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Sample records for anisn format dot

  1. MARS-ORNL, Processing Program Collection for AMPX, CCCC, ANISN, DOT, MORSE Format Library. LINX, MINX Library Utility, Data Merge. BINX, MINX Utility and SPHINX Utility, BCD to BIN Library Conversion. CINX, MINX Utility and SPHINX Utility, Library Data Collapsing

    International Nuclear Information System (INIS)

    Description of problem or function: MARS-ORNL is a selection of computer codes for the generation of problem-dependent multigroup cross section libraries. They are selected modules from the AMPX-2 system for AMPX interface format libraries, LASL codes for CCCC interfaces, and processing codes for libraries to be used by ANISN, DOT, or MORSE codes. The codes in the collection are used in connection with the following DLC data libraries: ZZ-LIB-IV (DLC-0040), ZZ-VITAMIN-C (DLC-0041), VITAMIN-4C (DLC-0053), ZZ-CLEAR/42B (DLC-0042), ZZ-CSRL/43B (DLC-0043), and EPRMASTER (DLC-0052). The functions of these processing codes are briefly described: A. AMPX Modules: AIM: Converts AMPX Master Interface Files from EBCDIC to binary form and back. AJAX: Merges, collects, assembles, re-orders, joins, and copies selected nuclides from AMPX Master Interfaces. BONAMI: Accesses Bondarenko factors from an AMPX Master Library and performs resonance self-shielding calculations. CHOX: Produces a coupled interface library in AMPX format by combining neutron libraries (generated by module XLACS), gamma libraries (generated by module SMUG), and photon production libraries (generated by module LAPHNGAS). CHOXM: Combines self-shielding factors as generated by the code SPHINX (PSR-0129) and an infinite dilution neutron master interface (generated by XLACS) to generate a self-shielded neutron AMPX Interface File. The interface produced by CHOXM is an input to the NITAWL module of AMPX. CHOXM is a modified version of CHOX. COMAND: Collapses ANISN cross section libraries. DIAL: Produces edits from AMPX Master Interfaces. ICE-II: Accepts cross sections from an AMPX working library and produces mixed cross sections in four formats: (1) AMPX working library format; (2) ANISN format; (3) group-independent ANISN format; (4) Monte Carlo processed cross section library format. NITAWL: Produces self-shielded and working cross section libraries in the formats required by the ANISN, DOT, or MORSE codes

  2. TEST, Sort, Delete, List ANISN and DOT Cross-Sections Library Data

    International Nuclear Information System (INIS)

    1 - Description of program or function: Test is an auxiliary program for sorting, deleting and listing data contents of ANISN and DOT cross section libraries, generated with AMICO or any other program. 2 - Restrictions on the complexity of the problem: No restrictions on the number of energy groups or materials are noted because the program uses the variable dimension technique

  3. Study and application of ANISN and DOT-II nuclear cores in reactor physics problems

    International Nuclear Information System (INIS)

    To solve time-independent neutrons and/or gamma rays transport problems in nuclear reactors, two codes available at IPEN were studied and applied to solve benchmark problems. The ANISN code solves the one-dimensional Boltzmann transport equation for neutrons or gamma rays, in plane, spherical, or cylindrical geometries. The DOT-II code solves the same equation in two-dimensional space for plane, cylindrical and circular geometries. General anisotropic scattering allowed in both codes. Moreover, pointwise convergence criteria, and alternate step function difference equations are also used in order to remove the oscillating flux distributions, sometimes found in discrete ordinates solutions. Basic theories and numerical techniques used in these codes are studied and summarized. Benchmark problems have been solved using these codes. Comparisons of the results show that both codes can be used with confidence in the analysis of nuclear problems. (author)

  4. ZZ DLC-2D/100G, 100 Neutron-Group Cross-Section Library by SUPERTOG Calculation for ANISN, DOT

    International Nuclear Information System (INIS)

    1 - Nature of physical problem solved: Format: ANISN, DOT or DTF-4; Number of groups: 100; Nuclides: H, D, He, He-3, Li-6, Li-7, Be-9, B-10, B-11, C-12, N-14, O-16, Na-23, Mg, Al-27, Si, Cl, K, Ca, V, Cr, Mn-55, Fe, Co-59, Ni, Cu, Cu-63, Cu-65, Nb, Mo, Ag-107, Xe-135, Cs-133, Sm-149, Eu-151, Eu-153, Gd, Dy-164, Lu-175, Lu-176, Ta-181, Ta-182, W-182, W-183, W-184, W-186, Re-185, Re-187, Au-197, Pb, Th-232, Pa-233, U-234, U-235, U-238, Pu-238, Pu-239, Pu-240, Pu-241, Pu-242, Am-241, Am-243, and Cm-244. Origin: The nuclides in DLC-2 are those which have been released as category I ENDF/B by the National Neutron Cross Section Center, Brookhaven National Laboratory. Weighting spectrum: The explicit assumption was made that the flux has the shape of a fission spectrum joined at 0.0674 MeV by a 1/E tail. Neutron transport calculations can be performed with DLC-2 data. Since the data are intended for use in multigroup discrete-ordinates or Monte Carlo transport codes which treat anisotropic scattering, possible cross section angular expansion is limited only by the options available in the particular code used. Specifically, the retrieval program manipulates DLC-2 such that it conforms to input requirements of the ANISN, DOT, or DTF-4 codes, or any computer code using data in the ANISN or DTF-4 format. The nuclides in DLC-2 are those which have been released as category I ENDF/B by the National Neutron Cross Section Center, Brookhaven National Laboratory. The library contains data for H, D, He, 3-He, 6-Li, 7-Li, 9-Be, 10-B, 11-B, 12-C, 14-N, 16-O, 23-Na, Mg, 27-Al, Si, Cl, K, Ca, V, Cr, 55-Mn, Fe, 59-Co, Ni, Cu, 63-Cu, 65-Cu, Nb, Mo, 107-Ag, 135-Xe, 133-Cs, 149-Sm, 151-Eu, 153-Eu, Gd, 164-Dy, 175-Lu, 176-Lu, 181-Ta, 182-Ta, 182-W, 183-W, 184-W, 186-W, 185-Re, 187-Re, 197-Au, Pb, 232-Th, 233-Pa, 234-U, 235-U, 238-U, 238-Pu, 239-Pu, 240-Pu, 241-Pu, 242-Pu, 241-Am, 243-Am, and 244-Cm. 2 - Method of solution: DLC-2 was generated by SUPERTOG from nuclear data in either point

  5. ANISN-E, 1-D Transport Program ANISN with Exponential Model. ANISN-JR, 1-D Transport Program ANISN with ZZ JSD Data and Flux Plot

    International Nuclear Information System (INIS)

    A - Nature of physical problem solved: The ANISN system treats neutron and gamma transport in one- dimensional plane, spherical and cylinder geometry. The multigroup cross sections prepared by the programs LIANE and SUPERTOG are processed by the program RETTOG, which produces a binary library with Legendre expansions. The binary library can be updated and edited with the program LGR/B. The photon multigroup cross sections are created with the program GAMLEG/A. If the bulk of the data is too large, the program TAPEMA produces a special group-by-group library. The volume sources are calculated from a reduced set of input data and punched in a format suitable for input to ANISN, using the program PRESOU. ANISN calculates fluxes by groups, space intervals, angle and any number of reaction rates. The energy and space dependent fluxes are stored on tape and can be reprocessed, edited and plotted with the program ANISEX, which also permits to calculate supplementary reaction rates. The program ANISN can condense cross sections into a reduced number of groups. The ANISN system is used as a reference system for the evaluation of approximation methods (space-diffusion or point kernel) or for the preparation of multigroup libraries for two-dimensional transport codes (DOT). In particular it is used for shielding problems with high attenuation in water reactors and fast reactors. ANISN-E solves the same problems as the original ANISN code. Some modifications concern weighted cross sections output and fixed distributed sources input/output. ANISN-E (CCC-0082/09): The CYBER 175 version of ANISN-E also contains the free-format input capability. ANISN-JR extends the applicability of the original ANISN code for shielding analyses by adding options of calculating the reaction rates distributions from detector response, generating the volume- flux weighted cross sections in arbitrary regions or zones and plotting the neutron or gamma-ray spectra and the reaction rates distributions

  6. Study and application of the ANISN and DOT 3.5 codes to problems in nuclear radiation shielding

    International Nuclear Information System (INIS)

    The application of the Sn transport codes ANISN and DOT 3.5 to problems in radiation shielding is reviewed. In addition, a large array of codes involved in radiation shielding calculations is described and applied in this work. The ANISN and DOT 3.5 codes solve the multigroup transport equation in plane, cylindrical and spherical geometries, the first in one dimension and the second in two dimensions, by using the Sn approximation and were designed to solve coupled neutron-photon transport problems commonly found in reactor shielding calculations. In this work the numerical methods used in these codes are reviewed and their basic application to deep-penetration and void problems is discussed. Benchmark problems are solved by employing the array of codes previously mentioned. In particular, the ability of the ISOFLUXO program coupled to the DOT 3.5 code of mapping contours of regions with approximately the same scalar fluxes is illustrated, showing that they can be efficiently used in shielding analysis. (Author)

  7. Extension of ANISN and DOT 3.5 transport computer codes to calculate heat generation by radiation and temperature distribution in nuclear reactors

    International Nuclear Information System (INIS)

    The ANISN and DOT 3.5 codes solve the transport equation using the discrete ordinate method, in one and two-dimensions, respectively. The objectives of the study were to modify these two codes, frequently used in reactor shielding problems, to include nuclear heating calculations due to the interaction of neutrons and gamma-rays with matter. In order to etermine the temperature distribution, a numerical algorithm was developed using the finite difference method to solve the heat conduction equation, in one and two-dimensions, considering the nuclear heating from neutron and gamma-rays, as the source term. (Author)

  8. ZZ-IRAN-LIB, Multigroup Neutron Gamma Cross-Section Library for 33 Elements in ANISN Format

    International Nuclear Information System (INIS)

    Description of program or function: - Format: ANISN/PC; - Number of groups: IRAN1.LIB (22 neutrons 18 gammas); IRAN2.LIB (17 neutrons, 18 gammas); IRAN3.LIB (7 neutrons, 18 gammas); IRAN4.LIB (7 neutrons, 6 gammas); IRAN5.LIB (5 neutrons, 4 gammas); IRAN6.LIB (2 neutrons, 4 gammas). - Nuclides: H-1, H-2, Li-6, Li-7, Be-9, B-10, C-12, N-14, O-16, Na, Mg, Al-27, Si, K, V, Cr, Mn-55, Fe, Ni, Nb-93, Pb, U-235, U-238, Pu-239, Ba-134, Ba-135, Ba-136, Ba-137, Ba-140, Bi-209, Ca-nat, Zr-nat, Cd-nat. - Origin: VITAMIN-4C; ENDF/B-IV and V, and JENDL-3. Weighting spectrum: IRAN.LIB's data (microscopic cross sections) is suitable for neutron, gamma and coupled neutron- gamma transport calculation (shielding). It is intended for use by the multigroup discrete ordinates code ANISN/PC (CCC-0514) using anisotropic scattering by Legendre expansion up to order P-3. IRAN.LIB is a collection of libraries for elements (H-1; H-2; Li-6; Li-7; Be-9; B-10; C-12; N-14; O-16; Na; Mg; Al-27; Si; K; V; Cr; Mn-55; Fe; Ni; Nb-93; Pb; U-235; U-238; Pu-239; Ba-134; Ba-135; Ba-136; Ba-137; Ba-140; Bi-209; Ca-nat; Zr-nat; Cd-nat) in ISOTXS format with a different group structure for each library, that is, IRAN1.LIB (22 neutrons, 18 gammas); IRAN2.LIB (17 neutrons, 18 gammas); IRAN3.LIB (7 neutrons, 18 gammas); IRAN4.LIB (7 neutrons, 6 gammas); IRAN5.LIB (5 neutrons, 4 gammas); IRAN6.LIB (2 neutrons, 4 gammas). 2 - Method of solution: The basic data sources were VITAMIN-4C; ENDF/B-IV and V and JENDL-3. Most of the data were taken from VITAMIN-4C (H-1, H-2, Li-6, Li-7, Be-9, B-10, C-12, N-14, O-16, Na, Mg, Al-27, Si, K, V, Cr, Mn-55, Fe, Ni, Nb-93, Pb, U-235, U-238, Pu-239) and collapsing them using AMPX-II modules. The AJAX module extracts the neutron cross sections of desired elements from VITAMIN-4C. CHOX module combines master neutron, gamma production and gamma interaction libraries into a coupled neutron-gamma library. MALOCS module collapses the cross sections into given energy groups and

  9. APPLE, Plot of 1-D Multigroup Neutron Flux and Gamma Flux and Reaction Rates from ANISN

    International Nuclear Information System (INIS)

    A - Description of problem or function: The APPLE-2 code has the following functions: (1) It plots multi-group energy spectra of neutron and/or gamma ray fluxes calculated by ANISN, DOT-3.5, and MORSE. (2) It gives an overview plot of multi-group neutron fluxes calculated by ANISN and DOT-3.5. The scalar neutron flux phi(r,E) is plotted with the spatial parameter r linear along the Y-axis, logE along the X-axis and log phi(r,E) in the Z direction. (3) It calculates the spatial distribution and region volume integrated values of reaction rates using the scalar flux calculated with ANISN and DOT-3.5. (4) Reaction rate distribution along the R or Z direction may be plotted. (5) An overview plot of reaction rates or scalar fluxes summed over specified groups may be plotted. R(ri,zi) or phi(ri,zi) is plotted with spatial parameters r and z along the X- and Y-axes in an orthogonal coordinate system. (6) Angular flux calculated by ANISN is rearranged and a shell source at any specified spatial mesh point may be punched out in FIDO format. The shell source obtained may be employed in solving deep penetration problems with ANISN, when the entire reactor system is divided into two or more parts and the neutron fluxes in two adjoining parts are connected by using the shell source. B - Method of solution: (a) The input data specification is made as simple as possible by making use of the input data required in the radiation transport code. For example, geometry related data in ANISN and DOT are transmitted to APPLE-2 along with scalar flux data so as to reduce duplicity and errors in reproducing these data. (b) Most the input data follow the free form FIDO format developed at Oak Ridge National Laboratory and used in the ANISN code. Furthermore, the mixture specifying method used in ANISN is also employed by APPLE-2. (c) Libraries for some standard response functions required in fusion reactor design have been prepared and are made available to users of the 42-group neutron

  10. Computer code ANISN multiplying media and shielding calculation 2. Code description (input/output)

    International Nuclear Information System (INIS)

    The new code CCC-0514-ANISN/PC is described, as well as a ''GENERAL DESCRIPTION OF ANISN/PC code''. In addition to the ANISN/PC code, the transmittal package includes an interactive input generation programme called APE (ANISN Processor and Evaluator), which facilitates the work of the user in giving input. Also, a 21 group photon cross section master library FLUNGP.LIB in ISOTX format, which can be edited by an executable file LMOD.EXE, is included in the package. The input and output subroutines are reviewed. 6 refs, 1 fig., 1 tab

  11. ZZ DLC-14 AIR, Group Constant Library of Secondary Gamma Transport in Air for ANISN Calculation

    International Nuclear Information System (INIS)

    1 - Nature of physical problem solved: Format: ANISN, DOT, MORSE (FIDO format); Number of groups: 22 neutron / 18 gamma-ray; Nuclides: air; Origin: ENDF/B for neutron cross sections, DLC-4/HPIC for gamma-ray and DLC-12/POPLIB for secondary gamma-ray production. Weighting spectrum: 1/E for neutron cross sections. The basic idea behind the distribution of this ANISN input data is to allow potential users to repeat the ANISN calculations reported in ref. (1). It is felt that it will be more economical to repeat the calculations rather than to distribute the results of the Straker-Gritzner (1) calculations. However, the cross section part of the data can actually be used in DOT or MORSE or any transport code which will accept input cross section in the FIDO format. 2 - Method of solution: The sample input data for ANISN are for a P5, S16 calculation of the transport of neutrons and secondary gamma-rays from a 12.2 to 15 MeV point neutron source in an infinite air medium. The source is actually uniformly distributed in the first interval (500 cm radius) of a spherical medium of air with radius 3005 meters. The problem is set up for calculating various 'detector responses' by means of the 'activity' option available with ANISN. This is accomplished by providing a cross section table for a 'material' which has detector responses in certain table positions. Then the inclusion of appropriate input data for 22$ and 23$ arrays causes the group fluxes to be multiplied by the group response function values to give the desired answer. The neutron detector responses calculated by this sample problem are Henderson tissue dose, Snyder-Neufeld dose, tissue kerma, and air kerma. The gamma-ray response functions calculated are Henderson tissue dose and air kerma. The neutron cross sections were first reduced from point data from ENDF/B to a 104 fine group structure with a modified version of CSP, assuming a 1/E weighting factor. The gamma-ray data were reduced from point data from DLC

  12. 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.

  13. 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.

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

    Science.gov (United States)

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-01

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

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

    International Nuclear Information System (INIS)

    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

  16. Formation and ordering of epitaxial quantum dots

    Science.gov (United States)

    Atkinson, Paola; Schmidt, Oliver G.; Bremner, Stephen P.; Ritchie, David A.

    2008-10-01

    Single quantum dots (QDs) have great potential as building blocks for quantum information processing devices. However, one of the major difficulties in the fabrication of such devices is the placement of a single dot at a pre-determined position in the device structure, for example, in the centre of a photonic cavity. In this article we review some recent investigations in the site-controlled growth of InAs QDs on GaAs by molecular beam epitaxy. The method we use is ex-situ patterning of the GaAs substrate by electron beam lithography and conventional wet or dry etching techniques to form shallow pits in the surface which then determine the nucleation site of an InAs dot. This method is easily scalable and can be incorporated with marker structures to enable simple post-growth lithographic alignment of devices to each site-controlled dot. We demonstrate good site-control for arrays with up to 10 micron spacing between patterned sites, with no dots nucleating between the sites. We discuss the mechanism and the effect of pattern size, InAs deposition amount and growth conditions on this site-control method. Finally we discuss the photoluminescence from these dots and highlight the remaining challenges for this technique. To cite this article: P. Atkinson et al., C. R. Physique 9 (2008).

  17. Computer code ANISN multiplying media and shielding calculation II. Code description (input/output)

    International Nuclear Information System (INIS)

    The user manual of the ANISN computer code describing input and output subroutines is presented. ANISN code was developed to solve one-dimensional transport equation for neutron or gamma rays in slab, sphere or cylinder geometry with general anisotropic scattering. The solution technique is the discrete ordinate method. (M.C.K.)

  18. Dynamic Trap Formation and Elimination in Colloidal Quantum Dots

    KAUST Repository

    Voznyy, O.

    2013-03-21

    Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers\\' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping. © 2013 American Chemical Society.

  19. ANISN-JR, a one-dimensional discrete ordinates code for neutron and gamma-ray transport calculations

    International Nuclear Information System (INIS)

    The ANISN code available from RSIC is designed to solve the one-dimensional Boltzmann equation for deep penetration problems taking into consideration the anisotropic scattering by Legendre expansion of the scattering cross sections. To extend its applicability for shielding analyses, the code has been modified by adding options of calculating the reaction rates distributions from detector response, generating the volume-flux weighted cross sections in arbitrary regions or zones and plotting the neutron or gamma-ray spectra and the reaction rates distributions. The formats of input data necessary in the options are described in detail. (auth.)

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

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    Ted Thorbeck

    2015-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-08-15

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

  3. LEPRICON, PWR Vessel Dose Analysis with DORT and ANISN Program

    International Nuclear Information System (INIS)

    1 - Description of program or function: The LEPRICON system provides state-of-the-art routines to prepare input to and process results from the discrete ordinates codes CCC-484/DORT and CCC-254/ANISN to determine best estimates with uncertainties of group fluences in pressure vessels of pressurized water reactors. The system anticipates availability of results of dosimetry measurements performed in the reactor as well as sources operating during the time of exposure. 2 - Method of solution: Effects of time-dependent core source spatial distributions, when necessary, are treated by the use of an adjoint function coupled with a scaling technique. Sources are generated by combining the results of the diffusion theory code PDQ-7 pin-wise calculations with in-core assembly-wise instrumentation and are converted from X-Y to R-theta geometry. Fluxes calculated by the discrete ordinates codes are then synthesized to form 3-D distributions, and the resulting calculated dosimeter responses compared with the measurements, and adjustments performed in a generalized linear least-squares combination procedure. Through correlations generated from the input, adjustments to the originally calculated group fluxes at a selected point in the pressure vessel are then made, and the best estimates of the fluences accumulated during the time period analyzed are output along with their reduced uncertainties. 3 - Restrictions on the complexity of the problem: Much of the input data to the adjustment routine may be defaulted to 'built-in' values by proper choice of the input options. However, these values may not apply to every reactor, and a caveat must be issued that the user might have to alter some of the definitions of the flux bias factors to describe additional uncertainties peculiar to his own reactor. One may also override any default input if other values are judged more appropriate. The ISOPLOT4 source, sample input and output files are included on tape but were not tested by RSIC

  4. The Formation Site of Noninterfacial Misfit Dislocations in InAs/GaAs Quantum Dots

    Directory of Open Access Journals (Sweden)

    Shuai Zhou

    2014-01-01

    Full Text Available Taking elastic anisotropy into consideration, we use a dislocation position dependent model to calculate the preferential formation site of noninterfacial 60° mixed dislocation segment in ellipsoid shaped InAs/GaAs quantum dots (QDs which is observed in the experiment. From the result, it is clear that the positions near the right edge of the quantum dot are the energy favorable areas for the noninterfacial 60° mixed dislocations.

  5. Dotted collar placed around carotid artery induces asymmetric neointimal lesion formation in rabbits without intravascular manipulations

    Directory of Open Access Journals (Sweden)

    Kivelä Antti

    2012-10-01

    Full Text Available Abstract Background Neointimal formation in atherosclerosis has been subject for intense research. However, good animal models mimicking asymmetrical lesion formation in human subjects have been difficult to establish. The aim of this study was to develop a model which would lead to the formation of eccentric lesions under macroscopically intact non-denuded endothelium. Methods We have developed a new collar model where we placed two cushions or dots inside the collar. Arterial lesions were characterized using histology and ultrasound methods. Results When this dotted collar was placed around carotid and femoral arteries it produced asymmetrical pressure on adventitia and a mild flow disturbance, and hence a change in shear stress. Our hypothesis was that this simple procedure would reproducibly produce asymmetrical lesions without any intraluminal manipulations. Intima/media ratio increased towards the distal end of the collar with the direction of blood flow under macroscopically intact endothelium. Macrophages preferentially accumulated in areas of the thickest neointima thus resembling early steps in human atherosclerotic plaque formation. Proliferating cells in these lesions and underlying media were scarce at eight weeks time point. Conclusion The improved dotted collar model produces asymmetrical human-like atherosclerotic lesions in rabbits. This model should be useful in studies regarding the pathogenesis and formation of eccentric atherosclerotic lesions.

  6. Reproducible formation of single magnetic bubbles in an array of patterned dots

    Science.gov (United States)

    Liu, T.; Puliafito, V.; Montaigne, F.; Petit, S.; Deranlot, C.; Andrieu, S.; Ozatay, O.; Finocchio, G.; Hauet, T.

    2016-06-01

    The formation conditions of single magnetic bubbles through in-plane field demagnetization are investigated in an array of Co/Ni circular dots by magnetic force microscopy and compared to micromagnetic calculations. We demonstrate high success rates in nucleating stable bubbles. The efficiency of single bubble formation is found to depend not only on the dot size, material thickness and intrinsic material parameters but also on the bubble nucleation path. Experimental phase diagrams and micromagnetic calculations highlight the influence of the starting in-plane field amplitude and dipolar interactions in stabilizing the bubble. The identification of a systematic procedure for controlling nucleation of single bubbles, multidomain states or a uniform state is important from a technological point of view, opening a path toward the realization of reprogrammable magnonic crystals for the control of spin-wave propagation.

  7. Dynamical entanglement formation and dissipation effects in two double quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Contreras-Pulido, L D [Centro de Investigacion CientIfica y de Educacion Superior de Ensenada, Apartado Postal 2732, Ensenada, BC 22860 (Mexico); Rojas, F [Departamento de Fisica Teorica, Centro de Ciencias de la Materia Condensada, Universidad Nacional Autonoma de Mexico, Ensenada, Baja California 22800 (Mexico)

    2006-11-01

    We study the static and dynamic formation of entanglement in charge states of a two double quantum dot array with two mobile electrons under the effect of an external driving field. We include dissipation via contact with a phonon bath. By using the density matrix formalism and an open quantum system approach, we describe the dynamical behaviour of the charge distribution (polarization), concurrence (measure of the degree of entanglement) and Bell state probabilities (two qubit states with maximum entanglement) of such a system, including the role of dot asymmetry and temperature effects. Our results show that it is possible to obtain entangled states as well as a most probable Bell state, which can be controlled by the driving field. We also evaluate how the entanglement formation based on charge states deteriorates as the temperature or asymmetry increases.

  8. Nuclear criticality for thermal reactors using the two-group neutron Albedo method and ANISN code

    International Nuclear Information System (INIS)

    The neutron Albedo method applied to criticality calculations in nuclear reactors is characterized by following the neutron currents, allowing the detailed analyses of the physics phenomena about interactions of the neutrons with the core-reflector group, by the determination of the probabilities of reflection, absorption and transmission. Under two-group neutron Albedo method, the effective neutron multiplication factor, keff, explicitly appears and therefore it is possible to obtain an explicit result from the variation of keff. In the present work, motivated for excellent results presented in previous studies applied to thermal reactors and shieldings, the methodology using Albedo's method was described for the criticality analysis of thermal reactors by using two energy neutron groups admitting variable reflection and absorption coefficients of the core to each reentrant current. The obtained results were compared to the results for keff obtained with the ANISN code and the Diffusion method, both presenting very good concordance. (author)

  9. Analysis of a water moderated critical assembly with anisn-Vitamin C

    International Nuclear Information System (INIS)

    A tightly packed water moderated 233UO2--ThO2 critical assembly was analyzed with the Vitamin C library and the 1-D S/s n/ code, ANISN (S8,P3). The purpose of the study was to provide validation of this calculational model as applied to water-cooled hybrid fusion blankets. The quantities compared were the core eigenvalue and various activation shapes. The calculated eigenvalue was 1.02 +- 0.01. The 233U fission and 232Th capture shapes were found to be in good agreement (+-5%) with experiment, except near water--metal boundaries where differences up to 24% were observed. No such error peaking was observed in the 232Th fast fission shape. We conclude that the model provides good volume averaged reaction rates in water-cooled systems. However, care must be exercised near water boundaries where thermally dependent reaction rates are significantly underestimated

  10. InGaAs/GaAs (110) quantum dot formation via step meandering

    Energy Technology Data Exchange (ETDEWEB)

    Diez-Merino, Laura; Tejedor, Paloma [Department of Nanostructures and Surfaces, Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049-Madrid (Spain)

    2011-07-01

    InGaAs (110) semiconductor quantum dots (QDs) offer very promising prospects as a material base for a new generation of high-speed spintronic devices, such as single electron transistors for quantum computing. However, the spontaneous formation of InGaAs QDs is prevented by two-dimensional (2D) layer-by-layer growth on singular GaAs (110) substrates. In this work we have studied, by using atomic force microscopy and photoluminescence spectroscopy (PL), the growth of InGaAs/GaAs QDs on GaAs (110) stepped substrates by molecular beam epitaxy (MBE), and the modification of the adatom incorporation kinetics to surface steps in the presence of chemisorbed atomic hydrogen. The as-grown QDs exhibit lateral dimensions below 100 nm and emission peaks in the 1.35-1.37 eV range. It has been found that a step meandering instability derived from the preferential attachment of In adatoms to [110]-step edges relative to [11n]-type steps plays a key role in the destabilization of 2D growth that leads to 3D mound formation on both conventional and H-terminated vicinal substrates. In the latter case, the driving force for 3D growth via step meandering is enhanced by H-induced upward mass transport in addition to the lower energy cost associated with island formation on H-terminated substrates, which results in a high density array of InGaAs/GaAs dots selectively nucleated on the terrace apices with reduced lateral dimensions and improved PL efficiency relative to those of conventional MBE-grown samples.

  11. ZZ SINEX, 100 Neutron-Group Neutron Reaction Cross-Section Library from ENDF/B by SUPERTOG for ANISN

    International Nuclear Information System (INIS)

    1 - Nature of physical problem solved: Format: ANISN; Number of groups: 100 group reaction cross sections for neutron interactions. Nuclides: H, D, He, He-3, Li-6, Li-7, Be-9, B-10, B-11, C-12, N-14, O-16, Na-23, Mg, Al-27, Si, Cl, K, Ca, V, Cr, Mn-55, Fe, Co-59, Ni, Cu, Cu-63, Cu-65, Nb, Mo, Ag-107, Ag-109, Xe-135, Cs-133, Sm-149, Eu-151, Eu-153, Gd, Dy-164, Lu-175, Lu-176, Ta-181, Ta-182, W-182, W-183, W-184, W-186, Re-185, Re-187, Au-197, Pb, Th-232, Pa-233, U-234, U-235, U-238, Pu-238, Pu-239, Pu-240, Pu-241, Pu-242, Am-241, Am-243, and Cm-244. Origin: ENDF/B; Weighting spectrum: For the top 99 groups, the explicit assumption was made that the flux (weighting function) has the shape of a fission spectrum jointed at 0.0674 MeV by a 1/E tail. For the thermal group (group 100), values for all materials except hydrogen were taken from the Maxwellian average values derived from the ENDF/B data. The data can be used in combination with 100 group neutron transport calculations (using, e. g., the DLC-2 library) to determine the spatial distribution of individual reaction rates. In particular, the retrieval program allows the preparation of dummy materials based on DLC-24 which can be used in the activity calculation option in ANISN to calculate the desired reaction rates. The library consists of 100 group reaction cross sections for neutron interactions as follows - total, elastic, inelastic, (n,2n), fission, (n,n'α), (n,n'3α), (n,2nα), absorption, (n,n'p), capture, (n,γ), (n,p), (n,d), (n,t), (n,He3), (n,α), (n,2α), and ν-bar. The units are barns, except that ν-bar is the average number of neutrons per fission event. A table listing the reactions included for each material is found in ref.1. The nuclides in DLC-24 are those which have been released as category I ENDF/B by the National Neutron Cross Section Center, Brookhaven National Laboratory. The library contains data for H, D, He, 3-He, 6-Li, 7-Li, 9-Be, 10-B, 11-B, 12-C, 14-N, 16-O, 23-Na, Mg, 27-Al, Si

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

    International Nuclear Information System (INIS)

    We report a model for metalorganic vapor-phase epitaxy on non-planar substrates, specifically V-grooves and pyramidal recesses, which we apply to the growth of InGaAs nanostructures. This model—based on a set of coupled reaction-diffusion equations, one for each facet in the system—accounts for the facet-dependence of all kinetic processes (e.g., precursor decomposition, adatom diffusion, and adatom lifetimes) and has been previously applied to account for the temperature-, concentration-, and temporal-dependence of AlGaAs nanostructures on GaAs (111)B surfaces with V-grooves and pyramidal recesses. In the present study, the growth of In0.12Ga0.88As quantum wires at the bottom of V-grooves is used to determine a set of optimized kinetic parameters. Based on these parameters, we have modeled the growth of In0.25Ga0.75As nanostructures formed in pyramidal site-controlled quantum-dot systems, successfully producing a qualitative explanation for the temperature-dependence of their optical properties, which have been reported in previous studies. Finally, we present scanning electron and cross-sectional atomic force microscopy images which show previously unreported facetting at the bottom of the pyramidal recesses that allow quantum dot formation

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-04-28

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

  14. Formation of uniform high-density and small-size Ge/Si quantum dots by scanning pulsed laser annealing of pre-deposited Ge/Si film

    Science.gov (United States)

    Qayyum, Hamza; Lu, Chieh-Hsun; Chuang, Ying-Hung; Lin, Jiunn-Yuan; Chen, Szu-yuan

    2016-05-01

    The capability to fabricate Ge/Si quantum dots with small dot size and high dot density uniformly over a large area is crucial for many applications. In this work, we demonstrate that this can be achieved by scanning a pre-deposited Ge thin layer on Si substrate with a line-focused pulsed laser beam to induce formation of quantum dots. With suitable setting, Ge/Si quantum dots with a mean height of 2.9 nm, a mean diameter of 25 nm, and a dot density of 6×1010 cm-2 could be formed over an area larger than 4 mm2. The average size of the laser-induced quantum dots is smaller while their density is higher than that of quantum dots grown by using Stranski-Krastanov growth mode. Based on the dependence of the characteristics of quantum dots on the laser parameters, a model consisting of laser-induced strain, surface diffusion, and Ostwald ripening is proposed for the mechanism underlying the formation of the Ge/Si quantum dots. The technique demonstrated could be applicable to other materials besides Ge/Si.

  15. Formation of uniform high-density and small-size Ge/Si quantum dots by scanning pulsed laser annealing of pre-deposited Ge/Si film

    Directory of Open Access Journals (Sweden)

    Hamza Qayyum

    2016-05-01

    Full Text Available The capability to fabricate Ge/Si quantum dots with small dot size and high dot density uniformly over a large area is crucial for many applications. In this work, we demonstrate that this can be achieved by scanning a pre-deposited Ge thin layer on Si substrate with a line-focused pulsed laser beam to induce formation of quantum dots. With suitable setting, Ge/Si quantum dots with a mean height of 2.9 nm, a mean diameter of 25 nm, and a dot density of 6×1010 cm−2 could be formed over an area larger than 4 mm2. The average size of the laser-induced quantum dots is smaller while their density is higher than that of quantum dots grown by using Stranski-Krastanov growth mode. Based on the dependence of the characteristics of quantum dots on the laser parameters, a model consisting of laser-induced strain, surface diffusion, and Ostwald ripening is proposed for the mechanism underlying the formation of the Ge/Si quantum dots. The technique demonstrated could be applicable to other materials besides Ge/Si.

  16. TDA, Time-Dependent 1-D Neutron Transport, Gamma Transport by ANISN Method in Slab, Spherical, Cylindrical Geometry

    International Nuclear Information System (INIS)

    1 - Nature of physical problem solved: TDA (Time-Dependent ANISN) solves the one-dimensional time- dependent Boltzmann transport equation for neutrons and/or gamma- rays in slab, sphere or cylindrical geometries. Delayed neutron and other time-dependent effects are not considered in the present version. A choice of two types of sources and one initial condition specification is given (A. Space and energy distributed source with a step function time distribution. B. Analytical first collision source). 2 - Method of solution: TDA is based on the steady-state SN code ANISN for reasons of stability and generality. The weighted difference equations are used. 3 - Restrictions on the complexity of the problem: Limited only by available main storage

  17. Theory of multiple quantum dot formation in strained-layer heteroepitaxy

    Science.gov (United States)

    Du, Lin; Maroudas, Dimitrios

    2016-07-01

    We develop a theory for the experimentally observed formation of multiple quantum dots (QDs) in strained-layer heteroepitaxy based on surface morphological stability analysis of a coherently strained epitaxial thin film on a crystalline substrate. Using a fully nonlinear model of surface morphological evolution that accounts for a wetting potential contribution to the epitaxial film's free energy as well as surface diffusional anisotropy, we demonstrate the formation of multiple QD patterns in self-consistent dynamical simulations of the evolution of the epitaxial film surface perturbed from its planar state. The simulation predictions are supported by weakly nonlinear analysis of the epitaxial film surface morphological stability. We find that, in addition to the Stranski-Krastanow instability, long-wavelength perturbations from the planar film surface morphology can trigger a nonlinear instability, resulting in the splitting of a single QD into multiple QDs of smaller sizes, and predict the critical wavelength of the film surface perturbation for the onset of the nonlinear tip-splitting instability. The theory provides a fundamental interpretation for the observations of "QD pairs" or "double QDs" and other multiple QDs reported in experimental studies of epitaxial growth of semiconductor strained layers and sets the stage for precise engineering of tunable-size nanoscale surface features in strained-layer heteroepitaxy by exploiting film surface nonlinear, pattern forming phenomena.

  18. Analysis on radiation field around HT-7U tokamak device using 1-D discrete ordinates transport code ANISN

    International Nuclear Information System (INIS)

    Calculation and analysis on radiation field around HT-7U Tokamak device under the condition of D-D discharge have been performed with the one-dimensional discrete ordinate transport calculation code ANISN. The effects of concrete wall and borated water with different thicknesses on shielding have been analyzed. The spatial distribution of fluxes of neutrons and induced photons and dose rate equivalent can be used as a reference to the radiation protection design and environmental assessment of HT-7U device

  19. In situ formation and photo patterning of emissive quantum dots in small organic molecules.

    Science.gov (United States)

    Bansal, Ashu K; Sajjad, Muhammad T; Antolini, Francesco; Stroea, Lenuta; Gečys, Paulius; Raciukaitis, Gediminas; André, Pascal; Hirzer, Andreas; Schmidt, Volker; Ortolani, Luca; Toffanin, Stefano; Allard, Sybille; Scherf, Ullrich; Samuel, Ifor D W

    2015-07-01

    Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. Here we report a novel method for the fabrication and patterning of metal selenide nanoparticles in organic semiconductor films that is compatible with solution processable large area device manufacturing. Our approach is based upon the controlled in situ decomposition of a cadmium selenide precursor complex in a film of the electron transporting material 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBI) by thermal and optical methods. In particular, we show that the photoluminescence quantum yield (PLQY) of the thermally converted CdSe quantum dots (QDs) in the TPBI film is up to 15%. We also show that laser illumination can form the QDs from the precursor. This is an important result as it enables direct laser patterning (DLP) of the QDs. DLP was performed on these nanocomposites using a picosecond laser. Confocal microscopy shows the formation of emissive QDs after laser irradiation. The optical and structural properties of the QDs were also analysed by means of UV-Vis, PL spectroscopy and transmission electron microscopy (TEM). The results show that the QDs are well distributed across the film and their emission can be tuned over a wide range by varying the temperature or irradiated laser power on the blend films. Our findings provide a route to the low cost patterning of hybrid electroluminescent devices. PMID:26062105

  20. Transport through a triple quantum dot system: Formation of resonance band and its application as a spin filter

    Energy Technology Data Exchange (ETDEWEB)

    He, Zelong [Institute of Condensed-Matter Science and Technology, Harbin Institute of Technology, Harbin 150080 (China); Institute of Optoelectronic Technology, Heilongjiang Institute of Technology, Harbin 150050 (China); Lü, Tianquan, E-mail: ltq@hit.edu.cn [Institute of Condensed-Matter Science and Technology, Harbin Institute of Technology, Harbin 150080 (China)

    2012-07-23

    A three-quantum-dot spin filter based on nonequilibrium Green's function technique is proposed with external magnetic flux, Rashba spin orbit interaction, and intradot coulomb interaction taken into consideration. Numerical results indicate a spin filter can be made efficient by adjusting external magnetic flux and Rashba spin orbit interaction. Moreover, the formation of a resonance band is discussed through calculation. It is observed that the possibility of transition from one peak to other three peaks in the conductance spectrum increases with increasing interdot coupling strength. -- Highlights: ► Investigation of the conductance through a triple quantum dot system. ► Proposal of an efficient spin-filter device. ► Discussion on the formation of the resonance band. ► Study on spin polarization with intradot Coulomb interaction taken into consideration.

  1. The (Un)Lonely Planet Guide: Formation and Evolution of Planetary Systems from a `Blue Dots' Perspective

    OpenAIRE

    Meyer, Michael R.

    2010-01-01

    In this contribution I summarize some recent successes, and focus on remaining challenges, in understanding the formation and evolution of planetary systems in the context of the Blue Dots initiative. Because our understanding is incomplete, we cannot yet articulate a "design reference mission" engineering matrix suitable for an exploration mission where success is defined as obtaining a spectrum of a potentially habitable world around a nearby star. However, as progress accelerates, we can i...

  2. Assessing the occurrence of the dibromide radical (Br{sub 2}{sup -{center_dot}}) in natural waters: Measures of triplet-sensitised formation, reactivity, and modelling

    Energy Technology Data Exchange (ETDEWEB)

    De Laurentiis, Elisa; Minella, Marco; Maurino, Valter; Minero, Claudio [Universita degli Studi di Torino, Dipartimento di Chimica, Via P. Giuria 5, 10125 Torino (Italy); Mailhot, Gilles; Sarakha, Mohamed [Clermont Universite, Universite Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6296, ICCF, F-63171 Aubiere (France); Brigante, Marcello, E-mail: marcello.brigante@univ-bpclermont.fr [Clermont Universite, Universite Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6296, ICCF, F-63171 Aubiere (France); Vione, Davide, E-mail: davide.vione@unito.it [Universita degli Studi di Torino, Dipartimento di Chimica, Via P. Giuria 5, 10125 Torino (Italy); Universita degli Studi di Torino, Centro Interdipartimentale NatRisk, Via Leonardo da Vinci 44, 10095 Grugliasco (Italy)

    2012-11-15

    The triplet state of anthraquinone-2-sulphonate (AQ2S) is able to oxidise bromide to Br{sup {center_dot}}/Br{sub 2}{sup -{center_dot}}, with rate constant (2-4) Dot-Operator 10{sup 9} M{sup -1} s{sup -1} that depends on the pH. Similar processes are expected to take place between bromide and the triplet states of naturally occurring chromophoric dissolved organic matter ({sup 3}CDOM*). The brominating agent Br{sub 2}{sup -{center_dot}} could thus be formed in natural waters upon oxidation of bromide by both {sup {center_dot}}OH and {sup 3}CDOM*. Br{sub 2}{sup -{center_dot}} would be consumed by disproportionation into bromide and bromine, as well as upon reaction with nitrite and most notably with dissolved organic matter (DOM). By using the laser flash photolysis technique, and phenol as model organic molecule, a second-order reaction rate constant of {approx} 3 Dot-Operator 10{sup 2} L (mg C){sup -1} s{sup -1} was measured between Br{sub 2}{sup -{center_dot}} and DOM. It was thus possible to model the formation and reactivity of Br{sub 2}{sup -{center_dot}} in natural waters, assessing the steady-state [Br{sub 2}{sup -{center_dot}}] Almost-Equal-To 10{sup -13}-10{sup -12} M. It is concluded that bromide oxidation by {sup 3}CDOM* would be significant compared to oxidation by {sup {center_dot}}OH. The {sup 3}CDOM*-mediated process would prevail in DOM-rich and bromide-rich environments, the latter because elevated bromide would completely scavenge {sup {center_dot}}OH. Under such conditions, {sup {center_dot}}OH-assisted formation of Br{sub 2}{sup -{center_dot}} would be limited by the formation rate of the hydroxyl radical. In contrast, the formation rate of {sup 3}CDOM* is much higher compared to that of {sup {center_dot}}OH in most surface waters and would provide a large {sup 3}CDOM* reservoir for bromide to react with. A further issue is that nitrite oxidation by Br{sub 2}{sup -{center_dot}} could be an important source of the nitrating agent {sup {center_dot

  3. Polyol-mediated C-dot formation showing efficient Tb3+/Eu3+ emission.

    Science.gov (United States)

    Dong, Hailong; Kuzmanoski, Ana; Gössl, Dorothee M; Popescu, Radian; Gerthsen, Dagmar; Feldmann, Claus

    2014-07-18

    C-dots (3-5 nm in diameter) obtained by most simple heating of polyols (glycerol, diethylene glycol and PEG 400) show intense blue and green emission (50% quantum yield). Upon modification with TbCl3/EuCl3, energy transfer from the C-dots to the rare-earth metal results in line-type Tb(3+) (green)/Eu(3+) (red) emission with quantum yields up to 85%. PMID:24887063

  4. Quantum dot formation and dynamic scaling behavior of SnO2 nanocrystals induced by pulsed delivery

    Science.gov (United States)

    Chen, Z. W.; Lai, J. K. L.; Shek, C. H.

