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1

The confinement energy of quantum dots

One of the most significant research interests in the field of electronics is that on quantum dot, because such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. Confinement energy is a very important property of quantum dot. In this study, quantum confinement energy of a quantum dot is concluded to be h2/8md2 (d being the diameter of the confinement) and not h2/8ma2 (a being the radius of the confinement), as reported in the available literature. This is in the light of a recent study [1]. This finding should have a significant impact in the understanding of the physics of quantum dot and its technological application.

Dey, Samrat; Chakraborty, kishan; Dasgupta, Debasmita; Bordoloi, Darsana; Saikia, Rituja; Neog, Darsana; Shimray, Shishila; Paul, Supriyanka; Brahma, Kabita; Dey, Joydeep; Choudhury, Saurav

2012-01-01

2

Comparison of quantum confinement effects between quantum wires and dots

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

Atomic and Molecular Quantum Theory Course Number: C561 10 Quantum Confinement in "Quantum dots "niche" area called quantum dots. 1. A quantum dot is a very small chunk of semiconductor material changes the spectroscopic properties of quantum dots. Chemistry, Indiana University 84 c 2003, Srinivasan

Iyengar, Srinivasan S.

4

Quantum Dots-in-a-Well (DWELL) Infrared Photodetectors with Confinement Enhancing Barriers

Quantum Dots-in-a-Well (DWELL) Infrared Photodetectors with Confinement Enhancing Barriers Ajit V@chtm.unm.edu Abstract: Improvement in the performance of quantum dots-in-a-well (DWELL) detectors with confinementGaAs barrier layers around the dots in a well (DWELL) structure to enhance the quantum confinement of carriers

Krishna, Sanjay

5

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

6

Quantum confinement effects on charge-transfer between PbS quantum dots and 4-mercaptopyridine

We obtain the surface enhanced Raman spectra of 4-mercaptopyridine on lead sulfide (PbS) quantum dots as a function of nanoparticle size and excitation wavelength. The nanoparticle radii are selected to be less than the exciton Bohr radius of PbS, enabling the observation of quantum confinement effects on the spectrum. We utilize the variation of nontotally symmetric modes of both b{sub 1} and b{sub 2} symmetry as compared to the totally symmetric a{sub 1} modes to measure the degree of charge-transfer between the molecule and quantum dot. We find both size dependent and wavelength dependent resonances in the range of these measurements, and attribute them to charge-transfer resonances which are responsible for the Raman enhancement.

Fu Xiaoqi [Department of Chemistry, City College of New York, New York, N.Y. 10031 (United States); Key Laboratory for Soft Chemistry and Functional Materials of Ministry Education, Nanjing University of Science and Technology, Nanjing 210094 (China); School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Pan Yi; Lombardi, John R. [Department of Chemistry, City College of New York, New York, N.Y. 10031 (United States); Wang Xin [Key Laboratory for Soft Chemistry and Functional Materials of Ministry Education, Nanjing University of Science and Technology, Nanjing 210094 (China)

2011-01-14

7

Efficient Exciton Transport Between Strongly Quantum-Confined Silicon Quantum Dots

NASA Astrophysics Data System (ADS)

First-order perturbation theory and many-body Green function analysis are used to quantify the influence of size, surface reconstruction and surface treatment on exciton transport between small silicon quantum dots. Competing radiative processes are also considered in order to determine how exciton transport efficiency is influenced. The analysis shows that quantum confinement causes small (˜ 1 nm) Si quantum dots to exhibit exciton transport efficiencies far exceeding that of their larger counterparts. We also find that surface reconstruction significantly influences the absorption cross-section and leads to a large reduction in both transport rate and efficiency. Exciton transport efficiency is higher for hydrogen-passivated dots as compared with those terminated with more electronegative ligands. This is because such ligands delocalize electron wave functions towards the surface and result in a lower dipole moment. This work [1] is a first step in the development of a framework for the design of quantum dot assemblies with improved exciton transfer efficiency. 2mm [1] Z. Lin, A. Franceschetti and M. T. Lusk, arXiv:1110.6456v1 [cond-mat.mes-hall

Lusk, Mark; Lin, Zhibin; Franceschetti, Alberto

2012-02-01

8

Spectral properties of quantum dots influenced by a confining potential model

NASA Astrophysics Data System (ADS)

We obtain the exact energy spectra and corresponding wave functions of the spherical quantum dots for any (n,l) state in the presence of a combination of pseudo-harmonic, Coulomb and linear confining potential terms within the exact analytical iteration method (EAIM). The interaction potential model under consideration is labeled as the Cornell modified-plus-harmonic (CMpH) type which is a correction form to the harmonic, Coulomb and linear confining potential terms.

Ikhdair, Sameer M.; Hamzavi, Majid

2012-12-01

9

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.

10

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots provide a platform for studying and exploiting individual electron spins as they interact with a complex solid state environment. Colloidal nanocrystal quantum dots are of particular interest for potential applications, because they can achieve sufficient confinement to operate at room temperature with relatively robust electron spin coherence. The strong confinement in these nanostructures leads to significant effects caused by mixing of valence subbands and variation in particle size and shape. These effects influence the processes of carrier spin initialization and detection. We have performed ensemble time-resolved Faraday rotation experiments as well as single-dot photoluminescence excitation measurements to study how the strong quantum confinement affects the spin physics in these systems. Single dot PLE measurements reveal mechanisms of transition broadening that are relevant at room temperature, including thermal broadening and spectral diffusion due to mobile charges in the surrounding environment. We find that the mixing of valence subbands in the confined hole states largely determines the efficiency of optical spin pumping and Faraday-rotation-based spin detection. By studying these effects, we take a step towards controlling and exploiting spin coherence in this flexible room temperature platform.

Berezovsky, Jesse; Fumani, Ahmad K.; Wolf, Michael

2014-08-01

11

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

12

Quantum dot resonant tunneling spectroscopy

NASA Astrophysics Data System (ADS)

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

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

13

Carrier confinement in Ge/Si quantum dots grown with an intermediate ultrathin oxide layer

NASA Astrophysics Data System (ADS)

We present computational results for strain effects on charge carrier confinement in GexSi1-x quantum dots (QDs) grown on an oxidized Si surface. The strain and free carrier probability density distributions are obtained using the continuum elasticity theory and the effective-mass approximation implemented by a finite-element modeling scheme. Using realistic parameters and conditions for hemisphere and pyramid QDs, it is pointed out that an uncapped hemisphere dot deposited on the Si surface with an intermediate ultrathin oxide layer offers advantageous electron-hole separation distances with respect to a square-based pyramid grown directly on Si. The enhanced separation is associated with a larger electron localization depth in the Si substrate for uncapped hemisphere dots. Thus, for dot diameters smaller than 15-20 nm and surface density of the dots (nQD) ranging from about 1010 to 1012 cm-2, the localization depth may be enhanced from about 8 nm for a pyramid to 38 nm for a hemisphere dot. We find that the effect in a hemisphere dot is very sensitive to the dot density and size, whereas the localization depth is not significantly affected by the variation of the Ge fraction x in GexSi1-x and the aspect ratio of the dot. We also calculate the effect of the fixed oxide charge (Qox) with densities ranging from 10-9 to 10-7 C/cm2 for 10-?cm p-type Si wafers on the carrier confinement. Although the confinement potential can be strongly perturbed by the charge at nQD less than ?4×1011 cm-2, it is not very sensitive to the value of Qox at higher nQD. Since, to our knowledge, there are no data on carrier confinement for Ge QDs deposited on oxidized Si surfaces, these results might be applicable to functional devices utilizing separated electrons and holes such as photovoltaic devices, spin transistors, and quantum computing components. The use of hemisphere QDs placed on oxidized Si rather than pyramid dots grown on bare Si may help to confine charge carriers deeper inside the Ge/Si heterostructure in order to reduce the influence of surfaces and interfaces on transport properties of the structures.

Kuryliuk, V.; Korotchenkov, O.; Cantarero, A.

2012-02-01

14

Confined Franz-Keldysh effect in ZnO quantum dots

NASA Astrophysics Data System (ADS)

Within the framework of the effective mass approximation, the confined Franz-Keldysh effect is investigated theoretically in a cylindrical ZnO quantum dot (QD). Numerical results show that the application of an electric field can decrease the strength and the threshold energy of the optical absorption coefficient in ZnO QD. There are additional oscillations in the absorption above the effective band gap, which are due to the Franz-Keldysh effect which occurs in the presence of the electric field. Our results also show that the electric field has a more obviously influence on the optical absorption in cylindrical ZnO QD with larger dot height.

Xia, Congxin; Spector, Harold N.

2010-03-01

15

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

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

16

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

17

NASA Astrophysics Data System (ADS)

The diffusion-controlled growth of CdS quantum dots (QDs) dispersed in a silicate glass matrix was investigated. It was found that the size of CdS QDs can be controlled by either heat treatment at various temperatures for a fixed duration or varying times at a constant temperature. Pastel yellow colored glass samples were obtained due to the presence of CdS petite crystals. X-ray diffraction (XRD) was used for determining the average dot size which varied from 3.8 to 30 nm. The typical quantum confinement effect was clearly observed from the blue shift measured in the optical absorption edge with decreasing dot size in the absorption spectroscopy. The band gap of CdS QDs ranges from 2.41 to 2.82 eV. Measured photoluminescence (PL) at an excitation wavelength of 350 nm showed the red shift of emission wavelength with increasing thermal treatment time and temperature in agreement with the increasing dot sizes. The half-width of PL spectra seems to indicate qualitatively the size distribution of dots and is consistent with the treatment parameters.

Mishra, Rakesh K.; Vedeshwar, A. G.; Tandon, R. P.

2014-02-01

18

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

19

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. PMID:23826867

2013-01-01

20

Dynamics of a Mn spin coupled to a single hole confined in a quantum dot

NASA Astrophysics Data System (ADS)

Using the emission of the positively charged exciton as a probe, we analyze the dynamics of the optical pumping and the dynamics of the relaxation of a Mn spin exchange coupled with a confined hole spin in a II-VI semiconductor quantum dot. The hole-Mn spin can be efficiently initialized in a few tens of ns under optical injection of spin-polarized carriers. We show that this optical pumping process and its dynamics are controlled by electron-Mn flip-flops within the positively charged exciton-Mn complex. The pumping mechanism and its magnetic field dependence are theoretically described by a model including the dynamics of the electron-Mn complex in the excited state and the dynamics of the hole-Mn complex in the ground state of the positively charged quantum dot. We measure at zero magnetic field a spin-relaxation time of the hole-Mn spin in the ?s range or shorter. This hole-Mn spin relaxation is induced by the presence of valence-band mixing in self-assembled quantum dots.

Varghese, B.; Boukari, H.; Besombes, L.

2014-09-01

21

NASA Astrophysics Data System (ADS)

We investigate the excitation kinetics of a repulsive impurity doped quantum dot initiated by oscillations of various confinement sources. The dopant is considered to be propagating under damped condition. For simplicity, we have considered an inherently linear motion of the dopant and the impurity potential has been assumed to have a Gaussian nature. The damping strength and the oscillation frequencies of dot confinement sources of electric and magnetic origin have been found to fabricate the said kinetics in a delicate way. The present study sheds light on how the individual or combined oscillations of different confinement sources could design the excitation kinetics in presence of damping.

Pal, Suvajit; Ghosh, Manas

2013-12-01

22

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

23

NASA Astrophysics Data System (ADS)

Monolayer transition metal dichalcogenides (TMDs) offer new opportunities for realizing quantum dots (QDs) in the ultimate two-dimensional (2D) limit. Given the rich control possibilities of electron valley pseudospin discovered in the monolayers, this quantum degree of freedom can be a promising carrier of information for potential quantum spintronics exploiting single electrons in TMD QDs. An outstanding issue is to identify the degree of valley hybridization, due to the QD confinement, which may significantly change the valley physics in QDs from its form in the 2D bulk. Here we perform a systematic study of the intervalley coupling by QD confinement potentials on extended TMD monolayers. We find that the intervalley coupling in such geometry is generically weak due to the vanishing amplitude of the electron wavefunction at the QD boundary, and hence valley hybridization will be well quenched by the much stronger spin–valley coupling in monolayer TMDs and the QDs can well inherit the valley physics of the 2D bulk. We also discover sensitive dependence of intervalley coupling strength on the central position and the lateral length scales of the confinement potentials, which may possibly allow tuning of intervalley coupling by external controls.

Liu, Gui-Bin; Pang, Hongliang; Yao, Yugui; Yao, Wang

2014-10-01

24

We achieved room temperature laser operation, around 1.5 mum, with a single layer of InAs\\/InP quantum dots in a photonic crystal structure using confined slow light. The lasing threshold is a few hundred muW.

F. Bordas; C. Seassal; E. Dupuy; P. Regreny; M. Gendry; M. J. Steel; A. Rahmani

2007-01-01

25

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

26

The electrical and the optical properties of InAs\\/GaAs quantum dots (QDs) grown by using atomic layer epitaxy (ALE) technique were investigated by using capacitance–voltage (C–V) and photoluminescence (PL) measurements. C–V curves showed that the plateaus related to the zero-dimensional carrier confinement effect existed and that the number of electrons occupying the InAs QD was approximately 7. The full width at

J. H. Kim; Y. J. Park; Y. M. Park; J. D. Song; J. I. Lee; T. W. Kim

2007-01-01

27

The electrical and the optical properties of InAs\\/GaAs quantum dots (QDs) grown by using atomic layer epitaxy (ALE) technique were investigated by using capacitance voltage (C V) and photoluminescence (PL) measurements. C V curves showed that the plateaus related to the zero-dimensional carrier confinement effect existed and that the number of electrons occupying the InAs QD was approximately 7. The

J. H. Kim; Y. J. Park; Y. M. Park; J. D. Song; J. I. Lee; T. W. Kim

2007-01-01

28

NASA Astrophysics Data System (ADS)

The optical analysis of multilayer structures formed from the topmost layer of InGaAs/GaAs quantum rings (QRs) grown on a vertically stacked and laterally aligned InGaAs/GaAs quantum dot (QD) superlattice has been performed to elucidate the nature of the contribution from each layer. These hybrid structures representing a coupled QR chain layer and the layers of self-assembled QD chains display strong optical anisotropy. Unusually strong oscillations are observed in the circularly polarized photoluminescence (PL) intensities under magnetic field for emissions in the spectral range of the QD structure and these oscillations occur simultaneously with weaker oscillations related to the Aharonov-Bohm interference that modulates the emissions from the QR top layer of the structure. The behavior seen in the magneto-PL spectrum is interpreted in terms of joint effects associated to strain, spatial, and magnetic field confinements on the valence band states forming the magnetoexciton ground state of this multilayered structure. The result can be ascribed to a magnetically induced dark exciton contribution where the heavy-hole (type II) state becomes localized outside, whereas light-hole (type I) as well as electron states remain inside the spatial confinement area of the QD.

Lopes-Oliveira, Vivaldo; Mazur, Yuriy I.; de Souza, Leonardo Dias; Marçal, Lucas A. Bernardes; Wu, Jiang; Teodoro, Marcio Daldin; Malachias, Angelo; Dorogan, Vitaliy G.; Benamara, Mourad; Tarasov, Georgiy G.; Marega, Euclydes; Marques, Gilmar E.; Wang, Zhiming M.; Orlita, Milan; Salamo, Gregory J.; Lopez-Richard, Victor

2014-09-01

29

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

30

NASA Astrophysics Data System (ADS)

We investigate the excitation kinetics of a repulsive impurity doped quantum dot as the dopant is propagating. The study assumes importance because of its intimate connection with impurity drift in nanodevices. The problem has been made more realistic by considering the dopant propagation to be damped. For simplicity, we have considered an inherently linear motion of the dopant with a Gaussian potential. The damping strength and the dot confinement sources of electric and magnetic origin have been found to fabricate the said kinetics in a delicate way. The present study sheds light on how the individual or combined variation of different confinement sources could design the excitation kinetics in presence of damping. However, in the overdamped region, we find attainment of stabilization in the excitation rate. The present investigation is believed to provide some useful perceptions in the phenomenon of damping that has potential importance in nanoelectronic applications.

Pal, Suvajit; Ghosh, Manas

2013-09-01

31

NASA Astrophysics Data System (ADS)

Optically tunable mesoscale structures offer unparalleled potential for photonic device applications. Here, we report the creation of composite photonic structures consisting of CdSxSe1-x quantum dots (QDs) customized within lines, first written in a glass by femtosecond laser pulses. CdSxSe1-x-doped borosilicate glasses were pulsed with a fs-laser using a 473 kHz repetition rate to create chemically distinct microscopic regions. Upon further heat treatment, these regions served as "micro-crucibles" within which quantum dots were precipitated exclusively. These results open prospects of developing other semiconductor doped glasses for versatile photonic structures useful over broader optical wavelengths.

Mardilovich, Pavel; Yang, Lihmei; Huang, Huan; Krol, Denise M.; Risbud, Subhash H.

2013-04-01

32

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

33

POSSIBLE DEFINTION OF QUANTUM BITS IN COUPLED QUANTUM DOTS

POSSIBLE DEFINTION OF QUANTUM BITS IN COUPLED QUANTUM DOTS Robert H. Blick and Heribert Lorenz, 80539 Munich, Germany. ABSTRACT In this work we investigate laterally defined quantum dots confined interaction in these artificial molecules. We probe the wave function entanglement of two coupled quantum dots

Ludwig-Maximilians-UniversitÃ¤t, MÃ¼nchen

34

Understanding electronic systems in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

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

Ciftja, Orion

2013-11-01

35

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

36

Transport through graphene quantum dots

NASA Astrophysics Data System (ADS)

We review transport experiments on graphene quantum dots and narrow graphene constrictions. In a quantum dot, electrons are confined in all lateral dimensions, offering the possibility for detailed investigation and controlled manipulation of individual quantum systems. The recently isolated two-dimensional carbon allotrope graphene is an interesting host to study quantum phenomena, due to its novel electronic properties and the expected weak interaction of the electron spin with the material. Graphene quantum dots are fabricated by etching mono-layer flakes into small islands (diameter 60-350 nm) with narrow connections to contacts (width 20-75 nm), serving as tunneling barriers for transport spectroscopy. Electron confinement in graphene quantum dots is observed by measuring Coulomb blockade and transport through excited states, a manifestation of quantum confinement. Measurements in a magnetic field perpendicular to the sample plane allowed to identify the regime with only a few charge carriers in the dot (electron-hole transition), and the crossover to the formation of the graphene specific zero-energy Landau level at high fields. After rotation of the sample into parallel magnetic field orientation, Zeeman spin splitting with a g-factor of g ? 2 is measured. The filling sequence of subsequent spin states is similar to what was found in GaAs and related to the non-negligible influence of exchange interactions among the electrons.

Güttinger, J.; Molitor, F.; Stampfer, C.; Schnez, S.; Jacobsen, A.; Dröscher, S.; Ihn, T.; Ensslin, K.

2012-12-01

37

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

38

NASA Astrophysics Data System (ADS)

We demonstrate in this work controllable synthesis of cubic InN nanocrystals` through Mn doping. We show that the pristine nanocrystal has the wurtzite structure, but can be converted into the zinc-blende (ZB) structure when it is doped with Mn. Our first-principles calculations show that the phase transition is caused by the stronger p-d coupling between the host p valence state and the impurity d level in the ZB structure, which makes the hole generation in the ZB structure easier. Quantum confinement in the nanocrystals further enhanced this effect. This observation lays an important foundation for defects control of crystal phases.

Meng, Xiuqing; Chen, Zhanghui; Chen, Zhuo; Wu, Fengmin; Li, Shu-Shen; Li, Jingbo; Wu, Junqiao; Wei, Su-Huai

2013-12-01

39

We demonstrate in this work controllable synthesis of cubic InN nanocrystals through Mn doping. We show that the pristine nanocrystal has the wurtzite structure, but can be converted into the zinc-blende (ZB) structure when it is doped with Mn. Our first-principles calculations show that the phase transition is caused by the stronger p-d coupling between the host p valence state and the impurity d level in the ZB structure, which makes the hole generation in the ZB structure easier. Quantum confinement in the nanocrystals further enhanced this effect. This observation lays an important foundation for defects control of crystal phases.

Meng, Xiuqing; Wu, Fengmin [Zhejiang Normal University, Jinhua, Zhejiang Province 321004 (China)] [Zhejiang Normal University, Jinhua, Zhejiang Province 321004 (China); Chen, Zhanghui; Li, Shu-Shen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China)] [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Chen, Zhuo [Department of Physics, Beijing Institute of Technology, Beijing 100081 (China)] [Department of Physics, Beijing Institute of Technology, Beijing 100081 (China); Li, Jingbo, E-mail: jbli@semi.ac.cn, E-mail: swei@nrel.gov [Zhejiang Normal University, Jinhua, Zhejiang Province 321004 (China) [Zhejiang Normal University, Jinhua, Zhejiang Province 321004 (China); State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Wu, Junqiao [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States)] [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Wei, Su-Huai, E-mail: jbli@semi.ac.cn, E-mail: swei@nrel.gov [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

2013-12-16

40

Electrochromic Nanocrystal Quantum Dots

NASA Astrophysics Data System (ADS)

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 of the narrow band-edge photoluminescence. Reversible switching of these optical properties of nanocrystals by the convenient electrochemical method has been demonstrated for the first time. This approach opens the road to a new class of electrochromic materials with unique properties that may find applications in infrared communication, "night-vision," and display technology. More broadly, the redox properties of molecules have been extended to semiconductor "artificial atoms."

Wang, Congjun; Shim, Moonsub; Guyot-Sionnest, Philippe

2001-03-01

41

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

42

We have designed, fabricated, and characterized an InP photonic crystal slab structure that supports a cavity-confined slow-light mode, i.e. a bandgap-confined valence band-edge mode. Three dimensional finite difference in time domain calculations predict that this type of structure can support electromagnetic modes with large quality factors and small mode volumes. Moreover these modes are robust with respect to fabrication imperfections. In this paper, we demonstrate room-temperature laser operation at 1.5 mum of a cavity-confined slow-light mode under pulsed excitation. The gain medium is a single layer of InAs/InP quantum dots. An effective peak pump power threshold of 80 microW is reported. PMID:19333310

Bordas, Frédéric; Seassal, Christian; Dupuy, Emmanuel; Regreny, Philippe; Gendry, Michel; Viktorovitch, Pierre; Steel, M J; Rahmani, Adel

2009-03-30

43

Quantum versus classical hyperfine-induced dynamics in a quantum dot* W. A. Coisha

Quantum versus classical hyperfine-induced dynamics in a quantum dot* W. A. Coisha and Daniel Loss spin dynamics for electrons confined to semiconductor quantum dots due to the contact hyperfine.1063/1.2722783 I. INTRODUCTION Prospects for future quantum information processing with quantum-dot

Yuzbashyan, Emil

44

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

Vukmirovic, Nenad; Wang, Lin-Wang

2009-11-10

45

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

46

Quantum Monte Carlo study of quantum dots in magnetic fields

We have studied the ground state energies and quantum numbers of confined two-dimensional (2D) electrons in weak and intermediate magnetic field strengths using quantum Monte Carlo methods. These 2D quantum dots are of theoretical interest, because it is possible to go from a weakly to a strongly correlated system by tuning the relative strength of the external potential to the

Wolfgang Geist; Lang Zeng; Mei-Yin Chou

2004-01-01

47

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

48

A quantum dot heterojunction photodetector

This thesis presents a new device architecture for photodetectors utilizing colloidally grown quantum dots as the principle photo-active component. We implement a thin film of cadmium selenide (CdSe) quantum dot sensitizers, ...

Arango, Alexi Cosmos, 1975-

2005-01-01

49

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

50

Quantum dot device tunable from single to triple dot system

We present a lateral quantum dot device which has a tunable number of quantum dots. Depending on easily tunable gate voltages, one, two or three quantum dots are found. They are investigated in transport and charge detection.

Rogge, M. C.; Haug, R. J. [Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstrasse 2, 30167 Hannover (Germany); Pierz, K. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

2013-12-04

51

Numerical simulation of a laterally confined double dot with tunable interaction potential

Recent technological advances have allowed for the construction of small (on the order of 100-1000 nm) systems of confined electrons called quantum dots. Often kept within semiconductor heterostructures, these systems are ...

Finck, Aaron David Kiyoshi

2005-01-01

52

NASA Astrophysics Data System (ADS)

Magneto-LO-polaron in a cylindrical GaAs0.9P0.1/GaAs0.6P0.4 quantum dot is studied taking into consideration of geometrical confinement. The effect of phonon on the exciton binding energy is computed applying variational method within the single band effective mass approximation numerically. And the nonlinear optical properties with the incident photon energy are investigated in the presence of magnetic field strength and the phonon effect using compact density matrix method. Optical susceptibilities of generation of second and third harmonic as a function of incident energy for a confined exciton in the presence of magnetic field strength in a GaAsP quantum dot with and without the phonon effect are carried out. Our results show that the second and third harmonic generations have influence on the effects of geometrical confinement, the phonon and the magnetic field strength.

Vinolin, Ada; John Peter, A.; Lee, Chang Woo

2014-11-01

53

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

54

Quantum dot infrared photodetectors

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

55

NASA Astrophysics Data System (ADS)

Among recent proposals for next-generation, non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate voltages (Rev. Mod. Phys.79, 1217 (2007)). In this talk we present numerical simulations of Berry Phase of electron spins in single electron devices for realistic asymmetric confining potentials in support of experimental work at the University at Albany, State University of New York aimed at the practical development of post-CMOS concepts and devices. We solve the Schr"odinger equation including spin-orbit effects using a numerical finite-element based technique. We will discuss the calculation of Berry Phase for electrons (Phys. Rev. B 73, 125330 (2006)) in electrostatically defined quantum dots including the Rashba and Dresselhaus spin-orbit interactions computed numerically from realistic asymmetric confining potentials. The new simulation results open the possibility of spin manipulation through the gate induced Berry phase. This work is supported through funding from the DARPA/NRI INDEX center.

Prabhakar, Sanjay; Raynolds, James

2009-03-01

56

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

2014-01-01

57

Quantum optics of a quantum dot: Local-field effects G. Ya. Slepyan* and S. A. Maksimenko

Quantum optics of a quantum dot: Local-field effects G. Ya. Slepyan* and S. A. Maksimenko Institute electrodynamics of isolated quantum dot QD has been analyzed. The system is modeled as a strongly confined properties of quantum dots QDs is currently an area of active investigation owing to promis- ing potential

Nabben, Reinhard

58

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

59

Correlated electrons in coupled quantum dots and related phenomena

NASA Astrophysics Data System (ADS)

Three topics related to correlated electrons in coupled quantum dots are discussed. The first is quasi-resonance between multi-electron states, which causes hitherto unremarked types of resonant absorption in coupled quantum dots. The second is electron tunneling through a Hubbard gap, which is induced by an increase in the density of electrons in a quantum-dot chain under an overall confining potential. The third is Mott transition in a two-dimensional quantum-dot array induced by an external electric field. In this system, the metal-insulator transition goes through a heavy electron phase in which the density of correlated electrons fluctuates.

Ugajin, Ryuichi

1998-01-01

60

Adiabatic description of nonspherical quantum dot models

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

61

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.

National Science Foundation GK-12 and Research Experience for Teachers (RET) Programs,

62

Quantum Computing with Quantum Dots

NASA Astrophysics Data System (ADS)

We report recent results on the spin dynamics of coupled quantum dots and their potential as quantum computer devices. Using the Heitler-London approach, we obtain the exchange coupling J(B,a) between the excess electrons of coupled dots.(D.P. DiVincenzo and D. Loss, Quantum Computation is Physical), to appear in Superlattices and Microstructures. Special Issue on the occasion of Rolf Landauer's 70th Birthday, ed. S. Datta. See cond- mat/9710259. The dependence of J on the magnetic field B and the interdot distance 2a is of great importance for controlling the coherent time-evolution of the two-spin system as required for quantum computation.(D. Loss and D.P. DiVincenzo, Phys. Rev. A, in press. See cond- mat/9701055.) Our result, which is in good agreement with a more refined LCAO calculation, is accessible to experimental tests via magnetic response measurements.

Burkard, Guido; Loss, Daniel

1998-03-01

63

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

64

Zeno Quantum Gates in Semiconductor Quantum Dots

We propose a scheme for a two-qubit conditional phase gate by quantum Zeno effect with semiconductor quantum dots. The system consists of two charged dots and one ancillary dot that can perform Rabi oscillations under a resonant laser pulse. The quantum Zeno effect is induced by phonon-assisted exciton relaxation between the ancillary dot and the charged dots, which is equivalent to a continuous measurement. We solve analytically the master equation and simulate the dynamics of the system using a realistic set of parameters. In contrast to standard schemes, larger phonon relaxation rates increase the fidelity of the operations.

K. J. Xu; Y. P. Huang; M. G. Moore; C. Piermarocchi

2008-10-24

65

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

66

Quantum Monte Carlo studies of quantum dots in magnetic fields

We have studied the ground and excited states of confined two-dimensional (2D) electrons in various magnetic field strengths by the variational and diffusion Monte Carlo methods. These 2D quantum dots are of great theoretical interest, because it is possible to go from a weakly to a strongly correlated system by tuning the relative strength of the external potential to the

Wolfgang Geist; Lang Zeng; Mei-Yin Chou; Cyrus Umrigar; Francesco Pederiva

2003-01-01

67

Optical Aharonov-Bohm effect on Wigner molecules in type-II semiconductor quantum dots

We theoretically examine the magnetoluminescence from a trion and a biexciton in a type-II semiconductor quantum dot, in which holes are confined inside the quantum dot and electrons are in a ring-shaped region surrounding the quantum dot. First, we show that two electrons in the trion and biexciton are strongly correlated to each other, forming a Wigner molecule: Since the

Rin Okuyama; Mikio Eto; Hiroyuki Hyuga

2011-01-01

68

Single hole quantum dot transistors in silicon Effendi Leobandung, Lingjie Guo, and Stephen Y-dot transistors were fabricated in silicon-on-insulator. Strong oscillations in the drain current as a function third from the quantum confinement effect. The realization of single hole quantum-dot transistors opens

69

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

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. PMID:21314178

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

2011-01-01

70

1 Quantum Dot Applications forQuantum Dot Applications for Flash Memory, SemiconductorFlash Memory cell #12;3 5 Quantum dots and highQuantum dots and high--K tunnelingK tunneling oxide reduce size and quantum dots 6 HighHigh--K tunneling layerK tunneling layer Replace current materials with a high

Lightsey, Glenn

71

Quantum soldering of individual quantum dots.

Making contact to a quantum dot: Single quantum-dot electronic circuits are fabricated by wiring atomically precise metal chalcogenide clusters with conjugated molecular connectors. These wired clusters can couple electronically to nanoscale electrodes and be tuned to control the charge-transfer characteristics (see picture). PMID:23135896

Roy, Xavier; Schenck, Christine L; Ahn, Seokhoon; Lalancette, Roger A; Venkataraman, Latha; Nuckolls, Colin; Steigerwald, Michael L

2012-12-01

72

An optically driven quantum dot quantum computer

We propose a quantum computer structure based on coupled asymmetric single-electron quantum dots. Adjacent dots are strongly coupled by means of electric dipole-dipole interactions enabling rapid computation rates. Further, the asymmetric structures can be tailored for a long coherence time. The result maximizes the number of computation cycles prior to loss of coherence.

G. D. Sanders; K. W. Kim; W. C. Holton

1999-09-22

73

Self-assembly Drives Quantum Dot Photoluminescence

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

74

Quantum dot strain engineering of InAs/InGaAs nanostructures L. Seravalli,a

and the confining layers' composition, the energy gap of the quantum dot material and the band discontinuities-assembled islands embedded in layers of semiconductor materials with larger energy gap and suitable band.55 m the room-temperature light emission of InAs quantum dots embedded in InGaAs confining layers grown

75

Photoionization cross sections of atomic impurities in spherical quantum dots

NASA Astrophysics Data System (ADS)

Quantum dots with atomic impurities have attracted considerable attention due to not only its theoretical but also practical significance. The confinement potentials associated with the structure of quantum dots are often described by the rectangular potential well or harmonic oscillator potential. However, the non-parabolic shape at the center for the rectangular well and the infinite depth for the harmonic oscillator potential make the models unrealistic in practical applications. Recently, the finite oscillator and Gaussian potentials are proposed to mimic the spherical quantum dots, which are defined respectively as VFO(r)=-A(1+Br / Br ?A . - ?A )(-Br / Br ?A . - ?A ) and VG(r)=-C(-r^2 / -r^2 D^2 . - D^2) with the confining strengths A and C, and the radii of quantum dots 1/B and D. In this work, the method of complex-coordinate rotation in the finite-element discrete variable representation is implemented to study the photoionization of atomic impurities in spherical quantum dots. We explore the energy spectra and photoionization of atomic impurities influenced by the quantum confinement. The shifting of Cooper minima caused by the quantum confinement is observed.

