WorldWideScience

Sample records for epitaxial quantum dots

  1. Advanced Epitaxial Lift-Off Quantum Dot Photovoltaic Devices Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to develop a high-efficiency, triple-junction, epitaxial lift-off (ELO) solar cell by incorporating quantum dots (QDs) within the current-limiting...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-07-01

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

  3. Epitaxial Heterostructures of Lead Selenide Quantum Dots on Hematite Nanowires.

    Science.gov (United States)

    Selinsky, Rachel S; Shin, Sanghun; Lukowski, Mark A; Jin, Song

    2012-06-21

    We present a novel method for synthesizing epitaxial quantum dot-nanowire (QD-NW) heterostructures using the example of colloidal PbSe QDs decorated on furnace-grown hematite (α-Fe2O3) NWs. The direct heterogeneous nucleation of QDs on Fe2O3 NWs relies upon an aggressive surface dehydration of the as-synthesized Fe2O3 NWs at 350 °C under vacuum and subsequent introduction of colloidal reactants resulting in direct growth of PbSe QDs on Fe2O3. The synthesis is tunable: the QD diameter distribution and density of QDs on the NWs increase with increased dehydration time, and QD diameters and size distributions decrease with decreased injection temperature of the colloidal synthesis. Transmission electron microscopy (TEM) structural analysis reveals direct heteroepitaxial heterojunctions where the matching faces can be PbSe (002) and Fe2O3 (003) with their respective [11̅0] crystallographic directions aligned. This can be a general approach for integrating colloidal and furnace synthetic techniques, thus broadening possible material combinations for future high-quality, epitaxial nanoscale heterostructures for solar applications.

  4. Self-assembly of vertically aligned quantum ring-dot structure by Multiple Droplet Epitaxy

    Science.gov (United States)

    Elborg, Martin; Noda, Takeshi; Mano, Takaaki; Kuroda, Takashi; Yao, Yuanzhao; Sakuma, Yoshiki; Sakoda, Kazuaki

    2017-11-01

    We successfully grow vertically aligned quantum ring-dot structures by Multiple Droplet Epitaxy technique. The growth is achieved by depositing GaAs quantum rings in a first droplet epitaxy process which are subsequently covered by a thin AlGaAs barrier. In a second droplet epitaxy process, Ga droplets preferentially position in the center indentation of the ring as well as attached to the edge of the ring in [ 1 1 bar 0 ] direction. By designing the ring geometry, full selectivity for the center position of the ring is achieved where we crystallize the droplets into quantum dots. The geometry of the ring and dot as well as barrier layer can be controlled in separate growth steps. This technique offers great potential for creating complex quantum molecules for novel quantum information technologies.

  5. Long-range ordered self-assembled InAs quantum dots epitaxially grown on (110) GaAs

    Science.gov (United States)

    Bauer, J.; Schuh, D.; Uccelli, E.; Schulz, R.; Kress, A.; Hofbauer, F.; Finley, J. J.; Abstreiter, G.

    2004-11-01

    We report on a promising approach for positioning of self-assembled InAs quantum dots on (110) GaAs with nanometer precision. By combining self-assembly of quantum dots with molecular beam epitaxy on previously grown and in situ cleaved substrates (cleaved-edge overgrowth), arrays of long-range ordered InAs quantum dots have been fabricated. Both atomic force microscopy and micro-photoluminescence measurements demonstrate the ability to control size, position, and ordering of the quantum dots. Furthermore, single dot photoluminescence investigations confirm the high optical quality of the quantum dots fabricated.

  6. Self-assembly of triangular quantum dots on (111)A substrates by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Jo, M.; Mano, T.; Abbarchi, M.; Kuroda, T. [Advanced Photonics Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Sakoda, K. [Advanced Photonics Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan and Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan)

    2014-05-15

    We report the self-assembly of triangular GaAs quantum dots (QDs) on (111)A substrates using droplet epitaxy. Shape transition from hexagonal to triangular QDs is observed with increasing crystallizing temperature. The mechanism of the morphological change is discussed in terms of different growth rates of step edges on a (111)A substrate.

  7. Single-photon emission from electrically driven InP quantum dots epitaxially grown on CMOS-compatible Si(001).

    Science.gov (United States)

    Wiesner, M; Schulz, W-M; Kessler, C; Reischle, M; Metzner, S; Bertram, F; Christen, J; Roßbach, R; Jetter, M; Michler, P

    2012-08-24

    The heteroepitaxy of III-V semiconductors on silicon is a promising approach for making silicon a photonic platform. Mismatches in material properties, however, present a major challenge, leading to high defect densities in the epitaxial layers and adversely affecting radiative recombination processes. However, nanostructures, such as quantum dots, have been found to grow defect-free even in a suboptimal environment. Here we present the first realization of indium phosphide quantum dots on exactly oriented Si(001), grown by metal-organic vapour-phase epitaxy. We report electrically driven single-photon emission in the red spectral region, meeting the wavelength range of silicon avalanche photodiodes' highest detection efficiency.

  8. Growth and characterization of InP ringlike quantum-dot molecules grown by solid-source molecular beam epitaxy.

    Science.gov (United States)

    Jevasuwan, Wipakorn; Boonpeng, Poonyasiri; Panyakeow, Somsak; Ratanathammaphan, Somchai

    2010-11-01

    In this paper, we have studied the fabrication of InP ringlike quantum-dot molecules on GaAs(001) substrate grown by solid-source molecular beam epitaxy using droplet epitaxy technique and the effect of In deposition rate on the physical and optical properties of InP ringlike quantum-dot molecules. The In deposition rate is varied from 0.2 ML/s to 0.4, 0.8 and 1.6 ML/s. The surface morphology and cross-section were examined by ex-situ atomic force microscope and transmission electron microscope, respectively. The increasing of In deposition rate results in the decreasing of outer and inner diameters of InP ringlike quantum-dot molecules and height of InP quantum dots but increases the InP quantum dot and ringlike quantum-dot molecule densities. The photoluminescence peaks of InP ringlike quantum-dot molecules are blue-shifted and FWHM is narrower when In deposition rate is bigger.

  9. Intersublevel infrared photodetector with strain-free GaAs quantum dot pairs grown by high-temperature droplet epitaxy.

    Science.gov (United States)

    Wu, Jiang; Shao, Dali; Dorogan, Vitaliy G; Li, Alvason Z; Li, Shibin; DeCuir, Eric A; Manasreh, M Omar; Wang, Zhiming M; Mazur, Yuriy I; Salamo, Gregory J

    2010-04-14

    Normal incident photodetection at mid infrared spectral region is achieved using the intersublevel transitions from strain-free GaAs quantum dot pairs in Al(0.3)Ga(0.7)As matrix. The GaAs quantum dot pairs are fabricated by high temperature droplet epitaxy, through which zero strain quantum dot pairs are obtained from lattice matched materials. Photoluminescence, photoluminescence excitation optical spectroscopy, and visible-near-infrared photoconductivity measurement are carried out to study the electronic structure of the photodetector. Due to the intersublevel transitions from GaAs quantum dot pairs, a broadband photoresponse spectrum is observed from 3 to 8 microm with a full width at half-maximum of approximately 2.0 microm.

  10. A modified gradient approach for the growth of low-density InAs quantum dot molecules by molecular beam epitaxy

    Science.gov (United States)

    Sharma, Nandlal; Reuter, Dirk

    2017-11-01

    Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

  11. Growth mode of tensile-strained Ge quantum dots grown by molecular beam epitaxy

    Science.gov (United States)

    Zhang, Z. P.; Song, Y. X.; Chen, Q. M.; Wu, X. Y.; Zhu, Z. Y. S.; Zhang, L. Y.; Li, Y. Y.; Wang, S. M.

    2017-11-01

    Growth mode of tensile-strained Ge quantum dots on different III–V buffers by molecular beam epitaxy is studied by a combination of reflection high-energy electron diffraction, atomic force microscopy and transmission electron microscopy. The Ge-QDs growth on the InAlAs buffer lattice matched to InP and on InAs buffer on GaSb follows the Volmer–Weber growth mode with round Ge QDs and no Ge wetting layer, while it obeys the Stranski–Krastanov growth mode on GaSb, AlSb and AlGaSb on GaSb substrates, showing rectangular shaped platelets and a clear Ge wetting layer. The discovery of the Volmer–Weber growth mode is essential to avoid forming a wetting layer and the subsequent antiphase-domain defects when capping III–Vs on Ge-QDs, important for potential optoelectronic applications.

  12. Composition profiling of GaAs/AlGaAs quantum dots grown by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bocquel, J.; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Giddings, A. D.; Prosa, T. J.; Larson, D. J. [CAMECA Instruments, Inc., 5500 Nobel Drive, Madison, Wisconsin 53711 (United States); Mano, T. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)

    2014-10-13

    Droplet epitaxy (DE) is a growth method which can create III-V quantum dots (QDs) whose optoelectronic properties can be accurately controlled through the crystallisation conditions. In this work, GaAs/AlGaAs DE-QDs have been analyzed with the complimentary techniques of cross-sectional scanning tunneling microscopy and atom probe tomography. Structural details and a quantitative chemical analysis of QDs of different sizes are obtained. Most QDs were found to be pure GaAs, while a small proportion exhibited high intermixing caused by a local etching process. Large QDs with a high aspect ratio were observed to have an Al-rich crown above the GaAs QD. This structure is attributed to differences in mobility of the cations during the capping phase of the DE growth.

  13. Site-controlled and advanced epitaxial Ge/Si quantum dots: fabrication, properties, and applications

    Science.gov (United States)

    Brehm, Moritz; Grydlik, Martyna

    2017-09-01

    In this review, we report on fabrication paths, challenges, and emerging solutions to integrate group-IV epitaxial quantum dots (QDs) as active light emitters into the existing standard Si technology. Their potential as laser gain material for the use of optical intra- and inter-chip interconnects as well as possibilities to combine a single-photon-source-based quantum cryptographic means with Si technology will be discussed. We propose that the mandatory addressability of the light emitters can be achieved by a combination of organized QD growth assisted by templated self-assembly, and advanced inter-QD defect engineering to boost the optical emissivity of group-IV QDs at room-temperature. Those two main parts, the site-controlled growth and the light emission enhancement in QDs through the introduction of single defects build the main body of the review. This leads us to a roadmap for the necessary further development of this emerging field of CMOS-compatible group-IV QD light emitters for on-chip applications.

  14. Site-controlled and advanced epitaxial Ge/Si quantum dots: fabrication, properties, and applications.

    Science.gov (United States)

    Brehm, Moritz; Grydlik, Martyna

    2017-09-29

    In this review, we report on fabrication paths, challenges, and emerging solutions to integrate group-IV epitaxial quantum dots (QDs) as active light emitters into the existing standard Si technology. Their potential as laser gain material for the use of optical intra- and inter-chip interconnects as well as possibilities to combine a single-photon-source-based quantum cryptographic means with Si technology will be discussed. We propose that the mandatory addressability of the light emitters can be achieved by a combination of organized QD growth assisted by templated self-assembly, and advanced inter-QD defect engineering to boost the optical emissivity of group-IV QDs at room-temperature. Those two main parts, the site-controlled growth and the light emission enhancement in QDs through the introduction of single defects build the main body of the review. This leads us to a roadmap for the necessary further development of this emerging field of CMOS-compatible group-IV QD light emitters for on-chip applications.

  15. Hybrid Double Quantum Dots

    DEFF Research Database (Denmark)

    Sherman, D.; Yodh, J. S.; Albrecht, S. M.

    2016-01-01

    Epitaxial semiconductor-superconductor hybrid materials are an excellent basis for studying mesoscopic and topological superconductivity, as the semiconductor inherits a hard superconducting gap while retaining tunable carrier density. Here, we investigate double-quantum-dot devices made from InA...... that the individual dots host weakly hybridized Majorana modes....

  16. Quantum Nanostructures by Droplet Epitaxy

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2009-02-01

    Full Text Available Droplet epitaxy is an alternative growth technique for several quantum nanostructures. Indium droplets are distributed randomly on GaAs substrates at low temperatures (120-350'C. Under background pressure of group V elements, Arsenic and Phosphorous, InAs and InP nanostructures are created. Quantum rings with isotropic shape are obtained at low temperature range. When the growth thickness is increased, quantum rings are transformed to quantum dot rings. At high temperature range, anisotropic strain gives rise to quantum rings with square holes and non-uniform ring stripe. Regrowth of quantum dots on these anisotropic quantum rings, Quadra-Quantum Dots (QQDs could be realized. Potential applications of these quantum nanostructures are also discussed.

  17. A detailed study of self-assembled (Al,Ga)InP quantum dots grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Baumann, Vasilij; Roedel, Reinhold; Heidemann, Matthias; Schneider, Christian; Kamp, Martin; Hoefling, Sven [Technische Physik, Physikalisches Institut, Wilhelm Conrad Roentgen Research Center for Complex Material Systems, Universitaet Wuerzburg (Germany)

    2014-11-15

    We report on the structural and optical properties of self-assembled (Al,Ga)InP quantum dots (QDs) with varying material composition embedded in a (Al{sub 0.30}Ga{sub 0.70}){sub 0.51}In{sub 0.49}P matrix. The samples were grown by gas-source molecular beam epitaxy. Atomic force microscopy was used to study the structural properties of the quantum dots, revealing a strong dependence of the morphology on the material composition. Low-temperature ensemble photoluminescence was observed between 590 nm and 720 nm. Temperature and excitation power dependent, as well as time resolved measurements were performed, indicating a significantly reduced electron confinement and a reduced overlap of the electron/hole wavefunctions for Al- and/or Ga-rich compositions. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Optimization of Quantum-Dot Molecular Beam Epitaxy for Broad Spectral Bandwidth Devices

    KAUST Repository

    Majid, Mohammed Abdul

    2012-12-01

    The optimization of the key growth parameters for broad spectral bandwidth devices based on quantum dots is reported. A combination of atomic force microscopy, photoluminescence of test samples, and optoelectronic characterization of superluminescent diodes (SLDs) is used to optimize the growth conditions to obtain high-quality devices with large spectral bandwidth, radiative efficiency (due to a reduced defective-dot density), and thus output power. The defective-dot density is highlighted as being responsible for the degradation of device performance. An SLD device with 160 nm of bandwidth centered at 1230 nm is demonstrated.

  19. Metal organic vapor-phase epitaxy of InAs/InGaAsP quantum dots for laser applications at 1.5 μm

    DEFF Research Database (Denmark)

    Semenova, Elizaveta; Kulkova, Irina; Kadkhodazadeh, Shima

    2011-01-01

    The epitaxial growth of InAs/InGaAsP/InP quantum dots (QDs) for emission around 1.5 mu m by depositing a thin layer of GaAs on top of the QDs is presented in this letter. The infuence of various growth parameters on the properties of the QDs, in particular, size, shape, chemical composition...

  20. Droplet epitaxial growth of highly symmetric quantum dots emitting at telecommunication wavelengths on InP(111)A

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Neul; Kuroda, Takashi [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Graduate School of Engineering, Kyushu University, NIMS, Tsukuba 305-0044 (Japan); Liu, Xiangming; Mano, Takaaki, E-mail: mano.takaaki@nims.go.jp; Mitsuishi, Kazutaka; Noda, Takeshi; Sakuma, Yoshiki; Sakoda, Kazuaki [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Castellano, Andrea [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Dip. di Scienza dei Materiali, Università di Milano Bicocca, Via Cozzi 55, I-20125 Milano (Italy); Sanguinetti, Stefano [Dip. di Scienza dei Materiali, Università di Milano Bicocca, Via Cozzi 55, I-20125 Milano (Italy)

    2014-04-07

    We demonstrate the formation of InAs quantum dots (QDs) on InAlAs/InP(111)A by means of droplet epitaxy. The C{sub 3v} symmetry of the (111)A substrate enabled us to realize highly symmetric QDs that are free from lateral elongations. The QDs exhibit a disk-like truncated shape with an atomically flat top surface. Photoluminescence signals show broad-band spectra at telecommunication wavelengths of 1.3 and 1.5 μm. Strong luminescence signals are retained up to room temperature. Thus, our QDs are potentially useful for realizing an entangled photon-pair source that is compatible with current telecommunication fiber networks.

  1. Formation of GaN quantum dots by molecular beam epitaxy using NH{sub 3} as nitrogen source

    Energy Technology Data Exchange (ETDEWEB)

    Damilano, B., E-mail: bd@crhea.cnrs.fr; Brault, J.; Massies, J. [CRHEA-CNRS, Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Rue B. Grégory, Valbonne 06560 (France)

    2015-07-14

    Self-assembled GaN quantum dots (QDs) in Al{sub x}Ga{sub 1−x}N (0.3 ≤ x ≤ 1) were grown on c-plane sapphire and Si (111) substrates by molecular beam epitaxy using ammonia as nitrogen source. The QD formation temperature was varied from 650 °C to 800 °C. Surprisingly, the density and size of QDs formed in this temperature range are very similar. This has been explained by considering together experimental results obtained from reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence to discuss the interplay between thermodynamics and kinetics in the QD formation mechanisms. Finally, possible ways to better control the QD optical properties are proposed.

  2. Au-assisted growth of anisotropic and epitaxial cdse colloidal nanocrystals via in situ dismantling of quantum dots

    KAUST Repository

    Fernàndez-Altable, Víctor

    2015-03-10

    Metallic nanocrystals have been revealed in the past years as valuable materials for the catalytic growth of semiconductor nanowires. Yet, only low melting point metals like Bi have been reported to successfully assist the growth of elongated CdX (X = S, Se, Te) systems in solution, and the possibility to use plasmonic noble metals has become a challenging task. In this work we show that the growth of anisotropic CdSe nanostructures in solution can also be efficiently catalyzed by colloidal Au nanoparticles, following a preferential crystallographic alignment between the metallic and semiconductor domains. Noteworthy, we report the heterodox use of semiconductor quantum dots as a homogeneous and tunable source of reactive monomer species to the solution. The mechanistic studies reveal that the in situ delivery of these cadmium and chalcogen monomer species and the formation of AuxCdy alloy seeds are both key factors for the epitaxial growth of elongated CdSe domains. The implementation of this method suggests an alternative synthetic approach for the assembly of different semiconductor domains into more complex heterostructures.

  3. Surface potential, charging and local current transport of individual Ge quantum dots grown by molecular beam epitaxy

    Science.gov (United States)

    Singha, R. K.; Manna, S.; Bar, R.; Das, S.; Ray, S. K.

    2017-06-01

    It is fundamentally important to understand the nanoscale electronic properties of a single quantum dot (QD) contrary to an ensemble of QDs. Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM) are two important tools, which could be employed to probe surface potential, charging phenomena, and current transport mechanism of individual QD. We demonstrate the aforementioned characteristics of self-assembled Ge QDs, which was grown on Si substrates by solid source molecular beam epitaxy driven by the Stranski-Krastanov method. Study reveals that each Ge QD acts as charge storage node even at zero applied bias. The shape, size and density of QDs could be well probed by CAFM and KPFM, whereas QD facets could be better resolved by the conductive tip. The CAFM investigation further reveals that there exists a composition gradient within the QDs and Ge core can be charged more efficiently than the Si-Ge periphery at low level of bias. Schematic energy band diagram at the tip-sample contact is presented to explain the current transport mechanism, charging/discharging characteristics and the threshold voltages of I-V characteristics of the individual Ge QDs.

  4. Epitaxial growth of quantum dots on InP for device applications operating at the 1.55 μm wavelength range

    DEFF Research Database (Denmark)

    Semenova, Elizaveta; Kulkova, Irina; Kadkhodazadeh, Shima

    2014-01-01

    The development of epitaxial technology for the fabrication of quantum dot (QD) gain material operating in the 1.55 μm wavelength range is a key requirement for the evolvement of telecommunication. High performance QD material demonstrated on GaAs only covers the wavelength region 1-1.35 μm...... dependence, and low laser quantum efficiency. Here, we demonstrate that with tailored growth conditions, which suppress surface migration of adatoms during the SK QD formation, much smaller base diameter (13.6nm versus 23nm) and an improved aspect ratio are achieved. In order to gain advantage of non...

  5. Self-assembly of InAs quantum dots on GaAs(001) by molecular beam epitaxy

    Science.gov (United States)

    Wu, Ju; Jin, Peng

    2015-02-01

    Currently, the nature of self-assembly of three-dimensional epitaxial islands or quantum dots (QDs) in a lattice-mismatched heteroepitaxial growth system, such as InAs/GaAs(001) and Ge/Si(001) as fabricated by molecular beam epitaxy (MBE), is still puzzling. The purpose of this article is to discuss how the self-assembly of InAs QDs in MBE InAs/GaAs(001) should be properly understood in atomic scale. First, the conventional kinetic theories that have traditionally been used to interpret QD self-assembly in heteroepitaxial growth with a significant lattice mismatch are reviewed briefly by examining the literature of the past two decades. Second, based on their own experimental data, the authors point out that InAs QD self-assembly can proceed in distinctly different kinetic ways depending on the growth conditions and so cannot be framed within a universal kinetic theory, and, furthermore, that the process may be transient, or the time required for a QD to grow to maturity may be significantly short, which is obviously inconsistent with conventional kinetic theories. Third, the authors point out that, in all of these conventional theories, two well-established experimental observations have been overlooked: i) A large number of "floating" indium atoms are present on the growing surface in MBE InAs/GaAs(001); ii) an elastically strained InAs film on the GaAs(001) substrate should be mechanically unstable. These two well-established experimental facts may be highly relevant and should be taken into account in interpreting InAs QD formation. Finally, the authors speculate that the formation of an InAs QD is more likely to be a collective event involving a large number of both indium and arsenic atoms simultaneously or, alternatively, a morphological/structural transformation in which a single atomic InAs sheet is transformed into a three-dimensional InAs island, accompanied by the rehybridization from the sp 2-bonded to sp 3-bonded atomic configuration of both indium

  6. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    1999-01-01

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

  7. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

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

  8. Surface potential, charging and local current transport of individual Ge quantum dots grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Singha, R.K. [Department of Physics, Visva-Bharati, Santiniketan 731235 (India); Manna, S.; Bar, R.; Das, S. [Department of Physics, Indian Institute of Technology-Kharagpur, Kharagpur 721302 (India); Ray, S.K., E-mail: physkr@phy.iitkgp.ernet.in [Department of Physics, Indian Institute of Technology-Kharagpur, Kharagpur 721302 (India)

    2017-06-15

    Highlights: We have elaborately explained the individual Ge QD charging phenomena and current transport, which is very important to understand the Ge/Si nano devices. This paper will give a flavor to properly understand these phenomena linked together along with the photocurrent mechanism which is related to the Ge/Si valence band offset. • Both the CAFM and KPFM techniques point out the functionality of doping nature of the underneath Si substrate on the aforementioned characteristics of Ge QDs. • Analysis of the surface potential mapping using KPFM technique yields an approximate valence band offset measurement which is required to understand the intra-valence transition of holes for the realization of long wavelength infrared photodetector. • KPFM and CAFM can be utilized to explore the charging/discharging phenomena of dots and their composition variations. • Current-voltage (I–V) characteristics of the individual Ge QD strongly depends on the individual QD size. • Energy band diagrams for diamond tip and Ge QD shows the higher barrier for electrons and lower barrier for holes allowing the easy tunneling for holes to dominate the transport. - Abstract: It is fundamentally important to understand the nanoscale electronic properties of a single quantum dot (QD) contrary to an ensemble of QDs. Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM) are two important tools, which could be employed to probe surface potential, charging phenomena, and current transport mechanism of individual QD. We demonstrate the aforementioned characteristics of self-assembled Ge QDs, which was grown on Si substrates by solid source molecular beam epitaxy driven by the Stranski-Krastanov method. Study reveals that each Ge QD acts as charge storage node even at zero applied bias. The shape, size and density of QDs could be well probed by CAFM and KPFM, whereas QD facets could be better resolved by the conductive tip. The CAFM investigation

  9. Hybrid AlGaAs/GaAs/AlGaAs nanowires with a quantum dot grown by molecular beam epitaxy on silicon

    Energy Technology Data Exchange (ETDEWEB)

    Cirlin, G. E., E-mail: cirlin@beam.ioffe.ru; Shtrom, I. V.; Reznik, R. R.; Samsonenko, Yu. B.; Khrebtov, A. I.; Bouravleuv, A. D.; Soshnikov, I. P. [St. Petersburg Academic University, Russian Academy of Sciences (Russian Federation)

    2016-11-15

    Data on the growth features and physical properties of GaAs inserts embedded in AlGaAs nanowires grown on Si(111) substrates by Au-assisted molecular beam epitaxy are presented. It is shown that by varying the growth parameters it is possible to form structures like quantum dots emitting in a wide wavelength range for both active and barrier regions. The technology proposed opens up new possibilities for the integration of direct-band III–V materials on silicon.

  10. GaIn As Quantum Dots (QD) grown by Liquid Phase Epitaxy (LPE)

    Energy Technology Data Exchange (ETDEWEB)

    Ortiz Vazquez, F E; Mishurnyi, V A; Gorbatchev, A Yu; De Anda, F [Universidad Autonoma de San Luis Potosi, Instituto de Investigation en Comunicacion Optica, Av. Karakorum 1470, Col. Lomas 4a Sec., San Luis Potosi, SLP, CP 78210 (Mexico); Elyukhin, V A, E-mail: fcoe_ov@prodigy.net.m, E-mail: andre@cactus.iico.uaslp.m [CINVESTAV-IPN, Av. IPN 2508, Col. San Pedro Zacatenco, Mexico D.F., CP 07360 (Mexico)

    2009-05-01

    The majority of the semiconductor structures with QD today are grown by MBE and MOCVD. It is known that the best material quality can be achieved by LPE because, in contrast to MBE and MOCVD, this method is realized at near-equilibrium conditions. To develop QD LPE technology first of all it is necessary to find out a growth technique allowing the crystallization of epitaxial materials with very small volume. This can be done by means of different techniques. In this work we apply a low temperature short-time growth method, which allows the production not only of single, but also of multilayer heterostructures. We have grown Ga{sub x}In{sub 1-z}As QD on GaAs (100) substrates at 450 C. The details of the QD formation, depending on composition of the Ga{sub x}In{sub -x} As solid solutions, have been studied by atom-force microscopy. The photoluminescence spectra of investigated samples show, in addition to a short-wave GaAs related peak, a longer wavelength line, which disappears after removal of the grown GaInAs material using an etching solution. This fact, together with atom-force microscopy results can be interpreted as a proof that QD heterostructures were grown successfully by LPE.

  11. Epitaxial grown InP quantum dots on a GaAs buffer realized on GaP/Si(001) templates

    Energy Technology Data Exchange (ETDEWEB)

    Hartwig, Walter; Wiesner, Michael; Koroknay, Elisabeth; Paul, Matthias; Jetter, Michael; Michler, Peter [Institut fuer Halbleiteroptik und Funktionelle Grenzflaechen und Research Center SCoPE, Universitaet Stuttgart, Allmandring 3, 70569 Stuttgart (Germany)

    2013-07-01

    The increasing necessity of higher computational capacity and security in the information technology requires originally technical solutions, which today's standard microelectronics, as their technical limits are close, can't provide anymore. One way out offers the integration of III-V semiconductor photonics with low-dimensional structures in current CMOS technology, enabling on-chip quantum optical applications, like quantum cryptography or quantum computing. Challenges in the heteroepitaxy of III-V semiconductors and silicon are the mismatches in material properties of the both systems. Defects, like dislocations and anti-phase domains (APDs), inhibit the monolithic integration of III-V semiconductor on Si. We present the growth of a thin GaAs buffer on CMOS-compatible oriented Si(001) by metal-organic vapor-phase epitaxy. To circumvent the forming APDs in the GaAs buffer a GaP on Si template (provided by NAsP{sub III/V} GmbH) was used. The dislocation density was then reduced by integrating several layers of InAs quantum dots in the GaAs buffer to bend the threading misfit dislocations. On top of this structure we grew InP quantum dots embedded in a Al{sub x}Ga{sub 1-x}InP composition and investigated the photoluminescence properties.

  12. Effects of in situ annealing of GaAs(100) substrates on the subsequent growth of InAs quantum dots by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Cortes, H; Mejia-Garcia, C [Escuela Superior de Fisica y Matematicas del IPN, UPALM, Edif. 9, Col. Lindavista, Mexico DF 07738 (Mexico); Mendez-GarcIa, V H; Vazquez-Cortes, D [Coordinacion para la Innovacion y la Aplicacion de la Ciencia y la TecnologIa, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis PotosI, S L P 78000 (Mexico); Rojas-Ramirez, J S; Contreras-Guerrero, R; RamIrez-Lopez, M; Martinez-Velis, I; Lopez-Lopez, M, E-mail: mlopez@fis.cinvestav.mx [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14-740, Mexico DF 07000 (Mexico)

    2010-04-02

    In the present work, we study the growth by molecular beam epitaxy of InAs self-assembling quantum dots (SAQDs) on GaAs(100) substrates subjected to an in situ annealing treatment. The annealing process consists of the exposition of the GaAs buffer layer surface to high temperatures for a few seconds with the shutter of an arsenic Knudsen cell closed. The purpose of the annealing is to obtain a better uniformity of the SAQD sizes. In our study we prepared different samples using the Stranski-Krastanov growth method to obtain InAs/GaAs(100) quantum dot samples with different annealing times and temperatures. Their structural and optical properties were studied by reflection high-energy electron diffraction (RHEED), high-resolution scanning electron microscopy (HRSEM), atomic force microscopy (AFM), and photoreflectance spectroscopy (PR). According to the results of AFM and HRSEM, by the thermal treatment we obtained a better distribution of quantum dot sizes in comparison with a reference sample with no treatment. The PR spectra from 0.9 to 1.35 eV presented two transitions associated with SAQDs. The energy transitions were obtained by fitting the PR spectra using the third derivative model.

  13. Influence of a GaN Cap Layer on the Morphology and the Physical Properties of Embedded Self-Organized InN Quantum Dots on GaN(0001) Grown by Metal-Organic Vapour Phase Epitaxy

    Science.gov (United States)

    Ivaldi, Francesco; Meissner, Christian; Domagala, Jarosław; Kret, Sławomir; Pristovsek, Markus; Högele, Michael; Kneissl, Michael

    2011-03-01

    Self-organized InN quantum dots were grown on GaN(0001) by metal-organic vapour phase epitaxy. Transmission electron microscopy (TEM) measurements found no wetting layer, i.e., the dots grow directly in Volmer-Weber growth mode. The dots were capped with GaN by three different procedures. Direct overgrowth at the same temperature as the dot formation produced the smoothest surfaces. Cubic and hexagonal GaN was observed in the cap layer, as well as strong indium intermixing. The dot size and volume was reduced during overgrowth. The dots were ˜90% relaxed with many dislocations at the interface from GaN to InN. The photoluminescence of the dots was very weak due to the dislocation.

  14. Photoluminescence and photocurrent from InP nanowires with InAsP quantum dots grown on Si by molecular beam epitaxy

    Science.gov (United States)

    Kuyanov, P.; LaPierre, R. R.

    2015-08-01

    InP nanowires with InAsP quantum dots (QDs) were grown by molecular beam epitaxy on a Si (111) substrates. The structure of the InAsP QDs were studied using transmission electron microscopy, allowing the development of a model where QD growth occurs by group V desorption from the surrounding substrate surface. Micro-photoluminescence was performed at 10 K showing emission at 1.47-1.49 eV from the InP wurtzite structure, and various emission peaks between 0.93 and 1.33 eV attributed to the QDs. The emission was tuned by the QD composition. The effectiveness of an AlInP passivation shell was demonstrated via an improvement in the photoluminescence intensity. Spectrally-resolved photocurrent measurements at room temperature demonstrated infrared response due to absorption within the QDs. The absorption red-shifted with increasing As composition of the QD.

  15. Quantum Dots: Theory

    Energy Technology Data Exchange (ETDEWEB)

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

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

  16. Synthesis of quantum dots

    Science.gov (United States)

    McDaniel, Hunter

    2017-10-17

    Common approaches to synthesizing alloyed quantum dots employ high-cost, air-sensitive phosphine complexes as the selenium precursor. Disclosed quantum dot synthesis embodiments avoid these hazardous and air-sensitive selenium precursors. Certain embodiments utilize a combination comprising a thiol and an amine that together reduce and complex the elemental selenium to form a highly reactive selenium precursor at room temperature. The same combination of thiol and amine acts as the reaction solvent, stabilizing ligand, and sulfur source in the synthesis of quantum dot cores. A non-injection approach may also be used. The optical properties of the quantum dots synthesized by this new approach can be finely tuned for a variety of applications by controlling size and/or composition of size and composition. Further, using the same approach, a shell can be grown around a quantum dot core that improves stability, luminescence efficiency, and may reduce toxicity.

  17. Enhanced performance of solution-processed broadband photodiodes by epitaxially blending MAPbBr3 quantum dots and ternary PbSxSe1‑x quantum dots as the active layer

    Science.gov (United States)

    Sulaman, Muhammad; Yang, Shengyi; Jiang, Yurong; Tang, Yi; Zou, Bingsuo

    2017-12-01

    Organic–inorganic hybrid photodetectors attract more and more interest, since they can combine the advantages of both organic and inorganic materials into one device, and broadband photodetectors are widely used in many scientific and industrial fields. In this work, we demonstrate the enhanced-performance solution-processed broadband photodiodes by epitaxially blending organo-lead halide perovskite (MAPbBr3) colloidal quantum dots (CQDs) with ternary PbSxSe1‑x CQDs as the active layer. As a result, the interfacial features of the hetero-epitaxial nanocomposite MAPbBr3:PbSxSe1‑x enables the design and perception of functionalities that are not available for the single-phase constituents or layered devices. By combining the high electrical transport properties of MAPbBr3 QDs with the highly radiative efficiency of PbS0.4Se0.6 QDs, the photodiodes ITO/ZnO/PbS0.4Se0.6:MAPbBr3/Au exhibit a maximum photoresponsivity and specific detectivity of 21.48 A W‑1 and 3.59 × 1013 Jones, 22.16 A W‑1 and 3.70 × 1013 Jones at room temperature under 49.8 μW cm‑2 532 nm laser and 62 μW cm‑2 980 nm laser, respectively. This is higher than that of the layered photodiodes ITO/ZnO/PbS0.4Se0.6/MAPbBr3/Au, pure perovskite (MAPbBr3) (or PbS0.4Se0.6) QD-based photodiodes reported previously, and it is also better than the traditional inorganic semiconductor-based photodetectors. Our experimental results indicate that epitaxially-aligned nanocomposites (MAPbBr3:PbSxSe1‑x) exhibit remarkable optoelectronic properties that are traceable to their atomic-scale crystalline coherence, and one can utilize the excellent photocarrier diffusion from PbSxSe1‑x into the perovskite to enhance the device performance from the UV-visible to infrared region.

  18. Optical anisotropy in vertically coupled quantum dots

    DEFF Research Database (Denmark)

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

    1999-01-01

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

  19. Quantum dot molecules

    CERN Document Server

    Wu, Jiang

    2014-01-01

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

  20. Graphene quantum dots

    CERN Document Server

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

    2014-01-01

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

  1. Double quantum dot memristor

    Science.gov (United States)

    Li, Ying; Holloway, Gregory W.; Benjamin, Simon C.; Briggs, G. Andrew D.; Baugh, Jonathan; Mol, Jan A.

    2017-08-01

    Memristive systems are generalizations of memristors, which are resistors with memory. In this paper, we present a quantum description of quantum dot memristive systems. Using this model we propose and experimentally demonstrate a simple and practical scheme for realizing memristive systems with quantum dots. The approach harnesses a phenomenon that is commonly seen as a bane of nanoelectronics, i.e., switching of a trapped charge in the vicinity of the device. We show that quantum dot memristive systems have hysteresis current-voltage characteristics and quantum jump-induced stochastic behavior. While our experiment requires low temperatures, the same setup could, in principle, be realized with a suitable single-molecule transistor and operated at or near room temperature.

  2. Quantum dot solar cells

    CERN Document Server

    Wu, Jiang

    2013-01-01

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

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

    Science.gov (United States)

    Qiu, Y.; Uhl, D.

    2002-01-01

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

  4. Hexagonal graphene quantum dots

    KAUST Repository

    Ghosh, Sumit

    2016-12-05

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

  5. Nanocrystal quantum dots

    CERN Document Server

    Klimov, Victor I

    2010-01-01

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

  6. Quantum-dot-in-perovskite solids

    KAUST Repository

    Ning, Zhijun

    2015-07-15

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

  7. Carbon nanotube quantum dots

    NARCIS (Netherlands)

    Sapmaz, S.

