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Sample records for anisn format dot

  1. Reentrant formation of magnetic polarons in quantum dots

    Science.gov (United States)

    Pientka, J. M.; Oszwałdowski, R.; Petukhov, A. G.; Han, J. E.; Žutić, Igor

    2012-10-01

    We propose a model of magnetic polaron formation in semiconductor quantum dots doped with magnetic ions. A wetting layer serves as a reservoir of photogenerated holes, which can be trapped by the adjacent quantum dots. For certain hole densities, the temperature dependence of the magnetization induced by the trapped holes is reentrant: it disappears for some temperature range and reappears at higher temperatures. We demonstrate that this peculiar effect is not an artifact of the mean-field approximation and persists after statistical spin fluctuations are accounted for. We predict fingerprints of reentrant magnetic polarons in photoluminescence spectra.

  2. 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.

  3. Inducing vortex formation in multilayered circular dots using remanent curves

    Science.gov (United States)

    Kim, Dong-Ok; Ryeol Lee, Dong; Choi, Yongseong; Metlushko, Vitali; Park, Jihwey; Kim, Jae-Young; Bong Lee, Ki

    2012-11-01

    We report field manipulation of magnetic vortex states in Co(30 nm)/Cu(3 nm)/Ni80Fe20 (20 nm)-multilayer dot arrays via remanent curve. The element-resolved resonant x-ray magnetic measurements, combined with micromagnetic simulations, show vortex formation in the Co layer but not in the NiFe layer along the major hysteresis loop. Although the two magnetic layers are not directly coupled due to the presence of the Cu interlayer, the NiFe layer is strongly influenced by the dipolar field from uncompensated magnetic poles in the Co layer. Using remanent curves, we demonstrate that the single vortex state can be induced simultaneously in both layers.

  4. The formation of acetylcholine receptor clusters visualized with quantum dots

    Directory of Open Access Journals (Sweden)

    Peng H Benjamin

    2009-07-01

    Full Text Available Abstract Background Motor innervation of skeletal muscle leads to the assembly of acetylcholine receptor (AChR clusters in the postsynaptic membrane at the vertebrate neuromuscular junction (NMJ. Synaptic AChR aggregation, according to the diffusion-mediated trapping hypothesis, involves the establishment of a postsynaptic scaffold that "traps" freely diffusing receptors into forming high-density clusters. Although this hypothesis is widely cited to explain the formation of postsynaptic AChR clusters, direct evidence at molecular level is lacking. Results Using quantum dots (QDs and live cell imaging, we provide new measurements supporting the diffusion-trap hypothesis as applied to AChR cluster formation. Consistent with published works, experiments on cultured Xenopus myotomal muscle cells revealed that AChRs at clusters that formed spontaneously (pre-patterned clusters, also called hot spots and at those induced by nerve-innervation or by growth factor-coated latex beads were very stable whereas diffuse receptors outside these regions were mobile. Moreover, despite the restriction of AChR movement at sites of synaptogenic stimulation, individual receptors away from these domains continued to exhibit free diffusion, indicating that AChR clustering at NMJ does not involve an active attraction of receptors but is passive and diffusion-driven. Conclusion Single-molecular tracking using QDs has provided direct evidence that the clustering of AChRs in muscle cells in response to synaptogenic stimuli is achieved by two distinct cellular processes: the Brownian motion of receptors in the membrane and their trapping and immobilization at the synaptic specialization. This study also provides a clearer picture of the "trap" that it is not a uniformly sticky area but consists of discrete foci at which AChRs are immobilized.

  5. 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.

  6. 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.

  7. Sb mediated formation of Ge/Si quantum dots: Growth and properties

    Energy Technology Data Exchange (ETDEWEB)

    Tonkikh, A.A., E-mail: tonkikh@mpi-halle.de [Max-Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany); Institute for Physics of Microstructures RAS, Nizhniy Novgorod (Russian Federation); Zakharov, N.D. [Max-Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany); Novikov, A.V.; Kudryavtsev, K.E. [Institute for Physics of Microstructures RAS, Nizhniy Novgorod (Russian Federation); Talalaev, V.G. [ZIK SiLi-nano, Martin Luther University Halle-Wittenberg (Germany); Fuhrmann, B.; Leipner, H.S. [Interdisciplinary Center of Materials Science, Martin Luther University Halle-Wittenberg (Germany); Werner, P. [Max-Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany)

    2012-02-01

    The phenomenon of surfactant (Sb) mediated formation of Ge/Si(100) islands (quantum dots) by means of molecular beam epitaxy is discussed. The limited diffusivity of Si and Ge adatoms caused by the Sb layer leads to a reduction of the size of Ge islands, the increase in the island density, and the sharpening of the interfaces of Ge islands. Thereby, a thin Sb layer is considered to be a powerful tool that provides more freedom in designing Ge quantum dot features. Ge quantum dots, grown via a thin Sb layer and embedded coherently in a Si p-n junction, are revealed to be the origin of the intense photo- and electroluminescence in the spectral range of about 1.5 {mu}m at room temperature.

  8. 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.

  9. Formation mechanism of dot-line square superlattice pattern in dielectric barrier discharge

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Weibo; Dong, Lifang, E-mail: donglfhbu@163.com, E-mail: pyy1616@163.com; Wang, Yongjie; Zhang, Xinpu [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); College of Quality and Technical Supervision, Hebei University, Baoding 071002 (China); Pan, Yuyang, E-mail: donglfhbu@163.com, E-mail: pyy1616@163.com [College of Quality and Technical Supervision, Hebei University, Baoding 071002 (China)

    2014-11-15

    We investigate the formation mechanism of the dot-line square superlattice pattern (DLSSP) in dielectric barrier discharge. The spatio-temporal structure studied by using the intensified-charge coupled device camera shows that the DLSSP is an interleaving of three different subpatterns in one half voltage cycle. The dot square lattice discharges first and, then, the two kinds of line square lattices, which form square grid structures discharge twice. When the gas pressure is varied, DLSSP can transform from square superlattice pattern (SSP). The spectral line profile method is used to compare the electron densities, which represent the amounts of surface charges qualitatively. It is found that the amount of surface charges accumulated by the first discharge of DLSSP is less than that of SSP, leading to a bigger discharge area of the following discharge (lines of DLSSP instead of halos of SSP). The spatial distribution of the electric field of the surface charges is simulated to explain the formation of DLSSP. This paper may provide a deeper understanding for the formation mechanism of complex superlattice patterns in DBD.

  10. Film formation of CdSe quantum dot embedded phosphate glass on an FTO glass substrate

    Science.gov (United States)

    Han, Karam; Kim, Yoon Hwa; Im, Won Bin; Chung, Woon Jin

    2015-07-01

    A thick film with CdSe quantum dot (QD) embedded glass was formed on a fluorine-doped tin oxide (FTO) glass substrate. Phosphate glasses with different CdO and ZnSe concentrations were synthesized, and the heat treatment conditions were varied to determine the appropriate QD and film formation conditions. Phosphate glass with 1 mol. % CdO and 1.5 mol. % ZnSe showed controlled crystallization of CdSe QDs when they were heat treated at 550℃ for 1 hr. Absorption spectra and Raman spectroscopy identified the QD formation. Precursor glass was ground into powder and pasted onto FTO only and TiO2/FTO glass substrates via the screen printing method. Glass film embedded with QDs was successfully formed after sintering, thus demonstrating its potential for film applications. [Figure not available: see fulltext.

  11. 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.

  12. 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.

  13. Unconventional application of conventional enzymatic substrate: first fluorogenic immunoassay based on enzymatic formation of quantum dots.

    Science.gov (United States)

    Malashikhina, Natalia; Garai-Ibabe, Gaizka; Pavlov, Valeri

    2013-07-16

    In this study, a simple fluorogenic immunoassay based on in situ formation of semiconductor quantum dots (QDs) is described. We discovered that alkaline phosphatase (ALP), the enzyme broadly used in enzyme-linked immuno-sorbent assay (ELISA), is able to trigger formation of fluorescent CdS QDs. ALP-catalyzed hydrolysis of p-nitrophenyl phosphate (pNPP) leads to the formation of p-nitrophenol and inorganic phosphate. The latter stabilizes CdS QDs produced in situ through interaction of Cd(2+) with S(2-) ions. So, the specific interaction of analyte (antibody) with ALP-labeled antibody can be detected through formation of CdS QDs, monitored by recording emission spectra at λex = 290 nm. The fluorescence intensity showed to be dependent on the concentration of target antibody. This method allowed us to detect as low as 0.4 ng mL(-1) of analyte antibody with a linear range up to 10 ng mL(-1). The sensitivity of this novel assay showed to be 1 order of magnitude better than that of the standard method based on colorimetric p-nitrophenyl phosphate assay.

  14. 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.

  15. Formation mechanism of highly luminescent silica capsules incorporating multiple hydrophobic quantum dots with various emission wavelengths.

    Science.gov (United States)

    Li, Chunliang; Murase, Norio

    2013-12-01

    A synthesis process was reconsidered for encapsulating hydrophobic quantum dots (QDs) into silica capsules with high photoluminescent (PL) efficiency. The process comprises three steps: silanization of QD surfaces, seed formation by assembly of the QDs, and coating of the QD seeds with a silica shell. Analysis of the encapsulation mechanism enabled this process to be adapted for application to CdSe-based core-shell QDs with various organic ligands such as oleic acid and with various emission wavelengths. Formation of the seeds is the key step in synthesizing the silica capsules, so that they have high PL efficiency. Due to the differences in QD size and in the affinity of the ligands on their surfaces, the concentration of QDs used in the synthesis must be optimized to maximize emission efficiency. Contrary to an initial assumption, several ligands remained on the QD surfaces even after the QDs were transferred from organic solution to water. This greatly affected the size and PL efficiency of the seeds. Judicious selection of the conditions for seed and silica capsule synthesis resulted in seeds with PL efficiency greater than 70% and in silica capsules encapsulating multiple CdSe/CdZnS QDs with PL efficiency as high as 41%. Silica capsules incorporating QDs with various emission peak wavelengths from green to red were also prepared. The process presented serves as a guideline for encapsulating various types of hydrophobic QDs into silica capsules for biological tagging applications.

  16. Formation of emission line dots and extremely metal-deficient dwarfs from almost dark galaxies

    CERN Document Server

    Bekki, Kenji

    2015-01-01

    Recent observations have discovered a number of extremely gas-rich very faint dwarf galaxies possibly embedded in low-mass dark matter halos. We investigate star formation histories of these gas-rich dwarf ("almost dark") galaxies both for isolated and interacting/merging cases. We find that although star formation rates (SFRs) are very low (<10^-5 M_sun/yr) in the simulated dwarfs in isolation for the total halo masses (M_h) of 10^8-10^9 M_sun, they can be dramatically increased to be ~ 10^{-4} M_sun/yr when they interact or merge with other dwarfs. These interacting faint dwarfs with central compact HII regions can be identified as isolated emission line dots ("ELdots") owing to their very low surface brightness envelopes of old stars. The remnant of these interacting and merging dwarfs can finally develop central compact stellar systems with very low metallicities (Z/Z_sun<0.1), which can be identified as extremely metal-deficient ("XMD") dwarfs. These results imply that although there would exist ma...

  17. The influence of sodium nanoparticles formation on luminescent properties of fluorophosphate glasses containing molecular clusters and quantum dots of lead selenide

    Science.gov (United States)

    Lipatova, Zh. O.; Kolobkova, E. V.; Sidorov, A. I.; Nikonorov, N. V.

    2016-08-01

    The influence of sodium nanoparticles and secondary heat treatment conditions on the spectralluminescent characteristics of fluorophosphate glasses with PbSe molecular clusters and quantum dots is studied. Experiments with glasses containing no sodium nanoparticles show that their thermal treatment leads to the formation of molecular clusters with subsequent formation of quantum dots having an intense luminescence. The results of numerical simulation for glasses with sodium nanoparticles shows that heat treatment leads to formation of a sodium fluoride shell on the nanoparticles surface. It is shown that quenching of the luminescence of PbSe molecular clusters and quantum dots takes place in these glasses.

  18. Quantum dot-based molecular imaging of cancer cell growth using a clone formation assay.

    Science.gov (United States)

    Geng, Xia-Fei; Fang, Min; Liu, Shao-Ping; Li, Yan

    2016-10-01

    This aim of the present study was to investigate clonal growth behavior and analyze the proliferation characteristics of cancer cells. The MCF‑7 human breast cancer cell line, SW480 human colon cancer cell line and SGC7901 human gastric cancer cell line were selected to investigate the morphology of cell clones. Quantum dot‑based molecular targeted imaging techniques (which stained pan‑cytokeratin in the cytoplasm green and Ki67 in the cell nucleus yellow or red) were used to investigate the clone formation rate, cell morphology, discrete tendency, and Ki67 expression and distribution in clones. From the cell clone formation assay, the MCF‑7, SW480 and SGC7901 cells were observed to form clones on days 6, 8 and 12 of cell culture, respectively. These three types of cells had heterogeneous morphology, large nuclear:cytoplasmic ratios, and conspicuous pathological mitotic features. The cells at the clone periphery formed multiple pseudopodium. In certain clones, cancer cells at the borderline were separated from the central cell clusters or presented a discrete tendency. With quantum dot‑based molecular targeted imaging techniques, cells with strong Ki67 expression were predominantly shown to be distributed at the clone periphery, or concentrated on one side of the clones. In conclusion, cancer cell clones showed asymmetric growth behavior, and Ki67 was widely expressed in clones of these three cell lines, with strong expression around the clones, or aggregated at one side. Cell clone formation assay based on quantum dots molecular imaging offered a novel method to study the proliferative features of cancer cells, thus providing a further insight into tumor biology.

  19. 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

  20. Functional Si and CdSe quantum dots: synthesis, conjugate formation, and photoluminescence quenching by surface interactions.

    Science.gov (United States)

    Sudeep, P K; Emrick, Todd

    2009-12-22

    Silicon quantum dots (QDs) were prepared with a corona of di-n-octyl phosphine oxides, by performing hydrosilylation chemistry on the surface of hydrogen-terminated Si QDs. These novel Si QDs proved well-suited to serve as "ligands" for other semiconductor QDs, such as CdSe, by interaction of the phosphine oxide corona with the CdSe surface. A pronounced photoluminescence quenching of CdSe quantum dots was observed upon introduction of the phosphine oxide functionalized Si QDs to a CdSe QD solution. Surface functionalization of the Si QDs proved critically important to observing these effects, as conventional (alkane-covered) Si QD samples gave no evidence of electronic interactions with TOPO-covered CdSe. In a comparative system, phosphine oxide terminated oligo(phenylene vinylene) molecules acting as CdSe QD ligands provide a similar fluorescence quenching, with exciton decay kinetics supporting the formation of an electronically interacting hybrid materials system.

  1. 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.

  2. Effect of InAlGaAs and GaAs combination barrier thickness on the duration of dot formation in different layers of stacked InAs/GaAs quantum dot heterostructure grown by MBE.

    Science.gov (United States)

    Halder, N; Suseendran, J; Chakrabarti, S; Herrera, Miriam; Bonds, Marta; Browning, Nigel D

    2010-08-01

    Multilayer stacks of quantum dots (QDs) (10 periods) with a combination barrier layer of In0.21Al0.21 Ga0.58As (30 angstroms) and GaAs (70-180 angstroms) are grown by solid source molecular beam epitaxy (MBE) and reflection high-energy electron diffraction (RHEED) has been used for the in situ determination of the duration of dot formation in the QD layers. The increase in the duration of dot formation in the consecutive layers of the QD heterostructure with thinner barrier is attributed to the indium migration towards the defects in the strained QD layers. A thicker GaAs layer at 590 degrees C overgrown on the InAlGaAs is believed to remove the unevenness of the growth front for the subsequent QD layer resulting in good vertical stacking of islands till the final layer of the multilayer heterostructures.

  3. Mechanistic Insights into the Formation of InP Quantum Dots**

    Science.gov (United States)

    Allen, Peter M.; Walker, Brian J.

    2011-01-01

    This paper examines the molecular mechanism of InP colloidal quantum dot (QD) syntheses. Unlike methods for monodisperse PbSe and CdSe we found that existing InP syntheses result in total depletion of molecular phosphorous species following nucleation, so QD growth is due exclusively to non-molecular ripening. We find that amines inhibit precursor depletion via solvation, and these findings may lead to better synthetic methodology for InP QDs. PMID:20025010

  4. Dipolariton formation in quantum dot molecules strongly coupled to optical resonators

    CERN Document Server

    Domínguez, Marlon S; Ramírez, Hanz Y

    2016-01-01

    In this theoretical work, we study a double quantum dot interacting strongly with a microcavity, while undergoing resonant tunneling. Effects of interdot tunneling on the light-matter hybridized states are determined, and tunability of their brightness degrees and associated dipole moments is demonstrated. These results predict dipolariton generation in artificial molecules coupled to optical resonators, and provide a promising scenario for control of emission efficiency and coherence times of exciton polaritons.

  5. Formation of Ge quantum dots array in layer-cake technique for advanced photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Chien, C Y; Chang, Y J; Chang, J E; Lee, M S; Li, P W [Department of Electrical Engineering, National Central University, ChungLi, 320, Taiwan (China); Chen, W Y; Hsu, T M, E-mail: pwli@ee.ncu.edu.tw [Department of Physics and Center for Nano Science and Technology, National Central University, ChungLi, 32001, Taiwan (China)

    2010-12-17

    We report a simple and manageable growth method for placing dense three-dimensional Ge quantum dot (QD) arrays in a uniform or a graded size distribution, based on thermally oxidizing stacked poly-SiGe in a layer-cake technique. The QD size and spatial density in each stack can be modulated by conditions of the Ge content in poly-Si{sub 1-x}Ge{sub x}, oxidation, and the underlay buffer layer. Size-dependent internal structure, strain, and photoluminescence properties of Ge QDs are systematically investigated. Optimization of the processing conditions could be carried out for producing dense Ge QD arrays to maximize photovoltaic efficiency.

  6. Formation of spin droplet at ν =5/2 in an asymmetric quantum dot under quantum Hall conditions

    Science.gov (United States)

    Atci, H.; Siddiki, A.

    2017-01-01

    In this work, a quantum dot that is defined asymmetrically by electrostatic means induced on a GaAs/AlGaAs heterostructure is investigated to unravel the effect of geometric constraints on the formation of spin droplets under quantized Hall conditions. The incompressibility of the excited ν =5/2 state is explored by solving the Schrödinger equation within spin density functional theory, where the confinement potential is obtained self-consistently utilizing the Thomas-Fermi approximation. Our numerical investigations show that the spatial distribution of the ν =2 incompressible strips and electron occupation in the second lowest Landau level considerably differ from the results of the laterally symmetric quantum dots. Our findings yield two important consequences: first, the incompressibility of the intriguing ν =5/2 state is strongly affected by the asymmetry, and second, since the Aharonov-Bohm interference patterns depend on the velocity of the particles, asymmetry yields an additional parameter to adjust the oscillation period, which imposes a boundary condition dependency in observing quasiparticle phases.

