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1

Electronic confinement in modulation doped quantum dots  

NASA Astrophysics Data System (ADS)

Modulation doping, an effective way to dope quantum dots (QDs), modifies the confinement energy levels in the QDs. We present a self-consistent full multi-grid solver to analyze the effect of modulation doping on the confinement energy levels in large-area structures containing Si QDs in SiO2 and Si3N4 dielectrics. The confinement energy was found to be significantly lower when QDs were in close proximity to dopant ions in the dielectric. This effect was found to be smaller in Si3N4, while smaller QDs in SiO2 were highly susceptible to energy reduction. The energy reduction was found to follow a power law relationship with the QD size.

Puthen Veettil, B.; König, D.; Patterson, R.; Smyth, S.; Conibeer, G.

2014-04-01

2

Comparison of quantum confinement effects between quantum wires and dots  

SciTech Connect

Dimensionality is an important factor to govern the electronic structures of semiconductor nanocrystals. The quantum confinement energies in one-dimensional quantum wires and zero-dimensional quantum dots are quite different. Using large-scale first-principles calculations, we systematically study the electronic structures of semiconductor (including group IV, III-V, and II-VI) surface-passivated quantum wires and dots. The band-gap energies of quantum wires and dots have the same scaling with diameter for a given material. The ratio of band-gap-increases between quantum wires and dots is material-dependent, and slightly deviates from 0.586 predicted by effective-mass approximation. Highly linear polarization of photoluminescence in quantum wires is found. The degree of polarization decreases with the increasing temperature and size.

Li, Jingbo; Wang, Lin-Wang

2004-03-30

3

Correlation studies in weakly confining quantum dot potentials  

NASA Astrophysics Data System (ADS)

We investigate the electron correlation in few-electron closed-shell atomic systems and similarly in few-electron quantum dots under weak confinement. As usual we start with restricted Hartree-Fock (HF) calculations and add electron correlation in steps in a series of approximations based on the single particle Green's function approach: (i) second-order Green function (GF); (ii) 2ph-Tamm-Dancoff approximation (TDA); and (iii) an extended version thereof which introduces ground-state correlation into the TDA. Our studies exhibit similarities and differences between weakly confined quantum dots and standard atomic systems. The calculations support the application of HF, GF, and TDA techniques in the modeling of three-dimensional quantum dot systems. The observed differences emphasize the significance of confinement and electronic features unique to quantum dots, such as the increased binding of electrons with higher angular momentum and thus - compared to atomic systems - modified shell-filling sequences.

Kimani, Peter; Jones, Preston; Winkler, Peter

4

Persistent current through a semiconductor quantum dot with Gaussian confinement  

NASA Astrophysics Data System (ADS)

The persistent diamagnetic current in a GaAs quantum dot with Gaussian confinement is calculated. It is shown that except at very low temperature or at high temperature, the persistent current increases with decreasing temperature. It is also shown that as a function of the dot size, the diamagnetic current exhibits a maximum at a certain confinement length. It is furthermore shown that for a shallow potential, the persistent current shows an interesting maximum structure as a function of the depth of the potential. At low temperature, the peak structure is pretty sharp but becomes broader and broader with increasing temperature.

Boyacioglu, Bahadir; Chatterjee, Ashok

2012-09-01

5

Confinement of Dirac electrons in graphene quantum dots  

NASA Astrophysics Data System (ADS)

We observe spatial confinement of Dirac states on epitaxial graphene quantum dots with low-temperature scanning tunneling microscopy after using oxygen as an intercalant to suppress the surface state of Ir(111) and to effectively decouple graphene from its metal substrate. We analyze the confined electronic states with a relativistic particle-in-a-box model and find a linear dispersion relation. The oxygen-intercalated graphene is p doped [ED=0.64±0.07 eV] and has a Fermi velocity close to the one of free-standing graphene [vF=0.96±0.07×106 m/s].

Jolie, Wouter; Craes, Fabian; Petrovi?, Marin; Atodiresei, Nicolae; Caciuc, Vasile; Blügel, Stefan; Kralj, Marko; Michely, Thomas; Busse, Carsten

2014-04-01

6

The effect of quantum dot shape and position on electron confinement in dot-in-a-well structures  

Microsoft Academic Search

In this paper we present results of our study on electron confinement in dot-in-a-well (DWELL) structures. The structures under investigation consist of an InAs quantum dot (QD) confined in an InGaAs quantum well (QW), which in turn buried in GaAs bulk. We examine DWELL structures of various quantum dot shapes embedded in the same quantum well and calculate their electronic

N. Batenipour; K. Saghafi; M. K. Moravvej-Farshi

2010-01-01

7

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer  

Microsoft Academic Search

We demonstrate the high quantum efficiency InAs?In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also

H. S. Ling; S. Y. Wang; C. P. Lee; M. C. Lo

2008-01-01

8

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer  

Microsoft Academic Search

We demonstrate the high quantum efficiency InAs\\/In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also

H. S. Ling; S. Y. Wang; C. P. Lee; M. C. Lo

2008-01-01

9

Exciton States in a Quantum Dot with Parabolic Confinement  

NASA Astrophysics Data System (ADS)

In this study the electronic eigenstructure of an exciton in a parabolic quantum dot (QD) has been calculated with a high accuracy by using Finite element method (FEM). We have converted the coordinates of electron-light-hole system to relative and center of mass coordinate, then placed the Spherical Harmonics into Schrödinger equation analytically and obtained the Schrödinger equation which depends only on the radial variable. Finally we used FEM with only radial variable in order to get the accurate numerical results. We also showed first 21 energy level spectra of exciton depending on confinement and Coulomb interaction parameters.

Do?an, Ü.; Sakiro?lu, S.; Yildiz, A.; Akgüngör, K.; Epik, H.; Sökmen, I.; Sari, H.; Ergün, Y.

10

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer  

NASA Astrophysics Data System (ADS)

We demonstrate the high quantum efficiency InAs/In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also improves the escape probability of the photoelectrons. Compared with the conventional DWELL QDIPs, the quantum efficiency increases more than 20 times and the detectivity is about an order of magnitude higher at 77 K.

Ling, H. S.; Wang, S. Y.; Lee, C. P.; Lo, M. C.

2008-05-01

11

Quantum Dots  

NSDL National Science Digital Library

This topic-in-depth addresses the characteristics and numerous applications of the semiconductor nanocrystals, quantum dots. First, Evident Technologies' Nanotechnology website provides a great summary about the properties of quantum dots (1 ). Users can learn about quantum dots' photoluminescence spectra, molecular coupling, quantum confinement, and their absorption spectra. The second website, created by Gunjan Mishra at the University of Nevada - Reno, is a downloadable slideshow illustrating the history, formation, and application of quantum dots (2). While created as part of a lecture series, this website provides students with a concise outline of the unique characteristics of the particles. Third, UCLA describes the combined research of chemists and engineers to use quantum dots as an inexpensive means of creating nanoscale circuitry for molecular computers of the future (3). Users can learn how the particles' photocatalytic properties make them a great candidate for improving the current method of creating interconnecting lines on silicon chips. Next, Stanislaus Wong at Stony Brook University presents his research in carbon nanotubes and semiconductor nanocrystals (4 ). After a short introduction about quantum dots, users can discover his group's efforts to understand these particles in order to implement them in the fields of chemistry and biology. The fifth site is a downloadable document by Victor Klimov at Los Alamos National Laboratory discussing the development of a new laser based on quantum dots (5 ). The site supplies a series of figures illustrating the nonradiative multiparticle auger recombinations in nanocrystal quantum dots, amplified spontaneous emissions, and more. Next, Nanotechweb compares new quantum discoveries in the 21st century to the ball-bearing inventions in the 20th century (6 ). Users can learn why scientists believe the particles can be utilized in medicine, security, and electronics. In an online article, Carnegie Mellon discusses how chemists are researching quantum dots to evaluate their effectiveness in treating diseases such as cancer (7). Users can discover how the scientists were able to produce quantum dots that fluoresced for an unprecedented eight months. The last site promotes the 2004 Quantum Dots Conference (8). Researchers can learn about the conference scope, the venue, invited speakers, and more.

12

Quantum dots-in-a-well (DWELL) infrared photodetectors with confinement enhancing barriers  

Microsoft Academic Search

Improvement in the performance of quantum dots-in-a-well (DWELL) detectors with confinement enhancing (CE) barriers is presented. Higher responsivity and lower noise, with detectivity of 6.5×1010 cm.Hz1\\/2W?1 (77K, 0.6V, 7.5µm, ƒ\\/2) have been obtained.

Ajit V. Barve; Jun Oh Kim; Saumya Sengupta; Yagya D. Sharma; Jiayi Shao; Sourav Adhikary; Thomas Rottera; Sanjay Krishna

2011-01-01

13

Electronic structure and electron correlation in weakly confining spherical quantum dot potentials  

NASA Astrophysics Data System (ADS)

The electronic structure and electron correlations in weakly confining spherical quantum dots potentials are investigated. Following a common practice, the investigation starts with the restricted Hartree-Fock (HF) approximation. Then electron correlation is added in steps in a series of approximations based on the single particle Green's function approach: (i) Second-order Green function (GF) (ii) 2ph-Tamm-Dancoff approximation (TDA) and (iii) an extended version thereof (XTDA) which introduces ground-state correlation into the TDA. The study includes as well Hartree-Fock V (N-1) potential approximation in which framework the Hartree-Fock virtual orbitals are calculated in the field of the N-1 electrons as opposed to the regular but unphysical N-electron field Hartree-Fock calculation of virtual orbitals. For contrast and comparison, the same approximation techniques are applied to few-electron closed-shell atoms and few-electron negative ions for which pertinent data is readily available. The results for the weakly confining spherical quantum dot potentials and the standard atomic systems exhibit fundamental similarities as well as significant differences. For the most part the results of these calculations are in favor of application of HF, GF, and TDA techniques in the modeling of three-dimensional weakly confining quantum dot potentials. The observed differences emphasize the significance of confinement and electronic features unique to quantum dots such as the increased binding of electrons with higher angular momentum and the modified shell filling sequences.

Kimani, Peter Borgia Ndungu

14

XANES: observation of quantum confinement in the conduction band of colloidal PbS quantum dots  

NASA Astrophysics Data System (ADS)

The presented investigations aimed at development of inexpensive method for synthesized materials suitable for utilization of solar energy. This important issue was addressed by focusing, mainly, on electronic local structure studies with supporting x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis of colloidal galena nano-particles (NPs) and quantum dots (QDs) synthesized using wet chemistry under microwave irradiation. Performed x-ray absorption near edge structure (XANES) analysis revealed an evidence of quantum confinement for the sample with QDs, where the bottom of the conduction band was shifted to higher energy. The QDs were found to be passivated with oxides at the surface. Existence of sulfate/sulfite and thiosulfate species in pure PbS and QDs, respectively, was identified.

Demchenko, I. N.; Chernyshova, M.; He, X.; Minikayev, R.; Syryanyy, Y.; Derkachova, A.; Derkachov, G.; Stolte, W. C.; Piskorska-Hommel, E.; Reszka, A.; Liang, H.

2013-04-01

15

Two-electron quantum dot in tilted magnetic fields: Sensitivity to the confinement model  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots are conventionally treated within the effective-mass approximation and a harmonic model potential in the two-dimensional plane for the electron confinement. The validity of this approach depends on the type of the quantum-dot device as well as on the number of electrons confined in the system. Accurate modeling is particularly demanding in the few-particle regime, where screening effects are diminished and thus the system boundaries may have a considerable effect on the confining potential. Here we solve the numerically exact two-electron states in both harmonic and hard-wall model quantum dots subjected to tilted magnetic fields. Our numerical results enable direct comparison against experimental singlet-triplet energy splittings. Our analysis shows that hard and soft wall models produce qualitatively different results for quantum dots exposed to tilted magnetic fields. Hence, we are able to address the sensitivity of the two-body phenomena to the modeling, which is of high importance in realistic spin-qubit design.

Frostad, T.; Hansen, J. P.; Wesslén, C. J.; Lindroth, E.; Räsänen, E.

2013-10-01

16

Strongly confined excitons in self-assembled InGaAs quantum dot clusters  

NASA Astrophysics Data System (ADS)

Quantum dot clusters (QDCs) consisting of regular geometric patterns of six InGaAs quantum dots (QD) are grown on a GaAs substrate using a hybrid growth method that combines droplet homoepitaxy and Stranski-Krastonov growth. These novel structures have potential applications as tunable single photon sources, entangled photon sources, or error corrected qubits - devices critical to the fields of secure optical communications and quantum computing We study the photoluminescence arising from a single cluster using both continuous wave and ultrafast spectroscopic techniques with variations in the sample temperature and excitation power. Our results suggest excitons (bound electron-hole pairs) are strongly confined within the individual QDs rather than loosely confined throughout the entire QDC. The work at Texas is supported financially by NSF, ARO, AFOSR, ONR, the Welch Foundation, and the Alfred Sloan Foundation. The work at Arkansas is supported by the NSF.

Creasey, Megan; Li, Xiaoqin; Lee, Jihoon; Wang, Zhiming; Salamo, Gregory

2011-03-01

17

Strong coupling of two interacting excitons confined in a nanocavity-quantum dot system.  

PubMed

We present a study of the strong coupling between radiation and matter, considering a system of two quantum dots, which are in mutual interaction and interact with a single mode of light confined in a semiconductor nanocavity. We take into account dissipative mechanisms such as the escape of the cavity photons, decay of the quantum dot excitons by spontaneous emission, and independent exciton pumping. It is shown that the mutual interaction between the dots can be measured off-resonance only if the strong coupling condition is reached. Using the quantum regression theorem, a reasonable definition of the dynamical coupling regimes is introduced in terms of the complex Rabi frequency. Finally, the emission spectrum for relevant conditions is presented and compared with the above definition, demonstrating that the interaction between the excitons does not affect the strong coupling. PMID:21673402

Cárdenas, Paulo C; Quesada, Nicolás; Vinck-Posada, Herbert; Rodríguez, Boris A

2011-07-01

18

Realistic confinement potential for a square-patterned two-dimensional semiconductor quantum dot and its approximated circular counterpart  

NASA Astrophysics Data System (ADS)

Two-dimensional semiconductor quantum-dot systems are typical nanoscale structures in which a few number of electrons is confined in a small region of space by applying external electric gate potentials. While the detailed form of the confining potential depends on the specific experimental setup, the parabolic confinement model has commonly been used because of its simplicity. Clearly, on those instances in which the experimental setup involves placement of gate potentials with sharp geometric features, the area depleted of electrons; thus, the quantum-dot region cannot be considered circular. If, for simplicity, we consider the confinement region of the electrons as square in shape, then an accurate calculation of the properties of such square-patterned quantum dot should be made using a realistic confinement potential originating from that particular configuration. We calculated exactly such a confinement potential for a square quantum dot. The particular analytic form of this realistic potential is complicated given its dependence on the two-dimensional position coordinates, rather than simply the distance from the center of the quantum dot. In this work, we choose to substitute the realistic confinement potential for a square-patterned quantum dot with an approximated circular symmetric potential. We assess the quality of this approximation and discuss instances in which one can reliably use the approximated simplified potential instead of the computationally unyielding exact one.

Ciftja, Orion

2012-11-01

19

Excitons in artificial quantum dots in the weak spatial confinement regime  

NASA Astrophysics Data System (ADS)

The exciton states in individual quantum dots prepared by the selective interdiffusion method in CdTe/CdMgTe quantum wells are studied by the methods of steady-state optical spectroscopy. The annealing-induced diffusion of Mg atoms inward to the bulk of the quantum well, which is significantly enhanced under the SiO2 mask, leads to a modulation of the bandgap width in the plane of the well, with the minima of the potential being located in the mask aperture areas. A lateral potential that arises, whose height is in the range 30 270 meV and characteristic scale is about 100 nm, efficiently localizes carriers, which form quasi-zero-dimensional excitons in the weak spatial confinement regime. Detailed magnetooptical studies show that Coulomb correlations play a significant role in the formation of exciton states under such a regime, which, in particular, manifests itself in the localization of the wavefunction of carriers on scales that are considerably smaller than the scale of the lateral potential. The particular features of the interlevel splitting, of the biexciton binding energy, and of the diamagnetic shift are discussed. A strong dependence of the interlevel relaxation on the interlevel splitting (the phonon neck) indicates that alternative relaxation mechanisms in the quantum dots studied are weak. The excited states are populated according to the Pauli principle, which indicates that it is possible to apply the shell model of many-exciton states to quantum dots under the weak spatial confinement conditions.

Zaitsev, S. V.; Welsch, M. K.; Forchel, A.; Bacher, G.

2007-12-01

20

Low-threshold oxide-confined 1.3-?m quantum-dot laser  

Microsoft Academic Search

Data are presented on low threshold, 1.3-?m oxide-confined InGaAs-GaAs quantum dot lasers. A very low continuous-wave threshold current of 1.2 mA with a threshold current density of 28 A\\/cm2 is achieved with p-up mounting at room temperature. For slightly larger devices the continuous-wave threshold current density is as low as 19 A\\/cm2

O. B. Shchekin; D. L. Huffaker; D. G. Deppe

2000-01-01

21

Electronic structure and electron correlation in weakly confining spherical quantum dot potentials  

Microsoft Academic Search

The electronic structure and electron correlations in weakly confining spherical quantum dots potentials are investigated. Following a common practice, the investigation starts with the restricted Hartree-Fock (HF) approximation. Then electron correlation is added in steps in a series of approximations based on the single particle Green's function approach: (i) Second-order Green function (GF) (ii) 2ph-Tamm-Dancoff approximation (TDA) and (iii) an

Peter Borgia Ndungu Kimani

2008-01-01

22

Additive Gaussian white noise modulated excitation kinetics of impurity doped quantum dots: Role of confinement sources  

NASA Astrophysics Data System (ADS)

We investigate the excitation kinetics of a repulsive impurity doped quantum dot initiated by the application of additive Gaussian white noise. The noise and the dot confinement sources of electric and magnetic origin have been found to fabricate the said kinetics in a delicate way. In addition to this the dopant location also plays some prominent role. The present study sheds light on how the individual or combined variation of different confinement sources could design the excitation kinetics in presence of noise. The investigation reveals emergence of maximization and saturation in the excitation kinetics as a result of complex interplay between various parameters that affect the kinetics. The phase space plots are often invoked and they lend credence to the findings. The present investigation is believed to provide some useful perceptions of the functioning of mesoscopic systems where noise plays some profound role.

Ganguly, Jayanta; Pal, Suvajit; Ghosh, Manas

2013-11-01

23

Strongly confining bare core CdTe quantum dots in polymeric microdisk resonators  

NASA Astrophysics Data System (ADS)

We report on a simple route to the efficient coupling of optical emission from strongly confining bare core CdTe quantum dots (QDs) to the eigenmodes of a micro-resonator. The quantum emitters are embedded into QD/polymer sandwich microdisk cavities. This prevents photo-oxidation and yields the high dot concentration necessary to overcome Auger enhanced surface trapping of carriers. In combination with the very high cavity Q-factors, interaction of the QDs with the cavity modes in the weak coupling regime is readily observed. Under nanosecond pulsed excitation the CdTe QDs in the microdisks show lasing with a threshold energy as low as 0.33 ?J.

Flatae, Assegid; Grossmann, Tobias; Beck, Torsten; Wiegele, Sarah; Kalt, Heinz

2014-01-01

24

Quantum-confined hydrogenic impurity in a spherical quantum dot under the influence of parallel electric and magnetic fields  

NASA Astrophysics Data System (ADS)

A recently developed computational technique, the complex absorbing potential (CAP) method for locating complex poles of resonance states, is applied to calculate the field-induced energy shifts and widths of the ground stale of a hydrogenic donor in a quantum dot (QD) subjected to parallel electric and magnetic fields. The present model demonstrates that resonances in a confined hydrogen atom lead to an anomalous behaviour due to the quantum confinement of the atom. We have studied the influence of magnetic field on the quantum-confined Stark effect. With increasing magnetic field, resonances shift to higher level and the width gets narrower with less impact on the oscillation amplitude. We will discuss our results in terms of a QD system realized in the GaAs/Ga 1-xAl xAs sample.

Sahoo, Satyabrate; Lin, Y. C.; Ho, Y. K.

2008-09-01

25

Self-Induced Oscillation for Electron-Hole Pair Confined in Quantum Dot  

SciTech Connect

We study the time-dependent (TD) phenomena of the electron-hole or electron-electron pair confined in the square quantum dot (SQD) system by computationally solving TD Schroedinger equation under the unrestricted Hartree-Fock (UHF) approach. A typical vacillation is found both in the electron and hole when the charged pair is strongly confined in the SQD while the charged particles have initially the same orbital symmetry. The FFT analysis elucidates that the transition matrix element due to the coulomb interaction involves the eigen frequency {omega} being equal to the excitation energy when the resonative vacillation appears. Thus, Coulomb potential has a potential to cause the self-induced ''Rabi'' oscillation when the charged-particle pair is confined only in the QD.

Tagawa, Tomoki; Tsubaki, Atsushi; Ishizuki, Masamu; Takeda, Kyozaburo [Department of Electrical Engineering and Bioscience, Waseda University, Tokyo 169-8555 (Japan)

2011-12-23

26

A molecule to detect and perturb the confinement of charge carriers in quantum dots.  

PubMed

This paper describes unprecedented bathochromic shifts (up to 970 meV) of the optical band gaps of CdS, CdSe, and PbS quantum dots (QDs) upon adsorption of an organic ligand, phenyldithiocarbamate (PTC), and the use of PTC to map the quantum confinement of specific charge carriers within the QDs as a function of their radius. For a given QD material and physical radius, R, the magnitude of the increase in apparent excitonic radius (?R) upon delocalization by PTC directly reflects the degree of quantum confinement of one or both charge carriers. The plots of ?R vs R for CdSe and CdS show that exciton delocalization by PTC occurs specifically through the excitonic hole. Furthermore, the plot for CdSe, which spans a range of R over multiple confinement regimes for the hole, identifies the radius (R?1.9 nm) at which the hole transitions between regimes of strong and intermediate confinement. This demonstration of ligand-induced delocalization of a specific charge carrier is a first step toward eliminating current-limiting resistive interfaces at organic-inorganic junctions within solid-state hybrid devices. Facilitating carrier-specific electronic coupling across heterogeneous interfaces is especially important for nanostructured devices, which comprise a high density of such interfaces. PMID:22032799

Frederick, Matthew T; Amin, Victor A; Cass, Laura C; Weiss, Emily A

2011-12-14

27

Theory of confined states of positronium in spherical and circular quantum dots with Kane's dispersion law  

PubMed Central

Confined states of a positronium (Ps) in the spherical and circular quantum dots (QDs) are theoretically investigated in two size quantization regimes: strong and weak. Two-band approximation of Kane’s dispersion law and parabolic dispersion law of charge carriers are considered. It is shown that electron-positron pair instability is a consequence of dimensionality reduction, not of the size quantization. The binding energies for the Ps in circular and spherical QDs are calculated. The Ps formation dependence on the QD radius is studied.

2013-01-01

28

Theory of confined states of positronium in spherical and circular quantum dots with Kane's dispersion law  

NASA Astrophysics Data System (ADS)

Confined states of a positronium (Ps) in the spherical and circular quantum dots (QDs) are theoretically investigated in two size quantization regimes: strong and weak. Two-band approximation of Kane's dispersion law and parabolic dispersion law of charge carriers are considered. It is shown that electron-positron pair instability is a consequence of dimensionality reduction, not of the size quantization. The binding energies for the Ps in circular and spherical QDs are calculated. The Ps formation dependence on the QD radius is studied.

Dvoyan, Karen G.; Matinyan, Sergey G.; Vlahovic, Branislav

2013-07-01

29

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

NASA Astrophysics Data System (ADS)

In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C-H or Si-H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C-H termination and positive for the Si-H termination. The prediction of negative electron affinities in SiC quantum dots by simple C-H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems.In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C-H or Si-H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C-H termination and positive for the Si-H termination. The prediction of negative electron affinities in SiC quantum dots by simple C-H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr12099b

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

2012-02-01

30

Quantum Dots  

NASA Astrophysics Data System (ADS)

Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by Lithographic Techniques: III-V Semiconductors and Carbon: 15. Electrically controlling single spin coherence in semiconductor nanostructures Y. Dovzhenko, K. Wang, M. D. Schroer and J. R. Petta; 16. Theory of electron and nuclear spins in III-V semiconductor and carbon-based dots H. Ribeiro and G. Burkard; 17. Graphene quantum dots: transport experiments and local imaging S. Schnez, J. Guettinger, F. Molitor, C. Stampfer, M. Huefner, T. Ihn and K. Ensslin; Part VI. Single Dots for Future Telecommunications Applications: 18. Electrically operated entangled light sources based on quantum dots R. M. Stevenson, A. J. Bennett and A. J. Shields; 19. Deterministic single quantum dot cavities at telecommunication wavelengths D. Dalacu, K. Mnaymneh, J. Lapointe, G. C. Aers, P. J. Poole, R. L. Williams and S. Hughes; Index.

Tartakovskii, Alexander

2012-07-01

31

Spin blockade and exchange in Coulomb-confined silicon double quantum dots.  

PubMed

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits because of their long coherence times, exceeding seconds in isotopically purified bulk silicon. With the recent demonstrations of initialization, readout and coherent manipulation of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling in two tunnel-coupled phosphorus donors. Spin-to-charge conversion via Pauli spin blockade, an essential ingredient for reading out individual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (?45 meV), requiring large electric fields (>1 MV m(-1)) to transfer both electron spins onto the same donor. Here, in a carefully characterized double donor-dot device, we directly observe spin blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems. PMID:24727686

Weber, Bent; Tan, Y H Matthias; Mahapatra, Suddhasatta; Watson, Thomas F; Ryu, Hoon; Rahman, Rajib; Hollenberg, Lloyd C L; Klimeck, Gerhard; Simmons, Michelle Y

2014-06-01

32

Spin blockade and exchange in Coulomb-confined silicon double quantum dots  

NASA Astrophysics Data System (ADS)

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits because of their long coherence times, exceeding seconds in isotopically purified bulk silicon. With the recent demonstrations of initialization, readout and coherent manipulation of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling in two tunnel-coupled phosphorus donors. Spin-to-charge conversion via Pauli spin blockade, an essential ingredient for reading out individual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (~45 meV), requiring large electric fields (>1 MV m-1) to transfer both electron spins onto the same donor. Here, in a carefully characterized double donor-dot device, we directly observe spin blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems.

Weber, Bent; Tan, Y. H. Matthias; Mahapatra, Suddhasatta; Watson, Thomas F.; Ryu, Hoon; Rahman, Rajib; Hollenberg, Lloyd C. L.; Klimeck, Gerhard; Simmons, Michelle Y.

2014-06-01

33

Quantum Confinement in Amorphous Silicon Quantum Dots Embedded in Silicon Nitride  

Microsoft Academic Search

Amorphous silicon quantum dots ( a-Si QDs) were grown in a silicon nitride film by plasma enhanced chemical vapor deposition. Transmission electron micrographs clearly demonstrated that a-Si QDs were formed in the silicon nitride. Photoluminescence and optical absorption energy measurement of a-Si QDs with various sizes revealed that tuning of the photoluminescence emission from 2.0 to 2.76 eV is possible

Nae-Man Park; Chel-Jong Choi; Tae-Yeon Seong; Seong-Ju Park

2001-01-01

34

Heat capacity and entropy of a GaAs quantum dot with Gaussian confinement  

PubMed Central

The heat capacity and entropy effects in a GaAs quantum dot with Gaussian confinement are calculated in the presence of a magnetic field and its interaction with the electron spin using the canonical ensemble approach. It is shown that the heat capacity shows a Schottky-like anomaly at a low temperature, while it approaches a saturation value 2kB as the temperature increases. As a function of the magnetic field, the heat capacity shows a maximum and then reduces to zero. Also the width of the maximum becomes wider with temperature. It is also shown that the heat capacity remains constant up to a certain value of the confinement length beyond which it displays a monotonic increase. However as a function of the confinement strength, though the heat capacity initially shows a significant drop, it remains constant thereafter. At low temperatures like T?=?10 and 20?K, the entropy is found to decrease with increasing magnetic field, but at higher temperatures, it remains almost independent of the magnetic field. At high temperatures, entropy shows a monotonic increase with temperature, but at a sufficiently low temperature as the magnetic field decreases, the entropy is found to develop a shoulder which becomes more and more pronounced with decreasing magnetic field.

Boyacioglu, B.; Chatterjee, A.

2012-01-01

35

Electrochromic Nanocrystal Quantum Dots  

Microsoft Academic Search

The optical properties of colloidal semiconductor nanocrystal quantum dots can be tuned by an electrochemical potential. The injection of electrons into the Lowest Unoccupied Quantum Confined Orbital (LUQCO) leads to an extraordinary electrochromic response with novel characteristics. These include a strong size-tunable mid-infrared absorption corresponding to an intraband transition, a bleach of the visible interband exciton transitions and a quench

Congjun Wang; Moonsub Shim; Philippe Guyot-Sionnest

2001-01-01

36

Coulomb repulsive correlation in systems with radial confinement: quantum dots and the Overhauser model in an external magnetic field  

Microsoft Academic Search

The ground-state correlation energy of an electron-negative ion system in a spherical quantum dot (QD) with parabolic confinement in an external homogeneous magnetic field is investigated. Both cases of finite and infinite potential barrier on the QD surface are considered. The theoretical analysis is carried out using a variational approach. The ground state energy of a two-electron system in a

A. A. Avetisyan; K. Moulopoulos; A. P. Djotyan

2006-01-01

37

Photoinduced band filling in strongly confined colloidal PbS quantum dots  

NASA Astrophysics Data System (ADS)

Increase in continuous wave laser excitation (6 W/cm2 to 120 W/cm2) of colloidal PbS quantum dots in the strongly quantized regime (diameters 2.0 nm and 4.7 nm) deposited on semi-insulating GaAs and glass causes a clear blue shift (0.019 eV and 0.080 eV) of the emission spectra. Proof of the applicability of a dynamic three-dimensional band filling model is the significance of the presented results and demonstrates the effective electronic coupling in quantum dot arrays similar to superlattices. The work also reveals the influence of quantum dot sizes on photo-doping effects.

Ullrich, B.; Xi, H.; Wang, J. S.

2014-06-01

38

Quantum Dots  

NSDL National Science Digital Library

This presentation, created by Gunjan Mishra at the University of Nevada - Reno, is a downloadable slideshow illustrating the history, formation, and application of quantum dots. While created as part of a lecture series, this website provides students with a concise outline of the unique characteristics of the particles.

Mishra, Gunjan

2008-07-07

39

Quantum dots infrared photodetectors  

Microsoft Academic Search

We report a series of InAs quantum dots infrared photodetectors. By using InGaAs cap layers and InAIGaAs lateral potential confinement layers, the peak absorption can be manipulated in from ?5.6 ?m to ?9 ?m.

Zhengmao Ye; J. C. Campbell; Zhonghui Chen; Eui-Tae Kim; A. Madhukar

2003-01-01

40

Electron-hole excitations in CdSe quantum dots under strong and intermediate confinement conditions  

NASA Astrophysics Data System (ADS)

The absorption spectrum of cadmium selenide nanocrystals in a glassy fluorophosphate matrix has been investigated in the vicinity of the fundamental absorption edge 400-650 nm. The revealed oscillations of the absorption have been interpreted as a manifestation of the quantum-well effect for electrons and holes under strong and intermediate confinement conditions. The data obtained have demonstrated that the individual discrete confinement states arise from the band and exciton states of the bulk crystal. The results are in good agreement with those obtained from theoretical consideration of the intermediate confinement model.

Karpov, S. V.; Mikushev, S. V.

2010-08-01

41

Electron and boson clusters in confined geometries: Symmetry breaking in quantum dots and harmonic traps  

PubMed Central

We discuss the formation of crystalline electron clusters in semiconductor quantum dots and of crystalline patterns of neutral bosons in harmonic traps. In a first example, we use calculations for two electrons in an elliptic quantum dot to show that the electrons can localize and form a molecular dimer. The calculated singlet–triplet splitting (J) as a function of the magnetic field (B) agrees with cotunneling measurements with its behavior reflecting the effective dissociation of the dimer for large B. Knowledge of the dot shape and of J(B) allows determination of the degree of entanglement. In a second example, we study strongly repelling neutral bosons in two-dimensional harmonic traps. Going beyond the Gross–Pitaevskii (GP) mean-field approximation, we show that bosons can localize and form polygonal-ring-like crystalline patterns. The total energy of the crystalline phase saturates in contrast to the GP solution, and its spatial extent becomes smaller than that of the GP condensate.

Yannouleas, Constantine; Landman, Uzi

2006-01-01

42

Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy  

NASA Astrophysics Data System (ADS)

Confinement of electron-hole pairs (excitons) in semiconductor quantum dots (QDs) leads to novel quantum phenomena, tunable optical properties and enhanced Coulomb interactions, all of which are sensitive to the size, shape and material composition of the QDs. This thesis discusses our pursuit in unraveling the complex interrelation between morphology of a QD and its electronic and optical properties. A series of epitaxially-grown semiconductor nanostructures with different QD sizes and composition is studied using optical two-dimensional coherent spectroscopy (2DCS). With the unique capabilities of unambiguously identifying coupling between resonances, isolating quantum pathways and revealing homogeneous dephasing information in heterogeneous systems, 2DCS is a powerful tool for studying QD ensembles. Of paramount importance is the exciton homogeneous line width, which is inversely proportional to the dephasing time. As the dephasing time sets the duration for which coherence is maintained, knowledge of the principal dephasing mechanisms in QDs is essential. 2D spectra of excitons in weakly-confining GaAs QDs reveal that elastic exciton-phonon coupling and intra-dot exciton-exciton interactions are responsible for line width broadening beyond the radiative limit, and the interaction strength of both mechanisms increases for decreasing QD size. These results are compared to those obtained from InAs QDs, which exhibit an order-of-magnitude larger confinement, to illustrate the role quantum confinement plays in exciton dephasing. The lowest energy optical transitions in semiconductor QDs are modified by confinement-enhanced Coulomb interactions, such as exchange-mediated coupling between excitons and correlation effects that can lead to bound and anti-bound states of two excitons. 2D spectra particularly sensitive to these interactions reveal that the electron and hole wave functions -- and therefore the strength of Coulomb interactions -- are sensitive to variations in QD size for the GaAs ensemble. In the InAs QDs, however, the wave functions are remarkably independent of the details of confinement, leading to similar electronic and optical properties for all QDs. To provide additional insight, the spectra are modeled using perturbative density matrix calculations, and the results are compared to many-body calculations to reveal the significance of the strength and nature of Coulomb interactions on the optical properties of QDs.

Moody, Galan

43

Quantum optics with single nanowire quantum dots  

Microsoft Academic Search

In this paper we present our recent developments in control and manipulation of individual spins and photons in a single nanowire quantum dot. Specific examples include demonstration of optical excitation of single spin states, charge tunable quantum devices and single photon sources. We will also discuss our recent discovery of a new type of charge confinement - crystal phase quantum

N. Akopian; Weert van MHM; Kouwen van MP; RE Algra; L. Liu; G. Patriarche; J.-C. Harmand; EPAM Bakkers; LP Kouwenhoven; V. Zwiller

2010-01-01

44

Photoluminescence quantum yield of CdSe-ZnS/CdS/ZnS core-multishell quantum dots approaches 100% due to enhancement of charge carrier confinement  

NASA Astrophysics Data System (ADS)

Quantum dots (QDs) with the highest possible photoluminescence quantum yields are necessary for modern nanotechnology applications to biosensing and optoelectronics. To date, core-shell QDs are the best. We suggest and demonstrate a novel approach to enhancement of charge-carrier confinement in the core of CdSe QDs by creating a ZnS/CdS/ZnS shell with staggered potential barrier. The CdS interlayer breaks the ZnS-shell structure continuity, which allows combining the benefits of a single ZnS-monolayer inner shell, creating the highest possible confinement potential, with a sufficient overall shell thickness and suitability for common surface modification techniques. This approach allows the preparation of CdSe-ZnS/CdS/ZnS QDs with photoluminescence quantum yields approaching 100% and small photoluminescence peak width.

Samokhvalov, Pavel; Linkov, Pavel; Michel, Jean; Molinari, Michael; Nabiev, Igor

2014-03-01

45

The effect of an anisotropic confinement on the ground-state energy of a polaron in a parabolic quantum dot  

NASA Astrophysics Data System (ADS)

We study the ground-state energy of a large polaron in a quantum dot. The electron is treated as trapped in an anisotropic parabolic box while the coupling to bulk LO phonons is considered. An upper bound to the ground-state energy of the polaron is obtained using the Fock approximation of Matz and Burkey. With this treatment, we obtain variational results that are good to describe weak or strong electron-phonon coupling as well as the isotropic and the one- and two-dimensional confinement limits. The usual asymptotic limits are found for all of these cases. Numerical calculations carried out in order to study the validity of each of these limits as a function of the degree of anisotropy are presented. Also we discuss the effect that the anisotropy and the strength of the confining potential have on the self-energy of the polaron. We find that an anisotropic confinement is more effective as regards increasing the self-energy of the polaron than an isotropic confinement.