    2006-01-01

    Quantum dot formation and dynamic scaling behavior of SnO2 nanocrystals in coalescence regime for growth by pulsed-laser deposition is explored experimentally and theoretically, and the same is compared with that for continuous vapor deposition such as molecular-beam epitaxy. Using high-resolution transmission electron microscopy, unusual quantum dots of SnO2 nanocrystals are studied. We present kinetic Monte-Carlo simulations for pulsed-laser deposition in the submonolayer regime and give a description of the island distance versus pulse intensity. We found that the scaling exponent for pulsed-laser deposition is 1.28±0.03, which is significantly lower as compared to that for molecular-beam epitaxy (1.62±0.03). Theoretical simulations reveal that this attractive difference can be pursued to the large fraction of multiple droplet coalescence under pulsed vapor delivery.

  5. UV-initiated formation of noble metal nanoparticles on zinc oxide quantum dots

    International Nuclear Information System (INIS)

    Full text: Quantum dots (nanosized semiconductor particles) are a relatively new phenomenon. They exhibit unusual properties as a result of spatial electron confinement within the particles, including an increased band gap energy and blue-shifted fluorescence. Quantum dots and nanoparticles have attracted a lot of academic and industrial interest because of their special properties, including small size and potential as catalysts, 'tunable' fluorescence, and potential use in biomedical applications. Still, there are many properties of quantum dots that need further investigation if they are to be fully utilised. The interaction between nanosized noble metal colloids and zinc oxide quantum dots (Q-ZnO) under UV-irradiation provides valuable information about the electronic structure of Q-ZnO. In a sample containing Q-ZnO and Pt6+, Au+ or Ag+, electrons from excited Q-ZnO were transferred to the metal ions, and consequently, metal particles were reduced onto the Q-ZnO particles. The processes that occur can be followed spectroscopically. The results will be discussed during the presentation. A Transmission Electron Microscope image of a 3nm zinc oxide quantum dot, with lattice planes clearly visible is presented

  6. Formation and properties of selected quantum dots in maize amylopectin matrix

    Energy Technology Data Exchange (ETDEWEB)

    Khachatryan, Karen, E-mail: rrchacza@cyf-kr.edu.pl [Department of Chemistry and Physics, Agricultural University, Balicka Street 122, 30 149 Krakow (Poland); Khachatryan, Gohar; Fiedorowicz, Maciej [Department of Chemistry and Physics, Agricultural University, Balicka Street 122, 30 149 Krakow (Poland); Tomasik, Piotr [Krakow College of Health Promotion, Krowoderska Street 73, 31 158 Krakow (Poland)

    2014-09-01

    Highlights: • Synthesis of quantum dots in aqueous gel of amylopectin. • Generation of quantum dots in non-ionic polysaccharide. • Preparation of CdS, Ga{sub 2}S{sub 3} and ZnS quantum dots of the size below 10 nm. • The amylopectin matrix is not suitable for generation of CaS and Cs{sub 2}S quantum dots. - Abstract: CdS, ZnS, Ga{sub 2}S{sub 3}, CaS and Cs{sub 2}S quantum dots (QDs) were generated in the amylopectin (Ap) matrix. They all emitted a light between 460 (ZnS) and 475 (CdS) nm. Sizes of Ga{sub 2}S{sub 3} and CdS QDs were 7–9 nm and 5–7 nm, respectively. Single ZnS QDs had 6–7 nm but they readily aggregated. The CaS and Cs{sub 2}S appeared mainly as 30–100 nm aggregates. There were no significant interactions between QDs and the Ap matrix. Presented method appeared unsuitable for the generation of CaS and Cs{sub 2}S QDs as they as well as their substrates [Ca(NO{sub 3}){sub 2}] hydrolyzed. Calcium compounds formed complexes with Ap and alkaline solution from CsOH could produce cesium salts of Ap as well as cause oxidation of Ap.

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

    OpenAIRE

    Somsak Panyakeow

    2010-01-01

    Laterally close-packed quantum dots (QDs) called quantum dot molecules (QDMs) are grown by modified molecular beam epitaxy (MBE). Quantum dots could be aligned and cross hatched. Quantum rings (QRs) created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs) and quantum dot rings (QDRs). Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA) is late...

  8. ANISN-L, a CDC-7600 code which solves the one-dimensional, multigroup, time dependent transport equation by the method of discrete ordinates

    Energy Technology Data Exchange (ETDEWEB)

    Wilcox, T. P.

    1973-09-20

    The code ANISN-L solves the one-dimensional, multigroup, time-independent Boltzmann transport equation by the method of discrete ordinates. In problems involving a fissionable system, it can calculate the system multiplication or alpha. In such cases, it is also capable of determining isotopic concentrations, radii, zone widths, or buckling in order to achieve a given multiplication or alpha. The code may also calculate fluxes caused by a specified fixed source. Neutron, gamma, and coupled neutron--gamma problems may be solved in either the forward or adjoint (backward) modes. Cross sections describing upscatter, as well as the usual downscatter, may be employed. This report describes the use of ANISN-L; this is a revised version of ANISN which handles both large and small problems efficiently on CDC-7600 computers. (RWR)

  9. The (Un)Lonely Planet Guide: Formation and Evolution of Planetary Systems from a `Blue Dots' Perspective

    CERN Document Server

    Meyer, Michael R

    2010-01-01

    In this contribution I summarize some recent successes, and focus on remaining challenges, in understanding the formation and evolution of planetary systems in the context of the Blue Dots initiative. Because our understanding is incomplete, we cannot yet articulate a "design reference mission" engineering matrix suitable for an exploration mission where success is defined as obtaining a spectrum of a potentially habitable world around a nearby star. However, as progress accelerates, we can identify observational programs that would address fundamental scientific questions through hypothesis testing such that the null result is interesting.

  10. The (Un)Lonely Planet Guide: Formation and Evolution of Planetary Systems from a ``Blue Dots'' Perspective

    Science.gov (United States)

    Meyer, M. R.

    2010-10-01

    In this contribution I summarize some recent successes, and focus on remaining challenges, in understanding the formation and evolution of planetary systems in the context of the Blue Dots initiative. Because our understanding is incomplete, we cannot yet articulate a design reference mission engineering matrix suitable for an exploration mission where success is defined as obtaining a spectrum of a potentially habitable world around a nearby star. However, as progress accelerates, we can identify observational programs that would address fundamental scientific questions through hypothesis testing such that the null result is interesting.

  11. Formation of visible single-mode light sources using quantum dots

    Science.gov (United States)

    Baig, Sarfaraz; Xu, Jianfeng; Wu, Pengfei; Chen, Bing; Wang, Michael

    2008-08-01

    The market demands for innovative, efficient, small package and single-mode light sources are always high because of their broad applications in scientific, medical, industrial, and commercial fields. The high photoluminescence quantum yield, photophysical and photochemical stability, and tunable emission wavelength make quantum dots ideal for a new generation of solid state light sources. We report on the realization of various single-mode light sources in the visible spectral band by using semiconductor quantum dots. The effective use of a waveguide structure can help achieve the divergence control of the output light beam. This technique may benefit the development for next generation light emitting diodes, optical communication, intelligent optical sensors, microprocessors, and nanoscale optical imaging systems.

  12. Formation of quantum wires and dots on InP(001) by As/P exchange

    International Nuclear Information System (INIS)

    We report on the use of in situ scanning tunneling microscopy to study As/P exchange on InP(001) surfaces by molecular beam epitaxy. Results demonstrate that the exchange process can be controlled to selectively produce either quantum wires or quantum dots. 15 nm wide self-assembled nanowires are observed, and they are elongated along the dimer row direction of the InP(001)-2x4 surface with a length of over 1 μm and flat top 2x4 surfaces. In addition, when the nanowires are annealed with no arsenic overpressure, the surface reconstruction transforms from 2x4 to 4x2 and the nanowires transform into dots with a rectangular base and flat top. [copyright] 2001 American Institute of Physics

  13. 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.

  14. Formation of dot arrays with a pitch of 20 nm x 20 nm for patterned media using 30 keV EB drawing on thin calixarene resist

    Energy Technology Data Exchange (ETDEWEB)

    Mohamad, Zulfakri bin [Department of Nano-Material System, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan); Shirai, Masumi [Department of Nano-Material System, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan); Sone, Hayato [Department of Production Science and Technology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan); Hosaka, Sumio [Department of Production Science and Technology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan); Kodera, Masatoshi [Department of Electronics, Information and Communication Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585 (Japan)

    2008-01-16

    We studied the possibility of achieving very fine-pitch dot arrays with a pitch of 20 nm x 20 nm using 30 keV electron beam (EB) drawing on negative calixarene resist. In order to form such patterns, we studied the dependence on resist thickness of the dot size and the packing. We propose EB drawing on an extremely thin film for very highly packed dot-array formation. Our experimental results demonstrate the possibility of forming highly packed dot-array patterns with a pitch of 20 nm x 20 nm and a resist thickness of about 13 nm, which corresponds to about 1.6 Tbits in{sup -2}.

  15. The Role of Groove Periodicity in the Formation of Site-Controlled Quantum Dot Chains

    OpenAIRE

    Schramm, Andreas; Hakkarainen, Teemu V; Tommila, Juha; Guina, Mircea

    2015-01-01

    Structural and optical properties of InAs quantum dot (QD) chains formed in etched GaAs grooves having different periods from 200 to 2000 nm in [010] orientation are reported. The site-controlled QDs were fabricated by molecular beam epitaxy on soft UV-nanoimprint lithography-patterned GaAs(001) surfaces. Increasing the groove periods decreases the overall QD density but increases the QD size and the linear density along the groove direction. The effect of the increased QD size with larger pe...

  16. Ex situ formation of metal selenide quantum dots using bacterially derived selenide precursors

    International Nuclear Information System (INIS)

    Luminescent quantum dots were synthesized using bacterially derived selenide (SeII−) as the precursor. Biogenic SeII− was produced by the reduction of SeIV by Veillonella atypica and compared directly against borohydride-reduced SeIV for the production of glutathione-stabilized CdSe and β-mercaptoethanol-stabilized ZnSe nanoparticles by aqueous synthesis. Biological SeII− formed smaller, narrower size distributed QDs under the same conditions. The growth kinetics of biologically sourced CdSe phases were slower. The proteins isolated from filter sterilized biogenic SeII− included a methylmalonyl-CoA decarboxylase previously characterized in the closely related Veillonella parvula. XAS analysis of the glutathione-capped CdSe at the S K-edge suggested that sulfur from the glutathione was structurally incorporated within the CdSe. A novel synchrotron based XAS technique was also developed to follow the nucleation of biological and inorganic selenide phases, and showed that biogenic SeII− is more stable and more resistant to beam-induced oxidative damage than its inorganic counterpart. The bacterial production of quantum dot precursors offers an alternative, ‘green’ synthesis technique that negates the requirement of expensive, toxic chemicals and suggests a possible link to the exploitation of selenium contaminated waste streams. (paper)

  17. In(Ga)As quantum dot formation on group-III assisted catalyst-free InGaAs nanowires

    International Nuclear Information System (INIS)

    Growth of GaAs and InxGa1-xAs nanowires by the group-III assisted molecular beam epitaxy growth method on (001)GaAs/SiO2 substrates is studied in dependence on growth temperature, with the objective of maximizing the indium incorporation. Nanowire growth was achieved for growth temperatures as low as 550 deg. C. The incorporation of indium was studied by low temperature micro-photoluminescence spectroscopy, Raman spectroscopy and electron energy loss spectroscopy. The results show that the incorporation of indium achieved by lowering the growth temperature does not have the effect of increasing the indium concentration in the bulk of the nanowire, which is limited to 3-5%. For growth temperatures below 575 0C, indium rich regions form at the surface of the nanowires as a consequence of the radial growth. This results in the formation of quantum dots, which exhibit spectrally narrow luminescence.

  18. The Role of Groove Periodicity in the Formation of Site-Controlled Quantum Dot Chains.

    Science.gov (United States)

    Schramm, Andreas; Hakkarainen, Teemu V; Tommila, Juha; Guina, Mircea

    2015-12-01

    Structural and optical properties of InAs quantum dot (QD) chains formed in etched GaAs grooves having different periods from 200 to 2000 nm in [010] orientation are reported. The site-controlled QDs were fabricated by molecular beam epitaxy on soft UV-nanoimprint lithography-patterned GaAs(001) surfaces. Increasing the groove periods decreases the overall QD density but increases the QD size and the linear density along the groove direction. The effect of the increased QD size with larger periods is reflected in ensemble photoluminescence measurements as redshift of the QD emission. Furthermore, we demonstrate the photoluminescence emission from single QD chains. PMID:26058509

  19. Analysis of Cl center dot center dot center dot Cl and C-H center dot center dot center dot Cl intermolecular interactions involving chlorine in substituted 2-chloroquinoline derivatives

    OpenAIRE

    Hathwar, Venkatesha R.; Roopan, Mohana S; R. Subashini; Khan, Nawaz F; Row, Guru TN

    2010-01-01

    Six crystal structures of substituted 2-chloroquinoline derivatives have been analysed to evaluate the role of Cl atom as a self recognizing unit resulting in the formation of Cl center dot center dot center dot Cl and C-H center dot center dot center dot Cl interactions to generate supramolecular assembly in the solid state. The features of Type I and Type II geometries associated with Cl center dot center dot center dot Cl interactions have been analysed to show directional preferences lead...

  20. Water electrolysis with a conducting carbon cloth: subthreshold hydrogen generation and superthreshold carbon quantum dot formation.

    Science.gov (United States)

    Biswal, Mandakini; Deshpande, Aparna; Kelkar, Sarika; Ogale, Satishchandra

    2014-03-01

    A conducting carbon cloth, which has an interesting turbostratic microstructure and functional groups that are distinctly different from other ordered forms of carbon, such as graphite, graphene, and carbon nanotubes, was synthesized by a simple one-step pyrolysis of cellulose fabric. This turbostratic disorder and surface chemical functionalities had interesting consequences for water splitting and hydrogen generation when such a cloth was used as an electrode in the alkaline electrolysis process. Importantly, this work also gives a new twist to carbon-assisted electrolysis. During electrolysis, the active sites in the carbon cloth allow slow oxidation of its surface to transform the surface groups from COH to COOH and so forth at a voltage as low as 0.2 V in a two-electrode system, along with platinum as the cathode, instead of 1.23 V (plus overpotential), which is required for platinum, steel, or even graphite anodes. The quantity of subthreshold hydrogen evolved was 24 mL cm(-2)  h(-1) at 1 V. Interestingly, at a superthreshold potential (>1.23 V+overpotential), another remarkable phenomenon was found. At such voltages, along with the high rate and quantity of hydrogen evolution, rapid exfoliation of the tiny nanoscale (5-7 nm) units of carbon quantum dots (CQDs) are found in copious amounts due to an enhanced oxidation rate. These CQDs show bright-blue fluorescence under UV light. PMID:24492961

  1. Determination of neutron flux distribution by using ANISN, a one-dimensional discrete S sub n ordinates transport code with anisotropic scattering

    Science.gov (United States)

    Ghorai, S. K.

    1983-01-01

    The purpose of this project was to use a one-dimensional discrete coordinates transport code called ANISN in order to determine the energy-angle-spatial distribution of neutrons in a 6-feet cube rock box which houses a D-T neutron generator at its center. The project was two-fold. The first phase of the project involved adaptation of the ANISN code written for an IBM 360/75/91 computer to the UNIVAC system at JSC. The second phase of the project was to use the code with proper geometry, source function and rock material composition in order to determine the neutron flux distribution around the rock box when a 14.1 MeV neutron generator placed at its center is activated.

  2. Preparation and formation mechanism of strong violet luminescent CdS quantum dots by using a ligand exchange strategy

    International Nuclear Information System (INIS)

    A simple and general method has been proposed for preparing strong violet emitting CdS quantum dots, in which a ligand exchange strategy was applied to surface passivation and functionalization with good reproducibility. The resulting quantum dots showed a visible violet luminescence with emission peak centered near 423 nm and photoluminescence quantum yields reached over 30%. Additionally, different mercapto-compounds used as ligands can make different functionalized surfaces, favoring quantum dots dispersion in different media and their further applications. It was observed that the band edge emission has the main contribution to the bright violet luminescence

  3. Quantum dots

    CERN Document Server

    Borovitskaya, Elena

    2002-01-01

    In this book, leading experts on quantum dot theory and technology provide comprehensive reviews of all aspects of quantum dot systems. The following topics are covered: (1) energy states in quantum dots, including the effects of strain and many-body effects; (2) self-assembly and self-ordering of quantum dots in semiconductor systems; (3) growth, structures, and optical properties of III-nitride quantum dots; (4) quantum dot lasers. Contents: Low-Dimensional Systems (E Borovitskaya & M S Shur); Energy States in Quantum Dots (A J Williamson); Self-Organized Quantum Dots (A R Woll et al.); Grow

  4. Formation, atomic structure, and electronic properties of GaSb quantum dots in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Timm, R.

    2007-12-14

    In this work, cross-sectional scanning tunneling microscopy and spectroscopy are used for the first time to study the shape, size, strain, chemical composition, and electronic properties of capped GaSb/GaAs QDs at the atomic scale. By evaluating such structural results on a variety of nanostructures built using different epitaxy methods and growth conditions, details on the underlying QD formation processes can be revealed. A cross-over from flat quantum wells (QWs) to optically active QDs can be observed in samples grown by metalorganic chemical vapor deposition (MOCVD) with increasing amount of GaSb, including self-assembled Sb accumulations within a still two-dimensional layer and tiny three-dimensional GaSb islands probably acting as precursor structures. The QWs consist of significantly intermixed material with stoichiometries of maximally 50% GaSb, additionally exhibiting small gaps filled with GaAs. A higher GaSb content up to nearly pure material is found in the QDs, being characterized by small sizes of up to 8 nm baselength and about 2 nm height. In spite of the intermixing, all nanostructures have rather abrupt interfaces, and no significant Sb segregation in growth direction is observed. This changes completely when molecular beam epitaxy (MBE) is used as growth method, in which case individual Sb atoms are found to be distributed over several nm above the nanostructures. Massive group-V atomic exchange processes are causing this strong inter-mixing and Sb segregation during GaAs overgrowth. In combination with the large strain inherent to GaSb/GaAs QDs, this segregation upon overgrowth is assumed to be the reason for a unique structural phenomenon: All MBE-grown QDs, independent of the amount of deposited GaSb, exhibit a ring structure, consisting of a ring body of high GaSb content and a more or less extended central gap filled with GaAs. These rings have formed in a self-assembled way even when the initial GaSb layer was overgrown considerably fast

  5. Nanocrystalline silicon and silicon quantum dots formation within amorphous silicon carbide by plasma enhanced chemical vapour deposition method controlling the Argon dilution of the process gases

    International Nuclear Information System (INIS)

    Structural and optical properties of the amorphous silicon carbide (a-SiC:H) thin films deposited by radio frequency plasma enhanced chemical vapour deposition method from a mixture of silane (SiH4) and methane (CH4) diluted in argon (Ar) have been studied with variation of Ar dilution from 94% to 98.4%. It is observed that nanocrystalline silicon starts to form within the a-SiC:H matrix by increasing the dilution to 96%. With further increase in Ar dilution to 98% formation of the silicon nanocrystals (nc-Si) with variable size is enhanced. The optical band gap (Eg) of the a-SiC:H film decreases from 2.0 eV to 1.9 eV with increase in Ar dilution from 96% to 98% as the a-SiC:H films gradually become Si rich. On increasing the Ar dilution further to 98.4% leads to the appearance of crystalline silicon quantum dots (c-Si q-dots) of nearly uniform size of 3.5 nm. The quantum confinement effect is apparent from the sharp increase in the Eg value to 2.6 eV. The phase transformation phenomenon from nc-Si within the a-SiC:H films to Si q-dot were further studied by high resolution transmission electron microscopy and the grazing angle X-ray diffraction spectra. A relaxation in the lattice strain has been observed with the formation of Si q-dots.

  6. Formation polarity dependent improved resistive switching memory characteristics using nanoscale (1.3 nm) core-shell IrOx nano-dots

    OpenAIRE

    Banerjee, Writam; Maikap, Siddheswar; Lai, Chao-Sung; Chen, Yi-Yan; Tien, Ta-Chang; Lee, Heng-Yuan; Chen, Wei-Su; Chen, Frederick T; Kao, Ming-Jer; Tsai, Ming-Jinn; Yang, Jer-Ren

    2012-01-01

    Improved resistive switching memory characteristics by controlling the formation polarity in an IrOx/Al2O3/IrOx-ND/Al2O3/WOx/W structure have been investigated. High density of 1 × 1013/cm2 and small size of 1.3 nm in diameter of the IrOx nano-dots (NDs) have been observed by high-resolution transmission electron microscopy. The IrOx-NDs, Al2O3, and WOx layers are confirmed by X-ray photo-electron spectroscopy. Capacitance-voltage hysteresis characteristics show higher charge-trapping density...

  7. Formation of long single quantum dots in high quality InSb nanowires grown by molecular beam epitaxy

    Science.gov (United States)

    Fan, Dingxun; Li, Sen; Kang, N.; Caroff, Philippe; Wang, L. B.; Huang, Y. Q.; Deng, M. T.; Yu, C. L.; Xu, H. Q.

    2015-09-01

    We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO2 substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of ~700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Landé g-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of ~300 μeV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices.

  8. Formation of long single quantum dots in high quality InSb nanowires grown by molecular beam epitaxy.

    Science.gov (United States)

    Fan, Dingxun; Li, Sen; Kang, N; Caroff, Philippe; Wang, L B; Huang, Y Q; Deng, M T; Yu, C L; Xu, H Q

    2015-09-28

    We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO2 substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of ∼700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Landég-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of ∼300 μeV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices. PMID:26308470

  9. Verification of ANISN-F by calculating the neutron distribution from a Ra-Be source in water as well as by simple criticality calculations

    International Nuclear Information System (INIS)

    The one dimensional discrete ordinates code ANISN-F was used to calculate the thermal neutron flux distribution in water from a Ra-Be neutron source. The calculations were performed in order to investigate the different possibilities of the code as well as to verify the results of the calculations in terms of comparisons to corresponding experimental data. Two different group cross section libraries were used in the calculations and conclusions were drawn on the adequacy of these libraries for a fixed source type calculation. Furthermore, critically calculations were performed for an infinite homogeneous slab of multiplying material using different angular and spatial approximations. The results of these calculations were then compared to the corresponding results previously obtained at this department by a different method and a different code. (author)

  10. Neutron-photon energy deposition in CANDU reactor fuel channels: a comparison of modelling techniques using ANISN and MCNP computer codes

    International Nuclear Information System (INIS)

    In order to assess irradiation-induced corrosion effects, coolant radiolysis and the degradation of the physical properties of reactor materials and components, it is necessary to determine the neutron, photon, and electron energy deposition profiles in the fuel channels of the reactor core. At present, several different computer codes must be used to do this. The most recent, advanced and versatile of these is the latest version of MCNP, which may be capable of replacing all the others. Different codes have different assumptions and different restrictions on the way they can model the core physics and geometry. This report presents the results of ANISN and MCNP models of neutron and photon energy deposition. The results validate the use of MCNP for simplified geometrical modelling of energy deposition by neutrons and photons in the complex geometry of the CANDU reactor fuel channel. Discrete ordinates codes such as ANISN were the benchmark codes used in previous work. The results of calculations using various models are presented, and they show very good agreement for fast-neutron energy deposition. In the case of photon energy deposition, however, some modifications to the modelling procedures had to be incorporated. Problems with the use of reflective boundaries were solved by either including the eight surrounding fuel channels in the model, or using a boundary source at the bounding surface of the problem. Once these modifications were incorporated, consistent results between the computer codes were achieved. Historically, simple annular representations of the core were used, because of the difficulty of doing detailed modelling with older codes. It is demonstrated that modelling by MCNP, using more accurate and more detailed geometry, gives significantly different and improved results. (author). 9 refs., 12 tabs., 20 figs

  11. Formation of self-assembled quantum dots of iron oxide thin films by spray pyrolysis from non-aqueous medium

    International Nuclear Information System (INIS)

    Quantum dots (QDs) of iron oxide have been deposited onto ITO coated glass substrates by spray pyrolysis technique, using ferric chloride (FeCl3.7H2O) in non-aqueous medium as a starting material. The non-aqueous solvents namely methanol, ethanol, propanol, butanol and pentanol were used as solvents. The effect of solvents on the film structure and morphology was studied. The structural, morphological, compositional and optical properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), and optical absorption measurement techniques

  12. Thermodynamic Equilibrium-Driven Formation of Single-Sized Nanocrystals: Reaction Media Tuning CdSe Magic-Sized versus Regular Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kui [SIMS, NRC of Canada; Hu, Michael Z. [ORNL; Wang, Ruibing [SIMS, NRC of Canada; Le Piolet, Mickael [SIMS, NRC of Canada; Frotey, Marion [SIMS, NRC of Canada; Zaman, Md. Badruz [SIMS, NRC of Canada; Wu, Xiaohua [IMS, NRC of Canada; Leek, Donald M. [SIMS, NRC of Canada; Tao, Ye [IMS, NRC of Canada; Wilkinson, Diana [SIMS, NRC of Canada; Li, Chunsheng [National Research Council of Canada

    2010-01-01

    A concept for the fundamental science of nanoparticle synthesis, thermodynamic equilibrium-driven formation of colloidal single-sized nanoparticle ensembles, is proposed and demonstrated in this manuscript, which addresses the controlled formation of CdSe magic-sized and regular quantum dots (MSQDs and RQDs). During formation, the former are magic-sized nuclei without further growth in size, while the latter experience nucleation and growth. Both MSQDs and RQDs exhibit bandgap emission, while the former have homogeneous spectra broadening only and the latter both homogeneous and inhomogeneous spectra broadening. The former are single-sized and the latter have size distribution. With continuous and homogeneous nucleation, the thermodynamically driven formation of MSQDs was realized via our one-pot noninjection approach, which features highly synthetic reproducibility and large-scale capability. With the proper tuning of the synthetic parameters, such as the nature of the reaction medium, that affect the thermodynamic equilibria, various CdSe MSQDs and RQDs were synthesized discriminately under otherwise identical synthetic formulation and reaction conditions; the reaction media were noncoordinating 1-octadecene, coordinating trioctylphosphine, and mixtures of the two. The nature of Cd precursors, affected also by the reaction media, plays a major role in the formation of MSQDs versus RQDs. The present investigation on the thermodynamically driven formation of CdSe single-sized nanoparticles via tuning of the reaction medium, mainly, brings novel insights into the formation mechanism and into the surface ligands of the resulting colloidal nanocrystals. More importantly, the present study provides novel experimental design and approaches to single-sized nanoparticles desired for various applications.

  13. NMR structural studies of intramolecular (Y+) sub n ter dot (R+) sub n (Y minus ) sub n DNA triplexes in solution: Imino and amino proton and nitrogen markers of Gter dot TA base triple formation

    Energy Technology Data Exchange (ETDEWEB)

    Radhakrishnan, I.; de los Santos, C.; Patel, D.J. (Columbia Univ., New York, NY (United States)); Gao, Xiaolian (Glaxo Research Inst., Research Triangle Park, NC (United States)); Live, D. (California Inst. of Tech., Pasadena (United States))

    1991-09-17

    The authors reported previously on NMR studies of (Y+){sub n}{center dot}(R+){sub n}(Y{minus}){sub n}DNA triple helices containing one oligopurine strand (R){sub n} and two oligopyrimidine strands (Y){sub n} stabilized by T{center dot}AT and C{sup +}{center dot}GC base triples. Recently, it has been established that guanosine can recognize a thymidine{center dot}adenosine base pair to form a G{center dot}TA triple in an otherwise (Y+){sub n}{center dot}(R+){sub n}(Y{minus}){sub n} triple-helix motif. The present study extends the NMR research to the characterization of structural features of a 31-mer deoxyoligonucleotide that folds intramolecularly into a 7-mer (Y+){sub n}{center dot}(R+){sub n}(Y{minus}){sub n} triplex with the strands linked through two T{sub 5} loops and that contains a central G{center dot}TA triple flanked by T{center dot}AT triples. The NMR data are consistent with the proposed pairing alignment for the G{center dot}TA triple where the guanosine in an anti orientation pairs through a single hydrogen bond from one of its 2-amino protons to the 4-carbonyl group of thymidine in the Watson-Crick TA pair. They detect a set of NOEs between adjacent triples that establishes that the G{center dot}TA triple stacks between flanking T{center dot}AT triples in the G{center dot}TA triplex. These results demonstrate the capabilities of the NMR approach in monitoring individual base triples and their pairing alignments, as well as establishing that the G{center dot}TA triple can be readily accommodated in an otherwise intramolecular (Y+){sub n}{center dot}(R+){sub n}(Y{minus}){sub n} triple helix in solution.

  14. Three-dimensional nanoscale study of Al segregation and quantum dot formation in GaAs/AlGaAs core-shell nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Mancini, L.; Blum, I.; Vurpillot, F.; Rigutti, L., E-mail: lorenzo.rigutti@univ-rouen.fr [Groupe de Physique des Matériaux, UMR CNRS 6634, University and INSA of Rouen, Normandie University, 76800 St. Etienne du Rouvray (France); Fontana, Y.; Conesa-Boj, S.; Francaviglia, L.; Russo-Averchi, E.; Heiss, M.; Morral, A. Fontcuberta i [Laboratoire des Matériaux Semiconducteurs, École Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland); Arbiol, J. [Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, CAT (Spain); Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, CAT (Spain)

    2014-12-15

    GaAs/Al-GaAs core-shell nanowires fabricated by molecular beam epitaxy contain quantum confining structures susceptible of producing narrow photoluminescence (PL) and single photons. The nanoscale chemical mapping of these structures is analyzed in 3D by atom probe tomography (APT). The study allows us to confirm that Al atoms tend to segregate within the AlGaAs shells towards the vertices of the hexagons defining the nanowire cross section. We also find strong alloy fluctuations remaining AlGaAs shell, leading occasionally to the formation of quantum dots (QDs). The PL emission energies predicted in the framework of a 3D effective mass model for a QD analyzed by APT and the PL spectra measured on other nanowires from the same growth batch are consistent within the experimental uncertainties.

  15. Formation of colloidal GaAs and CdS quantum dots by laser ablation in liquid media

    International Nuclear Information System (INIS)

    In this work colloidal quantum dots (QDs) of GaAs and CdS semiconductors have been formed by laser ablation in the liquid media. The pulsed passive mode-locked Nd:YAG laser at 1064 nm wavelength with pulse duration τ imp = 33 ps and energy 30 mJ was used. The luminescence of the colloidal QDs was excited by irradiation at 355 nm, the third harmonic of the Nd:YAG laser. The optical absorption and the photoluminescence spectra of the GaAs and CdS colloidal QDs have been investigated. The large blue shift of the photoluminescence, connected to size effects, was evaluated. The location of the maximum of luminescence spectra at the wavelengths 405 nm (CdS) and 420 nm (GaAs) give calculated sizes of QDs of 2-3 nm

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

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

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

  17. Quantum dot immunoassays in renewable surface column and 96-well plate formats for the fluorescence detection of Botulinum neurotoxin using high-affinity antibodies

    Energy Technology Data Exchange (ETDEWEB)

    Warner, Marvin G.; Grate, Jay W.; Tyler, Abby J.; Ozanich, Richard M.; Miller, Keith D.; Lou, Jianlong; Marks, James D.; Bruckner-Lea, Cindy J.

    2009-09-01

    A fluorescence sandwich immunoassay using high affinity antibodies and quantum dot (QD) reporters has been developed for detection of botulinum toxin serotype A (BoNT/A). For the development of the assay, a nontoxic recombinant fragment of the holotoxin (BoNT/A-HC-fragment) has been used as a structurally valid simulant for the full toxin molecule. The antibodies used, AR4 and RAZ1, bind to nonoverlapping epitopes present on both the full toxin and on the recombinant fragment. In one format, the immunoassay is carried out in a 96-well plate with detection in a standard plate reader. Detection down to 31 pM of the BoNT/Hc-fragment was demonstrated with a total incubation time of 3 hours, using AR4 as the capture antibody and QD-coupled RAZ1 as the reporter. In a second format, the AR4 capture antibody was coupled to Sepharose beads, and the immunochemical reactions were carried out in microcentrifuge tubes with an incubation time of 1 hour. These beads were subsequently captured and concentrated in a rotating rod “renewable surface” flow cell as part of a sequential injection fluidic system. This flow cell was equipped with a fiber optic system for fluorescence measurements. In PBS buffer solution matrix, the BoNT/A-HC-fragment was detected to concentrations as low as 5 pM using the fluidic measurement approach.

  18. Effect of Bi isovalent dopants on the formation of homogeneous coherently strained InAs quantum dots in GaAs matrices

    International Nuclear Information System (INIS)

    The distribution of hydrostatic strains in Bi3+-doped InAs quantum dots embedded in a GaAs matrix are calculated in the context of the deformation-potential model. The dependences of strains in the material of spherical InAs quantum dots with substitutional (Bi → As) and interstitial (Bi) impurities on the quantum-dot size are derived. The qualitative correlation of the model with the experiment is discussed. The data on the effect of doping on the morphology of self-assembled InAs:Bi quantum dots in a GaAs matrix are obtained.

  19. Formation polarity dependent improved resistive switching memory characteristics using nanoscale (1.3 nm) core-shell IrOx nano-dots

    Science.gov (United States)

    Banerjee, Writam; Maikap, Siddheswar; Lai, Chao-Sung; Chen, Yi-Yan; Tien, Ta-Chang; Lee, Heng-Yuan; Chen, Wei-Su; Chen, Frederick T.; Kao, Ming-Jer; Tsai, Ming-Jinn; Yang, Jer-Ren

    2012-03-01

    Improved resistive switching memory characteristics by controlling the formation polarity in an IrOx/Al2O3/IrOx-ND/Al2O3/WOx/W structure have been investigated. High density of 1 × 1013/cm2 and small size of 1.3 nm in diameter of the IrOx nano-dots (NDs) have been observed by high-resolution transmission electron microscopy. The IrOx-NDs, Al2O3, and WOx layers are confirmed by X-ray photo-electron spectroscopy. Capacitance-voltage hysteresis characteristics show higher charge-trapping density in the IrOx-ND memory as compared to the pure Al2O3 devices. This suggests that the IrOx-ND device has more defect sites than that of the pure Al2O3 devices. Stable resistive switching characteristics under positive formation polarity on the IrOx electrode are observed, and the conducting filament is controlled by oxygen ion migration toward the Al2O3/IrOx top electrode interface. The switching mechanism is explained schematically based on our resistive switching parameters. The resistive switching random access memory (ReRAM) devices under positive formation polarity have an applicable resistance ratio of > 10 after extrapolation of 10 years data retention at 85°C and a long read endurance of 105 cycles. A large memory size of > 60 Tbit/sq in. can be realized in future for ReRAM device application. This study is not only important for improving the resistive switching memory performance but also help design other nanoscale high-density nonvolatile memory in future.

  20. Quadra-quantum Dots and Related Patterns of Quantum Dot Molecules:

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

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

  1. Connecting the dots: Investigating planet formation and composition through observations of carbon and oxygen species in stars, disks, and planets

    Science.gov (United States)

    Teske, Johanna Kavanagh

    What physical processes and sources of material contribute to exoplanet compositions? Specifically, what roles do the protoplanetary disk composition and structure, and host star abundances play in the different stages of planet formation? In this thesis, beginning with a brief literature review in Chapter 2, I trace oxygen and carbon species through these stages to inform how, when, and where planets form. In Chapter 3 I describe a study of the molecular emission from the warm inner disks of T Tauri stars, where terrestrial planets likely form. I report moderate correlations between HCN emission strength and both stellar accretion rate (measured from UV or optical excess emission associated with accretion) and X-ray luminosity. These correlations point towards accretion related processes being an important source of disk atmosphere heating, and suggests that efficient H2O formation and/or UV dissociation of N2 (both also associated with higher stellar accretion rates) may aid in the production of HCN. Studies following mine have further connected the abundance of HCN versus H2O to the growth and migration of planetesimals in the disk, which helps control the formation of both giant and terrestrial planets. I shift to an already-formed exoplanet in Chapter 4, where I present optical photometry of the best-observed transiting super-Earth GJ 1214b with the goal of constraining the short-wavelength slope of its transmission spectrum. Most previous observations suggested a flat spectrum from the near-IR to the optical, corresponding to a low-scale-height, high-molecular-weight atmosphere. My observations are in general agreement with these findings, keeping the "door open" for a H2O-rich atmosphere for GJ 1214b, which other published g-band observations appeared to contradict. Chapters 5-7 of my thesis focus on measuring stellar abundances, particularly C/O ratios, in transiting (mostly) hot Jupiter exoplanet host stars from high resolution optical spectroscopy. Host

  2. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    Energy Technology Data Exchange (ETDEWEB)

    Mahapatra, Suddhasatta

    2008-01-16

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at T{sub G}=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at T{sub G}<{proportional_to}240 C. In the second variant technique, formation of large and distinct islands is demonstrated by deposition of amorphous selenium (a-Se) onto a 2D CdSe epilayer at room temperature and its subsequent desorption at a higher temperature (T{sub D}=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  3. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    International Nuclear Information System (INIS)

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at TG=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at TGD=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  4. (In,Mn)As multilayer quantum dot structures

    International Nuclear Information System (INIS)

    (In,Mn)As multilayer quantum dots structures were grown by molecular beam epitaxy using a Mn selective doping of the central parts of quantum dots. The study of the structural and magneto-optical properties of the samples with three and five layers of (In,Mn)As quantum dots has shown that during the quantum dots assembly, the out-diffusion of Mn from the layers with (In,Mn)As quantum dots can occur resulting in the formation of the extended defects. To produce a high quality structures using the elaborated technique of selective doping, the number of (In,Mn)As quantum dot layers should not exceed three

  5. Microwave-assisted synthesis of CdSe quantum dots: can the electromagnetic field influence the formation and quality of the resulting nanocrystals?

    Science.gov (United States)

    Moghaddam, Mojtaba Mirhosseini; Baghbanzadeh, Mostafa; Keilbach, Andreas; Kappe, C Oliver

    2012-12-01

    Microwave-assisted syntheses of colloidal nanocrystals (NCs), in particular CdSe quantum dots (QDs), have gained considerable attention due to unique opportunities provided by microwave dielectric heating. The extensive use of microwave heating and the frequently suggested specific microwave effects, however, pose questions about the role of the electromagnetic field in both the formation and quality of the produced QDs. In this work a one-pot protocol for the tunable synthesis of monodisperse colloidal CdSe NCs using microwave dielectric heating under carefully controlled conditions is introduced. CdSe QDs are fabricated using selenium dioxide as a selenium precursor, 1-octadecene as a solvent and reducing agent, cadmium alkyl carboxylates or alkyl phosphonates as cadmium sources, 1,2-hexadecanediol to stabilize the cadmium complex and oleic acid to stabilize the resulting CdSe QDs. Utilizing the possibilities of microwave heating technology in combination with accurate online temperature control the influence of different reaction parameters such as reaction temperature, ramp and hold times, and the timing and duration of oleic acid addition have been carefully investigated. Optimum results were obtained by performing the reaction at 240 °C applying a 5 min ramp time, 2 min hold time before oleic acid addition, 90 s for oleic acid addition, and a 5 min hold time after oleic acid addition (8.5 min overall holding at 240 °C). By using different cadmium complexes in the microwave protocol CdSe QDs with a narrow size distribution can be obtained in different sizes ranging from 0.5-4 nm by simply changing the cadmium source. The QDs were characterized by TEM, HRTEM, UV-Vis, and photoluminescence methods and the size distribution was monitored by SAXS. Control experiments involving conventional conductive heating under otherwise identical conditions ensuring the same heating and cooling profiles, stirring rates, and reactor geometries demonstrate that the

  6. 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...

  7. 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...

  8. MAIL3.1 : a computer program generating cross section sets for SIMCRI, ANISN-JR, KENO IV, KENO V, MULTI-KENO, MULTI-KENO-2 and MULTI-KENO-3.0

    Energy Technology Data Exchange (ETDEWEB)

    Suyama, Kenya; Komuro, Yuichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Takada, Tomoyuki; Kawasaki, Hiromitsu; Ouchi, Keisuke

    1998-02-01

    This report is a user`s manual of the computer program MAIL3.1 which generates various types of cross section sets for neutron transport programs such as SIMCRI, ANISN-JR, KENO IV, KENO V, MULTI-KENO, MULTI-KENO-2 and MULTI-KENO-3.0. MAIL3.1 is a revised version of MAIL3.0 that was opened in 1990. It has all of abilities of MAIL3.0 and has two more functions as shown in following. 1. AMPX-type cross section set generating function for KENO V. 2. Enhanced function for user of 16 group Hansen-Roach library. (author)

  9. A colloidal quantum dot spectrometer

    Science.gov (United States)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

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

  10. Tunable light emission by exciplex state formation between hybrid halide perovskite and core/shell quantum dots: Implications in advanced LEDs and photovoltaics.

    Science.gov (United States)

    Sanchez, Rafael S; de la Fuente, Mauricio Solis; Suarez, Isaac; Muñoz-Matutano, Guillermo; Martinez-Pastor, Juan P; Mora-Sero, Ivan

    2016-01-01

    We report the first observation of exciplex state electroluminescence due to carrier injection between the hybrid lead halide perovskite (MAPbI3-xClx) and quantum dots (core/shell PbS/CdS). Single layers of perovskite (PS) and quantum dots (QDs) have been produced by solution processing methods, and their photoluminescent properties are compared to those of bilayer samples in both PS/QD and QD/PS configurations. Exciplex emission at lower energies than the band gap of both PS and QD has been detected. The exciplex emission wavelength of this mixed system can be simply tuned by controlling the QD size. Light-emitting diodes (LEDs) have been fabricated using those configurations, which provide light emission with considerably low turn-on potential. The "color" of the LED can also be tuned by controlling the applied bias. The presence of the exciplex state PS and QDs opens up a broad range of possibilities with important implications not only in tunable LEDs but also in the preparation of intermediate band gap photovoltaic devices with the potentiality of surpassing the Shockley-Queisser limit. PMID:26844299

  11. Detection and control of charge states in a quintuple quantum dot

    OpenAIRE

    Ito, Takumi; Otsuka, Tomohiro; Amaha, Shinichi; Delbecq, Matthieu R.; NAKAJIMA, TAKASHI; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Noiri, Akito; Kawasaki, Kento; Tarucha, Seigo

    2016-01-01

    A semiconductor quintuple quantum dot with two charge sensors and an additional contact to the center dot from an electron reservoir is fabricated to demonstrate the concept of scalable architecture. This design enables formation of the five dots as confirmed by measurements of the charge states of the three nearest dots to the respective charge sensor. The gate performance of the measured stability diagram is well reproduced by a capacitance model.These results provide an important step towa...

  12. Top-gate defined double quantum dots in InAs nanowires

    OpenAIRE

    Pfund, A.; Shorubalko, I.; Leturcq, R.; Ensslin, K.

    2006-01-01

    We present low temperature transport measurements on double quantum dots in InAs nanowires grown by metal-organic vapor phase epitaxy. Two dots in series are created by lithographically defined top-gates with a procedure involving no extra insulating layer. We demonstrate the full tunability from strong to weak coupling between the dots. The quantum mechanical nature of the coupling leads to the formation of a molecular state extending over both dots. The excitation spectra of the individual ...