    2006-01-01

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

  8. Self Organized Grown Stranski-Krastanow II-VI Quantum Dots Vs. Colloidal Nanocrystals Integrated In Epitaxial Nanostructures

    Science.gov (United States)

    Arens, Ch.; Schöps, O.; Artemyev, M. V.; Woggon, U.; Lischka, K.; Schikora, D.

    2007-04-01

    We have integrated colloidal CdSe nanocrystals (NC) in MBE-grown ZnSe layers. In this paper we compare their density, size, size distribution and their optical tuning range with that of self-organized grown Stranski-Krastanow (SK) CdSe-QDs which are used as a reference. We find that the density of epitaxially overgrown NCs can be varied in a wider range than the SK-QD density. The size and shape of NCs is variable and this leads to a wide optical tuning range of the NC emission. The size of SK-QD is fixed due to the thermodynamic formation process. Further we found, that the size distribution of overgrown NCs is in the range of the size distribution of SK-QDs or even smaller.

  9. Quantum-dot infrared photodetectors: a review

    Science.gov (United States)

    Stiff-Roberts, Adrienne D.

    2009-04-01

    Quantum-dot infrared photodetectors (QDIPs) are positioned to become an important technology in the field of infrared (IR) detection, particularly for high-temperature, low-cost, high-yield detector arrays required for military applications. High-operating temperature (>=150 K) photodetectors reduce the cost of IR imaging systems by enabling cryogenic dewars and Stirling cooling systems to be replaced by thermo-electric coolers. QDIPs are well-suited for detecting mid-IR light at elevated temperatures, an application that could prove to be the next commercial market for quantum dots. While quantum dot epitaxial growth and intraband absorption of IR radiation are well established, quantum dot non-uniformity remains as a significant challenge. Nonetheless, state-of-the-art mid-IR detection at 150 K has been demonstrated using 70-layer InAs/GaAs QDIPs, and QDIP focal plane arrays are approaching performance comparable to HgCdTe at 77 K. By addressing critical challenges inherent to epitaxial QD material systems (e.g., controlling dopant incorporation), exploring alternative QD systems (e.g., colloidal QDs), and using bandgap engineering to reduce dark current and enhance multi-spectral detection (e.g. resonant tunneling QDIPs), the performance and applicability of QDIPs will continue to improve.

  10. Quantum Phase Transitions in Quantum Dots

    OpenAIRE

    Rau, I. G.; Amasha, S.; Oreg, Y.; Goldhaber-Gordon, D.

    2013-01-01

    This review article describes theoretical and experimental advances in using quantum dots as a system for studying impurity quantum phase transitions and the non-Fermi liquid behavior at the quantum critical point.

  11. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

    a future challenge for the droplet-epitaxy technique. A multipolar theory of spontaneous emission from quantum dots is developed to explain the recent observation that In(Ga)As quantum dots break the dipole theory. The analysis yields a large mesoscopic moment, which contains magnetic-dipole and electric......The present thesis reports research on the optical properties of quantum dots by developing new theories and conducting optical measurements. We demonstrate experimentally singlephoton superradiance in interface-uctuation quantum dots by recording the temporal decay dynamics in conjunction...... with second-order correlation measurements and a theoretical model. We measure an oscillator strength of up to 960:8 and an average quantum eciency of (94:83:0)%. This enhanced light-matter coupling is known as the giant oscillator strength of quantum dots, which is shown to be equivalent to superradiance. We...

  12. Quantum dots for quantum information technologies

    CERN Document Server

    2017-01-01

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

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

    Science.gov (United States)

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

    2007-10-01

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

  14. Templated self-assembly of SiGe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Dais, Christian

    2009-08-19

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

  15. Wavelength extension beyond 1.5 µm in symmetric InAs quantum dots grown on InP(111)A using droplet epitaxy

    Science.gov (United States)

    Ha, Neul; Mano, Takaaki; Wu, Yu-Nien; Ou, Ya-Wen; Cheng, Shun-Jen; Sakuma, Yoshiki; Sakoda, Kazuaki; Kuroda, Takashi

    2016-10-01

    By using a C 3v symmetric (111) surface as a growth substrate, we can achieve high structural symmetry in self-assembled quantum dots, which are suitable for use as quantum-entangled-photon emitters. Here, we report on the wavelength controllability of InAs dots on InP(111)A, which we realized by tuning the ternary alloy composition of In(Al,Ga)As barriers that were lattice-matched to InP. We changed the peak emission wavelength systematically from 1.3 to 1.7 µm by barrier band gap tuning. The observed spectral shift agreed with the result of numerical simulations that assumed a measured shape distribution independent of the barrier choice.

  16. Density and size control of InP/GaInP quantum dots on GaAs substrate grown by gas source molecular beam epitaxy.

    Science.gov (United States)

    Rödel, R; Bauer, A; Kremling, S; Reitzenstein, S; Höfling, S; Kamp, M; Worschech, L; Forchel, A

    2012-01-13

    We demonstrate a method to controllably reduce the density of self-assembled InP quantum dots (QDs) by cyclic deposition with growth interruptions. Varying the number of cycles enabled a reduction of the QD density from 7.4 × 10(10) cm(-2) to 1.8 × 10(9) cm(-2) for the same total amount of deposited InP. Simultaneously, a systematic increase of the QD size could be observed. Emission characteristics of different-sized InP QDs were analyzed. Excitation power dependent and time-resolved measurements confirm a transition from type I to type II band alignment for large InP quantum dots. Photon autocorrelation measurements of type I QDs performed under pulsed excitation reveal pronounced antibunching (g((2))(τ = 0) = 0.06 ± 0.03) as expected for a single-photon emitter. The described growth routine has great promise for the exploitation of InP QDs as quantum emitters.

  17. Atomically precise, coupled quantum dots fabricated by cleaved edge overgrowth

    Science.gov (United States)

    Wegscheider, W.; Schedelbeck, G.; Bichler, M.; Abstreiter, G.

    Recent progress in the fabrication of quantum dots by molecular beam epitaxy along three directions in space is reviewed. The optical properties of different sample structures consisting of individual quantum dots, pairs of coupled dots as well as of linear arrays of dots are studied by microscopic photoluminescence spectroscopy. The high degree of control over shape, composition and position of the 7×7×7 nm3 size GaAs quantum dots, which form at the intesection of three orthogonal quantum wells, allows a detailed investigation of the influence of coupling between almost identical zero-dimensional objects. In contrast to the inhomogeneously broadened quantum well and quantum wire signals originating from the complex twofold cleaved edge overgrowth structure, the photoluminescence spetrum of an individual quantum dot exhibits a single sharp line (full width at half maximum denomination "artificial atoms" for the quantum dots. It is further demonstrated that an "artifical molecule", characterized by the existence of bonding and antibonding states can be assembled from two of such "artificial atoms". The coupling strength between the "artificial atoms" is adjusted by the "interatomic" distance and is reflected in the energetic separation of the bonding and antibonding levels and the linewidths of the corresponding interband transitions.

  18. Marvelous applications of quantum dots.

    Science.gov (United States)

    Cheki, M; Moslehi, M; Assadi, M

    2013-05-01

    Nanotechnology is developed to convert research, prevention, and treatment of cancer through the novel diagnostic imaging techniques and therapies. In particular, the imaging nanotechnology has gained substantial momentum in recent years. The main progress in nanotechnology has led to the production of novel fluorescent probes named quantum dots (QDs). Quantum dots develop a revolution in the molecular tagging processes within research, in vivo and in vitro studies. Due to unique physical and chemical features of QD probes, new possible techniques of early cancer detection and therapeutic management are being surveyed. Quantum dots have also dissolved many of the restrictions of organic fluorophores and are a talented option as a research tool. This review addresses on the present status of research, preclinical applications and also future visions of quantum dots.  

  19. Quantum dots in cell biology.

    Science.gov (United States)

    Barroso, Margarida M

    2011-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Grossi, D. F., E-mail: d.grossi@tue.nl; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven (Netherlands); Smereka, P. [Department of Mathematics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Keizer, J. G. [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven (Netherlands); Australian Research Council Centre of Excellence for Quantum Computation and Communications, School of Physics, University of New South Wales, Sydney 2052 (Australia); Ulloa, J. M. [Institute for Systems based on Optoelectronics and Microtechnology (ISOM), Universidad Politecnica de Madrid, Avenida Complutense 30, 28040 Madrid (Spain)

    2014-10-06

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

  1. Transport through graphene quantum dots

    Science.gov (United States)

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

    2012-12-01

    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.

  2. Stacking InAs quantum dots over ErAs semimetal nanoparticles on GaAs (0 0 1) using molecular beam epitaxy

    Science.gov (United States)

    Zhang, Yuanchang; Eyink, Kurt G.; Grazulis, Lawrence; Hill, Madelyn; Peoples, Joseph; Mahalingam, Krishnamurthy

    2017-11-01

    Hybrid nanostructures are known to elicit an enhanced optical response. We study the directed alignment of ErAs metal nanoparticle (NP) and InAs quantum dot (QD) using molecular beam eptaxy (MBE) in a GaAs matrix. Due to high surface free energy caused by the crystal structure difference, overgrowth of an ErAs NP with GaAs forms a depression that condenses subsequent InAs adatoms to form an inverted QD self-aligned to the underlying ErAs NP. The ErAs NP growth, GaAs overgrowth, and InAs QD deposition were carefully controlled and studied with transmission electron microscopy (TEM) and atomic force microscopy (AFM) to investigate their effects on the QD-NP alignment.

  3. Stability of quantum dots in live cells

    Science.gov (United States)

    Zhu, Zheng-Jiang; Yeh, Yi-Cheun; Tang, Rui; Yan, Bo; Tamayo, Joshua; Vachet, Richard W.; Rotello, Vincent M.

    2011-12-01

    Quantum dots are highly fluorescent and photostable, making them excellent tools for imaging. When using these quantum dots in cells and animals, however, intracellular biothiols (such as glutathione and cysteine) can degrade the quantum dot monolayer, compromising function. Here, we describe a label-free method to quantify the intracellular stability of monolayers on quantum dot surfaces that couples laser desorption/ionization mass spectrometry with inductively coupled plasma mass spectrometry. Using this new approach we have demonstrated that quantum dot monolayer stability is correlated with both quantum dot particle size and monolayer structure, with appropriate choice of both particle size and ligand structure required for intracellular stability.

  4. Growth scheme for quantum dots with low fine structure splitting at telecom wavelengths (Conference Presentation)

    Science.gov (United States)

    Muller, Tina; Skiba-Szymanska, Joanna; Stevenson, R. Mark; Varnava, Christiana; Felle, Martin; Huwer, Jan; Farrer, Ian; Krysa, Andrey B.; Spencer, Peter; Ritchie, David A.; Heffernan, Jon; Shields, Andrew J.

    2017-02-01

    Quantum dots based on InAs/InP hold the promise to deliver entangled photons with wavelength suitable for the standard telecom window around 1550 nm, which makes them predestined to be used in future quantum networks applications based on existing fiber optics infrastructure. A prerequisite for the generation of such entangled photons is a small fine structure splitting (FSS) in the quantum dot excitonic eigenstates, as well as the ability to integrate the dot into photonic structures to enhance and direct its emission. Using optical spectroscopy, we show that a growth strategy based on droplet epitaxy can simultaneously address both issues. Contrary to the standard Stranski-Krastanow technique, droplet epitaxy dots do not rely on material strains during growth, which results in a drastic improvement in dot symmetry. As a consequence, the average exciton FSS is reduced by more than a factor 4, which in fact makes all the difference between easily finding a dot with the required FSS and not finding one at all. Furthermore, we demonstrate that droplet epitaxy dots can be grown on the necessary surface (001) for high quality optical microcavities, which increases dot emission count rates by more than a factor of five. Together, these properties make droplet epitaxy quantum dots readily suitable for the generation of entangled photons at telecom wavelengths.

  5. Quantum-dot emitters in photonic nanostructures

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  6. Quantum-dot based photonic quantum networks

    Science.gov (United States)

    Lodahl, Peter

    2018-01-01

    Quantum dots (QDs) embedded in photonic nanostructures have in recent years proven to be a very powerful solid-state platform for quantum optics experiments. The combination of near-unity radiative coupling of a single QD to a photonic mode and the ability to eliminate decoherence processes imply that an unprecedent light–matter interface can be obtained. As a result, high-cooperativity photon-emitter quantum interfaces can be constructed opening a path-way to deterministic photonic quantum gates for quantum-information processing applications. In the present manuscript, I review current state-of-the-art on QD devices and their applications for quantum technology. The overarching long-term goal of the research field is to construct photonic quantum networks where remote entanglement can be distributed over long distances by photons.

  7. Controlled positioning of self-assembled InAs quantum dots on (1 1 0) GaAs

    Science.gov (United States)

    Schuh, D.; Bauer, J.; Uccelli, E.; Schulz, R.; Kress, A.; Hofbauer, F.; Finley, J. J.; Abstreiter, G.

    2005-02-01

    We report on a new approach for positioning of self-assembled InAs quantum dots on (1 1 0) GaAs with nanometer precision. By combining self-assembly of quantum dots with molecular beam epitaxy on in situ cleaved surfaces (cleaved-edge overgrowth) we have successfully fabricated arrays of long-range ordered InAs quantum dots. Both atomic force microscopy and micro-photoluminescence measurements demonstrate the ability to control position and ordering of the quantum dots with epitaxial precision as well as size and size homogeneity. Furthermore, photoluminescence investigations on dot ensembles and on single dots confirm the high homogeneity and the excellent optical quality of the quantum dots fabricated.

  8. Characterization of encapsulated quantum dots via electron channeling contrast imaging

    Science.gov (United States)

    Deitz, Julia I.; Carnevale, Santino D.; De Graef, Marc; McComb, David W.; Grassman, Tyler J.

    2016-08-01

    A method for characterization of encapsulated epitaxial quantum dots (QD) in plan-view geometry using electron channeling contrast imaging (ECCI) is presented. The efficacy of the method, which requires minimal sample preparation, is demonstrated with proof-of-concept data from encapsulated (sub-surface) epitaxial InAs QDs within a GaAs matrix. Imaging of the QDs under multiple diffraction conditions is presented, establishing that ECCI can provide effectively identical visualization capabilities as conventional two-beam transmission electron microscopy. This method facilitates rapid, non-destructive characterization of sub-surface QDs giving immediate access to valuable nanostructural information.

  9. Characterization of encapsulated quantum dots via electron channeling contrast imaging

    Energy Technology Data Exchange (ETDEWEB)

    Deitz, Julia I.; McComb, David W. [Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Carnevale, Santino D. [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); De Graef, Marc [Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Grassman, Tyler J., E-mail: grassman.5@osu.edu [Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

    2016-08-08

    A method for characterization of encapsulated epitaxial quantum dots (QD) in plan-view geometry using electron channeling contrast imaging (ECCI) is presented. The efficacy of the method, which requires minimal sample preparation, is demonstrated with proof-of-concept data from encapsulated (sub-surface) epitaxial InAs QDs within a GaAs matrix. Imaging of the QDs under multiple diffraction conditions is presented, establishing that ECCI can provide effectively identical visualization capabilities as conventional two-beam transmission electron microscopy. This method facilitates rapid, non-destructive characterization of sub-surface QDs giving immediate access to valuable nanostructural information.

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

    Energy Technology Data Exchange (ETDEWEB)

    Heiss, Dominik

    2009-10-15

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

  11. Optophononics with Coupled Quantum Dots

    Science.gov (United States)

    2014-02-18

    single InAs/GaAs quantum dots. Phys. Rev. B 68, 233301 (2003). 9. Bennemann, K.-H. & Ketterson, J. B. (eds), Superconductivity : Conventional and...superlattices. Science 338, 935–939 (2012). 17. Kim, J.-H. et al. Coherent phonons in carbon nanotubes and graphene . Chem. Phys. 413, 55–80 (2013). 18

  12. Polymer-coated quantum dots

    NARCIS (Netherlands)

    Tomczak, N.; Liu, Rongrong; Vancso, Gyula J.

    2013-01-01

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

  13. Nuclear Spins in Quantum Dots

    NARCIS (Netherlands)

    Erlingsson, S.I.

    2003-01-01

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

  14. Silicon quantum dots: surface matters

    NARCIS (Netherlands)

    Dohnalová, K.; Gregorkiewicz, T.; Kůsová, K.

    2014-01-01

    Silicon quantum dots (SiQDs) hold great promise for many future technologies. Silicon is already at the core of photovoltaics and microelectronics, and SiQDs are capable of efficient light emission and amplification. This is crucial for the development of the next technological frontiers—silicon

  15. Kondo physics in tunable semiconductor nanowire quantum dots

    OpenAIRE

    Jespersen, T. S.; Aagesen, M.; Soerensen, C.; Lindelof, P. E.; Nygaard, J.

    2006-01-01

    We have observed the Kondo effect in strongly coupled semiconducting nanowire quantum dots. The devices are made from indium arsenide nanowires, grown by molecular beam epitaxy, and contacted by titanium leads. The device transparency can be tuned by changing the potential on a gate electrode, and for increasing transparencies the effects dominating the transport changes from Coulomb Blockade to Universal Conductance Fluctuations with Kondo physics appearing in the intermediate region.

  16. Coherent control of quantum dots

    DEFF Research Database (Denmark)

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

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

  17. Ultrasensitive solution-cast quantum dot photodetectors.

    Science.gov (United States)

    Konstantatos, Gerasimos; Howard, Ian; Fischer, Armin; Hoogland, Sjoerd; Clifford, Jason; Klem, Ethan; Levina, Larissa; Sargent, Edward H

    2006-07-13

    Solution-processed electronic and optoelectronic devices offer low cost, large device area, physical flexibility and convenient materials integration compared to conventional epitaxially grown, lattice-matched, crystalline semiconductor devices. Although the electronic or optoelectronic performance of these solution-processed devices is typically inferior to that of those fabricated by conventional routes, this can be tolerated for some applications in view of the other benefits. Here we report the fabrication of solution-processed infrared photodetectors that are superior in their normalized detectivity (D*, the figure of merit for detector sensitivity) to the best epitaxially grown devices operating at room temperature. We produced the devices in a single solution-processing step, overcoating a prefabricated planar electrode array with an unpatterned layer of PbS colloidal quantum dot nanocrystals. The devices showed large photoconductive gains with responsivities greater than 10(3) A W(-1). The best devices exhibited a normalized detectivity D* of 1.8 x 10(13) jones (1 jones = 1 cm Hz(1/2) W(-1)) at 1.3 microm at room temperature: today's highest performance infrared photodetectors are photovoltaic devices made from epitaxially grown InGaAs that exhibit peak D* in the 10(12) jones range at room temperature, whereas the previous record for D* from a photoconductive detector lies at 10(11) jones. The tailored selection of absorption onset energy through the quantum size effect, combined with deliberate engineering of the sequence of nanoparticle fusing and surface trap functionalization, underlie the superior performance achieved in this readily fabricated family of devices.

  18. Synthetic Control of Exciton Behavior in Colloidal Quantum Dots.

    Science.gov (United States)

    Pu, Chaodan; Qin, Haiyan; Gao, Yuan; Zhou, Jianhai; Wang, Peng; Peng, Xiaogang

    2017-03-08

    Colloidal quantum dots are promising optical and optoelectronic materials for various applications, whose performance is dominated by their excited-state properties. This article illustrates synthetic control of their excited states. Description of the excited states of quantum-dot emitters can be centered around exciton. We shall discuss that, different from conventional molecular emitters, ground-state structures of quantum dots are not necessarily correlated with their excited states. Synthetic control of exciton behavior heavily relies on convenient and affordable monitoring tools. For synthetic development of ideal optical and optoelectronic emitters, the key process is decay of band-edge excitons, which renders transient photoluminescence as important monitoring tool. On the basis of extensive synthetic developments in the past 20-30 years, synthetic control of exciton behavior implies surface engineering of quantum dots, including surface cation/anion stoichiometry, organic ligands, inorganic epitaxial shells, etc. For phosphors based on quantum dots doped with transition metal ions, concentration and location of the dopant ions within a nanocrystal lattice are found to be as important as control of the surface states in order to obtain bright dopant emission with monoexponential yet tunable photoluminescence decay dynamics.

  19. Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control

    KAUST Repository

    Sun, Liangfeng

    2012-05-06

    Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr \\'1 m \\'2) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH 2 groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.© 2012 Macmillan Publishers Limited.

  20. Ultrafast spectroscopy of quantum dots

    CERN Document Server

    Foo, E

    2001-01-01

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

  1. Silicon Quantum Dots for Quantum Information Processing

    Science.gov (United States)

    2013-11-01

    16 2.2.2 Si/SiGe Heterostructures . . . . . . . . . . . . . . . . . . . 18 2.2.3 Silicon Nanowires ...Recently, silicon MOS, silicon/silicon- germanium (Si/SiGe) heterostructures and silicon nanowire architectures have also achieved spin manipulation and...Churchill, D. J. Reilly, J. Xiang, C. M. Lieber, and C. M. Marcus. A Ge/Si heterostructure nanowire -based double quantum dot with integrated charge

  2. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

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

    2002-01-01

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

  3. Quantum Dot Light Emitting Diode

    Energy Technology Data Exchange (ETDEWEB)

    Keith Kahen

    2008-07-31

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

  4. Quantum Dot Light Emitting Diode

    Energy Technology Data Exchange (ETDEWEB)

    Kahen, Keith

    2008-07-31

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

  5. Quantum ballistic transport in strained epitaxial germanium

    Science.gov (United States)

    Gul, Y.; Holmes, S. N.; Newton, P. J.; Ellis, D. J. P.; Morrison, C.; Pepper, M.; Barnes, C. H. W.; Myronov, M.

    2017-12-01

    Large scale fabrication using Complementary Metal Oxide Semiconductor compatible technology of semiconductor nanostructures that operate on the principles of quantum transport is an exciting possibility now due to the recent development of ultra-high mobility hole gases in epitaxial germanium grown on standard silicon substrates. We present here a ballistic transport study of patterned surface gates on strained Ge quantum wells with SiGe barriers, which confirms the quantum characteristics of the Ge heavy hole valence band structure in 1-dimension. Quantised conductance at multiples of 2e2/h is a universal feature of hole transport in Ge up to 10 × (2e2/h). The behaviour of ballistic plateaus with finite source-drain bias and applied magnetic field is elucidated. In addition, a reordering of the ground state is observed.

  6. Quantum dots: lasers and amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Bimberg, Dieter; Ledentsov, Nikolai [Institut fuer Festkoerperphysik, PN5-2, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 (Germany)

    2003-06-25

    Continuous wave room-temperature output power of {approx} 3 W for edge emitters and of 1.2 mW for vertical-cavity surface-emitting lasers is realized for GaAs-based devices using InAs quantum dots (QDs) operating at 1.3 {mu}m. Characteristic temperatures up to 170 K below 330 K are realized. Simultaneously, differential efficiency exceeds 80% for these devices. Lasers emitting up to 12 W at 1140-1160 nm are useful as pump sources for Tm{sup 3+}-doped fibres for frequency up-conversion to 470 nm. Both types of lasers show transparency current densities of 6 A cm{sup -2} per dot layer, {eta}{sub int} = 98% and {alpha}{sub i} around 1.5 cm{sup -1}. Long operation lifetimes (above 3000 h at 50 deg C heatsink temperature at 1.5 W CW) and improved radiation hardness as compared to quantum well (QW) devices are manifested. Cut-off frequencies of about 10 GHz at 1100 nm and 6 GHz at 1300 nm and low {alpha} factors resulting in reduced filamentation and improved M{sup 2} values in single-mode operation are realized. Quantum dot semiconductor optical amplifiers (QD SOAs) demonstrate gain recovery times of 120-140 fs, 4-7 times faster than bulk/QW SOAs. The breakthrough became possible due to the development of self-organized growth in QD technology. (topical review)

  7. Barrier Engineered Quantum Dot Infrared Photodetectors

    Science.gov (United States)

    2015-06-01

    AFRL-RV-PS- AFRL-RV-PS- TR-2015-0111 TR-2015-0111 BARRIER ENGINEERED QUANTUM DOT INFRARED PHOTODETECTORS Sanjay Krishna Center for High Technology...2011 – 22 May 2012 4. TITLE AND SUBTITLE Barrier Engineered Quantum Dot Infrared Photodetectors 5a. CONTRACT NUMBER FA9453-12-1-0336 5b. GRANT...is Unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT To investigate barrier engineered designs to reduce the dark current in quantum dot infrared

  8. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

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

  9. Preparation of tin oxide quantum dots

    Science.gov (United States)

    Fauzi, N. F. S. M.; Kamarulzaman, N.; Kasim, M. F.; Chayed, N. F.; Aziz, N. D. A.

    2017-09-01

    Quantum dots are interesting nanostructures with have novel physical and chemical characteristics. It is not an easy task to obtain quantum dots because materials tend to agglomerate. In this work, SnO2 quantum dots have been successfully synthesized via a simple and low cost method which is the sol-gel method. Thermal analysis of the precursors were carried out using a Simultaneous Thermogravimetric Analyzer (STA). The annealed samples were characterized using X-Ray Diffraction (XRD) for phase studies. Finally, the crystallite size and morphology of tin oxide quantum dots were determined using Field Emission Scanning Electron Microscopy (FESEM).

  10. POLARON IN CYLINDRICAL AND SPHERICAL QUANTUM DOTS

    Directory of Open Access Journals (Sweden)

    L.C.Fai

    2004-01-01

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

  11. Mixed-quantum-dot solar cells.

    Science.gov (United States)

    Yang, Zhenyu; Fan, James Z; Proppe, Andrew H; Arquer, F Pelayo García de; Rossouw, David; Voznyy, Oleksandr; Lan, Xinzheng; Liu, Min; Walters, Grant; Quintero-Bermudez, Rafael; Sun, Bin; Hoogland, Sjoerd; Botton, Gianluigi A; Kelley, Shana O; Sargent, Edward H

    2017-11-06

    Colloidal quantum dots are emerging solution-processed materials for large-scale and low-cost photovoltaics. The recent advent of quantum dot inks has overcome the prior need for solid-state exchanges that previously added cost, complexity, and morphological disruption to the quantum dot solid. Unfortunately, these inks remain limited by the photocarrier diffusion length. Here we devise a strategy based on n- and p-type ligands that judiciously shifts the quantum dot band alignment. It leads to ink-based materials that retain the independent surface functionalization of quantum dots, and it creates distinguishable donor and acceptor domains for bulk heterojunctions. Interdot carrier transfer and exciton dissociation studies confirm efficient charge separation at the nanoscale interfaces between the two classes of quantum dots. We fabricate the first mixed-quantum-dot solar cells and achieve a power conversion of 10.4%, which surpasses the performance of previously reported bulk heterojunction quantum dot devices fully two-fold, indicating the potential of the mixed-quantum-dot approach.

  12. Chiral quantum dot based materials

    Science.gov (United States)

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

    2014-05-01

    Recently, the use of stereospecific chiral stabilising molecules has also opened another avenue of interest in the area of quantum dot (QD) research. The main goal of our research is to develop new types of technologically important quantum dot materials containing chiral defects, study their properties and explore their applications. The utilisation of chiral penicillamine stabilisers allowed the preparation of new water soluble white emitting CdS quantum nanostructures which demonstrated circular dichroism in the band-edge region of the spectrum. It was also demonstrated that all three types of QDs (D-, L-, and Rac penicillamine stabilised) show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. In this work the chiral CdS based quantum nanostructures have also been doped by copper metal ions and new chiral penicilamine stabilized CuS nanoparticles have been prepared and investigated. It was found that copper doping had a strong effect at low levels in the synthesis of chiral CdS nanostructures. We expect that this research will open new horizons in the chemistry of chiral nanomaterials and their application in biotechnology, sensing and asymmetric synthesis.

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

    Data.gov (United States)

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

  14. Colloidal quantum dot photodetectors

    KAUST Repository

    Konstantatos, Gerasimos

    2011-05-01

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

  15. Metalorganic vapor phase epitaxy growth, transmission electron microscopy, and magneto-optical spectroscopy of individual InAsxP1 -x/Ga0.5In0.5P quantum dots

    Science.gov (United States)

    Del Pozo-Zamudio, O.; Puebla, J.; Krysa, A.; Toro, R.; Sanchez, A. M.; Beanland, R.; Tartakovskii, A. I.; Skolnick, M. S.; Chekhovich, E. A.

    2017-08-01

    We report on growth and characterization of individual InAsxP1 -x /GaInP quantum dots with variable nominal As molar fraction. Magnetophotoluminescence experiments reveal quantum dot emission in a wide range from 1.3 to 1.8 eV, confirming successful incorporation of As into the quantum dots. Transmission electron microscopy reveals a core-cap structure of InAsP quantum dots with an InAs-rich core capped by an InP-rich layer. Inside the core, an average As molar fraction up to x ≈0.15 is observed. The heavy-hole g factors are found to be strongly dependent on As molar fraction, while the electron g factors are close to the InP values. This suggests type-II carrier confinement in the studied InAsP dots with holes (electrons) localized in the core (cap) region. Finally, dynamic nuclear polarization is observed, which allows for further insight into structural properties using nuclear magnetic resonance.

  16. Spin Switching via Quantum Dot Spin Valves

    Science.gov (United States)

    Gergs, N. M.; Bender, S. A.; Duine, R. A.; Schuricht, D.

    2018-01-01

    We develop a theory for spin transport and magnetization dynamics in a quantum dot spin valve, i.e., two magnetic reservoirs coupled to a quantum dot. Our theory is able to take into account effects of strong correlations. We demonstrate that, as a result of these strong correlations, the dot gate voltage enables control over the current-induced torques on the magnets and, in particular, enables voltage-controlled magnetic switching. The electrical resistance of the structure can be used to read out the magnetic state. Our model may be realized by a number of experimental systems, including magnetic scanning-tunneling microscope tips and artificial quantum dot systems.

  17. Transmission and scarring in graphene quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Huang Liang; Lai Yingcheng; Ferry, David K; Akis, Richard; Goodnick, Stephen M [Department of Electrical Engineering, Arizona State University, Tempe, AZ 85287 (United States)

    2009-08-26

    We study electronic transport in quantum-dot structures made of graphene. Focusing on the rectangular dot geometry and utilizing the non-equilibrium Green's function to calculate the transmission in the tight-binding framework, we find significant fluctuations in the transmission as a function of the electron energy. The fluctuations are correlated with the formation of quantum scarring states, or pointer states in the dot. Both enhancement and suppression of transmission have been observed. As the size of the quantum dot is increased, more scarring states can be formed, leading to stronger transmission or conductance fluctuations.

  18. Thick-shell nanocrystal quantum dots

    Science.gov (United States)

    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

    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.

  19. Optical Properties of Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Perinetti, U.

    2011-01-01

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

  20. Effect of temperature on quantum dots

    Indian Academy of Sciences (India)

    MAHDI AHMADI BORJI

    2017-07-12

    Jul 12, 2017 ... applications. Quantum dot semiconductor lasers, due to the discrete density of states, low threshold current and temperature dependence, high optical gain and quan- tum efficiency and high modulation speed, ... elastic properties of neighbour materials, lattice mis- match, and geometry of the quantum dot ...

  1. Surround-gated vertical nanowire quantum dots

    NARCIS (Netherlands)

    Van Weert, M.H.M.; Den Heijer, M.; Van Kouwen, M.P.; Algra, R.E.; Bakkers, E.P.A.M.; Kouwenhoven, L.P.; Zwiller, V.

    2010-01-01

    We report voltage dependent photoluminescence experiments on single indium arsenide phosphide (InAsP) quantum dots embedded in vertical surround-gated indium phosphide (InP) nanowires. We show that by tuning the gate voltage, we can access different quantum dot charge states. We study the

  2. Optical studies of capped quantum dots

    NARCIS (Netherlands)

    Wuister, S.F.

    2005-01-01

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

  3. Many electron effects in semiconductor quantum dots

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 26; Issue 1. Many electron effects in ... Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as 'artificial atoms' by some, ... Our calculations have been performed in a three-dimensional quantum dot. We have carried out a study of ...

  4. InN Quantum Dot Based Infra-Red Photodetectors.

    Science.gov (United States)

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

    2016-01-01

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

  5. Exciton in closed and opened quantum dot

    Directory of Open Access Journals (Sweden)

    M.V.Tkach

    2007-01-01

    Full Text Available The theory of exciton spectrum in spherically symmetric states for the three- shell closed spherical quantum dot is proposed. The evolution of the exciton spectrum while varying the outer well thickness from zero (stationary spectrum of single closed spherical quantum dot to infinity (quasistationary spectrum of a single open spherical quantum dot is investigated. The mechanism of damping (semiwidth of quasistationary states due to the redistribution over the energy levels of probability of exciton location in the space of two inner shells of nanosystem is studied. It is shown that the three shell closed spherical quantum dot of a rather big thickness of the outer well quite sufficiently and exactly reflects the basic properties of the quasistationary exciton spectrum in a single open spherical quantum dot.

  6. Biocompatible Quantum Dots for Biological Applications

    Science.gov (United States)

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

    2011-01-01

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

  7. Biocompatible quantum dots for biological applications.

    Science.gov (United States)

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

    2011-01-28

    Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, size-tunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots. Copyright © 2011 Elsevier Ltd. All rights reserved.

  8. High-density InAs/GaAs{sub 1−x}Sb{sub x} quantum-dot structures grown by molecular beam epitaxy for use in intermediate band solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Debnath, M. C., E-mail: mdebnath@cnsi.ucla.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma 73019 (United States); California NanoSystems Institute and Electrical Engineering Department, University of California-Los Angeles (UCLA), Los Angeles, California 90095 (United States); Mishima, T. D.; Santos, M. B.; Cheng, Y.; Whiteside, V. R.; Sellers, I. R. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma 73019 (United States); Hossain, K. [Amethyst Research, Inc., 123 Case Circle, Ardmore, Oklahoma 73401 (United States); Laghumavarapu, R. B.; Liang, B. L.; Huffaker, D. L. [California NanoSystems Institute and Electrical Engineering Department, University of California-Los Angeles (UCLA), Los Angeles, California 90095 (United States)

    2016-03-21

    InAs quantum-dot structures were grown using a GaAs{sub 1−x}Sb{sub x} matrix on a GaAs(001) substrate. The use of GaAs{sub 1−x}Sb{sub x} for the buffer and cap layers effectively suppressed coalescence between dots and significantly increased the dot density. The highest density (∼3.5 × 10{sup 11}/cm{sup 2}) was obtained for a nominal 3.0 monolayer deposition of InAs with an Sb composition of x = 13–14% in the GaAs{sub 1−x}Sb{sub x} matrix. When the Sb composition was increased to 18%, the resulting large photoluminescent red shift (∼90 meV) indicated the release of compressive strain inside the quantum dots. For x > 13%, we observed a significant decrease in photoluminescence intensity and an increase in the carrier lifetime (≥4.0 ns). This is attributed to the type-II band alignment between the quantum dots and matrix material.

  9. Electron transport in quantum dots

    CERN Document Server

    2003-01-01

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

  10. Quantum dots: lasers and amplifiers

    CERN Document Server

    Bimberg, D

    2003-01-01

    Continuous wave room-temperature output power of approx 3 W for edge emitters and of 1.2 mW for vertical-cavity surface-emitting lasers is realized for GaAs-based devices using InAs quantum dots (QDs) operating at 1.3 mu m. Characteristic temperatures up to 170 K below 330 K are realized. Simultaneously, differential efficiency exceeds 80% for these devices. Lasers emitting up to 12 W at 1140-1160 nm are useful as pump sources for Tm sup 3 sup + -doped fibres for frequency up-conversion to 470 nm. Both types of lasers show transparency current densities of 6 A cm sup - sup 2 per dot layer, eta sub i sub n sub t = 98% and alpha sub i around 1.5 cm sup - sup 1. Long operation lifetimes (above 3000 h at 50 deg C heatsink temperature at 1.5 W CW) and improved radiation hardness as compared to quantum well (QW) devices are manifested. Cut-off frequencies of about 10 GHz at 1100 nm and 6 GHz at 1300 nm and low alpha factors resulting in reduced filamentation and improved M sup 2 values in single-mode operation are ...