Lépine, Y.; Bruneau, G.

1998-02-01

46

Effect of Rashba interaction and Coulomb correlation on the ground state energy of a GaAs quantum dot with parabolic confinement  

NASA Astrophysics Data System (ADS)

The ground state energy of a parabolically confined quantum dot placed in an external magnetic field is studied taking into account the effects of the Rashba spin-orbit interaction (SOI) and electron-electron interaction. With a simple and physically reasonable model potential for electron-electron interaction term, the problem is solved exactly to second order in the Rashba coupling constant.

Sanjeev Kumar, D.; Mukhopadhyay, Soma; Chatterjee, Ashok

2013-01-01

47

Effect of ZnS shell formation on the confined energy levels of ZnSe quantum dots  

Microsoft Academic Search

Photoluminescence excitation spectroscopy was employed to investigate the electronic structure of ZnSe\\/ZnS core\\/shell quantum dots. Four excited states viz. 1Se-1S3\\/2h , 1Se-2S3\\/2h , 1Pe-1P3\\/2h , and 1Se-1SSO are observed in ZnSe and ZnSe\\/ZnS core\\/shell quantum dots. The experimentally observed excited states for ZnSe\\/ZnS quantum dots are analyzed on the basis of reported ``effective mass approximation'' calculations. The photoluminescence quantum efficiency

Amit D. Lad; Shailaja Mahamuni

2008-01-01

48

Anisotropy effect on the nonlinear optical properties of a three-dimensional quantum dot confined at the center of a cylindrical nano-wire  

NASA Astrophysics Data System (ADS)

The effect of geometrical anisotropy is numerically investigated on the linear and nonlinear optical properties of a GaAs quantum dot which is located at the center of a Ga1-xAlxAs cylindrical nano-wire. The finite difference approximation has been used for obtaining energy eigenvalues and corresponding wave functions. Also, the compact density matrix formalism is applied to investigate linear, third order nonlinear and total optical absorption coefficients (ACs) and refractive index (RI) changes. The optical properties and oscillator strength are calculated as a function of the incident photon energy for different ellipsoid aspect ratio, dot radius and incident optical intensity for 1-2, 2-3 and 1-3 transitions. The results clearly reveal that the dot anisotropy plays an important role in determining the magnitude of nonlinear AC and RI changes which enable us to adjust saturation condition. We found that the dot anisotropy shifts absorption spectrum towards both lower and higher energies which depend on the shape of dot (spherical, prolate or oblate quantum dot), dot radius and states between which transitions will occur. Additionally, it is shown that the presence of nano-wire (second confinement) causes (I) a large increment in RI changes (II) a decrement in total AC for prolate QDs with respect to the dot radius (III) an increment in third order AC with respect to the ellipsoid aspect ratio and (IV) a blue shift in optical spectrum.

Safarpour, Gh.; Izadi, M. A.; Novzari, M.; Niknam, E.; Moradi, M.

2014-05-01

49

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots  

PubMed Central

A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model.

2011-01-01

50

Stark effect in parabolic quantum dot  

Microsoft Academic Search

We theoretically investigate the optical properties of the exciton confined in parabolic quantum-dot , with and without electric field, by means of perturbative-variational method. The quantum-dot size enhances the 1s eigenvalue ahd oscillator strength . In smaller dot the relative extension of the exciton wave function is equal to the size of the dot . The 1s exciton bihding energy

S. JAZIRI; G. BASTARD; R. BENNACEUR

1993-01-01

51

Large quantum dots with small oscillator strength  

NASA Astrophysics Data System (ADS)

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 intermixing inside the quantum dots.

Stobbe, S.; Schlereth, T. W.; Höfling, S.; Forchel, A.; Hvam, J. M.; Lodahl, P.

2010-12-01

52

Quantum confinement energy in nanocrystalline silicon dots from high-frequency conductance measurement  

Microsoft Academic Search

Electron charging and discharging processes in floating gate metal-oxide-semiconductor memory based on nanocrystalline silicon (nc-Si) dots were investigated at room temperature using capacitance-voltage and conductance-voltage (G-V) measurements. From charged nc-Si dots, a sequential electron discharging processes was clearly observed in G-V spectroscopy. The fine structure in the observed conductance peaks has been interpreted in terms of the Coulomb blockade and

Shaoyun Huang; Souri Banerjee; Raymond T. Tung; Shunri Oda

2003-01-01

53

Mid-Infrared Quantum Dot Emitters Utilizing Planar Photonic Crystal Technology.  

National Technical Information Service (NTIS)

The three-dimensional confinement inherent in InAs self-assembled quantum dots (SAQDs) yields vastly different optical properties compared to one-dimensionally confined quantum well systems. Intersubband transitions in quantum dots can emit light normal t...

B. Passmore E. A. Shaner G. Subramania J. Cederberg S. K. Lyo

2008-01-01

54

Resistive switching memory based on three-dimensionally confined Ag quantum dots embedded in ultra thin polyimide layers.  

PubMed

Resistive switching memory devices based on three-dimensionally confined Ag quantum dots (QDs) embedded in polyimide (PI) layers were fabricated by using spin-coating and thermal evaporation. The Ag QDs embedded in PI layer were distributed uniformly with sizes of approximately 4-6 nm and with surface density of approximately 1.25 x 10(11) cm(-2). The electrical properties of the Ag/PI (10 nm)/Ag QDs/PI (10 nm)/Ag devices were investigated at room temperature. Current-voltage (I-V) measurements on the devices showed a counterclockwise electrical hysteresis behavior with reliable and reproducible resistive switching to the existence of the Ag QDs. The memory device transformed from its original high-resistance state to low-resistance state under positive bias, and regained its original high-resistance state under negative bias. The maximum ON/OFF ratio of the current bistability was 1 x 10(4). The device also revealed excellent endurance ability at ambient conditions. The possible operating mechanisms concerning the interaction between Ag QDs and PI matrix for the resistance-transform phenomenon were analyzed on the basis of the I-V results. PMID:23646596

Wu, Chaoxing; Li, Fushan; Guo, Tailiang

2013-02-01

55

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

56

Electronic structure and photon absorption in semiconductor quantum dots  

Microsoft Academic Search

Quantum dot structures have been the subject of intense investigation in recent years with the advances of molecular beam epitaxy growth technology. Quantum dot infrared photodetector (QDIP) which rely on intersubband transitions in quantum wells or quantum dots for infrared detection, as the three-dimensional confinement of electrons leads to a distribution of energy levels which impedes electron-phonon scattering. This suggests

Gregory von Winckel

2006-01-01

57

Nanocrystalline-Si-dot multi-layers fabrication by chemical vapor deposition with H-plasma surface treatment and evaluation of structure and quantum confinement effects  

NASA Astrophysics Data System (ADS)

100-nm-thick nanocrystalline silicon (nano-Si)-dot multi-layers on a Si substrate were fabricated by the sequential repetition of H-plasma surface treatment, chemical vapor deposition, and surface oxidation, for over 120 times. The diameter of the nano-Si dots was 5-6 nm, as confirmed by both the transmission electron microscopy and X-ray diffraction analysis. The annealing process was important to improve the crystallinity of the nano-Si dot. We investigated quantum confinement effects by Raman spectroscopy and photoluminescence (PL) measurements. Based on the experimental results, we simulated the Raman spectrum using a phenomenological model. Consequently, the strain induced in the nano-Si dots was estimated by comparing the experimental and simulated results. Taking the estimated strain value into consideration, the band gap modulation was measured, and the diameter of the nano-Si dots was calculated to be 5.6 nm by using PL. The relaxation of the q ˜ 0 selection rule model for the nano-Si dots is believed to be important to explain both the phenomena of peak broadening on the low-wavenumber side observed in Raman spectra and the blue shift observed in PL measurements.

Kosemura, Daisuke; Mizukami, Yuki; Takei, Munehisa; Numasawa, Yohichiroh; Ohshita, Yoshio; Ogura, Atsushi

2014-01-01

58

Quantum computation with quantum dots  

Microsoft Academic Search

We propose an implementation of a universal set of one- and two-quantum-bit gates for quantum computation using the spin states of coupled single-electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a recently derived spin master equation incorporating decoherence caused by a prototypical

Daniel Loss; David P. Divincenzo

1998-01-01

59

Classical behavior of few-electron parabolic quantum dots  

Microsoft Academic Search

Quantum dots are intricate and fascinating systems to study novel phenomena of great theoretical and practical interest because low dimensionality coupled with the interplay between strong correlations, quantum confinement and magnetic field creates unique conditions for emergence of fundamentally new physics. In this work we consider two-dimensional semiconductor quantum dot systems consisting of few interacting electrons confined in an isotropic

O. Ciftja

2009-01-01

60

Exotic Kondo States in GaAs Quantum Dots  

Microsoft Academic Search

Using a unique double quantum dot geometry, we probe an exotic Kondo effect involving one quantum dot containing excess spin-1\\/2 simultaneously coupled to both open and confined reservoirs of electrons. Transport measurements through open reservoirs (normal leads) reveal single channel Kondo behavior. However, the addition of a third lead consisting of a large quantum dot drastically changes transport through the

R. M. Potok; I. G. Rau; C. M. Marcus; H. Shtrikman

2005-01-01

61

Transient nonlinear spectroscopy of single quantum dots  

Microsoft Academic Search

Quantum dots represent electrons confined in all three dimensions on nanometer length scales. They are already being integrated into novel optoelectronic devices, and their use in a wide range of additional quantum-based devices has been proposed, including solid state quantum computers. Successful implementation of these proposals requires an improved understanding of the physical properties of localized electrons in solids. In

Todd Harry Stievater

2001-01-01

62

Quantum Dot Solar Cells  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

63

Self-sustained pulsation in the oxide-confined vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots  

SciTech Connect

The authors report the observation of strong self-pulsations in molecular-beam epitaxy-grown oxide-confined vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots. At continuous-wave operation, self-pulsations with pulse durations of 100-300 ps and repetition rates of 0.2-0.6 GHz were measured. The average optical power of the pulsations was 0.5-1.0 mW at the laser continuous-wave current values of 1.5-2.5 mA.

Kuzmenkov, A. G.; Ustinov, V. M.; Sokolovskii, G. S.; Maleev, N. A.; Blokhin, S. A.; Deryagin, A. G.; Chumak, S. V.; Shulenkov, A. S.; Mikhrin, S. S.; Kovsh, A. R.; McRobbie, A. D.; Sibbett, W.; Cataluna, M. A.; Rafailov, E. U. [Saint-Petersburg Physics and Technology Centre for Research and Education of the Russian Academy of Sciences, St. Petersburg 199034 (Russian Federation); Ioffe Physico-Technical Institute, St. Petersburg 194021 (Russian Federation); Minsk R and D Institute of Radiomaterials, Minsk 220024 (Belarus); Innolume GmbH, 44263 Dortmund (Germany); School of Physics and Astronomy, University of St Andrews, St. Andrews KY16 9SS (United Kingdom); Division of Electronic Engineering and Physics, University of Dundee, Dundee, DD1 4HN (United Kingdom)

2007-09-17

64

Quantum Dots for Biophotonics  

PubMed Central

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

Yong, Ken-Tye

2012-01-01

65

Spontaneous emission and optical control of spins in quantum dots  

Microsoft Academic Search

Quantum dots are attractive due to their potential technological applications and the opportunity they provide for study of fundamental physics in the mesoscopic scale. This dissertation studies optically controlled spins in quantum dots in connection to quantum information processing. The physical realization of the quantum bit (qubit) consists of the two spin states of an extra electron confined in a

Sophia E. Economou

2006-01-01

66

Quantum Dot Solar Cells  

Microsoft Academic Search

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

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

2002-01-01

67

Quantum dots with single-atom precision.  

PubMed

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. PMID:24974937

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

2014-07-01

68

Quantum confinement controlled solar hydrogen production from hydrogen sulfide using a highly stable CdS0.5Se0.5/CdSe quantum dot-glass nanosystem  

NASA Astrophysics Data System (ADS)

We have demonstrated unique CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems with quantum confinement effect. The stable, monodispersed CdS0.5Se0.5 and CdSe quantum dots (QDs) of size 2 to 12 nm have been grown in a germanate glass matrix by a simple melt quench technique at moderate temperature. XRD and Raman studies show formation of hexagonal CdS0.5Se0.5 and CdSe in the glass matrix. The quantum confinement of CdS0.5Se0.5 and CdSe was studied using TEM and UV-Vis spectroscopy. The band gap of the glass nanosystem was tuned from 3.6 to 1.8 eV by controlling the CdS0.5Se0.5 quantum dot size in the glass matrix. It can be further tuned to 1.68 eV using growth of CdSe quantum dots in the glass matrix. Considering the tuneable band gap of the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystem for the visible light absorption, a study of size tuneable photocatalytic activity for hydrogen generation from hydrogen sulfide splitting was performed under visible light irradiation for the first time. The utmost hydrogen evolution, i.e. 8164.53 and 7257.36 ?mol h-1 g-1 was obtained for the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems, respectively. The apparent quantum yield (AQY) was observed to be 26% and 21% for the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems, respectively. It is noteworthy that the present glass nanosystem as a photocatalyst was found to be very stable as compared to naked powder photocatalysts.We have demonstrated unique CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems with quantum confinement effect. The stable, monodispersed CdS0.5Se0.5 and CdSe quantum dots (QDs) of size 2 to 12 nm have been grown in a germanate glass matrix by a simple melt quench technique at moderate temperature. XRD and Raman studies show formation of hexagonal CdS0.5Se0.5 and CdSe in the glass matrix. The quantum confinement of CdS0.5Se0.5 and CdSe was studied using TEM and UV-Vis spectroscopy. The band gap of the glass nanosystem was tuned from 3.6 to 1.8 eV by controlling the CdS0.5Se0.5 quantum dot size in the glass matrix. It can be further tuned to 1.68 eV using growth of CdSe quantum dots in the glass matrix. Considering the tuneable band gap of the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystem for the visible light absorption, a study of size tuneable photocatalytic activity for hydrogen generation from hydrogen sulfide splitting was performed under visible light irradiation for the first time. The utmost hydrogen evolution, i.e. 8164.53 and 7257.36 ?mol h-1 g-1 was obtained for the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems, respectively. The apparent quantum yield (AQY) was observed to be 26% and 21% for the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems, respectively. It is noteworthy that the present glass nanosystem as a photocatalyst was found to be very stable as compared to naked powder photocatalysts. Electronic supplementary information (ESI) available: S-1. XRD of as synthesized CdS0.5Se0.5 and standard CdSe powder; S-2. Raman spectra of as synthesized CdS0.5Se0.5 and standard CdSe Powder; S-3. UV-Vis spectra of as synthesized CdS0.5Se0.5 powder; S-4. Narrow distribution of Quantum dots; S-5. TEM images of as synthesised CdS0.5Se0.5 powder; S-6. Repeatability and reusability of photocatalyst, CdS0.5Se0.5/CdSe quantum dot-glass nanosystems; S-7. XRD pattern of reused glass photocatalysts; S-8. Raman spectra of reused glass photocatalysts; S-9. XRD pattern of as synthesized CdS0.5Se0.5 powder and CdS0.5Se0.5 powder after photocatalysis reaction; S-10. XRD pattern of CdSe powder and CdSe powder after photocatalysis reaction; S-11. Synthesis procedure of CdS0.5Se0.5 powder. See DOI: 10.1039/c3nr04898e

Apte, Sanjay K.; Garaje, Sunil N.; Naik, Sonali D.; Waichal, Rupali P.; Baeg, Jin-Ook; Kale, Bharat B.

2013-12-01

69

Quantum Dots: An Experiment for Physical or Materials Chemistry  

ERIC Educational Resources Information Center

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.

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

2005-01-01

70

Topic in Depth - Quantum Dots  

NSDL National Science Digital Library

This topic-in-depth addresses the characteristics and numerous applications of the semiconductor nanocrystals, quantum dots. Find out how quantum dot are being used in computer science, chemistry, and medicine.

2010-09-20

71

Barrier engineered superlattice and quantum dot detectors for HOT operation  

Microsoft Academic Search

In this paper, we demonstrate a high operating temperature (HOT) quantum dot-in-a-well (DWELL) infrared photodetector with enhanced normal incidence (s-polarization) radiation photocurrent. The s-to-p polarization ratio was increased to 50%, compared to the 20% in conventional quantum dot detectors. This improvement was achieved through engineering the dot geometry and the quantum confinement via post growth capping materials of the quantum

Jiayi Shao; Thomas E. Vandervelde; Ajit Barve; Woo-Yong Jang; Andreas Stintz; Sanjay Krishna

2011-01-01

72

Collective Modes and Optical Absorption in Parabolic Quantum Wells and Quantum Dots  

Microsoft Academic Search

Parabolic confinement arises in semiconductor microstructures by design, as in parabolic quantum wells, or as a by-product of the fabrication process, as in quantum -dot and quantum-wire systems. We use a variety of techniques to study collective modes and far-infrared optical absorption in parabolic quantum wells and quantum dots. For a model array of Coulombically-coupled parabolic quantum dots, we use

Jed Dempsey

1991-01-01

73

Quantum-Dot Cellular Automata  

Microsoft Academic Search

Quantum-dot Cellular Automata (QCA) [1] is a promising architecture which employs quantum dots for digital computation. It is a revolutionary approach that holds the promise of high device density and low power dissipation. A basic QCA cell consists of four quantum dots coupled capacitively and by tunnel barriers. The cell is biased to contain two excess electrons within the four

Gregory Snider

2000-01-01

74

Investigation on the lasing characteristics of InAs/InGaAsP quantum dots with additional confinement structures  

NASA Astrophysics Data System (ADS)

We report on morphological, optical, and lasing characteristics of InAs quantum dots (QDs) embedded in an In0.69Ga0.31As0.67P0.33 quantum well (having a bandgap energy corresponding to a wavelength of 1.35 ?m (1.35Q-InGaAsP)), which formed a dot-in-a-well (DWELL) structure. This DWELL was further sandwiched in In0.85Ga0.15As0.32P0.68 layers (1.15 ?m, 1.15Q-InGaAsP). A 2 monolayer-thick GaAs layer was simultaneously introduced right below the InAs QD layer in the DWELL structure (GDWELL). The emission wavelength of the InAs GDWELL was 1490 nm, which was slightly shorter than that of the InAs QDs embedded only in 1.15Q-InGaAsP layers. To evaluate the effects of the GDWELL structure on lasing characteristics, gain-guided broad-area (BA) and index-guided ridge-waveguide (RW) laser diodes (LDs) were fabricated. The BA-LDs with the InAs QDs embedded only in 1.15Q-InGaAsP layers did not show the lasing at room temperature (RT) even in pulsed mode. For the GDWELL structure, however, the lasing emissions from both the BA-LDs and RW-LDs were successfully achieved at RT in continuous-wave mode.

Jo, Byounggu; Lee, Cheul-Ro; Kim, Jin Soo; Han, Won Seok; Song, Jung Ho; Leem, Jae-Young; Noh, Sam Kyu; Ryou, Jae-Hyun; Dupuis, Russell D.

2014-05-01

75

Quantum optics with quantum dots in microcavities  

NASA Astrophysics Data System (ADS)

This dissertation describes several quantum optics experiments that rely on the coupling between an atomic-like system and the confined optical modes of a cavity as described by cavity quantum electrodynamics (QED). The novelty of these experiments is that they are performed in the solid-state and as such are extremely interesting for applications of quantum information. These results have been obtained through a collaborative effort between the research groups of D. Bouwmeester in Physics, P. M. Petroff in Materials and ECE, L. A. Coldren in Materials and ECE, and E. L. Hu in ECE. The first set of these experiments explores this coupling in photonic crystal defect cavities. The first of these experiments shows how very few quantum dots can act as a sufficient gain medium to generate extremely low-threshold lasing. This surprising result, which arises due to the non-atomic-like nature of the quantum dots, is verified by a measurement of the photon statistical transition of the cavity mode. This is done for a series of such devices to elucidate the differences between macroscopic lasers and nanolasers. Next, a short experiment is discussed which uses the adsorption of material inside the cryostat to spectrally tune the resonance of a photonic crystal cavity. This section of the dissertation concludes with an experiment demonstrating an all-optical scheme to precisely determine the spacial location of a single quantum dot. Then, using this location, a high-quality photonic crystal cavity is fabricated, and strong coupling between the quantum and cavity is realized. The second set of experiments employs a novel, electrically-gated, oxide-apertured micropillar cavity to demonstrate a bright source of optically-generated single photons as well as electrically-generated single photons. Furthermore, the intra-cavity electric field generated by the gating of the structures enabled the demonstration of cavity QED with charged quantum dots, which has important ramifications for solid-state quantum information schemes that use the spin of an electron (or hole) for manipulation. Finally, the intra-cavity field is used to achieve spectral resonance between a quantum dot and a cavity mode by the Stark effect. This effect, in combination with a slightly elliptical micropillar, is used to demonstrate a polarization-switchable single photon source.

Rakher, Matthew T.

76

Coherent control and decoherence of single semiconductor quantum dots in a microcavity  

Microsoft Academic Search

Semiconductor quantum dots tightly confine excited electron-hole pairs, called excitons, resulting in discrete energy levels similar to those of single atoms. Transition energies in the visible or near-infrared make quantum dots suitable for many applications in quantum optics and quantum information science, but to take advantage of all the properties of quantum dot emission, it is necessary to excite them

Edward B. Flagg II

2008-01-01

77

Image simulations of quantum dots.  

SciTech Connect

Quantum dot (QD) nanostructures have drawn increased interest in recent years. Their small size leads to quantum confinement of the electrons, which is responsible for their unique electronic and optical properties. They promise to find use in a wide range of devices ranging from semiconductor lasers (Bimberg et al (2001), Ribbat et al (2001)) to quantum computing. The properties of QDs are also determined by their shape and composition. All three parameters (size, shape and composition) have a significant impact on their contrast in the transmission electron microscope (TEM), and consequently the possibility arises that these parameters can be extracted from the images. Zone axis plan view images are especially sensitive to the composition of QDs, and image simulation is an important way to understand how the composition determines the contrast. This paper outlines a method of image simulation of QDs developed by Liao et. al. (1999) and presents an application of the method to QDs in wurtzite InN/GaN.

Lang, C. (Christian); Liao, Xiaozhou; Cockayne, D. J. (David J.)

2001-01-01

78

Quantum optics with single quantum dot devices  

Microsoft Academic Search

A single radiative transition in a single-quantum emitter results in the emission of a single photon. Single quantum dots are single-quantum emitters with all the requirements to generate single photons at visible and near-infrared wavelengths. It is also possible to generate more than single photons with single quantum dots. In this paper we show that single quantum dots can be

Valéry Zwiller; Thomas Aichele; Oliver Benson

2004-01-01

79

Guest Editorial: Quantum Dots.  

National Technical Information Service (NTIS)

Advances in quantum dot (QD) waveguides, lasers, photodetectors, and growth/synthesis technologies are the subject of this special section. The development of Stranski-Krastanow strain-layer QDs has led to the emergence of low-threshold and moderate to hi...

J. Xu M. Gerhold

2009-01-01

80

Quantum dot infrared photodetectors  

Microsoft Academic Search

We discuss key issues related to quantum dot infrared photodetectors. These are the normal incidence response, the dark current, and the responsivity and detectivity. It is argued that the present devices have not fully demonstrated the potential advantages. The dominant infrared response in devices so far is polarized in the growth direction. The observed dark currents are several orders of

H. C. Liu; J.-Y. Duboz; R. Dudek; Z. R. Wasilewski; S. Fafard; P. Finnie

2003-01-01

81

Quantum dot solar cells  

Microsoft Academic Search

Quantum dot (QD) solar cells have the potential to increase the maximum attainable thermodynamic conversion efficiency of solar photon conversion up to about 66% by utilizing hot photogenerated carriers to produce higher photovoltages or higher photocurrents. The former effect is based on miniband transport and collection of hot carriers in QD array photoelectrodes before they relax to the band edges

A. J Nozik

2002-01-01

82

Plasmonic fluorescent quantum dots  

Microsoft Academic Search

Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals

Yongdong Jin; Xiaohu Gao

2009-01-01

83

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

Microsoft Academic Search

Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron–hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot

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

2011-01-01

84

Quadra-quantum dots grown on quantum rings having square-shaped holes: Basic nanostructure for quantum dot cellular automata application  

Microsoft Academic Search

Preferable quantum dot (QD) nanostructure for quantum computation based on quantum cellular automata (QCA) is laterally close-packed quantum dot molecular (QDM) having 4 QDs at the corners of square configuration. We called this 4 QDs-set as quadra-quantum dots (QQDs). Aligned QQDs with 2 electron-confinements work like a wire for digital information transmission by Coulomb repulsion force which is high speed

P. Boonpeng; W. Jevasuwan; S. Suraprapapich; S. Ratanathammaphan; S. Panyakeow

2009-01-01

85

Bound states in continuum: Quantum dots in a quantum well  

NASA Astrophysics Data System (ADS)

We report on the existence of a bound state in the continuum (BIC) of quantum rods (QR). QRs are novel elongated InGaAs quantum dot nanostructures embedded in the shallower InGaAs quantum well. BIC appears as an excited confined dot state and energetically above the bottom of a well subband continuum. We prove that high height-to-diameter QR aspect ratio and the presence of a quantum well are indispensable conditions for accommodating the BIC. QRs are unique semiconductor nanostructures, exhibiting this mathematical curiosity predicted 83 years ago by Wigner and von Neumann.

Prodanovi?, Nikola; Milanovi?, Vitomir; Ikoni?, Zoran; Indjin, Dragan; Harrison, Paul

2013-11-01

86

Quantum-dot cellular automata  

Microsoft Academic Search

Quantum-dot Cellular Automata (QCA) is a promising architecture which employs quantum dots for digital computation. It is a revolutionary approach which addresses the issues of device density and power dissipation. With a dot size of 20 nm an entire full adder would occupy only one square micron, and the power delay product is as low as a few kT. A

G. L. Snider; A. O. Orlov; I. Amlani; G. H. Bernstein; C. S. Lent; J. L. Merz; W. Porod

1999-01-01

87

Spatially confined synthesis of SiOx nano-rod with size-controlled Si quantum dots in nano-porous anodic aluminum oxide membrane.  

PubMed

By depositing Si-rich SiOx nano-rod in nano-porous anodic aluminum oxide (AAO) membrane using PECVD, the spatially confined synthesis of Si quantum-dots (Si-QDs) with ultra-bright photoluminescence spectra are demonstrated after low-temperature annealing. Spatially confined SiOx nano-rod in nano-porous AAO membrane greatly increases the density of nucleated positions for Si-QD precursors, which essentially impedes the route of thermally diffused Si atoms and confines the degree of atomic self-aggregation. The diffusion controlled growth mechanism is employed to determine the activation energy of 6.284 kJ mole(-1) and diffusion length of 2.84 nm for SiO1.5 nano-rod in nano-porous AAO membrane. HRTEM results verify that the reduced geometric dimension of the SiOx host matrix effectively constrain the buried Si-QD size at even lower annealing temperature. The spatially confined synthesis of Si-QD essentially contributes the intense PL with its spectral linewidth shrinking from 210 to 140 nm and its peak intensity enhancing by two orders of magnitude, corresponding to the reduction on both the average Si-QD size and its standard deviation from 2.6 to 2.0 nm and from 25% to 12.5%, respectively. The red-shifted PL wavelength of the Si-QD reveals an inverse exponential trend with increasing temperature of annealing, which is in good agree with the Si-QD size simulation via the atomic diffusion theory. PMID:21263629

Pai, Yi-Hao; Lin, Gong-Ru

2011-01-17

88

Magnetic Polarons in Anisotropic Quantum Dots  

Microsoft Academic Search

Tunability of confinement in magnetically-doped quantum dots (QDs) allows to tailor magnetism to an extent not available in bulk semiconductors. Versatile control of magnetic ordering, along with piezomagnetism, has been predicted even at a fixed number of carriers [1]. Recent experiments on colloidal QDs revealed strongly bound magnetic polarons (MPs) [2]. Previous studies of MPs in bulk semiconductors showed that

Rafal Oszwaldowski; Andre Petukhov; Igor Zutic

2010-01-01

89

Positioning of quantum dots on metallic nanostructures  

Microsoft Academic Search

The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has

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

2010-01-01

90

Interacting electrons in parabolic quantum dots  

Microsoft Academic Search

The problem of interacting electrons in a parabolic confinement has attracted considerable attention recently since experiments on parabolic quantum dots have revealed peculiar properties. We investigate this phenomenon numerically. To this end we diagonalize the Hamiltonian for Coulomb as well as for short range interactions using the Hartree-Fock based exact diagonalization method. In addition to the ground state energy we

Michael Schreiber; Jens Siewert; Thomas Vojta

2001-01-01

91

Highly tunable hybrid quantum dots with charge detection  

Microsoft Academic Search

In order to employ solid state quantum dots as qubits, both a high degree of control over the confinement potential as well as sensitive charge detection are essential. We demonstrate that by combining local anodic oxidation with local Schottky-gates, these criteria are nicely fulfilled in the resulting hybrid device. To this end, a quantum dot with adjacent charge detector is

C. Rössler; B. Küng; S. Dröscher; T. Choi; T. Ihn; K. Ensslin; M. Beck

2010-01-01

92

QUANTUM-DOT DEVICES AND QUANTUM-DOT CELLULAR AUTOMATA  

Microsoft Academic Search

We discuss novel nanoelectronic architecture paradigms based on cells composed of coupled quantum-dots. Boolean logic functions may be implemented in specic arrays of cells repre- senting binary information, the so-called Quantum-Dot Cellular Automata (QCA). Cells may also be viewed as carrying analog information and we outline a network-theoretic description of such Quantum-Dot Nonlinear Networks (Q-CNN). In addition, we discuss possible

WOLFGANG POROD

1997-01-01

93

Quantum-dot devices and Quantum-dot Cellular Automata  

Microsoft Academic Search

We discuss novel nanoelectronic architecture paradigms based on cells composed of coupled quantum dots. Boolean logic functions may be implemented in specific arrays of cells representing binary information, the so-called Quantum-Dot Cellular Automata (QCA). Cells may also be viewed as carrying analog information, and we outline a network-theoretic description of such Quantum-Dot Nonlinear Networks (Q-CNN). In addition, we discuss possible

Wolfgang Porod

1997-01-01

94

Quantum-dot cellular automata: computing with coupled quantum dots  

Microsoft Academic Search

We discuss novel nanoelectronic architecture paradigms based on cells composed of coupled quantum-dots. Boolean logic functions may be implemented in speci® c arrays of cells representing binary information, the so-called quantum-dot cellular automata (QCA). Cells may also be viewed as carrying analogue information and we outline a network-theoretic description of such quantum-dot nonlinear net- works (Q-CNN). In addition, we discuss

WOLFGANG POROD; CRAIG S. LENT; GARY H. BERNSTEIN; ALEXEI O. ORLOV; ISLAMSHAH AMLANI; GREGORY L. SNIDER; JAMES L. MERZ

1999-01-01

95

Positioning of quantum dots on metallic nanostructures.  

PubMed

The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has thus far been elusive. Placing an emission source within the influence of plasmonic structures now requires accuracy approaching molecular length scales. In this paper we report the ability to reliably position nanoscale functional objects, specifically quantum dots, with sub-100-nm accuracy, which is several times smaller than the diffraction limit of a quantum dot's emission light. Electron beam lithography-defined masks on metallic surfaces and a series of surface chemical functionalization processes allow the programmed assembly of DNA-linked colloidal quantum dots. The quantum dots are successfully functionalized to areas as small as (100 nm)(2) using the specific binding of thiolated DNA to Au/Ag, and exploiting the streptavidin-biotin interaction. An analysis of the reproducibility of the process for various pattern sizes shows that this technique is potentially scalable to the single quantum dot level with 50 nm accuracy accompanied by a moderate reduction in yield. PMID:20234079

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

2010-04-01

96

Quantum dots and spin qubits in graphene.  

PubMed

This is a review on graphene quantum dots and their use as a host for spin qubits. We discuss the advantages but also the challenges to use graphene quantum dots for spin qubits as compared to the more standard materials like GaAs. We start with an overview of this young and fascinating field and then discuss gate-tunable quantum dots in detail. We calculate the bound states for three different quantum dot architectures where a bulk gap allows for confinement via electrostatic fields: (i) graphene nanoribbons with armchair boundaries, (ii) a disc in single-layer graphene, and (iii) a disc in bilayer graphene. In order for graphene quantum dots to be useful in the context of spin qubits, one needs to find reliable ways to break the valley degeneracy. This is achieved here, either by a specific termination of graphene in (i) or in (ii) and (iii) by a magnetic field, without the need of a specific boundary. We further discuss how to manipulate spin in these quantum dots and explain the mechanism of spin decoherence and relaxation caused by spin-orbit interaction in combination with electron-phonon coupling, and by hyperfine interaction with the nuclear-spin system. PMID:20603538

Recher, Patrik; Trauzettel, Björn

2010-07-30

97

PREFACE: Quantum Dot 2010  

NASA Astrophysics Data System (ADS)

These conference proceedings contain the written papers of the contributions presented at Quantum Dot 2010 (QD2010). The conference was held in Nottingham, UK, on 26-30 April 2010. The conference addressed topics in research on: 1. Epitaxial quantum dots (including self-assembled and interface structures, dots defined by electrostatic gates etc): optical properties and electron transport quantum coherence effects spin phenomena optics of dots in cavities interaction with surface plasmons in metal/semiconductor structures opto-electronics applications 2. Novel QD structures: fabrication and physics of graphene dots, dots in nano-wires etc 3. Colloidal quantum dots: growth (shape control and hybrid nanocrystals such as metal/semiconductor, magnetic/semiconductor) assembly and surface functionalisation optical properties and spin dynamics electrical and magnetic properties applications (light emitting devices and solar cells, biological and medical applications, data storage, assemblers) The Editors Acknowledgements Conference Organising Committee: Maurice Skolnick (Chair) Alexander Tartakovskii (Programme Chair) Pavlos Lagoudakis (Programme Chair) Max Migliorato (Conference Secretary) Paola Borri (Publicity) Robert Taylor (Proceedings) Manus Hayne (Treasurer) Ray Murray (Sponsorship) Mohamed Henini (Local Organiser) International Advisory Committee: Yasuhiko Arakawa (Tokyo University, Japan) Manfred Bayer (Dortmund University, Germany) Sergey Gaponenko (Stepanov Institute of Physics, Minsk, Belarus) Pawel Hawrylak (NRC, Ottawa, Canada) Fritz Henneberger (Institute for Physics, Berlin, Germany) Atac Imamoglu (ETH, Zurich, Switzerland) Paul Koenraad (TU Eindhoven, Nethehrlands) Guglielmo Lanzani (Politecnico di Milano, Italy) Jungil Lee (Korea Institute of Science and Technology, Korea) Henri Mariette (CNRS-CEA, Grenoble, France) Lu Jeu Sham (San Diego, USA) Andrew Shields (Toshiba Research Europe, Cambridge, UK) Yoshihisa Yamamoto (Stanford University, USA) Artur Zrenner (Paderborn University, Germany) International Programme Committee: Alexander Eychmüller (TU Dresden, Germany) Jonathan Finley (TU Munich, Germany) Dan Gammon (NRL, Washington, USA) Alexander Govorov (Ohio University, USA) Neil Greenham (Cavendish Laboratory, UK) Vladimir Korenev (Ioffe Institute, Russia) Leo Kouwenhoven (TU Delft, Netherlands) Wolfgang Langbein (Cardiff University, UK) Xavier Marie (CNRS Toulouse, France) David Ritchie (Cambridge, UK) Andrew Sachrajda (IMS, Ottawa, Canada) Katerina Soulantica (University of Toulouse, France) Seigo Tarucha (University of Tokyo, Japan) Carlos Tejedor (UAM, Madrid, Spain) Euijoon Yoon (Seoul National University, Korea) Ulrike Woggon (Tu Berlin, Germany) Proceedings edited and compiled by Profesor Robert A Taylor, University of Oxford

Taylor, Robert A.

