China); Yin, Jianbo [College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); Liang, Jia; Sun, Wentao; Shen, Ziyong [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China)

    2015-01-15

    Zinc oxide (ZnO) nanostructures sensitized with cadmium sulfide quantum dots (CdS QDs) were fabricated using a simple and inexpensive solution method. ZnO nanostructures, in the form of either nanocones or nanorods, were first grown directly from fluorine-doped tin oxide (FTO) substrates in aqueous solutions of zinc nitrate (Zn(NO{sub 3}){sub 2}) and hexamethylenetetramine (HMTA, C{sub 6}H{sub 12}N{sub 4}) under external voltages. Then, CdS QDs were attached to these ZnO nanostructures via reactions in the mixed aqueous solutions of cadmium nitrate (Cd(NO{sub 3}){sub 2}) and thioacetamide (C{sub 2}H{sub 5}NS). Photovoltaic responses were obtained from the quantum dot sensitized solar cells (QDSSCs) in which these CdS QD-covered ZnO nanostructures were employed as the photoanodes. The morphologies of the ZnO nanostructures, which could be effectively modulated via the substrate location in the solutions during the fabrication, were found to have played an important role in determining the properties of the QDSSCs.

  1. Active doping of B in silicon nanostructures and development of a Si quantum dot solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Seung Hui; Kim, Yong Sung; Lee, Woo; Kim, Young Heon; Song, Jae Yong; Jang, Jong Shik; Park, Jae Hee; Kim, Kyung Joong [Korea Research Institute of Standards and Science (KRISS), Yuseong, 305-340 Daejeon (Korea, Republic of); Choi, Suk-Ho, E-mail: kjkim@kriss.re.kr [Department of Applied Physics, Kyung Hee University, Yongin 446-701 (Korea, Republic of)

    2011-10-21

    Active doping of B was observed in nanometer silicon layers confined in SiO{sub 2} layers by secondary ion mass spectrometry (SIMS) depth profiling analysis and confirmed by Hall effect measurements. The uniformly distributed boron atoms in the B-doped silicon layers of [SiO{sub 2} (8 nm)/B-doped Si(10 nm)]{sub 5} films turned out to be segregated into the Si/SiO{sub 2} interfaces and the Si bulk, forming a distinct bimodal distribution by annealing at high temperature. B atoms in the Si layers were found to preferentially substitute inactive three-fold Si atoms in the grain boundaries and then substitute the four-fold Si atoms to achieve electrically active doping. As a result, active doping of B is initiated at high doping concentrations above 1.1 x 10{sup 20} atoms cm{sup -3} and high active doping of 3 x 10{sup 20} atoms cm{sup -3} could be achieved. The active doping in ultra-thin Si layers was implemented for silicon quantum dots (QDs) to realize a Si QD solar cell. A high energy-conversion efficiency of 13.4% was realized from a p-type Si QD solar cell with B concentration of 4 x 10{sup 20} atoms cm{sup -3}.

  2. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films

    Science.gov (United States)

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates.

  3. Quantum Dots: Theory

    Energy Technology Data Exchange (ETDEWEB)

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

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

  4. Effect of ligand self-assembly on nanostructure and carrier transport behaviour in CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Li, Kuiying, E-mail: kuiyingli@ysu.edu.cn; Xue, Zhenjie

    2014-11-14

    Adjustment of the nanostructure and carrier behaviour of CdSe quantum dots (QDs) by varying the ligands used during QD synthesis enables the design of specific quantum devices via a self-assembly process of the QD core–shell structure without additional technologies. Surface photovoltaic (SPV) technology supplemented by X-ray diffractometry and infrared absorption spectroscopy were used to probe the characteristics of these QDs. Our study reveals that while CdSe QDs synthesized in the presence of and capped by thioglycolic acid, 3-mercaptopropionic acid, mercaptoethanol or α-thioglycerol ligands display zinc blende nanocrystalline structures, CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures, because different end groups in these ligands induce distinctive nucleation and growth mechanisms. Carboxyl end groups in the ligand served to increase the SPV response of the QDs, when illuminated by hν ≥ E{sub g,nano-CdSe}. Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit photo-generated free charge carrier (FCC) transfer transitions of CdSe QDs illuminated by photon energy of 4.13 to 2.14 eV. The terminal hydroxyl group might better accommodate energy released in the non-radiative de-excitation process of photo-generated FCCs in the ligand's lowest unoccupied molecular orbital in the 300–580 nm wavelength region, when compared with other ligand end groups. - Highlights: • CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures. • Carboxyl end groups in the ligand serve to increase the SPV response of CdSe QDs. • Terminal hydroxyl group in the ligand might accommodate non-radiative de-excitation process in CdSe QDs. • Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit carriers transport of CdSe QDs.

  5. Chiral quantum dot based materials

    Science.gov (United States)

    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.

  6. Quantum Dot Solar Cells

    Science.gov (United States)

    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. Coupled quantum dot-ring structures by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Somaschini, C; Bietti, S; Koguchi, N; Sanguinetti, S, E-mail: stefano.sanguinetti@unimib.it [L-NESS and Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Via Cozzi 53, I-20125 Milano (Italy)

    2011-05-06

    The fabrication, by pure self-assembly, of GaAs/AlGaAs dot-ring quantum nanostructures is presented. The growth is performed via droplet epitaxy, which allows for the fine control, through As flux and substrate temperature, of the crystallization kinetics of nanometer scale metallic Ga reservoirs deposited on the surface. Such a procedure permits the combination of quantum dots and quantum rings into a single, multi-functional, complex quantum nanostructure.

  8. Incoherent control of Goos-Hänchen shifts in a four-level InGaN/GaN quantum dot nanostructure

    Science.gov (United States)

    Solookinejad, G.; Panahi, M.; Ahmadi Sangachin, E.; Asadpour, Seyyed Hossein

    2016-04-01

    In this paper, we propose a new configuration for manipulating Goos-Hänchen (GH) shifts in reflected and transmitted probe beams in a fixed geometrical scheme with a confined four-level InGaN/GaN quantum dot nanostructure. Here, the four-level quantum dot nanostructure is driven by a weak probe light, a coherent coupling field, and two broadband polarized fields that serve as the incoherent pumping fields. We theoretically show that by modulation of the external coupling field, incoherent pumping rates, and detuning of the probe light, the GH shifts in the reflected and transmitted probe light can be controlled. Our results show that enhanced GH shifts of reflected and transmitted probe beams can be obtained by simultaneous use of incoherent pumping rates and detuning of the probe light. Moreover, we find that the GH shifts in both reflected and transmitted probe beams can be negative or positive at certain angles of the incident probe field. Thus, these results may provide some new possibilities for technological applications in all-optical systems based on nanostructure devices.

  9. Quantum dot molecules

    CERN Document Server

    Wu, Jiang

    2014-01-01

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

  10. CdS quantum dots sensitized Cu doped ZnO nanostructured thin films for solar cell applications

    Science.gov (United States)

    Poornima, K.; Gopala Krishnan, K.; Lalitha, B.; Raja, M.

    2015-07-01

    ZnO nanorods and Cu doped ZnO nanorods thin films have been prepared by simple hydrothermal method. CdS quantum dots are sensitized with Cu doped ZnO nanorod thin films using successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction study reveals that ZnO nanorods, and CdS quantum dot sensitized Cu doped ZnO nanorods exhibit hexagonal structure. The scanning electron microscope image shows the presence of ZnO nanorods. The average diameter and length of the aligned nanorod is 300 nm and 1.5 μm respectively. The absorption spectra shows that the absorption edge of CdS quantum dot sensitized ZnO nanorod thin film is shifted toward longer wavelength region when compared to the absorption edge of ZnO nanorods film. The conversion efficiency of the CdS quantum dot sensitized Cu doped ZnO nanorod thin film solar cell is 1.5%.

  11. Chiral Graphene Quantum Dots.

    Science.gov (United States)

    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. MBE growth of Quantum nanostructures for optoelectronics

    OpenAIRE

    2014-01-01

    Molecular Beam Epitaxy (MBE) is a powerful tech-nique for the fabrication of several self-assembled III-V nanostructures such as quantum rings, quantum dots, (Garcia 2013) and quantum wires that can cover a wide range of the spectrum from 0.98 ¿m to 1.6 ¿m. The possibility of performing in-situ, real-time, measurements of accumulated stress (¿¿) dur-ing growth of these nanostructures enables to achieve a deep understanding of the growth processes. For example, whereas quantum rings (QR) f...

  13. Mesoscopic quantum emitters coupled to plasmonic nanostructures

    DEFF Research Database (Denmark)

    Andersen, Mads Lykke

    This thesis reports research on quantum dots coupled to dielectric and plasmonic nano-structures by way of nano-structure fabrication, optical measurements, and theoretical modeling. To study light-matter interaction, plasmonic gap waveguides with nanometer dimensions as well as samples for studies...... of quantum dots in proximity to semiconductor/air and semiconductor/metal interfaces, were fabricated. We measured the decay dynamics of quantum dots near plasmonic gap waveguides and observed modied decay rates. The obtainable modications with the fabricated structures are calculated to be too small...... for the spontaneous emission of mesoscopic quantum emitters is developed. The light-matter interaction is in this model modied beyond the dipole expectancy and found to both suppress and enhance the coupling to plasmonic modes in excellent agreement with our measurements. We demonstrate that this mesoscopic effect...

  14. Quantum dot solar cells

    CERN Document Server

    Wu, Jiang

    2013-01-01

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

  15. Hexagonal graphene quantum dots

    KAUST Repository

    Ghosh, S.

    2016-12-05

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

  16. Characterization of Nanostructured TiO2 Electrodes Sensitized with CdSe Quantum Dots Using Photoacoustic and Photoelectrochemical Current Methods

    Science.gov (United States)

    Shen, Qing; Toyoda, Taro

    2004-05-01

    Two types of nanostructured titanium dioxide (TiO2) electrodes were prepared with anatase TiO2 nanoparticles of different sizes (average diameters of 15 and 27 nm). CdSe quantum dots were adsorbed onto each of the two types of TiO2 electrodes, by a chemical deposition (CD) technique, the average sizes of which increased to 7 nm on increasing the deposition time. Optical absorption and photoelectrochemical properties were characterized by using photoacoustic (PA) and photoelectrochemical (PEC) current methods. Redshift of the PA and PEC current spectra with increasing CdSe sizes was clearly observed, which indicates quantum confinement effects and photosensitization by the CdSe quantum dots. It was found that the PEC current spectra in the visible region were quite different for the two types of TiO2 electrodes for the same deposition time, although the PA spectra were very similar to each other. The correlation of the PEC current spectra with the microstructures of the two types of TiO2 electrodes was discussed, which provided information that could lead to the optimization of dye-sensitized solar cells (DSSC).

  17. Nanocrystal quantum dots

    CERN Document Server

    Klimov, Victor I

    2010-01-01

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

  18. Valley blockade quantum switching in Silicon nanostructures.

    Science.gov (United States)

    Prati, Enrico

    2011-10-01

    In analogy to the Coulomb and the Pauli spin blockade, based on the electrostatic repulsion and the Pauli exclusion principle respectively, the concept of valley blockade in Silicon nanostructures is explored. The valley parity operator is defined. Valley blockade is determined by the parity conservation of valley composition eigenvectors in quantum transport. A Silicon quantum changeover switch based on a triple of donor quantum dots capable to separate electrons having opposite valley parity by virtue of the valley parity conservation is proposed. The quantum changeover switch represents a novel kind of hybrid quantum based classical logic device.

  19. Carbon nanotube quantum dots

    NARCIS (Netherlands)

    Sapmaz, S.

    2006-01-01

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

  20. Carbon nanotube quantum dots

    NARCIS (Netherlands)

    Sapmaz, S.

    2006-01-01

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

  1. Dipole-dipole-induced giant Goos-Hänchen shift in a photonic crystal doped with quantum dot nanostructures

    Science.gov (United States)

    Panahi, M.; Solookinejad, G.; Ahmadi Sangachin, E.; Hossein Asadpour, Seyyed

    2016-07-01

    The impact of the dipole-dipole interaction on the Goo-Hänchen (GH) shifts in reflected and transmitted lights is investigated. A weak probe beam is incident on a cavity containing the donor and acceptor quantum dots embedded in a nonlinear photonic crystal. We deduced that the GH shifts can be easily adjusted via controlling the corresponding parameters of the system in the presence or absence of dipole-dipole interaction. Our proposed model may be useful to developing the all-optical devices based on photonic materials doped with nanoparticles.

  2. Dissipative tunneling in structures with quantum dots and quantum molecules

    OpenAIRE

    Dahnovsky, Yu. I.; Krevchik, V. D.; Semenov, M. B.; Yamamoto, K.; Zhukovsky, V. Ch.; Aringazin, A. K.; Kudryashov, E. I.; Mayorov, V. G.

    2005-01-01

    The problem of tunneling control in systems "quantum dot - quantum well" (as well as "quantum dot - quantum dot" or quantum molecule) and "quantum dot - bulk contact" is studied as a quantum tunneling with dissipation process in the semiclassical (instanton) approximation. For these systems temperature and correlation between a quantum dot radius and a quantum well width (or another quantum dot radius) are considered to be control parameters. The condition for a single electron blockade is fo...

  3. A unique structure for the multiplexer in quantum-dot cellular automata to create a revolution in design of nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Naji Asfestani, Mazaher; Rasouli Heikalabad, Saeed, E-mail: s.rasouli@iaut.ac.ir

    2017-05-01

    Quantum-dot cellular automata (QCA) is the advent of technology and suitable replacement for semiconductor transistor technology. In this paper, a unique structure for the 2:1 multiplexer is presented in QCA. The structure of this component is simple, ultra-efficient and very useful to implement the various logical functions. The proposed structure does not follow any Boolean function. It takes advantage of the inherent characteristics of quantum technology to produce the desired output. Based on these principles, we design the new and efficient structures for the 4:1 multiplexer and 8:1 multiplexer in the QCA technology. These structures are designed with QCADesigner simulator and simulation results are examined. Investigation results indicate the amazing performance of proposed structure compared to existing structures in terms of area, complexity, power consumption and latency.

  4. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

    a future challenge for the droplet-epitaxy technique. A multipolar theory of spontaneous emission from quantum dots is developed to explain the recent observation that In(Ga)As quantum dots break the dipole theory. The analysis yields a large mesoscopic moment, which contains magnetic-dipole and electric......-matter interaction of both electric and magnetic character. Our study demonstrates that In(Ga)As quantum dots lack parity symmetry and, as consequence, can be employed for locally probing the parity symmetry of complex photonic nanostructures. This opens the prospect for interfacing quantum dots with optical......The present thesis reports research on the optical properties of quantum dots by developing new theories and conducting optical measurements. We demonstrate experimentally singlephoton superradiance in interface-uctuation quantum dots by recording the temporal decay dynamics in conjunction...

  5. Single quantum dot nanowire photodetectors

    NARCIS (Netherlands)

    Van Kouwen, M.P.; Van Weert, M.H.M.; Reimer, M.E.; Akopian, N.; Perinetti, U.; Algra, R.E.; Bakkers, E.P.A.M.; Kouwenhoven, L.P.; Zwiller, V.

    2010-01-01

    We report InP nanowire photodetectors with a single InAsP quantum dot as light absorbing element. With excitation above the InP band gap, the nanowire photodetectors are efficient (quantum efficiency of 4%). Under resonant excitation of the quantum dot, the photocurrent amplitude depends on the line

  6. Single quantum dot nanowire photodetectors

    NARCIS (Netherlands)

    Van Kouwen, M.P.; Van Weert, M.H.M.; Reimer, M.E.; Akopian, N.; Perinetti, U.; Algra, R.E.; Bakkers, E.P.A.M.; Kouwenhoven, L.P.; Zwiller, V.

    2010-01-01

    We report InP nanowire photodetectors with a single InAsP quantum dot as light absorbing element. With excitation above the InP band gap, the nanowire photodetectors are efficient (quantum efficiency of 4%). Under resonant excitation of the quantum dot, the photocurrent amplitude depends on the

  7. Research progress of self-organized Ge quantum dots on Si substrate

    Institute of Scientific and Technical Information of China (English)

    HUANG Changjun; YU Jinzhong; WANG Qiming

    2004-01-01

    A review is presented on recent research development of self-organized Ge/Si quantum dots (QDs).Emphasis is put on the morphological evolution of the Ge quantum dots grown on Si (001) substrate,the structure analysis of multilayer Ge QDs,the optical and electronic properties of these nanostructures,and the approaches to fabricating ordered Ge quantum dots.

  8. Quantum mechanical effects analysis of nanostructured solar cell models

    Directory of Open Access Journals (Sweden)

    Badea Andrei

    2016-01-01

    Full Text Available The quantum mechanical effects resulted from the inclusion of nanostructures, represented by quantum wells and quantum dots, in the i-layer of an intermediate band solar cell will be analyzed. We will discuss the role of these specific nanostructures in the increasing of the solar cells efficiency. InAs quantum wells being placed in the i-layer of a gallium arsenide (GaAs p-i-n cell, we will analyze the quantum confined regions and determine the properties of the eigenstates located therein. Also, we simulate the electroluminescence that occurs due to the nanostructured regions.

  9. Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Maldonado, D., E-mail: david.hernandez@uca.es [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Herrera, M.; Sales, D.L. [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Alonso-Gonzalez, P.; Gonzalez, Y.; Gonzalez, L. [Instituto de Microelectronica de Madrid (CNM-CSIC), Isaac Newton 8 (PTM), 28760 Tres Cantos, Madrid (Spain); Pizarro, J.; Galindo, P.L. [Departamento de Lenguajes y Sistemas Informaticos, CASEM, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Molina, S.I. [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain)

    2010-07-01

    The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.

  10. Quantum dots for quantum information technologies

    CERN Document Server

    2017-01-01

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

  11. Electron correlations in quantum dots

    CERN Document Server

    Tipton, D L J

    2001-01-01

    Quantum dot structures confine electrons in a small region of space. Some properties of semiconductor quantum dots, such as the discrete energy levels and shell filling effects visible in addition spectra, have analogies to those of atoms and indeed dots are sometimes referred to as 'artificial atoms'. However, atoms and dots show some fundamental differences due to electron correlations. For real atoms, the kinetic energy of electrons dominates over their mutual Coulomb repulsion energy and for this reason the independent electron approximation works well. For quantum dots the confining potential may be shallower than that of real atoms leading to lower electron densities and a dominance of mutual Coulomb repulsion over kinetic energy. In this strongly correlated regime the independent electron picture leads to qualitatively incorrect results. This thesis concentrates on few-electron quantum dots in the strongly correlated regime both for quasi-one-dimensional and two-dimensional dots in a square confining p...

  12. Cd-free Cu-Zn-In-S/ZnS quantum dots@SiO2 multiple cores nanostructure: preparation and application for white LEDs.

    Science.gov (United States)

    Jiang, Tongtong; Shen, Mohan; Dai, Peng; Wu, Mingzai; Yu, Xinxin; Li, Guang; Xu, Xiaoliang; Zeng, Haibo

    2017-10-27

    The work reports the fabrication of Cu doped Zn-In-S (CZIS) alloy quantum dots (QDs) using dodecanethiol and oleic acid as stabilizing ligands. With the increase of doped Cu element, the photoluminescence (PL) peak is monotonically red shifted. After coating ZnS shell, the PL quantum yield of CZIS QDs can reach 78%. Using reverse micelle microemulsion method, CZIS/ZnS QDs@SiO2 multi-core nanospheres were synthesized to improve the colloidal stability and avoid the aggregation of QDs. The obtained multi-core nanospheres were dispersed in curing adhesive, and applied as a color conversion layer in down converted light-emitting diodes. After encapsulation in curing adhesive, the newly designed LEDs show artifically regulated color coordinates with varying the weight ratio of green QDs and red QDs, and the concentrations of these two types of QDs. Moreover, natural white and warm white LEDs with correlated color temperature of 5287, 6732, 2731, and 3309 K can be achieved, which indicates that CZIS/ZnS QDs@SiO2 nanostructures are promising color conversion layer material for solid-state lighting application.

  13. Quantum dots for terahertz generation

    Energy Technology Data Exchange (ETDEWEB)

    Liu, H C; Aslan, B; Gupta, J A; Wasilewski, Z R; Aers, G C; SpringThorpe, A J; Buchanan, M [Institute for Microstructural Sciences, National Research Council, Ottawa, K1A 0R6 (Canada)], E-mail: h.c.liu@nrc.ca

    2008-09-24

    Nanostructures made of semiconductors, such as quantum wells and quantum dots (QD), are well known, and some have been incorporated in practical devices. Here we focus on novel structures made of QDs and related devices for terahertz (THz) generation. Their potential advantages, such as low threshold current density, high characteristic temperature, increased differential gain, etc, make QDs promising candidates for light emitting applications in the THz region. Our idea of using resonant tunneling through QDs is presented, and initial results on devices consisting of self-assembled InAs QDs in an undoped GaAs matrix, with a design incorporating a GaInNAs/GaAs short period superlattice, are discussed. Moreover, shallow impurities are also being explored for possible THz emission: the idea is based on the tunneling through bound states of individual donor or acceptor impurities in the quantum well. Initial results on devices having an AlGaAs/GaAs double-barrier resonant tunneling structure are discussed.

  14. Charged-Exciton Complexes in Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang

    2001-01-01

    It is known experimentally that stable charged-exciton complexes can exist in low-dimensional semiconductor nanostructures. Much less is known about the properties of such charged-exciton complexes since three-body problems are very difficult to be solved, even numerically. Here we introduce the correlated hyperspherical harmonics as basis functions to solve the hyperangular equation for negatively and positively charged excitons (trions) in a harmonic quantum dot. By using this method, we have calculated the energy spectra of the low-lying states of a charged exciton as a function of the radius of quantum dot. Based on symmetry analysis, the level crossover as the dot radius increases can be fully explained as the results of symmetry constraint.``

  15. Comparison of strain fields in truncated and un-truncated quantum dots in stacked InAs/GaAs nanostructures with varying stacking periods

    CERN Document Server

    Shin, H; Yoo, Y H

    2003-01-01

    Strain fields in truncated and un-truncated InAs quantum dots with the same height and base length have been compared numerically when the dots are vertically stacked in a GaAs matrix at various stacking periods. The compressive hydrostatic strain in truncated dots decreases slightly as compared with the un-truncated dots without regard to the stacking period studied. However, the reduction in tensile biaxial strain, compressive radial strain and tensile axial strain was salient in the truncated dot and the reduction increased with decreasing stacking period. From such changes in strain, changes in the band gap and related properties are anticipated.

  16. Semiconductor quantum optics with tailored photonic nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Laucht, Arne

    2011-06-15

    This thesis describes detailed investigations of the effects of photonic nanostructures on the light emission properties of self-assembled InGaAs quantum dots. Nanoscale optical cavities and waveguides are employed to enhance the interaction between light and matter, i.e. photons and excitons, up to the point where optical non-linearities appear at the quantum (single photon) level. Such non-linearities are an essential component for the realization of hardware for photon based quantum computing since they can be used for the creation and detection of non-classical states of light and may open the way to new genres of quantum optoelectronic devices such as optical modulators and optical transistors. For single semiconductor quantum dots in photonic crystal nanocavities we investigate the coupling between excitonic transitions and the highly localized mode of the optical cavity. We explore the non-resonant coupling mechanisms which allow excitons to couple to the cavity mode, even when they are not spectrally in resonance. This effect is not observed for atomic cavity quantum electrodynamics experiments and its origin is traced to phonon-assisted scattering for small detunings ({delta}E<{proportional_to}5 meV) and a multi-exciton-based, Auger-like process for larger detunings ({delta}E >{proportional_to}5 meV). For quantum dots in high-Q cavities we observe the coherent coupling between exciton and cavity mode in the strong coupling regime of light-matter interaction, probe the influence of pure dephasing on the coherent interaction at high excitation levels and high lattice temperatures, and examine the coupling of two spatially separated quantum dots via the exchange of real and virtual photons mediated by the cavity mode. Furthermore, we study the spontaneous emission properties of quantum dots in photonic crystal waveguide structures, estimate the fraction of all photons emitted into the propagating waveguide mode, and demonstrate the on-chip generation of

  17. Understanding the electronic structure of CdSe quantum dot-fullerene (C60) hybrid nanostructure for photovoltaic applications

    Science.gov (United States)

    Sarkar, Sunandan; Rajbanshi, Biplab; Sarkar, Pranab

    2014-09-01

    By using the density-functional tight binding method, we studied the electronic structure of CdSe quantum dot(QD)-buckminsterfullerene (C60) hybrid systems as a function of both the size of the QD and concentration of the fullerene molecule. Our calculation reveals that the lowest unoccupied molecular orbital energy level of the hybrid CdSeQD-C60 systems lies on the fullerene moiety, whereas the highest occupied molecular orbital (HOMO) energy level lies either on the QD or the fullerene depending on size of the CdSe QD. We explored the possibility of engineering the energy level alignment by varying the size of the CdSe QD. With increase in size of the QD, the HOMO level is shifted upward and crosses the HOMO level of the C60-thiol molecule resulting transition from the type-I to type-II band energy alignment. The density of states and charge density plot support these types of band gap engineering of the CdSe-C60 hybrid systems. This type II band alignment indicates the possibility of application of this nanohybrid for photovoltaic purpose.

  18. Optical phonons in nanostructured thin films composed by zincblende zinc selenide quantum dots in strong size-quantization regime: Competition between phonon confinement and strain-related effects

    Energy Technology Data Exchange (ETDEWEB)

    Pejova, Biljana, E-mail: biljana@pmf.ukim.mk

    2014-05-01

    Raman scattering in combination with optical spectroscopy and structural studies by X-ray diffraction was employed to investigate the phonon confinement and strain-induced effects in 3D assemblies of variable-size zincblende ZnSe quantum dots close packed in thin film form. Nanostructured thin films were synthesized by colloidal chemical approach, while tuning of the nanocrystal size was enabled by post-deposition thermal annealing treatment. In-depth insights into the factors governing the observed trends of the position and half-width of the 1LO band as a function of the average QD size were gained. The overall shifts in the position of 1LO band were found to result from an intricate compromise between the influence of phonon confinement and lattice strain-induced effects. Both contributions were quantitatively and exactly modeled. Accurate assignments of the bands due to surface optical (SO) modes as well as of the theoretically forbidden transverse optical (TO) modes were provided, on the basis of reliable physical models (such as the dielectric continuum model of Ruppin and Englman). The size-dependence of the ratio of intensities of the TO and LO modes was studied and discussed as well. Relaxation time characterizing the phonon decay processes in as-deposited samples was found to be approximately 0.38 ps, while upon post-deposition annealing already at 200 °C it increases to about 0.50 ps. Both of these values are, however, significantly smaller than those characteristic for a macrocrystalline ZnSe sample. - Graphical abstract: Optical phonons in nanostructured thin films composed by zincblende zinc selenide quantum dots in strong size-quantization regime: competition between phonon confinement and strain-related effects. - Highlights: • Phonon confinement vs. strain-induced effects in ZnSe 3D QD assemblies were studied. • Shifts of the 1LO band result from an intricate compromise between the two effects. • SO and theoretically forbidden TO modes were

  19. Quantum dots for next-generation photovoltaics

    Directory of Open Access Journals (Sweden)

    Octavi E. Semonin

    2012-11-01

    Full Text Available Colloidal quantum-confined semiconductor nanostructures are an emerging class of functional material that are being developed for novel solar energy conversion strategies. One of the largest losses in a bulk or thin film solar cell occurs within a few picoseconds after the photon is absorbed, as photons with energy larger than the semiconductor bandgap produce charge-carriers with excess kinetic energy, which is then dissipated via phonon emission. Semiconductor nanostructures, where at least one dimension is small enough to produce quantum confinement effects, provide new pathways for controlling energy flow and therefore have the potential to increase the efficiency of the primary photoconversion step. In this review, we provide the current status of research efforts towards utilizing the unique properties of colloidal quantum dots (nanocrystals confined in three dimensions in prototype solar cells and demonstrate that these unique systems have the potential to bypass the Shockley-Queisser single-junction limit for solar photon conversion.