  11. InAs quantum dot growth on Al{sub x}Ga{sub 1−x}As by metalorganic vapor phase epitaxy for intermediate band solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Jakomin, R., E-mail: robertojakomin@xerem.ufrj.br [Campus de Xerém, Universidade Federal do Rio de Janeiro, UFRJ, Duque de Caxias-RJ (Brazil); Campus de Xerém, Universidade Federal do Rio de Janeiro, UFRJ, Duque de Caxias-RJ (Brazil); Kawabata, R. M. S.; Souza, P. L. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutoires–DISSE–PUC-Rio, RJ (Brazil); Pontificia Universidade Católica do Rio de Janeiro, Marques de São Vicente 225, Rio de Janeiro, 22452-900 RJ (Brazil); Mourão, R. T.; Pires, M. P. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutoires–DISSE–PUC-Rio, RJ (Brazil); Instituto de Física, Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro-RJ (Brazil); Micha, D. N. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutoires–DISSE–PUC-Rio, RJ (Brazil); Instituto de Física, Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro-RJ (Brazil); Coordenação de Licenciatura em Física, CEFET/RJ, Petrópolis-RJ (Brazil); Xie, H.; Fischer, A. M.; Ponce, F. A. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)

    2014-09-07

    InAs quantum dot multilayers have been grown using Al{sub x}Ga{sub 1−x}As spacers with dimensions and compositions near the theoretical values for optimized efficiencies in intermediate band photovoltaic cells. Using an aluminium composition of x = 0.3 and InAs dot vertical dimensions of 5 nm, transitions to an intermediate band with energy close to the ideal theoretical value have been obtained. Optimum size uniformity and density have been achieved by capping the quantum dots with GaAs following the indium-flush method. This approach has also resulted in minimization of crystalline defects in the epilayer structure.

  12. Thermoelectric transport through quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Merker, Lukas Heinrich

    2016-06-30

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

  13. Phonon bottleneck in GaAs/AlxGa1−xAs quantum dots

    Directory of Open Access Journals (Sweden)

    Y. C. Chang

    2015-06-01

    Full Text Available We report low-temperature photoluminescence measurements on highly-uniform GaAs/AlxGa1−xAs quantum dots grown by droplet epitaxy. Recombination between confined electrons and holes bound to carbon acceptors in the dots allow us to determine the energies of the confined states in the system, as confirmed by effective mass calculations. The presence of acceptor-bound holes in the quantum dots gives rise to a striking observation of the phonon-bottleneck effect.

  14. Lasing characteristics of InAs quantum dot laers on InP substrate

    Science.gov (United States)

    Yang, Y.; Qiu, D.; Uhl, R.; Chacon, R.

    2003-01-01

    Single-stack InAs self-assembled quantum dots (QD) lasers based on InP substrate have been grown by metalorganic vapor phase epitaxy. The narrow ridge waveguide lasers lased up to 260 K in continuous wave operation, and near room temperature in pulsed mode, with wavelengths between 1.59 to 1.74 mu m.

  15. Quantum dots with single-atom precision.

    Science.gov (United States)

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

    2014-07-01

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

  16. Large quantum dots with small oscillator strength

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  17. Excitonic quasimolecules in nanosystems of quantum dots

    Science.gov (United States)

    Pokutnyi, Sergey I.

    2017-09-01

    The theory of excitonic quasimolecules (biexcitons) (formed of spatially separated electrons and holes) in a nanosystem that consists of semiconductor quantum dots synthesized in a borosilicate glass matrix is presented. It is shown that exciton quasimolecule formation is of a threshold character and is possible in nanosystem, if the spacing between the quantum dots surfaces is larger than a certain critical spacing. It was found that the binding energy of the singlet ground state of an exciton quasimolecule, consisting of two semiconductor quantum dots is a significant large values, larger than the binding energy of the biexciton in a semiconductor single crystal by almost two orders of magnitude.

  18. Fluorescent Quantum Dots for Biological Labeling

    Science.gov (United States)

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

    2003-01-01

    Fluorescent semiconductor quantum dots that can serve as "on/off" labels for bacteria and other living cells are undergoing development. The "on/off" characterization of these quantum dots refers to the fact that, when properly designed and manufactured, they do not fluoresce until and unless they come into contact with viable cells of biological species that one seeks to detect. In comparison with prior fluorescence-based means of detecting biological species, fluorescent quantum dots show promise for greater speed, less complexity, greater sensitivity, and greater selectivity for species of interest. There are numerous potential applications in medicine, environmental monitoring, and detection of bioterrorism.

  19. Parallel carbon nanotube quantum dots and their interactions

    OpenAIRE

    Goss K.; Leijnse M.; Smerat S.; Wegewijs M.R.; Schneider C.M.; Meyer C

    2012-01-01

    We present quantum transport measurements of interacting parallel quantum dots formed in the strands of a carbon nanotube rope. In this molecular quantum dot system, transport is dominated by one quantum dot, while additional resonances from parallel side dots appear, which exhibit a weak gate coupling. This differential gating effect provides a tunability of the quantum dot system with only one gate electrode and provides control over the carbon nanotube strand that carries the current. By t...

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

    OpenAIRE

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

    2015-01-01

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

  1. Stranski-Krastanov InN/InGaN quantum dots grown directly on Si(111)

    Energy Technology Data Exchange (ETDEWEB)

    Soto Rodriguez, Paul E. D., E-mail: p.soto@isom.upm.es; Aseev, Pavel; Gómez, Victor J.; Kumar, Praveen; Ul Hassan Alvi, Naveed; Calleja, Enrique [Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM), Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Mánuel, José M.; Jiménez, Juan J.; García, Rafael [Dep. Ciencia de los Materiales e IM y QI., F. Ciencias, Universidad de Cádiz, 11510-Puerto Real, Cádiz (Spain); Morales, Francisco M. [Dep. Ciencia de los Materiales e IM y QI., F. Ciencias, Universidad de Cádiz, 11510-Puerto Real, Cádiz (Spain); IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz, Cádiz (Spain); Senichev, Alexander [Max Planck Institute of Microstructure Physics, Weinberg 2, Halle 06120 (Germany); Lienau, Christoph [Institut für Physik, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg (Germany); Nötzel, Richard, E-mail: noetzel500@gmail.com [L-NESS and Dipartimento di Scienza dei Materiali, Universitá di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy)

    2015-01-12

    The authors discuss and demonstrate the growth of InN surface quantum dots on a high-In-content In{sub 0.73}Ga{sub 0.27}N layer, directly on a Si(111) substrate by plasma-assisted molecular beam epitaxy. Atomic force microscopy and transmission electron microscopy reveal uniformly distributed quantum dots with diameters of 10–40 nm, heights of 2–4 nm, and a relatively low density of ∼7 × 10{sup 9} cm{sup −2}. A thin InN wetting layer below the quantum dots proves the Stranski-Krastanov growth mode. Near-field scanning optical microscopy shows distinct and spatially well localized near-infrared emission from single surface quantum dots. This holds promise for future telecommunication and sensing devices.

  2. Ge Quantum Dot Infrared Imaging Camera Project

    Data.gov (United States)

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

  3. Carbon Quantum Dots for Zebrafish Fluorescence Imaging

    National Research Council Canada - National Science Library

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-01-01

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties...

  4. Nanomaterials: Earthworms lit with quantum dots

    Science.gov (United States)

    Tilley, Richard D.; Cheong, Soshan

    2013-01-01

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

  5. Submonolayer Quantum Dot Infrared Photodetector

    Science.gov (United States)

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

    2010-01-01

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

  6. Adiabatic pumping through interacting quantum dots

    OpenAIRE

    Splettstoesser, Janine; Governale, Michele; König, Jürgen; Fazio, Rosario

    2005-01-01

    We present a general formalism to study adiabatic pumping through interacting quantum dots. We derive a formula that relates the pumped charge to the local, instantaneous Green function of the dot. This formula is then applied to the infinite-U Anderson model both for weak and strong tunnel-coupling strengths.

  7. Quantum Dots Coupled to a Superconductor

    DEFF Research Database (Denmark)

    Jellinggaard, Anders Robert

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

  8. Quantum dots and spin qubits in graphene

    Energy Technology Data Exchange (ETDEWEB)

    Recher, Patrik; Trauzettel, Bjoern, E-mail: precher@physik.uni-wuerzburg.de, E-mail: trauzettel@physik.uni-wuerzburg.de [Institut fuer Theoretische Physik und Astrophysik, University of Wuerzburg, 97074 Wuerzburg (Germany)

    2010-07-30

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

  9. Semiconductor Quantum Dots with Photoresponsive Ligands.

    Science.gov (United States)

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

    2016-10-01

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

  10. Charge transport through single molecules, quantum dots and quantum wires.

    Science.gov (United States)

    Andergassen, S; Meden, V; Schoeller, H; Splettstoesser, J; Wegewijs, M R

    2010-07-09

    We review recent progress in the theoretical description of correlation and quantum fluctuation phenomena in charge transport through single molecules, quantum dots and quantum wires. Various physical phenomena are addressed, relating to cotunneling, pair-tunneling, adiabatic quantum pumping, charge and spin fluctuations, and inhomogeneous Luttinger liquids. We review theoretical many-body methods to treat correlation effects, quantum fluctuations, non-equilibrium physics, and the time evolution into the stationary state of complex nanoelectronic systems.

  11. Effect of Sb and As spray on emission characteristics of InAs quantum dots with AlAs capping layer

    Science.gov (United States)

    Zhang, Z.; Tan, S.; Kim, Y.; Liu, Z.; Reece, P. J.; Bremner, S. P.

    2017-10-01

    We report on the influence of an Sb/As combined spray on the physical and optical characteristics of AlAs-capped InAs/GaAs quantum dots grown by Molecular Beam Epitaxy. Photoluminescence emission from the quantum dots shows a significant peak position shift under different Sb/As spray sequences. A blue-shifted quantum dot emission peak with an initial Sb rest indicates a large-to-small quantum dots transition process, with a bi-modal quantum dot size distribution inferred. High-resolution Transmission Electron Microscopy results reveal a large density of small quantum dots when the Sb spray is treated first. Furthermore, defect passivation in the vicinity of the quantum dots by use of Sb spray was detected.

  12. Low strain quantum dots in a double well infrared detector

    Science.gov (United States)

    Shenoi, R. V.; Hou, J.; Sharma, Y.; Shao, J.; Vandervelde, T. E.; Krishna, S.

    2008-08-01

    We report the fabrication of low strain quantum-dots-in-a-double-well (DDWELL) infrared photodetector where the net strain on the system has been reduced by limiting the total indium content in the system. The detector consists of InAs dots embedded in In0.15Ga0.85As and GaAs wells with a Al0.1Ga0.9As barrier, as opposed to In0.15Ga0.85As wells and a GaAs barrier in standard dots-in-a-well (DWELL) detector. The structure was a result of multilevel optimization involving the dot, well layers above and below the dot for achieving the desired wavelength response and higher absorption, and the thickness of the barriers for reduction in dark current. Detector structures grown using solid source molecular beam epitaxy (MBE) were processed and characterized. The reduction in total strain has enabled the growth of higher number of active region layers resulting in enhanced absorption of light. The detector shows dual color response with peaks in the mid-wave infrared (MWIR) and the long-wave infrared (LWIR) region. A peak detectivity of 6.7×1010 cm.√ Hz/W was observed at 8.7μm. The detector shows promise in raising the operating temperature of DWELL detectors, thereby enabling cheaper operation.

  13. Hole spin relaxation in quantum dots

    Science.gov (United States)

    Woods, L. M.; Reinecke, T. L.; Kotlyar, R.

    2004-03-01

    We present results for relaxation of the spin of a hole in a cylindrical quantum dot due to acoustic phonon assisted spin flips at low temperatures with an applied magnetic field. The hole dispersion is calculated by numerical diagonalization of the Luttinger Hamiltonian and applying perturbation theory with respect to the magnetic field, and the hole-phonon coupling is described by the Bir-Pikus Hamiltonian. We find that the decoherence time for hole spins for dots ≲20 nm is on the order of 10-8 s. This is several orders smaller than the decoherence time due to phonon assisted processes for electron spins in similar dots and is comparable to the total decoherence time of an electron spin in a quantum dot, which is controlled by the hyperfine interaction with nuclei. We obtain the dependence of the relaxation rate of the hole spin on dot size and hole mass.

  14. Computational intelligence applied to the growth of quantum dots

    Science.gov (United States)

    Singulani, Anderson P.; Vilela Neto, Omar P.; Aurélio Pacheco, Marco C.; Vellasco, Marley B. R.; Pires, Maurício P.; Souza, Patrícia L.

    2008-11-01

    We apply two computational intelligence techniques, namely, artificial neural network and genetic algorithm to the growth of self-assembled quantum dots. The method relies on an existing database of growth parameters with a resulting quantum dot characteristic to be able to later obtain the growth parameters needed to reach a specific value for such a quantum dot characteristic. The computational techniques were used to associate the growth input parameters with the mean height of the deposited quantum dots. Trends of the quantum dot mean height behavior as a function of growth parameters were correctly predicted and the growth parameters required to minimize the quantum dot mean height were provided.

  15. Characterizing and engineering tunable spin functionality inside indium arsenide/gallium arsenide quantum dot molecules

    Science.gov (United States)

    Liu, Weiwen

    The continual downsizing of the basic functional units used in the electronics industry has motivated the study of the quantum computation and related topics. To overcome the limitations of classical physics and engineering, some unique quantum mechanical features, especially entanglement and superpositions have begun to be considered as important properties for future bits. Including these quantum mechanical features is attractive because the ability to utilize quantum mechanics can dramatically enhance computational power. Among the various ways of constructing the basic building blocks for quantum computation, we are particularly interested in using spins inside epitaxially grown InAs/GaAs quantum dot molecules as quantum bits (qubits). The ability to design and engineer nanostructures with tailored quantum properties is critical to engineering quantum computers and other novel electro-optical devices and is one of the key challenges for scaling up new ideas for device application. In this thesis, we will focus on how the structure and composition of quantum dot molecules can be used to control spin properties and charge interactions. Tunable spin and charge properties can enable new, more scalable, methods of initializing and manipulating quantum information. In this thesis, we demonstrate one method to enable electric-field tunability of Zeeman splitting for a single electron spin inside a quantum dot molecules by using heterostructure engineering techniques to modify the barrier that separates quantum dots. We describe how these structural changes to the quantum dot molecules also change charge interactions and propose ways to use this effect to enable accurate measurement of coulomb interactions and possibly charge occupancy inside these complicated quantum dot molecules.

  16. Electron Spins in Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Hanson, R.

    2005-01-01

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

  17. AlInAs quantum dots

    Science.gov (United States)

    Gaisler, A. V.; Derebezov, I. A.; Gaisler, V. A.; Dmitriev, D. V.; Toropov, A. I.; Kozhukhov, A. S.; Shcheglov, D. V.; Latyshev, A. V.; Aseev, A. L.

    2017-01-01

    A system of quantum dots on the basis of AlxIn1-xAs/AlyGa1-y As solid solutions has been studied. The usage of broadband AlxIn1-x solid solutions as the basis of quantum dots makes it possible to expand considerably the spectral emission range into the short-wave region, including the wavelength region near 770 nm being of interest for the design of aerospace systems of quantum cryptography. The optical characteristics of single AlxIn1-xAs quantum dots grown according to the Stranski-Krastanov mechanism are studied by the cryogenic microphotoluminescence method. The fine structure of exciton states of quantum dots is studied in the wavelength region near 770 nm. It is shown that the splitting of exciton states is comparable with the natural width of exciton lines, which is of great interest for the design of emitters of pairs of entangled photons on the basis of AlxAs1-x quantum dots.

  18. Magnetoconductivity of quantum dots with Rashba interaction

    Science.gov (United States)

    Lipparini, E.; Barranco, M.; Malet, F.; Pi, M.

    2009-03-01

    We address the magnetoconductivity of a quantum dot with Rashba spin-orbit interaction within linear-response theory. As a consequence of the generalized Kohn’s theorem, the magnetoconductivity of the dot is zero when the spin-orbit coupling is neglected. The inclusion of the spin-orbit interaction violates the mentioned theorem and gives rise to a nonzero magnetoconductivity. We derive a simple expression for this quantity valid up to the second order in the Rashba parameter. In the limit of vanishing lateral confinement, i.e., for a quantum well, a similar calculation yields the quantum Hall-effect result.

  19. Diamond LED substrate and novel quantum dots.

    Science.gov (United States)

    Sung, James C; Sung, Michael

    2009-02-01

    Nitride LED (e.g., GaN) has become the mainstream of blue light source. The blue light can be converted to white light by exciting a phosphor (e.g., Nichia's YAG or Osram's TAG) with the complementary yellow emission. However, GaN is typically deposited on sapphire (Al2O3) substrates formed by crystal pulling or hexagonal (e.g., 4 H or 6 H) SiC wafers condensed from SiC vapor. In either case, the nitride lattice is ridden (e.g., 10(9)/cm2) with dislocations. The high dislocation density with sapphire is due to the large (>13%) lattice mismatch; and with hexagonal SiC, because of intrinsic defects. Cubic (beta) SiC may be deposited epitaxially using a CVD reactor onto silicon wafer by diffusing the interface and by chemical gradation. A reactive echant (e.g., hydrogen or fluorine) can be introduced periodically to gasify mis-aligned atoms. In this case, large single crystal wafers would be available for the manufacture of high bright LED with superb electro-optical efficiency. The SiC wafer may be coated with diamond film that can eliminate heat in real time. As a result of lower temperature, the nitride LED can be brighter and it will last longer. The blue light of GaN LED formed on SiC on Diamond (SiCON) LED may also be scattered by using novel quantum dots (e.g., 33 atom pairs of CdSe) to form a broad yellow light that blend in with the original blue light to form sunlight-like white light. This would be the ideal source for general illumination (e.g., for indoor) or backlighting (e.g., for LCD).

  20. A comparison between semi-spheroid- and dome-shaped quantum dots coupled to wetting layer

    Energy Technology Data Exchange (ETDEWEB)

    Shahzadeh, Mohammadreza; Sabaeian, Mohammad, E-mail: Sabaeian@scu.ac.ir [Physics Department, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, 61357-43135 (Iran, Islamic Republic of)

    2014-06-15

    During the epitaxial growth method, self-assembled semi-spheroid-shaped quantum dots (QDs) are formed on the wetting layer (WL). However for sake of simplicity, researchers sometimes assume semi-spheroid-shaped QDs to be dome-shaped (hemisphere). In this work, a detailed and comprehensive study on the difference between electronic and transition properties of dome- and semi-spheroid-shaped quantum dots is presented. We will explain why the P-to-S intersubband transition behaves the way it does. The calculated results for intersubband P-to-S transition properties of quantum dots show two different trends for dome-shaped and semi-spheroid-shaped quantum dots. The results are interpreted using the probability of finding electron inside the dome/spheroid region, with emphasis on the effects of wetting layer. It is shown that dome-shaped and semi-spheroid-shaped quantum dots feature different electronic and transition properties, arising from the difference in lateral dimensions between dome- and semi-spheroid-shaped QDs. Moreover, an analogy is presented between the bound S-states in the quantum dots and a simple 3D quantum mechanical particle in a box, and effective sizes are calculated. The results of this work will benefit researchers to present more realistic models of coupled QD/WL systems and explain their properties more precisely.

  1. MOVPE GROWTH OF SMALL AND UNIFORM INP/GAINP QUANTUM DOTS

    OpenAIRE

    Ren, Hong-Wen; Sugisaki, Mitsuru; LEE, JEONG-SIK; SUGOU, SHIGEO; Masumoto, Yasuaki

    1998-01-01

    InP self-assembled quantum dots embedded in Ga0.5In0.5P were fabricated by metal-organic vaporphase epitaxy. Small size and highly uniform InP dots were obtained at lower growth temperatureby using tertiarybutyl-phosphine instead of phosphine. Growth of 4ML InP on a 4ML GaP spacerat 550oC resulted in InP islands of about 30nm in base diameter and 7nm in height within 10%deviation. The formation of the dots was sensitively monitored by a fast-nulling ellipsometer. Byinserting another 2ML GaP s...

  2. Quantum efficiency of a double quantum dot microwave photon detector

    Science.gov (United States)

    Wong, Clement; Vavilov, Maxim

    Motivated by recent interest in implementing circuit quantum electrodynamics with semiconducting quantum dots, we study charge transfer through a double quantum dot (DQD) capacitively coupled to a superconducting cavity subject to a microwave field. We analyze the DQD current response using input-output theory and determine the optimal parameter regime for complete absorption of radiation and efficient conversion of microwave photons to electric current. For experimentally available DQD systems, we show that the cavity-coupled DQD operates as a photon-to-charge converter with quantum efficiencies up to 80% C.W. acknowledges support by the Intelligence Community Postdoctoral Research Fellowship Program.

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

    Science.gov (United States)

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

    2008-01-01

    Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material

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

    Science.gov (United States)

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

    2014-08-26

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

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

    KAUST Repository

    Hoogland, Sjoerd H.

    2012-01-01

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

  6. Surface treatment of nanocrystal quantum dots after film deposition

    Science.gov (United States)

    Sykora, Milan; Koposov, Alexey; Fuke, Nobuhiro

    2015-02-03

    Provided are methods of surface treatment of nanocrystal quantum dots after film deposition so as to exchange the native ligands of the quantum dots for exchange ligands that result in improvement in charge extraction from the nanocrystals.

  7. Few-quantum-dot lasing in photonic crystal nanocavities

    DEFF Research Database (Denmark)

    Liu, Jin; Ates, Serkan; Stobbe, Søren

    2012-01-01

    A very smooth lasing transition in photonic crystal nanocavities with embedded quantum dots is observed and compared to the theory. Decay rate measurements reveal that only a few quantum dots are feeding the cavity....

  8. Double quantum dots defined in bilayer graphene

    Science.gov (United States)

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

    2017-07-01

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

  9. Coherent transport through interacting quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hiltscher, Bastian

    2012-10-05

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

  10. Coherence and dephasing in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    2003-01-01

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

  11. Modulation Response of Semiconductor Quantum Dot Nanocavity Lasers

    DEFF Research Database (Denmark)

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

    2011-01-01

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

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

    Science.gov (United States)

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

    2017-08-22

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

  13. Angiogenic Profiling of Synthesized Carbon Quantum Dots.

    Science.gov (United States)

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

    2015-10-20

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

  14. Moment of inertia in elliptical quantum dots

    Science.gov (United States)

    Serra, Llorenç; Puente, Antonio; Lipparini, Enrico

    The moment of inertia of deformed quantum dots and its experimental relevance in relation to the dot spectroscopic features is theoretically investigated. A strong link to the low-energy orbital current mode that manifests in the magnetic dipole (M1) spectrum is stressed. The moment of inertia is obtained by solving the cranked Kohn-Sham equations within the local-spin-density approximation and the results discussed in comparison with the predictions of an analytical non-interacting model. The results as a function of deformation and size indicate that the existence of spin transitions in the dot ground state has an important effect on the moment of inertia.

  15. Odd triplet superconductivity in ultrasmall quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, Stephan; Koenig, Juergen [Theoretische Physik, Universitaet Duisburg-Essen and CENIDE (Germany); Sothmann, Bjoern [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg (Germany)

    2016-07-01

    We report on the possibility to create odd frequency Cooper pairs in proximized interacting quantum dots attached to ferromagnetic leads. Spin blockade effects together with induced superconductivity allow electron pairs with same spin at different times to carry superconducting correlations. Besides the conventional finite singlet pairing amplitude on the dot, only odd frequency triplet pairing is possible here. This is in contrast to the double dot case. We demonstrate how the order parameter for odd-frequency triplet pairing as well as the differential Andreev conductance are influenced when tuning gate and/or bias voltages, the angle of magnetizations of the leads and the coupling to the nearby superconductor.

  16. High resolution STEM of quantum dots and quantum wires

    DEFF Research Database (Denmark)

    Kadkhodazadeh, Shima

    2013-01-01

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

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

    DEFF Research Database (Denmark)

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

    2012-01-01

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

  18. Bright infrared LEDs based on colloidal quantum-dots

    KAUST Repository

    Sun, Liangfeng

    2013-01-01

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

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

    DEFF Research Database (Denmark)

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

    2009-01-01

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

  20. Thermoelectric properties of hexagonal graphene quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Yonghong, E-mail: yhyan@fudan.edu.cn [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Liang, Qi-Feng [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Zhao, Hui [Department of Physics, Tongji University, Shanghai 200092 (China); Wu, Chang-Qin [Department of Physics, Fudan University, Shanghai 200433 (China)

    2012-02-27

    By using the atomistic nonequilibrium Green's function method, we investigate the thermoelectric properties of graphene nanoribbons in the presence of two constrictions (or hexagonal graphene quantum dots). With decreasing widths of the constrictions, the thermal conductance of the nanoribbon can be reduced largely while S{sup 2}G{sub e} (S is the Seebeck coefficient and G{sub e} is the electronic conductance) remains still high as compared with the results of the pristine nanoribbon. Thus, the thermoelectric figure of merit ZT can be enhanced largely. In fact, in the presence of narrowest constrictions the ZT values of the zigzag quantum dots can exceed one at room temperature, while the ZT values of the armchair quantum dots may be close to one, depending on the size of the dot. -- Highlights: ► We study thermoelectric properties of hexagonal graphene quantum dots. ► By point contacts to two leads, the thermal conductance can be reduced greatly while keeping the power factor still high. ► Thermoelectric figure of merit (ZT) can exceed unity.

  1. Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry

    Science.gov (United States)

    Lüker, S.; Kuhn, T.; Reiter, D. E.

    2017-12-01

    Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches, the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach, we show that, indeed, lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatiotemporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot, the phonon emission is strongly concentrated along the direction of the smallest axis of the dot, which is important for the use of phonons for the communication between different dots.

  2. Covalent functionalized black phosphorus quantum dots

    Science.gov (United States)

    Scotognella, Francesco; Kriegel, Ilka; Sassolini, Simone

    2018-01-01

    Black phosphorus (BP) nanostructures enable a new strategy to tune the electronic and optical properties of this atomically thin material. In this paper we show, via density functional theory calculations, the possibility to modify the optical properties of BP quantum dots via covalent functionalization. The quantum dot selected in this study has chemical formula P24H12 and has been covalent functionalized with one or more benzene rings or anthracene. The effect of functionalization is highlighted in the absorption spectra, where a red shift of the absorption is noticeable. The shift can be ascribed to an electron delocalization in the black phosphorus/organic molecule nanostructure.

  3. Cadmium telluride quantum dots advances and applications

    CERN Document Server

    Donegan, John

    2013-01-01

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

  4. Potential clinical applications of quantum dots

    Science.gov (United States)

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

    2008-01-01

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

  5. Spin qubits in graphene quantum dots

    OpenAIRE

    Trauzettel, Björn; Bulaev, Denis V.; Loss, Daniel; Burkard, Guido

    2006-01-01

    We propose how to form spin qubits in graphene. A crucial requirement to achieve this goal is to find quantum dot states where the usual valley degeneracy in bulk graphene is lifted. We show that this problem can be avoided in quantum dots based on ribbons of graphene with semiconducting armchair boundaries. For such a setup, we find the energies and the exact wave functions of bound states, which are required for localized qubits. Additionally, we show that spin qubits in graphene can not on...

  6. High-Yield Fabrication of Entangled Photon Emitters for Hybrid Quantum Networking Using High-Temperature Droplet Epitaxy.

    Science.gov (United States)

    Basso Basset, Francesco; Bietti, Sergio; Reindl, Marcus; Esposito, Luca; Fedorov, Alexey; Huber, Daniel; Rastelli, Armando; Bonera, Emiliano; Trotta, Rinaldo; Sanguinetti, Stefano

    2018-01-10

    Several semiconductor quantum dot techniques have been investigated for the generation of entangled photon pairs. Among the other techniques, droplet epitaxy enables the control of the shape, size, density, and emission wavelength of the quantum emitters. However, the fraction of the entanglement-ready quantum dots that can be fabricated with this method is still limited to around 5%, and matching the energy of the entangled photons to atomic transitions (a promising route toward quantum networking) remains an outstanding challenge. Here, we overcome these obstacles by introducing a modified approach to droplet epitaxy on a high symmetry (111)A substrate, where the fundamental crystallization step is performed at a significantly higher temperature as compared with previous reports. Our method drastically improves the yield of entanglement-ready photon sources near the emission wavelength of interest, which can be as high as 95% due to the low values of fine structure splitting and radiative lifetime, together with the reduced exciton dephasing offered by the choice of GaAs/AlGaAs materials. The quantum dots are designed to emit in the operating spectral region of Rb-based slow-light media, providing a viable technology for quantum repeater stations.

  7. Hybrid quantum-classical modeling of quantum dot devices

    Science.gov (United States)

    Kantner, Markus; Mittnenzweig, Markus; Koprucki, Thomas

    2017-11-01

    The design of electrically driven quantum dot devices for quantum optical applications asks for modeling approaches combining classical device physics with quantum mechanics. We connect the well-established fields of semiclassical semiconductor transport theory and the theory of open quantum systems to meet this requirement. By coupling the van Roosbroeck system with a quantum master equation in Lindblad form, we introduce a new hybrid quantum-classical modeling approach, which provides a comprehensive description of quantum dot devices on multiple scales: it enables the calculation of quantum optical figures of merit and the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way. We construct the interface between both theories in such a way, that the resulting hybrid system obeys the fundamental axioms of (non)equilibrium thermodynamics. We show that our approach guarantees the conservation of charge, consistency with the thermodynamic equilibrium and the second law of thermodynamics. The feasibility of the approach is demonstrated by numerical simulations of an electrically driven single-photon source based on a single quantum dot in the stationary and transient operation regime.

  8. Probing silicon quantum dots by single-dot techniques

    Science.gov (United States)

    Sychugov, Ilya; Valenta, Jan; Linnros, Jan

    2017-02-01

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

  9. Biomedical and biological applications of quantum dots.

    Science.gov (United States)

    Abbasi, Elham; Kafshdooz, Tayebeh; Bakhtiary, Mohsen; Nikzamir, Nasrin; Nikzamir, Nasim; Nikzamir, Mohammad; Mohammadian, Mozhdeh; Akbarzadeh, Abolfazl

    2016-05-01

    Quantum dots (QDs) as colloidal nanocrystalline semiconductors have exceptional photophysical properties, due to their quantum confinement effects. Depending on their sizes and chemical compositions, QDs emit different wavelengths over a broad range of the light spectrum, from visible to infrared. QDs are typically extensively used for optical applications due to their high extinction coefficient. This article reviews biomedical applications of QDs, especially the application of QDs in cell targeting, delivery, diagnostics, cancer therapy, and imaging for cancer research.

  10. Growth of Low-Density Vertical Quantum Dot Molecules with Control in Energy Emission

    Directory of Open Access Journals (Sweden)

    Fuster D

    2010-01-01

    Full Text Available Abstract In this work, we present results on the formation of vertical molecule structures formed by two vertically aligned InAs quantum dots (QD in which a deliberate control of energy emission is achieved. The emission energy of the first layer of QD forming the molecule can be tuned by the deposition of controlled amounts of InAs at a nanohole template formed by GaAs droplet epitaxy. The QD of the second layer are formed directly on top of the buried ones by a strain-driven process. In this way, either symmetric or asymmetric vertically coupled structures can be obtained. As a characteristic when using a droplet epitaxy patterning process, the density of quantum dot molecules finally obtained is low enough (2 × 108 cm−2 to permit their integration as active elements in advanced photonic devices where spectroscopic studies at the single nanostructure level are required.

  11. Electrostatically confined trilayer graphene quantum dots

    Science.gov (United States)

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

    2017-04-01

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

  12. Evidence for Phase-Separated Quantum Dots in Cubic InGaN Layers from Resonant Raman Scattering

    Science.gov (United States)

    Lemos, V.; Silveira, E.; Leite, J. R.; Tabata, A.; Trentin, R.; Scolfaro, L. M. R.; Frey, T.; As, D. J.; Schikora, D.; Lischka, K.

    2000-04-01

    The emission of light in the blue-green region from cubic InxGa1-xN alloys grown by molecular beam epitaxy is observed at room temperature and 30 K. By using selective resonant Raman spectroscopy (RRS) we demonstrate that the emission is due to quantum confinement effects taking place in phase-separated In-rich quantum dots formed in the layers. RRS data show that the In content of the dots fluctuates across the volume of the layers. We find that dot size and alloy fluctuation determine the emission wavelengths.

  13. Comparison of quantum discord and local quantum uncertainty in a vertical quantum dot

    OpenAIRE

    Faizi, E.; Eftekhari, H.

    2014-01-01

    In this paper, we consider quantum correlations (quantum discord and local quantum uncertainty) in a vertical quantum dot. Their dependencies on magnetic field and temperature are presented in detail. It is noticeable that, quantum discord and local quantum uncertainty behavior is similar to a large extent. In addition, the time evolution of quantum discord and local quantum uncertainty under dephasing and amplitude damping channels is investigated. It has been found that, for some Belldiagon...

  14. Magnon cotunneling through a quantum dot

    Science.gov (United States)

    Karwacki, Łukasz

    2017-11-01

    I consider a single-level quantum dot coupled to two reservoirs of spin waves (magnons). Such systems have been studied recently from the point of view of possible coupling between electronic and magnonic spin currents. However, usually weakly coupled systems were investigated. When coupling between the dot and reservoirs is not weak, then higher order processes play a role and have to be included. Here I consider cotunneling of magnons through a spin-occupied quantum dot, which can be understood as a magnon (spin) leakage current in analogy to leakage currents in charge-based electronics. Particular emphasis has been put on investigating the effect of magnetic field and temperature difference between the magnonic reservoirs.

  15. Spin-wave excitations in quantum dots

    Science.gov (United States)

    Lipparini, Enrico; Serra, Llorenç

    1998-03-01

    The transverse response function for a quantum dot in a uniform magnetic field B is calculated using current-density-functional theory. The poles corresponding to the ΔLz=+/-1 and ΔSz=+/-1 spin waves are investigated as a function of B.

  16. Orbital current mode in elliptical quantum dots

    Science.gov (United States)

    Serra, Llorenç; Puente, Antonio; Lipparini, Enrico

    1999-11-01

    An orbital current mode peculiar to deformed quantum dots is theoretically investigated; first by using a simple model that makes it possible to analytically interpret its main characteristics, and second, by numerically solving the microscopic equations of time evolution after an initial perturbation within the time-dependent local-spin-density approximation. Results for different deformations and sizes are shown.

  17. Competing interactions in semiconductor quantum dots

    NARCIS (Netherlands)

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

    2014-01-01

    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

  18. Decoherence in Nearly-Isolated Quantum Dots

    DEFF Research Database (Denmark)

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

    2000-01-01

    Decoherence in nearly-isolated GaAs quantum dots is investigated using the change in average Coulomb blockade peak height upon breaking time-reversal symmetry. The normalized change in average peak height approaches the predicted universal value of 1/4 at temperatures well below the single...

  19. System and method for making quantum dots

    KAUST Repository

    Bakr, Osman M.

    2015-05-28

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

  20. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

    Semiconductor quantum dots are often described as "artificial atoms": They are small nanometre-sized structures in which electrons only are allowed to exist at certain discrete levels due to size quantization, thus allowing the engineering of fundamental properties such as the coupling to light. ...

  1. Assembling quantum dots via critical Casimir forces

    NARCIS (Netherlands)

    Marino, E.; Kodger, T.E.; Hove, J.B. ten; Velders, A.H.; Schall, P.

    2016-01-01

    Programmed assembly of colloidal inorganic nanocrystal superstructures is crucial for the realization of future artificial solids as well as present optoelectronic applications. Here, we present a new way to assemble quantum dots reversibly using binary solvents. By tuning the temperature and

  2. Doppler broadening effects in plasmonic quantum dots

    Science.gov (United States)

    Alves, R. A.; Silva, Nuno A.; Costa, J. C.; Gomes, M.; Guerreiro, A.

    2017-08-01

    In this paper we analyse the effects of the Doppler shift on the optical response of a nanoplasmonic system. Through the development of a simplified model based on the Hydrodynamic Drude model we analyse the response of a quantum dot embed in a moving fluid, predicting the Doppler broadening and the shift of the spectral line.

  3. Quantum dot waveguides: ultrafast dynamics and applications

    DEFF Research Database (Denmark)

    Chen, Yaohui; Mørk, Jesper

    2009-01-01

    In this paper we analyze, based on numerical simulations, the dynamics of semiconductor devices incorporating quantum dots (QDs). In particular we emphasize the unique ultrafast carrier dynamics occurring between discrete QD bound states, and its influence on QD semiconductor optical amplifiers...