  7. Ex Situ Formation of Metal Selenide Quantum Dots Using Bacterially Derived Selenide Precursors

    Energy Technology Data Exchange (ETDEWEB)

    Fellowes, Jonathan W.; Pattrick, Richard; Lloyd, Jon; Charnock, John M.; Coker, Victoria S.; Mosselmans, JFW; Weng, Tsu-Chien; Pearce, Carolyn I.

    2013-04-12

    Luminescent quantum dots were synthesized using bacterially derived selenide (SeII-) as the precursor. Biogenic SeII- was produced by the reduction of Se-IV by Veillonella atypica and compared directly against borohydride-reduced Se-IV for the production of glutathione-stabilized CdSe and beta-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.

  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. 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

    Energy Technology Data Exchange (ETDEWEB)

    Kole, Arindam; Chaudhuri, Partha, E-mail: erpc@iacs.res.in

    2012-11-01

    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 (SiH{sub 4}) and methane (CH{sub 4}) 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 (E{sub g}) 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 E{sub g} 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.

  10. 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

  11. Influence of reaction temperature on the formation process of ZnO quantum dots and the optical properties

    Institute of Scientific and Technical Information of China (English)

    庄晋艳; 李岚; 张晓松; 徐建萍; 魏军

    2009-01-01

    ZnO quantum dots (QDs)with the sizes of 3.0-5.6 nm are synthesized by solution-phase method at different temperatures. We find that temperature has great influence on the size of ZnO QDs. The growth process is the most sensitive to temperature, and the process is well explained by Lifshitz-Slyozov-Wagner (LSW) model. By photoluminescence (PL) spectra of the quantum dots at different temperatures and reactive time, we come to a conclusion that ultraviolet emission is mainly due to surface defects, and the or...

  12. Lateral variation of interface disorder in wetting layer on formation of InAs/InP quantum dots visualized by near-field imaging spectroscopy

    Science.gov (United States)

    Tojinbara, Hiroki; Takahashi, Motoki; Tsumori, Nobuhiro; Mizuno, Dai; Kubota, Ryosuke; Sakuma, Yoshiki; Saiki, Toshiharu

    2012-01-01

    Near-field photoluminescence imaging spectroscopy of a wetting layer of InAs/InP quantum dots (QDs) at the critical thickness of 2.4 monolayers (ML) is used to visualize the spatial variation of the interface disorder. The wetting layer has a significantly lower density of carrier localization centers than a 2-ML thick InAs/InP quantum well, particularly in the vicinity of the QDs. This indicates that atomic-scale interface disorder is reduced during the initial stages of QD formation; in contrast, disorder remained far from the QDs.

  13. Nano-dot formation using self-assembled 3-mercaptopropionic acid thin films prepared by facile atmospheric-vapor-adsorption method on Au(1 1 1)

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Tohru; Kimura, Ryota; Sakai, Hideki; Abe, Masahiko; Kondoh, Hiroshi; Ohta, Toshiaki; Matsumoto, Mutsuyoshi

    2002-12-30

    Nanometer scale structures of self-assembled films consisting of 3-mercaptopropionic acid (MPA) were formed by using electric stimuli between scanning tunng microscope (STM) Au tips and gold surfaces. The obtained structures were compared with those using bare gold surfaces and hexanethiol films on Au(1 1 1) under the same conditions. X-ray photoelectron spectroscopy measurements revealed that self-assembled ultrathin films of the corresponding thiol molecules were fabricated on Au(1 1 1) by a facile atmospheric-vapor-adsorption (AVA) method without solvent. Comparison of nano-structure formation suggested that the self-assembled thin films of 3-mercatopropionic acid molecules gave nano-dots below the height of voltage pulses where gold atom emission from Au tips and surface evaporation of Au(1 1 1) take place. It was found that 3-mercaptopropionic acid films easily produced much better nano-dots on Au(1 1 1) than hexanethiol films probably due to the formation of hydrogen bonding networks and/or the reactions of 3-mercaptopropionic acid when electric pulses were applied to the films.

  14. CdSe quantum dot formation: alternative paths to relaxation of a strained CdSe layer and influence of the capping conditions.

    Science.gov (United States)

    Robin, I C; Aichele, T; Bougerol, C; André, R; Tatarenko, S; Bellet-Amalric, E; Van Daele, B; Van Tendeloo, G

    2007-07-01

    CdSe/ZnSe quantum dot formation is investigated by studying different steps of the growth. To precisely control the critical thickness of CdSe grown on a ZnSe buffer layer, the CdSe self-regulated growth rate in atomic layer epitaxy growth mode is determined by reflection high-energy electron diffraction (RHEED) measurements for a temperature range between 180 and 280 °C. Then, the two-dimensional-three-dimensional (2D-3D) transition of a strained CdSe layer on (001)-ZnSe induced by the use of amorphous selenium is studied. The formation of CdSe islands is found when 3 monolayers (ML) of CdSe are deposited. When only 2.5 ML of CdSe are deposited, another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. We also studied the evolution of the surface morphology when 2.7 ML are deposited, to study the boundary between those two phenomena. The influence of capping on quantum dot morphology is investigated. It is found that cadmium is redistributed within the layer during capping. Our results show that the cadmium distribution after capping depends on the capping temperature and on the strain of the CdSe layer. Cadmium incorporation after capping is also studied. It is found that the amount of incorporated cadmium depends on the strain of the CdSe layer before capping.

  15. CdSe quantum dot formation: alternative paths to relaxation of a strained CdSe layer and influence of the capping conditions

    Energy Technology Data Exchange (ETDEWEB)

    Robin, I C [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Aichele, T [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Bougerol, C [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Andre, R [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Tatarenko, S [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Bellet-Amalric, E [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group, Departement de Recherche Fondamentale sur la Matiere Condensee/SP2M CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France); Daele, B Van [IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Tendeloo, G van [EMAT University of Antwerp (RUCA), Groenenborgerlaan 171, 2020 Antwerp (Belgium)

    2007-07-04

    CdSe/ZnSe quantum dot formation is investigated by studying different steps of the growth. To precisely control the critical thickness of CdSe grown on a ZnSe buffer layer, the CdSe self-regulated growth rate in atomic layer epitaxy growth mode is determined by reflection high-energy electron diffraction (RHEED) measurements for a temperature range between 180 and 280 deg. C. Then, the two-dimensional-three-dimensional (2D-3D) transition of a strained CdSe layer on (001)-ZnSe induced by the use of amorphous selenium is studied. The formation of CdSe islands is found when 3 monolayers (ML) of CdSe are deposited. When only 2.5 ML of CdSe are deposited, another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. We also studied the evolution of the surface morphology when 2.7 ML are deposited, to study the boundary between those two phenomena. The influence of capping on quantum dot morphology is investigated. It is found that cadmium is redistributed within the layer during capping. Our results show that the cadmium distribution after capping depends on the capping temperature and on the strain of the CdSe layer. Cadmium incorporation after capping is also studied. It is found that the amount of incorporated cadmium depends on the strain of the CdSe layer before capping.

  16. 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.

  17. Formation of a Colloidal CdSe and ZnSe Quantum Dots via a Gamma Radiolytic Technique

    Directory of Open Access Journals (Sweden)

    Aeshah Salem

    2016-09-01

    Full Text Available Colloidal cadmium selenide (CdSe and zinc selenide (ZnSe quantum dots with a hexagonal structure were synthesized by irradiating an aqueous solution containing metal precursors, poly (vinyl pyrrolidone, isopropyl alcohol, and organic solvents with 1.25-MeV gamma rays at a dose of 120 kGy. The radiolytic processes occurring in water result in the nucleation of particles, which leads to the growth of the quantum dots. The physical properties of the CdSe and ZnSe nanoparticles were measured by various characterization techniques. X-ray diffraction (XRD was used to confirm the nanocrystalline structure, energy-dispersive X-ray spectroscopy (EDX was used to estimate the material composition of the samples, transmission electron microscopy (TEM was used to determine the morphologies and average particle size distribution, and UV-visible spectroscopy was used to measure the optical absorption spectra, from which the band gap of the CdSe and ZnSe nanoparticles could be deduced.

  18. 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.

  19. 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.

  20. 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.

  1. 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.)

  2. Dot1-dependent histone H3K79 methylation promotes the formation of meiotic double-strand breaks in the absence of histone H3K4 methylation in budding yeast.

    Directory of Open Access Journals (Sweden)

    Mohammad Bani Ismail

    Full Text Available Epigenetic marks such as histone modifications play roles in various chromosome dynamics in mitosis and meiosis. Methylation of histones H3 at positions K4 and K79 is involved in the initiation of recombination and the recombination checkpoint, respectively, during meiosis in the budding yeast. Set1 promotes H3K4 methylation while Dot1 promotes H3K79 methylation. In this study, we carried out detailed analyses of meiosis in mutants of the SET1 and DOT1 genes as well as methylation-defective mutants of histone H3. We confirmed the role of Set1-dependent H3K4 methylation in the formation of double-strand breaks (DSBs in meiosis for the initiation of meiotic recombination, and we showed the involvement of Dot1 (H3K79 methylation in DSB formation in the absence of Set1-dependent H3K4 methylation. In addition, we showed that the histone H3K4 methylation-defective mutants are defective in SC elongation, although they seem to have moderate reduction of DSBs. This suggests that high levels of DSBs mediated by histone H3K4 methylation promote SC elongation.

  3. LUMINESCENCE OF CADMIUM SULFIDE QUANTUM DOTS IN FLUOROPHOSPHATE GLASSES

    OpenAIRE

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

    2015-01-01

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

  4. 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

    2012-12-07

    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

  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

    2012-11-01

    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. Thermodynamics of formation of double salts M{sub 2}SO{sub 4} {center_dot} M{sup '}SO{sub 4} {center_dot} 6H{sub 2}O and M{sub 2}SeO{sub 4} {center_dot} M{sup '}SeO{sub 4} {center_dot} 6H{sub 2}O where M denotes Rb, or Cs and M{sup '} denote Co, Ni, or Zn[Pitzer model; Solubility diagram; Rubidium, and cesium sulfate and selenate; Cobalt, nickel, and zinc sulfate and selenate; M2SO4{center_dot}M'SO4{center_dot}6H2O- and M2SeO4{center_dot}M'SeO4{center_dot}nH2O-double salts; Gibbs free energy

    Energy Technology Data Exchange (ETDEWEB)

    Christov, Christomir. E-mail: hhristov@chem.ucsd.edu

    2003-11-01

    Gibbs free energy of formation) of the solid phases (simple salts, six sulfate - M{sub 2}SO{sub 4} {center_dot} M{sup '}SO{sub 4} {center_dot} 6H{sub 2}O, and five selenate - M{sub 2}SeO{sub 4} {center_dot} M{sup '}SeO{sub 4} {center_dot} 6H{sub 2}O - double salts) crystallizing in the systems under consideration are determined.

  7. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

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

  8. 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...

  9. Formation of N, S-codoped fluorescent carbon dots from biomass and their application for the selective detection of mercury and iron ion

    Science.gov (United States)

    Ye, Qianghua; Yan, Fanyong; Luo, Yunmei; Wang, Yinyin; Zhou, Xuguang; Chen, Li

    2017-02-01

    Biomass is regarded as an excellent candidate for the preparation of heteroatom-doped carbon nanomaterials. We have developed a simple and facile one-pot synthesis of nitrogen and sulfur codoped fluorescent carbon dots from pigeon feathers, egg and manure via the pyrolysis carbonization method. The as-prepared four PCDs have high fluorescence quantum yield about 24.87% (PCDs-f), 17.48% (PCDs-w), 16.34% (PCDs-y), 33.50% (PCDs-m), respectively, which is higher than the other carbon dots preparing from biomass. We found that the preparation of PCDs-m with pigeon manure has no favourable selectively with heavy metal ions. However, other PCDs exhibit highly sensitive and selective detection behavior of Hg2 +/Fe3 + ions with a low detection limit of 10.3 and 60.9 nM. They were applied to imaging of human umbilical vein endothelial cells, showing low cytotoxicity and good biocompatibility.

  10. First-step nucleation growth dependence of InAs/InGaAs/InP quantum dot formation in two-step growth.

    Science.gov (United States)

    Yin, Zongyou; Tang, Xiaohong; Zhang, Jixuan; Deny, Sentosa; Teng, Jinghua; Du, Anyan; Chin, Mee Koy

    2008-02-27

    First-step nucleation growth has an important impact on the two-step growth of high-quality mid-infrared emissive InAs/InGaAs/InP quantum dots (QDs). It has been found that an optimized growth rate for first-step nucleation is critical for forming QDs with narrow size distribution, high dot density and high crystal quality. High growth temperature has an advantage in removing defects in the QDs formed, but the dot density will be reduced. Contrasting behavior in forming InAs QDs using metal-organic vapor phase epitaxy (MOVPE) by varying the input flux ratio of group-V versus group-III source (V/III ratio) in the first-step nucleation growth has been observed and investigated. High-density, 2.5 × 10(10) cm(-2), InAs QDs emitting at>2.15 µm have been formed with narrow size distribution, ∼1 nm standard deviation, by reducing the V/III ratio to zero in first-step nucleation growth.

  11. Connecting dots

    DEFF Research Database (Denmark)

    Murakami, Kyoko; Jacobs, Rachel L.

    2017-01-01

    of connecting the dots of recalled moments of individual family members lives and is geared towards building a family’s shared future for posterity. Lastly, we consider a wider implication of family reminiscence in terms of human development. http://www.infoagepub.com/products/Memory-Practices-and-Learning...... and Middleton, 1995). A reminiscence conversation is a dynamic talk-in-interaction, which can produce valuable learning experience for the participants involved. Reminiscence talk contains rich, personal, historic data that can reveal and inform family members of an unknown past. In this seminar/chapter, we...... shall present a discursive approach, a methodology that captures the dynamics of reminiscence. We analyse collected conversational data of British family members reminiscing on their past as a joint family activity. Through such talk-in-interaction, the family members develop continuity within...

  12. 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.

  13. Alkanols and chlorophenols cause different physiological adaptive responses on the level of cell surface properties and membrane vesicle formation in Pseudomonas putida DOT-T1E.

    Science.gov (United States)

    Baumgarten, Thomas; Vazquez, José; Bastisch, Christian; Veron, Wilfried; Feuilloley, Marc G J; Nietzsche, Sandor; Wick, Lukas Y; Heipieper, Hermann J

    2012-01-01

    In order to cope with the toxicity imposed by the exposure to environmental hydrocarbons, many bacteria have developed specific adaptive responses such as modifications in the cell envelope. Here we compared the influence of n-alkanols and chlorophenols on the surface properties of the solvent-tolerant bacterium Pseudomonas putida DOT-T1E. In the presence of toxic concentrations of n-alkanols, this strain significantly increased its cell surface charge and hydrophobicity with changes depending on the chain length of the added n-alkanols. The adaptive response occurred within 10 min after the addition of the solvent and was demonstrated to be of physiological nature. Contrary to that, chlorophenols of similar hydrophobicity and potential toxicity as the corresponding alkanols caused only minor effects in the surface properties. To our knowledge, this is the first observation of differences in the cellular adaptive response of bacteria to compound classes of quasi equal hydrophobicity and toxicity. The observed adaptation of the physico-chemical surface properties of strain DOT-T1E to the presence of alkanols was reversible and correlated with changes in the composition of the lipopolysaccharide content of the cells. The reaction is explained by previously described reactions allowing the release of membrane vesicles that was demonstrated for cells affected by 1-octanol and heat shock, whereas no membrane vesicles were released after the addition of chlorophenols.

  14. Synthesis and characterisation of multifunctional alginate microspheres via the in situ formation of ZnO quantum dots and the graft of 4-(1-pyrenyl) butyric acid to sodium alginate.

    Science.gov (United States)

    Luo, Guilin; Wang, Jianxin; Wang, Yingying; Feng, Bo; Weng, Jie

    2015-01-01

    Growth factor-loaded fluorescent alginate microspheres, which can realise sustained growth factor release and fluorescence imaging, were synthesised by in situ formation of ZnO quantum dots (QDs) and covalent graft of 4-(1-pyrenyl) butyric acid (PBA). BSA was chosen as a growth factor model protein to study the release kinetic of growth factors from alginate microspheres. The microsphere size and fluorescent properties were also investigated. Investigations of cell culture were used for evaluating biocompatibility of BSA-loaded fluorescent microspheres and fluorescence imaging property of ZnO QDs and PBA-grafted sodium alginate from the microspheres. The results show that they have good fluorescent property either to microspheres or to cells and fluorescent microspheres have good biocompatibility and property in sustained release of growth factors. The obtained microspheres will be expected to realise the imaging of cells and materials and also the release of growth factor in tissue engineering or in cell culture.

  15. Formats

    Directory of Open Access Journals (Sweden)

    Gehmann, Ulrich

    2012-03-01

    Full Text Available In the following, a new conceptual framework for investigating nowadays’ “technical” phenomena shall be introduced, that of formats. The thesis is that processes of formatting account for our recent conditions of life, and will do so in the very next future. It are processes whose foundations have been laid in modernity and which will further unfold for the time being. These processes are embedded in the format of the value chain, a circumstance making them resilient to change. In addition, they are resilient in themselves since forming interconnected systems of reciprocal causal circuits.Which leads to an overall situation that our entire “Lebenswelt” became formatted to an extent we don’t fully realize, even influencing our very percep-tion of it.

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

    Science.gov (United States)

    Al-Agel, Faisal A.; Suleiman, Jamal; Khan, Shamshad A.

    2017-03-01

    In this research work, we have synthesized silicon quantum dots at different substrate temperatures 193, 153 and 123 K at a fixed working pressure 5 Torr. of Argon gas. The structural studies of these silicon quantum dots have been undertaken using X-ray diffraction, Field Emission Scanning Electron Microscopy (FESEM) and High Resolution Transmission Electron Microscopy (HRTEM). The optical and electrical properties have been studied using UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Fluorescence spectroscopy and I-V measurement system. X-ray diffraction pattern of Si quantum dots prepared at different temperatures show the amorphous nature except for the quantum dots synthesized at 193 K which shows polycrystalline nature. FESEM images of samples suggest that the size of quantum dots varies from 2 to 8 nm. On the basis of UV-visible spectroscopy measurements, a direct band gap has been observed for Si quantum dots. FTIR spectra suggest that as-grown Si quantum dots are partially oxidized which is due exposure of as-prepared samples to air after taking out from the chamber. PL spectra of the synthesized silicon quantum dots show an intense peak at 444 nm, which may be attributed to the formation of Si quantum dots. Temperature dependence of dc conductivity suggests that the dc conductivity enhances exponentially by raising the temperature. On the basis above properties i.e. direct band gap, high absorption coefficient and high conductivity, these silicon quantum dots will be useful for the fabrication of solar cells.