2010-09-01

98

Quantum-Dot Sources for Single Photons and Entangled Photon Pairs  

Microsoft Academic Search

Quantum dots show excellent promise as triggered sources of both single and polarization entangled photons for quantum information applications. Our recent progress developing nonclassical light sources with single quantum dots is presented in this paper. Following radiative emission of an exciton confined in a quantum dot, there is a finite delay before re-excitation can occur; this results in an anti-bunching

Robert J. Young; David J. P. Ellis; R. Mark Stevenson; Anthony J. Bennett; Paola Atkinson; Ken Cooper; David A. Ritchie; Andrew J. Shields

2007-01-01

99

Probing relaxation times in graphene quantum dots  

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

100

Probing relaxation times in graphene quantum dots  

PubMed Central

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.

Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Muller, Andre; Stampfer, Christoph

2013-01-01

101

Amphoteric Nanocrystalline Quantum Dots  

NASA Astrophysics Data System (ADS)

The Nanocrystalline Quantum Dot (NQDs) 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 dc voltage across the pair, thin films of the Dots were deposited on both the positive and the negative electrodes. Extensive characterization including SEM, AFM, 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 number 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. Similar results were seen in maghemite (?-Fe2O3) NQDs. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of NQDs.

Islam, Mohammad

2007-03-01

102

Quantum Dots: Building Blocks of Quantum Devices?  

Microsoft Academic Search

Among other systems quantum dots have been considered as one of the prime candidates for a solid state quantum information processing that is scalable up to a large number of quantum bits. After some general considerations we focus here on an essential building block of a quantum processor, a quantum gate for entangling the states of two quantum bits. A

Manfred Bayer; G. Ortner; A. Larionov; D. R. Yakovlev; M. Schwab; P. Borri; W. Langbein; U. Woggon; I. Yugova; G. Baldassarri Höger von Högersthal; Y. B. Lyanda-Geller; T. L. Reinecke; S. Fafard; Z. Wasilewski; M. Korkusinski; P. Hawrylak; A. Forchel; J. P. Reithmaier

2004-01-01

103

Quantum Dots and Colors  

NSDL National Science Digital Library

Students are introduced to the physical concept of the colors of rainbows as light energy in the form of waves with distinct wavelengths, but in a different manner than traditional kaleidoscopes. Looking at different quantum dot solutions, they make observations and measurements, and graph their data. They come to understand how nanoparticles interact with absorbing photons to produce colors. They learn the dependence of particle size and color wavelength and learn about real-world applications for using these colorful liquids.

University Of Houston

104

Silicon quantum dots: surface matters.  

PubMed

Silicon quantum dots (SiQDs) hold great promise for many future technologies. Silicon is already at the core of photovoltaics and microelectronics, and SiQDs are capable of efficient light emission and amplification. This is crucial for the development of the next technological frontiers-silicon photonics and optoelectronics. Unlike any other quantum dots (QDs), SiQDs are made of non-toxic and abundant material, offering one of the spectrally broadest emission tunabilities accessible with semiconductor QDs and allowing for tailored radiative rates over many orders of magnitude. This extraordinary flexibility of optical properties is achieved via a combination of the spatial confinement of carriers and the strong influence of surface chemistry. The complex physics of this material, which is still being unraveled, leads to new effects, opening up new opportunities for applications. In this review we summarize the latest progress in this fascinating research field, with special attention given to surface-induced effects, such as the emergence of direct bandgap transitions, and collective effects in densely packed QDs, such as space separated quantum cutting. PMID:24713583

Dohnalová, K; Gregorkiewicz, T; K?sová, K

2014-04-30

105

Silicon quantum dots: surface matters  

NASA Astrophysics Data System (ADS)

Silicon quantum dots (SiQDs) hold great promise for many future technologies. Silicon is already at the core of photovoltaics and microelectronics, and SiQDs are capable of efficient light emission and amplification. This is crucial for the development of the next technological frontiers—silicon photonics and optoelectronics. Unlike any other quantum dots (QDs), SiQDs are made of non-toxic and abundant material, offering one of the spectrally broadest emission tunabilities accessible with semiconductor QDs and allowing for tailored radiative rates over many orders of magnitude. This extraordinary flexibility of optical properties is achieved via a combination of the spatial confinement of carriers and the strong influence of surface chemistry. The complex physics of this material, which is still being unraveled, leads to new effects, opening up new opportunities for applications. In this review we summarize the latest progress in this fascinating research field, with special attention given to surface-induced effects, such as the emergence of direct bandgap transitions, and collective effects in densely packed QDs, such as space separated quantum cutting.

Dohnalová, K.; Gregorkiewicz, T.; K?sová, K.

2014-04-01

106

Adiabatic description of nonspherical quantum dot models  

SciTech Connect

Within the effective mass approximation an adiabatic description of spheroidal and dumbbell quantum dot models in the regime of strong dimensional quantization is presented using the expansion of the wave function in appropriate sets of single-parameter basis functions. The comparison is given and the peculiarities are considered for spectral and optical characteristics of the models with axially symmetric confining potentials depending on their geometric size, making use of the complete sets of exact and adiabatic quantum numbers in appropriate analytic approximations.

Gusev, A. A., E-mail: gooseff@jinr.ru; Chuluunbaatar, O.; Vinitsky, S. I. [Joint Institute for Nuclear Research (Russian Federation); Dvoyan, K. G.; Kazaryan, E. M.; Sarkisyan, H. A. [Russian-Armenian (Slavonic) University (Armenia); Derbov, V. L.; Klombotskaya, A. S.; Serov, V. V. [Saratov State University (Russian Federation)

2012-10-15

107

Quantum dots in biology and medicine  

Microsoft Academic Search

Semiconductor quantum dots (QDs) are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. In comparison with organic dyes and fluorescent proteins, these quantum-confined nanoparticles are brighter, more stable against photobleaching, and can be excited for multicolor emission with a single light source. Recent advances have shown that nanometer-sized semiconductor

Robert E. Bailey; Andrew M. Smith; Shuming Nie

2004-01-01

108

Ultralow Noise Monolithic Quantum Dot Photonic Oscillators.  

National Technical Information Service (NTIS)

Three different nanostructured semiconductor lasers were studied - the quantum dot passively mode-locked laser, the dual-mode quantum dot laser, and the optically-injected quantum dot distributed feedback laser. The key milestones achieved were: (1) the u...

A. Hurtado J. Mee L. F. Lester N. Naderi R. Raghunathan

2013-01-01

109

Quantum Simulation in Quantum Dot Arrays.  

National Technical Information Service (NTIS)

The authors use electrostatically defined quantum dot arrays to study quantum simulation, examining both large arrays to explore the ground state and excitations of the Fermi-Hubbard model, and to examine very small arrays of 3-4 quantum dots as the basis...

L. Vandersypen

2013-01-01

110

Characteristics of ultralow threshold quantum dot lasers using indium-arsenide\\/indium-gallium arsenide dots-in-a- well structures  

Microsoft Academic Search

Semiconductor quantum dot lasers have an active medium that makes use three-dimensional quantum confinement effects and have been predicted to have many unique properties as compared to quantum well and double heterostructure lasers. In particular, they were expected to have low threshold current densities and temperature insensitive threshold currents. In this dissertation, a new quantum dot laser structure called the

Guangtian Liu

2000-01-01

111

Circular polarization memory in single Quantum Dots  

SciTech Connect

Under quasi-resonant circularly polarized optical excitation, charged quantum dots may emit polarized light. We measured various transitions with either positive, negative or no circular-polarization memory. We explain these observations and quantitatively calculate the polarization spectrum. Our model use the full configuration-interaction method, including the electron-hole exchange interaction, for calculating the quantum dot's confined many-carrier states, along with one assumption regarding the spin relaxation of photoexcited carriers: Electrons maintain their initial spin polarization, while holes do not.

Khatsevich, S.; Poem, E.; Benny, Y.; Marderfeld, I.; Gershoni, D. [Physics Department and Solid State Institute, Technion, Haifa 32000 (Israel); Badolato, A.; Petroff, P. M. [Materials Department, University of California Santa Barbara, Santa Barbara, California 93106 (United States)

2010-01-04

112

Mid-infrared HgTe colloidal quantum dot photodetectors  

Microsoft Academic Search

Today's infrared imaging devices are based on bulk and quantum-confined epitaxial materials and would benefit greatly from higher operating temperatures and lower cost. Imaging chips based on colloidal quantum dot technology could offer a convenient lower-cost alternative, but, to date, the spectral range of operation of colloidal quantum dots has been limited. In this Letter, we report colloidal HgTe quantum

Sean Keuleyan; Emmanuel Lhuillier; Vuk Brajuskovic; Philippe Guyot-Sionnest

2011-01-01

113

Lateral photodetectors with Ge quantum dots in Si  

Microsoft Academic Search

Lateral photodetectors with semiconductor quantum dots are novel devices using intrinsic properties of quantum dots such as the three dimensional confinement potential for carriers. On the InAs\\/GaAs material system they have proven their potential for highly efficient normal incidence operation. In this paper we present a detailed study of lateral photodetectors using intra-valence band transitions in self-assembled Ge dots. Two

C. Miesner; K. Brunner; G. Abstreiter

2001-01-01

114

Growth and control of optically active quantum dots  

Microsoft Academic Search

\\u000a We provide a general overview on the different methods employed to fabricate optically active quantum dots, i.e., quantum\\u000a dots which confine both electrons and holes in three dimensions. All the techniques are based on epitaxial growth of semiconductor\\u000a heterostructures. We first discuss bottom-up methods based on self-assembled growth, since they are the most used for single\\u000a dot investigations. We then

Armando Rastelli; Suwit Kiravittaya; Oliver G. Schmidt

2009-01-01

115

Superradiance of quantum dots  

NASA Astrophysics Data System (ADS)

In 1954, Dicke pointed out that the description of a spontaneously radiating gas has to include the fact that all atoms or molecules interact with a common radiation field. Consequently, the individual particles may not be considered as independent sources of radiation. In this regard, the question arises of whether quantum dot (QD) systems may also exhibit signatures of cooperative radiation and hence have to be considered as coupled quantum systems. Here, we present experimental evidence for a long-range electromagnetic interaction between laterally arranged QDs. The experimental results suggest that the QDs do not behave like independent objects as long as they form an ensemble of QDs. By removing QDs from the sample, we found that the coupling was reduced. The range of interaction is shown to be at least 150nm. This may therefore provide a mechanism to couple discrete quantum objects on a large scale.

Scheibner, Michael; Schmidt, Thomas; Worschech, Lukas; Forchel, Alfred; Bacher, Gerd; Passow, Thorsten; Hommel, Detlef

2007-02-01

116

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

117

Optical anisotropy of a donor in ellipsoidal quantum dots  

NASA Astrophysics Data System (ADS)

A system of an electron with a hydrogenic impurity confined in anisotropic quantum dots with ellipsoidal shape has been investigated. The linear and nonlinear optical absorptions as well as refractive index changes associated with intersubband transitions has been calculated. The results are presented as a function of the incident photon energy. The results show that the optical properties of a donor in ellipsoidal quantum dots are strongly affected by the anisotropy degree and the dot size. The dot anisotropy is shown to play a fundamental role in determining the dot properties.

Xie, Wenfang

2012-12-01

118

Induced Quantum Dots and Wires: Electron Storage and Delivery  

NASA Astrophysics Data System (ADS)

We show that quantum dots and quantum wires are formed underneath metal electrodes deposited on a planar semiconductor heterostructure containing a quantum well. The confinement is due to the self-focusing mechanism of an electron wave packet interacting with the charge induced on the metal surface. Induced quantum wires guide the transfer of electrons along metal paths and induced quantum dots store the electrons in specific locations of the nanostructure. Induced dots and wires can be useful for devices operating on the electron spin. An application for a spin readout device is proposed.

Bednarek, S.; Szafran, B.; Dudek, R. J.; Lis, K.

2008-03-01

119

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  

NASA Astrophysics Data System (ADS)

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.

Pejova, Biljana

2014-05-01

120

Quantum-dot cellular automata  

Microsoft Academic Search

An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two

G. L. Snider; A. O. Orlov; I. Amlani; G. H. Bernstein; C. S. Lent; J. L. Merz; W. Porod

1999-01-01

121

Quantum dot micropatterning on si.  

PubMed

Using InP and PbSe quantum dots, we demonstrate that the Langmuir-Blodgett technique is well-suited to coat nonflat surfaces with quantum dot monolayers. This allows deposition on silicon substrates covered by a developed patterned resist, which results in monolayer patterns with micrometer resolution. Atomic force microscopy and scanning electron microscopy reveal the formation of a densely packed monolayer that replicates predefined structures with high selectivity after photoresist removal. A large variety of shapes can be reproduced and, due to the excellent adhesion of the quantum dots to the substrate, the hybrid approach can be repeated on the same substrate. This final possibility leads to complex, large-area quantum dot monolayer structures with micrometer spatial resolution that may combine different types of quantum dots. PMID:18442279

Lambert, K; Moreels, I; Thourhout, D Van; Hens, Z

2008-06-01

122

Size and shape effects in electromagnetic response of quantum dots and quantum dot arrays  

Microsoft Academic Search

Size and shape effects in electromagnetic response of quantum dots (QDs) such as depolarization shift of the exciton resonance and fine structure of the gain band are considered on the basis of a unified concept of light confinement. We show that at sufficiently large oscillator strength of the transition, QD behaves itself as a microcavity and excitation of cavity eigenmodes

S. A Maksimenko; G. Ya Slepyan; V. P Kalosha; N. N Ledentsov; A Hoffmann; D Bimberg

2001-01-01

123

Efficient Quantum Dot-Quantum Dot and Quantum Dot-Dye Energy Transfer in Biotemplated Assemblies  

PubMed Central

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

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

2011-01-01

124

Spin interactions, relaxation and decoherence in quantum dots  

Microsoft Academic Search

We review recent studies on spin decoherence of electrons and holes in quasi-two-dimensional quantum dots, as well as electron-spin relaxation in nanowire quantum dots. The spins of confined electrons and holes are considered major candidates for the realization of quantum information storage and processing devices, provided that sufficiently long coherence and relaxation times can be achieved. The results presented here

Jan Fischer; Mircea Trif; W. A. Coish; Daniel Loss

2009-01-01

125

High-performance mid-infrared quantum dot infrared photodetectors  

Microsoft Academic Search

Quantum dot infrared photodetectors (QDIPs) have emerged as attractive devices for sensing long wavelength radiation. Their principle of operation is based on intersublevel transitions in quantum dots (QDs). Three-dimensional quantum confinement offers the advantages of normal incidence operation, low dark currents and high-temperature operation. The performance characteristics of mid-infrared devices with three kinds of novel heterostructures in the active region

S. Chakrabarti; A. D. Stiff-Roberts; X. H. Su; P. Bhattacharya; G. Ariyawansa; A. G. U. Perera

2005-01-01

126

Mesoscopic Theory for Quantum Dot Lasers  

Microsoft Academic Search

In this chapter we present a mesoscopic theory for the spatio-temporal carrier and light field dynamics in quantum dot lasers. Quantum dot Maxwell--Bloch equations (QDMBEs) are set up that mesoscopically describe the spatiotemporal light field and inter\\/intra-level carrier dynamics in each quantum dot (QD) of a typical QD ensemble in quantum dot lasers.

Ortwin Hess

127

TOPICAL REVIEW: Quantum dot micropillars  

Microsoft Academic Search

This topical review provides an overview of quantum dot micropillars and their application in cavity quantum electrodynamics (cQED) experiments. The development of quantum dot micropillars is motivated by the study of fundamental cQED effects in solid state and their exploitation in novel light sources. In general, light-matter interaction occurs when the dipole of an emitter couples to the ambient light

S. Reitzenstein; A. Forchel

2010-01-01

128

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

Microsoft Academic Search

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

Pablo Bianucci

2007-01-01

129

Coherent three-level mixing in an electronic quantum dot.  

PubMed

We observe magnetic-field-induced level mixing and quantum superposition phenomena between three approaching single-particle states in a quantum dot probed via the ground state of an adjacent quantum dot by single-electron resonant tunneling. The mixing is attributed to anisotropy and anharmonicity in realistic dot confining potentials. The pronounced anticrossing and transfer of strengths (both enhancement and suppression) between resonances can be understood with a simple coherent level mixing model. Superposition can lead to the formation of a dark state by complete cancellation of an otherwise strong resonance, an effect resembling coherent population trapping in a three-level-system of quantum and atom optics. PMID:19257308

Payette, C; Yu, G; Gupta, J A; Austing, D G; Nair, S V; Partoens, B; Amaha, S; Tarucha, S

2009-01-16

130

InAs quantum dots infrared photodetectors  

Microsoft Academic Search

In this paper, we present a study of a series of InAs quantum dot infrared photodetectors (QDIPs) with unintentionally doped active regions. The wavelength tunability will be demonstrated by changes of the content of In and Al in the InGaAs cap layers and InAlGaAs lateral potential confinement layers. The samples were grown on semi-insulating GaAs(001) substrates by solid-source molecular beam

Zhengmao Ye; J. C. Campbell; Zhonghui Chen; E. T. Kim; A. Madhukar

2003-01-01

131

The pinning effect in quantum dots  

NASA Astrophysics Data System (ADS)

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.

Monisha, P. J.; Mukhopadhyay, Soma

2014-04-01

132

The scalable quantum computation based on quantum dot systems  

Microsoft Academic Search

We propose a scheme for realizing the scalable quantum computation based on nonidentical quantum dots trapped in a single-mode waveguide. In this system, the quantum dots simultaneously interact with a large detuned waveguide and classical light fields. During the process, neither the waveguide mode nor the quantum dots are excited, while the sub-system composed of any two quantum dots can

Jian-Qi Zhang; Ya-Fei Yu; Xun-Li Feng; Zhi-Ming Zhang

2011-01-01

133

Self-assembly Drives Quantum Dot Photoluminescence  

Microsoft Academic Search

Engineering the spectral properties of quantum dots can be achieved by a control of the quantum dots organization on a substrate.\\u000a Indeed, many applications of quantum dots as LEDs are based on the realization of a 3D architecture of quantum dots. In this\\u000a contribution, we present a systematic study of the quantum dot organization obtained on different chemically modified substrates.

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

2009-01-01

134

Circuit Quantum Electrodynamics with Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

Research on semiconductor quantum dots has tremendously contributed to the understanding of the physics of individual charges and spins in a solid state environment. Typically, quantum dots are investigated by direct current transport measurements or using quantum point contacts for charge sensing. Instead, we have realized a novel device in which a semiconductor double quantum dot is dipole coupled to a GHz-frequency high-quality tranmission line resonator. This approach allows us to characterize the properties of the double dot by measuring both its dispersive and dissipative interaction with the resonator [1]. In addition to providing a new readout mechanism, this architecture has the potential to isolate the dots from the environment and to provide long distance coupling between spatially separated dots. These features are expected to improve the potential for realizing a quantum information processor with quantum dots as previously demonstrated for superconducting circuits making use of circuit quantum electrodynamics. [1] T. Frey et al., arXiv:1108.5378v1 (2011)

Wallraff, Andreas; Frey, Tobias; Leek, Peter J.; Beck, Matthias; Blais, Alexandre; Ihn, Thomas; Ensslin, Klaus

2012-02-01

135

Quantum Wires and Quantum Dots for Optoelectronics: Recent Advances with Epitaxial Growth on Nonplanar Substrates  

Microsoft Academic Search

\\u000a The lateral quantum confinement imposed on electrons and holes in semiconductor quantum wires (QWRs) and quantum dots (QDs)\\u000a has been predicted to bring about significant advantages for optoelectronic device applications. Early on, the increasingly\\u000a sharp density of states (DOS) achieved with more degrees of confinement was expected to dramatically enhance optical absorption\\u000a and emission due to the spectral confinement of

E. Kapon

136

Quantum Confinement-Tunable Ultrafast Charge Transfer at the PbS Quantum Dot and Phenyl-C61-butyric Acid Methyl Ester Interface.  

PubMed

Quantum dot (QD) solar cells have emerged as promising low-cost alternatives to existing photovoltaic technologies. Here, we investigate charge transfer and separation at PbS QDs and phenyl-C61-butyric acid methyl ester (PCBM) interfaces using a combination of femtosecond broadband transient absorption (TA) spectroscopy and steady-state photoluminescence quenching measurements. We analyzed ultrafast electron injection and charge separation at PbS QD/PCBM interfaces for four different QD sizes and as a function of PCBM concentration. The results reveal that the energy band alignment, tuned by the quantum size effect, is the key element for efficient electron injection and charge separation processes. More specifically, the steady-state and time-resolved data demonstrate that only small-sized PbS QDs with a bandgap larger than 1 eV can transfer electrons to PCBM upon light absorption. We show that these trends result from the formation of a type-II interface band alignment, as a consequence of the size distribution of the QDs. Transient absorption data indicate that electron injection from photoexcited PbS QDs to PCBM occurs within our temporal resolution of 120 fs for QDs with bandgaps that achieve type-II alignment, while virtually all signals observed in smaller bandgap QD samples result from large bandgap outliers in the size distribution. Taken together, our results clearly demonstrate that charge transfer rates at QD interfaces can be tuned by several orders of magnitude by engineering the QD size distribution. The work presented here will advance both the design and the understanding of QD interfaces for solar energy conversion. PMID:24521255

El-Ballouli, Ala'a O; Alarousu, Erkki; Bernardi, Marco; Aly, Shawkat M; Lagrow, Alec P; Bakr, Osman M; Mohammed, Omar F

2014-05-14

137

Numerical simulation of optical feedback on a quantum dot lasers  

SciTech Connect

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

Al-Khursan, Amin H., E-mail: ameen_2all@yahoo.com [Thi-Qar University, Nassiriya Nanotechnology Research Laboratory (NNRL), Science College (Iraq); Ghalib, Basim Abdullattif [Babylon University, Laser Physics Department, Science College for Women (Iraq); Al-Obaidi, Sabri J. [Al-Mustansiriyah University, Physics Department, Science College (Iraq)

2012-02-15

138

Coupled quantum dots as quantum gates  

Microsoft Academic Search

We consider a quantum-gate mechanism based on electron spins in coupled semiconductor quantum dots. Such gates provide a general source of spin entanglement and can be used for quantum computers. We determine the exchange coupling J in the effective Heisenberg model as a function of magnetic (B) and electric fields, and of the interdot distance a within the Heitler-London approximation

Guido Burkard; Daniel Loss; David P. Divincenzo

1999-01-01

139

Quantum Dot Light Emitting Diode.  

National Technical Information Service (NTIS)

The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, an...

K. Kahen

2008-01-01

140

Investigation of Quantum Dot Lasers.  

National Technical Information Service (NTIS)

Since the first demonstration of room-temperature operation of self- assembled quantum dot (QD) lasers about a decade ago, there have been great strides in improving the characteristics and performance of these lasers. They currently match or surpass the ...

P. Bhattacharya

2004-01-01

141

Quantum Dots in Cell Biology  

PubMed Central

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.

Barroso, Margarida M.

2011-01-01

142

Quantum-Dot Infrared Photodetectors  

Microsoft Academic Search

We present a study of a series of n-i-n InAs quantum-dot infrared photodetectors (QDIPs) with unintentionally doped active regions. Different quantum-dot capping layer materials (GaAs, InGaAs, and AlGaAs) are utilized to tune the operating wavelength and modify the QDIP performance. Normal-incidence operation with high detectivity in the mid (3-5 ) and long (8-12 ) wavelength regimes and the potential for

Joe C. Campbell; Anupam Madhukar

2007-01-01

143

Improving the operating temperature of quantum dots-in-a-well detectors  

Microsoft Academic Search

In this paper, we report some of our recent results on improving the operating temperature of dots-in-a-well (DWELL) infrared photodetectors. This was achieved by engineering the dot geometry and the interrelated quantum confinement by varying the growth conditions and composition of the subsequent capping of the quantum dots (QDs). The influence of these conditions was determined by examining the optical

Jiayi Shao; Thomas E. Vandervelde; Woo-Yong Jang; Andreas Stintz; Sanjay Krishna

2010-01-01

144

Practical issues in the realization of quantum-dot cellular automata  

Microsoft Academic Search

Several practical issues in the development and operation of quantum-dot cellular automata (QCA) cells and systems are discussed. The need for adiabatic clocking of QCA systems and modeling of electrostatic confinement of quantum dots are presented. Experimental data on dot coupling and applications to QCA detectors in a 2-dimensional electron gas (2DEG) are presented. We report a charge detection scheme

Gary H. Bernstein; Greg Bazan; Minhan Chen; Craig S. Lent; James L. Merz; Alexei O. Orlov; Wolfgang Porod; G. L. Snider; P. Douglas Tougaw

1996-01-01

145

Temperature dependence of polarization relaxation in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The decay time of the linear polarization degree of the luminescence in strongly confined semiconductor quantum dots with asymmetrical shape is calculated in the frame of second-order quasielastic interaction between quantum dot charge carriers and LO phonons. The phonon bottleneck does not prevent significantly the relaxation processes and the calculated decay times can be of the order of a few tens picoseconds at temperature T~=100 K, consistent with recent experiments by Paillard et al. [Phys. Rev. Lett. 86, 1634 (2001)].

Tsitsishvili, E.; Baltz, R. V.; Kalt, H.

2002-10-01

146

Multi-million atom electronic structure calculations for quantum dots  

Microsoft Academic Search

Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In

Muhammad Usman

2010-01-01

147

Surface plasmon polariton-controlled tunable quantum-dot emission  

NASA Astrophysics Data System (ADS)

The unique properties of surface plasmon polaritons, such as strong field confinement and local field enhancement effects, make them ideal candidates to enhance and shape the emission of luminescent nanoparticles. Of these nanoparticles, quantum dots are highly versatile, suitable for vastly different applications due to their size and material tunability. In many cases however, the emission wavelength of the quantum dots is fixed after manufacturing, allowing no control over the in situ emission properties. Here, we show fully optical, in situ tunability of the emission wavelength of quantum dots, with shifts of over 30 nm, employing surface plasmon polaritons to control the emission wavelength.

Moerland, R. J.; Rekola, H. T.; Sharma, G.; Eskelinen, A.-P.; Väkeväinen, A. I.; Törmä, P.

2012-05-01

148

Emission in Mn-Doped Quantum Dot  

NASA Astrophysics Data System (ADS)

We theoretically investigate the magneto-PL of Mn2+doped semiconductor core-shell colloidal quantum dot to explain the experiment result from a recent magnetophotoluminescence study of strongly confined diluted magnetic semiconductor (DMS) in Mn2+-doped ZnSe/CdSe core-shell colloidal nanocrystals. The yellow emission characterized for in Mn2+-which is associated with the d-d internal transition 4T1-6A1, was reported not suppressed in an applied B //z magnetic field and unpolarized as usual and instead, a Mn PL circular polarization has been observed. The in Mn2+- photoluminescence has been found to have a large splitting between ? + and ? {- }components which depends on the applied field. We show that this behavior, which has not been found in characteristics of the Mn2+ PL in bulks and other conventional DMS materials, is the result of the strong confinement of the nanocrystal and its properties. Our theory and calculation show that the reasons the yellow Mn2+ PL band in quantum dots is not suppressed under applied magnetic field originate due to the existence of the internal piezoelectric dipole moment and the Coulomb exchange interaction of the impurity ions with the confined electrons inside the dot.

Huong Nguyen, Que; Birman, Joseph L.

2013-03-01

149

Quantum dots investigated with charge detection techniques  

Microsoft Academic Search

The detection of the quantum dot charge state using a quantum point contact charge detector has opened a new exciting route for the investigation of quantum dot devices in recent years. In particular, time-resolved charge detection allowed the precise measurement of quantum dot shot noise at sub-femtoampere current levels, and the full counting statistics of the current. The technique can

Thomas Ihn; Simon Gustavsson; Urszula Gasser; Bruno Küng; Thomas Müller; Roland Schleser; Martin Sigrist; Ivan Shorubalko; Renaud Leturcq; Klaus Ensslin

2009-01-01

150

Novel Routes to Amphiphillic Ag Quantum Dots  

Microsoft Academic Search

Quantum dots are nanometer-sized particles that contain a few thousand atoms. Individually they possess both quantum and classical properties due to their size, and ensembles of quantum dots also display novel properties. Our goal is to synthesize amphiphillic quantum dots that will assemble as finite numbered structures in solution. Silver quantum dots are created in both a one-phase and two-phase

Andrew D. Dwoskin; Chau Sophia Nguyen; Jill K. Sakata

2003-01-01

151

Diamagnetic Exciton Properties in Quantum Dot Molecules  

NASA Astrophysics Data System (ADS)

The magnetic properties of nanostructures like quantum dots and rings are the subject of intense research. In particular, magnetic control of coupled quantum dots (artificial molecules) has become subject of interest. The diamagnetic shift of confined excitons complexes has been used as a measured of the wave function spatial extent in semiconductor nanostructures. In weak magnetic field, the diamagnetic shift is expected to exhibit quadratic dependence. However, for exciton complexes the diamagnetic behavior is expected to exhibit more complicated features related to electron-hole asymmetry effects on Coulomb interactions. In this work we study the magnetic response of neutral and charged excitons in InAs/GaAs asymmetric artificial molecules By using a first order perturbation approach, and within the effective mass approximation, we calculate magnetic field dependent electronic structures of confined excitons and trions in vertically coupled quantum dots. These predicted regions, which show coexistence of crossing and anticrossing exciton states, because of allowing control of charge localization and polarization of emitted photons. .

Ricardo, Fino Puerto Nelson; Hanz Yecid, Ramirez; S, Camacho Angela

2012-02-01

152

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

PubMed

Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots. PMID:21946709

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

2011-11-01

153

Quantum optics with quantum dots in microcavities  

Microsoft Academic Search

This dissertation describes several quantum optics experiments that rely on the coupling between an atomic-like system and the confined optical modes of a cavity as described by cavity quantum electrodynamics (QED). The novelty of these experiments is that they are performed in the solid-state and as such are extremely interesting for applications of quantum information. These results have been obtained

Matthew T. Rakher

2008-01-01

154

Magnetic field and symmetry effects in small quantum dots  

NASA Astrophysics Data System (ADS)

Shell phenomena in small quantum dots with a few electrons under a perpendicular magnetic field are discussed within a simple model. It is shown that various kinds of shell structures, which occur at specific values for the magnetic field lead to a disappearance of the orbital magnetization for particular magic numbers for noninteracting electrons in small quantum dots. Including the Coulomb interaction between two electrons, we found that the magnetic field gives rise to dynamical symmetries of a three-dimensional axially symmetric two-electron quantum dot with a parabolic confinement. These symmetries manifest themselves as near-degeneracy in the quantum spectrum at specific values of the magnetic field and are robust at any strength of the electron-electron interaction. A remarkable agreement between experimental data and calculations exhibits the important role of the thickness for the two-electron quantum dot for analysis of ground state transitions in a perpendicular magnetic field.

Nazmitdinov, R. G.

2009-01-01

155

Coherent optical spectroscopy of a strongly driven quantum dot.  

PubMed

Quantum dots are typically formed from large groupings of atoms and thus may be expected to have appreciable many-body behavior under intense optical excitation. Nonetheless, they are known to exhibit discrete energy levels due to quantum confinement effects. We show that, like single-atom or single-molecule two- and three-level quantum systems, single semiconductor quantum dots can also exhibit interference phenomena when driven simultaneously by two optical fields. Probe absorption spectra are obtained that exhibit Autler-Townes splitting when the optical fields drive coupled transitions and complex Mollow-related structure, including gain without population inversion, when they drive the same transition. Our results open the way for the demonstration of numerous quantum level-based applications, such as quantum dot lasers, optical modulators, and quantum logic devices. PMID:17702938

Xu, Xiaodong; Sun, Bo; Berman, Paul R; Steel, Duncan G; Bracker, Allan S; Gammon, Dan; Sham, L J

2007-08-17

156

NREL Certifies First All-Quantum-Dot Photovoltaic Cell; Demonstrates Stability, Performance (Fact Sheet)  

SciTech Connect

Researchers at the National Renewable Energy Laboratory (NREL) have certified the first all-quantum-dot photovoltaic cell, which was based on lead sulfide and demonstrated reasonable quantum dot solar cell performance for an initial efficiency measurement along with good stability. The certified open-circuit voltage of the quantum dot cell is greater than that possible from bulk lead sulfide because of quantum confinement.

Not Available

2011-02-01

157

A Review of Quantum Confinement  

SciTech Connect

A succinct history of the Confined Atom problem is presented. The hydrogen atom confined to the centre of an impenetrable sphere counts amongst the exactly soluble problems of physics, alongside much more noted exact solutions such as Black Body Radiation and the free Hydrogen atom in absence of any radiation field. It shares with them the disadvantage of being an idealisation, while at the same time encapsulating in a simple way particular aspects of physical reality. The problem was first formulated by Sommerfeld and Welker - henceforth cited as SW - in connection with the behaviour of atoms at very high pressures, and the solution was published on the occasion of Pauli's 60th birthday celebration. At the time, it seemed that there was not much other connection with physical reality beyond a few simple aspects connected to the properties of atoms in solids, for which more appropriate models were soon developed. Thus, confined atoms attracted little attention until the advent of the metallofullerene, which provided the first example of a confined atom with properties quite closely related to those originally considered by SW. Since then, the problem has received much more attention, and many more new features of quantum confinement, quantum compression, the quantum Faraday cage, electronic reorganisation, cavity resonances, etc have been described, which are relevant to real systems. Also, a number of other situations have been uncovered experimentally to which quantum confinement is relevant. Thus, studies of the confined atom are now more numerous, and have been extended both in terms of the models used and the systems to which they can be applied. Connections to thermodynamics are explored through the properties of a confined two-level atom adapted from Einstein's celebrated model, and issues of dynamical screening of electromagnetic radiation by the confining shell are discussed in connection with the Faraday cage produced by a confining conducting shell. The conclusions are shown to be relevant to a proposed 'quantum computer'. The description of the actual geometry of C{sub 60}, as opposed to a purely spherical approximation, leads to some qualification of the computed results.

Connerade, Jean-Patrick [Quantum Optics and Laser Science Group, Physics Department, Imperial College, London (United Kingdom)

2009-12-03

158

Gluon Confinement and Quantum Censorship  

NASA Astrophysics Data System (ADS)

The dynamical Maxwell-cut, a degeneracy is shown to be a precursor of condensate in the ?4 and the sine-Gordon models. The difference of the way the Maxwell-cut is obtained is pointed out and quantum censorship, the generation of semiclassically looking phenomenon by loop-corrections is conjectured in the sine-Gordon model. It is argued that quantum censorship and gluon confinement exclude each other.

Polónyi, János

2011-04-01

159

Quantum-Dot Cellular Automata  

NASA Astrophysics Data System (ADS)

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

Snider, Gregory

2000-03-01

160

Quantum dot quantum cascade infrared photodetector  

NASA Astrophysics Data System (ADS)

We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3 ?m. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski-Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64 × 1011 and 4.83 × 106 Jones at zero bias were obtained at 80 K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging.

Wang, Xue-Jiao; Zhai, Shen-Qiang; Zhuo, Ning; Liu, Jun-Qi; Liu, Feng-Qi; Liu, Shu-Man; Wang, Zhan-Guo

2014-04-01

161

Self-assembly drives quantum dot photoluminescence.  