  4. Enabling biomedical research with designer quantum dots

    NARCIS (Netherlands)

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

    2012-01-01

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

  5. Electron Scattering in Intrananotube Quantum Dots

    NARCIS (Netherlands)

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

    2009-01-01

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

  6. Ostwald's ripening of nanostructures with quantum dots

    CERN Document Server

    Vengrenovich, R D; Yarema, S V

    2001-01-01

    The scenario of quantum dots shaping during ripening three-dimensional islands obtained by heteroepitaxy in a Stranski-Krastanow mode, is offered. It is shown that throughout the growth of dislocations with their subsequent separation from the island bottom, the size distribution function becomes narrower with noticeable diminishing the dispersion. The possible reasons for signal attenuation of Ostwald's ripening islands are analyzed

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

    Science.gov (United States)

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

    2017-06-27

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Aouassa, Mansour, E-mail: mansour.aouassa@yahoo.fr [LMON, Faculté des Sciences de Monastir, Avenue de l’environnement Monastir 5019 (Tunisia); Jadli, Imen [LMON, Faculté des Sciences de Monastir, Avenue de l’environnement Monastir 5019 (Tunisia); Bandyopadhyay, Anup [Department of Mechanical Engineering, Texas A& M University, College Station, TX 77843 (United States); Kim, Sung Kyu [Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Yuseong-daero 1689-gil, Yuseong-gu, Daejeon (Korea, Republic of); Department of Materials Science and Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon (Korea, Republic of); Karaman, Ibrahim [Department of Mechanical Engineering, Texas A& M University, College Station, TX 77843 (United States); Lee, Jeong Yong [Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Yuseong-daero 1689-gil, Yuseong-gu, Daejeon (Korea, Republic of); Department of Materials Science and Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon (Korea, Republic of)

    2017-03-01

    Highlights: • We report the new fabrication approach for producing a self- assembled Mn dpoed Ge quantum dots (QDs) on SiO{sub 2} thin film with a Curie temperature above room temperature. These magnetic QDs are crystalline, monodisperse and have a well-defined shape and a controlled size. The investigation opens new routes for elaboration of self-assembled magnetic nanocrystals - Abstract: In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO{sub 2} thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO{sub 2} thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.

  9. The equilibrium shape of InAs quantum dots grown on a GaAs(001) substrate

    CERN Document Server

    Pehlke, E; Scheffler, M; Pehlke, Eckhard; Moll, Nikolaj; Scheffler, Matthias

    1996-01-01

    The equilibrium shape of strained InAs quantum dots grown epitaxially on a GaAs(001) substrate is derived as a function of volume. InAs surface energies are calculated within density-functional theory, and a continuum approach is applied for the elastic relaxation energies.

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

    Science.gov (United States)

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

    2013-10-14

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

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

    KAUST Repository

    El Afandy, Rami

    2011-07-07

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

  12. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

    of this Thesis we discuss a novel type of photonic crystal waveguide and show its applications for on-chip quantum information processing. This structure was designed for the ecient mapping of two orthogonal circular dipole transitions to dierent propagation paths of the emitted photon, i.e. exhibits chiral...... quantum-dot-waveguide coupling. Such a structure is ideally suited for a number of applications in quantum information processing and among others we propose an on-chip spin-photon interface, a single photon transistor, and a deterministic cNOT gate....

  13. Universal Growth Scheme for Quantum Dots with Low Fine-Structure Splitting at Various Emission Wavelengths

    Science.gov (United States)

    Skiba-Szymanska, Joanna; Stevenson, R. Mark; Varnava, Christiana; Felle, Martin; Huwer, Jan; Müller, Tina; Bennett, Anthony J.; Lee, James P.; Farrer, Ian; Krysa, Andrey B.; Spencer, Peter; Goff, Lucy E.; Ritchie, David A.; Heffernan, Jon; Shields, Andrew J.

    2017-07-01

    Efficient sources of individual pairs of entangled photons are required for quantum networks to operate using fiber-optic infrastructure. Entangled light can be generated by quantum dots (QDs) with naturally small fine-structure splitting (FSS) between exciton eigenstates. Moreover, QDs can be engineered to emit at standard telecom wavelengths. To achieve sufficient signal intensity for applications, QDs have been incorporated into one-dimensional optical microcavities. However, combining these properties in a single device has so far proved elusive. Here, we introduce a growth strategy to realize QDs with small FSS in the conventional telecom band, and within an optical cavity. Our approach employs ``droplet-epitaxy'' of InAs quantum dots on (001) substrates. We show the scheme improves the symmetry of the dots by 72%. Furthermore, our technique is universal, and produces low FSS QDs by molecular beam epitaxy on GaAs emitting at ˜900 nm , and metal-organic vapor-phase epitaxy on InP emitting at ˜1550 nm , with mean FSS 4 × smaller than for Stranski-Krastanow QDs.

  14. Quantum Dots and Their Multimodal Applications: A Review

    Science.gov (United States)

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

    2010-01-01

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

  15. Efficient Luminescence from Perovskite Quantum Dot Solids

    KAUST Repository

    Kim, Younghoon

    2015-11-18

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

  16. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    Science.gov (United States)

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

    1998-01-01

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

  17. Imaging Few-Electron Double Quantum Dots in InAs/InP Nanowires

    Science.gov (United States)

    Trodahl, Halvar J.; Boyd, Erin E.; Bleszynski, Ania; Westervelt, R. M.; Froberg, Linus E.; Samuelson, Lars

    2007-03-01

    InAs quantum dots formed in InAs/InP nanowire heterostructures are attractive candidates for nanoelectronics, spintronics and quantum information processing. Tunnel-coupled double InAs dots defined by InP barriers can be grown using chemical beam epitaxy; each dot can be small enough to hold just a few electrons. It is difficult to lithographically define gates small enough to individually address each dot. With use of a liquid-He cooled scanning probe microscope (SPM), the Coulomb blockade conductance of a single InAs quantum dot in an InAs/InP nanowire has been imaged, using the SPM tip as a movable gate [1]. This approach can individually tune the charge on each InAs dot in an InAs/InP nanowire. We plan to use this technique to investigate tunnel-coupled InAs double dots. [1] A. Bleszynski et al., 28th Int. Conf. on the Physics of Semiconductors, 2006.

  18. Electron-hole confinement symmetry in silicon quantum dots

    NARCIS (Netherlands)

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

    2015-01-01

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

  19. Mitigation of quantum dot cytotoxicity by microencapsulation.

    Science.gov (United States)

    Romoser, Amelia; Ritter, Dustin; Majitha, Ravish; Meissner, Kenith E; McShane, Michael; Sayes, Christie M

    2011-01-01

    When CdSe/ZnS-polyethyleneimine (PEI) quantum dots (QDs) are microencapsulated in polymeric microcapsules, human fibroblasts are protected from acute cytotoxic effects. Differences in cellular morphology, uptake, and viability were assessed after treatment with either microencapsulated or unencapsulated dots. Specifically, QDs contained in microcapsules terminated with polyethylene glycol (PEG) mitigate contact with and uptake by cells, thus providing a tool to retain particle luminescence for applications such as extracellular sensing and imaging. The microcapsule serves as the "first line of defense" for containing the QDs. This enables the individual QD coating to be designed primarily to enhance the function of the biosensor.

  20. Mitigation of quantum dot cytotoxicity by microencapsulation.

    Directory of Open Access Journals (Sweden)

    Amelia Romoser

    Full Text Available When CdSe/ZnS-polyethyleneimine (PEI quantum dots (QDs are microencapsulated in polymeric microcapsules, human fibroblasts are protected from acute cytotoxic effects. Differences in cellular morphology, uptake, and viability were assessed after treatment with either microencapsulated or unencapsulated dots. Specifically, QDs contained in microcapsules terminated with polyethylene glycol (PEG mitigate contact with and uptake by cells, thus providing a tool to retain particle luminescence for applications such as extracellular sensing and imaging. The microcapsule serves as the "first line of defense" for containing the QDs. This enables the individual QD coating to be designed primarily to enhance the function of the biosensor.

  1. Probing relaxation times in graphene quantum dots

    Science.gov (United States)

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

    2013-01-01

    Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100 ns. PMID:23612294

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

    Science.gov (United States)

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

    2017-03-22

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

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

    CERN Document Server

    2003-01-01

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

  4. Photon-mediated interaction between distant quantum dot circuits.

    Science.gov (United States)

    Delbecq, M R; Bruhat, L E; Viennot, J J; Datta, S; Cottet, A; Kontos, T

    2013-01-01

    Engineering the interaction between light and matter is an important goal in the emerging field of quantum opto-electronics. Thanks to the use of cavity quantum electrodynamics architectures, one can envision a fully hybrid multiplexing of quantum conductors. Here we use such an architecture to couple two quantum dot circuits. Our quantum dots are separated by 200 times their own size, with no direct tunnel and electrostatic couplings between them. We demonstrate their interaction, mediated by the cavity photons. This could be used to scale up quantum bit architectures based on quantum dot circuits or simulate on-chip phonon-mediated interactions between strongly correlated electrons.

  5. Semiconductor nanocrystals or quantum dots

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 18; Issue 8. Various Quantum Mechanical Concepts for Confinements in Semiconductor Nanocrystals. Jayakrishna Khatei Karuna Kar Nanda. Classroom Volume 18 Issue 8 August 2013 pp 771-776 ...

  6. Quantum optics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Cadeddu, Davide; Teissier, Jean

    2016-01-01

    We present an exploration of the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter's properties with the highest sensitivity, allowing...... the detection of thermal excitation of the mechanical mode at 4 K....

  7. Quantum Hall effect in epitaxial graphene with permanent magnets.

    Science.gov (United States)

    Parmentier, F D; Cazimajou, T; Sekine, Y; Hibino, H; Irie, H; Glattli, D C; Kumada, N; Roulleau, P

    2016-12-06

    We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.

  8. Andreev molecules in semiconductor nanowire double quantum dots

    NARCIS (Netherlands)

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

    2017-01-01

    Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum

  9. Synthesis of Cesium Lead Halide Perovskite Quantum Dots

    Science.gov (United States)

    Shekhirev, Mikhail; Goza, John; Teeter, Jacob D.; Lipatov, Alexey; Sinitskii, Alexander

    2017-01-01

    Synthesis of quantum dots is a valuable experiment for demonstration and discussion of quantum phenomena in undergraduate chemistry curricula. Recently, a new class of all-inorganic perovskite quantum dots (QDs) with a formula of CsPbX[subscript 3] (X = Cl, Br, I) was presented and attracted tremendous attention. Here we adapt the synthesis of…

  10. Quantum Dot Devices for Optical Signal Processing

    DEFF Research Database (Denmark)

    Chen, Yaohui

    with other semiconductor materials. The understanding of such properties is important in order to improve the performance of existing devices and to trigger the development of new semiconductor devices for dierent optical signal processing functionalities in the future. We present a detailed quantum dot...... and the continuum. Additional to the conventional time-domain modeling scheme, a small-signal perturbation analysis has been used to assist the investigation of harmonic modulation properties. The static properties of quantum dot devices, for example high saturation power, have been quantitatively analyzed....... Additional to the static linear amplication properties, we focus on exploring the gain dynamics on the time scale ranging from sub-picosecond to nanosecond. In terms of optical signals that have been investigated, one is the simple sinusoidally modulated optical carrier with a typical modulation frequency...

  11. The Silicon:Colloidal Quantum Dot Heterojunction

    KAUST Repository

    Masala, Silvia

    2015-10-13

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

  12. Transverse dipole spin modes in quantum dots

    Science.gov (United States)

    Lipparini, E.; Barranco, M.; Emperador, A.; Pi, M.; Serra, Ll.

    1999-09-01

    We have carried out a systematic analysis of the transverse dipole spin response of a large-size quantum dot within time-dependent current density functional theory. Results for magnetic fields corresponding to integer filling factors are reported, as well as a comparison with the longitudinal dipole spin response. As in the two-dimensional electron gas, the spin response at high-spin magnetization is dominated by a low-energy transverse mode.

  13. Spin response of unpolarized quantum dots

    Science.gov (United States)

    Serra, L.; Lipparini, E.

    1997-12-01

    The spin response function for electrons confined in a quantum dot is studied within the time-dependent local spin density approximation (TDLSDA) of density functional theory. In the long-wavelength regime we predict the existence of a low-energy collective dipole (ell = 1) spin mode. The evolution with electron number of the spin response is studied and compared with that of the density response. Predictions for the static dipole polarizability are given.

  14. Pharmaceutical and biomedical applications of quantum dots.

    Science.gov (United States)

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

    2016-05-01

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

  15. Dark pulse quantum dot diode laser.

    Science.gov (United States)

    Feng, Mingming; Silverman, Kevin L; Mirin, Richard P; Cundiff, Steven T

    2010-06-21

    We describe an operating regime for passively mode-locked quantum dot diode laser where the output consists of a train of dark pulses, i.e., intensity dips on a continuous background. We show that a dark pulse train is a solution to the master equation for mode-locked lasers. Using simulations, we study stability of the dark pulses and show they are consistent with the experimental results.

  16. Depleted Bulk Heterojunction Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Barkhouse, D. Aaron R.

    2011-05-26

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

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

    Directory of Open Access Journals (Sweden)

    LI Zhi-min

    2017-08-01

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

  18. In situ electron-beam polymerization stabilized quantum dot micelles.

    Science.gov (United States)

    Travert-Branger, Nathalie; Dubois, Fabien; Renault, Jean-Philippe; Pin, Serge; Mahler, Benoit; Gravel, Edmond; Dubertret, Benoit; Doris, Eric

    2011-04-19

    A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a "clean" electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions. © 2011 American Chemical Society

  19. Single-charge tunneling in ambipolar silicon quantum dots

    NARCIS (Netherlands)

    Müller, Filipp

    2015-01-01

    Spin qubits in coupled quantum dots (QDs) are promising for future quantum information processing (QIP). A quantum bit (qubit) is the quantum mechanical analogon of a classical bit. In general, each quantum mechanical two-level system can represent a qubit. For the spin of a single charge carrier

  20. Influence of semiconductor-dielectric transition border on the electron states in spherical quantum dots.

    CERN Document Server

    Ghazaryan, E M; Sarkisyan, H A

    2002-01-01

    Electron states in spherical quantum dots are studied, taking into account boundary conditions. The threshold habit of level appearance inside the quantum dots is revealed. The electron energy dependences on the quantum dots radius and confinement potential height

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

    Science.gov (United States)

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

    2017-08-01

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

  2. Imaging ligand-gated ion channels with quantum dots

    Science.gov (United States)

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

    2007-02-01

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

  3. Core–shell quantum dots: Properties and applications

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-07-05

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-08-03

    Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure.

  5. High performance tunnel injection InGaN/GaN quantum Dot light emitting diodes emitting in the green (λ=495nm)

    KAUST Repository

    Zhang, Meng

    2011-05-01

    InGaN/GaN self-organized quantum dots with density of (2-5)×10 10 cm-2, internal quantum efficiency of 32% and a reduced recombination lifetime of 0.6 ns were grown by plasma assisted molecular beam epitaxy. The photoluminescence spectra of the dots peak at 495 nm at 300 K. The characteristics of tunnel injection InGaN/GaN quantum dot light emitting diodes are presented. The current density at maximum efficiency is 90.2 A/cm 2, which is superior to equivalent multiquantum well devices. © 2010 Elsevier B.V. All rights reserved.

  6. Single quantum dot spectroscopy of CdSe/ZnSe grown on vicinal GaAs substrates

    Science.gov (United States)

    Makino, T.; André, R.; Gérard, J.-M.; Romestain, R.; Dang, Le Si; Bartels, M.; Lischka, K.; Schikora, D.

    2003-04-01

    We investigated the optical properties of two monolayers of CdSe sandwiched by ZnSe layers grown by molecular-beam epitaxy on GaAs substrates with a vicinal tilt of 2° in the [111] direction. By varying the spatial resolution from 10 μm down to 500 nm, sharp photoluminescence lines due to the recombination of excitons confined into quantum dots could be observed at low temperature. The dot density could be as low as ≈109 dots/cm2, which is smaller than previously reported values by at least one order of magnitude.

  7. Epitaxy of advanced nanowire quantum devices

    NARCIS (Netherlands)

    Gazibegovic, S.; Car, D.; Zhang, H.; Balk, S.C.; Logan, J.A.; Moor, M.W.A. de; Cassidy, M.C.; Schmits, R.; Xu, D.; Wang, G.; Krogstrup, P.; Veld, R.L.M. op het; Zuo, K.; Vos, Y.; Shen, J.; Bouman, D.; Shojaei, B.; Pennachio, D.; Lee, J.S.; Veldhoven, P.J. van; Koelling, S.; Verheijen, M.A.; Kouwenhoven, L.P.; Palmstrøm, C.J.; Bakkers, E.P.A.M.

    2017-01-01

    Semiconductor nanowires are ideal for realizing various low-dimensional quantum devices. In particular, topological phases of matter hosting non-Abelian quasiparticles (such as anyons) can emerge when a semiconductor nanowire with strong spin-orbit coupling is brought into contact with a

  8. Site-Control of InAs/GaAs Quantum Dots with Indium-Assisted Deoxidation

    Directory of Open Access Journals (Sweden)

    Sajid Hussain

    2016-03-01

    Full Text Available Site-controlled epitaxial growth of InAs quantum dots on GaAs substrates patterned with periodic nanohole arrays relies on the deterministic nucleation of dots into the holes. In the ideal situation, each hole should be occupied exactly by one single dot, with no nucleation onto planar areas. However, the single-dot occupancy per hole is often made difficult by the fact that lithographically-defined holes are generally much larger than the dots, thus providing several nucleation sites per hole. In addition, deposition of a thin GaAs buffer before the dots tends to further widen the holes in the [110] direction. We have explored a method of native surface oxide removal by using indium beams, which effectively prevents hole elongation along [110] and greatly helps single-dot occupancy per hole. Furthermore, as compared to Ga-assisted deoxidation, In-assisted deoxidation is efficient in completely removing surface contaminants, and any excess In can be easily re-desorbed thermally, thus leaving a clean, smooth GaAs surface. Low temperature photoluminescence showed that inhomogeneous broadening is substantially reduced for QDs grown on In-deoxidized patterns, with respect to planar self-assembled dots.

  9. Hybrid passivated colloidal quantum dot solids

    KAUST Repository

    Ip, Alex

    2012-07-29

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

  10. Nonrenewal statistics in transport through quantum dots

    Science.gov (United States)

    Ptaszyński, Krzysztof

    2017-01-01

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

  11. Single-photon emission from InAsP quantum dots embedded in density-controlled InP nanowires

    Science.gov (United States)

    Yanase, Shougo; Sasakura, Hirotaka; Hara, Shinjiro; Motohisa, Junichi

    2017-04-01

    We attempted to control the density and size of InP-based nanowires (NWs) and nanowire quantum dots (NW-QDs) during selective-area metalorganic vapor phase epitaxy. InP nanowire arrays with a 5 µm pitch and an average NW diameter d of 67 nm were successfully grown by optimization of growth conditions. InAsP quantum dots were embedded in these density-controlled InP NW arrays, and clear single-photon emission and exciton-biexciton cascaded emission were confirmed by excitation-dependent photoluminescence and photon correlation measurements.

  12. Comparative Study of 1.3 and 1.5 μm Light-Emitting Diodes GaAs-Based InAs/InGaAs and InAs/(Ga, In) (N, As) Self-Assembled Quantum Dots

    OpenAIRE

    O.A. Niasse; Ba, B.; Ndiaye, A.; F. Mbaye; A; Lo; A. Bèye; Tottereau, O

    2013-01-01

    This study presents self-assembled quantum dots structures made on GaAs substrate. The samples were grown by Molecular Beam Epitaxy (MBE) in the Stranski-Krastanow (SK) growth mode. Two types of quantum dots structures are performed under different growth conditions and are compared: the first type is composed of two structures with InAs quantum dots encapsulated with (Ga, In) (N, As) and the second one with boxes wrapped with InGaAs. The influence of encapsulation of quantum dots is highligh...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-02-08

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

  14. Resonance fluorescence from a telecom-wavelength quantum dot

    CERN Document Server

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

    2016-01-01

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

  15. Non-Markovian coherent feedback control of quantum dot systems

    Science.gov (United States)

    Xue, Shibei; Wu, Rebing; Hush, Michael R.; Tarn, Tzyh-Jong

    2017-03-01

    In this paper we present a non-Markovian coherent feedback scheme for decoherence suppression in single quantum dot systems. The feedback loop is closed via a quantum tunnelling junction between the natural source and drain baths of the quantum dot. The exact feedback-controlled non-Markovian Langevin equation is derived for describing the dynamics of the quantum dot. To deal with the nonlinear memory function in the Langevin equation, we analyse the Green’s function-based root locus, from which we show that the decoherence of the quantum dot can be suppressed via increasing the feedback coupling strength. The effectiveness of decoherence suppression induced by non-Markovian coherent feedback is demonstrated by a single quantum dot example bathed with Lorentzian noises.

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

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg

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

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

    KAUST Repository

    Liu, Huan

    2012-01-01

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

  18. Synthesis of silicon quantum dots showing high quantum efficiency.

    Science.gov (United States)

    Cho, Bomin; Baek, Sangsoo; Woo, Hee-Gweon; Sohn, Honglae

    2014-08-01

    Quantum efficiencies of Si quantum dots (QDs) have been investigated from the reaction of magnesium silicide and ammonium chloride. The change of quantum yield and optical characterization of Si QDs are measured depending on the reaction time. Highly luminescent Si QDs were obtained as the reaction time increased. Absorption measurement indicated that the Si QDs consisted of only silicon and hydrogen atom. Optical characterizations of Si QDs were measured by UV-Vis and PL spectroscopy. The size distribution and orientation of Si QDs were measured by TEM and XRD. TEM image displays the spherical Si QDs with the size of 3-4 nm. As the reaction time increased, Si QDs grew and their emission wavelength shifted to the longer wavelength. The monotonic shift of the PL as a function of excitation wavelength resulted in the excitation of different sizes of QDs that had different optical transition energies. Photoluminescence quantum yields exceeding 60% have been achieved.

  19. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

    Claudon, Julien; Munsch, Matthieu; Bleuse, Joel

    2012-01-01

    Besides microcavities and photonic crystals, photonic nanowires have recently emerged as a novel resource for solidstate quantum optics. We will review recent studies which demonstrate an excellent control over the spontaneous emission of InAs quantum dots (QDs) embedded in single-mode Ga......As photonic wires. On the basic side, we have demonstrated a strong inhibition (x 1/16) of QD SpE in thin wires (d0.95 for d~λ/n), and polarization control in elliptical nanowires. A single QD in a photonic wire is thus an attractive system to explore the physics of the "one-dimensional atom" and build novel...

  20. Quantum photonics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Kuhlmann, Andreas; Cadeddu, Davide

    2016-01-01

    We present results from the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter’s properties with the highest sensitivity. Weperform...... a detailed analysis of the noise in the device and reveal in particular the thermal excitation of mechanical modes at 4 K....

  1. Imaging Electrons in Few-Electron Quantum Dots

    Science.gov (United States)

    Fallahi, P.; Hanson, M.

    2005-03-01

    Single-electron quantum dots are important candidates for quantum information processing. We have developed a new technique to image electrons inside a single-electron quantum dot in the Coulomb blockade regime, using a scanning probe microscope (SPM) at liquid He temperatures (1). A single-electron quantum dot was formed in a two-dimensional electron gas (2DEG) inside a GaAs/AlGaAs heterostructure by surface gates. Spatial images of an electron inside the dot were obtained by fixing the tip voltage and recording the dot conductance while scanning the SPM tip above the quantum dot. The images show a ring of increased conductance about the center of the dot, where the dot conductance is on the Coulomb blockade conductance peak between 0 and 1 electrons. Simulations show that this technique can be used to extract the wavefunction of electrons inside the dot if the tip perturbation is narrower than the wave function (2). A charged SPM tip promised to be a useful tool for manipulating electrons in quantum dot circuits. 1) P. Fallahi, A.C. Bleszynski, et al submitted to Nanoletters. 2) P. Fallahi, et al Proc. 27 Int. Conf. on Physics and Semiconductors (ICPS27), Flagstaff, July 26-30, 2004, in press. *This work was supported at Harvard University by DARPA DAAD19-01-1-0659 and by the NSEC, NSF PHY-01-17795, and at UCSB by QUEST NSF Science and Technology Center.

  2. Nano-laser on silicon quantum dots

    Science.gov (United States)

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

    2011-04-01

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

  3. Colloidal Quantum Dot Photovoltaics: A Path Forward

    KAUST Repository

    Kramer, Illan J.

    2011-11-22

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

  4. Quantum computation with nuclear spins in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Christ, H.

    2008-01-24

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

  5. Plasmon assisted photonic crystal quantum dot sensors

    Science.gov (United States)

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

    2007-09-01

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

  6. Lateral excitonic switching in vertically stacked quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Jarzynka, Jarosław R.; McDonald, Peter G.; Galbraith, Ian [Institute of Photonics and Quantum Sciences, SUPA, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Shumway, John [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)

    2016-06-14

    We show that the application of a vertical electric field to the Coulomb interacting system in stacked quantum dots leads to a 90° in-plane switching of charge probability distribution in contrast to a single dot, where no such switching exists. Results are obtained using path integral quantum Monte Carlo with realistic dot geometry, alloy composition, and piezo-electric potential profiles. The origin of the switching lies in the strain interactions between the stacked dots hence the need for more than one layer of dots. The lateral polarization and electric field dependence of the radiative lifetimes of the excitonic switch are also discussed.

  7. Chains of quantum dot molecules grown on Si surface pre-patterned by ion-assisted nanoimprint lithography

    Energy Technology Data Exchange (ETDEWEB)

    Smagina, Zh. V.; Stepina, N. P., E-mail: stepina@isp.nsc.ru; Zinovyev, V. A.; Kuchinskaya, P. A. [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Lavrenteva 13, 630090 Novosibirsk (Russian Federation); Novikov, P. L.; Dvurechenskii, A. V. [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Lavrenteva 13, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogova, 2, 630090 Novosibirsk (Russian Federation)

    2014-10-13

    An original approach based on the combination of nanoimprint lithography and ion irradiation through mask has been developed for fabrication of large-area periodical pattern on Si(100). Using the selective etching of regions amorphized by ion irradiation ordered structures with grooves and ridges were obtained. The shape and depth of the relief were governed by ion energy and by the number of etching stages as well. Laterally ordered chains of Ge quantum dots were fabricated by molecular beam epitaxy of Ge on the pre-patterned Si substrates. For small amount of Ge deposited chains contain separate quantum dot molecules. The increase of deposition amount leads to overlapping of quantum dot molecules with formation of dense homogeneous chains of quantum dots. It was shown that the residual irradiation-induced bulk defects underneath the grooves suppress nucleation of Ge islands at the bottom of grooves. On pre-patterned substrates with whole defect regions, etched quantum dots grow at the bottom of grooves. The observed location of Ge quantum dots is interpreted in terms of local strain-mediated surface chemical potential which controls the sites of islands nucleation. The local chemical potential is affected by additional strain formed by the residual defects. It was shown by molecular dynamics calculations that these defects form the compressive strain at the bottom of grooves.

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

    NARCIS (Netherlands)

    Van der Wiel, W.G.

    2002-01-01

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

  9. Electron spin and charge in semiconductor quantum dots

    NARCIS (Netherlands)

    Elzerman, J.M.

    2004-01-01

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

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offe...

  11. Stark effect and polarizability of graphene quantum dots

    DEFF Research Database (Denmark)

    Pedersen, Thomas Garm

    2017-01-01

    The properties of graphene quantum dots can be manipulated via lateral electric fields. Treating electrons in such structures as confined massless Dirac fermions, we derive an analytical expression for the quadratic Stark shift valid for arbitrary angular momentum and quantum dot size. Moreover, we...

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

    DEFF Research Database (Denmark)

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

    2000-01-01

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

  13. Biexciton in nanoheterostructures of germanium quantum dots

    Science.gov (United States)

    Pokutnyi, Sergey I.

    2017-06-01

    The theory of biexciton (formed from spatially separated electrons and holes) in a nanosystem consisting of double quantum dots (QDs) of germanium synthesized in a silicon matrix is presented. It is shown that the major contribution to the biexciton binding energy is made by the energy of the exchange interaction of electrons with holes and this contribution is much more substantial than the contribution of the energy of Coulomb interaction between the electrons and holes. The position of the biexciton state energy band depends both on the mean radius of the QDs and the distance between their surfaces, which enables one to purposefully control it by varying these parameters of the nanostructure.

  14. Protease sensing using nontoxic silicon quantum dots

    Science.gov (United States)

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

    2017-08-01

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

  15. Self-polarization in spherical quantum dot

    Directory of Open Access Journals (Sweden)

    Stojanović Dušanka P.

    2015-01-01

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

  16. Polymorphic Architectures of Graphene Quantum Dots.

    Science.gov (United States)

    Kim, Sejung; Song, Youngjun; Heller, Michael J

    2017-08-01

    A systematic strategy for designing structured nanomaterials is demonstrated through self-assembly of graphene quantum dots. The approach reveals that graphene derivatives at the nanoscale assemble into various architectures of nanocrystals in a binary solution system. The shapes of the nanocrystals continue to evolve in terms of the intimate association of organic molecules with the dispersion medium, obtaining a high index faceted superlattice. This facile synthetic process provides a versatile strategy for designing particles to new structured materials systems, exploiting the crystallization of layered graphitic carbon structures within single crystals. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Graphene Quantum Dots for Theranostics and Bioimaging.

    Science.gov (United States)

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

    2016-10-01

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

  18. Transcending binary logic by gating three coupled quantum dots.

    Science.gov (United States)

    Klein, Michael; Rogge, S; Remacle, F; Levine, R D

    2007-09-01

    Physical considerations supported by numerical solution of the quantum dynamics including electron repulsion show that three weakly coupled quantum dots can robustly execute a complete set of logic gates for computing using three valued inputs and outputs. Input is coded as gating (up, unchanged, or down) of the terminal dots. A nanosecond time scale switching of the gate voltage requires careful numerical propagation of the dynamics. Readout is the charge (0, 1, or 2 electrons) on the central dot.

  19. Quantum dot blueing and blinking enables fluorescence nanoscopy.

    Science.gov (United States)

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

    2011-01-12

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

  20. Nonequilibrium composition profiles of alloy quantum dots and their correlation with the growth mode.

    Science.gov (United States)

    Niu, X B; Stringfellow, G B; Liu, Feng

    2011-08-12

    Equilibrium composition profiles (CPs) of epitaxial alloy quantum dots (QDs) are well established theoretically. However nonequilibrium CPs may occur experimentally. Using an atomistic-strain-model Monte Carlo simulation method, we demonstrate a striking correlation between the nonequilibrium CPs of QDs and the kinetic growth mode: the layer-by-layer growth (LG) and faceted growth (FG) form a core-shell structure having the triangle core of the unstrained and V-shaped core of the strained component, respectively, and both are distinctly different from the equilibrium CP. Comparing simulations with experiments, we infer that the InGaAs dots on GaAs grow by FG, while GeSi dots on Si grow first by LG followed by FG. Our findings suggest a possible method for controlling the CPs of QDs by selecting the growth mode.

  1. GaAs quantum dot molecules filled into droplet etched nanoholes

    Science.gov (United States)

    Heyn, Ch.; Küster, A.; Gräfenstein, A.; Ungeheuer, A.; Graf, A.; Hansen, W.

    2017-11-01

    We fabricate self-aligned vertically stacked GaAs quantum dot molecules (QDMs) by filling of self-assembled nanoholes in AlGaAs. The tunable nanoholes are created using local droplet etching (LDE) combining conventional molecular beam epitaxy with self-assembled, lithography-free patterning. The optical emission from single, strain-free QDMs shows clear excitonic features with linewidths below 150 μeV after optimizations of the fabrication process. This allows investigations of the coupling among the individual dots forming a QDM. In electric fields oriented along the axis of the QDM, luminescence emission from direct and indirect transitions can be clearly distinguished. Furthermore, an anti-crossing behaviour demonstrates inter-dot coupling in the QDM.

  2. 3D super-resolution imaging with blinking quantum dots

    Science.gov (United States)

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

    2013-01-01

    Quantum dots are promising candidates for single molecule imaging due to their exceptional photophysical properties, including their intense brightness and resistance to photobleaching. They are also notorious for their blinking. Here we report a novel way to take advantage of quantum dot blinking to develop an imaging technique in three-dimensions with nanometric resolution. We first applied this method to simulated images of quantum dots, and then to quantum dots immobilized on microspheres. We achieved imaging resolutions (FWHM) of 8–17 nm in the x-y plane and 58 nm (on coverslip) or 81 nm (deep in solution) in the z-direction, approximately 3–7 times better than what has been achieved previously with quantum dots. This approach was applied to resolve the 3D distribution of epidermal growth factor receptor (EGFR) molecules at, and inside of, the plasma membrane of resting basal breast cancer cells. PMID:24093439

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

    Science.gov (United States)

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

    2010-03-01

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

  4. Semiconductor quantum dot-sensitized solar cells

    Directory of Open Access Journals (Sweden)

    Jianjun Tian

    2013-10-01

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

  5. Silicon quantum dots for biological applications.

    Science.gov (United States)

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

    2014-01-01

    Semiconductor nanoparticles (or quantum dots, QDs) exhibit unique optical and electronic properties such as size-controlled fluorescence, high quantum yields, and stability against photobleaching. These properties allow QDs to be used as optical labels for multiplexed imaging and in drug delivery detection systems. Luminescent silicon QDs and surface-modified silicon QDs have also been developed as potential minimally toxic fluorescent probes for bioapplications. Silicon, a well-known power electronic semiconductor material, is considered an extremely biocompatible material, in particular with respect to blood. This review article summarizes existing knowledge related to and recent research progress made in the methods for synthesizing silicon QDs, as well as their optical properties and surface-modification processes. In addition, drug delivery systems and in vitro and in vivo imaging applications that use silicon QDs are also discussed. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Biosensing with Luminescent Semiconductor Quantum Dots

    Directory of Open Access Journals (Sweden)

    Hedi Mattoussi

    2006-08-01

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

  7. Electron states in semiconductor quantum dots.

    Science.gov (United States)

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

    2014-11-28

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

  8. Scaling of the Coulomb Energy Due to Quantum Fluctuations in the Charge on a Quantum Dot

    DEFF Research Database (Denmark)

    Molenkamp, L. W; Flensberg, Karsten; Kemerink, M.

    1995-01-01

    The charging energy of a quantum dot is measured through the effect of its potential on the conductance of a second dot. This technique allows a measurement of the scaling of the dot's charging energy with the conductance of the tunnel barriers leading to the dot. We find that the charging energy...

  9. Andreev molecules in semiconductor nanowire double quantum dots.

    Science.gov (United States)

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

    2017-09-19

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

  10. Interference and interactions in open quantum dots

    CERN Document Server

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

    2003-01-01

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

  11. Ferritin-Templated Quantum-Dots for Quantum Logic Gates

    Science.gov (United States)

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

    2005-01-01

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

  12. Colloidal quantum dot light-emitting devices

    Directory of Open Access Journals (Sweden)

    Vanessa Wood

    2010-07-01

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

  13. Quantum dots for lasers, amplifiers and computing

    Energy Technology Data Exchange (ETDEWEB)

    Bimberg, Dieter [Technische Universitaet Berlin, Hardenbergstr. 36, 10623, Berlin (Germany)

    2005-07-07

    For InAs-GaAs based quantum dot lasers emitting at 1300 nm, digital modulation showing an open eye pattern up to 12 Gb s{sup -1} at room temperature is demonstrated, at 10 Gb s{sup -1} the bit error rate is below 10{sup -12} at -2 dB m receiver power. Cut-off frequencies up to 20 GHz are realised for lasers emitting at 1.1 {mu}m. Passively mode-locked QD lasers generate optical pulses with repetition frequencies between 5 and 50 GHz, with a minimum Fourier limited pulse length of 3 ps. The uncorrelated jitter is below 1 ps. We use here deeply etched narrow ridge waveguide structures which show excellent performance similar to shallow mesa structures, but a circular far field at a ridge width of 1 {mu}m, improving coupling efficiency into fibres. No beam filamentation of the fundamental mode, low a-factors and strongly reduced sensitivity to optical feedback are observed. QD lasers are thus superior to QW lasers for any system or network. Quantum dot semiconductor optical amplifier (QD SOAs) demonstrate gain recovery times of 120-140 fs, 4-7 times faster than bulk/QW SOAs, and a net gain larger than 0.4 dB/(mm*QD-layer) providing us with novel types of booster amplifiers and Mach-Zehnder interferometers. These breakthroughs became possible due to systematic development of self-organized growth technologies.