  17. The formation and transformation of the spatial weak-light bright and dark solitons in a quantum dot molecule with the interdot tunneling coupling

    Science.gov (United States)

    Zeng, Kuanhong; Wang, Denglong; She, Yanchao; Luo, Xiaoqin

    2013-11-01

    We study analytically the properties of the optical absorption and the spatial weak-light solitons in a quantum dot molecule system with the interdot tunneling coupling (ITC). It is shown that, for the linear case, there exists tunneling induced transparency (TIT) in the context of a weak ITC, while the TIT can be replaced by Autler-Townes splitting in the presence of a strong ITC. For the nonlinear case, it is probable to realize the spatial optical solitons even under weak light intensity. Interestingly, we find that there appears transformation behavior between the bright and dark solitons by properly turning both the ITC strength and the detuning of the probe field. Meanwhile, the transformation condition of the bright and dark solitons is obtained. Additionally it is also found that the amplitude of the solitons first descends and then rises with the increasing of ITC strength. Our results may have potential applications for nonlinear optical experiments and optical telecommunication engineering in solid systems.

  18. From DOT to Dotty

    CERN Document Server

    CERN. Geneva

    2017-01-01

    - Module types are interfaces, which can be abstracted. In this talk Martin will present DOT, a particularly simple calculus that can express systems following these principles. DOT has been developed as the foundation of the next version of Scala. He will also report on dotty, a new Scala compiler that implements the constructs of DOT in its core data structures and that uses the lessons learned to drive Scala’s evolution.

  19. 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.

  20. Manipulating surface diffusion and elastic interactions to obtain quantum dot multilayer arrangements over different length scales

    Energy Technology Data Exchange (ETDEWEB)

    Placidi, E., E-mail: ernesto.placidi@ism.cnr.it; Arciprete, F. [Istituto di Struttura della Materia, CNR, Via del Fosso del Cavaliere 100, 00133 Rome (Italy); Università di Roma “Tor Vergata”, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy); Latini, V.; Latini, S.; Patella, F. [Università di Roma “Tor Vergata”, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy); Magri, R. [Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università di Modena e Reggio Emilia, and Centro S3 CNR-Istituto Nanoscienze, Via Campi 213/A, 4100 Modena (Italy); Scuderi, M.; Nicotra, G. [CNR-IMM, Strada VIII, 5, 95121 Catania (Italy)

    2014-09-15

    An innovative multilayer growth of InAs quantum dots on GaAs(100) is demonstrated to lead to self-aggregation of correlated quantum dot chains over mesoscopic distances. The fundamental idea is that at critical growth conditions is possible to drive the dot nucleation only at precise locations corresponding to the local minima of the Indium chemical potential. Differently from the known dot multilayers, where nucleation of new dots on top of the buried ones is driven by the surface strain originating from the dots below, here the spatial correlations and nucleation of additional dots are mostly dictated by a self-engineering of the surface occurring during the growth, close to the critical conditions for dot formation under the fixed oblique direction of the incoming As flux, that drives the In surface diffusion.

  1. Quantum Dot Solar Cells

    Science.gov (United States)

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

    2002-01-01

    We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in the synthesis process. We will present XRD, TEM, SEM and EDS characterization of our initial attempts at fabricating these quantum dots. Investigation of the size distributions of these nanoparticles via laser light scattering and scanning electron microscopy will be presented. Theoretical estimates on appropriate quantum dot composition, size, and inter-dot spacing along with potential scenarios for solar cell fabrication will be discussed.

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

    Science.gov (United States)

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

    2016-12-01

    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 towards realizing controllable large scale multiple quantum dot systems.

  3. LUMINESCENCE OF CADMIUM SULFIDE QUANTUM DOTS IN FLUOROPHOSPHATE GLASSES

    Directory of Open Access Journals (Sweden)

    Z. O. Lipatova

    2015-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-04

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

  5. Synthesis of biocompatible multicolor luminescent carbon dots for bioimaging applications

    Directory of Open Access Journals (Sweden)

    Nagaprasad Puvvada, B N Prashanth Kumar, Suraj Konar, Himani Kalita, Mahitosh Mandal and Amita Pathak

    2012-01-01

    Full Text Available Water-soluble carbon dots (C-dots were prepared through microwave-assisted pyrolysis of an aqueous solution of dextrin in the presence of sulfuric acid. The C-dots produced showed multicolor luminescence in the entire visible range, without adding any surface-passivating agent. X-ray diffraction and Fourier transform infrared spectroscopy studies revealed the graphitic nature of the carbon and the presence of hydrophilic groups on the surface, respectively. The formation of uniformly distributed C-dots and their luminescent properties were, respectively, revealed from transmission electron microscopy and confocal laser scanning microscopy. The biocompatible nature of C-dots was confirmed by a cytotoxicity assay on MDA-MB-468 cells and their cellular uptake was assessed through a localization study.

  6. Volmer–Weber InAs quantum dot formation on InP (113)B substrates under the surfactant effect of Sb

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Yu, E-mail: yu.zhao@insa-rennes.fr; Bertru, Nicolas; Folliot, Hervé; Rohel, Tony [Université Européenne de Bretagne, INSA, FOTON, UMR-CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes Cedex 7 (France); Mauger, Samuel J. C.; Koenraad, Paul M. [COBRA Inter-University Research Institute, Eindhoven University of Technology, P.O. Box 513, NL-5600MB Eindhoven (Netherlands)

    2014-07-21

    We report on Sb surfactant growth of InAs nanostructures on GaAs{sub 0.51}Sb{sub 0.49} layers deposited on InP (001) and on (113)B oriented substrates. On the (001) orientation, the presence of Sb significantly favors the two-dimensional growth regime. Even after the deposition of 5 mono-layers of InAs, the epitaxial film remains flat and InAs/GaAs{sub 0.51}Sb{sub 0.49} type-II quantum wells are achieved. On (113)B substrates, same growth runs resulted in formation of high density InAs islands. Microscopic studies show that wetting layer is missing on (113)B substrates, and thus, a Volmer-Weber growth mode is concluded. These different behaviors are attributed to the surface energy changes induced by Sb atoms on surface.

  7. Initial stage growth of GexSi1-x layers and Ge quantum dot formation on GexSi1-x surface by MBE.

    Science.gov (United States)

    Nikiforov, Aleksandr I; Timofeev, Vyacheslav A; Teys, Serge A; Gutakovsky, Anton K; Pchelyakov, Oleg P

    2012-10-09

    Critical thicknesses of two-dimensional to three-dimensional growth in GexSi1-x layers were measured as a function of composition for different growth temperatures. In addition to the (2 × 1) superstructure for a Ge film grown on Si(100), the GexSi1-x layers are characterized by the formation of (2 × n) reconstruction. We measured n for all layers of Ge/GexSi1-x/Ge heterosystem using our software with respect to the video recording of reflection high-energy electron diffraction (RHEED) pattern during growth. The n reaches a minimum value of about 8 for clear Ge layer, whereas for GexSi1-x films, n is increased from 8 to 14. The presence of a thin strained film of the GexSi1-x caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array for the top Ge layer. Based on the RHEED data, the hut-like island form, which has not been previously observed by us between the hut and dome islands, has been detected. Data on the growth of Ge/GexSi1-x/Ge heterostructures with the uniform array of islands in the second layer of the Ge film have been received.

  8. 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

  9. Correlation effects in strain-induced quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Rinaldi, R.; DeVittorio, M.; Cingolani, R.; Molinari, E. [Ist. Nazionale per la Fisica della Materia (INFM) and Dipt. di Ingegneria dell' Innovazione, Univ. Lecce (Italy); Hohenester, U. [INFM and Dipt. di Fisica, Univ. Modena e Reggio E. (Italy); Lipsanen, H.; Tulkki, J. [Optoelectronics Lab. and Lab. of Computational Engineering, Helsinki Univ. of Technology (Finland); Ahopelto, J. [VTT Electronics (Finland); Uchida, K.; Miura, N. [Inst. for Solid State Physics, Univ. of Tokyo (Japan); Arakawa, Y. [Inst. of Industrial Science, Univ. of Tokyo (Japan)

    2001-03-08

    We report on Coulomb correlation effects in the luminescence of strain-induced quantum dots. In single dots, under low power excitation, we observe the rising of sharp lines associated to the formation of excitonic molecules. In the grand-ensemble, in magnetic fields up to 45 T, we observe Darwin-Fock states of the dots to merge into a unique Landau level, with a considerable reduction in the total diamagnetic shift due to the enhanced electron-hole correlation caused by the increased degeneracy of the state. (orig.)

  10. Neutron and gamma ray total dose rate determination using anisn

    Science.gov (United States)

    Amin, E.; Ashoub, N.; Elkady, A.

    1994-07-01

    The National Center for Nuclear Safety and Radiation Control is in the process of acquiring a computer software library based mainly on internationally widely used computer codes. These codes are to be used as basic tools in safety analysis and radiation control and risk assessment. A complementary part of this activity is to validate the computer codes and set standard procedures with the limits of confidence for the different areas of applications of the one or the other code or set of codes. The present work has been then initiated in order to develop a standard shielding calculating procedure to be applied for the different applications of interest to the center, namely: shielding of nuclear installations, such as the ET-RR-1 reactor, the gamma unit, nuclear accelerator, radiotherapy units; shielding of nuclear sources (mainly neutron and gamma sources); shielding of transportation containers. In developing such a standard method, the sources of error to the final results (i.e. the dose rate and dose rate distribution) have to been identified and the error to be quantified. Through applying the developed procedure to benchmark PWR shielding problems, and to documented results for fission sources in water and concrete, the levels of confidence of the procedure in different application areas have been set.

  11. Neutron and gamma ray total dose rate determination using ANISN

    Energy Technology Data Exchange (ETDEWEB)

    Amin, E.; Elkady, A. [Atomic Energy Authority, Cairo (Egypt). National Center for Nuclear Safety and Radiation Control; Ashoub, N. [Nuclear Research Center, Cairo (Egypt)

    1994-07-01

    The National Center for Nuclear Safety and Radiation Control is in the process of acquiring a computer software library based mainly on internationally widely used computer codes. These codes are to be used as basic tools in safety analysis and radiation control and risk assessment. A complementary part of this activity is to validate the computer codes and set standard procedures with the limits of confidence for the different areas of applications of the one or the other code or set of codes. The present work has been then initiated in order to develop a standard shielding calculating procedure to be applied for the different applications of interest to the center, namely: shielding of nuclear installations, such as the ET-RR-1 reactor, the gamma unit, nuclear accelerator, radiotherapy units; shielding of nuclear sources (mainly neutron and gamma sources); shielding of transportation containers. In developing such a standard method, the sources of error to the final results (i.e. the dose rate and dose rate distribution) have to be identified and the error to be quantified. Through applying the developed procedure to benchmark PWR shielding problems, and to documented results for fission sources in water and concrete, the levels of confidence of the procedure in different application areas have been set. (author).

  12. dot-app: a Graphviz-Cytoscape conversion plug-in [version 1; referees: 1 approved, 2 approved with reservations

    Directory of Open Access Journals (Sweden)

    Braxton Fitts

    2016-10-01

    Full Text Available dot-app is a Cytoscape 3 app that allows Cytoscape to import and export Graphviz (*.dot, *.gv files, also known as DOT files due to the *.dot extension and their conformance to the DOT language syntax. The DOT format was originally created in the early 2000s to represent graph topologies, layouts and formatting. DOT-encoded files are produced and consumed by a number of open-source graph applications, including GraphViz, Gephi, neato, smyrna, and others. While DOT-based graph applications are popular, they emphasize general graph layout and styling over the topological and semantic analysis functions available in domain-focused applications such as Cytoscape. While domain-focused applications have easy access to large networks (10,000 to 100,000 nodes and advanced analysis and formatting, they do not offer all of the styling options that DOT-based applications (particularly GraphViz do. dot-app enables the interchange of networks between Cytoscape and DOT-based applications so that users can benefit from the features of both. dot-app was first deployed to the Cytoscape App Store in August 2015, has since registered more than 1,200 downloads, and has been highly rated by more than 20 users.

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

    Science.gov (United States)

    2010-01-01

    To fabricate quantum dot arrays with programmable periodicity, functionalized DNA origami nanotubes were developed. Selected DNA staple strands were biotin-labeled to form periodic binding sites for streptavidin-conjugated quantum dots. Successful formation of arrays with periods of 43 and 71 nm demonstrates precise, programmable, large-scale nanoparticle patterning; however, limitations in array periodicity were also observed. Statistical analysis of AFM images revealed evidence for steric hindrance or site bridging that limited the minimum array periodicity. PMID:20681601

  14. Hexagonal graphene quantum dots

    KAUST Repository

    Ghosh, S.

    2016-12-05

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

  15. 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

  16. Optically induced magnetization in diluted magnetic quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    John Peter, A. [Government Arts College, Melur 625 106, Madurai (India)], E-mail: a_johnpeter@rediffmail.com; Lily Mary Eucharista, K. [Arul Anandar College, Karumathur 625 514, Madurai (India)

    2009-03-15

    We report the effect of intense laser field on donor impurities in a semimagnetic Cd{sub 1-x{sub in}}Mn{sub x{sub in}}Te/Cd{sub 1-x{sub out}}Mn{sub x{sub out}}Te quantum dot. The spin polaronic energy of different Mn{sup 2+} is evaluated for different dot radii using a mean field theory in the presence of laser field. Magnetization is calculated for various concentrations of Mn{sup 2+} ions with different dot sizes. Significant magnetization of Mn spins can be obtained through the formation of polarized exciton magnetic polarons (EMPs). A rapid decrease of the laser dressed donor ionization energy for different values of dot sizes with increasing field intensity is predicted. Also, it is found that the polarization of EMPs increases rapidly at higher excitation energies.

  17. Fuzzy Dot Structure of BG-algebras

    Directory of Open Access Journals (Sweden)

    Tapan Senapati

    2014-09-01

    Full Text Available 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.

  18. 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...

  19. Carbon nanotube quantum dots

    NARCIS (Netherlands)

    Sapmaz, S.

    2006-01-01

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

  20. Reversible photoluminescence quenching of CdSe/ZnS quantum dots embedded in porous glass by ammonia vapor.

    Science.gov (United States)

    Orlova, A O; Gromova, Yu A; Maslov, V G; Andreeva, O V; Baranov, A V; Fedorov, A V; Prudnikau, A V; Artemyev, M V; Berwick, K

    2013-08-23

    The photoluminescence response of semiconductor CdSe/ZnS quantum dots embedded in a borosilicate porous glass matrix to exposure to ammonia vapor is investigated. The formation of surface complexes on the quantum dots results in quenching of the photoluminescence and a shortening of the luminescence decay time. The process is reversible, desorption of ammonia molecules from the quantum dot surface causes the photoluminescence to recover. The sensitivity of the quantum dot luminescence intensity and decay time to the interaction time and the reversibility of the photoluminescence changes make the CdSe/ZnS quantum dots in porous glass system a candidate for use as an optical sensor of ammonia.

  1. Reversible photoluminescence quenching of CdSe/ZnS quantum dots embedded in porous glass by ammonia vapor

    Science.gov (United States)

    Orlova, A. O.; Gromova, Yu A.; Maslov, V. G.; Andreeva, O. V.; Baranov, A. V.; Fedorov, A. V.; Prudnikau, A. V.; Artemyev, M. V.; Berwick, K.

    2013-08-01

    The photoluminescence response of semiconductor CdSe/ZnS quantum dots embedded in a borosilicate porous glass matrix to exposure to ammonia vapor is investigated. The formation of surface complexes on the quantum dots results in quenching of the photoluminescence and a shortening of the luminescence decay time. The process is reversible, desorption of ammonia molecules from the quantum dot surface causes the photoluminescence to recover. The sensitivity of the quantum dot luminescence intensity and decay time to the interaction time and the reversibility of the photoluminescence changes make the CdSe/ZnS quantum dots in porous glass system a candidate for use as an optical sensor of ammonia.

  2. 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

  3. 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.

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

    Science.gov (United States)

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

    2016-12-01

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

  5. Nanocrystal quantum dots

    CERN Document Server

    Klimov, Victor I

    2010-01-01

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

  6. Quantum dot 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.

  7. 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.

  8. Dislocation-induced Charges in Quantum Dots: Step Alignment and Radiative Emission

    Science.gov (United States)

    Leon, R.; Okuno, J.; Lawton, R.; Stevens-Kalceff, M.; Phillips, M.; Zou, J.; Cockayne, D.; Lobo, C.

    1999-01-01

    A transition between two types of step alignment was observed in a multilayered InGaAs/GaAs quantum-dot (QD) structure. A change to larger QD sizes in smaller concentrations occurred after formation of a dislocation array.

  9. Interference and interactions in open quantum dots

    CERN Document Server

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

    2003-01-01

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

  10. Single quantum dot nanowire photodetectors

    NARCIS (Netherlands)

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

    2010-01-01

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

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

    Science.gov (United States)

    Kłopotowski, Ł.; Wojnar, P.; Kret, S.; Parlińska-Wojtan, M.; Fronc, K.; Wojtowicz, T.; Karczewski, G.

    2015-06-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kłopotowski, Ł., E-mail: lukasz.klopotowski@ifpan.edu.pl; Wojnar, P.; Kret, S.; Fronc, K.; Wojtowicz, T.; Karczewski, G. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Parlińska-Wojtan, M. [Facility for Electron Microscopy and Sample Preparation, Center for Microelectronics and Nanotechnology, Faculty of Mathematics and Natural Sciences, University of Rzeszów, ul. Pigonia 1, 35-959 Rzeszów (Poland)

    2015-06-14

    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.

  13. A non-genetic approach to labelling acute myeloid leukemia and bone marrow cells with quantum dots.

    Science.gov (United States)

    Zheng, Yanwen; Tan, Dongming; Chen, Zheng; Hu, Chenxi; Mao, Zhengwei J; Singleton, Timothy P; Zeng, Yan; Shao, Xuejun; Yin, Bin

    2014-06-01

    The difficulty in manipulation of leukemia cells has long hindered the dissection of leukemia pathogenesis. We have introduced a non-genetic approach of marking blood cells, using quantum dots. We compared quantum dots complexed with different vehicles, including a peptide Tat, cationic polymer Turbofect and liposome. Quantum dots-Tat showed the highest efficiency of marking hematopoietic cells among the three vehicles. Quantum dots-Tat could also label a panel of leukemia cell lines at varied efficiencies. More uniform intracellular distributions of quantum dots in mouse bone marrow and leukemia cells were obtained with quantum dots-Tat, compared with the granule-like formation obtained with quantum dots-liposome. Our results suggest that quantum dots have provided a photostable and non-genetic approach that labels normal and malignant hematopoietic cells, in a cell type-, vehicle-, and quantum dot concentration-dependent manner. We expect for potential applications of quantum dots as an easy and fast marking tool assisting investigations of various types of blood cells in the future.