PubMed

Engineering the spectral properties of quantum dots can be achieved by a control of the quantum dots organization on a substrate. Indeed, many applications of quantum dots as LEDs are based on the realization of a 3D architecture of quantum dots. In this contribution, we present a systematic study of the quantum dot organization obtained on different chemically modified substrates. By varying the chemical affinity between the quantum dots and the substrate, the quantum dot organization is strongly modified from the 2D monolayer to the 3D aggregates. Then the photoluminescence of the different obtained samples has been systematically studied and correlated with the quantum dot film organization. We clearly show that the interaction between the substrate and the quantum dot must be stronger than the quantum dot-quantum dot interaction to avoid 3D aggregation and that these organization strongly modified the photoluminescence of the film rather than intrinsic changes of the quantum dot induced by pure surface chemistry. PMID:18792763

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

2009-03-01

162

Clocked molecular quantum-dot cellular automata  

Microsoft Academic Search

Quantum-dot cellular automata (QCA) is an approach to computing that eliminates the need for current switches by representing binary information as the configuration of charge among quantum dots. For molecular QCA, redox sites of molecules serve as the quantum dots. The Coulomb interaction between neighboring molecules provides device-device coupling. By introducing clocked control of the QCA cell, power gain, reduced

Craig S. Lent; Beth Isaksen

2003-01-01

163

Inkjet printing of light emitting quantum dots  

Microsoft Academic Search

We demonstrate the fabrication of diodes having inkjet printed light emitting quantum dots layer. Close packing of printed layer is shown to be influenced by surface morphology of the underlying polymer layer and size variance of quantum dots used. We extend our approach to printing quantum dots onto a quarter video graphics array substrate (76 800 monochrome pixels). The purity

Hanna M. Haverinen; Risto A. Myllylä; Ghassan E. Jabbour

2009-01-01

164

Applications of quantum dots in cell biology  

Microsoft Academic Search

Quantum dots promise to revolutionize the way fluorescence imaging is used in the Cell Biology field. The unique fluorescent spectral characteristics, high photostability, low photobleaching and tight emission spectra of quantum dots, position them above traditional dyes. Here we will address the ability of EviTags, which are water stabilized quantum dot products from Evident Technologies, to behave as effective FRET

Margarida Barroso; Roshanak Mehdibeigi; Louise Brogan

2006-01-01

165

Characteristics of electron transport through vertical double-barrier quantum-dot structures: Effects of symmetric and asymmetric variations of the lateral confinement potentials  

NASA Astrophysics Data System (ADS)

We report on a theoretical study of the electron transport through laterally-confined, vertical double-barrier resonant-tunneling (DBRT) structures, defined as one-dimensional (1D)-0D-1D systems, with a tunable lateral confinement. The current and the differential conductance of the systems are calculated and the influence caused by varying the lateral confinement on the device characteristics is investigated. Three representative systems are studied. First of all, a 1D-0D-1D device, symmetric with respect to the current flow, with a variable lateral confinement in the double-barrier quantum-well (DBQW) region, is investigated. This device would in an experimental setup correspond to the structure in which a thin, lateral metallic gate is placed in the DBQW region. Subsequently, calculations are performed for two asymmetric 1D-0D-1D devices, in which the strongest, but varying, lateral confinement is placed either in the collector or in the emitter region. In experiments, these two devices would correspond to the situations where a lateral metallic gate is positioned below or on top of the DBQW structure. The calculations predict several phenomena for the device characteristics. It is shown that as the lateral confinement increases, in addition to those normally observed current onsets and pinch-offs that move toward higher bias voltages, several current onsets and pinch-offs move towards lower bias voltages. These negative shifts of the current onsets and pinch-offs with increasing of the lateral confinement have so far not been expected for gated DBRT devices. It is also found that the threshold voltages, at which the current onsets and pinch-offs appear, depend strongly on the strength and position of the lateral confinement and on the Fermi levels in the collector and the emitter. The models that explain these predictions are presented and discussed.

Csontos, Dan; Xu, H. Q.

2002-11-01

166

Zeno-logic applications of semiconductor quantum dots  

SciTech Connect

Microscopic calculations show that CdSe-based semiconductor quantum dots with confined exciton and biexciton states are suitable candidates for Zeno-logic applications. The frequencies of the control and signal fields are chosen to guarantee very high transmission of the individual beams. If both fields are present simultaneously, they are strongly absorbed due to efficient ground-state-to-biexciton transitions. The optical Bloch equations for a three-level quantum-dot model with self-consistent light-matter coupling are solved numerically. The influence of dephasing and/or inhomogeneous dot distributions is analyzed and the conditions for satisfactory device operation are identified.

Schneebeli, L.; Peyghambarian, N. [Optical Sciences Center, University of Arizona, Tucson, Arizona 85721 (United States); Feldtmann, T.; Kira, M. [Department of Physics and Material Sciences Center, Philipps-University, D-35032 Marburg (Germany); Koch, S. W. [Optical Sciences Center, University of Arizona, Tucson, Arizona 85721 (United States); Department of Physics and Material Sciences Center, Philipps-University, D-35032 Marburg (Germany)

2010-05-15

167

Synthesis and applications of quantum dots and magnetic quantum dots  

Microsoft Academic Search

We have developed a new synthetic method for producing high-quality quantum dots (QDs) in aqueous solution for biological imaging applications. The glutathione-capped CdTe, ZnSe and Zn1-xCdxSe alloyed QDs derived are tunable in fluorescence emissions between 360 nm and 700 nm. They show high quantum yields (QYs) of up to 50%, with narrow bandwidths of 19-55 nm. The synthesis of glutathione-capped

Jackie Y. Ying; Yuangang Zheng; S. Tamil Selvan

2008-01-01

168

Analytical model for quantum well to quantum dot tunneling  

Microsoft Academic Search

This paper presents an analytical model of elastic tunneling from a quantum well to a quantum dot, applicable to the modeling of single electron transistor and memory charging. The main differences between tunneling to a quantum dot and to a continuum of states have been carefully addressed. The impact of quantum decoherence factors such as temperature and dot size dispersion

Raphaël Clerc; Gérard Ghibaudo; Georges Pananakakis

2003-01-01

169

Pseudosymmetric bias and correct estimation of Coulomb/confinement energy for unintentional quantum dot in channel of metal-oxide-semiconductor field-effect transistor  

NASA Astrophysics Data System (ADS)

We describe a measurement method that enables the correct estimation of the charging energy of an unintentional quantum dot (QD) in the channel of a metal-oxide-semiconductor field-effect transistor (MOSFET). If the channel has a single dominant QD with a large charging energy and an array of stray QDs with much weaker charging, this method eliminates the additional voltage drops due to stray QDs by regarding the stray QDs as series resistors. We apply this method to a short-channel MOSFET and find that the charging energy of the dominant QD can indeed be smaller than the size of the Coulomb diamond.

Ono, K.; Tanamoto, T.; Ohguro, T.

2013-10-01

170

Optical control of single excitons in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The fundamental building block of quantum information processing technologies is the quantum-bit a ‘qubit.’ These technologies require the ability to prepare, control, and read out a qubit state. Spins confined in self-assembled quantum dots are promising candidates for a quantum bit, because semiconductors are compatible with mature modern opto- and micro-electronics. These quantum dot systems offer two more advantages: they are excellent interfaces between the spin state—an anchored qubit and a photon—a ‘flying qubit’ and they provide means to coherently control the spin qubit by ultrashort optical pulses. In this review, we thoroughly discuss the qubit provided by an optically-excited electron in a quantum dot–the exciton qubit. We demonstrate its spin state initialization, coherent control and read-out using ultrashort optical pulses.

Kodriano, Y.; Schmidgall, E. R.; Benny, Y.; Gershoni, D.

2014-05-01

171

Gate-defined quantum confinement in suspended bilayer graphene.  

PubMed

Quantum-confined devices that manipulate single electrons in graphene are emerging as attractive candidates for nanoelectronics applications. Previous experiments have employed etched graphene nanostructures, but edge and substrate disorder severely limit device functionality. Here we present a technique that builds quantum-confined structures in suspended bilayer graphene with tunnel barriers defined by external electric fields that open a bandgap, thereby eliminating both edge and substrate disorder. We report clean quantum dot formation in two regimes: at zero magnetic field B using the energy gap induced by a perpendicular electric field and at B>0 using the quantum Hall ?=0 gap for confinement. Coulomb blockade oscillations exhibit periodicity consistent with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates single electron transport with high device quality and access to vibrational modes, enabling broad applications from electromechanical sensors to quantum bits. PMID:22760633

Allen, M T; Martin, J; Yacoby, A

2012-01-01

172

Quantum optics in coupled quantum dots  

NASA Astrophysics Data System (ADS)

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

Garrido, Mauricio

173

Nuclear spin physics in quantum dots: An optical investigation  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

174

Group-velocity slowdown in quantum-dots and quantum-dot molecules  

NASA Astrophysics Data System (ADS)

We investigate theoretically the slowdown of optical pulses due to quantum-coherence effects in InGaAs-based quantum dots and quantum dot molecules. Simple models for the electronic structure of quantum dots and, in particular, quantum-dot molecules are described and calibrated using numerical simulations. It is shown how these models can be used to design optimized quantum-dot molecules for quantum coherence applications. The wave functions and energies obtained from the optimizations are used as input for a microscopic calculation of the quantum-dot material dynamics including carrier scattering and polarization dephasing. The achievable group velocity slowdown in quantum-coherence V schemes consisting of quantum-dot molecule states is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots.

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

2014-03-01

175

The linear optical properties of a multi-shell spherical quantum dot of a parabolic confinement for cases with and without a hydrogenic impurity  

NASA Astrophysics Data System (ADS)

Throughout this work, we aim to explore the linear optical properties of a semiconductor multi-shell spherical quantum dot with and without a hydrogenic donor impurity. The core and well layers are defined by the parabolic electronic potentials in the radial direction. The energy levels and corresponding wavefunctions of the structure are calculated by using the shooting technique in the framework of the effective-mass approximation. We investigate the intersublevel absorption coefficients of a single electron and the hydrogenic donor impurity comparatively as a function of the photon energy. In addition, we carry out the effect of a donor impurity and the layer thickness on the oscillator strengths and magnitude and position of absorption coefficient peaks. We illustrate the electron probability distribution and variation of the energy levels in cases with and without the impurity for different thicknesses of layers. This kind of structure gives an opportunity to tune and control the absorption coefficient of the system by changing three different thickness parameters. Also it provides a possibility to separate 0s and 1p electrons in different regions of the quantum dot.

?ahin, Mehmet; Köksal, Koray

2012-12-01

176

Quantum Dots for Molecular Pathology  

PubMed Central

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

True, Lawrence D.; Gao, Xiaohu

2007-01-01

177

Biological applications of quantum dots  

Microsoft Academic Search

Quantum dots (QDs) are a novel class of inorganic fluorophore which are gaining widespread recognition as a result of their exceptional photophysical properties. They are rapidly being applied to existing and emerging technologies, and could have an important role in many areas. Significant challenges remain, however, which must be understood and more fully defined before they can be widely validated.This

Timothy Jamieson; Raheleh Bakhshi; Daniela Petrova; Rachael Pocock; Mo Imani; Alexander M. Seifalian

2007-01-01

178

Optically Controlled Quantum Dot Spins for Scaleable Quantum Computing.  

National Technical Information Service (NTIS)

The objective of this program has been to work towards development of spin based quantum dots for optically driven quantum information processing. Using a combination of ultrahigh resolution laser spectroscopy to study the physics of the dots and ultrafas...

D. G. Steel

2005-01-01

179

Quantum optics in coupled quantum dots  

Microsoft Academic Search

Coupled quantum dots present an active field of study, both at the fundamental and applied level, due to their atomic and molecular-like energy structure and the ability to design and tune their parameters. Being single-photon emitters, they are systems that behave fully according to the laws of quantum mechanics. The work presented here involved the experimental study of the electro-optical

Mauricio Garrido

2010-01-01

180

Optically controlled spins in semiconductor quantum dots  

Microsoft Academic Search

Spins in charged semiconductor quantum dots are currently generating much interest, both from a fundamental physics standpoint, as well as for their potential technological relevance. Being naturally a two-level quantum system, each of these spins can encode a bit of quantum information. Optically controlled spins in quantum dots possess several desirable properties: their spin coherence times are long, they allow

Sophia Economou

2010-01-01

181

Charge transfer magnetoexciton formation at vertically coupled quantum dots  

PubMed Central

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

2012-01-01

182

High Operating Temperature Quantum-Dot Infrared Photodetector Using Advanced Capping Techniques  

Microsoft Academic Search

We demonstrate an improvement in the operating temperature of a quantum dot-in-a-well (DWELL)-based infrared photodetector with spectral response observable till 250 K. This improvement was achieved through engineering the dot geome- try and the quantum confinement via postgrowth capping of the quantum dots (QDs) by selecting overlying materials under vari- ous growth conditions. The effect of the capping procedures was

Jiayi Shao; Thomas E. Vandervelde; Woo-Yong Jang; Andreas Stintz; Sanjay Krishna

2011-01-01

183

Hole storage in GaSb\\/GaAs quantum dots for memory devices  

Microsoft Academic Search

The hole confinement of self-organized GaSb\\/GaAs quantum dots embedded in n+p-diodes is investigated experimentally by admittance spectroscopy. The highest thermal activation energy obtained, 400 meV, refers to only weakly charged quantum dots. Detailed bias-dependent investigations allow to study state- filling and Coulomb charging effects. State filling lowers the activation energy down to 150 meV in quantum dots charged with the

M. Geller; C. Kapteyn; L. Müller-Kirsch; R. Heitz; D. Bimberg

2003-01-01

184

Ge\\/Si Self-Assembled Quantum Dots and Their Optoelectronic Device Applications  

Microsoft Academic Search

In recent years, quantum dots have been successfully grown by self-assembling processes. For optoelectronic device applications, the quantum-dot structures have advantages such as reduced phonon scattering, longer carrier lifetime, and lower detector noise due to low-dimensional confinement effect. Comparing to traditional optoelectronic III-V and other materials, self-assembled Ge quantum dots grown on Si substrates have a potential to be monolithically

Kang L. Wang; Dongho Cha; Jianlin Liu; Christopher Chen

2007-01-01

185

Confined Quantum Time of Arrivals  

NASA Astrophysics Data System (ADS)

We show that formulating the quantum time of arrival problem in a segment of the real line suggests rephrasing the quantum time of arrival problem to finding states that evolve to unitarily collapse at a given point at a definite time. For the spatially confined particle, we show that the problem admits a solution in the form of an eigenvalue problem of a compact and self-adjoint time of arrival operator derived by a quantization of the classical time of arrival, which is canonically conjugate with the Hamiltonian in a closed subspace of the Hilbert space.

Galapon, Eric A.; Caballar, Roland F.; Ricardo, T., Jr.

2004-10-01

186

Scalable qubit architecture based on holes in quantum dot molecules  

NASA Astrophysics Data System (ADS)

Spins confined in quantum dots are a leading candidate for solid-state quantum bits that can be coherently controlled by optical pulses. There are, however, many challenges to developing a scalable multibit information processing device based on spins in quantum dots, including the natural inhomogeneous distribution of quantum dot energy levels, the difficulty of creating all-optical spin manipulation protocols compatible with nondestructive readout, and the substantial electron-nuclear hyperfine interaction-induced decoherence. Here, we present a scalable qubit design and device architecture based on the spin states of single holes confined in a quantum dot molecule. The quantum dot molecule qubit enables a new strategy for optical coherent control with dramatically enhanced wavelength tunability. The use of hole spins allows the suppression of decoherence via hyperfine interactions and enables coherent spin rotations using Raman transitions mediated by a hole-spin-mixed optically excited state. Because the spin mixing is present only in the optically excited state, dephasing and decoherence are strongly suppressed in the ground states that define the qubits and nondestructive readout is possible. We present the qubit and device designs and analyze the wavelength tunability and fidelity of gate operations that can be implemented using this strategy. We then present experimental and theoretical progress toward implementing this design.

Economou, Sophia E.; Climente, Juan I.; Badolato, Antonio; Bracker, Allan S.; Gammon, Daniel; Doty, Matthew F.

2012-08-01

187

Synthesis of colloidal SnSe quantum dots by electron beam irradiation  

NASA Astrophysics Data System (ADS)

Water-soluble orthorhombic colloidal SnSe quantum dots with an average diameter of 4 nm were successfully prepared by a novel irradiation route using an electronic accelerator as a radiation source and hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant. The quantum dots exhibit a large direct bandgap of 3.89 eV, greatly blue shifted compared with that of bulk SnSe (1.0 eV) due to the quantum confinement effect. The quantum dots show blue photoluminescence at ˜420 nm. The influence of CTAB on the growth of the quantum dots was investigated and a possible reaction/growth mechanism was proposed.

Li, Zhen; Peng, Liwei; Fang, Yaoguo; Chen, Zhiwen; Pan, Dengyu; Wu, Minghong

2011-12-01

188

A tunable few electron triple quantum dot  

Microsoft Academic Search

We report on a new design to realize a fully tunable lateral triple quantum dot. The electrostatically defined quantum dots are arranged in series. The number of electrons in the quantum dots can be controlled and fundamental electronic configurations such as the (0,0,0) and (1,1,1) are obtained. Control of the number of electrons is important to perform quantum information processes

Louis Gaudreau; Alicia Kam; Ghislain Granger; Piotr Zawadzki; Sergei Studenikin; Aashish Clerk; Andrew Sachrajda

2010-01-01

189

Optical Interaction of Light with Semiconductor Quantum-Confined States at the Nanoscale  

NASA Astrophysics Data System (ADS)

In this chapter, near-field imaging spectroscopy of quantum-confined systems with a spatial resolution as high as 10-30 nm is described. Spatial profiles of local density of states and exciton wavefunctions confined in quantum dots are visualized. The fundamental aspects of localized and delocalized electrons in interface and alloy disorder systems are also discussed.

Saiki, Toshiharu

190

Electron spins in quantum dots for spintronics and quantum computation  

Microsoft Academic Search

Coherent manipulation, filtering, and measurement of electronic spin in quantum dots and other nanostructures have promising applications in conventional and in quantum information processing and transmission. We present an overview of our theoretical proposal to implement a quantum computer using electron spins in quantum dots as qubits. We discuss all necessary requirements towards a scalable quantum computer including one- and

Hans-Andreas Engel; Patrik Recher; Daniel Loss

2001-01-01

191

Quantum computing with quantum-dot cellular automata  

Microsoft Academic Search

Quantum-dot cellular automata (QCA), arrays of coupled quantum-dot devices, are proposed for quantum computing. The notion of coherent QCA (CQCA) is introduced in order to distinguish QCA applied to quantum computing from classical digital QCA. Information is encoded in the spatial state of the electrons in the multidot system. A line of CQCA cells can work as a quantum register.

Géza Tóth; Craig S. Lent

2001-01-01

192

Negative-Band-Gap Quantum Dots  

NASA Astrophysics Data System (ADS)

The spectrum of quantum dots (QDs) made from semiconductors like HgTe and HgS changes from negative gap to positive gap with decreasing size. Furthermore, intrinsic surface states, which are not related to dangling bonds, appear in the negative gap regime. We investigate theoretically the evolution of the spectrum of HgS QDs with decreasing size and show how states evolve from a negative gap to a positive gap as confinement is increased. The lowest confined electron level evolves into an intrinsic surface state with increasing size. This surface state is not derived from a bulk HgS bands. We demonstrate that surface states found do not have characteristic topological properties.

Malkova, Natalia; Bryant, Garnett W.

2011-12-01

193

Zero-energy states in graphene quantum dots and rings  

SciTech Connect

We present exact analytical zero-energy solutions for a class of smooth-decaying potentials, showing that the full confinement of charge carriers in electrostatic potentials in graphene quantum dots and rings is indeed possible without recourse to magnetic fields. These exact solutions allow us to draw conclusions on the general requirements for the potential to support fully confined states, including a critical value of the potential strength and spatial extent.

Downing, C. A.; Stone, D. A. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Portnoi, M. E. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); International Institute of Physics, Av. Odilon Gomes de Lima, 1722, Capim Macio, CEP: 59078-400, Natal - RN (Brazil)

2011-10-15

194

Quantum Dots Based Rad-Hard Computing and Sensors  

NASA Technical Reports Server (NTRS)

Quantum Dots (QDs) are solid-state structures made of semiconductors or metals that confine a small number of electrons into a small space. The confinement of electrons is achieved by the placement of some insulating material(s) around a central, well-conducting region. Thus, they can be viewed as artificial atoms. They therefore represent the ultimate limit of the semiconductor device scaling. Additional information is contained in the original extended abstract.

Fijany, A.; Klimeck, G.; Leon, R.; Qiu, Y.; Toomarian, N.

2001-01-01

195

Single Dot Spectroscopy of Two-Color Quantum Dot\\/Quantum Shell Nanostructures  

Microsoft Academic Search

Single dot spectroscopy is performed on two-color CdSe\\/ZnS\\/CdSe core\\/barrier\\/shell nanostructures. Unlike quantum dots cores, these systems have two phases with which to emit and ultimately examine for blinking analysis. These particles are brighter than conventional quantum dots and also show the photoluminescence (PL) intensity and energy fluctuations characteristic of quantum dots. Single dot spectral diffusion analysis yields no measureable energy

Eva A. Dias; Amy F. Grimes; Douglas S. English; Patanjali Kambhampati

2008-01-01

196

Electron tunneling rate in quantum dots under a uniform electric field  

Microsoft Academic Search

A stabilization method is used to evaluate the tunneling rate of an electron in isolated quantum dots of conical shape under uniform electric field. A stabilization graph is obtained by plotting the eigenvalues of a single quantum dot embedded in a confining box made of barrier material as functions of the size of the box. The eigenvalues of the system

David M.-T. Kuo; Yia-Chung Chang

2000-01-01

197

Self-assembly of heterojunction quantum dots(HeQuaDs)  

Microsoft Academic Search

Quantum dots (QDs) have been receiving considerable attention due to the unique properties, which arise due to the confinement of the electron and holes in a lower band gap material. The InAs on GaAs material system is one of the most studied combinations in which quantum dots form during epitaxy. These QDs form in a Stranski Krastanov manner via a

K. G. Eyink; D. H. Tomich; L. Grazulis; J. J. Pitz; K. Mahalingam; J. Shank; S. Munshi; B. Ulrich

2006-01-01

198

Fabrication of CdSe quantum dots-PHF organic hybrid light emitting diodes  

Microsoft Academic Search

Quantum dots (QDs) have been attracted an active interest for light emitting device due to their unique high luminescence efficiency and narrow emission spectra as a result of the strong electrons confinement in its nanoscale core that is potential for production of pure colour light emission. In this work, a CdSe quantum dot-PHF organic hybrid light emitting devices have been

T. H. T. Aziz; M. M. Salleh; M. Yahaya; A. A. Umar

2008-01-01

199

Probing collective modes of correlated states of few electrons in semiconductor quantum dots  

Microsoft Academic Search

Low-lying collective excitations above highly correlated ground states of few interacting electrons confined in GaAs semiconductor quantum dots are probed by resonant inelastic light scattering. We highlight that separate studies of the changes in the spin and charge degrees of freedom offer unique access to the fundamental interactions. The case of quantum dots with four electrons is found to be

S. Kalliakos; M. Rontani; V. Pellegrini; A. Pinczuk; A. Shinga; C. P. Garcia; G. Goldoni; E. Molinari; L. N. Pfeiffer; K. W. West

2009-01-01

200

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

Microsoft Academic Search

We apply discoveries in nanoscience towards applications relevant to health, environment, security, and connectedness. A materials fundamental to our research is the quantum dot. Each quantum dot is a particle of semiconductor only a few nanometers in diameter. These semiconductor nanoparticles confine electrons to within their characteristic wavelength. Thus, just as changing the length of a guitar string changes the

Edward H. Sargent

2006-01-01

201

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

Microsoft Academic Search

This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum

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

2011-01-01

202

Quantum Entanglement and Teleportation in a Vertical Quantum Dot  

NASA Astrophysics Data System (ADS)

We study the thermal entanglement and teleportation using quantum dot as the quantum channel. We firstly investigate the evolution of entanglement in the vertical quantum dot, then focus on the effects of the important parameters of the system on the teleported fidelity under different conditions. We obtain the critical temperature of suddenly dead entanglement. Based on Bell measurements in two subspaces, the isotropy and anisotropy subspaces, we can find that the anisotropy measurements always overmatch the isotropy ones. Moreover, we obtain the high-fidelity teleportation for quantum dot as quantum channel when the parameters are adjusted. The possible applications of quantum dot are expected in quantum teleportation

Qin, Li-Guo; Tian, Li-Jun; Yang, Guo-Hong

2013-12-01

203

Quantum dots in biology and medicine  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots (QDs) are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. In comparison with organic dyes and fluorescent proteins, these quantum-confined nanoparticles are brighter, more stable against photobleaching, and can be excited for multicolor emission with a single light source. Recent advances have shown that nanometer-sized semiconductor particles can be covalently linked with biorecognition molecules such as peptides, antibodies, nucleic acids, or small-molecule ligands for use as biological labels. High-quality QDs are also well suited for optical encoding and multiplexing applications due to their broad excitation profiles and narrow/symmetric emission spectra. In this article, we discuss recent developments in QD synthesis and bioconjugation, their applications in molecular and cellular imaging, as well as promising directions for future research.

Bailey, Robert E.; Smith, Andrew M.; Nie, Shuming

2004-10-01

204

Semiconductor quantum dot-sensitized solar cells  

PubMed Central

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.

Tian, Jianjun; Cao, Guozhong

2013-01-01

205

Strong optical confinement and multimode emission of organic photonic dots  

Microsoft Academic Search

We report on the optical mode structure of laterally confined organic microcavities. For preparation, an organic semiconductor is evaporated through a mask with square sized holes, resulting in photonic dots with approximately 5 mum diameter. Using a microscope setup, we observe a complex mode structure in transmission and photoluminescence. From the mode mapping, we conclude a strong three-dimensional optical confinement.

M. Langner; R. Gehlhaar; C. Schriever; H. Fröb; V. G. Lyssenko; K. Leo

2007-01-01

206

Quantum dot nanophotonics - from waveguiding to integration  

Microsoft Academic Search

Due to its unique optoelectronic properties, the quantum dot (QD) has become a promising material for realizing photonic components and devices with high quantum efficiencies. Quantum dots in colloidal form can have their surfaces modified with various molecules, which enables new fabrication process utilizing molecular self-assembly and can result in new QD photonic device structures in nano-scale. In this review

Lih Y. Lin; Chia-Jean Wang; Michael C. Hegg; Ludan Huangb

2009-01-01

207

Electronic states and curved surface effect of silicon quantum dots  

NASA Astrophysics Data System (ADS)

The calculation results show that the bonding energy and electronic states of silicon quantum dots (Si QDs) are different on various curved surfaces (CS), for example, a Si-O-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet. Curved surface breaks symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in band gap. The red-shifting of photoluminescence spectra on smaller silicon quantum dots can be explained by CS effect. In CS effect, surface curvature is determined by the shape of Si QDs or silicon nanostructures, which is independent of their sizes. The CS effect has the interesting fundamental physical properties in nanophysics as that of quantum confinement effect.

Huang, Wei-Qi; Huang, Zhong-Mei; Cheng, Han-Qiong; Miao, Xin-Jian; Shu, Qin; Liu, Shi-Rong; Qin, Chao-Jian

2012-10-01

208

Quantum Dot Light Emitting Diode  

SciTech Connect

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

Kahen, Keith

2008-07-31

209

Quantum Dot Light Emitting Diode  

SciTech Connect

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

Keith Kahen

2008-07-31

210

Renal clearance of quantum dots.  

PubMed

The field of nanotechnology holds great promise for the diagnosis and treatment of human disease. However, the size and charge of most nanoparticles preclude their efficient clearance from the body as intact nanoparticles. Without such clearance or their biodegradation into biologically benign components, toxicity is potentially amplified and radiological imaging is hindered. Using intravenously administered quantum dots in rodents as a model system, we have precisely defined the requirements for renal filtration and urinary excretion of inorganic, metal-containing nanoparticles. Zwitterionic or neutral organic coatings prevented adsorption of serum proteins, which otherwise increased hydrodynamic diameter by >15 nm and prevented renal excretion. A final hydrodynamic diameter <5.5 nm resulted in rapid and efficient urinary excretion and elimination of quantum dots from the body. This study provides a foundation for the design and development of biologically targeted nanoparticles for biomedical applications. PMID:17891134

Choi, Hak Soo; Liu, Wenhao; Misra, Preeti; Tanaka, Eiichi; Zimmer, John P; Itty Ipe, Binil; Bawendi, Moungi G; Frangioni, John V

2007-10-01

211

Impurity effects on coupled quantum dot spin qubits in semiconductors  

NASA Astrophysics Data System (ADS)

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

Nguyen, Nga; Das Sarma, Sankar

2011-03-01

212

Electron counting in quantum dots  

Microsoft Academic Search

We use time-resolved charge detection techniques to investigate single-electron tunneling in semiconductor quantum dots. The ability to detect individual charges in real-time makes it possible to count electrons one-by-one as they pass through the structure. The setup can thus be used as a high-precision current meter for measuring ultra-low currents, with resolution several orders of magnitude better than that of

S. Gustavsson; R. Leturcq; M. Studer; I. Shorubalko; T. Ihn; K. Ensslin; D. C. Driscoll; A. C. Gossard

2009-01-01

213

(Indium,gallium)arsenide quantum dot materials for solar cell applications: Effect of strain-reducing and strain-compensated barriers on quantum dot structural and optical properties  

Microsoft Academic Search

The last few years have seen rapid advances in nanoscience and nanotechnology, allowing unprecedented manipulation of nanostructures controlling solar energy capture, conversion, and storage. Quantum confined nanostructures, such as quantum wells (QWs) and quantum dots (QDs) have been projected as potential candidates for the implementation of some high efficiency photovoltaic device concepts, including the intermediate band solar cell (IBSC). In

Anup Pancholi

2008-01-01

214

Decay dynamics and exciton localization in large GaAs quantum dots grown by droplet epitaxy  

NASA Astrophysics Data System (ADS)

We investigate the optical emission and decay dynamics of excitons confined in large strain-free GaAs quantum dots grown by droplet epitaxy. From time-resolved measurements combined with a theoretical model we show that droplet-epitaxy quantum dots have a quantum efficiency of about 75% and an oscillator strength between 8 and 10. The quantum dots are found to be fully described by a model for strongly confined excitons, in contrast to the theoretical prediction that excitons in large quantum dots exhibit the so-called giant oscillator strength. We attribute these findings to localized ground-state excitons in potential minima created by material intermixing during growth. We provide further evidence for the strong-confinement regime of excitons by extracting the size of electron and hole wave functions from the phonon-broadened photoluminescence spectra. Furthermore, we explore the temperature dependence of the decay dynamics and, for some quantum dots, observe a pronounced reduction in the effective transition strength with temperature. We quantify and explain these effects as being an intrinsic property of large quantum dots owing to thermal excitation of the ground-state exciton. Our results provide a detailed understanding of the optical properties of large quantum dots in general, and of quantum dots grown by droplet epitaxy in particular.

Tighineanu, P.; Daveau, R.; Lee, E. H.; Song, J. D.; Stobbe, S.; Lodahl, P.

2013-10-01

215

Quantum Logic Using Excitonic Quantum Dots in External Optical Microcavities.  

National Technical Information Service (NTIS)

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

M. G. Raymer

2003-01-01

216

Magneto-Optical Transitions in a Coulomb Coupled Pair of Quantum Dots (Abstract Only).  

National Technical Information Service (NTIS)

Optical transitions for a pair of Coulomb coupled quantum dots in a magnetic field are investigated. It is shown that for a parabolic confinement potential, the electric dipole transition energies reveal interesting anticrossing behavior which is due to t...

T. Chakraborty V. Halonen P. Pietilainen

1991-01-01

217

Fluoroimmunoassays using antibody-conjugated quantum dots.  

PubMed

Luminescent colloidal semiconductor nanocrystals (quantum dots) are robust inorganic fluoro phores that have the potential to circumvent some of the functional limitations encountered by organic dyes in sensing and biotechnological applications. Quantum dots exhibit size-dependent tunable, narrow fluorescence emission spectra that span the visible spectrum and have broad absorption spectra. This allows simultaneous excitation of several particle sizes at a single wavelength with emission at multiple wavelengths. Quantum dots also provide a high-resistance threshold to chemical degradation and photodegradation. We have developed a conjugation strategy for the attachment of antibodies to quantum dots based on electrostatic interactions between negatively charged dihydrolipoic acid (DHLA)-capped CdSe-ZnS core-shell quantum dots and positively charged proteins (natural or engineered) that serve to bridge the quantum dot and antibody. This chapter details the materials and methods for synthesis of the DHLA-capped CdSe-ZnS core-shell quantum dots, the construction and preparation of recombinant proteins, the conjugation of antibodies to quantum dots, and the use of antibody-coated quantum dots in a fluoroimmunoassay. PMID:15923672

Goldman, Ellen R; Mattoussi, Hedi; Anderson, George P; Medintz, Igor L; Mauro, J Matthew

2005-01-01

218

Electron counting in quantum dots  

NASA Astrophysics Data System (ADS)

We use time-resolved charge detection techniques to investigate single-electron tunneling in semiconductor quantum dots. The ability to detect individual charges in real-time makes it possible to count electrons one-by-one as they pass through the structure. The setup can thus be used as a high-precision current meter for measuring ultra-low currents, with resolution several orders of magnitude better than that of conventional current meters. In addition to measuring the average current, the counting procedure also makes it possible to investigate correlations between charge carriers. Electron correlations are conventionally probed in noise measurements, which are technically challenging due to the difficulty to exclude the influence of external noise sources in the experimental setup. Using real-time charge detection techniques, we circumvent the problem by studying the electron correlation directly from the counting statistics of the tunneling electrons. In quantum dots, we find that the strong Coulomb interaction makes electrons try to avoid each other. This leads to electron anti-bunching, giving stronger correlations and reduced noise compared to a current carried by statistically independent electrons. The charge detector is implemented by monitoring changes in conductance in a nearby capacitively coupled quantum point contact. We find that the quantum point contact not only serves as a detector but also causes a back-action onto the measured device. Electron scattering in the quantum point contact leads to emission of microwave radiation. The radiation is found to induce an electronic transition between two quantum dots, similar to the absorption of light in real atoms and molecules. Using a charge detector to probe the electron transitions, we can relate a single-electron tunneling event to the absorption of a single photon. Moreover, since the energy levels of the double quantum dot can be tuned by external gate voltages, we use the device as a frequency-selective single-photon detector operating at microwave energies. The ability to put an on-chip microwave detector close to a quantum conductor opens up the possibility to investigate radiation emitted from mesoscopic structures and gives a deeper understanding of the role of electron-photon interactions in quantum conductors. A central concept of quantum mechanics is the wave-particle duality; matter exhibits both wave- and particle-like properties and cannot be described by either formalism alone. To investigate the wave properties of the electrons, we perform experiments on a structure containing a double quantum dot embedded in the Aharonov-Bohm ring interferometer. Aharonov-Bohm rings are traditionally used to study interference of electron waves traversing different arms of the ring, in a similar way to the double-slit setup used for investigating interference of light waves. In our case, we use the time-resolved charge detection techniques to detect electrons one-by-one as they pass through the interferometer. We find that the individual particles indeed self-interfere and give rise to a strong interference pattern as a function of external magnetic field. The high level of control in the system together with the ability to detect single electrons enables us to make direct observations of non-intuitive fundamental quantum phenomena like single-particle interference or time-energy uncertainty relations.

Gustavsson, S.; Leturcq, R.; Studer, M.; Shorubalko, I.; Ihn, T.; Ensslin, K.; Driscoll, D. C.; Gossard, A. C.

2009-06-01

219

Plasmon assisted photonic crystal quantum dot sensors  

NASA Astrophysics Data System (ADS)

We report Quantum Dot Infrared Detectors (QDIP) where light coupling to the self assembled quantum dots is achieved through plasmons occurring at the metal-semiconductor interface. The detector structure consists of an asymmetric InAs/InGaAs/GaAs dots-in-a-well (DWELL) structure and a thick layer of GaAs sandwiched between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The aperture of the detector is covered with a thin metallic layer which along with the dielectric layer confines light in the vertical direction. Sub-wavelength two-dimensional periodic patterns etched in the metallic layer covering the aperture of the detector and the active region creates a micro-cavity that concentrate light in the active region leading to intersubband transitions between states in the dot and the ones in the well. The sidewalls of the detector were also covered with metal to ensure that there is no leakage of light into the active region other than through the metal covered aperture. An enhanced spectral response when compared to the normal DWELL detector is obtained despite the absence of any aperture in the detector. The spectral response measurements show that the Long Wave InfraRed (LWIR) region is enhanced when compared to the Mid Wave InfraRed (MWIR) region. This may be due to coupling of light into the active region by plasmons that are excited at the metal-semiconductor interface. The patterned metal-dielectric layers act as an optical resonator thereby enhancing the coupling efficiency of light into the active region at the specified frequency. The concept of plasmon-assisted coupling is in principle technology agnostic and can be easily integrated into present day infrared sensors.

Shenoi, R. V.; Ramirez, D. A.; Sharma, Y.; Attaluri, R. S.; Rosenberg, J.; Painter, O. J.; Krishna, S.

2007-10-01

220

Vertically stacked quantum dot pairs fabricated by nanohole filling.  

PubMed

Strain-free, vertically coupled GaAs quantum dots (QDs) with an ultra-low density below [Formula: see text] [Formula: see text] are fabricated by filling of self-assembled nanoholes with a GaAs/AlGaAs/GaAs layer sequence. The sizes of the two QDs, forming a QD pair (QDP), as well as the AlGaAs tunnel-barrier between the dots are tuned independently. We present atomic force microscopy studies of the QDP formation steps. We have performed photoluminescence studies of single QDPs with varied dot size and tunnel-barrier thickness. The data indicate non-resonant tunnelling between the dots. Furthermore, we apply the quantum confined Stark effect to tune the photoluminescence energy by up to 25 meV. PMID:24784358

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

2014-05-30

221

Vertically stacked quantum dot pairs fabricated by nanohole filling  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

222

The Rashba Effect on the Bound Polaron in a Parabolic Quantum Dot  

NASA Astrophysics Data System (ADS)

The bound polaron ground state energy is calculated by the variational method of Pekar considering the influence of the Rashba SO interaction on the condition of electric-LO phonon strong coupling in a parabolic quantum dot (QD). The relations on the bound polaron ground state energy with the parallel confinement length, the electron-LO phonon coupling constant, the perpendicular confinement length and the Coulomb binding parameter are derived for a parabolic quantum dot.