  14. Using quantum dot photoluminescence for load detection

    Directory of Open Access Journals (Sweden)

    M. Moebius

    2016-08-01

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

  15. Study of metallothionein-quantum dots interactions.

    Science.gov (United States)

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

    2014-05-01

    Nanoparticles have gained increasing interest in medical and in vivo applications. Metallothionein (MT) is well known as a maintainer of metal ions balance in intracellular space. This is due to high affinity of this protein to any reactive species including metals and reactive oxygen species. The purpose of this study was to determine the metallothionein-quantum dots interactions that were investigated by spectral and electrochemical techniques. CuS, CdS, PbS, and CdTe quantum dots (QDs) were analysed. The highest intensity was shown for CdTe, than for CdS measured by fluorescence. These results were supported by statistical analysis and considered as significant. Further, these interactions were analysed using gel electrophoresis, where MT aggregates forming after interactions with QDs were detected. Using differential pulse voltammetry Brdicka reaction, QDs and MT were studied. This method allowed us to confirm spectral results and, moreover, to observe the changes in MT structure causing new voltammetric peaks called X and Y, which enhanced with the prolonged time of interaction up to 6 h. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. Charge-extraction strategies for colloidal quantum dot photovoltaics

    KAUST Repository

    Lan, Xinzheng

    2014-02-20

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Ferry, D K; Huang, L; Yang, R; Lai, Y-C; Akis, R, E-mail: ferry@asu.ed [School of Electrical, Computer, and Energy Engineering and Center for Solid State Electronics Research, Arizona State University, Tempe, AZ 85287-5706 (United States)

    2010-04-01

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

  18. Quantum transport in superlattice and quantum dot structures

    CERN Document Server

    Murphy, H M

    2000-01-01

    manifestation of oscillations in the current -voltage characteristics of superlattices in the Wannier-Stark transport regime when strong lateral confinement is provided due either to gaps in the folded phonon spectrum or phonon momentum meeting the condition for Bragg reflection. Current-voltage measurements are shown in this chapter for superlattice devices in the Wannier-Stark regime for a range of electric and magnetic fields (B//I). Many oscillations are clearly observed in the I(V) data presented, the possible origins of which are then fully explored. Moving away from superlattices, data involving tunnelling through quantum dots embedded in the barrier of a GaAs/AIAs/GaAs resonant tunnelling diode are presented in chapter 5. Quasi-hydrostatic pressure is used to tune tunnelling through the dots. These results lead to a new picture for the conduction band potential profile of this device, and give us important new information relating to devices incorporating self-assembled quantum dots. More importantly,...

  19. Universal decay cascade model for dynamic quantum dot initialization

    OpenAIRE

    Kashcheyevs, Vyacheslavs; Kaestner, Bernd

    2009-01-01

    Dynamic quantum dots can be formed by time-dependent electrostatic potentials in nanoelectronic devices, such as gate- or surface-acoustic-wave-driven electron pumps. Ability to control the number of captured electrons with high precision is required for applications in fundamental metrology and quantum information processing. In this work we propose and quantify a scheme to initialize quantum dots with a controllable number of electrons. It is based on the stochastic decrease in the electron...

  20. Ultraclean emission from InAsP quantum dots in defect-free wurtzite InP nanowires.

    Science.gov (United States)

    Dalacu, Dan; Mnaymneh, Khaled; Lapointe, Jean; Wu, Xiaohua; Poole, Philip J; Bulgarini, Gabriele; Zwiller, Val; Reimer, Michael E

    2012-11-14

    We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires. Using a two-step growth process combining selective-area and vapor-liquid-solid epitaxy, we grow defect-free wurtzite InP nanowires with embedded InAsP quantum dots, which are clad to diameters sufficient for waveguiding at λ ~ 950 nm. The absence of nearby traps, at both the nanowire surface and along its length in the vicinity of the quantum dot, manifests in excitonic transitions of high spectral purity. Narrow emission line widths (30 μeV) and very-pure single photon emission with a probability of multiphoton emission below 1% are achieved, both of which were not possible in previous work where stacking fault densities were significantly higher.

  1. Optical studies on a single GaAs laterally coupled quantum dot in comparison with an uncoupled quantum dot

    Science.gov (United States)

    Kim, Heedae; Song, Jin Dong

    2018-01-01

    We performed spectroscopy studies on a single GaAs laterally coupled quantum dot and an uncoupled quantum dot. Photoluminescence spectra confirmed the presence of optical coupling in the coupled quantum dot through dipole-dipole interactions. The optical coupling was investigated in terms of the integrated photoluminescence intensities and redshift of emission energies as the excitation power was increased. The excitation intensity was increased with linearly polarized light in the lateral coupling direction 1 1 bar 0 , which resulted in excitons X1 and X2 of the coupled quantum dot showing a clear photoluminescence peak shift to lower energy with drastically different power factors. These results were obtained by integrating the PL spectrum and comparing it to that of a single quantum dot. We also found that the decay rates of X1 and X2 in the coupled quantum dot increased significantly as a consequence of overlap of electron and hole wavefunctions extended via optical coupling in individual dots of the coupled quantum dot system.

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

    Science.gov (United States)

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

    2005-01-01

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

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

    DEFF Research Database (Denmark)

    Chen, Yaohui; Öhman, Filip; Mørk, Jesper

    2008-01-01

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

  4. Competitive performance of carbon "quantum" dots in optical bioimaging.

    Science.gov (United States)

    Cao, Li; Yang, Sheng-Tao; Wang, Xin; Luo, Pengju G; Liu, Jia-Hui; Sahu, Sushant; Liu, Yamin; Sun, Ya-Ping

    2012-01-01

    Carbon-based "quantum" dots or carbon dots are surface-functionalized small carbon nanoparticles. For bright fluorescence emissions, the carbon nanoparticles may be surface-doped with an inorganic salt and then the same organic functionalization. In this study, carbon dots without and with the ZnS doping were prepared, followed by gel-column fractionation to harvest dots of 40% and 60% in fluorescence quantum yields, respectively. These highly fluorescent carbon dots were evaluated for optical imaging in mice, from which bright fluorescence images were obtained. Of particular interest was the observed competitive performance of the carbon dots in vivo to that of the well-established CdSe/ZnS QDs. The results suggest that carbon dots may be further developed into a new class of high-performance yet nontoxic contrast agents for optical bioimaging.

  5. Exciton dephasing in single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    2000-01-01

    . The homogeneous and inhomogeneous broadening of InGaAs quantum dot luminescence is of central importance for the potential application of this material system in optoelectronic devices. Recent measurements of MOCVD-grown InAs/InGaAs quantum dots indicate a large homogeneous broadening at room temperature due......The homogeneous linewidth of excitonic transitions is a parameter of fundamental physical importance. In self-assembled quantum dot systems, a strong inhomogeneous broadening due to dot size fluctuations masks the homogeneous linewidth associated with transitions between individual states...... to fast dephasing. We present an investigation of the low-temperature homogeneous linewidth of individual PL lines from MBE-grown In0.5Ga0.5As/GaAs quantum dots....

  6. Ultrafast atomic-scale visualization of acoustic phonons generated by optically excited quantum dots.

    Science.gov (United States)

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

    2017-07-01

    Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots-grown by Droplet Epitaxy on AlGaAs-with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism. The transient behavior of the measured diffraction pattern reveals the nonequilibrium phonon dynamics both within the dots and in the region surrounding them. The experimental results are interpreted within the theoretical framework of a non-Markovian decoherence, according to which the optical excitation creates a localized polaron within the dot and a travelling phonon wavepacket that leaves the dot at the speed of sound. These findings indicate that integration of a phononic emitter in opto-electronic devices based on quantum dots for controlled communication processes can be fundamentally feasible.

  7. Behavior of optical bistability in multifold quantum dot molecules

    Science.gov (United States)

    Hamedi, H. R.; Mehmannavaz, M. R.

    2015-02-01

    We analyze the optical bistability (OB) behavior in a multifold quantum dot (QD) molecule composed of five quantum dots controlled by the tunneling coupling. It is shown that the optical bistability can strongly be affected by the tunneling inter-dot coupling coefficients as well as detuning parameters. In addition, we find that the rate of an incoherent pump field has a leading role in modification of the OB threshold. We then generalize our analysis to the case of multifold quantum dot molecules where the number of the quantum dots is N (with a center dot and N-1 satellite dots). We compare the OB features that could occur in a multifold QD system consist of three (N= ), four (N=\\text{4} ), and five (N = 5) quantum dots. We realize that the OB threshold increases as the number of satellite QDs increases. Such controllable optical bistability in multiple QD molecules may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  9. Quantum efficiency and oscillator strength of site-controlled InAs quantum dots

    DEFF Research Database (Denmark)

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

    2010-01-01

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

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

    NARCIS (Netherlands)

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

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

  11. A study of self-assembled InSb quantum dots grown on GaSb

    CERN Document Server

    Alphandery, E

    2002-01-01

    In this thesis, we study the system of self-assembled InSb quantum dots grown on GaSb by metalorganic vapor phase epitaxy. The luminescence of the samples is first studied as a function of different growth parameters. In the series of high growth rate samples, a 'low energy peak' is observed at 0.72-0.74 eV for longer deposition times than 2 seconds and for growth temperatures of 460-500 degC. This peak is attributed to dots that are strongly confined in the growth direction. As the growth rate is halved, a new 'high energy peak' appears in the PL spectra at 0.755-0.79 eV that we assign to another family of big alloyed quantum dots. The luminescence of the high growth rate samples is then studied as a function of excitation power, temperature and magnetic field. When the excitation power is increased the quantum dot transition increases in energy by approx 7-11 meV and further transitions are observed from the wetting layer, bulk acceptor, bound (BE3) and free excitons. Magneto-PL is used to calculate the in-...

  12. Vertical stacking of InAs quantum dots for polarization-insensitive semiconductor optical amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, T; Asada, M; Kita, T; Wada, O [Department of Electrical and Electronic Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan); Yasuoka, N, E-mail: t_inoue@person.kobe-u.ac.j [Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197 (Japan)

    2010-09-01

    In this paper, we report a control of the polarization property in quantum dot semiconductor optical amplifiers (QD-SOAs) using vertically-stacked, electronically-coupled InAs/GaAs QDs grown by molecular beam epitaxy. By optimizing the number of stacked layers and intermediate GaAs thickness, the 9-stacked QDs demonstrated the polarization-insensitive operation within 1.2 dB in the 1.3-mm optical communication band. Our results demonstrate that the electronically-coupled QDs are useful to realize the polarization-insensitive QD-SOAs.

  13. Dilute nitride InNP quantum dots: Growth and photoluminescence mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Kuang, Y. J. [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Takabayashi, K.; Kamiya, I. [Quantum Interface Laboratory, Toyota Technological Institute, Nagoya 468-8511 (Japan); Sukrittanon, S. [Material Science and Engineering Program, University of California, San Diego, La Jolla, California 92093 (United States); Pan, J. L.; Tu, C. W. [Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093 (United States)

    2014-10-27

    Self-assembled dilute nitride InNP quantum dots (QDs) in GaP matrix grown under the Stranski-Krastanov mode by gas-source molecular beam epitaxy are studied. The N-related localized states inside the InNP QDs provide a spatially direct recombination channel, in contrast to the spatially indirect channel through the strained In(N)P QDs/GaP interface states. The N incorporation into InP QDs therefore causes a blueshift and double-peak features in photoluminescence, which are not observed in other dilute nitride materials.

  14. Enhanced thermoelectric properties in boron nitride quantum-dot

    Directory of Open Access Journals (Sweden)

    Changning Pan

    Full Text Available We have investigated the ballistic thermoelectric properties in boron nitride quantum dots by using the nonequilibrium Green’s function approach and the Landauer transport theory. The result shows that the phonon transport is substantially suppressed by the interface in the quantum dots. The resonant tunneling effect of electron leads to the fluctuations of the electronic conductance. It enhances significantly the Seebeck coefficient. Combined with the low thermal conductance of phonon, the high thermoelectric figure of merit ZT ∼0.78 can be obtained at room temperature T = 300 K and ZT ∼0.95 at low temperature T = 100 K. It is much higher than that of graphene quantum dots with the same geometry parameters, which is ZT ∼0.29 at room temperature T = 300 K and ZT ∼0.48 at low temperature T = 100 K. The underlying mechanism is that the boron nitride quantum dots possess higher thermopower and lower phonon thermal conductance than the graphene quantum dots. Thus the results indicate that the thermoelectric properties of boron nitride can be significantly enhanced by the quantum dot and are better than those of graphene. Keywords: Thermoelectric properties, Boron nitride quantum dot, Electron transport, Phonon transport

  15. Long-Wavelength Infrared (LWIR) Quantum Dot Infrared Photodetector (QDIP) Focal Plane Array

    Science.gov (United States)

    Gunapala, Sarath D.; Bandara, S. V.; Liu, J. K.; Hill, C. J.; Rafol, S. B.; Mumolo, J. M.; Shott, C. A.

    2006-01-01

    We have exploited the artificial atomlike properties of epitaxially self-assembled quantum dots for the development of high operating temperature long wavelength infrared (LWIR) focal plane arrays. Quantum dots are nanometer-scale islands that form spontaneously on a semiconductor substrate due to lattice mismatch. QDIPs are expected to outperform quantum well infrared detectors (QWIPs) and are expected to offer significant advantages over II-VI material based focal plane arrays. QDIPs are fabricated using robust wide bandgap III-V materials which are well suited to the production of highly uniform LWIR arrays. We have used molecular beam epitaxy (MBE) technology to grow multi-layer LWIR quantum dot structures based on the InAs/InGaAs/GaAs material system. JPL is building on its significant QWIP experience and is basically building a Dot-in-the-Well (DWELL) device design by embedding InAs quantum dots in a QWIP structure. This hybrid quantum dot/quantum well device offers additional control in wavelength tuning via control of dot-size and/or quantum well sizes. In addition the quantum wells can trap electrons and aide in ground state refilling. Recent measurements have shown a 10 times higher photoconductive gain than the typical QWIP device, which indirectly confirms the lower relaxation rate of excited electrons (photon bottleneck) in QDPs. Subsequent material and device improvements have demonstrated an absorption quantum efficiency (QE) of approx. 3%. Dot-in-the-well (DWELL) QDIPs were also experimentally shown to absorb both 45 deg. and normally incident light. Thus we have employed a reflection grating structure to further enhance the quantum efficiency. JPL has demonstrated wavelength control by progressively growing material and fabricating devices structures that have continuously increased in LWIR response. The most recent devices exhibit peak responsivity out to 8.1 microns. Peak detectivity of the 8.1 micrometer devices has reached approx. 1 x 10(exp 10

  16. Detection of bioconjugated quantum dots passivated with different ligands for bio-applications.

    Science.gov (United States)

    Singh, Gurpal; Zaidi, Neelam Hazoor; Soni, Udit; Gautam, Manoj; Jackeray, Richa; Singh, Harpal; Sapra, Sameer

    2011-05-01

    Bioconjugation of quantum dots has resulted in a significant increase in resolution of biological fluorescent labeling. This intrinsic property of quantum dots can be utilized for sensitive detection of target analytes with high sensitivity; including pathogenic bacteria and cancer monitoring. The quantum dots and quantum dot doped silica nanoparticles exhibit prominent emission peaks when excited at 400 nm but on conjugation to model rabbit antigoat antibodies exhibit diminished intensity of emission peak at 600 nm. It shows that photoluminescence intensity of conjugated quantum dots and quantum dot doped silica nanoparticles could permit the detection of bioconjugation. Samples of conjugated and unconjugated quantum dots and quantum dot doped silica nanoparticles were subjected to enzyme linked immunosorbent assay for further confirmation of bioconjugation. In the present study ligand exchange, bioconjugation, fluorescence detection of bioconjugated quantum dots and quantum dot doped silica nanoparticles and further confirmation of bioconjugation by enzyme linked immunosorbent assay has been described.

  17. Polarizability in Quantum Dots via Correlated Quantum Monte Carlo

    Science.gov (United States)

    Colletti, L.; Pederiva, F.; Lipparini, E.; Umrigar, C. J.

    2008-06-01

    In this paper we review the calculations of charge-density and spin-density polarizabilities in small quantum dots by using a correlated Monte Carlo scheme. In the limit of small external fields, knowledge of polarizability implies, thanks to the commonly used "sum rules", prediction of the excitation energy of the dipole mode. The need of a numerical approach arises when spin-density polarizability is pursued, while the charge-density mode is analytically calculable as long as the confinement is maintained parabolic.

  18. Photolithographic process for the patterning of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-09-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-14

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

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

    Science.gov (United States)

    SalmanOgli, A.; Rostami, R.

    2013-10-01

    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.

  1. Solvothermal synthesis of InP quantum dots.

    Science.gov (United States)

    Nag, Angshuman; Sarma, D D

    2009-09-01

    We report an efficient and fast solvothermal route to prepare highly crystalline monodispersed InP quantum dots. This solvothermal route, not only ensures inert atmosphere, which is strictly required for the synthesis of phase pure InP quantum dots but also allows a reaction temperature as high as 430 degrees C, which is otherwise impossible to achieve using a typical solution chemistry; the higher reaction temperature makes the reaction more facile. This method also has a judicious control over the size of the quantum dots and thus in tuning the bandgap.

  2. Quantum Dots Microstructured Optical Fiber for X-Ray Detection

    Science.gov (United States)

    DeHaven, Stan; Williams, Phillip; Burke, Eric

    2015-01-01

    Microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide are presented. These quantum dots are applied inside the microstructured optical fibers using capillary action. The x-ray photon counts of these fibers are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The results of the fiber light output and associated effects of an acrylate coating and the quantum dot application technique are discussed.

  3. Electron transport in InAs nanowire quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Fuhrer, Andreas [Nanometer Structure Consortium, Lund Universtity, Box 118, S-221 00 Lund (Sweden); School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); Fasth, Carina; Samuelson, Lars [Nanometer Structure Consortium, Lund Universtity, Box 118, S-221 00 Lund (Sweden)

    2008-07-01

    We investigate electron transport in single and double quantum dots defined in catalytically grown InAs nanowires containing down to a single electron. We determine g-factor and strength of the spin-orbit interaction directly from excited state measurements in these few electron quantum dots. Using local gates to deplete homogeneous InAs nanowires offers a high degree of tunability for defining double quantum dots. Here we show that such systems are ideally suited to manipulate single spins and charges for electron pumping, charge read-out and spin manipulation applications.

  4. Tunable RKKY interaction in a double quantum dot nanoelectromechanical device

    Science.gov (United States)

    Parafilo, A. V.; Kiselev, M. N.

    2018-01-01

    We propose a realization of mechanically tunable Ruderman-Kittel-Kasuya-Yosida interaction in a double quantum dot nanoelectromechanical device. The coupling between spins of two quantum dots suspended above a metallic plate is mediated by conduction electrons. We show that the spin-mechanical interaction can be driven by a slow modulation of charge density in the metallic plate. We propose to use Stückelberg oscillations as a sensitive tool for detection of the spin and charge states of the coupled quantum dots. Theory of mechanical back action induced by a dynamical spin-spin interaction is discussed.

  5. Imaging GABAc Receptors with Ligand-Conjugated Quantum Dots

    Directory of Open Access Journals (Sweden)

    Ian D. Tomlinson

    2007-01-01

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

  6. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... is obtained by exciting and detecting the photoluminescence through a microscope objective which is located inside the cryostat. Furthermore, e-beam lithography and mesa etching have been used to reduce the size of the detection area to a few hundred nanometers in diameter. These techniques allow us...

  7. Germanium epitaxy on silicon

    Directory of Open Access Journals (Sweden)

    Hui Ye

    2014-03-01

    Full Text Available With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics.

  8. Finite element modelling of threading dislocation effect on polar GaN/AlN quantum dot

    Science.gov (United States)

    Jurczak, Grzegorz; Dłużewski, Paweł

    2018-01-01

    In this paper the effect of adjacent threading dislocation at the edge of the GaN/AlN quantum dot is analysed by use of the finite element analysis. Elastic as well electric effects related to dislocation core are taken into account. Two types of threading dislocations: edge- and screw-type, common for III-nitride epitaxial layers, are considered. Also, three different QD geometries are considered to estimate the impact of the threading dislocation on the quantum heterostructure. It is demonstrated that the local elastic and electric fields around dislocation affect local piezoelectric fields built-in the quantum dot. Local lattice deformation near the dislocation core reduce residual strains in the quantum dot. It is prominent in the case of edge-type dislocation. The presence of an electric charge along dislocation line provides significant shift of the total potential towards the negative values. However, estimated difference in band-to-band transition energy for edge- and screw-type dislocations are rather small, what suggest low sensitivity to the charge density along dislocation line. Unexpectedly, local strain field around the edge-type dislocation, slightly compensate the negative affect of the electrostatic potential.

  9. PREFACE: Quantum dots as probes in biology

    Science.gov (United States)

    Cieplak, Marek

    2013-05-01

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

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

    Directory of Open Access Journals (Sweden)

    Altaisky Mikhail V.

    2016-01-01

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

  11. Excitonic physics in a Dirac quantum dot

    Science.gov (United States)

    Raca, V.; Milovanović, M. V.

    2017-11-01

    We present a description of vacuum polarization in a circular Dirac quantum dot in two spatial dimensions assuming α —the relative strength of the Coulomb interaction small enough to render an approximation with a single electron (hole) lowest energy level relevant. Applying this approximation, we find that for αc≈1.05 the lowest level is half filled irrespective of the number of flavors that are present. The ground state can be represented as a superposition of particular (even number) excitonic states which constitute an excitonic cloud that evolves in a crossover manner. The ground state is degenerate with an intervalley excitonic state at αc≈1.05 , a critical strength, that in our approximation marks a point with single electron and exciton resonances.

  12. Tellurium quantum dots: Preparation and optical properties

    Science.gov (United States)

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

    2017-08-01

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

  13. Electronic levels of cubic quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Aristone, Flavio [Federal De Mato Grosso Do Sul Univ., Campo Grande (Brazil); Sanchez-Dehesa, Jose [Autonoma De Madrid Univ., Madrid (Spain); Marques, Gilmar E. [Federal De Sao Carlos Univ., Sao Carlos (Brazil)

    2003-09-01

    We introduce an efficient variational method to solve the three-dimensional Schroedinger equation for any arbitrary potential V(x,y,z). The method uses a basis set of localized functions which are build up as products of one-dimensional cubic {beta}-splines. We calculated the energy levels of GaAs/AlGaAs cubic quantum dots and make a comparison with the results from two well-known simplification schemes based on a decomposition of the full potential problem into three separate one-dimensional problems. We show that the scheme making a sequential decomposition gives eigenvalues in better agreement with the ones obtained variationally, but an exact solution is necessary when looking for highly precise values.

  14. Semiconductor quantum dot-inorganic nanotube hybrids.

    Science.gov (United States)

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

    2012-03-28

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

  15. Recent advances in quantum dot surface chemistry.

    Science.gov (United States)

    Hines, Douglas A; Kamat, Prashant V

    2014-03-12

    Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, this review addresses three main issues: (i) how surface chemistry affects the optical properties of QDs, (ii) how it influences the excited state dynamics, and (iii) how one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles, and in self-assembled QD monolayers.

  16. Double quantum dots in carbon nanotubes

    Science.gov (United States)

    von Stecher, Javier; Wunsch, Bernhard; Lukin, Mikhail; Demler, Eugene; Rey, Ana Maria

    2010-03-01

    We study the behavior of few-electrons confined in a double-well quantum dot in semiconducting carbon nanotubes. These carbon nanostructures exhibit richer physics than GaAs ones due to the additional valley degree of freedom. We calculate and characterize the low energy eigenstates in the presence of a magnetic field and double-well detuning. Spin-orbit coupling lifts the spin and valley degeneracy and, in the presence of exchange interactions, leads, at small detunings and weak magnetic fields, to a spin-valley antisymmetric two-electron ground state which is not a pure spin-singlet state. At large detuning, the strong Coulomb interactions accessible in carbon nanotubes can substantially modify the non-interacting eigenstates via higher orbital-level mixing. The latter manifest in current transport experiments by the disappearance of the Pauli blockade.

  17. Application of Quantum Dots in Biological Imaging

    Directory of Open Access Journals (Sweden)

    Shan Jin

    2011-01-01

    Full Text Available Quantum dots (QDs are a group of semiconducting nanomaterials with unique optical and electronic properties. They have distinct advantages over traditional fluorescent organic dyes in chemical and biological studies in terms of tunable emission spectra, signal brightness, photostability, and so forth. Currently, the major type of QDs is the heavy metal-containing II-IV, IV-VI, or III-V QDs. Silicon QDs and conjugated polymer dots have also been developed in order to lower the potential toxicity of the fluorescent probes for biological applications. Aqueous solubility is the common problem for all types of QDs when they are employed in the biological researches, such as in vitro and in vivo imaging. To circumvent this problem, ligand exchange and polymer coating are proven to be effective, besides synthesizing QDs in aqueous solutions directly. However, toxicity is another big concern especially for in vivo studies. Ligand protection and core/shell structure can partly solve this problem. With the rapid development of QDs research, new elements and new morphologies have been introduced to this area to fabricate more safe and efficient QDs for biological applications.

  18. High density InAlAs/GaAlAs quantum dots for non-linear optics in microcavities

    Energy Technology Data Exchange (ETDEWEB)

    Kuszelewicz, R.; Benoit, J.-M.; Barbay, S.; Lemaitre, A.; Patriarche, G.; Meunier, K. [Laboratoire de Photonique et Nanostructures, Route de Nozay, Marcoussis 91460 (France); Tierno, A.; Ackemann, T. [University of Strathclyde, Glasgow (United Kingdom)

    2012-02-15

    Structural and optical properties of InAlAs/GaAlAs quantum dots grown by molecular beam epitaxy are studied using transmission electron microscopy and temperature- and time-resolved photoluminescence. The control of the recombination lifetime (50 ps-1.25 ns) and of the dot density (5.10{sup -8}-2.10{sup 11} cm{sup -3}) strongly suggest that these material systems can find wide applications in opto-electronic devices as focusing non-linear dispersive materials as well as fast saturable absorbers.

  19. Electrical And Optical Properties Of Colloidal Quantum Dots And Quantum Dot Networks: Role Of Surface States And Using Biomolecular Links In Network Assembly

    National Research Council Canada - National Science Library

    Stroscio, Michael A; Dutta, Mitra; Ramadurai, Dinakar; Shi, Peng; Li, Yang; Alexson, Dimitri; Kohanpour, Babak; Sethuraman, Akil; Saini, Vikas; Raichura, Amit; Yang, Jianyong

    2004-01-01

    .... Absorption spectra and photoluminescence (PL) spectra of colloidal cadmium sulfide (CdS) quantum dots are analyzed to investigate the role of surface states in determining the electrical and optical properties of these semiconductor quantum dots...

  20. Influence of electron-phonon interaction on quantum phase transition in a triangular triple quantum dot

    Science.gov (United States)

    Kim, Chang-Il; Kang, Chol-Jin; Yun, Chol-Song; Choe, Myong-Il; Ahn, Jong-Kwan

    2017-11-01

    We investigate the quantum phase transition in triple quantum dot system with triangular geometry, in which one of the dots is connected to metallic leads and electrons in the dot interact with a local phonon mode. The influence of electron-phonon interaction on the quantum phase transition between local moment phase and Kondo screened strong coupling phase at the particle-hole symmetric point is studied based on the analytical arguments and the numerical renormalization group method. The results show that the critical value of tunnel-coupling between side dots decreases with the increase of electron-phonon coupling in "spin Kondo" regime. Furthermore, at a certain critical value of electron-phonon coupling, there appears only strong coupling phase, irrespective of tunnel-coupling between dots. The study of the influence of electron-phonon interaction on the quantum phase transition in triple quantum dot has the great importance for clarifying the mechanism of Kondo screening in the system.

  1. Collective Rabi dynamics of electromagnetically coupled quantum-dot ensembles

    Science.gov (United States)

    Glosser, Connor; Shanker, B.; Piermarocchi, Carlo

    2017-09-01

    Rabi oscillations typify the inherent nonlinearity of optical excitations in quantum dots. Using an integral kernel formulation to solve the three-dimensional Maxwell-Bloch equations in ensembles of up to 104 quantum dots, we observe features in Rabi oscillations due to the interplay of nonlinearity, nonequilibrium excitation, and electromagnetic coupling between the dots. This approach allows us to observe the dynamics of each dot in the ensemble without resorting to spatial averages. Our simulations predict synchronized multiplets of dots that exchange energy, dots that dynamically couple to screen the effect of incident external radiation, localization of the polarization due to randomness and interactions, as well as wavelength-scale regions of enhanced and suppressed polarization.

  2. Non-equilibrium Josephson current through interacting quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Pala, M.G. [IMEP-MINATEC (UMR CNRS/INPG/UJF), Grenoble (France); Governale, M.; Koenig, J. [Inst. fuer Theoretische Physik III, Ruhr-Univ. Bochum (Germany)

    2007-07-01

    We study transport through a quantum dot weakly coupled to both normal and superconducting leads. To this aim, we generalize a diagrammatic real-time transport theory to account for superconductivity in the leads. In particular, we consider a system consisting of a quantum dot tunnel coupled to one normal and two superconducting leads. A finite voltage can be applied between the normal and the superconducting leads to drive the dot out of equilibrium. The dot is described by a single, spin-degenerate level, with arbitrary Coulomb repulsion U. The tunnel coupling to the superconducting leads induces a coherent superposition of the empty and doubly occupied dot states (proximity effect). In turn, this may mediate a Josephson current between the two superconductors. We find a situation in which the Josephson current is switched on due to the interplay of Coulomb interaction and non-equilibrium in the dot. (orig.)

  3. Non-equilibrium transport in a series of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Xu Qingqiang; Xiong Shijie [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China)

    2006-11-15

    We investigate non-equilibrium transport properties in a series of quantum dots in which the Kondo resonance is influenced by the coupling between dots. Based on the Anderson Hamiltonian in the strongly interacting limit, we show the splitting of the Kondo resonance at the Fermi surface and the appearance of negative differential conductance when the magnitude of the interdot coupling is in the order of the coupling between the dots and the leads. We illustrate the relationship between the negative differential conductance and the local densities of states at the dots under different biases. We also show the profile of energies of dots in the series when a finite bias is applied. Furthermore, the differences in transport properties between even and odd numbers of quantum dots in the series are investigated.

  4. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications

    Science.gov (United States)

    Wen, Lin; Qiu, Liping; Wu, Yongxiang; Hu, Xiaoxiao; Zhang, Xiaobing

    2017-01-01

    Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided. PMID:28788080

  5. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications.

    Science.gov (United States)

    Wen, Lin; Qiu, Liping; Wu, Yongxiang; Hu, Xiaoxiao; Zhang, Xiaobing

    2017-07-28

    Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

  6. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications

    Directory of Open Access Journals (Sweden)

    Lin Wen

    2017-07-01

    Full Text Available Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

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

    Science.gov (United States)

    Usman, Muhammad

    Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined

  8. Comparative analysis of germanium–silicon quantum dots formation on Si(100), Si(111) and Sn/Si(100) surfaces

    Science.gov (United States)

    Lozovoy, Kirill; Kokhanenko, Andrey; Voitsekhovskii, Alexander

    2018-02-01

    In this paper theoretical modeling of formation and growth of germanium–silicon quantum dots in the method of molecular beam epitaxy (MBE) on different surfaces is carried out. Silicon substrates with crystallographic orientations (100) and (111) are considered. Special attention is paid to the question of growth of quantum dots on the silicon surface covered by tin, since germanium–silicon–tin system is extremely important for contemporary nano- and optoelectronics: for creation of photodetectors, solar cells, light-emitting diodes, and fast-speed transistors. A theoretical approach for modeling growth processes of such semiconductor compounds during the MBE is presented. Both layer-by-layer and island nucleation stages in the Stranski–Krastanow growth mode are described. A change in free energy during transition of atoms from the wetting layer to an island, activation barrier of the nucleation, critical thickness of 2D to 3D transition, as well as surface density and size distribution function of quantum dots in these systems are calculated with the help of the established model. All the theoretical speculations are carried out keeping in mind possible device applications of these materials. In particular, it is theoretically shown that using of the Si(100) surface covered by tin as a substrate for Ge deposition may be very promising for increasing size homogeneity of quantum dot array for possible applications in low-noise selective quantum dot infrared photodetectors.

  9. Controlled Photon Switch Assisted by Coupled Quantum Dots

    Science.gov (United States)

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

    2015-01-01

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

  10. Quantum dot conjugates in a sub-micrometer fluidic channel

    Science.gov (United States)

    Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.

    2010-04-13

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  11. Quenched dynamics of entangled states in correlated quantum dots

    Science.gov (United States)

    Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.

    2017-10-01

    The time evolution of an initially prepared entangled state in the system of coupled quantum dots has been analyzed by means of two different theoretical approaches: equations of motion for all orders localized electron correlation functions, considering interference effects, and kinetic equations for the pseudoparticle occupation numbers with constraint on the possible physical states. Results obtained by means of different approaches were carefully analyzed and compared to each other. Revealing a direct link between concurrence (degree of entanglement) and quantum dots pair correlation functions allowed us to follow the changes of entanglement during the time evolution of the coupled quantum dots system. It was demonstrated that the degree of entanglement can be controllably tuned during the time evolution of quantum dots system.

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

    DEFF Research Database (Denmark)

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

    is coupled efficiently to a single enhanced mode. One popular approach has been to couple single quantum dots to a nanocavity but a limiting factor in this configuration is that in order to apply the photon it should subsequently be coupled out of the cavity, reducing the overall efficiency significantly....... An alternative approach is to couple the quantum dot directly to the propagating mode of a photonic waveguide. We demonstrate the coupling of single quantum dots to a photonic crystal waveguide using time-resolved spontaneous emission measurements. A pronounced effect is seen in the decay rates of dots coupled......Efficient and high quality single-photon sources is a key element in quantum information processing using photons. As a consequence, much current research is focused on realizing all-solid-state nanophotonic single-photon sources. Single photons can be harvested with high efficiency if the emitter...

  13. Quantum Dots in the Therapy: Current Trends and Perspectives.

    Science.gov (United States)

    Pohanka, Miroslav

    2017-01-01

    Quantum dots are an emerging nanomaterial with broad use in technical disciplines; however, their application in the field of biomedicine becomes also relevant and significant possibilities have appeared since the discovery in 1980s. The current review is focused on the therapeutic applications of quantum dots which become an emerging use of the particles. They are introduced as potent carriers of drugs and as a material well suited for the diagnosis of disparate pathologies like visualization of cancer cells or pathogenic microorganisms. Quantum dots toxicity and modifications for the toxicity reduction are discussed here as well. Survey of actual papers and patents in the field of quantum dots use in the biomedicine is provided. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  14. Nonequilibrium electron transport through quantum dots in the Kondo regime

    DEFF Research Database (Denmark)

    Wölfle, Peter; Paaske, Jens; Rosch, Achim

    2005-01-01

    Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how...

  15. Coal as an abundant source of graphene quantum dots

    National Research Council Canada - National Science Library

    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

    .... 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...

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

    Energy Technology Data Exchange (ETDEWEB)

    Abdelsalam, Hazem, E-mail: hazem.abdelsalam@etu.u-picardie.fr [Laboratory of Condensed Matter Physics, University of Picardie, Amiens 80039 (France); Department of Theoretical Physics, National Research Center, Cairo 12622 (Egypt); Talaat, Mohamed H. [Physics Department, Faculty of Science, Ain Shams University, Cairo (Egypt); Lukyanchuk, Igor [Laboratory of Condensed Matter Physics, University of Picardie, Amiens 80039 (France); L. D. Landau Institute for Theoretical Physics, Moscow (Russian Federation); Portnoi, M. E. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Saroka, V. A., E-mail: v.saroka@exeter.ac.uk [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Institute for Nuclear Problems, Belarusian State University, Bobruiskaya 11, 220030 Minsk (Belarus)

    2016-07-07

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

  17. Graphene quantum dots as the electrolyte for solid state supercapacitors

    National Research Council Canada - National Science Library

    Zhang, Su; Li, Yutong; Song, Huaihe; Chen, Xiaohong; Zhou, Jisheng; Hong, Song; Huang, Minglu

    2016-01-01

    We propose that graphene quantum dots (GQDs) with a sufficient number of acidic oxygen-bearing functional groups such as -COOH and -OH can serve as solution- and solid- type electrolytes for supercapacitor...

  18. Quantum dot conjugates in a sub-micrometer fluidic channel

    Science.gov (United States)

    Stavis, Samuel M [Ithaca, NY; Edel, Joshua B [Brookline, MA; Samiee, Kevan T [Ithaca, NY; Craighead, Harold G [Ithaca, NY

    2008-07-29

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  19. Electronic structure of double Ge quantum dots in Si

    Science.gov (United States)

    Yakimov, A. I.

    2012-09-01

    Theoretical investigations of the electronic structure of elastically stressed double Ge quantum dots in Si performed in the six-band kp approximation with the Bir-Pikus Hamiltonian and with the configuration interaction method are reviewed. The existence of the antibonding ground state of holes has been revealed. It has been found that, when quantum dots approach each other, the exchange energy of two-particle states has a minimum at the point of the intersection of bonding and antibonding levels; the singlet and triplet states at this point are degenerate. For the lowest spin singlet, it has been revealed that Coulomb correlations in the motion of two holes are manifested in the localization of the two-particle wavefunction at opposite quantum dots when the distance between the dots increases. It has been shown that the degree of entanglement of the singlet quantum states reaches 50% in the case of the manifestation of such spatial correlations.