Lin, Chih-Yuan; Ho, Y. K.

2012-02-01

76

-mass confinement. In graphene dots, edge magnetization might produce such an effective mass term at the edgesSymmetry Classes in Graphene Quantum Dots: Universal Spectral Statistics, Weak Localization August 2008; published 6 February 2009) We study the symmetry classes of graphene quantum dots, both open

Baranger, Harold U.

77

processes in quantum dots coupled to field-effect transistors Farhan Rana Department of Electrical that are a consequence of quantum confinement and Coulomb blockade. A quantum dot coupled to a metal. The memory state of this unit cell is a function of the number of electrons stored in the quantum dot

Afshari, Ehsan

78

Quantum dot sensitized solar cells

Metal sulfide (CdS or PbS) quantum dots were synthesized in nanoporous TiO2 films for applications in solar energy conversion devices. Several electrolytes were investigated for the functioning redox activity in sandwich type regenerative solar cells, based on the quantum dots sensitized TiO2 film. A high IPCE was attained by optimizing the polysulfide electrolyte composition. The CdS QD shows a higher

Y. Tachibana; H. Y. Akiyama; K. Umekita; Y. Otsuka; T. Torimoto; S. Kuwabata

2008-01-01

79

Negative U Molecular Quantum Dot

While the correlated transport in mesoscopic systems with repulsive electron-electron correlations received considerable attention\\u000a in the past, and continues to be the focus of intense investigations, much less has been known about a role of attractive correlations in molecular nanowires and quantum dots. Here a negative-U Hubbard model of a d -fold degenerate quantum dot is reviewed. The attractive electron

A. S. Alexandrov

80

Energy levels in self-assembled quantum arbitrarily shaped dots.

A model to determine the electronic structure of self-assembled quantum arbitrarily shaped dots is applied. This model is based principally on constant effective mass and constant potentials of the barrier and quantum dot material. An analysis of the different parameters of this model is done and compared with those which take into account the variation of confining potentials, bands, and effective masses due to strain. The results are compared with several spectra reported in literature. By considering the symmetry, the computational cost is reduced with respect to other methods in literature. In addition, this model is not limited by the geometry of the quantum dot. PMID:15740390

Tablero, C

2005-02-01

81

Size-dependent band gap of colloidal quantum dots

The size-dependent band gap of semiconductor quantum dots is a well-known and widely studied quantum confinement effect. In order to understand the size-dependent band gap, different theoretical approaches have been adopted, including the effective-mass approximation with infinite or finite confinement potentials, the tight-binding method, the linear combination of atomic orbitals method, and the empirical pseudopotential method. In the present work

Sotirios Baskoutas; Andreas F. Terzis

2006-01-01

82

Quantum buses and quantum computer architecture based on quantum dots

We propose a quantum computer architecture based on quantum dots both for short distance and for long distance communication/computation. Our scheme exploits the natural characteristics of self-assembled quantum dots and it is scalable. It is centered on the idea of a quantum bus based on semiconductor self-assembled quantum dots. This allows for transmission of qubits between the different quantum registers, and could be integrated in most of the present proposal for semiconductor quantum dot-based quantum computation. Our proposal exploits the peculiar properties of {\\it relatively short} spin-chains, and advantages and disadvantages of two possible implementations, both based on spin-chain global dynamics, are discussed in details. A clear advantage of the scheme is to avoid the use of microcavities for long distance communication between different elements of the quantum computer. In this respect our scheme is comparatively faster than hybrid quantum dot-microcavity schemes.

Irene D'Amico

2005-11-18

83

Charge controlled optical switching in nanocrystal quantum dots

NASA Astrophysics Data System (ADS)

Electron injection into quantum confined conduction band of semiconductor nanocrystal quantum dot colloids and films is reversibly controlled by applying an electrochemical potential. This has led to charge-tunable optical switching in nanocrystal quantum dots, including a complete bleach in visible interband transition, strong midinfrared intraband absorption, and significant quenching of the photoluminescence. The observed optical properties of nanocrystal quantum dot colloids and thin films are novel and unique with strong and rapid electrochromic changes occurring in narrow and tunable spectral response covering both the visible and midinfrared. Redox concepts have also been extended to these nanometer-sized "artificial atoms." A spectroelectrochemical method has been used to measure the size-dependent reduction potentials of nanocrystal quantum dots.

Wang, Congjun; Shim, Moonsub; Guyot-Sionnest, Philippe

2002-03-01

84

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

85

All inorganic colloidal quantum dot LEDs

This thesis presents the first colloidal quantum dot light emitting devices (QD-LEDs) with metal oxide charge transport layers. Colloidally synthesized quantum dots (QDs) have shown promise as the active material in ...

Wood, Vanessa Claire

2007-01-01

86

from a resonantly driven quantum- dot transition. The Mollow triplet8 in the scattered photon spectrum above the higher-lying confined states of the quantum dot. This excitation method leads to photon-emission-time computing algorithms15 , even if the quantum dot is coupled to a cavity. In an attempt to both address

Loss, Daniel

87

Clocked molecular quantum-dot cellular automata

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

88

Nanometer Distance Measurements between Multicolor Quantum Dots

Nanometer Distance Measurements between Multicolor Quantum Dots Josh Antelman, Connie Wilking at Los Angeles, Los Angles, California 90095 Received April 10, 2009 ABSTRACT Quantum dot dimers made of short double-stranded DNA molecules labeled with different color quantum dots at each end were imaged

Michalet, Xavier

89

Probing the Cytotoxicity of Semiconductor Quantum Dots

Probing the Cytotoxicity of Semiconductor Quantum Dots Austin M. Derfus, Warren C. W. Chan With their bright, photostable fluorescence, semiconductor quantum dots (QDs) show promise as alternativesSe-core quantum dots are an example of a nanomaterial that has been shown to be useful as an alternative

Bhatia, Sangeeta

90

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

91

The quantum confined Stark effect in silicon nanocrystals.

The quantum confined Stark effect (QCSE) in Si nanocrystals embedded in a SiO(2) matrix is demonstrated by photoluminescence (PL) spectroscopy at room and cryogenic temperatures. It is shown that the PL peak position shifts to higher wavelengths with increasing applied electric field, which is expected from carrier polarization within the quantum dots. It is observed that the effect is more pronounced at lower temperatures due to the improved carrier localization at the lowest energy states of the quantum dots. Experimental results are shown to be in good agreement with phenomenological model developed for the QCSE model. PMID:21832777

Kulakci, Mustafa; Serincan, Ugur; Turan, Rasit; Finstad, Terje G

2008-11-12

92

Spin pumping through quantum dots

NASA Astrophysics Data System (ADS)

We propose schemes for generating spin currents into a semiconductor by adiabatic or non-adiabatic pumping of electrons through interacting quantum dots. The appeal of such schemes lies in the possibility to tune the pumping characteristics via gate voltages that control the properties of the quantum dot. The calculations are based on a systematic perturbation expansion in the tunnel-coupling strength and the pumping frequency, expressed within a diagrammatic real-time technique. Special focus is put on the possibility of pure spin pumping, i.e., of pumping spin currents without charge currents.

Rojek, Stephan; Governale, Michele; König, Jürgen

2014-09-01

93

Coherent Electron Spin Dynamics in Quantum Dots

NASA Astrophysics Data System (ADS)

The coherent spin dynamics of electrons in confined in quantum dots is discussed. A new measurement technique, mode-locking of electron spin precession by and with a pulsed excitation laser is used to address the coherence, which otherwise would be masked in ensemble studies by dephasing. The background of nuclei leads to a refocusing such that all optically excited electron spins become synchronized with the laser. With this tool spin coherence times in the microseconds range are demonstrated at cryogenic temperatures. The mode locking can be tailored by the laser excitation protocol such that strong signals at arbitrary times can be generated in Faraday rotation experiments.

Bayer, Manfred; Greilich, Alex; Yakovlev, Dmitri R.

94

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

95

Quantum dot in a graphene layer with topological defects

NASA Astrophysics Data System (ADS)

In this paper we use an exactly solvable model in order to investigate a magnetization and persistent current of massless Dirac fermions confined in a quantum dot in a graphene layer with a topological defect. We study the low-energy electronic spectrum of a graphene layer structure using the continuum approach and introduce a disclination by means of the geometric theory of defects. The model of the confining potential is introduced into the system via the Dirac oscillator, which provides a harmonic confinement for quasiparticles, in order to study a behaviour of quantum dots in graphene. The exact energy spectrum and wave functions are obtained analytically for the model, in the case where a thin magnetic flux confined to the dot centre, and the arising of persistent currents is investigated. A uniform magnetic field is introduced in a quantum dot, and this model is used to study persistent currents and magnetization in the graphene dot. We have derived exact expressions both for the magnetic moment and for the current carried by quasiparticle states.

Bueno, M. J.; Lemos de Melo, J.; Furtado, Claudio; de M. Carvalho, Alexandre M.

2014-09-01

96

Optical Fiber Sensing Using Quantum Dots

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

Jorge, Pedro; Martins, Manuel Antonio; Trindade, Tito; Santos, Jose Luis; Farahi, Faramarz

2007-01-01

97

Charge transfer magnetoexciton formation at vertically coupled quantum dots

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

2012-01-01

98

Quantum phase transition in a single-molecule quantum dot

LETTERS Quantum phase transition in a single-molecule quantum dot Nicolas Roch1 , Serge Florens1 demonstrate this possibility in a single-molecule quantum dot, where a gate voltage induces a crossing of two dif- ferent types of electron spin state (singlet and triplet) at zero magnetic field. The quantum dot

Canet, LÃ©onie

99

Fabrication Methods for Positioning of Quantum Dots

NASA Astrophysics Data System (ADS)

Quantum dot positioning is highly useful in terms of integrating nanoemitters into nanostructures, such as nanocavities and quantum dot waveguides. Demonstration of control over the positioning of quantum dots has proven difficult, and consequently construction of single-photon emitting systems has been hindered. We report the ability to reliably position nanoscale functional objects, specifically quantum dots, within a well-defined location. Programmed assembly of DNA linked quantum dots on both gold and silver substrates is obtained by Electron Beam Lithography patterning and a series of surface chemical functionalizations. A single quantum dot was successfully positioned within 100 nm of the desired location in 36 percent of the experiments. Furthermore, the method was completely reproducible within 500 nm accuracy. This method has the potential to functionalize quantum dots in even smaller pattern sizes.

Kramer, Rebecca; Oulton, Rupert; Sorger, Volker; Pholchai, Nitipat; Zhang, Xiang

2009-03-01

100

Reduced surface sidewall recombination and diffusion in quantum-dot lasers

We examine the surface recombination rate in quantum-dot semiconductor lasers and determine the diffusion length (1.0 mum) and, for the first time, provide a value for surface recombination velocity (5times104 cm\\/s) in quantum-dot material. As a result of strong carrier confinement in the dots, these values are much lower than in comparable quantum-well lasers (5times105 cm\\/s and 5 mum, respectively)

Stephen A. Moore; Liam O'Faolain; Maria Ana Cataluna; Michael B. Flynn; Maria V. Kotlyar; Thomas F. Krauss

2006-01-01

101

Quantum dot-based theranostics

Luminescent semiconductor nanocrystals, also known as quantum dots (QDs), have advanced the fields of molecular diagnostics and nanotherapeutics. Much of the initial progress for QDs in biology and medicine has focused on developing new biosensing formats to push the limit of detection sensitivity. Nevertheless, QDs can be more than passive bio-probes or labels for biological imaging and cellular studies. The

Yi-Ping Ho; Kam W. Leong

2010-01-01

102

Deformation potential dominated phonons in ZnS quantum dots

Strong deformation potential (DP) dominated Raman spectra are reported for quantum confined cubic ZnS nanoclusters under off-resonance conditions allowed only in quantum dots. A flurry of zone boundary phonons is demonstrated in the scattering process. Transverse optic (TO) mode in the multi-phonon process shows only even order overtones suggesting the dominance of a two-phonon process (having large DP value in ZnS) and its integral multiples. Two-phonon TO modes corresponding to A1 and B2 symmetries are also demonstrated under off-resonance conditions which are allowed only in quantum dots.

S. Dhara; A. K. Arora; Jay Ghatak; K. H. Chen; C. P. Liu; L. C. Chen; Y. Tzeng; Baldev Raj

2007-09-12

103

Resonant tunneling quantum-dot diodes - Physics, limitations, and technological prospects

NASA Astrophysics Data System (ADS)

The authors discuss the electronic structure and properties of the present generation of resonant-tunneling quantum-dot structures. Quantum dots are zero-dimensional semiconductor nanostructures, i.e., structures in which an electron is quantum-mechanically confined in all three spatial dimensions. Quantum dots appear to represent a viable structure to allow the continued downscaling of critical circuit geometries beyond the currently perceived limits for conventional VLSI devices. As they are currently fabricated, however, quantum-dot diodes have impediments which prevent the full realization of their potential. The authors assess these limitations and discuss measures for their solution.

Luscombe, James H.; Randall, John N.; Bouchard, Ann Marie

1991-08-01

104

A statistical model of quantum dot arrays with Coulomb coupling

We present a study of a statistical model of arrays of quantum dots, in which electrons are confined by semiconductor heterojunctions in all three dimensions, with Coulomb coupling. Our model describes repulsively interacting localized electrons whose number can vary with changes in chemical potential. By means of a Monte Carlo simulation, it is shown that, at low temperatures, some stable

Toshi-Kazu Suzuki; Kazumasa Nomoto; Ryuichi Ugajin; Ichiro Hase

1995-01-01

105

CORRELATIONS IN CONFINED QUANTUM PLASMAS

This is the final report for the project 'Correlations in Confined Quantum Plasmas', NSF-DOE Partnership Grant DE FG02 07ER54946, 8/1/2007 - 7/30/2010. The research was performed in collaboration with a group at Christian Albrechts University (CAU), Kiel, Germany. That collaboration, almost 15 years old, was formalized during the past four years under this NSF-DOE Partnership Grant to support graduate students at the two institutions and to facilitate frequent exchange visits. The research was focused on exploring the frontiers of charged particle physics evolving from new experimental access to unusual states associated with confinement. Particular attention was paid to combined effects of quantum mechanics and confinement. A suite of analytical and numerical tools tailored to the specific inquiry has been developed and employed

DUFTY J W

2012-01-11

106

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

Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots C. Robert,1,a) M. O of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix

Boyer, Edmond

107

NASA Astrophysics Data System (ADS)

This work presents an experimental method to tune the degree of heavy-hole (HH) and light-hole (LH) mixing of the ground state of quantum dots (QDs). A ferroelectric crystal is used to apply reversible anisotropic biaxial stress to thin nanomembranes, containing GaAs/AlGaAs QDs. The stress-induced modification of the QD anisotropy leads to a change of the relative intensity of the two emission lines produced by the recombination of neutral bright excitonic states. Such a change is ascribed to a variation of the degree of HH-LH mixing. At the same time the modified anisotropy produces a change of the excitonic fine structure splitting (FSS). Model calculations provide a qualitative insight into the relation between strain, HH-LH mixing, and the FSS in epitaxial GaAs/AlGaAs QDs.

Plumhof, J. D.; Trotta, R.; K?ápek, V.; Zallo, E.; Atkinson, P.; Kumar, S.; Rastelli, A.; Schmidt, O. G.

2013-02-01

108

Hybrid LSDA\\/Diffusion Quantum Monte-Carlo Method for Spin Sequences in Vertical Quantum Dots

We present an new hybrid Diffusion Quantum Monte-Carlo (DQMC)\\/Local Spin Density Approximation (LSDA) method, to compute the electronic structure of vertical quantum dots (VQD). The exact many-body electronic configuration is computed with a realistic confining potential. Our model confirms the atomic-like model of 2D shell structures obeying Hund's rule already predicted by LSDA.

P. Matagne; T. Wilkens; J. P. Leburton; R. Martin

2002-01-01

109

Spin-Orbit Effects in Coupled Quantum Dots

NASA Astrophysics Data System (ADS)

While in some materials, such as GaAs, the spin-orbit (SOE) effects are of relatively minor importance, it has been recently shown that they are very important for quantum dots in materials with narrow gap and small effective-mass electrons [1]. Then, spin and orbital enginnering could be more easily achieved with these materials. Coupled dots, due to the double-well confinement potential, are expected to show even stronger effects, which might be useful in the design of quantum computers and spintronic devices. Here we study SOE in pairs of coupled-dots. Competition between the terms derived from the confinement potential, magnetic field and their effects on the single- and two-particle spectra are analyzed. Circular quantum dots are considered and geometrics aspects of the confinement such as barrier height, separation between the dots, etc., are varied. The single-particle wave functions are determined for a given geometry using the finite-element method. Additional terms in the Hamiltonian are considered within a full-diagonalization scheme. and include different SOE, as well as Coulomb interactions in the case of multiple electrons. [1] See C.F. Destefani, et. al., cond-mat/0307027 and references therein.

Meza-Montes, Lilia; Ulloa, Sergio. E.

2004-03-01

110

Electron states in semiconductor quantum dots.

In this work, the electronic structures of quantum dots (QDs) of nine direct band gap semiconductor materials belonging to the group II-VI and III-V families are investigated, within the empirical tight-binding framework, in the effective bond orbital model. This methodology is shown to accurately describe these systems, yielding, at the same time, qualitative insights into their electronic properties. Various features of the bulk band structure such as band-gaps, band curvature, and band widths around symmetry points affect the quantum confinement of electrons and holes. These effects are identified and quantified. A comparison with experimental data yields good agreement with the calculations. These theoretical results would help quantify the optical response of QDs of these materials and provide useful input for applications. PMID:25429952

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

2014-11-28

111

Semiconductor quantum dot-sensitized solar cells

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

Tian, Jianjun; Cao, Guozhong

2013-01-01

112

The influence of bio-conjugation on photoluminescence of CdSe/ZnS quantum dots

NASA Astrophysics Data System (ADS)

We report a considerable blue shift in the luminescence spectra of CdSe/ZnS quantum dots conjugated to anti-interleukin-10 antibodies. This phenomenon can be explained theoretically by accounting for bio-conjugation as a process causing electrostatic interaction between a quantum dot and an antibody, which reduces effective volume of the dot core. To solve the Schrödinger equation for an exciton confined in the quantum dot, we use mirror boundary conditions that were successfully tested for different geometries of quantum wells.

Torchynska, Tetyana V.; Vorobiev, Yuri V.; Makhniy, Victor P.; Horley, Paul P.

2014-11-01

113

Quantitative multiplexed quantum dot immunohistochemistry

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

Sweeney, E.; Ward, T.H. [Clinical and Experimental Pharmacology, Paterson Institute for Cancer Research, Wilmslow Road, Manchester, 420 4BX (United Kingdom); Gray, N.; Womack, C. [AstraZeneca, Alderley Park, Macclesfield, Cheshire, SK10 4TG (United Kingdom); Jayson, G. [Translational Angiogenesis Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester, M20 4BX (United Kingdom); Hughes, A. [AstraZeneca, Alderley Park, Macclesfield, Cheshire, SK10 4TG (United Kingdom); Dive, C. [Clinical and Experimental Pharmacology, Paterson Institute for Cancer Research, Wilmslow Road, Manchester, 420 4BX (United Kingdom); Byers, R. [School of Cancer and Imaging Studies, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT (United Kingdom); Department of Histopathology, Manchester Royal Infirmary, Oxford Road, Manchester, M13 9WL (United Kingdom)], E-mail: richard.byers@cmmc.nhs.uk

2008-09-19

114

Nanobeam photonic crystal cavity quantum dot laser

Nanobeam photonic crystal cavity quantum dot laser Yiyang Gong*, Bryan Ellis, Gary Shambat, Tomas). 6. B. Ellis, I. Fushman, D. Englund, B. Zhang, Y. Yamamoto, and J. VuckoviÂ´c, "Dynamics of Quantum. Badolato, L. C. Andreani, E. L. Hu, P. M. Petroff, and D. Bouwmeester, "Self-Tuned Quantum Dot Gain

Vuckovic, Jelena

115

Quantum-Dot Cellular Automata Konrad Walus

Quantum-Dot Cellular Automata (QCA) Konrad Walus UBC Electrical and Computer Engineering #12;QCA full advantage of molecular scales Where is the benefit of small? #12;Fabricated QCA Devices "dot" = metal island electrometers 70-300 mK Al/AlOx on SiO2 Metal-dot QCA implementation #12;QCA Â· Nonlinear

Plotkin, Steven S.

116

Synthesis and applications of quantum dots and magnetic quantum dots

NASA Astrophysics Data System (ADS)

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 Zn 1-xCd xSe 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 QDs is simple and cost-effective compared to the conventional organometallic approaches. It can be easily scaled up for the commercial production of alloyed nanocrystals of various compositions. We have also demonstrated the fabrication of magnetic quantum dots (MQDs) through a seed-mediated approach. The formation and assembly of these bifunctional nanocomposites have been elucidated by high-resolution transmission electron microscopy (HRTEM). The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components in this hybrid system. We have created biocompatible silica-coated MQDs that effectively target the cell membranes.

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

2008-02-01

117

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

118

Optical properties of wurtzite and zinc-blende GaNAlN quantum dots Vladimir A. Fonoberova)

progress in GaN technology has led to an increasing number of publications on fabrication2-blende GaN/AlN quantum dots with heights from 1.5 to 4.5 nm. The quantum dot size corresponds to the strong quantum confinement regime. It has been established that the built-in piezoelectric field at the GaN

Fonoberov, Vladimir

119

Correlation energy of anisotropic quantum dots

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

Zhao Yan; Loos, Pierre-Francois; Gill, Peter M. W. [Research School of Chemistry, Australian National University, Canberra, ACT 0200 (Australia)

2011-09-15

120

Ultranarrow Luminescence Lines from Single Quantum Dots

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

121

Dynamics of Quantum Dot Photonic Crystal Lasers

Quantum dot photonic crystal membrane lasers were fabricated and the large signal modulation characteristics were studied. We find that the modulation characteristics of quantum dot lasers can be significantly improved using cavities with large spontaneous emission coupling factor. Our experiments show, and simulations confirm, that the modulation rate is limited by the rate of carrier capture into the dots to around 30GHz in our present system.

Bryan Ellis; Ilya Fushman; Dirk Englund; Bingyang Zhang; Yoshihisa Yamamoto; Jelena Vuckovic

2007-03-07

122

Single Quantum Dots as Local Temperature Markers

of this technique could go down to the size of a single quantum dot using far-field optics for temperature, a thermocouple has a spatial resolution of 100 Âµm and a temperature-sensitive paint of 1 Âµm.3,4 Recently, submi We propose in this work to use semiconductor nanocrystalline particles or quantum dots (QDs

Lin, Liwei

123

Theory of random population for quantum dots

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

124

Thick-shell nanocrystal quantum dots

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

125

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

126

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

127

QCAD Simulation and Optimization of Semiconductor Quantum Dots

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.

Xujiao Gao; Erik Nielsen; Richard P. Muller; Ralph W. Young; Andrew G. Salinger; Nathan C. Bishop; Michael P. Lilly; Malcolm S. Carroll

2014-03-28

128

Quantum measurement of coherent tunneling between quantum dots

NASA Astrophysics Data System (ADS)

We describe the conditional and unconditional dynamics of two coupled quantum dots when one dot is subjected to a measurement of its occupation number by coupling it to a third readout dot via the Coulomb interaction. The readout dot is coupled to source and drain leads under weak bias, and a tunnel current flows through a single bound state when energetically allowed. The occupation of the quantum dot near the readout dot shifts the bound state of the readout dot from a low conducting state to a high conducting state. The measurement is made by continuously monitoring the tunnel current through the readout dot. We show that there is a difference between the time scale for the measurement-induced decoherence between the localized states of the dots, and the time scale on which the system becomes localized due to the measurement.

Wiseman, H. M.; Utami, Dian Wahyu; Sun, He Bi; Milburn, G. J.; Kane, B. E.; Dzurak, A.; Clark, R. G.

2001-06-01

129

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

130

Quantum Optics: Colloidal Fluorescent Semiconductor Nanocrystals (Quantum Dots)

U ncorrected Proof Chapter 3 Quantum Optics: Colloidal Fluorescent Semiconductor Nanocrystals (Quantum Dots) in Single-Molecule Detection and Imaging Laurent A. Bentolila, Xavier Michalet, and Shimon quantum dots (QDs), have emerged as new powerful fluorescent probes for in vitro and in vivo biological

Michalet, Xavier

131

Decoherence of nuclear spin quantum memory in a quantum dot

Recently, an ensemble of nuclear spins in a quantum dot have been proposed as a long-lived quantum memory. A quantum state of an electron spin in the dot can be faithfully transfered into nuclear spins through controlled hyperfine coupling. Here we study the decoherence of this memory due to nuclear spin dipolar coupling and inhomogeneous hyperfine interaction during the storage

Changxue Deng; Xuedong Hu

2005-01-01

132

Disordered quantum dots: A diffusion quantum Monte Carlo study

We report diffusion quantum Monte Carlo (DQMC) calculations of disordered quantum dots in the presence of an external magnetic field. The addition spectra, spin configuration, Hund's rule, and many-body densities are investigated up to 13 electrons. The data from DQMC is in excellent agreement with exact diagonalization for disorder-free quantum dots, and in marked difference with those obtained from unrestricted

A. D. Güçlü; Jian-Sheng Wang; Hong Guo

2003-01-01

133

Ferritin-Templated Quantum-Dots for Quantum Logic Gates.

National Technical Information Service (NTIS)

Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The w...

S. H. Choi, J. W. Kim, S. H. Chu, Y. Park, G. C. King

2005-01-01

134

Fabrication and optical properties of quantum dots and wires

NASA Astrophysics Data System (ADS)

We describe photoluminescence measurements made on mesa geometry quantum dots and wires with exposed side walls fabricated by laterally patterning undoped GaAs/AlGaAs quantum wells using electron beam lithography and dry etching. At low temperature the photoluminescence efficiency of many but not all of the GaAs quantum dot arrays scales with the volume of quantum well material down to lateral dimensions of 50nm. This behaviour contrasts with that found in wires produced at the same time where the intensity falls off rapidly with decreasing wire width for dimensions below 500nm but is recovered by overgrowth with indium tin oxide, possibly as a result of strain. Narrow overgrown wires exhibit anisotropy in polarized excitation spectra which is discussed in relation to strain and lateral confinement effects.

Andrews, S. R.; Arnot, H. E. G.

135

Imaging Electrons in Few-Electron Quantum Dots

Imaging Electrons in Few-Electron Quantum Dots A thesis presented by Parisa Fallahi to The Division Electrons in Few-Electron Quantum Dots Abstract Electrons in a one-electron quantum dot were imaged images are obtained by scanning a charged tip above the surface of the quantum dot and recording

Heller, Eric

136

Quantum Dot Circuits: Single-Electron Switch and

Quantum Dot Circuits: Single-Electron Switch and Few-Electron Quantum Dots A thesis presented August 2003 #12;Â© 2003 Ian Hin-Yun Chan All rights reserved. #12;iii Abstract Quantum Dot Circuits: Single-Electron Switch and Few-Electron Quantum Dots Advisor: Robert M. Westervelt Author: Ian H. Chan

137

Quantum dots DOI: 10.1002/smll.200700148

Quantum dots DOI: 10.1002/smll.200700148 Specific Integrin Labeling in Living Cells Using Kessler, and Andreas R. Bausch* We present an integrin labeling method using functionalized quantum dots Â· quantum dots 1. Introduction Quantum dot (QD) bioimaging has recently been de- scribed as the most

Bausch, Andreas

138

Exciton spin relaxation in resonantly excited CdTe/ZnTe self-assembled quantum dots

We study the exciton spin relaxation in CdTe self-assembled quantum dots by using polarized photoluminescence spectroscopy in magnetic field. The experiments on single CdTe quantum dots and on large quantum dot ensembles show that by combining phonon-assisted absorption with circularly polarized resonant excitation the spin-polarized excitons are photo-excited directly into the ground states of quantum dots. We find that for single symmetric quantum dots at B=0 T, where the exciton levels are degenerate, the spins randomize very rapidly, so that no net spin polarization is observed. In contrast, when this degeneracy is lifted by applying external magnetic field, optically created spin-polarized excitons maintain their polarization on a time scale much longer than the exciton recombination time. We also observe that the exciton spin polarization is conserved when the splitting between exciton states is caused by quantum dot shape asymmetry. Similar behavior is found in a large ensemble of CdTe quantum dots. These results show that while exciton spins scatter rapidly between degenerate states, the spin relaxation time increases by orders of magnitude as the exciton spin states in a quantum dot become non-degenerate. Finally, due to strong electronic confinement in CdTe quantum dots, the large spin polarization of excitons shows no dependence on the number of phonons emitted between the virtual state and the exciton ground state during the excitation.

S. Mackowski; T. A. Nguyen; T. Gurung; K. Hewaparkarama; H. E. Jackson; L. M. Smith; J. Wrobel; K. Fronc; J. Kossut; G. Karczewski

2003-07-28

139

Density of states in randomly shaped graphene quantum dots

By numerical diagonalization of honeycomb-lattice tight-binding Hamiltonian we calculate the density of state (DOS) of irregularly shaped graphene quantum dots fabricated in the form of graphene nano-flakes. The finite-size electron confinement and the edge states result in the central peak of DOS that is located at the zero-energy Dirac point. The amplitude and width of the peak are provided by

T. Espinosa-Ortega; Igor A. Luk’yanchuk; Yuri G. Rubo

2011-01-01

140

Ultralong Dephasing Time in InGaAs Quantum Dots

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

141

Level rearrangement in exotic atoms and quantum dots

A presentation and a generalisation are given of the phenomenon of level rearrangement, which occurs when an attractive long-range potential is supplemented by a short-range attractive potential of increasing strength. This problem has been discovered in condensate-matter physics and has also been studied in the physics of exotic atoms. A similar phenomenon occurs in a situation inspired by quantum dots, where a short-range interaction is added to an harmonic confinement.

Monique Combescure; Avinash Khare; Ashok Raina; Jean-Marc Richard; Carole Weydert

2006-12-30

142

Surface morphology of self-assembled vertically stacked InAs quantum dots by atomic force microscopy

In quantum dots (QDs) three-dimensional confinement of carriers leads to energy level discreteness to exhibit a rich spectrum of phenomena including quantum confinement, exchange splittings, Coulomb blockade, and multiexciton transitions. In this paper, five-period vertically stacked samples with size-controlled growth were grown by molecular-beam epitaxy (MBE) with solid sources, and the surface morphologies of self-assembled vertically stacked InAs quantum dots

Shuwei Li; Kazuto Koike

2005-01-01

143

Theory of Electro-optic Modulation via a Quantum Dot Coupled to a Nano-resonator

In this paper, we analyze the performance of an electro-optic modulator based on a single quantum dot strongly coupled to a nano-resonator, where electrical control of the quantum dot frequency is achieved via quantum confined Stark effect. Using realistic system parameters, we show that modulation speeds of a few tens of GHz are achievable with this system, while the energy per switching operation can be as small as 0.5 fJ. In addition, we study the non-linear distortion, and the effect of pure quantum dot dephasing on the performance of the modulator.