Yin, Ji-Wen; Li, Wei-Ping; Yu, Yi-Fu; Xiao, Jing-Lin

2011-04-01

223

Raman-Controlled Quantum Dots for Quantum Computing.  

National Technical Information Service (NTIS)

Optical control is fundamental to our project objective of demonstration of key quantum operations for quantum computation with spin qubits of electrons in semiconductor quantum dots. Sophia Economou, the graduate student supported by this fellowship, wor...

L. J. Sham

2005-01-01

224

InP quantum dots: Electronic structure, surface effects, and the redshifted emission  

Microsoft Academic Search

We present pseudopotential plane-wave electronic-structure calculations on InP quantum dots in an effort to understand quantum confinement and surface effects and to identify the origin of the long-lived and redshifted luminescence. We find that (i) unlike the case in small GaAs dots, the lowest unoccupied state of InP dots is the Gamma1c-derived direct state rather than the X1c-derived indirect state

Huaxiang Fu; Alex Zunger

1997-01-01

225

Stress Relaxation Phenomena in Buried Quantum Dots  

Microsoft Academic Search

We report on the results of experimental and theoretical investigation of mechanical stress relaxation in heterostructures with buried quantum dots. Quan- tum dot is viewed as a dilatational inclusion with eigenstrain (transformation strain) caused by crystal lattice mismatch between the dot and matrix materials. Stresses and energies for spheroid inclusions in an infinite medium, in a half-space, and in a

N. A. Bert; V. V. Chaldyshev; A. L. Kolesnikova; A. E. Romanov

226

A light-hole exciton in a quantum dot  

NASA Astrophysics Data System (ADS)

A light-hole exciton is a quasiparticle formed from a single electron bound to a single light hole. This type of fundamental excitation, if confined inside a semiconductor quantum dot, could be advantageous in quantum information science and technology. However, it has been difficult to access it so far, because confinement and strain in conventional quantum dots favour a ground-state single-particle hole with a predominantly heavy-hole character. Here we demonstrate the creation of a light-hole exciton ground state by applying elastic stress to an initially unstrained quantum dot. Its signature is clearly distinct from that of the well-known heavy-hole exciton and consists of three orthogonally polarized bright optical transitions and a fine-structure splitting of hundreds of microelectronvolts between in-plane and out-of-plane components. This work paves the way for the exploration of the fundamental properties and of the potential relevance of three-dimensionally confined light-hole states in quantum technologies.

Huo, Y. H.; Witek, B. J.; Kumar, S.; Cardenas, J. R.; Zhang, J. X.; Akopian, N.; Singh, R.; Zallo, E.; Grifone, R.; Kriegner, D.; Trotta, R.; Ding, F.; Stangl, J.; Zwiller, V.; Bester, G.; Rastelli, A.; Schmidt, O. G.

2014-01-01

227

Nonlinear thermoelectric response of quantum dots  

NASA Astrophysics Data System (ADS)

The thermoelectric transport properties of nanostructured devices continue to attract attention from theorists and experimentalist alike as the spatial confinement allows for a controlled approach to transport properties of correlated matter. Most of the existing work, however, focuses on thermoelectric transport in the linear regime despite the fact that the nonlinear conductance of correlated quantum dots has been studied in some detail throughout the last decade. To go beyond the linear response regime, we use a recently developed scheme [1], to address the low-energy behavior near the strong-coupling fixed point at finite bias voltage and finite temperature drop at the quantum dot. We test the reliability of the method against the numerical renormalization group [2] and determine the charge, energy, and heat current through the nanostructure. This allows us to determine the nonlinear transport coefficients, the entropy production, and the fate of the Wiedemann-Franz law in the non-thermal steady-state [3].[4pt] [1] E. Munoz et al, arXiv:1111.4076.[0pt] [2] L. Merker et al, in preparation.[0pt] [3] S. Kirchner, F. Zamani, and E. Munoz, in ``New Materials for Thermoelectric Applications: Theory and Experiment,'' Springer (2012).

Kirchner, Stefan; Zamani, Farzaneh; Munoz, Enrique; Merker, Lukas; Costi, Theo

2013-03-01

228

A quantum dot in topological insulator nanofilm.  

PubMed

We introduce a quantum dot in topological insulator nanofilm as a bump at the surface of the nanofilm. Such a quantum dot can localize an electron if the size of the dot is large enough, ?5 nm. The quantum dot in topological insulator nanofilm has states of two types, which belong to two ('conduction' and 'valence') bands of the topological insulator nanofilm. We study the energy spectra of such defined quantum dots. We also consider intraband and interband optical transitions within the dot. The optical transitions of the two types have the same selection rules. While the interband absorption spectra have multi-peak structure, each of the intraband spectra has one strong peak and a few weak high frequency satellites. PMID:24590177

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

2014-03-19

229

Magneto Electronics with Quantum Dots  

NASA Astrophysics Data System (ADS)

In contrast to solid state physics, there is a common regime in quantum transport where electron-electron interaction effects are dominant: the Coulomb blockade regime. In the context of nanostructure Quantum dots (such as carbon nanotube, semiconductor heterostructures), the discreteness of electron spectrum becomes important together with Coulomb interaction. A measuring device composed of two electrodes and the bridging dot allows us to probe these quantum properties (energy levels, orbitals) of a molecule directly. Here, carbon nanotubes (CNTs) are very interesting active elements, where the observed electron transport crucially depends on the intensity of coupling to the electrodes. Moreover, the possibility of combining different electronic orders (ferromagnets, superconductors etc.) or dimensionalities (3D electrodes, nanoparticles, Fullerenes, molecular magnets etc.) makes these electronic circuits more fascinating. This work discusses the spin-torque effect in a spin valve made out of two ferromagnetic leads connected through a carbon nanotube. Due to Coulomb bolckade in the QD and the strong spin polarization in the electrode, a bias dependent spin-torque has been observed.

Datta, Subhadeep

2013-03-01

230

Quantum dot photonic crystal detectors  

NASA Astrophysics Data System (ADS)

In this paper we report the use of a photonic crystal resonant cavity to increase the quantum efficiency, detectivity (D*) and the background limited infrared photodetector (BLIP) temperature of a quantum dot detector. The photonic crystal is incorporated in InAs/InGaAs/GaAs dots-in-well (DWELL) detector using Electron beam lithography. From calibrated blackbody measurements, the conversion efficiency of the detector with the photonic crystal (DWELL-PC) is found to be 58.5% at -2.5 V while the control DWELL detectors have quantum efficiency of 7.6% at the same bias. We observed no significant reduction in the dark current of the photonic crystal devices compared to the normal structure. The generation-recombination limited D* at 77K with a 300K F1.7 background, is estimated to be 6 x 1010 cmHz1/2/W at -3V bias for the DWELL-PC which is a factor of 20 higher than that of the control sample. We also observed a 20% increase in the BLIP temperature for the DWELL-PCs.

Posani, Kalyan T.; Tripathi, Vaibhav; Annamalai, Senthil; Krishna, Sanjay; Perahia, Raviv; Crisafulli, Orion; Painter, Oskar

2006-03-01

231

Nonlinear Optical Properties of Quantum Dot Composites  

Microsoft Academic Search

As novel nanoscale materials become more integral to technological advances, a deeper understanding of their fundamental properties is required. A quantum dot is a semiconductor particle fabricated from various materials and at various sizes on the nanometer scale. Our experiments aim to understand the nonlinear optical properties of quantum dot composites, which will pave the way for applications in lithography,

Anthony Kolodzinski

2010-01-01

232

Intraband transitions in colloidal quantum dots  

Microsoft Academic Search

Semiconductor quantum dots represent new opportunies as materials in the mid infrared, in ranges of atmospheric transparencies (3-5 and 8-12 microns). Chemically synthesized colloidal quantum dots are unique in that they share the convenient processing aspects of organic materials, while displaying strong tunable optical response from 2 to 20 microns, and they are potential materials for infared lasers and various

Philippe Guyot-Sionnest; Congjun Wang

2002-01-01

233

Theory of random population for quantum dots  

Microsoft Academic Search

Carrier capture and recombination in quantum dots are random processes. Conventional rate equation models do not take into account this property. Based on our theory of random population we predict recombination spectra, transients, and gain of quantum-dot ensembles. Even with infinitely fast interlevel energy relaxation excited levels become considerably populated. The impact of a slowdown of energy relaxation is modeled

M. Grundmann; D. Bimberg

1997-01-01

234

Molecular quantum-dot cellular automata  

Microsoft Academic Search

Quantum-dot cellular automata (QCA) is an approach to computing which eliminates the need for transistors by representing binary digits as charge configurations rather than current levels. Coulomb interactions provide device-device coupling without current flow. Clocked control of the device allows power gain, control of power dissipation, and pipelined computation. Molecular QCA uses redox sites of molecules as quantum dots. We

Beth Isaksen; Craig S. Lent

2003-01-01

235

Thick-shell nanocrystal quantum dots  

DOEpatents

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.

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

2011-05-03

236

Charging colloidal quantum dots by electrochemistry  

Microsoft Academic Search

.  The combination of electrochemistry and spectroscopy has allowed to establish novel charge induced phenomena in colloidal\\u000a quantum dots thin films, including tuning the optical bandgap, modifying the fluorescence properties, and achieving conductivity.\\u000a This is a brief review on the topic of charging colloidal quantum dots by electrochemistry.

Philippe Guyot-Sionnest

2008-01-01

237

Ultranarrow Luminescence Lines from Single Quantum Dots  

Microsoft Academic Search

We report ultranarrow \\\\(<0.15 meV\\\\) cathodoluminescence lines originating from single InAs quantum dots in a GaAs matrix for temperatures up to 50 K, directly proving their delta-function-like density of electronic states. The quantum dots have been prepared by molecular beam epitaxy utilizing a strain-induced self-organizing mechanism. A narrow dot size distribution of width 12+\\/-1 nm is imaged by plan-view transmission

M. Grundmann; J. Christen; N. N. Ledentsov; J. Böhrer; D. Bimberg; S. S. Ruvimov; P. Werner; U. Richter; U. Gösele; J. Heydenreich; V. M. Ustinov; A. Yu. Egorov; A. E. Zhukov; P. S. Kop'ev; Zh. I. Alferov

1995-01-01

238

Photoluminescence of quantum-confined semiconductor structures  

NASA Astrophysics Data System (ADS)

Different aspects of the photoluminescence from semiconductor quantum-confined structures are studied in this dissertation, for a better understanding of fundamental physics of semiconductors. The precursor of any photoluminescence study is the characterization of the linear optical properties of the semiconductor structures. High resolution absorption measurements were performed in order to study the interplay of disorder and acoustic phonon scattering in a quantum well. Also, reflectivity measurements, together with a fitting procedure based on the transfer matrix formalism, are used to determine the thickness of samples. Excitons are atom-like quasi-particles, formed from a bound electron-hole pair. They follow a Bose-Einstein statistic, so in principle it is possible to achieve an excitonic Bose-Einstein condensate. Time resolved photoluminescence measurements were performed over an extensive range of lattice temperatures and carrier concentrations, in order to determine the fraction of excitons formed from the electron-hole plasma in a quantum well, after non-resonant excitation. The experimental spectra were compared to a pure plasma calculation first, then excitons were taken into account-The highest fraction of formed excitons is found for low temperatures and intermediate carrier densities. This fraction is found to be very small, and this has clear implications on the excitonic Bose-Einstein condensation studies. The photoluminescence emitted left and right from a quantum well is interfered in a modified Mach-Zender interferometer. It is shown that the light emitted on the two paths will interfere for a V-shape geometry and will not for any other paths. A structure formed by placing a quantum well in a field antinode of a resonant planar microcavity exhibits normal mode coupling: splitting of the resonance spectral line. For the case of resonant excitation, a third peak appears at higher excitation levels. The coherence properties of the photoluminescence from a normal-mode-coupling microcavity are studied using another version of the Mach-Zender interferometer. The degree of coherence measured in this way depends greatly on the pump wavelength and intensity, ranging from zero to 0.8. However, direct observation of the emission speckle shows significant coherence in all cases. The difference is explained by the different methods used to evaluate the coherence. The strong coupling between a quantum dot and a photonic crystal nanocavity is investigated by observation of photoluminescence. A new method of tunning the cavity wavelength by deposition of a thin film of solid Xenon on all the surfaces of the sample is presented. The method allows the scanning of the cavity wavelength with about 5 nm without a decrease in the quality factor and without changing the temperature. Finally, an extensive study of the quality factors of quantum dot photonic crystal nanocavities is presented. The role of the quantum dot ensemble absorption is investigated. At higher excitation levels, lasing is observed and discussed.

Mosor, Sorin

239

Energy Gaps and Interaction Blockade in Confined Quantum Systems  

SciTech Connect

We investigate universal properties of strongly confined particles that turn out to be dramatically different from what is observed for electrons in atoms and molecules. For a large class of harmonically confined systems, such as small quantum dots and optically trapped atoms, many-body particle addition and removal energies, and energy gaps, are accurately obtained from single-particle eigenvalues. Transport blockade phenomena are related to the derivative discontinuity of the exchange-correlation functional. This implies that they occur very generally, with Coulomb blockade being a particular realization of a more general phenomenon. In particular, we predict a van der Waals blockade in cold atom gases in traps.

Capelle, K. [Departamento de Fisica e Informatica, Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, 13560-970 Sao Carlos, SP (Brazil); Mathematical Physics, LTH, Lund University, 22100 Lund (Sweden); Borgh, M.; Kaerkkaeinen, K.; Reimann, S. M. [Mathematical Physics, LTH, Lund University, 22100 Lund (Sweden)

2007-07-06

240

Classical behavior of few-electron parabolic quantum dots  

NASA Astrophysics Data System (ADS)

Quantum dots are intricate and fascinating systems to study novel phenomena of great theoretical and practical interest because low dimensionality coupled with the interplay between strong correlations, quantum confinement and magnetic field creates unique conditions for emergence of fundamentally new physics. In this work we consider two-dimensional semiconductor quantum dot systems consisting of few interacting electrons confined in an isotropic parabolic potential. We study the many-electron quantum ground state properties of such systems in presence of a perpendicular magnetic field as the number of electrons is varied using exact numerical diagonalizations and other approaches. The results derived from the calculations of the quantum model are then compared to corresponding results for a classical model of parabolically confined point charges who interact with a Coulomb potential. We find that, for a wide range of parameters and magnetic fields considered in this work, the quantum ground state energy is very close to the classical energy of the most stable classical configuration under the condition that the classical energy is properly adjusted to incorporate the quantum zero point motion.

Ciftja, O.

2009-06-01

241

Red-Emitting Semiconductor Quantum Dot Lasers  

NASA Astrophysics Data System (ADS)

Visible-stimulated emission in a semiconductor quantum dot (QD) laser structure has been demonstrated. Red-emitting, self-assembled QDs of highly strained InAlAs have been grown by molecular beam epitaxy on a GaAs substrate. Carriers injected electrically from the doped regions of a separate confinement heterostructure thermalized efficiently into the zero-dimensional QD states, and stimulated emission at ~707 nanometers was observed at 77 kelvin with a threshold current of 175 milliamperes for a 60-micrometer by 400-micrometer broad area laser. An external efficiency of ~8.5 percent at low temperature and a peak power greater than 200 milliwatts demonstrate the good size distribution and high gain in these high-quality QDs.

Fafard, S.; Hinzer, K.; Raymond, S.; Dion, M.; McCaffrey, J.; Feng, Y.; Charbonneau, S.

1996-11-01

242

Changes in luminescence emission induced by proton irradiation: InGaAs/GaAs quantum wells and quantum dots  

NASA Technical Reports Server (NTRS)

The photoluminescence emission from InGaAs/GaAs quantum-well and quantum-dot (QD) structures are compared after controlled irradiation with 1.5 MeV proton fluxes. Results presented here show a significant enhancement in radiation tolerance with three-dimensional quantum confinement.

Leon, R.; Swift, G. M.; Magness, B.; Taylor, W. A.; Tang, Y. S.; Wang, K. L.; Dowd, P.; Zhang, Y. H.

2000-01-01

243

Polymer-coated quantum dots.  

PubMed

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 additional functional groups used in further chemical derivatization of the nanoparticles. We review the coating methods, including multidentate and amphiphilic polymeric coatings, and grafting-to and grafting-from approaches. We highlight the most commonly used polymers and discuss how their chemical structure influences the coating properties. PMID:24136705

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

2013-12-21

244

Biocompatible Quantum Dots for Biological Applications  

SciTech Connect

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.

Rosenthal, Sandra [ORNL; Chang, Jerry [Vanderbilt University; Kovtun, Oleg [Department of Chemistry, Vanderbilt University, 7300 Stevenson Ctr Ln, Nashville, TN 37235, USA.; McBride, James [Vanderbilt University; Tomlinson, Ian [Oak Ridge National Laboratory (ORNL)

2011-01-01

245

Decoherence dynamics of two charge qubits in vertically coupled quantum dots  

SciTech Connect

The decoherence dynamics of two charge qubits in a double quantum dot is investigated theoretically. We consider the quantum dynamics of two interacting electrons in a vertically coupled quantum dot driven by an external electric field. We derive the equations of motion for the density matrix, in which the presence of an electron confined in the double dot represents one qubit. A Markovian approach to the dynamical evolution of the reduced density matrix is adopted. We evaluate the concurrence of two qubits in order to study the effect of acoustic phonons on the entanglement. We also show that the disentanglement effect depends on the double dot parameters and increases with the temperature.

Ben Chouikha, W.; Bennaceur, R. [Laboratoire de Physique de la Matiere Condensee, Departement de Physique, Faculte des Sciences de Tunis, 1060 Tunis (Tunisia); Jaziri, S. [Departement de Physique, Faculte des Sciences de Bizerte, Jarzouna 7021 Bizerte (Tunisia)

2007-12-15

246

Nearly monodisperse graphene quantum dots fabricated by amine-assisted cutting and ultrafiltration  

NASA Astrophysics Data System (ADS)

We report a novel procedure involving polyethylenimine-assisted hydrothermal cutting and subsequent ultrafiltration for fabricating nearly monodisperse graphene quantum dots with a uniform lateral size and confined layer number. The isolated monolayer quantum dots exhibit a sharp band-edge absorption feature and strong photoluminescence (quantum yield of 21%) independent of excitation wavelength and pH. Their preliminary application in bioimaging has been demonstrated.We report a novel procedure involving polyethylenimine-assisted hydrothermal cutting and subsequent ultrafiltration for fabricating nearly monodisperse graphene quantum dots with a uniform lateral size and confined layer number. The isolated monolayer quantum dots exhibit a sharp band-edge absorption feature and strong photoluminescence (quantum yield of 21%) independent of excitation wavelength and pH. Their preliminary application in bioimaging has been demonstrated. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03623e

Xue, Qi; Huang, He; Wang, Liang; Chen, Zhiwen; Wu, Minghong; Li, Zhen; Pan, Dengyu

2013-11-01

247

Effect of organic materials used in the synthesis on the emission from CdSe quantum dots  

NASA Astrophysics Data System (ADS)

Quantum-dot nanocrystals have particular optical properties due to the quantum confinement effect and the surface effect. This study focuses on the effect of surface conditions on the emission from quantum dots. The quantum dots prepared with 1-hexadecylamine (HDA) in the synthesis show strong emission while the quantum dots prepared without HDA show weak emission, as well as emission from surface energy traps. The comparison of the X-ray patterns of these two sets of quantum dots reveals that HDA forms a layer on the surface of quantum dot during the synthesis. This surface passivation with a layer of HDA reduces surface energy traps, therefore the emission from surface trap levels is suppressed in the quantum dots synthesized with HDA.

Lee, Jae-Won; Yang, Ho-Soon; Hong, K. S.; Kim, S. M.

2013-12-01

248

Nanometer Distance Measurements Between Multicolor Quantum Dots  

PubMed Central

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

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

2009-01-01

249

Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots  

SciTech Connect

Low-dimensional semiconductors have attracted great interest due to the potential for tailoring their linear and nonlinear optical properties over a wide-range. Semiconductor nanocrystals (NC's) represent a class of quasi-zero-dimensional objects or quantum dots. Due to quantum cordhement and a large surface-to-volume ratio, the linear and nonlinear optical properties, and the carrier dynamics in NC's are significantly different horn those in bulk materials. napping at surface states can lead to a fast depopulation of quantized states, accompanied by charge separation and generation of local fields which significantly modifies the nonlinear optical response in NC's. 3D carrier confinement also has a drastic effect on the energy relaxation dynamics. In strongly confined NC's, the energy-level spacing can greatly exceed typical phonon energies. This has been expected to significantly inhibit phonon-related mechanisms for energy losses, an effect referred to as a phonon bottleneck. It has been suggested recently that the phonon bottleneck in 3D-confined systems can be removed due to enhanced role of Auger-type interactions. In this paper we report femtosecond (fs) studies of ultrafast optical nonlinearities, and energy relaxation and trap ping dynamics in three types of quantum-dot systems: semiconductor NC/glass composites made by high temperature precipitation, ion-implanted NC's, and colloidal NC'S. Comparison of ultrafast data for different samples allows us to separate effects being intrinsic to quantum dots from those related to lattice imperfections and interface properties.

Klimov, V.; McBranch, D.; Schwarz, C.

1998-08-10

250

Quantum dot detectors for mid-infrared sensing: bias-controlled spectral tuning and matched filtering  

Microsoft Academic Search

Quantum-dot infrared photodetectors (QDIPs), based on intersubband transitions in nanoscale self-assembled dots, are perceived as a promising technology for mid-infrared-regime sensing since they are based on a mature GaAs technology, are sensitive to normal incidence radiation, exhibit large quantum confined stark effect that can be exploited for hyperspectral imaging, and have lower dark currents than their quantum well counterparts. High

Unal Sakoglu; Zhipeng Wang; Majeed M. Hayat; J. Scott Tyo; Senthil Annamalai; Philip Dowd; Sanjay Krishna

2004-01-01

251

Synthesis and optical property of lead sulfide quantum dot materials by the sol-gel method  

Microsoft Academic Search

This research has attempted to investigate the effect of nanocrystallite surface on the quantum confinement using PbS quantum dot materials since the surface-to-volume ratio of such small nanocrystallites becomes very large in the small size region. The fabrication processes of PbS quantum dot materials have been established using the sol-gel method. Two types of matrices, 5\\/20\\/75 sodium borosilicates (Na2O :

Yasukazu Hoshino

2002-01-01

252

Optical Spin Initialization and Non-Destructive Measurement in a Quantum Dot Molecule  

Microsoft Academic Search

The spin of an electron is an ideal two level system for realizing a quantum bit. Spatial confinement in a self-assembled InAs quantum dot greatly extends its spin coherence times as well as making them optically addressable. Through the excited trion state the electron can be initialized, coherently manipulated, and read out: the essential operations for quantum information processing. For

Danny Kim

2009-01-01

253

Investigations on Landé factor in a strained GaxIn1-xAs/GaAs quantum dot  

NASA Astrophysics Data System (ADS)

The effective excitonic g-factor as functions of dot radius and the Ga alloy content, in a strained GaxIn1-xAs/GaAs quantum dot, is numerically measured. The heavy hole excitonic states are studied for various Ga alloy content taking into account the anisotropy, non-parabolicity of the conduction band and the geometrical confinement effects. The quantum dot is considered as spherical dot of InAs surrounded by a GaAs barrier material.

Kumar, N. R. Senthil; Peter, A. John

2014-04-01

254

Biodetection using fluorescent quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2002-07-01

255

Quantum dots as luminescent probes in biological systems  

Microsoft Academic Search

This review describes the recent progress made in exploiting the light emitting properties of quantum dots as luminescent probes for the investigation of non-covalent interactions between two or more biological molecules. The properties of quantum dots and conventional fluorescent probes are compared and methods for attaching quantum dots to biomolecules examined. Such attachment generally involves two stages: quantum dot capping\\/coating

Andrew J Sutherland

2002-01-01

256

The flnal report: Quantum dots: from fundamental physics to applications  

Microsoft Academic Search

BACKGROUND The research performed during the fellowship focused on the physics of quantum dots. Quantum dots are nano-sized semiconductors which exhibit strong conflne- ment efiects. In complete contrast to traditional semi- conductors with an energy band structure, electrons and holes in quantum dots are completely conflned and form bound states, somewhat reminiscent of an atom. In inorganic semiconductor quantum dots,

Richard J. Warburton

257

Quantum dot loaded immunomicelles for tumor imaging  

Microsoft Academic Search

BACKGROUND: Optical imaging is a promising method for the detection of tumors in animals, with speed and minimal invasiveness. We have previously developed a lipid coated quantum dot system that doubles the fluorescence of PEG-grafted quantum dots at half the dose. Here, we describe a tumor-targeted near infrared imaging agent composed of cancer-specific monoclonal anti-nucleosome antibody 2C5, coupled to quantum

Aristarchos Papagiannaros; Jaydev Upponi; William Hartner; Dmitriy Mongayt; Tatyana Levchenko; Vladimir Torchilin

2010-01-01

258

Realistic model of a vertical pillar quantum dot: Analysis of individual dot data  

NASA Astrophysics Data System (ADS)

An accurate model of a vertical pillar quantum dot is described. The full three-dimensional structure of the device containing the dot is taken into account and this leads to an effective two-dimensional model in which electrons move in the two lateral dimensions, the confinement is parabolic, and the interaction potential is very different from the bare Coulomb potential. The potentials are found from the device structure and a few adjustable parameters. Numerically stable calculation procedures for the interaction potential are detailed and procedures for deriving parameter values from experimental addition energy and chemical potential data are described. The model is able to explain magnetic-field-dependent addition energy and chemical potential data for an individual dot to an accuracy of about 5%, the accuracy level needed to determine ground-state quantum numbers from experimental transport data. Applications to excited state transport data are also described.

Maksym, P. A.; Nishi, Y.; Austing, D. G.; Hatano, T.; Kouwenhoven, L. P.; Aoki, H.; Tarucha, S.

2009-03-01

259

Realization of quantum-dot cellular automata using semiconductor quantum dots  

Microsoft Academic Search

We demonstrate that a quantum-dot cellular automata device can be fabricated using electron beam lithographically defined gates on GaAs\\/AlGaAs heterostructure materials, and that by tuning the four quantum dot (J. Phys. C: Solid State Phys. 21 (1988) L893) system polarization of one double dot can lead to polarization in the neighboring double dot (Phys. Rev. B 67 (2003) 033302). The

C. G Smith; S. Gardelis; A. W Rushforth; R. Crook; J. Cooper; D. A Ritchie; E. H Linfield; Y. Jin; M. Pepper

2003-01-01

260

Four-wave mixing in InAlGaAs quantum dots  

Microsoft Academic Search

Summary form only given. The nonlinear optical properties of semiconductor quantum dots are of interest, both fundamentally and for potential device applications. Large optical nonlinearities are predicted due to the three dimensional confinement but the small active volume of the dots and their large inhomogeneous broadening strongly reduce the interaction with the electromagnetic field. Until now, four-wave mixing (FWM) in

K. Leosson; D. Birkedal; J. M. Hvam

2001-01-01

261

Modeling of long wavelength quantum-dot lasers with dots-in-a-well structure  

Microsoft Academic Search

Summary form only given. The zero-dimensional nature and three-dimensional confinement of QDs give rise to widely-spaced discrete states, resulting in carrier dynamics and lasing characteristics that differ significantly from double heterostructure or quantum well lasers. In this paper, we propose a rate equation model for the dots-in-a-well (DWELL) structure, and analyze the steady-state and transient behavior of the DWELL lasers

Xiaodong Huang; A. Stintz; Hua Li; J. Cheng; K. J. Malloy

2002-01-01

262

Characteristics of electron transport through vertical double-barrier quantum-dot structures: Effects of symmetric and asymmetric variations of the lateral confinement potentials  

Microsoft Academic Search

We report on a theoretical study of the electron transport through laterally-confined, vertical double-barrier resonant-tunneling (DBRT) structures, defined as one-dimensional (1D)-0D-1D systems, with a tunable lateral confinement. The current and the differential conductance of the systems are calculated and the influence caused by varying the lateral confinement on the device characteristics is investigated. Three representative systems are studied. First of

Dan Csontos; H. Q. Xu

2002-01-01

263

Interacting Electrons in a Quantum Dot: Quantum Monte Carlo Studies.  

National Technical Information Service (NTIS)

An efficient optimization method for the quantum Monte Carlo many-body wave functions, called the stochastic gradient approximation (SGA), is presented. Using this method, the states of interacting electrons in a semiconductor quantum dot are studied for ...

A. Harju

1999-01-01

264

Ultralong Dephasing Time in InGaAs Quantum Dots  

Microsoft Academic Search

We measure a dephasing time of several hundred picoseconds at low temperature in the ground-state transition of strongly confined InGaAs quantum dots, using a highly sensitive four-wave mixing technique. Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic exciton-acoustic phonon interactions.

P. Borri; W. Langbein; S. Schneider; U. Woggon; R. L. Sellin; D. Ouyang; D. Bimberg

2001-01-01

265

Electric transport through circular graphene quantum dots: Presence of disorder  

Microsoft Academic Search

The electronic states of an electrostatically confined cylindrical graphene quantum dot and the electric transport through this device are studied theoretically within the continuum Dirac-equation approximation and compared with numerical results obtained from a tight-binding lattice description. A spectral gap, which may originate from strain effects, additional adsorbed atoms, or substrate-induced sublattice-symmetry breaking, allows for bound and scattering states. As

G. Pal; W. Apel; L. Schweitzer

2011-01-01

266

On-chip quantum optics with quantum dot microcavities.  

PubMed

A novel concept for on-chip quantum optics using an internal electrically pumped microlaser is presented. The microlaser resonantly excites a quantum dot microcavity system operating in the weak coupling regime of cavity quantum electrodynamics. This work presents the first on-chip application of quantum dot microlasers, and also opens up new avenues for the integration of individual microcavity structures into larger photonic networks. PMID:23044860

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

2013-02-01

267

Solid-state quantum optics with quantum dots in photonic nanostructures  

NASA Astrophysics Data System (ADS)

Quantum nanophotonics has become a new research frontier where quantum optics is combined with nanophotonics in order to enhance and control the interaction between strongly confined light and quantum emitters. Such progress provides a promising pathway towards quantum-information processing on an all-solid-state platform. Here we review recent progress on experiments with quantum dots in nanophotonic structures with special emphasis on the dynamics of single-photon emission. Embedding the quantum dots in photonic band-gap structures offers a way of controlling spontaneous emission of single photons to a degree that is determined by the local light-matter coupling strength. Introducing defects in photonic crystals implies new functionalities. For instance, efficient and strongly confined cavities can be constructed enabling cavity-quantum-electrodynamics experiments. Furthermore, the speed of light can be tailored in a photonic-crystal waveguide forming the basis for highly efficient single-photon sources where the photons are channeled into the slowly propagating mode of the waveguide. Finally, we will discuss some of the surprises that arise in solid-state implementations of quantum-optics experiments in comparison to their atomic counterparts. In particular, it will be shown that the celebrated point-dipole description of light-matter interaction can break down when quantum dots are coupled to plasmon nanostructures.

Lodahl, Peter; Stobbe, Søren

2013-02-01

268

On the calculation of energy eigenstates of electrons in a spherical quantum dot  

NASA Astrophysics Data System (ADS)

The fundamental problem in the investigation of the properties of a quantum dot is the calculation of the energy eigen values of its confined charge carriers and evaluation of their corresponding wave functions. The quantum dots may be approximated as spheres whose surfaces constitute infinite potential barriers for carriers. Consequently, the motion of electrons and holes (which are confined inside the dot) can be analyzed by effective mass approximation applied to noninteracting particles. An attempt has been made here to solve the Schrödinger's equation for particles inside the infinite spherical potential well to determine their allowed energy eigen values and eigen functions.

Purohit, Pranati; Roy, Dilip K.; Pati, Shankar P.

2012-10-01

269

Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots  

NASA Astrophysics Data System (ADS)

The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

Robert, C.; Nestoklon, M. O.; Pereira da Silva, K.; Pedesseau, L.; Cornet, C.; Alonso, M. I.; Goñi, A. R.; Turban, P.; Jancu, J.-M.; Even, J.; Durand, O.

2014-01-01

270

Energy levels of few-electron quantum dots imaged and characterized by atomic force microscopy  

PubMed Central

Strong confinement of charges in few-electron systems such as in atoms, molecules, and quantum dots leads to a spectrum of discrete energy levels often shared by several degenerate states. Because the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum results from a change in cantilever resonance frequency and dissipation when an electron tunnels on/off a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the quantitative measurement of predicted temperature-dependent shifts of Coulomb blockade peaks. Scanning the surface shows that several quantum dots may reside on what topographically appears to be just one. Relative coupling strengths can be estimated from these images of grouped coupled dots.

Cockins, Lynda; Miyahara, Yoichi; Bennett, Steven D.; Clerk, Aashish A.; Studenikin, Sergei; Poole, Philip; Sachrajda, Andrew; Grutter, Peter

2010-01-01

271

Amplification Without Inversion in Semiconductor Quantum Dot  

NASA Astrophysics Data System (ADS)

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.

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

272

Inkjet printing of light emitting quantum dots  

NASA Astrophysics Data System (ADS)

We demonstrate the fabrication of diodes having inkjet printed light emitting quantum dots layer. Close packing of printed layer is shown to be influenced by surface morphology of the underlying polymer layer and size variance of quantum dots used. We extend our approach to printing quantum dots onto a quarter video graphics array substrate (76 800 monochrome pixels). The purity of emitted electroluminescent spectra of resulting devices is related to coverage integrity of printed layer, which in turn is shown to be affected by the number of printed drops per pixel.

Haverinen, Hanna M.; Myllylä, Risto A.; Jabbour, Ghassan E.

2009-02-01

273

Fluorescent Quantum Dots for Biological Labeling  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

274

Magneto-Absorption in Ellipsoidal Quantum Dot  

NASA Astrophysics Data System (ADS)

The absorption of light in ellipsoidal quantum dot in the presence of a magnetic field is discussed using perturbation theory. Also the same problem is discussed using the normal modes. Quantum dot absorption coefficient is calculated - as well as threshold frequency of absorption - as a function of applied magnetic field. Theoretical results are compared with experimental data obtained by magneto-luminescence method in In0.53Ga0.47As quantum dot (M. Bayer et al, PRB vol.53, pp. 15810-15814, 1996).

Dvoyan, K. G.; Evoyan, V. V.; Kazaryan, E. M.; Nazmitdinov, R. G.; Sarkisyan, H. A.

275

CNT Quantum dots as Terahertz detectors  

NASA Astrophysics Data System (ADS)

We study Carbon Nanotube (CNT) quantum dots as detectors of THz radiation via photon assisted single electron tunneling. Although successful detection was recently demonstrated [1], the coupling between the CNT and THz radiations was very weak. Here, we implement a novel device design where the radiation is effectively coupled to the CNT quantum dot through broad band on-chip antennas. We show that the enhanced coupling yields a highly sensitive broad band Terahertz sensor. [4pt] [1] Y. Kawano, S. Toyokawa, T. Uchida and K. Ishibashi, THz photon assisted tunneling in carbon-nanotube quantum dots, Journal of Applied Physics 103, 034307 (2008).

Rinzan, Mohamed; Jenkins, Greg; Drew, Dennis; Shafranjuk, Serhii; Barbara, Paola

2011-03-01

276

Single to quadruple quantum dots with tunable tunnel couplings  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

277

An All-Optical Quantum Gate in a Semiconductor Quantum Dot  

Microsoft Academic Search

We report coherent optical control of a biexciton (two electron-hole pairs), confined in a single quantum dot, that shows coherent oscillations similar to the excited-state Rabi flopping in an isolated atom. The pulse control of the biexciton dynamics, combined with previously demonstrated control of the single-exciton Rabi rotation, serves as the physical basis for a two-bit conditional quantum logic gate.

Xiaoqin Li; Yanwen Wu; Duncan Steel; D. Gammon; T. H. Stievater; D. S. Katzer; C. Piermarocchi; L. J. Sham

2003-01-01

278

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

279

Confinement and single-electron tunneling in Schottky-gated, laterally squeezed double-barrier quantum-well heterostructures  

Microsoft Academic Search

The conductance of laterally confined double-barrier quantum-well resonant-tunneling heterostructures is investigated. The confinement is provided by a Schottky gate and can be varied in a continuous way, giving direct proof of the quantum size effect. Data for dots with nominal diameters in the submicron range are reported. Possible evidence for a modulation of the Coulomb blockade by quantum confinement is

P. Gueret; N. Blanc; R. Germann; H. Rothuizen

1992-01-01

280

Purification of functionalized quantum dots.  