  20. Controlling light-matter interaction with mesoscopic quantum dots

    DEFF Research Database (Denmark)

    Stobbe, Søren; Kristensen, Philip Trøst; Lodahl, Peter

    2012-01-01

    Semiconductor quantum dots (QDs) enable efficient coupling between light and matter, which is useful in applications such as light-harvesting and all-solid-state quantum information processing. This coupling can be increased by placing QDs in nanostructured optical environments such as photonic...

  1. Nanostructures based on quantum dots for application in promising methods of single- and multiphoton imaging and diagnostics

    Science.gov (United States)

    Nabiev, I. R.

    2017-01-01

    Molecules recognizing biomarkers of diseases (monoclonal antibodies (monoABs)) are often too large for biomedical applications, and the conditions that are used to bind them with nanolabels lead to disordered orientation of monoABs with respect to the nanoparticle surface. Extremely small nanoprobes, designed via oriented conjugation of quantum dots (QDs) with single-domain antibodies (sdABs) derived from the immunoglobulin of llama and produced in the E. coli culture, have a hydrodynamic diameter less than 12 nm and contain equally oriented sdAB molecules on the surface of each QD. These nanoprobes exhibit excellent specificity and sensitivity in quantitative determination of a small number of cells expressing biomarkers. In addition, the higher diffusion coefficient of sdABs makes it possible to perform immunohistochemical analysis in bulk tissue, inaccessible for conventional monoABs. The necessary conditions for implementing high-quality immunofluorescence diagnostics are a high specificity of labeling and clear differences between the fluorescence of nanoprobes and the autofluorescence of tissues. Multiphoton micros-copy with excitation in the near-IR spectral range, which is remote from the range of tissue autofluorescence excitation, makes it possible to solve this problem and image deep layers in biological tissues. The two-photon absorption cross sections of CdSe/ZnS QDs conjugated with sdABs exceed the corresponding values for organic fluorophores by several orders of magnitude. These nanoprobes provide clear discrimination between the regions of tumor and normal tissues with a ratio of the sdAB fluorescence to the tissue autofluorescence upon two-photon excitation exceeding that in the case of single-photon excitation by a factor of more than 40. The data obtained indicate that the sdAB-QD conjugates used as labels provide the same, or even better, quality as the "gold standard" of immunohistochemical diagnostics. The developed nanoprobes are expected to

  2. Quantum dots: Rethinking the electronics

    Science.gov (United States)

    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.

  3. Interface phonon effect on optical spectra of quantum nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Maslov, Alexander Yu., E-mail: maslov.ton@mail.ioffe.r [Ioffe Physical Technical Institute, Polytechnicheskaya st., 26, 194021 Saint Petersburg (Russian Federation); Proshina, Olga V.; Rusina, Anastasia N. [Ioffe Physical Technical Institute, Polytechnicheskaya st., 26, 194021 Saint Petersburg (Russian Federation)

    2009-12-15

    This paper deals with theory of large radius polaron effect in quantum wells, wires and dots. The interaction of charge particles and excitons with both bulk and interface optical phonons is taken into consideration. The analytical expression for polaron binding energy is obtained for different types of nanostructures. It is shown that the contribution of interface phonons to the polaron binding energy may exceed the bulk phonon part. The manifestation of polaron effects in optical spectra of quantum nanostructures is discussed.

  4. Quantum dots in cell biology.

    Science.gov (United States)

    Barroso, Margarida M

    2011-03-01

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

  5. Hydrophobin-Encapsulated Quantum Dots.

    Science.gov (United States)

    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.

  6. Quantum Dots in Cell Biology

    OpenAIRE

    Barroso, Margarida M.

    2011-01-01

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

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

    Science.gov (United States)

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

    2016-05-01

    In this paper, we develop a theory for discrete solitons interaction with a string of coupled quantum dots in view of the local field effects. Discrete nonlinear Schrodinger (DNLS) equations are used to describe the dynamics of the string. Numerical calculations are carried out and results are analyzed with the help of matlab software. With the help of numerical solutions we demonstrate that in the quantum dots string, Rabi oscillations (RO) are self trapped into stable bright Rabi solitons. The Rabi oscillations in different types of nanostructures have potential applications to the elements of quantum logic and quantum memory.

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

    Energy Technology Data Exchange (ETDEWEB)

    Pozner, R.; Lifshitz, E. [Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Peskin, U., E-mail: uri@tx.technion.ac.il [Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Lise Meitner Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

    2015-09-14

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

  9. Optically active quantum dots

    Science.gov (United States)

    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.

  10. Optical phonons in nanostructured thin films composed by zincblende zinc selenide quantum dots in strong size-quantization regime: Competition between phonon confinement and strain-related effects

    Science.gov (United States)

    Pejova, Biljana

    2014-05-01

    Raman scattering in combination with optical spectroscopy and structural studies by X-ray diffraction was employed to investigate the phonon confinement and strain-induced effects in 3D assemblies of variable-size zincblende ZnSe quantum dots close packed in thin film form. Nanostructured thin films were synthesized by colloidal chemical approach, while tuning of the nanocrystal size was enabled by post-deposition thermal annealing treatment. In-depth insights into the factors governing the observed trends of the position and half-width of the 1LO band as a function of the average QD size were gained. The overall shifts in the position of 1LO band were found to result from an intricate compromise between the influence of phonon confinement and lattice strain-induced effects. Both contributions were quantitatively and exactly modeled. Accurate assignments of the bands due to surface optical (SO) modes as well as of the theoretically forbidden transverse optical (TO) modes were provided, on the basis of reliable physical models (such as the dielectric continuum model of Ruppin and Englman). The size-dependence of the ratio of intensities of the TO and LO modes was studied and discussed as well. Relaxation time characterizing the phonon decay processes in as-deposited samples was found to be approximately 0.38 ps, while upon post-deposition annealing already at 200 °C it increases to about 0.50 ps. Both of these values are, however, significantly smaller than those characteristic for a macrocrystalline ZnSe sample.

  11. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

    a future challenge for the droplet-epitaxy technique. A multipolar theory of spontaneous emission from quantum dots is developed to explain the recent observation that In(Ga)As quantum dots break the dipole theory. The analysis yields a large mesoscopic moment, which contains magnetic-dipole and electric......-matter interaction of both electric and magnetic character. Our study demonstrates that In(Ga)As quantum dots lack parity symmetry and, as consequence, can be employed for locally probing the parity symmetry of complex photonic nanostructures. This opens the prospect for interfacing quantum dots with optical...... metamaterials for tailoring light-matter interaction at the single-electron and single-photon level....

  12. Mesoscopic Cavity Quantum Electrodynamics with Quantum Dots

    CERN Document Server

    Childress, L I; Lukin, M D

    2003-01-01

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

  13. Beer's law in semiconductor quantum dots

    CERN Document Server

    Adamashvili, G T

    2010-01-01

    The propagation of a coherent optical linear wave in an ensemble of semiconductor quantum dots is considered. It is shown that a distribution of transition dipole moments of the quantum dots changes significantly the polarization and Beer's absorption length of the ensemble of quantum dots. Explicit analytical expressions for these quantities are presented.

  14. Nanoscale quantum-dot supercrystals

    Science.gov (United States)

    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.

  15. Dye- and quantum dot-sensitized solar cells based on nanostructured wide-bandgap semiconductors via an integrated experimental and modeling study

    Science.gov (United States)

    Xin, Xukai

    Dye-sensitized solar cells (DSSCs) and quantum dot-sensitized solar cells (QDSSCs) are two promising alternative, cost-effective concepts for solar-to-electric energy conversion that have been offered to challenge conventional Si solar cells over the past decade. The configuration of a DSSC or a QDSSC consists of sintered TiO2 nanoparticle films, ruthenium-based dyes or quantum dots (QDs) (i.e., sensitizers), and electrolytes. Upon the absorption of photons, the dyes or QDs generate excitons (i.e., electron-hole pairs). Subsequently, the electrons inject into the TiO2 photoanode to generate photocurrent; scavenged by a redox couple, holes transport to the cathode. The overall power conversion efficiency (PCE) of a DSSC or QDSSC is dictated by the light harvest efficiency, quantum yield for charge injection, and charge collection efficiency at the electrodes. The goal of our research is to understand the fundamental physics and performance of DSSCs and QDSSCs with improved PCE at the low cost based on rational engineering of TiO2 nanostructures, sensitizers, and electrodes through an integrated experimental and modeling study. In this presentation, I will discuss three aspects that I have accomplished over the last several years. (1) Effects of surface treatment and structural modification of photoanode on the performance of DSSCs. First, our research indicates that the surface treatment with both TiCl4 and oxygen plasma yields the most efficient dye-sensitized TiO2-nanoparticle solar cells. A maximum PCE is achieved with a 21 microm thick TiO2 film; the PCE further increases to 8.35% after TiCl4 and O 2 plasma treatments, compared to the untreated TiO2 ( PCE = 3.86%). Second, we used a layer of TiO2 nanoparticle film coated on the FTO glass, and a bilayer of TiO2nanoparticle/freestanding TiO2 nanotube film deposited on the FTO glass as photoanodes. The J˜V parameter analysis acquired by equivalent circuit model simulation reveals that nanotubular structures are

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

    Energy Technology Data Exchange (ETDEWEB)

    Heiss, Dominik

    2009-10-15

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

  17. Many-particle theory of optical properties in low-dimensional nanostructures. Dynamics in single-walled carbon nanotubes and semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Malic, Ermin

    2008-09-02

    This work focuses on the theoretical investigation of optical properties of low-dimensional nanostructures, specifically single-walled carbon nanotubes (CNTs) and self-assembled InAs/GaAs quantum dots (QDs). The density-matrix formalism is applied to explain recent experimental results and to give insight into the underlying physics. A microscopic calculation of the absorption coefficient and the Rayleigh scattering cross section is performed by a novel approach combining the density-matrix formalism with the tight-binding wave functions. The calculated spectra of metallic nanotubes show a double-peaked structure resulting from the trigonal warping effect. The intensity ratios of the four lowest-lying transitions in both absorption and Rayleigh spectra can be explained by the different behavior of the optical matrix elements along the high-symmetry lines K-{gamma} and K-M. The Rayleigh line shape is predicted to be asymmetric, with an enhanced cross section for lower photon energies arising from non-resonant contributions of the optical susceptibility. Furthermore, the Coulomb interaction is shown to be maximal when the momentum transfer is low. For intersubband processes with a perpendicular momentum transfer, the coupling strength is reduced to less than 5%. The chirality and diameter dependence of the excitonic binding energy and the transition frequency are presented in Kataura plots. Furthermore, the influence of the surrounding environment on the optical properties of CNTs is investigated. Extending the confinement to all three spatial dimensions, semiconductor Bloch equation are derived to describe the dynamics in QD semiconductor lasers and amplifiers. A detailed microscopic analysis of the nonlinear turn-on dynamics of electrically pumped InAs/GaAs QD lasers is performed, showing the generation of relaxation oscillations on a nanosecond time scale in both the photon and charge carrier density. The theory predicts a strong damping of relaxation oscillations

  18. Nuclear Spins in Quantum Dots

    NARCIS (Netherlands)

    Erlingsson, S.I.

    2003-01-01

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

  19. Colloidal quantum dot solar cells

    Science.gov (United States)

    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.

  20. Polymer-coated quantum dots

    NARCIS (Netherlands)

    Tomczak, Nikodem; Liu, Rongrong; Vancso, Julius G.

    2013-01-01

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

  1. Anomalous Temperature Dependence of Photoluminescence in InAs/InAlGaAs/InP Quantum Wire and Dot Hybrid Nanostructures

    Institute of Scientific and Technical Information of China (English)

    YANG Xin-Rong; XU Bo; WANG Hai-Fei; ZHAO Guo-Qing; SHI Shu-Hui; SHEN Xiao-Zhi; LI Jun-Feng; WANG Zhan-Guo

    2011-01-01

    Self-assembled InAs quantum wires (QWRs) are fabricated on an InP substrate by solid-source molecular beam epitaxy (SSMBE). Photoluminescence (PL) spectra are investigated in these nanostructures as a function of temperature. An anomalous enhancement of PL intensity and a temperature insensitive PL emission are observed from lnAs nanostructures grown on InP substrates using lnAIGaAs as the matrix layer and the origin of this phenomenon is discussed. We attribute the anomalous temperature dependence of photoluminescence to the formation of Al-rich and In-rich region in the InAlGaAs buffer layer and the cap layer.%@@ Self-assembled InAs quantum wires (QWRs) are fabricated on an InP substrate by solid-source molecular beam epitaxy (SSMBE).Photoluminescence (PL) spectra are investigated in these nanostructures as a function of temperature.An anomalous enhancement of PL intensity and a temperature insensitive PL emission are observed from InAs nanostructures grown on InP substrates using InAlGaAs as the matrix layer and the origin of this phenomenon is discussed.We attribute the anomalous temperature dependence of photoluminescence to the formation of Al-rich and In-rich region in the InAlGaAs buffer layer and the cap layer.

  2. Quantum-size-controlled photoelectrochemical etching of semiconductor nanostructures

    Science.gov (United States)

    Fischer, Arthur J.; Tsao, Jeffrey Y.; Wierer, Jr., Jonathan J.; Xiao, Xiaoyin; Wang, George T.

    2016-03-01

    Quantum-size-controlled photoelectrochemical (QSC-PEC) etching provides a new route to the precision fabrication of epitaxial semiconductor nanostructures in the sub-10-nm size regime. For example, quantum dots (QDs) can be QSC-PEC-etched from epitaxial InGaN thin films using narrowband laser photoexcitation, and the QD sizes (and hence bandgaps and photoluminescence wavelengths) are determined by the photoexcitation wavelength.

  3. Virtual photonic couplings of quantum nanostructures

    DEFF Research Database (Denmark)

    Matsueda, H.; Hvam, Jørn Märcher; Ducommun, Yann

    nanotechnology on the basis of what is really happening in the nanostructures. Therefore, we have first focused on dipole-dipole interaction, especially the resonance dynamic dipole- dipole interaction (RDDDI) among transition dipoles, publishing on the generation of an intrinsic nonlinear localized mode...... scheme into physics of solids, mainly because the range of the mediating photon was not long enough to cover the distance of usual concerns, e.g. size of devices in conventional integrated circuits. However, this retardation should be lifted not just to improve our understanding, but to refine our...... as early as 1996, and subsequently on quantum gate application with quantum dots (QDs), coherent modes in an ensemble of QDs, a parity conserving dynamic Förster type mechanism between identical tuned QDs involving a real photon (RPH) or virtual photon (VPH), and the RDDDI mechanism between nonidentical...

  4. Coherent control of quantum dots

    DEFF Research Database (Denmark)

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

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

  5. Semiconductor double quantum dot micromaser.

    Science.gov (United States)

    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.

  6. Coherent control of quantum dots

    DEFF Research Database (Denmark)

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

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

  7. Brightness-equalized quantum dots

    Science.gov (United States)

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

    2015-10-01

    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.

  8. Colloidal quantum dots: synthesis, properties and applications

    Science.gov (United States)

    Brichkin, S. B.; Razumov, V. F.

    2016-12-01

    Key recent results obtained in studies of a new class of luminophores, colloidal quantum dots, are analyzed. Modern methods for the synthesis and post-synthetic treatment of colloidal quantum dots that make it possible to achieve record high quantum yield of luminescence and to modify their characteristics for specific applications are considered. Currently important avenues of research on colloidal quantum dots and the problems in and prospects for their practical applications in various fields are discussed. The bibliography includes 272 references.

  9. Quantum Computer Using Coupled Quantum Dot Molecules

    CERN Document Server

    Wu, N J; Natori, A; Yasunaga, H; Wu*, Nan-Jian

    1999-01-01

    We propose a method for implementation of a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively.The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates by using a box-shaped quantum dot model and numerically solving a time-dependent Schridinger equation, and demonstrate that the quantum gates can perform the quantum computation. The operating speed of the gates is about one operation per 4ps. The reading operation of the output of the quantum computer can...

  10. Thermoelectric energy harvesting with quantum dots.

    Science.gov (United States)

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

    2015-01-21

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

  11. Ultrafast spectroscopy of quantum dots

    CERN Document Server

    Foo, E

    2001-01-01

    exchange-correlation interactions among the confined carriers inside the dots are suggested to be responsible. A density functional calculation for BGR of the ground state transition shows good agreement with our experimental results, especially in the high dot occupancy regime. Many-particle state scattering gives rise to large homogeneous spectral broadening of the PL peaks, from which an intradot relaxation time approx 300 fs is estimated. This observation supports the results obtained by direct excitation of carriers within the QDs. Femtosecond time-resolved photoluminescence measured by frequency up-conversion has been used to investigate carrier dynamics in InAs/GaAs self-assembled quantum dots (QDs). Our results reveal ultrafast carrier relaxation and sequential state filling. Carrier relaxation is proposed to occur by Auger-type processes, and the sequential state filling suggests that intradot relaxation is much faster than carrier capture from the InAs wetting layer. Measurements obtained by direct ...

  12. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

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

    2002-01-01

    We have produced GaAs-based quantum-dot edge-emitting lasers operating at 1.16 mu m with record-low transparency current, high output power, and high internal quantum efficiencies. We have also realized GaAs-based quantum-dot lasers emitting at 1.3 mu m, both high-power edge emitters and low...

  13. Semiconductor quantum dots for electron spin qubits

    NARCIS (Netherlands)

    van der Wiel, Wilfred Gerard; Stopa, M.; Kodera, T.; Hatano, T.; Tarucha, S.

    2006-01-01

    We report on our recent progress in applying semiconductor quantum dots for spin-based quantum computation, as proposed by Loss and DiVincenzo (1998 Phys. Rev. A 57 120). For the purpose of single-electron spin resonance, we study different types of single quantum dot devices that are designed for

  14. Colloidal Quantum Dot Photovoltaics Enhanced by Perovskite Shelling.

    Science.gov (United States)

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

    2015-11-11

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

  15. Ultrasmall colloidal PbS quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Reilly, Nick; Wehrung, Michael; O' Dell, Ryan Andrew [Department of Physics and Astronomy, Bowling Green State University, Bowling Green, OH 43403 (United States); Sun, Liangfeng, E-mail: lsun@bgsu.edu [Department of Physics and Astronomy, Bowling Green State University, Bowling Green, OH 43403 (United States); Center for Photochemical Sciences, Bowling Green State University, Bowling Green, OH 43403 (United States)

    2014-09-15

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

  16. POLARON IN CYLINDRICAL AND SPHERICAL QUANTUM DOTS

    Directory of Open Access Journals (Sweden)

    L.C.Fai

    2004-01-01

    Full Text Available Polaron states in cylindrical and spherical quantum dots with parabolic confinement potentials are investigated applying the Feynman variational principle. It is observed that for both kinds of quantum dots the polaron energy and mass increase with the increase of Frohlich electron-phonon coupling constant and confinement frequency. In the case of a spherical quantum dot, the polaron energy for the strong coupling is found to be greater than that of a cylindrical quantum dot. The energy and mass are found to be monotonically increasing functions of the coupling constant and the confinement frequency.

  17. Activation of silicon quantum dots for emission

    Institute of Scientific and Technical Information of China (English)

    Huang Wei-Qi; Miao Xin-Jian; Huang Zhong-Mei; Liu Shi-Rong; Qin Chao-Jian

    2012-01-01

    The emission of silicon quantum dots is weak when their surface is passivated well. Oxygen or nitrogen on the surface of silicon quantum dots can break the passivation to form localized electronic states in the band gap to generate active centers where stronger emission occurs.From this point of view,we can build up radiative matter for emission.Emissions of various wavelengths can be obtained by controlling the surface bonds of silicon quantum dots.Our experimental results demonstrate that annealing is important in the treatment of the activation,and stimulated emissions at about 600 and 700 nm take place on active silicon quantum dots.

  18. Synthetic Developments of Nontoxic Quantum Dots.

    Science.gov (United States)

    Das, Adita; Snee, Preston T

    2016-03-03

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

  19. Spin transport through quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Lima, A.T. da Cunha; Anda, Enrique V. [Pontificia Univ. Catolica do Rio de Janeiro (PUC-Rio), RJ (Brazil)

    2003-07-01

    Full text: We investigate the spin polarized transport properties of a nanoscopic device constituted by a quantum dot connected to two leads. The electrical current circulates with a spin polarization that is modulated via a gate potential that controls the intensity of the spin-orbit coupling, the Rashba effect. We study a polarized field-effect transistor when one of its parts is constituted by a small quantum dot, which energies are controlled by another gate potential operating inside the confined region. The high confinement and correlation suffered by the charges inside the dot gives rise to novel phenomena. We show that through the manipulation of the gate potential applied to the dot it is possible to control, in a very efficient way, the intensity and polarization of the current that goes along the system. Other crucial parameters to be varied in order to understand the behavior of this system are the intensity of the external applied electric and magnetic field. The system is represented by the Anderson Impurity Hamiltonian summed to a spin-orbit interaction, which describes the Rashba effect. To obtain the current of this out-of-equilibrium system we use the Keldysh formalism.The solution of the Green function are compatible with the Coulomb blockade regime. We show that under the effect of a external magnetic field, if the dot is small enough the device operates as a complete spin filter that can be controlled by the gate potential. The behavior of this device when it is injected into it a polarized current and modulated by the Rashba effect is as well studied. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Ramírez-Porras, A., E-mail: aramirez@fisica.ucr.ac.cr [Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); García, O. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Vargas, C. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Corrales, A. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Solís, J.D. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica)

    2015-08-30

    Highlights: • PL spectra of porous silicon samples have been studied using a stochastic model. • This model can deconvolute PL spectra into three components. • Quantum dots, quantum wires and localized states have been identified. • Nanostructure diameters are in the range from 2.2 nm to 4.0 nm. • Contributions from quantum wires are small compared to the others. - Abstract: Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models.

  1. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

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

  2. Quantum Optics with Quantum Dots in Photonic Nanowires

    DEFF Research Database (Denmark)

    Gérard, J.-M.; Claudon, J.; Bleuse, J.;

    2011-01-01

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

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

    Science.gov (United States)

    Li, Lijie; Jiang, Jian-Hua

    2016-08-01

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

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

    Science.gov (United States)

    Li, Lijie; Jiang, Jian-Hua

    2016-01-01

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

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

    Science.gov (United States)

    Li, Lijie; Jiang, Jian-Hua

    2016-08-23

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

  6. Colloidal quantum dots as optoelectronic elements

    Science.gov (United States)

    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.

  7. Quantum Dot Spectrum Converters for Enhanced High Efficiency Photovoltaics Project

    Data.gov (United States)

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

  8. Exciton in type-II quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Sierra-Ortega, J; Escorcia, R A [Universidad del Magdalena, A. A. 731, Santa Marta (Colombia); Mikhailov, I D, E-mail: jsierraortega@gmail.co [Universidad Industrial de Santander, A. A. 678, Bucaramanga (Colombia)

    2009-05-01

    We study the quantum-size effect and the influence of the external magnetic field on the exciton ground state energy in the type-II InP quantum disk, lens and pyramid deposited on a wetting layer and embedded in a GaInP matrix. We show that the charge distribution over and below quantum dot and wetting layer induced by trapped exciton strongly depends on the quantum dot morphology and the strength of the magnetic field.

  9. Colloidal quantum dot photodetectors

    KAUST Repository

    Konstantatos, Gerasimos

    2011-05-01

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

  10. Fabrication and optical properties of multishell InAs quantum dots on GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xin; Zhang, Xia, E-mail: xzhang@bupt.edu.cn; Li, Junshuai; Cui, Jiangong; Ren, Xiaomin [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

    2015-02-07

    Hybrid nanostructures combining nanowires with quantum dots promote the development of nanoelectronic and nanophotonic devices with integrated functionalities. In this work, we present a complex nanostructure with multishell quantum dots grown on nanowires. 1–4 shells of Stranski-Krastanov InAs quantum dots are grown on the sidewalls of GaAs nanowires by metal organic chemical vapor deposition. Different dot shells are separated by 8 nm GaAs spacer shells. With increasing the number of shells, the quantum dots become sparser and tend to align in one array, which is caused by the shrinkage of facets on which dots prefer to grow as well as the strain fields produced by the lower set of dots which influences the migration of In adatoms. The size of quantum dots increases with the increase of shell number due to enhanced strain fields coupling. The spectra of multishell dots exhibit multiwavelength emission, and each peak corresponds to a dot shell. This hybrid structure may serve as a promising element in nanowire intermediate band solar cells, infrared nanolasers, and photodetectors.

  11. Optical studies of capped quantum dots

    NARCIS (Netherlands)

    Wuister, S.F.

    2005-01-01

    This thesis describes the synthesis and spectroscopy of CdSe and CdTe semiconductor quantum dots (QDs). The first chapter gives an introduction into the unique size dependent properties of semiconductor quantum dots. Highly luminescent QDs of CdSe and CdTe were prepared via a high temperature method

  12. Detecting the chirality for coupled quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Cao Huijuan [Institute for Condensed Matter Physics, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510631 (China); Hu Lian [Institute for Condensed Matter Physics, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510631 (China)], E-mail: huliancaohj@yahoo.com

    2008-04-21

    We propose a scheme to detect the chirality for a system consisting of three coupled quantum dots. The chirality is found to be determined by the frequency of the transition between chiral states under the chiral symmetry broken perturbation. The results are important to construct quantum gates and to demonstrate chiral entangle states in the triangle spin dots.

  13. Optically active quantum-dot molecules.

    Science.gov (United States)

    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.

  14. Research on Self-Assembling Quantum Dots.

    Science.gov (United States)

    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)

  15. Thick-shell nanocrystal quantum dots

    Science.gov (United States)

    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.

  16. Optical Properties of Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Perinetti, U.

    2011-01-01

    This thesis presents different optical experiments performed on semiconductor quantum dots. These structures allow to confine a small number of electrons and holes to a tiny region of space, some nm across. The aim of this work was to study the basic properties of different types of quantum dots

  17. Optical Properties of Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Perinetti, U.

    2011-01-01

    This thesis presents different optical experiments performed on semiconductor quantum dots. These structures allow to confine a small number of electrons and holes to a tiny region of space, some nm across. The aim of this work was to study the basic properties of different types of quantum dots mad

  18. Quantum-dot supercrystals for future nanophotonics

    Science.gov (United States)

    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. Biocompatible quantum dots for biological applications.

    Science.gov (United States)

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

    2011-01-28

    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.

  20. Tailoring Magnetism in Quantum Dots

    Science.gov (United States)

    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.

  1. Coherent optoelectronics with single quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-11-12

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

  2. Coherent optoelectronics with single quantum dots

    Science.gov (United States)

    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.

  3. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

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

  4. Electron transport in quantum dots

    CERN Document Server

    2003-01-01

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

  5. One-pot synthesis of graphene oxide sheets and graphene oxide quantum dots from graphite nanofibers

    Energy Technology Data Exchange (ETDEWEB)

    Abdul Rashid, Suraya, E-mail: suraya-ar@upm.edu.my; Mohd Zobir, Syazwan Afif [Universiti Putra Malaysia, Materials Processing and Technology Laboratory, Nanomaterials and Nanotechnology Group, Institute of Advanced Technology (Malaysia); Krishnan, Shutesh; Hassan, Mohd Murshid [Graphene Nanochem Sdn. Bhd., Level 9, WORK@Clearwater (Malaysia); Lim, Hong Ngee [Universiti Putra Malaysia, UPM, Department of Chemistry, Faculty of Science (Malaysia)

    2015-05-15

    A one-pot synthesis of graphene oxide (GO) sheets and GO quantum dots using graphite nanofibers (GNF) as starting material is reported. Two types of GNF starting materials, namely herringbone and platelet structures, were used. HRTEM revealed that platelet GNF produces quantum dots typically less than 10 nm in size while herringbone GNF produces relatively larger GO sheets. SAED patterns indicate that the produced GO sheets have a hexagonal crystal structure. UV–Vis, PL, XPS, and Raman show salient differences between the produced GO nanostructures which correlate well with the morphological analysis. Unlike the GO sheets, the GO quantum dots are photoluminescent. The difference in PL properties was attributed to the higher oxygen content in GO quantum dots which were shown by XPS. The results offer a new insight to the importance of starting material in the synthesis of graphene nanostructures.