  13. DOT 3.5-E (DOT 3.5-E/JEF-1) analysis of the PCA-Replica (H2O/FE) shielding benchmark for the LWR-PV damage prediction

    International Nuclear Information System (INIS)

    The results of a DOT 3.5-E/JEF-1 validation on the (H2O/Fr) PCA-REPLICA (UKAEA-Winfith) low-flux shielding benchmark are presented. The PCA-REPLICA experiments reproduces the excore radial geometry of a PWR and is closely related to LWR safety since it is dedicated to test the accuracy of the calculated neutron exposure parameters (fast fluence and iron displacement rates) in a pressure vessel simulator. The NJOY/THEMIS data processing system is employed to obtain the neutron damage-energy cross sections for the JEF-1 iron file. The SN 1-D ANISN code is used to collapse cross sections from the VITAMIN-J (175 n) shielding library, based on the JEF-1 data, to a 28 group working library for 2-D calculations. A 3-D-equivalent synthesis (X,Y,Z) of 2-D and 1-D DOT 3.5-E SN calculations in a plane geometry, gives the integral and spectral results for comparison with the respective experimental data. The underprediction of the in-vessel dosimeter experimental activities depends probably on an overestimation of the iron inelastic scattering cross section of the JEF-1 file

  14. 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.

  15. Ultrasmall silicon quantum dots

    NARCIS (Netherlands)

    Zwanenburg, F.A.; Van Loon, A.A.; Steele, G.A.; Rijmenam, C.E.W.M.; Balder, T.; Fang, Y.; Lieber, C.M.; Kouwenhoven, L.P.

    2009-01-01

    We report the realization of extremely small single quantum dots in p-type silicon nanowires, defined by Schottky tunnel barriers with Ni and NiSi contacts. Despite their ultrasmall size the NiSi–Si–NiSi nanowire quantum dots readily allow spectroscopy of at least ten consecutive holes, and addition

  16. Quantum Dots: Theory

    OpenAIRE

    Vukmirovic, Nenad

    2010-01-01

    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.

  17. Effects of formation of mini-bands in two-dimensional array of silicon nanodisks with SiC interlayer for quantum dot solar cells

    International Nuclear Information System (INIS)

    A sub-10 nm, high-density, periodic silicon nanodisk (Si-ND) array with a SiC interlayer has been fabricated using a new top-down process that involves a 2D array of a bio-template etching mask and damage-free neutral beam etching. Optical and electrical measurements were carried out to clarify the formation of mini-bands due to wavefunction coupling. We found that the SiC interlayer could enhance the optical absorption coefficient in the layer of Si-NDs due to the stronger coupling of wavefunctions. Theoretical simulation also indicated that wavefunction coupling was effectively enhanced in Si-NDs with a SiC interlayer, which precisely matched the experimental results. Furthermore, the I–V properties of a 2D array of Si-NDs with a SiC interlayer were studied through conductive AFM measurements, which indicated conductivity in the structure was enhanced by strong lateral electronic coupling between neighboring Si-NDs. We confirmed carrier generation and less current degradation in the structure due to high photon absorption and conductivity by inserting the Si-NDs into p–i–n solar cells. (paper)

  18. Quantum Dots for Biophotonics

    OpenAIRE

    Ken-Tye Yong

    2012-01-01

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

  19. 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

  20. Entanglement creation in semiconductor quantum dot charge qubit

    CERN Document Server

    Buscemi, Fabrizio; Bertoni, Andrea

    2010-01-01

    We study theoretically the appearance of quantum correlations in two- and three-electron scattering in single and double dots. The key role played by transport resonances into entanglement formation between the single-particle states is shown. Both reflected and transmitted components of the scattered particle wavefunction are used to evaluate the quantum correlations between the incident carrier and the bound particle(s) in the dots. Our investigation provides a guideline for the analysis of decoherence effects due to the Coulomb scattering in semiconductor quantum dots structures.

  1. Optical properties of charged semiconductor quantum dots

    Science.gov (United States)

    Jha, Praket P.

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

  2. Quantum dot cascade laser

    OpenAIRE

    Zhuo, Ning; Liu, Feng Qi; Zhang, Jin Chuan; Wang, Li Jun; Liu, Jun Qi; Zhai, Shen Qiang; Wang, Zhan Guo

    2014-01-01

    We demonstrated an unambiguous quantum dot cascade laser based on InGaAs/GaAs/InAs/InAlAs heterostructure by making use of self-assembled quantum dots in the Stranski-Krastanow growth mode and two-step strain compensation active region design. The prototype generates stimulated emission at λ ~ 6.15 μm and a broad electroluminescence band with full width at half maximum over 3 μm. The characteristic temperature for the threshold current density within the temperature range of 82 to 162 K is up...

  3. 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

  4. Fuzzy Dot Structure of BG-algebras

    OpenAIRE

    Tapan Senapati; Monoranjan Bhowmik; Madhumangal Pal

    2014-01-01

    In this paper, the notions of fuzzy dot subalgebras is introduced together with fuzzy normal dot subalgebras and fuzzy dot ideals of BG-algebras. The homomorphic image and inverse image are investigated in fuzzy dot subalgebras and fuzzy dot ideals of BG-algebras. Also, the notion of fuzzy relations on the family of fuzzy dot subalgebras and fuzzy dot ideals of BG-algebras are introduced with some related properties.

  5. Electron correlations in quantum dots

    CERN Document Server

    Tipton, D L J

    2001-01-01

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

  6. Colloidal Double Quantum Dots

    Science.gov (United States)

    2016-01-01

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

  7. Colloidal Double Quantum Dots.

    Science.gov (United States)

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

    2016-05-17

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

  8. Fabrication and evaluation of series-triple quantum dots by thermal oxidation of silicon nanowire

    International Nuclear Information System (INIS)

    Series-connected triple quantum dots were fabricated by a simple two-step oxidation technique using the pattern-dependent oxidation of a silicon nanowire and an additional oxidation of the nanowire through the gap of the fine gates attached to the nanowire. The characteristics of multi-dot single-electron devices are obtained. The formation of each quantum dot beneath an attached gate is confirmed by analyzing the electrical characteristics and by evaluating the gate capacitances between all pairings of gates and quantum dots. Because the gate electrode is automatically attached to each dot, the device structure benefits from scalability. This technique promises integrability of multiple quantum dots with individual control gates

  9. Fabrication and evaluation of series-triple quantum dots by thermal oxidation of silicon nanowire

    Energy Technology Data Exchange (ETDEWEB)

    Uchida, Takafumi, E-mail: takafumi-uchida@frontier.hokudai.ac.jp; Jo, Mingyu; Tsurumaki-Fukuchi, Atsushi; Arita, Masashi; Takahashi, Yasuo [Graduate School of Information Science and Technology, Hokkaido University, Sapporo, 060-0814 Japan (Japan); Fujiwara, Akira [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, 243-0198 Japan (Japan)

    2015-11-15

    Series-connected triple quantum dots were fabricated by a simple two-step oxidation technique using the pattern-dependent oxidation of a silicon nanowire and an additional oxidation of the nanowire through the gap of the fine gates attached to the nanowire. The characteristics of multi-dot single-electron devices are obtained. The formation of each quantum dot beneath an attached gate is confirmed by analyzing the electrical characteristics and by evaluating the gate capacitances between all pairings of gates and quantum dots. Because the gate electrode is automatically attached to each dot, the device structure benefits from scalability. This technique promises integrability of multiple quantum dots with individual control gates.

  10. Quantum Dot Sensitized Photoelectrodes

    OpenAIRE

    Thomas Nann; Thomas J. Macdonald

    2011-01-01

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

  11. Quantum Dot Sensitized Photoelectrodes

    Directory of Open Access Journals (Sweden)

    Thomas Nann

    2011-11-01

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

  12. Plasmonic fluorescent quantum dots

    OpenAIRE

    Jin, Yongdong; Gao, Xiaohu

    2009-01-01

    Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem1,2. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence3,4. So far, the combination of...

  13. Quantum dots in graphene

    OpenAIRE

    Silvestrov, P.G.; Efetov, K. B.

    2006-01-01

    We suggest a way of confining quasiparticles by an external potential in a small region of a graphene strip. Transversal electron motion plays a crucial role in this confinement. Properties of thus obtained graphene quantum dots are investigated theoretically for different types of the boundary conditions at the edges of the strip. The (quasi)bound states exist in all systems considered. At the same time, the dependence of the conductance on the gate voltage carries an information about the s...

  14. Quantum dot nanostructures

    Directory of Open Access Journals (Sweden)

    Mohamed Henini

    2002-06-01

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

  15. Quantum dot solar cell

    International Nuclear Information System (INIS)

    Full text: The much awaited desire of replacing fossil fuel with photovoltaic will remain a fairy tale if the myriad of issues facing solar cell development are marginalized. Foremost in the list is the issue of cost. Silicon has reached a stage where its use on large scale can no longer be lavishly depended upon. The demand for high grade silicon from the microelectronics and solar industries has soared leading to scarcity. New approach has to be sought. Notable is the increased attention on thin films such as cadmium telluride, copper indium gallium diselenide, amorphous silicon, and the not so thin non-crystalline family of silicon. While efforts to address the issues of stability, toxicity and efficiency of these systems are ongoing, another novel approach is quietly making its appearance - quantum dots. Quantum dots seem to be promising candidates for solar cells because of the opportunity to manipulate their energy levels allowing absorption of a wider solar spectrum. Utilization of minute quantity of these nano structures is enough to bring the cost of solar cell down and to ascertain sustainable supply of useful material. The paper outlines the progress that has been made on quantum dot solar cells. (author)

  16. Photophysical and structural characterisation of in situ formed quantum dots.

    Science.gov (United States)

    Bansal, A K; Antolini, F; Sajjad, M T; Stroea, L; Mazzaro, R; Ramkumar, S G; Kass, K-J; Allard, S; Scherf, U; Samuel, I D W

    2014-05-28

    Conjugated polymer-semiconductor quantum dot (QD) composites are attracting increasing attention due to the complementary properties of the two classes of materials. We report a convenient method for in situ formation of QDs, and explore the conditions required for light emission of nanocomposite blends. In particular we explore the properties of nanocomposites of the blue emitting polymer poly[9,9-bis(3,5-di-tert-butylphenyl)-9H-fluorene] together with cadmium sulphide (CdS) and cadmium selenide (CdSe) precursors. We show the formation of emissive quantum dots of CdSe from thermally decomposed precursor. The dots are formed inside the polymer matrix and have a photoluminescence quantum yield of 7.5%. Our results show the importance of appropriate energy level alignment, and are relevant to the application of organic-inorganic systems in optoelectronic devices. PMID:24727793

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

    Indian Academy of Sciences (India)

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

    2009-05-01

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

  18. From single dots to interacting arrays

    OpenAIRE

    Gudmundsson, Vidar; Manolescu, Andrei; Krahne, Roman; Heitmann, Detlef

    2001-01-01

    We explore the structural changes in charge the density and the electron configuration of quantum dots caused by the presence of other dots in an array, and the interaction of neighboring dots. We discuss what recent measurements and calculation of the far-infrared absorption reveal about almost isolated quantum dots and investigate some aspects of the complex transition from isolated dots to dots with strongly overlapping electron density. We also address the the effects on the magnetization...

  19. Intrinsic Photoluminescence Emission from Subdomained Graphene Quantum Dots.

    Science.gov (United States)

    Yoon, Hyewon; Chang, Yun Hee; Song, Sung Ho; Lee, Eui-Sup; Jin, Sung Hwan; Park, Chanae; Lee, Jinsup; Kim, Bo Hyun; Kang, Hee Jae; Kim, Yong-Hyun; Jeon, Seokwoo

    2016-07-01

    The photoluminescence (PL) origin of bright blue emission arising from intrinsic states in graphene quantum dots (GQDs) is investigated. The bright PL of intercalatively acquired GQDs is attributed to favorably formed subdomains composed of four to seven carbon hexagons. Random and harsh oxidation which hinders the energetically favorable formation of subdomains causes weak and redshifted PL. PMID:27153519

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

    Directory of Open Access Journals (Sweden)

    Damalakiene L

    2013-02-01

    Full Text Available Leona Damalakiene,1 Vitalijus Karabanovas,2 Saulius Bagdonas,1 Mindaugas Valius,3 Ricardas Rotomskis1,21Biophotonics Group, Laser Research Center, Faculty of Physics, 2Biomedical Physics Laboratory, Institute of Oncology, 3Proteomics Center, Institute of Biochemistry, Vilnius University, Vilnius, LithuaniaBackground: The purpose of this study was to elucidate the mechanism of natural uptake of nonfunctionalized quantum dots in comparison with microinjected quantum dots by focusing on their time-dependent accumulation and intracellular localization in different cell lines.Methods: The accumulation dynamics of nontargeted CdSe/ZnS carboxyl-coated quantum dots (emission peak 625 nm was analyzed in NIH3T3, MCF-7, and HepG2 cells by applying the methods of confocal and steady-state fluorescence spectroscopy. Intracellular colocalization of the quantum dots was investigated by staining with Lysotracker®.Results: The uptake of quantum dots into cells was dramatically reduced at a low temperature (4°C, indicating that the process is energy-dependent. The uptake kinetics and imaging of intracellular localization of quantum dots revealed three accumulation stages of carboxyl-coated quantum dots at 37°C, ie, a plateau stage, growth stage, and a saturation stage, which comprised four morphological phases: adherence to the cell membrane; formation of granulated clusters spread throughout the cytoplasm; localization of granulated clusters in the perinuclear region; and formation of multivesicular body-like structures and their redistribution in the cytoplasm. Diverse quantum dots containing intracellular vesicles in the range of approximately 0.5–8 µm in diameter were observed in the cytoplasm, but none were found in the nucleus. Vesicles containing quantum dots formed multivesicular body-like structures in NIH3T3 cells after 24 hours of incubation, which were Lysotracker-negative in serum-free medium and Lysotracker-positive in complete medium. The

  1. Electrochromic nanocrystal quantum dots.

    Science.gov (United States)

    Wang, C; Shim, M; Guyot-Sionnest, P

    2001-03-23

    Incorporating nanocrystals into future electronic or optoelectronic devices will require a means of controlling charge-injection processes and an understanding of how the injected charges affect the properties of nanocrystals. We show that the optical properties of colloidal semiconductor nanocrystal quantum dots can be tuned by an electrochemical potential. The injection of electrons into the quantum-confined states of the nanocrystal leads to an electrochromic response, including a strong, size-tunable, midinfrared absorption corresponding to an intraband transition, a bleach of the visible interband exciton transitions, and a quench of the narrow band-edge photoluminescence. PMID:11264530

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

    Science.gov (United States)

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

    2015-05-01

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

  3. Growth and temperature dependent photoluminescence of InGaAs quantum dot chains

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Haeyeon, E-mail: haeyeon.yang@sdsmt.edu [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); Colton, John S.; Park, Tyler; Meyer, David; Jones, Aaron M.; Thalman, Scott; Smith, Dallas; Clark, Ken; Brown, Steve [Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602 (United States)

    2014-03-01

    Highlights: • We examine the optical properties of novel quantum dot chains. • Study shows that platelets evolve into quantum dots during heating of the InGaAs platelets encapsulated with GaAs. • Single stack of quantum dots emits light at room temperature. • Quantum dots are of high quality, confirmed by cross-section TEM images and photoluminescence. • Light emission at room temperature weakens beyond the detection limit when the quantum dots form above the critical annealing temperature. - Abstract: We report a study of growth and photoluminescence from a single stack of MBE-grown In{sub 0.4}Ga{sub 0.6}As quantum dot chains. The InGaAs epilayers were grown at a low temperature so that the resulting surfaces remain flat with platelets even though their thicknesses exceed the critical thickness of the conventional Stranski–Krastanov growth mode. The flat InGaAs layers were then annealed at elevated temperatures to induce the formation of quantum dot chains. A reflection high energy electron diffraction study suggests that, when the annealing temperature is at or below 480 °C, the surface of growth front remains flat during the periods of annealing and growth of a 10 nm thick GaAs capping layer. Surprisingly, transmission electron microscopy images do indicate the formation of quantum dot chains, however, so the dot-chains in those samples may form from precursory platelets during the period of temperature ramping and subsequent capping with GaAs due to intermixing of group III elements. The optical emission from the quantum dot layer demonstrates that there is a critical annealing temperature of 480–500 °C above which the properties of the low temperature growth approach are lost, as the optical properties begin to resemble those of quantum dots produced by the conventional Stranski–Krastanov technique.

  4. Printer model for dot-on-dot halftone screens

    Science.gov (United States)

    Balasubramanian, Raja

    1995-04-01

    A printer model is described for dot-on-dot halftone screens. For a given input CMYK signal, the model predicts the resulting spectral reflectance of the printed patch. The model is derived in two steps. First, the C, M, Y, K dot growth functions are determined which relate the input digital value to the actual dot area coverages of the colorants. Next, the reflectance of a patch is predicted as a weighted combination of the reflectances of the four solid C, M, Y, K patches and their various overlays. This approach is analogous to the Neugebauer model, with the random mixing equations being replaced by dot-on-dot mixing equations. A Yule-Neilsen correction factor is incorporated to account for light scattering within the paper. The dot area functions and Yule-Neilsen parameter are chosen to optimize the fit to a set of training data. The model is also extended to a cellular framework, requiring additional measurements. The model is tested with a four color xerographic printer employing a line-on-line halftone screen. CIE L*a*b* errors are obtained between measurements and model predictions. The Yule-Neilsen factor significantly decreases the model error. Accuracy is also increased with the use of a cellular framework.

  5. Quantum dot cascade laser

    Science.gov (United States)

    2014-01-01

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

  6. ANALYTICAL REVIEW FOR DIFFERENT ASPECTS OF DOT GAIN

    OpenAIRE

    Parag Dnyandeo Nathe

    2013-01-01

    This document gives information about Dot reproduction, Dot gain, factors affecting dot gain, calculation of dot gain measurement and control over dot gain in different controlling parameters. Dot generation in print reproduction and different aspects which causes dot gain during image generation with photochemical process, during printing with mechanical process and during visual inspection of print dot gain is occurred. This document gives information about all causes of dot gain and contr...

  7. Engineering the hole confinement for CdTe-based quantum dot molecules

    International Nuclear Information System (INIS)

    We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum dots grown in a vertical stack. We achieve this by using materials with a different lattice constant for the growth of the outer and inner barriers. We monitor the resulting dot morphology with transmission electron microscopy studies and correlate the results with ensemble quantum dot photoluminescence. Furthermore, we embed the double quantum dots into diode structures and study photoluminescence as a function of bias voltage. We show that in properly engineered structures, it is possible to achieve a resonance of the hole states by tuning the energy levels with electric field. At the resonance, we observe signatures of a formation of a molecular state, hybridized over the two dots

  8. 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.

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

    Science.gov (United States)

    Altaisky, Mikhail V.; Zolnikova, Nadezhda N.; Kaputkina, Natalia E.; Krylov, Victor A.; Lozovik, Yurii E.; Dattani, Nikesh S.

    2016-02-01

    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.

  10. Investigations of segregation phenomena in highly strained Mn-doped Ge wetting layers and Ge quantum dots embedded in silicon

    International Nuclear Information System (INIS)

    In this Letter, we investigate manganese diffusion and the formation of Mn precipitates in highly strained, few monolayer thick, Mn-doped Ge wetting layers and nanometric size Ge quantum dot heterostructures embedded in silicon. We show that in this Ge(Mn)/Si system manganese always precipitates and that the size and the position of Mn clusters (precipitates) depend on the growth temperature. At high growth temperature, manganese strongly diffuses from germanium to silicon, whereas decreasing the growth temperature reduces the manganese diffusion. In the germanium quantum dots layers, Mn precipitates are detected, not only in partially relaxed quantum dots but also in fully strained germanium wetting layers between the dots

  11. Semiconductor nanocrystals inside spherical microcavities: A case of quantum dots in photonic dots

    OpenAIRE

    Artemyev, M. V.

    2003-01-01

    Quantum dots in photonic dots, a new type of microstructures involving highly luminescent II-VI semiconductor nanocrystals has been proposed and realized by incorporating nanocrystals (quantum dots) into glass and polymeric microspheres. The high quality micron-size microspheres represent simplest fully three-dimensional microcavities (photonic dots). Coupling of discrete electron states of quantum dots and photon states inside photonic dots strongly affects onto both stationary and dynamic p...

  12. Quantum dots: Rethinking the electronics

    Science.gov (United States)

    Bishnoi, Dimple

    2016-05-01

    In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including "waste heat" from the sun's energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate band setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.

  13. DOT Official County Highway Map

    Data.gov (United States)

    Minnesota Department of Natural Resources — The County Highway Map theme is a scanned and rectified version of the original MnDOT County Highway Map Series. The cultural features on some of these maps may be...

  14. Spin pumping through quantum dots

    OpenAIRE

    Rojek, Stephan; Governale, Michele; König, Jürgen

    2013-01-01

    We propose schemes for generating spin currents into a semiconductor by adiabatic or non-adiabatic pumping of electrons through interacting quantum dots. The appeal of such schemes lies in the possibility to tune the pumping characteristics via gate voltages that control the properties of the quantum dot. The calculations are based on a systematic perturbation expansion in the tunnel-coupling strength and the pumping frequency, expressed within a diagrammatic real-time technique. Special focu...

  15. Photonics of shungite quantum dots

    OpenAIRE

    Razbirin, Boris S.; Rozhkova, Natalia N.; Sheka, Elena F.

    2014-01-01

    Shungite quantum dots are associated with nanosize fragments of reduced graphene oxide similarly to synthetic graphene quantum dots thus forming a common class of GQDs. Colloidal dispersions of powdered shungite in water, carbon tetrachloride, and toluene form the ground for the GQD photonic peculiarities manifestation. Morphological study shows a steady trend of GQDs to form fractals and a drastic change in the colloids fractal structure caused by solvent was reliably established. Spectral s...

  16. Dot arrays of L11 type Co-Pt ordered alloy perpendicular films

    International Nuclear Information System (INIS)

    Magnetic properties of dot arrays of L11 type Co-Pt ordered alloy perpendicular films were studied. L11-Co-Pt films with a large uniaxial magnetic anisotropy Ku of the order of 107 erg/cm3 were fabricated at a substrate temperature of 360 deg. C using ultrahigh vacuum sputter film deposition. Dot patterns with dot diameters of 70-200 nm were made using high resolution e-beam lithography and reactive ion etching (RIE). The values of Ku were measured by the GST method using the Anomalous Hall Effect; we observed the averaged signals of 6000 dots. The values of Ku for dot arrays of 10-nm-thick L11-Co50Pt50 films deposited on MgO(111) substrates (single crystal films) and glass disks (polycrystalline films) were nearly the same as those of the original films independent of D, indicating no significant etching damage by the RIE process. Magnetic force microscopy images revealed that all dots were single domains in the present D region. The coercivity Hc of the dot arrays was 25.0 kOe [MgO(111) substrate, D=70 nm] and 14.3 kOe (glass disks, D=80 nm). The switching field distribution σ/Hc was relatively small, σ/Hc=0.15, even for dot arrays fabricated on glass disks, indicating the homogeneous formation of a L11 type ordered structure in the Co50Pt50 layers

  17. Bioactivation of water-soluble peptidic quantum dot through biotin-streptavidin binding

    Science.gov (United States)

    Dif, A.; Touchet, S.; Nagarajan, S.; Baudy-Floc'h, M.; Dahan, M.; Piehler, J.; Marchi-Artzner, V.

    2008-02-01

    This paper describes the preparation of bioactive water-soluble fluorescent CdSe/ZnS semi-conductor quantum dots with a small hydrodynamic diameter of 10 nm. These quantum dots are functionalized with a biotinylated peptide that can be introduced at different ratios onto the surface of the quantum dots. Their ability to bind to streptavidin in solution is tested by using gel electrophoresis and fluorescence resonance energy transfer with a fluorescent labeled-streptavidin. The binding of these quantum dots to Agarose micrometric beads coated with streptavidin is also analyzed by fluorescent optical microscopy. A synthetic pegylated peptide is successfully used to prevent the non specific adsorption of streptavidin onto the quantum dots. A specific binding to the streptavidin results in the formation of a very stable streptavidin-quantum dot complex without any significant aggregation. The average number of streptavidin per quantum dot is found to be to 4 at the most. Such bioactivate quantum dots can be further conjugated to any biotinylated biomolecule and used in biological medium.

  18. Scalable Quantum Computing with "Enhancement" Quantum Dots

    CERN Document Server

    Lyanda-Geller, Y B; Yang, M J

    2005-01-01

    We propose a novel scheme of solid state realization of a quantum computer based on single spin "enhancement mode" quantum dots as building blocks. In the enhancement quantum dots, just one electron can be brought into initially empty dot, in contrast to depletion mode dots based on expelling of electrons from multi-electron dots by gates. The quantum computer architectures based on depletion dots are confronted by several challenges making scalability difficult. These challenges can be successfully met by the approach based on ehnancement mode, capable of producing square array of dots with versatile functionalities. These functionalities allow transportation of qubits, including teleportation, and error correction based on straightforward one- and two-qubit operations. We describe physical properties and demonstrate experimental characteristics of enhancement quantum dots and single-electron transistors based on InAs/GaSb composite quantum wells. We discuss the materials aspects of quantum dot quantum compu...

  19. A high quality liquid-type quantum dot white light-emitting diode

    Science.gov (United States)

    Sher, Chin-Wei; Lin, Chin-Hao; Lin, Huang-Yu; Lin, Chien-Chung; Huang, Che-Hsuan; Chen, Kuo-Ju; Li, Jie-Ru; Wang, Kuan-Yu; Tu, Hsien-Hao; Fu, Chien-Chung; Kuo, Hao-Chung

    2015-12-01

    This study demonstrates a novel package design to store colloidal quantum dots in liquid format and integrate them with a standard LED. The high efficiency and high quality color performance at a neutral white correlated color temperature is demonstrated. The experimental results indicate that the liquid-type quantum dot white light-emitting diode (LQD WLED) is highly efficient and reliable. The luminous efficiency and color rendering index (CRI) of the LQD WLED can reach 271 lm Wop-1 and 95, respectively. Moreover, a glass box is employed to prevent humidity and oxygen erosion. With this encapsulation design, our quantum dot box can survive over 1000 hours of storage time.

  20. Fuzzy dot ideals and fuzzy dot H-ideals of BCH-algebras

    Institute of Scientific and Technical Information of China (English)

    PENG Jia-yin

    2008-01-01

    The notions of fuzzy dot ideals and fuzzy dot H-ideals in BCH-algebras are intro duced,several appropriate examples are provided,and their some properties are investigated.The relations among fuzzy ideal,fuzzy H-ideal,fuzzy dot ideal and fuzzy dot H-ideals in BCH algebras are discussed,several equivalent depictions of fuzzy dot ideal are obtained. How to deal with the homomorphic image and inverse image of fuzzy dot ideals (fuzzy dot H-ideals) are studied. The relations between a fuzzy dot ideal (fuzzy dot H-ideal) in BCH-algebras and a fuzzy dot ideal (fuzzy dot H-ideal) in the product algebra of BCH-algebras are given.

  1. Studies on formation and structures of ultrafine Cu precipitates in Fe-Cu model alloys for reactor pressure vessel steels using positron quantum dot confinement in the precipitates by their positron affinity. JAERI's nuclear research promotion program, H11-034 (Contract research)

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, Masayuki; Nagai, Yasuyoshi; Tang, Zheng; Yubuta, Kunio [Tohoku Univ., Sendai (Japan). Inst. for Materials Research; Suzuki, Masahide [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2003-03-01

    Positron annihilation experiments on Fe-Cu model dilute alloys of nuclear reactor pressure vessel (RPV) steels have been performed after neutron irradiation in JMTR. Nanovoids whose inner surfaces were covered by Cu atoms were clearly observed. The nanovoids transformed to ultrafine Cu precipitates by dissociating their vacancies after annealing at around 400degC. The nanovoids and the ultrafine Cu precipitates are strongly suggested to be responsible for irradiation-induced embrittlement of RPV steels. Effects of Ni, Mn and P addition on the nanovoid and Cu precipitate formations were also studied. The nanovoid formation was enhanced by Ni and P, but suppressed by Mn. The Cu precipitates after annealing around 400degC were almost free from these doping elements and hence were pure Cu in the chemical composition. Furthermore the Fermi surface of the 'embedded' Cu precipitates with a body centered cubic crystal structure was obtained from two dimensional angular correlation of annihilation radiation (2D-ACAR) in a Fe-Cu single crystal and was agreed well with that from a band structure calculation. Theoretical calculation of positron confinement in Fe-Cu model alloys showed that a positron quantum dot state induced by positron affinity is attained for the embedded precipitates larger than 1 nm. A new position sensitive detector with a function of one dimensional angular correlation of annihilation radiation (1D-ACAR) has been developed that enables high resolution experiments over wide ranges of momentum distribution. (author)

  2. Studies on formation and structures of ultrafine Cu precipitates in Fe-Cu model alloys for reactor pressure vessel steels using positron quantum dot confinement in the precipitates by their positron affinity. JAERI's nuclear research promotion program, H11-034 (Contract research)

    International Nuclear Information System (INIS)

    Positron annihilation experiments on Fe-Cu model dilute alloys of nuclear reactor pressure vessel (RPV) steels have been performed after neutron irradiation in JMTR. Nanovoids whose inner surfaces were covered by Cu atoms were clearly observed. The nanovoids transformed to ultrafine Cu precipitates by dissociating their vacancies after annealing at around 400degC. The nanovoids and the ultrafine Cu precipitates are strongly suggested to be responsible for irradiation-induced embrittlement of RPV steels. Effects of Ni, Mn and P addition on the nanovoid and Cu precipitate formations were also studied. The nanovoid formation was enhanced by Ni and P, but suppressed by Mn. The Cu precipitates after annealing around 400degC were almost free from these doping elements and hence were pure Cu in the chemical composition. Furthermore the Fermi surface of the 'embedded' Cu precipitates with a body centered cubic crystal structure was obtained from two dimensional angular correlation of annihilation radiation (2D-ACAR) in a Fe-Cu single crystal and was agreed well with that from a band structure calculation. Theoretical calculation of positron confinement in Fe-Cu model alloys showed that a positron quantum dot state induced by positron affinity is attained for the embedded precipitates larger than 1 nm. A new position sensitive detector with a function of one dimensional angular correlation of annihilation radiation (1D-ACAR) has been developed that enables high resolution experiments over wide ranges of momentum distribution. (author)

  3. SCAMPI, Problem Dependent Library Preprocessing in AMPX Format

    International Nuclear Information System (INIS)

    1 - Description of program or function: SCAMPI (Scale and Ampx Processing Interface) was prepared to facilitate the calculational procedure for creating problem-dependent cross sections (working format) from problem-independent multigroup data (master library). It consists primarily of modules derived from AMPX-77 (PSR-0315) and SCALE-4.3 (CCC-0545). Included in the package are AIM, AJAX, ALE, ALPO, BONAMI, COMPOZ, CORECTOL, CSAS, FILTER, GIP, ICE, LAVA, MALOCS, NITAWL, PERFUME, RADE, SMILER, UNITAB, WAX, and XSDRN. The CSASIN full-screen PC input processor that guides the user through the CSAS module input has been modified for SCAMPI an is also included. The CSAS module was modified to remove the interface with KENO and automatically provide output of an ANISN-formatted working library for use with codes such as TORT-DORT (CCC-0543), ANISN-ORNL (CCC-0254), or MORSE-CGA (CCC-0474. The GIP program was extracted from the TORT-DORT-2.12.14 package (CCC-0543). Note that no data libraries are included in SCAMPI. PSR-0352/05: The original version of SCAMPI was upgraded to contain the following features: - A bug in the fission matrix collapsing was corrected in the MALOCS code. - The RGENDF subroutine was corrected and modified in the SMILER module to read GENDF double precision binary files from NJOY-99. - The listing length of the output data was increased from 1000 to 10000 records in the MILER subroutine of the SMILER module. - The SMILER and MALOCS modules treat now, in addition to the prompt fission spectrum, the delayed fission spectrum, and prepare the total (prompt part + delayed part) fission spectrum. - MALOCS can now process rectangular fission matrices. - Truncation of the up-scatter terms with the full effective use of the trigger options IOPT7=0, 1, 2, 3 and 4 of the MALOCS module. This new release includes all pre-2006 MALOCS module modifications made by the ENEA-Bologna Nuclear Data Group. 2 - Method of solution: The CSAS control module in SCAMPI uses

  4. Production of three-dimensional quantum dot lattice of Ge/Si core–shell quantum dots and Si/Ge layers in an alumina glass matrix

    International Nuclear Information System (INIS)

    We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells. (paper)

  5. Three-Dimensional Dissipative Optical Solitons in a Dielectric Medium with Quantum Dots

    Directory of Open Access Journals (Sweden)

    Gubin M.Yu.

    2015-01-01

    Full Text Available We consider the problem of formation of three-dimensional spatio-temporal dissipative solitons (laser bullets in a dense ensemble of two-level quantum dots. The principal possibility of effective laser bullets generation in an all-dielectric metamaterials with quantum dots is shown. The phenomenon arises due to the simultaneous appearance of strong local field effects and significant corrections to diffraction effects during the propagation of short optical pulses in such medium.

  6. Fabrication and characterization of silicon quantum dots in Si-rich silicon carbide films.

    Science.gov (United States)

    Chang, Geng-Rong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2011-12-01

    Amorphous Si-rich silicon carbide films were prepared by magnetron co-sputtering and subsequently annealed at 900-1100 degrees C. After annealing at 1100 degrees C, this configuration of silicon quantum dots embedded in amorphous silicon carbide formed. X-ray photoelectron spectroscopy was used to study the chemical modulation of the films. The formation and orientation of silicon quantum dots were characterized by glancing angle X-ray diffraction, which shows that the ratio of silicon and carbon significantly influences the species of quantum dots. High-resolution transmission electron microscopy investigations directly demonstrated that the formation of silicon quantum dots is heavily dependent on the annealing temperatures and the ratio of silicon and carbide. Only the temperature of about 1100 degrees C is enough for the formation of high-density and small-size silicon quantum dots due to phase separation and thermal crystallization. Deconvolution of the first order Raman spectra shows the existence of a lower frequency peak in the range 500-505 cm(-1) corresponding to silicon quantum dots with different atom ratio of silicon and carbon. PMID:22409005

  7. Optical Fiber Sensing Using Quantum Dots

    OpenAIRE

    Faramarz Farahi; José Luís Santos; Tito Trindade; Manuel António Martins; Pedro Jorge

    2007-01-01

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

  8. Crystal structure of Legionella DotD: insights into the relationship between type IVB and type II/III secretion systems.

    Directory of Open Access Journals (Sweden)

    Noboru Nakano

    Full Text Available The Dot/Icm type IVB secretion system (T4BSS is a pivotal determinant of Legionella pneumophila pathogenesis. L. pneumophila translocate more than 100 effector proteins into host cytoplasm using Dot/Icm T4BSS, modulating host cellular functions to establish a replicative niche within host cells. The T4BSS core complex spanning the inner and outer membranes is thought to be made up of at least five proteins: DotC, DotD, DotF, DotG and DotH. DotH is the outer membrane protein; its targeting depends on lipoproteins DotC and DotD. However, the core complex structure and assembly mechanism are still unknown. Here, we report the crystal structure of DotD at 2.0 Å resolution. The structure of DotD is distinct from that of VirB7, the outer membrane lipoprotein of the type IVA secretion system. In contrast, the C-terminal domain of DotD is remarkably similar to the N-terminal subdomain of secretins, the integral outer membrane proteins that form substrate conduits for the type II and the type III secretion systems (T2SS and T3SS. A short β-segment in the otherwise disordered N-terminal region, located on the hydrophobic cleft of the C-terminal domain, is essential for outer membrane targeting of DotH and Dot/Icm T4BSS core complex formation. These findings uncover an intriguing link between T4BSS and T2SS/T3SS.

  9. Quantum dot field effect transistors

    Directory of Open Access Journals (Sweden)

    Frederik Hetsch

    2013-09-01

    Full Text Available Solution processed colloidal semiconductor quantum dots offer a high potential for decreasing costs and expanding versatility of many electronic and optoelectronic devices. Initially used as a research tool to study charge carrier mobilities in closely packed quantum dot thin films, field effect transistors with quantum dots as the active layer have recently experienced a breakthrough in performance (achievement of mobilities higher than 30 cm2 V−1 s−1 as a result of a proper choice of surface ligands and/or improved chemical treatment of the nanoparticle films during device processing. Here we review these innovative developments and the continuing work that may soon lead to commercial grade electronic components.

  10. Beer's law in semiconductor quantum dots

    CERN Document Server

    Adamashvili, G T

    2010-01-01

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

  11. 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....

  12. Chaos and Interactions in Quantum Dots

    OpenAIRE

    Alhassid, Y.

    2001-01-01

    Quantum dots are small conducting devices containing up to several thousand electrons. We focus here on closed dots whose single-electron dynamics are mostly chaotic. The mesoscopic fluctuations of the conduction properties of such dots reveal the effects of one-body chaos, quantum coherence and electron-electron interactions.

  13. MOVPE overgrowth of InN quantum dot like structures

    International Nuclear Information System (INIS)

    Indium nitride (InN) quantum dots could be used an alternative material for applications at the standard telecommunication wavelength of 1.55 μm. We showed that the density and size of InN quantum dots grown in Volmer-Weber growth mode can be controlled by growth temperature and total amount of InN on the surface. For light emitting devices those quantum dot like structures need to be overgrown. Therefore, we studied systematically the overgrowth process by MOVPE of InN quantum dots on GaN/sapphire with a density of 1010 cm-2. Different capping strategies were monitored by in-situ ellipsometry which allows investigations on a submonolayer scale of the InN/GaN system with 11% lattice mismatch. Additional characterisation was done by atomic force microscopy, x-ray and photoluminescence measurements. The main problem of indium segregation from InN QDs into the first capping layers and the formation of InGaN is observed by XRD with a gallium content of less than 20%. Thus for overgrowth a high growth rate is needed, but the material quality must still be maintained. Further investigations with InGaN capping layers to reduce the strain during overgrowth have been done.

  14. Surface processes during purification of InP quantum dots

    Directory of Open Access Journals (Sweden)

    Natalia Mordvinova

    2014-08-01

    Full Text Available Recently, a new simple and fast method for the synthesis of InP quantum dots by using phosphine as phosphorous precursor and myristic acid as surface stabilizer was reported. Purification after synthesis is necessary to obtain samples with good optical properties. Two methods of purification were compared and the surface processes which occur during purification were studied. Traditional precipitation with acetone is accompanied by a small increase in photoluminescence. It occurs that during the purification the hydrolysis of the indium precursor takes place, which leads to a better surface passivation. The electrophoretic purification technique does not increase luminescence efficiency but yields very pure quantum dots in only a few minutes. Additionally, the formation of In(OH3 during the low temperature synthesis was explained. Purification of quantum dots is a very significant part of postsynthetical treatment that determines the properties of the material. But this subject is not sufficiently discussed in the literature. The paper is devoted to the processes that occur at the surface of quantum dots during purification. A new method of purification, electrophoresis, is investigated and described in particular.

  15. Spatially correlated two-dimensional arrays of semiconductor and metal quantum dots in GaAs-based heterostructures

    International Nuclear Information System (INIS)

    A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix

  16. Spatially correlated two-dimensional arrays of semiconductor and metal quantum dots in GaAs-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Nevedomskiy, V. N., E-mail: nevedom@mail.ioffe.ru; Bert, N. A.; Chaldyshev, V. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Preobrazhernskiy, V. V.; Putyato, M. A.; Semyagin, B. R. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2015-12-15

    A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix.

  17. Environmental conditions influence for real-time hologram formation on dichromated polyvinyl alcohol NiCl{sub 2}{center_dot}6H{sub 2}O doped films

    Energy Technology Data Exchange (ETDEWEB)

    Fontanilla-Urdaneta, R C; Olivares-Perez, A; Fuentes-Tapia, I; Rios-Velasco, M A, E-mail: rfontanilla@inaoep.mx, E-mail: olivares@inaoep.mx, E-mail: ifuentes@inaoep.mx, E-mail: moni_arv@hotmail.com [Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Luis Enrique Erro No. 1 Tonantzintla, Puebla (Mexico)

    2011-01-01

    The real-time holographic gratings recording are studied by the presence of a metallic salt. The experimental process refers to analysis of diffraction efficiency by the influence of humidity in the coating solution on holograms formation in presence of electrical potential. The diffraction efficiency is measured as a function of the exposure energy until reach the saturation. The influence of the hologram parameters to get the diffraction efficiency is studied at room conditions.

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

    International Nuclear Information System (INIS)

    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 T1=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T1∝B-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 T1∝T-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 T1h in the microsecond range, therefore, comparable with electron spin

  19. 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

  20. Ambient-Processed Colloidal Quantum Dot Solar Cells via Individual Pre-Encapsulation of Nanoparticles

    KAUST Repository

    Debnath, Ratan

    2010-05-05

    We report colloidal quantum dot solar cells fabricated under ambient atmosphere with an active area of 2.9 mm2 that exhibit 3.6% solar power conversion efficiency. The devices are based on PbS tuned via the quantum size effect to have a first excitonic peak at 950 nm. Because the formation of native oxides and sulfates on PbS leads to p-type doping and deep trap formation and because such dopants and traps dramatically influence device performance, prior reports of colloidal quantum dot solar cells have insisted on processing under an inert atmosphere. Here we report a novel ligand strategy in which we first encapsulate the quantum dots in the solution phase with the aid of a strongly bound N-2,4,6-trimethylphenyl-N-methyldithiocarbamate ligand. This allows us to carry out film formation and all subsequent device fabrication under an air atmosphere. © 2010 American Chemical Society.

  1. Luminescent Surface Quaternized Carbon Dots

    KAUST Repository

    Bourlinos, Athanasios B.

    2012-01-10

    Thermal oxidation of a salt precursor made from the acid base combination of tris(hydroxymethyl)aminomethane and betaine hydrochloride results in light-emitting surface quaternized carbon dots that are water-dispersible, display anion exchange properties, and exhibit uniform size/surface charge. © 2011 American Chemical Society.

  2. On triaxial ellipsoidal quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Voon, L C Lew Yan; Willatzen, M [Mads Clausen Institute, University of Southern Denmark, Grundtvigs Alle 150, DK-6400 Soenderborg (Denmark)

    2004-02-25

    The bound-state problem for triaxial ellipsoidal infinite-barrier quantum dots has been solved. It is exactly solvable in terms of ellipsoidal coordinates and the eigenmodes are written in terms of Lame wavefunctions. The need for all eight types of functions is shown. This presents a generalization over previous work on spheres and spheroids. Splitting of degeneracy and level crossing are obtained.

  3. DOT strategies versus orbiter strategies

    NARCIS (Netherlands)

    Rutten, R.J.

    2001-01-01

    The Dutch Open Telescope is a high-resolution solar imager coming on-line at La Palma. The definition of the DOT science niche, strategies, and requirements resemble Solar Orbiter considerations and deliberations. I discuss the latter in the light of the former, and claim that multi-line observation

  4. Quantum dot photonic crystal lasers

    OpenAIRE

    Yoshie, T.; Shchekin, O. B.; Chen, H.; Deppe, D. G.; Scherer, A.

    2002-01-01

    Coupled cavity designs on two-dimensional square lattice photonic crystal slabs were used to demonstrate optically pumped indium arsenide quantum dot photonic crystal lasers at room temperature. Threshold pump powers of 120 and 370 μW were observed for coupled cavities including two and four defect cavities defined in optimised photonic crystals.

  5. Star Formation in Luminous Quasars at 2

    CERN Document Server

    Harris, Kathryn; Schulz, Bernhard; Hatziminaoglou, Evanthia; Viero, Marco; Anderson, Nick; Bethermin, Matthieu; Chapman, Scott; Clements, David L; Cooray, Asantha; Efstathiou, Andreas; Feltre, Anne; Hurley, Peter; Ibar, Eduardo; Lacy, Mark; Oliver, Sebastian; Page, Mathew J; Perez-Fournon, Ismael; Petty, Sara M; Pitchford, Lura K; Rigopoulou, Dimitra; Scott, Douglas; Symeonidis, Myrto; Vieira, Joaquin; Wang, Lingyu

    2016-01-01

    We investigate the relation between star formation rates ($\\dot{M}_{s}$) and AGN properties in optically selected type 1 quasars at $2dot{\\rm{M}}_s$ remains approximately constant with redshift, at $300\\pm100~\\rm{M}_{\\odot}$yr$^{-1}$. Conversely, $\\dot{\\rm{M}}_s$ increases with AGN luminosity, up to a maximum of $\\sim600~\\rm{M}_{\\odot}$yr$^{-1}$, and with CIV FWHM. In context with previous results, this is consistent with a relation between $\\dot{\\rm{M}}_s$ and black hole accretion rate ($\\dot{\\rm{M}}_{bh}$) existing in only parts of the $z-\\dot{\\rm{M}}_{s}-\\dot{\\rm{M}}_{bh}$ plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between $\\dot{\\rm{M}}_s$ and both AGN luminosity and CIV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates...