PubMed

Semiconductor quantum dots (QDs) are fluorescent nanoparticles that can be used for biological imaging. Because of their brightness and photostability, which is far superior to those of organic dyes and fluorescent proteins, they can be detected at the single-particle level over long periods of time using standard fluorescence microscopy techniques. QDs can be conjugated to biomolecules and then used to track the motion of these molecules. Commercial, soluble QDs are available either unconjugated or functionalized with specific biomolecules. In the latter case, biomolecules such as streptavidin, Protein A, or antibodies are attached to the QD surface. Free biomolecules are often present in the QD solution, and these can be detrimental for live-cell imaging or other fluorescence assays. It is thus desirable to purify the functionalized QDs from these contaminating free biomolecules using size-exclusion chromatography. This article describes a simple procedure for purifying functionalized QDs using MicroSpin SR-400 columns. PMID:24086059

Courty, Sébastien; Dahan, Maxime

2013-10-01

281

Spatio-temporal fluctuations and disorder in quantum dot lasers  

Microsoft Academic Search

The quantum dot laser is a complex nonlinear system in which light fields dynamically interact with the charge carriers in the dots and the embedding quantum well medium. In real laser systems, typical dot-to-dot variations in size, energy levels and material parameters exist. In addition, the dots are not equally positioned on a grid within the layers. The respective variance

Dietmar W. Reschner; Edeltraud Gehrig; Ortwin G. Hess

2004-01-01

282

Quantum Dots-in-a-Well Focal Plane Arrays  

Microsoft Academic Search

In this paper, the basics and some of the recent developments in quantum dots-in-a-well (DWELL) focal plane arrays (FPAs) are reviewed. Fundamentally, these detectors represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP), in which the active region consists of quantum dots (QDs) embedded in a quantum well (QW). This hybridization

Thomas E. Vandervelde; Michael C. Lenz; Eric Varley; Ajit Barve; Jiayi Shao; Rajeev V. Shenoi; David A. Ramirez; Wooyong Jang; Yagya D. Sharma; Sanjay Krishna

2008-01-01

283

Electric field control of exciton states in quantum dot molecules  

Microsoft Academic Search

Semiconductor nanostructures have attracted considerable interest during the recent years in view of the potential application in quantum information processing. In particular, quantum dots have been suggested to fulfill an essential requirement for quantum computation: controllable interaction that couples two quantum dot qubits. Previous experiments on two vertically aligned quantum dots have demonstrated the formation of coupled exciton states. We

G. Ortner; M. Bayer; A. Kress; A. Forchel; Y. B Lyanda-Geller; T. L Reinecke

2004-01-01

284

Quantum optics of a quantum dot: Local-field effects  

SciTech Connect

The role of local fields in quantum electrodynamics of isolated quantum dot (QD) has been analyzed. The system is modeled as a strongly confined in space two-level quantum oscillator illuminated by quantum light. Relation between local and acting fields in QD has been derived in the dipole approximation from the integral Maxwell equations for electromagnetic field operators. A formalism of the electromagnetic field quantization in electrically small scatterers has been developed. As a result, Hamiltonian of the system has been formulated in terms of the acting field with a separate term responsible for the effect of depolarization. Schroedinger equation with that Hamiltonian has been solved in linear approximation. Interaction of QD with different quantum states of light, such as Fock states, coherent states, Fock qubits, entangled states, has been analyzed. It has been shown that the local-fields induce a fine structure of the QD absorption (emission) spectrum: instead of a single line with the frequency corresponding to the exciton transition, a doublet appears with one component shifted to the blue (red). The value of the shift depends only on the geometrical and electronic properties of QD while the intensities of components are completely determined by the quantum light statistics. It has been demonstrated that in the limiting cases of classical light and single-photon state the doublet is reduced to a singlet shifted in the former case and unshifted in the latter one. A physical interpretation of the predicted effect has been proposed. Possible ways of experimental observation of the effect has been discussed together with the potentiality of its utilization in the quantum information processing.

Slepyan, G.Ya.; Maksimenko, S.A.; Hoffmann, A.; Bimberg, D. [Institute of Nuclear Problems, Belarus State University, Bobruiskaya 11, 220050 Minsk (Belarus); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

2002-12-01

285

Nanoscale imaging and spontaneous emission control with a single nano-positioned quantum dot.  

PubMed

Plasmonic nanostructures confine light on the nanoscale, enabling ultra-compact optical devices that exhibit strong light-matter interactions. Quantum dots are ideal for probing plasmonic devices because of their nanoscopic size and desirable emission properties. However, probing with single quantum dots has remained challenging because their small size also makes them difficult to manipulate. Here we demonstrate the use of quantum dots as on-demand probes for imaging plasmonic nanostructures, as well as for realizing spontaneous emission control at the single emitter level with nanoscale spatial accuracy. A single quantum dot is positioned with microfluidic flow control to probe the local density of optical states of a silver nanowire, achieving 12 nm imaging accuracy. The high spatial accuracy of this scanning technique enables a new method for spontaneous emission control where interference of counter-propagating surface plasmon polaritons results in spatial oscillations of the quantum dot lifetime as it is positioned along the wire axis. PMID:23385591

Ropp, Chad; Cummins, Zachary; Nah, Sanghee; Fourkas, John T; Shapiro, Benjamin; Waks, Edo

2013-01-01

286

Optical Signatures of Coupled Quantum Dots  

Microsoft Academic Search

An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can be understood as a superposition of charge and spin configurations of the two dots. Coulomb interactions shift the

E. A. Stinaff; M. Scheibner; A. S. Bracker; I. V. Ponomarev; V. L. Korenev; M. E. Ware; M. F. Doty; T. L. Reinecke; D. Gammon

2006-01-01

287

Quantum Dots Investigated for Solar Cells  

NASA Technical Reports Server (NTRS)

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 their fluorescence (see the photograph).

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

2001-01-01

288

Femtosecond laser deposition of semiconductor quantum dot films  

NASA Astrophysics Data System (ADS)

We report new results on the deposition of high-density films of semiconductor nanostructures by ultrafast pulsed laser deposition (UFPLD). Such materials are of interest for advanced optoelectronic applications such as quantum dot lasers and energy harvesting devices. The deposition method utilizes the interaction of a focused chirped pulse amplified (CPA) Ti-sapphire laser beam with a solid target (a rotating semiconductor wafer) to produce a hot-dense plasma at the target surface with a power density in excess of 1014 W/cm2. The plasma then undergoes rapid expansion and the resulting condensation process produces a high density of nanoscale particles (average size of a few nm) on a substrate placed a few cm from the target. We have investigated several semiconductor quantum dot systems including silicon and germanium. We observed a significant blue-shift of the optical absorption edge indicating quantum confinement effects which may be of interest for photovoltaic applications.

Oraiqat, Ibrahim; Kennedy, Jack; Mathis, James; Clarke, Roy

2012-07-01

289

Final Report, Quantum Dot Light Emitting Diode.  

National Technical Information Service (NTIS)

The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, an...

K. Kahen R. Egidi

2012-01-01

290

Towards registered single quantum dot photonic devices  

NASA Astrophysics Data System (ADS)

We have registered the position and wavelength of a single InGaAs quantum dot using an innovative cryogenic laser lithography technique. This approach provides accurate marking of the location of self-organized dots and is particularly important for realizing any solid-state cavity quantum electrodynamics scheme where the overlap of the spectral and spatial characteristics of an emitter and a cavity is essential. We demonstrate progress in two key areas towards efficient single quantum dot photonic device implementation. Firstly, we show the registration and reacquisition of a single quantum dot with 50 and 150 nm accuracy, respectively. Secondly, we present data on the successful fabrication of a photonic crystal L3 cavity following the registration process.

Lee, K. H.; Brossard, F. S. F.; Hadjipanayi, M.; Xu, X.; Waldermann, F.; Green, A. M.; Sharp, D. N.; Turberfield, A. J.; Williams, D. A.; Taylor, R. A.

2008-11-01

291

Towards registered single quantum dot photonic devices.  

PubMed

We have registered the position and wavelength of a single InGaAs quantum dot using an innovative cryogenic laser lithography technique. This approach provides accurate marking of the location of self-organized dots and is particularly important for realizing any solid-state cavity quantum electrodynamics scheme where the overlap of the spectral and spatial characteristics of an emitter and a cavity is essential. We demonstrate progress in two key areas towards efficient single quantum dot photonic device implementation. Firstly, we show the registration and reacquisition of a single quantum dot with 50 and 150 nm accuracy, respectively. Secondly, we present data on the successful fabrication of a photonic crystal L3 cavity following the registration process. PMID:21832772

Lee, K H; Brossard, F S F; Hadjipanayi, M; Xu, X; Waldermann, F; Green, A M; Sharp, D N; Turberfield, A J; Williams, D A; Taylor, R A

2008-11-12

292

Quantum Dots and the Harkess Method  

NSDL National Science Digital Library

Students explore the applications of quantum dots by researching a journal article and answering framing questions used in a classwide discussion. This "Harkness-method" discussion helps students become critical readers of scientific literature.

Vu Bioengineering Ret Program

293

Nanomaterials: Earthworms lit with quantum dots  

NASA Astrophysics Data System (ADS)

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

Tilley, Richard D.; Cheong, Soshan

2013-01-01

294

Carbon Nanotube Quantum Dots as THz Detectors.  

National Technical Information Service (NTIS)

In this project we developed very sensitive broadband THz detectors using carbon nanotube quantum dots coupled to antenna-shaped source and drain electrodes. The sensing mechanism is photon-assisted tunneling and leads to a counterintuitive effect: the TH...

P. Barbara

2012-01-01

295

Strain-Induced Localized States Within the Matrix Continuum of Self-Assembled Quantum Dots  

SciTech Connect

Quantum dot-based infrared detectors often involve transitions from confined states of the dot to states above the minimum of the conduction band continuum of the matrix. We discuss the existence of two types of resonant states within this continuum in self-assembled dots: (i) virtual bound states, which characterize square wells even without strain and (ii) strain-induced localized states. The latter emerge due to the appearance of 'potential wings' near the dot, related to the curvature of the dots. While states (i) do couple to the continuum, states (ii) are sheltered by the wings, giving rise to sharp absorption peaks.

Popescu, V.; Bester, G.; Zunger, A.

2009-07-01

296

Probing the size and environment induced phase transformation in CdSe quantum dots  

SciTech Connect

The structural and electronic properties of CdSe quantum dots in toluene and drop-casted on Si wafer were investigated by in-situ micro X-ray diffraction, X-ray photoelectron spectroscopy and UV-Vis absorption and emission spectroscopy. The in-situ micro diffraction data show that the CdSe quantum dots capped with TOPO or hexadecylamine (HDA) in toluene exhibit predominantly wurtzite crystal structure, which undergoes a phase transformation to zinc blende crystal structure following drop casting on Si and this phase transition increases with decreasing the size of the CdSe quantum dots. Decreasing the size of quantum dots also increases the Se vacancies that facilitate the phase transformation. The X-ray photoelectron spectra show a systematic increase in the core level binding energies of Cd 3d and Se 3d, the band gap and the Cd/Se ratio as the size of the quantum dots decreases from 6.6nm to 2.1nm. This is attributed to the quantum confinement of CdSe crystallites by the capping ligands in toluene which increases with decreasing the size of the quantum dots. However, drop-casting quantum dots on Si alter the density and arrangement of capping ligands and solvent molecules on the quantum dots which causes significant phase transformation.

Karakoti, Ajay S.; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Yang, Ping; Thevuthasan, Suntharampillai

2011-11-17

297

Wavelength agile superlattice quantum dot infrared photodetector  

Microsoft Academic Search

A dual-band superlattice quantum dot infrared photodetector, providing bias-selectability of the response peaks, is demonstrated. The active region consists of two quantum dot superlattices separated by a graded barrier, enabling photocurrent generation only in one superlattice for a given bias polarity. Two response bands, one consisting of three peaks at 2.9, 3.2, and 4.9 mum and the other consisting of

G. Ariyawansa; A. G. U. Perera; G. Huang; P. Bhattacharya

2009-01-01

298

Semiconductor clusters nanocrystals, and quantum dots  

Microsoft Academic Search

Current research into semiconductor clusters is focused on the properties on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the

A. P. Alivisatos

1996-01-01

299

Integrated photonics using colloidal quantum dots  

Microsoft Academic Search

Integrated photonic devices were realized using colloidal quantum dot composites such as flexible microcavity laser, microdisk emitters and integrated active-passive waveguides. The microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP\\/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a

Vinod M. Menon; Saima Husaini; Nicky Okoye; Nikesh V. Valappil

2009-01-01

300

Photon-Assisted Tunneling in Quantum Dots  

Microsoft Academic Search

The manipulation and quantification of the effects produced by an rf field in a mesoscopic structure are fundamental issues\\u000a in view of developing single-spin-based qubits. Here, we review the experiments on electron transport in quantum dots under\\u000a microwave irradiation. The electromagnetic vector potential provides excitation of electrons in the leads and in the quantum\\u000a dot, and an electromotive potential at

Enrico Prati; Rossella Latempa; Marco Fanciulli

2009-01-01

301

Germanium quantum dots: Optical properties and synthesis  

Microsoft Academic Search

Three different size distributions of Ge quantum dots (?200, 110, and 60 A?) 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

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

1994-01-01

302

Quantum confinement-induced tunable exciton states in graphene oxide  

NASA Astrophysics Data System (ADS)

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology.

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M.; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-07-01

303

Quantum confinement-induced tunable exciton states in graphene oxide  

PubMed Central

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology.

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M.; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

304

Submonolayer Quantum Dot Infrared Photodetector  

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

305

Quantum versus classical hyperfine-induced dynamics in a quantum dot  

NASA Astrophysics Data System (ADS)

In this article we analyze spin dynamics for electrons confined to semiconductor quantum dots due to the contact hyperfine interaction. We compare mean-field (classical) evolution of an electron spin in the presence of a nuclear field with the exact quantum evolution for the special case of uniform hyperfine coupling constants. We find that (in this special case) the zero-magnetic-field dynamics due to the mean-field approximation and quantum evolution are similar. However, in a finite magnetic field, the quantum and classical solutions agree only up to a certain time scale t

Coish, W. A.; Loss, Daniel; Yuzbashyan, E. A.; Altshuler, B. L.

2007-04-01

306

Toward quantum entanglement in a quantum-dot nanocavity  

Microsoft Academic Search

Our semiconductor normal-mode-coupling microcavities, each containing a single narrow-linewidth quantum well (QW), exhibit record many-oscillator vacuum-field Rabi splitting (VRS). The question addressed here is: can the vacuum field be increased sufficiently by reducing the cavity-mode volume, so that a single quantum dot can exhibit VRS similar to an atom in a high-finesse cavity? The quantum-dot nanocavity has two advantages: a

H. M. Gibbs; G. Khitrova; E. S. Lee; C. Ell; D. G. Deppe; D. L. Huffaker

1999-01-01

307

Resonant Raman scattering in self-assembled quantum dots  

SciTech Connect

A theoretical treatment for first-order resonant Raman scattering in self-assembled quantum dots (SAQD's) of different materials is presented. The dots are modeled as cylindrical disks with elliptical cross section, to simulate shape and confinement anisotropies obtained from the SAQD growth conditions. Coulomb interaction between electron and hole is considered in an envelope function Hamiltonian approach and the eigenvalues and eigenfunctions are obtained by a matrix diagonalization technique. By including excitonic intermediate states in the Raman process, the scattering efficiency and cross section are calculated for long-range Froehlich exciton-phonon interaction. The Froehlich interaction in the SAQD is considered in an approach in which both the mechanical and electrostatic matching boundary conditions are fulfilled at the SAQD interfaces. Exciton and confined phonon selection rules are derived for Raman processes. Characteristic results for SAQD's are presented, including InAs dots in GaAs, as well as CdSe dots in ZnSe substrates. We analyze how Raman spectroscopy would give information on carrier masses, confinement anisotropy effects, and SAQD geometry. (c) 1999 The American Physical Society.

Menendez-Proupin, E. [Department of Theoretical Physics, Havana University, Vedado 10400, Havana, (Cuba); Trallero-Giner, C. [Department of Theoretical Physics, Havana University, Vedado 10400, Havana, (Cuba); Ulloa, S. E. [Department of Physics and Astronomy and Condensed Matter and Surface Sciences Program, Ohio University, Athens, Ohio 45701-2979 (United States)

1999-12-15

308

Single electron-spin memory with a semiconductor quantum dot  

NASA Astrophysics Data System (ADS)

We show storage of the circular polarization of an optical field, transferring it to the spin-state of an individual electron confined in a single semiconductor quantum dot. The state is subsequently read out through the electronically-triggered emission of a single photon. The emitted photon shares the same polarization as the initial pulse but has a different energy, making the transfer of quantum information between different physical systems possible. With an applied magnetic field of 2 T, spin memory is preserved for at least 1000 times more than the exciton's radiative lifetime.

Young, Robert J.; Dewhurst, Samuel J.; Stevenson, R. Mark; Atkinson, Paola; Bennett, Anthony J.; Ward, Martin B.; Cooper, Ken; Ritchie, David A.; Shields, Andrew J.

2007-10-01

309

Scanning Tunneling Spectroscopy of Semiconductor Quantum Dots and Nanocrystals  

Microsoft Academic Search

\\u000a Quantum dots (QDs) and nanocrystals (NCs) have attracted great attention for applications in nano- and opto-electronics, quantum\\u000a computation, biosensing, and nanomedicine. Three-dimensional electronic confinement can be achieved based on lateral or vertical\\u000a QDs in a two-dimensional electron gas, by strain-induced QDs, or by colloidal NCs.\\u000a \\u000a \\u000a In this chapter, we will focus on tunneling spectroscopy on semiconductor QDs and NCs. First,

Giuseppe Maruccio; Roland Wiesendanger

2010-01-01

310

Molecular states in graphene double quantum dots  

NASA Astrophysics Data System (ADS)

We present a double quantum dot structure based on an armchair graphene nanoribbon with three serial narrow constrictions. With appropriate geometry and size, each region in between two constrictions behaves as a tunneling quantum dot. Within the low energy range around the Dirac point, conductance of the structure shows strong resonances. The paired resonance peaks are related to the quasibound molecular states in the tunnel-coupled dots. The quasibound states and the interdot coupling can be effectively tuned by only the geometrical parameters of the structure.

Xiong, Yong-Jian

2013-12-01

311

Finite-Temperature Effects on Correlation of Electrons in Quantum Dots  

Microsoft Academic Search

The path-integral Monte Carlo method is used to examine the two-electron state of a model quantum dot. Electrons in the two-dimensional quantum dot are confined by a harmonic oscillator potential of strength hbaromega=1eV. Mixed state densities, energies and pair correlation functions are evaluated at various temperatures, and their temperature dependencies are analyzed. Also, the two-electron pure state energetics is resolved

Markku Leino; Tapio T. Rantala

2004-01-01

312

Size dependence in tunneling spectra of PbSe quantum-dot arrays  

Microsoft Academic Search

Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic, and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. Developments of cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional

Y. C. Ou; S. F. Cheng; W. B. Jian

2009-01-01

313

Semiconductor quantum-dot nanostructures: Their application in a new class of infrared photodetectors  

Microsoft Academic Search

Semiconductor quantum-dot nanostructures are interesting objects for fundamental as well as practical reasons. Fundamentally, they can form the basis of systems in which to study the quantum mechanics of electrons confined in zero-dimensional (0-D) space. In practice, the dots can be embedded in the active regions of a new class of electronic and optoelectronic devices with novel functionalities. This paper

Elias Towe; Dong Pan

2000-01-01

314

Colloidal quantum-dot photodetectors exploiting multiexciton generation.  

PubMed

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. Here, we report a class of solution-processed photoconductive detectors, sensitive in the ultraviolet, visible, and the infrared, in which the internal gain is dramatically enhanced for photon energies Ephoton greater than 2.7 times the quantum-confined bandgap Ebandgap. Three thin-film devices with different quantum-confined bandgaps (set by the size of their constituent lead sulfide nanoparticles) show enhancement determined by the bandgap-normalized photon energy, Ephoton/Ebandgap, which is a clear signature of MEG. The findings point to a valuable role for MEG in enhancing the photocurrent in a solid-state optoelectronic device. We compare the conditions on carrier excitation, recombination, and transport for photoconductive versus photovoltaic devices to benefit from MEG. PMID:19541992

Sukhovatkin, Vlad; Hinds, Sean; Brzozowski, Lukasz; Sargent, Edward H

2009-06-19

315

Colloidal Quantum-Dot Photodetectors Exploiting Multiexciton Generation  

NASA Astrophysics Data System (ADS)

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. Here, we report a class of solution-processed photoconductive detectors, sensitive in the ultraviolet, visible, and the infrared, in which the internal gain is dramatically enhanced for photon energies Ephoton greater than 2.7 times the quantum-confined bandgap Ebandgap. Three thin-film devices with different quantum-confined bandgaps (set by the size of their constituent lead sulfide nanoparticles) show enhancement determined by the bandgap-normalized photon energy, Ephoton/Ebandgap, which is a clear signature of MEG. The findings point to a valuable role for MEG in enhancing the photocurrent in a solid-state optoelectronic device. We compare the conditions on carrier excitation, recombination, and transport for photoconductive versus photovoltaic devices to benefit from MEG.

Sukhovatkin, Vlad; Hinds, Sean; Brzozowski, Lukasz; Sargent, Edward H.

2009-06-01

316

Engineered quantum dot structures: fabrication and applications  

NASA Astrophysics Data System (ADS)

Quantum dot structures with tailored geometries were developed for different high power laser applications by molecular beam epitaxy based self-assembly techniques. 920 nm quantum dot laser material with new record values of 0.08 nm/K in temperature dependent wavelength shift could be obtained, which is a factor of 4 lower than for quantum well lasers. Tapered distributed Bragg reflector laser devices were processed, which exhibit single mode output powers of more than 1 W in cw with an M2 value of 2. For display applications based on frequency doubling, 1060 nm quantum dot laser material is developed with and without tunnel injection quantum well active zones. With this new type of laser material an output power of 4.5 W could be obtained on 100 ?m broad area lasers. An overview is given on this recent work performed within the frame of the EU project "WWW_BRIGHTER_EU".

Reithmaier, Johann Peter; Pavelescu, Emil-Mihai; Gilfert, Christian; Gushterov, A.; Kaiser, Wolfgang; Weinmann, Pia; Kamp, Martin; Forchel, Alfred; Martín-Mínguez, Alfredo; Esquivias, Ignacio

2009-01-01

317

Advancements in the Field of Quantum Dots  

NASA Astrophysics Data System (ADS)

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.

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

2012-08-01

318

Thermoelectric properties of hexagonal graphene quantum dots  

NASA Astrophysics Data System (ADS)

By using the atomistic nonequilibrium Green's function method, we investigate the thermoelectric properties of graphene nanoribbons in the presence of two constrictions (or hexagonal graphene quantum dots). With decreasing widths of the constrictions, the thermal conductance of the nanoribbon can be reduced largely while SG (S is the Seebeck coefficient and G is the electronic conductance) remains still high as compared with the results of the pristine nanoribbon. Thus, the thermoelectric figure of merit ZT can be enhanced largely. In fact, in the presence of narrowest constrictions the ZT values of the zigzag quantum dots can exceed one at room temperature, while the ZT values of the armchair quantum dots may be close to one, depending on the size of the dot.

Yan, Yonghong; Liang, Qi-Feng; Zhao, Hui; Wu, Chang-Qin

2012-02-01

319

Cryogenic spectroscopy of ultra-low density colloidal lead chalcogenide quantum dots on chip-scale optical cavities towards single quantum dot near-infrared cavity QED.  

PubMed

We present evidence of cavity quantum electrodynamics from a sparse density of strongly quantum-confined Pb-chalcogenide nanocrystals (between 1 and 10) approaching single-dot levels on moderately high-Q mesoscopic silicon optical cavities. Operating at important near-infrared (1500-nm) wavelengths, large enhancements are observed from devices and strong modifications of the QD emission are achieved. Saturation spectroscopy of coupled QDs is observed at 77K, highlighting the modified nanocrystal dynamics for quantum information processing. PMID:20052171

Bose, Ranojoy; Gao, Jie; McMillan, James F; Williams, Alex D; Wong, Chee Wei

2009-12-01

320

Cryogenic spectroscopy of ultra-low density colloidal lead chalcogenide quantum dots on chip-scale optical cavities towards single quantum dot near-infrared cavity QED  

SciTech Connect

We present evidence of cavity quantum electrodynamics from a sparse density of strongly quantum-confined Pb-chalcogenide nanocrystals (between 1 and 10) approaching single-dot levels on moderately high-Q mesoscopic silicon optical cavities. Operating at important near-infrared (1500-nm) wavelengths, large enhancements are observed from devices and strong modifications of the QD emission are achieved. Saturation spectroscopy of coupled QDs is observed at 77K, highlighting the modified nanocrystal dynamics for quantum information processing.

Bose, Ranojoy; Gao, Feng; McMillan, James F.; Williams, Alex D.; Wong, Chee Wei

2009-01-01

321

Searching for spin coherence in single quantum dots  

Microsoft Academic Search

Quantum dots form the basis of many spin-based quantum computing architectures, yet the transverse coherence time T2 of a single electron spin in a quantum dot has not been measured. These measurements are challenging, due to the relatively weak interaction with light and the difficulty of resolving signatures from large ensembles of quantum dots. We describe our efforts to isolate

Petru Fodor; Gilberto Medeiros-Ribeiro; Jeremy Levy

2004-01-01

322

Evaluation of the fundamental properties of quantum dot infrared detectors  

Microsoft Academic Search

The physical properties of detectors based on intraband optical absorption in quantum dots is described and examined in the interest of providing a competitive alternative infrared (IR) detector technology. These quantum dot detectors are an extension of quantum well infrared photodetectors and are expected to have a large performance advantage. A model is developed for quantum dot infrared photodetectors based

Jamie Phillips

2002-01-01

323

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

SciTech Connect

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

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

2012-01-01

324

Connecting the (quantum) dots: Towards hybrid photovoltaic devices based on chalcogenide gels  

PubMed Central

CdSe(ZnS) core(shell) aerogels were prepared from the assembly of quantum dots into mesoporous colloidal networks. The sol-gel method produces inorganic particle interfaces with low resistance to electrical transport while maintaining quantum-confinement. The photoelectrochemical properties of aerogels and their composites with poly(3-hexylthiophene) are reported for the first time.

De Freitas, Jilian N.; Korala, Lasantha; Reynolds, Luke X.; Haque, Saif A.

2014-01-01

325

Transparent conducting films of CdSe(ZnS) core(shell) quantum dot xerogels  

PubMed Central

A method of fabricating sol-gel quantum dot (QD) films is demonstrated, and their optical, structural and electrical properties are evaluated. The CdSe(ZnS) xerogel films remain quantum confined, yet are highly conductive (10?3 S· cm?1). This approach provides a pathway for the exploitation of QD gels in optoelectronic applications.

Korala, Lasantha; Li, Li

2012-01-01

326

Full-colour quantum dot displays fabricated by transfer printing  

Microsoft Academic Search

Light-emitting diodes with quantum dot luminophores show promise in the development of next-generation displays, because quantum dot luminophores demonstrate high quantum yields, extremely narrow emission, spectral tunability and high stability, among other beneficial characteristics. However, the inability to achieve size-selective quantum dot patterning by conventional methods hinders the realization of full-colour quantum dot displays. Here, we report the first demonstration

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

2011-01-01

327

The quantum dot molecule from an optical point of view  

Microsoft Academic Search

For over ten years the techniques of single quantum dot optical spectroscopy has enabled rapid progress in the fundamental understanding of quantum dots and in the application of quantum information concepts [1]. We now apply these ever improving optical techniques to two self-assembled InAs\\/GaAs quantum dots that are coherently coupled through tunneling - that is, a quantum dot molecule [2].

Daniel Gammon

2009-01-01

328

Quasi-periodic quantum dot arrays produced by electrochemical synthesis.  

National Technical Information Service (NTIS)

We discuss a ''gentle'' electrochemical technique for fabricating quasi-periodic quantum dot arrays. The technique exploits a self-organizing phenomenon to produce quasi-periodic arrangement of dots and provides excellent control over dot size and interdo...

S. Bandyopadhyay A. E. Miller D. F. Yue G. Banerjee R. E. Ricker

1994-01-01

329

Optical properties of charged semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The effect of n-type doping on the luminescence properties of II-VI quantum dots is studied. The addition of two shells of CdS on CdSe quantum dots prevents the creation of surface traps and makes the system stable under reducing environment. The injection of electrons into films of quantum dots leads to lower photoluminescence (PL) efficiency, with the extent of quenching dependent on both the number and the quantum states of the spectator charges in the nanocrystal. It is found that a 1Pe electron is an eightfold better PL quencher than the 1Se electron. Reduced threshold for stimulated emission is also observed in doped CdSe/CdS films. Time resolved photoluminescence measurements are used to extract the recombination rates of a charged exciton, called trion. It is observed that the negative trion has a radiative rate ˜2.2 +/- 0.4x faster than a neutral exciton, while its non-radiative recombination rate is slower than the biexciton non-radiative recombination rate by a factor of 7.5 +/- 1.7. The knowledge of the recombination rates of the trion enables us to calculate the quantum yield of a negative trion to be ˜10% for the nanocrystals investigated in our work. This is larger than the off state quantum yield from a single quantum dot photoluminescence trajectory and eliminates the formation of negative trion as the possible reason for the PL blinking of single quantum dots. Single quantum dot electrochemistry has also been achieved. It is shown that by varying the Fermi level of the system electrons can be reversibly injected into and extracted out of single CdSe/CdS and CdSe/ZnS nanoparticles to modulate the photoluminescence.

Jha, Praket P.

330

Quantum Dots: Fundamentals, Applications, and Frontiers  

Microsoft Academic Search

This volume contains papers delivered at a NATO Advanced Research Workshop and provides a broad introduction to all major aspects of quantum dot structures. Such structures have been produced for studies of basic physical phenomena, for device fabrication and, on a more speculative level, have been suggested as components of a solid-state realization of a quantum computer. The book is

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

2005-01-01

331

Universal quantum computing with nanowire double quantum dots  

NASA Astrophysics Data System (ADS)

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

Xue, Peng

2011-10-01

332

Quantum dot-nanocavity devices for information processing  

Microsoft Academic Search

A combination of a single quantum emitter (a semiconductor quantum dot) with a semiconductor optical nanocavity has been employed to demonstrate devices ranging from optical switches and modulators controlled with sub-fJ energies, to quantum sources. Quantum dots in photonic crystals are interesting both as a testbed for fundamental cavity quantum electrodynamics (QED) experiments, as well as a platform for quantum

Jelena Vuckovic; Kelley Rivoire; Arka Majumdar; Erik Kim; Sonia Buckley; Pierre Petroff

2011-01-01

333

Pulse-gated quantum dot hybrid qubit  

NASA Astrophysics Data System (ADS)

A quantum dot hybrid qubit formed from three electrons in a double quantum dot has the potential for great speed, due to presence of level crossings where the qubit becomes charge-like. Here, we show how to exploit the level crossings to implement fast pulsed gating. We develop one- and two-qubit dc quantum gates that are simpler than the previously proposed ac gates [1]. We obtain closed-form solutions for the control sequences and show that the gates are fast (sub-nanosecond) and can achieve high fidelities. [4pt] [1] Z. Shi, et al., Phys. Rev. Lett. 108, 140503 (2012).

Coppersmith, S. N.; Koh, Teck Seng; King Gamble, John; Eriksson, M. A.; Friesen, Mark

2013-03-01

334

Quantum Dots: Fundamentals, Applications, and Frontiers  

NASA Astrophysics Data System (ADS)

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

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

335

Biological applications of quantum dots.  

PubMed

Quantum dots (QDs) are a novel class of inorganic fluorophore which are gaining widespread recognition as a result of their exceptional photophysical properties. They are rapidly being applied to existing and emerging technologies, and could have an important role in many areas. Significant challenges remain, however, which must be understood and more fully defined before they can be widely validated. This review provides on overview of QD technology, covering QD characteristics, synthesis methods, and the applications in which they have been put to use. The influence of synthesis methods on QD characteristics and their subsequent suitability to different applications is discussed, and a broad outline of the technologies into which they have been incorporated is presented, and the relative merits and weaknesses of their incorporation are evaluated. The potential for further development, and inclusion in other technologies is also discussed, and barriers restricting further progress specified, particularly with regard to the poorly understood surface chemistry of QDs, the potential for alteration of function of biological molecules when complexed with QDs, and on a larger scale the significant potential for cytotoxicity both in vitro and in vivo. PMID:17686516

Jamieson, Timothy; Bakhshi, Raheleh; Petrova, Daniela; Pocock, Rachael; Imani, Mo; Seifalian, Alexander M

2007-11-01

336

Experimental demonstration of quantum-dot cellular automata  

Microsoft Academic Search

We present the experimental demonstration of a basic cell of quantum-dot cellular automata (QCA), a transistorless computation paradigm which addresses the issues of device density and interconnection. The device presented is a six-dot quantum-dot cellular system consisting of a four-dot QCA cell and two electrometer dots. The system is fabricated using metal dots which are connected by capacitors and tunnel

G. L. Snider; A. O. Orlov; I. Amlani; G. H. Bernstein; C. S. Lent; J. L. Merz; W. Porod

1998-01-01

337

Cavity quantum electrodynamics with quantum dot - photonic crystal nanocavities  

NASA Astrophysics Data System (ADS)

High quality factor, small mode volume photonic crystal cavities and single emitter quantum dots are the topic of this dissertation. They are studied as both a combined system with InAs quantum dots grown in the center of a 2D GaAs photonic crystal slab nanocavity as well as individually. The individual studies are concerned with passive 1D silicon photonic crystal nanobeam cavities and deterministic, site-selectively grown arrays of InAs quantum dots. For the combined system, strong light matter coupling in a quantum dot photonic crystal slab nanocavity is discussed. Vacuum Rabi splitting is seen when the interaction strength exceeds the dissipative processes of the coupled system. In order to increase the probability of a spectral matching between cavity modes and quantum dot transitions, a technique for condensing an inert gas onto a sample is used. This can lead to a spectral tuning of up to 4 nm of the cavity mode with minimal change in the cavity quality factor while maintaining cryogenic temperatures down to 4 K. The effect of a large density of quantum dots within a quantum dot photonic crystal slab nanocavity is also addressed. Gain and absorption effects are found to occur, changing the cavity emission linewidth from that of its intrinsic value, as well as lasing with a low number of quantum dots and with high spontaneous emission coupling factors. Additionally, methods for improving the quality factor of GaAs photonic crystal cavities and better understanding different loss mechanisms are discussed. In the individual studies, the site-selective growth of InAs quantum dots on pre-structured GaAs wafers is shown as a promising method for the eventual deterministic fabrication of photonic crystal cavities to single quantum dots. An in-situ annealing step is used to reduce quantum dot density, helping ensure that dots are not grown in unwanted locations. Given silicon's potential for achieving higher quality factors than its GaAs counterpart, a study of 1D passive silicon photonic crystal nanobeam cavities is carried out. Transmission through a coupled microfiber is used to measure quality factors of the cavities and compared with that of a crossed polarized resonant scattering measurement.

Hendrickson, Joshua R.

338

Imaging a coupled quantum dot-quantum point contact system  

Microsoft Academic Search

We have quantitatively studied the effect of charge traps on the electrical conductance of a quantum dot and a capacitively coupled quantum point contact. Using the sharp metallic tip of a low-temperature scanning force microscope as a scanned gate, we could localize the traps. The quantum point contact served as a charge detector and allowed us to distinguish single electron

A. E. Gildemeister; T. Ihn; R. Schleser; K. Ensslin; D. C. Driscoll; A. C. Gossard

2007-01-01

339

Quantum computer aided design simulation and optimization of semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling multi-dimensional quantum devices, particularly silicon multi-quantum dots (QDs) developed for quantum bits (qubits). This finite-element simulator has three differentiating features: (i) its core contains nonlinear Poisson, effective mass Schrodinger, and Configuration Interaction solvers that have massively parallel capability for high simulation throughput and can be run individually or combined self-consistently for 1D/2D/3D quantum devices; (ii) the core solvers show superior convergence even at near-zero-Kelvin temperatures, which is critical for modeling quantum computing devices; and (iii) it interfaces directly with the full-featured optimization engine Dakota. In this work, we describe the capabilities and implementation of the QCAD simulation tool and show how it can be used to both analyze existing experimental QD devices through capacitance calculations and aid in the design of few-electron multi-QDs. In particular, we observe that computed capacitances are in rough agreement with experiment, and that quantum confinement increases capacitance when the number of electrons is fixed in a quantum dot. Coupling of QCAD with the optimizer Dakota allows for rapid identification and improvement of device layouts that are likely to exhibit few-electron quantum dot characteristics.