  6. Negative Differential Resistance Probe for Interdot Interactions in a Double Quantum Dot Array.

    Science.gov (United States)

    Pozner, Roni; Lifshitz, Efrat; Peskin, Uri

    2015-05-07

    Colloidal quantum dots are free-standing nanostructures with chemically tunable electronic properties. In this work, we consider a new STM tip-double quantum dot (DQD)-surface setup with a unique connectivity, in which the tip is coupled to a single dot and the coupling to the surface is shared by both dots. Our theoretical analysis reveals a unique negative differential resistance (NDR) effect attributed to destructive interference during charge transfer from the DQD to the surface. This NDR can be used as a sensitive probe for interdot interactions in DQD arrays.

  7. Generation of heralded entanglement between distant quantum dot hole spins

    Science.gov (United States)

    Delteil, Aymeric

    Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of

  8. Quantum Computing with Electron Spins in Quantum Dots

    CERN Document Server

    Vandersypen, L M K; Van Beveren, L H W; Elzerman, J M; Greidanus, J S; De Franceschi, S; Kouwenhoven, Leo P

    2002-01-01

    We present a set of concrete and realistic ideas for the implementation of a small-scale quantum computer using electron spins in lateral GaAs/AlGaAs quantum dots. Initialization is based on leads in the quantum Hall regime with tunable spin-polarization. Read-out hinges on spin-to-charge conversion via spin-selective tunneling to or from the leads, followed by measurement of the number of electron charges on the dot via a charge detector. Single-qubit manipulation relies on a microfabricated wire located close to the quantum dot, and two-qubit interactions are controlled via the tunnel barrier connecting the respective quantum dots. Based on these ideas, we have begun a series of experiments in order to demonstrate unitary control and to measure the coherence time of individual electron spins in quantum dots.

  9. Hybrid nanostructures of well-organized arrays of colloidal quantum dots and a self-assembled monolayer of gold nanoparticles for enhanced fluorescence

    Science.gov (United States)

    Liu, Xiaoying; McBride, Sean P.; Jaeger, Heinrich M.; Nealey, Paul F.

    2016-07-01

    Hybrid nanomaterials comprised of well-organized arrays of colloidal semiconductor quantum dots (QDs) in close proximity to metal nanoparticles (NPs) represent an appealing system for high-performance, spectrum-tunable photon sources with controlled photoluminescence. Experimental realization of such materials requires well-defined QD arrays and precisely controlled QD-metal interspacing. This long-standing challenge is tackled through a strategy that synergistically combines lateral confinement and vertical stacking. Lithographically generated nanoscale patterns with tailored surface chemistry confine the QDs into well-organized arrays with high selectivity through chemical pattern directed assembly, while subsequent coating with a monolayer of close-packed Au NPs introduces the plasmonic component for fluorescence enhancement. The results show uniform fluorescence emission in large-area ordered arrays for the fabricated QD structures and demonstrate five-fold fluorescence amplification for red, yellow, and green QDs in the presence of the Au NP monolayer. Encapsulation of QDs with a silica shell is shown to extend the design space for reliable QD/metal coupling with stronger enhancement of 11 times through the tuning of QD-metal spatial separation. This approach provides new opportunities for designing hybrid nanomaterials with tailored array structures and multiple functionalities for applications such as multiplexed optical coding, color display, and quantum transduction.

  10. Thermoelectric transport through quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Merker, Lukas Heinrich

    2016-06-30

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

  11. Colloidal quantum dot materials for infrared optoelectronics

    Science.gov (United States)

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

    2015-09-01

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

  12. Quantum dots with single-atom precision.

    Science.gov (United States)

    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.

  13. Recombination in quantum dot sensitized solar cells.

    Science.gov (United States)

    Mora-Seró, Iván; Giménez, Sixto; Fabregat-Santiago, Francisco; Gómez, Roberto; Shen, Qing; Toyoda, Taro; Bisquert, Juan

    2009-11-17

    Quantum dot sensitized solar cells (QDSCs) have attracted significant attention as promising third-generation photovoltaic devices. In the form of quantum dots (QDs), the semiconductor sensitizers have very useful and often tunable properties; moreover, their theoretical thermodynamic efficiency might be as high as 44%, better than the original 31% calculated ceiling. Unfortunately, the practical performance of these devices still lags behind that of dye-sensitized solar cells. In this Account, we summarize the strategies for depositing CdSe quantum dots on nanostructured mesoporous TiO(2) electrodes and discuss the methods that facilitate improvement in the performance and stability of QDSCs. One particularly significant factor for solar cells that use polysulfide electrolyte as the redox couple, which provides the best performance among QDSCs, is the passivation of the photoanode surface with a ZnS coating, which leads to a dramatic increase of photocurrents and efficiencies. However, these solar cells usually show a poor current-potential characteristic, so a general investigation of the recombination mechanisms is required for improvements. A physical model based on recombination through a monoenergetic TiO(2) surface state that takes into account the effect of the surface coverage has been developed to better understand the recombination mechanisms of QDSCs. The three main methods of QD adsorption on TiO(2) are (i) in situ growth of QDs by chemical bath deposition (CBD), (ii) deposition of presynthesized colloidal QDs by direct adsorption (DA), and (iii) deposition of presynthesized colloidal QDs by linker-assisted adsorption (LA). A systematic investigation by impedance spectroscopy of QDSCs prepared by these methods showed a decrease in the charge-transfer resistance and increased electron lifetimes for CBD samples; the same result was found after ZnS coating because of the covering of the TiO(2) surface. The increase of the lifetime with the ZnS treatment

  14. Quantum information processing in nanostructures Quantum optics; Quantum computing

    CERN Document Server

    Reina-Estupinan, J H

    2002-01-01

    Since information has been regarded os a physical entity, the field of quantum information theory has blossomed. This brings novel applications, such as quantum computation. This field has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineering, to the physical sciences. Thus, we now have an interdisciplinary field where great efforts are being made in order to build devices that should allow for the processing of information at a quantum level, and also in the understanding of the complex structure of some physical processes at a more basic level. This thesis is devoted to the theoretical study of structures at the nanometer-scale, 'nanostructures', through physical processes that mainly involve the solid-state and quantum optics, in order to propose reliable schemes for the processing of quantum information. Initially, the main results of quantum information theory and quantum computation are briefly reviewed. Next, the state-of-the-art of ...

  15. Large quantum dots with small oscillator strength

    DEFF Research Database (Denmark)

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

    2010-01-01

    We have measured the oscillator strength and quantum efficiency of excitons confined in large InGaAs quantum dots by recording the spontaneous emission decay rate while systematically varying the distance between the quantum dots and a semiconductor-air interface. The size of the quantum dots...... is measured by in-plane transmission electron microscopy and we find average in-plane diameters of 40 nm. We have calculated the oscillator strength of excitons of that size assuming a quantum-dot confinement given by a parabolic in-plane potential and a hard-wall vertical potential and predict a very large...... oscillator strength due to Coulomb effects. This is in stark contrast to the measured oscillator strength, which turns out to be so small that it can be described by excitons in the strong confinement regime. We attribute these findings to exciton localization in local potential minima arising from alloy...

  16. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

    Semiconductor quantum dots are often described as "artificial atoms": They are small nanometre-sized structures in which electrons only are allowed to exist at certain discrete levels due to size quantization, thus allowing the engineering of fundamental properties such as the coupling to light....... The main property of semiconductor quantum dots compared to bulk material or even quantum well structures is the discrete nature of the allowed states, which means that inversion of the medium can be obtained for very low electron densities. This has led to the fabrication of quantum dot lasers with record......-low threshold currents and amplifiers with record-high power levels. In this tutorial we will review the basic properties of quantum dots, emphasizing the properties which are important for laser and amplifier applications, as well as devices for all-optical signal processing. The high-speed properties...

  17. Scanning gate microscopy of ultra clean carbon nanotube quantum dots

    OpenAIRE

    Xue, Jiamin; Dhall, Rohan; Cronin, Stephen B.; LeRoy, Brian J.

    2015-01-01

    We perform scanning gate microscopy on individual suspended carbon nanotube quantum dots. The size and position of the quantum dots can be visually identified from the concentric high conductance rings. For the ultra clean devices used in this study, two new effects are clearly identified. Electrostatic screening creates non-overlapping multiple sets of Coulomb rings from a single quantum dot. In double quantum dots, by changing the tip voltage, the interactions between the quantum dots can b...

  18. Electronic properties of aperiodic quantum dot chains

    Science.gov (United States)

    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.

  19. Amplification Without Inversion in Semiconductor Quantum Dot

    Science.gov (United States)

    Hajibadali, A.; Abbasian, K.; Rostami, A.

    In this paper, we have realized amplification without inversion (AWI) in quantum dot (QD). A Y-type four-level system of InxGa1-xN quantum dot has been obtained and investigated for AWI. It has been shown that, with proper setting of control fields' amplitude, we can obtain reasonable gain. With proper setting of phase difference of control fields and probe field, we can obtain considerable gain in resonant wavelength. We have designed this system by solving the Schrödinger-Poisson equations for InxGa1-xN quantum dot in GaN substrate, self-consistently.

  20. Time-bin Entanglement from Quantum Dots

    CERN Document Server

    Weihs, Gregor; Predojević, Ana

    2016-01-01

    The desire to have a source of single entangled photon pairs can be satisfied using single quantum dots as emitters. However, we are not bound to pursue only polarization entanglement, but can also exploit other degrees of freedom. In this chapter we focus on the time degree of freedom, to achieve so-called time-bin entanglement. This requires that we prepare the quantum dot coherently into the biexciton state and also build special interferometers for analysis. Finally this technique can be extended to achieve time-bin and polarization hyper-entanglement from a suitable quantum dot.

  1. Fluorescent Quantum Dots for Biological Labeling

    Science.gov (United States)

    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.

  2. Quantum dot heterojunction solar cells: the mechanism of device operation and impacts of quantum dot oxidation

    OpenAIRE

    Ihly, Rachelle

    2014-01-01

    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 s...

  3. Quantum Dots in Vertical Nanowire Devices

    NARCIS (Netherlands)

    Van Weert, M.

    2010-01-01

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

  4. A Ge/Si heterostructure nanowire-based double quantum dot with integrated charge sensor

    DEFF Research Database (Denmark)

    Hu, Yongjie; Churchill, Hugh; Reilly, David

    2007-01-01

    : the predominance of spin-zero nuclei suppresses the hyperfine interaction and chemical synthesis creates a clean and defect-free system with highly controllable properties. Here we present a top gate-defined double quantum dot based on Ge/Si heterostructure nanowires with fully tunable coupling between the dots......Coupled electron spins in semiconductor double quantum dots hold promise as the basis for solid-state qubits. To date, most experiments have used III-V materials, in which coherence is limited by hyperfine interactions. Ge/Si heterostructure nanowires seem ideally suited to overcome this limitation...... and to the leads. We also demonstrate a novel approach to charge sensing in a one-dimensional nanostructure by capacitively coupling the double dot to a single dot on an adjacent nanowire. The double quantum dot and integrated charge sensor serve as an essential building block required to form a solid-state spin...

  5. Non-adiabatic geometrical quantum gates in semiconductor quantum dots

    CERN Document Server

    Solinas, P; Zanghì, N; Rossi, F; Solinas, Paolo; Zanardi, Paolo; Zanghì, Nino; Rossi, Fausto

    2003-01-01

    In this paper we study the implementation of non-adiabatic geometrical quantum gates with in semiconductor quantum dots. Different quantum information enconding/manipulation schemes exploiting excitonic degrees of freedom are discussed. By means of the Aharanov-Anandan geometrical phase one can avoid the limitations of adiabatic schemes relying on adiabatic Berry phase; fast geometrical quantum gates can be in principle implemented

  6. Single to quadruple quantum dots with tunable tunnel couplings

    Energy Technology Data Exchange (ETDEWEB)

    Takakura, T.; Noiri, A.; Obata, T.; Yoneda, J.; Yoshida, K. [Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Otsuka, T.; Tarucha, S. [Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); RIKEN, Center for Emergent Matter Science, 3-1 Wako-shi, Saitama 351-0198 (Japan)

    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.

  7. Optical and morphological properties of InGaAs/AIGaAs self-assembled quantum dot nanostructures for 980 nm room temperature emission

    Institute of Scientific and Technical Information of China (English)

    G. Trevisi; P. Frigeri; M. Minelli; P. Allegri; V. Avanzini; S. Franchi

    2007-01-01

    This work deals with the study of optical and morphological properties of InGaAs/AlGaAs quantum dot (QD) structures grown by molecular beam epitaxy (MBE). Photoluminescence (PL) emission energies, activation energies of PL quenching and QD sizes are studied as functions of the Al content in the AlyGal_yAs confining layers (CL). We show that the PL emission energy of In(Ga)As/AlyGal-yAs QD structures increases with increasing y and that the sizes of InAs/AlyGal-yAs QDs decrease with increasing y. By the comparison of the experimental results with those of an effective-mass model developed to calculate the QD fundamental transition energies, we show that the blueshift of emission energy has to be ascribed not only to the increase in barrier discontinuities that confine the carriers into QDs but even to effects related to changes of the QD morphology dependent on CL composition. Moreover, we show that the Al content in the barriers determines also the activation energy of thermal quenching of PL, which depends on the thermal escape of carriers from QD levels. These studies resulted in the preparation of structures with efficient light-emission in the 980 nm spectral window of interest for lightwave communications.

  8. Quantum Dots Investigated for Solar Cells

    Science.gov (United States)

    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

  9. Optical anisotropy in vertically coupled quantum dots

    DEFF Research Database (Denmark)

    Yu, Ping; Langbein, Wolfgang Werner; Leosson, Kristjan;

    1999-01-01

    We have studied the polarization of surface and edge-emitted photoluminescence (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD's) grown by molecular beam epitaxy. The PL polarization is found to be strongly dependent on the number of stacked layers. While single...... number due to increasing dot size....

  10. Double Acceptor Interaction in Semimagnetic Quantum Dot

    Directory of Open Access Journals (Sweden)

    A. Merwyn Jasper D. Reuben

    2011-01-01

    Full Text Available The effect of geometry of the semimagnetic Quantum Dot on the Interaction energy of a double acceptor is computed in the effective mass approximation using the variational principle. A peak is observed at the lower dot sizes as a magnetic field is increased which is attributed to the reduction in confinement.

  11. Quantum Dots Coupled to a Superconductor

    DEFF Research Database (Denmark)

    Jellinggaard, Anders Robert

    are tuned electrostatically. This includes tuning the odd occupation of the dot through a quantum phase transition, where it forms a singlet with excitations in the superconductor. We detail the fabrication of these bottom gated devices, which additionally feature ancillary sensor dots connected...

  12. Ge Quantum Dot Infrared Imaging Camera Project

    Data.gov (United States)

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

  13. Chaotic quantum dots with strongly correlated electrons

    OpenAIRE

    Shankar, R.

    2007-01-01

    Quantum dots pose a problem where one must confront three obstacles: randomness, interactions and finite size. Yet it is this confluence that allows one to make some theoretical advances by invoking three theoretical tools: Random Matrix theory (RMT), the Renormalization Group (RG) and the 1/N expansion. Here the reader is introduced to these techniques and shown how they may be combined to answer a set of questions pertaining to quantum dots

  14. Start Shift of Individual Quantum Dots

    Science.gov (United States)

    1999-06-18

    We will here describe the results of the influence of electric field on InP quantum dots embedded in GalnP, lattice matched to GaAs. Experimental...details The sample we used was grown by metal-organic vapour phase epitaxy, and contained InP quantum dots in GanP, lattice matched to GaAs (n-type

  15. Germanium quantum dots: Optical properties and synthesis

    OpenAIRE

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

    1994-01-01

    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. Col...

  16. Renormalization in Periodically Driven Quantum Dots.

    Science.gov (United States)

    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.

  17. Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysics

    Directory of Open Access Journals (Sweden)

    Emrick Todd

    2007-01-01

    Full Text Available AbstractCdSe quantum dots functionalized with oligo-(phenylene vinylene (OPV ligands (CdSe-OPV nanostructures represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures.

  18. Submonolayer Quantum Dot Infrared Photodetector

    Science.gov (United States)

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

    2010-01-01

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

  19. Quantum dots as biophotonics tools.

    Science.gov (United States)

    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.

  20. Quantum Dot Solar Cells. The Next Big Thing in Photovoltaics.

    Science.gov (United States)

    Kamat, Prashant V

    2013-03-21

    The recent surge in the utilization of semiconductor nanostructures for solar energy conversion has led to the development of high-efficiency solar cells. Some of these recent advances are in the areas of synthesis of new semiconductor materials and the ability to tune the electronic properties through size, shape, and composition and to assemble quantum dots as hybrid assemblies. In addition, processes such as hot electron injection, multiple exciton generation (MEG), plasmonic effects, and energy-transfer-coupled electron transfer are gaining momentum to overcome the efficiency limitations of energy capture and conversion. The recent advances as well as future prospects of quantum dot solar cells discussed in this perspective provide the basis for consideration as "The Next Big Thing" in photovoltaics.

  1. Titanium-based silicide quantum dot superlattices for thermoelectrics applications.

    Science.gov (United States)

    Savelli, Guillaume; Stein, Sergio Silveira; Bernard-Granger, Guillaume; Faucherand, Pascal; Montès, Laurent; Dilhaire, Stefan; Pernot, Gilles

    2015-07-10

    Ti-based silicide quantum dot superlattices (QDSLs) are grown by reduced-pressure chemical vapor deposition. They are made of titanium-based silicide nanodots scattered in an n-doped SiGe matrix. This is the first time that such nanostructured materials have been grown in both monocrystalline and polycrystalline QDSLs. We studied their crystallographic structures and chemical properties, as well as the size and the density of the quantum dots. The thermoelectric properties of the QDSLs are measured and compared to equivalent SiGe thin films to evaluate the influence of the nanodots. Our studies revealed an increase in their thermoelectric properties-specifically, up to a trifold increase in the power factor, with a decrease in the thermal conductivity-making them very good candidates for further thermoelectric applications in cooling or energy-harvesting fields.

  2. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

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

  3. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

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

  4. Inter-dot coupling effects on transport through correlated parallel coupled quantum dots

    Indian Academy of Sciences (India)

    Shyam Chand; G Rajput; K C Sharma; P K Ahluwalia

    2009-05-01

    Transport through symmetric parallel coupled quantum dot system has been studied, using non-equilibrium Green function formalism. The inter-dot tunnelling with on-dot and inter-dot Coulomb repulsion is included. The transmission coefficient and Landaur–Buttiker like current formula are shown in terms of internal states of quantum dots. The effect of inter-dot tunnelling on transport properties has been explored. Results, in intermediate inter-dot coupling regime show signatures of merger of two dots to form a single composite dot and in strong coupling regime the behaviour of the system resembles the two decoupled dots.

  5. Advancements in the Field of Quantum Dots

    Science.gov (United States)

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

    2012-08-01

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

  6. Quantum-dot-in-perovskite solids

    KAUST Repository

    Ning, Zhijun

    2015-07-15

    © 2015 Macmillan Publishers Limited. All rights reserved. Heteroepitaxy - atomically aligned growth of a crystalline film atop a different crystalline substrate - is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned \\'dots-in-a-matrix\\' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  7. Quantum Dots and Their Multimodal Applications: A Review

    OpenAIRE

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

    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 ...

  8. PREFACE: Quantum dots as probes in biology

    Science.gov (United States)

    Cieplak, Marek

    2013-05-01

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

  9. Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

    Directory of Open Access Journals (Sweden)

    Manvir S. Kushwaha

    2014-12-01

    Full Text Available Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding the size of the quantum dots: resulting into a blue (red shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower magneto-optical transitions survive even in the extreme instances. However, the intra

  10. Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Kushwaha, Manvir S. [Department of Physics and Astronomy, Rice University, P.O. Box 1892, Houston, TX 77251 (United States)

    2014-12-15

    Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level

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

    Science.gov (United States)

    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. Phonons in Quantum-Dot Quantum Well

    Institute of Scientific and Technical Information of China (English)

    QINGuo-Yi

    2004-01-01

    Phonon modes of A1As/GaAs/A1As and GaAs/A1As/metal Pb quantum-dot quantum wells (QDQW's) with the whole scale up to 90 AО are calculated by using valence force field model (VFFM) based on group theory.Their optical frequency spectra are divided into two nonoverlapping bands, the AlAs-like band and the GaAs-like band,originated from and having frequency interval inside the bulk AlAs optical band and bulk GaAs optical band, respectively.The GaAs-LO (Г)-like modes of QDQW's that have maximum bulk GaAs-LO (Г) parentages in all modes covering thewhole frequency region and all symmetries have always A1 symmetry. Its frequency is controllable by adjusting thestructure parameters. In A1As/GaAs/A1As, it may be controlled to meet any designed frequency in GaAs-like band.The results on GaAs/A1As/metal Pb QDQW's show the same effect of reducing in interface optical phonons by using the metal/semiconductor interface revealed ever by macroscopic model The frequency spectra in both GaAs-like andAlAs-like optical phonon bands are independent of the thickness of Pb shell as long as the thickness of Pb shell is no less than 5 AО Defects at metal/A1As interface have significant influence to AlAs-like optical modes but have only minor influence to GaAs-like optical modes. All these results are important for the studying of the e-ph interaction in QD structures.

  13. Phonons in Quantum-Dot Quantum Well

    Institute of Scientific and Technical Information of China (English)

    QIN Guo-Yi

    2004-01-01

    Phonon modes of AlAs/GaAs/AlAs and GaAs/AlAs/metal Pb quantum-dot quantum wells (QDQW's)with the whole scale up to 90 A are calculated by using valence force field model (VFFM) based on group theory.Their optical frequency spectra are divided into two nonoverlapping bands, the AMs-like band and the GaAs-like band,originated from and having frequency interval inside the bulk AlAs optical band and bulk GaAs optical band, respectively.The GaAs-LO (F)-like modes of QDQW's that have maximum bulk GaAs-LO (F) parentages in all modes covering the whole frequency region and all symmetries have always A1 symmetry. Its frequency is controllable by adjusting the structure parameters. In AlAs/GaAs/AlAs, it may be controlled to meet any designed frequency in GaAs-like band.The results on GaAs/AMs/metal Pb QDQW's show the same effect of reducing in interface optical phonons by using the metal/semiconductor interface revealed ever by macroscopic model. The frequency spectra in both GaAs-like and AlAs-like optical phonon bands are independent of the thickness of Pb shell as long as the thickness of Pb shell is no less than 5 A. Defects at metal/AlAs interface have significant influence to AMs-like optical modes but have only minor influence to GaAs-like optical modes. All these results are important for the studying of the e-ph interaction in QD structures.

  14. Electron Spins in Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Hanson, R.

    2005-01-01

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

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

    Science.gov (United States)

    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.

  16. Electromechanical transition in quantum dots

    Science.gov (United States)

    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.

  17. Optical and Micro-Structural Characterization of MBE Grown Indium Gallium Nitride Polar Quantum Dots

    KAUST Repository

    El Afandy, Rami

    2011-07-07

    Gallium nitride and related materials have ushered in scientific and technological breakthrough for lighting, mass data storage and high power electronic applications. These III-nitride materials have found their niche in blue light emitting diodes and blue laser diodes. Despite the current development, there are still technological problems that still impede the performance of such devices. Three-dimensional nanostructures are proposed to improve the electrical and thermal properties of III-nitride optical devices. This thesis consolidates the characterization results and unveils the unique physical properties of polar indium gallium nitride quantum dots grown by molecular beam epitaxy technique. In this thesis, a theoretical overview of the physical, structural and optical properties of polar III-nitrides quantum dots will be presented. Particular emphasis will be given to properties that distinguish truncated-pyramidal III-nitride quantum dots from other III-V semiconductor based quantum dots. The optical properties of indium gallium nitride quantum dots are mainly dominated by large polarization fields, as well as quantum confinement effects. Hence, the experimental investigations for such quantum dots require performing bandgap calculations taking into account the internal strain fields, polarization fields and confinement effects. The experiments conducted in this investigation involved the transmission electron microscopy and x-ray diffraction as well as photoluminescence spectroscopy. The analysis of the temperature dependence and excitation power dependence of the PL spectra sheds light on the carrier dynamics within the quantum dots, and its underlying wetting layer. A further analysis shows that indium gallium nitride quantum dots through three-dimensional confinements are able to prevent the electronic carriers from getting thermalized into defects which grants III-nitrides quantum dot based light emitting diodes superior thermally induced optical

  18. Quantum Piston - Quantum Preservation, Simulation and Transfer In Oxide Nanostructures

    Science.gov (United States)

    2016-06-28

    of the host material that is performing the simulation. A lot of the research that was conducted involves basic characterization (quantum transport ... semiconductor with long-lived defect complexes (nitrogen-vacanc 15. SUBJECT TERMS oxide nanoelectronics, superconductivity, quantum information 16...to develop the unique properties of superconducting semiconductors to achieve Quantum Preservation, Simulation and Transfer in Oxide Nanostructures

  19. Two optically active molybdenum disulfide quantum dots as tetracycline sensors

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhuosen; Lin, Jintai [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Gao, Jinwei [Institute for Advanced Materials, Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006 (China); Wang, Qianming, E-mail: qmwang@scnu.edu.cn [Key Laboratory of Theoretical Chemistry of Environment, Ministry of Education, School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Guangzhou Key Laboratory of Materials for Energy Conversion and Storage, 510006 (China)

    2016-08-01

    In this work, we use the hydrothermal method to develop two luminescent MoS{sub 2} quantum dots (QDs) from L-cysteine and glutathione as sulfur precursors. The special blue emissions give rise to an instantaneous determination of tetracycline (TC) through the quenching of its luminescence. The accessibility of the optical materials and recognition mechanism have been extensively studied. This strategy demonstrated that MoS{sub 2} could act as a new platform for anchoring bioactive species or particular functional moieties. - Highlights: • MoS{sub 2} nanostructures with water solubility have been fabricated. • Blue emission has been achieved. • It displays selective detection to tetracyclines in water.

  20. Quantum Yield Heterogeneity among Single Nonblinking Quantum Dots Revealed by Atomic Structure-Quantum Optics Correlation.

    Science.gov (United States)

    Orfield, Noah J; McBride, James R; Wang, Feng; Buck, Matthew R; Keene, Joseph D; Reid, Kemar R; Htoon, Han; Hollingsworth, Jennifer A; Rosenthal, Sandra J

    2016-02-23

    Physical variations in colloidal nanostructures give rise to heterogeneity in expressed optical behavior. This correlation between nanoscale structure and function demands interrogation of both atomic structure and photophysics at the level of single nanostructures to be fully understood. Herein, by conducting detailed analyses of fine atomic structure, chemical composition, and time-resolved single-photon photoluminescence data for the same individual nanocrystals, we reveal inhomogeneity in the quantum yields of single nonblinking "giant" CdSe/CdS core/shell quantum dots (g-QDs). We find that each g-QD possesses distinctive single exciton and biexciton quantum yields that result mainly from variations in the degree of charging, rather than from volume or structure inhomogeneity. We further establish that there is a very limited nonemissive "dark" fraction (<2%) among the studied g-QDs and present direct evidence that the g-QD core must lack inorganic passivation for the g-QD to be "dark". Therefore, in contrast to conventional QDs, ensemble photoluminescence quantum yield is principally defined by charging processes rather than the existence of dark g-QDs.