  6. Imaging Pseudomonas aeruginosa Biofilm Extracellular Polymer Scaffolds with Amphiphilic Carbon Dots.

    Science.gov (United States)

    Ritenberg, Margarita; Nandi, Sukhendu; Kolusheva, Sofiya; Dandela, Rambabu; Meijler, Michael M; Jelinek, Raz

    2016-05-20

    Biofilm formation is a critical facet of pathogenesis and resilience of human, animal, and plant bacteria. Extracellular polymeric substances (EPS) constitute the physical scaffolding for bacterial biofilms and thus play central roles in their development and virulence. We show that newly synthesized amphiphilic fluorescent carbon dots (C-dots) readily bind to the EPS scaffold of Pseudomonas aeruginosa, a major biofilm-forming pathogen, resulting in unprecedented microscopic visualization of the EPS structural features. Fluorescence microscopy analysis utilizing the C-dots reveals that the P. aeruginosa EPS matrix exhibits a remarkable dendritic morphology. The experiments further illuminate the growth kinetics of the EPS and the effect of external factors such as temperature. We also show that the amphiphilic C-dot platform enabled screening of substances disrupting biofilm development, specifically quorum sensing inhibitors. PMID:26882175

  7. Multi-band silicon quantum dots embedded in an amorphous matrix of silicon carbide.

    Science.gov (United States)

    Chang, Geng-rong; Ma, Fei; Ma, Da-yan; Xu, Ke-wei

    2010-11-19

    Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized by a magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy, glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the chemical composition and the microstructural properties. The results show that the sizes and size distribution of silicon quantum dots can be tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon in the matrix. A physicochemical mechanism is proposed to demonstrate this formation process. Photoluminescence measurements indicate a multi-band configuration due to the quantum confinement effect of silicon quantum dots with different sizes. The PL spectra are further widened as a result of the existence of amorphous silicon quantum dots. This multi-band configuration would be extremely advantageous in improving the photoelectric conversion efficiency of photovoltaic solar cells. PMID:20975214

  8. Multi-band silicon quantum dots embedded in an amorphous matrix of silicon carbide

    International Nuclear Information System (INIS)

    Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized by a magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy, glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the chemical composition and the microstructural properties. The results show that the sizes and size distribution of silicon quantum dots can be tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon in the matrix. A physicochemical mechanism is proposed to demonstrate this formation process. Photoluminescence measurements indicate a multi-band configuration due to the quantum confinement effect of silicon quantum dots with different sizes. The PL spectra are further widened as a result of the existence of amorphous silicon quantum dots. This multi-band configuration would be extremely advantageous in improving the photoelectric conversion efficiency of photovoltaic solar cells.

  9. Hyperdense dots mimicking microcalcifications : Mammographic findings

    International Nuclear Information System (INIS)

    To differentiate fine hyperdense dots mimicking microcalcifications from true microcalcifications on mammography. Mammograms showing hyperdense dots in ten patients (mean age, 59 years) were evaluated. Two radiologists were asked to differentiate with the naked eye the hyperdense dots seen on ten mammograms and proven microcalcifications seen on ten mammograms. Densitometry was also performed for all lesions and the contrast index was calculated. The shape and distribution of the hyperdense dots were evaluated and enquires were made regarding any history of breast disease and corresponding treatment. Biopsies were performed for two patients with hyperdense dots. Two radiologists made correct diagnoses in 19/20 cases(95%). The contrast index was 0.10-0.88 (mean 0.58) for hyperdense dots and 0.02-0.45 (mean 0.17) for true microcalcifications. The hyperdense dots were finer and homogeneously rounder than the microcalcifications. Distribution of the hyperdense dots was more superficial in subcutaneous fat (seven cases) and subareolar area (six cases). All ten patients with hyperdense dots had history of mastitis and abscesses and had been treated by open drainage (six cases) and/or folk remedy (four cases). In eight patients, herb patches had been attached. Biopsies of hyperdense dots did not show any microcalcification or evidence of malignancy. These hyperdense dots were seen mainly in older patients. Their characteristic density, shape, distribution and clinical history makes differential diagnosis from true microcalcifications easy and could reduce unnecessary diagnostic procedures such as surgical biopsy

  10. Hyperdense dots mimicking microcalcifications : Mammographic findings

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Nam Hyeon; Park, Jeong Mi; Goo, Hyun Woo; Bang, Sun Woo [Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of)

    1996-12-01

    To differentiate fine hyperdense dots mimicking microcalcifications from true microcalcifications on mammography. Mammograms showing hyperdense dots in ten patients (mean age, 59 years) were evaluated. Two radiologists were asked to differentiate with the naked eye the hyperdense dots seen on ten mammograms and proven microcalcifications seen on ten mammograms. Densitometry was also performed for all lesions and the contrast index was calculated. The shape and distribution of the hyperdense dots were evaluated and enquires were made regarding any history of breast disease and corresponding treatment. Biopsies were performed for two patients with hyperdense dots. Two radiologists made correct diagnoses in 19/20 cases(95%). The contrast index was 0.10-0.88 (mean 0.58) for hyperdense dots and 0.02-0.45 (mean 0.17) for true microcalcifications. The hyperdense dots were finer and homogeneously rounder than the microcalcifications. Distribution of the hyperdense dots was more superficial in subcutaneous fat (seven cases) and subareolar area (six cases). All ten patients with hyperdense dots had history of mastitis and abscesses and had been treated by open drainage (six cases) and/or folk remedy (four cases). In eight patients, herb patches had been attached. Biopsies of hyperdense dots did not show any microcalcification or evidence of malignancy. These hyperdense dots were seen mainly in older patients. Their characteristic density, shape, distribution and clinical history makes differential diagnosis from true microcalcifications easy and could reduce unnecessary diagnostic procedures such as surgical biopsy.

  11. ZZ BP-3, 104-Group Neutron Cross-Section Library for Transport Calculation. ZZ BP-6, 104 Group Neutron and Gamma-Ray Multigroup Cross-Section Library for Transport Calculation

    International Nuclear Information System (INIS)

    1 - Description of program or function: specified on ORNL-RSIC-25, shielding benchmark problems. - BP-3 (Neutron cross sections): Format: ANISN, DOT and MORSE; Number of groups: 22 neutron / 18 gamma-ray; Nuclides: air; Origin: ENDF/B; Weighting spectrum: 1/E; - BP-6 (neutron and gamma-ray cross sections): Format: ANISN, DOT and MORSE; Number of groups: 22 neutron / 18 gamma-ray; Nuclides: Borated Polyethylene (C-12, H, and B-10); Origin: ENDF/B-II. The cross section data can be used to repeat the Shielding Benchmark Problems 3.0 and 6.0 for testing against the results published in ORNL-RSIC-25. 2 - Method of solution: ZZ-BP-3 neutron cross sections from the CCC-17/05R library were processed into 104 neutron groups using the PSR-9/CSP code. The fine-group neutron cross sections were collapsed to 22 broad groups using CCC-254/ANISN with an equilibrium fission spectrum source. The resulting multigroup cross sections are P5 coefficients punched on cards in format suitable for input to ANISN, DOT, and MORSE. ZZ-BP-6 neutron and gamma-ray cross sections for 12C, H, and 10B were from ENDF/B-II data. The neutron multigroup cross sections were generated into 104 neutron groups using the PSR-13/SUPERTOG code. The fine-group neutron cross sections were collapsed to 22 broad groups using CCC-254/ANISN with an equilibrium fission spectrum source. The gamma-ray multigroup cross sections were generated using PSR-7/MUG. The neutron-gamma-ray coupling utilized yield data from the DLC-12/POPOP4 library (data sets 010101, 060101, 060301, and 05100201). The neutron-gamma-ray coupled multigroup cross-section set was generated using the SAMPLE COUPLING CODE (ASCC). The multigroup cross sections are in a 22-18 group structure with P3 coefficients punched on cards in format suitable for input to ANISN, DOT, and MORSE

  12. Systematic safety evaluation on photoluminescent carbon dots

    Science.gov (United States)

    Wang, Kan; Gao, Zhongcai; Gao, Guo; Wo, Yan; Wang, Yuxia; Shen, Guangxia; Cui, Daxiang

    2013-03-01

    Photoluminescent carbon dots (C-dots) were prepared using the improved nitric acid oxidation method. The C-dots were characterized by tapping-mode atomic force microscopy, and UV-vis absorption spectroscopy. The C-dots were subjected to systematic safety evaluation via acute toxicity, subacute toxicity, and genotoxicity experiments (including mouse bone marrow micronuclear test and Salmonella typhimurium mutagenicity test). The results showed that the C-dots were successfully prepared with good stability, high dispersibility, and water solubility. At all studied C-dot dosages, no significant toxic effect, i.e., no abnormality or lesion, was observed in the organs of the animals. Therefore, the C-dots are non-toxic to mice under any dose and have potential use in fluorescence imaging in vivo, tumor cell tracking, and others.

  13. DNA derived fluorescent bio-dots for sensitive detection of mercury and silver ions in aqueous solution

    International Nuclear Information System (INIS)

    Highlights: • First application of a DNA derived fluorescent bio-dot for metal sensing. • Bio-dot was conveniently obtained via a mild thermal hydro-thermal synthesis. • Bio-dot was directly used for fluorescent sensing without further modification. • Bio-dot showed good fluorescent sensing property for Hg(II) and Ag(I). • Formation of T–Hg–T and C–Ag–C structures played key roles in sensing. - Abstract: Inspired by the high affinity between heavy metal ions and bio-molecules as well as the low toxicity of carbon-based quantum dots, we demonstrated the first application of a DNA derived carbonaceous quantum dots, namely bio-dots, in metal ion sensing. The present DNA-derived bio-dots contain graphitic carbon layers with 0.242 nm lattice fringes, exhibit excellent fluorescence property and can be obtained via a facile hydrothermal preparation procedure. Hg(II) and Ag(I) are prone to be captured by the bio-dots due to the existence of residual thymine (T) and cytosine (C) groups, resulting in a quenched fluorescence while other heavy metal ions would cause negligible changes on the fluorescent signals of the bio-dots. The bio-dots could be used as highly selective toxic-free biosensors, with two detecting linear ranges of 0–0.5 μM and 0.5–6 μM for Hg(II) and one linear range of 0–10 μM for Ag(I). The detection limits (at a signal-to-noise ratio of 3) were estimated to be 48 nM for Hg(II) and 0.31 μM for Ag(I), respectively. The detection of Hg(II) and Ag(I) could also be realized in the real water sample analyses, with satisfying recoveries ranging from 87% to 100%

  14. DNA derived fluorescent bio-dots for sensitive detection of mercury and silver ions in aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    Song, Ting [Laboratory of Environmental Science and Technology, Xinjiang Technical Institute of Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhu, Xuefeng, E-mail: zhuxf@ms.xjb.ac.cn [Laboratory of Environmental Science and Technology, Xinjiang Technical Institute of Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011 (China); Zhou, Shenghai [Laboratory of Environmental Science and Technology, Xinjiang Technical Institute of Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011 (China); Yang, Guang [Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an 710049 (China); Gan, Wei [Laboratory of Environmental Science and Technology, Xinjiang Technical Institute of Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011 (China); Yuan, Qunhui, E-mail: yuanqh@ms.xjb.ac.cn [Laboratory of Environmental Science and Technology, Xinjiang Technical Institute of Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011 (China)

    2015-08-30

    Highlights: • First application of a DNA derived fluorescent bio-dot for metal sensing. • Bio-dot was conveniently obtained via a mild thermal hydro-thermal synthesis. • Bio-dot was directly used for fluorescent sensing without further modification. • Bio-dot showed good fluorescent sensing property for Hg(II) and Ag(I). • Formation of T–Hg–T and C–Ag–C structures played key roles in sensing. - Abstract: Inspired by the high affinity between heavy metal ions and bio-molecules as well as the low toxicity of carbon-based quantum dots, we demonstrated the first application of a DNA derived carbonaceous quantum dots, namely bio-dots, in metal ion sensing. The present DNA-derived bio-dots contain graphitic carbon layers with 0.242 nm lattice fringes, exhibit excellent fluorescence property and can be obtained via a facile hydrothermal preparation procedure. Hg(II) and Ag(I) are prone to be captured by the bio-dots due to the existence of residual thymine (T) and cytosine (C) groups, resulting in a quenched fluorescence while other heavy metal ions would cause negligible changes on the fluorescent signals of the bio-dots. The bio-dots could be used as highly selective toxic-free biosensors, with two detecting linear ranges of 0–0.5 μM and 0.5–6 μM for Hg(II) and one linear range of 0–10 μM for Ag(I). The detection limits (at a signal-to-noise ratio of 3) were estimated to be 48 nM for Hg(II) and 0.31 μM for Ag(I), respectively. The detection of Hg(II) and Ag(I) could also be realized in the real water sample analyses, with satisfying recoveries ranging from 87% to 100%.

  15. Synthesis, Characterization and Application Of PbS Quantum Dots

    International Nuclear Information System (INIS)

    Lead Chalcogenides (PbS, PbSe, PbTe) quantum dots (QDs) are ideal for fundamental studies of strongly quantum confined systems with possible technological applications. Tunable electronic transitions at near--infrared wavelengths can be obtained with these QDs. Applications of lead chalcogenides encompass quite a good number of important field viz. the fields of telecommunications, medical electronics, optoelectronics etc. Very recently, it has been proposed that 'memristor'(Memory resistor) can be realized in nanoscale systems with coupled ionic and electronic transports. The hystersis characteristics of 'memristor' are observed in many nanoscale electronic devices including semiconductor quantum dot devices. This paper reports synthesis of PbS QDs by chemical route. The fabricated samples are characterized by UV-Vis, XRD, SEM, TEM, EDS, etc. Observed characteristics confirm nano formation. I-V characteristics of the sample are studied for investigating their applications as 'memristor'.

  16. Analysis of biodistribution attributes of radiopharmaceuticals by BioDOT

    International Nuclear Information System (INIS)

    An important component of radiopharmaceuticals quality evaluation is determination of biological distribution attributes by animal study. This is subjective, time consuming, and difficult to quantify. A user friendly graphical statistical analysis software (BioDOT) was developed using Visual Basic 6.0 for repeatable, objective evaluate of biological distribution attribute of radiopharmaceuticals in animal. The software measured the organs mass, organs radioactivity, radioactivity decay correction, radioactivity per gram of organs, and calculate radioactivity target to non-target ratios. Radiopharmaceuticals quality assessment by a BioDOT was used to estimate post injected biological distribution, and organs radioactivity and uniformity ratio was calculated. The software quantified percent injected dose of radiopharmaceutical in selected organs of the animal study. Total percent injected dose was quantified and correlated with the standard value of BP Pharmacopoeia. The method objectively measured distribution quality attributes of radiopharmaceuticals and generate full report in pdf format in less than 10 min per study. (author)

  17. Quantum dot loading in strong alkaline: improved performance in quantum-dot sensitized solar cells

    International Nuclear Information System (INIS)

    For the first time, we demonstrate that the conversion efficiency of CdTe quantum-dot sensitized solar cells could be effectively improved by using a strong alkaline environment during deposition of quantum dots (QDs) onto the TiO2 mesoporous electrode. Alkalis play three unique roles during the deposition: (i) decreasing the inter-particle electrostatic force between TiO2 nanoparticles and QDs to improve QD deposition; (ii) spontaneous formation of Cd(OH)2 during the deposition, which contributes to improvement of device efficiency; (iii) enhancing QD stability by hindering ligands' detachment from QD surface. With these advantages, improved QD loading onto a TiO2 photoanode has been achieved, from barely loading to dense, uniform QD loading with an optimized NaOH addition. Using this method, the overall efficiency of CdTe sensitized solar cell exceeds 2.1% when coupled with a Cu2S cathode—an almost 40% increase of efficiency compared with QDs deposited under a relatively low pH environment. (paper)

  18. Lateral patterning of multilayer InAs/GaAs(001) quantum dot structures by in vacuo focused ion beam

    International Nuclear Information System (INIS)

    We report on the effects of patterning and layering on multilayer InAs/GaAs(001) quantum dot structures laterally ordered using an in vacuo focused ion beam. The patterned hole size and lateral pattern spacing affected the quantum dot size and the fidelity of the quantum dots with respect to the lateral patterns. 100% pattern fidelity was retained after six layers of dots for a 9.0 ms focused ion beam dwell time and 2.0 µm lateral pattern spacing. Analysis of the change in quantum dot size as a function of pattern spacing provided a means of estimating the maximum average adatom surface diffusion length to be approximately 500 nm, and demonstrated the ability to alter the wetting layer thickness via pattern spacing. Increasing the number of layers from six to 26 resulted in mound formation, which destroyed the pattern fidelity at close pattern spacings and led to a bimodal quantum dot size distribution as measured by atomic force microscopy. The bimodal size distribution also affected the optical properties of the dots, causing a split quantum dot photoluminescence peak where the separation between the split peaks increased with increasing pattern spacing. (paper)

  19. Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity

    Science.gov (United States)

    Kaur, Gurvir; Tripathi, S. K.

    2015-01-01

    The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent.

  20. Nanoscaled redox active protein adsorption on Au-dot arrays: An electrochemical scanning probe microscopic investigation for application in nano-biodevices

    Energy Technology Data Exchange (ETDEWEB)

    Yagati, Ajay Kumar; Jung, Mi; Kim, Sang-Uk [Interdisciplinary Program of Integrated Biotechnology, Sogang University, 1 Shinsu-dong, Mapo-gu, Seoul 121-742 (Korea, Republic of); Min, Junhong [College of Bionanotechnology, Kyungwon University, Bokjung-dong, Sujung-gu, Seongnam 461-701 (Korea, Republic of); Choi, Jeong-Woo, E-mail: jwchoi@sogang.ac.k [Interdisciplinary Program of Integrated Biotechnology, Sogang University, 1 Shinsu-dong, Mapo-gu, Seoul 121-742 (Korea, Republic of); Department of Chemical and Biomolecular Engineering, Interdisciplinary Program of Integrated Biotechnology Sogang University, 1 Shinsu-dong, Mapo-gu, Seoul 121-742 (Korea, Republic of)

    2009-11-30

    Highly dense and uniform protein dot arrays on Au-nanodots using size controllable method were fabricated on indium tin oxide (ITO) substrate in order to develop an electrochemical nanobiochip. Cysteine modified azurin was directly immobilized on the fabricated Au-nanodots without any linker materials. Atomic force microscopy was used for characterizing Au-dots formed on ITO substrate. Electrochemical scanning tunneling microscopy (ECSTM) revealed the monolayer formation with an in situ cyclic voltammetry to observe redox behaviour of both bare Au-dots and protein immobilized Au-dots. I-V characteristics were obtained on both bare Au-dots and protein immobilized Au-dots structured on ITO conductive electrodes.

  1. 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

  2. Adiabatic pumping through quantum dots

    International Nuclear Information System (INIS)

    A finite charge can be pumped through a mesoscopic system in the absence of an applied bias voltage by changing periodically in time some parameters of the system. If these parameters change slowly with respect to all internal time scales of the system, pumping is adiabatic. The scope of this work is to investigate adiabatic pumping through a quantum dot, in particular the influence of Coulomb interaction between electrons in the dot on the pumped charge. On one hand we develop a formalism based on Green's functions, in order to calculate the pumped charge from the weak-tunnel-coupling regime down to the Kondo regime. We extend our calculations to a system with a superconducting contact. On the other hand we use a systematic perturbation expansion for the calculation of the pumped charge, giving us the possibility to analyze processes which contribute to charge pumping and to highlight the important role of interaction-induced level renormalization. (orig.)

  3. Quantum dots: promises and accomplishments

    Directory of Open Access Journals (Sweden)

    Dieter Bimberg

    2011-09-01

    Full Text Available Exploration of the Stranski-Krastanow growth of strained semiconductor heterostructures marked the major breakthrough for easy fabrication of defect-free quantum dots (QDs. For the first time, single QDs are facilitating the development of electrically operated emitters of single polarized or entangled photons on demand: an essential component for quantum communication systems. QDs inserted in quantum wells, stacked in planes upon each other, have led to semiconductor lasers that can operate at wavelengths that were previously impossible, or at least difficult to reach, for a given semiconductor family. These lasers show excellent temperature stability, large radiation resistance, and excellent temporal and spatial stability. In this review we discuss recent progress in the field of quantum dot devices.

  4. Charging graphene nanoribbon quantum dots

    OpenAIRE

    Żebrowski, D. P.; B. Szafran

    2015-01-01

    We describe charging a quantum dot induced electrostatically within a semiconducting graphene nanoribbon by electrons or holes. The applied model is based on a tight-binding approach with the electron-electron interaction introduced by a mean field local spin density approximation. The numerical approach accounts for the charge of all the $p_z$ electrons and screening of external potentials by states near the charge neutrality point. Both a homogenous ribbon and a graphene flake embedded with...

  5. FRET sensor with quantum dot

    Czech Academy of Sciences Publication Activity Database

    Datinská, Vladimíra; Klepárník, Karel; Belšánová, Barbora; Minárik, M.; Foret, František

    Veszprém: PANNON Egyetem, 2015 - (Mizsey, P.), s. 20-23 ISBN 978-963-396-072-1. [Műszaki Kémiai Napok 2015. Veszprém (HU), 21.04.2015-23.04.2015] R&D Projects: GA ČR(CZ) GA14-28254S; GA TA ČR(CZ) TA02010672 Institutional support: RVO:68081715 Keywords : FRET * quantum dot * sensor Subject RIV: CB - Analytical Chemistry, Separation

  6. FRET sensor with quantum dot

    Czech Academy of Sciences Publication Activity Database

    Datinská, Vladimíra; Klepárník, Karel; Belšánová, Barbora; Minárik, M.; Foret, František

    Veszprém : PANNON Egyetem, 2015 - (Mizsey, P.), s. 20-23 ISBN 978-963-396-072-1. [Műszaki Kémiai Napok 2015. Veszprém (HU), 21.04.2015-23.04.2015] R&D Projects: GA ČR(CZ) GA14-28254S; GA TA ČR(CZ) TA02010672 Institutional support: RVO:68081715 Keywords : FRET * quantum dot * sensor Subject RIV: CB - Analytical Chemistry, Separation

  7. 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-power...... biased to positive net gain. We have further measured gain recovery times in quantum dot amplifiers that are significantly lower than in bulk and quantum-well semiconductor optical amplifiers. This is promising for future demonstration of quantum dot devices with high modulation bandwidth...... surface emitting VCSELs. We investigated the ultrafast dynamics of quantum-dot semiconductor optical amplifiers. The dephasing time at room temperature of the ground-state transition in semiconductor quantum dots is around 250 fs in an unbiased amplifier, decreasing to below 50 fs when the amplifier is...

  8. Ultrasmall colloidal PbS quantum dots

    International Nuclear Information System (INIS)

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

  9. Few-electron quantum dots

    International Nuclear Information System (INIS)

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

  10. Photoactivation of silicon quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Lockwood, R., E-mail: rossl@ualberta.c [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada); McFarlane, S. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada); Rodriguez Nunez, J.R. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Wang, X.Y. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada); Veinot, J.G.C. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Meldrum, A. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada)

    2011-07-15

    We show that free-standing silicon quantum dots (QDs) can be photoactivated by blue or UV optical irradiation. The luminescence intensity increases by an order of magnitude for irradiation times of several minutes under moderate optical power. The cut-off energy for photoactivation is between 2.1 and 2.4 eV, not very different from the activation energy for hydrogen dissociation from bulk silicon surfaces. We propose the mechanism for this effect is associated with silicon-hydride bond breaking and the subsequent oxidation of dangling bonds. This phenomenon could be used to 'write' luminescent quantum dots into pre-determined arrays. - Research highlights: {yields}Laser light causes increased photoluminescence intensity in silicon quantum dots. {yields} The photoactivation process is effective for wavelengths of 514 nm and shorter. {yields} Hydrogen bound to the Si-QDs is replaced by oxygen in a two-step process. {yields} Patterning is possible but limited by physical dispersion of Si-QDs.

  11. Energy transfer in complexes of water-soluble quantum dots and chlorin e6 molecules in different environments

    Directory of Open Access Journals (Sweden)

    Irina V. Martynenko

    2013-12-01

    Full Text Available The photoexcitation energy transfer is found and investigated in complexes of CdSe/ZnS cationic quantum dots and chlorin e6 molecules formed by covalent bonding and electrostatic interaction in aqueous solution and in porous track membranes. The quantum dots and chlorin e6 molecules form stable complexes that exhibit Förster resonance energy transfer (FRET from quantum dots to chlorin e6 regardless of complex formation conditions. Competitive channels of photoexcitation energy dissipation in the complexes, which hamper the FRET process, were found and discussed.

  12. Extracellular Synthesis of Luminescent CdS Quantum Dots Using Plant Cell Culture.

    Science.gov (United States)

    Borovaya, Mariya N; Burlaka, Olga M; Naumenko, Antonina P; Blume, Yaroslav B; Yemets, Alla I

    2016-12-01

    The present study describes a novel method for preparation of water-soluble CdS quantum dots, using bright yellow-2 (BY-2) cell suspension culture. Acting as a stabilizing and capping agent, the suspension cell culture mediates the formation of CdS nanoparticles. These semiconductor nanoparticles were determined by means of an UV-visible spectrophotometer, photoluminescence, high-resolution transmission electron microscopy (HRTEM), and XRD. Followed by the electron diffraction analysis of a selected area, transmission electron microscopy indicated the formation of spherical, crystalline CdS ranging in diameter from 3 to 7 nm and showed wurtzite CdS quantum dots. In the present work, the toxic effect of synthesized CdS quantum dots on Nicotiana tabacum protoplasts as a very sensitive model was under study. The results of this research revealed that biologically synthesized CdS nanoparticles in low concentrations did not induce any toxic effects. PMID:26909780

  13. Dark states and Aharonov—Bohm oscillations in multi-quantum-dot systems

    International Nuclear Information System (INIS)

    We study the formation of dark states and the Aharonov—Bohm effect in symmetrically/asymmetrically coupled three- and four-quantum-dot systems. It is found that without a transverse magnetic field, destructive interference can trap an electron in a dark state. However, the introduction of a transverse magnetic field can disrupt the dark state, giving rise to oscillation in current. For symmetrically structured quantum-dot systems, the oscillation has a period of one flux quanta. But for asymmetrically structured dot systems, the period of oscillation is halved. In addition, the dephasing due to charge noise also blocks the formation of dark states, while it does not change the period of oscillation. (general)

  14. Extracellular Synthesis of Luminescent CdS Quantum Dots Using Plant Cell Culture

    Science.gov (United States)

    Borovaya, Mariya N.; Burlaka, Olga M.; Naumenko, Antonina P.; Blume, Yaroslav B.; Yemets, Alla I.

    2016-02-01

    The present study describes a novel method for preparation of water-soluble CdS quantum dots, using bright yellow-2 (BY-2) cell suspension culture. Acting as a stabilizing and capping agent, the suspension cell culture mediates the formation of CdS nanoparticles. These semiconductor nanoparticles were determined by means of an UV-visible spectrophotometer, photoluminescence, high-resolution transmission electron microscopy (HRTEM), and XRD. Followed by the electron diffraction analysis of a selected area, transmission electron microscopy indicated the formation of spherical, crystalline CdS ranging in diameter from 3 to 7 nm and showed wurtzite CdS quantum dots. In the present work, the toxic effect of synthesized CdS quantum dots on Nicotiana tabacum protoplasts as a very sensitive model was under study. The results of this research revealed that biologically synthesized CdS nanoparticles in low concentrations did not induce any toxic effects.

  15. Time Dependent Study of Multiple Exciton Generation in Nanocrystal Quantum Dots

    Science.gov (United States)

    Damtie, Fikeraddis A.; Wacker, Andreas

    2016-03-01

    We study the exciton dynamics in an optically excited nanocrystal quantum dot. Multiple exciton formation is more efficient in nanocrystal quantum dots compared to bulk semiconductors due to enhanced Coulomb interactions and the absence of conservation of momentum. The formation of multiple excitons is dependent on different excitation parameters and the dissipation. We study this process within a Lindblad quantum rate equation using the full many-particle states. We optically excite the system by creating a single high energy exciton ESX in resonance to a double exciton EDX. With Coulomb electron-electron interaction, the population can be transferred from the single exciton to the double exciton state by impact ionisation (inverse Auger process). The ratio between the recombination processes and the absorbed photons provide the yield of the structure. We observe a quantum yield of comparable value to experiment assuming typical experimental conditions for a 4 nm PbS quantum dot.

  16. Charge State Hysteresis in Semiconductor Quantum Dots

    OpenAIRE

    Yang, C. H.; Rossi, A; Lai, N. S.; Leon, R.; Lim, W. H.; Dzurak, A.S.

    2014-01-01

    Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which acc...

  17. Optical Fiber Sensing Using Quantum Dots

    Directory of Open Access Journals (Sweden)

    Faramarz Farahi

    2007-12-01

    Full Text Available Recent advances in the application of semiconductor nanocrystals, or quantumdots, as biochemical sensors are reviewed. Quantum dots have unique optical properties thatmake them promising alternatives to traditional dyes in many luminescence basedbioanalytical techniques. An overview of the more relevant progresses in the application ofquantum dots as biochemical probes is addressed. Special focus will be given toconfigurations where the sensing dots are incorporated in solid membranes and immobilizedin optical fibers or planar waveguide platforms.

  18. Spintronics and Quantum Computing with Quantum Dots

    OpenAIRE

    Recher, P.; Loss, D.; Levy, J

    2000-01-01

    The creation, coherent manipulation, and measurement of spins in nanostructures open up completely new possibilities for electronics and information processing, among them quantum computing and quantum communication. We review our theoretical proposal for using electron spins in quantum dots as quantum bits. We present single- and two qubit gate mechanisms in laterally as well as vertically coupled quantum dots and discuss the possibility to couple spins in quantum dots via superexchange. We ...

  19. Resonant electron transfer between quantum dots

    OpenAIRE

    Openov, Leonid A.

    1999-01-01

    An interaction of electromagnetic field with a nanostructure composed of two quantum dots is studied theoretically. An effect of a resonant electron transfer between the localized low-lying states of quantum dots is predicted. A necessary condition for such an effect is the existence of an excited bound state whose energy lies close to the top of the barrier separating the quantum dots. This effect may be used to realize the reversible quantum logic gate NOT if the superposition of electron s...

  20. Quasibound states in graphene quantum-dot nanostructures generated by concentric potential barrier rings

    Institute of Scientific and Technical Information of China (English)

    Jiang Zhao-Tan; Yu Cheng-Long; Dong Quan-Li

    2012-01-01

    We study the quasibound states in a graphene quantum-dot structure generated by the single-,double-,and triple-barrier electrostatic potentials.It is shown that the strongest quasibound states are mainly determined by the innermost barrier.Specifically,the positions of the quasibound states are determined by the barrier height,the number of the quasibound states is determined by the quantum-dot radius and the angular momentum,and the localization degree of the quasibound states is influenced by the width of the innermost barrier,as well as the outside barriers.Furthermore,according to the study on the double- and triple-barrier quantum dots,we find that an effective way to generate more quasibound states with even larger energy level spacings is to design a quantum dot defined by many concentric barriers with larger barrier-height differences.Last,we extend our results into the quantum dot of many barriers,which gives a complete picture about the formation of the quasibound states in the kind of graphene quantum dot created by many concentric potential barrier rings.

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

    Science.gov (United States)

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

    2016-04-01

    In this work, selective electrodeposition of silver on quantum dots is described. The particular characteristics of the nanostructured silver thus obtained are studied by electrochemical and microscopic techniques. On one hand, quantum dots were found to catalyze the silver electrodeposition, and on the other hand, a strong adsorption between electrodeposited silver and quantum dots was observed, indicated by two silver stripping processes. Nucleation of silver nanoparticles followed different mechanisms depending on the surface (carbon or quantum dots). Voltammetric and confocal microscopy studies showed the great influence of electrodeposition time on surface coating, and high-resolution transmission electron microscopy (HRTEM) imaging confirmed the initial formation of Janus-like Ag@QD nanoparticles in this process. By use of moderate electrodeposition conditions such as 50 μM silver, -0.1 V, and 60 s, the silver was deposited only on quantum dots, allowing the generation of localized nanostructured electrode surfaces. This methodology can also be employed for sensing applications, showing a promising ultrasensitive electrochemical method for quantum dot detection. PMID:26910270

  2. Random Feature Maps for Dot Product Kernels

    CERN Document Server

    Kar, Purushottam

    2012-01-01

    Approximating non-linear kernels using feature maps has gained a lot of interest in recent years due to applications in reducing training and testing times of SVM classifiers and other kernel based learning algorithms. We extend this line of work and present low distortion embeddings for dot product kernels into linear Euclidean spaces. We base our results on a classical result in harmonic analysis characterizing all dot product kernels and use it to define randomized feature maps into explicit low dimensional Euclidean spaces in which the native dot product provides an approximation to the dot product kernel with high confidence.

  3. Activation of silicon quantum dots for emission

    Institute of Scientific and Technical Information of China (English)

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

    2012-01-01

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

  4. Thermoelectric energy harvesting with quantum dots

    International Nuclear Information System (INIS)

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

  5. 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...

  6. Electrochemical tuning of optical properties of graphitic quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ge, Juan [Department of Inorganic Nonmetallic Material, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Li, Yan, E-mail: liyan2011@ustb.edu.cn [Department of Inorganic Nonmetallic Material, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Zhang, Bo-Ping [Department of Inorganic Nonmetallic Material, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Ma, Ning [Department of Material Physics and Chemistry, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Wang, Jun; Pu, Chang; Xiang, Ying-Chang [Department of Inorganic Nonmetallic Material, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-10-15

    Graphitic quantum dots (GQDs), as a new class of quantum dots, possess unique properties. Among the various reported approaches for their fabrication, electrochemical method possesses numerous advantages compared with others. In particular, the formation process of the GQDs could be precisely controlled by this method through adjusting the electrochemical parameters and environment. In this study, GQDs with multi-color fluorescence (FL) were obtained by this method through tuning only the applied potential window of cycling voltammetry. The luminescence mechanism of those GQDs was discussed and explained by the ultraviolet (UV)–visible, photoluminescence (PL), and photoluminescence excitation (PLE) spectra. The influence of the applied potential window on the PL properties of GQDs and the relationship between the degree of surface oxidation and PL properties were also investigated. - Highlights: • We produced the graphite quantum dots (GQDs) by an electrochemical method. • We changed the applied potentials of cycling voltammetry (CV). • Varying of applied potentials changed surface oxygen-containing groups of GQDs. • Higher surface oxidation degree resulted in the red-shift of PL spectra.

  7. Profiteering from the Dot-com Bubble, Sub-Prime Crisis and Asian Financial Crisis

    NARCIS (Netherlands)

    M.J. McAleer (Michael); J. Suen (John); W-K. Wong (Wing-Keung)

    2013-01-01

    textabstractThis paper explores the characteristics associated with the formation of bubbles that occurred in the Hong Kong stock market in 1997 and 2007, as well as the 2000 dot-com bubble of Nasdaq. It examines the profitability of Technical Analysis (TA) strategies generating buy and sell signals

  8. Electron-electron interactions in graphene field-induced quantum dots in a high magnetic field

    DEFF Research Database (Denmark)

    Orlof, A.; Shylau, Artsem; Zozoulenko, I. V.

    2015-01-01

    We study the effect of electron-electron interaction in graphene quantum dots defined by an external electrostatic potential and a high magnetic field. To account for the electron-electron interaction, we use the Thomas-Fermi approximation and find that electron screening causes the formation of ......, we discuss how our predictions can be observed using the Kelvin probe force microscope measurements....

  9. 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. PMID:26781285

  10. Quantum Gates Between Two Spins in a Triple Dot System with an Empty Dot

    CERN Document Server

    Coello, Jose Garcia

    2011-01-01

    We propose a scheme for implementing quantum gates and entanglement between spin qubits in the outer dots of a triple-dot system with an empty central dot. The voltage applied to the central dot can be tuned to realize the gate. Our scheme exemplifies the possibility of quantum gates outside the regime where each dot has an electron, so that spin-spin exchange interaction is not the only relevant mechanism. Analytic treatment is possible by mapping the problem to a t-J model. The fidelity of the entangling quantum gate between the spins is analyzed in the presence of decoherence stemming from a bath of nuclear spins, as well as from charge fluctuations. Our scheme provides an avenue for extending the scope of two qubit gate experiments to triple-dots, while requiring minimal control, namely that of the potential of a single dot, and may enhance the qubit separation to ease differential addressability.

  11. 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

  12. Porous silicon: silicon quantum dots for photonic applications

    International Nuclear Information System (INIS)

    Porous silicon formation and structure characterization are briefly illustrated. Its luminescence properties rae presented and interpreted on the basis of exciton recombination in quantum dot structures: the trap-controlled hopping mechanism is used to describe the recombination dynamics. Porous silicon application to photonic devices is considered: porous silicon multilayer in general, and micro cavities in particular are described. The present situation in the realization of porous silicon LEDs is considered, and future developments in this field of research are suggested. (author). 30 refs., 30 figs., 13 tabs

  13. Photoluminescence from germanium quantum dots formed by pulsed laser deposition

    International Nuclear Information System (INIS)

    The time-resolved photoluminescence of GeOx films (x ≤ 2) containing Ge nanocrystals is carried out in the energy range of 1.4 - 3.2 eV and the relaxation time of 50 μs. The thin films are formed by the pulsed laser deposition from direct and particle flow of an erosive torch in an atmosphere of oxygen and argon. The dependence of photoluminescence properties of films on parameters of deposition and doping by gold is investigated. The results are explained in the framework of excitonic model of photoluminescence from Ge quantum dots whose sizes are determined by conditions of their formation

  14. COULOMB BLOCKADE EFFECT IN SELF-ASSEMBLED GOLD QUANTUM DOTS

    Institute of Scientific and Technical Information of China (English)

    Shu-Fen Hu; Ru-Ling Yeh; Ru-Shi Liu

    2004-01-01

    Nanometer-scale Au quantum dots have been assembled on SiO2 by controlling the reaction of raw materials to form a citrate Au sol and an aminosilane/dithiol-treated patterned Si wafer. The detailed formation mechanism has been studied. Three gold colloidal particles (~15 nm), aligned in a chain to form a one-dimensional current path, was bridged across an 80-nm gap between source and drain metal electrodes. The device exhibited a Coulomb blockade effect at 33 K.

  15. Suspension Synthesis of Surfactant-Free Cuprous Oxide Quantum Dots

    OpenAIRE

    Dongzhi Lai; Tao Liu; Xinyun Gu; Ying Chen; Jin Niu; Lingmin Yi; Wenxing Chen

    2015-01-01

    Suspension methods were used to synthesize surfactant-free Cu2O quantum dots (Cu2O-QDs) in high precursor concentrations using sodium hypophosphite as a reducing agent. Transmission electron microscopy (TEM) observations indicated that a large amount of Cu2O-QDs were synthesized with diameters ranging from 7 to 10 nm. We propose a mechanism where DMSO acts as a surface passivation agent, explaining the possible formation of Cu2O-QDs. Noticeably, the Cu2O-QDs exhibited high and stable catalyti...

  16. Suspension Synthesis of Surfactant-Free Cuprous Oxide Quantum Dots

    Directory of Open Access Journals (Sweden)

    Dongzhi Lai

    2015-01-01

    Full Text Available Suspension methods were used to synthesize surfactant-free Cu2O quantum dots (Cu2O-QDs in high precursor concentrations using sodium hypophosphite as a reducing agent. Transmission electron microscopy (TEM observations indicated that a large amount of Cu2O-QDs were synthesized with diameters ranging from 7 to 10 nm. We propose a mechanism where DMSO acts as a surface passivation agent, explaining the possible formation of Cu2O-QDs. Noticeably, the Cu2O-QDs exhibited high and stable catalytic activity for the reduction of rhodamine B.

  17. Optical anisotropy in vertically coupled quantum dots

    DEFF Research Database (Denmark)

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

    1999-01-01

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

  18. Double Acceptor Interaction in Semimagnetic Quantum Dot

    Directory of Open Access Journals (Sweden)

    A. Merwyn Jasper D. Reuben

    2011-01-01

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

  19. Thick-shell nanocrystal quantum dots

    Science.gov (United States)

    Hollingsworth, Jennifer A.; Chen, Yongfen; Klimov, Victor I.; Htoon, Han; Vela, Javier

    2011-05-03

    Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

  20. Photoinduced electron transfers with carbon dots

    OpenAIRE

    Wang, Xin; Cao, Li; Lu, Fushen; Meziani, Mohammed J.; Li, Heting; Qi, Gang; Zhou, Bing; Harruff, Barbara A.; Kermarrec, Fabien; Sun, Ya-Ping

    2009-01-01

    The photoluminescence in carbon dots (surface-passivated small carbon nanoparticles) could be quenched efficiently by electron acceptor or donor molecules in solution, namely that photo-excited carbon dots are both excellent electron donors and excellent electron acceptors, thus offering new opportunities for their potential uses in light energy conversion and related applications.

  1. Photoluminescence of hybrid quantum dots

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Bratislava: Slovak Expert Group of Solid State Chemistry and Physics , 2013 - (Koman, M.; Jorík, V.; Kožíšek, Z.). s. 28-28 ISBN 978-80-970896-5-8. [Joint Seminar – Development of materials science in research and education /23./. 09.09.2013-13.09.2013, Kežmarské Žľaby] R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : energy transfer * quantum dots Subject RIV: BM - Solid Matter Physics ; Magnetism; JA - Electronics ; Optoelectronics, Electrical Engineering (UMCH-V)

  2. 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 with...

  3. Semiconductor double quantum dot micromaser.

    Science.gov (United States)

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

    2015-01-16

    The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication. Here we demonstrate a maser that is driven by single-electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside a high-quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. PMID:25593187

  4. Model-based clustered-dot screening

    Science.gov (United States)

    Kim, Sang Ho

    2006-01-01

    I propose a halftone screen design method based on a human visual system model and the characteristics of the electro-photographic (EP) printer engine. Generally, screen design methods based on human visual models produce dispersed-dot type screens while design methods considering EP printer characteristics generate clustered-dot type screens. In this paper, I propose a cost function balancing the conflicting characteristics of the human visual system and the printer. By minimizing the obtained cost function, I design a model-based clustered-dot screen using a modified direct binary search algorithm. Experimental results demonstrate the superior quality of the model-based clustered-dot screen compared to a conventional clustered-dot screen.

  5. Photoluminescence of a quantum-dot molecule

    International Nuclear Information System (INIS)

    The coherent coupling of quantum dots is a sensitive indicator of the energy and phase relaxation processes taking place in the nanostructure components. We formulate a theory of low-temperature, stationary photoluminescence from a quantum-dot molecule composed of two spherical quantum dots whose electronic subsystems are resonantly coupled via the Coulomb interaction. We show that the coupling leads to the hybridization of the first excited states of the quantum dots, manifesting itself as a pair of photoluminescence peaks with intensities and spectral positions strongly dependent on the geometric, material, and relaxation parameters of the quantum-dot molecule. These parameters are explicitly contained in the analytical expression for the photoluminescence differential cross section derived in the paper. The developed theory and expression obtained are essential in interpreting and analyzing spectroscopic data on the secondary emission of coherently coupled quantum systems

  6. Bound states in the continuum and spin filter in quantum-dot molecules

    Energy Technology Data Exchange (ETDEWEB)

    Ramos, J.P. [Departamento de Física, Universidad Católica del Norte, Casilla 1280, Antofagasta (Chile); Orellana, P.A., E-mail: pedro.orellana@usm.cl [Departamento de Física, Universidad Técnica Federico Santa María, Vicuña Mackenna 3939, Santiago (Chile)

    2014-12-15

    In this paper we study the formation of bound states in the continuum in a quantum dot molecule coupled to leads and their potential application in spintronics. Based on the combination of bound states in the continuum and Fano effect, we propose a new design of a spin-dependent polarizer. By lifting the spin degeneracy of the carriers in the quantum dots by means of a magnetic field the system can be used as a spin-polarized device. A detailed analysis of the spin-dependent conductance and spin polarization as a function of the applied magnetic field and gate voltages is carried out.