Gao, X.; Nielsen, E.; Muller, R. P.; Young, R. W.; Salinger, A. G.; Bishop, N. C.; Lilly, M. P.; Carroll, M. S.

2013-10-01

340

Evaporation-Induced Assembly of Quantum Dots into Nanorings  

PubMed Central

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

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

2011-01-01

341

Dot-in-Well Quantum-Dot Infrared Photodetectors  

NASA Technical Reports Server (NTRS)

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 system is expected to enable achievement of greater densities of QDs and correspondingly greater quantum efficiencies. The host GaAs/AlGaAs MQW structures are highly compatible with mature fabrication processes that are now used routinely in making QWIP FPAs. The hybrid InGaAs-dot/GaAs/AlGaAs-well system also offers design advantages in that the effects of variability of dot size can be partly compensated by engineering quantum-well sizes, which can be controlled precisely.

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

2008-01-01

342

Theoretical modeling and experimental characterization of InAs\\/InGaAs quantum dots in a well detector  

Microsoft Academic Search

Theoretical modeling and experimental characterization of InGaAs\\/GaAs quantum dots-in-a-well (DWELL) intersubband heterostructures, grown by molecular beam epitaxy are reported. In this heterostructure, the self-assembled dots are confined to the top half of a 110 A˚ InGaAs well which in turn is placed in a GaAs matrix. Using transmission electron microscopy, the quantum dots are found to be pyramidal in shape

A. Amtout; S. Raghavan; P. Rotella; G. von Winckel; A. Stintz; S. Krishna

2004-01-01

343

Direct Interband Light Absorption in a Spherical Quantum Dot with the Modified PÖSCHEL-TELLER Potential  

NASA Astrophysics Data System (ADS)

The energy levels and direct interband absorption of light in a spherical quantum dot with a modified Pöschel-Teller confining potential are studied. Analytical expressions for the particle energy spectrum and absorption threshold frequencies in the regime of strong size quantization are obtained. Selection rules for quantum transitions are revealed. Red shift and blue shift of absorption threshold has been observed depending on the values of half-width and depth of confining potential, correspondingly.

Tevosyan, H. Kh.; Hayrapetyan, D. B.; Dvoyan, K. G.; Kazaryan, E. M.

344

Negative-band-gap quantum dots: Gap collapse, intrinsic surface states, excitonic response, and excitonic insulator phase  

NASA Astrophysics Data System (ADS)

The spectrum of quantum dots made from semiconductors such as HgTe and HgS changes from negative gap to positive gap with decreasing size. Furthermore, intrinsic surface states, which are not related to dangling bonds, appear in the negative-gap regime. We investigate theoretically the evolution of the spectrum of HgS quantum dots with decreasing size and show how states evolve from a negative gap to a positive gap as confinement is increased. The lowest confined electron level evolves into an intrinsic surface state with increasing size and, thus, is not derived directly from a bulk HgS band. Due to strong band mixing in narrow-gap semiconductors, spacing between confined levels decreases more slowly with increasing size than for quantum dots made from wide-gap semiconductors. Moreover, dielectric screening becomes nearly metallic as the gap closes. As a consequence, confinement energies dominate exciton binding energies for all dot sizes up to the gap closure. Excitons remain in the strong confinement limit as size increases until the gap closes. Nonetheless, the exciton binding exceeds the single-particle gap for sizes near gap closure, opening up the possibility of an excitonic insulator phase in quantum dots not possible in positive-gap quantum dots. Signatures in the quantum-dot optical response for gap collapse and surface states are identified.

Malkova, Natalia; Bryant, Garnett W.

2010-10-01

345

Unconventional Nodal Wavefunctions in Quantum Dots  

NASA Astrophysics Data System (ADS)

In a single band model such as one electron in a box, it is well known that the ground state wavefunction has no node maximizing its spatial symmetry. However, the ordering of eigenstates in a multiband system e.g., p-doped semiconductor quantum dots (QDs) can be very different due to spin-orbit interaction, symmetry of the underlying lattice and geometry of the confinement. Such unconventional ordering of states has appeared in the literature [1, 2] but it is often ignored or merely considered a shortcoming of k.p model [3]. We investigate spatial structure of hole envelope-wavefunctions in QDs with a focus on its symmetry. Our calculation shows a counter-intuitive ordering of eigenstates where a single hole ``ground-state'' has a node at the center. For simplicity, we start with a 2D QD tight-binding model and extend the discussion to 3D QD tight-binding and k.p models. We also discuss experimental implications of the wavefunction ordering described above. [1] K. V'yborn'y et al., PRB 85, 155312 (2012) [2] A. Bagga et al., PRB 71, 115327 (2005); P. Horodyská et al., PRB 81, 045301 (2010); J. Xia and J. Li, PRB 60, 11540 (1999) [3] L. W. Wang et al., APL 76, 339 (2000)

Lee, Jeongsu; Výborný, Karel; žuti?, Igor; Han, Jong

2013-03-01

346

Controlled exchange interaction for quantum logic operations with spin qubits in coupled quantum dots  

SciTech Connect

A two-electron system confined in two coupled semiconductor quantum dots is investigated as a candidate for performing quantum logic operations with spin qubits. We study different processes of swapping the electron spins by a controlled switching on and off of the exchange interaction. The resulting spin swap corresponds to an elementary operation in quantum-information processing. We perform direct simulations of the time evolution of the two-electron system. Our results show that, in order to obtain the full interchange of spins, the exchange interaction should change smoothly in time. The presence of jumps and spikes in the time characteristics of the confinement potential leads to a considerable increase of the spin-swap time. We propose several mechanisms to modify the exchange interaction by changing the confinement potential profile and discuss their advantages and disadvantages.

Moskal, S.; Bednarek, S.; Adamowski, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Cracow (Poland)

2007-09-15

347

Characteristics of ultralow threshold quantum dot lasers using indium-arsenide/indium-gallium arsenide dots-in-a- well structures  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dot lasers have an active medium that makes use three-dimensional quantum confinement effects and have been predicted to have many unique properties as compared to quantum well and double heterostructure lasers. In particular, they were expected to have low threshold current densities and temperature insensitive threshold currents. In this dissertation, a new quantum dot laser structure called the ``dots-in-a-well'' (DWELL) laser, was successfully demonstrated and shown to have the lowest room temperature threshold current density (16 A cm-2) ever reported for any semiconductor laser. The internal efficiency, modal gain, and characteristic temperature of the DWELL lasers were systematically studied as a function of the DWELL-laser design parameters. It was noticed that the low modal gain of this and other quantum dot lasers is a factor limiting the performance of these devices. Different ways to improve the modal gain and characteristic temperature at the cost of higher threshold current densities are suggested. A quasi-equilibrium theory and rate equation model for the combined quantum well and quantum dot system are also used to investigate the properties of the DWELL structure.

Liu, Guangtian

348

Optically Detected Magnetic Resonance of Semiconductor Quantum Dots.  

National Technical Information Service (NTIS)

Semiconductor quantum dots have attracted large scientific and technological interests in the last decade. This document describes our attempts to characterize the localization of carriers in CdSe and CdS quantum dots. utilizing optically detected spin an...

A. Glozman E. Lifshitz I. D. Litvin

2000-01-01

349

Quantum-dot Cellular Automata Devices and Architectures.  

National Technical Information Service (NTIS)

We discuss novel nanoelectronic architecture paradigms based on cells composed of coupled quantum dots. Boolean logic functions may be implemented in specific arrays of cells representing binary inlormation, the so-called Quantum Dot Cellular Automata (QC...

W. Porod

1998-01-01

350

Energy transfer from CdSe quantum dots to graphene  

NASA Astrophysics Data System (ADS)

Graphene-CdSe quantum dots hybrid is a promising structure to combine unique properties of graphene and quantum dots. In this work, graphene was firstly prepared on a 300 nm SiO2/Si substrate by mechanical exfoliation of a highly oriented pyrolytic graphite using scotch tape. Then the samples were immersed in CdSe quantum dots solutions for 15 minutes and followed by water flush. The graphene-CdSe quantum dots hybrid structures were obtained due to the electrostatic adsorption of CdSe quantum dots on graphene. Fluorescence quenching of CdSe quantum dots on graphene was found, which probably indicates the energy transfer from CdSe quantum dots to graphene. The results suggest that graphene is a good candidate for manipulating energy transfer of quantum dots due to its extremely high carrier mobility.

Liao, Chunyan; Zhu, Xiuhong

2013-12-01

351

An all-optical quantum gate in a semiconductor quantum dot.  

PubMed

We report coherent optical control of a biexciton (two electron-hole pairs), confined in a single quantum dot, that shows coherent oscillations similar to the excited-state Rabi flopping in an isolated atom. The pulse control of the biexciton dynamics, combined with previously demonstrated control of the single-exciton Rabi rotation, serves as the physical basis for a two-bit conditional quantum logic gate. The truth table of the gate shows the features of an all-optical quantum gate with interacting yet distinguishable excitons as qubits. Evaluation of the fidelity yields a value of 0.7 for the gate operation. Such experimental capability is essential to a scheme for scalable quantum computation by means of the optical control of spin qubits in dots. PMID:12907794

Li, Xiaoqin; Wu, Yanwen; Steel, Duncan; Gammon, D; Stievater, T H; Katzer, D S; Park, D; Piermarocchi, C; Sham, L J

2003-08-01

352

Optically controlled magnetization of zero-dimensional magnetic polarons in CdMnTe self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

We find strong optically induced magnetization of zero-dimensional magnetic polarons confined to CdMnTe quantum dots. The spin alignment of magnetic ions at B = 0 T is created through circularly polarized resonant excitation and it is probed by polarization-resolved photoluminescence. This observation clearly demonstrates that in the CdMnTe quantum dots the exciton spin relaxation time is significantly longer than the formation time of magnetic polaron. Importantly, the spatial confinement characteristic of quantum dots increases the stability of magnetic polarons so that significant polarizaton of the emission is observed for temperatures higher than 120 K.

Mackowski, S.; Gurung, T.; Nguyen, T. A.; Jackson, H. E.; Smith, L. M.; Kossut, J.; Karczewski, G.

2004-02-01

353

Quantum Zeno effect rationalizes the phonon bottleneck in semiconductor quantum dots.  

PubMed

Quantum confinement can dramatically slow down electron-phonon relaxation in nanoclusters. Known as the phonon bottleneck, the effect remains elusive. Using a state-of-the-art time-domain ab initio approach, we model the observed bottleneck in CdSe quantum dots and show that it occurs under quantum Zeno conditions. Decoherence in the electronic subsystem, induced by elastic electron-phonon scattering, should be significantly faster than inelastic scattering. Achieved with multiphonon relaxation, the phonon bottleneck is broken by Auger processes and structural defects, rationalizing experimental difficulties. PMID:23683182

Kilina, Svetlana V; Neukirch, Amanda J; Habenicht, Bradley F; Kilin, Dmitri S; Prezhdo, Oleg V

2013-05-01

354

Quantum Dots: The New Little Nanosemiconductors  

NASA Astrophysics Data System (ADS)

The recent arrival of nanomaterials has brought a nifty device called the Quantum Dot. They have intriguing and useful properties. They release light when electricity, heat or light excites their electrons. Their tunable bandgaps allow for the wavelength range they release to be controlled. Free Dots can be attached to a variety of molecules via metal coordinating functional groups. Some of These groups include thiol, phosphine oxide, phosphonic acid, amine, nitrile, phosphine, carboxylic acid or others ligands. This allows the Dots to be dispersed or dissolved in almost any solvent as well as incorporated into a large number of inorganic and organic films. quantum dots can also be tuned to emit in sharp Gaussian peaks in visible or infrared light. Their uses vary from counter counterfeiting to tracking terrorist movement across a large empty landscape.

Harenza, Chance

2006-10-01

355

Cavity quantum electrodynamics with quantum dot - photonic crystal nanocavities  

Microsoft Academic Search

High quality factor, small mode volume photonic crystal cavities and single emitter quantum dots are the topic of this dissertation. They are studied as both a combined system with InAs quantum dots grown in the center of a 2D GaAs photonic crystal slab nanocavity as well as individually. The individual studies are concerned with passive 1D silicon photonic crystal nanobeam

Joshua R. Hendrickson

2010-01-01

356

Controlled Population Transfer in a Double Quantum Dot System  

SciTech Connect

We study the potential for controlled population transfer between the ground states of two anharmonic coupled quantum dots. We propose a method based on the interaction of the quantum dot structure with external electromagnetic fields. The interaction of the quantum dot system with the electromagnetic fields is studied with the use of the time-dependent Schroedinger equation. We present numerical results for an asymmetric quantum dot structure.

Fountoulakis, Antonios; Terzis, Andreas F. [Physics Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece); Paspalakis, Emmanuel [Materials Science Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece)

2007-12-26

357

Microscopic study of relaxation oscillations in quantum-dot VCSELs  

Microsoft Academic Search

We propose a theoretical model to investigate the switch-on dynamics of electrically pumped quantum dot vertical-cavity surface-emitting lasers. The model is based on the self-consistently combined quantum dot-wetting layer Maxwell–Bloch equations incorporating microscopically calculated Coulomb and phonon-assisted scattering processes between the quantum dot and the quantum dot-embedding wetting layer states. Our approach allows the calculation of the time delay before

Jeong Eun Kim; Matthias-Rene Dachner; Alexander Wilms; Marten Richter; Ermin Malic

2011-01-01

358

Electric Field Effect on Optical Absorption of Quantum Confined CdSe Nanoplatelets  

NASA Astrophysics Data System (ADS)

We studied electro-optical effects in 2D quantum confined CdSe nanoplatelets synthesized by colloidal chemistry. They were incorporated into transparent polymeric film sandwiched between two ITO electrodes to which the electric potential has been applied. The electro-optical response in the nanoplatelets has a Stark-like character similar to observed elsewhere for CdSe quantum dots and nanorods. However, the magnitude of the Stark effect in the platelets is of the order of magnitude higher than that in quantum dots or nanorods of an equivalent diameter. The electro-optical response from the nanoplatelets is partially polarized.

Artemyev, M. V.; Prudnikau, A. V.; Ermolenko, M. V.; Gurinovich, L. I.; Gaponenko, S. V.

2013-05-01

359

Generation of singlet oxygen and other radical species by quantum dot and carbon dot nanosensitizers  

Microsoft Academic Search

Medicinal applications of luminescent semiconductor quantum dots are of growing interest. In spite of the fact that their fabrication and imaging applications have been extensively investigated for the last decade, very little is documented on photodynamic action of quantum dots. In this study we demonstrate generation of singlet oxygen and other radical species upon exposure of quantum dots to blue

Roman Generalov; Ingeborg L. Christensen; Wei Chen; Ya-Ping Sun; Solveig Kristensen; Petras Juzenas

2009-01-01

360

Dirac electrons in graphene-based quantum wires and quantum dots.  

PubMed

In this paper we analyse the electronic properties of Dirac electrons in finite-size ribbons and in circular and hexagonal quantum dots. We show that due to the formation of sub-bands in the ribbons it is possible to spatially localize some of the electronic modes using a p-n-p junction. We also show that scattering of confined Dirac electrons in a narrow channel by an infinitely massive wall induces mode mixing, giving a qualitative reason for the fact that an analytical solution to the spectrum of Dirac electrons confined in a square box has not yet been found. A first attempt to solve this problem is presented. We find that only the trivial case k = 0 has a solution that does not require the existence of evanescent modes. We also study the spectrum of quantum dots of graphene in a perpendicular magnetic field. This problem is studied in the Dirac approximation, and its solution requires a numerical method whose details are given. The formation of Landau levels in the dot is discussed. The inclusion of the Coulomb interaction among the electrons is considered at the self-consistent Hartree level, taking into account the interaction with an image charge density necessary to keep the back-gate electrode at zero potential. The effect of a radial confining potential is discussed. The density of states of circular and hexagonal quantum dots, described by the full tight-binding model, is studied using the Lanczos algorithm. This is necessary to access the detailed shape of the density of states close to the Dirac point when one studies large systems. Our study reveals that zero-energy edge states are also present in graphene quantum dots. Our results are relevant for experimental research in graphene nanostructures. The style of writing is pedagogical, in the hope that newcomers to the subject will find this paper a good starting point for their research. PMID:21715777

Peres, N M R; Rodrigues, J N B; Stauber, T; Lopes Dos Santos, J M B

2009-08-26

361

Electron transport through a quantum dot assisted by cavity photons  

NASA Astrophysics Data System (ADS)

We investigate transient transport of electrons through a single quantum dot controlled by a plunger gate. The dot is embedded in a finite wire with length Lx assumed to lie along the x-direction with a parabolic confinement in the y-direction. The quantum wire, originally with hard-wall confinement at its ends, ±Lx/2, is weakly coupled at t = 0 to left and right leads acting as external electron reservoirs. The central system, the dot and the finite wire, is strongly coupled to a single cavity photon mode. A non-Markovian density-matrix formalism is employed to take into account the full electron-photon interaction in the transient regime. In the absence of a photon cavity, a resonant current peak can be found by tuning the plunger-gate voltage to lift a many-body state of the system into the source-drain bias window. In the presence of an x-polarized photon field, additional side peaks can be found due to photon-assisted transport. By appropriately tuning the plunger-gate voltage, the electrons in the left lead are allowed to undergo coherent inelastic scattering to a two-photon state above the bias window if initially one photon was present in the cavity. However, this photon-assisted feature is suppressed in the case of a y-polarized photon field due to the anisotropy of our system caused by its geometry.

Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

2013-11-01

362

Functional microspheres of graphene quantum dots  

NASA Astrophysics Data System (ADS)

Graphene-quantum-dot microspheres (GQDSs) have been prepared by assembly of graphene quantum dots (GQDs) via a water-in-oil (W/O) emulsion technique without the addition of any surfactants. Although made of quantum-sized graphene dots, the as-formed GQDSs are solid and remain intact after slight ultrasonication. The versatile W/O emulsion method allows the in situ intercalation of functional nanocomponents into the GQDSs for specific applications. As exemplified by the Fe3O4-containing GQDSs, Fe3O4-GQDSs exhibit a large magnetic response. Furthermore, the embedded Fe3O4 nanoparticles in GQDSs can act as the catalysts for the growth of carbon nanotubes (CNTs), which opens the opportunities for fabricating new complex structures of CNTs surrounding GQDSs by simple chemical vapor deposition.

Ding, Yi; Cheng, Huhu; Zhou, Ce; Fan, Yueqiong; Zhu, Jia; Shao, Huibo; Qu, Liangti

2012-06-01

363

Quantum Dot Research: Current State and Future Prospects  

Microsoft Academic Search

This article reviews the current state of research involving semiconductor quantum dots, provides a brief review of the theory behind their unique properties, and an introduction explaining the importance of quantum dot research. The characteristic shifting of the band gap energy with quantum dot size, as predicted from the density of states for low-dimensional structures, allows experimental measurements to determine

Tracie J. Bukowski; Joseph H. Simmons

2002-01-01

364

A device architecture for computing with quantum dots  

Microsoft Academic Search

We describe a paradigm for computing with interacting quantum dots, quantum-dot cellular automata (QCA). We show how arrays of quantum-dot cells could be used to perform useful computations. A new adiabatic switching paradigm is developed which permits clocked control, eliminates metastability problems, and enables a pipelined architecture

CRAIG S. LENT; P. DOUGLAS TOUGAW

1997-01-01

365

Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots  

Microsoft Academic Search

The development of optical gain in chemically synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal quantum dot lasers. We examined the competing dynamical processes involved in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative Auger recombination, large optical gain can be developed at

V. I. Klimov; A. A. Mikhailovsky; Su Xu; A. Malko; J. A. Hollingsworth; C. A. Leatherdale; H.-J. Eisler; M. G. Bawendi

2000-01-01

366

Experimental studies of clocked quantum-dot cellular automata devices  

Microsoft Academic Search

Devices based on the quantum-dot cellular automata (QCA) computational approach (Lent et al, 1993) use interacting quantum dots to encode and process binary information. In this transistorless approach to computation, logic levels are represented by the configurations of single electrons in coupled quantum-dot systems. In the last few years, significant progress has been made towards the realization of basic QCA

A. O. Orlov; G. Toth; I. Amlani; R. Kummamuru; R. Ramasubramaniam; C. S. Lent; G. H. Bernstein; G. L. Snider

2000-01-01

367

Computing with Quantum-dot Cellular Automata: Adiabatic Switching  

Microsoft Academic Search

We describe a paradigm for computing with interacting quantum dots, quantum-dot cellular automata (QCA). We show how arrays of quantum-dot cells could be used to perform useful computations. A new adiabatic switching scheme is developed which permits clocked control, eliminates metastability problems, and enables a pipelined architecture. We discuss implementation in semiconductor and metallic tunnel-junction systems.

Craig S. Lent; P. Douglas Tougaw; Weiwen Weng; Yuriy Brazhnik

1997-01-01

368

Synthesis and Applications of Luminescent Quantum Dots in Bioassays  

Microsoft Academic Search

Luminescent quantum dot (QD) based probes have gained significance in the last decade for optical imaging of cells, tissues and in bioassays as alternatives to conventional organic fluorophores. The main objective of my PhD dissertation was to develop luminescent quantum dot based bioassays for real time monitoring of enzyme activity and simultaneous detection of several biomarkers. The quantum dot based

Venkata Ramana Kethineedi

2011-01-01

369

Long-Wavelength Quantum-Dot Infrared Photodetectors With Operating Temperature Over 200 K  

Microsoft Academic Search

We demonstrate the high-temperature operation of confinement enhanced dots-in-a-well (CE-DWELL) quantum-dot infrared photodetectors (QDIPs). The thin Al0.3Ga0.7As barrier layer added above the InAs QDs greatly improve the lateral confinement of QD states in the In0.15Ga0.85As DWELL structure and the device performance. With better device parameters of CE-DWELL, it is possible to achieve high quantum efficiency, high operating temperature, and long-wavelength

Hong-Shi Ling; Shiang-Yu Wang; Chien-Ping Lee; Ming-Cheng Lo

2009-01-01

370

Disorder-mediated electron valley resonance in carbon nanotube quantum dots.  

PubMed

We propose a scheme for coherent rotation of the valley isospin of a single electron confined in a carbon nanotube quantum dot. The scheme exploits the ubiquitous atomic disorder of the nanotube crystal lattice, which induces time-dependent valley mixing as the confined electron is pushed back and forth along the nanotube axis by an applied ac electric field. Using experimentally determined values for the disorder strength we estimate that valley Rabi oscillations with a period on the nanosecond time scale are feasible. The valley resonance effect can be detected in the electric current through a double quantum dot in the single-electron transport regime. PMID:21405589

Pályi, András; Burkard, Guido

2011-02-25

371

Spin states in graphene quantum dots  

NASA Astrophysics Data System (ADS)

Graphene quantum dots [1,2], douple dots [3], rings [4] and nanoribbons [5] have been fabricated by electron beam lithography and dry etching. The orbital [1] properties of graphene quantum dots have been investigated in perpendicular magnetic fields and the details of the electron-hole crossover in graphene leads to a situation where electron (hole) states move down (up) in magnetic field opposite to what has been observed in standard semiconductor based quantum dots. Graphene quantum dots are thought to be good candidates for spin-based quantum information processing since spin-orbit interactions and hyperfine coupling are both expected to be weak. We investigated graphene quantum dots in the single-level transport regime in in-plane magnetic fields where orbital effects are expected to have a minor effect [6]. The g-factor is found to be g 2 and the spin filling sequence of orbital levels can be understood in view of the strength of the exchange interaction which is independent of carrier density in graphene. [4pt] [1] J. Guttinger, C. Stampfer, F. Libisch, T. Frey, J. Burgdoerfer, T. Ihn, K. Ensslin, Phys. Rev. Lett. 103, 046810 (2009) [0pt] [2] T. Ihn, J. Guttinger, F. Molitor, S. Schnez, E. Schurtenberger, A. Jacobsen, S. Hellmuller, T. Frey, S. Droscher, C. Stampfer, and K. Ensslin, Materials Today 13, 44 (2010) [0pt] [3] F. Molitor, H. Knowles, S. Droscher, U. Gasser, T. Choi, P. Roulleau, J. Guttinger, A. Jacobsen, C. Stampfer, K. Ensslin and T. Ihn, Europhys. Lett. 89, 67005 (2010) [0pt] [4] M. Huefner, F. Molitor, A. Jacobsen, A. Pioda, C.Stampfer, K. Ensslin and T. Ihn, N. J. of Phys. 12, 043054 (2010) [0pt] [5] C. Stampfer, J. Guttinger, S. Hellmuller, F. Molitor, K. Ensslin, and T. Ihn, Phys. Rev. Lett. 102, 056403 (2009) [0pt] [6] J. Guttinger, T. Frey, C. Stampfer, T. Ihn, and K. Ensslin, Phys. Rev. Lett. 105, 116801 (2010)

Ensslin, Klaus

2011-03-01

372

Coherent versus incoherent dynamics in InAs quantum-dot active wave guides  

SciTech Connect

Coherent dynamics measured by time-resolved four-wave mixing is compared to incoherent population dynamics measured by differential transmission spectroscopy on the ground-state transition at room temperature of two types of InAs-based quantum dots with different confinement energies. The measurements are performed with heterodyne detection on quantum-dot active wave guides to enhance the light{endash}matter interaction length. An elastic nature of the measured dephasing is revealed which is independent of the dot energy level scheme. {copyright} 2001 American Institute of Physics.

Borri, P.; Langbein, W.; Hvam, J. M.; Heinrichsdorff, F.; Mao, M.-H.; Bimberg, D.

2001-06-01

373

Strain-induced active tuning of the coherent tunneling in quantum dot molecules  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally the possibility to manipulate the coupling strength in an asymmetric pair of electronically coupled InGaAs quantum dots by using externally induced strain fields. The coupling strength of holes confined in the dots increases linearly with increasing tensile strain. A model based on k .p theory explains the effect in terms of modified weight of the light hole component mediating the coupling in the barrier. Our results are relevant to the creation and control of entangled states in optically active quantum dots.

Zallo, E.; Trotta, R.; K?ápek, V.; Huo, Y. H.; Atkinson, P.; Ding, F.; Šikola, T.; Rastelli, A.; Schmidt, O. G.

2014-06-01

374

Trion X+ in vertically coupled type II quantum dots in threading magnetic field  

PubMed Central

We analyze the energy spectrum of a positively charged exciton confined in a semiconductor heterostructure formed by two vertically coupled, axially symmetrical type II quantum dots located close to each other. The electron in the structure is mainly located inside the dots, while the holes generally move in the exterior region close to the symmetry axis. The solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are shown for bonding and anti-bonding lowest-lying of the trion states corresponding to the different quantum dots morphologies, dimensions, separation between them, thicknesses of the wetting layers, and the magnetic field strength.

2012-01-01

375

Mid-infrared quantum dot emitters utilizing planar photonic crystal technology.  

SciTech Connect

The three-dimensional confinement inherent in InAs self-assembled quantum dots (SAQDs) yields vastly different optical properties compared to one-dimensionally confined quantum well systems. Intersubband transitions in quantum dots can emit light normal to the growth surface, whereas transitions in quantum wells emit only parallel to the surface. This is a key difference that can be exploited to create a variety of quantum dot devices that have no quantum well analog. Two significant problems limit the utilization of the beneficial features of SAQDs as mid-infrared emitters. One is the lack of understanding concerning how to electrically inject carriers into electronic states that allow optical transitions to occur efficiently. Engineering of an injector stage leading into the dot can provide current injection into an upper dot state; however, to increase the likelihood of an optical transition, the lower dot states must be emptied faster than upper states are occupied. The second issue is that SAQDs have significant inhomogeneous broadening due to the random size distribution. While this may not be a problem in the long term, this issue can be circumvented by using planar photonic crystal or plasmonic approaches to provide wavelength selectivity or other useful functionality.

Subramania,Ganapathi Subramanian; Lyo, Sungkwun Kenneth; Cederberg, Jeffrey George; Passmore, Brandon Scott; El-Kady, Ihab Fathy; Shaner, Eric Arthur

2008-09-01

376

Compact quantum-dot-based ultrafast lasers  

NASA Astrophysics Data System (ADS)

Solid-state lasers that can generate optical pulses in the picosecond and femtosecond domains have progressed rapidly over the past decade from laboratory systems to an impressive range of commercial systems. Novel materials, notably quantum-dot semiconductor structures, have enhanced the characteristics of such lasers and opened up new possibilities in ultrafast science and technology. In our most recent work we have shown that quantum-dot devices can be designed to provide efficient means of generating and amplifying ultrashort optical pulses at high repetition rate rates.

Sibbett, W.; Rafailov, E. U.

2008-03-01

377

Potential clinical applications of quantum dots  

PubMed Central

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

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

2008-01-01

378

Bilayer graphene quantum dot defined by topgates  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

379

Quantum Dot Infrared Photodetector Using Modulation Doped InAs Self-Assembled Quantum Dots  

Microsoft Academic Search

We report the quantum dot infrared photodetector using the modulation dopedInAs self-assembledquantum dots. By modulation doping, it is possible to remove the effect ofthe dopants on the energylevel in InAs dots and to attribute clearly the infrared photocurrent to the carrier excitation in InAsdots. The infrared photocurrent in the detector was clearly observed up to30 K. The peak energyand the

Naoto Horiguchi; Toshiro Futatsugi; Yoshiaki Nakata; Naoki Yokoyama; Tanaya Mankad; Pierre M. Petroff

1999-01-01

380

Optical properties of amorphous silicon quantum dots (a-Si QDs) with various dot size using extended Hückel theory  

NASA Astrophysics Data System (ADS)

A high quality amorphous silicon (a-Si) nanostructures has grown experimentally to study the origin of light emission and the quantum confinement effect in a-Si. The quantum confinement effect increases the band gap of material as the size of quantum structure decreases, which results in a blue shift in optical luminescence and energy absorption. Here we demonstrate this effect using extended Hückel method to calculate fundamental band gap and optical absorption energy of a-Si samples with various dot sizes. As result, when the dot size was decreased from 2.2 to 1.0 nm, the absorption spectra peak shifted toward higher energy from 2.278 eV to 3.856 eV.

Setianto; Men, Liu Kin; Faizal, Ferry; Wibawa, Bambang Mukti; Hardjo, Doy Hardoyo; Panatarani, Camellia; Joni, I. Made

2013-09-01

381

Structural Origin of Enhanced Luminescence Efficiency of Antimony Irradiated InAs Quantum Dots  

SciTech Connect

We report that Sb irradiation combined with the presence of a GaAs intermediate layer previous to the deposition of a GaSb layer over InAs quantum dots grown by molecular beam epitaxy improves the crystalline quality of these nanostructures. Moreover, this approach to develop III-V-Sb nanostructures causes the formation of quantum dots buried by a confining GaSb layer and, in this way, achieving a type II band alignment. Both phenomena, studied by Conventional transmission electron microscopy (CTEM) and scanning-transmission electron microscope (STEM) techniques are keys to achieve the best room temperature photoluminescence results from InAs/GaAs (001) quantum dots. The Sb flux contributes to the preservation of the quantum dots size and at the same time reduces In diffusion from the wetting layer.

Beltran, AM [Universidad de Cadiz, Spain; Ben, Teresa [Universidad de Cadiz, Spain; Sales, David [Universidad de Cadiz, Spain; Sanchez, AM [University of Warwick, UK; Ripalda, JM [Instituto de Microelectronica de Madrid (CNM, CSIC); Taboada, Alfonso G [Instituto de Microelectronica de Madrid (CNM, CSIC); Varela del Arco, Maria [ORNL; Pennycook, Stephen J [ORNL; Molina, S. I. [Universidad de Cadiz, Spain

2011-01-01

382

Full-colour quantum dot displays fabricated by transfer printing  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

383

Quantum dots-in-a-well infrared photodetectors  

Microsoft Academic Search

Novel InAs\\/InGaAs quantum dots-in-a-well (DWELL) infrared photodetectors are reported. These detectors, in which the active region consists of InAs quantum dots embedded in an InGaAs well quantum well, represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP). Like QDIPs, the DWELL detectors display normal incidence operation without gratings or optocouplers while

Sanjay Krishna

2005-01-01

384

Mid infrared quantum dots in a well infrared photodetectors  

Microsoft Academic Search

The design, growth, fabrication and characterization of novel InAs\\/ InGaAs quantum dots-in-a-well (DWELL) infrared photodetectors are presented. These detectors, in which the active region consists of InAs quantum dots embedded in an InGaAs quantum well, represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP). Like QDIPs, the DWELL detectors display normal

S. Krishna

2005-01-01

385

Coherent nonlinear optical spectroscopy of coupled quantum dots  

Microsoft Academic Search

Quantum dots have been the focus of both fundamental and applied research due to their atomic-like properties. The delta-function-like density of states along with strong nonlinear optical properties have made quantum dots the focus of novel opto-electronic devices and of quantum computing proposals. The key issue for implementing quantum dots in devices such as quantum computers is the ability to

Elizabeth Tabak Batteh

2003-01-01

386

Quantum Information Processing Using Quantum Dot Spins and Cavity QED  

Microsoft Academic Search

The electronic spin degrees of freedom in semiconductors typically have decoherence times that are several orders of magnitude longer than other relevant time scales. A solid-state quantum computer based on localized electron spins as qubits is therefore of potential interest. Here, a scheme that realizes controlled interactions between two distant quantum dot spins is proposed. The effective long-range interaction is

D. D. Awschalom; G. Burkard; D. P. Divincenzo; D. Loss; M. Sherwin; A. Small

1999-01-01

387

Hyperfine interactions and quantum information processing in quantum dots  

Microsoft Academic Search

This thesis explores the feasibility of using electron spins in semiconductor quantum dots as fundamental building blocks for quantum information processing. We start from a general perspective, evaluating the possible limits to operation of such a spin-based system. We show that the coherence properties of electron spins are limited by their interaction with lattice nuclear spins. We then consider approaches

Jacob Mason Taylor

2006-01-01

388

Low-energy trions in graphene quantum dots  

NASA Astrophysics Data System (ADS)

We investigate, within the envelope function approximation, the low-energy states of trions in graphene quantum dots (QDs). The presence of valley pseudospin in graphene as an electron degree of freedom apart from spin adds convolution to the interplay between exchange symmetry and the electron-electron interaction in the trion, leading to new states of trions as well as a low-energy trion spectrum different from those in semiconductors. Due to the involvement of valley pseudospin, it is found that the low-energy spectrum is nearly degenerate and consists of states all characterized by having an antisymmetric (pseudospin) ? (spin) component in the wave function, with the spin (pseudospin) part being either singlet (triplet) or triplet (singlet), as opposed to the spectrum in a semiconductor whose ground state is known to be nondegenerate and always a spin singlet in the case of X- trions. We investigate trions in the various regimes determined by the competition between quantum confinement and electron-electron interaction, both analytically and numerically. The numerical work is performed within a variational method accounting for electron mass discontinuity across the QD edge. The result for electron-hole correlation in the trion is presented. Effects of varying quantum dot size and confinement potential strength on the trion binding energy are discussed. The "relativistic effect" on the trion due to the unique relativistic type electron energy dispersion in graphene is also examined.

Cheng, H.-C.; Lue, N.-Y.; Chen, Y.-C.; Wu, G. Y.

2014-06-01

389

Spectral and threshold performance of patterned quantum dot lasers  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots have been widely researched as a means of improving the performance of optoelectronic devices. Self-assembly has been the dominant method of fabricating quantum dots because of its relative ease compared to more explicit techniques. We have developed a method for fabricating quantum dots in a more explicit manner using electron beam lithography and selective-area metal-organic chemical vapor deposition crystal growth. By eliminating the dependence on strain-driven self-assembly, we can avoid the size distribution and resulting inhomogeneously broadened emission spectrum associated with self-assembled quantum dot ensembles. We report on the threshold and spectral properties of patterned quantum dot lasers.

Elarde, V. C.; Coleman, J. J.

2006-03-01

390

Coherent spin manipulation with a triple quantum dot  

NASA Astrophysics Data System (ADS)

Recently, Landau-Zener-Stuckelberg (LZS) oscillations have been demonstrated in a double quantum dot device [1]. In this talk we demonstrate LZS oscillations in a triple quantum dot environment. Our triple quantum dot design allows us to tune to either the charge or spin qubit regimes. Using a pulsing technique in the spin qubit regime, we create a superposition of triple quantum dot states, allow for phase accumulation, and interfere. We demonstrate coherent LZS oscillations with three spins across the triple quantum dot structure. We investigate their dependence on pulse rise time, separation time, energy detuning, and magnetic field. [4pt] [1] J. R. Petta et al., Science 327, 669 (2010).