  20. Mini array of quantum Hall devices based on epitaxial graphene

    Energy Technology Data Exchange (ETDEWEB)

    Novikov, S.; Lebedeva, N. [Department of Micro and Nanosciences, Aalto University, Micronova, Tietotie 3, Espoo (Finland); Hämäläinen, J.; Iisakka, I.; Immonen, P.; Manninen, A. J.; Satrapinski, A. [VTT Technical Research Centre of Finland Ltd., Centre for Metrology MIKES, P.O. Box 1000, 02044 VTT (Finland)

    2016-05-07

    Series connection of four quantum Hall effect (QHE) devices based on epitaxial graphene films was studied for realization of a quantum resistance standard with an up-scaled value. The tested devices showed quantum Hall plateaux R{sub H,2} at a filling factor v = 2 starting from a relatively low magnetic field (between 4 T and 5 T) when the temperature was 1.5 K. The precision measurements of quantized Hall resistance of four QHE devices connected by triple series connections and external bonding wires were done at B = 7 T and T = 1.5 K using a commercial precision resistance bridge with 50 μA current through the QHE device. The results showed that the deviation of the quantized Hall resistance of the series connection of four graphene-based QHE devices from the expected value of 4×R{sub H,2} = 2 h/e{sup 2} was smaller than the relative standard uncertainty of the measurement (<1 × 10{sup −7}) limited by the used resistance bridge.

  1. Bismides: 2D structures and quantum dots

    Science.gov (United States)

    Pačebutas, Vaidas; Butkutė, Renata; Čechavičius, Bronislovas; Stanionytė, Sandra; Pozingytė, Evelina; Skapas, Martynas; Selskis, Algirdas; Geižutis, Andrejus; Krotkus, Arūnas

    2017-09-01

    The growth and characterization of ternary GaAsBi and quaternary GaInAsBi compound quantum wells (QWs) on GaAs substrates is presented in this study. The influence of technological parameters, such as different growth modes, substrate temperatures, beam equivalent pressure ratios and thermal treating on structural and luminescent properties of QWs is discussed. The complex structural investigations using x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy revealed high crystal structure, smooth surfaces and abrupt interfaces of both GaAsBi and GaInAsBi QWs. The temperature dependent photoluminescence measurements demonstrated emission wavelengths up to 1.43 µm in room temperature PL spectra measured for GaAsBi/GaAs QWs containing 12% Bi, whereas GaInAsBi QWs with 4.2% of bismuth inserted between GaAs barriers has reached 1.25 µm. Moreover, the annealing at high temperatures of GaAsBi/AlAs QWs stimulated agglomeration of bismuth to quantum dots in the well layers, emitting at 1.5 µm. The achieved wavelengths are the longest ones declared for the GaAsBi and GaInAsBi QW structures grown on the GaAs substrate, therefore bismide-based QWs are the promising structures for applications in infrared devices.

  2. Anisotropic Pauli spin blockade in hole quantum dots

    NARCIS (Netherlands)

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

    2016-01-01

    We present measurements on gate-defined double quantum dots in Ge-Si core-shell nanowires, which we tune to a regime with visible shell filling in both dots. We observe a Pauli spin blockade and can assign the measured leakage current at low magnetic fields to spin-flip cotunneling, for which we

  3. The Wigner molecule in a 2D quantum dot

    OpenAIRE

    Akman, N.; Tomak, M.

    1999-01-01

    The charge density and pair correlation function of three interacting electrons confined within a two-dimensional disc-like hard wall quantum dot are calculated by full numerical diagonalization of the Hamiltonian. The formation of a Wigner-molecule in the form of equilateral triangular configuration for electrons is observed as the size of the dot is increased.

  4. Electron Energy Level Statistics in Graphene Quantum Dots

    NARCIS (Netherlands)

    De Raedt, H.; Katsnellson, M. I.; Katsnelson, M.I.

    2008-01-01

    Motivated by recent experimental observations of size quantization of electron energy levels in graphene quantum dots [7] we investigate the level statistics in the simplest tight-binding model for different dot shapes by computer simulation. The results are in a reasonable agreement with the

  5. Ultrafast gain and index dynamics in quantum dot amplifiers

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang; Mørk, Jesper

    1999-01-01

    The ultrafast dynamics of gain and refractive index in an InAs/GaAs quantum dot amplifier are investigated at room temperature. The gain is observed to recover with a 90 fs time constant, ruling out problems of slow carrier capture into the dots, and making this component promising for high...

  6. Long lived coherence in self-assembled quantum dots

    DEFF Research Database (Denmark)

    Birkedal, Dan; Leosson, Kristjan; Hvam, Jørn Märcher

    2001-01-01

    We report measurements of ultralong coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mu eV, which is significantly smaller than the linewidth observed in single-dot lum...

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

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Vijendra, E-mail: vsmedphysics@gmail.com; Swami, O. P., E-mail: omg1789@gmail.com; Nagar, A. K., E-mail: ajaya.nagar@gmail.com [Department of Physics, Govt. Dungar College, Bikaner, Rajasthan 334001 (India); Taneja, S., E-mail: sachintaneja9@gmail.com [Department of Radiotherapy, CHAF Bangalore, Karnataka 560007 (India)

    2016-05-06

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

  8. Dispersive microwave readout of a silicon double quantum dot

    Science.gov (United States)

    Schmidt, Andrew; Henry, Edward; House, M. G.; Wang, Y. T.; Lo, C. C.; Li, H.; Greenman, L.; Pan, H.; Xiao, M.; Whaley, K. B.; Jiang, H. W.; Yablonovitch, E.; Bokor, J.; Siddiqi, I.

    2012-02-01

    Microwave resonators coupled to quantum systems have been used for fast dispersive measurement in several different architectures in solid state and atomic physics. The electronic states of a semiconductor quantum dot represent a promising candidate for quantum information processing. Our work is geared toward developing a fast, non-demolition readout of a semiconductor qubit as realized in silicon by coupling to a superconducting resonant circuit. We report progress on a novel design of a lateral double quantum dot with a unique accumulation gate that allows for control of the spatial location of the 2DEG on the device, allowing the lossy 2DEG to be decoupled from the resonator.

  9. Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Cundiff, Steven T. [Univ. of Colorado, Boulder, CO (United States)

    2016-05-03

    This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.

  10. Ultrafast optical signal processing using semiconductor quantum dot amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper

    2002-01-01

    The linear and nonlinear properties of quantum dot amplifiers are discussed on the basis of an extensive theoretical model. These devices show great potential for linear amplification as well as ultrafast signal processing.......The linear and nonlinear properties of quantum dot amplifiers are discussed on the basis of an extensive theoretical model. These devices show great potential for linear amplification as well as ultrafast signal processing....

  11. Noise and saturation properties of semiconductor quantum dot optical amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper

    2002-01-01

    We present a detailed theoretical analysis of quantum dot optical amplifiers. Due to the presence of a reservoir of wetting layer states, the saturation and noise properties differ markedly from bulk or QW amplifiers and may be significantly improved.......We present a detailed theoretical analysis of quantum dot optical amplifiers. Due to the presence of a reservoir of wetting layer states, the saturation and noise properties differ markedly from bulk or QW amplifiers and may be significantly improved....

  12. Spin-orbit-enhanced Wigner localization in quantum dots

    DEFF Research Database (Denmark)

    Cavalli, Andrea; Malet, F.; Cremon, J. C.

    2011-01-01

    We investigate quantum dots with Rashba spin-orbit coupling in the strongly-correlated regime. We show that the presence of the Rashba interaction enhances the Wigner localization in these systems, making it achievable for higher densities than those at which it is observed in Rashba-free quantum...... dots. Recurring shapes in the pair distribution functions of the yrast spectrum, which might be associated with rotational and vibrational modes, are also reported....

  13. Ultrafast optical properties of lithographically defined quantum dot amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Miaja-Avila, L.; Verma, V. B.; Mirin, R. P.; Silverman, K. L. [Quantum Electronics and Photonics Division, National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Coleman, J. J. [Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801 (United States)

    2014-02-10

    We measure the ultrafast optical response of lithographically defined quantum dot amplifiers at 40 K. Recovery of the gain mostly occurs in less than 1 picosecond, with some longer-term transients attributable to carrier heating. Recovery of the absorption proceeds on a much longer timescale, representative of relaxation between quantum dot levels and carrier recombination. We also measure transparency current-density in these devices.

  14. Quantum Dot Semiconductor Optical Amplifiers - Physics and Applications

    OpenAIRE

    Berg, Tommy Winther; Mørk, Jesper

    2004-01-01

    This thesis describes the physics and applications of quantum dot semiconductor optical amplifiers based on numerical simulations. These devices possess a number of unique properties compared with other types of semiconductor amplifiers, which should allow enhanced performance of semiconductor devices in communication systems in the future. The basic properties of quantum dot devices are investigated, especially regarding the potential of realizing amplification and signal processing without ...

  15. High-Temperature Luminescence Quenching of Colloidal Quantum Dots

    OpenAIRE

    Zhao, Y.; Riemersma, C.; Pietra, F; de Mello Donega, C.; Meijerink, A.

    2012-01-01

    Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300–500 K) luminescence studies are reported for highly efficient CdSe core–shell quantum dots (QDs), aimed at obtaining insight into temperature quenching of QD emission. Through thermal cycling (yoyo) experiments for QDs in polymer matrices, reversible and irreversible luminescence quen...

  16. Programmable Periodicity of Quantum Dot Arrays with DNA Origami Nanotubes

    OpenAIRE

    Bui, Hieu; Onodera, Craig; Kidwell, Carson; Tan, Yerpeng; Graugnard, Elton; Kuang, Wan; Lee, Jeunghoon; Knowlton, William B.; Yurke, Bernard; Hughes, William L.

    2010-01-01

    To fabricate quantum dot arrays with programmable periodicity, functionalized DNA origami nanotubes were developed. Selected DNA staple strands were biotin-labeled to form periodic binding sites for streptavidin-conjugated quantum dots. Successful formation of arrays with periods of 43 and 71 nm demonstrates precise, programmable, large-scale nanoparticle patterning; however, limitations in array periodicity were also observed. Statistical analysis of AFM images revealed evidence for steric h...

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

    Science.gov (United States)

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

    2017-10-01

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

  18. Noncovalently silylated carbon nanotubes decorated with quantum dots

    OpenAIRE

    Bottini, Massimo; Magrini, Andrea; Dawson, Marcia I.; Rosato, Nicola; Bergamaschi, Antonio; Mustelin, Tomas

    2007-01-01

    A nanoassembly of single-walled carbon nanotubes coated by a thin layer of silica followed by quantum dots was prepared. That the quantum dots retained their photoluminescent properties after deposition onto the silylated carbon nanotubes suggests that the thin layer of silica prevented the quenching of the fluorescence by the nanotubes. This fluorescent nanoassembly represents an excellent building block for photoelectric and optical devices and biological nanoprobes.

  19. Solution-Processed Nanocrystal Quantum Dot Tandem Solar Cells

    KAUST Repository

    Choi, Joshua J.

    2011-06-03

    Solution-processed tandem solar cells created from nanocrystal quantum dots with size-tuned energy levels are demonstrated. Prototype devices featuring interconnected quantum dot layers of cascaded energy gaps exhibit IR sensitivity and an open circuit voltage, V oc, approaching 1 V. The tandem solar cell performance depends critically on the optical and electrical properties of the interlayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Science.gov (United States)

    Qiu, Yueming

    2006-01-01

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

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

    Science.gov (United States)

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

    2009-06-01

    Medicinal applications of luminescent semiconductor quantum dots are of growing interest. In spite of the fact that their fabrication and imaging applications have been extensively investigated for the last decade, very little is documented on photodynamic action of quantum dots. In this study we demonstrate generation of singlet oxygen and other radical species upon exposure of quantum dots to blue light and therapeutic red light. Extent of radical production can be readily modified by antioxidants. Lay and scientific communities are two sites concerning potential hazards and enthusiastic applications of nanotechnology. Synthesis of quantum dots composed of less toxic materials is of great interest. A new candidate is a ubiquitous element carbon, which on nanoscale exhibits strong photoluminescence.

  2. Ultrafast atomic-scale visualization of acoustic phonons generated by optically excited quantum dots

    Directory of Open Access Journals (Sweden)

    Giovanni M. Vanacore

    2017-07-01

    Full Text Available Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots—grown by Droplet Epitaxy on AlGaAs—with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism. The transient behavior of the measured diffraction pattern reveals the nonequilibrium phonon dynamics both within the dots and in the region surrounding them. The experimental results are interpreted within the theoretical framework of a non-Markovian decoherence, according to which the optical excitation creates a localized polaron within the dot and a travelling phonon wavepacket that leaves the dot at the speed of sound. These findings indicate that integration of a phononic emitter in opto-electronic devices based on quantum dots for controlled communication processes can be fundamentally feasible.

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

    NARCIS (Netherlands)

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

    2016-01-01

    We define single quantum dots of lengths varying from 60 nm up to nearly half a micron in Ge-Si core-shell nanowires. The charging energies scale inversely with the quantum dot length between 18 and 4 meV. Subsequently, we split up a long dot into a double quantum dot with a separate control over

  4. Colloidal quantum dot photovoltaics: The effect of polydispersity

    KAUST Repository

    Zhitomirsky, David

    2012-02-08

    The size-effect tunability of colloidal quantum dots enables facile engineering of the bandgap at the time of nanoparticle synthesis. The dependence of effective bandgap on nanoparticle size also presents a challenge if the size dispersion, hence bandgap variability, is not well-controlled within a given quantum dot solid. The impact of this polydispersity is well-studied in luminescent devices as well as in unipolar electronic transport; however, the requirements on monodispersity have yet to be quantified in photovoltaics. Here we carry out a series of combined experimental and model-based studies aimed at clarifying, and quantifying, the importance of quantum dot monodispersity in photovoltaics. We successfully predict, using a simple model, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using this same experimentally tested model the implications of a broadened quantum dot population on device performance. We report that present-day colloidal quantum dot photovoltaic devices with typical inhomogeneous linewidths of 100-150 meV are dominated by surface traps, and it is for this reason that they see marginal benefit from reduction in polydispersity. Upon eliminating surface traps, achieving inhomogeneous broadening of 50 meV or less will lead to device performance that sees very little deleterious impact from polydispersity. © 2012 American Chemical Society.

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

    Science.gov (United States)

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

    2014-11-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Schindel, Daniel G. [Department of Mathematics and Statistics, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB, R3B 2E9 (Canada); Singh, Mahi R. [Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 3K7 (Canada)

    2014-03-31

    We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

  7. Rhizopus stolonifer mediated biosynthesis of biocompatible cadmium chalcogenide quantum dots.

    Science.gov (United States)

    Mareeswari, P; Brijitta, J; Harikrishna Etti, S; Meganathan, C; Kaliaraj, Gobi Saravanan

    2016-12-01

    We report an efficient method to biosynthesize biocompatible cadmium telluride and cadmium sulphide quantum dots from the fungus Rhizopus stolonifer. The suspension of the quantum dots exhibited purple and greenish-blue luminescence respectively upon UV light illumination. Photoluminescence spectroscopy, X-ray diffraction, and transmission electron microscopy confirms the formation of the quantum dots. From the photoluminescence spectrum the emission maxima is found to be 424 and 476nm respectively. The X-ray diffraction of the quantum dots matches with results reported in literature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability evaluation carried out on 3-days transfer, inoculum 3×10(5) cells, embryonic fibroblast cells lines shows that more than 80% of the cells are viable even after 48h, indicating the biocompatible nature of the quantum dots. A good contrast in imaging has been obtained upon incorporating the quantum dots in human breast adenocarcinoma Michigan Cancer Foundation-7 cell lines. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Nonequilibrium transport of helical Luttinger liquids through a quantum dot

    Science.gov (United States)

    Chao, Sung-Po; Silotri, Salman A.; Chung, Chung-Hou

    2013-08-01

    We study a steady-state nonequilibrium transport between two interacting helical edge states of a two-dimensional topological insulator, described by helical Luttinger liquids, through a quantum dot. For a noninteracting dot, the current is obtained analytically by including the self-energy correction to the dot's Green function. For an interacting dot, we use the equation-of-motion method to study the influence of weak on-site Coulomb interaction on the transport. We find the metal-to-insulator quantum phase transition for attractive or repulsive interactions in the leads when the magnitude of the interaction strength characterized by a charge sector Luttinger parameter K goes beyond a critical value. The critical Luttinger parameter Kcr depends on the hopping strengths between the dot and the leads, as well as the energy level of the dot with respect to the Fermi levels of the leads, ranging from the weak-interaction regime for the dot level off-resonance to the strong-interaction regime for the dot in resonance with the equilibrium Fermi level. Near the transition, there are various singular behaviors of current noise, dot density of state, and the decoherence rate (inverse of lifetime) of the dot, which are briefly discussed.

  9. High quantum yield ZnO quantum dots synthesizing via an ultrasonication microreactor method.

    Science.gov (United States)

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

    2016-11-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. Structural and electrooptical characteristics of quantum dots emitting at 1.3 μm on gallium arsenide

    DEFF Research Database (Denmark)

    Fiore, A.; Oesterle, U.; Stanley, R.P.

    2001-01-01

    of approximate to1.8 ns is measured at room temperature, which confirms the excellent structural quality. A fast PL rise (tau (rise) = 10 +/-2 ps) is observed at all temperatures, indicating the potential for high-speed modulation. High-efficiency light-emitting diodes (LEDs) based on these dots are demonstrated......We present a comprehensive study of the structural and emission properties of self-assembled InAs quantum dots emitting at 1.3 mum. The dots are grown by molecular beam epitaxy on gallium arsenide substrates. Room-temperature emission at 1.3 mum is obtained by embedding the dots in an InGaAs layer...

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

    Science.gov (United States)

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

    2016-12-01

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

  12. Efficiency vs. multi-photon contribution test for quantum dots.

    Science.gov (United States)

    Predojević, Ana; Ježek, Miroslav; Huber, Tobias; Jayakumar, Harishankar; Kauten, Thomas; Solomon, Glenn S; Filip, Radim; Weihs, Gregor

    2014-02-24

    The development of linear quantum computing within integrated circuits demands high quality semiconductor single photon sources. In particular, for a reliable single photon source it is not sufficient to have a low multi-photon component, but also to possess high efficiency. We investigate the photon statistics of the emission from a single quantum dot with a method that is able to sensitively detect the trade-off between the efficiency and the multi-photon contribution. Our measurements show, that the light emitted from the quantum dot when it is resonantly excited possess a very low multi-photon content. Additionally, we demonstrated, for the first time, the non-Gaussian nature of the quantum state emitted from a single quantum dot.

  13. Semitransparent quantum dot light-emitting diodes by cadmium-free colloidal quantum dots.

    Science.gov (United States)

    Kim, Yohan; Ippen, Christian; Greco, Tonino; Oh, Min Suk; Chul, Jong Han; Lee, Jeongno; Wedel, Armin; Kim, Jiwan

    2014-11-01

    The InP/ZnSe/ZnS multishell colloidal quantum dots (QDs) were prepared by convenient heating-up method for an emission layer of semitransparent quantum dot light-emitting diodes (QD-LEDs). The synthesized InP/ZnSe/ZnS multishell QDs exhibited an emission peak at 545 nm for clear green color with a full-width at half-maximum (FWHM) of 50 nm, and photoluminescent (PL) quantum yield (QY) of 45%. The multishell on the indium phosphide (InP) core helped increasing QY and stability by reducing interfacial defects. Using a Ca/Ag cathode, the whole QD-LEDs were semitransparent throughout the visible wavelengths. The maximum brightness and currernt efficiency of semitransparent QD-LEDs reached 587 cd/m2 and 1.52 cd/A by controlling the thickness of Ca/Ag cathode, which is comparable to the device with opaque LiF/Al cathode (1444 cd/m2 and 1.98 cd/A). The performance of our semitransparent and eco-friendly device is not matched with traditional cadmium (Cd) based QD-LEDs yet, but it shows the great potential for various window-type information displays.

  14. Exploring the Physics of Semiconductor Quantum Dots using Circuit Quantum Electrodynamics

    Science.gov (United States)

    Stockklauser, Anna; Maisi, Ville; Ihn, Thomas; Ensslin, Klaus; Wallraff, Andreas

    2015-03-01

    Semiconductor quantum dots and superconducting qubits both possess excitations in the microwave domain for which a wide range of novel approaches to create, store, manipulate and detect individual photons have been developed. A key ingredient are coplanar waveguide resonators in which the field energy of an excitation is distributed over a small mode volume. This feature creates sizable electromagnetic fields at the level of individual microwave photons mediating strong electromagnetic interactions with a variety of quantum systems. In an approach known as circuit quantum electrodynamics (QED) we both probe fundamental quantum optical effects and demonstrate basic features of quantum information processing. In this presentation, I will discuss experiments exploring the physics of semiconductor quantum dots in the context of circuit QED. We investigate the coherent dipole coupling of double dots to microwave photons and detect radiation emitted from the dots in inelastic electron tunneling processes. This approach may allow us to explore quantum coherent interfaces between semiconducting and superconducting qubits.

  15. Quantitative analysis of quantum dot dynamics and emission spectra in cavity quantum electrodynamics

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg; Lodahl, Peter

    2013-01-01

    -resolved measurements reveal that the actual coupling strength is significantly smaller than anticipated from the spectral measurements and that the quantum dot is rather weakly coupled to the cavity. We suggest that the observed Rabi splitting is due to cavity feeding by other quantum dots and/or multi...

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

    Energy Technology Data Exchange (ETDEWEB)

    Beltako, Katawoura; Cavassilas, Nicolas; Michelini, Fabienne [Universités Aix Marseille et Toulon, CNRS, IM2NP, UMR 7334, 13288 Marseille (France)

    2016-08-15

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

  17. Reducing inhomogeneity in the dynamic properties of quantum dots via self-aligned plasmonic cavities.

    Science.gov (United States)

    Demory, Brandon; Hill, Tyler A; Teng, Chu-Hsiang; Deng, Hui; Ku, P C

    2018-01-05

    A plasmonic cavity is shown to greatly reduce the inhomogeneity of dynamic optical properties such as quantum efficiency and radiative lifetime of InGaN quantum dots. By using an open-top plasmonic cavity structure, which exhibits a large Purcell factor and antenna quantum efficiency, the resulting quantum efficiency distribution for the quantum dots narrows and is no longer limited by the quantum dot inhomogeneity. The standard deviation of the quantum efficiency can be reduced to 2% while maintaining the overall quantum efficiency at 70%, making InGaN quantum dots a viable candidate for high-speed quantum cryptography and random number generation applications.

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

    Directory of Open Access Journals (Sweden)

    Stephan Michael

    2016-05-01

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

  19. Relaxation of a Hole Spin in a Quantum Dot.

    Science.gov (United States)

    Woods, L. M.; Reinecke, T. L.; Kotlyar, R.

    2004-03-01

    Theoretical results for relaxation of the spin of a hole in cylindrical quantum dots due to acoustic phonon assisted flips at low temperatures with an applied magnetic field are presented. The hole dispersion is calculated by numerical diagonalization of the Luttinger Hamiltonian and applying perturbation theory with respect to the magnetic field,and the hole-phonon coupling is described by the Bir-Pikus Hamiltonian. We find that the decoherence time for hole spins for dots < ˜ 20 nm is on the order of 10-8 s. This is several orders smaller than the decoherence time due to phonon assisted processes for electron spins in similar dots and is comparable to the total decoherence time of an electron spin in a quantum dot, which is controlled by the hyperfine interaction with nuclei. We obtain the dependence of the relaxation rate of the hole spin on dot size, hole mass.

  20. Quantum confinement induced shift in energy band edges and band gap of a spherical quantum dot

    Science.gov (United States)

    Borah, P.; Siboh, D.; Kalita, P. K.; Sarma, J. K.; Nath, N. M.

    2018-02-01

    We have proposed and validated an ansatz as effective potential for confining electron/hole within a spherical quantum dot in order to understand quantum confinement and its consequences associated with energy states and band gap of Spherical Quantum Dots. Within effective mass approximation formalism, we have considered an ansatz incorporating a conjoined harmonic oscillator and Coulomb interaction as the effective potential for confining an electron or a hole within a spherical quantum dot and by employing appropriate boundary conditions, we have calculated the shifts in energy of minimum of conduction band (CBM) and maximum of valence band (VBM) with respect to size of spherical quantum dots. We have also determined the quantum confinement induced shift in band gap energy of spherical quantum dots. In order to verify our theoretical predictions as well as to validate our ansatz, we have performed phenomenological analysis in comparison with available experimental results for quantum dots made of CdSe and observe a very good agreement in this regard. Our experimentally consistent theoretical results also help in mapping the probability density of electron and hole inside a spherical quantum dot. The consistency of our results with available experimental data signifies the capability as well as applicability of the ansatz for the effective confining potential to have reasonable information in the study of real nano-structured spherical systems.

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

    Directory of Open Access Journals (Sweden)

    Tyler D. Park

    2014-12-01

    Full Text Available Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

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

    Energy Technology Data Exchange (ETDEWEB)

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K. [Department of Physics and Astronomy, Brigham Young University, Provo UT 84602 (United States); Yang, Haeyeon [Department of Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, SD 57701 (United States); Kim, Dong Jun [IPG Photonics Corporation, Oxford, MA 01540 (United States)

    2014-12-15

    Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

  3. Fabrication of quantum-dot devices in graphene

    Directory of Open Access Journals (Sweden)

    Satoshi Moriyama, Yoshifumi Morita, Eiichiro Watanabe, Daiju Tsuya, Shinya Uji, Maki Shimizu and Koji Ishibashi

    2010-01-01

    Full Text Available We describe our recent experimental results on the fabrication of quantum-dot devices in a graphene-based two-dimensional system. Graphene samples were prepared by micromechanical cleavage of graphite crystals on a SiO2/Si substrate. We performed micro-Raman spectroscopy measurements to determine the number of layers of graphene flakes during the device fabrication process. By applying a nanofabrication process to the identified graphene flakes, we prepared a double-quantum-dot device structure comprising two lateral quantum dots coupled in series. Measurements of low-temperature electrical transport show the device to be a series-coupled double-dot system with varied interdot tunnel coupling, the strength of which changes continuously and non-monotonically as a function of gate voltage.

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

    Energy Technology Data Exchange (ETDEWEB)

    Baart, T. A.; Vandersypen, L. M. K. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Eendebak, P. T. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Netherlands Organisation for Applied Scientific Research (TNO), P.O. Box 155, 2600 AD Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)

    2016-05-23

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

  5. Influence of GaAs Substrate Orientation on InAs Quantum Dots: Surface Morphology, Critical Thickness, and Optical Properties

    Directory of Open Access Journals (Sweden)

    Liang BL

    2007-01-01

    Full Text Available AbstractInAs/GaAs heterostructures have been simultaneously grown by molecular beam epitaxy on GaAs (100, GaAs (100 with a 2° misorientation angle towards [01−1], and GaAs (n11B (n = 9, 7, 5 substrates. While the substrate misorientation angle increased from 0° to 15.8°, a clear evolution from quantum dots to quantum well was evident by the surface morphology, the photoluminescence, and the time-resolved photoluminescence, respectively. This evolution revealed an increased critical thickness and a delayed formation of InAs quantum dots as the surface orientation departed from GaAs (100, which was explained by the thermal-equilibrium model due to the less efficient of strain relaxation on misoriented substrate surfaces.

  6. Self-assembly of heterojunction quantum dots(HeQuaDs)

    Science.gov (United States)

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

    2006-02-01

    Quantum dots (QDs) have been receiving considerable attention due to the unique properties, which arise due to the confinement of the electron and holes in a lower band gap material. The InAs on GaAs material system is one of the most studied combinations in which quantum dots form during epitaxy. These QDs form in a Stranski Krastanov manner via a self-assembly process in which the dots nucleate at a critical adatom coverage on a wetting layer of InAs. QDs may be vertically aligned by using the residual strain above a buried dot layer to enhance the nucleation of the second layer of dots. In this work, we show the formation of QDs, which are composed of multiple materials, can be formed through a marriage of these two concepts. In this particular demonstration, we formed InAs dots on GaAs andcrowned the QDs with GaSb and encapsulated the entire structure with GaAs. Atomic Force Microscopy shows additional nucleation between the InAs layers has been minimized and cross-sectional transmission electron microscopy shows the formation the composite structure. Transmission electron microscopy indicated a clear boundary between the GaSb and InAs regions. AFM analysis of the HeQuaD structure shows that GaSb material grows mainly on the two (1 1 0) inclined facets. Thus, the HeQuaD is elongated along the (1 1 0) direction. We have also obtained preliminary photoluminescence (PL) from a 3 layer GaS/InAs HeQuaD structure with a peak around 1.3 microns.

  7. High-Temperature Luminescence Quenching of Colloidal Quantum Dots

    NARCIS (Netherlands)

    Zhao, Y.|info:eu-repo/dai/nl/355358352; Riemersma, C.; Pietra, F|info:eu-repo/dai/nl/355358395; de Mello Donega, C.|info:eu-repo/dai/nl/125593899; Meijerink, A.|info:eu-repo/dai/nl/075044986

    2012-01-01

    Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300–500 K) luminescence studies are reported for highly efficient CdSe core–shell quantum

  8. Highly luminescent water-soluble CdTe quantum dots

    NARCIS (Netherlands)

    Wuister, SF; Swart, A.N.; van Driel, F; Hickey, SG; Donega, CD; Swart, Ingmar|info:eu-repo/dai/nl/304837652

    Colloidal CdTe quantum dots prepared in TOP/DDA (trioctylphosphine/dodecylamine) are transferred into water by the use of aminoethanethiol.HCl (AET) or mercaptopropionic acid (MPA). This results in an increase in the photoluminescence quantum efficiency and a longer exciton lifetime. For the first

  9. Quantum dot mediated imaging of atherosclerosis

    Energy Technology Data Exchange (ETDEWEB)

    Jayagopal, Ashwath; Haselton, Frederick R [Department of Biomedical Engineering, Vanderbilt University School of Medicine, Nashville, TN 37232 (United States); Su Yanru; Blakemore, John L; Linton, MacRae F; Fazio, Sergio [Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232 (United States)], E-mail: rick.haselton@vanderbilt.edu

    2009-04-22

    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{sup -/-} 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.

  10. Optical orientation in self assembled quantum dots

    CERN Document Server

    Stevens, G C

    2002-01-01

    We examined Zeeman splitting in a series of ln sub x Ga sub ( sub 1 sub - sub x sub ) As/GaAs self assembled quantum dots (SAQD's) with different pump polarisations. All these measurements were made in very low external magnetic fields where direct determination of the Zeeman splitting energy is impossible due to its small value in comparison to the photoluminescence linewidths. The use of a technique developed by M. J. Snelling allowed us to obtain the Zeeman splitting and hence the excitonic g-factors indirectly. We observed a linear low field splitting, becoming increasingly non-linear at higher fields. We attribute this non-linearity to field induced level mixing. It is believed these are the first low field measurements in these structures. A number of apparent nuclear effects in the Zeeman splitting measurements led us onto the examination of nuclear effects in these structures. The transverse and oblique Hanie effects then allowed us to obtain the sign of the electronic g-factors in two of our samples,...

  11. Quantum dot mediated imaging of atherosclerosis

    Science.gov (United States)

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

    2009-04-01

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

  12. Carbon Quantum Dots for Zebrafish Fluorescence Imaging.

    Science.gov (United States)

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-07-02

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. Herein, we describe fluorescence bioimaging of zebrafish using C-QDs as probe in terms of the preparation of C-QDs, zebrafish husbandry, embryo harvesting, and introduction of C-QDs into embryos and larvae by soaking and microinjection. The multicolor of C-QDs was validated with their imaging for zebrafish embryo. The distribution of C-QDs in zebrafish embryos and larvae were successfully observed from their fluorescence emission. the bio-toxicity of C-QDs was tested with zebrafish as model and C-QDs do not interfere to the development of zebrafish embryo. All of the results confirmed the high biocompatibility and low toxicity of C-QDs as imaging probe. The absorption, distribution, metabolism and excretion route (ADME) of C-QDs in zebrafish was revealed by their distribution. Our work provides the useful information for the researchers interested in studying with zebrafish as a model and the applications of C-QDs. The operations related zebrafish are suitable for the study of the toxicity, adverse effects, transport, and biocompatibility of nanomaterials as well as for drug screening with zebrafish as model.

  13. Synthesis, optimization and characterization of carbon quantum dots

    Science.gov (United States)

    Deshpande, Vibha

    Quantum dots are Nano-sized structures of semiconductors with unique optical properties that make them a very valuable tool in a wide range of interesting and important applications. Quantum dots can be designed to emit a particular colored light by altering their size; they are long-lived and fluoresce brightly. Consequently, they have been used extensively in biological imaging studies, where they have facilitated the observation of detailed biological processes at the molecular level. The thesis work focuses on understanding the fundamental electronic properties of low dimensional material and their Biological applications. Carbon based Quantum Dots is the main subject in our project due to their biocompatibility and novel optical properties. Here we studied the structural, luminescence, biological properties and applications of carbon based different sizes of quantum dots. Our main goal lied in the formulation of highly florescent, broad range pH and ionic-stable N/S-doped Carbon based Quantum Dots for the purpose of determining or studying Inter and intra Cellular Functions and Imaging Live Cells. The Studies also include the effect of doping carbon based Quantum Dots. Our interest also lies in using scanning probe microscopy to investigate these quantum dots. Since the carbon element is the basis of all biological materials, full carbon nanomaterial's have a lower toxicity compared with other nanomaterial's; simultaneously, the particle size of CQDs is smaller and thus more convenient to enter the cell in vivo, which makes CQDs having great potential applications in the biological fields. In addition, the surface of CQDs contains a lot of functional groups, so that it can be modified with organic, inorganic, polymer, and other substances endowing different functional properties.

  14. Physical optimization of quantum error correction circuits with spatially separated quantum dot spins.

    Science.gov (United States)

    Wang, Hong-Fu; Zhu, Ai-Dong; Zhang, Shou

    2013-05-20

    We propose an efficient protocol for optimizing the physical implementation of three-qubit quantum error correction with spatially separated quantum dot spins via virtual-photon-induced process. In the protocol, each quantum dot is trapped in an individual cavity and each two cavities are connected by an optical fiber. We propose the optimal quantum circuits and describe the physical implementation for correcting both the bit flip and phase flip errors by applying a series of one-bit unitary rotation gates and two-bit quantum iSWAP gates that are produced by the long-range interaction between two distributed quantum dot spins mediated by the vacuum fields of the fiber and cavity. The protocol opens promising perspectives for long distance quantum communication and distributed quantum computation networks.

  15. Carbon quantum dots and applications in photocatalytic energy conversion.

    Science.gov (United States)

    Fernando, K A Shiral; Sahu, Sushant; Liu, Yamin; Lewis, William K; Guliants, Elena A; Jafariyan, Amirhossein; Wang, Ping; Bunker, Christopher E; Sun, Ya-Ping

    2015-04-29

    Quantum dots (QDs) generally refer to nanoscale particles of conventional semiconductors that are subject to the quantum-confinement effect, though other nanomaterials of similar optical and redox properties are also named as QDs even in the absence of strictly defined quantum confinement. Among such nanomaterials that have attracted tremendous recent interest are carbon dots, which are small carbon nanoparticles with some form of surface passivation, and graphene quantum dots in various configurations. In this article, we highlight these carbon-based QDs by focusing on their syntheses, on their photoexcited state properties and redox processes, and on their applications as photocatalysts in visible-light carbon dioxide reduction and in water-splitting, as well as on their mechanistic similarities and differences.

  16. Folded-light-path colloidal quantum dot solar cells.

    KAUST Repository

    Koleilat, Ghada I

    2013-01-01

    Colloidal quantum dot photovoltaics combine low-cost solution processing with quantum size-effect tuning to match absorption to the solar spectrum. Rapid advances have led to certified solar power conversion efficiencies of over 7%. Nevertheless, these devices remain held back by a compromise in the choice of quantum dot film thickness, balancing on the one hand the need to maximize photon absorption, mandating a thicker film, and, on the other, the need for efficient carrier extraction, a consideration that limits film thickness. Here we report an architecture that breaks this compromise by folding the path of light propagating in the colloidal quantum dot solid. Using this method, we achieve a substantial increase in short-circuit current, ultimately leading to improved power conversion efficiency.