  14. Photoconductive gain and quantum efficiency of remotely doped Ge/Si quantum dot photodetectors

    Science.gov (United States)

    Yakimov, A. I.; Kirienko, V. V.; Armbrister, V. A.; Bloshkin, A. A.; Dvurechenskii, A. V.; Shklyaev, A. A.

    2016-10-01

    We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

  15. 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.

  16. Hydrophobin-Encapsulated Quantum Dots.

    Science.gov (United States)

    Taniguchi, Shohei; Sandiford, Lydia; Cooper, Maggie; Rosca, Elena V; Ahmad Khanbeigi, Raha; Fairclough, Simon M; Thanou, Maya; Dailey, Lea Ann; Wohlleben, Wendel; von Vacano, Bernhard; de Rosales, Rafael T M; Dobson, Peter J; Owen, Dylan M; Green, Mark

    2016-02-01

    The phase transfer of quantum dots to water is an important aspect of preparing nanomaterials that are suitable for biological applications, and although numerous reports describe ligand exchange, very few describe efficient ligand encapsulation techniques. In this report, we not only report a new method of phase transferring quantum dots (QDs) using an amphiphilic protein (hydrophobin) but also describe the advantages of using a biological molecule with available functional groups and their use in imaging cancer cells in vivo and other imaging applications.

  17. Quantum Dots in Cell Biology

    OpenAIRE

    Barroso, Margarida M.

    2011-01-01

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

  18. Quantum dots in cell biology.

    Science.gov (United States)

    Barroso, Margarida M

    2011-03-01

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

  19. Self-organized dots of GaN:Mn grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kuroda, S.; Marcet, S. [CEA-CNRS Group ' ' Nanophysique et Semiconducteurs' ' , Laboratoire de Spectrometrie Physique, Universite Joseph Fourier, Grenoble I and CEA/DRFMC/SP2M, 17 avenue des Martyrs, 38054 Grenoble, Cedex 9 (France); Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Halley, D.; Ferrand, D.; Mariette, H. [CEA-CNRS Group ' ' Nanophysique et Semiconducteurs' ' , Laboratoire de Spectrometrie Physique, Universite Joseph Fourier, Grenoble I and CEA/DRFMC/SP2M, 17 avenue des Martyrs, 38054 Grenoble, Cedex 9 (France); Cibert, J. [Laboratoire Louis Neel, CNRS, BP 166, 38042 Grenoble (France); Yamamoto, S.; Sakai, T.; Ohshima, T.; Itoh, H. [Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gumma 370-1292 (Japan)

    2006-07-01

    Self-organized dots of Mn-doped GaN were grown on AlN by plasma-assisted molecular beam epitaxy. The growth was performed in the nitrogen-rich growth regime with the addition of small amount of Mn flux. The in-situ surface observation using reflection high energy electron diffraction (RHEED) and the ex-situ examination using atomic force microscope (AFM) revealed that the dot formation was observed only in the case where the amount of Mn flux was small. The estimate of Mn composition using particle induced X-ray emission (PIXE) experiment showed that the Mn composition in the dots layer was much higher than in thick (Ga,Mn)N layers grown with the same amount of Mn flux. The maximum Mn composition for the high-density dot formation was about x=0.01. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Fabrication of self-organized dots of GaN:Mn using plasma-assisted MBE

    Science.gov (United States)

    Kuroda, S.; Marcet, S.; Bellet-Amalric, E.; Halley, D.; Ferrand, D.; Cibert, J.; Mariette, H.

    2005-02-01

    The growth of self-organized dots of Mn-doped GaN on AlN by plasma-assisted molecular beam epitaxy was studied. The observations of reflection high-energy electron diffraction (RHEED) revealed that the transition of the growth mode from 2D to 3D was delayed by adding a small amount of Mn flux and it disappeared with the further increase in Mn flux. By atomic force microscope (AFM) measurement on a surface with uncapped dots, it was found that the 2D-3D transition occurs with the formation of high dots density only when a tiny amount of Mn flux was added. A possible mechanism for the suppression of the dot formation by additional Mn atoms is discussed.

  1. 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.

  2. Single to quadruple quantum dots with tunable tunnel couplings

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-03-17

    We prepare a gate-defined quadruple quantum dot to study the gate-tunability of single to quadruple quantum dots with finite inter-dot tunnel couplings. The measured charging energies of various double dots suggest that the dot size is governed by the gate geometry. For the triple and quadruple dots, we study the gate-tunable inter-dot tunnel couplings. For the triple dot, we find that the effective tunnel coupling between side dots significantly depends on the alignment of the center dot potential. These results imply that the present quadruple dot has a gate performance relevant for implementing spin-based four-qubits with controllable exchange couplings.

  3. 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.

  4. 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)

  5. Optically active quantum dots

    Science.gov (United States)

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

    2015-10-01

    The main goal of our research is to develop new types of technologically important optically active quantum dot (QD) based materials, study their properties and explore their biological applications. For the first time chiral II-VI QDs have been prepared by us using microwave induced heating with the racemic (Rac), D- and L-enantiomeric forms of penicillamine as stabilisers. Circular dichroism (CD) studies of these QDs have shown that D- and L-penicillamine stabilised particles produced mirror image CD spectra, while the particles prepared with a Rac mixture showed only a weak signal. It was also demonstrated that these QDs show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. These QDs have demonstrated highly specific chiral recognition of various biological species including aminoacids. The utilisation of chiral stabilisers also allowed the preparation of new water soluble white emitting CdS nano-tetrapods, which demonstrated circular dichroism in the band-edge region of the spectrum. Biological testing of chiral CdS nanotetrapods displayed a chiral bias for an uptake of the D- penicillamine stabilised nano-tetrapods by cancer cells. It is expected that this research will open new horizons in the chemistry of chiral nanomaterials and their application in nanobiotechnology, medicine and optical chemo- and bio-sensing.

  6. 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.

  7. Nanopatterned Quantum Dot Lasers for High Speed, High Efficiency, Operation

    Science.gov (United States)

    2015-04-27

    SUBTITLE 13. SUPPLEMENTARY NOTES 12. DISTRIBUTION AVAILIBILITY STATEMENT 6. AUTHORS 7. PERFORMING ORGANIZATION NAMES AND ADDRESSES 15. SUBJECT TERMS ...growth using metalorganic chemical vapor deposition (MOCVD). These methods allowed us to realize quantum dot active regions in which the injected carriers...temperature sensitivity , commonly observed in self-assembled QD lasers2. An alternate approach to SK QD formation is the use of nanopatterning with

  8. The histone H3K79 methyltransferase Dot1L is essential for mammalian development and heterochromatin structure.

    Directory of Open Access Journals (Sweden)

    Brendan Jones

    Full Text Available Dot1 is an evolutionarily conserved histone methyltransferase specific for lysine 79 of histone H3 (H3K79. In Saccharomyces cerevisiae, Dot1-mediated H3K79 methylation is associated with telomere silencing, meiotic checkpoint control, and DNA damage response. The biological function of H3K79 methylation in mammals, however, remains poorly understood. Using gene targeting, we generated mice deficient for Dot1L, the murine Dot1 homologue. Dot1L-deficient embryos show multiple developmental abnormalities, including growth impairment, angiogenesis defects in the yolk sac, and cardiac dilation, and die between 9.5 and 10.5 days post coitum. To gain insights into the cellular function of Dot1L, we derived embryonic stem (ES cells from Dot1L mutant blastocysts. Dot1L-deficient ES cells show global loss of H3K79 methylation as well as reduced levels of heterochromatic marks (H3K9 di-methylation and H4K20 tri-methylation at centromeres and telomeres. These changes are accompanied by aneuploidy, telomere elongation, and proliferation defects. Taken together, these results indicate that Dot1L and H3K79 methylation play important roles in heterochromatin formation and in embryonic development.

  9. 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.

  10. Chiral Graphene Quantum Dots.

    Science.gov (United States)

    Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; Qu, Zhi-Bei; Kim, Kyoungwon; Jiang, Shuang; Baumeister, Elizabeth; Lee, Jaewook; Yeom, Bongjun; Bahng, Joong Hwan; Lee, Jaebeom; Violi, Angela; Kotov, Nicholas A

    2016-02-23

    Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

  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. 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.

  13. Membrane analysis with amphiphilic carbon dots.

    Science.gov (United States)

    Nandi, Sukhendu; Malishev, Ravit; Parambath Kootery, Kaviya; Mirsky, Yelena; Kolusheva, Sofiya; Jelinek, Raz

    2014-09-14

    Newly-synthesized amphiphilic carbon dots were used for spectroscopic analysis and multicolour microscopic imaging of membranes and live cells. We show that Förster resonance energy transfer (FRET) occurred from the amphiphilic carbon dots to different membrane-associated fluorescence acceptors. The amphiphilic carbon dots enabled imaging of membrane disruption by the beta-amyloid peptide.

  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. Surface processes during purification of InP quantum dots.

    Science.gov (United States)

    Mordvinova, Natalia; Emelin, Pavel; Vinokurov, Alexander; Dorofeev, Sergey; Abakumov, Artem; Kuznetsova, Tatiana

    2014-01-01

    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(OH)3 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.

  16. Imaging electrostatically confined Dirac fermions in graphene quantum dots

    Science.gov (United States)

    Lee, Juwon; Wong, Dillon; Velasco, Jairo, Jr.; Rodriguez-Nieva, Joaquin F.; Kahn, Salman; Tsai, Hsin-Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid S.; Crommie, Michael F.

    2016-11-01

    Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries. Reflection and transmission at these boundaries affect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions.

  17. Quantum dots formed in InSb/AlAs and AlSb/AlAs heterostructures

    Science.gov (United States)

    Abramkin, D. S.; Rumynin, K. M.; Bakarov, A. K.; Kolotovkina, D. A.; Gutakovskii, A. K.; Shamirzaev, T. S.

    2016-06-01

    The crystal structure of new self-assembled InSb/AlAs and AlSb/AlAs quantum dots grown by molecularbeam epitaxy has been investigated by transmission electron microscopy. The theoretical calculations of the energy spectrum of the quantum dots have been supplemented by the experimental data on the steady-state and time-resolved photoluminescence spectroscopy. Deposition of 1.5 ML of InSb or AlSb on the AlAs surface carried out in the regime of atomic-layer epitaxy leads to the formation of pseudomorphically strained quantum dots composed of InAlSbAs and AlSbAs alloys, respectively. The quantum dots can have the type-I and type-II energy spectra depending on the composition of the alloy. The ground hole state in the quantum dot belongs to the heavy-hole band and the localization energy of holes is much higher than that of electrons. The ground electron state in the type-I quantum dots belongs to the indirect X XY valley of the conduction band of the alloy. The ground electron state in the type-II quantum dots belongs to the indirect X valley of the conduction band of the AlAs matrix.

  18. InAs Colloidal Quantum Dots Synthesis via Aminopnictogen Precursor Chemistry.

    Science.gov (United States)

    Grigel, Valeriia; Dupont, Dorian; De Nolf, Kim; Hens, Zeger; Tessier, Mickael D

    2016-10-05

    Despite their various potential applications, InAs colloidal quantum dots have attracted considerably less attention than more classical II-VI materials because of their complex syntheses that require hazardous precursors. Recently, amino-phosphine has been introduced as a cheap, easy-to-use and efficient phosphorus precursor to synthesize InP quantum dots. Here, we use aminopnictogen precursors to implement a similar approach for synthesizing InAs quantum dots. We develop a two-step method based on the combination of aminoarsine as the arsenic precursor and aminophosphine as the reducing agent. This results in state-of-the-art InAs quantum dots with respect to the size dispersion and band-gap range. Moreover, we present shell coating procedures that lead to the formation of InAs/ZnS(e) core/shell quantum dots that emit in the infrared region. This innovative synthesis approach can greatly facilitate the research on InAs quantum dots and may lead to synthesis protocols for a wide range of III-V quantum dots.

  19. Nanoscale quantum-dot supercrystals

    Science.gov (United States)

    Baimuratov, Anvar S.; Turkov, Vadim K.; Rukhlenko, Ivan D.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-09-01

    We develop a theory allowing one to calculate the energy spectra and wave functions of collective excitations in twoand three-dimensional quantum-dot supercrystals. We derive analytical expressions for the energy spectra of twodimensional supercrystals with different Bravias lattices, and use them to analyze the possibility of engineering the supercrystals' band structure. We demonstrate that the variation of the supercrystal's parameters (such as the symmetry of the periodic lattice and the properties of the quantum dots or their environment) enables an unprecedented control over its optical properties, thus paving a way towards the development of new nanophotonics materials.

  20. 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

  1. 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.

  2. 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

    2010-11-01

    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.

  3. 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...

  4. 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.

  5. ZnS semiconductor quantum dots production by an endophytic fungus Aspergillus flavus

    Energy Technology Data Exchange (ETDEWEB)

    Uddandarao, Priyanka, E-mail: uddandaraopriyanka@gmail.com; B, Raj Mohan, E-mail: rajmohanbala@gmail.com

    2016-05-15

    Graphical abstract: - Highlights: • Endophytic fungus Aspergillus flavus isolated from a medicinal plant Nothapodytes foetida was used for the synthesis of quantum dots. • Morris-Weber kinetic model and Lagergren's pseudo-first-order rate equation were used to study the biosorption kinetics. • Polycrystalline ZnS quantum dots of 18 nm and 58.9 nm from TEM and DLS, respectively. - Abstract: The development of reliable and eco-friendly processes for the synthesis of metal sulphide quantum dots has been considered as a major challenge in the field of nanotechnology. In the present study, polycrystalline ZnS quantum dots were synthesized from an endophytic fungus Aspergillus flavus. It is noteworthy that apart from being rich sources of bioactive compounds, endophytic fungus also has the ability to mediate the synthesis of nanoparticles. TEM and DLS revealed the formation of spherical particles with an average diameter of about 18 nm and 58.9 nm, respectively. The ZnS quantum dots were further characterized using SEM, EDAX, XRD, UV–visible spectroscopy and FTIR. The obtained results confirmed the synthesis of polycrystalline ZnS quantum dots and these quantum dots are used for studying ROS activity. In addition this paper explains kinetics of metal sorption to study the role of biosorption in synthesis of quantum dots by applying Morris-Weber kinetic model. Since Aspergillus flavus is isolated from a medicinal plant Nothapodytes foetida, quantum dots synthesized from this fungus may have great potential in broad environmental and medical applications.

  6. Polymer-coated quantum dots

    NARCIS (Netherlands)

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

    2013-01-01

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

  7. 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

  8. Nuclear Spins in Quantum Dots

    NARCIS (Netherlands)

    Erlingsson, S.I.

    2003-01-01

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

  9. 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.

  10. Ultrafast laser-induced formation of surface micro-structuring on quantum dot coated glass%超快激光对涂有量子点玻璃表面的微构造

    Institute of Scientific and Technical Information of China (English)

    任玉; 王玥; 秦沛; 胡思怡; 刘丽炜; 李野

    2016-01-01

    The fabrication induced by ultrafast laser illumination on solid surface has been widely illustrated in the field of la-ser physics.A new nanoscale-structure fabrication method based on the local surface plasmon resonance of the quantum dots (QDs)which are adhered on the substrate is demonstrated.By illuminating a K9 substrate which has been coated by Cu2 S QDs with femtosecond laser,a series of grating-like and sub-wavelength period strips are achieved.The interval between each strip is nearly 34 nm when the central wavelength,pulse duration and illumination power of the laser are 1300 nm,50 fs and 230 mW re-spectively.Moreover,the mechanism of inducing period strips has been demonstrated by the simulated near field distribution of the adhered QDs on substrate.The result shows that the period strips result from the interference between femtosecond laser and localized plasmon induced by QDs.This preparation method can not only reduce the laser threshold of nanoscale-structure fabrica-tion of transparent medium,but also improve the processing technology of the micro-nano structure on the surface of the trans-parent substrate.%基于金属量子点的局域等离激元效应,提出一种新的固体介质表面微结构的制备方法。利用飞秒激光辐照涂有 Cu2 S 量子点的 K9玻璃,在其表面制备出了类似光栅结构的亚波长周期性条纹。当飞秒激光的中心波长为1300 nm、脉宽为50 fs、激光功率为230 mW 时,玻璃表面的亚波长周期性条纹结构尺寸为34 nm。通过模拟得到了附有 Cu2 S 量子点玻璃表面的近场分布,模拟结果表明,出现这种周期性条纹结构是入射飞秒激光与量子点产生的等离激元场之间产生干涉引起的。该制备方法可以降低透明介质微构造的激光功率阈值,改善了透明基质表面的微纳结构加工工艺。

  11. Silanization of Low-Temperature-Plasma Synthesized Silicon Quantum Dots for Production of a Tunable, Stable, Colloidal Solution

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, I. E.; Shircliff, R. A.; Macauley, C.; Smith, D. K.; Lee, B. G.; Agrawal, S.; Stradins, P.; Collins, R. T.

    2012-02-16

    We present a method for grafting silanes onto low-temperature-plasma synthesized silicon quantum dots. The resulting solution of dots is characterized with Fourier transform infrared spectroscopy and transmission electron microscopy, and determined to be a colloidal suspension. The silane is attached at a single point on the quantum dot surface to avoid cross-linking and multilayer formation, and photoluminescence spectroscopy shows the colloidal suspension of dots is stable for over two months in air. The hydroxyl-terminated surfaces required for silanization are created by wet chemical etch, which can be used to tune the luminescence of the silicon dots in the green- to red-wavelength range. We find, however, that the wet etch cannot move the emission into the blue-wavelength range and discuss this observation in terms of the nature of etching process and origin of the emission. In addition, we discuss the photoluminescence quantum yield in the context of other passivation and synthetic techniques.

  12. Spin transport through quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2003-07-01

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

  13. 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%.

  14. Carbon dots as antioxidants and prooxidants.

    Science.gov (United States)

    Christensen, Ingeborg Lie; Sun, Ya-Ping; Juzenas, Petras

    2011-10-01

    In this study we report the effect of classical CdSe/ZnS quantum dots and novel spherical carbon dots on generation of singlet oxygen and other reactive oxygen species (ROS) in aqueous solutions in vitro. Free radicals were initiated either chemically using 2,2'-azodiisobutyramidine dihydrochloride (AAPH) or by radiation with a blue light source emitting 390-470 nm (peak 420 nm). Two reagents, dihydrorhodamine 123 (Dhr123) and singlet oxygen sensor green (SOSG), were used as radical probes. Quantum dots and carbon dots inhibited oxidation of the radical probes under decomposition of AAPH. However, when subjected to the blue light both the quantum dots and carbon dots induced oxidation of Dhr123 to a greater extent than SOSG in water. Generation of singlet oxygen was remarkably enhanced in deuterium oxide solutions while oxidation of Dhr123 remained unchanged. For comparison, traditional photosensitizer protoporphyrin IX mainly induced oxidation of SOSG in water. In conclusion, upon external radiation carbon dots or quantum dots generate reactive oxygen species acting as prooxidants. Carbon dots or quantum dots also scavenge free radicals that are generated chemically by an azo compound. Such dual properties of these nanoparticles can be used for photodynamic and photocatalytic or antioxidant applications.