  7. Magnetic properties of large aspect ratio Co dots electrodeposited on prestructured silicon substrates

    International Nuclear Information System (INIS)

    A silicon substrate, pre-structured by focused ion beam (FIB), is used for selective electrodeposition of cylindrical cobalt nanodots with a large aspect ratio of depth to diameter of 2. These nanostructures are characterised by magnetic force microscopy (MFM) and ferromagnetic resonance (FMR). Cobalt dots grown in the pulsed mode are single domain in the remnant state with an easy magnetization perpendicular to the substrate. On the contrary, some of the dots grown, in the continuous mode, present a Co cap on top, which leads to the formation of magnetic vortices with an in-plane magnetization component

  8. Tensile-strained GaAsN quantum dots on InP

    OpenAIRE

    Pohjola, P.; Hakkarainen, T.; Koskenvaara, H.; Sopanen, Markku; Lipsanen, Harri; Sainio, J.

    2007-01-01

    Self-assembled quantum dots are typically fabricated from compressive-strained material systems, e.g., InAs on GaAs. In this letter, self-assembled quantum dots from tensile-strained GaAsN on InP are demonstrated. GaAsN on InP has type-I band alignment. Stranski-Krastanov growth mode is not observed, but in situannealing of the uncapped samples results in the formation of islands. Photoluminescence spectra from the buried GaAsN show separate peaks due to a wetting layer and islands around the...

  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. Silicon quantum dots: surface matters

    International Nuclear Information System (INIS)

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

  11. Evolution of excitonic states in two-phase systems with quantum dots of II-VI semiconductors near the percolation threshold

    Science.gov (United States)

    Bondar, N. V.; Brodyn, M. S.

    2010-03-01

    In two-phase disordered media composed of borosilicate glass with ZnSe or CdS quantum dots, the formation of a phase percolation transition of carriers for near-threshold concentrations that are manifested in optical spectra has been observed. Microscopic fluctuations of the quantum-dot density near the percolation threshold were found that resembled the phenomenon of critical opalescence, where similar fluctuations of the density of a pure substance appear near to a phase transition. It is proposed that the dielectric mismatch between a matrix and ZnSe or CdS quantum dots plays a significant role in the carrier (exciton) delocalization, resulting in the appearance of a “dielectric Coulomb trap” beyond the QD border and the formation of surface states of excitons. The spatial overlapping of excitonic states at the critical density of quantum dots results in a tunneling of carriers and the formation of a phase percolation transition in such media.

  12. One-electron oxidation of the hydroquinonic form of vitamin K by OHter dot and N sub 3 ter dot free radicals. A steady-state gamma radiolysis study. Activation radicalaire d'un modele de vitamine K par les radicaux OHter dot et N sub 3 ter dot. Etude par radiolyse gamma

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen Van Binh, E.; Gardes-Albert, M.; Ferradini, C.; Acher, F.; Azerad, R. (Paris-5 Univ., 75 (FR))

    1991-06-01

    The oxidation of a water-soluble model of vitamin K hydroquinone, symbolised by KH{sub 2}p, has been studied by {gamma} radiolysis using OH{center dot} or N{sub 3}{center dot} free radicals as oxidants. Irradiation doses were up to 300 Gy. The analysis of final products by spectrophotometric absorption and HPLC allowed to characterize the formation of the quinone K and to estimate the initial yield of KH{sub 2}p-disappearance and K-formation. N{sub 3}{center dot} radicals led selectively to the formation of the quinone K with a G-value of (3.0 {+-} 0.3) x 10{sup -7} mol/J, thus involving a simple one-electron oxidation mechanism. On the contrary, when OH{center dot} radicals oxidized KH{sub 2}p, in addition to the quinone, other non identified species were simultaneously produced during the radiolysis, thus requiring a more complex oxidation mechanism.

  13. Near-infrared nano-spectroscopy and emission energy control of semiconductor quantum dots using a phase-change material

    International Nuclear Information System (INIS)

    We have proposed a method to achieve near-field imaging spectroscopy of single semiconductor quantum dots with high sensitivity by using an optical mask layer of a phase-change material. Sequential formation and elimination of an amorphous aperture allows imaging spectroscopy with high spatial resolution and high collection efficiency. We present numerical simulation and experimental result that show the effectiveness of this technique. Inspired by this optical mask effect, a new approach which can precisely control the emission energy of semiconductor quantum dots has been proposed. This method uses the volume expansion of a phase change material upon amorphization, which allows reversible emission energy tuning of quantum dots. A photoluminescence spectroscopy of single quantum dots and simulation were conducted to demonstrate and further explore the feasibility of this method

  14. Role of surface states and defects in the ultrafast nonlinear optical properties of CuS quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Mary, K. A. Ann; Unnikrishnan, N. V., E-mail: nvu100@yahoo.com [School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam 686560 (India); Philip, Reji [Light and Matter Physics Group, Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore 560080 (India)

    2014-07-01

    We report facile preparation of water dispersible CuS quantum dots (2–4 nm) and nanoparticles (5–11 nm) through a nontoxic, green, one-pot synthesis method. Optical and microstructural studies indicate the presence of surface states and defects (dislocations, stacking faults, and twins) in the quantum dots. The smaller crystallite size and quantum dot formation have significant effects on the high energy excitonic and low energy plasmonic absorption bands. Effective two-photon absorption coefficients measured using 100 fs laser pulses employing open-aperture Z-scan in the plasmonic region of 800 nm reveal that CuS quantum dots are better ultrafast optical limiters compared to CuS nanoparticles.

  15. Influence of finite superconducting gaps on the proximity effect in interacting quantum dots

    International Nuclear Information System (INIS)

    The tunnel coupling of superconductors to an interacting quantum dot leads to the formation of Andreev-bound states (ABS), which are the excitation energies of the proximized dot. In the limit of large superconducting gaps in the leads, Δ→∞, the hybrid system of dot and superconductors can be described exactly by an effective Hamiltonian. Since in real systems the superconducting gap is usually not a large quantity it is an interesting question whether the predictions of the Δ→∞ calculations still have significance for real systems with finite gaps. In order to investigate this question we perform two different calculations: first, a systematic 1/Δ expansion where we find that the occurring currents show only small changes but we find indications that a finite Δ renormalizes the ABSs. To quantify the last statement we perform a second calculation where we resume the coupling to the superconductors at arbitrary values for Δ neglecting vertex corrections.

  16. Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Jemsson, Tomas; Machhadani, Houssaine; Karlsson, K. Fredrik; Hsu, Chih-Wei; Holtz, Per-Olof [Department of Physics, Chemistry, and Biology (IFM), Semiconductor Materials, Linköping University, S-58183 Linköping (Sweden)

    2014-08-25

    We report on the observation of linearly polarized single photon antibunching in the excitonic emission from a site-controlled InGaN quantum dot. The measured second order coherence function exhibits a significant dip at zero time difference, corresponding to g{sub m}{sup 2}(0)=0.90 under continuous laser excitation. This relatively high value of g{sub m}{sup 2}(0) is well understood by a model as the combination of short exciton life time (320 ps), limited experimental timing resolution and the presence of an uncorrelated broadband background emission from the sample. Our result provides the first rigorous evidence of InGaN quantum dot formation on hexagonal GaN pyramids, and it highlights a great potential in these dots as fast polarized single photon emitters if the background emission can be eliminated.

  17. Optical study of GaAs quantum dots embedded into AlGaAs nanowires

    International Nuclear Information System (INIS)

    We report the photoluminescence characterization of GaAs quantum dots embedded in AlGaAs nanowires. Time-integrated and time-resolved photoluminescence was measured for both arrays and single quantum dot/nanowires. The optical spectroscopy data show the influence of growth temperature on the distribution of diameters and the presence of different crystalline phases in the AlGaAs nanowires. By means of scanning and transmission electron microscopy and photoluminescence we observed that the growth temperature has a strong influence on the homogeneity of the nanowires, in size and density. In photoluminescence spectra of a single quantum dot, spectral diffusion was observed in the exciton line. Formation of various crystalline phases in the AlGaAs nanowires leads to very long decay times for the nanowire luminescence, around 20 ns

  18. Synthesis of colloidal SnSe quantum dots by electron beam irradiation

    International Nuclear Information System (INIS)

    Water-soluble orthorhombic colloidal SnSe quantum dots with an average diameter of 4 nm were successfully prepared by a novel irradiation route using an electronic accelerator as a radiation source and hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant. The quantum dots exhibit a large direct bandgap of 3.89 eV, greatly blue shifted compared with that of bulk SnSe (1.0 eV) due to the quantum confinement effect. The quantum dots show blue photoluminescence at ∼420 nm. The influence of CTAB on the growth of the quantum dots was investigated and a possible reaction/growth mechanism was proposed. - Highlights: → A rapid, facile and green strategy is developed to synthesize SnSe QDs. → The raw materials are green and easily obtained. → The surfactant CTAB plays an important role in the formation of SnSe quantum dots. → The obtained SnSe QDs is well-dispersed with the average size of around 4 nm.

  19. Auger recombination in In(Ga)Sb/InAs quantum dots

    International Nuclear Information System (INIS)

    We report on the epitaxial formation of type II In0.5Ga0.5Sb/InAs and InSb/InAs quantum dot ensembles using metal organic vapor phase epitaxy. Employing scanning tunneling spectroscopy, we determine spatial quantum dot dimensions smaller than the de Broglie wavelength of InGaSb, which strongly indicates a three dimensional hole confinement. Photoluminescence spectroscopy at low temperatures yields an enhanced radiative recombination in the mid-infrared regime at energies of 170–200 meV. This luminescence displays a strong excitation power dependence with a blueshift indicating a filling of excited quantum dot hole states. Furthermore, a rate equation model is used to extract the Auger recombination coefficient from the power dependent intensity at 77 K yielding values of 1.35 × 10−28 cm6/s for In0.5Ga0.5Sb/InAs quantum dots and 1.47 × 10−27 cm6/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices

  20. Time-bin Entanglement from Quantum Dots

    CERN Document Server

    Weihs, Gregor; Predojević, Ana

    2016-01-01

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

  1. Magnon-driven quantum dot refrigerators

    Science.gov (United States)

    Wang, Yuan; Huang, Chuankun; Liao, Tianjun; Chen, Jincan

    2015-12-01

    A new model of refrigerator consisting of a spin-splitting quantum dot coupled with two ferromagnetic reservoirs and a ferromagnetic insulator is proposed. The rate equation is used to calculate the occupation probabilities of the quantum dot. The expressions of the electron and magnon currents are obtained. The region that the system can work in as a refrigerator is determined. The cooling power and coefficient of performance (COP) of the refrigerator are derived. The influences of the magnetic field, applied voltage, and polarization of two leads on the performance are discussed. The performances of two different magnon-driven quantum dot refrigerators are compared.

  2. Introduction to the physics of quantum dots

    International Nuclear Information System (INIS)

    Quantum dots contain only a few well-defined energy levels for electron and/or holes as a result of the confinement of charge in all three spatial dimensions. Here, we describe both the application of photoluminescence spectroscopy and transport measurements to the characterisation of quantum dots and the novel phenomena that they exhibit. These include the Coulomb blockade, single electron tunneling and single photon detection. The impact of quantum dots on future electronics and directions for future research, such as in quantum computing and cryptography, are discussed. (author)

  3. Nonuniform magnetization reversals in elliptical permalloy dots

    Energy Technology Data Exchange (ETDEWEB)

    Lai, M.-F.; Wei, Z.-H. E-mail: zhwei@phys.ntu.edu.tw; Chang, Ching-Ray; Usov, N.A.; Wu, J.C.; Lai, Jun-Yang

    2004-11-01

    Reversible and irreversible magnetization processes of the single-domain elliptical permalloy dot are studied by simulation. The magnetization curve of the reversible process obtained by applying the field along the hard axis of the elliptical dot is almost linear, as is the case in the single-domain ellipsoidal particle. Due to the occurrence of the non uniform reversal, the switching field is reduced significantly compared to that predicted by the Stoner-Wohlfarth model. The nucleation fields of elliptical dots are calculated as a function of ellipse's aspect ratio, and the function reveals a step-like behavior.

  4. Structural and optical characterization of Si/Ge quantum dots

    OpenAIRE

    Wigblad, Dan

    2008-01-01

    In this study silicon-germanium quantum dots grown on silicon have been investigated. The aim of the work was to find quantum dots suitable for use as a thermistor material. The quantum dots were produced at KTH, Stockholm, using a RPCVD reactor that is designed for industrial production. The techniques used to study the quantum dots were: HRSEM, AFM, HRXRD, FTPL, and Raman spectroscopy. Quantum dots have been produced in single and multilayer structures. As a result of this work a multilayer...

  5. Quantum Dots-based Reverse Phase Protein Microarray

    Energy Technology Data Exchange (ETDEWEB)

    Shingyoji, Masato; Gerion, Daniele; Pinkel, Dan; Gray, Joe W.; Chen, Fanqing

    2005-07-15

    CdSe nanocrystals, also called quantum dots (Qdots) are a novel class of fluorophores, which have a diameter of a few nanometers and possess high quantum yield, tunable emission wavelength and photostability. They are an attractive alternative to conventional fluorescent dyes. Quantum dots can be silanized to be soluble in aqueous solution under biological conditions, and thus be used in bio-detection. In this study, we established a novel Qdot-based technology platform that can perform accurate and reproducible quantification of protein concentration in a crude cell lysate background. Protein lysates have been spiked with a target protein, and a dilution series of the cell lysate with a dynamic range of three orders of magnitude has been used for this proof-of-concept study. The dilution series has been spotted in microarray format, and protein detection has been achieved with a sensitivity that is at least comparable to standard commercial assays, which are based on horseradish peroxidase (HRP) catalyzed diaminobenzidine (DAB) chromogenesis. The data obtained through the Qdot method has shown a close linear correlation between relative fluorescence unit and relative protein concentration. The Qdot results are in almost complete agreement with data we obtained with the well-established HRP-DAB colorimetric array (R{sup 2} = 0.986). This suggests that Qdots can be used for protein quantification in microarray format, using the platform presented here.

  6. Structural characterization of InAs quantum dot chains grown by molecular beam epitaxy on nanoimprint lithography patterned GaAs(100)

    International Nuclear Information System (INIS)

    We combine nanoimprint lithography and molecular beam epitaxy for the site-controlled growth of InAs quantum dot chains on GaAs(100) substrates. We study the influence of quantum dot growth temperature and regrowth buffer thickness on the formation of the quantum dot chains. In particular, we show that by carefully tuning the growth conditions we can achieve equal quantum dot densities and photoluminescence ground state peak wavelengths for quantum dot chains grown on patterns oriented along the [011], [011-bar], [011] and [001] directions. Furthermore, we identify the crystal facets that form the sidewalls of the grooves in the differently oriented patterns after capping and show that the existence of (411)A sidewalls causes reduction of the QD density as well as sidewall roughening.

  7. Structural characterization of InAs quantum dot chains grown by molecular beam epitaxy on nanoimprint lithography patterned GaAs(100)

    Energy Technology Data Exchange (ETDEWEB)

    Hakkarainen, T V; Tommila, J; Schramm, A; Tukiainen, A; Ahorinta, R; Dumitrescu, M; Guina, M, E-mail: teemu.hakkarainen@tut.fi [Optoelectronics Research Centre, Tampere University of Technology, PO Box 692, FIN-33101 Tampere (Finland)

    2011-07-22

    We combine nanoimprint lithography and molecular beam epitaxy for the site-controlled growth of InAs quantum dot chains on GaAs(100) substrates. We study the influence of quantum dot growth temperature and regrowth buffer thickness on the formation of the quantum dot chains. In particular, we show that by carefully tuning the growth conditions we can achieve equal quantum dot densities and photoluminescence ground state peak wavelengths for quantum dot chains grown on patterns oriented along the [011], [011-bar], [011] and [001] directions. Furthermore, we identify the crystal facets that form the sidewalls of the grooves in the differently oriented patterns after capping and show that the existence of (411)A sidewalls causes reduction of the QD density as well as sidewall roughening.

  8. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

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

  9. 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...

  10. 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...

  11. 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.

  12. Neutron spectra calculation in material in order to compute irradiation damage

    International Nuclear Information System (INIS)

    This short presentation will be on neutron spectra calculation methods in order to compute the damage rate formation in irradiated structure. Three computation schemes are used in the French C.E.A.: (1) 3-dimensional calculations using the line of sight attenuation method (MERCURE IV code), the removal cross section being obtained from an adjustment on a 1-dimensional transport calculation with the discrete ordinate code ANISN; (2) 2-dimensional calculations using the discrete ordinates method (DOT 3.5 code), 20 to 30 group library obtained by collapsing the 100 group a library on fluxes computed by ANISN; (3) 3-dimensional calculations using the Monte Carlo method (TRIPOLI system). The cross sections which originally came from UKNDL 73 and ENDF/B3 are now processed from ENDF B IV. (author)

  13. Magnetic quantum dots and magnetic edge states

    International Nuclear Information System (INIS)

    Starting with defining the magnetic edge state in a magnetic quantum dot, which becomes quite popular nowadays conjunction with a possible candidate for a high density memory device or spintronic materials, various magnetic nano-quantum structures are reviewed in detail. We study the magnetic edge states of the two dimensional electron gas in strong perpendicular magnetic fields. We find that magnetic edge states are formed along the boundary of the magnetic dot, which is formed by a nonuniform distribution of magnetic fields. These magnetic edge states circulate either clockwise or counterclockwise, depending on the number of missing flux quanta, and exhibit quite different properties, as compared to the conventional ones which are induced by electrostatic confinements in the quantum Hall system. We also find that a close relation between the quantum mechanical eigenstates and the classical trajectories in the magnetic dot. When a magnetic dot is located inside a quantum wire, the edge-channel scattering mechanism by the magnetic quantum dot is very different from that by electrostatic dots. Here, the magnetic dot is formed by two different magnetic fields inside and outside the dot. We study the ballistic edge-channel transport and magnetic edge states in this situation. When the inner field is parallel to the outer one, the two-terminal conductance is quantized and shows the features of a transmission barrier and a resonator. On the other hand, when the inner field is reversed, the conductance is not quantized and all channels can be completely reflected in some energy ranges. The difference between the above two cases results from the distinct magnetic confinements. We also describe successfully the edge states of magnetic quantum rings and others in detail

  14. Coherent scattering in a small quantum dot

    International Nuclear Information System (INIS)

    Ballistic transport in an open small (100 nm) three-terminal quantum dot based on the high-mobility two-dimensional electron gas of the AlGaAs/GaAs heterojunction has been analyzed. It has been shown that the gate oscillations of resistance of such a dot arise due to the coherent scattering of electrons on its quasidiscrete levels being suppressed by a weak magnetic field

  15. Exploring Extragalactic Emission: The Hα Dot Survey

    Science.gov (United States)

    Rampalli, Rayna; Salzer, John Joseph

    2016-01-01

    The Hα Dot Survey was established as a result of finding point sources of strong line emission in the data obtained for the ALFALFA Hα Survey (Van Sistine et al. 2015). In the latter survey, broad-band R and narrow-band Hα filters were used to examine target galaxies from the ALFALFA blind HI survey (Giovanelli et al. 2005, Haynes et al. 2011). In the process of reducing the ALFALFA Hα Survey data the "Hα Dots" were discovered (Kellar et al. 2008, 2012). Using specialized image analysis tools, a large population of dots has already been detected in the more than 1500 ALFALFA Hα narrow-band images taken with the 0.9m WIYN and 2.1m KPNO telescopes. Follow-up spectra of over 200 Hα Dots discovered from the 0.9m images reveal that these objects are a mix of nearby low-luminosity star-forming galaxies, compact starbursts and Seyfert 2 galaxies at intermediate redshifts, and high-redshift QSOs. Here we present the first list of Hα Dots detected using 2.1m telescope data. The 2.1m images yield a sample of Dots that average almost two magnitudes fainter than those detected with the 0.9m. The current REU project is designed to characterize the set of Hα Dots detected in the deeper 2.1m telescope images, while the broad goals of the Hα Dot Survey include the desire to understand better the chemical evolution of galaxies over cosmic time. This project was supported in part by the NSF REU grant 1358980, by the Maria Mitchell Association (Nantucket, MA), and by the Massachusetts Space Grant Consortium.

  16. Quantum dot cascade laser: Arguments in favor

    OpenAIRE

    Dmitriev, I. A.; Suris, R. A.

    2007-01-01

    Quantum cascade lasers are recognized as propitious candidates for future terahertz optoelectronics. Here we demonstrate several definite advantages of quantum dot cascade structures over quantum well devices, which suffer fundamental performance limitations owing to continuous carrier spectrum. The discrete spectrum of quantum dots opens an opportunity to control the non-radiative relaxation and optical loss and also provides for more flexibility in the choice of an optical and electrical de...

  17. Electronic Commerce Beyond the "dot com" Boom

    OpenAIRE

    James A. Senn

    2000-01-01

    The explosion of interest in electronic commerce stemming from commercial use of the Internet triggered high expectations, and accompanying high stock market value for public companies specializing in the delivery of products and services through this channel. However, the boom in the market value of these so-called "dot com" companies appears to be over. This paper examines the factors underlying the fall off in the value of "dot com" companies, focusing on the manner in which fundamental bu...

  18. Positioning of quantum dots on metallic nanostructures

    International Nuclear Information System (INIS)

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

  19. 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.

  20. 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

  1. Coherent transport through interacting quantum dots

    International Nuclear Information System (INIS)

    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

  2. InSb quantum dots and quantum rings on InAs-rich surface

    International Nuclear Information System (INIS)

    We report a study of InSb nanoobjects (quantum dots and quantum rings) grown on InAs-rich surface by liquid phase epitaxy. Characterization of the sample surface was performed using atomic force microscopy (AFM). The bimodal formation of the uncapped InSb quantum dots (QDs) was observed for the growing on a binary InAs substrate. Uniform high-density (1 x 1010 cm-2) quantum dots with a height of 3 nm were obtained at T = 420-430 deg. C, whereas low-density (5 x 108 cm-2) big quantum dots were 9 nm in height. As a buffer layer, lattice-matched InAsSb0.12P0.25 solid solution was deposed on InAs substrate using metal-organic vapour phase epitaxy. Deposition from the InSb melt on the buffer layer resulted in the formation of InSb nanoobjects with density as high as 3 x 1010 cm-2.

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

    NARCIS (Netherlands)

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

    2009-01-01

    An accurate model of a vertical pillar quantum dot is described. The full three-dimensional structure of the device containing the dot is taken into account and this leads to an effective two-dimensional model in which electrons move in the two lateral dimensions, the confinement is parabolic, and t

  4. Precise control of size and density of self-assembled Ge dot on Si(1 0 0) by carbon-induced strain-engineering

    International Nuclear Information System (INIS)

    In order to produce dome-shaped Ge dots with small size and high density, C submonolayers (C-SMLs) were incorporated at the interface between Ge wetting layers and Ge dots. The C atoms are considered to induce a local strain field by forming Ge-C bonding. Such strain field enhanced dome formation even at low temperature (10 cm-2. The Ge domes thus prepared exhibited intensive photoluminescence (PL) compared to those prepared by a conventional self-assembling technique

  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. Photonic Enhancement of Colloidal Quantum Dot Photovoltaics

    Science.gov (United States)

    Labelle, Andre Jean-Romeo Richard

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

  7. Non-Equilibrium Electron Transport through a Double Quantum Dot System: Study of Two Exchange Coupled Quantum Dots in a 4-Terminal Geometry

    OpenAIRE

    Koerting, Verena

    2007-01-01

    In this thesis we study two exchange-coupled quantum dots with an emphasis on non-equilibrium physics. Assuming a single electron on each quantum dot, the double quantum dot system is characterized by an interplay between the Kondo spin coupling of the dots with the leads and the spin-exchange coupling between the dots. We find that a finite voltage on one quantum dot drives the other quantum dot out of equilibrium.

  8. InGaN quantum dot growth in the limits of Stranski-Krastanov and spinodal decomposition

    Energy Technology Data Exchange (ETDEWEB)

    Figge, Stephan; Tessarek, Christian; Aschenbrenner, Timo; Hommel, Detlef [Institute of Solid State Physics, Section Semiconductor Epitaxy, University of Bremen (Germany)

    2011-08-15

    Most commonly used for the self-assembling of InGaN quantum dots is a Stranski-Krastanov growth scheme. Often neglected is the influence of spinodal decomposition, although it is frequently discussed with quantum well growth. In this publication we will expose the influence of both mechanisms on the formation process of quantum dots. This paper gives an insight in the theoretical background of quantum dot formation and covers the growth by molecular beam epitaxy and metal organic vapor phase epitaxy. Stranski-Krastanov like growth has been verified by the surface evolution beyond the critical thickness as seen by atomic force microscopy on uncapped samples. The overgrowth of such samples led to dissolution of the quantum dots. Indium compositions within the miscibility gap below critical thickness yielded spinodal phase separation in meander like structures These structures are in agreement with the theory from Hilliard and Cahn. Based on spinodal decomposition overgrowth schemes have been developed which showed reliable quantum dot emission. Such layers have been implemented into device structures such as LEDs and laser structures. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Writing Electron Dot Structures: Abstract of Issue 9905M

    Science.gov (United States)

    Magnell, Kenneth R.

    1999-10-01

    Writing Electron Dot Structures is a computer program for Mac OS that provides drill with feedback for students learning to write electron dot structures. While designed for students in the first year of college general chemistry it may also be used by high school chemistry students. A systematic method similar to that found in many general chemistry texts is employed: determine the number of valence shell electrons, select the central atom, construct a skeleton, add electrons to complete octets, examine the structure for resonance forms. During the construction of a structure, the student has the option of quitting, selecting another formula, or returning to a previous step. If an incorrect number of electrons is entered the student may not proceed until the correct number is entered. The symbol entered for the central atom must follow accepted upper/lower case practice, and entry of the correct symbol must be accomplished before proceeding to the next step. A periodic table is accessible and feedback provides assistance for these steps. Construction of the skeleton begins with the placement of the central atom. Atoms can be added, moved, or removed. Prompts and feedback keep the student informed of progress and problems. A correct skeleton is required before proceeding to the next step. Completion of the structure begins with the addition of electron pairs to form the required bonds. Remaining electrons are added to complete the formation of multiple bonds, assure compliance with the octet rule, and form expanded octets. Resonance forms are made by moving or removing and replacing electron pairs in the existing skeleton. Prompts and feedback guide the student through this process. A running tally of bond pairs, unshared pairs, octets, electrons used, and electrons remaining is provided during this step. Screens from Writing Electron Dot Structures Hardware and Software Requirements Hardware and software requirements for Writing Electron Dot Structures are shown

  10. Colloidal Quantum dot photovoltaics: Tuning optoelectronic properties

    International Nuclear Information System (INIS)

    Full text: Colloidal quantum dots combine processing from the solution phase with tunability of the bandgap. Via the size-effect the optical properties can be matched to the solar spectrum for a wide-range photon harvesting. To engineer photovoltaic devices, quantum dots are compressed from their colloidal form into a close-packed nanocrystal matrix, while undergoing a systematic layer-by-layer process. The resulting quantum dot solid is treated as semiconductor medium - one having electron-hole mobilites, free carrier densities and a dielectric constant. While the size-effect determined the band-gap before, it is now the nature of ligand and the treatment route, that influences mentioned electronic parameters. We took the view on the processing steps and found a concept for analysing trap states, moblility and device performance in real quantum dot solids. Our findings emphasize the interplay of mobility and trap-distribution with routes that take special care on the nanocrystal surface and hence conserve optoelectronic qualities of quantum dots for efficient photovoltaic cells. (author)

  11. Nanosized Carbon Dots from Organic Matter and Biomass

    Institute of Scientific and Technical Information of China (English)

    LI Yuanyuan; CHEN Tong; MA Yulong

    2016-01-01

    Carbon nanoparticles (C-dots) were prepared by relfuxing the combustion soots of candles and corn stalk in nitric acid. The synthesized C-dots were characterized. The results showed a sharp increase in oxygen content and a sharp decrease in carbon content after oxidation. The C-dots had -OH and -CO2H groups introduced which made them hydrophilic. However, their difference was also obvious. The C-dots from candle soot had a 10-45 nm broad particle size distribution, and those from corn stalk soot had a 6-18 nm relatively small and narrow size distribution. The C-dots were mainly ofsp2 andsp3 carbon structure different from the C-dots of diamond-like structure from candle soot. Interestingly, two kinds of C-dots all exhibited unique photoluminescent properties. The obtained C-dots have potential applications in a broad range of areas.

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

    Science.gov (United States)

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

    2016-08-01

    A system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines for maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.

  13. Quantum dot optoelectronic devices: lasers, photodetectors and solar cells

    International Nuclear Information System (INIS)

    Nanometre-scale semiconductor devices have been envisioned as next-generation technologies with high integration and functionality. Quantum dots, or the so-called ‘artificial atoms’, exhibit unique properties due to their quantum confinement in all 3D. These unique properties have brought to light the great potential of quantum dots in optoelectronic applications. Numerous efforts worldwide have been devoted to these promising nanomaterials for next-generation optoelectronic devices, such as lasers, photodetectors, amplifiers, and solar cells, with the emphasis on improving performance and functionality. Through the development in optoelectronic devices based on quantum dots over the last two decades, quantum dot devices with exceptional performance surpassing previous devices are evidenced. This review describes recent developments in quantum dot optoelectronic devices over the last few years. The paper will highlight the major progress made in 1.3 μm quantum dot lasers, quantum dot infrared photodetectors, and quantum dot solar cells. (topical review)

  14. 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.

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

    OpenAIRE

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

    2015-01-01

    In optoelectronic devices based on quantum dot arrays, thin nanolayers of gold are preferred as stable metal contacts and for connecting recombination centers. The optimal morphology requirements are uniform arrays with precisely controlled positions and sizes over a large area with long range ordering since this strongly affects device performance. To understand the development of gold layer nanomorphology, the detailed mechanism of structure formation are probed with time-resolved grazing i...

  16. Site-controlled quantum dots coupled to a photonic crystal molecule

    Energy Technology Data Exchange (ETDEWEB)

    Rigal, B.; Jarlov, C.; Gallo, P.; Dwir, B.; Rudra, A.; Calic, M.; Kapon, E. [Laboratory of Physics of Nanostructures, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland)

    2015-10-05

    Two site-controlled quantum dots (QDs) were integrated in a photonic crystal molecule (PCM) formed by L3 nanocavities. A statistical analysis of the coupled cavity modes demonstrated the formation of bonding and anti-bonding delocalized PCM states. Excitonic transitions belonging to each QD were identified by scanning micro-photoluminescence spectroscopy. Co-polarization of the QDs photoluminescence with the coupled cavity modes provides evidence for the simultaneous coupling of two spatially separated QDs to the same PCM mode.

  17. Site-controlled quantum dots coupled to a photonic crystal molecule

    International Nuclear Information System (INIS)

    Two site-controlled quantum dots (QDs) were integrated in a photonic crystal molecule (PCM) formed by L3 nanocavities. A statistical analysis of the coupled cavity modes demonstrated the formation of bonding and anti-bonding delocalized PCM states. Excitonic transitions belonging to each QD were identified by scanning micro-photoluminescence spectroscopy. Co-polarization of the QDs photoluminescence with the coupled cavity modes provides evidence for the simultaneous coupling of two spatially separated QDs to the same PCM mode

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

    DEFF Research Database (Denmark)

    Liu, Jin; Ates, Serkan; Stobbe, Søren; Lorke, Michael; Lodahl, Peter

    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.......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....

  19. Luminescence Spectra of a Quantum-Dot Cascade Laser

    OpenAIRE

    Apalkov, Vadim; Chakraborty, Tapash

    2000-01-01

    A quantum cascade laser where the quantum wells in the active regions are replaced by quantum dots with their atom-like discrete energy levels is an interesting system to study novel features in optical spectroscopy. We study structures suitable for diagonal lasing transitions in coupled dots, and vertical lasing transitions in a single dot, in the active regions of the laser device. The luminescence spectra as a function of electron number and dot size show that for diagonal transitions, a s...

  20. Short-wave infrared colloidal quantum dot photodetectors on silicon

    OpenAIRE

    Hu, Chen; Gassenq, Alban; Justo, Yolanda; Yakunin, Sergii; Heiss, Wolfgang; Hens, Zeger; Roelkens, Gunther

    2013-01-01

    In this paper, two kinds of colloidal quantum dots, PbS and HgTe, are explored for SWIR photodetectors application. The colloidal dots are prepared by hot injection chemical synthesis, with organic ligands around the dots keeping them stable in solution. For the purpose of achieving efficient carrier transport between the dots in a film, these long organic ligands are replaced by shorter, inorganic ligands. We report uniform, ultra-smooth colloidal QD films without cracks realized by dip-coat...

  1. Optical properties of a Quantum-Dot Cascade Structure

    OpenAIRE

    Apalkov, V. M.; Chakraborty, Tapash

    2001-01-01

    We report on our theoretical studies of the luminescence spectra of a quantum cascade laser where the quantum wells in the active regions are replaced by parabolic quantum dots. We analyze the influence of shape and size of the dots on the luminescence spectra. The emission spectra have interaction induced blueshift which increases almost linearly with increasing electron number. The blueshift is smaller for larger and non-circular dots. For large dots, shape of the emission line has weak dep...

  2. Excitonic Properties in GaAs Parabolic Quantum Dots

    OpenAIRE

    Jaziri, S.; Bennaceur, R.

    1995-01-01

    Certain classes of semiconductor quantum dots being actually fabricated exhibit a nearly parabolic confinement for both the electron and the hole. In undoped quantum dots, excitonic effects are important. In this work, first we present theoretical results on exciton properties in parabolic quantum dots: resonance energy, binding energy and oscillator strength. Then, we investigate the effects of external electric and magnetic fields on exciton in quantum dots.

  3. Nanodots formation with slow highly charged ions

    Energy Technology Data Exchange (ETDEWEB)

    Yamazaki, Yasunori [Graduate School of Arts and Sciences, University of Tokyo and RIKEN (Japan)

    2007-06-15

    We have been developing a compact electron beam ion source with a high-T{sub c}superconductor as a solenoid magnet, which can be operated at liquid nitrogen temperature, and can deliver slow highly-charged ions as high as q 42. With this ion source together with other ion sources, nanodot formation processes were studied for a highly oriented pyrolytic graphite (HOPG) plate as a target. The impact site was observed with both the scanning tunnelling microscope (STM) mode and non-contact atomic force microscope (NCAFM) mode. It was found that protrusion-like dots were observed for both modes at the same position, and one HCI induced one dot. The dot size (diameter) and height were observed to be more or less the same for both modes, i.e, an HCI impact induces topographic modification on the HOPG surface. The dot size and height were measured as functions of the charge state (q = 8-46) and the kinetic energy (E = 1-300 keV) of highly-charged ions. It was found that the dot size increased linearly with the charge state, although the dependence on the kinetic energy was very weak if any.

  4. Barrier Li Quantum Dots in Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

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

    2003-01-01

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

  5. Branch management into micropipeline joint dot

    Directory of Open Access Journals (Sweden)

    Dimitar Tyanev

    2011-11-01

    Full Text Available This paper considers problems related to hardware implementation of computational process with conditional jumps. Hardware refers to asynchronous pipeline organization at microoperational level. Exploration is dedicated to one of the tasks presented in (Tyanev, D., 2009 concerning to micropipeline controller design to control micropipeline stage into joint dot of branch algorithm. Joint dot is the point at which few preceding branches are combined. It appears inevitably into conditional jump structures and this is the reason for the actuality of its problem. Analysis of this new task is presented and request arbitration functioning principles are formulated for the incoming to joint dot requests. The arbiter is responsible for the fair choice on which depends steady peformance of separate pipeline brances. Paper also describes pipeline controller synthesis and analysis of its operation in two variants: about 2-phase and 4-phase data transfer protocol. The synthesized asynchronous arbiter scheme is invariant to the type of pipeline protocol.

  6. 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.

  7. 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 (cotunneli...

  8. Weak localization in arrays of metallic quantum dots

    OpenAIRE

    Golubev, Dmitri S.; Zaikin, Andrei D.

    2006-01-01

    Combining scattering matrix formalism with non-linear $\\sigma$-model technique we analyze weak localization effects in arrays of chaotic quantum dots connected via barriers with arbitrary distribution of channel transmissions. With the aid of our approach we evaluate magnetoconductance of two arbitrarily connected quantum dots as well as of $N\\times M$ arrays of identical quantum dots.

  9. AHE measurements of very thin films and nanosized dots

    NARCIS (Netherlands)

    Kikuchi, N.; Murillo, R.; Lodder, J.C.

    2005-01-01

    In this paper we present anomalous Hall effect analysis from very thin Co (0.5 nm) film, Co/Pt multilayers and large areas of nanosized dots as well as from a few magnetic dots having a diameter of 120 nm. The dot arrayis prepared from Co/Pt multilayer by using laser interference lithography (LIL) w

  10. Edge-state blockade of transport in quantum dot arrays

    Science.gov (United States)

    Benito, Mónica; Niklas, Michael; Platero, Gloria; Kohler, Sigmund

    2016-03-01

    We propose a transport blockade mechanism in quantum dot arrays and conducting molecules based on an interplay of Coulomb repulsion and the formation of edge states. As a model we employ a dimer chain that exhibits a topological phase transition. The connection to a strongly biased electron source and drain enables transport. We show that the related emergence of edge states is manifest in the shot noise properties as it is accompanied by a crossover from bunched electron transport to a Poissonian process. For both regions we develop a scenario that can be captured by a rate equation. The resulting analytical expressions for the Fano factor agree well with the numerical solution of a full quantum master equation.

  11. Hydrophilic colloidal quantum dots with long peptide chain coats.

    Science.gov (United States)

    Dąbrowska, Anna; Nyk, Marcin; Worch, Remigiusz; Grzyb, Joanna

    2016-09-01

    Here, the transition of colloidal CdSe quantum dots (QDs) from hydrophobic to hydrophilic environments after coating the surface with long peptide chains of membrane scaffold proteins (MSP) is reported. The intermediate step included the solubilization of QDs with detergents, where n-octyl glucoside was the most promising ligand. Furthermore, size analysis by fluorescence correlation spectroscopy, gel filtration and atomic force microscopy suggested that the obtained QD-MSP conjugates were primarily discoidal and were likely formed from single QDs tightly encircled by helix belts. In addition, Fourier-transformed infrared spectroscopy analysis confirmed the preservation of the secondary structure of most proteins during conjugate formation, with no signs of denaturation. The obtained QD-MSP conjugates were optimal in terms of stability in water environments, suggesting that it is possible to obtain QDs with single peptide coats and providing the first guidelines for future research in this direction. PMID:27289307

  12. Chiroptical activity in colloidal quantum dots coated with achiral ligands.

    Science.gov (United States)

    Melnikau, Dzmitry; Savateeva, Diana; Gaponik, Nikolai; Govorov, Alexander O; Rakovich, Yury P

    2016-01-25

    We studied the chiroptical properties of colloidal solution of CdSe and CdSe/ZnS quantum dots (QDs) with a cubic lattice structure which were initially prepared without use of any chiral molecules and coated with achiral ligands. We demonstrate circular dichroism (CD) activity around first and second excitonic transition of these CdSe based nanocrystals. We consider that this chiroptical activity is caused by imbalance in racemic mixtures of QDs between the left and right handed nanoparticles, which appears as a result of the formation of various defects or incorporation of impurities into crystallographic structure during their synthesis. We demonstrate that optical activity of colloidal solution of CdSe QDs with achiral ligands weakly depends on the QDs size and number of ZnS monolayers, but does not depend on the nature of achiral ligands or polarity of the solution. PMID:26832599

  13. Molecular Andreev bound states and Majorana modes in a double dot system

    Science.gov (United States)

    Vernek, Edson; Silva, Joelson F.

    Nanostructured systems such as quantum dots (QD) connected to superconductors has attracted a lot of attention in the recent years. One of the well known phenomena in such a system is the formation of a pair of bound called Andreev bound states (ABS). Recently, it have been shown that when a QD is coupled to a topological superconductor wire, a Majorana bound state (MBS) leaks from the end of the wire into the dot. The character of these bound states is much reacher in structures like molecules and is far from being completely understood. In this work we study a system composed by a two inter-connected QDs in which one of then is coupled to a normal superconductor and to a normal lead while the other is coupled to a topological superconductor and to a distinct normal metallic lead. We show that in the atomic limit (for small interdot coupling), one of the dot has a pair of ABS whereas the other has a single a MBS. More interestingly, in the molecular regime (large inter-dot coupling) we observe a localized Majorana mode coexisting with a delocalized molecular ABS. We would like to thank financial support from the Brazilian agencies CNPq, CAPES and FAPEMIG.

  14. Optical control of nonlinearly dressed states in an individual quantum dot

    Science.gov (United States)

    Ardelt, P.-L.; Koller, M.; Simmet, T.; Hanschke, L.; Bechtold, A.; Regler, A.; Wierzbowski, J.; Riedl, H.; Finley, J. J.; Müller, K.

    2016-04-01

    We report nonlinear resonance fluorescence of an individual semiconductor quantum dot. By driving a single semiconductor quantum dot via a two-photon transition, we probe the linewidth of two-photon excitation processes and show that, similar to their single-photon counterparts, they are close to being Fourier limited at low temperatures. The evolution of the population of excitonic states with increasing Rabi energy exhibits a clear S-shaped behavior, indicative of the nonlinear response via the two-photon excitation process. Numerical calculations of the nonlinear response using a four-level atomic system representing the manifold of excitonic and biexcitonic states in the quantum dot are in excellent agreement with our experiments and reveal the effect of interactions with LA phonons in the solid-state environment. Finally, we demonstrate the formation of dressed states emerging from a nonlinear two-photon interaction between the quantum dot and the optical excitation field. The nonlinear optical dressing induces a mixing of all four excitonic states that allows direct optical tuning of the polarization selection rules and energies of the dressed states in the artificial atom. We expect our results to play a pivotal role for the generation of nonclassical photon pairs desired for applications in quantum communication and fundamental experiments on quantum optical properties of photons.

  15. Optical studies of capped quantum dots

    OpenAIRE

    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 in a glovebox. These QDs are soluble in organics but can be transferred into water or ethanol after exchange of the surfactants by various thiols (HS-R). For CdTe the exchange with thiols has a be...

  16. Nonuniform micromagnetic states in thin circular dots

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Z.-H. E-mail: zhwei@phys.ntu.edu.tw; Lai, M.-F.; Chang, C.-R.; Usov, N.A.; Wu, J.C.; Lai, J.-Y

    2004-11-01

    Micromagnetic states are strongly related to sizes of nano-dots. The quasiuniform state becomes unstable and transforms to a new nonuniform state as the diameter of the permalloy circular dot exceeds some critical size. The magnetization curvature increases gradually as the diameter increases. Finally, when the diameter is larger than another critical size, the new nonuniform state becomes unstable and a vortex enters the particle. Hence the new nonuniform state plays an intermediate role in the evolution from the quasiuniform state to the vortex state as the diameter increases.