Arka Majumdar; Nicolas Manquest; Andrei Faraon; Jelena Vuckovic

2009-11-27

144

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

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. PMID:20457938

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

2010-01-01

145

Quantum dot loaded immunomicelles for tumor imaging

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

146

Entanglement and Quantum Phase Transition in a One-Dimensional System of quantum Dots with Disorder

Entanglement and Quantum Phase Transition in a One-Dimensional System of quantum Dots with Disorder We study the entanglement of formation and quantum phase transition in a one-dimensional quantum dots, quantum computer based on quantum dots is a prominent one[9, 10]. Quantum dots are clusters of atoms

Kais, Sabre

147

ac Josephson transport through interacting quantum dots

NASA Astrophysics Data System (ADS)

We investigate the ac Josephson current through a quantum dot with strong Coulomb interaction attached to two superconducting and one normal lead. To this end, we perform a perturbation expansion in the tunneling couplings within a diagrammatic real-time technique. The ac Josephson current is connected to the reduced density matrix elements that describe superconducting correlations induced on the quantum dot via proximity effect. We analyze the dependence of the ac signal on the level position of the quantum dot, the charging energy, and the applied bias voltages.

Hiltscher, Bastian; Governale, Michele; König, Jürgen

2012-12-01

148

Quantum dot-based theranostics

NASA Astrophysics Data System (ADS)

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

Ho, Yi-Ping; Leong, Kam W.

2010-01-01

149

Double superexchange in quantum dot mesomaterials

dynamics are quantified from first-principles for a model system composed of small silicon quantum dots as the critical obstacles to dramatic enhancements in the energy conversion efficiency of photovoltaic cells based attractive for photovoltaic and opto- electronic applications.1Â4 Compared with dots of greater size

Wu, Zhigang

150

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

151

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

152

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

153

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

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

154

Creating atomic order in semiconductors quantum dots

1 Creating atomic order in semiconductors quantum dots Peter Moeck Department of Physics (MC 273 in the invention of the integrated circuit" Jack S. Kilby (Â½): creating first integrated circuit in Ge, September

Moeck, Peter

155

Synthesis and characterization of infrared quantum dots

This thesis focuses on the development of synthetic methods to create application ready quantum dots (QDs) in the infrared for biological imaging and optoelectronic devices. I concentrated primarily on controlling the size ...

Harris, Daniel Kelly

2014-01-01

156

Quantum Dot Array Formation through Biomolecular Nanopatterning.

National Technical Information Service (NTIS)

Report developed under SBIR contract for Topic A98-028: The objective is to demonstrate the feasibility of forming precisely ordered and precisely located arrays of semiconductor quantum dots by using biomolecular templates and Low Energy Electron Enhance...

H. P. Gillis

1999-01-01

157

Photodetectors based on colloidal quantum dots

Inspired by recent work demonstrating photocurrent enhancement in quantum-dot (QD) solids via post-deposition chemical annealing and by recent successes incorporating single monolayers of QDs in light-emitting devices ...

Oertel, David C. (David Charles)

2007-01-01

158

Quantum-confined graphene-like electronic states are directly observed in graphene oxide and photothermally reduced graphene oxide via transient spectroscopy. An unexpected novel hybrid state arising from amorphous carbon-like peripheral structure with high sp(3) /sp(2) carbon ratio in close vicinity of confined graphene-like states is found commonly existent in various carbon nanomaterials, including graphene oxide, graphene quantum dots, and carbon dots. PMID:24030902

Wang, Lei; Wang, Hai-Yu; Wang, Yan; Zhu, Shou-Jun; Zhang, Yong-Lai; Zhang, Jun-Hu; Chen, Qi-Dai; Han, Wei; Xu, Huai-Liang; Yang, Bai; Sun, Hong-Bo

2013-12-01

159

Semiconductor clusters nanocrystals, and quantum dots

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

160

Optimal spin-state transition in singly occupied quantum dots network

NASA Astrophysics Data System (ADS)

We present a general model to study the spin-state transition in a network of singly occupied lateral quantum dots. The perturbative expansion of the extended Hubbard model is used to describe the dynamics of confined electrons as an effective spin Hamiltonian in the strong correlation regime. To optimize the transition, we apply the gradient ascent pulse engineering algorithm to control the exchange couplings constrained to the manifolds evaluated by Heitler-London approximation. The method is applicable to an arbitrary number of quantum dots in any arrangement. Results of the method applied to the case of triple quantum dot are presented for linear and triangular topologies.

Yaghouti, M.; Sharifi, M. J.; Kazemi, A.

2013-01-01

161

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

162

Single electron-spin memory with a semiconductor quantum dot

We show storage of the circular polarisation 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 readout through the electronically-triggered emission of a single photon. The emitted photon shares the same polarisation 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 Tesla, spin memory is preserved for at least 1000 times more than the exciton's radiative lifetime.

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

2007-06-14

163

Quantum confinement in Si and Ge nanostructures: Theory and experiment

NASA Astrophysics Data System (ADS)

The role of quantum confinement (QC) in Si and Ge nanostructures (NSs) including quantum dots, quantum wires, and quantum wells is assessed under a wide variety of fabrication methods in terms of both their structural and optical properties. Structural properties include interface states, defect states in a matrix material, and stress, all of which alter the electronic states and hence the measured optical properties. We demonstrate how variations in the fabrication method lead to differences in the NS properties, where the most relevant parameters for each type of fabrication method are highlighted. Si embedded in, or layered between, SiO2, and the role of the sub-oxide interface states embodies much of the discussion. Other matrix materials include Si3N4 and Al2O3. Si NSs exhibit a complicated optical spectrum, because the coupling between the interface states and the confined carriers manifests with varying magnitude depending on the dimension of confinement. Ge NSs do not produce well-defined luminescence due to confined carriers, because of the strong influence from oxygen vacancy defect states. Variations in Si and Ge NS properties are considered in terms of different theoretical models of QC (effective mass approximation, tight binding method, and pseudopotential method). For each theoretical model, we discuss the treatment of the relevant experimental parameters.

Barbagiovanni, Eric G.; Lockwood, David J.; Simpson, Peter J.; Goncharova, Lyudmila V.

2014-03-01

164

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

165

Design and simulation of an electrically tunable quantum dot cascade laser

to their use in infrared counter measures (IRCM), they are used in multiple other applications, which include of wide quantum-well (QW) subband spectrum, corresponding to a free-electronic in-plane motion (motion in quantum dot 15 have been tried to confine electrons. But these methods have intrinsic disadvantages like

Mohseni, Hooman

166

Thermal runaway and optical efficiency in InAs\\/GaAs quantum dot lasers

In contrast to quantum well lasers, we show thermal runaway effects are prominent for quantum dot (QD) lasers emitting at 1300 nm. In addition to the surface states at the cleaved facet and the effect of strain relaxation, which can couple confined states with surface states, the exposed relaxed QDs at the cleaved facet can themselves contribute to extra nonradiative

C. K. Chia; M. Suryana; M. Hopkinson

2009-01-01

167

Stark Effect of Interactive Electron-hole pairs in Spherical Semiconductor Quantum Dots

. Abstract. We present a theoretical approach, based on the effective mass approximation model are found to be in good agreement with experimental data over a significant domain of quantum dot sizes,7]. The characteristic blue-shift observed in optical spectra of such strongly quantum-confined systems emerges

168

Thermoelectric transport through strongly correlated quantum dots

The thermoelectric properties of strongly correlated quantum dots, described by a single level Anderson model coupled to conduction electron leads, is investigated using Wilson's numerical renormalization group method. We calculate the electronic contribution, $K_{\\rm e}$, to the thermal conductance, the thermopower, $S$, and the electrical conductance, $G$, of a quantum dot as a function of both temperature, $T$, and gate voltage, ${\\rm v}_g$, for strong, intermediate and weak Coulomb correlations, $U$, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures $T_{1}({\\rm v}_g)$ and $T_{2}({\\rm v}_g)$ with $T_{1}< T_{2}$. Such sign changes in $S(T)$ are particularly sensitive signatures of strong correlations and Kondo physics. The relevance of this to recent thermopower measurements of Kondo correlated quantum dots is discussed. We discuss the figure of merit, power factor and the degree of violation of the Wiedemann-Franz law in quantum dots. The extent of temperature scaling in the thermopower and thermal conductance of quantum dots in the Kondo regime is also assessed.

T. A. Costi; V. Zlatic

2010-04-09

169

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.

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

2008-12-01

170

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

171

Open Quantum Dots in Graphene: Scaling Relativistic Pointer States

1 Open Quantum Dots in Graphene: Scaling Relativistic Pointer States D K Ferry1 , L Huang, R Yang quantum dots provide a window into the connection between quantum and classical physics, particularly in graphene and bilayer graphene quantum dots with this recursive Green's function method. Finally, we examine

Zhang, Junshan

172

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

173

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

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

174

Quantum Dots versus Quantum Wells on Silicon Alan Y. Liua, Chong Zhangb, Justin Normana,

1 Quantum Dots versus Quantum Wells on Silicon Alan Y. Liua, Chong Zhangb, Justin Normana, Andrew with semiconductor quantum dots [2]. Recent success with In(Ga)As quantum dot lasers epitaxially grown on silicon on silicon are lacking [3]ï¿½[5]. Here we directly compare the optical properties of In(Ga)As quantum dot

Bowers, John

175

Quantum dots for light emitting diodes.

In this article we discuss the development and key advantages of quantum dot based light emitting diode (QD-LED) and other applications based on their color purity, stability, and solution processibility. Analysis of quantum dot based LEDs and the main challenges faced in this field, such as the QD luminescence quenching, QD charging in thin films, and external quantum efficiency are discussed in detail. The description about how different optical down-conversion and structures enabled researchers to overcome these challenges and to commercialize the products. The recent developments about how to overcome these difficulties have also been discussed in this article. PMID:23858829

Qasim, Khan; Lei, Wei; Li, Qing

2013-05-01

176

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

177

Electron tunneling and spin relaxation in a lateral quantum dot

We report measurements that use real-time charge sensing to probe a single-electron lateral quantum dot. The charge sensor is a quantum point contact (QPC) adjacent to the dot and the sensitivity is comparable to other ...

Amasha, Sami

2008-01-01

178

Wigner Function for an Impurity in a Parabolic Quantum Dot

High sensitivity of quantum dots with impurities can be linked with phase space high sensitivity to initial conditions. We present the Wigner function for an impurity in a parabolic quantum dot obtained from a variational wavefunction.

Gary Snyder; Majd Mayassi; Praveen Nittala; Tomas Materdey

2006-01-01

179

Nanostructured architectures for colloidal quantum dot solar cells

This thesis introduces a novel ordered bulk heterojunction architecture for colloidal quantum dot (QD) solar cells. Quantum dots are solution-processed nanocrystals whose tunable bandgap energies make them a promising ...

Jean, Joel, S.M. Massachusetts Institute of Technology

2013-01-01

180

Quantum dots to monitor RNAi delivery and improve gene silencing

Quantum dots to monitor RNAi delivery and improve gene silencing Alice A. Chen1 , Austin M. Derfus2RNA delivery that combines unmodified siRNA with seminconductor quantum dots (QDs) as multi color biological

Bhatia, Sangeeta

181

Spatial variation of available electronic excitations within individual quantum dots.

Quantum dots (QDs) allow for manipulation of the position and energy levels of electrons at sub-10 nm length scales through control of material chemistry, size, and shape. It is known from optical studies that the bandgap of semiconductor QDs increases as their size decreases due to the narrowing of the quantum confinement potential. The mechanism of quantum confinement also indicates that the localized properties within individual QDs should depend on their shape in addition to their size, but direct observations of this effect have proven challenging due to the limited spatial resolution of measurement techniques at this scale and the ability to remove contributions from the surroundings. Here we present experimental evidence of spatial variations in the lowest available electron transition energy within a series of single electrically isolated QDs due to a dome-shaped geometry, measured using electron energy-loss spectroscopy in a (scanning) transmission electron microscope [(S)TEM-EELS]. We observe a consistent increase in the energy onset of electronic excitations from the lateral center of the dot toward the edges, which we attribute purely to shape. This trend is in qualitative agreement with a simple quantum simulation of the local density of states in a dome-shaped QD. PMID:23276278

Jung, Hee Joon; Dasgupta, Neil P; Van Stockum, Philip B; Koh, Ai Leen; Sinclair, Robert; Prinz, Fritz B

2013-02-13

182

Quantum phase transition in a single-molecule quantum dot.

Quantum criticality is the intriguing possibility offered by the laws of quantum mechanics when the wave function of a many-particle physical system is forced to evolve continuously between two distinct, competing ground states. This phenomenon, often related to a zero-temperature magnetic phase transition, is believed to govern many of the fascinating properties of strongly correlated systems such as heavy-fermion compounds or high-temperature superconductors. In contrast to bulk materials with very complex electronic structures, artificial nanoscale devices could offer a new and simpler means of understanding quantum phase transitions. Here we demonstrate this possibility in a single-molecule quantum dot, where a gate voltage induces a crossing of two different types of electron spin state (singlet and triplet) at zero magnetic field. The quantum dot is operated in the Kondo regime, where the electron spin on the quantum dot is partially screened by metallic electrodes. This strong electronic coupling between the quantum dot and the metallic contacts provides the strong electron correlations necessary to observe quantum critical behaviour. The quantum magnetic phase transition between two different Kondo regimes is achieved by tuning gate voltages and is fundamentally different from previously observed Kondo transitions in semiconductor and nanotube quantum dots. Our work may offer new directions in terms of control and tunability for molecular spintronics. PMID:18509439

Roch, Nicolas; Florens, Serge; Bouchiat, Vincent; Wernsdorfer, Wolfgang; Balestro, Franck

2008-05-29

183

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

184

Three-dimensional optical control of individual quantum dots.

We show that individual colloidal CdSe-core quantum dots can be optically trapped and manipulated in three dimensions by an infrared continuous wave laser operated at low laser powers. This makes possible utilizing quantum dots not only for visualization but also for manipulation, an important advantage for single molecule experiments. Moreover, we provide quantitative information about the magnitude of forces applicable to a single quantum dot and of the polarizability of an individual quantum dot. PMID:18767883

Jauffred, Liselotte; Richardson, Andrew C; Oddershede, Lene B

2008-10-01

185

Electrical control of quantum dot spin qubits

NASA Astrophysics Data System (ADS)

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

Laird, Edward Alexander

186

Using resonantly excited photoluminescence along with photoluminescence excitation spectroscopies, we study the carrier excitation processes in CdTe/ZnTe and CdSe/ZnSe self-assembled quantum dots. Photoluminescence excitation spectra of single CdTe quantum dots reflect two major mechanisms for carrier excitation: The first, associated with the presence of sharp and intense lines in the spectrum, is a direct excited state ? ground state transition. The second, associated with the appearance of up to four much broader excitation lines, is a LO phonon-assisted absorption directly into the quantum dot ground states. LO phonons with energies of both quantum dots and ZnTe barrier material are identified in the photoluminescence excitation spectra. Resonantly excited PL measurements for the dot ensemble as a function of excitation energy makes it possible to separate the contributions of these two mechanisms. We find that for CdTe quantum dots the distribution of excited states coupled to the ground states reflects the energy distribution of the quantum dot emission, but shifted up in energy by 100 meV. This large splitting between excited and ground states in CdTe quantum dots suggests strong spatial confinement. In contrast, the LO phonon-assisted absorption shows significant size selectivity. In the case of CdTe dots the exciton-LO phonon coupling is strongly enhanced for smaller-sized dots which have higher emission energies. In contrast, for CdSe quantum dots the exciton-LO phonon coupling is uniform over the ensemble ? that is, the energy distribution determines the intensities of LO phonon replicas. We show that for CdTe quantum dots after annealing, that is after an increase in the average dot size, the exciton-LO phonon interaction reflects the dot energy distribution, as observed for CdSe quantum dots.

T. A. Nguyen; S. Mackowski; H. E. Jackson; L. M. Smith; J. Wrobel; K. Fronc; G. Karczewski; J. Kossut; M. Dobrowolska J. K. Furdyna; W. Heiss

2003-09-17

187

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

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

188

Imaging vasculature and lymphatic flow in mice using quantum dots.

Quantum dots are ideal probes for fluorescent imaging of vascular and lymphatic tissues. On injection into appropriate sites, red- and near-infrared-emitting quantum dots provide excellent definition of vasculature, lymphoid organs, and lymph nodes draining both normal tissues and tumors. We detail methods for use with commercially available quantum dots and discuss common difficulties. PMID:19685300

Ballou, Byron; Ernst, Lauren A; Andreko, Susan; Fitzpatrick, James A J; Lagerholm, B Christoffer; Waggoner, Alan S; Bruchez, Marcel P

2009-01-01

189

Charge detection in graphene quantum dots J. Gttinger,a

as a CD, as shown below. The sample is fabricated by mechanical exfoliation of natural bulk graphite.21Charge detection in graphene quantum dots J. GÃ¼ttinger,a C. Stampfer, S. HellmÃ¼ller, F. Molitor, T on a graphene quantum dot with an integrated graphene charge detector. The quantum dot device consists

Ihn, Thomas

190

Molecular Imaging: Physics and Bioapplications of Quantum Dots

CHAPTER 8 Molecular Imaging: Physics and Bioapplications of Quantum Dots Xavier Michalet, Laurent A. Bentolila, and Shimon Weiss 111 8.1 Introduction 112 8.2 Brief Overview of Quantum Dot Physics 112 8 Properties of Quantum Dots 115 8.3.1 Absorption and Emission Spectra 115 8.3.2 Fluorescence Intermittency 115

Michalet, Xavier

191

Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots

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

192

Lighting Up Individual DNA Binding Proteins with Quantum Dots

Lighting Up Individual DNA Binding Proteins with Quantum Dots Yuval Ebenstein,*,, Natalie Gassman. Fluorescent quantum dots (QD) are used to label proteins bound to DNA, allowing multicolor, nanometer optical contrast mechanism, such as fluorescence. Quantum dots (QDs), with their narrow, "tunable

Michalet, Xavier

193

Resonances from perturbed symmetry in open quantum dots

Resonances from perturbed symmetry in open quantum dots Pierre Duclos a;b , Pavel Exner c quantum dot, i.e., a straight hardÂwall channel with a potential well. If this potential dependsÂ¨o] investigated the case of a wire with ``quantum dot'' modeled by a potential well and the resonances which

194

A device architecture for computing with quantum dots

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

195

A nonlinear Bloch model for Coulomb interaction in quantum dots

A nonlinear Bloch model for Coulomb interaction in quantum dots Brigitte Bidegaray-Fesquet and Kole a Coulomb Hamiltonian for electronÂ electron interaction in quantum dots in the Heisenberg picture. Then we-Bloch model, quantum dot, Coulomb interaction, Cauchy problem, Liouville model, positiveness properties. 1

196

Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics

Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics X. Michalet,1 * F. F. Pinaud,1 * L. A,3 * Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over quantum dots are single crystals a few nanometers in diameter whose size and shape can be precisely

Nielsen, Steven O.

197

Optically mapping the electronic structure of coupled quantum dots

LETTERS Optically mapping the electronic structure of coupled quantum dots M. SCHEIBNER*, M. YAKES@bloch.nrl.navy.mil; gammon@nrl.navy.mil Published online: 10 February 2008; doi:10.1038/nphys882 In a network of quantum dots' (LACS) technique in which the ladder of orbital energy levels of one quantum dot is used to probe

Loss, Daniel

198

Quantum dot thermal spectroscopy for biological optical tweezer applications

Quantum dot thermal spectroscopy for biological optical tweezer applications William T Ramsay1. Quantum dots can be fabricated to hold particular emission properties and can be labelled to target specific binding sites in biological samples to act as biomarkers [1]. Many quantum dots have been observed

Greenaway, Alan

199

Single Electron Charging in Optically Active Nanowire Quantum Dots

Single Electron Charging in Optically Active Nanowire Quantum Dots Maarten P. van Kouwen, Michael E report optical experiments of a charge tunable, single nanowire quantum dot subject to an electric field the tunnel coupling of the quantum dot with the contacts. Such charge control is a first requirement for opto

200

Exciton binding energy in semiconductor quantum dots

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

Pokutnii, S. I., E-mail: Pokutnyi_Sergey@inbox.ru [National Academy of Sciences of Ukraine, G.V. Kurdjumov Institute for Metal Physics (Ukraine)

2010-04-15

201

Quantum teleportation in one-dimensional quantum dots system Hefeng Wang, Sabre Kais *

Quantum teleportation in one-dimensional quantum dots system Hefeng Wang, Sabre Kais * Department of quantum teleportation protocol based on one-dimensional quantum dots system. Three quantum dots with three electrons are used to perform teleportation, the unknown qubit is encoded using one electron spin on quantum

Kais, Sabre

202

Quantum Teleportation in Quantum Dots System Hefeng Wang and Sabre Kais

Quantum Teleportation in Quantum Dots System Hefeng Wang and Sabre Kais Department of Chemistry of quantum teleportation protocol based on one-dimensional quantum dots system. Three quantum dots with three electrons are used to perform teleportation, the unknown qubit is encoded using one electron spin on quantum

Kais, Sabre

203

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

204

Potential clinical applications of quantum dots

The use of luminescent colloidal quantum dots in biological investigations has increased dramatically over the past several years due to their unique size-dependent optical properties and recent advances in biofunctionalization. In this review, we describe the methods for generating high-quality nanocrystals and report on current and potential uses of these versatile materials. Numerous examples are provided in several key areas including cell labeling, biosensing, in vivo imaging, bimodal magnetic-luminescent imaging, and diagnostics. We also explore toxicity issues surrounding these materials and speculate about the future uses of quantum dots in a clinical setting. PMID:18686776

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

2008-01-01

205

Imaging a coupled quantum dot-quantum point contact system

NASA Astrophysics Data System (ADS)

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 charging events in several traps from charging events on the dot. We used the quantum dot to analyze the tip-induced potential quantitatively and found its shape to be independent of the voltage applied to the tip within a certain range of parameters. We estimate that the trap density is below 0.1% of the doping density, that the charging energy of a trap is three times higher than that of the quantum dot, and that the interaction energy between the quantum dot and a trap is a significant portion of the dot's charging energy. Possibly, such charge traps are the reason for frequently observed parametric charge rearrangements.

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

2007-10-01

206

Semiconductor Quantum Dots and Quantum Dot Arrays and Applications of Multiple Exciton Generation 6885 6.1.3. Quantum Dots Dispersed in Organic Semiconductor Polymer Matrices 6885 6.2. Schottky. Acknowledgments 6887 9. Note Added after ASAP Publication 6887 10. References 6887 1. Introduction Semiconductors

George, Steven C.

207

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

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

Ugur, A.; Hatami, F.; Masselink, W. T. [Department of Physics, Humboldt-Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin (Germany); Vamivakas, A. N.; Lombez, L.; Atatuere, M. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2008-10-06

208

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

209

NASA Astrophysics Data System (ADS)

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.

2011-08-01

210

Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

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 [Department of Electrical Engineering, University of Notre Dame, Indiana 46556 (United States)] [Department of Electrical Engineering, University of Notre Dame, Indiana 46556 (United States)

2013-01-28

211

NASA Astrophysics Data System (ADS)

We report a Ti-TiOx/quantum dot based bipolar nonvolatile resistive memory device. The device has ON/OFF ratio 100 and is reproducible. The memory device showed good retention characteristics under stress and excellent stability even after 100 000 cycles of switching operation. The memory devices are solution processed at room temperature in ambient atmosphere. The operating mechanism is discussed based on charge trapping in quantum dots resulting in Coulomb blockade effect with the metal-oxide layer acting as the barrier to confine the trapped charges. The mechanism is supported by negative differential resistance (NDR) observed exclusively in the ON state.

Kannan, V.; Rhee, J. K.

2011-10-01

212

Magnetic properties of graphene quantum dots

NASA Astrophysics Data System (ADS)

Using the tight-binding approximation we calculated the diamagnetic susceptibility of graphene quantum dots (GQDs) of different geometrical shapes and characteristic sizes of 2-10 nm, when the magnetic properties are governed by the electron edge states. Two types of edge states can be discerned: the zero-energy states (ZESs), located exactly at the zero-energy Dirac point, and the dispersed edge states (DESs), with the energy close but not exactly equal to zero. DESs are responsible for a temperature-independent diamagnetic response, while ZESs provide a temperature-dependent spin paramagnetism. Hexagonal, circular, and randomly shaped GQDs contain mainly DESs, and, as a result, they are diamagnetic. The edge states of the triangular GQDs are of ZES type. These dots reveal the crossover between spin paramagnetism, dominating for small dots and at low temperatures, and orbital diamagnetism, dominating for large dots and at high temperatures.

Espinosa-Ortega, T.; Luk'yanchuk, I. A.; Rubo, Y. G.

2013-05-01

213

Germanium quantum dots: Optical properties and synthesis

NASA Astrophysics Data System (ADS)

Three different size distributions of Ge quantum dots (?200, 110, and 60 Å) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray photoemission, infrared spectroscopy, and Raman spectroscopy. Colloidal suspensions of these quantum dots were prepared and their extinction spectra are measured with ultraviolet/visible (UV/Vis) and near infrared (IR) spectroscopy, in the regime from 0.6 to 5 eV. The optical spectra are correlated with a Mie theory extinction calculation utilizing bulk optical constants. This leads to an assignment of three optical features to the E(1), E(0'), and E(2) direct band gap transitions. The E(0') transitions exhibit a strong size dependence. The near IR spectra of the largest dots is dominated by E(0) direct gap absorptions. For the smallest dots the near IR spectrum is dominated by the ?25?L indirect transitions.

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

1994-07-01

214

Near-field resonant energy transfer between spherical quantum dots

NASA Astrophysics Data System (ADS)

Non-radiative (Forster-type) energy transfer of an exciton between two quantum dots (QDs) plays an important role in artificial structures where semiconductor nanocrystal QDs play the role of building blocks. We theoretically study the effect of surrounding medium (e.g. dielectric substrate) on the transfer rate. Applying a simple model to describe the QDs, we demonstrate that the transfer rate can be strongly enhanced in the vicinity of a metal surface if the donor QD is excited in resonance with surface plasmons characteristic of this surface. Then the scaling law with the interdot distance becomes more complex than R-6 and the characteristic Forster radius can increase by an order of magnitude. We also show that transfer rate between two QDs is not exactly / R-6 even within the dipole-dipole approximation, in free space if the electron and hole in the dot are in the weak confinement regime

Peres, Filipa C. R.; Vasilevskiy, Mikhail I.

2014-08-01

215

Electron Transport Through Laterally Coupled Double Quantum Dots

NASA Astrophysics Data System (ADS)

We study electron transport through laterally coupled double quantum dots. We introduce the coupling parameter ?, which characterizes the strength of the coupling via the reservoirs between quantum dots. We find that the visibility decreases as |?| increases. We also examine the pseudo-spin Kondo effect in the laterally coupled double quantum dots. The differential conductance shows the additional structure in the spilt peak by the inter-dot tunnel coupling due to the asymmetry of the spectral density of states.

Kubo, T.; Tokura, Y.; Hatano, T.; Tarucha, S.

2008-10-01

216

Quantum dots A survey of rigorous results

such systems are called quantum wells. In quantum wires the electrons can move freely in one dimension has in recent years made it possible to fabriÂ cate ultrasmall structures that confine electrons but are restricted in the other two. Structures that restrict the motion of the electrons in all directions

217

Optical properties of quantum-dot-doped liquid scintillators

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

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

2014-01-01

218

Optical properties of quantum-dot-doped liquid scintillators

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

219

Unraveling the mesoscopic character of quantum dots in nanophotonics

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

Tighineanu, Petru; Stobbe, Søren; Lodahl, Peter

2014-01-01

220

NASA Astrophysics Data System (ADS)

We report on the nonlinear optical properties of a quantum dot including the Rashba spin-orbit interaction (RSOI) with external electric and magnetic fields. The effect of dot size is considered. We do not make any assumptions about the strength of the confinement. We use the numerical diagonalization of the Hamiltonian to determine the electronic structure. The confining potential is taken to be of the Woods-Saxon type. We find the effect of RSOI on nonlinear optical coefficients.

Aytekin, O.; Turgut, S.; Tomak, M.

2014-11-01

221

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

222

Triggered Single Photons from a Quantum Dot

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

223

Nanocomposites of POC and quantum dots

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

224

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

225

Fast Electrical Control of a Quantum Dot Strongly Coupled to a Nano-resonator

The resonance frequency of an InAs quantum dot strongly coupled to a GaAs photonic crystal cavity was electrically controlled via quantum confined Stark effect. Stark shifts up to 0.3meV 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 150MHz, limited by the RC constant of the transmission line. The coupling rate and the magnitude of the Stark shift with electric field were investigated while coherently probing the system.

Andrei Faraon; Arka Majumdar; Hyochul Kim; Pierre Petroff; Jelena Vuckovic

2009-06-03

226

Interaction effects in the mesoscopic regime: A quantum Monte Carlo study of irregular quantum dots

Interaction effects in the mesoscopic regime: A quantum Monte Carlo study of irregular quantum dots-state properties of isolated irregular quantum dots. Quantum Monte Carlo techniques are used to calculate- mation overpredicts the effects of interactions in quantum dots. DOI: 10.1103/PhysRevB.71.241306 PACS

Baranger, Harold U.

227

Tuning the optical properties of dilute nitride site controlled quantum dots

NASA Astrophysics Data System (ADS)

We show that deterministic control of the properties of pyramidal site-controlled quantum dots (QD) could be achieved by exposing the QD layer to nitrogen precursor unsymmetrical dimethylhydrazine (UDMHy). The properties that could be tuned include an expected emission reduction in dilute nitride materials, excitonic pattern (biexciton binding energy) and improved carrier confinement potential symmetry (reduced fine-structure splitting).

Juska, G.; Dimastrodonato, V.; Mereni, L. O.; Gocalinska, A.; Pelucchi, E.

2013-12-01

228

Tuning the optical properties of dilute nitride site controlled quantum dots

We show that deterministic control of the properties of pyramidal site-controlled quantum dots (QD) could be achieved by exposing the QD layer to nitrogen precursor unsymmetrical dimethylhydrazine (UDMHy). The properties that could be tuned include an expected emission reduction in dilute nitride materials, excitonic pattern (biexciton binding energy) and improved carrier confinement potential symmetry (reduced fine-structure splitting)

Juska, G.; Dimastrodonato, V.; Mereni, L. O.; Gocalinska, A.; Pelucchi, E. [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland)

2013-12-04

229

Quantum Information Processing Using Quantum Dot Spins and Cavity QED

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

230

Ultrafast gain dynamics in InP quantum-dot optical amplifiers

NASA Astrophysics Data System (ADS)

We measured the gain dynamics at the ground-state transition in an electrically pumped InP/AlGaInP quantum-dot optical amplifier at room temperature by femtosecond differential transmission. The gain shows an ultrafast recovery within 200 fs, even faster than in state-of-the-art InAs/GaAs quantum-dot amplifiers. This finding, likely to be due to the less confined and more closely spaced hole levels in InP dots, is promising for optical signal processing at high bit rates. We furthermore measured the pump-induced refractive index changes and deduced a linewidth enhancement factor similar to the one in InAs/GaAs quantum dots.

Langbein, Wolfgang; Cesari, Valentina; Masia, Francesco; Krysa, Andrey B.; Borri, Paola; Smowton, Peter M.

2010-11-01

231

Optical levitation of microdroplet containing a single quantum dot

Semiconductor nanocrystals, also known as quantum dots (QDs), are key ingredients in current quantum optics experiments. They serve as quantum emitters and memories and have tunable energy levels that depend not only on the material but also, through the quantum confinement effect, on the size. The resulting strongly confined electron and hole wave functions lead to large transition dipole moments, which opens a path to ultra strong coupling and even deep strong coupling between light and matter. Such efficient coupling requires the precise positioning of the QD in an optical cavity with a high quality factor and small mode volume, such as micro-Fabry--Perot cavity, whispering-gallery-mode microcavity, or photonic-crystal cavity. However, the absence of a technique for free-space positioning has limited the further research on QD-based cavity quantum electrodynamics. In this paper, we present a technique to overcome this challenge by demonstrating the optical levitation or trapping in helium gas of a single Q...