  15. Probing silicon quantum dots by single-dot techniques

    Science.gov (United States)

    Sychugov, Ilya; Valenta, Jan; Linnros, Jan

    2017-02-01

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

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

    Science.gov (United States)

    Martynenko, Irina V; Orlova, Anna O; Maslov, Vladimir G; Baranov, Alexander V; Fedorov, Anatoly V; Artemyev, Mikhail

    2013-01-01

    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.

  17. 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

  18. Brightness-equalized quantum dots

    Science.gov (United States)

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

    2015-10-01

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices.

  19. 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.

  20. Transport through a strongly coupled graphene quantum dot in perpendicular magnetic field

    Directory of Open Access Journals (Sweden)

    Güttinger Johannes

    2011-01-01

    Full Text Available Abstract We present transport measurements on a strongly coupled graphene quantum dot in a perpendicular magnetic field. The device consists of an etched single-layer graphene flake with two narrow constrictions separating a 140 nm diameter island from source and drain graphene contacts. Lateral graphene gates are used to electrostatically tune the device. Measurements of Coulomb resonances, including constriction resonances and Coulomb diamonds prove the functionality of the graphene quantum dot with a charging energy of approximately 4.5 meV. We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level. Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.

  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

    2016-04-05

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

  2. Synthesis and applications of carbon dots

    OpenAIRE

    Nolan, Andrew Steven

    2015-01-01

    The use of non-invasive methods to visualise and monitor processes inside living organisms is vital in the understanding and diagnosis of disease. The work in this thesis details the synthesis and applications of a new imaging modality; carbon dots, whose inherent fluorescence and non-toxic nature makes them attractive alternatives to more traditional ‘quantum dots’. In this thesis, different methods of carbon dot synthesis were attempted in order to produce carbon dots of t...

  3. Colloidal quantum dots: synthesis, properties and applications

    Science.gov (United States)

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

    2016-12-01

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

  4. Thermoelectric energy harvesting with quantum dots.

    Science.gov (United States)

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

    2015-01-21

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

  5. 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.

  6. Synthetic Developments of Nontoxic Quantum Dots.

    Science.gov (United States)

    Das, Adita; Snee, Preston T

    2016-03-03

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

  7. POLARON IN CYLINDRICAL AND SPHERICAL QUANTUM DOTS

    Directory of Open Access Journals (Sweden)

    L.C.Fai

    2004-01-01

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

  8. 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.

  9. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

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

    2002-01-01

    -power 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 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...

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

    OpenAIRE

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

    2005-01-01

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

  11. 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...

  12. Prognostic and therapeutic value of disruptor of telomeric silencing-1-like (DOT1L expression in patients with ovarian cancer

    Directory of Open Access Journals (Sweden)

    Xiaoxue Zhang

    2017-01-01

    Full Text Available Abstract Background Epigenetics has been known to play a critical role in regulating the malignant phenotype. This study was designed to examine the expression of DOT1L (histone 3 lysine 79 methyltransferase and H3K79 methylation in normal ovarian tissues and ovarian tumors and to explore the function of DOT1L and its underline mechanisms in ovarian cancer. Methods The expression of DOT1L and H3K79 methylation in 250 ovarian tumor samples and 24 normal ovarian samples was assessed by immunohistochemistry. The effects of DOT1L on cell proliferation in vitro were evaluated using CCK8, colony formation and flow cytometry. The DOT1L-targeted genes were determined using chromatin immune-precipitation coupled with high-throughput sequencing (ChIP-seq and ChIP-PCR. Gene expression levels were measured by real-time PCR and immunoblotting. The effects of DOT1L on tumor growth in vivo were evaluated using an orthotopic ovarian tumor model. Results DOT1L expression and H3K79 methylation was significantly increased in malignant ovarian tumors. High DOT1L expression was associated with International Federation of Gynecology and Obstetrics (FIGO stage, histologic grade, and lymphatic metastasis. DOT1L was an independent prognostic factor for the overall survival (OS and progression-free survival (PFS of ovarian cancer, and higher DOT1L expression was associated with poorer OS and PFS. Furthermore, DOT1L regulates the transcription of G1 phase genes CDK6 and CCND3 through H3K79 dimethylation; therefore, blocking DOT1L could result in G1 arrest and thereby impede the cell proliferation in vitro and tumor growth in vivo. Conclusions Our findings first demonstrate that DOT1L over-expression has important clinical significance in ovarian cancer and also clarify that it drives cell cycle progression through transcriptional regulation of CDK6 and CCND3 through H3K79 methylation, suggesting that DOT1L might be potential target for prognostic assessment and

  13. 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.

  14. Low-temperature synthesis of CdSe nanocrystal quantum dots.

    Science.gov (United States)

    Siy, Jacqueline T; Brauser, Eric M; Bartl, Michael H

    2011-01-07

    A method for fabricating colloidal CdSe nanocrystals at low reaction temperatures was developed. The transition from CdSe clusters to continuously-growing nanocrystals was found to be crucial in the formation of high-quality quantum dots with narrow size distribution and efficient, tunable optical properties.

  15. Thermochemistry of uranium compounds: XVI, Calorimetric determination of the standard molar enthalpy of formation at 298.15 K, low-temperature heat capacity, and high-temperature enthalpy increments of UO{sub 2}(OH){sub 2} {center_dot} H{sub 2}O (schoepite)

    Energy Technology Data Exchange (ETDEWEB)

    Tasker, I.R.; O`Hare, P.A.G.; Lewis, B.M.; Johnson, G.K.; Cordfunke, E.H.P.

    1987-08-01

    Three precise calorimetric methods, viz., low-temperature adiabatic, high-temperatuare drop, and solution-reaction, have been used to determine as a function of temperature the key chemical thermodynamic properties of a pure sample of schoepite, UO{sub 2}(OH){sub 2} {center_dot} H{sub 2}O. The following results have been obtained at the standard reference temperature T = 298.15 K:standard molar enthalpy of formation {Delta}/sub f/H/sub m/{sup 0}(T) = {minus}1825.4 +- 2.1 kJ mol/sup {minus}1/; molar heat capacity C/sub p,m/{sup 0}(T) = 172.07 +- 0.34 JK/sup {minus}1/; and the standard molar entropy S/sub m/{sup 0}(T) = 188.54 +- 0.38 JK/sup {minus}1/ mol/sup {minus}1/. The molar enthalpy increments relative to 298.15 K and the molar heat capacity are given by the polynomials: {H{sub m}{sup 0}(T) {minus} H{sub m}{sup 0}(298.15 K)}/(J mol/sup {minus}1/) = {minus}38209.0 + 84.2375 (T/K) + 0.1472958 (T/K){sup 2} and C/sub p,m/{sup 0}(T)/(JK/sup {minus}1/ mol/sup {minus}1/) = 84.238 + 0.294592 (T/K), where 298.15 K < T < 400 K. The present result for {Delta}/sup f/H/sub m/{sup 0} at 298.15 K has been combined with three other closely-agreeing values from the literature to give a recommended weighted mean {Delta}/sub f/H/sub m/{sup 0} = {minus}1826.4 +- 1.7 kJ mol/sup {minus}1/, from which is calculated the standard Gibbs energy of formation {Delta}/sub f/G/sub m/{sup 0} = {minus}1637.0 +- 1.7 kJ mol/sup {minus}1/ at 298.15 K. Complete thermodynamic properties of schoepite are tabulated from 298.15 to 423.15 K. 19 refs., 6 tabs.

  16. 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.

  17. 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.

  18. Optically active quantum-dot molecules.

    Science.gov (United States)

    Shlykov, Alexander I; Baimuratov, Anvar S; Baranov, Alexander V; Fedorov, Anatoly V; Rukhlenko, Ivan D

    2017-02-20

    Chiral molecules made of coupled achiral semiconductor nanocrystals, also known as quantum dots, show great promise for photonic applications owing to their prospective uses as configurable building blocks for optically active structures, materials, and devices. Here we present a simple model of optically active quantum-dot molecules, in which each of the quantum dots is assigned a dipole moment associated with the fundamental interband transition between the size-quantized states of its confined charge carriers. This model is used to analytically calculate the rotatory strengths of optical transitions occurring upon the excitation of chiral dimers, trimers, and tetramers of general configurations. The rotatory strengths of such quantum-dot molecules are found to exceed the typical rotatory strengths of chiral molecules by five to six orders of magnitude. We also study how the optical activity of quantum-dot molecules shows up in their circular dichroism spectra when the energy gap between the molecular states is much smaller than the states' lifetime, and maximize the strengths of the circular dichroism peaks by optimizing orientations of the quantum dots in the molecules. Our analytical results provide clear design guidelines for quantum-dot molecules and can prove useful in engineering optically active quantum-dot supercrystals and photonic devices.

  19. Research on Self-Assembling Quantum Dots.

    Science.gov (United States)

    1995-10-30

    0K. in a second phase of this contract we turned our efforts to the fabrication and studies of self assembled quantum dots . We first demonstrated a...method for producing InAs-GasAs self assembled quantum dots (SAD) using MBE. (AN)

  20. 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.

  1. Quantum Dots Coupled to a Superconductor

    DEFF Research Database (Denmark)

    Jellinggaard, Anders Robert

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

  2. Detecting the chirality for coupled quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-04-21

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

  3. 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....

  4. Optical studies of capped quantum dots

    NARCIS (Netherlands)

    Wuister, S.F.

    2005-01-01

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

  5. Optical Properties of Semiconductor Quantum Dots

    NARCIS (Netherlands)

    Perinetti, U.

    2011-01-01

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

  6. 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

  7. 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...

  8. Biocompatible quantum dots for biological applications.

    Science.gov (United States)

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

    2011-01-28

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

  9. Quantum-dot supercrystals for future nanophotonics

    Science.gov (United States)

    Baimuratov, Anvar S.; Rukhlenko, Ivan D.; Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-01-01

    The study of supercrystals made of periodically arranged semiconductor quantum dots is essential for the advancement of emerging nanophotonics technologies. By combining the strong spatial confinement of elementary excitations inside quantum dots and exceptional design flexibility, quantum-dot supercrystals provide broad opportunities for engineering desired optical responses and developing superior light manipulation techniques on the nanoscale. Here we suggest tailoring the energy spectrum and wave functions of the supercrystals' collective excitations through the variation of different structural and material parameters. In particular, by calculating the excitonic spectra of quantum dots assembled in two-dimensional Bravais lattices we demonstrate a wide variety of spectrum transformation scenarios upon alterations in the quantum dot arrangement. This feature offers unprecedented control over the supercrystal's electromagnetic properties and enables the development of new nanophotonics materials and devices.

  10. Red luminescence from strain-induced GaInP quantum dots

    OpenAIRE

    1996-01-01

    The strain of self‐organized InP islands is used to induced quantum dots in near‐surface GaInP/AlGaInP quantum wells. To obtain quantum dotluminescence in a widely tunable wavelength range of 630–700 nm, the composition and thickness of the GaInP quantum well is varied. The effect of different cap layer materials, i.e., GaAs, AlGaAs, GaInP, and AlGaInP on the InP island formation and quantum dotluminescenceproperties is investigated. The luminescence intensity ratio of the quantum dot peak to...

  11. Charge-driven feedback loop in the resonance fluorescence of a single quantum dot

    Science.gov (United States)

    Merkel, B.; Kurzmann, A.; Schulze, J.-H.; Strittmatter, A.; Geller, M.; Lorke, A.

    2017-03-01

    We demonstrate a feedback loop that manifests itself in a strong hysteresis and bistability of the exciton resonance fluorescence signal. Field ionization of photogenerated quantum dot excitons leads to the formation of a charged interface layer that drags the emission line along over a frequency range of more than 30 GHz . These measurements are well described by a rate equation model. With a time-resolved resonance fluorescence measurement we determined the buildup times for the hole gas in the orders of milliseconds. This internal charge-driven feedback loop could be used to reduce the spectral wandering in the emission spectra of single self-assembled quantum dots.

  12. 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 compressible strips in the potential profile and the electron density. We numerically solve the Dirac equations describing the electron dynamics in quantum dots, and we demonstrate that compressible strips lead to the appearance of plateaus in the electron energies as a function of the magnetic field. Finally...

  13. Quantum interference and control of the optical response in quantum dot molecules

    Energy Technology Data Exchange (ETDEWEB)

    Borges, H. S.; Sanz, L.; Villas-Boas, J. M.; Alcalde, A. M. [Instituto de Física, Universidade Federal de Uberlândia, 38400-902 Uberlândia-MG (Brazil)

    2013-11-25

    We discuss the optical response of a quantum molecule under the action of two lasers fields. Using a realistic model and parameters, we map the physical conditions to find three different phenomena reported in the literature: the tunneling induced transparency, the formation of Autler-Townes doublets, and the creation of a Mollow-like triplet. We found that the electron tunneling between quantum dots is responsible for the different optical regime. Our results not only explain the experimental results in the literature but also give insights for future experiments and applications in optics using quantum dots molecules.

  14. Blood Compatibility Evaluations of Fluorescent Carbon Dots.

    Science.gov (United States)

    Li, Sha; Guo, Zhong; Zhang, Yi; Xue, Wei; Liu, Zonghua

    2015-09-02

    Because of their unique advantages, fluorescent carbon dots are gaining popularity in various biomedical applications. For these applications, good biosafety is a prerequisite for their use in vivo. Studies have reported the preliminary biocompatibility evaluations of fluorescent carbon dots (mainly cytotoxicity); however, to date, little information is available about their hemocompatibility, which could impede their development from laboratory to bedside. In this work, we evaluated the hemocompatibility of fluorescent carbon dots, which we prepared by hydrothermal carbonization of α-cyclodextrin. The effects of the carbon dots on the structure and function of key blood components were investigated at cellular and molecular levels. In particular, we considered the morphology and lysis of human red blood cells, the structure and conformation of the plasma protein fibrinogen, the complement activation, platelet activation, and in vitro and in vivo blood coagulation. We found that the carbon dots have obvious concentration-dependent effects on the blood components. Overall, concentrations of the fluorescent carbon dots at ≤0.1 mg/mL had few adverse effects on the blood components, but at higher doses, the carbon dots impair the structure and function of the blood components, causing morphological disruptions and lysis of red blood cells, interference in the local microenvironments of fibrinogen, activation of the complement system, and disturbances in the plasma and whole blood coagulation function in vitro. However, the carbon dots tend to activate platelets only at low concentrations. Intravenous administration of the carbon dots at doses up to 50 mg/kg did not impair the blood coagulation function. These results provide valuable information for the clinical application of fluorescent carbon dots.

  15. Peptide dot immunoassay and immunoblotting: electroblotting from aluminum thin-layer chromatography plates and isoelectric focusing gels to activated nitrocellulose

    DEFF Research Database (Denmark)

    Bjerrum, O.J.; Holm, A.; Lauritzen, Edgar;

    1993-01-01

    Peptide dot immunoassay, electroblotting, activated nitrocellulose, dot blot, membranes, peptides and proteins......Peptide dot immunoassay, electroblotting, activated nitrocellulose, dot blot, membranes, peptides and proteins...

  16. 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...

  17. Chiral quantum dot based materials

    Science.gov (United States)

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

    2014-05-01

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

  18. Exciton dynamics in GaAs/(Al,Ga)As core-shell nanowires with shell quantum dots

    Science.gov (United States)

    Corfdir, Pierre; Küpers, Hanno; Lewis, Ryan B.; Flissikowski, Timur; Grahn, Holger T.; Geelhaar, Lutz; Brandt, Oliver

    2016-10-01

    We study the dynamics of excitons in GaAs/(Al,Ga)As core-shell nanowires by continuous-wave and time-resolved photoluminescence and photoluminescence excitation spectroscopy. Strong Al segregation in the shell of the nanowires leads to the formation of Ga-rich inclusions acting as quantum dots. At 10 K, intense light emission associated with these shell quantum dots is observed. The average radiative lifetime of excitons confined in the shell quantum dots is 1.7 ns. We show that excitons may tunnel toward adjacent shell quantum dots and nonradiative point defects. We investigate the changes in the dynamics of charge carriers in the shell with increasing temperature, with particular emphasis on the transfer of carriers from the shell to the core of the nanowires. We finally discuss the implications of carrier localization in the (Al,Ga)As shell for fundamental studies and optoelectronic applications based on core-shell III-As nanowires.

  19. 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.

  20. 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.

  1. Quantum dots with single-atom precision.

    Science.gov (United States)

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

    2014-07-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Li Zhen; Peng Liwei; Fang Yaoguo; Chen Zhiwen [Shanghai Applied Radiation Institute, Shanghai University, Shanghai 201800 (China); Pan Dengyu [Institute of Nanochemistry and Nanobiology, Shanghai University, Shanghai 201800 (China); Wu Minghong, E-mail: mhwu@staff.shu.edu.cn [Shanghai Applied Radiation Institute, Shanghai University, Shanghai 201800 (China)

    2011-12-15

    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 {approx}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.

  3. Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

    Science.gov (United States)

    Knapp, T. J.; Mohr, R. T.; Li, Yize Stephanie; Thorgrimsson, Brandur; Foote, Ryan H.; Wu, Xian; Ward, Daniel R.; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

    2016-04-01

    We report the fabrication and characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. In the past, all gate-defined quantum dots in Si/SiGe heterostructures were formed on top of strain-graded virtual substrates. The strain grading process necessarily introduces misfit dislocations into a heterostructure, and these defects introduce lateral strain inhomogeneities, mosaic tilt, and threading dislocations. The use of a SiGe nanomembrane as the virtual substrate enables the strain relaxation to be entirely elastic, eliminating the need for misfit dislocations. However, in this approach the formation of the heterostructure is more complicated, involving two separate epitaxial growth procedures separated by a wet-transfer process that results in a buried non-epitaxial interface 625 nm from the quantum dot. We demonstrate that in spite of this buried interface in close proximity to the device, a double quantum dot can be formed that is controllable enough to enable tuning of the inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of an applied magnetic field.

  4. Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

    Science.gov (United States)

    Knapp, T. J.; Mohr, R. T.; Li, Yize Stephanie; Thorgrimsson, Brandur; Foote, Ryan H.; Wu, Xian; Ward, Daniel R.; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

    We report the characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. Previously, all heterostructures used to form quantum dots were created using the strain-grading method of strain relaxation, a method that necessarily introduces misfit dislocations into a heterostructure and thereby degrades the reproducibility of quantum devices. Using a SiGe nanomembrane as a virtual substrate eliminates the need for misfit dislocations but requires a wet-transfer process that results in a non-epitaxial interface in close proximity to the quantum dots. We show that this interface does not prevent the formation of quantum dots, and is compatible with a tunable inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of the applied magnetic field. This work was supported in part by ARO (W911NF-12-0607), NSF (DMR-1206915, PHY-1104660), and the United States Department of Defense. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressly or implied, of the US Government. T.J. Knapp et al. (2015). arXiv:1510.08888 [cond-mat.mes-hall].