  1. Quantum Phase Extraction in Isospectral Electronic Nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Christopher

    2010-04-28

    Quantum phase is not a direct observable and is usually determined by interferometric methods. We present a method to map complete electron wave functions, including internal quantum phase information, from measured single-state probability densities. We harness the mathematical discovery of drum-like manifolds bearing different shapes but identical resonances, and construct quantum isospectral nanostructures possessing matching electronic structure but divergent physical structure. Quantum measurement (scanning tunneling microscopy) of these 'quantum drums' [degenerate two-dimensional electron states on the Cu(111) surface confined by individually positioned CO molecules] reveals that isospectrality provides an extra topological degree of freedom enabling robust quantum state transplantation and phase extraction.

  2. Could nanostructure be unspeakable quantum system?

    CERN Document Server

    Aristov, V V

    2010-01-01

    Heisenberg, Bohr and others were forced to renounce on the description of the objective reality as the aim of physics because of the paradoxical quantum phenomena observed on the atomic level. The contemporary quantum mechanics created on the base of their positivism point of view must divide the world into speakable apparatus which amplifies microscopic events to macroscopic consequences and unspeakable quantum system. Examination of the quantum phenomena corroborates the confidence expressed by creators of quantum theory that the renunciation of realism should not apply on our everyday macroscopic world. Nanostructures may be considered for the present as a boundary of realistic description for all phenomena including the quantum one.

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

    Science.gov (United States)

    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

  4. Quantum computation with two-dimensional graphene quantum dots

    Institute of Scientific and Technical Information of China (English)

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

    2012-01-01

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

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

    Science.gov (United States)

    Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

    2014-08-26

    A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

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

    Science.gov (United States)

    2014-08-01

    method is also applicable to bare nanoparticles in polar solvents. 15. SUBJECT TERMS Quantum Dots, Nonlinear Optical Materials , Energy...TERMS Quantum Dots, Nonlinear Optical Materials , Energy Conservation, Up-conversion 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT

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

    KAUST Repository

    Hoogland, Sjoerd H.

    2012-01-01

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

  8. Diffraction of quantum dots reveals nanoscale ultrafast energy localization.

    Science.gov (United States)

    Vanacore, Giovanni M; Hu, Jianbo; Liang, Wenxi; Bietti, Sergio; Sanguinetti, Stefano; Zewail, Ahmed H

    2014-11-12

    Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent "ballistic" behavior of lattice vibrations, the phonons. If dominant, such behavior would determine the mechanism for transport and relaxation in various energy-conversion applications. In order to study this coherent limit, both the spatial and temporal resolutions must be sufficient for the length-time scales involved. Here, we report observation of the lattice dynamics in nanoscale quantum dots of gallium arsenide using ultrafast electron diffraction. By varying the dot size from h = 11 to 46 nm, the length scale effect was examined, together with the temporal change. When the dot size is smaller than the inelastic phonon mean-free path, the energy remains localized in high-energy acoustic modes that travel coherently within the dot. As the dot size increases, an energy dissipation toward low-energy phonons takes place, and the transport becomes diffusive. Because ultrafast diffraction provides the atomic-scale resolution and a sufficiently high time resolution, other nanostructured materials can be studied similarly to elucidate the nature of dynamical energy localization.

  9. Quantum Dot Based Photovoltaics Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Hybrid photovoltaic cells that combine nanostructured inorganic semiconductors with organic conductors such as the cell proposed, show promise for energy generation...

  10. Coherent transport through interacting quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hiltscher, Bastian

    2012-10-05

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

  11. Coherence and dephasing in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    2003-01-01

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

  12. Modulation Response of Semiconductor Quantum Dot Nanocavity Lasers

    DEFF Research Database (Denmark)

    Lorke, Michael; Nielsen, Torben Roland; Mørk, Jesper

    2011-01-01

    The modulation response of quantum-dot based nanocavity devices is investigated using a semiconductor theory. We show that high modulation bandwidth is achieved even in the presence of inhomogeneous broadening of the quantum dot ensemble.......The modulation response of quantum-dot based nanocavity devices is investigated using a semiconductor theory. We show that high modulation bandwidth is achieved even in the presence of inhomogeneous broadening of the quantum dot ensemble....

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. LUMINESCENCE OF CADMIUM SULFIDE QUANTUM DOTS IN FLUOROPHOSPHATE GLASSES

    OpenAIRE

    Z. O. Lipatova; E. V. Kolobkova; V. A. Aseev

    2015-01-01

    Cadmium sulfide quantum dots are perspective materials in optics, medicine, biology and optoelectronics. Fluorophosphate glasses, doped with cadmium sulfide quantum dots, were examined in the paper. Heat treatment led to the formation of quantum dots with diameters equal to 2.8 nm, 3.0 nm and 3.8 nm. In view of such changes in the quantum dots size the fundamental absorption edge shift and the luminescence band are being displaced to the long wavelengths. Luminescence lifetime has been fou...

  15. Atomic and Electronic Structure of Quantum Dots Measured with Scanning Probe Techniques

    NARCIS (Netherlands)

    Sun, Z.

    2012-01-01

    This thesis deals with low temperature scanning tunneling microscopy/spectroscopy and atomic force microscopy (LT-STM/STS and AFM) studies on colloidal semiconductor and graphene quantum dots (g-QDs). These nanostructures are interesting because they show tunable electrical and optical properties du

  16. Plasmonic Effect on Exciton and Multiexciton Emission of Single Quantum Dots.

    Science.gov (United States)

    Dey, Swayandipta; Zhao, Jing

    2016-08-04

    Quantum dots are nanoscale quantum emitters with high quantum yield and size-dependent emission wavelength, holding promises in many optical and electronic applications. When quantum dots are situated close to noble metal nanoparticles, their emitting behavior can be conveniently tuned because of the interaction between the excitons of the quantum dots and the plasmons of the metal nanoparticles. This interaction at the single quantum dot level gives rise to reduced or suppressed photoluminescence blinking and enhanced multiexciton emission, which is difficult to achieve in isolated quantum dots. However, the mechanism of how plasmonic structures cause the changes in the quantum dot emission remains unclear. Because of the complexity of the system, the interfaces between metal, semiconductor, and ligands must be considered, in addition to factors such as geometry, interparticle distance, and spectral overlap. The challenges in the design and fabrication of the hybrid nanostructures as well as in understanding the exciton-plasmon coupling mechanism can be overcome by a cooperative effort in synthesis, optical spectroscopy, and theoretical modeling.

  17. Design of tunneling injection quantum dot lasers

    Institute of Scientific and Technical Information of China (English)

    JIA Guo-zhi; YAO Jiang-hong; SHU Yong-chun; WANG Zhan-guo

    2007-01-01

    To implement high quality tunneling injection quantum dot lasers,effects of primary factors on performance of the tunneling injection quantum dot lasers were investigated. The considered factors were tunneling probability,tunneling time and carriers thermal escape time from the quantum well. The calculation results show that with increasing of the ground-state energy level in quantum well,the tunneling probability increases and the tunneling time decreases,while the thermal escape time decreases because the ground-state energy levelis shallower. Longitudinal optical phonon-assisted tunneling can be an effective method to solve the problem that both the tunneling time and the thermal escape time decrease simultaneously with the ground-state energy level increasing in quantum well.

  18. Angiogenic Profiling of Synthesized Carbon Quantum Dots.

    Science.gov (United States)

    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.

  19. Optical properties of geometrically optimized graphene quantum dots

    Science.gov (United States)

    Bugajny, Paweł; Szulakowska, Ludmiła; Jaworowski, Błazej; Potasz, Paweł

    2017-01-01

    We derive effective tight-binding model for geometrically optimized graphene quantum dots and based on it we investigate corresponding changes in their optical properties in comparison to ideal structures. We consider hexagonal and triangular dots with zigzag and armchair edges. Using density functional theory methods we show that displacement of lattice sites leads to changes in atomic distances and in consequence modifies their energy spectrum. We derive appropriate model within tight-binding method with edge-modified hopping integrals. Using group theoretical analysis, we determine allowed optical transitions and investigate oscillatory strength between bulk-bulk, bulk-edge and edge-edge transitions. We compare optical joint density of states for ideal and geometry optimized structures. We also investigate an enhanced effect of sites displacement which can be designed in artificial graphene-like nanostructures. A shift of absorption peaks is found for small structures, vanishing with increasing system size.

  20. Bright infrared LEDs based on colloidal quantum-dots

    KAUST Repository

    Sun, Liangfeng

    2013-01-01

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

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

    Science.gov (United States)

    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

  2. Photoreflectance and photoluminescence study of InAs dots-in-a-well nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Nedzinskas, Ramūnas; Čechavičius, Bronislovas; Kavaliauskas, Julius; Karpus, Vytautas; Valušis, Gintaras [Semiconductor Physics Institute, Center for Physical Sciences and Technology, A. Goštauto 11, LT-01108 Vilnius (Lithuania); Li, Lianhe; Khanna, Suraj P.; Linfield, Edmund H. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2013-12-04

    InAs quantum dots (QDs), embedded within InGaAs/GaAs/AlAs and GaAs/AlAs quantum wells (QWs), are examined by photoreflectance and photoluminescence techniques. Optical properties and electronic structure of two differently designed dots-in-a-well nanostructures is revealed focusing on the effect of strain-reducing InGaAs layer, which is discussed in detail. It is found that the use of InGaAs capping layer red-shifts the QD ground-state interband transition energy by about 100 meV maintaining strong quantization of the electronic states. The changes in InAs QD electronic properties are ascribed mainly to QD size/shape variation due to decomposition of InGaAs layer during growth process.

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

    Energy Technology Data Exchange (ETDEWEB)

    Moroni, Stefano T.; Dimastrodonato, Valeria; Chung, Tung-Hsun; Juska, Gediminas; Gocalinska, Agnieszka; Pelucchi, Emanuele [Tyndall National Institute, “Lee Maltings,” University College Cork, Cork (Ireland); Vvedensky, Dimitri D. [The Blackett Laboratory, Imperial College London, London SW7 2AZ (United Kingdom)

    2015-04-28

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

  4. Resonant tunneling in graphene pseudomagnetic quantum dots.

    Science.gov (United States)

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

    2013-06-12

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

  5. Cadmium telluride quantum dots advances and applications

    CERN Document Server

    Donegan, John

    2013-01-01

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

  6. Bilayer graphene quantum dot defined by topgates

    Energy Technology Data Exchange (ETDEWEB)

    Müller, André; Kaestner, Bernd; Hohls, Frank; Weimann, Thomas; Pierz, Klaus; Schumacher, Hans W., E-mail: hans.w.schumacher@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    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.

  7. Free spin quantum computation with semiconductor nanostructures

    CERN Document Server

    Zhang, W M; Soo, C; Zhang, Wei-Min; Wu, Yin-Zhong; Soo, Chopin

    2005-01-01

    Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two electrons which is then converted into spin entanglement states by using single spin rotations. Deterministic two-qubit quantum gates can also be manipulated using only single spin rotations with help of QCA. A single-short read-out of spin states can be realized by coupling the unit cell to a quantum point contact.

  8. High resolution STEM of quantum dots and quantum wires

    DEFF Research Database (Denmark)

    Kadkhodazadeh, Shima

    2013-01-01

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

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

    DEFF Research Database (Denmark)

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

    2012-01-01

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

  10. A Polaron in a Quantum Dot Quantum Well

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; XIE HongJing; CHEN ChuanYu

    2002-01-01

    The polaron effect in a quantum dot quantum well (QDQW)system is investigated by using the perturbation method. Both the bound electron states outside and inside the shell well are taken into account . Numerical calculation on the CdS/HgS QDQW shows that the phonon correction to the electron ground state energy is quite significant and cannot be neglected.

  11. Photonic Enhancement of Colloidal Quantum Dot Photovoltaics

    Science.gov (United States)

    Labelle, Andre Jean-Romeo Richard

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

  12. Probing silicon quantum dots by single-dot techniques

    Science.gov (United States)

    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.

  13. Local Gate Control of a Carbon Nanotube Double Quantum Dot

    Science.gov (United States)

    2016-04-04

    Nanotube Double Quantum Dot N. Mason,*† M. J. Biercuk,* C. M. Marcus† We have measured carbon nanotube quantum dots with multiple electro- static gates and...used the resulting enhanced control to investigate a nano- tube double quantum dot. Transport measurements reveal honeycomb charge stability diagrams...This ability to control electron interactions in the quantum regime in a molecular conductor is important for applications such as quantum

  14. Investigation of confinement effects in ZnO quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Haranath, D; Sahai, Sonal; Joshi, Amish G; Gupta, Bipin K; Shanker, V, E-mail: haranath@nplindia.or [National Physical Laboratory, Council of Scientific and Industrial Research, Dr K S Krishnan Road, New Delhi-110 012 (India)

    2009-10-21

    We report a simple method for the synthesis of Na{sup +} doped and stable zinc oxide quantum dots, using the quantum confinement atom method. An intense broad green photoluminescence (PL) was observed with a maximum located at {approx}535 nm when excited by UV radiation of 332 nm. The PL peak intensity is found to be highly dependent on the size of the quantum dots (QDs). Electron microscopy observation revealed that the radius of the QD was {approx}1 nm, which clearly indicated that the QDs are in the strong quantum confinement region (exciton Bohr radius, r{sub B}, for bulk ZnO is 1.8 nm). Phase purity of ZnO and the presence of Na{sup +} was confirmed by x-ray diffraction (XRD) and atomic absorption spectroscopy (AAS), respectively. The results are well incremented by x-ray photoelectron spectroscopy (XPS) studies. Intentional ageing of QDs for several days under controlled experimental conditions such as temperature, relative humidity and pH etc, facilitated the formation of various nanostructures with a slight red shift in the PL peak position. Time resolved emission spectroscopy measurements indicated that PL decay time changes from 35 ns for QDs to 1660 {mu}s for nanocrystals. The observed high-intensity and stable green PL emissions have been analyzed and thoroughly discussed.

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

    Science.gov (United States)

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

    2017-06-27

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

  16. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    1999-01-01

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

  17. Germanium quantum dots: Optical properties and synthesis

    Science.gov (United States)

    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.

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

    Institute of Scientific and Technical Information of China (English)

    Yu Tao; Zhu Ai-Dong; Zhang Shou

    2012-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Neetu, E-mail: singh.neetu1985@gmail.com; Kapoor, Avinashi [Department of Electronic Science, University of Delhi South Campus, New Delhi-110 021 (India); Kumar, Vinod [Department of Physics, University of the Free State, Bloemfontein, ZA9300 (South Africa); Mehra, R. M. [School of Engineering and Technology, Sharda University, Greater Noida-201 306, U.P. (India)

    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.

  20. Oscillator strength reduction induced by external electric fields in self-assembled quantum dots and rings

    OpenAIRE

    2007-01-01

    We have carried out continuous wave and time resolved photoluminescence experiments in self-assembled In(Ga)As quantum dots and quantum rings embedded in field effect structure devices. In both kinds of nanostructures, we find a noticeable increase of the exciton radiative lifetime with the external voltage bias that must be attributed to the field-induced polarizability of the confined electron hole pair. The interplay between the exciton radiative recombination and the electronic carrier tu...

  1. Saturating optical resonances in quantum dots

    Science.gov (United States)

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

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

  2. System and method for making quantum dots

    KAUST Repository

    Bakr, Osman M.

    2015-05-28

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

  3. Quantum dot waveguides: ultrafast dynamics and applications

    DEFF Research Database (Denmark)

    Chen, Yaohui; Mørk, Jesper

    2009-01-01

    In this paper we analyze, based on numerical simulations, the dynamics of semiconductor devices incorporating quantum dots (QDs). In particular we emphasize the unique ultrafast carrier dynamics occurring between discrete QD bound states, and its influence on QD semiconductor optical amplifiers...... (SOAs). Also the possibility of realizing an all-optical regenerator by incorporating a QD absorber section in an amplifier structure is discussed....

  4. Electron Scattering in Intrananotube Quantum Dots

    NARCIS (Netherlands)

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

    2009-01-01

    Intratube quantum dots showing particle-in-a-box-like states with level spacings up to 200 meV are realized in metallic single-walled carbon nanotubes by means of low dose medium energy Ar+ irradiation. Fourier-transform scanning tunneling spectroscopy compared to results of a Fabry-Perot electron r

  5. Producing Quantum Dots by Spray Pyrolysis

    Science.gov (United States)

    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.

  6. Enabling biomedical research with designer quantum dots

    NARCIS (Netherlands)

    Tomczak, N.; Janczewski, D.; Dorokhin, D.V.; Han, M-Y; Vancso, G.J.; Navarro, Melba; Planell, Josep A.

    2012-01-01

    Quantum Dots (QDs) are a new class of semiconductor nanoparticulate luminophores, which are actively researched for novel applications in biology and nanomedicine. In this review, the recent progress in the design and applications of QD labels for in vitro and in vivo imaging of cells is presented.

  7. Single Molecule Applications of Quantum Dots

    DEFF Research Database (Denmark)

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

    2013-01-01

    Fluorescent nanocrystals composed of semiconductor materials were first introduced for biological applications in the late 1990s. The focus of this review is to give a brief survey of biological applications of quantum dots (QDs) at the single QD sensitivity level. These are described as follows: 1...

  8. Spin Wigner molecules in quantum dots

    Science.gov (United States)

    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. Optical Properties of Quantum-Dot-Doped Liquid Scintillators

    CERN Document Server

    Aberle, C; Weiss, S; Winslow, L

    2013-01-01

    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.

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

    Science.gov (United States)

    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.

  11. Room Temperature Single-Photon Emission from Individual Perovskite Quantum Dots.

    Science.gov (United States)

    Park, Young-Shin; Guo, Shaojun; Makarov, Nikolay S; Klimov, Victor I

    2015-10-27

    Lead-halide-based perovskites have been the subject of numerous recent studies largely motivated by their exceptional performance in solar cells. Electronic and optical properties of these materials have been commonly controlled by varying the composition (e.g., the halide component) and/or crystal structure. Use of nanostructured forms of perovskites can provide additional means for tailoring their functionalities via effects of quantum confinement and wave function engineering. Furthermore, it may enable applications that explicitly rely on the quantum nature of electronic excitations. Here, we demonstrate that CsPbX3 quantum dots (X = I, Br) can serve as room-temperature sources of quantum light, as indicated by strong photon antibunching detected in single-dot photoluminescence measurements. We explain this observation by the presence of fast nonradiative Auger recombination, which renders multiexciton states virtually nonemissive and limits the fraction of photon coincidence events to ∼6% on average. We analyze limitations of these quantum dots associated with irreversible photodegradation and fluctuations ("blinking") of the photoluminescence intensity. On the basis of emission intensity-lifetime correlations, we assign the "blinking" behavior to random charging/discharging of the quantum dot driven by photoassisted ionization. This study suggests that perovskite quantum dots hold significant promise for applications such as quantum emitters; however, to realize this goal, one must resolve the problems of photochemical stability and photocharging. These problems are largely similar to those of more traditional quantum dots and, hopefully, can be successfully resolved using advanced methodologies developed over the years in the field of colloidal nanostructures.

  12. Two- versus three-dimensional quantum confinement in indium phosphide wires and dots.

    Science.gov (United States)

    Yu, Heng; Li, Jingbo; Loomis, Richard A; Wang, Lin-Wang; Buhro, William E

    2003-08-01

    The size dependence of the bandgap is the most identifiable aspect of quantum confinement in semiconductors; the bandgap increases as the nanostructure size decreases. The bandgaps in one-dimensional (1D)-confined wells, 2D-confined wires, and 3D-confined dots should evolve differently with size as a result of the differing dimensionality of confinement. However, no systematic experimental comparisons of analogous 1D, 2D or 3D confinement systems have been made. Here we report growth of indium phosphide (InP) quantum wires having diameters in the strong-confinement regime, and a comparison of their bandgaps with those previously reported for InP quantum dots. We provide theoretical evidence to establish that the quantum confinement observed in the InP wires is weakened to the expected extent, relative to that in InP dots, by the loss of one confinement dimension. Quantum wires sometimes behave as strings of quantum dots, and we propose an analysis to generally distinguish quantum-wire from quantum-dot behaviour.

  13. Exploring semiconductor quantum dots and wires by high resolution electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Molina, S I [Departamento de Ciencia de los Materiales e Ing Metalurgica y Q. Inorganica, F. de Ciencias, Universidad de Cadiz, Campus Rio San Pedro. 11510 Puerto Real (Cadiz) (Spain); Galindo, P L [Departamento de Lenguajes y Sistemas Informaticos, CASEM, Universidad de Cadiz, Campus Rio San Pedro. 11510 Puerto Real (Cadiz) (Spain); Gonzalez, L; Ripalda, J M [Instituto de Microelectronica de Madrid (CNM, CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid (Spain); Varela, M; Pennycook, S J, E-mail: sergio.molina@uca.e [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge TN 37831 (United States)

    2010-02-01

    We review in this communication our contribution to the structural characterisation of semiconductor quantum dots and wires by high resolution electron microscopy, both in phase-contrast and Z-contrast modes. We show how these techniques contribute to predict the preferential sites of nucleation of these nanostructures, and also determine the compositional distribution in 1D and 0D nanostructures. The results presented here were produced in the framework of the European Network of Excellence entitled {sup S}elf-Assembled semiconductor Nanostructures for new Devices in photonics and Electronics (SANDiE){sup .}

  14. Probing the quantum-classical connection with open quantum dots

    Science.gov (United States)

    Ferry, D. K.; Akis, R.; Brunner, R.

    2015-10-01

    Open quantum dots provide a natural system in which to study both classical and quantum features of transport. From the classical point of view these dots possess a mixed phase space which yields families of closed, regular orbits as well as an expansive sea of chaos. As a closed test bed, they provide a natural system with a very rich set of eigen-states. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which eventually couple to the classical states discussed above. The manner of this connection is governed strongly by decoherence theory. The remaining coherent states possess all the properties of pointer states. Here, we discuss the quantum-classical connection and how it appears within the experimental world.

  15. Quantum Dots and Their Multimodal Applications: A Review

    Directory of Open Access Journals (Sweden)

    Paul H. Holloway

    2010-03-01

    Full Text Available 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.

  16. Efficient Luminescence from Perovskite Quantum Dot Solids

    KAUST Repository

    Kim, Younghoon

    2015-11-18

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

  17. Light emission from Si quantum dots

    Directory of Open Access Journals (Sweden)

    Philippe M. Fauchet

    2005-01-01

    Full Text Available Si quantum dots (QDs as small as ∼2 nm in diameter have been synthesized by a variety of techniques. Because of quantum confinement and the elimination of bulk or surface defects, these dots can emit light from the near infrared throughout the visible with quantum efficiencies in excess of 10%. The luminescence wavelength range has been extended to longer wavelengths by the addition of light-emitting rare earths such as erbium (Er. Light-emitting devices (LEDs have been fabricated and their performances are starting to approach those of direct band gap semiconductor or organic LEDs. A search for a Si QD-based laser is even under way. The state-of-the-art in the materials science, physics, and device development of luminescent Si QDs is reviewed and areas of future research are pointed out.

  18. Quantum Size- Dependent Third- Order Nonlinear Optical Susceptibility in Semiconductor Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    SUN Ting; XIONG Gui-guang

    2005-01-01

    The density matrix approach has been employed to investigate the optical nonlinear polarization in a single semiconductor quantum dot(QD). Electron states are considered to be confined within a quantum dot with infinite potential barriers. It is shown, by numerical calculation, that the third-order nonlinear optical susceptibilities for a typical Si quantum dot is dependent on the quantum size of the quantum dot and the frequency of incident light.

  19. Charge transport-induced recoil and dissociation in double quantum dots.

    Science.gov (United States)

    Pozner, Roni; Lifshitz, Efrat; Peskin, Uri

    2014-11-12

    Colloidal quantum dots (CQDs) are free-standing nanostructures with chemically tunable electronic properties. This combination of properties offers intriguing new possibilities for nanoelectromechanical devices that were not explored yet. In this work, we consider a new scanning tunneling microscopy setup for measuring ligand-mediated effective interdot forces and for inducing motion of individual CQDs within an array. Theoretical analysis of a double quantum dot structure within this setup reveals for the first time voltage-induced interdot recoil and dissociation with pronounced changes in the current. Considering realistic microscopic parameters, our approach enables correlating the onset of mechanical motion under bias voltage with the effective ligand-mediated binding forces.

  20. Local Quantum Dot Tuning on Photonic Crystal Chips

    CERN Document Server

    Faraon, Andrei; Fushman, Ilya; Stoltz, Nick; Petroff, Pierre; Vuckovic, Jelena

    2007-01-01

    Quantum networks based on InGaAs quantum dots embedded in photonic crystal devices rely on QDs being in resonance with each other and with the cavities they are embedded in. We developed a new technique based on temperature tuning to spectrally align different quantum dots located on the same chip. The technique allows for up to 1.8nm reversible on-chip quantum dot tuning.

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

    DEFF Research Database (Denmark)

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

    2000-01-01

    Semiconductor quantum dots, especially those formed by self-organized growth, are considered a promising material system for future optical devices [1] and the optical properties of quantum dot ensembles have been investigated in detail over the past years. Recently, considerable interest has...... developed in the study of single quantum dots, characterized by sharp atomic-like transition lines revealing their zero-dimensional density of states. Substantial information about the fundamental properties of individual quantum dots, as well as their interactions with other dots and the host lattice, can...

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

    Science.gov (United States)

    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.

  3. Coupling of single quantum dots to a photonic crystal waveguide

    DEFF Research Database (Denmark)

    Lund-Hansen, Toke; Stobbe, Søren; Julsgaard, Brian

    . An alternative approach is to couple the quantum dot directly to the propagating mode of a photonic waveguide. We demonstrate the coupling of single quantum dots to a photonic crystal waveguide using time-resolved spontaneous emission measurements. A pronounced effect is seen in the decay rates of dots coupled...

  4. Electron-hole confinement symmetry in silicon quantum dots

    NARCIS (Netherlands)

    Müller, F.; Mueller, Filipp; Konstantaras, Georgios; Spruijtenburg, P.C.; van der Wiel, Wilfred Gerard; Zwanenburg, Floris Arnoud

    2015-01-01

    We report electrical transport measurements on a gate-defined ambipolar quantum dot in intrinsic silicon. The ambipolarity allows its operation as either an electron or a hole quantum dot of which we change the dot occupancy by 20 charge carriers in each regime. Electron−hole confinement symmetry is

  5. Coupling of single quantum dots to a photonic crystal waveguide

    DEFF Research Database (Denmark)

    Lund-Hansen, Toke; Stobbe, Søren; Julsgaard, Brian;

    . An alternative approach is to couple the quantum dot directly to the propagating mode of a photonic waveguide. We demonstrate the coupling of single quantum dots to a photonic crystal waveguide using time-resolved spontaneous emission measurements. A pronounced effect is seen in the decay rates of dots coupled...