Minowa, Yosuke; Ashida, Masaaki

2014-01-01

232

Quantum-dot cellular automata at a molecular scale

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

233

Entangling distant quantum dots using classical interference

NASA Astrophysics Data System (ADS)

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

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

2008-10-01

234

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

235

Thermoelectric transport through strongly correlated quantum dots

The thermoelectric properties of strongly correlated quantum dots, described by a single level Anderson model coupled to conduction electron leads, is investigated using Wilson's numerical renormalization group method. We calculate the electronic contribution, $K_{\\rm e}$, to the thermal conductance, the thermopower, $S$, and the electrical conductance, $G$, of a quantum dot as a function of both temperature, $T$, and gate voltage, ${\\rm v}_g$, for strong, intermediate and weak Coulomb correlations, $U$, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures $T_{1}({\\rm v}_g)$ and $T_{2}({\\rm v}_g)$ with $T_{1}< T_{2}$. Such sign changes in $S(T)$ are particularly sensitive signatures of strong correlations and Kondo physics. The relevance of this to recent thermopower measurements of Kondo correlated quantum dots is discussed. We discuss the figure of merit, power factor and the degree of violation of the Wiedemann-Franz law in ...

Costi, T A; 10.1103/PhysRevB.81.235127

2010-01-01

236

Local Quantum Dot Tuning on Photonic Crystal Chips

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

Andrei Faraon; Dirk Englund; Ilya Fushman; Nick Stoltz; Pierre Petroff; Jelena Vuckovic

2007-03-28

237

Quantum confinement in CdSe nanocrystallites

Quantum confinement increases the spacing between energy levels as the nanocrystallite size is decreased. Its qualitative features hold both for states localized near the center of a nanocrystallite and those near the surface, such as states due primarily to dangling bonds. However, different quantitative features are expected because of the different size constraints on each of these states. Since the

K. E. Andersen; C. Y. Fong; W. E. Pickett

2002-01-01

238

Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

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

Generalov, Roman; Kavaliauskiene, Simona; Westr?m, Sara; Chen, Wei; Kristensen, Solveig; Juzenas, Petras

2011-01-01

239

Principles of conjugating quantum dots to proteins via carbodiimide chemistry

NASA Astrophysics Data System (ADS)

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

Song, Fayi; Chan, Warren C. W.

2011-12-01

240

Quantum confinement and band offsets in amorphous silicon quantum wells

NASA Astrophysics Data System (ADS)

Quantum wells (QWs) are nanostructures consisting of alternating layers of a low and high band-gap semiconductor. The band gap of QWs can be tuned by changing the thickness of the low band-gap layer, due to quantum confinement effects. Although this principle is well established for crystalline materials, there is still controversy for QWs fabricated from amorphous materials: How strong are the confinement effects in amorphous QWs, where, because of the disorder, the carriers are localized to start with? We prepare an atomistic model of QWs based on a-Si:H to gain insight into this problem. The electronic structure of our atomistic QWs model is described with first-principles density functional theory, allowing us to study the confinement effects directly. We find that the quantum confinement effect is rather weak, compared to experimental results on a similar system.

Jarolimek, K.; de Groot, R. A.; de Wijs, G. A.; Zeman, M.

2014-09-01

241

Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots

NASA Astrophysics Data System (ADS)

Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 ?s relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 ?s and T2 to be 6.5 ?s in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 ?s at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.

He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

2012-02-01

242

Quantum-dot-induced phase shift in a pillar microcavity

We perform high-resolution reflection spectroscopy of a quantum dot resonantly coupled to a pillar microcavity. We show the change in reflectivity as the quantum dot is tuned through the cavity resonance and measure the quantum-dot-induced phase shift using an ultrastable interferometer. The macroscopic phase shift we measure could be extended to the study of charged quantum dot pillar microcavity systems, where it could be exploited to realize a high-efficiency spin photon interface for hybrid quantum information schemes.

Young, A. B.; Hu, C. Y.; Rarity, J. G. [Merchant Venturers School of Engineering, Woodland Road, Bristol, BS8 1UB (United Kingdom); Oulton, R. [Merchant Venturers School of Engineering, Woodland Road, Bristol, BS8 1UB (United Kingdom); H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Thijssen, A. C. T. [H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Schneider, C.; Reitzenstein, S.; Kamp, M.; Hoefling, S.; Worschech, L.; Forchel, A. [Technische Physik, Physikalisches Institut and Wilhelm Conrad Roentgen-Center for Complex Material Systems, Universitaet Wuerzburg, Am Hubland, D-97474 Wuerzburg (Germany)

2011-07-15

243

Quantum modeling of laser-quantum dot interaction Brigitte Bidgaray-Fesquet

Quantum modeling of laser-quantum dot interaction Brigitte BidÃ©garay-Fesquet Laboratoire Jeanth 2008 B. BidÃ©garay-Fesquet (LJK) Laser-quantum dot interaction Luminy, October 30th 2008 1 / 17 #12 + . . . B. BidÃ©garay-Fesquet (LJK) Laser-quantum dot interaction Luminy, October 30th 2008 2 / 17 #12;Bloch

Bidegaray, Brigitte

244

Light absorption enhancement in closely packed Ge quantum dots

NASA Astrophysics Data System (ADS)

Multilayers of Ge quantum dots (QDs, 3 nm in diameter) embedded in SiO2, separated by SiO2 barrier layer (3, 9, or 20 nm thick), have been synthesized by sputter deposition and characterized by transmission electron microscopy and light absorption spectroscopy. Quantum confinement affects the optical bandgap energy (1.9 eV for QDs, 0.8 eV for bulk Ge); moreover, the absorption probability greatly depends on the QD-QD distance. A strong electronic coupling among Ge QDs is evidenced, with a significant increase of the light absorption efficiency when the QD-QD distance is reduced. These data unveil promising aspects for light harvesting with nanostructures.

Mirabella, S.; Cosentino, S.; Failla, M.; Miritello, M.; Nicotra, G.; Simone, F.; Spinella, C.; Franzò, G.; Terrasi, A.

2013-05-01

245

Electric Field effects on quantum correlations in semiconductor quantum dots

We study the effect of external electric bias on the quantum correlations in the array of optically excited coupled semiconductor quantum dots. The correlations are characterized by the quantum discord and concurrence and are observed using excitonic qubits. We employ the lower bound of concurrence for thermal density matrix at different temperatures. The effect of the F\\"orster interaction on correlations will be studied. Our theoretical model detects nonvanishing quantum discord when the electric field is on while concurrence dies, ensuring the existence of nonclassical correlations as measured by the quantum discord.

S. Shojaei; M. Mahdian; R. Yousefjani

2012-04-18

246

First-principles study of the electronic structure of CdS/ZnSe coupled quantum dots

NASA Astrophysics Data System (ADS)

We have studied the electronic structure of CdS/ZnSe coupled quantum dots, a novel heterostructure at the nanoscale. Our calculations reveal CdS/ZnSe coupled quantum dots are type II in nature where the anion p states play an important role in deciding the band offset for the highest occupied molecular orbitals (HOMO). We show that the offsets of HOMO as well as the lowest unoccupied molecular orbitals (LUMO) can be tuned by changing the sizes of the components of the coupled quantum dots, thereby providing an additional control parameter to tune the band gap and the optical properties. Our investigations also suggest that the formation of an alloy near the interface has very little influence on the band offsets, although it affects the spatial localization of the quantum states from the individual components. Comparing the influence of strain on coupled quantum dots and core-shell nanowires, we find strain practically has no role in the electronic structure of coupled quantum dots as the small effective area of the interface in a coupled quantum dot helps a large part of the structure remain free from any substantial strain. We argue that in contrast to core-shell nanowires, quantum confinement is the key parameter that controls the electronic properties of coupled quantum dots and should therefore be an ideal candidate for the design of a quantum device.

Ganguli, Nirmal; Acharya, S.; Dasgupta, I.

2014-06-01

247

Conductance peaks in open quantum dots

We present a simple measure of the conductance fluctuations in open ballistic chaotic quantum dots, extending the number of maxima method originally proposed for the statistical analysis of compound nuclear reactions. The average number of extreme points (maxima and minima) in the dimensionless conductance, $T$, as a function of an arbitrary external parameter $Z$, is directly related to the autocorrelation function of $T(Z)$. The parameter $Z$ can be associated to an applied gate voltage causing shape deformation in quantum dot, an external magnetic field, the Fermi energy, etc.. The average density of maxima is found to be $ = \\alpha_{Z}/Z_c$, where $\\alpha_{Z}$ is a universal constant and $Z_c$ is the conductance autocorrelation length, which is system specific. The analysis of $$ does not require large statistic samples, providing a quite amenable way to access information about parametric correlations, such as $Z_c$.

J. G. G. S. Ramos; D. Bazeia; M. S. Hussein; C. H. Lewenkopf

2011-09-26

248

Carrier dynamics in strain-induced InGaAsP\\/InP quantum dots

Carrier dynamics of strain-induced InGaAsP\\/InP quantum dots (QDs) is investigated. In this structure, self-assembled InAs islands on the surface act as stressors and create a lateral confinement potential in the near surface InGaAsP\\/InP quantum well. Photoluminescence (PL) measurements reveal that decreasing the distance from the QD to the surface significantly diminishes the QD–PL intensity, presumably due to surface states of

H. Koskenvaara; J. Riikonen; J. Sormunen; M. Sopanen; H. Lipsanen

2006-01-01

249

Theory of dynamic nuclear polarization and feedback in quantum dots

An electron confined in a quantum dot interacts with its local nuclear spin environment through the hyperfine contact interaction. This interaction combined with external control and relaxation or measurement of the electron spin allows for the generation of dynamic nuclear polarization. The quantum nature of the nuclear bath, along with the interplay of coherent external fields and incoherent dynamics in these systems renders a wealth of intriguing phenomena seen in recent experiments such as electron Zeeman frequency focusing, hysteresis, and line dragging. We develop in detail a fully quantum, self-consistent theory that can be applied to such experiments and that moreover has predictive power. Our theory uses the operator sum representation formalism in order to incorporate the incoherent dynamics caused by the additional, Markovian bath, which in self-assembled dots is the vacuum field responsible for electron-hole optical recombination. The beauty of this formalism is that it reduces the complexity of the problem by encoding the joint dynamics of the external coherent and incoherent driving in an effective dynamical map that only acts on the electron spin subspace. This together with the separation of timescales in the problem allows for a tractable and analytically solvable formalism. The key role of entanglement between the electron spin and the nuclear spins in the formation of dynamic nuclear polarization naturally follows from our solution. We demonstrate the theory in detail for an optical pulsed experiment and present an in-depth discussion and physical explanation of our results.

Sophia E. Economou; Edwin Barnes

2013-12-19

250

Ultraviolet-blue photoluminescence of ZnSe quantum dots.

Zinc blende, sphericity, monodisperse, high luminescence ZnSe quantum dots (QDs) were synthesized by a one-step mild hydrothermal route with Zn and Se dissolved in aqueous NaOH as the source material. The structure and the morphology of the sample were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicated that the products were cubic blende ZnSe ranging from 3.2 to 4.5 nm in size. TEM images showed that the QDs have very good dispersibility and distribution. The characteristic features of the absorption and photoluminescence spectra of ZnSe quantum dots were studied at room temperature. Compared with the bulk ZnSe, the absorption edges and luminescent peaks of ZnSe QDs were blue shifted to higher energies due to the quantum confinement effect. Photoluminescence at ultraviolet excitation showed the strong emission at 390 nm related to the higher excitonic states. ZnSe QDs exhibiting photoluminescence line widths as narrow as 40-60 nm. Meanwhile, we simply explored the theoretical mechanism of luminescence in ZnSe QDs and analogized the relation of various point defect concentrations of ZnSe. PMID:20355637

Peng, Ling Ling; Wang, Yu Hua; Li, Cheng Yan

2010-03-01

251

Theory of dynamic nuclear polarization and feedback in quantum dots

NASA Astrophysics Data System (ADS)

An electron confined in a quantum dot interacts with its local nuclear spin environment through the hyperfine contact interaction. This interaction combined with external control and relaxation or measurement of the electron spin allows for the generation of dynamic nuclear polarization. The quantum nature of the nuclear bath, along with the interplay of coherent external fields and incoherent dynamics in these systems renders a wealth of intriguing phenomena seen in recent experiments such as electron Zeeman frequency focusing, hysteresis, and line dragging. We develop in detail a fully quantum, self-consistent theory that can be applied to such experiments and that moreover has predictive power. Our theory uses the operator sum representation formalism in order to incorporate the incoherent dynamics caused by the additional, Markovian bath, which in self-assembled dots is the vacuum field responsible for electron-hole optical recombination. The beauty of this formalism is that it reduces the complexity of the problem by encoding the joint dynamics of the external coherent and incoherent driving in an effective dynamical map that only acts on the electron spin subspace. This, together with the separation of time scales in the problem, allows for a tractable and analytically solvable formalism. The key role of entanglement between the electron spin and the nuclear spins in the formation of dynamic nuclear polarization naturally follows from our solution. We demonstrate the theory in detail for an optical pulsed experiment and present an in-depth discussion and physical explanation of our results.

Economou, Sophia E.; Barnes, Edwin

2014-04-01

252

Electrical properties of semiconductor quantum dots

A method, which makes it possible to obtain semiconductor particles V Almost-Equal-To 10{sup -20} cm{sup 3} in volume (quantum dots) with a concentration of up to 10{sup 11} cm{sup -2} and electrical contacts to each of them, is suggested. High variability in the electrical properties of such particles from a metal oxide (CuO or NiO) after the chemisorption of gas molecules is found.

Kharlamov, V. F., E-mail: kharl@ostu.ru; Korostelev, D. A.; Bogoraz, I. G.; Milovidova, O. A.; Sergeyev, V. O. [State University, Educational-Research-Production Complex (Russian Federation)

2013-04-15

253

Gain characteristics of quantum dot injection lasers

Gain characteristics of injection lasers based on self-organized quantum dots (QDs) were studied experimentally for two systems: InGaAs QDs in an AlGaAs matrix on a GaAs substrate and InAs QDs in an InGaAs matrix on an InP substrate. A ground-to-excited state transition was observed with increasing threshold gain. An empirical equation is proposed to fit the current density dependence of

A. E. Zhukov; A. R. Kovsh; V. M. Ustinov; A. Yu Egorov; N. N. Ledentsov; A. F. Tsatsul'nikov; M. V. Maximov; Yu M. Shernyakov; V. I. Kopchatov; A. V. Lunev; P. S. Kop'ev; D. Bimberg; Zh I. Alferov

1999-01-01

254

Quantum-dot cellular automata adders

In this paper, a novel quantum-dot cellular automata (QCA) adder design is presented that reduces the number of QCA cells compared to previously reported designs. The proposed one-bit QCA adder structure is based on a new algorithm that requires only three majority gates and two inverters for the QCA addition. By connecting n one-bit QCA adders, we can obtain an

Wei Wang; Konrad Walus; G. A. Jullien

2003-01-01

255

Singly ionized double-donor complex in vertically coupled quantum dots

The electronic states of a singly ionized on-axis double-donor complex (D2+) confined in two identical vertically coupled, axially symmetrical quantum dots in a threading magnetic field are calculated. 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 antibonding lowest-lying artificial molecule states corresponding to different quantum dot morphologies, dimensions, separation between them, thicknesses of the wetting layers, and magnetic field strength. PMID:22937880

2012-01-01

256

Polarization Resolved Single Dot Spectroscopy of (211)B InAs Quantum Dots

We report on single dot spectroscopy of (211)B InAs quantum dots, grown by molecular beam epitaxy. The dots exhibit sharp emission lines, the origin of which has been identified. Polarization dependent microphotoluminescence spectra confirm fine structure splittings from 20{mu}eV down to the determination limit of our setup (10 {mu}eV).

Germanis, S.; Dialynas, G. E.; Deligeorgis, G.; Hatzopoulos, Z. [Physics Department, University of Crete, P.O. Box 2208, 71003 Heraklion, Crete (Greece); Savvidis, P. G.; Pelekanos, N. T. [Materials Science and Technology Department, University of Crete, P.O. Box 2208, 71003 Heraklion, Crete (Greece)

2011-12-23

257

spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We calculations. Published by Elsevier Inc. Keywords: Computational nano-technology; Electronic structure nano-science is to predict electronic properties and their changes due to quantum confinement effects

Dongarra, Jack

258

Deposition of colloidal quantum dots by microcontact printing for LED display technology

This thesis demonstrates a new deposition method of colloidal quantum dots within a quantum dot organic light-emitting diode (QD-LED). A monolayer of quantum dots is microcontact printed as small as 20 ,Lm lines as well ...

Kim, LeeAnn

2006-01-01

259

Thermoelectric conversion in Silicon quantum-dots

NASA Astrophysics Data System (ADS)

Quantum dot-based devices have specific thermoelectric properties. Thanks to their delta-like density of states, they are expected to exhibit high Seebeck coefficient, nearly zero electronic thermal conductance and ultra-low phononic thermal conductance if embedded in an oxide matrix. Using a physical simulator dedicated to the sequential transport through quantum dots (QDs), the thermoelectric properties of devices based on Silicon QDs embedded in silicon oxide are assessed. Fully self-consistent 3D Poisson/Schrödinger simulation is performed. From the accurate computation of tunneling rates, a Monte-Carlo algorithm is used to solve the master equation and to extract the current-voltage characteristics for different temperature gradients applied between the electrodes. The evolution of both the Seebeck coefficient and the electronic conductivity resulting from a temperature bias are investigated for dissymmetric spherical and cubic quantum-dot-based (QD) single-electron transistors (SETs). Finally, the validity of the linear regime and the potentiality of semiconducting SETs in the field of Seebeck nanoscale metrology are discussed.

Talbo, V.; Saint-Martin, J.; Apertet, Y.; Retailleau, S.; Dollfus, P.

2012-11-01

260

Ultra-bright alkylated graphene quantum dots

NASA Astrophysics Data System (ADS)

Highly efficient and stable photoluminescence (PL) are urgently desired for graphene quantum dots (GQDs) to facilitate their prospective applications as optical materials. Here, we report the facile and straightforward synthesis of alkylated graphene quantum dots (AGQDs) via the solvothermal reaction of propagatively alkylated graphene sheets (PAGenes). In contrast to most GQDs reported so far, the synthesized AGQDs process pH-independent and ultra-bright PL with a relative quantum yield of up to 65%. Structural and chemical composition characterization demonstrated that the synthesized AGQDs are nearly oxygen-defect-free with alkyl groups decorated on edges and basal plane, which may contribute to their greatly improved pH tolerance and high quantum efficiency. The photocatalytic performance of AGQDs-P25 nanocomposites was evaluated by the degradation of Rhodamine B under visible light. The photocatalytic rate is ca. 5.9 times higher than that of pure P25, indicating that AGQDs could harness the visible spectrum of sunlight for energy conversion or environmental therapy.Highly efficient and stable photoluminescence (PL) are urgently desired for graphene quantum dots (GQDs) to facilitate their prospective applications as optical materials. Here, we report the facile and straightforward synthesis of alkylated graphene quantum dots (AGQDs) via the solvothermal reaction of propagatively alkylated graphene sheets (PAGenes). In contrast to most GQDs reported so far, the synthesized AGQDs process pH-independent and ultra-bright PL with a relative quantum yield of up to 65%. Structural and chemical composition characterization demonstrated that the synthesized AGQDs are nearly oxygen-defect-free with alkyl groups decorated on edges and basal plane, which may contribute to their greatly improved pH tolerance and high quantum efficiency. The photocatalytic performance of AGQDs-P25 nanocomposites was evaluated by the degradation of Rhodamine B under visible light. The photocatalytic rate is ca. 5.9 times higher than that of pure P25, indicating that AGQDs could harness the visible spectrum of sunlight for energy conversion or environmental therapy. Electronic supplementary information (ESI) available: Additional figures (Fig. S1-S12). See DOI: 10.1039/c4nr03506b

Feng, Lan; Tang, Xing-Yan; Zhong, Yun-Xin; Liu, Yue-Wen; Song, Xue-Huan; Deng, Shun-Liu; Xie, Su-Yuan; Yan, Jia-Wei; Zheng, Lan-Sun

2014-10-01

261

Engineered quantum dot single-photon sources

NASA Astrophysics Data System (ADS)

Fast, high efficiency and low error single-photon sources are required for the implementation of a number of quantum information processing applications. The fastest triggered single-photon sources to date have been demonstrated using epitaxially grown semiconductor quantum dots (QDs), which can be conveniently integrated with optical microcavities. Recent advances in QD technology, including demonstrations of high temperature and telecommunications wavelength single-photon emission, have made QD single-photon sources more practical. Here we discuss the applications of single-photon sources and their various requirements, before reviewing the progress made on a QD platform in meeting these requirements.

Buckley, Sonia; Rivoire, Kelley; Vu?kovi?, Jelena

2012-12-01

262

Imaging ligand-gated ion channels with quantum dots

NASA Astrophysics Data System (ADS)

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

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

2007-02-01

263

Versatile mode-locked quantum-dot laser diodes

NASA Astrophysics Data System (ADS)

Semiconductor quantum-dots have been recently showing great promise for the generation of ultrashort pulses, forming the basis of very compact and efficient ultrafast laser sources. In this paper we discuss how the unique properties of quantum-dot materials can be exploited in novel and versatile mode-locking regimes in InAs/GaAs quantum-dot edge-emitting lasers, both in monolithic and external cavity configurations. We present the current status of our research on ultrashort pulse generation involving ground (1260nm) and excited-state (1180nm) transitions, as well as the recent progress in external-cavity broadband tunable quantum-dot lasers.

Cataluna, M. A.; Rafailov, E. U.

2010-04-01

264

Progress on compact ultrafast quantum dot based lasers

NASA Astrophysics Data System (ADS)

In this paper we review the recent progress on the development of novel quantum-dot structures and laser devices. The investigation of novel regimes of ultrashort pulse generation in quantum-dot edge-emitting lasers will be presented. We illustrate how new functionalities have been opened up, such as dual-wavelength mode-locking and enhanced tunability, through the exploitation of the excited-state transitions in the quantum dots as an additional degree of freedom in these ultrafast lasers. Progress on novel design rules for quantum-dot based vertical external cavity lasers and SESAMs are also considered.

Rafailov, E. U.; Cataluna, M. A.

2010-02-01

265

Quantum Size Effects of Hydrogen Impurity at Off-Center Donor Atom in Spherical Quantum Dots

NASA Astrophysics Data System (ADS)

We obtain the numerical solutions for a single electron energy level of a hydrogen impurity confined inside an off-center donor in a spherical quantum dot. The energy spectrum of single electron impurity for off-center donor atom subject to screened Coulomb's attractive potential barrier well is presented. Using B-spline finite element method, we generate a complete set of wavefunctions within the central unit cell, and through the perturbation theory, the whole energy spectrum of an impurity at low temperature can be explored. We find that the energy splitting and different related magnetic quantum number ml, i.e., (n, l, ml) varies with quantum dot size. This is due to the fact that quantum confinement effect lifts the degeneracy which comes from the Coulomb interaction. On the other hand, the phenomena of energy spectrum splitting under this model is an analogous case, considering that degeneracy of hydrogen energy levels in free space has been lifted by an external magnetic field (Zeeman effect).

Huang, Yung Sheng; Huang, Jung Sheng; Lee, Kuan Wei; Chang, Fang-Ling

266

Enhanced performance of quantum dot solar cells based on type II quantum dots

NASA Astrophysics Data System (ADS)

The characteristics of quantum dot solar cells (QDSCs) based on type II QDs are investigated theoretically. Based on a drift-diffusion model, we obtained a much higher open circuit voltage (Voc) as well as conversion efficiency in a type II QDSC, compared to type I QDSCs. The improved Voc and efficiency are mainly attributed to the much longer Auger recombination lifetime in type II QDs. Moreover, the influence of the carrier lifetime on devices' performance is discussed and clarified. In addition, an explicit criterion to determine the role of quantum dots in solar cells is put forward.

Xu, Feng; Yang, Xiao-Guang; Luo, Shuai; Lv, Zun-Ren; Yang, Tao

2014-10-01

267

We investigate the possibility of achieving scalable photonic quantum computing by the giant optical circular birefringence induced by a quantum-dot spin in a double-sided optical microcavity as a result of cavity quantum electrodynamics. We construct a deterministic controlled-not gate on two photonic qubits by two single-photon input-output processes and the readout on an electron-medium spin confined in an optical resonant microcavity. This idea could be applied to multi-qubit gates on photonic qubits and we give the quantum circuit for a three-photon Toffoli gate. High fidelities and high efficiencies could be achieved when the side leakage to the cavity loss rate is low. It is worth pointing out that our devices work in both the strong and the weak coupling regimes. PMID:23938640

Wei, Hai-Rui; Deng, Fu-Guo

2013-07-29

268

Two-dimensional magnetoexcitons in type-II semiconductor quantum dots

NASA Astrophysics Data System (ADS)

We have investigated the excitons formed in planar type-II semiconductor structures as function of an applied magnetic field. The type-II structure studied confines the electron inside a quantum dot and keeps the hole outside; the exciton is formed by the electron-hole Coulomb attraction. The shape of the dots is varied from circular to ellipsoidal, with smooth or rough potential walls. The effects of a lattice defect and of a shallow hydrogenic impurity located close the dot are also investigated. The problem is solved numerically for two interacting particles in a two-dimensional model with the magnetic field aligned perpendicularly to the dot plane. A simpler solution with separable wave functions for the electron and the hole was used to obtain the contributions of the excited states. The exciton spectra exhibit many energy-level crossings with angular-momentum changes in agreement with the Aharonov-Bohm effect. Our results for systems with reduced symmetry (elliptical and/or rough quantum dots or with the impurity or defect) have shown anticrossings of the exciton energy levels, leading to modulations on the average energy and on the optical oscillator strength of the exciton as function of the magnetic field. Similar modulations have been observed for type-II quantum dots and they were discussed considering the reduced dot symmetry and a selective optical excitation and relaxation processes contributing to the photoluminescence signal.

Degani, Marcos H.; Maialle, Marcelo Z.; Medeiros-Ribeiro, Gilberto; Ribeiro, Evaldo

2008-08-01

269

Digital Logic Gate Using Quantum-Dot Cellular Automata

A functioning logic gate based on quantum-dot cellular automata is presented, where digital data are encoded in the positions of only two electrons. The logic gate consists of a cell, composed of four dots connected in a ring by tunnel junctions, and two single-dot electrometers. The device is operated by applying inputs to the gates of the cell. The logic

Islamshah Amlani; Alexei O. Orlov; Geza Toth; Gary H. Bernstein; Craig S. Lent; Gregory L. Snider

1999-01-01

270

The Effects of Electric Field on a Triangular Bound Potential Quantum Dot Qubit

NASA Astrophysics Data System (ADS)

On the condition of electron-LO-phonon strong coupling in a triangular bound potential quantum dot, we obtain the eigenenergy and eigenfuctions of the ground state and the first-excited state by using the Pekar type of variational method. This two-level system in a quantum dot can be employed as a qubit, which is a basic unit for quantum information operation and storage. Our numerical results indicate that the oscillation period of this qubit is an increasing function of the confinement length and the electric field. The influence of electric field on the period of oscillation becomes greater when the confinement length is increased. The electron probability density of the qubit is an increasing function of the electron-LO-phonon coupling constant. On the contrary, it is a decreasing function of the electric field. Meanwhile, the electron probability density varies periodically with the polar angle.

Yin, Ji-wen; Yu, Yi-fu; Li, Hong-juan

2014-10-01

271

Size-dependent absorption properties of CdX (X = S, Se, Te) quantum dots

NASA Astrophysics Data System (ADS)

A unified nanothermodynamic model was developed to study the size effects on first absorption peak energy and molar extinction coefficient of semiconductor quantum dots (QDs) based on size-dependent cohesive energy and quantum confinement effect. It is found that: (1) the first absorption peak energy increases as QD size decreases; (2) the molar extinction coefficient decreases with decreasing QD size in strong confinement regime and (3) tunable absorption properties of semiconductor QDs are caused by size-induced cohesive energy variation owing to severe bond dangling. The accuracy of the developed model was verified with experimental data of CdS, CdSe and CdTe QDs.

Yang, C. C.; Mai, Y.-W.

2012-05-01

272

Optical Aharonov-Bohm effect on Wigner molecules in type-II semiconductor quantum dots

NASA Astrophysics Data System (ADS)

We theoretically examine the magnetoluminescence from a trion and a biexciton in a type-II semiconductor quantum dot, in which holes are confined inside the quantum dot and electrons are in a ring-shaped region surrounding the quantum dot. First, we show that two electrons in the trion and biexciton are strongly correlated to each other, forming a Wigner molecule: Since the relative motion of electrons is frozen, they behave as a composite particle whose mass and charge are twice those of a single electron. As a result, the energy of the trion and biexciton oscillates as a function of magnetic field with half the period of the single-electron Aharonov-Bohm oscillation. Next, we evaluate the photoluminescence. Both the peak position and peak height change discontinuously at the transition of the many-body ground state, implying a possible observation of the Wigner molecule by the optical experiment.

Okuyama, Rin; Eto, Mikio; Hyuga, Hiroyuki

2011-05-01

273

Ultra-bright alkylated graphene quantum dots.

Highly efficient and stable photoluminescence (PL) are urgently desired for graphene quantum dots (GQDs) to facilitate their prospective applications as optical materials. Here, we report the facile and straightforward synthesis of alkylated graphene quantum dots (AGQDs) via the solvothermal reaction of propagatively alkylated graphene sheets (PAGenes). In contrast to most GQDs reported so far, the synthesized AGQDs process pH-independent and ultra-bright PL with a relative quantum yield of up to 65%. Structural and chemical composition characterization demonstrated that the synthesized AGQDs are nearly oxygen-defect-free with alkyl groups decorated on edges and basal plane, which may contribute to their greatly improved pH tolerance and high quantum efficiency. The photocatalytic performance of AGQDs-P25 nanocomposites was evaluated by the degradation of Rhodamine B under visible light. The photocatalytic rate is ca. 5.9 times higher than that of pure P25, indicating that AGQDs could harness the visible spectrum of sunlight for energy conversion or environmental therapy. PMID:25192187

Feng, Lan; Tang, Xing-Yan; Zhong, Yun-Xin; Liu, Yue-Wen; Song, Xue-Huan; Deng, Shun-Liu; Xie, Su-Yuan; Yan, Jia-Wei; Zheng, Lan-Sun

2014-10-01

274

Si, Ge, and SiGe quantum wires and quantum dots

NASA Astrophysics Data System (ADS)

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

Pearsall, T. P.