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

    Energy Technology Data Exchange (ETDEWEB)

    Zabel, T., E-mail: zabel@kth.se; Reuterskiöld Hedlund, C.; Gustafsson, O.; Berggren, J.; Ernerheim-Jokumsen, C.; Soldemo, M.; Weissenrieder, J.; Götelid, M.; Hammar, M. [School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, S-164 40 Kista (Sweden); Karim, A.; Wang, Q. [Acreo AB, Electrum 236. 16440 Kista (Sweden)

    2015-01-05

    We report on the epitaxial formation of type II In{sub 0.5}Ga{sub 0.5}Sb/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{sup −28} cm{sup 6}/s for In{sub 0.5}Ga{sub 0.5}Sb/InAs quantum dots and 1.47 × 10{sup −27} cm{sup 6}/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices.

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

    Science.gov (United States)

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

    2006-02-01

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

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

    OpenAIRE

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

    2015-01-01

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

  8. 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.

  9. Fluorescent Quantum Dots for Biological Labeling

    Science.gov (United States)

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

    2003-01-01

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

  10. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

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

  11. Electronic properties of aperiodic quantum dot chains

    Science.gov (United States)

    Korotaev, P. Yu.; Vekilov, Yu. Kh.; Kaputkina, N. E.

    2012-04-01

    The electronic spectral and transport properties of aperiodic quantum dot chains are investigated. The systems with singular continuous energy spectrum are considered: Thue-Morse chain, double-periodic chain, Rudin-Shapiro chain. The influence of electronic energy in quantum dot on the spectral properties, band structure, density of states and spectral resistivity, is discussed. Low resistivity regions correspond to delocalized states and these states could be current states. Also we discuss the magnetic field application as the way to tune electronic energy in quantum dot and to obtain metallic or insulating conducting states of the systems.

  12. Amplification Without Inversion in Semiconductor Quantum Dot

    Science.gov (United States)

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

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

  13. Quantum Dots Investigated for Solar Cells

    Science.gov (United States)

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

    2001-01-01

    The NASA Glenn Research Center has been investigating the synthesis of quantum dots of CdSe and CuInS2 for use in intermediate-bandgap solar cells. Using quantum dots in a solar cell to create an intermediate band will allow the harvesting of a much larger portion of the available solar spectrum. Theoretical studies predict a potential efficiency of 63.2 percent, which is approximately a factor of 2 better than any state-of-the-art devices available today. This technology is also applicable to thin-film devices--where it offers a potential four-fold increase in power-to-weight ratio over the state of the art. Intermediate-bandgap solar cells require that quantum dots be sandwiched in an intrinsic region between the photovoltaic solar cell's ordinary p- and n-type regions (see the preceding figure). The quantum dots form the intermediate band of discrete states that allow sub-bandgap energies to be absorbed. However, when the current is extracted, it is limited by the bandgap, not the individual photon energies. The energy states of the quantum dot can be controlled by controlling the size of the dot. Ironically, the ground-state energy levels are inversely proportional to the size of the quantum dots. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Ba Wendi et al., in the early 1990's. The most studied quantum dots prepared by this method have been of CdSe. To produce these dots, researchers inject a syringe of the desired organometallic precursors into heated triocytlphosphine oxide (TOPO) that has been vigorously stirred under an inert atmosphere (see the following figure). The solution immediately begins to change from colorless to yellow, then orange and red/brown, as the quantum dots increase in size. When the desired size is reached, the heat is removed from the flask. Quantum dots of different sizes can be identified by placing them under a "black light" and observing the various color differences in

  14. 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.

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

    OpenAIRE

    Ihly, Rachelle

    2014-01-01

    This thesis explores the understanding of the chemistry and physics of colloidal quantum dots for practical solar energy photoconversion. Solar cell devices that make use of PbS quantum dots generally rely on constant and unchanged optical properties such that band gap energies remain tuned within the device. The design and development of unique experiments to ascertain mechanisms of optical band gap shifts occurring in PbS quantum dot thin-films exposed to air are discussed. The systematic s...

  16. Tailoring Magnetism in Quantum Dots

    Science.gov (United States)

    Zutic, Igor; Abolfath, Ramin; Hawrylak, Pawel

    2007-03-01

    We study magnetism in magnetically doped quantum dots as a function of particle numbers, temperature, confining potential, and the strength of Coulomb interaction screening. We show that magnetism can be tailored by controlling the electron-electron Coulomb interaction, even without changing the number of particles. The interplay of strong Coulomb interactions and quantum confinement leads to enhanced inhomogeneous magnetization which persists at substantially higher temperatures than in the non-interacting case or in the bulk-like dilute magnetic semiconductors. We predict a series of electronic spin transitions which arise from the competition between the many-body gap and magnetic thermal fluctuations. Cond-mat/0612489. [1] R. Abolfath, P. Hawrylak, I. Zuti'c, preprint.

  17. Synthesis of Cu-doped InP nanocrystals (d-dots) with ZnSe diffusion barrier as efficient and color-tunable NIR emitters.

    Science.gov (United States)

    Xie, Renguo; Peng, Xiaogang

    2009-08-05

    Efficient Cu-doped InP quantum dots (Cu:InP d-dots) emitters were successfully synthesized by epitaxial growth of a ZnSe diffusion barrier for the dopants. The Cu dopant emission of the Cu:InP/ZnSe core/shell d-dots covered the important red and near-infrared (NIR) window for biomedical applicaitons, from 630 to 1100 nm, by varying the size of the InP host nanocrystals. These new d-dots emitters not only compensate for the emission wavelength of the existing noncadmium d-dots emitters, Cu- and Mn-doped ZnSe d-dots (450-610 nm), but also offer a complete series of efficient nanocrystal emitters based on InP nanocrystals. The one-pot synthetic scheme for the formation of Cu:InP/ZnSe core/shell d-dots was successfully established by systematically studying the doping process, the dopant concentration-dependent photophysical properties, and the dopant diffusion during shell epitaxy, etc. Complete elimination of InP bandgap emission and efficient pure dopant emission (with photoluminescence quantum yield as high as between 35-40%) of the core/shell d-dots were achieved by optimizing the final doping level and the diffusion barrier thickness.

  18. 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...

  19. 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...

  20. Start Shift of Individual Quantum Dots

    Science.gov (United States)

    1999-06-18

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

  1. Exciton in type-II quantum dot

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-05-01

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

  2. Random Feature Maps for Dot Product Kernels

    OpenAIRE

    Kar, Purushottam; Karnick, Harish

    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 explic...

  3. Chaotic quantum dots with strongly correlated electrons

    OpenAIRE

    Shankar, R.

    2007-01-01

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

  4. Dot-dye-immunoassay for the diagnosis of schistosomiasis mansoni

    Directory of Open Access Journals (Sweden)

    Ana Lúcia Teles Rabello

    1992-06-01

    Full Text Available A new serological assay dot-dye-immunoassay (dot-DIA was evaluated for the diagnosis of schistosomiasis mansoni. This method consist of four steps: (a biding of antigens to a nitrocellulose membrane (NC; (b blocking of free sites of the NC; (c incubation in specific primary antibody; (d detection of primary antibody reactivity by color development using second antibody coupled to textile dyes. Sera from 82 individuals, 61 with Schistosoma mansoni eggs in the stool and 21 stool negative were tested by ELISA, dot-ELISA, and dotDIA. A high level of agreement between the methods tested was observed for all sera tested: ELISA x dot-ELISA: 95.1%, ELISA x dot-DIA: 92.7% and dot-ELISA x dot-DIA: 97.6%. In this study, dot-DIA proved to be a feasible, sensitive, rapid and practical test for the diagnosis of shcistosomiasis.

  5. 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.

  6. 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

  7. Characterization and Effect of Thermal Annealing on InAs Quantum Dots Grown by Droplet Epitaxy on GaAs(111)A Substrates.

    Science.gov (United States)

    Bietti, Sergio; Esposito, Luca; Fedorov, Alexey; Ballabio, Andrea; Martinelli, Andrea; Sanguinetti, Stefano

    2015-12-01

    We report the study on formation and thermal annealing of InAs quantum dots grown by droplet epitaxy on GaAs (111)A surface. By following the changes in RHEED pattern, we found that InAs quantum dots arsenized at low temperature are lattice matched with GaAs substrate, becoming almost fully relaxed when substrate temperature is increased. Morphological characterizations performed by atomic force microscopy show that annealing process is able to change density and aspect ratio of InAs quantum dots and also to narrow size distribution.

  8. Si-doped carbon quantum dots: a facile and general preparation strategy, bioimaging application, and multifunctional sensor.

    Science.gov (United States)

    Qian, Zhaosheng; Shan, Xiaoyue; Chai, Lujing; Ma, Juanjuan; Chen, Jianrong; Feng, Hui

    2014-05-14

    Heteroatom doping of carbon quantum dots not only enables great improvement of fluorescence efficiency and tunability of fluorescence emission, but also provides active sites in carbon dots to broaden their application in sensor. Silicon as a biocompatible element offers a promising direction for doping of carbon quantum dots. Si-doped carbon quantum dots (SiCQDs) were synthesized through a facile and effective approach. The as-prepared Si-doped carbon quantum dots possess visible fluorescence with high quantum yield up to 19.2%, owing to fluorescence enhancement effect of introduced silicon atoms into carbon dots. The toxicity test on human Hela cells showed that SiCQDs have lower cellular toxicity than common CQDs, and bioimaging experiments clearly demonstrated their excellent biolabelling ability and outstanding performance in resistance to photobleaching. Strong fluorescence quenching effect of Fe(III) on SiCQDs can be used for its selective detection among general metal ions. Specific electron transfer between SiCQDs and hydrogen peroxide enables SiCQDs as a sensitive fluorescence sensing platform for hydrogen peroxide. The subsequent fluorescence recovery induced by removal of hydrogen peroxide from SiCQDs due to formation of the stable adducts between hydrogen peroxide and melamine was taken advantage of to construct effective sensor for melamine.

  9. Real-time in situ probing of high-temperature quantum dots solution synthesis.

    Science.gov (United States)

    Abécassis, Benjamin; Bouet, Cécile; Garnero, Cyril; Constantin, Doru; Lequeux, Nicolas; Ithurria, Sandrine; Dubertret, Benoit; Pauw, Brian Richard; Pontoni, Diego

    2015-04-08

    Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-angle X-ray scattering to experimentally monitor the formation of CdSe quantum dots synthesized in solution through the heating up of precursors in octadecene at 240 °C. Our experiment yields a complete movie of the structure of the solution from the self-assembly of the precursors to the formation of the quantum dots. We show that the initial cadmium precursor lamellar structure melts into small micelles at 100 °C and that the first CdSe nuclei appear at 218.7 °C. The size distributions and concentration in nanocrystals are measured in a quantitative fashion as a function of time. We show that a short nucleation burst lasting 30 s is followed by a slow decrease of nanoparticle concentration. The rate-limiting process of the quantum dot formation is found to be the thermal activation of selenium.

  10. Advancements in the Field of Quantum Dots

    Science.gov (United States)

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

    2012-08-01

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

  11. 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.

  12. Quantum dots as biophotonics tools.

    Science.gov (United States)

    Cesar, Carlos L

    2014-01-01

    This chapter provides a short review of quantum dots (QDs) physics, applications, and perspectives. The main advantage of QDs over bulk semiconductors is the fact that the size became a control parameter to tailor the optical properties of new materials. Size changes the confinement energy which alters the optical properties of the material, such as absorption, refractive index, and emission bands. Therefore, by using QDs one can make several kinds of optical devices. One of these devices transforms electrons into photons to apply them as active optical components in illumination and displays. Other devices enable the transformation of photons into electrons to produce QDs solar cells or photodetectors. At the biomedical interface, the application of QDs, which is the most important aspect in this book, is based on fluorescence, which essentially transforms photons into photons of different wavelengths. This chapter introduces important parameters for QDs' biophotonic applications such as photostability, excitation and emission profiles, and quantum efficiency. We also present the perspectives for the use of QDs in fluorescence lifetime imaging (FLIM) and Förster resonance energy transfer (FRET), so useful in modern microscopy, and how to take advantage of the usually unwanted blinking effect to perform super-resolution microscopy.

  13. Electromechanical transition in quantum dots

    Science.gov (United States)

    Micchi, G.; Avriller, R.; Pistolesi, F.

    2016-09-01

    The strong coupling between electronic transport in a single-level quantum dot and a capacitively coupled nanomechanical oscillator may lead to a transition towards a mechanically bistable and blocked-current state. Its observation is at reach in carbon-nanotube state-of-art experiments. In a recent publication [Phys. Rev. Lett. 115, 206802 (2015), 10.1103/PhysRevLett.115.206802] we have shown that this transition is characterized by pronounced signatures on the oscillator mechanical properties: the susceptibility, the displacement fluctuation spectrum, and the ring-down time. These properties are extracted from transport measurements, however the relation between the mechanical quantities and the electronic signal is not always straightforward. Moreover the dependence of the same quantities on temperature, bias or gate voltage, and external dissipation has not been studied. The purpose of this paper is to fill this gap and provide a detailed description of the transition. Specifically we find (i) the relation between the current-noise and the displacement spectrum; (ii) the peculiar behavior of the gate-voltage dependence of these spectra at the transition; (iii) the robustness of the transition towards the effect of external fluctuations and dissipation.

  14. Quantum dots for terahertz generation

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-09-24

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

  15. 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

  16. Polyhedral Oligomeric Silsesquioxane Functionalized Carbon Dots for Cell Imaging.

    Science.gov (United States)

    Wang, Wen-Jing; Hai, Xin; Mao, Quan-Xing; Chen, Ming-Li; Wang, Jian-Hua

    2015-08-05

    In the present study, octa-aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS) functionalized carbon dots (CDs/POSS) are prepared by a one-pot approach with glycerol as carbon source and solvent medium. OA-POSS serves as a passivation agent, and it is obtained via hydrolytic condensation of 3-aminopropyltriethoxysilane (APTES). During the functionalization process, the amino groups on OA-POSS combine with carboxylic groups on the bare CDs via formation of amide bond to construct organic-inorganic hybrid carbon dots. The obtained CDs/POSS are well dispersed in aqueous medium with a diameter of ca. 3.6 nm. It is demonstrated that CDs/POSS provide favorable photoluminescent property with a quantum yield of 24.0%. They also exhibit resistance to photobleaching and excellent photoluminescence stability in the presence of biological sample matrix (characterized by heavy metals and organic molecules), which facilitate cell imaging in biological systems. Both the photoluminescent emission wavelength and the fluorescence intensity depend closely on the excitation wavelength, and thus, it provides a potential for multicolor imaging as demonstrated with HeLa cells and MCF-7 cells.

  17. Investigation of confinement effects in ZnO quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-10-21

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

  18. 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

  19. 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.

  20. Photoluminescence of carbon dots from mesoporous silica

    Science.gov (United States)

    Nelson, D. K.; Razbirin, B. S.; Starukhin, A. N.; Eurov, D. A.; Kurdyukov, D. A.; Stovpiaga, E. Yu; Golubev, V. G.

    2016-09-01

    Photophysical properties of carbon dots were investigated under various excitation conditions and over a wide temperature region - from room to liquid helium temperatures. The carbon dots (CDs) were synthesized using mesoporous silica particles as a reactor and (3-aminopropyl)triethoxysilane (APTES) as a precursor. The photoluminescence spectra of CDs exhibit a strong dependence on the excitation wavelength and demonstrate a significant inhomogeneous broadening. Lowering sample temperature reveals the doublet structure of the spectra, which is associated with the vibronic structure of radiative transitions. The vibration energy ∼1200 cm-1 is close to the energy of Csbnd O stretching vibration. Long-lived phosphorescence of carbon dots with its decay time ∼0.2 s at T = 80 K was observed. The fluorescence and phosphorescence spectra are shown to be spectrally separated. The long-lived component of the emission was ascribed to optically forbidden triplet-singlet transitions. The value of the singlet-triplet splitting was found to be about 0.3 eV. Photo-induced polarization of the luminescence of carbon dots was revealed. The degree of the linear polarization is dependent on the wavelengths of both excitation and emitted light. The effect indicates a hidden anisotropy of optical dipole transitions in the dots and demonstrates the loss of the dipole orientation during the electron energy relaxation.

  1. Core-Shell Structure and Photoluminescence of CdS Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    邹炳锁; 武振羽; 曹立; 戴建华; 张泽勃; 聂玉昕; 解思深

    2001-01-01

    A double-potential-well model is proposed to describe the core-shell thickness-dependent photoluminescence peaks and energy relaxations in semiconductor quantum dots (QDs). The surface effect plays an important role in the formation of new states-polaronic states around the surface of QDs. The polaronic states formed emit light due to the strong interaction between the core state (confined state) and the surface state with an enhanced participation of the size effect.

  2. Coherence and dephasing in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    2003-01-01

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

  3. Quantum Dots and Their Multimodal Applications: A Review

    OpenAIRE

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

    2010-01-01

    Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons ...

  4. Filtering algorithm for dotted interferences

    Energy Technology Data Exchange (ETDEWEB)

    Osterloh, K., E-mail: kurt.osterloh@bam.de [Federal Institute for Materials Research and Testing (BAM), Division VIII.3, Radiological Methods, Unter den Eichen 87, 12205 Berlin (Germany); Buecherl, T.; Lierse von Gostomski, Ch. [Technische Universitaet Muenchen, Lehrstuhl fuer Radiochemie, Walther-Meissner-Str. 3, 85748 Garching (Germany); Zscherpel, U.; Ewert, U. [Federal Institute for Materials Research and Testing (BAM), Division VIII.3, Radiological Methods, Unter den Eichen 87, 12205 Berlin (Germany); Bock, S. [Technische Universitaet Muenchen, Lehrstuhl fuer Radiochemie, Walther-Meissner-Str. 3, 85748 Garching (Germany)

    2011-09-21

    An algorithm has been developed to remove reliably dotted interferences impairing the perceptibility of objects within a radiographic image. This particularly is a major challenge encountered with neutron radiographs collected at the NECTAR facility, Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II): the resulting images are dominated by features resembling a snow flurry. These artefacts are caused by scattered neutrons, gamma radiation, cosmic radiation, etc. all hitting the detector CCD directly in spite of a sophisticated shielding. This makes such images rather useless for further direct evaluations. One approach to resolve this problem of these random effects would be to collect a vast number of single images, to combine them appropriately and to process them with common image filtering procedures. However, it has been shown that, e.g. median filtering, depending on the kernel size in the plane and/or the number of single shots to be combined, is either insufficient or tends to blur sharp lined structures. This inevitably makes a visually controlled processing image by image unavoidable. Particularly in tomographic studies, it would be by far too tedious to treat each single projection by this way. Alternatively, it would be not only more comfortable but also in many cases the only reasonable approach to filter a stack of images in a batch procedure to get rid of the disturbing interferences. The algorithm presented here meets all these requirements. It reliably frees the images from the snowy pattern described above without the loss of fine structures and without a general blurring of the image. It consists of an iterative, within a batch procedure parameter free filtering algorithm aiming to eliminate the often complex interfering artefacts while leaving the original information untouched as far as possible.