  6. Coupling single quantum dots to plasmonic nanocones: optical properties.

    Science.gov (United States)

    Meixner, Alfred J; Jäger, Regina; Jäger, Sebastian; Bräuer, Annika; Scherzinger, Kerstin; Fulmes, Julia; Krockhaus, Sven zur Oven; Gollmer, Dominik A; Kern, Dieter P; Fleischer, Monika

    2015-01-01

    Coupling a single quantum emitter, such as a fluorescent molecule or a quantum dot (QD), to a plasmonic nanostructure is an important issue in nano-optics and nano-spectroscopy, relevant for a wide range of applications, including tip-enhanced near-field optical microscopy, plasmon enhanced molecular sensing and spectroscopy, and nanophotonic amplifiers or nanolasers, to mention only a few. While the field enhancement of a sharp nanoantenna increasing the excitation rate of a very closely positioned single molecule or QD has been well investigated, the detailed physical mechanisms involved in the emission of a photon from such a system are, by far, less investigated. In one of our ongoing research projects, we try to address these issues by constructing and spectroscopically analysing geometrically simple hybrid heterostructures consisting of sharp gold cones with single quantum dots attached to the very tip apex. An important goal of this work is to tune the longitudinal plasmon resonance by adjusting the cones' geometry to the emission maximum of the core-shell CdSe/ZnS QDs at nominally 650 nm. Luminescence spectra of the bare cones, pure QDs and hybrid systems were distinguished successfully. In the next steps we will further investigate, experimentally and theoretically, the optical properties of the coupled systems in more detail, such as the fluorescence spectra, blinking statistics, and the current results on the fluorescence lifetimes, and compare them with uncoupled QDs to obtain a clearer picture of the radiative and non-radiative processes.

  7. Mitigation of quantum dot cytotoxicity by microencapsulation.

    Directory of Open Access Journals (Sweden)

    Amelia Romoser

    Full Text Available 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.

  8. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    Science.gov (United States)

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

    1998-01-01

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

  9. Coherent transport through interacting quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hiltscher, Bastian

    2012-10-05

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

  10. Quantum theory of plasmons in nanostructures

    DEFF Research Database (Denmark)

    Winther, Kirsten Trøstrup

    . For a theoretical description of plasmon in such materials, where the electrons are heavily confined in one or more directions, a quantum mechanical description of the electrons in the material is necessary. In this thesis, the ab initio methods Density functional theory (DFT) and linear response time-dependent DFT......In this thesis, ab initio quantum-mechanical calculations are used to study the properties of plasmons in nanostructures that involve atomic length-scales. The plasmon is an electronic excitation that corresponds to oscillations in the electron charge density in metals, often visualized as water...... are applied to calculate the properties of plasmons in nanostructures in different dimensions. In order to identify and visualize localized plasmon modes, a method for calculating plasmon eigenmodes within the ab initio framework has been developed. In the studied materials, quantum mechanical effects...

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  13. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

    Directory of Open Access Journals (Sweden)

    Generalov R

    2011-09-01

    Full Text Available Roman Generalov1,2, Simona Kavaliauskiene1, Sara Westrøm1, Wei Chen3, Solveig Kristensen2, Petras Juzenas11Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway; 2School of Pharmacy, University of Oslo, Oslo, Norway; 3Department of Physics, The University of Texas at Arlington, Arlington, TX, USAAbstract: 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.Keywords: fluorescence lifetime, free radicals, liposomes, lipodots, reactive oxygen species

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

    CERN Document Server

    2003-01-01

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

  15. Mode Competition in Dual-Mode Quantum Dots Semiconductor Microlaser

    CERN Document Server

    Chusseau, Laurent; Viktorovitch, P; Letartre, Xavier

    2013-01-01

    This paper describes the modeling of quantum dots lasers with the aim of assessing the conditions for stable cw dual-mode operation when the mode separation lies in the THz range. Several possible models suited for InAs quantum dots in InP barriers are analytically evaluated, in particular quantum dots electrically coupled through a direct exchange of excitation by the wetting layer or quantum dots optically coupled through the homogeneous broadening of their optical gain. A stable dual-mode regime is shown possible in all cases when quantum dots are used as active layer whereas a gain medium of quantum well or bulk type inevitably leads to bistable behavior. The choice of a quantum dots gain medium perfectly matched the production of dual-mode lasers devoted to THz generation by photomixing.

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

    Science.gov (United States)

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

    2017-03-22

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

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

    Science.gov (United States)

    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.

  18. SU(4) Kondo entanglement in double quantum dot devices

    Science.gov (United States)

    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.

  19. Probing relaxation times in graphene quantum dots

    Science.gov (United States)

    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

  20. Free standing luminescent silicon quantum dots: evidence of quantum confinement and defect related transitions

    Energy Technology Data Exchange (ETDEWEB)

    Ray, Mallar [School of Materials Science and Engineering, Bengal Engineering and Science University, Shibpur, Howrah: 711103, West Bengal (India); Hossain, Syed Minhaz [Department of Physics, Bengal Engineering and Science University, Shibpur, Howrah: 711103, West Bengal (India); Klie, Robert F [Department of Physics, University of Illinois at Chicago, Chicago, IL 60607 (United States); Banerjee, Koushik; Ghosh, Siddhartha, E-mail: mray@matsc.becs.ac.in [Department of Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, 60607 (United States)

    2010-12-17

    We report the synthesis of luminescent, free standing silicon quantum dots by dry and wet etching of silicon and silicon oxide core/shell nanostructures, which are synthesized by controlled oxidation of mechanically milled silicon. Dry and wet etching performed with CF{sub 4} plasma and aqueous HF, respectively, result in the removal of the thick oxide shell of the core/shell nanostructures and affect an additional step of size reduction. HF etch is capable of producing isolated, spherical quantum dots of silicon with dimensions {approx} 2 nm. However, the etching processes introduce unsaturated bonds at the surface of the nanocrystals which are subsequently passivated by oxygen on exposure to ambient atmosphere. The photoluminescence spectra of the colloidal suspensions of these nanocrystals are characterized by double peaks and excitation dependent shift of emission energy. Comparison of the structural, absorption and luminescence characteristics of the samples provides evidence for two competing transition processes-quantum confinement induced widened band gap related transitions and oxide associated interface state mediated transitions. The results enable us to experimentally distinguish between the contributions of the two different transition mechanisms, which has hitherto been a challenging problem.

  1. Effect of magnetic field on an electronic structure and intraband quantum transitions in multishell quantum dots

    Science.gov (United States)

    Holovatsky, V. A.; Voitsekhivska, O. M.; Yakhnevych, M. Ya.

    2017-09-01

    The electron energy spectrum and wave functions in multishell spherical quantum dot, consisting of core and two spherical shells - potential wells separated by thin potential barriers, are obtained in the framework of the effective mass approximation and single band model. The investigations are performed within the matrix method for the nanostructure driven by magnetic field using the complete set of wave functions obtained without the magnetic field. The electron dipole momentum and oscillator strengths of intraband quantum transitions as functions of the magnetic field induction are numerically calculated. In order to increase the sensibility to magnetic field, the geometric parameters of the shells are chosen in such a way that the electron in the ground state is to be located in outer spherical well, but when the magnetic field induction becomes bigger, it moves into the core. It is shown that size of the middle potential well causes the smooth change of the electron location due to the effect of magnetic field, what is displayed on optical properties of nanostructure. The calculations are performed for multishell quantum dot CdSe/ZnS/CdSe/ZnS/CdSe.

  2. Opto-electronic and quantum transport properties of semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sabathil, M.

    2005-01-01

    In this work a novel and efficient method for the calculation of the ballistic transport properties of open semiconductor nanostructures connected to external reservoirs is presented. It is based on the Green's function formalism and reduces the effort to obtain the transmission and the carrier density to a single solution of a hermitian eigenvalue problem with dimensions proportional to the size of the decoupled device and the multiple inversion of a small matrix with dimensions proportional to the size of the contacts to the leads. Using this method, the 4-band GaAs hole transport through a 2-dimensional three-terminal T-junction device, and the resonant tunneling current through a 3-dimensional InAs quantum dot molecule embedded into an InP heterostructure have been calculated. The further extension of the method into a charge self-consistent scheme enables the efficient prediction of the IV-characteristics of highly doped nanoscale field effect transistors in the ballistic regime, including the influence of quasi bound states and the exchange-correlation interaction. Buettiker probes are used to emulate the effect of inelastic scattering on the current for simple 1D devices, systematically analyzing the dependence of the density of states and the resulting self-consistent potential on the scattering strength. The second major topic of this work is the modeling of the optical response of quantum confined neutral and charged excitons in single and coupled self-assembled InGaAs quantum dots. For this purpose the existing device simulator nextnano{sup 3} has been extended to incorporate particle-particle interactions within the means of density functional theory in local density approximation. In this way the exciton transition energies for neutral and charged excitons as a function of an externally applied electric field have been calculated, revealing a systematic reduction of the intrinsic dipole with the addition of extra holes to the exciton, a finding

  3. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-05-16

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

  4. Barrier Li Quantum Dots in Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    LIUYi-Min; LIXiao-Zhu; YANWen-Hong; BAOCheng-Guang

    2003-01-01

    The methods for the few-body system are introduced to investigate the states of the barrier Li quantum dots (QDs) in an arbitrary strength of magnetic field. The configuration, which consists of a positive ion located on the z-axis at a distaneed from the two-dimensional QD plane (the x-y plane) and three electrons in the dot plane bound by the positive ion, is called a barrier Li center. The system, which consists of three electrons in the dot plane bound by the ion,is called a barrier Li QD. The dependence of energy of the state of the barrier Li QD on an external magnetic field B and the distance d is obtained. The angular momentum L of the ground states is found to jump not only with the variation orB but also with d.

  5. The Study of Quantum Interference in Metallic Photonic Crystals Doped with Four-Level Quantum Dots

    Directory of Open Access Journals (Sweden)

    Hatef Ali

    2010-01-01

    Full Text Available Abstract In this work, the absorption coefficient of a metallic photonic crystal doped with nanoparticles has been obtained using numerical simulation techniques. The effects of quantum interference and the concentration of doped particles on the absorption coefficient of the system have been investigated. The nanoparticles have been considered as semiconductor quantum dots which behave as a four-level quantum system and are driven by a single coherent laser field. The results show that changing the position of the photonic band gap about the resonant energy of the two lower levels directly affects the decay rate, and the system can be switched between transparent and opaque states if the probe laser field is tuned to the resonance frequency. These results provide an application for metallic nanostructures in the fabrication of new optical switches and photonic devices.

  6. Quantum Entanglement of Quantum Dot Spin Using Flying Qubits

    Science.gov (United States)

    2015-05-01

    SPDC photon is teleported to a single quantum dot spin by a projective measurement using a Hong Ou Mandel (HOM) interferometer. The SPDC source...photo diode B: Blue CW: Continuous wave DBR: Distributed Bragg reflector EOM: Electro-optics modulator H: Horizontal HOM: Hong-Ou- Mandel InAs

  7. Quantum optics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Cadeddu, Davide; Teissier, Jean

    2016-01-01

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

  8. Quantum photonics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Kuhlmann, Andreas; Cadeddu, Davide;

    2016-01-01

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

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

    Science.gov (United States)

    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.

  10. Nanobeam photonic crystal cavity quantum dot laser

    CERN Document Server

    Gong, Yiyang; Shambat, Gary; Sarmiento, Tomas; Harris, James S; Vuckovic, Jelena

    2010-01-01

    The lasing behavior of one dimensional GaAs nanobeam cavities with embedded InAs quantum dots is studied at room temperature. Lasing is observed throughout the quantum dot PL spectrum, and the wavelength dependence of the threshold is calculated. We study the cavity lasers under both 780 nm and 980 nm pump, finding thresholds as low as 0.3 uW and 19 uW for the two pump wavelengths, respectively. Finally, the nanobeam cavity laser wavelengths are tuned by up to 7 nm by employing a fiber taper in near proximity to the cavities. The fiber taper is used both to efficiently pump the cavity and collect the cavity emission.

  11. Energy level statistics of quantum dots.

    Science.gov (United States)

    Tsau, Chien-Yu; Nghiem, Diu; Joynt, Robert; Woods Halley, J

    2007-05-08

    We investigate the charging energy level statistics of disordered interacting electrons in quantum dots by numerical calculations using the Hartree approximation. The aim is to obtain a global picture of the statistics as a function of disorder and interaction strengths. We find Poisson statistics at very strong disorder, Wigner-Dyson statistics for weak disorder and interactions, and a Gaussian intermediate regime. These regimes are as expected from previous studies and fundamental considerations, but we also find interesting and rather broad crossover regimes. In particular, intermediate between the Gaussian and Poisson regimes we find a two-sided exponential distribution for the energy level spacings. In comparing with experiment, we find that this distribution may be realized in some quantum dots.

  12. Many electron effects in semiconductor quantum dots

    Indian Academy of Sciences (India)

    R K Pandey; Manoj K Harbola; V Ranjan; Vijay A Singh

    2003-01-01

    Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as ‘artificial atoms’ by some, they are much larger (1 100 nm) than real atoms. One can study a variety of manyelectron effects in them, which are otherwise difficult to observe in a real atom. We have treated these effects within the local density approximation (LDA) and the Harbola–Sahni (HS) scheme. HS is free of the selfinteraction error of the LDA. Our calculations have been performed in a three-dimensional quantum dot. We have carried out a study of the size and shape dependence of the level spacing. Scaling laws for the Hubbard ‘’ are established.

  13. Energy level statistics of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Tsau, C-Y [University of Wisconsin-Madison, Madison, WI 53706 (United States); Nghiem, Diu [University of Wisconsin-Madison, Madison, WI 53706 (United States); Joynt, Robert [University of Wisconsin-Madison, Madison, WI 53706 (United States); Halley, J Woods [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)

    2007-05-08

    We investigate the charging energy level statistics of disordered interacting electrons in quantum dots by numerical calculations using the Hartree approximation. The aim is to obtain a global picture of the statistics as a function of disorder and interaction strengths. We find Poisson statistics at very strong disorder, Wigner-Dyson statistics for weak disorder and interactions, and a Gaussian intermediate regime. These regimes are as expected from previous studies and fundamental considerations, but we also find interesting and rather broad crossover regimes. In particular, intermediate between the Gaussian and Poisson regimes we find a two-sided exponential distribution for the energy level spacings. In comparing with experiment, we find that this distribution may be realized in some quantum dots.

  14. Energy level statistics of quantum dots

    Science.gov (United States)

    Tsau, Chien-Yu; Nghiem, Diu; Joynt, Robert; Halley, J. Woods

    2007-05-01

    We investigate the charging energy level statistics of disordered interacting electrons in quantum dots by numerical calculations using the Hartree approximation. The aim is to obtain a global picture of the statistics as a function of disorder and interaction strengths. We find Poisson statistics at very strong disorder, Wigner-Dyson statistics for weak disorder and interactions, and a Gaussian intermediate regime. These regimes are as expected from previous studies and fundamental considerations, but we also find interesting and rather broad crossover regimes. In particular, intermediate between the Gaussian and Poisson regimes we find a two-sided exponential distribution for the energy level spacings. In comparing with experiment, we find that this distribution may be realized in some quantum dots.

  15. Dual-channel spontaneous emission of quantum dots in magnetic metamaterials.

    Science.gov (United States)

    Decker, Manuel; Staude, Isabelle; Shishkin, Ivan I; Samusev, Kirill B; Parkinson, Patrick; Sreenivasan, Varun K A; Minovich, Alexander; Miroshnichenko, Andrey E; Zvyagin, Andrei; Jagadish, Chennupati; Neshev, Dragomir N; Kivshar, Yuri S

    2013-01-01

    Metamaterials, artificial electromagnetic media realized by subwavelength nano-structuring, have become a paradigm for engineering electromagnetic space, allowing for independent control of both electric and magnetic responses of the material. Whereas most metamaterials studied so far are limited to passive structures, the need for active metamaterials is rapidly growing. However, the fundamental question on how the energy of emitters is distributed between both (electric and magnetic) interaction channels of the metamaterial still remains open. Here we study simultaneous spontaneous emission of quantum dots into both of these channels and define the control parameters for tailoring the quantum-dot coupling to metamaterials. By superimposing two orthogonal modes of equal strength at the wavelength of quantum-dot photoluminescence, we demonstrate a sharp difference in their interaction with the magnetic and electric metamaterial modes. Our observations reveal the importance of mode engineering for spontaneous emission control in metamaterials, paving a way towards loss-compensated metamaterials and metamaterial nanolasers.

  16. Peptide-directed binding of quantum dots to integrins in human fibroblast.

    Science.gov (United States)

    Shi, Peng; Chen, Hongfeng; Cho, Michael R; Stroscio, Michael A

    2006-03-01

    There is currently a major international effort aimed at integrating semiconductor nanostructures with biological structures. This paper reports the use of peptide sequences with certain motifs like artinine-glycine-aspartic acid (RGD) and leucine-aspartic acid-valine (LDV) to functionalize zinc sulfide (ZnS)-capped cadmiun selenide (CdSe) quantum dots, so that the quantum dot-peptide complexes selectively bind to integrins on HT1080 human fibrosarcoma cells membrane. In this way, an interface between semiconductor nanocrystals and subcellular components was achieved, and the distribution pattern of RGD and LDV receptors on HT1080 cell membranes is revealed. These findings point the way to using a wide class of peptide-functionalized semiconductor quantum dots for the study of cellular processes involving integrins.

  17. Dirac gap-induced graphene quantum dot in an electrostatic potential

    Science.gov (United States)

    Giavaras, G.; Nori, Franco

    2011-04-01

    A spatially modulated Dirac gap in a graphene sheet leads to charge confinement, thus enabling a graphene quantum dot to be formed without the application of external electric and magnetic fields [G. Giavaras and F. Nori, Appl. Phys. Lett. 97, 243106 (2010)]. This can be achieved provided the Dirac gap has a local minimum in which the states become localized. In this work, the physics of such a gap-induced dot is investigated in the continuum limit by solving the Dirac equation. It is shown that gap-induced confined states couple to the states introduced by an electrostatic quantum well potential. Hence the region in which the resulting hybridized states are localized can be tuned with the potential strength, an effect which involves Klein tunneling. The proposed quantum dot may be used to probe quasirelativistic effects in graphene, while the induced confined states may be useful for graphene-based nanostructures.

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

    Directory of Open Access Journals (Sweden)

    LI Zhi-min

    2017-08-01

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

  19. DLTS measurements on GaSb/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hoegner, Annika; Nowozin, Tobias; Marent, Andreas; Bimberg, Dieter [Institut fuer Festkoerperphysik, TU Berlin (Germany); Tseng, Chi-Che [Institute of Photonics Technologies, NTHU (China); Lin, Shih-Yen [Institute of Optoelectronic Sciences, NTOU (China)

    2010-07-01

    Memory devices based on hole storage in self-organized quantum dots offer significant advantages with respect to storage time and scalability. Recently, we demonstrated a first prototype based on InAs/GaAs quantum dots at low temperatures. To enable feasible storage times at room temperature the localisation energy of the quantum dots has to be increased by using other material systems. A first step in this direction is the use of GaSb quantum dots within a GaAs matrix. We have characterized self-organized GaSb/GaAs quantum dots embedded into a n{sup +}p-diode structure. DLTS measurements on hole emission were conducted and yield a strong peak from which a mean emission energy of about 400 meV can be extracted. The reference sample without the quantum dots (containing only the wetting layer) shows no such peak.

  20. Quantum dot spectroscopy using a single phosphorus donor

    Science.gov (United States)

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

    2015-12-01

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

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

    Science.gov (United States)

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

    2016-09-01

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

  2. Decoherence in Nearly-Isolated Quantum Dots

    DEFF Research Database (Denmark)

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

    2000-01-01

    Decoherence in nearly-isolated GaAs quantum dots is investigated using the change in average Coulomb blockade peak height upon breaking time-reversal symmetry. The normalized change in average peak height approaches the predicted universal value of 1/4 at temperatures well below the single......-particle level spacing, but is greatly suppressed for temperature greater than the level spacing, suggesting that inelastic scattering or other dephasing mechanisms dominate in this regime....

  3. Quantum dot/glycol chitosan fluorescent nanoconjugates

    OpenAIRE

    Mansur, Alexandra AP; Herman S. Mansur

    2015-01-01

    In this study, novel carbohydrate-based nanoconjugates combining chemically modified chitosan with semiconductor quantum dots (QDs) were designed and synthesised via single-step aqueous route at room temperature. Glycol chitosan (G-CHI) was used as the capping ligand aiming to improve the water solubility of the nanoconjugates to produce stable and biocompatible colloidal systems. UV-visible (UV–vis) spectroscopy, photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR) spec...

  4. Depleted bulk heterojunction colloidal quantum dot photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Barkhouse, D.A.R. [Department of Electrical and Computer Engineering, University of Toronto, 10 King' s College Road, Toronto, Ontario M5S 3G4 (Canada); IBM Thomas J. Watson Research Center, Kitchawan Road, Yorktown Heights, NY, 10598 (United States); Debnath, Ratan; Kramer, Illan J.; Zhitomirsky, David; Levina, Larissa; Sargent, Edward H. [Department of Electrical and Computer Engineering, University of Toronto, 10 King' s College Road, Toronto, Ontario M5S 3G4 (Canada); Pattantyus-Abraham, Andras G. [Department of Electrical and Computer Engineering, University of Toronto, 10 King' s College Road, Toronto, Ontario M5S 3G4 (Canada); Quantum Solar Power Corporation, 1055 W. Hastings, Ste. 300, Vancouver, BC, V6E 2E9 (Canada); Etgar, Lioz; Graetzel, Michael [Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland)

    2011-07-26

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

  5. The Silicon:Colloidal Quantum Dot Heterojunction

    KAUST Repository

    Masala, Silvia

    2015-10-13

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

  6. Depleted Bulk Heterojunction Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Barkhouse, D. Aaron R.

    2011-05-26

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

  7. Pharmaceutical and biomedical applications of quantum dots.

    Science.gov (United States)

    Bajwa, Neha; Mehra, Neelesh K; Jain, Keerti; Jain, Narendra K

    2016-05-01

    Quantum dots (QDs) have captured the fascination and attention of scientists due to their simultaneous targeting and imaging potential in drug delivery, in pharmaceutical and biomedical applications. In the present study, we have exhaustively reviewed various aspects of QDs, highlighting their pharmaceutical and biomedical applications, pharmacology, interactions, and toxicological manifestations. The eventual use of QDs is to dramatically improve clinical diagnostic tests for early detection of cancer. In recent years, QDs were introduced to cell biology as an alternative fluorescent probe.

  8. The pinning effect in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Monisha, P. J., E-mail: pjmonisha@gmail.com [School of Physics, University of Hyderabad, Hyderabad-500046 (India); Mukhopadhyay, Soma [Department of Physics, D V R College of Engineering and Technology, Hyderabad-502285 (India)

    2014-04-24

    The pinning effect is studied in a Gaussian quantum dot using the improved Wigner-Brillouin perturbation theory (IWBPT) in the presence of electron-phonon interaction. The electron ground state plus one phonon state is degenerate with the electron in the first excited state. The electron-phonon interaction lifts the degeneracy and the first excited states get pinned to the ground state plus one phonon state as we increase the confinement frequency.

  9. Electrically addressing a single self-assembled quantum dot

    CERN Document Server

    Ellis, D J P; Atkinson, P; Ritchie, D A; Shields, A J

    2006-01-01

    We report on the use of an aperture in an aluminum oxide layer to restrict current injection into a single self-assembled InAs quantum dot, from an ensemble of such dots within a large mesa. The insulating aperture is formed through the wet-oxidation of a layer of AlAs. Under photoluminescence we observe that only one quantum dot in the ensemble exhibits a Stark shift, and that the same single dot is visible under electroluminescence. Autocorrelation measurements performed on the electroluminescence confirm that we are observing emission from a single quantum dot.

  10. Virtual photonic couplings of quantum nanostructures for quantum information technology

    DEFF Research Database (Denmark)

    Matsueda, H.; Hvam, Jørn Märcher; Ducommun, Y.

    2008-01-01

    of a model of resonance dynamic multipolemultipole interaction (RDMMI), on the basis of microphotoluminescence (μ-PL) experiment of a single asymmetric pair of GaAs/AlGaAs quantum dots (QDs). The ranges of the mediating photons in various RDMMI are estimated, proving the significance of RDMMI...

  11. Electron States of Few-Electron Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    戴振宏; 孙金祚; 张立德; 李作宏; 黄士勇; 隋鹏飞

    2002-01-01

    We study few-electron semiconductor quantum dots using the unrestricted Hartree-Fock-Roothaan method based on the Gaussian basis. Our emphasis is on the energy level calculation for quantum dots. The confinement potential in a quantum dot is assumed to be in a form of three-dimensional spherical finite potential well. Some valuable results, such as the rearrangement of the energy level, have been obtained.

  12. Semiconductor quantum dot scintillation under gamma-ray irradiation.

    Science.gov (United States)

    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.

  13. Controllability of multi-partite quantum systems and selective excitation of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Schirmer, S G [Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Pullen, I C H [Department of Applied Mathematics and Computing, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Solomon, A I [Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)

    2005-10-01

    We consider the degrees of controllability of multi-partite quantum systems, as well as necessary and sufficient criteria for each case. The results are applied to the problem of simultaneous control of an ensemble of quantum dots with a single laser pulse. Finally, we apply optimal control techniques to demonstrate selective excitation of individual dots for a simultaneously controllable ensemble of quantum dots.

  14. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

    Claudon, Julien; Munsch, Matthieu; Bleuse, Joel;

    2012-01-01

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

  15. Quantum transport through an array of quantum dots.

    Science.gov (United States)

    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.

  16. Understanding chemically processed solar cells based on quantum dots.

    Science.gov (United States)

    Malgras, Victor; Nattestad, Andrew; Kim, Jung Ho; Dou, Shi Xue; Yamauchi, Yusuke

    2017-01-01

    Photovoltaic energy conversion is one of the best alternatives to fossil fuel combustion. Petroleum resources are now close to depletion and their combustion is known to be responsible for the release of a considerable amount of greenhouse gases and carcinogenic airborne particles. Novel third-generation solar cells include a vast range of device designs and materials aiming to overcome the factors limiting the current technologies. Among them, quantum dot-based devices showed promising potential both as sensitizers and as colloidal nanoparticle films. A good example is the p-type PbS colloidal quantum dots (CQDs) forming a heterojunction with a n-type wide-band-gap semiconductor such as TiO2 or ZnO. The confinement in these nanostructures is also expected to result in marginal mechanisms, such as the collection of hot carriers and generation of multiple excitons, which would increase the theoretical conversion efficiency limit. Ultimately, this technology could also lead to the assembly of a tandem-type cell with CQD films absorbing in different regions of the solar spectrum.

  17. Understanding chemically processed solar cells based on quantum dots

    Science.gov (United States)

    Malgras, Victor; Nattestad, Andrew; Kim, Jung Ho; Dou, Shi Xue; Yamauchi, Yusuke

    2017-01-01

    Abstract Photovoltaic energy conversion is one of the best alternatives to fossil fuel combustion. Petroleum resources are now close to depletion and their combustion is known to be responsible for the release of a considerable amount of greenhouse gases and carcinogenic airborne particles. Novel third-generation solar cells include a vast range of device designs and materials aiming to overcome the factors limiting the current technologies. Among them, quantum dot-based devices showed promising potential both as sensitizers and as colloidal nanoparticle films. A good example is the p-type PbS colloidal quantum dots (CQDs) forming a heterojunction with a n-type wide-band-gap semiconductor such as TiO2 or ZnO. The confinement in these nanostructures is also expected to result in marginal mechanisms, such as the collection of hot carriers and generation of multiple excitons, which would increase the theoretical conversion efficiency limit. Ultimately, this technology could also lead to the assembly of a tandem-type cell with CQD films absorbing in different regions of the solar spectrum. PMID:28567179

  18. Tuning the quantum critical crossover in quantum dots

    Science.gov (United States)

    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)

  19. Investigation of Quantum Dot Lasers

    Science.gov (United States)

    2007-11-02

    Lett. 79, 722 (2001). 8. Report of Inventions None. 9. List of Scientific Personnel Supported, Degrees, Awards and Honors Siddhartha ...Ghosh, GSRA Sameer Pradhan, GSRA Sasan Fathpour, GSRA Zetian Mi, GSRA Siddhartha Ghosh, Ph.D., “Growth of In(Ga)As/GaAs self-organized quantum

  20. Nanoengineering the second order susceptibility in semiconductor quantum dot heterostructures.

    Science.gov (United States)

    Zielinski, Marcin; Winter, Shoshana; Kolkowski, Radoslaw; Nogues, Claude; Oron, Dan; Zyss, Joseph; Chauvat, Dominique

    2011-03-28

    We study second-harmonic generation from single CdTe/CdS core/shell rod-on-dot nanocrystals with different geometrical parameters, which allow to fine tune the nonlinear properties of the nanostructure. These hybrid semiconductor-semiconductor nanoparticles exhibit extremely strong and stable second-harmonic emission, although the size of CdTe core is still within the strong quantum confinement regime. The orientation sensitive polarization response is analyzed by means of a pointwise additive model of the third-order tensors associated to the nanoparticle components. These findings prove that engineering of semiconducting complex heterostructures at the single nanoparticle scale can lead to extremely bright nanometric nonlinear light sources.