275

Shape evolution of InAs quantum dots during overgrowth

The effects of strain and thickness of an InxGa1?xAs (x=0?0.2) cap layer grown at low temperature on large low-growth-rate InAs quantum dots (QDs) are systematically studied by atomic force microscopy. The dot height drastically reduces and the dot shape transforms into an elongated ridge-valley structure at the early stage of GaAs overgrowth, while the dots tend to preserve their shape

R. Songmuang; S. Kiravittaya; O. G. Schmidt

2003-01-01

276

Lifetime blinking in nonblinking nanocrystal quantum dots

Nanocrystal quantum dots are attractive materials for applications as nanoscale light sources. One impediment to these applications is fluctuations of single-dot emission intensity, known as blinking. Recent progress in colloidal synthesis has produced nonblinking nanocrystals; however, the physics underlying blinking suppression remains unclear. Here we find that ultra-thick-shell CdSe/CdS nanocrystals can exhibit pronounced fluctuations in the emission lifetimes (lifetime blinking), despite stable nonblinking emission intensity. We demonstrate that lifetime variations are due to switching between the neutral and negatively charged state of the nanocrystal. Negative charging results in faster radiative decay but does not appreciably change the overall emission intensity because of suppressed nonradiative Auger recombination for negative trions. The Auger process involving excitation of a hole (positive trion pathway) remains efficient and is responsible for charging with excess electrons, which occurs via Auger-assisted ionization of biexcitons accompanied by ejection of holes. PMID:22713750

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

2012-01-01

277

PREFACE: Quantum dots as probes in biology

NASA Astrophysics Data System (ADS)

The recent availability of nanostructured materials has resulted in an explosion of research focused on their unique optical, thermal, mechanical and magnetic properties. Optical imagining, magnetic enhancement of contrast and drug delivery capabilities make the nanoparticles of special interest in biomedical applications. These materials have been involved in the development of theranostics—a new field of medicine that is focused on personalized tests and treatment. It is likely that multimodal nanomaterials will be responsible for future diagnostic advances in medicine. Quantum dots (QD) are nanoparticles which exhibit luminescence either through the formation of three-dimensional excitons or excitations of the impurities. The excitonic luminescence can be tuned by changing the size (the smaller the size, the higher the frequency). QDs are usually made of semiconducting materials. Unlike fluorescent proteins and organic dyes, QDs resist photobleaching, allow for multi-wavelength excitations and have narrow emission spectra. The techniques to make QDs are cheap and surface modifications and functionalizations can be implemented. Importantly, QDs could be synthesized to exhibit useful optomagnetic properties and, upon functionalization with an appropriate biomolecule, directed towards a pre-selected target for diagnostic imaging and photodynamic therapy. This special issue on Quantum dots in Biology is focused on recent research in this area. It starts with a topical review by Sreenivasan et al on various physical mechanisms that lead to the QD luminescence and on using wavelength shifts for an improvement in imaging. The next paper by Szczepaniak et al discusses nanohybrids involving QDs made of CdSe coated by ZnS and combined covalently with a photosynthetic enzyme. These nanohybrids are shown to maintain the enzymatic activity, however the enzyme properties depend on the size of a QD. They are proposed as tools to study photosynthesis in isolated photosynthetic systems. The next paper, by Olejnik et al, discussed metallic QDs which enhance photosynthetic function in light-harvesting biomolecular complexes. Such hybrid structures with gold QDs are shown to exhibit a strong increase in the fluorescence quantum yield. The next two papers, by Sikora et al and Kaminska et al deal with the ZnO nanoparticles passivated by MgO. In the first of these two papers, the authors describe the behavior of ZnO/MgO when introduced to human cancer cells. In the second, the authors describe the QDs with an extra outer layer of Fe2O3 which makes the nanoparticles superparamagnetic and also capable of generation of reactive oxygen species which could be applied to form localized centers of toxicity for cancer treatment. Finally, in the last paper by Yatsunenko et al, the authors discuss several semiconducting QDs like ZnO with various rare-earth dopands. They propose a microwave-driven hydrothermal technology to make them, characterize their luminescence and demonstrate their usefulness in the early recognition of cancer tissues. Quantum dots as probes in biology contents Quantum dots as probes in biologyMarek Cieplak Luminescent nanoparticles and their applications in the life sciencesVarun K A Sreenivasan, Andrei V Zvyagin and Ewa M Goldys Ferredoxin:NADP+ oxidoreductase in junction with CdSe/ZnS quantum dots: characteristics of an enzymatically active nanohybrid Krzysztof Szczepaniak, Remigiusz Worch and Joanna Grzyb Spectroscopic studies of plasmon coupling between photosynthetic complexes and metallic quantum dotsMaria Olejnik, Bartosz Krajnik, Dorota Kowalska, Guanhua Lin and Sebastian Mackowski Luminescence of colloidal ZnO nanoparticles synthesized in alcohols and biological application of ZnO passivated by MgOBo?ena Sikora, Krzysztof Fronc, Izabela Kami?ska, Kamil Koper, Piotr St?pie? and Danek Elbaum Novel ZnO/MgO/Fe2O3 composite optomagnetic nanoparticles I Kami?ska, B Sikora, K Fronc, P Dziawa, K Sobczak, R Minikayev, W Paszkowicz and D Elbaum Impact of yttria stabilization on Tb3+ intra-shell luminescence efficiency in

Cieplak, Marek

2013-05-01

278

Design and fabrication of quantum-dot lasers

Semiconductor lasers using quantum-dots in their active regions have been reported to exhibit significant performance advantages over their bulk semiconductor and quantum-well counterparts namely: low threshold current, ...

Nabanja, Sheila

2008-01-01

279

Tuning the quantum critical crossover in quantum dots

NASA Astrophysics Data System (ADS)

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

Murthy, Ganpathy

2005-03-01

280

Two-electron volcano-shaped quantum dot

NASA Astrophysics Data System (ADS)

We propose a simple model of non-uniform volcano-shaped quantum dot that reflects the confinement details of the morphology of really fabricated GaAs/InAs nanorings and whose profile geometry, on the one hand, is described by means of simple analytical functions and, on the other hand, allows us to find exact one-particle wave functions. By using them as a basis function we calculate two-electron lower energies as functions of the external magnetic field applied along the growth axis. We show that the ring morphology and electron-electron interaction have great influence on the energy spectrum structure of nanoring and the Aharonov-Bohm oscillations.

Garcia, L. F.; Gutiérrez, W.; Mikhailov, I. D.

2014-12-01

281

Multi-electron double quantum dot spin qubits

NASA Astrophysics Data System (ADS)

Double quantum dot (DQD) spin quits in a solid state environment typically consist of two electron spins confined to a DQD potential. We analyze the viability and potential advantages of DQD qubits which use greater then two electrons, and present results for six-electron qubits using full configuration interaction methods. The principal results of this work are that such six electron DQDs can retain an isolated low-energy qubit space that is more robust to charge noise due to screening. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Nielsen, Erik; Kestner, Jason; Barnes, Edwin; Das Sarma, Sankar

2013-03-01

282

Quantum dots fluorescence quantum yield measured by Thermal Lens Spectroscopy.

An essential parameter to evaluate the light emission properties of fluorophores is the fluorescence quantum yield, which quantify the conversion efficiency of absorbed photons to emitted photons. We detail here an alternative nonfluorescent method to determine the absolute fluorescence quantum yield of quantum dots (QDs). The method is based in the so-called Thermal Lens Spectroscopy (TLS) technique, which consists on the evaluation of refractive index gradient thermally induced in the fluorescent material by the absorption of light. Aqueous dispersion carboxyl-coated cadmium telluride (CdTe) QDs samples were used to demonstrate the Thermal Lens Spectroscopy technical procedure. PMID:25103802

Estupiñán-López, Carlos; Dominguez, Christian Tolentino; Cabral Filho, Paulo E; Fontes, Adriana; de Araujo, Renato E

2014-01-01

283

Electrically injected quantum-dot photonic crystal microcavity light sources

The design, fabrication, and characterization of an electrically injected quantum-dot photonic crystal microcavity light source are described. The optical gain in the GaAs\\/AlGaAs-based device is provided by self-organized InGaAs quantum dots with ground-state room-temperature emission at 1.1 µm. The carriers are injected directly into the photonic crystal microcavity, which contains ˜50 dots, avoiding surface state recombination in the photonic crystal

J. Topol'Ancik; S. Chakravarty; P. Bhattacharya; S. Chakrabarti

2006-01-01

284

We report on the development and testing of a coplanar stripline antenna that is designed for integration in a magneto-photoluminescence experiment to allow coherent control of individual electron spins confined in single self-assembled semiconductor quantum dots. We discuss the design criteria for such a structure which is multi-functional in the sense that it serves not only as microwave delivery but also as electrical top gate and shadow mask for the single quantum dot spectroscopy. We present test measurements on hydrogenated amorphous silicon, demonstrating electrically detected magnetic resonance using the in-plane component of the oscillating magnetic field created by the coplanar stripline antenna necessary due to the particular geometry of the quantum dot spectroscopy. From reference measurements using a commercial electron spin resonance setup in combination with finite element calculations simulating the field distribution in the structure, we obtain a magnetic field of 0.12 mT at the position where the quantum dots would be integrated into the device. The corresponding ?-pulse time of ?0.5??s meets the requirements set by the high sensitivity optical spin read-out scheme developed for the quantum dot. PMID:21806214

Klotz, F; Huebl, H; Heiss, D; Klein, K; Finley, J J; Brandt, M S

2011-07-01

285

High Resolution and High Collection Efficiency of Single Quantum Dots.

High Resolution and High Collection Efficiency of Single Quantum Dots. A. N. Vamivakas1 ,Z. Liu2GaAs quantum dots (QDs) grown by Stranski-Krastanow self-assembly on GaAs substrates [1]. In self-assembled QD the resolution and collection efficiency of our optical microscopy system. In contrast to conventional Solid

286

Wavelength tunable mode-locked quantum-dot laser

NASA Astrophysics Data System (ADS)

We study the characteristics of wavelength tunable quantum-dot mode-locked lasers using a curved two-section device, external grating, and optical bandpass filter. Wide wavelength tunability is demonstrated due to the fact that the center wavelength of mode-locking is extended to excited state transitions as well as ground state transitions of the quantum-dot gain media.

Kim, Jimyung; Choi, Myoung-Taek; Lee, Wangkuen; Delfyett, Peter J., Jr.

2006-05-01

287

Modified Quantum Dots Could Lead to Improved Treatments for Cancer

NSDL National Science Digital Library

This online article from Carnegie Mellon Today, discusses how chemists are researching quantum dots to evaluate their effectiveness in treating diseases such as cancer. Readers can discover how the scientists were able to produce quantum dots that fluoresced for an unprecedented eight months, and how they might be useful in locating diseases like cancer.

Pavlak, Amy

1969-12-31

288

Spin storage and readout in self-organized quantum dots

NASA Astrophysics Data System (ADS)

We demonstrate optical charging of spectrally selected subensembles of self-organized quantum dots with single charge carriers. By circularly polarized excitation in an applied magnetic field, we are able to address the spin of single electron in the quantum dot. A spin-flip of the electron is observed after excitation in the upper Zeeman level.

Warming, T.; Wieczorek, W.; Geller, M.; Bimberg, D.; Cirlin, G. E.; Zhukov, A. E.; Ustinov, V. M.

2007-04-01

289

Nanocrystal Quantum Dots: From Fundamental Photophysics to Multicolor Lasing

NSDL National Science Digital Library

This PDF document was created by Victor Klimov of the Los Alamos National Laboratory. It discussing the development of a new laser based on quantum dots. The site supplies a series of figures illustrating the nonradiative multiparticle auger recombinations in nanocrystal quantum dots, amplified spontaneous emissions, and more.

Klimov, Victor

2008-07-04

290

Quantum confinement in Si and Ge nanostructures: effect of crystallinity

NASA Astrophysics Data System (ADS)

We look at the relationship between the preparation method of Si and Ge nanostructures (NSs) and the structural, electronic, and optical properties in terms of quantum confinement (QC). QC in NSs causes a blue shift of the gap energy with decreasing NS dimension. Directly measuring the effect of QC is complicated by additional parameters, such as stress, interface and defect states. In addition, differences in NS preparation lead to differences in the relevant parameter set. A relatively simple model of QC, using a `particle-in-a-box'-type perturbation to the effective mass theory, was applied to Si and Ge quantum wells, wires and dots across a variety of preparation methods. The choice of the model was made in order to distinguish contributions that are solely due to the effects of QC, where the only varied experimental parameter was the crystallinity. It was found that the hole becomes de-localized in the case of amorphous materials, which leads to stronger confinement effects. The origin of this result was partly attributed to differences in the effective mass between the amorphous and crystalline NS as well as between the electron and hole. Corrections to our QC model take into account a position dependent effective mass. This term includes an inverse length scale dependent on the displacement from the origin. Thus, when the deBroglie wavelength or the Bohr radius of the carriers is on the order of the dimension of the NS the carriers `feel' the confinement potential altering their effective mass. Furthermore, it was found that certain interface states (Si-O-Si) act to pin the hole state, thus reducing the oscillator strength.

Barbagiovanni, Eric G.; Lockwood, David J.; Costa Filho, Raimundo N.; Goncharova, Lyudmila V.; Simpson, Peter J.

2013-10-01

291

Quantum optics and cavity QED with quantum dots in photonic crystals

This chapter will primarily focus on the studies of quantum optics with semiconductor, epitaxially grown quantum dots embedded in photonic crystal cavities. We will start by giving brief introductions into photonic crystals and quantum dots, then proceed with the introduction to cavity quantum electrodynamics (QED) effects, with a particular emphasis on the demonstration of these effects on the quantum dot-photonic crystal platform. Finally, we will focus on the applications of such cavity QED effects.

Vuckovic, Jelena

2014-01-01

292

Intraband carrier photoexcitation in quantum dot lasers.

We unveil the role of bound-to-continuum photoexcitation of carriers as a relevant process that affects the performance of quantum dot (QD) lasers. We present the response of an InAs/InGaAs QD laser to a sub-band gap pump, showing an unexpected depletion of the emitted photons. We relate this observation with carrier photoexcitation through additional transmission and photocurrent measurements. We provide a theoretical support to the experimental data and highlight the important role of this process in the laser characteristics. PMID:18278879

Moreno, P; Richard, M; Rossetti, M; Portella-Oberli, M; Li, L H; Deveaud-Plédran, B; Fiore, A

2008-03-01

293

Superexchange blockade in triple quantum dots

We propose the interaction of two electrons in a triple quantum dot as a minimal system to control long range superexchange transitions. These are probed by transport spectroscopy. Narrow resonances appear indicating the transfer of charge from one side of the sample to the other with the central one being occupied only virtually. We predict that two different intermediate states establish the two arms of a one dimensional interferometer. Configurations of destructive interference of the two superexchage trajectories totally block the current through the system. We emphasize the role of spin correlations giving rise to lifetime-enhanced resonances.

Rafael Sánchez; Fernando Gallego-Marcos; Gloria Platero

2013-12-09

294

Ab initio computation of circular quantum dots

We perform coupled-cluster and diffusion Monte Carlo calculations of the energies of circular quantum dots up to 20 electrons. The coupled-cluster calculations include triples corrections and a renormalized Coulomb interaction defined for a given number of low-lying oscillator shells. Using such a renormalized Coulomb interaction brings the coupled-cluster calculations with triples correlations in excellent agreement with the diffusion Monte Carlo calculations. This opens up perspectives for doing ab initio calculations for much larger systems of electrons.

M. Pedersen Lohne; G. Hagen; M. Hjorth-Jensen; S. Kvaal; F. Pederiva

2010-09-24

295

Quantum dots in diagnostics and detection: principles and paradigms.

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

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

2014-06-21

296

Pristine graphene quantum dots and graphene oxide quantum dots are synthesized by chemical exfoliation from the graphite nanoparticles with high uniformity in terms of shape (circle), size (less than 4 nm), and thickness (monolayer). The origin of the blue and green photoluminescence of GQDs and GOQDs is attributed to intrinsic and extrinsic energy states, respectively. PMID:23712762

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

2013-07-19

297

Analysis of electronic structures of quantum dots using meshless Fourier transform k·p method

NASA Astrophysics Data System (ADS)

We develop a complete Fourier transform k.p method and present its application for a theoretical investigation on electronic structures of quantum dots with consideration of the built-in strain effects. The Fourier transform technique is applied to the periodic position-dependent Hamiltonian, and a simple and neat expression of the Hamiltonian matrix in the Fourier domain is formulated due to the orthogonality of exponential functions. Spurious solutions can be avoided due to the truncation of high Fourier frequencies. A kinetic Hamiltonian matrix in momentum domain is formulated by entering the analytical Fourier transform of the quantum-dot shape function into the neat Hamiltonian matrix easily, which allows meshless numerical implementation. The formulation of strain Hamiltonian matrix is done by convolution of Fourier series of strain components and Fourier series of the quantum-dot shape functions. Therefore, an original Fourier transform-based k.p approach is developed by combining the kinetic Hamiltonian matrix and the strain Hamiltonian. This approach is adopted to study the dimension effect and strain effect on the ground states of electrons and holes of pyramidal quantum dots that are truncated to different heights. The ground-state energy variation shows that the electron state is the most sensitive to these effects and the strain effect on E1, LH1, and HH1 is more prominent for sharperquantum dots. This investigation shows that band mixing between the conduction band and valence band, and band mixing between heavy-hole and light-hole bands are reduced due to the strain effect, whereas this effect is more prominent for nontruncated pyramidal quantum dots due to the stress concentration. Among the three ground states, light-hole states are more weakly confined in the nonpyramidal quantum dot and shift to the tip of the pyramid due to the strain.

Zhao, Qiuji; Mei, Ting

2011-03-01

298

Spin quantum jumps in a singly charged quantum dot

NASA Astrophysics Data System (ADS)

We model the population and coherence dynamics of a singly charged quantum dot driven by a constant optical field. Using a separation of time scales we predict the occurrence of quantum jumps in the spin state of the excess electron or hole. Our analysis extends the description of intermittent fluorescence from a three-level to a four-level description; the former is common in atomic systems, the later occurs in many solid-state systems. The statistics of the quantum jumps as function of the intensity of the driving field provide detailed information on physical processes that limit the ground-state coherence of these systems and their use as a solid-state quantum bit. In particular it enables a discrimination of coherent spin coupling, induced by the nuclear magnetic field, from incoherent spin flips; the coherent coupling can gradually be suppressed by increasing the pump intensity due to the quantum Zeno effect.

van Exter, M. P.; Gudat, J.; Nienhuis, G.; Bouwmeester, D.

2009-08-01

299

FIG. 1: Size-dependent color emission of quantum dots. This is a purely quantum mechanical effect. FIG. 2: Size-dependent color emission of quantum dots. This is a purely quantum mechanical effect. 1 #12;FIG. 3: Size-dependent color emission of quantum dots. This is a purely quantum mechanical effect

Nielsen, Steven O.

300

Rare-earth doped GaN and InGaN quantum dots grown by plasma assisted MBE

We report on the MBE growth of GaN and InGaN quantum dots (QDs) doped with rare earth ions, namely Eu, Tm and Tb exhibiting red, blue and green luminescence, respectively. Intense photoluminescence\\/cathodoluminescence is observed, resulting from the spatial localization of rare earth ions in dots combined with the confinement properties of the carriers. White light emission has been produced by

Y. Hori; T. Andreev; X. Biquard; E. Monroy; D. Jalabert; Le Si Dang; M. Tanaka; O. Oda; B. Daudin

2005-01-01

301

Universal Braess paradox in open quantum dots

NASA Astrophysics Data System (ADS)

We present analytical and numerical results that demonstrate the presence of the Braess paradox in chaotic quantum dots. The paradox that we identify, originally perceived in classical networks, shows that the addition of more capacity to the network can suppress the current flow in the universal regime. We investigate the weak localization term, showing that it presents the paradox encoded in a saturation minimum of the conductance, under the presence of hyperflow in the external leads. In addition, we demonstrate that the weak localization suffers a transition signal depending on the overcapacity lead and presents an echo on the magnetic crossover before going to zero due to the full time-reversal symmetry breaking. We also show that the quantum interference contribution can dominate the Ohm term in the presence of constrictions and that the corresponding Fano factor engenders an anomalous behavior.

Barbosa, A. L. R.; Bazeia, D.; Ramos, J. G. G. S.

2014-10-01

302

Semiconductor Quantum Dots for Biomedicial Applications

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

Shao, Lijia; Gao, Yanfang; Yan, Feng

2011-01-01

303

Effects of quantum dot characteristics on electronic spin-subband state entanglement

NASA Astrophysics Data System (ADS)

The entanglement dynamics of spin-subband states for an electron in a 2D isotropic Rashba quantum dot, with an applied magnetic field of arbitrary strength, is studied. We explicitly include the confining (gate) effects as a two-dimensional isotropic harmonic oscillator. The von Neumann entropy, as a measure of entanglement, is calculated as a function of time, by going to the Fock-Darwin representation. Our results indicate that the period and amplitude of the collapse-revival behavior of the entanglement between the spin states and the structural subbands strongly depend upon the size of the quantum dot (confining length) and choice of heterostructural materials. Our results, thereby, provide means of controlling the degree of entanglement by adjusting these factors.

Safaiee, R.; Foroozani, N.; Golshan, M. M.

2009-02-01

304

Competing interactions in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

305

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

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. PMID:23013605

2012-01-01

306

Exciton in vertically coupled type II quantum dots in threading magnetic field

NASA Astrophysics Data System (ADS)

We analyze the energy spectrum of a neutral 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 dots tunneling between them while the hole generally is placed in the exterior region close to the symmetry axis. Solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are presented for the energies of bonding and anti-bonding lowest-lying of the exciton states and for the density of states for different InP/GaInP quantum dots' morphologies and the magnetic field strength values.

Mendoza-Cantillo, J.; Escorcia-Salas, G. Elizabeth; Mikhailov, I. D.; Sierra-Ortega, J.

2014-11-01

307

Minimal self-contained quantum refrigeration machine based on four quantum dots.

We present a theoretical study of an electronic quantum refrigerator based on four quantum dots arranged in a square configuration, in contact with as many thermal reservoirs. We show that the system implements the minimal mechanism for acting as a self-contained quantum refrigerator, by demonstrating heat extraction from the coldest reservoir and the cooling of the nearby quantum dot. PMID:23829751

Venturelli, Davide; Fazio, Rosario; Giovannetti, Vittorio

2013-06-21

308

Discrete quantum Fourier transform in coupled semiconductor double quantum dot molecules

In this Letter, we present a physical scheme for implementing the discrete quantum Fourier transform in a coupled semiconductor double quantum dot system. The main controlled-R gate operation can be decomposed into many simple and feasible unitary transformations. The current scheme would be a useful step towards the realization of complex quantum algorithms in the quantum dot system.

Ping Dong; Ming Yang; Zhuo-Liang Cao

2007-04-17

309

Photovoltaic quantum dot quantum cascade infrared photodetector A. V. Barve and S. Krishna

Photovoltaic quantum dot quantum cascade infrared photodetector A. V. Barve and S. Krishna Citation subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions #12;Photovoltaic) Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared

Krishna, Sanjay

310

NASA Astrophysics Data System (ADS)

Efficient iso-entropic energy filtering of electronic waves can be realized through nanostructures with three dimensional confinement, such as quantum dot resonant tunneling structures. Large-area deployment of such structures is useful for energy selective contacts but such configuration is susceptible to structural disorders. In this work, the transport properties of quantum-dot-based wide-area resonant tunneling structures, subject to realistic disorder mechanisms, are studied. Positional variations of the quantum dots are shown to reduce the resonant transmission peaks while size variations in the device are shown to reduce as well as broaden the peaks. Increased quantum dot size distribution also results in a peak shift to lower energy which is attributed to large dots dominating transmission. A decrease in barrier thickness reduces the relative peak height while the overall transmission increases dramatically due to lower "series resistance." While any shift away from ideality can be intuitively expected to reduce the resonance peak, quantification allows better understanding of the tolerances required for fabricating structures based on resonant tunneling phenomena.

Puthen-Veettil, B.; Patterson, R.; König, D.; Conibeer, G.; Green, M. A.

2014-10-01

311

Quantum Dot Self-Assembly for Protein Detection with Sub-Picomolar Sensitivity

Quantum Dot Self-Assembly for Protein Detection with Sub-Picomolar Sensitivity Chinmay P. Soman and rapid antigen detection is described. In the presence of a specific antigen, quantum dot other things, the relative concentration of quantum dot conjugates and antigen molecules. Quantum dot

312

Electroluminescence of carbon ‘quantum' dots - From materials to devices

NASA Astrophysics Data System (ADS)

Carbon ‘quantum' dots or carbon dots have emerged as a new class of luminescent nanomaterials. While photoluminescence properties of carbon dots had targeted optical imaging and related usage, their unique excited state redox processes responsible for the luminescence emissions may find potentially significant optoelectronic applications. In this regard, we investigated the electroluminescence properties of the carbon dots integrated into multilayer light emitting diode devices. The devices emitted white light with a slight blue color, visible to naked eyes, thus validating the expectation that carbon dots may potentially serve as a new platform for electroluminescent nanomaterials.

Veca, L. Monica; Diac, Andreea; Mihalache, Iuliana; Wang, Ping; LeCroy, Gregory E.; Pavelescu, Emil Mihai; Gavrila, Raluca; Vasile, Eugeniu; Terec, Anamaria; Sun, Ya-Ping

2014-10-01

313

Quantum emission efficiency of nanocrystalline and amorphous Si quantum dots

The paper presents the comparison of emission efficiencies for crystalline Si quantum dots (QDs) and amorphous Si nanoclusters (QDs) embedded in hydrogenated amorphous (a-Si:H) films grown by the hot wire-CVD method (HW-CVD) at the variation of technological parameters. The correlations between the intensities of different PL bands and the volumes of Si nanocrystals (nc-Si:H) and\\/or an amorphous (a-Si:H) phase have

T. V. Torchynska

2011-01-01

314

RKKY interaction in a chirally coupled double quantum dot system

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

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

2013-12-04

315

Electron energy level calculations for cylindrical narrow gap semiconductor quantum dot

Three computational techniques are presented for approximation of the ground state energy and wave function of an electron confined by a disk-shaped InAs quantum dot (QD) embedded in GaAs matrix. The problem is treated with the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, and the Ben-Daniel Duke boundary conditions. To solve the three

Yiming Li; Jinn-Liang Liu; O. Voskoboynikov; C. P. Lee; S. M. Sze

2001-01-01

316

Acoustic-phonon Raman scattering in InAs\\/InP self-assembled quantum dots

Single layers of self-assembled InAs\\/InP quantum dots (QD) are studied by Raman scattering excited in resonance with the confined E1 transition of InAs. Intense periodic oscillations are observed in the low-frequency Stokes and anti-Stokes spectra of both capped and uncapped QD. By using a controlled chemical etching, we progressively reduced the thickness of the InP cap layer. We found that

J. R. Huntzinger; J. Groenen; M. Cazayous; A. Mlayah; N. Bertru; C. Paranthoen; O. Dehaese; H. Carrère; E. Bedel; G. Armelles

2000-01-01

317

Low chirp observed in directly modulated quantum dot lasers

We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as

Hideaki Saito; Kenichi Nishi; Akio Kamei; Shigeo Sugou

2000-01-01

318

Deterministic Coupling of Single Quantum Dots to Single Nanocavity Modes

We demonstrate a deterministic approach to the implementation of solid-state cavity quantum electrodynamics (QED) systems based on a precise spatial and spectral overlap between a single self-assembled quantum dot and a photonic crystal membrane nanocavity. By fine-tuning nanocavity modes with a high quality factor into resonance with any given quantum dot exciton, we observed clear signatures of cavity QED (such

Antonio Badolato; Kevin Hennessy; Mete Atatüre; Jan Dreiser; Evelyn Hu; Pierre M. Petroff; Atac Imamoglu

2005-01-01

319

Ferritin-templated quantum dots for quantum logic gates (Invited Paper)

Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The work presented here offers a new method to develop quantum-dots using a bio-template, called ferritin, that ensures QD

Sang H. Choi; Jae-Woo Kim; Sang-Hyon Chu; Glen C. King; Peter T. Lillehei; Seon-Jeong Kim; James R. Elliott

2005-01-01

320

Double quantum dot in a quantum dash: Optical properties

We study the optical properties of highly elongated, highly flattened quantum dot structures, also referred to as quantum dashes, characterized by the presence of two trapping centers located along the structure. Such a system can exhibit some of the properties characteristic for double quantum dots. We show that sub- and super-radiant states can form for certain quantum dash geometries, which is manifested by a pronounced transfer of intensity between spectral lines, accompanied by the appearance of strong electron-hole correlations. We also compare exciton absorption spectra and polarization properties of a system with a single and double trapping center and show how the geometry of multiple trapping centers influences the optical properties of the system. We show that for a broad range of trapping geometries the relative absorption intensity of the ground state is larger than that of the lowest excited states, contrary to the quantum dash systems characterized by a single trapping center. Thus, optical properties of these structures are determined by fine details of their morphology.

Kaczmarkiewicz, Piotr, E-mail: piotr.kaczmarkiewicz@pwr.wroc.pl; Machnikowski, Pawe? [Institute of Physics, Wroc?aw University of Technology, 50-370 Wroc?aw (Poland); Kuhn, Tilmann [Institut für Festkörpertheorie, Westfälische Wilhelms-Universität, 48149 Münster (Germany)

2013-11-14

321

Three-dimensional Si/Ge quantum dot crystals.

Modern nanotechnology offers routes to create new artificial materials, widening the functionality of devices in physics, chemistry, and biology. Templated self-organization has been recognized as a possible route to achieve exact positioning of quantum dots to create quantum dot arrays, molecules, and crystals. Here we employ extreme ultraviolet interference lithography (EUV-IL) at a wavelength of lambda = 13.5 nm for fast, large-area exposure of templates with perfect periodicity. Si(001) substrates have been patterned with two-dimensional hole arrays using EUV-IL and reactive ion etching. On these substrates, three-dimensionally ordered SiGe quantum dot crystals with the so far smallest quantum dot sizes and periods both in lateral and vertical directions have been grown by molecular beam epitaxy. X-ray diffractometry from a sample volume corresponding to about 3.6 x 10(7) dots and atomic force microscopy (AFM) reveal an up to now unmatched structural perfection of the quantum dot crystal and a narrow quantum dot size distribution. Intense interband photoluminescence has been observed up to room temperature, indicating a low defect density in the three-dimensional (3D) SiGe quantum dot crystals. Using the Ge concentration and dot shapes determined by X-ray and AFM measurements as input parameters for 3D band structure calculations, an excellent quantitative agreement between measured and calculated PL energies is obtained. The calculations show that the band structure of the 3D ordered quantum dot crystal is significantly modified by the artificial periodicity. A calculation of the variation of the eigenenergies based on the statistical variation in the dot dimensions as determined experimentally (+/-10% in linear dimensions) shows that the calculated electronic coupling between neighboring dots is not destroyed due to the quantum dot size variations. Thus, not only from a structural point of view but also with respect to the band structure, the 3D ordered quantum dots can be regarded as artificial crystal. PMID:17892317

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

2007-10-01

322

NASA Astrophysics Data System (ADS)

The energy spectrum of a positively charged exciton confined in vertically coupled type II quantum dots with different morphologies in the presence of the external magnetic field is studied. The effect of the quantum dot morphology on the curves of the lowest energy levels as functions of the magnetic field is analyzed. It is shown that a strong correlation presented in this system generates the Aharonov-Bohm oscillations of the lower energy levels similar to those in wide quantum ring. The novel curves of the trion energies dependences on the external magnetic field for the disk-like, lens-like, and cone-like structures are presented.

Horta-Piñeres, Sindi; Elizabeth Escorcia-Salas, G.; Mikhailov, I. D.; Sierra-Ortega, J.

2014-11-01

323

The size of silicon quantum dots (Si QDs) embedded in silicon nitride (SiN{sub x}) has been controlled by varying the total pressure in the plasma-enhanced chemical vapor deposition (PECVD) reactor. This is evidenced by transmission electron microscopy and results in a shift in the light emission peak of the quantum dots. We show that the luminescence in our structures is attributed to the quantum confinement effect. These findings give a strong indication that the quality (density and size distribution) of Si QDs can be improved by optimizing the deposition parameters which opens a route to the fabrication of an all-Si tandem solar cell.

Rezgui, B.; Sibai, A.; Nychyporuk, T.; Lemiti, M.; Bremond, G. [Universite de Lyon, Institut des Nanotechnologies de Lyon INL-UMR5270, CNRS, INSA de Lyon, Villeurbanne F-69621 (France); Maestre, D.; Palais, O. [IM2NP, CNRS UMR 6242, Universite Aix-Marseille, Avenue Escadrille Normandie Niemen, Case 142, 13397, Marseille Cedex 20 (France)

2010-05-03

324

Density and Depth of Natural Quantum Dots in Silicon MOS Structures

NASA Astrophysics Data System (ADS)

Electron spins in MOS structures have shown promise as qubits for quantum information processing. Typically, characteristics such as mobility, mid-gap interface states and oxide fixed charge are considered figures of merit for the Si/SiO2 interface, however, other properties may be important. Recently, we have shown that, by biasing the gate above threshold and then reducing VG to 0V, we freeze electrons into natural quantum dots, where 2D electrons are confined by interface disorder. The depth of these dots is determined by the temperature and can be extracted using a Schottky-Hall-Read model. Additionally, we measure the density of confined electron states from the magnitude of the ESR signal. These measurements offer us a means to characterize the interface disorder in these MOS structures. Experiments have been performed on devices from different labs. Preliminary results from industrial quality devices fabricated at Sandia National Laboratories indicate a shallower dot depth, though a similar mobility. The shallower confinement suggests a higher quality for single-electron quantum devices.

Jock, R. M.; Shankar, S.; Tyryshkin, A. M.; He, J.-H.; Lyon, S. A.; Eng, K.; Childs, K.; Tracy, L.; Lilly, M.; Carroll, M.