  5. 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.

  6. 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

  7. Evidence for curvilinear interpolation from dot alignment judgements

    NARCIS (Netherlands)

    van Assen, MA; Vos, PG

    1999-01-01

    Visual interpolation between dots responsible for rectilinear versus curvilinear contour interpretation was examined with the psychophysical forced directional response (FDR) paradigm. Regular four-dot polygon segments, together with a target dot, were presented to the subjects for 150 ms. Subjects

  8. Toward structurally defined carbon dots as ultracompact fluorescent probes.

    Science.gov (United States)

    LeCroy, Gregory Ethan; Sonkar, Sumit Kumar; Yang, Fan; Veca, L Monica; Wang, Ping; Tackett, Kenneth N; Yu, Jing-Jiang; Vasile, Eugeniu; Qian, Haijun; Liu, Yamin; Luo, Pengju George; Sun, Ya-Ping

    2014-05-27

    There has been much discussion on the need to develop fluorescent quantum dots (QDs) as ultracompact probes, with overall size profiles comparable to those of the genetically encoded fluorescent tags. In the use of conventional semiconductor QDs for such a purpose, the beautifully displayed dependence of fluorescence color on the particle diameter becomes a limitation. More recently, carbon dots have emerged as a new platform of QD-like fluorescent nanomaterials. The optical absorption and fluorescence emissions in carbon dots are not bandgap in origin, different from those in conventional semiconductor QDs. The absence of any theoretically defined fluorescence color-dot size relationships in carbon dots may actually be exploited as a unique advantage in the size reduction toward having carbon dots serve as ultracompact QD-like fluorescence probes. Here we report on carbon dots of less than 5 nm in the overall dot diameter with the use of 2,2'-(ethylenedioxy)bis(ethylamine) (EDA) molecules for the carbon particle surface passivation. The EDA-carbon dots were found to be brightly fluorescent, especially over the spectral range of green fluorescent protein. These aqueous soluble smaller carbon dots also enabled more quantitative characterizations, including the use of solution-phase NMR techniques, and the results suggested that the dot structures were relatively simple and better-defined. The potential for these smaller carbon dots to serve as fluorescence probes of overall sizes comparable to those of fluorescent proteins is discussed.

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

    DEFF Research Database (Denmark)

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

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

  10. Charged-Exciton Complexes in Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang

    2001-01-01

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

  11. 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.

  12. 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.

  13. Angiogenic Profiling of Synthesized Carbon Quantum Dots.

    Science.gov (United States)

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

    2015-10-20

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

  14. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

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

  15. Molecular beam epitaxy of InN dots on nitrided sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Romanyuk, Yaroslav E.; Dengel, Radu-Gabriel; Stebounova, LarissaV.; Leone, Stephen R.

    2007-04-20

    A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-06-01

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

  17. Dot Detection of Braille Images Using A Mixture of Beta Distributions

    Directory of Open Access Journals (Sweden)

    Amany Al-Saleh

    2011-01-01

    Full Text Available Problem statement: Braille is a tactile format of written communication for people with low vision and blindness worldwide. Optical Braille Recognition (OBR offers many benefits to Braille users and people who work with them. Approach: This study presents an algorithm for detecting dots composing braille characters in an image of embossed braille material obtained by an optical scanner. We assumed that a mixture of Beta distributions could model the histogram of a scanned braille document. The core of the proposed method was the use of stability of thresholding with Beta distribution to initiate the process of thresholds estimation. Segmented Braille image was used to form a grid that contains recto dots and another one that contains verso dots. Results: Braille dots composing characters on both singlesided and double-sided documents were automatically identified from those grids with excellent accuracy. Conclusion: The experiment showed that the proposed method obtained very good results but it requires more testing on different scanned Braille document images.

  18. Glowing graphene quantum dots and carbon dots: properties, syntheses, and biological applications.

    Science.gov (United States)

    Zheng, Xin Ting; Ananthanarayanan, Arundithi; Luo, Kathy Qian; Chen, Peng

    2015-04-08

    The emerging graphene quantum dots (GQDs) and carbon dots (C-dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications.

  19. 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.

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

    OpenAIRE

    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. Resonant tunneling in graphene pseudomagnetic quantum dots.

    Science.gov (United States)

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

    2013-06-12

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

  2. 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

  3. Polymers in Carbon Dots: A Review

    Directory of Open Access Journals (Sweden)

    Yiqun Zhou

    2017-02-01

    Full Text Available Carbon dots (CDs have been widely studied since their discovery in 2004 as a green substitute of the traditional quantum dots due to their excellent photoluminescence (PL and high biocompatibility. Meanwhile, polymers have increasingly become an important component for both synthesis and modification of CDs to provide polymeric matrix and enhance their PL property. Furthermore, critical analysis of composites of CDs and polymers has not been available. Herein, in this review, we summarized the use of polymers in the synthesis and functionalization of CDs, and the applications of these CDs in various fields.

  4. Bilayer graphene quantum dot defined by topgates

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-06-21

    We investigate the application of nanoscale topgates on exfoliated bilayer graphene to define quantum dot devices. At temperatures below 500 mK, the conductance underneath the grounded gates is suppressed, which we attribute to nearest neighbour hopping and strain-induced piezoelectric fields. The gate-layout can thus be used to define resistive regions by tuning into the corresponding temperature range. We use this method to define a quantum dot structure in bilayer graphene showing Coulomb blockade oscillations consistent with the gate layout.

  5. Mitigation of quantum dot cytotoxicity by microencapsulation.

    Directory of Open Access Journals (Sweden)

    Amelia Romoser

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

  6. Spectroscopic characteristics of carbon dots (C-dots) derived from carbon fibers and conversion to sulfur-bridged C-dots nanosheets.

    Science.gov (United States)

    Vinci, John C; Ferrer, Ivonne M; Guterry, Nathan W; Colón, Verónica M; Destino, Joel F; Bright, Frank V; Colón, Luis A

    2015-09-01

    We synthesized sub-10 nm carbon nanoparticles (CNPs) consistent with photoluminescent carbon dots (C-dots) from carbon fiber starting material. The production of different C-dots fractions was monitored over seven days. During the course of the reaction, one fraction of C-dots species with relatively high photoluminescence was short-lived, emerging during the first hour of reaction but disappearing after one day of reaction. Isolation of this species during the first hour of the reaction was crucial to obtaining higher-luminescent C-dots species. When the reaction proceeded for one week, the appearance of larger nanostructures was observed over time, with lateral dimensions approaching 200 nm. The experimental evidence suggests that these larger species are formed from small C-dot nanoparticles bridged together by sulfur-based moieties between the C-dot edge groups, as if the C-dots polymerized by cross-linking the edge groups through sulfur bridges. Their size can be tailored by controlling the reaction time. Our results highlight the variety of CNP products, from sub-10 nm C-dots to ~200 nm sulfur-containing carbon nanostructures, that can be produced over time during the oxidation reaction of the graphenic starting material. Our work provides a clear understanding of when to stop the oxidation reaction during the top-down production of C-dots to obtain highly photoluminescent species or a target average particle size.

  7. Quantum dot-block copolymer hybrids with improved properties and their application to quantum dot light-emitting devices.

    Science.gov (United States)

    Zorn, Matthias; Bae, Wan Ki; Kwak, Jeonghun; Lee, Hyemin; Lee, Changhee; Zentel, Rudolf; Char, Kookheon

    2009-05-26

    To combine the optical properties of CdSe@ZnS quantum dots (QDs) with the electrical properties of semiconducting polymers, we prepared QD/polymer hybrids by grafting a block copolymer (BCP) containing thiol-anchoring moieties (poly(para-methyl triphenylamine-b-cysteamine acrylamide)) onto the surfaces of QDs through the ligand exchange procedure. The prepared QD/polymer hybrids possess improved processability such as enhanced solubility in various organic solvents as well as the film formation properties along with the improved colloidal stability derived from the grafted polymer shells. We also demonstrated light-emitting diodes based on QD/polymer hybrids, exhibiting the improved device performance (i.e., 3-fold increase in the external quantum efficiency) compared with the devices prepared by pristine (unmodified) QDs.

  8. Modified growth of Ge quantum dots using C{sub 2}H{sub 4} mediation by ultra-high vacuum chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lee, S.W. [Institute of Materials Science and Engineering, National Central University, Jhong-Li 32001, Taiwan (China)], E-mail: swlee@ncu.edu.tw; Chen, P.S. [Department of Materials Science and Engineering, Minghsin University of Science and Technology, Hsinchu 30401, Taiwan (China); Cheng, S.L. [Institute of Materials Science and Engineering, National Central University, Jhong-Li 32001, Taiwan (China); Department of Chemical and Materials Engineering, National Central University, Jhong-Li 32001, Taiwan (China); Lee, M.H. [Institute of Electro-optical Science and Technology, National Taiwan Normal University, Taipei 11677, Taiwan (China); Chang, H.T. [Institute of Materials Science and Engineering, National Central University, Jhong-Li 32001, Taiwan (China); Lee, C.-H.; Liu, C.W. [Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2008-07-30

    C{sub 2}H{sub 4} mediations were used to modify the Stranski-Krastanow growth mode of Ge dots on Si(0 0 1) at 550 deg. C by ultra-high vacuum chemical vapor deposition. With appropriate C{sub 2}H{sub 4}-mediation to modify the Si surface, the elongated Ge hut clusters can be transformed to highly uniform Ge domes with a high Ge composition at the core. These C{sub 2}H{sub 4}-mediated Ge dots, almost bounded by {l_brace}1 1 3{r_brace} facets, have an average diameter and height of 55 and 9 nm, respectively. We propose two major mechanisms to depict the formation of these C{sub 2}H{sub 4}-mediated Ge dots: (i) an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation, and (ii) the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. This work provides a useful scheme to tune the topography of Ge dots in an UHV/CVD condition for possible optoelectronic applications.

  9. 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....

  10. The Influence of Formulating a Damping Solution on Dot Gain

    Directory of Open Access Journals (Sweden)

    Povilas Mikalainis

    2011-02-01

    Full Text Available Difference in dot gain using various additives to the damping solution was investigated on two offset web presses. Dot gain was measured using a densitometer and calculated considering CIE L*a*b* coordinates. It was found that while using a non alcohol additive instead of the alcohol one, dot gain became smaller and printing stability was lower. Changes in dot gain depend on the ink that may vary in colours. The influence of changes in dot gain on the colour was determined. Besides, it was found that differences in colour were unacceptable in many cases.Article in Lithuanian

  11. Photoluminescent carbon dots from 1,4-addition polymers.

    Science.gov (United States)

    Jiang, Zhiqiang; Nolan, Andrew; Walton, Jeffrey G A; Lilienkampf, Annamaria; Zhang, Rong; Bradley, Mark

    2014-08-25

    Photoluminescent carbon dots were synthesised directly by thermopyrolysis of 1,4-addition polymers, allowing precise control of their properties. The effect of polymer composition on the properties of the carbon dots was investigated by TEM, IR, XPS, elemental analysis and fluorescence analysis, with carbon dots synthesised from nitrogen-containing polymers showing the highest fluorescence. The carbon dots with high nitrogen content were observed to have strong fluorescence in the visible region, and culture with cells showed that the carbon dots were non-cytotoxic and readily taken up by three different cell lines.

  12. 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.

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

    Science.gov (United States)

    O'Brien, D; Hegarty, S P; Huyet, G; Uskov, A V

    2004-05-15

    The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor.

  14. 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...

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Electron Scattering in Intrananotube Quantum Dots

    NARCIS (Netherlands)

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

    2009-01-01

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

  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...... (SOAs). Also the possibility of realizing an all-optical regenerator by incorporating a QD absorber section in an amplifier structure is discussed....

  3. Amphoteric CdSe nanocrystalline quantum dots.

    Science.gov (United States)

    Islam, Mohammad A

    2008-06-25

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

  4. 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

  5. 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...

  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. Saturating optical resonances in quantum dots

    Science.gov (United States)

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

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

  8. Single Molecule Applications of Quantum Dots

    DEFF Research Database (Denmark)

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

    2013-01-01

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

  9. Carbon dots (C-dots) from cow manure with impressive subcellular selectivity tuned by simple chemical modification.

    Science.gov (United States)

    D'Angelis do E S Barbosa, Cintya; Corrêa, José R; Medeiros, Gisele A; Barreto, Gabrielle; Magalhães, Kelly G; de Oliveira, Aline L; Spencer, John; Rodrigues, Marcelo O; Neto, Brenno A D

    2015-03-23

    Improved cellular selectivity for nucleoli staining was achieved by simple chemical modification of carbon dots (C-dots) synthesized from waste carbon sources such as cow manure (or from glucose). The C-dots were characterized and functionalized (amine-passivated) with ethylenediamine, affording amide bonds that resulted in bright green fluorescence. The new modified C-dots were successfully applied as selective live-cell fluorescence imaging probes with impressive subcellular selectivity and the ability to selectively stain nucleoli in breast cancer cell lineages (MCF-7). The C-dots were also tested in four other cellular models and showed the same cellular selection in live-cell imaging experiments.

  10. A Quick and Parallel Analytical Method Based on Quantum Dots Labeling for ToRCH-Related Antibodies

    Directory of Open Access Journals (Sweden)

    Li Ding

    2009-01-01

    Full Text Available Abstract Quantum dot is a special kind of nanomaterial composed of periodic groups of II–VI, III–V or IV–VI materials. Their high quantum yield, broad absorption with narrow photoluminescence spectra and high resistance to photobleaching, make them become a promising labeling substance in biological analysis. Here, we report a quick and parallel analytical method based on quantum dots for ToRCH-related antibodies including Toxoplasma gondii, Rubella virus, Cytomegalovirus and Herpes simplex virus type 1 (HSV1 and 2 (HSV2. Firstly, we fabricated the microarrays with the five kinds of ToRCH-related antigens and used CdTe quantum dots to label secondary antibody and then analyzed 100 specimens of randomly selected clinical sera from obstetric outpatients. The currently prevalent enzyme-linked immunosorbent assay (ELISA kits were considered as “golden standard” for comparison. The results show that the quantum dots labeling-based ToRCH microarrays have comparable sensitivity and specificity with ELISA. Besides, the microarrays hold distinct advantages over ELISA test format in detection time, cost, operation and signal stability. Validated by the clinical assay, our quantum dots-based ToRCH microarrays have great potential in the detection of ToRCH-related pathogens.

  11. A rapid fluorescence "switch-on" assay for glutathione detection by using carbon dots-MnO2 nanocomposites.

    Science.gov (United States)

    Cai, Qi-Yong; Li, Jie; Ge, Jia; Zhang, Lin; Hu, Ya-Lei; Li, Zhao-Hui; Qu, Ling-Bo

    2015-10-15

    Glutathione (GSH) serves many cellular functions and plays crucial roles in human pathologies. Simple and sensitive sensors capable of detecting GSH would be useful tools to understand the mechanism of diseases. In this work, a rapid fluorescence "switch-on" assay was developed to detect trace amount of GSH based on carbon dots-MnO2 nanocomposites, which was fabricated through in situ synthesis of MnO2 nanosheets in carbon dots colloid solution. Due to the formation of carbon dots-MnO2 nanocomposites, fluorescence of carbon dots could be quenched efficiently by MnO2 nanosheeets through fluorescence resonance energy transfer (FRET). However, the presence of GSH would reduce MnO2 nanosheets to Mn(2+) ions and subsequently release carbon dots, which resulted in sufficient recovery of fluorescent signal. This proposed assay demonstrated highly selectivity toward GSH with a detection limit of 300nM. Moreover, this method has also shown sensitive responses to GSH in human serum samples, which indicated its great potential to be used in disease diagnosis. As no requirement of any further functionalization of these as-prepared nanomaterials, this sensing system shows remarkable advantages including very fast and simple, cost-effective as well as environmental-friendly, which suggest that this new strategy could serve as an efficient tool for analyzing GSH level in biosamples.

  12. Fluorophotometric determination of critical micelle concentration (CMC) of ionic and non-ionic surfactants with carbon dots via Stokes shift.

    Science.gov (United States)

    Lavkush Bhaisare, Mukesh; Pandey, Sunil; Shahnawaz Khan, M; Talib, Abou; Wu, Hui-Fen

    2015-01-01

    A new and facile method for the determination of critical micelle concentration (CMC) of ionic and non-ionic surfactants is proposed in this article. Carbon dots exhibited substantial fluorescence and therefore enhanced the sensitivity of this evaluation. Understanding the formation of surfactant micelles is vital for the applications of biomedicine such as drug fabrication and smart molecular vehicles in delivering therapeutic dosage to various molecular sites. The fluorescence property of carbon dots was utilized for the first time to estimate the critical micelle concentration of surfactants. The central concept of the approach is based on the Stokes shift determination of a system composed of constant amount of carbon dots with varying concentrations of ionic and non-ionic surfactants. The synthesized carbon dots were characterized by FTIR, TEM, XRD, Raman, UV, and fluorescence spectroscope. The carbon dots were excited at 280 nm so as to obtain maximum emission for the Stokes shift measurement. The CMC value of cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), Triton X-100, dodecyldimethyl(3-sulfopropyl)ammonium hydroxide (SB-12) evaluated by this approach was found to be 0.98, 7.3, 0.19, and 3.5mM, respectively. The signals of spectra were assigned and explained in terms of both electron transitions between specific molecular orbital and the interaction with solvent.