  17. 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

  18. Engineered Quantum Dot Single Photon Sources

    CERN Document Server

    Buckley, Sonia; Vuckovic, Jelena

    2012-01-01

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

  19. Spintronic transport through an interacting Rashba dot

    International Nuclear Information System (INIS)

    We investigate the spin-dependent transport property through a quantum wire with local Rashba interaction based on fRG method. The Rashba field forms quasi-bound states which couple to the continuum states with an opposite spin direction. It is found that the transport through the Rashba dot strongly depends on an assumed spin polarization of the continuum states and on the Coulomb interaction U in the dot. The interaction U (U>UC) leads to the appearance of three conductance peaks. Two outer peaks are associated with the Coulomb blockade and the center peak is induced by correlation of the electrons with different spin

  20. Addition of Zn during the phosphine-based synthesis of indium phospide quantum dots: doping and surface passivation

    OpenAIRE

    Natalia E. Mordvinova; Vinokurov, Alexander A; Lebedev, Oleg I.; Kuznetsova, Tatiana A.; Dorofeev, Sergey G.

    2015-01-01

    Zinc-doped InP(Zn) colloidal quantum dots (QDs) with narrow size distribution and low defect concentration were grown for the first time via a novel phosphine synthetic route and over a wide range of Zn doping. We report the influence of Zn on the optical properties of the obtained quantum dots. We propose a mechanism for the introduction of Zn in the QDs and show that the incorporation of Zn atoms into the InP lattice leads to the formation of Zn acceptor levels and a luminescence tail in th...

  1. Quantum phase transition in trigonal triple quantum dots: The case of quantum dots deviated from particle–hole symmetric point

    International Nuclear Information System (INIS)

    We consider a triple quantum dot system in a triangular geometry with one of the dots connected to metallic leads. We investigate quantum phase transition between local moment phase and Kondo screened strong coupling phase in triple quantum dots where energy levels of dots are deviated from the particle–hole symmetric point. The effect of on-site energy of dots on quantum phase transition between local moment phase and Kondo screened strong coupling phase in triple quantum dots 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 when the energy level of embedded dot rises up from the symmetric point to the Fermi level and the critical value increases when the energy levels of two side dots rise up. The study of the influence of on-site-energy changes on the quantum phase transitions in triple quantum dots has the importance for clarifying the mechanism of Kondo screening in triple quantum dots where energy levels of dots are deviated from the particle–hole symmetric point

  2. A study of the lunisolar secular resonance $2\\dot{\\omega}+\\dot{\\Omega}=0$

    CERN Document Server

    Celletti, Alessandra

    2016-01-01

    The dynamics of small bodies around the Earth has gained a renewed interest, since the awareness of the problems that space debris can cause in the nearby future. A relevant role in space debris is played by lunisolar secular resonances, which might contribute to an increase of the orbital elements, typically of the eccentricity. We concentrate our attention on the lunisolar secular resonance described by the relation $2\\dot{\\omega}+\\dot{\\Omega}=0$, where $\\omega$ and $\\Omega$ denote the argument of perigee and the longitude of the ascending node of the space debris. We introduce three different models with increasing complexity. We show that the growth in eccentricity, as observed in space debris located in the MEO region at the inclination about equal to $56^\\circ$, can be explained as a natural effect of the secular resonance $2\\dot{\\omega}+\\dot{\\Omega}=0$, while the chaotic variations of the orbital parameters are the result of interaction and overlapping of nearby resonances.

  3. A study of the lunisolar secular resonance $2dot{omega}+dot{Omega}=0$

    Directory of Open Access Journals (Sweden)

    Alessandra eCelletti

    2016-03-01

    Full Text Available The dynamics of small bodies around the Earth has gained a renewed interest,since the awareness of the problems that space debris can cause in thenearby future. A relevant role in space debris is played by lunisolarsecular resonances, which might contribute to an increase of the orbitalelements, typically of the eccentricity. We concentrate our attention onthe lunisolar secular resonance described by the relation$2dot{omega}+dot{Omega}=0$, where $omega$ and $Omega$ denotethe argument of perigee and the longitude of the ascending node of the space debris.We introduce three different models with increasing complexity. We show that the growth in eccentricity, as observed in space debris located in the MEO region at the inclination about equal to $56^circ$, can be explained as a natural effect of the secular resonance $2dot{omega}+dot{Omega}=0$, while the chaotic variations of the orbital parameters are the result of interaction and overlapping of nearby resonances.

  4. A study of the lunisolar secular resonance 2dot{ω}+dot{Ω}=0

    Science.gov (United States)

    Celletti, Alessandra; Gales, Catalin

    2016-03-01

    The dynamics of small bodies around the Earth has gained a renewed interest, since the awareness of the problems that space debris can cause in the nearby future. A relevant role in space debris is played by lunisolar secular resonances, which might contribute to an increase of the orbital elements, typically of the eccentricity. We concentrate our attention on the lunisolar secular resonance described by the relation 2dot{ω}+dot{Ω}=0, where ω and Ω denote the argument of perigee and the longitude of the ascending node of the space debris. We introduce three different models with increasing complexity. We show that the growth in eccentricity, as observed in space debris located in the MEO region at the inclination about equal to 56°, can be explained as a natural effect of the secular resonance 2dot{ω}+dot{Ω}=0, while the chaotic variations of the orbital parameters are the result of interaction and overlapping of nearby resonances.

  5. Electrically addressing a single self-assembled quantum dot

    CERN Document Server

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

    2006-01-01

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

  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...... to resolve luminescence lines from individual quantum dots, revealing an atomic-like spectrum of sharp transition lines. A parameter of fundamental importance is the intrinsic linewidth of these transitions. Using high-resolution spectroscopy we have determined the linewidth and investigated its dependence...... on temperature, which gives information about how the exciton confined to the quantum dot interacts with the surrounding lattice....

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

    DEFF Research Database (Denmark)

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

    2000-01-01

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

  8. Lateral excitonic switching in vertically stacked quantum dots

    Science.gov (United States)

    Jarzynka, Jarosław R.; McDonald, Peter G.; Shumway, John; Galbraith, Ian

    2016-06-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-24

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

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

    International Nuclear Information System (INIS)

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

  11. Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

    International Nuclear Information System (INIS)

    We report on numerical simulations of InP surface lateral quantum-dot molecules on In0.48Ga0.52 P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k→·p→ bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots

  12. Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

    Energy Technology Data Exchange (ETDEWEB)

    Barettin, Daniele, E-mail: Daniele.Barettin@uniroma2.it; Auf der Maur, Matthias [Department of Electronic Engineering, University of Rome “Tor Vergata,” Via del Politecnico 1, 00133, Rome (Italy); De Angelis, Roberta; Prosposito, Paolo; Casalboni, Mauro [Department of Industrial Engineering, University of Rome Tor Vergata, Via del Politecnico 1 00133 Rome, Italy and INSTM, Unitá di ricerca dell' Universitá di Roma “Tor Vergata,” Via della Ricerca Scientifica 1, 00133, Rome (Italy); Pecchia, Alessandro [CNR-ISMN, via Salaria Km. 29.300, 00017 Monterotondo, Rome (Italy)

    2015-03-07

    We report on numerical simulations of InP surface lateral quantum-dot molecules on In{sub 0.48}Ga{sub 0.52 }P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k{sup →}·p{sup →} bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.

  13. Emission spectra of a laser based on an In(Ga)As/GaAs quantum-dot superlattice

    International Nuclear Information System (INIS)

    The spectral characteristics of a laser with an active region based on a ten-layer system of In(Ga)As/GaAs vertically correlated quantum dots with 4.5-nm GaAs spacer layers between InAs quantum dots are studied under the conditions of spontaneous and stimulated emission, depending on the current and the duration of pump pulses. Data obtained by transmission electron microscopy and electroluminescence and absorption polarization anisotropy measurements make it possible to demonstrate that the investigated system of tunnel-coupled InAs quantum dots separated by thin GaAs barriers represents a quantum-dot superlattice. With an increase in the laser pump current, the electroluminescence intensity increases linearly and the spectral position of the electroluminescence maximum shifts to higher energies, which is caused by the dependence of the miniband density-of-states distribution on the pump current. Upon exceeding the threshold current, multimode lasing via the miniband ground state is observed. One of the lasing modes can be attributed to the zero-phonon line, and the other is determined by the longitudinal-optical phonon replica of quantum-dot emission. The results obtained give evidence that, under conditions of the laser pumping of an In(Ga)As/GaAs quantum-dot superlattice, strong coupling between the discrete electron states in the miniband and optical phonons takes place. This leads to the formation of quantum-dot polarons, resulting from the resonant mixing of electronic states whose energy separation is comparable to the optical-phonon energy

  14. Tunneling Processes in Optically Excited Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    LI Xiu-Ping; WEI Hua-Rong; XU Li-Ping; GONG Jian-Ping; YAN Wei-Xian

    2011-01-01

    The single-electron tunneling processes in optically excited coupled quantum dots can be divided into two parts: the electron and the hole parts, which are analytically obtained in the framework of the Keldysh formalism. The tunneling process is selective tunneling, which results in dark tunneling states. The tunneling currents are co-determined by the resonance energies and probability distributions of the particular quantum channels defined by the electron-hole complex resonant states.%The single-electron tunneling processes in optically excited coupled quantum dots can be divided into two parts:the electron and the hole parts,which are analytically obtained in the framework of the Keldysh formalism.The tunneling process is selective tunneling,which results in dark tunneling states.The tunneling currents are co-determined by the resonance energies and probability distributions of the particular quantum channels defined by the electron-hole complex resonant states.Probing the fine-energy structure of the exciton complexes[1-10] in an optically excited quantum dot is an important way of exploring new mechanisms in nanostructures.Single electron tunneling (SET) devices consisting of a central quantum dot (QD) and a tunneling coupled source and drain have become important optoelectronic nano-devices.[11,12

  15. Quantum dot quantum cascade infrared photodetector

    International Nuclear Information System (INIS)

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

  16. 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

  17. Ostwald's ripening of nanostructures with quantum dots

    International Nuclear Information System (INIS)

    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

  18. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

    This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission into the...... 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.......This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission into the...... mode exceeding 98% for emitters spectrally close to the band-edge of the waveguide mode. In addition we illustrate the broadband nature of the underlying eects, by obtaining coupling eciencies above 90% for quantum dots detuned from the band edge by as far as 20nm. These values are in good agreement...

  19. Multiple exciton generation effect in quantum dots

    International Nuclear Information System (INIS)

    Full text: Recently among various investigations in the field of nanophysics a great intensification in studying of multiple exciton generation (MEG) effect in quantum dots at absorption of photons with the energy several times higher than the gap in electronic spectra (hν>>Eg) has been made [1-2]. There have been proposed four theoretical approaches to explain the MEG effect. However, the statistic approach basing on the Fermi theory of multiple pi-mesons generation (1950) is the most adequate related to others. In this work: 1. the results of statistic approach have been generalized; 2. the microscopic mechanism basing on theory of electronic 'shaking' has been proposed; 3. the problem of deviation of mean multiplicity of MEG effect from the Poisson law of fluctuations has been investigated that is a evidence of strong non-linear and non-equilibrium character of exciton generation process; 4. the role of interface electronic states of quantum dot and ligand has been considered by means of perturbation theory of closed states related to surface Tamm electronic states of quantum dot and legend; 5. the problem of size optimization of quantum dot to receive the maximum multiplicity has been studied; 6. the efficiency of MEG effect for the third generation of solar cells has been calculated on the basis of proposed theory. (authors)

  20. Linear Kondo conductance in a quantum dot

    International Nuclear Information System (INIS)

    In a tunnelling experiment across a quantum dot it is possible to change the coupling between the dot and the contacts at will, by properly tuning the transparency of the barriers and the temperature. Gate voltages allow for changes of the relative position of the dot addition energies and the Fermi level of the leads. Here we discuss the two limiting cases: weak and strong coupling in the tunnelling Hamiltonian. In the latter case Kondo resonant conductance can emerge at low temperature in a Coulomb blockade valley. We give a pedagogical approach to the single-channel Kondo physics at equilibrium and review the Nozieres scattering picture of the correlated fixed point. We emphasize the effect of an applied magnetic field and show how an orbital Kondo effect can take place in vertical quantum dots tuned both to an even and to an odd number of electrons at a level crossing. We extend the approach to the two-channel overscreened Kondo case and discuss recent proposals for detecting the non-Fermi liquid fixed point which could be reached at strong coupling

  1. Incipient Wigner localization in circular quantum dots

    Science.gov (United States)

    Ghosal, Amit; Güçlü, A. D.; Umrigar, C. J.; Ullmo, Denis; Baranger, Harold U.

    2007-08-01

    We study the development of electron-electron correlations in circular quantum dots as the density is decreased. We consider a wide range of both electron number, N⩽20 , and electron gas parameter, rs≲18 , using the diffusion quantum Monte Carlo technique. Features associated with correlation appear to develop very differently in quantum dots than in bulk. The main reason is that translational symmetry is necessarily broken in a dot, leading to density modulation and inhomogeneity. Electron-electron interactions act to enhance this modulation ultimately leading to localization. This process appears to be completely smooth and occurs over a wide range of density. Thus there is a broad regime of “incipient” Wigner crystallization in these quantum dots. Our specific conclusions are (i) the density develops sharp rings while the pair density shows both radial and angular inhomogeneity; (ii) the spin of the ground state is consistent with Hund’s (first) rule throughout our entire range of rs for all 4⩽N⩽20 ; (iii) the addition energy curve first becomes smoother as interactions strengthen—the mesoscopic fluctuations are damped by correlation—and then starts to show features characteristic of the classical addition energy; (iv) localization effects are stronger for a smaller number of electrons; (v) finally, the gap to certain spin excitations becomes small at the strong interaction (large rs ) side of our regime.

  2. 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...

  3. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

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

    2010-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...

  4. 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...

  5. Enabling biomedical research with designer quantum dots

    NARCIS (Netherlands)

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

    2012-01-01

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

  6. 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.

  7. Photoluminescence of hybrid quantum dot systems

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    2015-01-01

    Roč. 7, č. 4 (2015), 347-349. ISSN 2164-6627 R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

  8. Grating image with desired shaped dots

    Science.gov (United States)

    Honma, Hideaki; Toda, Toshiki; Takahashi, Susumu; Sawamura, Chikara; Iwata, Fujio

    2000-03-01

    A new type of Grating Image we dominate as `Sparklegram' is presented. The Sparklegram is characterized because it provides high quality and better design flexibility. These features are achieved by constructing it with shaped dots as desired. Each dot can be designed as an individual shape, for example, a star or a triangle. As dot shapes, we can use not only geometric patterns, but also some kind of symbols. Not only flexibility of each consists dot shape, but also the quality of reconstructed image is remarkably increased too. Because of these features, the constructed image with the new type of Grating Image, Sparklegram has high quality and high flexibility. It can be applied to security use, for example on credit-cards, tickets, etc., and also can be applied to the package of software products, CDs, videos and other kind of items requiring security. And with these features of flexibility and high quality, Sparklegram has also advantages to be applied to other use, for example amusement use, comics and game characters' goods and packages.

  9. Producing Quantum Dots by Spray Pyrolysis

    Science.gov (United States)

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

    2006-01-01

    An improved process for making nanocrystallites, commonly denoted quantum dots (QDs), is based on spray pyrolysis. Unlike the process used heretofore, the improved process is amenable to mass production of either passivated or non-passivated QDs, with computer control to ensure near uniformity of size.

  10. Language, visual working memory, and dot subtraction: What counts?

    Science.gov (United States)

    Briere, Jennifer L; Campbell, Jamie I D

    2016-03-01

    To investigate cognitive factors affecting subtraction of visual objects, we adapted the dot subtraction task developed by Pica, Lemer, Izard, and Dehaene (2004), who used it to investigate calculation by the Mundurukú, an indigene group in Brazil that has a limited number word vocabulary. In the dot subtraction task, briefly displayed arrays of moving dots are used to represent the quantities for subtraction. We tested 40 Canadian university students' dot enumeration, Arabic digit subtraction, visual working memory, and performance on the dot subtraction task with dot display durations of 2, 1.5, 1, and .5 s. In the 2 s condition, error rates were uniformly low, whereas in the .5 s condition, error rates increased sharply as the minuend increased from 4 to 8, as was observed with the Mundurukú. Individual differences in dot subtraction accuracy were predicted by dot enumeration skill with longer dot display durations but were predicted by visual working memory efficiency with shorter durations. Pica et al. (2004) attributed the Mundurukú participants' very poor subtraction to the absence of counting words, but our results show that a shift to reliance on visual working memory is a nonlinguistic factor that comes into play in the dot subtraction task when time to encode the dot arrays is limited. (PsycINFO Database Record PMID:26372056

  11. Growth and structural characterization of pyramidal site-controlled quantum dots with high uniformity and spectral purity

    CERN Document Server

    Dimastrodonato, Valeria; Young, Robert J; Pelucchi, Emanuele

    2010-01-01

    This work presents some fundamental features of pyramidal site-controlled InGaAs Quantum Dots (QDs) grown by MetalOrganic Vapour Phase Epitaxy on patterned GaAs (111)B substrate. The dots self-form inside pyramidal recesses patterned on the wafer via pre-growth processing. The major advantage of this growth technique is the control it provides over the dot nucleation posi-tion and the dimensions of the confined structures onto the sub-strate. The fundamental steps of substrate patterning and the QD forma-tion mechanism are described together with a discussion of the structural particulars. The post-growth processes, including sur-face etching and substrate removal, which are required to facili-tate optical characterization, are discussed. With this approach extremely high uniformity and record spectral purity are both achieved.

  12. Nonequilibrium transport via spin-induced subgap states in superconductor/quantum dot/normal metal cotunnel junctions

    Science.gov (United States)

    Koerting, V.; Andersen, B. M.; Flensberg, K.; Paaske, J.

    2010-12-01

    We study low-temperature transport through a Coulomb blockaded quantum dot (QD) contacted by a normal (N) and a superconducting (S) electrode. Within an effective cotunneling model the conduction electron self-energy is calculated to leading order in the cotunneling amplitudes and subsequently resummed to obtain the nonequilibrium T matrix, from which we obtain the nonlinear cotunneling conductance. For even-occupied dots the system can be conceived as an effective S/N-cotunnel junction with subgap transport mediated by Andreev reflections. The net spin of an odd-occupied dot, however, leads to the formation of subgap resonances inside the superconducting gap which give rise to a characteristic peak-dip structure in the differential conductance, as observed in recent experiments.

  13. Coherence and dephasing in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    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 cohere...... 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.......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...

  14. Inhomogeneous charging and screening effects in semiconductor quantum dot arrays

    Energy Technology Data Exchange (ETDEWEB)

    Wetzler, R [Institut fuer Theoretische Physik, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Kunert, R [Institut fuer Theoretische Physik, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Wacker, A [Fysiska Institutionen, Lunds Universitet, Box 118, 22100 Lund (Sweden); Schoell, E [Institut fuer Theoretische Physik, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany)

    2004-07-01

    The electronic properties of quantum dot (QD) arrays are strongly influenced by the Coulomb interaction of electrons within the dot as well as with those in neighbouring dots. In this paper, we investigate this behaviour taking into account screening by a free electron gas in the vicinity of the QDs. We find pronounced effects for standard capacitance[ndash]voltage (CV) measurements of QD structures embedded in a pn-diode. In particular, we show that the three-dimensional nature of the problem is crucial for devices with low dot-density, whereas the self-consistency between electron depletion in the bulk layer and dot occupation is important for high dot-densities. The Coulomb interaction between the dots induces a broadening of the peaks in the CV characteristic which is comparable with the effect of disordered QD arrays, where we considered realistic size and position fluctuations obtained by a kinetic Monte Carlo simulation.

  15. Optical Properties of Quantum-Dot-Doped Liquid Scintillators

    CERN Document Server

    Aberle, C; Weiss, S; Winslow, L

    2013-01-01

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

  16. Growth and characterization of InP/In0.48Ga0.52P quantum dots optimized for single-photon emission

    International Nuclear Information System (INIS)

    In this work the growth of self-assembled InP/InGaP quantum dots, as well as their optical and structural properties are presented and discussed. The QDs were grown on In0.48Ga0.52P, lattice matched to GaAs. Self-assembled InP quantum dots are grown using gas-source molecular beam epitaxy over a wide range of InP deposition rates, using an ultra-low growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/μm2 is realized. The resulting isolated InP quantum dots are individually characterized without the need for lithographical patterning and masks on the substrate. Both excitonic and biexcitonic emissions are observed from single dots, appearing as doublets with a fine-structure splitting of 320 μeV. Hanbury Brown-Twiss correlation measurements for the excitonic emission under cw excitation show anti-bunching behavior with an autocorrelation value of g(2)(0)=0.2. This system is applicable as a single-photon source for applications such as quantum cryptography. The formation of well-ordered chains of InP quantum dots on GaAs (001) substrates by using self-organized In0.48Ga0.52P surface undulations as a template is also demonstrated. The ordering requires neither stacked layers of quantum dots nor substrate misorientation. The structures are investigated by polarization-dependent photoluminescence together with transmission electron microscopy. Luminescence from the In0.48Ga0.52P matrix is polarized in one crystallographic direction due to anisotropic strain arising from a lateral compositional modulation. The photoluminescence measurements show enhanced linear polarization in the alignment direction of quantum dots. A polarization degree of 66% is observed. The optical anisotropy is achieved with a straightforward heterostructure, requiring only a single layer of QDs.

  17. Optically controlled spins in semiconductor quantum dots

    Science.gov (United States)

    Economou, Sophia

    2010-03-01

    Spins in charged semiconductor quantum dots are currently generating much interest, both from a fundamental physics standpoint, as well as for their potential technological relevance. Being naturally a two-level quantum system, each of these spins can encode a bit of quantum information. Optically controlled spins in quantum dots possess several desirable properties: their spin coherence times are long, they allow for all-optical manipulation---which translates into fast logic gates---and their coupling to photons offers a straightforward route to exchange of quantum information between spatially separated sites. Designing the laser fields to achieve the unprecedented amount of control required for quantum information tasks is a challenging goal, towards which there has been recent progress. Special properties of hyperbolic secant optical pulses enabled the design of single qubit rotations, initially developed about the growth axis z [1], and later about an arbitrary direction [2]. Recently we demonstrated our theoretical proposal [1] in an ensemble of InAs/GaAs quantum dots by implementing ultrafast rotations about the z axis by an arbitrary angle [3], with the angle of rotation as a function of the optical detuning in excellent agreement with the theoretical prediction. We also developed two-qubit conditional control in a quantum dot `molecule' using the electron-hole exchange interaction [4]. In addition to its importance in quantum dot-based quantum computation, our two-qubit gate can also play an important role in photonic cluster state generation for measurement-based quantum computing [5]. [1] S. E. Economou, L. J. Sham, Y. Wu, D. S. Steel, Phys. Rev. 74, 205415 (2006) [2] S. E. Economou and T. L. Reinecke, Phys. Rev. Lett., 99, 217401 (2007) [3] A. Greilich, S. E. Economou et al, Nature Phys. 5, 262 (2009) [4] S. E. Economou and T. L. Reinecke, Phys. Rev. B, 78, 115306 (2008) [5] S. E. Economou, N. H. Lindner, and T. Rudolph, in preparation

  18. Evolution of visible photoluminescence of Si quantum dots embedded in silicon oxide matrix

    Energy Technology Data Exchange (ETDEWEB)

    Karlash, Anna Yu., E-mail: anna_karlash@ukr.net [Institute of High Technologies, Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska str., Kyiv 01601 (Ukraine); Skryshevsky, Valeriy A.; Kuznetsov, Gennady V. [Institute of High Technologies, Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska str., Kyiv 01601 (Ukraine); Kladko, Vasyl P. [Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 41, pr. Nauki, Kyiv 03028 (Ukraine)

    2013-11-15

    Highlights: •Nanocomposites were created by pressing of silica aerogel and porous Si powder. •Photoluminescence properties of nc-Si/SiO{sub x} nanocomposites were studied. •The increase of forming pressure results in photoluminescence blue shift. •Aging of nanocomposites leads to the strong increase of emission efficiency. •The transformation of photoluminescence kinetics was observed for aged nanocomposites. -- Abstract: Photoluminescence properties of nc-Si/SiO{sub x} nanocomposites produced by pressing the mixture of the silica aerogel powder with the porous silicon have been studied. The transformation of emission spectra of Si quantum dots, its quantum yield and emission kinetics during the long time (few months) aging in ambient conditions and formation conditions (external pressure) were observed. The different behavior of short and long wave range emission of Si quantum dots embedded in silicon oxide matrix has been obtained. The observed blue-shifting (from 2.02 to 2.05 eV) of emission peak associated with the free exciton recombination in Si quantum dots at forming pressure increasing is explained by the reduction of average Si quantum dot dimension due to the breaking away the surface irregularities and smoothing of the Si nanoparticles surface. Effect of a strong increase in intensity (more than 1 order) and blue shifting of emission of Si quantum dots were discovered in nc-Si/SiO{sub x} nanocomposites at few months’ storage in ambient conditions. Such effects were explained in terms of both surface passivation and the carrier confinement. It was also confirmed by the fact that for aged composites the photoluminescence kinetics transforms by adding the stretched exponential term to the single exponential low.

  19. Fluorescence behavior of glutathione capped CdTe@ZnS quantum dots chemically coordinated to zinc octacarboxy phthalocyanines

    International Nuclear Information System (INIS)

    Core–shell CdTe@ZnS quantum dots capped with glutathione (CdTe@ZnS–GSH) were covalently linked to zinc octacarboxy phthalocyanine (ZnPc(COOH)8). The conjugate was characterized by UV/Vis, infrared and X-Ray photoelectron spectroscopies as well as transmission electron and atomic force microscopies. The fluorescence quantum yields of the core CdTe capped with thioglycolic acid increased upon formation of the core-shell. Upon conjugation with ZnPc(COOH)8, the fluorescence quantum yield of CdTe@ZnS–GSH decreased due to energy transfer from the latter to the Pc. The average fluorescence lifetime of the CdTe@ZnS–GSH QD also decreased upon conjugation from 26.2 to 13.3 ns. -- Graphical Abstract: CdTe@ZnS quantum dots capped with glutathione (CdTe@ZnS-GSH) and covalently linked to zinc octacarboxy phthalocyanine (ZnPc(COOH)8), showed decreased fluorescence quantum yield and lifetime of the CdTe@ZnS-GSH following conjugation due to energy transfer. Highlights: ► CdTe@ZnS quantum dots capped with glutathione were synthesized. ► The quantum dots were chemically linked to zinc octacarboxy phthalocyanine. ► The fluorescence quantum yields of the quantum dots decreased on conjugation. ► Fluorescence lifetimes also decreased due to energy transfer

  20. ZZ VITAMIN-J/KERMA, Gas Production Cross-Sections, Neutron and Gamma Kerma in FOURACES Format

    International Nuclear Information System (INIS)

    1 - Description of program or function: Format: ANISN; Number of groups: 175 neutron plus 38 photon energy groups; Nuclides: H-1, D-2, T-3, Li-6, Li-7, Be-9, B-10, B-11, C, O-16, Al-27, Si, Ti, V, Cr, Mn-55, Fe, Ni, Cu, Zr, Nb-93, Mo, Ba-134, Ba-135, Ba-136, Ba-137, Ba-138, W-182, W-183, W-184, W-186, Pb, Bi-209, He-3, He-4, N-14, Mg, P-31, S, Ca, Co-59, In, Sn, Ta-181, Re Origin: EFF-1, DLC-99 (HUGO) data library; Weighting spectrum: Maxwellian plus 1/E plus fission spectrum plus fusion peak. Library of gas production cross sections, neutron kerma factors and photon kerma factors in FOURACES format according to GEFF-1 specifications. Kerma factors have been calculated for temperatures 300 K and 800 K. 2 - Method of solution: For the gas production cross sections, the lump reactions 203 and 207 included in EFF-1 had been assumed as the basic of the computation. The neutronics kerma factors have been calculated with the module KERMA of THEMIS. The photonic kerma factors have been calculated with the module GROUPG of THEMIS, starting from the DLC-99 (HUGO) data library of gamma interactions

  1. Quantum dot-sized organic fluorescent dots for long-term cell tracing

    Science.gov (United States)

    Li, Kai; Tang, Ben Zhong; Liu, Bin

    2014-03-01

    Fluorescence techniques have been extensively employed to develop non-invasive methodologies for tracking and understanding complex biological processes both in vitro and in vivo, which is of high importance in modern life science research. Among a variety of fluorescent probes, inorganic semiconductor quantum dots (QDs) have shown advantages in terms of better photostability, larger Stokes shift and more feasible surface functionalization. However, their intrinsic toxic heavy metal components and unstable fluorescence at low pH greatly impede the applications of QDs in in vivo studies. In this work, we developed novel fluorescent probes that can outperform currently available QD based probes in practice. Using conjugated oligomer with aggregation-induced emission characteristics as the fluorescent domain and biocompatible lipid-PEG derivatives as the encapsulation matrix, the obtained organic dots have shown higher brightness, better stability in biological medium and comparable size and photostability as compared to their counterparts of inorganic QDs. More importantly, unlike QD-based probes, the organic fluorescent dots do not blink, and also do not contain heavy metal ions that could be potentially toxic when applied for living biosubstrates. Upon surface functionalization with a cell-penetrating peptide, the organic dots greatly outperform inorganic quantum dots in both in vitro and in vivo long-term cell tracing studies, which will be beneficial to answer crucial questions in stem cell/immune cell therapies. Considering the customized fluorescent properties and surface functionalities of the organic dots, a series of biocompatible organic dots will be developed to serve as a promising platform for multifarious bioimaging tasks in future.

  2. Functionalized manganese-doped zinc sulfide quantum dot-based fluorescent probe for zinc ion

    International Nuclear Information System (INIS)

    We report on a simple strategy for the determination of zinc ion by using surface-modified quantum dots. The probe consists of manganese-doped quantum dots made from zinc sulfide and capped N-acetyl-L-cysteine. The particles exhibit bright yellow-orange emission with a peak at 598 nm which can be attributed to the 4T1→6A1 transition of Mn(II). This bright fluorescence is effectively quenched by modifying the sulfur anion which suppresses the radiative recombination process. The emission of the probe can then be restored by adding Zn(II) which causes the formation of a ZnS passivation layer around the QDs. The fluorescence enhancement caused is linear in the 1. 25 to 30 μM zinc concentration range, and the limit of detection is 0. 67 μM. (author)

  3. Optimization of process parameter for synthesis of silicon quantum dots using low pressure chemical vapour deposition

    Indian Academy of Sciences (India)

    Dipika Barbadikar; Rashmi Gautam; Sanjay Sahare; Rajendra Patrikar; Jatin Bhatt

    2013-06-01

    Si quantum dots-based structures are studied recently for performance enhancement in electronic devices. This paper presents an attempt to get high density quantum dots (QDs) by low pressure chemical vapour deposition (LPCVD) on SiO2 substrate. Surface treatment, annealing and rapid thermal processing (RTP) are performed to study their effect on size and density of QDs. The samples are also studied using Fourier transformation infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence study (PL). The influence of Si–OH bonds formed due to surface treatment on the density of QDs is discussed. Present study also discusses the influence of surface treatment and annealing on QD formation.

  4. 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.

  5. Double-walled carbon nanotubes synthesized using carbon black as the dot carbon source

    Science.gov (United States)

    Chen, Zhi-Gang; Li, Feng; Ren, Wen-Cai; Cong, Hongtao; Liu, Chang; Qing Lu, Gao; Cheng, Hui-Ming

    2006-07-01

    Double-walled carbon nanotubes (DWNTs) were synthesized used carbon black as the dot carbon source by a semi-continuous hydrogen arc discharge process. High-resolution transmission electron microscopy (HRTEM) observations revealed that most of the tubes were DWNTs with outer and inner diameters in the range of 2.67-4 nm and 1.96-3.21 nm, respectively. Most of the DWNTs were in a bundle form of about 10-30 nm in diameter with high purity (about 70%) from thermal gravimetric analysis (TGA), resonant laser Raman spectroscopy, scanning electron microscopy (SEM) and TEM characterizations. It was found that carbon black as the dot carbon source could be easy controlled to synthesize one type of nanotube. A simple process combining oxidation and acid treatment to purify the DWNT bundles was used without damaging the bundles. The structure of carbon black, as the key element for influencing purity, bundle formation and purification of DWNTs, is discussed.

  6. Novel cookie-with-chocolate carbon dots displaying extremely acidophilic high luminescence

    Science.gov (United States)

    Lu, Siyu; Zhao, Xiaohuan; Zhu, Shoujun; Song, Yubin; Yang, Bai

    2014-10-01

    A fluorescent carbon dot with a cookie-with-chocolate film structure (about 5 × 5 μm2) showed a high fluorescence quantum yield (61.12%) at low pH. It was hydrothermally synthesized from l-serine and l-tryptophan. The formation mechanism of the film with carbon dots (CDs) was investigated. The film structure was formed by hydrogen bonding and π-π stacking interactions between aromatic rings. The strong blue fluorescence of the CDs increased under strong acidic conditions owing to the changes in the N-groups. These cookie-like CDs are attractive for their potential use as effective fluorescent probes for the sensitive detection of aqueous H+ and Fe3+.A fluorescent carbon dot with a cookie-with-chocolate film structure (about 5 × 5 μm2) showed a high fluorescence quantum yield (61.12%) at low pH. It was hydrothermally synthesized from l-serine and l-tryptophan. The formation mechanism of the film with carbon dots (CDs) was investigated. The film structure was formed by hydrogen bonding and π-π stacking interactions between aromatic rings. The strong blue fluorescence of the CDs increased under strong acidic conditions owing to the changes in the N-groups. These cookie-like CDs are attractive for their potential use as effective fluorescent probes for the sensitive detection of aqueous H+ and Fe3+. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03965c

  7. Interference effects in a double quantum dot system with inter-dot Coulomb correlations

    International Nuclear Information System (INIS)

    Electron transport through a double quantum dot system is studied with the use of the Green function formalism based on the equation of motion method, and an interplay between interference and Coulomb blockade effects due to inter-dot correlations is discussed. A double structure with two Fano resonances (or antiresonances) is found in the conductance spectrum. Fano features are weakly influenced by the presence of Coulomb interaction but the conductance is strongly suppressed in the energy region with the Fermi level in the leads close to the aligned levels of both dots. This Coulomb blockade effect takes place when the coupling between the dots is of repulsive character. On the other hand, the conductance of an artificial molecule with attractive inter-dot coupling is only slightly modified in this energy region. As a sign of the coupling can be easily changed in a presence of an external magnetic field by changes of the magnetic flux there is the possibility to control variations of the conductance, which may be important from the application point of view

  8. 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.

  9. Barrier Li Quantum Dots in Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    LIU Yi-Min; LI Xiao-Zhu; YAN Wen-Hong; BAO Cheng-Guang

    2003-01-01

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

  10. Facile labeling of lipoglycans with quantum dots

    International Nuclear Information System (INIS)

    Bacterial endotoxins or lipopolysaccharides (LPS) are among the most potent activators of the innate immune system, yet mechanisms of their action and in particular the role of glycans remain elusive. Efficient non-invasive labeling strategies are necessary for studying interactions of LPS glycans with biological systems. Here we report a new method for labeling LPS and other lipoglycans with luminescent quantum dots. The labeling is achieved by partitioning of hydrophobic quantum dots into the core of various LPS aggregates without disturbing the native LPS structure. The biofunctionality of the LPS-Qdot conjugates is demonstrated by the labeling of mouse monocytes. This simple method should find broad applicability in studies concerned with visualization of LPS biodistribution and identification of LPS binding agents.

  11. 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...

  12. Quantum features of semiconductor quantum dots

    International Nuclear Information System (INIS)

    The exact solutions of the two-dimensional Schrodinger equation with the position-dependent mass for the square well potential in the semiconductor quantum dots system are obtained. The eigenvalues, which are closely related to the position-dependent masses μ1 and μ2, the potential well depth V0 and the radius of the quantum dots r0, can be calculated from two boundary conditions. We generalize this quantum system to three-dimensional case. The special cases for the angular momentum quantum number l=0, 1, 2 are studied in some detail. We find that the energy levels are proportional to the parameters μ2, V0 and r0 for l=0. The relations between them for l=1, 2 become very complicated. The scattering states of this quantum system are mentioned briefly

  13. Quantum dot/glycol chitosan fluorescent nanoconjugates

    Science.gov (United States)

    Mansur, Alexandra AP; Mansur, Herman S.

    2015-04-01

    In this study, novel carbohydrate-based nanoconjugates combining chemically modified chitosan with semiconductor quantum dots (QDs) were designed and synthesised via single-step aqueous route at room temperature. Glycol chitosan (G-CHI) was used as the capping ligand aiming to improve the water solubility of the nanoconjugates to produce stable and biocompatible colloidal systems. UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were used to characterise the synthesis and the relative stability of biopolymer-capped semiconductor nanocrystals. The results clearly demonstrated that the glycol chitosan derivative was remarkably effective at nucleating and stabilising semiconductor CdS quantum dots in aqueous suspensions under acidic, neutral, and alkaline media with an average size of approximately 2.5 nm and a fluorescent activity in the visible range of the spectra.

  14. Thermal annealing of selected individual quantum dots

    International Nuclear Information System (INIS)

    Cathodoluminescence spectra of single InAs/GaAs quantum dots were recorded before and after consecutive thermal annealing steps. The annealing process leads to an overall blueshift of the spectra indicating In/Ga interdiffusion. Excitonic fine-structure splitting and binding energies of charged and neutral excitonic complexes were monitored. A drastic reduction of the fine-structure splitting from 170 μeV to less than 20 μeV can be observed accompanied by a change of the character of the biexciton from anti-binding to binding with respect to the exciton. Tailoring the fine-structure splitting is especially important for the use of single quantum dots in opto-electronic devices for quantum key distribution where a degeneracy of the exciton ground state (i.e. a fine-structure splitting below the homogeneous linewidth) is required for the on-demand production of entangled photon pairs

  15. Many electron effects in semiconductor quantum dots

    Indian Academy of Sciences (India)

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

    2003-01-01

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

  16. Protease-activated quantum dot probes

    Science.gov (United States)

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

    2006-04-01

    We demonstrate a novel quantum dot based probe with inherent signal amplification upon interaction with a targeted proteolytic enzyme. This probe may be useful for imaging in cancer detection and diagnosis. In this system, quantum dots (QDs) are bound to gold nanoparticles (AuNPs) via a proteolytically-degradable peptide sequence to non-radiatively suppress luminescence. A 71% reduction in luminescence was achieved with conjugation of AuNPs to QDs. Peptide cleavage results in release of AuNPs and restores radiative QD photoluminescence. Initial studies observed a 52% rise in luminescence over 47 hours of exposure to 0.2 mg/mL collagenase. These probes can be customized for targeted degradation simply by changing the sequence of the peptide linker.

  17. 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.

  18. Light emission from Si quantum dots

    Directory of Open Access Journals (Sweden)

    Philippe M. Fauchet

    2005-01-01

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

  19. Magnetoconductance fluctuations in open bismuth quantum dots

    Science.gov (United States)

    Hackens, B.; Minet, J. P.; Farhi, G.; Crahay, A.; Faniel, S.; Gustin, C.; Bayot, V.

    2002-03-01

    We investigate the low temperature (300 mK - 10 K) magnetoconductance of open circular bismuth quantum dots (diameter: 500 nm). The structures are fabricated using a combination of electron beam lithography, lift off and plasma etching techniques on bismuth thin films evaporated on heated SiO2 substrates. We observe reproducible magnetoconductance fluctuations (UCFs) up to 5T, qualitatively similar to conductance fluctuations evidenced in open quantum dots patterned in high mobility semiconductor heterostructures. In our samples, UCFs are superposed on a slowly varying negative magnetoconductance background. We also observe a sharp conductance maximum centered in B=0, which is reminescent of the spin-orbit induced anti-localisation phenomenon. The behavior of UCFs and of the conductance maximum is discussed as a function of the temperature, thickness and degree of cristallinity of the cavity.

  20. Trajectory phases of a quantum dot model

    International Nuclear Information System (INIS)

    We present a thermodynamic formalism to study the trajectories of charge transport through a quantum dot coupled to two leads in the resonant-level model. We show that a close analogue of equilibrium phase transitions exists for the statistics of transferred charge; by tuning an appropriate ‘counting field’, crossovers to different trajectory phases are possible. Our description reveals a mapping between the statistics of a given device and current measurements over a range of devices with different dot–lead coupling strengths. Furthermore insight into features of the trajectory phases are found by studying the occupation of the dot conditioned on the transported charge between the leads; this is calculated from first principles using a trajectory biased two-point projective measurement scheme. (paper)

  1. Ratiometric Temperature Sensing with Semiconducting Polymer Dots

    OpenAIRE

    Ye, Fangmao; Wu, Changfeng; Jin, Yuhui; Chan, Yang-Hsiang; Zhang, Xuanjun; Chiu, Daniel T.

    2011-01-01

    This communication describes ultra-bright single-nanoparticle ratiometric temperature sensors based on semiconducting polymer dots (Pdots). We attached the temperature sensitive dye—Rhodamine B (RhB), whose emission intensity decreases with increasing temperature—within the matrix of Pdots. The as-prepared Pdot-RhB nanoparticle showed excellent temperature sensitivity and high brightness because it took advantage of the light harvesting and amplified energy transfer capability of Pdots. More ...

  2. Lyophilization of Semiconducting Polymer Dot Bioconjugates

    OpenAIRE

    Sun, Wei; Ye, Fangmao; Gallina, Maria E.; Yu, Jiangbo; Wu, Changfeng; Chiu, Daniel T.

    2013-01-01

    Semiconducting polymer dot (Pdot) bioconjugates are a new class of ultrabright fluorescent probes. Here, we report a procedure for lyophilizing Pdot bioconjugates so that they successfully retain their optical properties, colloidal stability, and cell-targeting capability during storage. We found that when Pdot bioconjugates were lyophilized in the presence of 10% sucrose, the rehydrated Pdot bioconjugates did not show any signs of aggregation and exhibited the same hydrodynamic diameters as ...

  3. SPECTRAL PROPERTIES OF SHUNGITE QUANTUM DOTS

    OpenAIRE

    RAZBIRIN B.S.; ROZHKOVA N.N.; Sheka, E. F.; Nelson, D. K.; Starukhin, A. N.; Goryunov, A. S.

    2014-01-01

    A low-temperature study has been performed for aqueous shungite, carbon tetrachloride, and toluene dispersions. Spectral characteristics for graphene quantum dots (GQDs) of shungite, attributed to individual fragments of reduced graphene oxide (rGO), reveal a dual character of the dispersions emitting centers: individual GQDs are responsible for the spectra position while fractal structure of GQD colloids provides large broadening of the spectra due to structural inhomogeneity of the colloida...

  4. 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.

  5. Quantum dot/glycol chitosan fluorescent nanoconjugates

    OpenAIRE

    Mansur, Alexandra AP; Mansur, Herman S.

    2015-01-01

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

  6. Kondo Effect in Mesoscopic Quantum Dots

    OpenAIRE

    Grobis, M.; Rau, I. G.; Potok, R. M.; Goldhaber-Gordon, D.

    2006-01-01

    A dilute concentration of magnetic impurities can dramatically affect the transport properties of an otherwise pure metal. This phenomenon, known as the Kondo effect, originates from the interactions of individual magnetic impurities with the conduction electrons. Nearly a decade ago, the Kondo effect was observed in a new system, in which the magnetic moment stems from a single unpaired spin in a lithographically defined quantum dot, or artificial atom. The discovery of the Kondo effect in a...

  7. Shot noise of coupled semiconductor quantum dots

    OpenAIRE

    Kiesslich, G.; Wacker, A; Schoell, E.

    2003-01-01

    The low-frequency shot noise properties of two electrostatically coupled semiconductor quantum dot states which are connected to emitter/collector contacts are studied. A master equation approach is used to analyze the bias voltage dependence of the Fano factor as a measure of temporal correlations in tunneling current caused by Pauli's exclusion principle and the Coulomb interaction. In particular, the influence of the Coulomb interaction on the shot noise behavior is discussed in detail and...