2011-03-01

325

Quantum dot nanoparticle conjugation, characterization, and applications in neuroscience

NASA Astrophysics Data System (ADS)

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

Pathak, Smita

326

Electron and nuclear spins in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

The electron and nuclear spin degrees of freedom in two-dimensional semiconductor quantum dots are studied as important resources for such fields as spintronics and quantum information. The coupling of electron spins to their orbital motion, via the spin-orbit interaction, and to nuclear spins, via the hyperfine interaction, are important for understanding spin-dynamics in quantum dot systems. This work is concerned with both of these interactions as they relate to two-dimensional semiconductor quantum dots. We first consider the spin-orbit interaction in many-electron quantum dots, studying its role in conductance fluctuations. We further explore the creation and destruction of spin-polarized currents by chaotic quantum dots in the strong spin-orbit limit, finding that even without magnetic fields or ferromagnets (i.e., with time reversal symmetry) such systems can produce large spin-polarizations in currents passing through a small number of open channels. We use a density matrix formalism for transport through quantum dots, allowing consideration of currents entangled between different leads, which we show can have larger fluctuations than currents which are not so entangled. Second, we consider the hyperfine interaction between electrons and approximately 106 nuclei in two-electron double quantum dots. The nuclei in each dot collectively form an effective magnetic field interacting with the electron spins. We show that a procedure originally explored with the intent to polarize the nuclei can also equalize the effective magnetic fields of the nuclei in the two quantum dots or, in other parameter regimes, can cause the effective magnetic fields to have large differences.

Krich, Jacob Jonathan

327

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

We study the coupling between a photonic crystal cavity and an off-resonant quantum dot under resonant excitation of the cavity or the quantum dot. Linewidths of the quantum dot and the cavity as a function of the excitation laser power are measured. We show that the linewidth of the quantum dot, measured by observing the cavity emission, is significantly broadened compared to the theoretical estimate. This indicates additional incoherent coupling between the quantum dot and the cavity.

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

2010-03-11

328

Optimal tunneling enhances the quantum photovoltaic effect in double quantum dots

We investigate the quantum photovoltaic effect in double quantum dots by applying the nonequilibrium quantum master equation. A drastic suppression of the photovoltaic current is observed near the open circuit voltage, ...

Wang, Chen

329

Full counting statistics of quantum dot resonance fluorescence

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

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

2014-01-01

330

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

NASA Technical Reports Server (NTRS)

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

Qiu, Y.; Uhl, D.

2002-01-01

331

Electric control of the exciton fine structure in nonparabolic quantum dots

NASA Astrophysics Data System (ADS)

We show that the nonparabolic confinement potential is responsible for the nonmonotonic behavior and sign change of the exciton fine-structure splitting (FSS) in optically active self-assembled quantum dots. This insight is important for the theoretical understanding and practical control by electric fields of the quantum state of the emitted light from a biexciton cascade recombination process. We find that a hard-wall (box) confinement potential leads to a FSS that is in better agreement with experimentally measured FSS than a harmonic potential. We then show that a finite applied electric field can be used to remove the FSS entirely, thus allowing for the creation of maximally entangled photons, being vital to the growing field of quantum communication and quantum key distribution.

Welander, Erik; Burkard, Guido

2012-10-01

332

NEST Scientific Report 2007-2009 Probing collective modes of correlated states of few electrons electrons confined in GaAs quantum dots (QDs) are probed by resonant inelastic light scattering. We to the fundamental interactions. The case of QDs with four electrons is found to be determined by a competition

Abbondandolo, Alberto

333

National Technical Information Service (NTIS)

We use magnetotunnelling spectroscopy as a non-invasive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The images reveal clearly the elliptical symmetry of ...

A. Levin, A. Patane, E. E. Vdovin, L. Eaves, P. C. Main

2001-01-01

334

Inserting one single Mn ion into a quantum dot

A method of growth to get one single Mn in self-assembled semiconductor quantum dot is presented. With a simple quantitative model, the appropriate low Mn density needed prior to the quantum dot nucleation is estimated. Such a low Mn concentration was reached by inserting a thin ZnTe spacer between a Zn{sub 1-x}Mn{sub x}Te buffer and the CdTe quantum dot layer. The control of Mn density is made by changing the thickness of the ZnTe spacer, with good reproducibility. Qualitative and quantitative comparisons of optical spectra for different samples assess the relevance of this growth method.

Maingault, Laurent; Besombes, L.; Leger, Y.; Bougerol, C.; Mariette, H. [CEA-CNRS-UJF Group Nanophysics and Semiconductor, Laboratoire de Spectrometrie Physique, Universite Joseph Fourier Grenoble, BP 87, 38402 St Martin d'Heres, France and CEA/DRFMC/SP2M, 17 Av. des Martyrs, 38000 Grenoble (France)

2006-11-06

335

Inserting one single Mn ion into a quantum dot

NASA Astrophysics Data System (ADS)

A method of growth to get one single Mn in self-assembled semiconductor quantum dot is presented. With a simple quantitative model, the appropriate low Mn density needed prior to the quantum dot nucleation is estimated. Such a low Mn concentration was reached by inserting a thin ZnTe spacer between a Zn1-xMnxTe buffer and the CdTe quantum dot layer. The control of Mn density is made by changing the thickness of the ZnTe spacer, with good reproducibility. Qualitative and quantitative comparisons of optical spectra for different samples assess the relevance of this growth method.

Maingault, Laurent; Besombes, L.; Léger, Y.; Bougerol, C.; Mariette, H.

2006-11-01

336

Imaging GABAc Receptors with Ligand-Conjugated Quantum Dots

We report a methodology for labeling the GABAc receptor on the surface membrane of intact cells. This work builds upon our earlier work with serotonin-conjugated quantum dots and our studies with PEGylated quantum dots to reduce nonspecific binding. In the current approach, a PEGylated derivative of muscimol was synthesized and attached via an amide linkage to quantum dots coated in an amphiphilic polymer derivative of a modified polyacrylamide. These conjugates were used to image GABAC receptors heterologously expressed in Xenopus laevis oocytes. PMID:18437227

Tomlinson, Ian D.; Gussin, Hélène A.; Little, Deborah M.; Warnement, Michael R.; Qian, Haohua; Pepperberg, David R.; Rosenthal, Sandra J.

2007-01-01

337

NASA Astrophysics Data System (ADS)

The binding energy of hydrogenic impurity associated with the ground state and some low-lying states in a GaAs spherical parabolic quantum dot with taking into account hydrostatic pressure and electric field are theoretically studied by using the configuration-integration method. The binding energies of these low-lying states of the impurity depend sensitively on the hydrostatic pressure, electric field and the strength of the parabolic confinement. Based on the analysis of these impurity states, we propose a way for preparation of quantum bit (qubit) by using the strong quantum confinement to the impurity in the quantum dot. Also we calculate the wave functions of some low-lying states to discuss the oscillator strength which is related to the electronic dipole-allowed transitions from 0s state to 0p state. The results show that the electronic dipole-allowed transitions mostly happen between the 0s state and 0p state, especially for the quantum confinement large enough.

Yuan, Jian-Hui; Zhang, Yan; Li, Meng; Wu, Zhi-Hui; Mo, Hua

2014-10-01

338

Hyper-parallel photonic quantum computation with coupled quantum dots

NASA Astrophysics Data System (ADS)

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

Ren, Bao-Cang; Deng, Fu-Guo

2014-04-01

339

Hyper-parallel photonic quantum computation with coupled quantum dots

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

Bao-Cang Ren; Fu-Guo Deng

2013-09-01

340

Hyper-parallel photonic quantum computation with coupled quantum dots.

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

Ren, Bao-Cang; Deng, Fu-Guo

2014-01-01

341

Hybrid entanglement in a triple-quantum-dot shuttle device

NASA Astrophysics Data System (ADS)

We study the H3×N hybrid entanglement between charge and vibrational modes in a triple-quantum-dot shuttle system. Three quantum dots are linearly connected, with the outer dots fixed and the central dot oscillating, described as a quantum harmonic oscillator with oscillation modes that are entangled with the electronic states of the quantum dots. The entangled states are characterized by the Schmidt number as a function of the parameters of the system: detuning and inverse tunneling length. We show that at steady state, as a function of detuning, the excited states of lower energy present Bell-type entanglement 2×N, with the participation of two quantum dots, while the more energetic excited states present 3×N entanglement, with the participation of three quantum dots. In the stationary regime, we find qualitative relationships between the maxima of the electronic current and the Schmidt number. Also, the time evolution of the degree of entanglement for a particular initial condition is studied in the presence of a time-dependent electric field and we evaluate the effects on entanglement of the condition of coherent destruction of tunneling.

Mora, J.; Cota, E.; Rojas, F.

2014-10-01

342

Ferritin-Templated Quantum-Dots for Quantum Logic Gates

NASA Technical Reports Server (NTRS)

Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The work presented here offers a new method to develop quantum-dots using a bio-template, called ferritin, that ensures QD production in uniform size of nano-scale proportion. The bio-template for uniform yield of QD is based on a ferritin protein that allows reconstitution of core material through the reduction and chelation processes. One of the biggest challenges for developing QLG is the requirement of ordered and uniform size of QD for arrays on a substrate with nanometer precision. The QD development by bio-template includes the electrochemical/chemical reconsitution of ferritins with different core materials, such as iron, cobalt, manganese, platinum, and nickel. The other bio-template method used in our laboratory is dendrimers, precisely defined chemical structures. With ferritin-templated QD, we fabricated the heptagonshaped patterned array via direct nano manipulation of the ferritin molecules with a tip of atomic force microscope (AFM). We also designed various nanofabrication methods of QD arrays using a wide range manipulation techniques. The precise control of the ferritin-templated QD for a patterned arrangement are offered by various methods, such as a site-specific immobilization of thiolated ferritins through local oxidation using the AFM tip, ferritin arrays induced by gold nanoparticle manipulation, thiolated ferritin positioning by shaving method, etc. In the signal measurements, the current-voltage curve is obtained by measuring the current through the ferritin, between the tip and the substrate for potential sweeping or at constant potential. The measured resistance near zero bias was 1.8 teraohm for single holoferritin and 5.7 teraohm for single apoferritin, respectively.

Choi, Sang H.; Kim, Jae-Woo; Chu, Sang-Hyon; Park, Yeonjoon; King, Glen C.; Lillehei, Peter T.; Kim, Seon-Jeong; Elliott, James R.

2005-01-01

343

NASA Astrophysics Data System (ADS)

We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of electron impurity doped quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength ( ?c), and harmonic confinement potential ( ?0), the influence of impurity location ( x0,y0) on the diagonal components of frequency dependent linear ( ?xx and ?yy), and the first ( ?xxx and ?yyy) NLO responses of the dot is computed through linear variational route. The non-linear polarizabilities undergo maximization at some typical oscillation frequency of the external field depending upon the impurity location.

Sarkar, Kanchan; Kumar Datta, Nirmal; Ghosh, Manas

2010-03-01

344

Continuous flow purification of nanocrystal quantum dots.

Colloidal quantum dot (QD) purification is typically conducted via repeating precipitation-redispersion involving massive amounts of organic solvents and has been the main obstacle in mass production of QDs with dependable surface properties. Our results show that the electric field apparently affects the streamlining of QDs and that we could continuously collect stably dispersed QDs by the electrophoretic purification process. The purification yield increases as the electric potential difference increases or the flow rate decreases, but reaches an asymptotic value. The yield can be further improved by raising the absolute magnitude of the mobility of QDs with the addition of solvents with high dielectric constants. The continuous purification process sheds light on industrial production of colloidal nanomaterials. PMID:25340305

Kim, Duckjong; Park, Hye Kyung; Choi, Hyekyoung; Noh, Jaehong; Kim, Kyungnam; Jeong, Sohee

2014-11-01

345

Capillary electrophoresis of quantum dots: minireview.

It has been already three decades, since the fluorescent nanocrystals called quantum dots (QDs) appeared and attracted attention of a broad scientific community. Their excellent not only optical but also electronic properties predetermined QDs for utilization in a variety of areas. Besides lasers, solar cells, and/or computers, QDs have established themselves in the field of (bio)chemical labeling as well as medical imaging. However, due to the numerous application possibilities of QDs, there are high demands on their properties that need to be precisely controlled and characterized. CE with its versatile modes and possibilities of detection was found to be an effective tool not only for characterization of QDs size and/or surface properties but also for monitoring of their interactions with other molecules of interest. In this minireview, we are giving short insight in analysis of QDs by CE, and summarizing the advantages of this method for QDs characterization. PMID:24648211

Stanisavljevic, Maja; Vaculovicova, Marketa; Kizek, Rene; Adam, Vojtech

2014-07-01

346

Quantum dots: synthesis, bioapplications, and toxicity

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

2012-01-01

347

Monolithic mode-locked quantum dot lasers

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

348

Coherent electronhole correlations in quantum dots Lars Jonsson,a)

Coherent electronÂhole correlations in quantum dots Lars JoÂ¨nsson,a) Matthew M. Steiner, and John W. These effects are im- portant for two reasons: first, optical properties, e.g., the ex- citonic recombination dot of size 5 25 25 nm3 denoted x, y, and z directions, respec- tively . Within the effective

Wilkins, John

349

Spectroscopy of electronic states in InSb quantum dots

Arrays of quantum dots on InSb have been realized, and intraband transitions between their discrete (zero-dimensional) electronic states have been observed with far-infrared magnetospectroscopy. In the devices, the number of electrons can be adjusted by a gate voltage, and less than five electrons per dot are detectable.

Ch. Sikorski; U. Merkt

1989-01-01

350

The scaling of the effective band gaps in indium-arsenide quantum dots and wires.

Colloidal InAs quantum wires having diameters in the range of 5-57 nm and narrow diameter distributions are grown from Bi nanoparticles by the solution-liquid-solid (SLS) mechanism. The diameter dependence of the effective band gaps (DeltaE(g)s) in the wires is determined from photoluminescence spectra and compared to the experimental results for InAs quantum dots and rods and to the predictions of various theoretical models. The DeltaE(g) values for InAs quantum dots and wires are found to scale linearly with inverse diameter (d(-1)), whereas the simplest confinement models predict that DeltaE(g) should scale with inverse-square diameter (d(-2)). The difference in the observed and predicted scaling dimension is attributed to conduction-band nonparabolicity induced by strong valence-band-conduction-band coupling in the narrow-gap InAs semiconductor. PMID:19206431

Wang, Fudong; Yu, Heng; Jeong, Sohee; Pietryga, Jeffrey M; Hollingsworth, Jennifer A; Gibbons, Patrick C; Buhro, William E

2008-09-23

351

Scanning Gate Measurements on a Coupled Quantum Dot — Quantum Point Contact System

NASA Astrophysics Data System (ADS)

We use the metallic tip of a low-temperature scanning force microscope as a movable gate to study a quantum dot and an adjacent quantum point contact. By scanning the tip we can add single electrons to the dot and detect them with the quantum point contact. Additionally, we detect other charging events which we attribute to charge traps.

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

2007-04-01

352

Observation of inter-sub-level transitions in modulation-doped Ge quantum dots

Observation of inter-sub-level transitions in modulation-doped Ge quantum dots J. L. Liu,a) W. G-doped Ge quantum dots are observed. The dot structure is grown by molecular-beam epitaxy, and consists of 30 periods of Ge quantum dots sandwiched by two 6 nm boron-doped Si layers. An absorption peak

353

Semiconductor Few-Electron Quantum Dots as Spin Qubits

a natural two- level system suitable as a qubit in a quantum computer [1]. In this work, we describe, as such a spin qubit [2]. The outline is as follows. Section 1 serves as an introduction into quantum computing and quantum dots. Section 2 describes the development of the "hardware" for the spin qubit: a device

354

We present a comparison of the 8-band k{center_dot}p and empirical pseudopotential approaches to describing the electronic structure of pyramidal InAs/GaAs self-assembled quantum dots. We find a generally good agreement between the two methods. The most significant differences found in the k(centre dot)p calculation are (i) a reduced splitting of the electron p states (3 vs 24 meV), (ii) an incorrect in-plane polarization ratio for electron-hole dipole transitions (0.97 vs 1.24), and (iii) an over confinement of both electron (48 meV) and hole states (52 meV), resulting in a band gap error of 100 meV. We introduce a ''linear combination of bulk bands'' technique which produces results similar to a full direct diagonalization pseudopotential calculation, at a cost similar to the k{center_dot}p method. (c) 2000 American Institute of Physics.

Wang, L. W. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Williamson, A. J. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Zunger, Alex [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Jiang, H. [Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)] [Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan 48109-2122 (United States); Singh, J. [Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)] [Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)

2000-01-17

355

Growth of cubic GaN quantum dots

Zinc-blende GaN quantum dots were grown on 3C-AlN(001) by two different methods in a molecular beam epitaxy system. The quantum dots in method A were fabricated by the Stranski-Krastanov growth process. The quantum dots in method B were fabricated by droplet epitaxy, a vapor-liquid-solid process. The density of the quantum dots was controllable in a range of 10{sup 8} cm{sup -2} to 10{sup 12} cm{sup -2}. Reflection high energy electron diffraction analysis confirmed the zinc-blende crystal structure of the QDs. Photoluminescence spectroscopy revealed the optical activity of the QDs, the emission energy was in agreement with the exciton ground state transition energy of theoretical calculations.

Schupp, T.; Lischka, K.; As, D. J. [Universitaet Paderborn, Department Physik, Warburger Str.100, 33095 Paderborn (Germany); Meisch, T.; Neuschl, B.; Feneberg, M.; Thonke, K. [Institut fuer Quantenmaterie, Universitaet Ulm, 89069 Ulm (Germany)

2010-11-01

356

Coal as an abundant source of graphene quantum dots

NASA Astrophysics Data System (ADS)

Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

Ye, Ruquan; Xiang, Changsheng; Lin, Jian; Peng, Zhiwei; Huang, Kewei; Yan, Zheng; Cook, Nathan P.; Samuel, Errol L. G.; Hwang, Chih-Chau; Ruan, Gedeng; Ceriotti, Gabriel; Raji, Abdul-Rahman O.; Martí, Angel A.; Tour, James M.

2013-12-01

357

Hybrid organic/quantum dot thin film structures and devices

Organic light emitting diodes have undergone rapid advancement over the course of the past decade. Similarly, quantum dot synthesis has progressed to the point that room temperature highly efficient photoluminescence can ...

Coe-Sullivan, Seth (Seth Alexander)

2005-01-01

358

Coal as an abundant source of graphene quantum dots.

Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites. PMID:24309588

Ye, Ruquan; Xiang, Changsheng; Lin, Jian; Peng, Zhiwei; Huang, Kewei; Yan, Zheng; Cook, Nathan P; Samuel, Errol L G; Hwang, Chih-Chau; Ruan, Gedeng; Ceriotti, Gabriel; Raji, Abdul-Rahman O; Martí, Angel A; Tour, James M

2013-01-01

359

We propose and demonstrate a technique for tailoring the emission bandwidth of ?1.3 ?m quantum dot superluminescent light-emitting diodes. A broadening of the emission is achieved by incorporating the InAs quantum dot layers in InGaAs quantum wells of different indium compositions. These structures exhibit a broader and flatter emission compared to a simple dot-in well structure comprised of wells of

S. K. Ray; K. M. Groom; M. D. Beattie; H. Y. Liu; M. Hopkinson; R. A. Hogg

2006-01-01

360

Chlorine doped graphene quantum dots: Preparation, properties, and photovoltaic detectors

NASA Astrophysics Data System (ADS)

Graphene quantum dots (GQDs) are becoming one of the hottest advanced functional materials because of the opening of the bandgap due to quantum confinement effect, which shows unique optical and electrical properties. The chlorine doped GQDs (Cl-GQDs) have been fabricated by chemical exfoliation of HCl treated carbon fibers (CFs), which were prepared from degreasing cotton through an annealing process at 1000 °C for 30 min. Raman study shows that both G and 2D peaks of GQDs may be redshifted (softened) by chlorine doping, leading to an n-type doping. The first vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbing and electron-accepting roles for (Cl)-GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ˜105 at room temperature using a 405 nm laser irradiation under the reverse bias voltage. The study expands the application of (Cl)-GQDs to the important optoelectronic detection devices.

Zhao, Jianhong; Tang, Libin; Xiang, Jinzhong; Ji, Rongbin; Yuan, Jun; Zhao, Jun; Yu, Ruiyun; Tai, Yunjian; Song, Liyuan

2014-09-01

361

Raman phonon emission in a driven double quantum dot.

The compound semiconductor gallium-arsenide (GaAs) provides an ultra-clean platform for storing and manipulating quantum information, encoded in the charge or spin states of electrons confined in nanostructures. The absence of inversion symmetry in the zinc-blende crystal structure of GaAs however, results in a strong piezoelectric interaction between lattice acoustic phonons and qubit states with an electric dipole, a potential source of decoherence during charge-sensitive operations. Here we report phonon generation in a GaAs double quantum dot, configured as a single- or two-electron charge qubit, and driven by the application of microwaves via surface gates. In a process that is a microwave analogue of the Raman effect, phonon emission produces population inversion of the two-level system and leads to rapid decoherence of the qubit when the microwave energy exceeds the level splitting. Comparing data with a theoretical model suggests that phonon emission is a sensitive function of the device geometry. PMID:24759675

Colless, J I; Croot, X G; Stace, T M; Doherty, A C; Barrett, S D; Lu, H; Gossard, A C; Reilly, D J

2014-01-01

362

Graphene-quantum-dot nonvolatile charge-trap flash memories.

Nonvolatile flash-memory capacitors containing graphene quantum dots (GQDs) of 6, 12, and 27 nm average sizes (d) between SiO2 layers for use as charge traps have been prepared by sequential processes: ion-beam sputtering deposition (IBSD) of 10 nm SiO2 on a p-type wafer, spin-coating of GQDs on the SiO2 layer, and IBSD of 20 nm SiO2 on the GQD layer. The presence of almost a single array of GQDs at a distance of ?13 nm from the SiO2/Si wafer interface is confirmed by transmission electron microscopy and photoluminescence. The memory window estimated by capacitance-voltage curves is proportional to d for sweep voltages wider than ± 3 V, and for d = 27 nm the GQD memories show a maximum memory window of 8 V at a sweep voltage of ± 10 V. The program and erase speeds are largest at d = 12 and 27 nm, respectively, and the endurance and data-retention properties are the best at d = 27 nm. These memory behaviors can be attributed to combined effects of edge state and quantum confinement. PMID:24896068

Sin Joo, Soong; Kim, Jungkil; Kang, Soo Seok; Kim, Sung; Choi, Suk-Ho; Hwang, Sung Won

2014-06-27

363

Copper-indium-selenide quantum dot-sensitized solar cells.

We present a new synthetic process of near infrared (NIR)-absorbing copper-indium-selenide (CISe) quantum dots (QDs) and their applications to efficient and completely heavy-metal-free QD-sensitized solar cells (QDSCs). Lewis acid-base reaction of metal iodides and selenocarbamate enabled us to produce chalcopyrite-structured CISe QDs with controlled sizes and compositions. Furthermore, gram-scale production of CISe QDs was achieved with a high reaction yield of ~73%, which is important for the commercialization of low-cost photovoltaic (PV) devices. By changing the size and composition, electronic band alignment of CISe QDs could be finely tuned to optimize the energetics of the effective light absorption and injection of electrons into the TiO2 conduction band (CB). These energy-band-engineered QDs were applied to QDSCs, and the quantum-confinement effect on the PV performances was clearly demonstrated. Our best cell yielded a conversion efficiency of 4.30% under AM1.5G one sun illumination, which is comparable to the performance of the best solar cells based on toxic lead chalcogenide or cadmium chalcogenide QDs. PMID:24177572

Yang, Jiwoong; Kim, Jae-Yup; Yu, Jung Ho; Ahn, Tae-Young; Lee, Hyunjae; Choi, Tae-Seok; Kim, Young-Woon; Joo, Jin; Ko, Min Jae; Hyeon, Taeghwan

2013-12-21

364

Prediction of an excitonic ground state in InAs/InSb quantum dots.

Using atomistic pseudopotential and configuration-interaction many-body calculations, we predict an excitonic ground state in the InAs/InSb quantum-dot system. For large dots, the conduction band minimum of the InAs dot lies below the valence band maximum of the InSb matrix. Due to quantum confinement, at a critical size calculated here for various shapes, the gap E(g) between InAs conduction states and InSb valence states vanishes. Strong electron-hole correlation effects are induced by the spatial proximity of the electron and hole wave functions, and by the lack of strong (exciton unbinding) screening, afforded by the existence of discrete 0D confined energy levels. These correlation effects overcome E(g), leading to the formation of a biexcitonic ground state (two electrons in InAs and two holes in InSb) being energetically more favorable (by approximately 15 meV) than the dot without excitons. PMID:15698111

He, Lixin; Bester, Gabriel; Zunger, Alex

2005-01-14

365

Long-distance coherent coupling in a quantum dot array.

Controlling long-distance quantum correlations is central to quantum computation and simulation. In quantum dot arrays, experiments so far rely on nearest-neighbour couplings only, and inducing long-distance correlations requires sequential local operations. Here, we show that two distant sites can be tunnel-coupled directly. The coupling is mediated by virtual occupation of an intermediate site, with a strength that is controlled via the energy detuning of this site. It permits a single charge to oscillate coherently between the outer sites of a triple dot array without passing through the middle, as demonstrated through the observation of Landau-Zener-Stückelberg interference. The long-distance coupling significantly improves the prospects of fault-tolerant quantum computation using quantum dot arrays, and opens up new avenues for performing quantum simulations in nanoscale devices. PMID:23624695

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

2013-06-01

366

Colloidal chemical synthesis and characterization of InAs nanocrystal quantum dots

InAs nanocrystal quantum dots have been prepared via colloidal chemical synthesis using the reaction of InCl{sub 3} and As[Si(CH{sub 3}){sub 3}]{sub 3}. Sizes ranging from 25 to 60 A in diameter are produced and isolated with size distributions of {plus_minus}10{percent}{endash}15{percent} in diameter. The nanocrystals are crystalline and generally spherical with surfaces passivated by trioctylphosphine giving them solubility in common organic solvents. The dots have been structurally characterized by transmission electron microscopy (TEM) and powder x-ray diffraction (XRD) and the optical absorption and emission have been examined. Quantum confinement effects are evident with absorption onsets well to the blue of the bulk band gap and size dependent absorption and emission features. The emission is dominated by band edge luminescence. These quantum dots are particularly interesting as they provide an opportunity to make important comparisons with comparably sized InAs quantum dots synthesized by molecular beam epitaxy techniques. {copyright} {ital 1996 American Institute of Physics.}

Guzelian, A.A.; Banin, U.; Kadavanich, A.V.; Peng, X.; Alivisatos, A.P. [Department of Chemistry, University of California, Berkeley] [Department of Chemistry, University of California, Berkeley; [Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

1996-09-01

367

Silicon/silicon-germanium quantum dot spin qubits

NASA Astrophysics Data System (ADS)

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

Simmons, Christine B.

368

Synergetics in multiple exciton generation effect in quantum dots

NASA Astrophysics Data System (ADS)

We present detailed analysis of the non-Poissonian population of excitons produced by multiple exciton generation (MEG) effect in quantum dots on the base of statistic theory of MEG and synergetic approach for chemical reactions. From the analysis we can conclude that a non-Poissonian distribution of exciton population is evidence of nonlinear and nonequilibrium character of the process of multiple generation of excitons in quantum dots at a single photon absorption.

Turaeva, N. N.; Oksengendler, B. L.; Uralov, I.

2011-06-01

369

Quantum dot sensitized semiconductors for solar energy conversion

Metal sulfide (CdS or PbS) quantum dots were synthesized in nanoporous TiO2 films for applications in solar energy conversion devices. Sandwich type regenerative solar cells, based on the quantum dots sensitized TiO2 film, exhibit a high IPCE over visible wavelengths by optimizing the polysulfide electrolyte composition. The CdS QD shows a higher IPCE, compared to PbS, related to an increased

Hitomi Y. Akiyama; Tsukasa Torimoto; Yasuhiro Tachibana; Susumu Kuwabata

2006-01-01

370

Deformation potentials of CdSe quantum dots

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

Li, Jingbo; Wang, Lin-Wang

2004-06-02

371

Charge and spin storage in self-organized quantum dots

NASA Astrophysics Data System (ADS)

We demonstrate optical charging of spectrally selected subensembles of self-organized quantum dots with single charge carriers. In spectral hole burning experiments negative and positive trions are observed, representing quantum dots charged with single electrons and holes. By circularly polarized excitation in an applied magnetic field we are able to address the spin of single electrons. A spin flip of the electron is observed after excitation in the upper Zeeman level.

Wieczorek, W.; Warming, T.; Geller, M.; Bimberg, D.; Cirlin, G. E.; Zhukov, A. E.; Ustinov, V. M.

2006-05-01

372

Engineering of perturbation effects in onion-like heteronanocrystal quantum dot-quantum well

NASA Astrophysics Data System (ADS)

In this article, the perturbation influences on optical characterization of quantum dot and quantum dot-quantum well (modified quantum dot) heteronanocrystal is investigated. The original aim of this article is to investigate the quantum dot-quantum well heteronanocrystal advantages and disadvantages, when used as a functionalized particle in biomedical applications. Therefore, all of the critical features of quantum dots are fundamentally studied and their influences on optical properties are simulated. For the first time, the perturbation effects on optical characteristics are observed in the quantum dot-quantum well heteronanocrystals by 8-band K.P theory. The impact of perturbation on optical features such as photoluminescence and shifting of wavelength is studied. The photoluminescence and operation wavelength of quantum dots play a vital role in biomedical applications, where their absorption and emission in biological assays are altered by shifting of wavelength. Furthermore, in biomedical applications, by tuning the emission wavelengths of the quantum dot into far-red and near-infrared ranges, non-invasive in-vivo imaging techniques have been easily developed. In this wavelength window, tissue absorption, scattering and auto-fluorescence intensities have minimum quantities; thus fixing or minimizing of wavelength shifting can be regarded as an important goal which is investigated in this work.

SalmanOgli, A.; Rostami, R.

2013-10-01

373

Investigation of size dependent structural and optical properties of thin films of CdSe quantum dots

Research highlights: {yields} CdSe q-dots have been synthesized using simple chemical synthesis route. {yields} Thin film of CdSe quantum dots exhibited self-organized growth. {yields} Size dependent blue shift observed in the absorption edge of CdSe nanocrystallites. {yields} PL emission band corresponds to band edge luminescence and defect luminescence. {yields} Organized growth led to enhancement in luminescence yield of smaller size Q-dots. -- Abstract: Cadmium selenide (CdSe) quantum dots were grown on indium tin oxide substrate using wet chemical technique for possible application as light emitting devices. The structural, morphological and luminescence properties of the as deposited thin films of CdSe Q-dot have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. The quantum dots have been shown to deposit in an organized array on ITO/glass substrate. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the nanocrystalline CdSe exhibits intense photoluminescence as compared to the large grained polycrystalline CdSe films.

Sharma, Madhulika, E-mail: madhulikasharma1@gmail.com [Department of Physics, Bhopal University, Bhopal 462 026 (India) [Department of Physics, Bhopal University, Bhopal 462 026 (India); Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology, Bombay, Powai, Mumbai 400076 (India); Sharma, A.B.; Mishra, N. [Department of Physics, Bhopal University, Bhopal 462 026 (India)] [Department of Physics, Bhopal University, Bhopal 462 026 (India); Pandey, R.K. [University Institute of Technology, Barkatullah University, Bhopal 462026 (India)] [University Institute of Technology, Barkatullah University, Bhopal 462026 (India)

2011-03-15

374

Self-illuminating quantum dot conjugates for in vivo imaging.