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

    Energy Technology Data Exchange (ETDEWEB)

    See, Gloria G. [Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 208 North Wright Street, Urbana, Illinois 61801 (United States); Xu, Lu; Nuzzo, Ralph G. [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States); Sutanto, Erick; Alleyne, Andrew G. [Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, 154 Mechanical Engineering Building, Urbana, Illinois 61801 (United States); Cunningham, Brian T. [Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 208 North Wright Street, Urbana, Illinois 61801 (United States); Department of Bioengineering, University of Illinois at Urbana-Champaign, 1270 Digital Computer Laboratory, MC-278, Urbana, Illinois 61801 (United States)

    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.

  2. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum

    OpenAIRE

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

    2016-01-01

    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 pr...

  3. Core–shell quantum dots: Properties and applications

    Energy Technology Data Exchange (ETDEWEB)

    Vasudevan, D., E-mail: vasudevand@rediffmail.com [Electrodics and electrocatalysis division, CSIR-CECRI, Karaikudi 630006 (India); Gaddam, Rohit Ranganathan [Amity Institute of Nanotechnology, Amity University, Noida 201301 (India); Trinchi, Adrian; Cole, Ivan [CSIRO Materials Science and Engineering, Clayton South MDC, 3169 (Australia)

    2015-07-05

    Fluorescent quantum dots (QDs) are semiconducting nanocrystals (NCs) that find numerous applications in areas, such as bio labelling, sensors, lasers, light emitting diodes and medicine. Core–shell quantum dots were developed to improve the photoluminescence efficiency of single quantum dots. Capping their surface with organic ligands as well as their extraction into aqueous media enables their use in sensing applications. The current review highlights the importance and applications of core shell quantum dots as well as their surface modifications and applications in the field of medicine and as sensors for chemical and biochemical analysis.

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

    Science.gov (United States)

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

    2016-08-01

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

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

    Science.gov (United States)

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

    2016-09-22

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

  6. Quantum coherence in semiconductor nanostructures for improved lasers and detectors.

    Energy Technology Data Exchange (ETDEWEB)

    Chow, Weng Wah Dr. (; .); Lyo, Sungkwun Kenneth; Cederberg, Jeffrey George; Modine, Normand Arthur; Biefeld, Robert Malcolm

    2006-02-01

    The potential for implementing quantum coherence in semiconductor self-assembled quantum dots has been investigated theoretically and experimentally. Theoretical modeling suggests that coherent dynamics should be possible in self-assembled quantum dots. Our experimental efforts have optimized InGaAs and InAs self-assembled quantum dots on GaAs for demonstrating coherent phenomena. Optical investigations have indicated the appropriate geometries for observing quantum coherence and the type of experiments for observing quantum coherence have been outlined. The optical investigation targeted electromagnetically induced transparency (EIT) in order to demonstrate an all optical delay line.

  7. Utilization of down-shifting photoluminescent ZnO quantum dots on solar cells

    Science.gov (United States)

    Zazueta-Raynaud, A.; Lopez-Delgado, R.; Pelayo-Ceja, J. E.; Alvarez-Ramos, M. E.; Ayon, A.

    2017-07-01

    We report on the synthesis of photo luminescent zinc oxide (ZnO) quantum dots, their deployment on the window side of photovoltaic structures and the measured influence on the power conversion efficiency. Down-shifting effects were characterized by exciting the synthesized nanostructures with photons in the 340-350 nm range, and measuring the wavelength of the emitted photons observed to be ~500 nm. The colloidal ZnO quantum dots were synthesized in an ethanol-based solution, obtaining different sized nanostructures centered at 4 nm, optically recognizable by their emission in various colors. Subsequently, different concentrations of zinc oxide quantum dots were prepared and dispersed in poly-methyl-methacrylate (PMMA) to be spin cast on the window side of previously characterized solar cells. The observations made to date indicate an improvement of ~4.8% in the PCE. In this work, we discuss the results obtained and suggest pathways to further increase the power conversion efficiency of photovoltaic devices employing quantum dots.

  8. Near-Infrared Localized Surface Plasmon Resonances Arising from Free Carriers in Doped Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Prashant K.; Luther, Joey; Ewers, Trevor; Alivisatos, A. Paul

    2010-10-12

    Quantum confinement of electronic wavefunctions in semiconductor quantum dots (QDs) yields discrete atom-like and tunable electronic levels, thereby allowing the engineering of excitation and emission spectra. Metal nanoparticles, on the other hand, display strong resonant interactions with light from localized surface plasmon resonance (LSPR) oscillations of free carriers, resulting in enhanced and geometrically tunable absorption and scattering resonances. The complementary attributes of these nanostructures lends strong interest toward integration into hybrid nanostructures to explore enhanced properties or the emergence of unique attributes arising from their interaction. However, the physicochemical interface between the two components can be limiting for energy transfer and synergistic coupling within such a hybrid nanostructure. Therefore, it is advantageous to realize both attributes, i.e., LSPRs and quantum confinement within the same nanostructure. Here, we describe well-defined LSPRs arising from p-type carriers in vacancy-doped semiconductor quantum dots. This opens up possibilities for light harvesting, non-linear optics, optical sensing and manipulation of solid-state processes in single nanocrystals.

  9. Quantum-Dot-Based Telecommunication-Wavelength Quantum Relay

    Science.gov (United States)

    Huwer, J.; Stevenson, R. M.; Skiba-Szymanska, J.; Ward, M. B.; Shields, A. J.; Felle, M.; Farrer, I.; Ritchie, D. A.; Penty, R. V.

    2017-08-01

    The development of quantum relays for long-haul and attack-proof quantum communication networks operating with weak coherent laser pulses requires entangled photon sources at telecommunication wavelengths with intrinsic single-photon emission for most practical implementations. Using a semiconductor quantum dot emitting entangled photon pairs in the telecommunication O band, we demonstrate a quantum relay fulfilling both of these conditions. The system achieves a maximum fidelity of 94.5% for implementation of a standard four-state protocol with input states generated by a laser. We further investigate robustness against frequency detuning of the narrow-band input and perform process tomography of the teleporter, revealing operation for arbitrary pure input states, with an average gate fidelity of 83.6%. The results highlight the potential of semiconductor light sources for compact and robust quantum-relay technology that is compatible with existing communication infrastructures.

  10. Quantum Optomechanics with Silicon Nanostructures

    Science.gov (United States)

    Safavi-Naeini, Amir H.

    Mechanical resonators are the most basic and ubiquitous physical systems known. In on-chip form, they are used to process high frequency signals in every cell phone, television, and laptop. They have also been in the last few decades in different shapes and forms, a critical part of progress in quantum information sciences with kilogram scale mirrors for gravitational wave detection measuring motion at its quantum limits, and the motion of single ions being used to link qubits for quantum computation. Optomechanics is a field primarily concerned with coupling light to the motion of mechanical structures. This thesis contains descriptions of recent work with mechanical systems in the megahertz to gigahertz frequency range, formed by nanofabricating novel photonic/phononic structures on a silicon chip. These structures are designed to have both optical and mechanical resonances, and laser light is used to address and manipulate their motional degrees of freedom through radiation pressure forces. We laser cool these mechanical resonators to their ground states, and observe for the first time the quantum zero-point motion of a nanomechanical resonator. Conversely, we show that engineered mechanical resonances drastically modify the optical response of our structures, creating large effective optical nonlinearities not present in bulk silicon. We experimentally demonstrate aspects of these nonlinearities by proposing and observing ``electromagnetically induced transparency'' and light slowed down to 6 m/s, as well as wavelength conversion, and generation of nonclassical optical radiation. Finally, the application of optomechanics to longstanding problems in quantum and classical communications are proposed and investigated.

  11. Hybrid passivated colloidal quantum dot solids

    Science.gov (United States)

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

    2012-09-01

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

  12. Hybrid passivated colloidal quantum dot solids

    KAUST Repository

    Ip, Alex

    2012-07-29

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

  13. Nonrenewal statistics in transport through quantum dots

    Science.gov (United States)

    Ptaszyński, Krzysztof

    2017-01-01

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

  14. Production and targeting of monovalent quantum dots.

    Science.gov (United States)

    Seo, Daeha; Farlow, Justin; Southard, Kade; Jun, Young-Wook; Gartner, Zev J

    2014-10-23

    The multivalent nature of commercial quantum dots (QDs) and the difficulties associated with producing monovalent dots have limited their applications in biology, where clustering and the spatial organization of biomolecules is often the object of study. We describe here a protocol to produce monovalent quantum dots (mQDs) that can be accomplished in most biological research laboratories via a simple mixing of CdSe/ZnS core/shell QDs with phosphorothioate DNA (ptDNA) of defined length. After a single ptDNA strand has wrapped the QD, additional strands are excluded from the surface. Production of mQDs in this manner can be accomplished at small and large scale, with commercial reagents, and in minimal steps. These mQDs can be specifically directed to biological targets by hybridization to a complementary single stranded targeting DNA. We demonstrate the use of these mQDs as imaging probes by labeling SNAP-tagged Notch receptors on live mammalian cells, targeted by mQDs bearing a benzylguanine moiety.

  15. Amphoteric CdSe nanocrystalline quantum dots.

    Science.gov (United States)

    Islam, Mohammad A

    2008-06-25

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

  16. Assessment of quantum dots concentrators for photovoltaic electricity production; Evaluation du potentiel de concentrateurs a quantum dots pour la production d'electricite photovoltaique. Rapport final

    Energy Technology Data Exchange (ETDEWEB)

    Schueler, A.; Kostro, A.; Huriet, B.

    2006-07-01

    One of the most promising application of semiconductor nanostructures in the field of photovoltaics might be planar photoluminescent concentrators. Even for diffuse solar radiation, considerable concentration factors might be achieved. Such devices have originally been designed on the basis of organic dyes and might benefit from a considerably improved lifetime when replacing the organic fluorescent substances by inorganic semiconductor nanocrystals, so-called quantum dots. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the use of quantum dot solar concentrators in photovoltaic solar energy conversion, reliable computer simulations are needed. A tool for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte-Carlo methods that are applied to polarization-dependent reflection/transmission at interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent re-emission. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, such simulations allow to predict the total efficiency of the envisaged concentrating PV systems, and to optimize pane dimensions, photoluminescent emission frequencies, and choice of PV cell types. (author)

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

    Science.gov (United States)

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

    2005-01-01

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

  18. Resonance fluorescence from a telecom-wavelength quantum dot

    CERN Document Server

    Al-Khuzheyri, R; Huwer, J; Santana, T S; Szymanska, J Skiba-; Felle, M; Ward, M B; Stevenson, R M; Farrer, I; Tanner, M G; Hadfield, R H; Ritchie, D A; Shields, A J; Gerardot, B D

    2016-01-01

    We report on resonance fluorescence from a single quantum dot emitting at telecom wavelengths. We perform high-resolution spectroscopy and observe the Mollow triplet in the Rabi regime--a hallmark of resonance fluorescence. The measured resonance-fluorescence spectra allow us to rule out pure dephasing as a significant decoherence mechanism in these quantum dots. Combined with numerical simulations, the experimental results provide robust characterisation of charge noise in the environment of the quantum dot. Resonant control of the quantum dot opens up new possibilities for on-demand generation of indistinguishable single photons at telecom wavelengths as well as quantum optics experiments and direct manipulation of solid-state qubits in telecom-wavelength quantum dots.

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

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg

    deviations. Similar measurements on a quantum dot in a photonic-crystal cavity sow a Rabi splitting on resonance, while time-resolved measurements prove that the system is in the weak coupling regime. Whle tuning the quantum dot through resonance of the high-Q mode we observe a strong and surprisingly...... Successfully model the decay rates with a microscopic model that allows us to for the first time extract the effective phonon density of states, which we can model with bulk phonons. Studies on a quantum dot detuned from a low-Q mode of a photonic-crystal cavity show a high collection efficiency at the first......In this thesis we have performed quantum-electrodynamics experiments on quantum dots embedded in photonic-crystal cavities. We perform a quantitative comparison of the decay dynamics and emission spectra of quantum dots embedded in a micropillar cavity and a photonic-crystal cavity. The light...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-02-08

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

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width...... quantum optical properties for single photon application and quantum optics.......We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer...

  2. Surface plasmons in a metal nanowire coupled to colloidal quantum dots: Scattering properties and quantum entanglement

    OpenAIRE

    2014-01-01

    We investigate coherent single surface-plasmon transport in a metal nanowire strongly coupled to two colloidal quantum dots. Analytical expressions are obtained for the transmission and reflection coefficients by solving the corresponding eigenvalue equation. Remote entanglement of the wave functions of the two quantum dots can be created if the inter-dot distance is equal to a multiple half-wavelength of the surface plasmon. Furthermore, by applying classical laser pulses to the quantum dots...

  3. Quantum state preparation in semiconductor dots by adiabatic rapid passage

    OpenAIRE

    Wu, Yanwen; Piper, I.M.; Ediger, M.; Brereton, P.; Schmidgall, E. R.; Hugues, M.; Hopkinson, M.; Phillips, R.T.

    2010-01-01

    Preparation of a specific quantum state is a required step for a variety of proposed practical uses of quantum dynamics. We report an experimental demonstration of optical quantum state preparation in a semiconductor quantum dot with electrical readout, which contrasts with earlier work based on Rabi flopping in that the method is robust with respect to variation in the optical coupling. We use adiabatic rapid passage, which is capable of inverting single dots to a specified upper level. We d...

  4. Quantum dot/plasmonic nanoparticle metachromophores with quantum yields that vary with excitation wavelength.

    Science.gov (United States)

    Munechika, Keiko; Chen, Yeechi; Tillack, Andreas F; Kulkarni, Abhishek P; Jen-La Plante, Ilan; Munro, Andrea M; Ginger, David S

    2011-07-13

    Coupled plasmonic/chromophore systems are of interest in applications ranging from fluorescent biosensors to solar photovoltaics and photoelectrochemical cells because near-field coupling to metal nanostructures can dramatically alter the optical performance of nearby materials. We show that CdSe quantum dots (QDs) near single silver nanoprisms can exhibit photoluminescence lifetimes and quantum yields that depend on the excitation wavelength, in apparent violation of the Kasha-Vavilov rule. We attribute the variation in QD lifetime with excitation wavelength to the wavelength-dependent coupling of higher-order plasmon modes to different spatial subpopulations of nearby QDs. At the QD emission wavelength, these subpopulations are coupled to far-field radiation with varying efficiency by the nanoprism dipolar resonance. These results offer an easily accessible new route to design metachromophores with tailored optical properties.

  5. Colloidal Quantum Dot Photovoltaics: A Path Forward

    KAUST Repository

    Kramer, Illan J.

    2011-11-22

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

  6. Nano-laser on silicon quantum dots

    Science.gov (United States)

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

    2011-04-01

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

  7. An Exciton Bound to a Neutral Donor in Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    解文方

    2002-01-01

    The binding energies for an exciton (X) trapped in a two-dimensional quantum dot by a neutral donor have been calculated using the method of few-body physics for the heavy hole (σ= 0.196) and the light hole (σr = 0.707).We find that the (D0, X) complex confined in a quantum dot has in general a larger binding energy than those in a two-dimensional quantum well and a three-dimensional bulk semiconductor, and the binding energy increases with the decrease of the dot radius. At dot radius R →∞, we compare our calculated result with the previous results.

  8. Nonequilibrium Electron Transport Through a Quantum Dot from Kubo Formula

    Institute of Scientific and Technical Information of China (English)

    L(U) Rong; ZHANG Guang-Ming

    2005-01-01

    Based on the Kubo formula for an electron tunneling junction, we revisit the nonequilibrium transport properties through a quantum dot. Since the Fermi level of the quantum dot is set by the conduction electrons of the leads, we calculate the electron current from the left side by assuming the quantum dot coupled to the right lead as another side of the tunneling junction, and the other way round is used to calculate the current from the right side. By symmetrizing these two currents, an effective local density states on the dot can be obtained, and is discussed at high and low temperatures, respectively.

  9. Quantum spin transport in semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Schindler, Christoph

    2012-05-15

    In this work, we study and quantitatively predict the quantum spin Hall effect, the spin-orbit interaction induced intrinsic spin-Hall effect, spin-orbit induced magnetizations, and spin-polarized electric currents in nanostructured two-dimensional electron or hole gases with and without the presence of magnetic fields. We propose concrete device geometries for the generation, detection, and manipulation of spin polarization and spin-polarized currents. To this end a novel multi-band quantum transport theory, that we termed the multi-scattering Buettiker probe model, is developed. The method treats quantum interference and coherence in open quantum devices on the same footing as incoherent scattering and incorporates inhomogeneous magnetic fields in a gauge-invariant and nonperturbative manner. The spin-orbit interaction parameters that control effects such as band energy spin splittings, g-factors, and spin relaxations are calculated microscopically in terms of an atomistic relativistic tight-binding model. We calculate the transverse electron focusing in external magnetic and electric fields. We have performed detailed studies of the intrinsic spin-Hall effect and its inverse effect in various material systems and geometries. We find a geometry dependent threshold value for the spin-orbit interaction for the inverse intrinsic spin-Hall effect that cannot be met by n-type GaAs structures. We propose geometries that spin polarize electric current in zero magnetic field and analyze the out-of-plane spin polarization by all electrical means. We predict unexpectedly large spin-orbit induced spin-polarization effects in zero magnetic fields that are caused by resonant enhancements of the spin-orbit interaction in specially band engineered and geometrically designed p-type nanostructures. We propose a concrete realization of a spin transistor in HgTe quantum wells, that employs the helical edge channel in the quantum spin Hall effect.

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

    Science.gov (United States)

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

    2016-07-01

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

  11. Quantum dot mode locked lasers for coherent frequency comb generation

    Science.gov (United States)

    Martinez, A.; Calò, C.; Rosales, R.; Watts, R. T.; Merghem, K.; Accard, A.; Lelarge, F.; Barry, L. P.; Ramdane, A.

    2013-12-01

    Monolithic semiconductor passively mode locked lasers (MLL) are very attractive components for many applications including high bit rate telecommunications, microwave photonics and instrumentation. Owing to the three dimensional confinement of the charge carriers, quantum dot based mode-locked lasers have been the subject of intense investigations because of their improved performance compared to conventional material systems. Indeed, the inhomogeneous gain broadening and the ultrafast absorption recovery dynamics are an asset for short pulse generation. Moreover, the weak coupling of amplified spontaneous emission with the guided modes plus low loss waveguide leads to low timing jitter. Our work concentrates on InAs quantum dash nanostructures grown on InP substrate, intended for applications in the 1.55 μm telecom window. InAs/InP quantum dash based lasers, in particular, have demonstrated efficient mode locking in single section Fabry-Perot configurations. The flat optical spectrum of about 12 nm, combined with the narrow RF beat note linewidth of about 10 kHz make them a promising technology for optical frequency comb generation. Coherence between spectral modes was assessed by means of spectral phase measurements. The parabolic spectral phase profile indicates that short pulses can be obtained provided the intracavity dispersion can be compensated by inserting a single mode fiber.

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

    KAUST Repository

    Liu, Huan

    2012-01-01

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

  13. Exotic states in quantum nanostructures

    CERN Document Server

    2002-01-01

    Mesoscopic physics has made great strides in the last few years It is an area of research that is attractive to many graduate students of theoretical condensed matter physics The techniques that are needed to understand it go beyond the conventional perturbative approaches that still form the bulk of the graduate lectures that are given to students Even when the non-perturbative techniques are presented, they often are presented within an abstract context It is important to have lectures given by experts in the field, which present both theory and experiment in an illuminating and inspiring way, so that the impact of new methodology on novel physics is clear It is an apt time to have such a volume since the field has reached a level of maturity The pedagogical nature of the articles and the variety of topics makes it an important resource for newcomers to the field The topics range from the newly emerging area of quantum computers and quantum information using Josephson junctions to the formal mathematical me...

  14. Quantum Mechanics of Palladium Nanostructures

    Science.gov (United States)

    Hira, Ajit; McKeough, James; Ortiz, Bridget; Diaz, Juan

    We continue our interest in the chemisorption of different atomic and molecular species on small clusters of metallic elements, by examining the interactions of H, H2, Li and O adsorbates with Pdn clusters (n = 2 thru 20). The study of clusters can reveal the effects of substrate geometry on the behavior of adsorbates. Transition-metal clusters are especially suited for the study of quantum size effects and for formation of metallic states, and are ideal candidates for catalytic processes. Hybrid ab initio methods of quantum chemistry (particularly the DFT-B3LYP model) are used to derive optimal geometries for the clusters of interest. We compare calculated binding energies, bond-lengths, ionization potentials, electron affinities and HOMO-LUMO gaps for the clusters. Of particular interest are the comparisons of binding strengths at the three important types of sites: edge (E), hollow (H), on-top (T), threefold sites and fourfold sites. Effects of crystal symmetries corresponding to the bulk structures are investigated. The capacity of Pd clusters to adsorb H atoms will be compared to Ni clusters. Admixture with Pt atoms will also be considered.

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

    Science.gov (United States)

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

    2016-12-01

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

  16. A Nanowire-Based Plasmonic Quantum Dot Laser.

    Science.gov (United States)

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

    2016-04-13

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

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

    DEFF Research Database (Denmark)

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

    2000-01-01

    Semiconductor quantum dots, especially those formed by self-organized growth, are considered a promising material system for future optical devices [1] and the optical properties of quantum dot ensembles have been investigated in detail over the past years. Recently, considerable interest has dev...

  18. Transport through Zero-Dimensional States in a Quantum Dot

    NARCIS (Netherlands)

    Kouwenhoven, Leo P.; Wees, Bart J. van; Harmans, Kees J.P.M.; Williamson, John G.

    1990-01-01

    We have studied the electron transport through zero-dimensional (0D) states. 0D states are formed when one-dimensional edge channels are confined in a quantum dot. The quantum dot is defined in a two-dimensional electron gas with a split gate technique. To allow electronic transport, connection to

  19. Electron spin and charge in semiconductor quantum dots

    NARCIS (Netherlands)

    Elzerman, J.M.

    2004-01-01

    In this thesis, the spin and charge degree of freedom of electrons in semiconductor lateral and vertical quantum dots are experimentally investigated. The lateral quantum dot devices are defined in a two-dimensional electron gas (2DEG) below the surface of a GaAs/AlGaAs heterostructure, by metallic

  20. Exciton dephasing in single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    2000-01-01

    . The homogeneous and inhomogeneous broadening of InGaAs quantum dot luminescence is of central importance for the potential application of this material system in optoelectronic devices. Recent measurements of MOCVD-grown InAs/InGaAs quantum dots indicate a large homogeneous broadening at room temperature due...

  1. Negative Trions Trapped by a Spherical Parabolic Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this paper, a negatively charged exciton trapped by a spherical parabolic quantum dot has been investigated. The energy spectra of low-lying states are calculated by means of matrix diagonalization. The important feature of the low-lying states of the negatively charged excitons in a spherical quantum dot is obtained via an analysis of the energy spectra.

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

    DEFF Research Database (Denmark)

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

    2009-01-01

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

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

    DEFF Research Database (Denmark)

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

    2009-01-01

    Quantum dots are ideal probes for fluorescent imaging of vascular and lymphatic tissues. On injection into appropriate sites, red- and near-infrared-emitting quantum dots provide excellent definition of vasculature, lymphoid organs, and lymph nodes draining both normal tissues and tumors. We deta...

  4. Fast synthesize ZnO quantum dots via ultrasonic method.

    Science.gov (United States)

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

    2016-05-01

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

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

    NARCIS (Netherlands)

    Van der Wiel, W.G.

    2002-01-01

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

  6. Quantum computation with nuclear spins in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Christ, H.

    2008-01-24

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

  7. Gates controlled parallel-coupled bilayer graphene double quantum dot

    CERN Document Server

    Wang, Lin-Jun; Wei, Da; Cao, Gang; Tu, Tao; Xiao, Ming; Guo, Guang-Can; Chang, A M

    2011-01-01

    Here we report the fabrication and quantum transport measurements of gates controlled parallel-coupled bilayer graphene double quantum dot. It is shown that the interdot coupling strength of the parallel double dots can be effectively tuned from weak to strong regime by both the in-plane plunger gates and back gate. All the relevant energy scales and parameters of the bilayer graphene parallel-coupled double dot can be extracted from the honeycomb charge stability diagrams revealed through the transport measurements.

  8. Self-polarization in spherical quantum dot

    Directory of Open Access Journals (Sweden)

    Stojanović Dušanka P.

    2015-01-01

    Full Text Available The electronic structures of CdS quantum dot (QD with dielectric mismatch are calculated. Poisson equation is solved analitically in case of point charge placed inside semiconductor sphere embeded in dielectric matrix in case of different values of the dielectric permittivity of QD and matrix. The validity of the effective mass approximation for the conduction band is assumed. Schrödinger equation for one electron is solved analitically. On the basis of the Poisson equation solution self potential is examined and used as perturbation to calculate the self-polarization effect.

  9. Graphene Quantum Dots for Theranostics and Bioimaging.

    Science.gov (United States)

    Schroeder, Kathryn L; Goreham, Renee V; Nann, Thomas

    2016-10-01

    Since their advent in the early 1990s, nanomaterials hold promise to constitute improved technologies in the biomedical area. In particular, graphene quantum dots (GQDs) were conjectured to produce new or improve current methods used for bioimaging, drug delivery, and biomarker sensors for early detection of diseases. This review article critically compares and discusses current state-of-the-art use of GQDs in biology and health sciences. It shows the ability of GQDs to be easily functionalised for use as a targeted multimodal treatment and imaging platform. The in vitro and in vivo toxicity of GQDs are explored showing low toxicity for many types of GQDs.

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

    Science.gov (United States)

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-01-01

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

  11. Colloidal-quantum-dot spasers and plasmonic amplifiers

    CERN Document Server

    Kress, Stephan J P; Rohner, Patrik; Kim, David K; Antolinez, Felipe V; Zaininger, Karl-Augustin; Jayanti, Sriharsha V; Richner, Patrizia; McPeak, Kevin M; Poulikakos, Dimos; Norris, David J

    2016-01-01

    Colloidal quantum dots are robust, efficient, and tunable emitters now used in lighting, displays, and lasers. Consequently, when the spaser, a laser-like source of surface plasmons, was first proposed, quantum dots were specified as the ideal plasmonic gain medium. Subsequent spaser designs, however, have required a single material to simultaneously provide gain and define the plasmonic cavity, an approach ill-suited to quantum dots and other colloidal nanomaterials. Here we develop a more open architecture that decouples the gain medium from the cavity, leading to a versatile class of quantum-dot-based spasers that allow controlled generation, extraction, and manipulation of plasmons. We first create high-quality-factor, aberration-corrected, Ag plasmonic cavities. We then incorporate quantum dots via electrohydrodynamic printing18,19 or drop-casting. Photoexcitation under ambient conditions generates monochromatic plasmons above threshold. This signal is extracted, directed through an integrated amplifier,...