  8. Semiconductor Quantum Dots for Biomedicial Applications

    OpenAIRE

    Lijia Shao; Feng Yan; Yanfang Gao

    2011-01-01

    Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can...

  9. Quantum dots: synthesis, bioapplications, and toxicity

    OpenAIRE

    Valizadeh, Alireza; Mikaeili, Haleh; Samiei, Mohammad; Farkhani, Samad Mussa; Zarghami, Nosratalah; Kouhi, Mohammad; Akbarzadeh, Abolfazl; Davaran, Soodabeh

    2012-01-01

    This review introduces quantum dots (QDs) and explores their properties, synthesis, applications, delivery systems in biology, and their toxicity. QDs are one of the first nanotechnologies to be integrated with the biological sciences and are widely anticipated to eventually find application in a number of commercial consumer and clinical products. They exhibit unique luminescence characteristics and electronic properties such as wide and continuous absorption spectra, narrow emission spectra...

  10. 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.

  11. The quantum dot nanoconjugate tool box (Invited Paper)

    Science.gov (United States)

    Tomlinson, I. D.; Wright, D. W.; Giorgio, T. D.; Blakely, R. D.; Pennycook, S. J.; Hercules, D.; Bentzen, L.; Smith, R. A.; McBride, J.; Vergne, M. J.; Rosenthal, S.

    2005-04-01

    The surface coating of quantum dots has been characterised using Z-stem. Quantum dots have been pegylated to increase stability in aqueous solution. The fluorescence intensity of the quantum dots was modulated pegylation. PEG was coupled using different ratios of EDC, PEG and NHS. Optimum coupling conditions were found to occur when 2000 equivalents of PEG were reacted with 1 equivalent of dot in the presence of 1500 equivalents of NHS and EDC. Angiotensin II was also conjugated to quantum dots and these conjugates were shown to be biologically active. Quantum dots have also been surface functionalised with other peptides such as NGR with subsequent demonstration of cell surface binding and can be characterized by flow cytometry.

  12. 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

  13. Thermodynamic properties of a quantum Hall anti-dot interferometer

    Science.gov (United States)

    Levy Schreier, Sarah; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.

    2016-02-01

    We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov-Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.

  14. Modified magnetic quantum dot with electric confining potentials

    International Nuclear Information System (INIS)

    The electronic properties of a modified magnetic quantum dot are studied. The modified magnetic quantum dot is a quantum structure that is formed by spatially inhomogeneous distributions of magnetic fields. Electrons are magnetically confined to the plane where the magnetic fields inside and outside the dot are different from each other. The energy spectrum exhibits quite different features depending on the directions of the magnetic fields inside and outside the dot. In particular, the case of opposite directions of the fields is more interesting than that of the same direction. An electrostatic potential is introduced to the system to study the effects of an electric confining potential on the eigenenergy of a single electron in the modified magnetic quantum dot. The additional potential raises the whole energy spectrum and changes its shape. The ground-state angular momentum transitions occurring in a bare modified magnetic quantum dot disappear on introduction of the additional parabolic potential

  15. Controlling quantum dot energies using submonolayer bandstructure engineering

    International Nuclear Information System (INIS)

    We demonstrate control of energy states in epitaxially-grown quantum dot structures formed by stacked submonolayer InAs depositions via engineering of the internal bandstructure of the dots. Transmission electron microscopy of the stacked sub-monolayer regions shows compositional inhomogeneity, indicative of the presence of quantum dots. The quantum dot ground state is manipulated not only by the number of deposited InAs layers, but also by control of the thickness and material composition of the spacing layers between submonolayer InAs depositions. In this manner, we demonstrate the ability to shift the quantum dot ground state energy at 77 K from 1.38 eV to 1.88 eV. The results presented offer a potential avenue towards enhanced control of dot energies for a variety of optoelectronic applications.

  16. Quantum Dot Device Design Optimization for Resonator Coupling

    Science.gov (United States)

    King, Cameron; Coppersmith, S. N.; Friesen, Mark

    Coupling a semiconductor quantum dot qubit to a superconducting resonator broadens the possibilities for interqubit communication and potentially allows integration of quantum dots with other qubit systems. The major technological hurdle that must be overcome is reaching the strong coupling limit, where the coupling frequency between the resonator and the qubit is larger than both the qubit decoherence rate and the photon loss rate of the resonator. In this work, we examine optimization of the quantum dot device design. Using the Thomas-Fermi approximation in conjunction with a metallic dot capacitive model, we focus on improving the capacitive coupling between a resonator gate and a quantum dot while decreasing the cross-coupling to nearby dots. Through these simulations, we find that the optimization follows an intuitive geometric relation. This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), and ONR (N00014-15-1-0029).

  17. 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.

  18. Controlled coupling of quantum dots to nanowire plasmons

    International Nuclear Information System (INIS)

    Full text: The diameter of dielectric waveguides is limited by the wavelength of the guided light. In contrast, gold and silver nanowires can sustain propagating plasmon modes even for significantly smaller dimensions. Furthermore the strong eld localization of the nanowire plasmon modes leads to a strong interaction with nearby quantum emitters such as quantum dots. We use electron beam lithography, rst, to fabricate silver nanowires and, second, to position a few dots close to one nanowire end in a template-assisted process. Scanning a focused laser spot over the nanowire ends, we demonstrate both, the excitation of nanowire modes by quantum dots and the addressing of the same dots by plasmons. We use the fluorescence signals to quantify the quantum dots/plasmon coupling and show that part of the plasmon-induced dot fluorescence couples back to plasmonic modes. (author)

  19. Quantum Dots and Their Multimodal Applications: A Review

    Directory of Open Access Journals (Sweden)

    Paul H. Holloway

    2010-03-01

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

  20. The quantum Hall effect in quantum dot systems

    International Nuclear Information System (INIS)

    It is proposed to use quantum dots in order to increase the temperatures suitable for observation of the integer quantum Hall effect. A simple estimation using Fock-Darwin spectrum of a quantum dot shows that good part of carriers localized in quantum dots generate the intervals of plateaus robust against elevated temperatures. Numerical calculations employing local trigonometric basis and highly efficient kernel polynomial method adopted for computing the Hall conductivity reveal that quantum dots may enhance peak temperature for the effect by an order of magnitude, possibly above 77 K. Requirements to potentials, quality and arrangement of the quantum dots essential for practical realization of such enhancement are indicated. Comparison of our theoretical results with the quantum Hall measurements in InAs quantum dot systems from two experimental groups is also given

  1. Central dot sign in entities other than Caroli disease

    International Nuclear Information System (INIS)

    The purpose of this study was to describe central dot sign (tiny dots with strong contrast enhancement of the portal vein within dilated hepatic bile ducts on computed tomography) in entities other than Caroli disease, especially in peribiliary cysts with or without autosomal-dominant polycystic kidney disease. Computed tomography in 74 cases of peribiliary cysts and 134 cases of other liver diseases and states possibly showing central dot sign were retrospectively reviewed to examine the central dot sign. In three cases of peribiliary cysts, some part of the liver showed strongly enhanced portal radicles surrounded completely or partially by low-attenuation, enlarged peribiliary cysts, presenting ''central dot sign'' on contrast-enhanced computed tomography. We suggest that in addition to Caroli disease, some other entities and diseases of the liver may demonstrate central dot sign and this sign should not be considered a specific finding of Caroli disease. (author)

  2. Central dot sign in entities other than Caroli disease

    Energy Technology Data Exchange (ETDEWEB)

    Ahmadi, T.; Itai, Yuji [Tsukuba Univ., Ibaraki (Japan). Inst. of Clinical Medicine; Minami, Manabu

    1997-11-01

    The purpose of this study was to describe central dot sign (tiny dots with strong contrast enhancement of the portal vein within dilated hepatic bile ducts on computed tomography) in entities other than Caroli disease, especially in peribiliary cysts with or without autosomal-dominant polycystic kidney disease. Computed tomography in 74 cases of peribiliary cysts and 134 cases of other liver diseases and states possibly showing central dot sign were retrospectively reviewed to examine the central dot sign. In three cases of peribiliary cysts, some part of the liver showed strongly enhanced portal radicles surrounded completely or partially by low-attenuation, enlarged peribiliary cysts, presenting ``central dot sign`` on contrast-enhanced computed tomography. We suggest that in addition to Caroli disease, some other entities and diseases of the liver may demonstrate central dot sign and this sign should not be considered a specific finding of Caroli disease. (author)

  3. Ac response of a coupled double quantum dot

    Institute of Scientific and Technical Information of China (English)

    Xu Jie; W.Z. Shangguan; Zhan Shi-Chang

    2005-01-01

    The effect of phase-breaking process on the ac response of a coupled double quantum dot is studied in this paper based on the nonequilibrium Green function formalism. A general expression is derived for the ac current in the presence of electron-phonon interaction. The ac conductance is numerically computed and the results are compared with those in [Anatram M P and Datts S 1995 Phys. Rev. B 51 7632]. Our results reveal that the inter-dot electron tunnelling interplays with that between dots and electron reservoirs, and contributes prominently to the ac current when inter-dot tunnelling coupling is much larger than the tunnelling coupling between dots and electron reservoirs. In addition, the phase-breaking process is found to have a significant effect on the ac transport through the coupled double dot.

  4. The role of strain-driven in migration in the growth of self-assembled InAs quantum dots on InP

    CERN Document Server

    Yoon, S H; Lee, T W; Hwang, H D; Yoon, E J; Kim, Y D

    1999-01-01

    Self-assembled InAs quantum dots (SAQDs) were grown on InP by metalorganic chemical vapor deposition. The amount of excess InAs and the aspect ratio of the SAQD increased with temperature and V/III ratio. It is explained that the As/P exchange reaction at the surface played an important role in the kinetics of SAQD formation. Insertion of a lattice-matched InGaAs buffer layer suppressed the excess InAs formation, and lowered the aspect ratio. Moreover, the dots formed on InGaAs buffer layers were faceted, whereas those on InP were hemispherical, confirming the effect of the As/P exchange reaction. The shape of InAs quantum dots on InGaAs buffer layers was a truncated pyramid with four [136] facets and base edges parallel to directions.

  5. Study of inter-dot coupling in nano-patterned permalloy dots array

    International Nuclear Information System (INIS)

    We present a series of studies on interdot coupling in the nanometer-scaled permalloy dots array. A standard electron beam lithography in conjunction with lift-off process was employed for patterning 30 nm thick of millions of permalloy dots array with diameter (D) of 500 nm and the aspect ratio S/D of spacing (S) to diameter ranging from 0.2 to 1.25. The magnetization reversal processes were identified to evolve through the vortex nucleation, movement, and annihilation based on magnetic force microscopy (MFM) imaging in the presence of external magnetic fields. The nucleation field, annihilation field, and moving rate of vortex core were analyzed using M-H loops measured by the alternating gradient magnetometer (AGM). These behaviors are associated with the dipole-dipole interaction in dots array with various interdot spacings.

  6. InAs/InP quantum dots: from single to coupled dots applications

    Energy Technology Data Exchange (ETDEWEB)

    Cornet, C.; Dore, F.; Even, J.; Loualiche, S. [LENS-UMR FOTON 6082 au CNRS, INSA de Rennes, 20 Avenue des Buttes de Coesmes, 35043 Rennes Cedex (France); Schliwa, A.; Bimberg, D. [Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); Hayne, M.; Moshchalkov, V.V. [INPAC, Pulsed Fields Group, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Chauvin, N.; Bremond, G.; Bru-Chevallier, C. [LPM-UMR CNRS 5511, INSA de Lyon, 69621 Villeurbanne Cedex (France); Gendry, M. [LEOM-UMR CNRS 5512, Ecole centrale de Lyon, 69134 Ecully Cedex (France)

    2006-07-01

    We report a brief overview of recent research developments on InAs/InP quantum dots (QDs). Eight-band k . p calculations are performed on single InAs/InP QDs, and the impact of substrate orientation ((311)B or (100)) on electronic and optical properties is studied. A configuration interaction model is used to determine few-particle states of these dots and a comparison with micro-photoluminescence experiments on single InAs/InP QDs is made. It is then demonstrated that high QDs density can be reached on such a system, leading to lateral coupling between dots. Calculations and (magnetophoto-) (photo-) (electro-) luminescence experiments are used to demonstrate that the lateral coupling leads to miniband effects, and to a better charge carrier redistribution between QDs for laser applications. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. InAs/InP quantum dots: from single to coupled dots applications

    International Nuclear Information System (INIS)

    We report a brief overview of recent research developments on InAs/InP quantum dots (QDs). Eight-band k . p calculations are performed on single InAs/InP QDs, and the impact of substrate orientation ((311)B or (100)) on electronic and optical properties is studied. A configuration interaction model is used to determine few-particle states of these dots and a comparison with micro-photoluminescence experiments on single InAs/InP QDs is made. It is then demonstrated that high QDs density can be reached on such a system, leading to lateral coupling between dots. Calculations and (magnetophoto-) (photo-) (electro-) luminescence experiments are used to demonstrate that the lateral coupling leads to miniband effects, and to a better charge carrier redistribution between QDs for laser applications. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Nonlinear transport in coupled quantum dots: A stationary probability approach

    Institute of Scientific and Technical Information of China (English)

    GONG JianPing; DUAN SuQing; YAN WeiXian; ZHAO XianGeng

    2009-01-01

    The stationary tunneling current and differential conductance of the coupled quantum dots system with split-gates are calculated by generalizing the Beenaker's linear response theory for the description of the Coulomb-blockade oscillations of the conductance in the single quantum dot. The calculation of the charging diagram in parallel through the double dot as function of the two side-gate voltages shows a remarkable agreement with the recent experimental results by Hatano et al. (Science, 2005, 309: 268-271)

  9. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    OpenAIRE

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

    2016-01-01

    We present a novel reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consist of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired...

  10. Exciton dephasing in single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    2000-01-01

    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. The ho...... 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....

  11. Unraveling the mesoscopic character of quantum dots in nanophotonics

    OpenAIRE

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

    2014-01-01

    We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. At the microscopic level the deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, w...

  12. Induced quantum dots and wires: electron storage and delivery

    OpenAIRE

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

    2007-01-01

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

  13. Thermodynamic properties of a quantum Hall anti-dot interferometer

    OpenAIRE

    Schreier, Sarah Levy; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.

    2015-01-01

    We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop....

  14. Recent advances in carbon-based dots for electroanalysis.

    Science.gov (United States)

    Yulong, Ying; Xinsheng, Peng

    2016-04-25

    Carbon-based dots represent a new type of quantum dot with unique and well-defined properties owing to their quantum confinement and edge effects, which are widely employed in sensing, light-emitting diodes, nanomedicine, photocatalysis, electrocatalysis, bioimaging, etc. In this review, we update the latest research results of carbon-based dots in this rapidly evolving field of electroanalysis, place emphases on their applications as sensors and give future perspectives for developing more smart sensors. PMID:26797087

  15. Mid-infrared active PbTe/CdTe quantum dots: growth, optical properties and device applications

    International Nuclear Information System (INIS)

    The mid-infrared spectral region is of high interest for the field of molecular gas spectroscopy as most strong molecular absorption lines lie within this region. Applications of gas analysis are very widespread. For mid-infrared optoelectronic devices, the IV-VI or lead salt compounds are very well suited as these materials have almost mirror-like conduction and valence bands as well as low non-radiative Auger recombination rates. The use of quantum dots as active regions in such devices enables enhanced device performance because the reduction of the dimensionalty to zero results in discrete energy levels and a peaked electronic density of states. In this work, IV-VI PbTe quantum dots embedded in II-VI CdTe are investigated with respect to growth, luminescence and device applications. The dot formation is based on phase separation due to the immiscibility of narrow-gap PbTe and wide-gap CdTe and the minimization of the interface energies. Hence, two-dimensional PbTe layers embedded in CdTe spontaneously split up into isolated nanoprecipitates or quantum dots. The resulting dots are spherically shaped and exhibit atomically sharp interfaces. The miscibility gap arises from the difference in the crystal structure between rocksalt PbTe and zincblende CdTe. The emission wavelenght can be tuned by their size over a broad spectral region from 1.4 - 3.3 mym. The quantum dot size can be adjusted by the inital layer thickness or the PbTe growth temperature. The relation between the dot size and the emission energy was determined and compared to theoretical calculation. From transmission electron microscopy images, the dot size distributions were evaluated and the transition energies were obtained from photoluminescence experiments. The calculation of the transition energy as a function of dot size allows an energy to size conversion of the photoluminescence spectra. Additional control of the emission energy to higher values is obtained by alloying the PbTe quantum dots

  16. Oscillatory instabilities in dc-biased quantum dots

    International Nuclear Information System (INIS)

    We consider a 'quantum dot' in the Coulomb blockade regime, subject to an arbitrarily large source-drain voltage V. When V is small, quantum dots with odd electron occupation display the Kondo effect, giving rise to enhanced conductance. Here we investigate the regime where V is increased beyond the Kondo temperature and the Kondo resonance splits into two components. It is shown that interference between them results in spontaneous oscillations of the current through the dot. The theory predicts the appearance of 'Shapiro steps' in the current-voltage characteristics of an irradiated quantum dot; these would constitute an experimental signature of the predicted effect. (author). Letter-to-the-editor

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

    International Nuclear Information System (INIS)

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

  18. 我是中国DotA的希望(一)

    Institute of Scientific and Technical Information of China (English)

    少小帅

    2010-01-01

    我叫贾鹏我叫贾鹏,我是中国DotA的希望。他们一直这么评价我,而我对此深信不疑。在这个全民DotA的时代,我也不例外。我DotA玩的怎么样,我不好去评价,和我一起DotA的兄弟们是这么评价我的,"前期打得没的说!"邱涵说;"Gank打得没的说!"程龙说;

  19. Carbon Dot Based Sensing of Dopamine and Ascorbic Acid

    OpenAIRE

    Upama Baruah; Neelam Gogoi; Achyut Konwar; Manash Jyoti Deka; Devasish Chowdhury; Gitanjali Majumdar

    2014-01-01

    We demonstrate carbon dot based sensor of catecholamine, namely, dopamine and ascorbic acid. Carbon dots (CDs) were prepared from a green source: commercially available Assam tea. The carbon dots prepared from tea had particle sizes of ∼0.8 nm and are fluorescent. Fluorescence of the carbon dots was found to be quenched in the presence of dopamine and ascorbic acid with greater sensitivity for dopamine. The minimum detectable limits were determined to be 33 μM and 98 μM for dopamine and ascor...

  20. Second-harmonic imaging of semiconductor quantum dots

    DEFF Research Database (Denmark)

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

    2000-01-01

    Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of similar to 885 nm corresponding to the quantum-dot photoluminescence maxim...... further observe that second-harmonic images of the quantum-dot surface structure show wavelength-dependent spatial variations. Imaging at different wavelength is used to demonstrate second-harmonic generation from the semiconductor quantum dots. (C) 2000 American Institute of Physics....

  1. Highly fluorescent xerogels with entrapped carbon dots for organic scintillators

    Energy Technology Data Exchange (ETDEWEB)

    Quaranta, A., E-mail: quaranta@ing.unitn.it [University of Trento, Department of Industrial Engineering, via Mesiano, 77, 38123 Trento (Italy); Laboratori Nazionali di Legnaro, INFN, Viale dell' Università, 2, 35020 Legnaro (PD) (Italy); Carturan, S. [Laboratori Nazionali di Legnaro, INFN, Viale dell' Università, 2, 35020 Legnaro (PD) (Italy); University of Padova, Department of Physics and Astronomy “Galileo Galilei”, Via Marzolo, 8, 35131 Padova (Italy); Campagnaro, A.; Dalla Palma, M. [University of Trento, Department of Industrial Engineering, via Mesiano, 77, 38123 Trento (Italy); Laboratori Nazionali di Legnaro, INFN, Viale dell' Università, 2, 35020 Legnaro (PD) (Italy); Giarola, M.; Daldosso, N. [University of Verona, Department of Informatics, Strada le Grazie,15, 37134 Verona (Italy); Maggioni, G. [Laboratori Nazionali di Legnaro, INFN, Viale dell' Università, 2, 35020 Legnaro (PD) (Italy); University of Padova, Department of Physics and Astronomy “Galileo Galilei”, Via Marzolo, 8, 35131 Padova (Italy); Mariotto, G. [University of Verona, Department of Informatics, Strada le Grazie,15, 37134 Verona (Italy)

    2014-02-28

    Organically modified silicate thin film and bulk samples were prepared using [3-(2-aminoethylamino)propyl]trimethoxysilane (AEAP-TMOS) as precursor with the addition of different amounts of AEAP-TMOS functionalized C-dots, prepared by reaction of AEAP-TMOS and citric acid at high temperature. The synthesis of surface functionalized C-dots was followed by Fourier Transform Infrared (FTIR) spectroscopy, and the C-dots optical properties were characterized by optical absorption and UV–vis fluorescence. Thin xerogel films and bulk samples were studied by FTIR, Raman and fluorescence spectroscopy. Intense blue-green emission was observed by UV excitation of functionalized C-dots. Carbon quantum dot (CQD) luminescence was preserved also in the xerogel matrices, and the energy transfer from the matrix to CQDs, which is a key characteristic for scintillation detectors, was investigated in the two systems. - Highlights: • Functionalized carbon dots were synthesized. • Carbon dots were dispersed in hybrid xerogel bulk and thin film. • Carbon dots exhibit a strong tunable blue luminescence. • Xerogels were characterized by FT-IR, Raman and fluorescence spectroscopies. • Energy transfer processes were evidenced between C-dots and xerogel matrix.

  2. Core–shell quantum dots: Properties and applications

    International Nuclear Information System (INIS)

    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

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

    OpenAIRE

    Chusseau, Laurent; Philippe, Fabrice; Viktorovitch, Pierre; Letartre, Xavier

    2013-01-01

    This paper describes the modeling of quantum dots lasers with the aim of assessing the conditions for stable cw dual-mode operation when the mode separation lies in the THz range. Several possible models suited for InAs quantum dots in InP barriers are analytically evaluated, in particular quantum dots electrically coupled through a direct exchange of excitation by the wetting layer or quantum dots optically coupled through the homogeneous broadening of their optical gain. A stable dual-mode ...

  4. 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.

  5. 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.

  6. Emission switching in carbon dots coated CdTe quantum dots driving by pH dependent hetero-interactions

    International Nuclear Information System (INIS)

    Due to the different emission mechanism between fluorescent carbon dots and semiconductor quantum dots (QDs), it is of interest to explore the potential emission in hetero-structured carbon dots/semiconducting QDs. Herein, we design carbon dots coated CdTe QDs (CDQDs) and investigate their inherent emission. We demonstrate switchable emission for the hetero-interactions of the CDQDs. Optical analyses indicate electron transfer between the carbon dots and the CdTe QDs. A heterojunction electron process is proposed as the driving mechanism based on N atom protonation of the carbon dots. This work advances our understanding of the interaction mechanism of the heterostructured CDQDs and benefits the future development of optoelectronic nanodevices with new functionalities

  7. Emission switching in carbon dots coated CdTe quantum dots driving by pH dependent hetero-interactions

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Xiao; Wang, Hao; Yi, Qinghua; Wang, Yun; Cong, Shan; Zhao, Jie; Sun, Yinghui; Zou, Guifu, E-mail: zouguifu@suda.edu.cn, E-mail: jiexiong@uestc.edu.cn [College of Physics, Optoelectronics and Energy and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Qian, Zhicheng [School of Electronic and Information Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Huang, Jianwen; Xiong, Jie, E-mail: zouguifu@suda.edu.cn, E-mail: jiexiong@uestc.edu.cn [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Luo, Hongmei [Department of Chemical and Materials Engineering, New Mexico State University, Las Cruces, New Mexico 88003 (United States)

    2015-11-16

    Due to the different emission mechanism between fluorescent carbon dots and semiconductor quantum dots (QDs), it is of interest to explore the potential emission in hetero-structured carbon dots/semiconducting QDs. Herein, we design carbon dots coated CdTe QDs (CDQDs) and investigate their inherent emission. We demonstrate switchable emission for the hetero-interactions of the CDQDs. Optical analyses indicate electron transfer between the carbon dots and the CdTe QDs. A heterojunction electron process is proposed as the driving mechanism based on N atom protonation of the carbon dots. This work advances our understanding of the interaction mechanism of the heterostructured CDQDs and benefits the future development of optoelectronic nanodevices with new functionalities.

  8. SMM DotA大赛结束中国DotA战队囊括三甲

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    11月27至29日,国外著名DotA大赛Sendi Mutiara Multimedia Grand National DotA Tournament:Grand Firlals 2009(以下简称SMM09)在马来西亚马六甲州进行了为期三天的精彩大战.最终来自中国的三支战队sGty、cD、EHOME囊括三甲。成为SMM09的最大赢家。

  9. High-efficiency aqueous-solution-processed hybrid solar cells based on P3HT dots and CdTe nanocrystals.

    Science.gov (United States)

    Yao, Shiyu; Chen, Zhaolai; Li, Fenghong; Xu, Bin; Song, Jiaxing; Yan, Lulin; Jin, Gan; Wen, Shanpeng; Wang, Chen; Yang, Bai; Tian, Wenjing

    2015-04-01

    Without using any environmentally hazardous organic solution, we fabricated hybrid solar cells (HSCs) based on the aqueous-solution-processed poly(3-hexylthiophene) (P3HT) dots and CdTe nanocrystals (NCs). As a novel aqueous donor material, the P3HT dots are prepared through a reprecipitation method and present an average diameter of 2.09 nm. When the P3HT dots are mixed with the aqueous CdTe NCs, the dependence of the device performance on the donor-acceptor ratio shows that the optimized ratio is 1:24. Specifically, the dependence of the device performance on the active-layer thermal annealing conditions is investigated. As a result, the optimized annealing temperature is 265 °C, and the incorporation of P3HT dots as donor materials successfully reduced the annealing time from 1 h to 10 min. In addition, the transmission electron microscopy and atomic force microscopy measurements demonstrate that the size of the CdTe NCs increased as the annealing time increased, and the annealing process facilitates the formation of a smoother interpenetrating network in the active layer. Therefore, charge separation and transport in the P3HT dots:CdTe NCs layer are more efficient. Eventually, the P3HT dots:CdTe NCs solar cells achieved 4.32% power conversion efficiency. The polymer dots and CdTe NCs based aqueous-solution-processed HSCs provide an effective way to avoid a long-time thermal annealing process of the P3HT dots:CdTe NCs layer and largely broaden the donor materials for aqueous HSCs. PMID:25781480

  10. Intersubband Electronic Properties of InAs/GaAs Quantum Dot Molecules with Horizontal Spacer

    OpenAIRE

    A. Khaledi-Nasab; Shahzadeh, M.; Amouzegar, H.; Sabaeian, M.

    2013-01-01

    In this work the intersubband electronic properties of two laterally coupled dome-shaped InAs/GaAs quantum dots were investigated. The envelope functions and eigenenergies were calculated as function of distance between the dots. The coupling between the dots was studied using transition lifetime between the dots. The results showed that in close distances (smaller than 3 nm) the quantum dots are coupled and by increasing the distance transition lifetime fall down drastically and the dots bec...

  11. Homogeneous linewidth of self-assembled III-V quantum dots observed in single-dot photoluminescence

    DEFF Research Database (Denmark)

    Leosson, K.; Birkedal, Dan; Magnúsdóttir, Ingibjörg; Langbein, W.; Hvam, Jørn Märcher

    2003-01-01

    We report photoluminescence emission from single self-assembled InAlGaAs quantum dots, which is broadened purely by dephasing processes. We observe linewidths as low as 6+/-3@meV at 10K, which agrees with the homogeneous linewidth derived from four-wave mixing experiments. By selecting dots that...... are not affected by local field fluctuations and using high-energy excitation, we avoid additional sources of linewidth broadening typically present in single-dot photoluminescence spectra. We observe a strong LO-phonon coupling in InAlGaAs and InGaAs dots, which becomes the dominating contribution to...

  12. The Effectiveness of Family-Based DOTS versus Professional-Family Mix DOTS in Treating Smears Positive Tuberculosis

    Directory of Open Access Journals (Sweden)

    Hassan Yekrang Sis

    2014-07-01

    Full Text Available Background: The present study compared the effectiveness of Family-Based DOTS (FB-DOTS versus Professional-Family Mix DOTS (PFM-DOTS in smear positive tuberculosis (TB patients. Methods: This semi-experimental study was performed in Tuberculosis and Lung Diseases Research Center of Tabriz in 2011-2012, among 57 TB patients recruited into either FB-DOTS or PFM-DOTS groups. At the baseline of the study, knowledge of both patients and their supervisors were assessed while at the end point, smear and culture of sputum, quality of life, knowledge and satisfaction of the patients along with the knowledge and satisfaction of their super-visors were assessed. Results: The difference for sputum smear negative (culture was 16.2 (4.8% and 7.7(6.9% for the PFM-DOTS in comparison with FB DOTS by the end of the second and forth months of treatment, respectively. A significant difference was observed between the two groups in relation to knowledge, satisfaction (patients and supervisors and all four domains of quality of life: physical health (P=0.036, psychological health (P<0.001, social relations (P=0.026 and environmental health (P<0.001. Conclusion: The PFM-DOTS treatment strategy in which health experts follow the patients in their homes seems to be among most appropriate strategies in treating TB.

  13. Optical and structural properties of ensembles of colloidal Ag{sub 2}S quantum dots in gelatin

    Energy Technology Data Exchange (ETDEWEB)

    Ovchinnikov, O. V., E-mail: Ovchinnikov-O-V@rambler.ru; Smirnov, M. S. [Voronezh State University (Russian Federation); Shapiro, B. I. [Moscow State University of Fine Chemical Technologies (Russian Federation); Shatskikh, T. S.; Perepelitsa, A. S.; Korolev, N. V. [Voronezh State University (Russian Federation)

    2015-03-15

    The size dependences of the absorption and luminescence spectra of ensembles of hydrophilic colloidal Ag{sub 2}S quantum dots produced by the sol-gel method and dispersed in gelatin are analyzed. By X-ray diffraction analysis and transmission electron microscopy, the formation of core/shell nanoparticles is detected. The characteristic feature of the nanoparticles is the formation of crystalline cores, 1.5–2.0 nm in dimensions, and shells of gelatin and its complexes with the components of synthesis. The observed slight size dependence of the position of infrared photoluminescence bands (in the range 1000–1400 nm) in the ensembles of hydrophilic colloidal Ag{sub 2}S quantum dots is explained within the context of the model of the radiative recombination of electrons localized at structural and impurity defects with free holes.

  14. MOVPE growth of InAs quantum dots for mid-IR applications

    Institute of Scientific and Technical Information of China (English)

    TANG Xiao-hong; YIN Zong-you; DU An-yan; ZHAO Jing-hua; DENY S

    2006-01-01

    InAs quantum dots (QDs) grown on InxGa1-xAs/InP matrix by low pressure metal organic vapor phase epitaxy (LP-MOVPE) in nitrogen ambient were studied. Formation of the InAs QDs with different growth conditions was investigated. To improve the dot size uniformity,a two-step growth method was used and investigated. It is found that morphology of the InAs QDs formed on such InxGa1-xAs/InP matrix is very sensitive to the growth conditions. InAs QDs with high density of 1.3×1010 cm-2 are grown by using S-K growth method with fast growth rate. Using the two-step growth method,the InAs QDs size uniformity improves by 63% and 110% compared that of the dots grown by ordinary S-K method and ALE method,respectively. Narrow photoluminescence (PL) emission spectrum of the QDs grown by using the two-step growth method is received. FWHM of the PL curve is measured at 26 meV and the peak emission wavelength is larger than 2.3 μm at 77 K.

  15. Optical spin control in charged quantum dots with a single Mn atom

    International Nuclear Information System (INIS)

    In semiconductor quantum dots spins bear good prospects as basic elements for new quantum hardware such as quantum bits. In a single quantum dot containing a single Mn atom charged by an electron (hole) the excitation by laser light causes the formation of a trion complex, i.e. a positively or negatively charged exciton. The trion spin, like the carrier spin in the non-excited state, is coupled to the Mn spin via the exchange interaction. This coupling allows for the manipulation of the optically not directly accessible Mn spin via spin flip processes of either the electron (hole) or the trion and thus ultimately for the manipulation of the Mn spin by laser light. We consider a charged CdTe quantum dot doped with a single Mn atom and focus on electron and light hole processes as heavy holes do not induce spin flips. Starting from a well defined initial state we show that the six Mn spin states can be set by a series of ultrashort laser pulses. Thus besides the electron (hole)/trion spin also the Mn spin may be used as a basis for controlled operations in the field of spintronics.

  16. Electric-field controlled ferromagnetism in MnGe magnetic quantum dots

    Directory of Open Access Journals (Sweden)

    Faxian Xiu

    2011-03-01

    Full Text Available Electric-field control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and non-volatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (Tc>300 K and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs, materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metal-oxide-semiconductor (CMOS technology. Here, we review recent reports on the development of high-Curie temperature Mn0.05Ge0.95 quantum dots (QDs and successfully demonstrate electric-field control of ferromagnetism in the Mn0.05Ge0.95 quantum dots up to 300 K. Upon the application of gate-bias to a metal-oxide-semiconductor (MOS capacitor, the ferromagnetism of the channel layer (i.e. the Mn0.05Ge0.95 quantum dots was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism.

  17. Stellar formation

    CERN Document Server

    Reddish, V C

    1978-01-01

    Stellar Formation brings together knowledge about the formation of stars. In seeking to determine the conditions necessary for star formation, this book examines questions such as how, where, and why stars form, and at what rate and with what properties. This text also considers whether the formation of a star is an accident or an integral part of the physical properties of matter. This book consists of 13 chapters divided into two sections and begins with an overview of theories that explain star formation as well as the state of knowledge of star formation in comparison to stellar structure

  18. Electron charging in epitaxial germanium quantum dots on silicon (100)

    Science.gov (United States)

    Ketharanathan, Sutharsan

    The electron charging behavior of self assembled epitaxial Ge quantum dots on Si(100) grown using molecular beam epitaxy has been studied. Ge quantum dots encapsulated in n-type Si matrix were incorporated into Schottky diodes to investigate their charging behavior using capacitance-voltage measurements. These experimental results were interpreted in the context of theoretical models to assess the degree of charge localization to the dot. Experiments involving Ge quantum dot growth, growth of Sb-doped Si and morphological evolution during encapsulation of the Ge dots during Si overgrowth were performed in order to optimize the conditions for obtaining distinct Ge quantum dot morphologies. This investigation included finding a suitable method to minimize Sb segregation while maintaining good dot epitaxy and overall crystal quality. Holes are confined to the Ge dots for which the valence band offsets are large (˜650 meV). Electrons are confined to the strained Si regions adjacent to the Ge quantum dots which have relatively smaller confinement potentials (˜100--150 meV). Experimentally, it was found that but and pyramid clusters in the range from 20--40 nm in diameter confine ˜1electron per dot while dome clusters in the range from 60--80 nm diameter confine ˜6--8 electrons per dot. Theoretical simulations predict that similar pyramid structures confine ˜0.4 electrons per dot and dome structures confine ˜2.2--3 electrons per dot. Even though the theory and the experimental results disagree due to various uncertainties and approximations, the ratio between theory and experiment agree remarkably well for both island types. We also investigated constructive three-dimensional nanolithography. Nanoscale Au rich dots and pure Ge dots were deposited on SiO2 and Si3N4 substrates by decomposing adsorbed precursors using a focused electron beam in an environmental transmission electron microscope. Dimethyl acetylacetonate gold was used for Au and digermane was used to

  19. Illuminating microemulsions: ionic liquid-CdS quantum dots hybrid materials as potential white light harvesting systems.

    Science.gov (United States)

    Damarla, Krishnaiah; Bharmoria, Pankaj; Rao, K Srinivasa; Gehlot, Praveen Singh; Kumar, Arvind

    2016-05-01

    Microemulsions (MEs) comprising of 2-hydroxyethylammonium formate, (HO-EAF), isooctane and dioctylsulfosuccinate proliniumisopropylester ([ProC3]AOT) have been constructed and used to prepare and stabilize CdS Quantum Dots (QDs) at room temperature. Such hybrid materials exhibited tunable light emission wherein the photoluminescence chromaticity could be precisely adjusted to pure white with a quantum efficiency (QE) of ∼43%, by adjusting the droplet size of MEs. PMID:27087045

  20. Terbium to Quantum Dot FRET Bioconjugates for Clinical Diagnostics: Influence of Human Plasma on Optical and Assembly Properties

    OpenAIRE

    Niko Hildebrandt; Blanco-Canosa, Juan B.; Dawson, Philip E.; Stewart, Michael H.; Kimihiro Susumu; W. Russ Algar; Frank Morgner; Igor L. Medintz; Daniel Geißler; Stefan Stufler

    2011-01-01

    Förster resonance energy transfer (FRET) from luminescent terbium complexes (LTC) as donors to semiconductor quantum dots (QDs) as acceptors allows extraordinary large FRET efficiencies due to the long Förster distances afforded. Moreover, time-gated detection permits an efficient suppression of autofluorescent background leading to sub-picomolar detection limits even within multiplexed detection formats. These characteristics make FRET-systems with LTC and QDs excellent candidates for clinic...

  1. Galaxy formation

    International Nuclear Information System (INIS)

    Galaxy formation is at the forefront of observation and theory in cosmology. An improved understanding is essential for improving our knowledge both of the cosmological parameters, of the contents of the universe, and of our origins. In these lectures intended for graduate students, galaxy formation theory is reviewed and confronted with recent observational issues. In lecture 1, the following topics are presented: star formation considerations, including IMF, star formation efficiency and star formation rate, the origin of the galaxy luminosity function, and feedback in dwarf galaxies. In lecture 2, we describe formation of disks and massive spheroids, including the growth of supermassive black holes, negative feedback in spheroids, the AGN-star formation connection, star formation rates at high redshift and the baryon fraction in galaxies.

  2. Biphasic quantum dots of cubic and hexagonal Mn doped CdS; necessity of Rietveld analysis

    Energy Technology Data Exchange (ETDEWEB)

    Heiba, Zein K., E-mail: zein_kh@yahoo.com [Ain Shams University, Faculty of Science, Physics Department, Cairo (Egypt); Taif University, Faculty of Science, Physics Department (Saudi Arabia); Mohamed, Mohamed Bakr [Ain Shams University, Faculty of Science, Physics Department, Cairo (Egypt); Imam, N.G. [Experimental Physics Department, Nuclear Research Center, Atomic Energy Authority, 13759 Cairo (Egypt)

    2015-01-05

    Highlights: • Mn{sup 2+} doped CdS quantum dots (QDs) were prepared via a simple chemical synthesis procedure. • Biphasic composite of CdS QDs was revealed with maximum magnetism at 10 at.% of Mn{sup 2+}. • Rietveld structural analysis is a necessity for dealing with nano or quantum dots chalcogenides. • Full investigation of effects of Mn doping on the structural, optical and magnetic parameters. - Abstract: Mn{sup 2+} doped CdS quantum dots (QDs) were prepared via a simple chemical synthesis method. Incorporation of Mn ions into CdS QDs was monitored by structural, magnetic and optical spectroscopy analysis. Although the diffraction patterns seemed to be single wurtzite hexagonal structure, analysis revealed biphasic composite of CdS QDs hexagonal wurtzite and cubic zinc blende. The band gap, crystal phase and the morphology of CdS QDs were found not to be greatly affected by Mn{sup 2+} doping, however there was an optimal Mn{sup 2+} doping content of 10% where the magnetism is maximum. The recorded photoluminescence (PL) emission spectra, excited at 370 nm, depict emission lines in the UV and blue-shift regions. The emission band reveals that the band gap of pure CdS QDs is around 3 eV which is greater than that of bulk CdS (2.42 eV). The band gap of Mn:CdS QDs is almost independent of Mn content (x) and the crystallite size remains almost the same for all values of x. The observed structural, magnetic and optical properties have been explained on the basis of formation of two phases of CdS doped with Mn. This work aims to highlight recent advances in the synthesis of Mn:CdS diluted magnetic semiconductor quantum dots and their wonderful performance.

  3. Aminophosphines: A Double Role in the Synthesis of Colloidal Indium Phosphide Quantum Dots.

    Science.gov (United States)

    Tessier, Mickael D; De Nolf, Kim; Dupont, Dorian; Sinnaeve, Davy; De Roo, Jonathan; Hens, Zeger

    2016-05-11

    Aminophosphines have recently emerged as economical, easy-to-implement precursors for making InP nanocrystals, which stand out as alternative Cd-free quantum dots for optoelectronic applications. Here, we present a complete investigation of the chemical reactions leading to InP formation starting from InCl3 and tris(dialkylamino)phosphines. Using nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction, we demonstrate that injection of the aminophosphine in the reaction mixture is followed by a transamination with oleylamine, the solvent of the reaction. In addition, mass spectrometry and NMR indicate that the formation of InP concurs with that of tetra(oleylamino)phosphonium chloride. The chemical yield of the InP formation agrees with this 4 P(+III) → P(-III) + 3 P(+V) disproportionation reaction occurring, since full conversion of the In precursor was only attained for a 4:1 P/In ratio. Hence it underlines the double role of the aminophosphine as both precursor and reducing agent. These new insights will guide further optimization of high quality InP quantum dots and might lead to the extension of synthetic protocols toward other pnictide nanocrystals. PMID:27111735

  4. 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.

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

    International Nuclear Information System (INIS)

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

  6. InP based lasers and optical amplifiers with wire-/dot-like active regions

    International Nuclear Information System (INIS)

    Long wavelength lasers and semiconductor optical amplifiers based on InAs quantum wire-/dot-like active regions were developed on InP substrates dedicated to cover the extended telecommunication wavelength range between 1.4 and 1.65 μm. In a brief overview different technological approaches will be discussed, while in the main part the current status and recent results of quantum-dash lasers are reported. This includes topics like dash formation and material growth, device performance of lasers and optical amplifiers, static and dynamic properties and fundamental material and device modelling

  7. Static and dynamic properties of three-dimensional dot-type magnonic crystals

    Science.gov (United States)

    Maksymov, Artur; Spinu, Leonard

    2016-04-01

    The static and dynamic magnetization of three-dimensional magnonic metamaterials has been investigated. By numerical means it was analyzed the impact of space dimensionality on the properties of magnonic crystal with unit cell consisting of four dots. It is find out the possibility of multi-vortex core formation which is related to the increasing of the crystal height by three-dimensional periodicity of single crystal layer. Additionally is provided the analysis of ferromagnetic resonance phenomenon for two-dimensional and three-dimensional structures. For the unsaturated magnetization of three-dimensional crystal the several pronounced resonance frequencies were detected.

  8. A Nanowire-Based Plasmonic Quantum Dot Laser.

    Science.gov (United States)

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

    2016-04-13

    Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm(2) was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics. PMID:27030886

  9. A Multi-Chanel Speckle Imaging for the DOT

    NARCIS (Netherlands)

    Sütterlin, P.; Hammerschlag, R.H.; Bettonvil, F.C.M.; Rutten, R.J.; Skomorovsky, V.I.; Domyshev, G.N.

    2001-01-01

    The Dutch Open Telescope (DOT) had its initial observing campaighn in September 1999. Alhough only a simple video system was used, the results demonstrated the excellent high-resolution capabilities of the combination of the open-teloscope concept, the DOT optics, the remaining image degradation due

  10. Cotunneling effects in GaAs vertical double quantum dot

    OpenAIRE

    Badrutdinov, A. O.; Huang, S. M.; Kono, K; Ono, K.; Tayurskii, D. A.

    2010-01-01

    We observed lifting of Coulomb blockade in GaAs vertical double quantum dot with low potential barriers, induced by cotunneling mechanisms at dilution fridge temperature of 10 mK. Several distinct features were observed, compared to single dot case, and appropriate explanation for them was given

  11. Fractional decay of quantum dots in photonic crystals

    DEFF Research Database (Denmark)

    Kristensen, Philip Trøst; Koenderink, Femius; Lodahl, Peter; Tromborg, Bjarne; Mørk, Jesper

    2008-01-01

    We define a practical measure for the degree of fractional decay and establish conditions for the effect to be observable for quantum dots in photonic crystals exhibiting absorptive losses.......We define a practical measure for the degree of fractional decay and establish conditions for the effect to be observable for quantum dots in photonic crystals exhibiting absorptive losses....