  17. Simulating electron spin entanglement in a double quantum dot

    Science.gov (United States)

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

    2011-03-01

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

  18. Fast gain and phase recovery of semiconductor optical amplifiers based on submonolayer quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Herzog, Bastian, E-mail: BHerzog@physik.tu-berlin.de; Owschimikow, Nina; Kaptan, Yücel; Kolarczik, Mirco; Switaiski, Thomas; Woggon, Ulrike [Institut für Optik und Atomare Physik, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany); Schulze, Jan-Hindrik; Rosales, Ricardo; Strittmatter, André; Bimberg, Dieter; Pohl, Udo W. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

    2015-11-16

    Submonolayer quantum dots as active medium in opto-electronic devices promise to combine the high density of states of quantum wells with the fast recovery dynamics of self-assembled quantum dots. We investigate the gain and phase recovery dynamics of a semiconductor optical amplifier based on InAs submonolayer quantum dots in the regime of linear operation by one- and two-color heterodyne pump-probe spectroscopy. We find an as fast recovery dynamics as for quantum dot-in-a-well structures, reaching 2 ps at moderate injection currents. The effective quantum well embedding the submonolayer quantum dots acts as a fast and efficient carrier reservoir.

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

    Science.gov (United States)

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

    2016-02-01

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word 'RAHASIA'. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.

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

    Energy Technology Data Exchange (ETDEWEB)

    Isnaeni,, E-mail: isnaeni@lipi.go.id; Sugiarto, Iyon Titok [Research Center for Physics, Indonesian Institute of Science, Building 442 Puspiptek Serpong, South Tangerang, Banten, Indonesia 15314 (Indonesia); Bilqis, Ratu; Suseno, Jatmiko Endro [Department of Physics, Diponegoro University, Jl. Prof. Soedarto, Tembalang, Semarang, Indonesia 50275 (Indonesia)

    2016-02-08

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word ’RAHASIA’. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.

  1. Periodic Scarred States in Open Quantum Dots as Evidence of Quantum Darwinism

    Science.gov (United States)

    Burke, A. M.; Akis, R.; Day, T. E.; Speyer, Gil; Ferry, D. K.; Bennett, B. R.

    2010-04-01

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  2. Single-photon superradiance from a quantum dot

    DEFF Research Database (Denmark)

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

    2016-01-01

    and the hole comprising the exciton gives rise to an anharmonic spectrum, which we exploit to prepare the superradiant quantum state deterministically with a laser pulse. We observe a fivefold enhancement of the oscillator strength compared to conventional quantum dots. The enhancement is limited by the base...... temperature of our cryostat and may lead to oscillator strengths above 1000 from a single quantum emitter at optical frequencies....

  3. Sub-monolayer quantum dots in confinement enhanced dots-in-a-well heterostructure

    Science.gov (United States)

    Sengupta, S.; Kim, J. O.; Barve, A. V.; Adhikary, S.; Sharma, Y. D.; Gautam, N.; Lee, S. J.; Noh, S. K.; Chakrabarti, S.; Krishna, S.

    2012-05-01

    We have investigated optical properties and device performance of sub-monolayer quantum dots infrared photodetector with confinement enhancing (CE) barrier and compared with conventional Stranski-Krastanov quantum dots with a similar design. This quantum dots-in-a-well structure with CE barrier enables higher quantum confinement and increased absorption efficiency due to stronger overlap of wavefunctions between the ground state and the excited state. Normal incidence photoresponse peak is obtained at 7.5 μm with a detectivity of 1.2 × 1011 cm Hz1/2 W-1 and responsivity of 0.5 A/W (77 K, 0.4 V, f/2 optics). Using photoluminescence and spectral response measurements, the bandstructure of the samples were deduced semi-empirically.

  4. Tuning Single Quantum Dot Emission with a Micromirror.

    Science.gov (United States)

    Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul

    2018-01-11

    The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

  5. Imaging electrostatically confined Dirac fermions in graphene quantum dots

    Science.gov (United States)

    Lee, Juwon; Wong, Dillon; Velasco, Jairo, Jr.; Rodriguez-Nieva, Joaquin F.; Kahn, Salman; Tsai, Hsin-Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid S.; Crommie, Michael F.

    2016-11-01

    Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries. Reflection and transmission at these boundaries affect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions.

  6. Influence of surface states of CuInS{sub 2} quantum dots in quantum dots sensitized photo-electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Zhuoyin; Liu, Yueli [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China); Wu, Lei [School of Electronic and Electrical, Wuhan Railway Vocational College of Technology, Wuhan 430205 (China); Zhao, Yinghan; Chen, Keqiang [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China); Chen, Wen, E-mail: chenw@whut.edu.cn [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China)

    2016-12-01

    Graphical abstract: J–V curves of different ligands capped CuInS{sub 2} QDs sensitized TiO{sub 2} photo-electrodes. - Highlights: • DDT, OLA, MPA, and S{sup 2−} ligand capped CuInS{sub 2} quantum dot sensitized photo-electrodes are prepared. • Surface states of quantum dots greatly influence the electrochemical performance of CuInS{sub 2} quantum dot sensitized photo-electrodes. • S{sup 2−} ligand enhances the UV–vis absorption and electron–hole separation property as well as the excellent charge transfer performance of the photo-electrodes. - Abstract: Surface states are significant factor for the enhancement of electrochemical performance in CuInS{sub 2} quantum dot sensitized photo-electrodes. DDT, OLA, MPA, and S{sup 2−} ligand capped CuInS{sub 2} quantum dot sensitized photo-electrodes are prepared by thermolysis, solvethermal and ligand-exchange processes, respectively, and their optical properties and photoelectrochemical properties are investigated. The S{sup 2−} ligand enhances the UV–vis absorption and electron–hole separation property as well as the excellent charge transfer performance of the photo-electrodes, which is attributed to the fact that the atomic S{sup 2−} ligand for the interfacial region of quantum dots may improve the electron transfer rate. These S{sup 2−}-capped CuInS{sub 2} quantum dot sensitized photo-electrodes exhibit the excellent photoelectrochemical efficiency and IPCE peak value, which is higher than that of the samples with DDT, OLA and MPA ligands.

  7. Grow light for plant factory using quantum dot LED

    Directory of Open Access Journals (Sweden)

    Jin-Won Song

    2016-01-01

    Full Text Available The research on the LED base next generation lighting is actively accomplished in the field of lighting for the energy saving for the global warming prevention. In this study, made the multifunctional LED light source as research on the lighting equipment that using the Quantum Dot. Synthesized the quantum dot having the wavelength of 510nm, 610nm, 660nm and confirmed the possibility of characteristic evaluation result that it was applicable as the result LED fluorescent substance. We synthesized quantum dot that mixed the resin and was spread on the blue LED having the wavelength of 455nm. We make the multi-wavelength LED device in order to confirm the possibility for application for the plant factory and evaluated the electrical characteristic of the LED light source. Also, we evaluated the growth characteristic so that the quantum dot could confirm the possibility for application by plant growth light source. Finally we presented the possibility for application of the quantum dot with the multifunction LED light source.

  8. Long-lived population inversion in isovalently doped quantum dots.

    Science.gov (United States)

    Lahad, Ohr; Meir, Noga; Pinkas, Iddo; Oron, Dan

    2015-01-27

    Optical gain from colloidal quantum dots has been desired for several decades since their discovery. While gain from multiexcitations is by now well-established, nonradiative Auger recombination limits the lifetime of such population inversion in quantum dots. CdSe cores isovalently doped by one to few Te atoms capped with rod-shaped CdS are examined as a candidate system for enhanced stimulated emission properties. Emission depletion spectroscopy shows a behavior characteristic of 3-level gain systems in these quantum dots. This implies complete removal of the 2-fold degeneracy of the lowest energy electronic excitation due to the large repulsive exciton-exciton interaction in the doubly excited state. Using emission depletion measurements of the trap-associated emission from poorly passivated CdS quantum dots, we show that 3-level characteristics are typical of emission resulting from a band edge to trap state transition, but reveal subtle differences between the two systems. These results allow for unprecedented observation of long-lived population inversion from singly excited quantum dots.

  9. SELF-ORGANIZATION OF LEAD SULFIDE QUANTUM DOTS INTO SUPERSTRUCTURES

    Directory of Open Access Journals (Sweden)

    Elena V. Ushakova

    2014-11-01

    Full Text Available The method of X-ray structural analysis (X-ray scattering at small angles is used to show that the structures obtained by self-organization on a substrate of lead sulfide (PbS quantum dots are ordered arrays. Self-organization of quantum dots occurs at slow evaporation of solvent from a cuvette. The cuvette is a thin layer of mica with teflon ring on it. The positions of peaks in SAXS pattern are used to calculate crystal lattice of obtained ordered structures. Such structures have a primitive orthorhombic crystal lattice. Calculated lattice parameters are: a = 21,1 (nm; b = 36,2 (nm; c = 62,5 (nm. Dimensions of structures are tens of micrometers. The spectral properties of PbS QDs superstructures and kinetic parameters of their luminescence are investigated. Absorption band of superstructures is broadened as compared to the absorption band of the quantum dots in solution; the luminescence band is slightly shifted to the red region of the spectrum, while its bandwidth is not changed much. Luminescence lifetime of obtained structures has been significantly decreased in comparison with the isolated quantum dots in solution, but remained the same for the lead sulfide quantum dots close-packed ensembles. Such superstructures can be used to produce solar cells with improved characteristics.

  10. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum

    Directory of Open Access Journals (Sweden)

    Takaaki Yamaguchi

    2016-10-01

    Full Text Available CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were precipitated in the intracellular space, indicating that cadmium and selenium ions were incorporated into the cell and that the quantum dots were synthesized with intracellular metabolites. To reveal differences in F. oxysporum metabolism, cell extracts of F. oxysporum, before and after CdSe synthesis, were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE. The results suggested that the amount of superoxide dismutase (SOD decreased after CdSe synthesis. Fluorescence microscopy revealed that cytoplasmic superoxide increased significantly after CdSe synthesis. The accumulation of superoxide may increase the expression of various metabolites that play a role in reducing Se4+ to Se2− and inhibit the aggregation of CdSe to make nanoparticles.

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

    Science.gov (United States)

    Delteil, Aymeric

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

  12. A Quantum Dot with Spin-Orbit Interaction--Analytical Solution

    Science.gov (United States)

    Basu, B.; Roy, B.

    2009-01-01

    The practical applicability of a semiconductor quantum dot with spin-orbit interaction gives an impetus to study analytical solutions to one- and two-electron quantum dots with or without a magnetic field.

  13. Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots

    NARCIS (Netherlands)

    de Weerd, C.; Shin, Y.; Marino, E.; Kim, J.; Lee, H.; Saeed, S.; Gregorkiewicz, T.

    2017-01-01

    Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other

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

    Science.gov (United States)

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

    2014-12-04

    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.

  15. Carrier-phonon interaction in semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Seebeck, Jan

    2009-03-10

    In recent years semiconductor quantum dots have been studied extensively due to their wide range of possible applications, predominantly for light sources. For successful applications, efficient carrier scattering processes as well as a detailed understanding of the optical properties are of central importance. The aims of this thesis are theoretical investigations of carrier scattering processes in InGaAs/GaAs quantum dots on a quantum-kinetic basis. A consistent treatment of quasi-particle renormalizations and carrier kinetics for non-equilibrium conditions is presented, using the framework of non-equilibrium Green's functions. The focus of our investigations is the interaction of carriers with LO phonons. Important for the understanding of the scattering mechanism are the corresponding quasi-particle properties. Starting from a detailed study of quantum-dot polarons, scattering and dephasing processes are discussed for different temperature regimes. The inclusion of polaron and memory effects turns out to be essential for the description of the carrier kinetics in quantum-dot systems. They give rise to efficient scattering channels and the obtained results are in agreement with recent experiments. Furthermore, a consistent treatment of the carrier-LO-phonon and the carrier-carrier interaction is presented for the optical response of semiconductor quantum dots, both giving rise to equally important contributions to the dephasing. Beside the conventional GaAs material system, currently GaN based light sources are of high topical interest due to their wide range of possible emission frequencies. In this material additionally intrinsic properties like piezoelectric fields and strong band-mixing effects have to be considered. For the description of the optical properties of InN/GaN quantum dots a procedure is presented, where the material properties obtained from an atomistic tight-binding approach are combined with a many-body theory for non

  16. The effect of side quantum dots on conductance through four-quantum-dot combinations: study by non-equilibrium Greens function method

    Directory of Open Access Journals (Sweden)

    Z Darizin

    2016-06-01

    Full Text Available Electronic transport has been investigated in four-quantum-dot combination coupled to metal electrodes using the non-equilibrium Green’s function method, and curves I-V and conductance (dI/dV were analyzed for special combination. We have showed that the emergence of negative differential conductivity is due to asymmetric distribution of quantum dots in the central region, existence of non-coupled dots (side quantum dots, and the interference effect. We found that more side quantum dots lead to more negative differential conductance.

  17. Telegraph noise in coupled quantum dot circuits induced by a quantum point contact.

    Science.gov (United States)

    Taubert, D; Pioro-Ladrière, M; Schröer, D; Harbusch, D; Sachrajda, A S; Ludwig, S

    2008-05-02

    Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed.

  18. Polarization of the photoluminescence of quantum dots incorporated into quantum wires

    Energy Technology Data Exchange (ETDEWEB)

    Platonov, A. V., E-mail: alexei.platonov@mail.ioffe.ru; Kochereshko, V. P.; Kats, V. N.; Cirlin, G. E.; Bouravleuv, A. D.; Avdoshina, D. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Delga, A.; Besombes, L.; Mariette, H. [CEA, INAC, SP2M, and Institut Néel, CEA-CNRS group “Nanophysique et Semiconducteurs” (France)

    2016-12-15

    The photoluminescence spectra of individual quantum dots incorporated into a quantum wire are studied. From the behavior of the spectra in a magnetic field, it is possible to estimate the exciton binding energy in a quantum dot incorporated into a quantum wire. It is found that the exciton photoluminescence signal emitted from a quantum dot along the direction of the nanowire axis is linearly polarized. At the same time, the photoluminescence signal propagating in the direction orthogonal to the nanowire axis is practically unpolarized. The experimentally observed effect is attributed to the nonaxial arrangement of the dot in the wire under conditions of a huge increase in the exciton binding energy due to the effect of the image potential on the exciton.

  19. Quantum strain sensor with a topological insulator HgTe quantum dot

    Science.gov (United States)

    Korkusinski, Marek; Hawrylak, Pawel

    2014-05-01

    We present a theory of electronic properties of HgTe quantum dot and propose a strain sensor based on a strain-driven transition from a HgTe quantum dot with inverted bandstructure and robust topologically protected quantum edge states to a normal state without edge states in the energy gap. The presence or absence of edge states leads to large on/off ratio of conductivity across the quantum dot, tunable by adjusting the number of conduction channels in the source-drain voltage window. The electronic properties of a HgTe quantum dot as a function of size and applied strain are described using eight-band Luttinger and Bir-Pikus Hamiltonians, with surface states identified with chirality of Luttinger spinors and obtained through extensive numerical diagonalization of the Hamiltonian.

  20. Quantum strain sensor with a topological insulator HgTe quantum dot

    Science.gov (United States)

    Korkusinski, Marek; Hawrylak, Pawel

    2014-01-01

    We present a theory of electronic properties of HgTe quantum dot and propose a strain sensor based on a strain-driven transition from a HgTe quantum dot with inverted bandstructure and robust topologically protected quantum edge states to a normal state without edge states in the energy gap. The presence or absence of edge states leads to large on/off ratio of conductivity across the quantum dot, tunable by adjusting the number of conduction channels in the source-drain voltage window. The electronic properties of a HgTe quantum dot as a function of size and applied strain are described using eight-band Luttinger and Bir-Pikus Hamiltonians, with surface states identified with chirality of Luttinger spinors and obtained through extensive numerical diagonalization of the Hamiltonian. PMID:24811674

  1. Growth parameter optimization for fast quantum dot SESAMs.

    Science.gov (United States)

    Maas, D J H C; Bellancourt, A-R; Hoffmann, M; Rudin, B; Barbarin, Y; Golling, M; Südmeyer, T; Keller, U

    2008-11-10

    Semiconductor saturable absorber mirrors (SESAMs) using quantum dot (QD) absorbers exhibit a larger design freedom than standard quantum well absorbers. The additional parameter of the dot density in combination with the field enhancement allows for an independent control of saturation fluence and modulation depth. We present the first detailed study of the effect of QD growth parameters and post growth annealing on the macroscopic optical SESAM parameters, measuring both nonlinear reflectivity and recombination dynamics. We studied a set of self-assembled InAs QD-SESAMs optimized for an operation wavelength around 960 nm with varying dot density and growth temperature. We confirm that the modulation depth is controlled by the dot density. We present design guidelines for QD-SESAMs with low saturation fluence and fast recovery, which are for example important for modelocking of vertical external cavity surface emitting lasers (VECSELs).

  2. Silicon quantum dots for optical applications

    Science.gov (United States)

    Wu, Jeslin J.

    Luminescent silicon quantum dots (SiQDs) are emerging as attractive materials for optoelectronic devices, third generation photovoltaics, and bioimaging. Their applicability in the real world is contingent on their optical properties and long-term environmental stability; and in biological applications, factors such as water solubility and toxicity must also be taken into consideration. The aforementioned properties are highly dependent on the QDs' surface chemistry. In this work, SiQDs were engineered for the respective applications using liquid-phase and gas-phase functionalization techniques. Preliminary work in luminescent downshifting for photovoltaic systems are also reported. Highly luminescent SiQDs were fabricated by grafting unsaturated hydrocarbons onto the surface of hydrogen-terminated SiQDs via thermal and photochemical hydrosilylation. An industrially attractive, all gas-phase, nonthermal plasma synthesis, passivation (aided by photochemical reactions), and deposition process was also developed to reduce solvent waste. With photoluminescence quantum yields (PLQYs) nearing 60 %, the alkyl-terminated QDs are attractive materials for optical applications. The functionalized SiQDs also exhibited enhanced thermal stability as compared to their unfunctionalized counterparts, and the photochemically-hydrosilylated QDs further displayed photostability under UV irradiation. These environmentally-stable SiQDs were used as luminescent downshifting layers in photovoltaic systems, which led to enhancements in the blue photoresponse of heterojunction solar cells. Furthermore, the QD films demonstrated antireflective properties, improving the coupling efficiency of sunlight into the cell. For biological applications, oxide, amine, or hydroxyl groups were grafted onto the surface to create water-soluble SiQDs. Luminescent, water-soluble SiQDs were produced in by microplasma treating the QDs in water. Stable QYs exceeding 50 % were obtained. Radical-based and

  3. Charge transport in semiconductor nanocrystal quantum dots

    Science.gov (United States)

    Mentzel, Tamar Shoshana

    In this thesis, we study charge transport in arrays of semiconductor nanocrystal quantum dots. Nanocrystals are synthesized in solution, and an organic ligand on the surface of the nanocrystal creates a potential barrier that confines charges in the nanocrystal. Optical absorption measurements reveal discrete electronic energy levels in the nanocrystals resulting from quantum confinement. When nanocrystals are deposited on a surface, they self-assemble into a close-packed array forming a nanocrystal solid. We report electrical transport measurements of a PbSe nanocrystal solid that serves as the channel of an inverted field-effect transistor. We measure the conductance as a function of temperature, source-drain bias and. gate voltage. The data indicates that holes are the majority carriers; the Fermi energy lies in impurity states in the bandgap of the nanocrystal; and charges hop between the highest occupied valence state in the nanocrystals (the 1S h states). At low source-drain voltages, the activation energy for hopping is given by the energy required to generate holes in the 1Sh state plus activation over barriers resulting from site disorder. The barriers from site disorder are eliminated with a sufficiently high source-drain bias. From the gate effect, we extract the Thomas-Fermi screening length and a density of states that is consistent with the estimated value. We consider variable-range hopping as an alternative model, and find no self-consistent evidence for it. Next, we employ charge sensing as an alternative to current measurements for studying transport in materials with localized sites. A narrow-channel MOSFET serves as a charge sensor because its conductance is sensitive to potential fluctuations in the nearby environment caused by the motion of charge. In particular, it is sensitive to the fluctuation of single electrons at the silicon-oxide interface within the MOSFET. We pattern a strip of amorphous germanium within 100 nm of the transistor. The

  4. Shock Compression Spectroscopy of Quantum Dots

    Science.gov (United States)

    Christensen, James; Banishev, Alexandr; Dlott, Dana

    2017-06-01

    We have investigated CdSe quantum dots (QDs) as photoluminescent probes of shocked solids. They could be especially useful for composite materials, where the individual components could be tagged with different color QDs. The QDs are tiny (4 nm) spherical emitters, pumped by a continuous laser during shock or diamond anvil experiments up to 12 GPa. In the diamond anvil the QDs are hydrostatically compressed and the emission blueshifts with increasing pressure. By contrast, in shock experiments the QDs are embedded in a hard glass or a soft polymer matrix and subjected to uniaxial compression, which should mechanically deform them, and the emission redshifts with increasing pressure. We did hundreds of shock experiments with laser-driven flyer plates, measuring time-resolved intensities, spectral shifts and spectral widths with 1 ns time resolution. We also measured the time-dependent strain of the matrix using a fast optomechanical probe. We showed that the QD redshift can measure the strain in the glass or polymer with 1 ns time resolution. In the hard glass above 4 GPa the QDs behave oddly. When the shock arrives, the QDs redshift as the strain increases, but after about 20 ns, the redshift disappears for about 20 ns and then reappears. We think this redshift blinking behavior is related to the shear transients in the matrix, which suggests we might be able to use QDs to measure uniaxial strain and shear. This material is based on work supported by the Defense Threat Reduction Agency under Grant HDTRA1-12-1-0011.

  5. Biosensing with Quantum Dots: A Microfluidic Approach

    Science.gov (United States)

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

    2011-01-01

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

  6. Quantum dot labeling of mesenchymal stem cells

    Directory of Open Access Journals (Sweden)

    Cascio Wayne E

    2007-11-01

    Full Text Available Abstract Background Mesenchymal stem cells (MSCs are multipotent cells with the potential to differentiate into bone, cartilage, fat and muscle cells and are being investigated for their utility in cell-based transplantation therapy. Yet, adequate methods to track transplanted MSCs in vivo are limited, precluding functional studies. Quantum Dots (QDs offer an alternative to organic dyes and fluorescent proteins to label and track cells in vitro and in vivo. These nanoparticles are resistant to chemical and metabolic degradation, demonstrating long term photostability. Here, we investigate the cytotoxic effects of in vitro QD labeling on MSC proliferation and differentiation and use as a cell label in a cardiomyocyte co-culture. Results A dose-response to QDs in rat bone marrow MSCs was assessed in Control (no-QDs, Low concentration (LC, 5 nmol/L and High concentration (HC, 20 nmol/L groups. QD yield and retention, MSC survival, proinflammatory cytokines, proliferation and DNA damage were evaluated in MSCs, 24 -120 hrs post QD labeling. In addition, functional integration of QD labeled MSCs in an in vitro cardiomyocyte co-culture was assessed. A dose-dependent effect was measured with increased yield in HC vs. LC labeled MSCs (93 ± 3% vs. 50% ± 15%, p 90% of QD labeled cells were viable in all groups, however, at 120 hrs increased apoptosis was measured in HC vs. Control MSCs (7.2% ± 2.7% vs. 0.5% ± 0.4%, p Conclusion Fluorescent QDs label MSC effectively in an in vitro co-culture model. QDs are easy to use, show a high yield and survival rate with minimal cytotoxic effects. Dose-dependent effects suggest limiting MSC QD exposure.

  7. Signatures of Majorana zero-modes in nanowires, quantum spin Hall edges, and quantum dots

    NARCIS (Netherlands)

    Mi, Shuo

    2015-01-01

    This thesis focuses on the investigation of Majorana zero-modes and their quantum transport properties of topological insulators and topological superconductors in several low-dimensional systems, i.e. 1D nanowire system (Chapter 2), 2D quantum spin Hall system (Chapter 3, 4) and 0D quantum dot

  8. Coupling of self-assembled InAs quantum dots to surface plasmon polaritons

    DEFF Research Database (Denmark)

    Andersen, Mads Lykke; Stobbe, Søren; Johansen, Jeppe

    2008-01-01

    InAs quantum dots have been placed at different distances to a silver mirror. We extract the coupling of quantum dots to surface plasmon polaritons as a function of the distance by time-resolved spontaneous emission measurements.......InAs quantum dots have been placed at different distances to a silver mirror. We extract the coupling of quantum dots to surface plasmon polaritons as a function of the distance by time-resolved spontaneous emission measurements....

  9. Multi-bit dark state memory: Double quantum dot as an electronic quantum memory

    Science.gov (United States)

    Aharon, Eran; Pozner, Roni; Lifshitz, Efrat; Peskin, Uri

    2016-12-01

    Quantum dot clusters enable the creation of dark states which preserve electrons or holes in a coherent superposition of dot states for a long time. Various quantum logic devices can be envisioned to arise from the possibility of storing such trapped particles for future release on demand. In this work, we consider a double quantum dot memory device, which enables the preservation of a coherent state to be released as multiple classical bits. Our unique device architecture uses an external gating for storing (writing) the coherent state and for retrieving (reading) the classical bits, in addition to exploiting an internal gating effect for the preservation of the coherent state.

  10. Longitudinal modes of quantum dots in magnetic fields

    Science.gov (United States)

    Serra, Ll.; Pi, M.; Emperador, A.; Barranco, M.; Lipparini, E.

    The far infrared longitudinal spin and density responses of two-dimensional quantum dots are discussed within local spin-density functional theory. The influence of a partial spin polarization, induced by a perpendicular static magnetic field, is taken into account in the coupling of spin and density channels. As an illustrative application, the case of a dot made of 5 electrons in parabolic confinement is discussed.

  11. Gain recovery dynamics and limitations in quantum dot amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Bischoff, Svend; Magnúsdóttir, Ingibjörg

    2001-01-01

    gain recovery in a quantum dot amplifier, and it is thus not yet clear what the limiting processes for the device response are. We present the results of a comprehensive theoretical model, which agrees well with the experimental results, and indicates the importance of slow recovery of higher energy...... levels. The model used is of the rate-equation type with three energy levels: ground state (GS) and excited state (ES) dot levels and a wetting layer...

  12. QCAD simulation and optimization of semiconductor double quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Nielsen, Erik; Gao, Xujiao; Kalashnikova, Irina; Muller, Richard Partain; Salinger, Andrew Gerhard; Young, Ralph Watson

    2013-12-01

    We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling quantum devices, particularly silicon double quantum dots (DQDs) developed for quantum qubits. The simulator has three di erentiating features: (i) its core contains nonlinear Poisson, e ective mass Schrodinger, and Con guration Interaction solvers that have massively parallel capability for high simulation throughput, and can be run individually or combined self-consistently for 1D/2D/3D quantum devices; (ii) the core solvers show superior convergence even at near-zero-Kelvin temperatures, which is critical for modeling quantum computing devices; (iii) it couples with an optimization engine Dakota that enables optimization of gate voltages in DQDs for multiple desired targets. The Poisson solver includes Maxwell- Boltzmann and Fermi-Dirac statistics, supports Dirichlet, Neumann, interface charge, and Robin boundary conditions, and includes the e ect of dopant incomplete ionization. The solver has shown robust nonlinear convergence even in the milli-Kelvin temperature range, and has been extensively used to quickly obtain the semiclassical electrostatic potential in DQD devices. The self-consistent Schrodinger-Poisson solver has achieved robust and monotonic convergence behavior for 1D/2D/3D quantum devices at very low temperatures by using a predictor-correct iteration scheme. The QCAD simulator enables the calculation of dot-to-gate capacitances, and comparison with experiment and between solvers. It is observed that computed capacitances are in the right ballpark when compared to experiment, and quantum con nement increases capacitance when the number of electrons is xed in a quantum dot. In addition, the coupling of QCAD with Dakota allows to rapidly identify which device layouts are more likely leading to few-electron quantum dots. Very efficient QCAD simulations on a large number of fabricated and proposed Si DQDs have made it possible to provide fast feedback for design

  13. A tunable colloidal quantum dot photo field-effect transistor

    KAUST Repository

    Ghosh, Subir

    2011-01-01

    We fabricate and investigate field-effect transistors in which a light-absorbing photogate modulates the flow of current along the channel. The photogate consists of colloidal quantum dots that efficiently transfer photoelectrons to the channel across a charge-separating (type-II) heterointerface, producing a primary and sustained secondary flow that is terminated via electron back-recombination across the interface. We explore colloidal quantum dot sizes corresponding to bandgaps ranging from 730 to 1475 nm and also investigate various stoichiometries of aluminum-doped ZnO (AZO) channel materials. We investigate the role of trap state energies in both the colloidal quantum dot energy film and the AZO channel. © 2011 American Institute of Physics.

  14. Quantum Dot Semiconductor Optical Amplifiers - Physics and Applications

    DEFF Research Database (Denmark)

    Berg, Tommy Winther

    2004-01-01

    This thesis describes the physics and applications of quantum dot semiconductor optical amplifiers based on numerical simulations. These devices possess a number of unique properties compared with other types of semiconductor amplifiers, which should allow enhanced performance of semiconductor...... and QW devices and to experiments on quantum dot amplifiers. These comparisons outline the qualitative differences between the different types of amplifiers. In all cases focus is put on the physical processes responsible the differences....... devices in communication systems in the future. The basic properties of quantum dot devices are investigated, especially regarding the potential of realizing amplification and signal processing without introducing pattern dependence. Also the gain recovery of a single short pulse is modeled...

  15. Chemically fabricated magnetic quantum dots of InP:Mn.

    Science.gov (United States)

    Sahoo, Y; Poddar, P; Srikanth, H; Lucey, D W; Prasad, P N

    2005-08-18

    Quantum dots of InP:Mn are chemically prepared by following hot colloidal nanochemistry with starting precursors that obviate the need for external surfactant. These quantum dots are uniform spheres with 3-nm diameters; they are crystalline, photoluminescent, and magnetic. The crystallographic and optical properties are similar to those of undoped InP nanocrystallites, while the magnetism is consistent with the ferromagnetic response observed in a class of diluted magnetic semiconductors. Because of the ultrafine sizes, the sample shows superparamagnetic behavior, whereas ferromagnetic hysteresis loops are clearly seen below the blocking temperature. Structural characterization and analysis confirm that the magnetism in these quantum dots is not due to segregated binary MnP or MnO phases and that they truly represent a homogeneous dilute magnetic semiconductor.

  16. Colloidal quantum dot solids for solution-processed solar cells

    KAUST Repository

    Yuan, Mingjian

    2016-02-29

    Solution-processed photovoltaic technologies represent a promising way to reduce the cost and increase the efficiency of solar energy harvesting. Among these, colloidal semiconductor quantum dot photovoltaics have the advantage of a spectrally tuneable infrared bandgap, which enables use in multi-junction cells, as well as the benefit of generating and harvesting multiple charge carrier pairs per absorbed photon. Here we review recent progress in colloidal quantum dot photovoltaics, focusing on three fronts. First, we examine strategies to manage the abundant surfaces of quantum dots, strategies that have led to progress in the removal of electronic trap states. Second, we consider new device architectures that have improved device performance to certified efficiencies of 10.6%. Third, we focus on progress in solution-phase chemical processing, such as spray-coating and centrifugal casting, which has led to the demonstration of manufacturing-ready process technologies.

  17. Charge pumping in strongly coupled molecular quantum dots

    Science.gov (United States)

    Haughian, Patrick; Yap, Han Hoe; Gong, Jiangbin; Schmidt, Thomas L.

    2017-11-01

    The interaction between electrons and the vibrational degrees of freedom of a molecular quantum dot can lead to an exponential suppression of the conductance, an effect which is commonly termed Franck-Condon blockade. Here, we investigate this effect in a quantum dot driven by time-periodic gate voltages and tunneling amplitudes using nonequilibrium Green's functions and a Floquet expansion. Building on previous results showing that driving can lift the Franck-Condon blockade, we investigate driving protocols which can be used to pump charge across the quantum dot. In particular, we show that due to the strongly coupled nature of the system, the pump current at resonance is an exponential function of the drive strength.

  18. A prototype silicon double quantum dot with dispersive microwave readout

    Science.gov (United States)

    Schmidt, A. R.; Henry, E.; Lo, C. C.; Wang, Y.-T.; Li, H.; Greenman, L.; Namaan, O.; Schenkel, T.; Whaley, K. B.; Bokor, J.; Yablonovitch, E.; Siddiqi, I.

    2014-07-01

    We present a unique design and fabrication process for a lateral, gate-confined double quantum dot in an accumulation mode metal-oxide-semiconductor (MOS) structure coupled to an integrated microwave resonator. All electrostatic gates for the double quantum dot are contained in a single metal layer, and use of the MOS structure allows for control of the location of the two-dimensional electron gas via the location of the accumulation gates. Numerical simulations of the electrostatic confinement potential are performed along with an estimate of the coupling of the double quantum dot to the microwave resonator. Prototype devices are fabricated and characterized by transport measurements of electron confinement and reflectometry measurements of the microwave resonator.

  19. A prototype silicon double quantum dot with dispersive microwave readout

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, A. R., E-mail: andrewrobertschmidt@gmail.com; Henry, E.; Namaan, O.; Siddiqi, I., E-mail: irfan-siddiqi@berkeley.edu [Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720 (United States); Lo, C. C.; Wang, Y.-T.; Bokor, J.; Yablonovitch, E. [Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720 (United States); Li, H. [Department of Physics, University of California, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Greenman, L.; Whaley, K. B. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Schenkel, T. [Accelerator and Fusion Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2014-07-28

    We present a unique design and fabrication process for a lateral, gate-confined double quantum dot in an accumulation mode metal-oxide-semiconductor (MOS) structure coupled to an integrated microwave resonator. All electrostatic gates for the double quantum dot are contained in a single metal layer, and use of the MOS structure allows for control of the location of the two-dimensional electron gas via the location of the accumulation gates. Numerical simulations of the electrostatic confinement potential are performed along with an estimate of the coupling of the double quantum dot to the microwave resonator. Prototype devices are fabricated and characterized by transport measurements of electron confinement and reflectometry measurements of the microwave resonator.

  20. Valley blockade in a silicon double quantum dot

    Science.gov (United States)

    Perron, Justin K.; Gullans, Michael J.; Taylor, Jacob M.; Stewart, M. D.; Zimmerman, Neil M.

    2017-11-01

    Electrical transport in double quantum dots (DQDs) illuminates many interesting features of the dots' carrier states. Recent advances in silicon quantum information technologies have renewed interest in the valley states of electrons confined in silicon. Here we show measurements of dc transport through a mesa-etched silicon double quantum dot. Comparing bias triangles (i.e., regions of allowed current in DQDs) at positive and negative bias voltages we find a systematic asymmetry in the size of the bias triangles at the two bias polarities. Asymmetries of this nature are associated with blocked tunneling events due to the occupation of a metastable state. Several features of our data lead us to conclude that the states involved are not simple spin states. Rather, we develop a model based on selective filling of valley states in the DQD that is consistent with all of the qualitative features of our data.

  1. Electron Transport in Quantum Dots and Heat Transport in Molecules

    DEFF Research Database (Denmark)

    Kirsanskas, Gediminas

    Since the invention of the transistor in 1947 and the development of integrated circuits in the late 1950’s, there was a rapid progress in the development and miniaturization of the solid state devices and electronic circuit components. This miniaturization raises a question “How small do we have...... and to perform electrical transport experiments at temperatures below one Kelvin (1 K), and thus to address such question. In this thesis we are concerned with the theoretical description of one kind of such devices called quantum dots. As the name suggest a quantum dot is a system where particles are confined...... in all three directions, which makes it effectively zero dimensional and corresponds to discrete electronic orbitals (levels) and excitation spectrum. This is analogous to the situation in atoms, where confinement potential replaces the potential of the nucleus, thus quantum dots are often referred...

  2. Visible-Light-Activated Bactericidal Functions of Carbon "Quantum" Dots.

    Science.gov (United States)

    Meziani, Mohammed J; Dong, Xiuli; Zhu, Lu; Jones, Les P; LeCroy, Gregory E; Yang, Fan; Wang, Shengyuan; Wang, Ping; Zhao, Yiping; Yang, Liju; Tripp, Ralph A; Sun, Ya-Ping

    2016-05-04

    Carbon dots, generally defined as small carbon nanoparticles with various surface passivation schemes, have emerged as a new class of quantum-dot-like nanomaterials, with their optical properties and photocatalytic functions resembling those typically found in conventional nanoscale semiconductors. In this work, carbon dots were evaluated for their photoinduced bactericidal functions, with the results suggesting that the dots were highly effective in bacteria-killing with visible-light illumination. In fact, the inhibition effect could be observed even simply under ambient room lighting conditions. Mechanistic implications of the results are discussed and so are opportunities in the further development of carbon dots into a new class of effective visible/natural light-responsible bactericidal agents for a variety of bacteria control applications.

  3. Diffusion Monte Carlo study of circular quantum dots

    Science.gov (United States)

    Pederiva, Francesco; Umrigar, C. J.; Lipparini, E.