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

    Science.gov (United States)

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

    2015-02-01

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

  13. Second-harmonic imaging of semiconductor quantum dots

    DEFF Research Database (Denmark)

    Østergaard, John Erland; Bozhevolnyi, Sergey I.; Pedersen, Kjeld;

    2000-01-01

    Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of similar to 885 nm corresponding to the quantum-dot photoluminescence maximum....... In addition, the second-harmonic spectrum exhibits another smaller but well-pronounced peak at 765 nm not found in the linear experiments. We attribute this peak to the generation of second-harmonic radiation in the AlGaAs spacer layer enhanced by the local symmetry at the quantum-dot interface. We further...... observe that second-harmonic images of the quantum-dot surface structure show wavelength-dependent spatial variations. Imaging at different wavelength is used to demonstrate second-harmonic generation from the semiconductor quantum dots. (C) 2000 American Institute of Physics....

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

    Science.gov (United States)

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

    2014-06-21

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

  15. LUMINESCENCE OF CADMIUM SULFIDE QUANTUM DOTS IN FLUOROPHOSPHATE GLASSES

    Directory of Open Access Journals (Sweden)

    Z. O. Lipatova

    2015-03-01

    Full Text Available Cadmium sulfide quantum dots are perspective materials in optics, medicine, biology and optoelectronics. Fluorophosphate glasses, doped with cadmium sulfide quantum dots, were examined in the paper. Heat treatment led to the formation of quantum dots with diameters equal to 2.8 nm, 3.0 nm and 3.8 nm. In view of such changes in the quantum dots size the fundamental absorption edge shift and the luminescence band are being displaced to the long wavelengths. Luminescence lifetime has been found to be dependent on the registration wavelength in the range from 450 to 700 nm. Obtained fluorophosphate glasses with CdS quantum dots can find their application as fluorescent materials with intensive luminescence band and long excited-state natural lifetime.

  16. Interaction of porphyrins with CdTe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-05-13

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

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

    OpenAIRE

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

    2013-01-01

    Quantum dots embedded within nanowires represent one of the most promising technologies for applications in quantum photonics. Whereas the top-down fabrication of such structures remains a technological challenge, their bottom-up fabrication through self-assembly is a potentially more powerful strategy. However, present approaches often yield quantum dots with large optical linewidths, making reproducibility of their physical properties difficult. We present a versatile quantum-dot-innanowire...

  18. Templated self-assembly of SiGe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Dais, Christian

    2009-08-19

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

  19. The Electron-Hole Pair in a Single Quantum Dot and That in a Vertically Coupled Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    XIEWen-Fang; ZHUWu

    2003-01-01

    The energy spectra of low-lying states of an exciton in a single and a vertically coupled quantum dots are studied under the influence of a perpendicularly applied magnetic field. Calculations are made by using the method of numerical diagonalization of the Hamiltonian within the effective-mass approximation. We also calculated the binding energy of the ground and the excited states of an exciton in a single quantum dot and that in a vertically coupled quantum dot as a function of the dot radius for different vaJues of the distance and the magnetic field strength.

  20. Quantum transport in semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kubis, Tillmann Christoph

    2009-11-15

    The main objective of this thesis is to theoretically predict the stationary charge and spin transport in mesoscopic semiconductor quantum devices in the presence of phonons and device imperfections. It is well known that the nonequilibrium Green's function method (NEGF) is a very general and all-inclusive scheme for the description of exactly this kind of transport problem. Although the NEGF formalism has been derived in the 1960's, textbooks about this formalism are still rare to find. Therefore, we introduce the NEGF formalism, its fundamental equations and approximations in the first part of this thesis. Thereby, we extract ideas of several seminal contributions on NEGF in literature and augment this by some minor derivations that are hard to find. Although the NEGF method has often been numerically implemented on transport problems, all current work in literature is based on a significant number of approximations with often unknown influence on the results and unknown validity limits. Therefore, we avoid most of the common approximations and implement in the second part of this thesis the NEGF formalism as exact as numerically feasible. For this purpose, we derive several new scattering self-energies and introduce new self-adaptive discretizations for the Green's functions and self-energies. The most important improvements of our NEGF implementation, however, affect the momentum and energy conservation during incoherent scattering, the Pauli blocking, the current conservation within and beyond the device and the reflectionless propagation through open device boundaries. Our uncommonly accurate implementation of the NEGF method allows us to analyze and assess most of the common approximations and to unveil numerical artifacts that have plagued previous approximate implementations in literature. Furthermore, we apply our numerical implementation of the NEGF method on the stationary electron transport in THz quantum cascade lasers (QCLs) and answer

  1. Biosensing with Luminescent Semiconductor Quantum Dots

    Directory of Open Access Journals (Sweden)

    Hedi Mattoussi

    2006-08-01

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

  2. Semiconductor Quantum Dots for Biomedicial Applications

    Science.gov (United States)

    Shao, Lijia; Gao, Yanfang; Yan, Feng

    2011-01-01

    Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can be used as labels for the electrochemical detection of DNA or proteins. This article reviews the synthesis and toxicity of QDs and their optical and electrochemical bioanalytical applications. Especially the application of QDs in biomedicine such as delivering, cell targeting and imaging for cancer research, and in vivo photodynamic therapy (PDT) of cancer are briefly discussed. PMID:22247690

  3. Semiconductor quantum dot-sensitized solar cells.

    Science.gov (United States)

    Tian, Jianjun; Cao, Guozhong

    2013-10-31

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

  4. Semiconductor quantum dot-sensitized solar cells

    Directory of Open Access Journals (Sweden)

    Jianjun Tian

    2013-10-01

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

  5. Electron states in semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Dhayal, Suman S., E-mail: ssdhayal@gmail.com [Department of Physics, University of North Texas, P.O. Box 311427, Denton, Texas 76203 (United States); Ramaniah, Lavanya M., E-mail: lavanya@barc.gov.in [High Pressure and Synchrotron Radiation Physics Division, Physics Group, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Ruda, Harry E.; Nair, Selvakumar V., E-mail: selva.nair@utoronto.ca [Centre for Nanotechnology, University of Toronto, 170 College Street, Toronto, Ontario M5S 3E3 (Canada)

    2014-11-28

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

  6. Silicon quantum dots for biological applications.

    Science.gov (United States)

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

    2014-01-01

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

  7. Coherent spin dynamics in semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Amand, T.; Senes, M.; Marie, X.; Renucci, P. [Laboratoire de Nanophysique, Magnetisme et Optoelectronique-LPMC, INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Urbaszek, B. [Laboratoire de Nanophysique, Magnetisme et Optoelectronique-LPMC, INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Department of Physics, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Krebs, O.; Laurent, S.; Voisin, P. [Laboratoire de Photonique et Nanostructures, route de Nozay, 91460 Marcoussis (France); Warburton, R.J. [Department of Physics, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)

    2005-05-01

    The anisotropic exchange interaction (AEI) between electrons and holes is shown to play a central role in quantum dots (QDs) spin dynamics. In neutral QDs, AEI is at the origin of spin quantum beats observed under resonant excitation between the lowest energy doublet of linearly dipole-active eigenstates. In negatively charged QDs, AEI is at the origin of QD emission with opposite helicity to the optic al excitation, under non-resonant excitation conditions. Finally, the possibility of leaving a spin information in the system after recombination of the photo-injected electron-hole pair is discussed with respect to the type and the level of the doping. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Andreev molecules in semiconductor nanowire double quantum dots.

    Science.gov (United States)

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

    2017-09-19

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

  9. Interference and interactions in open quantum dots

    CERN Document Server

    Bird, J P; Ferry, D K; Moura, A P S; Lai, Y C; Indlekofer, K M

    2003-01-01

    In this report, we review the results of our joint experimental and theoretical studies of electron-interference, and interaction, phenomena in open electron cavities known as quantum dots. The transport through these structures is shown to be heavily influenced by the remnants of their discrete density of states, elements of which remain resolved in spite of the strong coupling that exists between the cavity and its reservoirs. The experimental signatures of this density of states are discussed at length in this report, and are shown to be related to characteristic wavefunction scarring, involving a small number of classical orbits. A semiclassical analysis of this behaviour shows it to be related to the effect of dynamical tunnelling, in which electrons are injected into the dot tunnel through classically forbidden regions of phase space, to access isolated regular orbits. The dynamical tunnelling gives rise to the formation of long-lived quasi-bound states in the open dots, and the many-body implications a...

  10. Semiconductor Nanostructures Quantum States and Electronic Transport

    CERN Document Server

    Ihn, Thomas

    2009-01-01

    This textbook describes the physics of semiconductor nanostructures with emphasis on their electronic transport properties. At its heart are five fundamental transport phenomena: quantized conductance, tunnelling transport, the Aharonov-Bohm effect, the quantum Hall effect, and the Coulomb blockade effect. The book starts out with the basics of solid state and semiconductor physics, such as crystal structure, band structure, and effective mass approximation, including spin-orbit interaction effects important for research in semiconductor spintronics. It contains material aspects such as band e

  11. Mn-doped Ge self-assembled quantum dots via dewetting of thin films

    Science.gov (United States)

    Aouassa, Mansour; Jadli, Imen; Bandyopadhyay, Anup; Kim, Sung Kyu; Karaman, Ibrahim; Lee, Jeong Yong

    2017-03-01

    In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO2 thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO2 thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.

  12. Electrons, holes, and excitons in superlattice of cylindrical quantum dots with weakest coupling of quasiparticles between quantum dots layers

    CERN Document Server

    Tkach, N V; Zegrya, G G

    2002-01-01

    The theoretical investigation of the spectrum of electrons, holes, and excitons in the superlattice of cylindrical quantum dots with weakest coupling of quasiparticles between vertical layers of quantum dots is carried out. The calculations are fulfilled by the example of cylindrical quantum dots of beta-HgS introduced into beta-CdS as the superlattice. It is shown that electron and hole in such system form quasi-two-dimensional energy minibands, but excitons are described by the Sugano-Shinada model. The dependence of quasiparticle spectra on geometric parameters of the superlattice with cylindrical quantum dots is studied. It is shown that the position of minibands of all quasiparticles is very sensitive to variation of the quantum dot height

  13. Using quantum dot photoluminescence for load detection

    Science.gov (United States)

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

    2016-08-01

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

  14. Colloidal quantum dot light-emitting devices

    Directory of Open Access Journals (Sweden)

    Vanessa Wood

    2010-07-01

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

  15. Study of metallothionein-quantum dots interactions.

    Science.gov (United States)

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

    2014-05-01

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

  16. Quantum dot imaging for embryonic stem cells

    Directory of Open Access Journals (Sweden)

    Gambhir Sanjiv S

    2007-10-01

    Full Text Available Abstract Background Semiconductor quantum dots (QDs hold increasing potential for cellular imaging both in vitro and in vivo. In this report, we aimed to evaluate in vivo multiplex imaging of mouse embryonic stem (ES cells labeled with Qtracker delivered quantum dots (QDs. Results Murine embryonic stem (ES cells were labeled with six different QDs using Qtracker. ES cell viability, proliferation, and differentiation were not adversely affected by QDs compared with non-labeled control cells (P = NS. Afterward, labeled ES cells were injected subcutaneously onto the backs of athymic nude mice. These labeled ES cells could be imaged with good contrast with one single excitation wavelength. With the same excitation wavelength, the signal intensity, defined as (total signal-background/exposure time in millisecond was 11 ± 2 for cells labeled with QD 525, 12 ± 9 for QD 565, 176 ± 81 for QD 605, 176 ± 136 for QD 655, 167 ± 104 for QD 705, and 1,713 ± 482 for QD 800. Finally, we have shown that QD 800 offers greater fluorescent intensity than the other QDs tested. Conclusion In summary, this is the first demonstration of in vivo multiplex imaging of mouse ES cells labeled QDs. Upon further improvements, QDs will have a greater potential for tracking stem cells within deep tissues. These results provide a promising tool for imaging stem cell therapy non-invasively in vivo.

  17. Using quantum dot photoluminescence for load detection

    Energy Technology Data Exchange (ETDEWEB)

    Moebius, M., E-mail: martin.moebius@zfm.tu-chemnitz.de; Hartwig, M. [Technische Universität Chemnitz, Reichenhainer Straße, 09126 Chemnitz (Germany); Martin, J. [Fraunhofer Institute for Electronic Nano Systems, Technologie-Campus 3, 09126 Chemnitz (Germany); Baumann, R. R.; Otto, T.; Gessner, T. [Technische Universität Chemnitz, Reichenhainer Straße, 09126 Chemnitz (Germany); Fraunhofer Institute for Electronic Nano Systems, Technologie-Campus 3, 09126 Chemnitz (Germany)

    2016-08-15

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

  18. Using quantum dot photoluminescence for load detection

    Directory of Open Access Journals (Sweden)

    M. Moebius

    2016-08-01

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

  19. Polymersomes containing quantum dots for cellular imaging

    Directory of Open Access Journals (Sweden)

    Camblin M

    2014-05-01

    Full Text Available Marine Camblin,1 Pascal Detampel,1 Helene Kettiger,1 Dalin Wu,2 Vimalkumar Balasubramanian,1,* Jörg Huwyler1,*1Division of Pharmaceutical Technology, 2Department of Chemistry, University of Basel, Basel, Switzerland*These authors contributed equally to this workAbstract: Quantum dots (QDs are highly fluorescent and stable probes for cellular and molecular imaging. However, poor intracellular delivery, stability, and toxicity of QDs in biological compartments hamper their use in cellular imaging. To overcome these limitations, we developed a simple and effective method to load QDs into polymersomes (Ps made of poly(dimethylsiloxane-poly(2-methyloxazoline (PDMS-PMOXA diblock copolymers without compromising the characteristics of the QDs. These Ps showed no cellular toxicity and QDs were successfully incorporated into the aqueous compartment of the Ps as confirmed by transmission electron microscopy, fluorescence spectroscopy, and fluorescence correlation spectroscopy. Ps containing QDs showed colloidal stability over a period of 6 weeks if stored in phosphate-buffered saline (PBS at physiological pH (7.4. Efficient intracellular delivery of Ps containing QDs was achieved in human liver carcinoma cells (HepG2 and was visualized by confocal laser scanning microscopy (CLSM. Ps containing QDs showed a time- and concentration-dependent uptake in HepG2 cells and exhibited better intracellular stability than liposomes. Our results suggest that Ps containing QDs can be used as nanoprobes for cellular imaging.Keywords: quantum dots, polymersomes, cellular imaging, cellular uptake

  20. Quantum transport in semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kubis, Tillmann Christoph

    2009-11-15

    The main objective of this thesis is to theoretically predict the stationary charge and spin transport in mesoscopic semiconductor quantum devices in the presence of phonons and device imperfections. It is well known that the nonequilibrium Green's function method (NEGF) is a very general and all-inclusive scheme for the description of exactly this kind of transport problem. Although the NEGF formalism has been derived in the 1960's, textbooks about this formalism are still rare to find. Therefore, we introduce the NEGF formalism, its fundamental equations and approximations in the first part of this thesis. Thereby, we extract ideas of several seminal contributions on NEGF in literature and augment this by some minor derivations that are hard to find. Although the NEGF method has often been numerically implemented on transport problems, all current work in literature is based on a significant number of approximations with often unknown influence on the results and unknown validity limits. Therefore, we avoid most of the common approximations and implement in the second part of this thesis the NEGF formalism as exact as numerically feasible. For this purpose, we derive several new scattering self-energies and introduce new self-adaptive discretizations for the Green's functions and self-energies. The most important improvements of our NEGF implementation, however, affect the momentum and energy conservation during incoherent scattering, the Pauli blocking, the current conservation within and beyond the device and the reflectionless propagation through open device boundaries. Our uncommonly accurate implementation of the NEGF method allows us to analyze and assess most of the common approximations and to unveil numerical artifacts that have plagued previous approximate implementations in literature. Furthermore, we apply our numerical implementation of the NEGF method on the stationary electron transport in THz quantum cascade lasers (QCLs) and answer

  1. Using a quantum dot system to realize perfect state transfer

    Institute of Scientific and Technical Information of China (English)

    Li Ji; Wu Shi-Hai; Zhang Wen-Wen; Xi Xiao-Qiang

    2011-01-01

    There are some disadvantages to Nikolopoulos et al.'s protocol [Nikolopoulos G M,Petrosyan D and Lambropoulos P 2004 Europhys.Lett.65 297] where a quantum dot system is used to realize quantum communication.To overcome these disadvantages,we propose a protocol that uses a quantum dot array to construct a four-qubit spin chain to realize perfect quantum state transfer (PQST).First,we calculate the interaction relation for PQST in the spin chain.Second,we review the interaction between the quantum dots in the Heitler-London approach.Third,we present a detailed program for designing the proper parameters of a quantum dot array to realize PQST.

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

    Science.gov (United States)

    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.

  3. Charge-extraction strategies for colloidal quantum dot photovoltaics

    KAUST Repository

    Lan, Xinzheng

    2014-02-20

    The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p-and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction. © 2014 Macmillan Publishers Limited.

  4. Quantum Electrodynamics of Quantum Dot-Metal Nanoparticles Molecules

    CERN Document Server

    Ridolfo, A; Fina, N; Saija, R; Savasta, S

    2010-01-01

    We study theoretically the quantum optical properties of hybrid molecules composed of an individual quantum dot and a metallic nanoparticle. We calculate the resonance fluorescence of this hybrid system. Its incoherent part, the one arising from nonlinear quantum processes, results to be enhanced by more than two orders of magnitude as compared to that in the absence of the metallic nanoparticle. Scattering spectra at different excitation powers and nonperturbative calculations of intensity-field correlation functions show that this system can act as a nonlinear ultra-compact two-photon switch for incident photons, where the presence (or absence) of a single incident photon field is sufficient to allow (or prevent) the scattering of subsequent photons. We also find that a small frequency shift of the incident light field may cause changes in the intensity field correlation function of orders of magnitude.

  5. Virtual photonic couplings of quantum nanostructures

    DEFF Research Database (Denmark)

    Matsueda, H.; Hvam, Jørn Märcher; Ducommun, Yann;

    scheme into physics of solids, mainly because the range of the mediating photon was not long enough to cover the distance of usual concerns, e.g. size of devices in conventional integrated circuits. However, this retardation should be lifted not just to improve our understanding, but to refine our...... nanotechnology on the basis of what is really happening in the nanostructures. Therefore, we have first focused on dipole-dipole interaction, especially the resonance dynamic dipole- dipole interaction (RDDDI) among transition dipoles, publishing on the generation of an intrinsic nonlinear localized mode......, we illustrate more general resonance dynamic multipole-multipole interactions (RDMMIs) by plotting the interaction energy and range as a function of inter-polar distance, see Fig. 2 [4]. This RDMMI should inevitably appear in the course of realizing quantum information devices such as quantum...

  6. Single-photon superradiance from a quantum dot

    DEFF Research Database (Denmark)

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

    2016-01-01

    We report on the observation of single-photon superradiance from an exciton in a semiconductor quantum dot. The confinement by the quantum dot is strong enough for it to mimic a two-level atom, yet sufficiently weak to ensure superradiance. The electrostatic interaction between the electron...... temperature of our cryostat and may lead to oscillator strengths above 1000 from a single quantum emitter at optical frequencies....

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

    DEFF Research Database (Denmark)

    Chen, Yaohui; Öhman, Filip; Mørk, Jesper

    2008-01-01

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

  8. RKKY interaction in a chirally coupled double quantum dot system

    Energy Technology Data Exchange (ETDEWEB)

    Heine, A. W.; Tutuc, D.; Haug, R. J. [Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2, 30167 Hannover (Germany); Zwicknagl, G. [Institut für Mathematische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig (Germany); Schuh, D. [Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätstr. 31, 93053 Regensburg (Germany); Wegscheider, W. [Laboratorium für Festkörperphysik, ETH Zürich, Schafmattstr. 16, 8093 Zürich, Switzerland and Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätstr. 31, 93053 Regens (Germany)

    2013-12-04

    The competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is investigated in a double quantum dots system, coupled via a central open conducting region. A perpendicular magnetic field induces the formation of Landau Levels which in turn give rise to the so-called Kondo chessboard pattern in the transport through the quantum dots. The two quantum dots become therefore chirally coupled via the edge channels formed in the open conducting area. In regions where both quantum dots exhibit Kondo transport the presence of the RKKY exchange interaction is probed by an analysis of the temperature dependence. The thus obtained Kondo temperature of one dot shows an abrupt increase at the onset of Kondo transport in the other, independent of the magnetic field polarity, i.e. edge state chirality in the central region.

  9. Optical and micro-structural characterizations of MBE grown indium gallium nitride polar quantum dots

    KAUST Repository

    Elafandy, Rami T.

    2011-12-01

    Comparison between indium rich (27%) InGaN/GaN quantum dots (QDs) and their underlying wetting layer (WL) is performed by means of optical and structural characterizations. With increasing temperature, micro-photoluminescence (μPL) study reveals the superior ability of QDs to prevent carrier thermalization to nearby traps compared to the two dimensional WL. Thus, explaining the higher internal quantum efficiency of the QD nanostructure compared to the higher dimensional WL. Structural characterization (X-ray diffraction (XRD)) and transmission electron microscopy (TEM)) reveal an increase in the QD indium content over the WL indium content which is due to strain induced drifts. © 2011 IEEE.

  10. Population Dynamics and the Optical Absorption in Hybrid Metal Nanoparticle - Semiconductor Quantum dot Nanosystem

    CERN Document Server

    Kim, Nam-Chol; Ko, Myong-Chol; So, Guang Hyok; Kim, Il-Guang

    2015-01-01

    We studied theoretically the population dynamics and the absorption spectrum of hybrid nanosystem consisted of a matal nanoparticle (MNP) and a semiconductor quantum dot(SQD). We investigated the exciton-plasmon coupling effects on the population dynamics and the absorption properties of the nanostructure. Our results show that the nonlinear optical response of the hybrid nanosystem can be greatly enhanced or depressed due to the exciton-plasmon couplings. The results obtained here may have the potential applications of nanoscale optical devices such as optical switches and quantum devices such as a single photon transistor.

  11. Quantum fluctuations in semiconductor quantum dots and their contributions to the self-energy functions of exciton states

    Science.gov (United States)

    Mutygullina, A. A.; Khamadeev, M. A.; Blum, D. O.; Shirdelhavar, A. H.

    2017-06-01

    Influence of quantum fluctuations in a system consisting of a quantum dot and the reservoir of acoustic phonons on processes in which the quantum dot takes part is investigated. Under some conditions this influence is shown to be very strong. We find a contribution from the quantum fluctuations to the self-energy function of the exciton coupled to the quantum dot.

  12. Spins of Andreev states in double quantum dots

    Science.gov (United States)

    Su, Zhaoen; Chen, Jun; Yu, Peng; Hocervar, Moira; Plissard, Sebastien; Car, Diana; Tacla, Alexandre; Daley, Andrew; Pekker, David; Bakkers, Erik; Frolov, Sergey

    Andreev (or Shiba) states in coupled double quantum dots is an open field. Here we demonstrate the realization of Andreev states in double quantum dots in an InSb nanowire coupled to two NbTiN superconductors. The magnetic field dependence of the Andreev states has been explored to resolve the spins in different double dot configurations. The experiment helps to understand the interplay between pair correlation, exchange energy and charging energy with a well-controlled system. It also opens the possibility to implement Majorana modes in Kitaev chains made of such dots.

  13. Quantum dot-induced viral capsid assembling in dissociation buffer

    Directory of Open Access Journals (Sweden)

    Gao D

    2013-06-01

    Full Text Available Ding Gao,1,2 Zhi-Ping Zhang,1 Feng Li,3 Dong Men,1 Jiao-Yu Deng,1 Hong-Ping Wei,1 Xian-En Zhang,1 Zong-Qiang Cui1 1State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 2Graduate University of Chinese Academy of Sciences, Beijing, 3Division of Nanobiomedicine and i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, People's Republic of China Abstract: Viruses encapsulating inorganic nanoparticles are a novel type of nanostructure with applications in biomedicine and biosensors. However, the encapsulation and assembly mechanisms of these hybridized virus-based nanoparticles (VNPs are still unknown. In this article, it was found that quantum dots (QDs can induce simian virus 40 (SV40 capsid assembly in dissociation buffer, where viral capsids should be disassembled. The analysis of the transmission electron microscope, dynamic light scattering, sucrose density gradient centrifugation, and cryo-electron microscopy single particle reconstruction experimental results showed that the SV40 major capsid protein 1 (VP1 can be assembled into ≈25 nm capsids in the dissociation buffer when QDs are present and that the QDs are encapsulated in the SV40 capsids. Moreover, it was determined that there is a strong affinity between QDs and the SV40 VP1 proteins (KD = 2.19E-10 M, which should play an important role in QD encapsulation in the SV40 viral capsids. This study provides a new understanding of the assembly mechanism of SV40 virus-based nanoparticles with QDs, which may help in the design and construction of other similar virus-based nanoparticles. Keywords: quantum dots, simian virus 40, self-assembly, encapsulation, virus-based nanoparticles

  14. Quantum dot density studies for quantum dot intermediate band solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Thomassen, Sedsel Fretheim; Zhou, Dayong; Vitelli, Stefano; Mayani, Maryam Gholami; Fimland, Bjoern-Ove; Reenaas, Turid Worren

    2010-07-01

    Quantum dots (QDs) have been an active area of research for many years and have been implemented in several applications, such as lasers and detectors. During the last years, some attempts have been made to increase the absorption and efficiency of solar cells by inserting QDs into the intrinsic region of pin solar cells. So far, these attempts have been successful in increasing the absorption, but not the cell efficiency. There are probably several reasons for this lack of efficiency increase, but we believe that one important reason is the low density of the implemented QDs. In this work, samples of single layer InAs QDs on n-GaAs(001) substrates have been grown by molecular beam epitaxy (MBE) and we have performed a systematic study of how deposition parameters affect the QD density. The aim is to achieve densities > 1011 cm-2. The nominal substrate temperature (360 - 500 deg. C), the InAs growth rate (0.085 - 1 ML/s) and thickness (2.0 - 2.8 ML) have been varied in a systematic way for two different deposition methods of InAs, i.e. continuous deposition or deposition with interruptions. In addition, we have for the continuous growth samples also varied the As-flux (0.5 - 6 centre dot10-6 torr). Scanning electron microscopy (SEM) has been the main characterization method to determine quantum dot sizes and densities, and atomic force microscopy (AFM) has been used for evaluation of the quantum dot heights. We find that the QD density increases with reduced growth temperature and that it is higher for samples grown continuously than for samples grown with growth interruptions. The homogeneity is also strongly affected by temperature, InAs deposition method and the As-flux. We have observed QD densities as high as 2.5 centre dot1011 cm-2 for the samples grown at the lowest growth temperatures. (Author)

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

    Science.gov (United States)

    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.

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

    DEFF Research Database (Denmark)

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

    2010-01-01

    We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled In(Ga)As quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD.......1±2.6 and an encouragingly high QE of (48±14)% for the SCQDs....

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

    NARCIS (Netherlands)

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

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

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

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

    DEFF Research Database (Denmark)

    Grodecka-Grad, Anna; Foerstner, Jens

    2011-01-01

    We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantum kinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual...... processes with relevant acoustic phonons. We show that the relaxation is dominated by phonon-assisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between...... the quantum dots is studied in detail. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)...