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

    NARCIS (Netherlands)

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

    1990-01-01

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

  13. 49 CFR 15.15 - SSI disclosed by DOT.

    Science.gov (United States)

    2010-10-01

    ... 49 Transportation 1 2010-10-01 2010-10-01 false SSI disclosed by DOT. 15.15 Section 15.15 Transportation Office of the Secretary of Transportation PROTECTION OF SENSITIVE SECURITY INFORMATION § 15.15 SSI... containing SSI are not available for public inspection or copying, nor does DOT release such records...

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

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg

    deviations. Similar measurements on a quantum dot in a photonic-crystal cavity sow a Rabi splitting on resonance, while time-resolved measurements prove that the system is in the weak coupling regime. Whle tuning the quantum dot through resonance of the high-Q mode we observe a strong and surprisingly...

  15. 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...

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

    DEFF Research Database (Denmark)

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

    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...

  17. Electronic properties of assemblies of zno quantum dots

    NARCIS (Netherlands)

    Roest, Aarnoud Laurens

    2003-01-01

    Electron transport in an assembly of ZnO quantum dots has been studied using an electrochemically gated transistor. The electron mobility shows a step-wise increase as a function of the electron occupation per quantum dot. When the occupation number is below two, transport occurs by tunnelling betwe

  18. X-ray scattering from periodic arrays of quantum dots

    International Nuclear Information System (INIS)

    Three-dimensional periodic arrays of self-organized quantum dots in semiconductor multilayers are investigated by high-resolution x-ray scattering. We demonstrate that the statistical parameters of the dot array can be determined directly from the scattering data without performing a numerical simulation of the scattered intensity.

  19. Quantum dots for multimodal molecular imaging of angiogenesis

    OpenAIRE

    Mulder, W.J.M.; Strijkers, G.J.; Nicolay, K.; Griffioen, A W

    2010-01-01

    Quantum dots exhibit unique optical properties for bioimaging purposes. We have previously developed quantum dots with a paramagnetic and functionalized coating and have shown their potential for molecular imaging purposes. In the current mini-review we summarize the synthesis procedure, the in vitro testing and, importantly, the in vivo application for multimodal molecular imaging of tumor angiogenesis.

  20. Quantum Wires and Quantum Dots for Neutral Atoms

    OpenAIRE

    Schmiedmayer, Joerg

    1998-01-01

    By placing changeable nanofabricated structures (wires, dots, etc.) on an atom mirror one can design guiding and trapping potentials for atoms. These potentials are similar to the electrostatic potentials which trap and guide electrons in semiconductor quantum devices like quantum wires and quantum dots. This technique will allow the fabrication of nanoscale atom optical devices.

  1. DOE evaluation document for DOT 7A Type A packaging

    International Nuclear Information System (INIS)

    This document, DOE Evaluation Document for DOT 7A Type A Packaging, March 1987, presents approximately 100 different packagings which have been determined to meet the requirements for a DOT Spec 7A Type A packaging (49 CFR 178.350) and satisfies the requirements of 49 CFR 174.315(a) concerning the requirements for a document

  2. Nonvolatile Quantum Dot Gate Memory (NVQDM): Tunneling Rate from Quantum Well Channel to Quantum Dot Gate

    Science.gov (United States)

    Hasaneen, El-Sayed; Heller, Evan; Bansal, Rajeev; Jain, Faquir

    2003-10-01

    In this paper, we compute the tunneling of electrons in a nonvolatile quantum dot memory (NVQDM) cell during the WRITE operation. The transition rate of electrons from a quantum well channel to the quantum dots forming the floating gate is calculated using a recently reported method by Chuang et al.[1]. Tunneling current is computed based on transport of electrons from the channel to the floating quantum dots. The maximum number of electrons on a dot is calculated using surface electric field and break down voltage of the tunneling dielectric material. Comparison of tunneling for silicon oxide and high-k dielectric gate insulators is also described. Capacitance-Voltage characteristics of a NVQDM device are calculated by solving the Schrodinger and Poisson equations self-consistently. In addition, the READ operation of the memory has been investigated analytically. Results for 70 nm channel length Si NVQDMs are presented. Threshold voltage is calculated including the effect of the charge on nanocrystal quantum dots. Current-voltage characteristics are obtained using BSIM3v3 model [2-3]. This work is supported by Office of Navel Research (N00014210883, Dr. D. Purdy, Program Monitor), Connecticut Innovations Inc./TranSwitch (CII # 00Y17), and National Science Foundation (CCR-0210428) grants. [1] S. L. Chuang and N. Holonyak, Appl. Phys. Lett., 80, pp. 1270, 2002. [2] Y. Chen et. al., BSIM3v3 Manual, Elect. Eng. and Comp. Dept., U. California, Berkeley, CA, 1996. [3] W. Liu, MOSFET Models for SPICE Simulation, John Wiley & Sons, Inc., 2001.

  3. Ultra-bright alkylated graphene quantum dots

    Science.gov (United States)

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

    2014-10-01

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

  4. Resonant Raman scattering off neutral quantum dots

    International Nuclear Information System (INIS)

    Resonant inelastic (Raman) light scattering off neutral GaAs quantum dots which contain a mean number, N=42, of electron-hole pairs is computed. We find Raman amplitudes corresponding to strongly collective final states (charge-density excitations) of similar magnitude as the amplitudes related to weakly collective or single-particle excitations. As a function of the incident laser frequency or the magnetic field, they are rapidly varying amplitudes. It is argued that strong Raman peaks should come out in the spin-density channels, not related to valence-band mixing effects in the intermediate states. (author)

  5. Fano-Rashba effect in quantum dots

    International Nuclear Information System (INIS)

    We consider the electronic transport through a Rashba quantum dot coupled to ferromagnetic leads. We show that the interference of localized electron states with resonant electron states leads to the appearance of the Fano-Rashba effect. This effect occurs due to the interference of bound levels of spin-polarized electrons with the continuum of electronic states with an opposite spin polarization. We investigate this Fano-Rashba effect as a function of the applied magnetic field and Rashba spin-orbit coupling

  6. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

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

    2010-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...... determined the oscillator strength, quantum efficiency and spin-flip rates of QD excitons as well as their dependencies on emission wavelength and QD size. Enhancement and inhibition of QD spontaneous emission in photonic crystal membranes (PCMs) is observed. Efficient coupling to PCM waveguides is...

  7. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

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

    2011-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...... determined the oscillator strength, quantum efficiency and spin-flip rates of QD excitons as well as their dependencies on emission wavelength and QD size. Enhancement and inhibition of QD spontaneous emission in photonic crystal membranes (PCMs) is observed. Efficient coupling to PCM waveguides is...

  8. Relaxation dynamics in correlated quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Andergassen, S. [Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Schuricht, D.; Pletyukhov, M.; Schoeller, H. [Institute for Theory of Statistical Physics, RWTH Aachen University and JARA-Fundamentals of Future Information Technology, 52056 Aachen (Germany)

    2014-12-04

    We study quantum many-body effects on the real-time evolution of the current through quantum dots. By using a non-equilibrium renormalization group approach, we provide analytic results for the relaxation dynamics into the stationary state and identify the microscopic cutoff scales that determine the transport rates. We find rich non-equilibrium physics induced by the interplay of the different energy scales. While the short-time limit is governed by universal dynamics, the long-time behavior features characteristic oscillations as well as an interplay of exponential and power-law decay.

  9. Quantum dot loaded immunomicelles for tumor imaging

    Directory of Open Access Journals (Sweden)

    Levchenko Tatyana

    2010-10-01

    Full Text Available Abstract Background Optical imaging is a promising method for the detection of tumors in animals, with speed and minimal invasiveness. We have previously developed a lipid coated quantum dot system that doubles the fluorescence of PEG-grafted quantum dots at half the dose. Here, we describe a tumor-targeted near infrared imaging agent composed of cancer-specific monoclonal anti-nucleosome antibody 2C5, coupled to quantum dot (QD-containing polymeric micelles, prepared from a polyethylene glycol/phosphatidylethanolamine (PEG-PE conjugate. Its production is simple and involves no special equipment. Its imaging potential is great since the fluorescence intensity in the tumor is twofold that of non-targeted QD-loaded PEG-PE micelles at one hour after injection. Methods Para-nitrophenol-containing (5% PEG-PE quantum dot micelles were produced by the thin layer method. Following hydration, 2C5 antibody was attached to the PEG-PE micelles and the QD-micelles were purified using dialysis. 4T1 breast tumors were inoculated subcutaneously in the flank of the animals. A lung pseudometastatic B16F10 melanoma model was developed using tail vein injection. The contrast agents were injected via the tail vein and mice were depilated, anesthetized and imaged on a Kodak Image Station. Images were taken at one, two, and four hours and analyzed using a methodology that produces normalized signal-to-noise data. This allowed for the comparison between different subjects and time points. For the pseudometastatic model, lungs were removed and imaged ex vivo at one and twenty four hours. Results The contrast agent signal intensity at the tumor was double that of the passively targeted QD-micelles with equally fast and sharply contrasted images. With the side views of the animals only tumor is visible, while in the dorsal view internal organs including liver and kidney are visible. Ex vivo results demonstrated that the agent detects melanoma nodes in a lung

  10. Prompt Planetesimal Formation beyond the Snow Line

    Science.gov (United States)

    Armitage, Philip J.; Eisner, Josh A.; Simon, Jacob B.

    2016-09-01

    We develop a simple model to predict the radial distribution of planetesimal formation. The model is based on the observed growth of dust to millimeter-sized particles, which drift radially, pile-up, and form planetesimals where the stopping time and dust-to-gas ratio intersect the allowed region for streaming instability-induced gravitational collapse. Using an approximate analytic treatment, we first show that drifting particles define a track in metallicity–stopping time space whose only substantial dependence is on the disk’s angular momentum transport efficiency. Prompt planetesimal formation is feasible for high particle accretion rates (relative to the gas, {\\dot{M}}p/\\dot{M}≳ 3× {10}-2 for α ={10}-2), which could only be sustained for a limited period of time. If it is possible, it would lead to the deposition of a broad and massive belt of planetesimals with a sharp outer edge. Numerically including turbulent diffusion and vapor condensation processes, we find that a modest enhancement of solids near the snow line occurs for centimeter-sized particles, but that this is largely immaterial for planetesimal formation. We note that radial drift couples planetesimal formation across radii in the disk, and suggest that considerations of planetesimal formation favor a model in which the initial deposition of material for giant planet cores occurs well beyond the snow line.

  11. 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.

  12. Double Rashba Quantum Dots Ring as a Spin Filter

    Directory of Open Access Journals (Sweden)

    Chi Feng

    2008-01-01

    Full Text Available AbstractWe theoretically propose a double quantum dots (QDs ring to filter the electron spin that works due to the Rashba spin–orbit interaction (RSOI existing inside the QDs, the spin-dependent inter-dot tunneling coupling and the magnetic flux penetrating through the ring. By varying the RSOI-induced phase factor, the magnetic flux and the strength of the spin-dependent inter-dot tunneling coupling, which arises from a constant magnetic field applied on the tunneling junction between the QDs, a 100% spin-polarized conductance can be obtained. We show that both the spin orientations and the magnitude of it can be controlled by adjusting the above-mentioned parameters. The spin filtering effect is robust even in the presence of strong intra-dot Coulomb interactions and arbitrary dot-lead coupling configurations.

  13. Silicon quantum dots: fine-tuning to maturity.

    Science.gov (United States)

    Morello, Andrea

    2015-12-18

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science. PMID:26584678

  14. Charge-tunable indium gallium nitride quantum dots

    Science.gov (United States)

    Zhang, Lei; Teng, Chu-Hsiang; Ku, Pei-Cheng; Deng, Hui

    2016-02-01

    III-Nitride quantum dots have emerged as a new chip-scale system for quantum information science, which combines electrical and optical interfaces on a semiconductor chip that is compatible with noncryogenic operating temperatures. Yet most work has been limited to optical excitations. To enable single-spin-based quantum optical and quantum information research, we demonstrate here quantized charging in optically active, site-controlled III-nitride quantum dots. Single-electron charging was confirmed by the voltage dependence of the energy, dipole moment, fine structures, and polarization properties of the exciton states in the quantum dots. The fundamental energy structures of the quantum dots were identified, including neutral and charged excitons, fine structures of excitons, and A and B excitons. The results lay the ground for coherent control of single charges in III-nitride quantum dots, opening a door to III-nitride-based spintronics and spin-qubit quantum information processing.

  15. Interaction of porphyrins with CdTe quantum dots

    International Nuclear Information System (INIS)

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

  16. Silicon quantum dots: fine-tuning to maturity

    Science.gov (United States)

    Morello, Andrea

    2015-12-01

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science.

  17. Representative longitudinal optical phonon modes in polar semiconductor quantum dots

    International Nuclear Information System (INIS)

    Highlights: ► We model the exciton-longitudinal optical phonon coupling for cylinder quantum dot. ► We predict a representative optical phonon mode for GaAs/AlAs quantum dot. ► Huang–Rhys factors increases with radius decreasing of GaAs/AlAs quantum dot. - Abstract: Existence of representative longitudinal optical (LO) phonon modes is theoretically discussed for the case of polar semiconductor cylindrical quantum dots embedded in a semiconductor matrix. The approach is developed within the dielectric continuum model considering the Fröhlich interaction between electrons and the confined LO phonons. The theory is applied to cylindrical GaAs/AlAs quantum dots within an adiabatic treatment.

  18. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

    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......-quadrupole contributions and may compete with the dipole moment in light-matter interactions. A theory for the quantum-dot wavefunctions is developed showing that the mesoscopic moment originates from distortions in the underlying crystal lattice. The resulting quantum-mechanical current density is curved leading to light......-matter interaction of both electric and magnetic character. Our study demonstrates that In(Ga)As quantum dots lack parity symmetry and, as consequence, can be employed for locally probing the parity symmetry of complex photonic nanostructures. This opens the prospect for interfacing quantum dots with optical...

  19. Extracellular biosynthesis of CdTe quantum dots by the fungus Fusarium oxysporum and their anti-bacterial activity

    Science.gov (United States)

    Syed, Asad; Ahmad, Absar

    2013-04-01

    The growing demand for semiconductor [quantum dots (Q-dots)] nanoparticles has fuelled significant research in developing strategies for their synthesis and characterization. They are extensively investigated by the chemical route; on the other hand, use of microbial sources for biosynthesis witnessed the highly stable, water dispersible nanoparticles formation. Here we report, for the first time, an efficient fungal-mediated synthesis of highly fluorescent CdTe quantum dots at ambient conditions by the fungus Fusarium oxysporum when reacted with a mixture of CdCl2 and TeCl4. Characterization of these biosynthesized nanoparticles was carried out by different techniques such as Ultraviolet-visible (UV-Vis) spectroscopy, Photoluminescence (PL), X-ray Diffraction (XRD), X-ray Photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and Fourier Transformed Infrared Spectroscopy (FTIR) analysis. CdTe nanoparticles shows antibacterial activity against Gram positive and Gram negative bacteria. The fungal based fabrication provides an economical, green chemistry approach for production of highly fluorescent CdTe quantum dots.

  20. Star formation rates in luminous quasars at 2 < z < 3

    Science.gov (United States)

    Harris, Kathryn; Farrah, Duncan; Schulz, Bernhard; Hatziminaoglou, Evanthia; Viero, Marco; Anderson, Nick; Béthermin, Matthieu; Chapman, Scott; Clements, David L.; Cooray, Asantha; Efstathiou, Andreas; Feltre, Anne; Hurley, Peter; Ibar, Eduardo; Lacy, Mark; Oliver, Sebastian; Page, Mathew J.; Pérez-Fournon, Ismael; Petty, Sara M.; Pitchford, Lura K.; Rigopoulou, Dimitra; Scott, Douglas; Symeonidis, Myrto; Vieira, Joaquin; Wang, Lingyu

    2016-04-01

    We investigate the relation between star formation rates (dot{{M}}_s) and AGN properties in optically selected type 1 quasars at 2 quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C IV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; Mi is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between dot{{M}}_s and dot{{M}}_{bh}. Finally, there is no strong relation between dot{{M}}_s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects.

  1. Quantum dot systems: artificial atoms with tunable properties

    International Nuclear Information System (INIS)

    Full text: Quantum dots - also called zero-dimensional electron systems or artificial atoms - are physical objects where the constituent electrons are confined in a small spatial region, leading to discrete eigenvalues for the energies of the confined electrons. Large quantum dots offer a dense energy spectrum comparable to that of metallic grains, whereas small quantum dots more closely resemble atoms in their electronic properties. Quantum dots can be linked to leads by tunnel barriers, hence permitting electrical transport measurements: Coulomb blockade and single-electron charging effects are observed due to the repulsive electron electron interaction on the quantum dot site. Usually fabricated by conventional semiconductor growth and processing technology, the advantage is that both simple and also more complex quantum dot systems can be designed to purpose, acting as model systems with in-situ tunable parameters such as the number of confined electrons in the quantum dot and the strength of the tunnel coupling to the leads, electrostatically controlled by the applied voltages to gate electrodes. With increasing the tunnel coupling to the leads, the virtual occupation of the quantum dot from the leads becomes more and more important -- the simple description of electrical transport by single-electron tunneling events breaks down. The basic physics is described by the Kondo physics based on the Anderson impurity model. A system consisting of strongly electrostatically coupled quantum dots with separate leads to each quantum dot represent another realization of the Anderson impurity model. Experiments to verify the analogy are presented. The experimental data embedded within this tutorial have been obtained with Alexander Huebel, Matthias Keller, Joerg Schmid, David Quirion, Armin Welker, Ulf Wilhelm, and Klaus von Klitzing. (author)

  2. Dead zones in colloidal quantum dot photovoltaics: evidence and implications

    KAUST Repository

    Barkhouse, D. Aaron R.

    2010-09-01

    In order to fabricate photovoltaic (PV) cells incorporating light-trapping electrodes, flexible foil substrates, or more than one junction, illumination through the top-contact (i.e.: non-substrate) side of a photovoltaic device is desirable. We investigate the relative collection efficiency for illumination through the top vs. bottom of PbS colloidal quantum dot (CQD) PV devices. The external quantum efficiency spectra of FTO/TiO2/PbS CQD/ITO PV devices with various PbS layer thicknesses were measured for illumination through either the top (ITO) or bottom (FTO) contacts. By comparing the relative shapes and intensities of these spectra with those calculated from an estimation of the carrier generation profile and the internal quantum efficiency as a function of distance from the TiO2 interface in the devices, a substantial dead zone, where carrier extraction is dramatically reduced, is identified near the ITO top contact. The implications for device design, and possible means of avoiding the formation of such a dead zone, are discussed.

  3. Photoluminescence of germanium quantum dots formed by pulsed laser ablation

    International Nuclear Information System (INIS)

    Time-resolved studies of photoluminescence in the energy range 1.4-3.2 eV are carried out for GeOx films (x ≤ 2) containing Ge nanoclusters. The relaxation times vary in the range from 50 ns to 20 μs. The films are produced by single-stage pulsed laser ablation and deposited from the direct and reverse fluxes of particles of the erosion spray in oxygen and argon atmosphere. The dependences of the photoluminescence properties of the films on the conditions of deposition and on doping with gold are studied. The photoluminescence bands, with peaks at the energies 1.42-2.1 eV, are narrow, slow, and close to each other in energy, whereas the other bands, with peaks near 2.5 eV and in the range 2.7-2.9 eV, are broad, faster, and only slightly overlapping in energy. The results are interpreted in the context of the model of photoluminescence in Ge quantum dots, whose dimensions are controlled by the conditions of their formation

  4. Photoluminescence Properties Research on Graphene Quantum Dots/Silver Composites.

    Science.gov (United States)

    Wang, Jun; Li, Yan; Zhang, Bo-Ping; Xie, Dan-Dan; Ge, Juan; Liu, Hui

    2016-04-01

    Graphene quantum dots (GQDs) possess unique properties of graphene and exhibit a series of new phenomena of 0 dimension (D) carbon materials. Thus, GQDs have attracted much attention from researchers and have shown great promise for many applications. Recently, many works focus on GQDs-metal ions and metal nanoparticles (NPs). Although, many researches point out that metal ions and metal NPs have significant effect on photoluminescence (PL) feature of GQDs, mainly focus on PL intensity. Here, for the first time, we reported that metal NPs also affected PL peak position which was dependent on the mix mechanism of metal and GQDs. When GQDs-silver (Ag) composite mixed by physical method and excited at a wavelength of 320 nm, PL peak position of composites first showed blue-shifted then red-shifted with increasing of Ag content. However, if GQDs-Ag composite prepared by chemical method, PL peak position of the composites blue-shifted. Furthermore, the shift of PL peak position of GQDs-Ag prepared both for physical and chemical method displayed excitation-dependent feature. When the excitation wavelength approached to Ag SPR peaks, no obvious PL shift was observed. The mechanism for different PL shifts and the phenomenon of excitation-dependent PL shift as well as the formation mechanism of GQDs-Ag composite by chemical method are discussed in detail in this paper. PMID:27451653

  5. Binding Quantum Dots to Silk Biomaterials for Optical Sensing

    Directory of Open Access Journals (Sweden)

    Disi Lu

    2015-01-01

    Full Text Available Quantum dots (QDs, have great potential for fabricating optical sensing devices and imaging biomaterial degradation in vivo. In the present study, 2-mercaptoethylamine- (MEA- and mercaptopropionic acid- (MPA- capped CdTe-QDs were physically incorporated in silk films that contained a high content (>30% of crystalline beta-sheet structure. The beta-sheets were induced by the addition of glycerol, water annealing, glycerol/annealing, or treatment with methanol. Incorporation of QDs did not influence the formation of beta-sheets. When the films were extracted with water, most QDs remained associated with the silk, based on the retention of photoluminescence in the silk films and negligible photoluminescence in the extracts. Compared to the solution state, photoluminescence intensity significantly decreased for MEA-QDs but not for MPA-QDs in the silk films, while the emission maximum blue shifted (≈4 nm slightly for both. Further film digestion using protease XIV, alpha-chymotrypsin, and the combination of the two proteases suggested that QDs may be bound to the silk beta-sheet regions but not the amorphous regions. QDs photoluminescence in silk films was quenched when the concentration of hydrogen peroxide (H2O2 was above 0.2-0.3 mM, indicating the QDs-incorporated silk films can be used to report oxidation potential in solution.

  6. Multiple Energy Exciton Shelves in Quantum-Dot-DNA Nanobioelectronics.

    Science.gov (United States)

    Goodman, Samuel M; Singh, Vivek; Ribot, Josep Casamada; Chatterjee, Anushree; Nagpal, Prashant

    2014-11-01

    Quantum dots (QDs) are semiconductor nanocrystallites with multiple size-dependent quantum-confined states that are being explored for utilizing broadband radiation. While DNA has been used for the self-assembly of nanocrystals, it has not been investigated for the formation of simultaneous conduction pathways for transporting multiple energy charges or excitons. These exciton shelves can be formed by coupling the conduction band, valence band, and hot-carrier states in QDs with different HOMO-LUMO levels of DNA nucleobases, resulting from varying degrees of conjugation in the nucleobases. Here we present studies on the electronic density of states in four naturally occurring nucleobases (guanine, thymine, cytosine, and adenine), which energetically couple to quantized states in semiconductor QDs. Using scanning tunneling spectroscopy of single nanoparticle-DNA constructs, we demonstrate composite DOS of chemically coupled DNA oligonucleotides and cadmium chalcogenide QDs (CdS, CdSe, CdTe). While perfectly aligned CdTe QD-DNA states lead to exciton shelves for multiple energy charge transport, mismatched energy levels in CdSe QD-DNA introduce intrabandgap states that can lead to charge trapping and recombination. Although further investigations are required to study the rates of charge transfer, recombination, and back-electron transfer, these results can have important implications for the development of a new class of nanobioelectronics and biological transducers. PMID:26278768

  7. Submonolayer Quantum Dots for High Speed Surface Emitting Lasers

    Directory of Open Access Journals (Sweden)

    Zakharov ND

    2007-01-01

    Full Text Available AbstractWe report on progress in growth and applications of submonolayer (SML quantum dots (QDs in high-speed vertical-cavity surface-emitting lasers (VCSELs. SML deposition enables controlled formation of high density QD arrays with good size and shape uniformity. Further increase in excitonic absorption and gain is possible with vertical stacking of SML QDs using ultrathin spacer layers. Vertically correlated, tilted or anticorrelated arrangements of the SML islands are realized and allow QD strain and wavefunction engineering. Respectively, both TE and TM polarizations of the luminescence can be achieved in the edge-emission using the same constituting materials. SML QDs provide ultrahigh modal gain, reduced temperature depletion and gain saturation effects when used in active media in laser diodes. Temperature robustness up to 100 °C for 0.98 μm range vertical-cavity surface-emitting lasers (VCSELs is realized in the continuous wave regime. An open eye 20 Gb/s operation with bit error rates better than 10−12has been achieved in a temperature range 25–85 °Cwithout current adjustment. Relaxation oscillations up to ∼30 GHz have been realized indicating feasibility of 40 Gb/s signal transmission.

  8. 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.

  9. Quantum Computer Using Coupled Quantum Dot Molecules

    CERN Document Server

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

    1999-01-01

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

  10. Colloidal quantum dot light-emitting devices.

    Science.gov (United States)

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

    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. PMID:22110863

  11. 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.

  12. Quantum chaos in open quantum dot arrays

    International Nuclear Information System (INIS)

    Full text: The discovery of chaos in macro-scale physical systems led to the emergence of a new understanding of laws in nature. Chaos should not exist at all in quantum systems - as laws of quantum mechanics actually forbid it. We will show in this work the footprints of quantum chaos in the dynamics of electron transport by studying ballistic open quantum dot arrays. We will apply quantum mechanical calculations and classical calculations in order to explain the low field magneto-transport through open quantum dots. To characterize the quantum/classical correspondence in this system and to understand the transport, it is necessary to invoke dynamical tunneling, a quantum-mechanical mechanism which allows tunneling of electrons between chaotic and regular regions in the phase space, a process which is classically forbidden. The relevant conclusions regarding dynamical tunneling are drawn by using Husimi representations. By comparing the classical trajectories with the electron probability density high accordance is achieved. The Husimi plots are used to visualize the wave function distribution in the vx-x-plane of the Poincare section. We show in the Husimi plots that the wave function has weight on the regular and chaotic regions alike. This represents a distribution in the phase space that cannot be generated by classical dynamics and supports the interpretation including dynamical tunneling. (author)

  13. Excitation transfer in stacked quantum dot chains

    International Nuclear Information System (INIS)

    Stacked InAs quantum dot chains (QDCs) on InGaAs/GaAs cross-hatch pattern (CHP) templates yield a rich emission spectrum with an unusual carrier transfer characteristic compared to conventional quantum dot (QD) stacks. The photoluminescent spectra of the controlled, single QDC layer comprise multiple peaks from the orthogonal QDCs, the free-standing QDs, the CHP, the wetting layers and the GaAs substrate. When the QDC layers are stacked, employing a 10 nm GaAs spacer between adjacent QDC layers, the PL spectra are dominated by the top-most stack, indicating that the QDC layers are nominally uncoupled. Under high excitation power densities when the high-energy peaks of the top stack are saturated, however, low-energy PL peaks from the bottom stacks emerge as a result of carrier transfers across the GaAs spacers. These unique PL signatures contrast with the state-filling effects in conventional, coupled QD stacks and serve as a means to quickly assess the presence of electronic coupling in stacks of dissimilar-sized nanostructures. (paper)

  14. Using quantum dot photoluminescence for load detection

    Science.gov (United States)

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

    2016-08-01

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

  15. 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.

  16. Cost Effectiveness of DOTS and Non-DOTS Strategies for Smear-positive Pulmonary Tuberculosis in Beijing

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The cost-effectiveness of DOTS (Directly Observed Treatment, short course) and non-DOTS strategies for smear-positive pulmonary tuberculosis in Beijing was evaluated. Cost calculation was based on the expenses of drugs, chest X-ray films, sputum smears and cultures for the patients. Effectiveness of the intervention was assessed in two aspects: direct benefits to the patients treated and indirect benefits to the others through reduced transmission of tuberculosis; disability adjusted life of year (DALY) was used as an index. The results showed that one DALY could be saved with 45.7 Yuan by DOTS and 471.4 Yuan by non-DOTS. DOTS is a good control strategy for smear-positive tuberculosis.

  17. Design optimization of large-size format edge-lit light guide units

    Science.gov (United States)

    Hastanin, J.; Lenaerts, C.; Fleury-Frenette, K.

    2016-04-01

    In this paper, we present an original method of dot pattern generation dedicated to large-size format light guide plate (LGP) design optimization, such as photo-bioreactors, the number of dots greatly exceeds the maximum allowable number of optical objects supported by most common ray-tracing software. In the proposed method, in order to simplify the computational problem, the original optical system is replaced by an equivalent one. Accordingly, an original dot pattern is splitted into multiple small sections, inside which the dot size variation is less than the ink dots printing typical resolution. Then, these sections are replaced by equivalent cells with continuous diffusing film. After that, we adjust the TIS (Total Integrated Scatter) two-dimensional distribution over the grid of equivalent cells, using an iterative optimization procedure. Finally, the obtained optimal TIS distribution is converted into the dot size distribution by applying an appropriate conversion rule. An original semi-empirical equation dedicated to rectangular large-size LGPs is proposed for the initial guess of TIS distribution. It allows significantly reduce the total time needed to dot pattern optimization.

  18. Coherent coupling of two quantum dots embedded in an Aharonov-Bohm ring

    OpenAIRE

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

    2000-01-01

    We define two laterally gated small quantum dots (~ 15 electrons) in an Aharonov-Bohm geometry in which the coupling between the two dots can be broadly changed. For weakly coupled quantum dots we find Aharonov-Bohm oscillations. In an intermediate coupling regime we concentrate on the molecular states of the double dot and extract the magnetic field dependence of the coherent coupling.

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

    DEFF Research Database (Denmark)

    Hu, Yongjie; Churchill, Hugh; Reilly, David;

    2007-01-01

    between the dots and to the leads. We also demonstrate a novel approach to charge sensing in a one-dimensional nanostructure by capacitively coupling the double dot to a single dot on an adjacent nanowire. The double quantum dot and integrated charge sensor serve as an essential building block required to...

  20. Ultrashort Dynamics in Quantum Dot Waveguides: Theoretical Analysis and Experimental Investigations

    DEFF Research Database (Denmark)

    Gehrig, E.; Poel, Mike van der; Birkedal, Dan;

    2004-01-01

    Experimental pump-probe measurements and computational modeling on the basis of spatially resolved Quantum Dot Maxwell-Bloch equations allow identification of the processes underlying the ultrafast dot dynamics.......Experimental pump-probe measurements and computational modeling on the basis of spatially resolved Quantum Dot Maxwell-Bloch equations allow identification of the processes underlying the ultrafast dot dynamics....

  1. Ultra-large scale synthesis of high electrochemical performance SnO2 quantum dots within 5 min at room temperature following a growth self-termination mechanism

    International Nuclear Information System (INIS)

    Highlights: • SnO2 quantum dots were prepared at an ultra-large scale at room temperature within 5 min. • The grinding of SnCl2⋅2H2O and ammonium persulphate with morpholine produces quantum dots. • The reactions were self-terminated through the rapid consumption of water. • The obtained SnO2 quantum dots own high electrochemical performance. - Abstract: SnO2 quantum dots are prepared at an ultra-large scale by a productive synthetic procedure without using any organic ligand. The grinding of solid mixture of SnCl2⋅2H2O and ammonium persulphate with morpholine in a mortar at room temperature produces 1.2 nm SnO2 quantum dots within 5 min. The formation of SnO2 is initiated by the reaction between tin ions and hydroxyl groups generated from hydrolysis of morpholine in the released hydrate water from SnCl2⋅2H2O. It is considered that as water is rapidly consumed by the hydrolysis reaction of morpholine, the growth process of particles is self-terminated immediately after their transitory period of nucleation and growth. As a result of simple procedure and high toleration to scaling up of preparation, at least 50 g of SnO2 quantum dots can be produced in one batch in our laboratory. The as prepared quantum dots present high electrochemical performance due to the effective faradaic reaction and the alternative trapping of electrons and holes

  2. Low-density InP-based quantum dots emitting around the 1.5 μm telecom wavelength range

    International Nuclear Information System (INIS)

    The authors report on low-density InAs quantum dots (QDs) grown on AlGaInAs surfaces lattice matched to InP using post-growth annealing by solid-source molecular beam epitaxy. Clearly spatially separated QDs with a dot density of about 5 × 108 cm−2 are obtained by using a special capping technique after the dot formation process. High-resolution micro-photoluminescence performed on optimized QD structures grown on distributed Bragg reflector exhibits single QD emissions around 1.5 μm with narrow excitonic linewidth below 50 μeV, which can be used as single photon source in the telecom wavelength range

  3. Silicon quantum dots embedded in amorphous SiC matrix for third-generation solar cells: Microstructure control by RF discharge power

    Science.gov (United States)

    Cheng, Qijin; Levchenko, Igor; Song, Denyuan; Xu, Shuyan; Ostrikov, Kostya Ken

    2015-04-01

    A low-frequency (460 kHz), low-pressure, thermally non-equilibrium, high-density inductively coupled plasma (ICP) has been used to synthesize a novel, advanced photovoltaic material suitable for fabrication of third-generation solar cells. Silicon quantum dots (SQDs) embedded in an amorphous silicon carbide matrix were prepared at a very low substrate temperature of approximately 200°C without any hydrogen dilution. The effect of the radio-frequency (RF) power of the plasma discharge on the morphology and structure of the embedded quantum dots was studied. A brief discussion on the possible mechanisms of the quantum dot formation in the ICP is presented. This study is relevant to third-generation photovoltaic solar cells.

  4. Zeros in single-channel transmission through double quantum dots.

    Science.gov (United States)

    Rotter, I; Sadreev, A F

    2005-04-01

    By using a simple model we consider single-channel transmission through a double quantum dot that consists of two single dots coupled by a wire of finite length L . Each of the two single dots is characterized by a few energy levels only, and the wire is assumed to have only one level whose energy depends on the length L . The transmission is described by using S matrix theory and the effective non-Hermitian Hamilton operator H(eff) of the system. The decay widths of the eigenstates of H(eff) depend strongly on energy. The model explains the origin of the transmission zeros of the double dot that is considered by us. Mostly, they are caused by (destructive) interferences between neighboring levels and are of first order. When, however, both single dots are identical and their transmission zeros are of first order, those of the double dot are of second order. First-order transmission zeros cause phase jumps of the transmission amplitude by pi, while there are no phase jumps related to second-order transmission zeros. In this latter case, a phase jump occurs due to the fact that the width of one of the states vanishes when crossing the energy of the transmission zero. The parameter dependence of the widths of the resonance states is determined by the spectral properties of the two single dots. PMID:15903767

  5. 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.

  6. Electric properties of Ge quantum dot embedded in Si matrix

    Institute of Scientific and Technical Information of China (English)

    MA Xi-ying; SHI Wei-lin

    2005-01-01

    The electric characteristics of Ge quantum dot grown by molecular beam epitaxy in Si matrix were investigated by admittance spectroscopy and deep level transient spectroscopy. The admittance spectroscopy measurements show that the activation energy of 0.341 eV can be considered as the emitting energy of hole from the ground state of the quantum dot. And the capacitance variation with temperature of the sample shows a platform at various frequencies with reverse bias 0.5 V, which indicates that the boundary of space charge region is located at the quantum dot layer where the large confined hole concentration blocks the further extension of space charge region. When the temperature increases from 120 K to 200 K, the holes in the dot emit out completely. The position of the platform shifting with the increase of the applied frequency shows the frequency effects of the charges in the quantum dot. The deep level transient spectroscopy results show that the charge concentration in the Ge quantum dot is a function of the pulse duration and the reverse bias voltage, the activation energy and capture cross-section of hole decrease with the increase of pulse duration due to the Coulomb charging effect. The valence-band offsets of hole in Ge dot obtained by admittance spectroscopy and deep level transient spectroscopy are 0.341 and 0.338 eV, respectively.

  7. Lead Chalcogenide Quantum Dots and Quantum Dot Hybrids for Optoelectronic Devices

    OpenAIRE

    Schornbaum, Julia

    2015-01-01

    Semiconductor quantum dots (QDs) exhibit remarkable properties, which include a size-tunable band gap and narrow emission bands. They are also suitable for large-area and low-cost fabrication, due to their solution-processability. Consequently, QDs are very promising for future applications in printable optoelectronic devices. Near-infrared (NIR) active lead chalcogenide QDs hold an enormous potential, as they exhibit optical properties in a wavelength regime, where efficient photoactive mate...

  8. Chemiluminescence behavior of the carbon dots and the reduced state carbon dots

    Energy Technology Data Exchange (ETDEWEB)

    Teng, Ping [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China); Xie, Jianxin [College of Resources and Environment, Yuxi Normal University, Yuxi, Yunnan 653100 (China); Long, Yijuan; Huang, Xiaoxiao; Zhu, Rui; Wang, Xiliang; Liang, Liping [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China); Huang, Yuming, E-mail: ymhuang@swu.edu.cn [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China); Zheng, Huzhi, E-mail: zhenghz@swu.edu.cn [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China)

    2014-02-15

    Potassium permanganate (KMnO{sub 4}) can react with two different carbon nanoparticles, i.e., carbon dots (CDs) and reduced state carbon dots (r-CDs), in a strong acid medium to generate chemiluminescence (CL). Furthermore, the different CL intensities and CL behaviors due to the different surface groups on these two kinds of carbon nanoparticles were confirmed. CL spectra, fluorescence spectra, UV–vis absorption spectra, and electron paramagnanetic resonance spectra were applied to investigate the CL mechanism. The main reaction pathways were proposed as follows: for the CL reaction between CDs and KMnO{sub 4}, the excited states of CDs (CDs{sup ⁎}) and Mn(II) (Mn(II){sup ⁎}) emerged as KMnO{sub 4} could inject holes into CDs, then, the CDs{sup ⁎} and Mn(II){sup ⁎} acted as luminophors to yield CL; in the r-CDs-KMnO{sub 4} system, r-CDs were oxidized by KMnO{sub 4} directly, and CDs{sup ⁎} and Mn(II){sup ⁎} were produced, at the same time, CL occurred. What is more interesting is that the CL intensity of the r-CD system is stronger than that of the CD system, which confirms that functional groups have strong effect on the CL behavior. It inspired us that new carbon nanoparticles with excellent luminous performance can be designed by tuning their surface groups. -- Highlights: • Carbon dots (CDs) and reduced state carbon dots (r-CDs) can react with potassium permanganate (KMnO{sub 4}) in a strong acid to generate chemiluminescence (CL). • With different surface groups, the CL intensity of r-CDs-KMnO{sub 4} system is different from that of CDs-KMnO{sub 4} system. • The CL mechanisms of the two systems were investigated.

  9. Extracting inter-dot tunnel couplings between few donor quantum dots in silicon

    Science.gov (United States)

    Gorman, S. K.; Broome, M. A.; Keizer, J. G.; Watson, T. F.; Hile, S. J.; Baker, W. J.; Simmons, M. Y.

    2016-05-01

    The long term scaling prospects for solid-state quantum computing architectures relies heavily on the ability to simply and reliably measure and control the coherent electron interaction strength, known as the tunnel coupling, t c. Here, we describe a method to extract the t c between two quantum dots (QDs) utilising their different tunnel rates to a reservoir. We demonstrate the technique on a few donor triple QD tunnel coupled to a nearby single-electron transistor (SET) in silicon. The device was patterned using scanning tunneling microscopy-hydrogen lithography allowing for a direct measurement of the tunnel coupling for a given inter-dot distance. We extract {t}{{c}}=5.5+/- 1.8 {{GHz}} and {t}{{c}}=2.2+/- 1.3 {{GHz}} between each of the nearest-neighbour QDs which are separated by 14.5 nm and 14.0 nm, respectively. The technique allows for an accurate measurement of t c for nanoscale devices even when it is smaller than the electron temperature and is an ideal characterisation tool for multi-dot systems with a charge sensor.

  10. Coupling capacitance between double quantum dots tunable by the number of electrons in Si quantum dots

    International Nuclear Information System (INIS)

    Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD

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

    DEFF Research Database (Denmark)

    Grodecka-Grad, Anna; Foerstner, Jens

    2011-01-01

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

  12. Universal parametric correlations of conductance peaks in quantum dots

    International Nuclear Information System (INIS)

    We compute the parametric correlation function of the conductance peaks in chaotic and weakly disordered quantum dots in the Coulomb blockade regime and demonstrate its universality upon an appropriate scaling of the parameter. For a symmetric dot we show that this correlation function is affected by breaking time-reversal symmetry but is independent of the details of the channels in the external leads. We derive a new scaling which depends on the eigenfunctions alone and can be extracted directly from the conductance peak heights. Our results are in excellent agreement with model simulations of a disordered quantum dot. copyright 1996 The American Physical Society

  13. Kondo effect in quantum dots and molecular devices

    Institute of Scientific and Technical Information of China (English)

    JIANG Lang; LI Hongxiang; HU Wenping; ZHU Daoben

    2005-01-01

    Kondo effect is a very important many-body phenomenon in condensed matter physics,which explains why the resistance increases as the temperature is lowered (usually <10 K) in dilute magnetic alloy, and why the conductance increases as temperature is decreased in quantum dots. This paper simply introduces equilibrium and non- equilibrium Kondo effects in quantum dots together with the Kondo effect in quantum dots with even number of electrons (when the singlet and triplet states are degenerate). Furthermore, Kondo effect in single atom/molecular transistors is introduced, which indicates a new way to study Kondo effect.

  14. Dielectrophoretic Manipulation and Separation of Microparticles Using Microarray Dot Electrodes

    Directory of Open Access Journals (Sweden)

    Bashar Yafouz

    2014-04-01

    Full Text Available This paper introduces a dielectrophoretic system for the manipulation and separation of microparticles. The system is composed of five layers and utilizes microarray dot electrodes. We validated our system by conducting size-dependent manipulation and separation experiments on 1, 5 and 15 μm polystyrene particles. Our findings confirm the capability of the proposed device to rapidly and efficiently manipulate and separate microparticles of various dimensions, utilizing positive and negative dielectrophoresis (DEP effects. Larger size particles were repelled and concentrated in the center of the dot by negative DEP, while the smaller sizes were attracted and collected by the edge of the dot by positive DEP.

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

    DEFF Research Database (Denmark)

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

    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...

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

    Science.gov (United States)

    DeHaven, Stan; Williams, Phillip; Burke, Eric

    2015-01-01

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

  17. 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.

  18. Imaging GABAc Receptors with Ligand-Conjugated Quantum Dots

    Directory of Open Access Journals (Sweden)

    Sandra J. Rosenthal

    2008-04-01

    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.

  19. Optically Modulated Bistability in Quantum Dot Resonant Tunneling Diodes

    Science.gov (United States)

    Weng, Qian-Chun; An, Zheng-Hua; Hou, Ying; Zhu, Zi-Qiang

    2013-04-01

    InAs quantum dots are introduced into resonant tunneling diodes to study the electronic transport behavior, and a wide bistability (ΔV ~ 0.8 V) is observed in the negative differential resistance region. Based on an analytic model, we attribute the observed distinct bistability of a resonant tunneling diodes with quantum dots to the feedback dependence of energy of the electron-storing quantum dots on the tunneling current density. Meanwhile, we find that this wide bistable region can be modulated sensitively by light illumination and becomes narrower with increasing light intensity. Our results suggest that the present devices can be potentially used as sensitive photodetectors in optoelectronic fields.

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

    International Nuclear Information System (INIS)

    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