Granger, Ghislain; Gaudreau, Louis; Kam, Alicia; Studenikin, Sergei; Zawadzki, Piotr; Aers, Geof; Pioro-Ladrière, Michel; Wasilewski, Zbigniew; Sachrajda, Andrew

2011-03-01

391

Nuclear spin effects in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The interaction of an electronic spin with its nuclear environment, an issue known as the central spin problem, has been the subject of considerable attention due to its relevance for spin-based quantum computation using semiconductor quantum dots. Independent control of the nuclear spin bath using nuclear magnetic resonance techniques and dynamic nuclear polarization using the central spin itself offer unique possibilities for manipulating the nuclear bath with significant consequences for the coherence and controlled manipulation of the central spin. Here we review some of the recent optical and transport experiments that have explored this central spin problem using semiconductor quantum dots. We focus on the interaction between 104-106 nuclear spins and a spin of a single electron or valence-band hole. We also review the experimental techniques as well as the key theoretical ideas and the implications for quantum information science.

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

2013-06-01

392

Anisotropic Spin Exchange in Coupled Quantum Dots  

NASA Astrophysics Data System (ADS)

We study the effect of spin-orbit coupling on the exchange interaction between spins in coupled quantum dots in III-V semiconductors. Our motivatation is recent work showing that spin-orbit induced anisotropic corrections to the isotropic Heisenberg exchange are potentially useful for quantum computation.ootnotetextD. Stepanenko and N.E. Bonesteel, PRL 93, 140501 (2004). We show that ferromagnetic direct exchange enhances the anisotropy of the interaction by reducing the size of the isotropic term --- an important effect if these terms are going to used for quantum computation. If only one orbital is kept per dot (Hund-Mulliken approximation) the effect of ferromagnetic direct exchange is overestimated for large dots.ootnotetextG. Burkard, D. Loss, and D.P. DiVincenzo, PRB 59, 2070 (1999). This can be seen, for example, by noting that the calculated isotropic exchange coupling becomes negative in zero magnetic field for some interdot distances, in violation of the Lieb-Mattis theorem. To reliably estimate the enhancement of the anisotropy, we therefore work within an approximation in which more than one orbital is kept per dot, and show that this new approximation is applicable to a wider range of dot parameters. Apart from the improved reliability of the approximation, adding more orbitals gives new insight into the symmetry of the resulting interaction.

Foster, Kerwin; Hormozi, Layla

2005-03-01

393

Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

394

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

Microsoft Academic Search

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

Ranojoy Bose

2009-01-01

395

Modulation-doped quantum dot infrared photodetectors using self-assembled InAs quantum dots  

Microsoft Academic Search

We have designed and fabricated a new quantum dot infrared photodetector which utilizes lateral transport of photoexcited carriers in the modulation-doped AlGaAs\\/GaAs two-dimensional (2D) channels. A broad photocurrent signal has been observed in the photon energy range of 100–300 meV due to bound-to-continuum intersubband absorption of normal incidence radiation in the self-assembled InAs quantum dots. The peak responsivity was as

S.-W Lee; K. Hirakawa; Y. Shimada

2000-01-01

396

Synthesis of CdSe quantum dots for quantum dot sensitized solar cell  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

397

Noise spectra of an interacting quantum dot  

NASA Astrophysics Data System (ADS)

We study the noise spectra of a many-level quantum dot coupled to two electron reservoirs, when interactions are taken into account only on the dot within the Hartree-Fock approximation. The dependence of the noise spectra on the interaction strength, the coupling to the leads, and the chemical potential are derived. For zero bias and zero temperature, we find that as a function of the (external) frequency, the noise exhibits steps and dips at frequencies reflecting the internal structure of the energy levels on the dot. Modifications due to a finite bias and finite temperatures are investigated for a noninteracting two-level dot. Possible relations to experiments are pointed out.

Gabdank, N.; Rothstein, E. A.; Entin-Wohlman, O.; Aharony, A.

2011-12-01

398

Surface passivation dependent photoluminescence from silicon quantum dot phosphors.  

PubMed

We demonstrate wavelength-tunable, air-stable and nontoxic phosphor materials based on silicon quantum dots (SiQDs). The phosphors, which are composed of micrometer-size silicon particles with attached SiQDs, are synthesized by an electrochemical etching method under ambient conditions. The photoluminescence (PL) peak wavelength can be controlled by the SiQD size due to quantum confinement effect, as well as the surface passivation chemistry of SiQDs. The red-emitting phosphors have PL quantum yield equal to 17%. The SiQD-phosphors can be embedded in polymers and efficiently excited by 405 nm light-emitting diodes for potential general lighting applications. PMID:23164908

Tu, Chang-Ching; Hoo, Ji-Hao; Böhringer, Karl F; Lin, Lih Y; Cao, Guozhong

2012-11-15

399

Solution-Processed Quantum Dot Photodetectors  

Microsoft Academic Search

Digital imaging has traditionally been enabled by single-crystalline photodetectors. This approach typically either mandates the use of silicon as photon-to-electron converter or requires a hybrid-integrated solution. In contrast, solution-processed optoelectronic materials offer convenient integration of light-sensing materials atop an electronic readout circuit. Colloidal quantum dots offer particular advantages, combining solution-processing with the spectral tunability afforded by the quantum size effect.

Gerasimos Konstantatos; Edward H. Sargent

2009-01-01

400

Carrier dynamics in quantum well and quantum dot lasers  

NASA Astrophysics Data System (ADS)

This dissertation concerns the high speed characteristics of semiconductor lasers. From analysis of the frequency dependence of optical modulation characteristics and small signal impedance, it has been possible to extract information about the carrier dynamics and particularly, the carrier capture time. Study of quantum dot high speed characteristics as a function of temperature have led to good understanding of their dynamics. Analysis of the room temperature impedance in quantum dot laser has shown typical capture times of about 30-40ps. The capture times agree reasonably well with values calculated values based on electron-hole scattering being the important capture mechanism. Measured modulation bandwidths of 20GHz at 80K are consistent with pump-probe measurements of capture time of about 10ps. Theoretical calculations show that the capture time is expected to reduce at low temperatures. The onset of severe capture time limitations was at about 150K which resulted in an extracted spacing between the ground and excited electron state of 60 meV, in good agreement with theoretical calculations of 56 meV. Hence, both the magnitude and temperature dependence of the modulation response are consistent with the mechanism for carrier capture being electron-hole scattering. In contrast, maximum modulation bandwidth of very high speed quantum well lasers has shown an increase of less than a factor of two between room temperature and cryogenic temperature. Extremely high speed 1.55?m tunneling injection lasers increased from 20 GHz bandwidth at room temperature to an extrapolated 35 GHz at cryogenic temperature, while the differential gain increased by a factor of fifty. The K-factor and hence the damping limit was almost independent of temperature. This suggest that the gain compression factor is proportional to differential gain. The general result is that for devices which are damping limited, no great improvement in bandwidth is expected from operating at lower temperature. A comparative study was made between a tunneling injection laser (TIL) and three different confinement heterostructure (SCH) 1.55 ?m devices with similar gain regions. The TIL showed more than twice the room temperature modulation bandwidth of the best of the SCH devices, double the differential gain, and the same K-factor. The TIL was limited much less by heating and somewhat less by capture time than the SCH devices. These differences between both their dynamic and DC characteristics are consistent with the tunneling injection mechanism resulting in a cold carrier distribution. Measurements of large-signal modulation characteristics are compared to full numerical rate equantion simulations and show reasonable agreement. An expression is determined for temporal photon density as a function of small signal parameters, and comparison of this expression with full numerical simulation shows that it is valid for output switching ratios up to about 2. The determined maximum digital transmission speed is approximately 23/K (ns) or 1.4/(capture time)(ns) in Gb/sec. This analysis indicates that large signal pulse widths are typically limited to K-factor in quantum well lasers, and are limited by both K-factor and capture time in quantum dot lasers. (Abstract shortened by UMI.)

Klotzkin, David J.

401

Theory of the Optical Response of Singleand Coupled Semiconductor Quantum Dots  

Microsoft Academic Search

Due to their quasi-zero-dimensional structure, quantum dots show optical properties which are different from those of nanostructures\\u000a with spatial confinement in less than three dimensions. In this chapter, the theory of both the linear optical properties\\u000a and nonlinear dynamics of semiconductor quan- tum dots is discussed. The main focus is on the experimentally accessible quantities\\u000a such as absorption\\/luminescence and pump-probe

C. Weber; M. Richter; S. Ritter; A. Knorr

402

Peptide Coated Quantum Dots for Biological Applications  

PubMed Central

Quantum dots (QDOTs) have been widely recognized by the scientific community and the biotechnology industry, as witnessed by the exponential growth of this field in the past several years. We describe the synthesis and characterization of visible and near infrared QDots—a critical step for engineering organic molecules like proteins and peptides for building nanocomposite materials with multifunctional properties suitable for biological applications.

Iyer, Gopal; Pinaud, Fabien; Tsay, James; Li, Jack J.; Bentolila, Laurent A.; Michalet, Xavier; Weiss, Shimon

2011-01-01

403

Spin Fluctuations in Magnetic Quantum Dots  

Microsoft Academic Search

We present a theoretical description of magnetism in quantum dots (QDs) doped with magnetic ions. It has been recognized that the mean-field theory (MFT) is inadequate for small magnetic systems, such as bound magnetic polarons (BMPs), at finite temperatures [1]. Magnetic QDs are in many respects similar to BMPs, however the latter are one-electron systems while the former may contain

A. G. Petukhov; R. M. Abolfath; Igor Zutic

2009-01-01

404

Optical Signatures of Coupled Quantum Dots.  

National Technical Information Service (NTIS)

An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can b...

A. S. Bracker E. A. Stinaff I. V. Ponomarev M. Scheibner V. L. Korenev

2006-01-01

405

Spin relaxation in graphene quantum dots  

NASA Astrophysics Data System (ADS)

With its low concentration of nuclear spins and relatively weak spin-orbit coupling, graphene is a promising host material for electron spin qubits. We have calculated the spin relaxation time T1 of a single spin in graphene quantum dots [1,2] as a function of the externally applied magnetic field B. We find that in quantum dots without coupling between the valleys K and K' in the graphene band structure, there is an effective time-reversal symmetry breaking which prevents the Van Fleck cancellation at B=0 known from semiconductor quantum dots. In combination with the lower dimensionality of the phonons in graphene, this leads to a distinct value of the exponent ? in the power law T1B^? which can be different from the value for semiconductor quantum dots. [4pt] [1] B. Trauzettel, D.V. Bulaev, D. Loss, and G. Burkard, Nature Phys. 3, 192 (2007).[0pt] [2] P. Recher, J. Nilsson, G. Burkard, and B. Trauzettel, Phys. Rev. B 79, 085407 (2009).

Burkard, Guido; Struck, Philipp

2010-03-01

406

Spin qubits in graphene quantum dots  

Microsoft Academic Search

The main characteristics of good qubits are long coherence times in combination with fast operating times. It is well known that carbon-based materials could increase the coherence times of spin qubits, which are among the most developed solid-state qubits. Here, we propose how to form spin qubits in graphene quantum dots. A crucial requirement to achieve this goal is to

Bjoern Trauzettel; Denis V. Bulaev; Daniel Loss; Guido Burkard

2007-01-01

407

Quantum Dot Based Infrared Focal Plane Arrays  

Microsoft Academic Search

In the past decade, there has been active research on infrared detectors based on intersubband transitions in self-assembled quantum dots (QDs). In the past two years, at least four research groups have independently demonstrated focal plane arrays based on this technology. In this paper, the progress from the first raster scanned image obtained with a QD detector to the demonstration

Sanjay Krishna; Sarath D. Gunapala; Sumith V. Bandara; Cory Hill; David Z. Ting

2007-01-01

408

Triggered Single Photons from a Quantum Dot  

Microsoft Academic Search

We demonstrate a new method for generating triggered single photons. After a laser pulse generates excitons inside a single quantum dot, electrostatic interactions between them and the resulting spectral shifts allow a single emitted photon to be isolated. Correlation measurements show a reduction of the two-photon probability to 0.12 times the value for Poisson light. Strong antibunching persists when the

Charles Santori; Matthew Pelton; Glenn Solomon; Yseulte Dale; Yoshihisa Yamamoto

2001-01-01

409

Producing Quantum Dots by Spray Pyrolysis  

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

410

Applications of quantum dots in cell biology  

NASA Astrophysics Data System (ADS)

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

Barroso, Margarida; Mehdibeigi, Roshanak; Brogan, Louise

2006-03-01

411

PLAs in Quantum-dot Cellular Automata  

Microsoft Academic Search

Various implementations of the Quantum-dot Cel- lular Automata (QCA) device architecture may help many performance scaling trends continue as we approach the nano- scale. Experimental success has led to the evolution of a research track that looks at QCA-based design. The work presented in this paper follows that track and looks at implementation friendly, programmable QCA circuits. Specifically, we present

Xiaobo Sharon Hu; Michael Crocker; Michael T. Niemier; Minjun Yan; Gary H. Bernstein

2006-01-01

412

Protease-activated quantum dot probes  

Microsoft Academic Search

We have developed a novel nanoparticulate luminescent probe with inherent signal amplification upon interaction with a targeted proteolytic enzyme. This construct may be useful for imaging in cancer detection and diagnosis. In this system, quantum dots (QDs) are bound to gold nanoparticles (AuNPs) via a proteolytically degradable peptide sequence to non-radiatively suppress luminescence. A 71% reduction in luminescence was achieved

Emmanuel Chang; Jordan S. Miller; Jiantang Sun; William W. Yu; Vicki L. Colvin; Rebekah. Drezek; Jennifer L.. West

2005-01-01

413

Quantum-Dot Cellular Automata Design Guideline  

Microsoft Academic Search

Quantum-dot Cellular Automata (QCA) can be considered as a candidate for the next generation digi- tal logic implementation technology due to their small feature sizes and ultra low power consumption. Up to now, several designs using QCA technology have been pro- posed. However, we found not all of the designs function properly. Furthermore, no general design guidelines have been proposed

Kyosun Kim; Kaijie Wu; Ramesh Karri

2006-01-01

414

New small quantum dots for neuroscience  

NASA Astrophysics Data System (ADS)

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

Selvin, Paul

2014-03-01

415

Assembling quantum dots in glasses and polymers  

Microsoft Academic Search

This paper is an overview of research in my group over the past 10 to 15 years. Our work has explored the synthesis, assembly, nanostructure characterization, and optical properties of a wide variety of semiconductor quantum dots in II-VI, III-V, and other systems. Our early work was aimed at applications in photonics and fiber optics but more recently we have

Subhash H. Risbud

2004-01-01

416

Theoretical analysis of quantum dot infrared photodetectors  

Microsoft Academic Search

Quantum dot infrared photodetectors (QDIPs) have many advantages compared with other types of semiconductor-based photodetectors. Therefore, it is important to evaluate their characteristics theoretically. In this paper our aim is to develop a simple algorithm for this interesting type of photodetector. This algorithm describes a non-trivial evaluation of the most important characteristics. It is used to calculate the dark current,

Mohamed B. El Mashade; M. Ashry; A. Nasr

2003-01-01

417

Dark Current in Quantum Dot Infrared Photodetectors  

Microsoft Academic Search

We present the results of a new analytical model for the analysis of the dark current in realistic quantum dot infrared photodetectors (QDIPs). This model includes the effect of the space charge formed by electrons captured in QDs and donors, the self-consistent electric potential in the QDIP active region, the activation character of the electron capture and its limitation by

Victor Ryzhii; Victor Pipa; Irina Khmyrova; Vladimir Mitin; Magnus Willander

2000-01-01

418

Controlling cavity reflectivity with a single quantum dot  

NASA Astrophysics Data System (ADS)

Solid-state cavity quantum electrodynamics (QED) systems offer a robust and scalable platform for quantum optics experiments and the development of quantum information processing devices. In particular, systems based on photonic crystal nanocavities and semiconductor quantum dots have seen rapid progress. Recent experiments have allowed the observation of weak and strong coupling regimes of interaction between the photonic crystal cavity and a single quantum dot in photoluminescence. In the weak coupling regime, the quantum dot radiative lifetime is modified; in the strong coupling regime, the coupled quantum dot also modifies the cavity spectrum. Several proposals for scalable quantum information networks and quantum computation rely on direct probing of the cavity-quantum dot coupling, by means of resonant light scattering from strongly or weakly coupled quantum dots. Such experiments have recently been performed in atomic systems and superconducting circuit QED systems, but not in solid-state quantum dot-cavity QED systems. Here we present experimental evidence that this interaction can be probed in solid-state systems, and show that, as expected from theory, the quantum dot strongly modifies the cavity transmission and reflection spectra. We show that when the quantum dot is coupled to the cavity, photons that are resonant with its transition are prohibited from entering the cavity. We observe this effect as the quantum dot is tuned through the cavity and the coupling strength between them changes. At high intensity of the probe beam, we observe rapid saturation of the transmission dip. These measurements provide both a method for probing the cavity-quantum dot system and a step towards the realization of quantum devices based on coherent light scattering and large optical nonlinearities from quantum dots in photonic crystal cavities.

Englund, Dirk; Faraon, Andrei; Fushman, Ilya; Stoltz, Nick; Petroff, Pierre; Vu?kovi?, Jelena

2007-12-01

419

Controlling cavity reflectivity with a single quantum dot.  

PubMed

Solid-state cavity quantum electrodynamics (QED) systems offer a robust and scalable platform for quantum optics experiments and the development of quantum information processing devices. In particular, systems based on photonic crystal nanocavities and semiconductor quantum dots have seen rapid progress. Recent experiments have allowed the observation of weak and strong coupling regimes of interaction between the photonic crystal cavity and a single quantum dot in photoluminescence. In the weak coupling regime, the quantum dot radiative lifetime is modified; in the strong coupling regime, the coupled quantum dot also modifies the cavity spectrum. Several proposals for scalable quantum information networks and quantum computation rely on direct probing of the cavity-quantum dot coupling, by means of resonant light scattering from strongly or weakly coupled quantum dots. Such experiments have recently been performed in atomic systems and superconducting circuit QED systems, but not in solid-state quantum dot-cavity QED systems. Here we present experimental evidence that this interaction can be probed in solid-state systems, and show that, as expected from theory, the quantum dot strongly modifies the cavity transmission and reflection spectra. We show that when the quantum dot is coupled to the cavity, photons that are resonant with its transition are prohibited from entering the cavity. We observe this effect as the quantum dot is tuned through the cavity and the coupling strength between them changes. At high intensity of the probe beam, we observe rapid saturation of the transmission dip. These measurements provide both a method for probing the cavity-quantum dot system and a step towards the realization of quantum devices based on coherent light scattering and large optical nonlinearities from quantum dots in photonic crystal cavities. PMID:18064008

Englund, Dirk; Faraon, Andrei; Fushman, Ilya; Stoltz, Nick; Petroff, Pierre; Vuckovi?, Jelena

2007-12-01

420

Nonlocal quantum cloning via quantum dots trapped in distant cavities  

NASA Astrophysics Data System (ADS)

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.

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

2012-05-01

421

Elastic light scattering by semiconductor quantum dots of arbitrary shape  

Microsoft Academic Search

Elastic light scattering by low-dimensional quantum objects without a change in the frequency is theoretically investigated in terms of the quantum perturbation theory. The differential cross section of resonance light scattering from any excitons in any quantum dots is calculated. It is demonstrated that, when the light wavelengths considerably exceed the quantum-dot size, the polarization and angular distribution of the

I. G. Lang; L. I. Korovin; S. T. Pavlov

2007-01-01

422

Phase coherent transport in two coupled quantum dots  

Microsoft Academic Search

Quantum dots by now offer a well-defined environment for studying quantum physics. Hence, various proposals have been introduced how to integrate these artificial molecules for building quantum computing devices. Crucial for operating such circuits is the realization of wave function coherence established in coupled quantum dots. Consequently, the foremost goal is to devise basic circuits for testing phase coherence and

R. H Blick; A. K Hüttel; A. W Holleitner; E. M Höhberger; H. Qin; J. Kirschbaum; J. Weber; W. Wegscheider; M. Bichler; K. Eberl; J. P Kotthaus

2003-01-01

423

Photoionization cross sections of hydrogen impurities in spherical quantum dots using the finite-element discrete-variable representation  

SciTech Connect

The method of complex-coordinate rotation in a finite-element discrete variable representation is implemented to study the photoionization of hydrogen impurity in spherical quantum dots which are modelled by finite oscillator and Gaussian potentials. The level splitting and crossing of hydrogen impurities due to the variation of dot radii and confining potentials are presented, as well as the shifting down of the energy of hydrogenic impurity toward the combined energy of the free hydrogen and the amplitude of the confining potential. We illustrate the staircaselike behavior in ground and excited energy curves varying with dot radii. The variation of photoionization cross sections with photoelectron energies are given for several dot radii. The cross sections as functions of quantum-dot radii and confining potentials for specific photon energies showing resonancelike profiles are observed and discussed.

Lin, C. Y.; Ho, Y. K. [Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 106, Taiwan (China)

2011-08-15

424

Fast electrical control of a quantum dot strongly coupled to a photonic-crystal cavity.  

PubMed

The resonance frequency of an InAs quantum dot strongly coupled to a GaAs photonic-crystal cavity was electrically controlled via the quadratic quantum confined Stark effect. Stark shifts up to 0.3 meV were achieved using a lateral Schottky electrode that created a local depletion region at the location of the quantum dot. We report switching of a probe laser coherently coupled to the cavity up to speeds as high as 150 MHz, limited by the RC constant of the transmission line. The coupling strength g and the magnitude of the Stark shift with electric field were investigated while coherently probing the system. PMID:20366737

Faraon, Andrei; Majumdar, Arka; Kim, Hyochul; Petroff, Pierre; Vuckovi?, Jelena

2010-01-29

425

Photocatalytic activity of quantum dots incorporated in molecular sieves for generation of hydrogen  

NASA Astrophysics Data System (ADS)

MCM-41 molecular sieve coupled with lead sulfide quantum dots (PbS-MCM-41) was prepared by ion-exchange method. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectroscopy, infrared spectroscopy (IR) and BET (Brunauer-Emmett-Teller) experiments. Exciton absorption peak at higher energy than the fundamental absorption edge of bulk lead sulfide indicates quantum confinement effects in quantum dots as a consequence of their small size. The hydrogen production rate from water photocatalytic decomposition under visible light irradiation (? > 400 nm) over PbS nanoparticles formed in mesoporous material was much higher compared to the bulk PbS.

Pourahmad, Afshin

426

Vertical quantum dot with a vertically coupled charge detector  

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

427

Using a quantum dot system to realize perfect state transfer  

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

428

Electronic states and oscillator strengths for interband transitions of a graded quantum dot quantum well structure  

NASA Astrophysics Data System (ADS)

A theoretical study of electron and hole electronic states and oscillator strength of interband transitions in a graded spherical HgS/CdS/HgS/CdS quantum dot quantum well (QDQW) nanostructure is presented; also the Coulomb interaction energies of excitons are calculated. The Finite Element Method (FEM) is used for solving the problem with the position dependent effective mass approximation. The results of calculations show that gradation of the potential decreases energies of confined particles and considerably reduces the oscillator strength for certain transitions. The gradation of the potential can be used as an additional parameter for experimental purposes to manipulate needed properties of the QDQW structure.

Bochorishvili, Beka

2011-02-01

429

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

430

Vertical quantum dot with a vertically coupled charge detector  

Microsoft Academic Search

We fabricated a vertical quantum dot equipped with a charge detector. The dot current flows vertically between the top and bottom contacts. The charge detector is formed at the bottom contact layer with a current channel constricted to the region just under the dot. This channel current is reduced by addition of an extra electron onto the dot due to

Koichiro Zaitsu; Yosuke Kitamura; Keiji Ono; Seigo Tarucha

2008-01-01

431

Practical issues in the realization of quantum-dot cellular automata  

NASA Astrophysics Data System (ADS)

Several practical issues in the development and operation of quantum-dot cellular automata (QCA) cells and systems are discussed. The need for adiabatic clocking of QCA systems and modeling of electrostatic confinement of quantum dots are presented. Experimental data on dot coupling and applications to QCA detectors in a 2-dimensional electron gas (2DEG) are presented. We report a charge detection scheme where we observe strong modulation in the detector signal, in addition to the detector exhibiting minimal effect on the dot being measured. With this investigation, we demonstrate these two key components required for QCA in AlGaAs/GaAs materials, namely dot coupling and charge-state detection.

Bernstein, Gary H.; Bazan, Greg; Chen, Minhan; Lent, Craig S.; Merz, James L.; Orlov, Alexei O.; Porod, Wolfgang; Snider, G. L.; Tougaw, P. Douglas

1996-12-01

432

GENERAL: The influence of electric field on a parabolic quantum dot qubit  

NASA Astrophysics Data System (ADS)

This paper calculates the time evolution of the quantum mechanical state of an electron by using variational method of Pekar type on the condition of electric-LO-phonon strong coupling in a parabolic quantum dot. It obtains the eigenenergies of the ground state and the first-excited state, the eigenfunctions of the ground state and the first-excited state This system in a quantum dot may be employed as a two-level quantum system qubit. The superposition state electron density oscillates in the quantum dot with a period when the electron is in the superposition state of the ground and the first-excited state. It studies the influence of the electric field on the eigenenergies of the ground state, the first-excited state and the period of oscillation at the different electron-LO-phonon coupling constant and the different confinement length.

Yin, Ji-Wen; Xiao, Jing-Lin; Yu, Yi-Fu; Wang, Zi-Wu

2009-02-01

433

Improved photoluminescence efficiency of patterned quantum dots incorporating a dots-in-the-well structure  

Microsoft Academic Search

InAs quantum dots embedded in InGaAs quantum well (DWELL: dots-in-the-well) structures grown on nanopatterned GaAs pyramids and planar GaAs(001) surface are comparatively investigated. Photoluminescence (PL) measurements demonstrate that the DWELL structure grown on the GaAs pyramids exhibits a broad quantum well PL band (full width at half-maximum ~ 90 meV) and a higher quantum dot emission efficiency than the DWELL

P. S. Wong; B. L. Liang; V. G. Dorogan; J. Tatebayashi; X. He; N. Nuntawong; Yu I. Mazur; G. J. Salamo; S. R. J. Brueck; D. L. Huffaker

2008-01-01

434

Laterally-biased quantum dot infrared photodetector  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

435

Progress towards single spin optoelectronics using quantum dot nanostructures  

Microsoft Academic Search

We summarise recent progress in our understanding of the physics of fundamental charge and spin excitations in quantum dot semiconductor nanostructures. Many novel potential applications of these nanostructures have arisen from the strong optical non-linearities that exist in the few-particle quantum dot absorption spectrum. By comparison, the interaction of the electron spin with other localised charges in the dot and

Domink Heiss; Miro Kroutvar; Jonathan J. Finley; Gerhard Abstreiter

2005-01-01

436

Quantum-dot cellular automata at a molecular scale  

Microsoft Academic Search

ABSTRACT: Quantum - dot cellular automata (QCA) is a scheme for molecular electronics in which information is transmitted and processed through electro - static interactions between charges in an array of quantum dots QCA wires, majority gates, clocked cell operation, and (recently) true power gain between QCA cells has been demonstrated in a metal - dot prototype system at cryogenic

M. Lieberman

2002-01-01

437

InP\\/GalnP Quantum Dot Lasers  

Microsoft Academic Search

\\u000a Over the last decade self-assembled semiconductor quantum dots have become a major issue in semiconductor physics [1–3] — both from a fundamental point of view as well as in respect to applications such as the quantum dot laser. Originally,\\u000a the quantum dot laser was proposed to outperform the well-established quantum well laser on the basis of properties such as\\u000a material

Oliver G. Schmidt; Yvonne M. Manz; Karl Eber

438

Investigation of potential profile effects in quantum dot and onion-like quantum dot-quantum well on optical properties  

NASA Astrophysics Data System (ADS)

This paper investigates GaAs/AlGaAs modified quantum dot nanocrystal and GaAs/AlGaAs/GaAs/AlGaAs quantum dot-quantum well heteronanocrystal. These quantum dots have been analyzed by the finite element numerical methods. Simulations carried out for state n=1, l=0, and m=0 which are original, orbital, and magnetic state of quantum numbers. The effects of variation in radius layers such as total radius, GaAs core, shell and AlGaAs barriers radius on the wavelength and emission coefficient are studied. For the best time, it has also investigated the effect of mole fraction on emission coefficient. Meanwhile, one of the problems in biological applications is alteration of the emission wavelength of a quantum dot by changing in its dimension. This problem will be resolved by changing in potential profile.

Elyasi, P.; SalmanOgli, A.

2014-05-01

439

Structural analysis of strained quantum dots using nuclear magnetic resonance  

NASA Astrophysics Data System (ADS)

Strained semiconductor nanostructures can be used to make single-photon sources, detectors and photovoltaic devices, and could potentially be used to create quantum logic devices. The development of such applications requires techniques capable of nanoscale structural analysis, but the microscopy methods typically used to analyse these materials are destructive. NMR techniques can provide non-invasive structural analysis, but have been restricted to strain-free semiconductor nanostructures because of the significant strain-induced quadrupole broadening of the NMR spectra. Here, we show that optically detected NMR spectroscopy can be used to analyse individual strained quantum dots. Our approach uses continuous-wave broadband radiofrequency excitation with a specially designed spectral pattern and can probe individual strained nanostructures containing only 1 × 105 quadrupole nuclear spins. With this technique, we are able to measure the strain distribution and chemical composition of quantum dots in the volume occupied by the single confined electron. The approach could also be used to address problems in quantum information processing such as the precise control of nuclear spins in the presence of strong quadrupole effects.

Chekhovich, E. A.; Kavokin, K. V.; Puebla, J.; Krysa, A. B.; Hopkinson, M.; Andreev, A. D.; Sanchez, A. M.; Beanland, R.; Skolnick, M. S.; Tartakovskii, A. I.

2012-10-01

440

Structural analysis of strained quantum dots using nuclear magnetic resonance.  

PubMed

Strained semiconductor nanostructures can be used to make single-photon sources, detectors and photovoltaic devices, and could potentially be used to create quantum logic devices. The development of such applications requires techniques capable of nanoscale structural analysis, but the microscopy methods typically used to analyse these materials are destructive. NMR techniques can provide non-invasive structural analysis, but have been restricted to strain-free semiconductor nanostructures because of the significant strain-induced quadrupole broadening of the NMR spectra. Here, we show that optically detected NMR spectroscopy can be used to analyse individual strained quantum dots. Our approach uses continuous-wave broadband radiofrequency excitation with a specially designed spectral pattern and can probe individual strained nanostructures containing only 1 × 10(5) quadrupole nuclear spins. With this technique, we are able to measure the strain distribution and chemical composition of quantum dots in the volume occupied by the single confined electron. The approach could also be used to address problems in quantum information processing such as the precise control of nuclear spins in the presence of strong quadrupole effects. PMID:22922539

Chekhovich, E A; Kavokin, K V; Puebla, J; Krysa, A B; Hopkinson, M; Andreev, A D; Sanchez, A M; Beanland, R; Skolnick, M S; Tartakovskii, A I

2012-10-01

441

Ground and first excited state energies of impurity-bound polaron in a parabolic quantum dot  

Microsoft Academic Search

A Landau–Pekar variational theory is employed to obtain the ground and the first excited state binding energies of an electron bound to a Coulomb impurity in a polar semiconductor quantum dot (QD) with parabolic confinement in both two and three dimensions. It is found that the binding energy increase with increasing the Coulomb binding parameter and increase with the decrease

Shi-Hua Chen; Jing-Lin Xiao

2008-01-01

442

Hydrogenic impurity bound polaron in a parabolic quantum dot with arbitrary electron–phonon coupling strength  

Microsoft Academic Search

A variational approach is employed to obtain the ground and the first excited state binding energies of an electron bound to a hydrogenic impurity in a polar semiconductor quantum dot (QD) with symmetric parabolic confinement in both two and three-dimensions. We perform calculations for the entire range of the electron–phonon coupling constant and the Coulomb binding parameter and for arbitrary

Shi-Hua Chen

2011-01-01

443

Third harmonic generation in quantum dot with Rashba spin orbit interaction  

NASA Astrophysics Data System (ADS)

Here we have investigated the influence of magnetic field and confinement potential on nonlinear optical property, third harmonic generation (THG) of a parabolically confinement quantum dot in the presence of Rashba spin orbit interaction. We have used density matrix formulation for obtaining optical properties within the effective mass approximation. The results are presented as a function of confining potential, magnetic field, Rashba spin orbit interaction strength and photon energy. Our results indicate that an increase of Rashba spin orbit interaction coefficient produces strong effect on the peak positions of THG. The role of confinement strength and spin orbit interaction strength as control parameters on THG have been demonstrated.

Kumar, Manoj; Gumber, Sukirti; Lahon, Siddhartha; Jha, Pradip Kumar; Mohan, Man

2014-03-01

444

(e,3e) process on a quantum dot  

SciTech Connect

The exact initial state wave function of an interacting electron pair in a quantum dot under parabolic confinement and neutralization of the dot by the substrate after ejection of electrons is exploited to obtain the fivefold differential cross section (X) of the (e,3e) process on the dot. The reflections of the center-of-mass (c.m.) motion and relative motion on X are decoupled if the incident and scattered electrons are energetic and the ejected electrons are slow. The results are studied in fixed mutual angle (with zero c.m. momentum K) and Bethe ridge modes which allow the 'cleanest' analysis of the contribution of the relative motion. The Coulomb interaction between the emitted electrons is found to qualitatively change the angular distribution of X. In the mode in which the magnitude of K is equal to the momentum transfer q, the angular distribution of X with respect to {theta}{sub Kq}=cos{sup -1}(K{center_dot}q) leads to a mapping of the initial c.m. wave function of the ejected pair. However, the c.m. motion is found to be best studied in the kinematics where the relative momentum k-vector of the ejected pair is equal to q-vector.

Srivastava, M.K. [Institute Instrumentation Centre, Indian Institute of Technology, Roorkee, 247 667, Uttaranchal (India)

2004-12-01

445

Si, Ge, and SiGe quantum wires and quantum dots  

Microsoft Academic Search

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

T. P. Pearsall

2007-01-01

446

The Rashba Effect on the Bound Polaron in a Parabolic Quantum Dot  

Microsoft Academic Search

The bound polaron ground state energy is calculated by the variational method of Pekar considering the influence of the Rashba\\u000a SO interaction on the condition of electric–LO phonon strong coupling in a parabolic quantum dot (QD). The relations on the\\u000a bound polaron ground state energy with the parallel confinement length, the electron–LO phonon coupling constant, the perpendicular\\u000a confinement length and

Ji-Wen Yin; Wei-Ping Li; Yi-Fu Yu; Jing-Lin Xiao

2011-01-01

447

Semiconductor quantum dot scintillation under gamma-ray irradiation  

SciTech Connect

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-ray irradiation, and compare the energy resolution of the 59 keV line of Americium 241 obtained with our quantum dot-glass nanocomposite material 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. These results demonstrate the potential of quantum dots for room-temperature gamma-ray detection, which has applications in medical imaging, environmental monitoring, as well as security and defense. Present technology in gamma radiation detection suffers from flexibility and scalability issues. For example, bulk Germanium provides fine energy resolution (0.2% energy resolution at 1.33 MeV) but requires operation at liquid nitrogen temperature. On the other hand, Cadmium-Zinc-Telluride is a good room temperature detector ( 1% at 662 keV) but the size of the crystals that can be grown is limited to a few centimeters in each direction. Finally, the most commonly used scintillator, Sodium Iodide (NaI), can be grown as large crystals but suffers from a lack of energy resolution (7% energy resolution at 662 keV). Recent advancements in nanotechnology6-10 have provided the possibility of controlling materials synthesis at the molecular level. Both morphology and chemical composition can now be manipulated, leading to radically new material properties due to a combination of quantum confinement and surface to volume ratio effects. One of the main consequences of reducing the size of semiconductors down to nanometer dimensions is to increase the energy band gap, leading to visible luminescence, which suggests that these materials could be used as scintillators. The visible band gap of quantum dots would also ensure both efficient photon counting (better coupling with photomultipliers optimized for the visible region), and high photon output (smaller individual photon energy results in more photons produced) at room temperature, which is essential for effective Poisson counting (the energy resolution {Delta}E/E is inversely proportional to the square root of the number of photons collected).

Letant, S E; Wang, T

2006-08-23

448

Entrapment in phospholipid vesicles quenches photoactivity of quantum dots  

PubMed Central

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 co