Fluorescent semiconductor quantum dots hold great potential for molecular imaging in vivo. However, the utility of existing quantum dots for in vivo imaging is limited because they require excitation from external illumination sources to fluoresce, which results in a strong autofluorescence background and a paucity of excitation light at nonsuperficial locations. Here we present quantum dot conjugates that luminesce by bioluminescence resonance energy transfer in the absence of external excitation. The conjugates are prepared by coupling carboxylate-presenting quantum dots to a mutant of the bioluminescent protein Renilla reniformis luciferase. We show that the conjugates emit long-wavelength (from red to near-infrared) bioluminescent light in cells and in animals, even in deep tissues, and are suitable for multiplexed in vivo imaging. Compared with existing quantum dots, self-illuminating quantum dot conjugates have greatly enhanced sensitivity in small animal imaging, with an in vivo signal-to-background ratio of > 10(3) for 5 pmol of conjugate. PMID:16501578

So, Min-Kyung; Xu, Chenjie; Loening, Andreas M; Gambhir, Sanjiv S; Rao, Jianghong

2006-03-01

375

Optical detection of brain tumors using quantum dots

NASA Astrophysics Data System (ADS)

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

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

2005-11-01

376

Cavity -Quantum Dot interactions and mode coupling in a nanocavity

NASA Astrophysics Data System (ADS)

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

Kasisomayajula, Vijay; Russo, Onofrio

2009-03-01

377

Long-Term Retention of Fluorescent Quantum Dots In Vivo

NASA Astrophysics Data System (ADS)

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

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

378

Electronic doping and trap reduction of quantum dots

NASA Astrophysics Data System (ADS)

Both undoped and doped semiconductor quantum dots (QDs) offer unique opportunities for studying the fundamental physics of quantum confinement. Obtaining a thorough understanding of their physical properties is necessary for development of efficient and robust materials for use in a wide range of applications such as optoelectronics (optical switches, light emitting diodes (LEDs), photovoltaics, and lasers), biosensing, and nanoelectronics. This thesis involves studies that look specifically at the effects of electronic doping and trap reduction in undoped and Mn2+ -doped QDs. Investigation of the effect of electron-Mn2+ exchange interactions on Mn 2+ luminescence in Mn2+:CdS nanocrystal films through an electrochemical method reveals effective Auger de-excitation of photoexcited Mn2+. The doped QDs demonstrate increased sensitivity to Auger de-excitation versus undoped QDs due to the long lifetime of the Mn2+ excited state. Photochemical electronic doping of colloidal CdSe nanocrystals is achieved for the first time through the use of a borohydride hole quencher, Li[Et3BH], and the high spectroscopic quality of the resulting n-type nanocrystals allows for advanced characterization by absorption and photoluminescence. Additionally, chemical titrations of the n-type nanocrystals confirm electron accumulation and suggest significant electron trapping for some of the nanocrystals. Spectroelectrochemical measurements on undoped and Mn2+-doped ZnSe QDs target charge injection into traps within the semiconductor bandgap. In both the undoped and doped QDs, transfer of electrons into the nanocrystal film is directly correlated with enhanced photoluminescence quantum yield and dubbed "electrobrightening." This method of brightening through trap passivation is extended to colloidal systems through the use of outer-sphere reductants and ultimately improves the ensemble photoluminescence quantum yield of Mn2+ -doped ZnSe QDs from 14% to 80%.

Thorsen, Amanda Leigh

379

Gain dynamics and excitonic transition in CdSe colloidal quantum dots

NASA Astrophysics Data System (ADS)

Dynamics of the photo-excited excitons in CdSe colloidal quantum dots was investigated by degenerate pump-probe measurement. Under resonant excitation, the lowest energy state of an electron-hole pair dominates two-step decay. The fast initial decay and long-term decay were attributed to the intrinsic Auger recombination and radiative recombination, respectively. As increasing the excited exciton density, a significant change of the later decay was seen before the absorption bleaching. As our nanocrystal is the case of strong confinement, in which an excitonic Bohr radius is smaller than the dot size, the biexciton-involved recombination is suggested to dominate at high carrier densities. Optical gain was measured by the variable stripe length method and broad gain spectrum was obtained due to the recombination of many excited levels between biexciton and exciton states. This result also supports biexcitons play an important role in the strong confinement regime at high carrier densities.

Kyhm, K.; Kim, J. H.; Kim, S. M.; Yang, Ho-soon

2007-09-01

380

Selecting of modes in nano-laser of silicon quantum dots

NASA Astrophysics Data System (ADS)

In a nano-laser of Si quantum dots (QD), the smaller QD fabricated by nanosecond pulse laser can form the pumping level tuned by the quantum confinement (QC) effect. Coupling between the active centers formed by localized states of surface bonds and the two-dimensional (2D) photonic crystal used to select model can produce a sharp peak at 2.076 eV in the nano-laser. It is interesting to make a comparison between the localized electronic states in gap due to defect formed by surface bonds and the localized photonic states in gap of photonic band due to defect of 2D photonic crystal.

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

2012-06-01

381

Zinc oxide quantum dots embedded films by metal organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) quantum dots (QDs) were fabricated on silicon substrates by metal organic chemical vapor deposition. Formation of QDs is due to the vigorous reaction of the precursors when a large amount of precursors was introduced during the growth. The size of the QDs ranged from 3 to 12 nm, which was estimated by high-resolution transmission electron microscopy. The photoluminescence measured at 80 K showed that the emission of QDs embedded film ranged from 3.0 to 3.6 eV. The broad near-band-edge emission was due to the quantum confinement effect of the QDs.

Tan, S. T.; Sun, X. W.; Zhang, X. H.; Chen, B. J.; Chua, S. J.; Yong, Anna; Dong, Z. L.; Hu, X.

2006-05-01

382

Magnetoluminescence from trion and biexciton in type-II quantum dot

NASA Astrophysics Data System (ADS)

We theoretically investigate optical Aharonov-Bohm (AB) effects on trion and biexciton in the type-II semiconductor quantum dots, in which holes are localized near the center of the dot, and electrons are confined in a ring structure formed around the dot. Many-particle states are calculated numerically by the exact diagonalization method. Two electrons in trion and biexciton are strongly correlated to each other, forming a Wigner molecule. Since the relative motion of electrons are frozen, the Wigner molecule behaves as a composite particle whose mass and charges are twice those of an electron. As a result, the period of AB oscillation for trion and biexciton becomes h/2 e as a function of magnetic flux penetrating the ring. We find that the magnetoluminescence spectra from trion and biexciton change discontinuously as the magnetic flux increases by h/2 e. PACS: 71.35.Ji, 73.21.-b, 73.21.La, 78.67.Hc

Okuyama, Rin; Eto, Mikio; Hyuga, Hiroyuki

2011-04-01

383

Correlation of structural and optical properties of self-organized quantum dots

NASA Astrophysics Data System (ADS)

Interaction between strongly localized charge carriers in zero-dimensional systems like quantum dots (QD) depends sensitively on the geometrical roperties of the dots. The recently observed monolayer splitting with eight well resolved peaks (in low excitation photoluminescence (PL)) together with eight-band kp theory as the appropriate tool for modeling electronic and optical properties offers direct spectroscopic access to details of the QD morphology. By this achievement it became possible to link single-dot spectra obtained by cathodoluminescence measurements via the exciton transition energy to structural properties of the probed QD. In view of theory this situation constitutes an ideal starting point to study few-particle interactions for realistic InAs QDs as a function of their structural properties. This is done using the configuration interaction method. The wavefunctions are obtained from eight-band kp calculations of single-particle states including explicitly piezoelectric effects in the confinement potential.

Schliwa, Andrei; Rodt, Sven; Guffarth, Florian; Poetschke, Konstantin; Warming, Till; Seguin, Robert; Bimberg, Dieter

2004-06-01

384

The performance of coupled (CdS:CdSe) quantum dot-sensitized TiO 2 nanofibrous solar cells

Highly porous networks and reduced grain boundaries with one-dimensional (1-D) nanofibrous morphology offer enhanced charge transport in solar cells applications. Quantum dot (QDs) decorated TiO2 nanofibrous electrodes, unlike organic dye sensitizers, can yield multiple carrier generations due to the quantum confinement effect. This paper describes the first attempt to combine these two novel approaches, in which CdS (?18nm) and CdSe

P. Sudhagar; June Hyuk Jung; Yong-Gun Lee; R. Sathyamoorthy; Yong Soo Kang; Heejoon Ahn

2009-01-01

385

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude.In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance.The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells. PMID:23912379

Mendes, Manuel J; Hernández, Estela; López, Esther; García-Linares, Pablo; Ramiro, Iñigo; Artacho, Irene; Antolín, Elisa; Tobías, Ignacio; Martí, Antonio; Luque, Antonio

2013-08-30

386

Atomic Ordering in Self-assembled Epitaxial and Endotaxial Compound and Element Semiconductor alloy quantum dots, the suggestion is made that atomically ordered quantum dots which are grown superior long term structural stability. Such atomically ordered quantum dots should, therefore

Moeck, Peter

387

Thermopower of few-electron quantum dots with Kondo correlations

NASA Astrophysics Data System (ADS)

The thermopower of few-electron quantum dots is crucially influenced by on-dot electron-electron interactions, particularly in the presence of Kondo correlations. In this paper, we present a comprehensive picture which elucidates the underlying relations between the thermopower and the spectral density function of two-level quantum dots. The effects of various electronic states, including the Kondo states originating from both spin and orbital degrees of freedom, are clearly unraveled. Such a physical picture is affirmed by accurate numerical data obtained with a hierarchical equations of motion approach. Our findings and understandings provide an effective and viable way to control the thermoelectric properties of strongly correlated quantum dot systems.

Ye, LvZhou; Hou, Dong; Wang, Rulin; Cao, Dewen; Zheng, Xiao; Yan, YiJing

2014-10-01

388

Ge quantum dot memory structure with laterally ordered highly dense arrays of Ge dots.

This work was devoted to the development of a Ge quantum dot memory structure of a MOSFET type with laterally ordered Ge quantum dots within the gate dielectric stack. Lateral ordering of the Ge dots was achieved by the combination of the following technological steps: (a) use of a focused ion beam (FIB) to create ordered two-dimensional arrays of regular holes on a field oxide on the silicon substrate, (b) chemical cleaning and restoring of the Si surface in the holes, (c) further oxidation to transfer the pattern from the field oxide to the silicon substrate, (d) removal of the field oxide and thermal re-oxidation of the sample in order to create a tunneling oxide of homogeneous thickness on the patterned silicon surface, and (e) self-assembly of the two-dimensional arrays of Ge dots on the patterned tunneling oxide. The charging properties of the obtained memory structure were characterized by electrical measurements. Charging of the Ge quantum dot layer by electrons injected from the substrate resulted in a large shift in the capacitance-voltage curves of the MOS structure. Charges were stored in deep traps in the charging layer, and consequently the erasing process was difficult, resulting in a limited memory window. The advantages of controlled positioning of the quantum dots in the charging layer will be discussed. PMID:17455497

Nassiopoulou, A G; Olzierski, A; Tsoi, E; Berbezier, I; Karmous, A

2007-01-01

389

Quantum master equation for electron transport through quantum dots and single molecules Upendra s : 73.63. b, 03.65.Yz, 05.60.Gg I. INTRODUCTION Electron transport through a quantum dot QD or a single in the fabrication of devices such as quantum dots whose size and geometry can be controlled with high precision14

Mukamel, Shaul

390

Stark E ect of Interactive Electron-hole pairs in Spherical Semiconductor Quantum Dots

Stark E#11;ect of Interactive Electron-hole pairs in Spherical Semiconductor Quantum Dots B model, on the quantum-con#12;nement Stark e#11;ects for spherical semiconducting quantum dots of quantum dot sizes. PACS numbers: 71.35.-y, 71.70.Ej Submitted to: Journal of Physics: Condensed Matter z

Recanati, Catherine

391

Charge sensing and controllable tunnel coupling in a Si/SiGe double quantum dot.

We report integrated charge sensing measurements on a Si/SiGe double quantum dot. The quantum dot is shown to be tunable from a single, large dot to a well-isolated double dot. Charge sensing measurements enable the extraction of the tunnel coupling t between the quantum dots as a function of the voltage on the top gates defining the device. Control of the voltage on a single such gate tunes the barrier separating the two dots. The measured tunnel coupling is an exponential function of the gate voltage. The ability to control t is an important step toward controlling spin qubits in silicon quantum dots. PMID:19645459

Simmons, C B; Thalakulam, Madhu; Rosemeyer, B M; Van Bael, B J; Sackmann, E K; Savage, D E; Lagally, M G; Joynt, R; Friesen, Mark; Coppersmith, S N; Eriksson, M A

2009-09-01

392

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

We demonstrate the emission and routing of single photons along a semiconductor chip originating from carrier recombination in an actively positioned InAs quantum dot. Device scale arrays of quantum dots are formed by a two step regrowth process. We precisely locate the propagating region of a unidirectional photonic crystal waveguide with respect to the quantum dot nucleation site. Under pulsed optical excitation, the multiphoton emission probability from the exit of the waveguide is 12 \\pm 5 % before any background correction. Our results are a major step towards the deterministic integration of a quantum emitter with the waveguiding components of photonic quantum circuits.

Jamil, Ayesha; Kalliakos, Sokratis; Schwagmann, Andre; Ward, Martin B; Brody, Yarden; Ellis, David J P; Farrer, Ian; Griffiths, Jonathan P; Jones, Geb A C; Ritchie, David A; Shields, Andrew J

2014-01-01

393

Role of quantum confinement in luminescence efficiency of group IV nanostructures

NASA Astrophysics Data System (ADS)

Experimental results obtained previously for the photoluminescence efficiency (PLeff) of Ge quantum dots (QDs) are theoretically studied. A log-log plot of PLeff versus QD diameter (D) resulted in an identical slope for each Ge QD sample only when EG˜(D2+D)-1. We identified that above D ? 6.2 nm: EG˜D-1 due to a changing effective mass (EM), while below D ? 4.6 nm: EG˜D-2 due to electron/hole confinement. We propose that as the QD size is initially reduced, the EM is reduced, which increases the Bohr radius and interface scattering until eventually pure quantum confinement effects dominate at small D.

Barbagiovanni, E. G.; Lockwood, D. J.; Rowell, N. L.; Costa Filho, R. N.; Berbezier, I.; Amiard, G.; Favre, L.; Ronda, A.; Faustini, M.; Grosso, D.

2014-01-01

394

Selective targeting of microglia by quantum dots

Background Microglia, the resident immune cells of the brain, have been implicated in brain injury and various neurological disorders. However, their precise roles in different pathophysiological situations remain enigmatic and may range from detrimental to protective. Targeting the delivery of biologically active compounds to microglia could help elucidate these roles and facilitate the therapeutic modulation of microglial functions in neurological diseases. Methods Here we employ primary cell cultures and stereotaxic injections into mouse brain to investigate the cell type specific localization of semiconductor quantum dots (QDs) in vitro and in vivo. Two potential receptors for QDs are identified using pharmacological inhibitors and neutralizing antibodies. Results In mixed primary cortical cultures, QDs were selectively taken up by microglia; this uptake was decreased by inhibitors of clathrin-dependent endocytosis, implicating the endosomal pathway as the major route of entry for QDs into microglia. Furthermore, inhibiting mannose receptors and macrophage scavenger receptors blocked the uptake of QDs by microglia, indicating that QD uptake occurs through microglia-specific receptor endocytosis. When injected into the brain, QDs were taken up primarily by microglia and with high efficiency. In primary cortical cultures, QDs conjugated to the toxin saporin depleted microglia in mixed primary cortical cultures, protecting neurons in these cultures against amyloid beta-induced neurotoxicity. Conclusions These findings demonstrate that QDs can be used to specifically label and modulate microglia in primary cortical cultures and in brain and may allow for the selective delivery of therapeutic agents to these cells. PMID:22272874

2012-01-01

395

Quantum dot mediated imaging of atherosclerosis

NASA Astrophysics Data System (ADS)

The progression of atherosclerosis is associated with leukocyte infiltration within lesions. We describe a technique for the ex vivo imaging of cellular recruitment in atherogenesis which utilizes quantum dots (QD) to color-code different cell types within lesion areas. Spectrally distinct QD were coated with the cell-penetrating peptide maurocalcine to fluorescently-label immunomagnetically isolated monocyte/macrophages and T lymphocytes. QD-maurocalcine bioconjugates labeled both cell types with a high efficiency, preserved cell viability, and did not perturb native leukocyte function in cytokine release and endothelial adhesion assays. QD-labeled monocyte/macrophages and T lymphocytes were reinfused in an ApoE-/- mouse model of atherosclerosis and age-matched controls and tracked for up to four weeks to investigate the incorporation of cells within aortic lesion areas, as determined by oil red O (ORO) and immunofluorescence ex vivo staining. QD-labeled cells were visible in atherosclerotic plaques within two days of injection, and the two cell types colocalized within areas of subsequent ORO staining. Our method for tracking leukocytes in lesions enables high signal-to-noise ratio imaging of multiple cell types and biomarkers simultaneously within the same specimen. It also has great utility in studies aimed at investigating the role of distinct circulating leukocyte subsets in plaque development and progression.

Jayagopal, Ashwath; Su, Yan Ru; Blakemore, John L.; Linton, MacRae F.; Fazio, Sergio; Haselton, Frederick R.

2009-04-01

396

Multiplexed modular genetic targeting of quantum dots.

While DNA-directed nanotechnology is now a well-established platform for bioinspired nanoscale assembly in vitro, the direct targeting of various nanomaterials in living biological systems remains a significant challenge. Hybrid biological systems with integrated and targeted nanomaterials may have interesting and exploitable properties, so methods for targeting various nanomaterials to precise biological locations are required. Fluorescence imaging has benefited from the use of nanoparticles with superior optical properties compared to fluorescent organic dyes or fluorescent proteins. While single-particle tracking (SPT) in living cells with genetically encoded proteins is limited to very short trajectories, the high photon output of genetically targeted and multiplexed quantum dots (QDs) would enable long-trajectory analysis of multiple proteins. However, challenges with genetic targeting of QDs limit their application in these experiments. In this report, we establish a modular method for targeting QD nanoparticles selectively to multiple genetically encoded tags by precomplexing QD-streptavidin conjugates with cognate biotinylated hapten molecules. This approach enables labeling and SPT of multiple genetically encoded proteins on living cells at high speed and can label expressed proteins in the cytosol upon microinjection into living cells. While we demonstrate labeling with three distinct QD conjugates, the approach can be extended to other specific hapten-affinity molecule interactions and alternative nanoparticles, enabling precise directed targeting of nanoparticles in living biological systems. PMID:25380615

Saurabh, Saumya; Beck, Lauren E; Maji, Suvrajit; Baty, Catherine J; Wang, Yi; Yan, Qi; Watkins, Simon C; Bruchez, Marcel P

2014-11-25

397

Immune cells tracing using quantum dots

NASA Astrophysics Data System (ADS)

Fluorescent nanoparticles, such as nanocrystal quantum dots (QDs), have potential to be applied to molecular biology and bioimaging, since some nanocrystals emit higher and longer lasting fluorescence than conventional organic probes do. Here we report an example of labeling immune cells by QDs. We collected splenic CD4 + T-lymphocyte and peritoneal macrophages from mice. Then cells were labeled with QDs. QDs are incorporated into the T-lymphocyte and macrophages immediately after addition and located in the cytoplasm via endocytosis pathway. The fluorescence of QDs held in the endosomes was easily detected for more than a week. In addition, T-lymphocytes labeled with QDs were stable and cell proliferation or cytokine production including IL-2 and IFN-? was not affected. When QD-labeled T-lymphocytes were adoptively transferred intravenously to mice, they remained in the peripheral blood and spleen up to a week. Using QD-labeled peritoneal macrophages, we studied cell traffic during inflammation on viscera in peritoneum cavity. QD-labeled macrophages were transplanted into the peritoneum of the mouse, and colitis was induced by intracolonic injection of a hapten, trinitrobenzensulfonic acid. With the aid of stong signals of QDs, we found that macrophage accumuled on the inflammation site of the colon. These results suggested that fluorescent probes of QDs might be useful as bioimaging tools for tracing target cells in vivo.

Hoshino, Akiyoshi; Fujioka, Kouki; Kawamura, Yuki I.; Toyama-Sorimachi, Noriko; Yasuhara, Masato; Dohi, Taeko; Yamamoto, Kenji

2006-02-01

398

Toxicity of carbon group quantum dots

NASA Astrophysics Data System (ADS)

Carbon group quantum dots (QDs) such as carbon, silicon and germanium, have potential for biomedical applications such as bio-imaging markers and drug delivery systems and are expected to demonstrate several advantages over conventional fluorescent QDs such as CdSe, especially in biocompatibility. We assessed biocompatibility of newly manufactured silicon QDs (Si-QDs), by means of both MTT assay and LDH assay for HeLa cells in culture and thereby detected the cellular toxicity by administration of high concentration of Si-QD (>1000 ?g/mL), while we detected the high toxicity by administration of over 100 ?g/mL of CdSe-QDs. As a hypothesis for the cause of the cellular toxicity, we measured oxy-radical generation from the QDs by means of luminol reaction method. We detected generation of oxy-radicals from the Si-QDs and those were decreased by radical scavenger such as superoxide dismutase (SOD) and N-acetyl cysteine (NAC). We concluded that the Si-QD application to cultured cells in high concentration led cell membrane damage by oxy-radicals and combination usage with radical scavenger is one of the answers.

Hanada, Sanshiro; Fujioka, Kouki; Hoshino, Akiyoshi; Manabe, Noriyoshi; Hirakuri, Kenji; Yamamoto, Kenji

2009-02-01

399

Tuning electrochemical rectification via quantum dot assemblies.

A novel approach to tuning electrochemical rectification using 2D assemblies of quantum dots (QDs) is presented. Asymmetric enhancement of the oxidation and reduction currents in the presence of the Fe(CN)(6)(3-/4-) redox couple is observed upon adsorption of QDs at thiol-modified Au electrodes. The extent of the electrochemical rectification is dependent on the average QD size. A molecular blocking layer is generated by self-assembling 11-mercaptoundecanoic acid (MUA) and an ultrathin film of poly(diallyldimethylammonium chloride) (PDADMAC) on the electrode. The polycationic film allows the electrostatic adsorption of 3-mercaptopropionic acid (MPA)-stabilized CdTe QDs, generating 2D assemblies with approximately 0.4% coverage. The QD adsorption activates a fast charge transfer across the blocking layer in which the reduction process is more strongly enhanced than the oxidation reaction. The partial electrochemical rectification is rationalized in terms of the relative position of the valence (VB) and conduction band (CB) edges with respect to the redox Fermi energy (?(redox)). Quantitative analysis of the exchange current density obtained from electrochemical impedance spectroscopy demonstrates that the enhancement of charge transport across the molecular barrier is strongly dependent on the position of the QD valence band edge relative to ?(redox). The average electron tunneling rate constant through the QD assemblies is estimated on the basis of the Gerischer model for electron transfer. PMID:21050000

Kissling, Gabriela P; Bünzli, Christa; Fermín, David J

2010-12-01

400

National Technical Information Service (NTIS)

We investigate resonant tunneling in GaAs/(AlGa)As double-barrier resonant-tunneling diodes (RTDs) in which a single layer of InAs self-assembled quantum dots (SAQDs) is embedded in the center of the GaAs quantum well. The dots provide a well-defined and ...

A. Patane, E. E. Vdovin, I. A. Larkin, P. N. Brounkov, Y. V. Dubrovskii

2001-01-01

401

Binding energy and exciton spectrum in double cylindrical quantum dot

The spectral characteristics of exciton in combined nanoheterosystem consisting of semiconductor cylindrical quantum wire containing two quantum dots separated by thin barrier-shell are investigated. It is shown that the binding energy non monotonously depends on the geometrical characteristics of nanoheterosystem approaching several minimum and maximum magnitudes.

O. M. Makhanets; M. M. Dovganiuk; J. O. Seti

2008-01-01

402

Manipulating Quantum Dots to Nanometer Precision by Control of Flow

accuracy for holding times exceeding one hour and the ability to take active quantum measurements on the dynamically manipulated QD. KEYWORDS Quantum dots, control, electroosmotic flow, subpixel averaging, photon to always move that object from its current location toward its desired position in discrete time steps

Waks, Edo

403

2 Micrometers InAsSb Quantum-dot Lasers

NASA Technical Reports Server (NTRS)

InAsSb quantum-dot lasers near 2 micrometers were demonstrated in cw operation at room temperature with a threshold current density of 733 A,/cm(sup 2), output power of 3 mW/facet and a differential quantum efficiency of 13%.

Qiu, Yueming; Uhl, David; Keo, Sam

2004-01-01

404

Electrical control of single hole spins in nanowire quantum dots.

The development of viable quantum computation devices will require the ability to preserve the coherence of quantum bits (qubits). Single electron spins in semiconductor quantum dots are a versatile platform for quantum information processing, but controlling decoherence remains a considerable challenge. Hole spins in III-V semiconductors have unique properties, such as a strong spin-orbit interaction and weak coupling to nuclear spins, and therefore, have the potential for enhanced spin control and longer coherence times. A weaker hyperfine interaction has previously been reported in self-assembled quantum dots using quantum optics techniques, but the development of hole-spin-based electronic devices in conventional III-V heterostructures has been limited by fabrication challenges. Here, we show that gate-tunable hole quantum dots can be formed in InSb nanowires and used to demonstrate Pauli spin blockade and electrical control of single hole spins. The devices are fully tunable between hole and electron quantum dots, which allows the hyperfine interaction strengths, g-factors and spin blockade anisotropies to be compared directly in the two regimes. PMID:23416794

Pribiag, V S; Nadj-Perge, S; Frolov, S M; van den Berg, J W G; van Weperen, I; Plissard, S R; Bakkers, E P A M; Kouwenhoven, L P

2013-03-01

405

As the priority of interconnects and active components in nanoscale optical and electronic devices, three-dimensional hyper-branched nanostructures came into focus of research. Recently, a novel crystallization route, named as "nonclassical crystallization," has been reported for three-dimensional nanostructuring. In this process, Quantum dots are used as building blocks for the construction of the whole hyper-branched structures instead of ions or single-molecules in conventional crystallization. The specialty of these nanostructures is the inheritability of pristine quantum dots' physical integrity because of their polycrystalline structures, such as quantum confinement effect and thus the luminescence. Moreover, since a longer diffusion length could exist in polycrystalline nanostructures due to the dramatically decreased distance between pristine quantum dots, the exciton-exciton interaction would be different with well dispersed quantum dots and single crystal nanostructures. This may be a benefit for electron transport in solar cell application. Therefore, it is very necessary to investigate the exciton-exciton interaction in such kind of polycrystalline nanostructures and their optical properites for solar cell application. In this research, we report a novel CdTe hyper-branched nanostructures based on self-assembly of CdTe quantum dots. Each branch shows polycrystalline with pristine quantum dots as the building units. Both steady state and time-resolved spectroscopy were performed to investigate the properties of carrier transport. Steady state optical properties of pristine quantum dots are well inherited by formed structures. While a suppressed multi-exciton recombination rate was observed. This result supports the percolation of carriers through the branches' network. PMID:23646691

Pan, Ling-Yun; Pan, Gen-Cai; Zhang, Yong-Lai; Gao, Bing-Rong; Dai, Zhen-Wen

2013-02-01

406

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 the presence of level crossings where the qubit becomes chargelike. 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. We obtain closed-form solutions for the control sequences and show that the gates are fast (subnanosecond) and can achieve high fidelities.

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

2012-12-01

407

Distance measurement along DNA molecules using fluorecent quantum dots

NASA Astrophysics Data System (ADS)

To create and design better micro- and nanofluidic devices, we need to understand how macromolecules behave when squeezed by lateral barriers to create pseudo-two-dimensional confinement. We present experiments in which we visualize DNA molecules of varying sizes (2 kbp - 50 kbp) trapped in 10 micrometer wide slits, the slit height varying from the radius of gyration of the unconfined molecule (micrometer) down to 25 nm (half the persistence length of DNA). We present data on the diffusion coefficient and electrophoretic mobility (no electroosmotic flow) of SYBR-gold labeled DNA molecules as a function of slit height. Simultaneously, we have assessed the DNA conformation by examining molecules that are end-labeled with differently colored fluorescent quantum dots. By determining the distance between labels, we measure directly the end-to-end distance - a conformational measure much discussed but rarely measured. Using the same approach but turning the problem around, we determined if contour length can be estimated from visualization experiments. The answer to this question becomes important when the distance between specific binding sites on the DNA backbone must be measured. One such application, for example, is the determination of haplotypes (genetic variability due to blocks of single nucleotide polymorphisms (SNP)) in diploid individuals.

Strey, Helmut

2005-03-01

408

NASA Astrophysics Data System (ADS)

The effects of electric field on carrier escape in InAs/GaAs quantum dots embedded in a p-i-n solar cell structures have been studied by quantum efficiency. Via band structure simulation, effective barrier height of carriers inside QDs is reduced with increasing local electric field, so tunneling and thermal escape are enhanced. At 300K, when electric field intensity is below 40kV/cm, thermal escape is dominant in all confined states in QDs; when electric field intensity is above 40kV/cm, tunneling is dominant in shallow confined states and thermal escape is dominant in the ground state of QDs.

Dai, Yushuai; Polly, Stephen; Hellström, Staffan; Driscoll, Kristina; Forbes, David V.; Hubbard, Seth M.; Roland, Paul J.; Ellingson, Randy J.

2014-03-01

409

Graphene quantum dots, graphene oxide, carbon quantum dots and graphite nanocrystals in coals.

Six coal samples of different ranks have been used to prepare single-layer graphene quantum dots (S-GQDs). After chemical oxidation and a series of centrifugation separation, every coal could be treated into two fractions, namely, CoalA and CoalB. According to the characterization results of TEM, AFM, XRD, Raman and FTIR, CoalA was revealed to be mainly composed of S-GQDs, which have an average height of about 0.5 nm and an average plane dimension of about 10 nm. The obtained S-GQDs showed excitation-dependent fluorescence and excellent electrochemiluminescence. CoalB was found to be some other carbon-based nanomaterials (CNMs), including agglomerated GQDs, graphene oxide, carbon quantum dots and agglomerated carbon nanocrystals. Generally, low-ranked coals might be more suitable for the preparation of S-GQDs. The production yield of S-GQDs from the six investigated coals decreased from 56.30% to 14.66% when the coal rank increased gradually. In contrast, high-ranked coals had high production yield of CoalB and might be more suitable for preparing other CNMs that were contained in CoalB, although those CNMs were difficult to separate from each other in our experiment. PMID:24875280

Dong, Yongqiang; Lin, Jianpeng; Chen, Yingmei; Fu, Fengfu; Chi, Yuwu; Chen, Guonan

2014-07-01

410

Understanding quantum confinement in nanowires: basics, applications and possible laws.

A comprehensive investigation of quantum confinement in nanowires has been carried out. Though applied to silicon nanowires (SiNWs), it is general and applicable to all nanowires. Fundamentals and applications of quantum confinement in nanowires and possible laws obeyed by these nanowires, have been investigated. These laws may serve as backbones of nanowire science and technology. The relationship between energy band gap and nanowire diameter has been studied. This relationship appears to be universal. A thorough review indicates that the first principles results for quantum confinement vary widely. The possible cause of this variation has been examined. Surface passivation and surface reconstruction of nanowires have been elucidated. It has been found that quantum confinement owes its origin to surface strain resulting from surface passivation and surface reconstruction and hence thin nanowires may actually be crystalline-core/amorphous-shell (c-Si/a-Si) nanowires. Experimental data available in the literature corroborate with the suggestion. The study also reveals an intrinsic relationship between quantum confinement and the surface amorphicity of nanowires. It demonstrates that surface amorphicity may be an important tool to investigate the electronic, optoelectronic and sensorial properties of quantum-confined nanowires. PMID:25245123

Mohammad, Noor S

2014-10-22

411

Understanding quantum confinement in nanowires: basics, applications and possible laws

NASA Astrophysics Data System (ADS)

A comprehensive investigation of quantum confinement in nanowires has been carried out. Though applied to silicon nanowires (SiNWs), it is general and applicable to all nanowires. Fundamentals and applications of quantum confinement in nanowires and possible laws obeyed by these nanowires, have been investigated. These laws may serve as backbones of nanowire science and technology. The relationship between energy band gap and nanowire diameter has been studied. This relationship appears to be universal. A thorough review indicates that the first principles results for quantum confinement vary widely. The possible cause of this variation has been examined. Surface passivation and surface reconstruction of nanowires have been elucidated. It has been found that quantum confinement owes its origin to surface strain resulting from surface passivation and surface reconstruction and hence thin nanowires may actually be crystalline-core/amorphous-shell (c-Si/a-Si) nanowires. Experimental data available in the literature corroborate with the suggestion. The study also reveals an intrinsic relationship between quantum confinement and the surface amorphicity of nanowires. It demonstrates that surface amorphicity may be an important tool to investigate the electronic, optoelectronic and sensorial properties of quantum-confined nanowires.