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

    Science.gov (United States)

    Winslow, Lindley; Conrad, Janet; Jerry, Ruel

    2010-02-01

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

  1. Photolithographic process for the patterning of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Na, Young Joo; Park, Sang Joon; Lee, Sang Wha [Department of Chemical and Bioengineering, Kyungwon University, Seongnam-si, Gyeonggi-Do 461-701 (Korea, Republic of); Kim, Jong Sung [Department of Chemical and Bioengineering, Kyungwon University, Seongnam-si, Gyeonggi-Do 461-701 (Korea, Republic of)], E-mail: jskim@kyungwon.ac.kr

    2008-09-15

    Recently, quantum dots have been used as molecular probes substituting for conventional organic fluorophores. Quantum dots are stable against photobleaching and have more controllable emission bands, broader absorption spectra, and higher quantum yields. In this study, an array of ZnS-coated CdSe quantum dots on a slide glass has been prepared by photolithographic method. The array pattern was prepared using a positive photoresist (AZ1518) and developer (AZ351). The patterned glass was silanized with 3-aminopropyltriethoxysilane (APTES), and carboxyl-coated quantum dots were selectively attached onto the array pattern. The silanization was examined by measuring contact angle and the surface of the array pattern was analyzed using AFM and fluorescent microscope.

  2. Linewidth broadening of a quantum dot coupled to an off-resonant cavity

    CERN Document Server

    Majumdar, Arka; Kim, Erik; Englund, Dirk; Kim, Hyochul; Petroff, Pierre; Vuckovic, Jelena

    2010-01-01

    We study the coupling between a photonic crystal cavity and an off-resonant quantum dot under resonant excitation of the cavity or the quantum dot. Linewidths of the quantum dot and the cavity as a function of the excitation laser power are measured. We show that the linewidth of the quantum dot, measured by observing the cavity emission, is significantly broadened compared to the theoretical estimate. This indicates additional incoherent coupling between the quantum dot and the cavity.

  3. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... is obtained by exciting and detecting the photoluminescence through a microscope objective which is located inside the cryostat. Furthermore, e-beam lithography and mesa etching have been used to reduce the size of the detection area to a few hundred nanometers in diameter. These techniques allow us...

  4. Second Bound State of Biexcitons in Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Eang

    2003-01-01

    The second bound state of the biexcitons in a quantum dot, with orbital angular momentum L = 1, is reported. By using the method of few-body physics, the binding energy spectra of the second bound state of a biexciton in a GaAs quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio and the quantum dot size. The fact that the biexcitons have a second bound state may aid in the better understanding of their binding mechanism.

  5. Kondo effect in quantum dots and molecular devices

    Institute of Scientific and Technical Information of China (English)

    JIANG Lang; LI Hongxiang; HU Wenping; ZHU Daoben

    2005-01-01

    Kondo effect is a very important many-body phenomenon in condensed matter physics,which explains why the resistance increases as the temperature is lowered (usually <10 K) in dilute magnetic alloy, and why the conductance increases as temperature is decreased in quantum dots. This paper simply introduces equilibrium and non- equilibrium Kondo effects in quantum dots together with the Kondo effect in quantum dots with even number of electrons (when the singlet and triplet states are degenerate). Furthermore, Kondo effect in single atom/molecular transistors is introduced, which indicates a new way to study Kondo effect.

  6. Thermal Rectification Effect of an Interacting Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    CHEN Xue-Ou; DONG Bing; LEI Xiao-Lin

    2008-01-01

    @@ We investigate the nonlinear thermal transport properties of a single interacting quantum dot with two energy levels tunnel-coupled to two electrodes using nonequilibrium Green function method and Hartree-Fock decoupling approximation. In the case of asymmetric tunnel-couplings to two electrodes, for example, when the upper level of the quantum dot is open for transport, whereas the lower level is blocked, our calculations predict a strong asymmetry for the heat (energy) current, which shows that the quantum dot system may act as a thermal rectifier in this specific situation.

  7. Quantum dot doped solid polymer electrolyte for device application

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Pramod K.; Kim, Kang Wook; Rhee, Hee-Woo [Department of Chemical and Biomolecular Engineering, Sogang University, Mapo-Gu, Seoul 121-742 (Korea)

    2009-06-15

    ZnS capped CdSe quantum dots embedded in PEO:KI:I{sub 2} polymer electrolyte matrix have been synthesized and characterized for dye sensitized solar cell (DSSC) application. The complex impedance spectroscopy shows enhance in ionic conductivity ({sigma}) due to charges provide by quantum dots (QD) while AFM affirm the uniform distribution of QD into polymer electrolyte matrix. Cyclic voltammetry revealed the possible interaction between polymer electrolyte, QD and iodide/iodine. The photovoltaic performances of the DSSC containing quantum dots doped polymer electrolyte was also found to improve. (author)

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

    Science.gov (United States)

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

    2016-02-01

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

  9. Emission redistribution from a quantum dot-bowtie nanoantenna

    OpenAIRE

    Regler, A.; Schraml, K.; Lyamkina, A.; Spiegl, M; Müller, K.; Vuckovic, J.; Finley, J. J.; Kaniber, M.

    2016-01-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby ($\\sim 25nm$) plasmonic antenna. Micro-photoluminescence spectroscopy shows a $\\sim 2.4\\times$ 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 $2.5\\mu W$ for both coupled and uncoupled quantum dot emission in polarization-resolved me...

  10. Graphene mediated Stark shifting of quantum dot energy levels

    Science.gov (United States)

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

    2016-05-01

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

  11. Semiconductor Quantum Dots in Chemical Sensors and Biosensors

    Directory of Open Access Journals (Sweden)

    Nikos Chaniotakis

    2009-09-01

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

  12. Imaging GABAc Receptors with Ligand-Conjugated Quantum Dots

    Directory of Open Access Journals (Sweden)

    Ian D. Tomlinson

    2007-01-01

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

  13. Infrared Focal Plane Arrays Based on Semiconductor Quantum Dots

    Science.gov (United States)

    2002-01-01

    studied in the framework of this, including the collaborating researchers in each of them, are detailed below: 1. “Ultra Small InAs/GaInP/ InP Quantum Dots ”: with...of detectors, which will be attached to Si based signal processors. D:\\FINAL REPORT.doc 4 Part 1 Ultra Small InAs/GaInP/ InP Quantum Dots The heights of...an ensemble of self-assembled InAs/GaAs or InAs/ InP quantum dots (QDs) are typically in the range of 10-30 monolayers [1]. Here, we report on InAs

  14. Temperature Studies of Single InP Quantum Dots

    Science.gov (United States)

    1999-06-18

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP012858 TITLE: Temperature Studies of Single InP Quantum Dots DISTRIBUTION...34 QWR/QD.07 St Petersburg, Russia, June 14-18, 1999 © 1999 loffe Institute Temperature studies of single InP quantum dots Valdry Zwiller, Mats-Erik...Information on the size and geometry of our self-assembled InP Quantum Dots grown on GamnP lattice matched to GaAs has been published elsewhere -I

  15. Solvothermal synthesis of InP quantum dots.

    Science.gov (United States)

    Nag, Angshuman; Sarma, D D

    2009-09-01

    We report an efficient and fast solvothermal route to prepare highly crystalline monodispersed InP quantum dots. This solvothermal route, not only ensures inert atmosphere, which is strictly required for the synthesis of phase pure InP quantum dots but also allows a reaction temperature as high as 430 degrees C, which is otherwise impossible to achieve using a typical solution chemistry; the higher reaction temperature makes the reaction more facile. This method also has a judicious control over the size of the quantum dots and thus in tuning the bandgap.

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

    Science.gov (United States)

    DeHaven, Stan; Williams, Phillip; Burke, Eric

    2015-01-01

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

  17. PL Emission and Shape of Silicon Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-0-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet. The red-shifting of PL spectra on smaller silicon quantum dots can be explained by curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided in curved surface effect.About The Author: Zhong-Mei Huang,Master in Guizhou University.

  18. Quantum Dot-Photonic Crystal Cavity QED Based Quantum Information Processing

    Science.gov (United States)

    2012-08-14

    Physical Review A, 2012] 3. Study of the off-resonant quantum dot-cavity coupling in solid-state cavity QED system, and the phonon mediated off...resonant interaction between two quantum dots [Majumdar et al., Physical Review B , 2012] 4. Coherent optical spectroscopy of a single quantum dot via an off...Resonant cavity - much simpler than in conventional approaches [Majumdar et al, Physical Review B, 2011; Papageorge et al., New. Journal of Physics

  19. Emissive ZnO-graphene quantum dots for white-light-emitting diodes.

    Science.gov (United States)

    Son, Dong Ick; Kwon, Byoung Wook; Park, Dong Hee; Seo, Won-Seon; Yi, Yeonjin; Angadi, Basavaraj; Lee, Chang-Lyoul; Choi, Won Kook

    2012-05-27

    Hybrid nanostructures combining inorganic materials and graphene are being developed for applications such as fuel cells, batteries, photovoltaics and sensors. However, the absence of a bandgap in graphene has restricted the electrical and optical characteristics of these hybrids, particularly their emissive properties. Here, we use a simple solution method to prepare emissive hybrid quantum dots consisting of a ZnO core wrapped in a shell of single-layer graphene. We then use these quantum dots to make a white-light-emitting diode with a brightness of 798 cd m(-2). The strain introduced by curvature opens an electronic bandgap of 250 meV in the graphene, and two additional blue emission peaks are observed in the luminescent spectrum of the quantum dot. Density functional theory calculations reveal that these additional peaks result from a splitting of the lowest unoccupied orbitals of the graphene into three orbitals with distinct energy levels. White emission is achieved by combining the quantum dots with other emissive materials in a multilayer light-emitting diode.

  20. The Electron-Hole Pair in a Single Quantum Dot and That in a Vertically Coupled Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang; ZHU Wu

    2003-01-01

    The energy spectra of low-lying states of an exciton in a single and a vertically coupled quantum dots arestudied under the influence of a perpendicularly applied magnetic field. Calculations are made by using the method ofnumerical diagonalization of the Hamiltonian within the effective-mass approximation. We also calculated the bindingenergy of the ground and the excited states of an exciton in a single quantum dot and that in a vertically coupledquantum dot as a function of the dot radius for different values of the distance and the magnetic field strength.

  1. Quantum computation in a quantum-dot-Majorana-fermion hybrid system

    CERN Document Server

    Xue, Zheng-Yuan

    2012-01-01

    We propose a scheme to implement universal quantum computation in a quantum-dot-Majorana-fermion hybrid system. Quantum information is encoded on pairs of Majorana fermions, which live on the the interface between topologically trivial and nontrivial sections of a quantum nanowire deposited on an s-wave superconductor. Universal single-qubit gates on topological qubit can be achieved. A measurement-based two-qubit Controlled-Not gate is produced with the help of parity measurements assisted by the quantum-dot and followed by prescribed single-qubit gates. The parity measurement, on the quantum-dot and a topological qubit, is achieved by the Aharonov- Casher effect.

  2. Single-photon emission from electrically driven InP quantum dots epitaxially grown on CMOS-compatible Si(001)

    Science.gov (United States)

    Wiesner, M.; Schulz, W.-M.; Kessler, C.; Reischle, M.; Metzner, S.; Bertram, F.; Christen, J.; Roßbach, R.; Jetter, M.; Michler, P.

    2012-08-01

    The heteroepitaxy of III-V semiconductors on silicon is a promising approach for making silicon a photonic platform. Mismatches in material properties, however, present a major challenge, leading to high defect densities in the epitaxial layers and adversely affecting radiative recombination processes. However, nanostructures, such as quantum dots, have been found to grow defect-free even in a suboptimal environment. Here we present the first realization of indium phosphide quantum dots on exactly oriented Si(001), grown by metal-organic vapour-phase epitaxy. We report electrically driven single-photon emission in the red spectral region, meeting the wavelength range of silicon avalanche photodiodes’ highest detection efficiency.

  3. Kondo effects in triangular triple quantum dots

    Science.gov (United States)

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

    2009-03-01

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

  4. Application of Quantum Dots in Biological Imaging

    Directory of Open Access Journals (Sweden)

    Shan Jin

    2011-01-01

    Full Text Available Quantum dots (QDs are a group of semiconducting nanomaterials with unique optical and electronic properties. They have distinct advantages over traditional fluorescent organic dyes in chemical and biological studies in terms of tunable emission spectra, signal brightness, photostability, and so forth. Currently, the major type of QDs is the heavy metal-containing II-IV, IV-VI, or III-V QDs. Silicon QDs and conjugated polymer dots have also been developed in order to lower the potential toxicity of the fluorescent probes for biological applications. Aqueous solubility is the common problem for all types of QDs when they are employed in the biological researches, such as in vitro and in vivo imaging. To circumvent this problem, ligand exchange and polymer coating are proven to be effective, besides synthesizing QDs in aqueous solutions directly. However, toxicity is another big concern especially for in vivo studies. Ligand protection and core/shell structure can partly solve this problem. With the rapid development of QDs research, new elements and new morphologies have been introduced to this area to fabricate more safe and efficient QDs for biological applications.

  5. Mitochondria as target of Quantum dots toxicity

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jiahan; Zhang, Yue; Xiao, Qi; Tian, Fangfang; Liu, Xiaorong; Li, Ran; Zhao, Guangyuan; Jiang, Fenglei [State Key Laboratory of Virology and Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China); Liu, Yi, E-mail: yiliuchem@whu.edu.cn [State Key Laboratory of Virology and Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China)

    2011-10-30

    Highlights: {yields} The present work investigated the toxicity of CdTe QDs on the function of mitochondria isolated from rat livers. {yields} These results will help us learn more about QDs toxicity at subcellular (mitochondrial) level. {yields} QDs toxicity on mitochondria indicates that the QDs require to be further improved before they can be safely used in clinic. - Abstract: Quantum dots (QDs) hold great promise in many biological applications, with the persistence of safety concerns about the environment and human health. The present work investigated the potential toxicity of CdTe QDs on the function of mitochondria isolated from rat livers by examining mitochondrial respiration, swelling, and lipid peroxidation. We observed that QDs can significantly affect the mitochondrial membrane properties, bioenergetics and induce mitochondrial permeability transition (MPT). These results will help us learn more about QDs toxicity at subcellular (mitochondrial) level.

  6. Optoelectronic Applications of Colloidal Quantum Dots

    Science.gov (United States)

    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.

  7. Quantum Dot Devices for Optical Signal Processing

    DEFF Research Database (Denmark)

    Chen, Yaohui

    . Additional to the static linear amplication properties, we focus on exploring the gain dynamics on the time scale ranging from sub-picosecond to nanosecond. In terms of optical signals that have been investigated, one is the simple sinusoidally modulated optical carrier with a typical modulation frequency...... range of 1-100 gigahertz. Our simulations reveal the role of ultrafast intradot carrier dynamics in enhancing modulation bandwidth of quantum dot semiconductor optical ampliers. Moreover, the corresponding coherent gain response also provides rich dispersion contents over a broad bandwidth. One...... important implementation is recently boosted by the research in slow light. The idea is to migrate such dynamical gain knowledge for the investigation of microwave phase shifter based on semiconductor optical waveguide. Our study reveals that phase shifting based on the conventional semiconductor optical...

  8. Semiconductor quantum dot-inorganic nanotube hybrids.

    Science.gov (United States)

    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. Tellurium quantum dots: Preparation and optical properties

    Science.gov (United States)

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

    2017-08-01

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

  10. Highly Fluorescent Noble Metal Quantum Dots

    Science.gov (United States)

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

    2009-01-01

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

  11. Theoretical study of quantum confined Stark shift in InAs/GaAs quantum dots

    Institute of Scientific and Technical Information of China (English)

    Guo Ru-Hai; Shi Hong-Yan; Sun Xiu-Dong

    2004-01-01

    The quantum confined Stark effect (QCSE) of the self-assembled InAs/GaAs quantum dots has been investigated theoretically. The ground-state transition energies for quantum dots in the shape of a cube, pyramid or "truncated pyramid" are calculated and analysed. We use a method based on the Green function technique for calculating the strain in quantum dots and an efficient plane-wave envelope-function technique to determine the ground-state electronic structure of them with different shapes. The symmetry of quantum dots is broken by the effect of strain. So the properties of carriers show different behaviours from the traditional quantum device. Based on these results, we also calculate permanent built-in dipole moments and compare them with recent experimental data. Our results demonstrate that the measured Stark effect in self-assembled InAs/GaAs quantum dot structures can be explained by including linear grading.

  12. Tunable Few-Electron Quantum Dots as Spin Qubits

    Science.gov (United States)

    Elzerman, Jeroen; Hanson, Ronald; Greidanus, Jacob; Willems van Beveren, Laurens; de Franceschi, Silvano; Vandersypen, Lieven; Tarucha, Seigo; Kouwenhoven, Leo

    2003-03-01

    Recently it was proposed to make a quantum bit using the spin of an electron in a quantum dot. We present the first experimental steps towards realizing a system of two coupled qubits. The Zeeman splitting between the two spin states defining the qubit is measured for a one-electron dot in a parallel magnetic field. For a two-electron dot, we control the spin singlet-triplet energy difference with a perpendicular magnetic field, and we induce a transition from singlet to triplet ground state. We find relaxation from triplet to singlet to be extremely slow (> 1 mus), which is promising for quantum computing. We couple two few-electron dots, creating the first fully tunable few-electron double dot. Its charge configuration can be read out with a nearby QPC acting as an integrated charge detector.

  13. Bound polarons in quantum dot quantum well structures

    Institute of Scientific and Technical Information of China (English)

    Xing Yan; Wang Zhi-Ping; Wang Xu

    2009-01-01

    The problem of bound polarons in quantum dot quantum well (QDQW) structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical (LO) and surface optical (SO) modes are derived in the framework of the diclectric continuum approximation. The electron-phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numcrical results reveal that there exist three branches of eigenfrequcncies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.

  14. Excitons in quantum-dot quantum-well nanoparticles

    Institute of Scientific and Technical Information of China (English)

    史俊杰

    2002-01-01

    A variational calculation is presented for the ground-state properties of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles. The relationship between the exciton states and structure parameters of QDQW nanoparticles is investigated, in which both the heavy-hole and the light-hole exciton states are considered. The results show that the confinement energies of the electron and hole states and the exciton binding energies depend sensitively on the well width and core radius of the QDQW structure. A detailed comparison between the heavy-hole and light-hole exciton states is given. Excellent agreement is found between experimental results and our calculated 1se-1sh transition energies.

  15. Exciton lifetime measurements on single silicon quantum dots.

    Science.gov (United States)

    Sangghaleh, Fatemeh; Bruhn, Benjamin; Schmidt, Torsten; Linnros, Jan

    2013-06-01

    We measured the exciton lifetime of single silicon quantum dots, fabricated by electron beam lithography, reactive ion etching and oxidation. The observed photoluminescence decays are of mono-exponential character with a large variation (5-45 μs) from dot to dot, even for the same emission energy. We show that this lifetime variation may be the origin of the heavily debated non-exponential (stretched) decays typically observed for ensemble measurements.

  16. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications

    Directory of Open Access Journals (Sweden)

    Lin Wen

    2017-07-01

    Full Text Available Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

  17. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications.

    Science.gov (United States)

    Wen, Lin; Qiu, Liping; Wu, Yongxiang; Hu, Xiaoxiao; Zhang, Xiaobing

    2017-07-28

    Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

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

    Energy Technology Data Exchange (ETDEWEB)

    Goldmann, Elias

    2014-07-23

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

  19. Nanoimprint-Transfer-Patterned Solids Enhance Light Absorption in Colloidal Quantum Dot Solar Cells.

    Science.gov (United States)

    Kim, Younghoon; Bicanic, Kristopher; Tan, Hairen; Ouellette, Olivier; Sutherland, Brandon R; García de Arquer, F Pelayo; Jo, Jea Woong; Liu, Mengxia; Sun, Bin; Liu, Min; Hoogland, Sjoerd; Sargent, Edward H

    2017-03-16

    Colloidal quantum dot (CQD) materials are of interest in thin-film solar cells due to their size-tunable bandgap and low-cost solution-processing. However, CQD solar cells suffer from inefficient charge extraction over the film thicknesses required for complete absorption of solar light. Here we show a new strategy to enhance light absorption in CQD solar cells by nanostructuring the CQD film itself at the back interface. We use two-dimensional finite-difference time-domain (FDTD) simulations to study quantitatively the light absorption enhancement in nanostructured back interfaces in CQD solar cells. We implement this experimentally by demonstrating a nanoimprint-transfer-patterning (NTP) process for the fabrication of nanostructured CQD solids with highly ordered patterns. We show that this approach enables a boost in the power conversion efficiency in CQD solar cells primarily due to an increase in short-circuit current density as a result of enhanced absorption through light-trapping.

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

    Science.gov (United States)

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

    2013-06-01

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

  1. Long lived coherence in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    2001-01-01

    We report measurements of ultralong coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mu eV, which is significantly smaller than the linewidth observed in single-dot lum...

  2. Ultrafast gain and index dynamics in quantum dot amplifiers

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang; Mørk, Jesper

    1999-01-01

    The ultrafast dynamics of gain and refractive index in an InAs/GaAs quantum dot amplifier are investigated at room temperature. The gain is observed to recover with a 90 fs time constant, ruling out problems of slow carrier capture into the dots, and making this component promising for high...

  3. Electron Energy Level Statistics in Graphene Quantum Dots

    NARCIS (Netherlands)

    De Raedt, H.; Katsnellson, M. I.; Katsnelson, M.I.

    2008-01-01

    Motivated by recent experimental observations of size quantization of electron energy levels in graphene quantum dots [7] we investigate the level statistics in the simplest tight-binding model for different dot shapes by computer simulation. The results are in a reasonable agreement with the experi

  4. Nonequilibrium electron transport through quantum dots in the Kondo regime

    DEFF Research Database (Denmark)

    Wölfle, Peter; Paaske, Jens; Rosch, Achim

    2005-01-01

    Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how the ...

  5. Non-Markovian spontaneous emission from a single quantum dot

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg; Ates, Serkan; Lund-Hansen, Toke;

    2011-01-01

    We observe non-Markovian dynamics of a single quantum dot when tuned into resonance with a cavity mode. Excellent agreement between experiment and theory is observed providing the first quantitative description of such a system....

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

    Science.gov (United States)

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

    2013-12-01

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

  7. Colloidal Quantum-Dot Photodetectors Exploiting Multiexciton Generation

    National Research Council Canada - National Science Library

    Vlad Sukhovatkin; Sean Hinds; Lukasz Brzozowski; Edward H. Sargent

    2009-01-01

    Multiexciton generation (MEG) has been indirectly observed in colloidal quantum dots, both in solution and the solid state, but has not yet been shown to enhance photocurrent in an optoelectronic device...

  8. Advanced Epitaxial Lift-Off Quantum Dot Photovoltaic Devices Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to develop a high-efficiency, triple-junction, epitaxial lift-off (ELO) solar cell by incorporating quantum dots (QDs) within the current-limiting...

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

    Science.gov (United States)

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

    2010-04-13

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  10. A fast "hybrid" silicon double quantum dot qubit

    CERN Document Server

    Shi, Zhan; Prance, J R; Gamble, John King; Koh, Teck Seng; Shim, Yun-Pil; Hu, Xuedong; Savage, D E; Lagally, M G; Eriksson, M A; Friesen, Mark; Coppersmith, S N

    2011-01-01

    We propose a quantum dot qubit architecture that has an attractive combination of speed and fabrication simplicity. It consists of a double quantum dot with one electron in one dot and two electrons in the other. The qubit itself is a set of two states with total spin quantum numbers $S^2=3/4$ ($S=\\half$) and $S_z = -\\half$, with the two different states being singlet and triplet in the doubly occupied dot. The architecture is relatively simple to fabricate, a universal set of fast operations can be implemented electrically, and the system has potentially long decoherence times. These are all extremely attractive properties for use in quantum information processing devices.

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

    Science.gov (United States)

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

    2016-12-01

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

  12. Type 2 quantum dots in Ge/Si system

    CERN Document Server

    Dvurechenskij, A V

    2001-01-01

    The results on the electronic structure of spatially indirect excitons, multiparticle excitonic complexes, and negative interband photoconductivity in arrays of Ge/Si type 2 quantum dots are presented. These data have been compared with the well known results for type 2 A sup I sup I sup I B sup V and A sup I sup I B sup V sup I -based heterostructures with quantum dots. Fundamental physical phenomena are found to be the result of an increase in the binding energy of excitons in quantum dots as compared with that of free excitons in bulk homogeneous materials; the shortwave shift of exciton transition energy at multiparticle complexes production (charges excitons, biexcitons), as well as the trapping of equilibrium carrier by localized states induced by the charged quantum dot electric field

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

    Science.gov (United States)

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

    2016-07-01

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

  14. Probing of Unembedded Metallic Quantum Dots with Positrons

    Energy Technology Data Exchange (ETDEWEB)

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

    2003-08-01

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

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

    Science.gov (United States)

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

    2016-12-01

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

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

    Science.gov (United States)

    Qiu, Y.; Uhl, D.

    2002-01-01

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

  17. Electric properties of Ge quantum dot embedded in Si matrix

    Institute of Scientific and Technical Information of China (English)

    MA Xi-ying; SHI Wei-lin

    2005-01-01

    The electric characteristics of Ge quantum dot grown by molecular beam epitaxy in Si matrix were investigated by admittance spectroscopy and deep level transient spectroscopy. The admittance spectroscopy measurements show that the activation energy of 0.341 eV can be considered as the emitting energy of hole from the ground state of the quantum dot. And the capacitance variation with temperature of the sample shows a platform at various frequencies with reverse bias 0.5 V, which indicates that the boundary of space charge region is located at the quantum dot layer where the large confined hole concentration blocks the further extension of space charge region. When the temperature increases from 120 K to 200 K, the holes in the dot emit out completely. The position of the platform shifting with the increase of the applied frequency shows the frequency effects of the charges in the quantum dot. The deep level transient spectroscopy results show that the charge concentration in the Ge quantum dot is a function of the pulse duration and the reverse bias voltage, the activation energy and capture cross-section of hole decrease with the increase of pulse duration due to the Coulomb charging effect. The valence-band offsets of hole in Ge dot obtained by admittance spectroscopy and deep level transient spectroscopy are 0.341 and 0.338 eV, respectively.

  18. The spectral analysis and threshold limits of quasi-supercontinuum self-assembled quantum dot interband lasers

    KAUST Repository

    Tan, Cheeloon

    2009-09-01

    This paper presents a theoretical model to explain the quasi-supercontinuum interband emission from InGaAs/GaAs self-assembled semiconductor quantum dot lasers by accounting for both inhomogeneous and homogeneous optical gain broadening. The experimental and theoretical agreement of a room temperature (293 K) broadband laser emission confirms the presence of multiple-state lasing actions in highly inhomogeneous dot ensembles. The corresponding full-width half-maximum of the photoluminescence is 76 meV as opposed to those wideband lasing coverage at only low temperature (∼60 K) from typical quantum dot lasers. A newly proposed change of homogeneous broadening with injection that occurs only in highly inhomogeneous quantum dot system is critical to account for the continuous wideband lasing but not the conventional ideas of carrier dynamics in semiconductor lasers. In addition, the analysis of threshold conditions reveals that broadband lasing only occurs when the energy spacing between quantized energy states is comparable to the inhomogeneous broadening of quantum-dot nanostructures. The study is important in providing a picture of this novel device and realization of broad lasing coverage for diverse applications, especially in the research field of short-pulse generation and ultra-fast phenomena in semiconductor quantum-dot laser. © 2009 IEEE.

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

    NARCIS (Netherlands)

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

    2016-01-01

    We define single quantum dots of lengths varying from 60 nm up to nearly half a micron in Ge-Si core-shell nanowires. The charging energies scale inversely with the quantum dot length between 18 and 4 meV. Subsequently, we split up a long dot into a double quantum dot with a separate control over

  20. Solution-Processed Nanocrystal Quantum Dot Tandem Solar Cells

    KAUST Repository

    Choi, Joshua J.

    2011-06-03

    Solution-processed tandem solar cells created from nanocrystal quantum dots with size-tuned energy levels are demonstrated. Prototype devices featuring interconnected quantum dot layers of cascaded energy gaps exhibit IR sensitivity and an open circuit voltage, V oc, approaching 1 V. The tandem solar cell performance depends critically on the optical and electrical properties of the interlayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.