    2000-09-01

    We present ground- and excited-state energies obtained from diffusion Monte Carlo (DMC) calculations, using accurate multiconfiguration wave functions, for N electrons (N<=13) confined to a circular quantum dot. We compare the density and correlation energies to the predictions of local spin density approximation (LSDA) theory and Hartree-Fock (HF) theory, and analyze the electron-electron pair-correlation functions. The DMC estimated change in electrochemical potential as a function of the number of electrons in the dot is compared to that from LSDA and HF calculations. Hund's first rule is found to be satisfied for all dots except N=4 for which there is a near degeneracy.

  4. Correlated Coulomb drag in capacitively coupled quantum-dot structures

    DEFF Research Database (Denmark)

    Kaasbjerg, Kristen; Jauho, Antti-Pekka

    2016-01-01

    We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs) -- a biasdriven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach which accounts for higher-order tunneling (cotunneling......) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multi-electron cotunneling processes. Our theory establishes the conditions for a nonzero drag as well as the direction of the drag current in terms of microscopic system parameters...... on Coulomb drag in CQD systems....

  5. Realization of electrically tunable single quantum dot nanocavities

    Energy Technology Data Exchange (ETDEWEB)

    Hofbauer, Felix Florian Georg

    2009-03-15

    We investigated the design, fabrication and optical investigation of electrically tunable single quantum dot-photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light matter interaction. We demonstrate that the quantum confined Stark effect can be employed to quickly and reversibly switch the dot-cavity coupling, simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by up to {proportional_to}4 meV relative to the nanocavity mode, before the emission quenches due to carrier tunneling escape from the dots. We directly probe spontaneous emission, irreversible polariton decay and the statistics of the emitted photons from a single-dot nanocavity in the weak and strong coupling regimes. New information is obtained on the nature of the dot-cavity coupling in the weak coupling regime and electrical control of zero dimensional polaritons is demonstrated for the first time. The structures investigated are p-i-n photodiodes consisting of an 180nm thick free-standing GaAs membrane into which a two dimensional photonic crystal is formed by etching a triangular lattice of air holes. Low mode volume nanocavities (V{sub mode}<1.6 ({lambda}/n){sup 3}) are realized by omitting 3 holes in a line to form L3 cavities and a single layer of InGaAs self-assembled quantum dots is embedded into the midpoint of the membrane. The nanocavities are electrically contacted via 35 nm thick p- and n-doped contact layers in the GaAs membrane. In the weak coupling regime, time resolved spectroscopy reveals a {proportional_to}7 x shortening of the spontaneous emission lifetime as the dot is tuned through the nanocavity mode, due to the Purcell effect. Upon strongly detuning the same quantum dot transition from the nanocavity mode we observe an additional {proportional_to}8 x lengthening of the spontaneous emission lifetime. These observations unequivocally highlight two regimes of dot

  6. Long coherence times in self-assembled semiconductor quantum dots

    DEFF Research Database (Denmark)

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

    2002-01-01

    We report measurements of ultra-long coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mueV, which is significantly smaller than the linewidth observed in single-dot...... luminescence. Time-resolved luminescence measurements show a lifetime of the dot ground state of 800 ps demonstrating the presence of pure dephasing at finite temperature. The homogeneous width is lifetime limited only at temperatures approaching 0 K....

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

    Science.gov (United States)

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

    2014-07-03

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

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

    Science.gov (United States)

    Rice, Charles V.; Giffin, Guinevere A.

    2008-01-01

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

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

    NARCIS (Netherlands)

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

    2016-01-01

    We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the

  10. Room-temperature dephasing in InAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang; Hvam, Jørn Märcher

    1999-01-01

    Summary form only given. Semiconductor quantum dots (QDs) are receiving increasing attention for fundamental studies on zero-dimensional confinement and for device applications. Quantum-dot lasers are expected to show superior performances, like high material gain, low and temperature...... stacked layers of InAs-InGaAs-GaAs quantum dots....

  11. Experimental realization of highly efficient broadband coupling of single quantum dots to a photonic crystal waveguide

    DEFF Research Database (Denmark)

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

    2008-01-01

    We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to a photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements -factors of up to 0...

  12. Fluorescent determination of graphene quantum dots in water samples

    Energy Technology Data Exchange (ETDEWEB)

    Benítez-Martínez, Sandra; Valcárcel, Miguel, E-mail: qa1meobj@uco.es

    2015-10-08

    This work presents a simple, fast and sensitive method for the preconcentration and quantification of graphene quantum dots (GQDs) in aqueous samples. GQDs are considered an object of analysis (analyte) not an analytical tool which is the most frequent situation in Analytical Nanoscience and Nanotechnology. This approach is based on the preconcentration of graphene quantum dots on an anion exchange sorbent by solid phase extraction and their subsequent elution prior fluorimetric analysis of the solution containing graphene quantum dots. Parameters of the extraction procedure such as sample volume, type of solvent, sample pH, sample flow rate and elution conditions were investigated in order to achieve extraction efficiency. The limits of detection and quantification were 7.5 μg L{sup −1} and 25 μg L{sup −1}, respectively. The precision for 200 μg L{sup −1}, expressed as %RSD, was 2.8%. Recoveries percentages between 86.9 and 103.9% were obtained for two different concentration levels. Interferences from other nanoparticles were studied and no significant changes were observed at the concentration levels tested. Consequently, the optimized procedure has great potential to be applied to the determination of graphene quantum dots at trace levels in drinking and environmental waters. - Highlights: • Development of a novel and simple method for determination of graphene quantum dots. • Preconcentration of graphene quantum dots by solid phase extraction. • Fluorescence spectroscopy allows fast measurements. • High sensitivity and great reproducibility are achieved.

  13. Preparation of carbon quantum dots based high photostability luminescent membranes.

    Science.gov (United States)

    Zhao, Jinxing; Liu, Cui; Li, Yunchuan; Liang, Jiyuan; Liu, Jiyan; Qian, Tonghui; Ding, Jianjun; Cao, Yuan-Cheng

    2017-06-01

    Urethane acrylate (UA) was used to prepare carbon quantum dots (C-dots) luminescent membranes and the resultants were examined with FT-IR, mechanical strength, scanning electron microscope (SEM) and quantum yields (QYs). FT-IR results showed the polyurethane acrylate (PUA) prepolymer -C = C-vibration at 1101 cm-1 disappeared but there was strong vibration at1687cm-1 which was contributed from the-C = O groups in cross-linking PUA. Mechanical strength results showed that the different quantity of C-dots loadings and UV-curing time affect the strength. SEM observations on the cross-sections of the membranes are uniform and have no structural defects, which prove that the C-dots are compatible with the water-soluble PUA resin. The C-dot loading was increased from 0 to 1 g, the maximum tensile stress was nearly 2.67 MPa, but the tensile strain was decreased from 23.4% to 15.1% and 7.2% respectively. QYs results showed that the C-dots in the membrane were stable after 120 h continuous irradiation. Therefore, the C-dots photoluminescent film is the promising material for the flexible devices in the future applications. Copyright © 2016 John Wiley & Sons, Ltd.

  14. Quantum size dependent optical nutation in CdSe/ZnS/CdSe quantum dot quantum well

    Science.gov (United States)

    Fang, Yinan; Xiao, Meng; Yao, Duanzheng

    2010-07-01

    The energy spectra and the optical nutation effect in CdSe/ZnS/CdSe quantum dot quantum well with core/shell/shell structure have been numerically studied and analyzed based on quantum theory and the effective mass approximation. For solving the uncertain coefficients A0, A1, B0, B1, A2, B2 and E, a new method has been used in the paper. It has been shown that the optical nutation signals of the CdSe/ZnS/CdSe quantum dot quantum well are dependent on the quantum size of the quantum dot quantum well and there exists an optimized condition for induced nutation signal, which is quite sensitive to the shells’ sizes of the QDQW with the core/shell/shell structure.

  15. Origin of luminescence quenching in structures containing CdSe/ZnSe quantum dots with a few Mn2 + ions

    Science.gov (United States)

    Oreszczuk, K.; Goryca, M.; Pacuski, W.; Smoleński, T.; Nawrocki, M.; Kossacki, P.

    2017-11-01

    We present a detailed spectroscopic study of photoluminescence quenching in epitaxial structures containing CdSe/ZnSe quantum dots doped with low concentration of Mn2 + ions. Our time-resolved and time-integrated experiments reveal the origin of the quenching observed in macro-photoluminescence studies of ensembles of such dots. We show that incorporation of even a few ions to an individual dot does not quench its luminescence effectively, although some fingerprints of expected spin-dependent quenching are visible. At the same time, the presence of Mn2 + ions in the sample significantly affects the luminescence intensity of the wetting layer, resulting in a quenching of the global luminescence from studied structure. On the other hand, the luminescence decay dynamics are found to be independent of the presence of Mn2 + ions, which suggests that the observed quenching occurs for the excited excitonic states.

  16. Quantum-dot based nanothermometry in optical plasmonic recording media

    Energy Technology Data Exchange (ETDEWEB)

    Maestro, Laura Martinez [Fluorescence Imaging Group, Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Autónoma de Madrid, Madrid 28049 (Spain); Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122 (Australia); Zhang, Qiming; Li, Xiangping; Gu, Min [Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122 (Australia); Jaque, Daniel [Fluorescence Imaging Group, Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Autónoma de Madrid, Madrid 28049 (Spain)

    2014-11-03

    We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media.

  17. Dynamics of semiconductor nanocrystals and quantum dot-dye assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Borczyskowski, Christian von [Center for Nanostructured Materials and Analytics (nanoMA), Chemnitz University of Technology, Chemnitz (Germany)

    2009-07-01

    Semiconductor quantum dots such as silicon or CdSe show rich dynamics of exciton formation and relaxation which can be investigated by single molecule techniques. Dynamics are controlled by electron-phonon coupling and photo-induced charge (blinking) and/or energy transfer (FRET). In this contribution we concentrate on the interplay of these processes. In general, this interplay can only be described properly by taking into account the spatial distribution of the exciton wave function. Moreover, we show that the wave function can be probed by single dye molecules attached to the surface of a single quantum dot.

  18. Gain dynamics and saturation in semiconductor quantum dot amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper; Hvam, Jørn Märcher

    2004-01-01

    Quantum dot (QD)-based semiconductor optical amplifiers offer unique properties compared with conventional devices based on bulk or quantum well material. Due to the bandfilling properties of QDs and the existence of a nearby reservoir of carriers in the form of a wetting layer, QD semiconductor...... optical amplifiers may be operated in regimes of high linearity, i.e. with a high saturation power, but can also show strong and fast nonlinearities by breaking the equilibrium between discrete dot states and the continuum of wetting layer states. In this paper, we analyse the interplay of these two...

  19. Device and Method of Scintillating Quantum Dots for Radiation Imaging

    Science.gov (United States)

    Burke, Eric R. (Inventor); DeHaven, Stanton L. (Inventor); Williams, Phillip A. (Inventor)

    2017-01-01

    A radiation imaging device includes a radiation source and a micro structured detector comprising a material defining a surface that faces the radiation source. The material includes a plurality of discreet cavities having openings in the surface. The detector also includes a plurality of quantum dots disclosed in the cavities. The quantum dots are configured to interact with radiation from the radiation source, and to emit visible photons that indicate the presence of radiation. A digital camera and optics may be used to capture images formed by the detector in response to exposure to radiation.

  20. Quantum Dots: Proteomics characterization of the impact on biological systems

    Science.gov (United States)

    Pozzi-Mucelli, Stefano; Boschi, F.; Calderan, L.; Sbarbati, A.; Osculati, F.

    2009-05-01

    Over the past few years, Quantum Dots have been tested in most biotechnological applications that use fluorescence, including DNA array technology, immunofluorescence assays, cell and animal biology. Quantum Dots tend to be brighter than conventional dyes, because of the compounded effects of extinction coefficients that are an order of magnitude larger than those of most dyes. Their main advantage resides in their resistance to bleaching over long periods of time (minutes to hours), allowing the acquisition of images that are crisp and well contrasted. This increased photostability is especially useful for three-dimensional (3D) optical sectioning, where a major issue is bleaching of fluorophores during acquisition of successive z-sections, which compromises the correct reconstruction of 3D structures. The long-term stability and brightness of Quantum Dots make them ideal candidates also for live animal targeting and imaging. The vast majority of the papers published to date have shown no relevant effects on cells viability at the concentration used for imaging applications; higher concentrations, however, caused some issues on embryonic development. Adverse effects are due to be caused by the release of cadmium, as surface PEGylation of the Quantum Dots reduces these issues. A recently published paper shows evidences of an epigenetic effect of Quantum Dots treatment, with general histones hypoacetylation, and a translocation to the nucleus of p53. In this study, mice treated with Quantum Dots for imaging purposes were analyzed to investigate the impact on protein expression and networking. Differential mono-and bidimensional electrophoresis assays were performed, with the individuation of differentially expressed proteins after intravenous injection and imaging analysis; further, as several authors indicate an increase in reactive oxygen species as a possible mean of damage due to the Quantum Dots treatment, we investigated the signalling pathway of APE1/Ref1, a

  1. Overview of Stabilizing Ligands for Biocompatible Quantum Dot Nanocrystals

    Directory of Open Access Journals (Sweden)

    Aaron Clapp

    2011-11-01

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

  2. Stark effect and polarizability of graphene quantum dots

    Science.gov (United States)

    Pedersen, Thomas Garm

    2017-09-01

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

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

    Science.gov (United States)

    Chou, Kenny F.; Dennis, Allison M.

    2015-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Kenny F. Chou

    2015-06-01

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

  5. Spin-dependent coupling between quantum dots and topological quantum wires

    Science.gov (United States)

    Hoffman, Silas; Chevallier, Denis; Loss, Daniel; Klinovaja, Jelena

    2017-07-01

    Considering Rashba quantum wires with a proximity-induced superconducting gap as physical realizations of Majorana bound states and quantum dots, we calculate the overlap of the Majorana wave functions with the local wave functions on the dot. We determine the spin-dependent tunneling amplitudes between these two localized states and show that we can tune into a fully spin polarized tunneling regime by changing the distance between dot and Majorana bound state. Upon directly applying this to the tunneling model Hamiltonian, we calculate the effective magnetic field on the quantum dot flanked by two Majorana bound states. The direction of the induced magnetic field on the dot depends on the occupation of the nonlocal fermion formed from the two Majorana end states which can be used as a readout for such a Majorana qubit.

  6. Glowing graphene quantum dots and carbon dots: properties, syntheses, and biological applications.

    Science.gov (United States)

    Zheng, Xin Ting; Ananthanarayanan, Arundithi; Luo, Kathy Qian; Chen, Peng

    2015-04-08

    The emerging graphene quantum dots (GQDs) and carbon dots (C-dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Quantum interference in a single anisotropic quantum dot near hyperbolic metamaterials.

    Science.gov (United States)

    Sun, Lu; Jiang, Chun

    2016-04-04

    We theoretically demonstrate an anisotropic quantum vacuum created by a judiciously designed hyperbolic metamaterial. An electric dipole located nearby shows strong orientation dependence in the decay rate. With a proper arrangement of the ellipsoid-shaped CdSe/ZnSe quantum dot relative to the Ag/TiO2 metamaterial, the anisotropies of quantum vacuum and quantum dot are harnessed to achieve an extraordinary quantum interference between radiative decay channels of orthogonal transitions. The ratio between cross damping term and spontaneous decay rate, Γij/Γii, which never exceeds unity in previously reported works reaches 1.04 in our numerical results. The corresponding evolution of excited state population in quantum dot is also dramatically modified.

  8. Complex dynamics in planar two-electron quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Schroeter, Sebastian Josef Arthur

    2013-06-25

    Quantum dots play an important role in a wide range of recent experimental and technological developments. In particular they are promising candidates for realisations of quantum bits and further applications in quantum information theory. The harmonically confined Hooke's atom model is experimentally verified and separates in centre-of-mass and relative coordinates. Findings that are contradictory to this separability call for an extension of the model, in particular changing the confinement potential. In order to study effects of an anharmonic confinement potential on spectral properties of planar two-electron quantum dots a sophisticated numerical approach is developed. Comparison between the Helium atom, Hooke's atom and an anharmonic potential model are undertaken in order to improve the description of quantum dots. Classical and quantum features of complexity and chaos are investigated and used to characterise the dynamics of the system to be mixed regular-chaotic. Influence of decoherence can be described by quantum fidelity, which measures the effect of a perturbation on the time evolution. The quantum fidelity of eigenstates of the system depends strongly on the properties of the perturbation. Several methods for solving the time-dependent Schrödinger equation are implemented and a high level of accuracy for long time evolutions is achieved. The concept of offset entanglement, the entanglement of harmonic models in the noninteracting limit, is introduced. This concept explains different questions raised in the literature for harmonic quantum dot models, recently. It shows that only in the groundstate the electrons are not entangled in the fermionic sense. The applicability, validity, and origin of Hund's first rule in general quantum dot models is further addressed. In fact Hund's first rule is only applicable, and in this case also valid, for one pair of singlet and triplet states in Hooke's atom. For more realistic models of two

  9. Self-assembled InAs quantum dots in an InGaAsN matrix on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Egorov, A.Yu. [Infineon Technologies, Corporate Research Photonics, Muenchen (Germany); Ioffe Physico-Technical Inst., St. Petersburg (Russian Federation); Bedarev, D. [Ioffe Physico-Technical Inst., St. Petersburg (Russian Federation); Bernklau, D.; Riechert, H. [Infineon Technologies, Corporate Research Photonics, Muenchen (Germany); Dumitras, G. [Technical Univ. of Munich, Garching (Germany). Dept. of Physics E16

    2001-04-01

    Self-assembled InAs quantum dots (QDs) are fabricated in In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01} and In{sub 0.06}Ga{sub 0.94}As{sub 0.98}N{sub 0.02} matrices on GaAs by solid source molecular beam epitaxy. The influence of InAs average layer thickness and matrix material on photoluminescence properties are studied. We observe a photoluminescence peak wavelength up to 1.49 {mu}m from structures with a nominal InAs thickness of four monolayers (ML). For QD structures emitting at 1.3 {mu}m, no saturation of ground state luminescence and no excited state photoluminescence are detected. This should lead to an improved performance of 1.3 {mu}m quantum dot lasers on GaAs. (orig.)

  10. Cavity length and stripe width dependent lasing characteristics of InAs/InP(1 0 0) quantum dot lasers

    Science.gov (United States)

    Li, S. G.; Gong, Q.; Wang, X. Z.; Cao, C. F.; Zhou, Z. W.; Wang, H. L.

    2016-03-01

    The lasing characteristics of InAs/InP(1 0 0) quantum dot lasers grown by gas source molecular beam epitaxy were carefully studied by varying cavity length and stripe width. With the increase of injection current, the lasers having a longer cavity length and a wider stripe width exhibited simultaneously two-lasing peaks or/three-lasing peaks. The high-energy peak undergoes continuous buleshift, while the low-energy peaks are somewhat fixed. At the same times, the injection current density decreased as the stripe width increase. When the lasers were applied to external cavity system, the shorter cavity length of InAs/InP quantum dot laser had a wider tunable range.

  11. 640 x 512 Pixels Long-Wavelength Infrared (LWIR) Quantum-Dot Infrared Photodetector (QDIP) Imaging Focal Plane Array

    Science.gov (United States)

    Gunapala, Sarath D.; Bandara, Sumith V.; Hill, Cory J.; Ting, David Z.; Liu, John K.; Rafol, Sir B.; Blazejewski, Edward R.; Mumolo, Jason M.; Keo, Sam A.; Krishna, Sanjay; hide

    2007-01-01

    Epitaxially grown self-assembled. InAs-InGaAs-GaAs quantum dots (QDs) are exploited for the development of large-format long-wavelength infrared focal plane arrays (FPAs). The dot-in-a-well (DWELL) structures were experimentally shown to absorb both 45 degrees and normal incident light, therefore, a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 micrometers, with peak detectivity reaching approximately 1 X 10(exp 10) Jones at 77 K. The devices were fabricated into the first long-wavelength 640 x 512 pixel QD infrared photodetector imaging FPA, which has produced excellent infrared imagery with noise equivalent temperature difference of 40 mK at 60-K operating temperature.

  12. Electron injection from colloidal PbS quantum dots into titanium dioxide nanoparticles.

    Science.gov (United States)

    Hyun, Byung-Ryool; Zhong, Yu-Wu; Bartnik, Adam C; Sun, Liangfeng; Abruña, Hector D; Wise, Frank W; Goodreau, Jason D; Matthews, James R; Leslie, Thomas M; Borrelli, Nicholas F

    2008-11-25

    Injection of photoexcited electrons from colloidal PbS quantum dots into TiO(2) nanoparticles is investigated. The electron affinity and ionization potential of PbS quantum dots, inferred from cyclic voltammetry measurements, show strong size dependence due to quantum confinement. On the basis of the measured energy levels, photoexcited electrons should transfer efficiently from the quantum dots into TiO(2) only for quantum-dot diameter below approximately 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of PbS quantum dots coupled to titanium dioxide nanoparticles are consistent with electron transfer for small quantum dots. The measured electron transfer time is surprisingly slow ( approximately 100 ns), and implications of this for future photovoltaics will be discussed. Initial results obtained from solar cells sensitized with PbS quantum dots are presented.

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

    Science.gov (United States)

    2011-01-01

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

  14. Temperature-dependent properties of single long-wavelength InGaAs quantum dots embedded in a strain reducing layer

    Science.gov (United States)

    Olbrich, Fabian; Kettler, Jan; Bayerbach, Matthias; Paul, Matthias; Höschele, Jonatan; Portalupi, Simone Luca; Jetter, Michael; Michler, Peter

    2017-05-01

    We report on temperature-dependent investigations of single metal-organic vapor phase epitaxy-grown In(Ga)As/GaAs quantum dots at wavelengths above 1 μm. Here, two types of samples are compared, whereas the quantum dots differ in the material composition and are embedded in a strain reducing layer to achieve an emission redshift. The analysis is performed by standard micro-photoluminescence spectroscopy, time-correlated photon counting, and intensity second-order autocorrelation measurements. It is found that the long-wavelength quantum dots experience a high charge carrier confinement (˜200 meV), but the thermal emission of carriers into the barrier or the wetting layer is mainly dominated by the shell spacing of individual dots. Additionally, we demonstrate that the single-dot carrier dynamics is reservoir-dominated. The influence of the strain reducing layers seems to cause this effect, leading to changes in the effective dot filling rate and charge configuration. Single-photon emission is preserved up to 77 K for a sample spectrally reaching the telecom O-band and then allowing for quantum dot single-photon operation at liquid nitrogen temperatures.

  15. Wave function mapping conditions in Open Quantum Dots structures

    OpenAIRE

    Mendoza, M.; Schulz, P. A.

    2003-01-01

    We discuss the minimal conditions for wave function spectroscopy, in which resonant tunneling is the measurement tool. Two systems are addressed: resonant tunneling diodes, as a toy model, and open quantum dots. The toy model is used to analyze the crucial tunning between the necessary resolution in current-voltage characteristics and the breakdown of the wave functions probing potentials into a level splitting characteristic of double quantum wells. The present results establish a parameter ...

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

    Science.gov (United States)

    Shuhui, Zhang; Lu, Wang; Zhenwu, Shi; Yanxiang, Cui; Haitao, Tian; Huaiju, Gao; Haiqiang, Jia; Wenxin, Wang; Hong, Chen; Liancheng, Zhao

    2012-01-25

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

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

    Science.gov (United States)

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

    2015-07-31

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

  18. Optimization and Characterization of Indium Arsenide Quantum Dots for Application in III-V Material Solar Cells

    Science.gov (United States)

    Podell, Adam P.

    In this work, InAs quantum dots grown by organometallic vapor-phase epitaxy (OMVPE) are investigated for application in III - V material solar cells. The first focus is on the opti- mization of growth parameters to produce high densities of uniform defect-free quantum dots via growth on 2" vicinal GaAs substrates. Parameters studied are InAs coverage, V/III ratio and growth rate. QDs are grown by the Stranski-Krastanov (SK) growth mode on (100) GaAs substrates misoriented toward (110) or (111) planes with various degrees of misorientation from 0° to 6°. Atomic force microscopy results indicated that as misorientation angle increased toward(110),critical thickness for quantum dot formation increased with theta c =1.8ML,1.9ML and 2.0 ML corresponding to 0°, 2° and 6°, respectively. Results for quantum dots grown on (111) misoriented substrates indicated, on average, that higher densities of quantum dots were achieved, compared with similar growths on substrates misoriented toward (110). Most notably, a stable average number density of 8 x 1010cm -2 was observed over a range of growth rates of 0.1ML/s - 0.4ML/s on (111) misoriented substrates compared with a decreasing number density as low as 2.85 x 1010cm -2 corresponding to a growth rate of 0.4ML/s grown on (110) misoriented substrates. p-i-n solar cell devices with a 10-layer quantum dot super- lattice imbedded in the i-region were also grown on (100) GaAs substrates misoriented 0°, 2° and 6° toward (110) as well as a set of devices grown on substrates misoriented toward (111). Device results showed a 1.0mA/cm2 enhancement to the short-circuit current for a v 2° misoriented device with 2.2 ML InAs coverage per quantum dot layer. Spectral response measurements were performed and integrated spectral response showed sub-GaAs bandgap short-circuit contribution which increased with increasing InAs coverage in the quantum dot layers from 0.04mA/cm2/ML, 0.28mA/cm2/ ML and 0.19mA/cm2/ML corresponding to 0°, 2

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-05-01

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

  20. Quantum efficiency of self-assembled quantum dots determined by a modified optical local density of states

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Stobbe, Søren; Nikolaev, I.S.

    2007-01-01

    We have measured time-resolved spontaneous emission from quantum dots near a dielectric interface with known photonic local density of states. We thus experimentally determine the quantum efficiency and the dipole moment, important for quantum optics.......We have measured time-resolved spontaneous emission from quantum dots near a dielectric interface with known photonic local density of states. We thus experimentally determine the quantum efficiency and the dipole moment, important for quantum optics....

  1. Far-infrared edge modes in quantum dots

    Science.gov (United States)

    Lipparini, E.; Barberán, N.; Barranco, M.; Pi, M.; Serra, Ll.

    1997-11-01

    We have investigated edge modes of different multipolarity sustained by quantum dots submitted to external magnetic fields. We present a microscopic description based on a variational solution of the equation of motion for any axially symmetric confining potential and multipole mode. Numerical results for dots with different numbers of electrons, whose ground state is described within a local current density-functional theory, are discussed. Two sum rules, which are exact within this theory, are derived. In the limit of a large neutral dot at B=0, we show that the classical hydrodynamic dispersion law for edge waves ω(q) ~q ln (q0/q) holds when quantum and finite-size effects are taken into account.

  2. Brueckner-Hartree-Fock study of circular quantum dots

    Science.gov (United States)

    Emperador, A.; Lipparini, E.; Serra, Ll.

    2006-06-01

    We calculate ground state energies in the Brueckner-Hartree-Fock theory for N electrons (with N⩽20 ) confined to a circular quantum dot and in presence of a static magnetic field. Comparison with the predictions of Hartree-Fock, local-spin-density and exact configuration-interaction theories is made. We find that the correlations taken into account in Brueckner-Hartree-Fock calculations give an important contribution to the ground state energies, especially in strongly confined dots. In this high-density range, corresponding in practice to self-assembled quantum dots, the results of Brueckner-Hartree-Fock calculations are close to the exact values and better than those obtained in the local-spin-density approximation.

  3. Out-of-Equilibrium Kondo Effect in Double Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Aguado, Ramon; Langreth, David C.

    2000-08-28

    The out-of-equilibrium transport properties of a double quantum dot system in the Kondo regime are studied theoretically by means of a two-impurity Anderson Hamiltonian with interimpurity hopping. The Hamiltonian is solved by means of a nonequilibrium generalization of the slave-boson mean-field theory. It is demonstrated that measurements of the differential conductance dI/dV , for appropriate values of voltages and tunneling couplings, can give a direct observation of the coherent superposition between the many-body Kondo states of each dot. For large voltages and arbitrarily large interdot tunneling, there is a critical voltage above which the physical behavior of the system again resembles that of two decoupled quantum dots. (c) 2000 The American Physical Society.

  4. Phonon mediated spin relaxation in a moving quantum dot

    Science.gov (United States)

    Zhao, Xinyu; Huang, Peihao; Hu, Xuedong

    2015-03-01

    We study decoherence of an electron spin qubit that is being transported in a moving quantum dot. Our focus is on spin relaxation due to phonon noise through the spin-orbit interaction. We find that the effective magnetic field caused by the motion of the electron can either enhance or suppress spin relaxation depending on the angle between the moving direction and the external magnetic field. At low external magnetic field (BAlt 0 . 5 T), the suppression effect can be significant, which indicates that a moving quantum dot can maintain spin coherence better than a static dot. We also find that the spin relaxation rate is not a monotonically increasing function of the applied magnetic field when the motion of the electron is taken into account. We thank financial support by US ARO and NSF PIF.

  5. Slow light in quantum dot photonic crystal waveguides

    DEFF Research Database (Denmark)

    Nielsen, Torben Roland; Lavrinenko, Andrei; Mørk, Jesper

    2009-01-01

    A theoretical analysis of pulse propagation in a semiconductor quantum dot photonic crystal waveguide in the regime of electromagnetically induced transparency is presented. The slow light mechanism considered here is based on both material and waveguide dispersion. The group index n......(g) for the combined system is significantly enhanced relative to slow light based on purely material or waveguide dispersion....

  6. Semiconductor quantum dot amplifiers for optical signal processing

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Uskov, A. V.; Bischoff, Svend

    2001-01-01

    The dynamics of quantum dot semiconductor amplifiers are investigated theoretically with respect to the potential for ultrafast signal processing. The high-speed signal processing capacity of these devices is found to be limited by the wetting layer dynamics in case of electrical pumping, while...... optical pumping partly removes this limitation. Also, the possibility of using spectral hole burning for signal processing is discussed....

  7. Recording force events of single quantum-dot endocytosis.

    Science.gov (United States)

    Shan, Yuping; Hao, Xian; Shang, Xin; Cai, Mingjun; Jiang, Junguang; Tang, Zhiyong; Wang, Hongda

    2011-03-28

    We applied force spectroscopy based on atomic force microscope (AFM) to demonstrate the possibility of measuring the interaction force between single quantum-dots (QDs) and living cells at single particle level under native conditions. In the force-distance cycle, we recorded the events of cellular uptake of single QDs and single QD detachment from the cell.

  8. Modelling exciton–phonon interactions in optically driven quantum dots

    DEFF Research Database (Denmark)

    Nazir, Ahsan; McCutcheon, Dara

    2016-01-01

    We provide a self-contained review of master equation approaches to modelling phonon effects in optically driven self-assembled quantum dots. Coupling of the (quasi) two-level excitonic system to phonons leads to dissipation and dephasing, the rates of which depend on the excitation conditions...

  9. Quantum dot amplifiers with high output power and low noise

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper

    2003-01-01

    Quantum dot semiconductor optical amplifiers have been theoretically investigated and are predicted to achieve high saturated output power, large gain, and low noise figure. We discuss the device dynamics and, in particular, show that the presence of highly inverted barrier states does not limit...

  10. Surface engineered quantum dots in photoelectrochemistry and supramolecular assembly

    NARCIS (Netherlands)

    Dorokhin, D.V.

    2010-01-01

    This thesis demonstrates the power of chemical surface engineering in the design and fabrication of functional hybrid materials made of Quantum Dots. The small size of the QDs, in the range of 1 to 10 nm, and related stability in solution, require a careful consideration of a proper surface

  11. Theory of coherent dynamic nuclear polarization in quantum dots

    DEFF Research Database (Denmark)

    Neder, Izhar; Rudner, Mark Spencer; Halperin, Bertrand

    2014-01-01

    We consider the production of dynamic nuclear spin polarization (DNP) in a two-electron double quantum dot, in which the electronic levels are repeatedly swept through a singlet-triplet avoided crossing. Our analysis helps to elucidate the intriguing interplay between electron-nuclear hyperfine c...

  12. Quantum Dots Embedded in Graphene Nanoribbons by Chemical Substitution

    DEFF Research Database (Denmark)

    Carbonell-Sanroma, Eduard; Brandimarte, Pedro; Balog, Richard

    2017-01-01

    Bottom-up chemical reactions of selected molecular precursors on a gold surface can produce high quality graphene nanoribbons (GNRs). Here, we report on the formation of quantum dots embedded in an armchair GNR by substitutional inclusion of pairs of boron atoms into the GNR backbone. The boron...

  13. Attachment of Quantum Dots on Zinc Oxide Nanorods

    Science.gov (United States)

    Seay, Jared; Liang, Huan; Harikumar, Parameswar

    2011-03-01

    ZnO nanorods grown by hydrothermal technique are of great interest for potential applications in photovoltaic and optoelectronic devices. In this study we investigate the optimization of the optical absorption properties by a low temperature, chemical bath deposition technique. Our group fabricated nanorods on indium tin oxide (ITO) substrate with precursor solution of zinc nitrate hexahydrate and hexamethylenetramine (1:1 molar ratio) at 95C for 9 hours. In order to optimize the light absorption characteristics of ZnO nanorods, CdSe/ZnS core-shell quantum dots (QDs) of various diameters were attached to the surface of ZnO nanostructures grown on ITO and gold-coated silicon substrates. Density of quantum dots was varied by controlling the number drops on the surface of the ZnO nanorods. For a 0.1 M concentration of QDs of 10 nm diameter, the PL intensity at 385 nm increased as the density of the quantum dots on ZnO nanostructures was increased. For quantum dots at 1 M concentration, the PL intensity at 385 nm increased at the beginning and then decreased at higher density. We will discuss the observed changes in PL intensity with QD concentration with ZnO-QD band structure and recombination-diffusion processes taking place at the interface.

  14. Ultrafast Dynamics of Quantum-Dot Semiconductor Optical Amplifiers

    DEFF Research Database (Denmark)

    Poel, Mike van der; Hvam, Jørn Märcher

    2007-01-01

    We report on a series of experiments on the dynamical properties of quantum-dot semiconductor optical amplifiers. We show how the amplifier responds to one or several ultrafast (170 fs) pulses in rapid succession and our results demonstrate applicability and ultimate limitations to application...

  15. Spontaneous emission of quantum dots in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren

    2010-01-01

    We report on the enhancement of the spontaneous emission rate of single semiconductor quantum dots embedded in a photonic crystal waveguide with engineered disorder. Random high-Q cavities, that are signature of Anderson localization, are measured in photoluminescence experiments and appear...

  16. THz Electro-absorption Effect in Quantum Dots

    DEFF Research Database (Denmark)

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

    2011-01-01

    In a THz pump - optical probe experiment we demonstrate an instantaneous electro-absorption effect in InGaAs/GaAs quantum dots, induced by the electric field of a single-cycle THz pulse with 3 THz bandwidth and with free-space peak electric field reaching 220 kV/cm. The transient modulation of QD...

  17. Dephasing in InAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang Werner; Mørk, Jesper

    1999-01-01

    The room-temperature dephasing in InAs/GaAs self-assembled quantum dots is measured using two independent methods: spectal-hole burning and four-wave mixing. Dephasing times weakly dependent on the excitation density are found, with a low density value of 290+/-80 fs from spectal-hole burning...

  18. Application of zinc oxide quantum dots in food safety

    Science.gov (United States)

    Zinc oxide quantum dots (ZnO QDs) are nanoparticles of purified powdered ZnO. The ZnO QDs were directly added into liquid foods or coated on the surface of glass jars using polylactic acid (PLA) as a carrier. The antimicrobial activities of ZnO QDs against Listeria monocytogenes, Salmonella Enteriti...

  19. One- and two-phonon capture processes in quantum dots

    DEFF Research Database (Denmark)

    Magnúsdóttir, Ingibjörg; Uskov, Alexander; Bischoff, Svend

    2002-01-01

    Multiphonon capture processes are investigated theoretically and found to contribute efficiently to the carrier injection into quantum dots. It is shown that two-phonon capture contributes where single-phonon capture is energetically inhibited and can lead to electron capture times of a few...

  20. Light emission in quantum dots and dyes doped polymer nanofibers

    Science.gov (United States)

    Li, Baojun; Cheng, Chang; Yang, Xianguang

    2018-01-01

    Polymer nanofibers are cheap and flexible building blocks for nanophotonic components. For high density nanophotonic integration, both passive and active polymer nanofibers are desirable. In contrast to passive polymer nanofibers, active polymer nanofibers are more desirable because they can act as a light source and waveguide simultaneously. In this talk, light emission in quantum dots and dyes doped polymer nanofibers will be introduced.