Mohammad, Noor S.

2014-10-01

412

Signatures of Wigner molecule formation in interacting Dirac fermion quantum dots

We study N interacting massless Dirac fermions confined in a two-dimensional quantum dot. Physical realizations of this problem include a graphene monolayer and the surface state of a strong topological insulator. We consider both a magnetic confinement and an infinite mass confinement. The ground-state energy is computed as a function of the effective interaction parameter {alpha} from the Hartree-Fock approximation and, alternatively, by employing the Mueller exchange functional. For N=2, we compare those approximations to exact diagonalization results. The Hartree-Fock energies are highly accurate for the most relevant interaction range {alpha} < or approx. 2, but the Mueller functional leads to an unphysical instability when {alpha} > or approx. 0.756. Up to 20 particles were studied using Hartree-Fock calculations. Wigner molecule formation was observed for strong but realistic interactions, accompanied by a rich peak structure in the addition energy spectrum.

Paananen, Tomi; Egger, Reinhold [Institut fuer Theoretische Physik, Heinrich-Heine-Universitaet, D-40225 Duesseldorf (Germany); Siedentop, Heinz [Mathematisches Institut, Ludwigs-Maximilians-Universitaet Muenchen, D-80333 Muenchen (Germany)

2011-02-15

413

Quantum-dot-tagged photonic crystal beads for multiplex detection of tumor markers.

Novel quantum-dot-tagged photonic crystal beads were fabricated for multiplex detection of tumor markers via self-assembly of quantum dot-embedded polystyrene nanospheres into photonic crystal beads through a microfluidic device. PMID:25308755

Li, Juan; Wang, Huan; Dong, Shujun; Zhu, Peizhi; Diao, Guowang; Yang, Zhanjun

2014-12-01

414

LDRD Final Report on Theory and Exploration of Quantum-Dot Optical Nonlinearities and Coherences.

National Technical Information Service (NTIS)

A microscopic theory for investigating quantum-dot optical properties was developed. The theory incorporated advances on various aspects of quantum-dot physics developed at Sandia and elsewhere. Important components are a non-Markovian treatment of polari...

W. W. Chow

2008-01-01

415

Synthesis and structural characterization of ZnTe/ZnSe core/shell tunable quantum dots

Colloidal semiconductor nanocrystals or quantum dots have attracted much attention recently with their unique optical properties. Here we present a novel approach to synthesize ZnTe/ZnSe core/shell tunable quantum dots. ...

Guan, Juan

2008-01-01

416

Fabrication and optimization of light emitting devices with core-shell quantum dots

Quantum dot light emitting devices (QD-LEDs) are promising options for the next generation of solid state lighting, color displays, and other optoelectronic applications. Overcoating quantum dots (QDs) -- semiconducting ...

Song, Katherine Wei

2013-01-01

417

Ultrafast optical control of individual quantum dot spin qubits.

Single spins in semiconductor quantum dots form a promising platform for solid-state quantum information processing. The spin-up and spin-down states of a single electron or hole, trapped inside a quantum dot, can represent a single qubit with a reasonably long decoherence time. The spin qubit can be optically coupled to excited (charged exciton) states that are also trapped in the quantum dot, which provides a mechanism to quickly initialize, manipulate and measure the spin state with optical pulses, and to interface between a stationary matter qubit and a 'flying' photonic qubit for quantum communication and distributed quantum information processing. The interaction of the spin qubit with light may be enhanced by placing the quantum dot inside a monolithic microcavity. An entire system, consisting of a two-dimensional array of quantum dots and a planar microcavity, may plausibly be constructed by modern semiconductor nano-fabrication technology and could offer a path toward chip-sized scalable quantum repeaters and quantum computers. This article reviews the recent experimental developments in optical control of single quantum dot spins for quantum information processing. We highlight demonstrations of a complete set of all-optical single-qubit operations on a single quantum dot spin: initialization, an arbitrary SU(2) gate, and measurement. We review the decoherence and dephasing mechanisms due to hyperfine interaction with the nuclear-spin bath, and show how the single-qubit operations can be combined to perform spin echo sequences that extend the qubit decoherence from a few nanoseconds to several microseconds, more than 5 orders of magnitude longer than the single-qubit gate time. Two-qubit coupling is discussed, both within a single chip by means of exchange coupling of nearby spins and optically induced geometric phases, as well as over longer-distances. Long-distance spin-spin entanglement can be generated if each spin can emit a photon that is entangled with the spin, and these photons are then interfered. We review recent work demonstrating entanglement between a stationary spin qubit and a flying photonic qubit. These experiments utilize the polarization- and frequency-dependent spontaneous emission from the lowest charged exciton state to single spin Zeeman sublevels. PMID:24006335

De Greve, Kristiaan; Press, David; McMahon, Peter L; Yamamoto, Yoshihisa

2013-09-01

418

Feedback-generated periodic pulse trains in quantum dot lasers

NASA Astrophysics Data System (ADS)

Quantum dot lasers have been shown to have greatly enhanced stability in the feedback configuration thanks to a high damping of the relaxation oscillations and they display different dynamics to those of conventional semiconductor lasers. For high feedback levels in conventional devices one obtains Low Frequency Fluctuations: sharp dropouts in intensity and subsequent gradual build-ups. Standard low frequency fluctuation-like traces are conspicuous by their absence in studies of feedback with quantum dot devices. We experimentally examine single mode quantum dot lasers at high feedback levels with a long delay and observe regular pulse-trains with a period equaling the external cavity round-trip time where each pulse features a distinctive broad trailing edge plateau. The distinctive pulse shape is very similar to the recently published strong pulse-asymmetry in two-section, passively mode-locked quantum dot lasers where this asymmetry was shown to result from the creation of different modal groups. We attribute the pulses in our experiment to the same phenomenon: each pulse corresponds to a simultaneous excitation of a number of the external cavity modes. We consider a model tailored specifically for quantum dot lasers with strong optical feedback and find it reproduces the experimentally observed trains extremely well.

Viktorov, Evgeny A.; Goulding, David; Hegarty, Stephen P.; Huyet, Guillaume; Erneux, Thomas; Kelleher, Bryan

2014-05-01

419

Temperature-dependent electron transport in quantum dot photovoltaics

NASA Astrophysics Data System (ADS)

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

Padilla, Derek J.

420

Detection of viral infections using colloidal quantum dots

NASA Astrophysics Data System (ADS)

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

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

2006-02-01

421

Effective Landé factor in a GaMnAs quantum dot; with the effects of sp-d exchange on a bound polaron

NASA Astrophysics Data System (ADS)

The effective g-factor of conduction (valence) band electron (hole) is obtained in the GaMnAs quantum dot. Magneto bound polaron in a GaMnAs/Ga0.6Al0.4As quantum dot is investigated with the inclusion of exchange interaction effects due to Mn alloy content and the geometrical confinement. The spin polaronic energy of the heavy hole exciton is studied with the spatial confinement using a mean field theory in the presence of magnetic field strength.

Lalitha, D.; Peter, A. John

2014-04-01

422

Local Phonon Modes in InAs/GaAs Quantum Dots

NASA Astrophysics Data System (ADS)

Local optical phonons in self-organized InAs/GaAs quantum dots (QDs) are investigated by Raman scattering under resonant excitation of the QD ground state transition. All QD sample structures, including single and stacked QD layers, pure InAs and InxGa1-xAs QDs as well as InAs QDs overgrown by GaAs and InxGa1-xAs quantum wells, show an interface mode at ˜36 meV, a LO-like confined InAs QD mode at ˜33 meV and a TO-like confined InAs QD mode at ˜31 meV. For all samples the interface mode shows the strongest exciton-phonon coupling, followed by the QD LO mode.

Paarmann, A.; Guffarth, F.; Warming, T.; Hoffmann, A.; Bimberg, D.

2005-06-01

423

Coherent excitation of a strongly coupled quantum dot - cavity system

We have studied the coherent excitation of a strongly coupled QD/photonic crystal cavity system. Time-resolved reflectivity measurements show the vacuum Rabi oscillation of the dot in the cavity. Next, we considered the resonant driving of a cavity-detuned dot, which efficiently populates the cavity mode. This cavity-controlled read-out channel allows high-resolution single quantum dot spectroscopy. Autocorrelation measurements on the cavity mode show antibunching and suggest the use of the resonantly driven QD/cavity system as an on-demand source of single photons with potentially near-unity indistinguishability.

Dirk Englund; Arka Majumdar; Andrei Faraon; Mitsuru Toishi; Nick Stoltz; Pierre Petroff; Jelena Vuckovic

2009-02-14

424

Generation of even harmonics in coupled quantum dots

Using the spatial-temporal symmetry principle we developed recently, we propose an effective scheme for even-harmonics generation in coupled quantum dots. The relative intensity of odd and even harmonic components in the emission spectrum can be controlled by tuning the dipole couplings among the dots, which can be realized in experiments by careful design of the nanostructures. In particular, pure 2nth harmonics and (2n+1)th harmonics (where n is an integer) can be generated simultaneously with polarizations in two mutual perpendicular directions in our systems. An experimental design of the coupled dots system is presented.

Guo Shifang; Duan Suqing; Yang Ning; Chu Weidong; Zhang Wei [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)

2011-07-15

425

GaAsSb-capped InAs quantum dots: From enlarged quantum dot height to alloy fluctuations

The Sb-induced changes in the optical properties of GaAsSb-capped InAs/GaAs quantum dots (QDs) are shown to be strongly correlated with structural changes. The observed redshift of the photoluminescence emission is shown to follow two different regimes. In the first regime, with Sb concentrations up to approx12%, the emission wavelength shifts up to approx1280 nm with a large enhancement of the luminescence characteristics. A structural analysis at the atomic scale by cross-sectional scanning tunneling microscopy shows that this enhancement arises from a gradual increase in QD height, which improves carrier confinement and reduces the sensitivity of the excitonic band gap to QD size fluctuations within the ensemble. The increased QD height results from the progressive suppression of QD decomposition during the capping process due to the presence of Sb atoms on the growth surface. In the second regime, with Sb concentrations above approx12%, the emission wavelength shifts up to approx1500 nm, but the luminescence characteristics progressively degrade with the Sb content. This degradation at high Sb contents occurs as a result of composition modulation in the capping layer and strain-induced Sb migration to the top of the QDs, together with a transition to a type-II band alignment.

Ulloa, J. M.; Gargallo-Caballero, R.; Moral, M. del; Guzman, A.; Hierro, A. [Institute for Systems based on Optoelectronics and Microtechnology (ISOM), Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Bozkurt, M.; Koenraad, P. M. [Photonics and Semiconductor Nanophysics, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven (Netherlands)

2010-04-15

426

Carrier dynamics and activation energy of CdTe quantum dots in a Cd{sub x}Zn{sub 1-x}Te quantum well

We investigate the optical properties of CdTe quantum dots (QDs) in a Cd{sub 0.3}Zn{sub 0.7}Te quantum well (QW) grown on GaAs (100) substrates. Carrier dynamics of CdTe/ZnTe QDs and quantum dots-in-a-well (DWELL) structure is studied using time-resolved photoluminescence (PL) measurements, which show the longer exciton lifetime of the DWELL structure. The activation energy of the electrons confined in the DWELL structure, as obtained from the temperature-dependent PL spectra, was also higher than that of electrons confined in the CdTe/ZnTe QDs. This behavior is attributed to the better capture of carriers into QDs within the surrounding QW.

Han, W. I.; Lee, J. H.; Yu, J. S.; Choi, J. C. [Department of Physics, Yonsei University, Wonju 220-710 (Korea, Republic of); Lee, H. S. [Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)

2011-12-05

427

Quantum interference in exciton-Mn spin interactions in a CdTe semiconductor quantum dot

We show theoretically and experimentally the existence of a new quantum interference(QI) effect between the electron-hole interactions and the scattering by a single Mn impurity. Theoretical model, including electron-valence hole correlations, the short and long range exchange interaction of Mn ion with the heavy hole and with electron and anisotropy of the quantum dot, is compared with photoluminescence spectroscopy of CdTe dots with single magnetic ions. We show how design of the electronic levels of a quantum dot enable the design of an exciton, control of the quantum interference and hence engineering of light-Mn interaction.

A. Trojnar; M. Korkusinski; E. Kadantsev; P. Hawrylak; M. Goryca; T. Kazimierczuk; P. Kossacki; P. Wojnar; M. Potemski

2011-05-04

428

Quantum description of nuclear spin cooling in a quantum dot

NASA Astrophysics Data System (ADS)

We study theoretically the cooling of an ensemble of nuclear spins coupled to the spin of a localized electron in a quantum dot. We obtain a master equation for the state of the nuclear spins interacting with a sequence of polarized electrons that allows us to study quantitatively the cooling process including the effect of nuclear spin coherences, which can lead to “dark states” of the nuclear system in which further cooling is inhibited. We show that the inhomogeneous Knight field mitigates this effect strongly and that the remaining dark-state limitations can be overcome by very few shifts of the electron wave function, allowing for cooling far beyond the dark-state limit. Numerical integration of the master equation indicates that polarizations larger than 90% can be achieved within a millisecond time scale.

Christ, H.; Cirac, J. I.; Giedke, G.

2007-04-01

429

A Quantum Dot Single-Photon Turnstile Device

Quantum communication relies on the availability of light pulses with strong quantum correlations among photons. An example of such an optical source is a single-photon pulse with a vanishing probability for detecting two or more photons. Using pulsed laser excitation of a single quantum dot, a single-photon turnstile device that generates a train of single-photon pulses was demonstrated. For a

P. Michler; A. Kiraz; C. Becher; W. V. Schoenfeld; P. M. Petroff; Lidong Zhang; E. Hu; A. Imamoglu

2000-01-01

430

InGaAs-GaAs quantum-dot lasers

Quantum-dot (QD) lasers provide superior lasing characteristics compared to quantum-well (QW) and QW wire lasers due to their delta like density of states. Record threshold current densities of 40 A·cm -2 at 77 K and of 62 A·cm-2 at 300 K are obtained while a characteristic temperature of 385 K is maintained up to 300 K. The internal quantum efficiency

D. Bimberg; N. Kirstaedter; N. N. Ledentsov; Zh. I. Alferov; P. S. Kop'ev; V. M. Ustinov

1997-01-01

431

Quantum forces of a gas confined in nano structures

NASA Astrophysics Data System (ADS)

In nano domains, thermodynamic properties of gases considerably differ from those in macro domains. One of the reasons for this difference is the quantum size effects, which become important when the thermal de Broglie wavelength of particles is not negligible in comparison with domain size. In this study, it is shown that quantum forces may appear in gases confined in nano structures due to the quantum boundary layer caused by quantum size effects. In the case of experimental verification of these quantum forces, a macroscopic manifestation of the effect of the quantum boundary layer on the thermodynamic behavior of gases can be confirmed.

Firat, Coskun; Sisman, Altug

2013-04-01

432

Optical absorption of semiconductor quantum dot solids

NASA Astrophysics Data System (ADS)

Several aspects concerning optical absorption in 3D assemblies of semiconductor quantum dots (QD solids) were studied. Considering the numerically simulated spectral dependences of the absorption coefficient in the case 3D QD assemblies with finite crystal size distribution, described by log-normal probability distribution functions (PDFs), several fundamental predictions were derived. First of all, it is predicted that the band gap energy of the QD solid should exhibit a certain ‘red-shift’ upon enlargement of the dispersion of the crystal size at a fixed average value thereof when the size-quantization regime in individual QDs has been entered. Furthermore, very large Urbach energy values are predicted, comparable to those characteristic for amorphous materials, for semiconductor QD solids with finite dispersion of the crystal size when the average QD size falls within the size-quantization interval. The Urbach energy in 3D assemblies composed by strongly quantized QDs with large dispersions of the PDFs characterizing the size distributions could be 100 times larger than the values in the non-quantized case (regardless of the size distribution in the latter case). Such large values are not due to the structural disorder inherent to individual QDs constituting the array, but a consequence of the disorder on the superlattice scale. Analogous arguments could be applied to predict large Urbach energies corresponding to the absorption tails in absorption spectra constructed from the spectral response of stationary nonequilibrium conductivity (photoconductivity). All these predictions are in excellent agreement with the available experimental data. Moreover, the presented approach could enable exact prediction of the optical absorption of a semiconductor QD solid if the PDF of the crystal size is known from the experiment. The smearing of excitonic absorption peaks in QD solids induced as a consequence of particle size distribution is considered and analyzed to some extent as well.

Pejova, Biljana

2014-04-01

433

Biosensing with Quantum Dots: A Microfluidic Approach

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

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

2011-01-01

434

Toxicity of Oxidatively Degraded Quantum Dots

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

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

2014-01-01

435

Microwave spectroscopy on a double quantum dot with an on-chip Josephson oscillator

Microwave spectroscopy on a double quantum dot with an on-chip Josephson oscillator A W Holleitner://www.njp.org/) Received 19 November 1999; online 18 February 2000 Abstract. We present measurements on microwave spectroscopy on a double quantum dot with an on-chip microwave source. The quantum dots are realized in the two

Ludwig-Maximilians-UniversitÃ¤t, MÃ¼nchen

436

Phase relaxation of one-particle states in closed quantum dots K. Held a,b

Â429 www.elsevier.com/locate/chaos #12;Quantum dots which contain a larger number of electrons N, OÃ°103 Ã?Phase relaxation of one-particle states in closed quantum dots K. Held a,b , E. Eisenberg a,b , B to analyze the effect of dephasing of one-particle states on the magnetocon- ductance of closed quantum dots

Eisenberg, Eli

437

Nanoprecipitation was utilized to synthesize biodegradable and surfactant-free nanoparticles loaded with quantum dots. This protocol also yielded nanoparticles coloaded with both quantum dots and hydrophobic drug (Coenzyme Q10) molecules. Importantly, even though surfactants were not utilized during the nanoprecipitation procedure, these loaded nanoparticles did not aggregate. Dialysis efficiently removed unencapsulated quantum dots from nanoparticle suspensions without altering the physical properties

Barrett J. Nehilla; Philip G. Allen; Tejal A. Desai

438

Quantum Dots in a Polymer Composite: A Convenient Particle-in-a-Box Laboratory Experiment

ERIC Educational Resources Information Center

Semiconductor quantum dots are at the forefront of materials science chemistry with applications in biological imaging and photovoltaic technologies. We have developed a simple laboratory experiment to measure the quantum-dot size from fluorescence spectra. A major roadblock of quantum-dot based exercises is the particle synthesis and handling;…

Rice, Charles V.; Giffin, Guinevere A.

2008-01-01

439

Self-organized formation of quantum dots of a material on a substrate

Systems and methods are described for fabricating arrays of quantum dots. A method for making a quantum dot device, includes: forming clusters of atoms on a substrate; and charging the clusters of atoms such that the clusters of atoms repel one another. The systems and methods provide advantages because the quantum dots can be ordered with regard to spacing and/or size.

Zhang, Zhenyu (232 Long Bow Rd., Knoxville, TN 37922); Wendelken, John F. (925 Suwanee Rd., Knoxville, TN 37923); Chang, Ming-Che (F4-2, No. 178 Sec 5 Minsheng East Rd., Taipei, TW); Pai, Woei Wu (1F, No. 17, Alley 11, Lane 202, Ming Chyuan Rd., Pan Chou City, Taipei County, TW)

2001-01-01

440

Pressure dependence of photoluminescence spectra of self-assembled InAs/GaAs quantum dots

Pressure dependence of photoluminescence spectra of self-assembled InAs/GaAs quantum dots F. J Photoluminescence (PL) measurements have been performed in InAs/GaAs self-assembled quantum dots (QDs) under high-organised quantum dots (QDs) studied under high excitation conditions at low temperatures and under high hydrostatic

Nabben, Reinhard

441

dots by double-quantum-coherence optical spectroscopy Benjamin P. Fingerhut,1 Marten Richter,1,2 Jun for utilization of quantum dots (QDs) for enhancing the efficiencies of solar cells, and for the generation-embedded quantum dots often leads to the association of single excitons into exciton complexes. The existence

Mukamel, Shaul

442

Correlations of conductance peaks and transmission phases in deformed quantum dots

Correlations of conductance peaks and transmission phases in deformed quantum dots Reinhard Baltin of a deformed ballistic quantum dot weakly coupled to leads. We show that preferred single--particle levels on ballistic quantum dots are discussed. PACS numbers: 73.23.Hk, 73.23.Ps, 73.40.Gk Published in Eur. Phys. J

Hackenbroich, Gregor

443

Distance-Engineered Plasmon-Enhanced Light Harvesting in CdSe Quantum Dots

Distance-Engineered Plasmon-Enhanced Light Harvesting in CdSe Quantum Dots Shengye Jin,,Â§, Erica De Supporting Information ABSTRACT: Improvement of light harvesting in semiconductor quantum dots (QDs. SECTION: Plasmonics, Optical Materials, and Hard Matter Semiconductor quantum dots (QDs) have received

444

Raman spectroscopy of electrochemically self-assembled CdS quantum dots

Raman spectroscopy of electrochemically self-assembled CdS quantum dots A. Balandina) Department the lowest two subbands. The results suggest that quantum dot arrays, produced by inexpensive robust0003-6951 00 02202-6 Quantum dots represent the ultimate test bed for size quantization of both

445

Quantum Dots Encapsulated within Phospholipid Membranes: Phase-Dependent Structure, Photostability is an efficient approach to transfer quantum dots (QDs) into aqueous solutions, which is important for renewable-Crick base-pairing. INTRODUCTION Luminescent semiconductor nanocrystals, or quantum dots (QDs), have

Salaita, Khalid

446

Observation of Individual Microtubule Motor Steps in Living Cells with Endocytosed Quantum Dots

Observation of Individual Microtubule Motor Steps in Living Cells with Endocytosed Quantum Dots by following movements of endocytic vesicles that contain quantum dots (QDs) with a fast camera. The brightness and photostability of quantum dots allow us to record motor displacement traces with 300 Âµs time resolution and 1

Chen, Peng

447

quantum dots This article has been downloaded from IOPscience. Please scroll down to see the full text. For example, in a quantum-dot system, the conductance can depend on the lead positions. We investigate, for graphene quantum dots, the conductance variations with the lead positions. Since for graphene the types

Lai, Ying-Cheng

448

Theory of time-resolved Raman scattering and fluorescence emission from semiconductor quantum dots

Theory of time-resolved Raman scattering and fluorescence emission from semiconductor quantum dots description of time-resolved Raman scattering and fluorescence emission of a coupled phonon-quantum dot system spectra of an InGaAs/GaAs-quantum dot are calculated for stationary and pulsed optical excitation

Nabben, Reinhard

449

Crossover from `mesoscopic' to `universal' phase for electron transmission in quantum dots

Crossover from `mesoscopic' to `universal' phase for electron transmission in quantum dots M in coherent electron systems--that is, `mesoscopic' systems such as quantum dots--can yield infor- mation measurements on relatively large quantum dots1 recently revealed that the phase evolution for electrons

Heiblum, Mordehai "Moty"

450

Eigenvalues imbedded in the band spectrum for the periodic array of quantum dots

Eigenvalues imbedded in the band spectrum for the periodic array of quantum dots V. A. Geyler a.ÂPetersburg, 197101, Russia Abstract Solvable model of a periodic array of quantum dots in a uniform magnetic field. II. Model We consider an array of quantum dots displaced in the nodes of a plane lattice \\Gamma which

451

Effect of the (OH) Surface Capping on ZnO Quantum Dots

Effect of the (OH) Surface Capping on ZnO Quantum Dots H. Zhou1 ) (a), H. Alves (a), D. M. Hofmann; S10.1 ZnO quantum dots were prepared by the reaction of Zn2+ with OHÂÂ in alcoholic solution transition of ZnO quantum dots is strongly correlated with the presence of the surface (OH) groups

Nabben, Reinhard

452

Quantum-dot based avalanche photodiodes for mid-infrared Majeed M. Hayat a

Quantum-dot based avalanche photodiodes for mid-infrared sensing Majeed M. Hayat a , Oh-Hyun Kwon b ABSTRACT A mid-infrared sensor is proposed in which an intersubband quantum-dot (QD) detector is integrated temperatures. Keywords: Quantum dots, avalanche photodiodes, infrared, sensors, mid-wave infrared, avalanche

Hayat, Majeed M.

453

Probing Electric and Magnetic Vacuum Fluctuations with Quantum Dots

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

454

Pulsed single-photon resonant-cavity quantum dot LED

NASA Astrophysics Data System (ADS)

We demonstrate electrical pumping of self-assembled InP/Ga 0.51In 0.49P quantum dots embedded in a p-i-n resonant-cavity-diode structure with emission in the red spectral region. A high aluminum containing Al 0.98Ga 0.02As layer allows wet thermal oxidation and implementation of a current restricting oxide aperture above the active region. The intended use of these InP-quantum dots in such a resonant-cavity-LED structure as a pulsed electrically driven single-photon emitter was confirmed by measuring the second order intensity correlation function g(?) with a Hanbury-Brown and Twiss type setup. The correlation measurements performed on a single quantum dot (?40 K) show a clear antibunching behavior ( g(0)<0.24) up to 200 MHz as expected for a single-photon emitter.

Schulz, W.-M.; Eichfelder, M.; Reischle, M.; Kessler, C.; Roßbach, R.; Jetter, M.; Michler, P.

2011-01-01

455

Probing electric and magnetic vacuum fluctuations with quantum dots

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

Petru Tighineanu; Mads Lykke Andersen; Anders Søndberg Sørensen; Søren Stobbe; Peter Lodahl

2014-04-04

456

Tunable optical Kerr effects of DNAs coupled to quantum dots

The coupling between DNA molecules and quantum dots can result in impressive nonlinear optical properties. In this paper, we theoretically demonstrate the significant enhancement of Kerr coefficient of signal light using optical pump-probe technique when the pump-exciton detuning is zero, and the probe-exciton detuning is adjusted properly to the frequency of DNA vibration mode. The magnitude of optical Kerr coefficient can be tuned by modifying the intensity of the pump beam. It is shown clearly that this phenomenon cannot occur without the DNA-quantum dot coupling. The present research will lead us to know more about the anomalous nonlinear optical behaviors in the hybrid DNA-quantum dot systems, which may have potential applications in the fields such as DNA detection. PMID:23194282

2012-01-01

457

Observation of dressed excitonic states in a single quantum dot.

We report the observation of dressed states of a quantum dot. The optically excited exciton and biexciton states of the quantum dot are coupled by a strong laser field and the resulting spectral signatures are measured using differential transmission of a probe field. We demonstrate that the anisotropic electron-hole exchange interaction induced splitting between the x- and y-polarized excitonic states can be completely erased by using the ac-Stark effect induced by the coupling field, without causing any appreciable broadening of the spectral lines. We also show that by varying the polarization and strength of a resonant coupling field, we can effectively change the polarization axis of the quantum dot. PMID:18518335

Jundt, Gregor; Robledo, Lucio; Högele, Alexander; Fält, Stefan; Imamo?lu, Atac

2008-05-01

458

Observation of Dressed Excitonic States in a Single Quantum Dot

NASA Astrophysics Data System (ADS)

We report the observation of dressed states of a quantum dot. The optically excited exciton and biexciton states of the quantum dot are coupled by a strong laser field and the resulting spectral signatures are measured using differential transmission of a probe field. We demonstrate that the anisotropic electron-hole exchange interaction induced splitting between the x- and y-polarized excitonic states can be completely erased by using the ac-Stark effect induced by the coupling field, without causing any appreciable broadening of the spectral lines. We also show that by varying the polarization and strength of a resonant coupling field, we can effectively change the polarization axis of the quantum dot.

Jundt, Gregor; Robledo, Lucio; Högele, Alexander; Fält, Stefan; Imamo?lu, Atac

2008-05-01

459

Peptide linkers for the assembly of semiconductor quantum dot bioconjugates

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

460

Probing electric and magnetic vacuum fluctuations with quantum dots

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

Tighineanu, Petru; Sørensen, Anders Søndberg; Stobbe, Søren; Lodahl, Peter

2014-01-01

461

Probing electric and magnetic vacuum fluctuations with quantum dots.

The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this Letter we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level. PMID:25105618

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

2014-07-25

462

Gate-controlled electron spins in quantum dots

In this paper we study the properties of anisotropic semiconductor quantum dots (QDs) formed in the conduction band in the presence of the magnetic field. The Kane-type model is formulated and is analyzed by using both analytical and finite element techniques. Among other things, we demonstrate that in such quantum dots, the electron spin states in the phonon-induced spin-flip rate can be manipulated with the application of externally applied anisotropic gate potentials. More precisely, such potentials enhance the spin flip rates and reduce the level crossing points to lower quantum dot radii. This happens due to the suppression of the g-factor towards bulk crystal. We conclude that the phonon induced spin-flip rate can be controlled through the application of spin-orbit coupling. Numerical examples are shown to demonstrate these findings.

Prabhakar, Sanjay [M2NeT Laboratory, Wilfrid Laurier University, Waterloo, ON, N2L3C5 (Canada); Melnik, Roderick [M2NeT Laboratory, Wilfrid Laurier University, Waterloo, ON, N2L3C5 and Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911, Leganes (Spain); Bonilla, Luis L. [Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911, Leganes, Spain and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 (United States)

2013-12-16

463

Group-velocity slowdown in a double quantum dot molecule

NASA Astrophysics Data System (ADS)

The slowdown of optical pulses due to quantum-coherence effects is investigated theoretically for an “active material” consisting of InGaAs-based double quantum dot molecules. These are designed to exhibit a long-lived coherence between two electronic levels, which is an essential part of a quantum-coherence scheme that makes use of electromagnetically induced transparency effects to achieve group-velocity slowdown. We apply a many-particle approach based on realistic semiconductor parameters that allows us to calculate the quantum dot material dynamics including microscopic carrier scattering and polarization dephasing dynamics. The group-velocity reduction is characterized in the frequency domain by a quasiequilibrium slowdown factor and in the time domain by the probe-pulse slowdown obtained from a calculation of the spatiotemporal material dynamics coupled to the propagating optical field. The group-velocity slowdown in the quantum dot molecule is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots. The dependencies of slowdown and shape of the propagating probe pulses on lattice temperature and drive intensities are investigated.

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

2013-09-01

464

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

NASA Astrophysics Data System (ADS)

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals' lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems.

Lodahl, Peter; Floris van Driel, A.; Nikolaev, Ivan S.; Irman, Arie; Overgaag, Karin; Vanmaekelbergh, Daniël; Vos, Willem L.

2004-08-01

465

Proposal for ultra-high performance infrared quantum dot.

In this paper, effect of an introduced defect on electrical and optical properties of quantum box and spherical quantum dot is studied. 3D-self-consistent solution of the Schrödinger-Poisson equations for evaluation of the proposed complex quantum box and analytical solution for spherical quantum dot are used. It is shown that with increasing the defect size and height a considerable enhancement in matrix element, optical nonlinearities (second order, quadratic electro-optic effect and the resonant third order nonlinear susceptibilities), optical linear absorption coefficient ( 4.5 -10 nm, 10(-4) approximately 10(-2) m.V(-1), 10(-12) approximately 10(-9) m(2) / V (2) , 10(-11) approximately 10(-9) m(2) / V(2) and 4.7 x 10(2) approximately 3.8 x 10(4) cm(-1) respectively) and electroabsorption properties associated with intersublevel transition of centered defect quantum dot are examined. Also, it is shown that enhancement of optical nonlinearity is approximately independent of defect position that is so excellent from practical implementation point of view. A THZ-IR photodetector based on resonant tunneling spherical centered defect quantum dot (RT-SCDQD) operating at room temperature is also investigated. Inserting the centered defect in quantum dot increases the dipole transition matrix element and so increases the absorption coefficient considerably (1.05 x 10(6) approximately 7.33 x 10(6)at 83 microm ). Therefore the quantum efficiency in SCDQD structure enhances which leads to increasing the responsivity of the proposed system. The double barrier reduces the dark current. These improvements concludes to ultra high detectivity 5 x 10(16) 2.25 x 10(9) cm H