  13. Origins of photoluminescence decay kinetics in CdTe colloidal quantum dots.

    Science.gov (United States)

    Califano, Marco

    2015-03-24

    Recent experimental studies have identified at least two nonradiative components in the fluorescence decay of solutions of CdTe colloidal quantum dots (CQDs). The lifetimes reported by different groups, however, differed by orders of magnitude, raising the question of whether different types of traps were at play in the different samples and experimental conditions and even whether different types of charge carriers were involved in the different trapping processes. Considering that the use of these nanomaterials in biology, optoelectronics, photonics, and photovoltaics is becoming widespread, such a gap in our understanding of carrier dynamics in these systems needs addressing. This is what we do here. Using the state-of-the-art atomistic semiempirical pseudopotential method, we calculate trapping times and nonradiative population decay curves for different CQD sizes considering up to 268 surface traps. We show that the seemingly discrepant experimental results are consistent with the trapping of the hole at unsaturated Te bonds on the dot surface in the presence of different dielectric environments. In particular, the observed increase in the trapping times following air exposure is attributed to the formation of an oxide shell on the dot surface, which increases the dielectric constant of the dot environment. Two types of traps are identified, depending on whether the unsaturated bond is single (type I) or part of a pair of dangling bonds on the same Te atom (type II). The energy landscape relative to transitions to these traps is found to be markedly different in the two cases. As a consequence, the trapping times associated with the different types of traps exhibit a strikingly contrasting sensitivity to variations in the dot environment. Based on these characteristics, we predict the presence of a sub-nanosecond component in all photoluminescence decay curves of CdTe CQDs in the size range considered here if both trap types are present. The absence of such a

  14. Electrochemiluminescent detection of Pb2+ by graphene/gold nanoparticles and CdSe quantum dots

    Science.gov (United States)

    Lu, Liping; Guo, Linqing; Li, Jiao; Kang, Tianfang; Cheng, Shuiyuan

    2016-12-01

    A highly sensitive electrochemiluminescent detection method for lead ions (Pb(II)) was fabricated based on the distance-dependent quenching of the electrochemiluminescence from CdSe quantum dots by nanocomposites of graphene and gold nanoparticles. Graphene/gold nanoparticles were electrochemically deposited onto a glassy carbon electrode through the constant potential method. Thiol-labeled DNA was then assembled on the surface of the electrode via gold-sulfur bonding, following which the amino-labeled terminal of the DNA was linked to carboxylated CdSe quantum dots by the formation of amide bonds. The 27-base aptamer was designed with two different domains: the immobilization and detection sequences. The immobilization sequence was paired with 12 complementary bases and immobilized on the gold electrode; the single-stranded detection sequence, rich in G bases, formed a G-quadruplex (G4) structure in the presence of Pb2+. The formation of G4 shortens the distance between the CdSe quantum dots and the Au electrode, which decreases the electrochemiluminescent intensity in a linear fashion, proportional to the concentration of Pb(II). The linear range of the sensor was 10-10 to 10-8 mol/L (R = 0.9819) with a detection limit of 10-10 mol/L. This sensor detected Pb(II) in real water samples with satisfactory results.

  15. Polycation-Capped CdS Quantum Dots Synthesized in Reverse Microemulsions

    Directory of Open Access Journals (Sweden)

    Karina Lemke

    2012-01-01

    Full Text Available This paper is focused on the formation and recovery of cadmium sulfide (CdS nanoparticles in two different types of polycation-modified reverse microemulsions using low molecular weight poly(diallyldimethylammonium chloride (PDADMAC and poly(ethyleneimine (PEI. Both polymers were incorporated in a quaternary w/o microemulsion consisting of water, toluene-pentanol (1 : 1, and sodium dodecyl sulfate (SDS, as well as in a ternary w/o microemulsion consisting of water, heptanol, and 3-(N,N-dimethyl-dodecylammonio-propanesulfonate (SB. UV-vis and fluorescence measurements in the microemulsion illustrate the capping effect of the polycations on the formation of the CdS quantum dots. The nanoparticles are redispersed in water and characterized by using UV-vis and fluorescence spectroscopy, in combination with dynamic light scattering. From the quaternary microemulsion, only nanoparticle aggregates of about 100 nm can be redispersed, but, from the ternary microemulsion, well-stabilized polycation-capped CdS quantum dots can be obtained. The results show that the electrostatic interactions between the polycation and the surfactant are of high relevance especially in the solvent evaporation and redispersion process. That means only that in the case of moderate polycation-surfactant interactions a redispersion of the polymer-capped CdS quantum dots without problems of aggregation is possible.

  16. Unified ZnO Q-dot growth mechanism from simultaneous UV-Vis and EXAFS monitoring of sol-gel reactions induced by different alkali base

    Science.gov (United States)

    Caetano, Bruno L.; Silva, Marlon N.; Santilli, Celso V.; Briois, Valérie; Pulcinelli, Sandra H.

    2016-11-01

    This article aims to give experimental evidences of the universality of main steps involved in ZnO nanoparticles formation and growth from sol-gel process. In this way, we revisit the effect of the alkali base (LiOH, NaOH, KOH) used to induce the hydrolysis-condensation reaction in order to unfold the ZnO Q-dot formation mechanisms by using simultaneous time resolved monitoring of zinc species and Q-dot size by combining EXAFS and UV-Vis spectroscopy. Irrespective of the alkali base used, nucleation and growth of ZnO Q-dots occur by consumption of zinc oxy-acetate precursor. Higher amounts of ZnO nanocrystal are produced as the strength of the base increases. After achieving the steady state equilibrium regime the Q-dot growth occurs initially by oriented attachment coalescence mechanism followed by the Ostwald ripening coarsening. The dependence of the formation and growth mechanisms on the base strength allows the fine tuning of the Q-dot size and photoluminescence properties.

  17. General and Efficient C-C Bond Forming Photoredox Catalysis with Semiconductor Quantum Dots.

    Science.gov (United States)

    Caputo, Jill A; Frenette, Leah C; Zhao, Norman; Sowers, Kelly L; Krauss, Todd D; Weix, Daniel J

    2017-03-29

    Photoredox catalysis has become an essential tool in organic synthesis because it enables new routes to important molecules. However, the best available molecular catalysts suffer from high catalyst loadings and rely on precious metals. Here we show that colloidal nanocrystal quantum dots (QDs) can serve as efficient and robust, precious-metal free, photoassisted redox catalysts. A single-sized CdSe quantum dot (3.0 ± 0.2 nm) can replace several different dye catalysts needed for five different photoredox reactions (β-alkylation, β-aminoalkylation, dehalogenation, amine arylation, and decarboxylative radical formation). Even without optimization of the QDs or the reaction conditions, efficiencies rivaling those of the best available metal dyes were obtained.

  18. A low temperature processed Si-quantum-dot poly-Si TFT nonvolatile memory device

    Institute of Scientific and Technical Information of China (English)

    Sun Wei

    2013-01-01

    This paper reports on a successful demonstration of poly-Si TFT nonvolatile memory with a much reduced thermal-budget.The TFT uses uniform Si quantum-dots (size ~10 nm and density ~1011 cm-2) asstorage media,obtained via LPCVD by flashing SiH4/H2 at 580 ℃ for 15 s on a Si3N4 surface.The poly-Si grain-enlargement step was shifted after source/drain formation.The NiSix-silicided source/drain enables a fast lateral-recrystallization,and thus grain-enlargement can be accomplished by a much reduced thermal-cycle (i.e.,550 ℃/4 h).The excellent memory characteristics suggest that the proposed poly-Si TFT Si quantum-dot memory and associated processes are promising for use in wider TFT applications,such as system-on-glass.

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

    Science.gov (United States)

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

    2009-09-01

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

  20. 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.

  1. Blocking transport resonances via Kondo many-body entanglement in quantum dots

    Science.gov (United States)

    Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena

    2016-08-01

    Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) \\xotime SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin.

  2. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

    Directory of Open Access Journals (Sweden)

    Generalov R

    2011-09-01

    Full Text Available Roman Generalov1,2, Simona Kavaliauskiene1, Sara Westrøm1, Wei Chen3, Solveig Kristensen2, Petras Juzenas11Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway; 2School of Pharmacy, University of Oslo, Oslo, Norway; 3Department of Physics, The University of Texas at Arlington, Arlington, TX, USAAbstract: Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers.Keywords: fluorescence lifetime, free radicals, liposomes, lipodots, reactive oxygen species

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

    Science.gov (United States)

    Generalov, Roman; Kavaliauskiene, Simona; Westrøm, Sara; Chen, Wei; Kristensen, Solveig; Juzenas, Petras

    2011-01-01

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

  4. 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

  5. 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.

  6. Nanobeam photonic crystal cavity quantum dot laser

    CERN Document Server

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

    2010-01-01

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

  7. 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.

  8. Mesoscopic Cavity Quantum Electrodynamics with Quantum Dots

    CERN Document Server

    Childress, L I; Lukin, M D

    2003-01-01

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

  9. Energy level statistics of quantum dots.

    Science.gov (United States)

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

    2007-05-08

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

  10. Design of tunneling injection quantum dot lasers

    Institute of Scientific and Technical Information of China (English)

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

    2007-01-01

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

  11. 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.

  12. Energy level statistics of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-05-08

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

  13. Energy level statistics of quantum dots

    Science.gov (United States)

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

    2007-05-01

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

  14. 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.

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

    Science.gov (United States)

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

    2017-03-22

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

  16. 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.

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

    Science.gov (United States)

    Song, Fayi; Chan, Warren C W

    2011-12-09

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

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

    CERN Document Server

    Chusseau, Laurent; Viktorovitch, P; Letartre, Xavier

    2013-01-01

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

  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. 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

  1. 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.

  2. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

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

  3. DLTS measurements on GaSb/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-07-01

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

  4. Quantum dot spectroscopy using a single phosphorus donor

    Science.gov (United States)

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

    2015-12-01

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

  5. 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.

  6. Controlled self-assembly of hydrophobic quantum dots through silanization.

    Science.gov (United States)

    Yang, Ping; Ando, Masanori; Murase, Norio

    2011-09-01

    We demonstrate the formation of one-, two-, and three-dimensional nanocomposites through the self-assembly of silanized CdSe/ZnS quantum dots (QDs) by using a controlled sol-gel process. The self-assembly behavior of the QDs was created when partially hydrolyzed silicon alkoxide monomers replaced hydrophobic ligands on the QDs. We examined systematically self-assembly conditions such as solvent components and QD sizes in order to elucidate the formation mechanism of various QD nanocomposites. The QD nanocomposites were assembled in water phase or on the interface of water and oil phase in emulsions. The partially hydrolyzed silicon alkoxides act as intermolecules to assemble the QDs. The QD nanocomposites with well-defined solid or hollow spherical, fiber-like, sheet-like, and pearl-like morphologies were prepared by adjusting the experimental conditions. The high photoluminescence efficiency of the prepared QD nanocomposites suggests partially hydrolyzed silicon alkoxides reduced the surface deterioration of QDs during self-assembly. These techniques are applicable to other hydrophobic QDs for fabricating complex QD nanocomposites.

  7. Mercaptoethanol capped CdSe quantum dots and CdSe/ZnS core/shell: synthesis, characterization and cytotoxicity evaluation.

    Science.gov (United States)

    Painuly, Diksha; Bhatt, Anugya; Krishnan, V Kalliyana

    2013-02-01

    CdSe Quantum dots (Q-dots) and CdSe/ZnS core/shell have been synthesized by wet chemical route using mercaptoethanol (ME) as cappant. The synthesized Q-dots and core/shell were characterized using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDS), Dynamic Light Scattering (DLS), Optical absorption and luminescence spectroscopy. The core/shell formation was confirmed by both XRD and TEM analysis. The luminescence was shown to be considerably enhanced in the core/shell sample. Effect of dialysis process on the optical properties of the Q-dots and core/shell has also been discussed. Cytotoxicity studies have been carried out for Q-dots and core/shell. CdSe/ZnS core/shell was found to be non-cytotoxic as compared to CdSe Q-dots up to a certain concentration range. Polyethylene glycol (PEG) coating enhances the non-cytotoxic nature of CdSe/ZnS core/shell when compared with bare core/shell.

  8. 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.

  9. 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.

  10. Pharmaceutical and biomedical applications of quantum dots.

    Science.gov (United States)

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

    2016-05-01

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

  11. Depleted bulk heterojunction colloidal quantum dot photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-07-26

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

  12. Barrier Engineered Quantum Dot Infrared Photodetectors

    Science.gov (United States)

    2015-06-01

    Advisor, Space Based Advanced Sensing and Protection //SIGNED// JOHN BEAUCHEMIN Chief Engineer, Spacecraft Technology Division Space Vehicles...QD based device can be further improved by planting the dots into a CE DWELL structure to reduce the operating bias while maintaining good...noteworthy low operating bias voltage indicates its feasibility for fabrication of FPA using commercially available silicon read-out circuits. Figure 3. (a

  13. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

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

    2011-01-01

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

  14. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  15. The pinning effect in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-24

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

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

    Science.gov (United States)

    2016-04-04

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

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

    CERN Document Server

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

    2011-01-01

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

  18. Electron States of Few-Electron Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    戴振宏; 孙金祚; 张立德; 李作宏; 黄士勇; 隋鹏飞

    2002-01-01

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

  19. Aerial measurement error with a dot planimeter: Some experimental estimates

    Science.gov (United States)

    Yuill, R. S.

    1971-01-01

    A shape analysis is presented which utilizes a computer to simulate a multiplicity of dot grids mathematically. Results indicate that the number of dots placed over an area to be measured provides the entire correlation with accuracy of measurement, the indices of shape being of little significance. Equations and graphs are provided from which the average expected error, and the maximum range of error, for various numbers of dot points can be read.

  20. Local Quantum Dot Tuning on Photonic Crystal Chips

    CERN Document Server

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

    2007-01-01

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

  1. Exciton lifetime measurements on single silicon quantum dots.

    Science.gov (United States)

    Sangghaleh, Fatemeh; Bruhn, Benjamin; Schmidt, Torsten; Linnros, Jan

    2013-06-01

    We measured the exciton lifetime of single silicon quantum dots, fabricated by electron beam lithography, reactive ion etching and oxidation. The observed photoluminescence decays are of mono-exponential character with a large variation (5-45 μs) from dot to dot, even for the same emission energy. We show that this lifetime variation may be the origin of the heavily debated non-exponential (stretched) decays typically observed for ensemble measurements.

  2. 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.

  3. Production and targeting of monovalent quantum dots.

    Science.gov (United States)

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

    2014-10-23

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

  4. Probing relaxation times in graphene quantum dots

    Science.gov (United States)

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

    2013-01-01

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

  5. Nonrenewal statistics in transport through quantum dots

    Science.gov (United States)

    Ptaszyński, Krzysztof

    2017-01-01

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

  6. 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

    2015-04-08

    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.

  7. Thermoelectric study of dissipative quantum-dot heat engines

    Science.gov (United States)

    De, Bitan; Muralidharan, Bhaskaran

    2016-10-01

    This paper examines the thermoelectric response of a dissipative quantum-dot heat engine based on the Anderson-Holstein model in two relevant operating limits, (i) when the dot phonon modes are out of equilibrium, and (ii) when the dot phonon modes are strongly coupled to a heat bath. In the first case, a detailed analysis of the physics related to the interplay between the quantum-dot level quantization, the on-site Coulomb interaction, and the electron-phonon coupling on the thermoelectric performance reveals that an n -type heat engine performs better than a p -type heat engine. In the second case, with the aid of the dot temperature estimated by incorporating a thermometer bath, it is shown that the dot temperature deviates from the bath temperature as electron-phonon interaction in the dot becomes stronger. Consequently, it is demonstrated that the dot temperature controls the direction of phonon heat currents, thereby influencing the thermoelectric performance. Finally, the conditions on the maximum efficiency with varying phonon couplings between the dot and all the other macroscopic bodies are analyzed in order to reveal the nature of the optimum junction.

  8. 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.

  9. 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.

  10. Multicolor Nitrogen-Doped Carbon Dots for Live Cell Imaging.

    Science.gov (United States)

    Du, Fengyi; Li, Jianan; Hua, Ye; Zhang, Miaomiao; Zhou, Zhou; Yuan, Jing; Wang, Jun; Peng, Wanxin; Zhang, Li; Xia, Sheng; Wang, Dongqing; Yang, Shiming; Xu, Wenrong; Gong, Aihua; Shao, Qixiang

    2015-05-01

    Doping carbon dots with nitrogen atoms considerably enhances their fluorescence properties. However, the mechanism by which the carbon dots are doped is not fully understood. We developed a facile bottom-up hydrothermal carbonization (HTC) process that uses glucose and glycine as precursors for the synthesis of photoluminescent nitrogen-doped carbon dots. The as-prepared nitrogen-doped carbon dots were mono-dispersed spherical particles with a diameter of -2.8 nm. The doped nitrogen atoms assumed pyridinic type and pyrrolic type configurations to participate in the nanocrystal structure of the carbon dots. It appeared that the nitrogen doping introduces a new internal structure. The aqueous solution of nitrogen-doped carbon dots showed excitation wavelength-dependent multicolor photoluminescence. Further, these nitrogen-doped carbon dots readily entered the cytoplasm of A549 cancer cells and showed no significant cytotoxicity. The internalized nitrogen-doped carbon dots were localized to the cell membrane and cytoplasm, particularly around the nucleus. Further, the as-prepared, biocompatible, nitrogen-doped carbon dots demonstrated the potential to be used as fluorescent probes for multicolor live cell labeling, tracking, and imaging.

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

    Institute of Scientific and Technical Information of China (English)

    解文方

    2002-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

    L(U) Rong; ZHANG Guang-Ming

    2005-01-01

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

  13. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum

    OpenAIRE

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

    2016-01-01

    CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum) were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were pr...

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

    Science.gov (United States)

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

    2016-09-22

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

  15. 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.

  16. Novel Growth Technologies for In Situ Formation of Semiconductor Quantum Wire Structures

    Science.gov (United States)

    1994-01-01

    situ formation of InP quantum dots . It has been observed that many strained systems exhibit Stranski-Krastanow growth, where the epitaxy initiates in two... quantum dots have been achieved. This ONR contract was key to our development of the less hazardous novel non-hydride sources, tertiarybutylarsine (TBA) and...Novel growth technologies were developed for low dimensional quantum materials and devices. Non-hydride MOCVD and use of strain to produce InP

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

    Institute of Scientific and Technical Information of China (English)

    XIEWen-Fang; ZHUWu

    2003-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang; ZHU Wu

    2003-01-01

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

  19. 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.

  20. 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.

  1. Silanization of plasma-grown silicon quantum dots for production of a tunable, stable, colloidal solution

    Science.gov (United States)

    Anderson, Ingrid E.; Shircliff, Rebecca A.; Lee, Benjamin G.; Simonds, Brian; Agarwal, Sumit; Stradins, Paul; Collins, Reuben T.

    2011-09-01

    Nanomaterials have the potential to revolutionize photovoltaics with the promise of new physics, novel architectures and low cost synthesis. Silicon quantum dots, relative to their II-VI counterparts, are understudied due to the difficulty of solution synthesis and chemical passivation. However, silicon is still an attractive solar cell material, providing an optimal band gap, low toxicity, and a very solid body of physical understanding of bulk silicon to draw from. We have synthesized silicon quantum dots with plasma enhanced chemical vapor deposition, and have developed a method for chemical passivation of these silicon quantum dots that can be used on particles created in a variety of ways. This versatile method utilizes oxidation via wet chemical etch and subsequent siloxane bond formation. The attachment of a silane to the SiOx shell leads to stability of the silicon core for over a month in air, and individual particles can be seen with TEM; thus a stable, colloidal suspension is formed. The future for this technique, including increasing quantum yield of the particles by changing the nature of the oxide, will be discussed.

  2. Synthesis and drug detection performance of nitrogen-doped carbon dots

    Energy Technology Data Exchange (ETDEWEB)

    Niu, Jingjing [Functional and Environment Materials Research Institute, College of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Nano Structure and Low Dimensional Physics Laboratory, Peking University, Beijing 100871 (China); Gao, Hui, E-mail: hope@lzu.edu.cn [Functional and Environment Materials Research Institute, College of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China)

    2014-05-01

    Recently, nitrogen-doped carbon dots (NCDs) have attracted considerable interest since nitrogen (N) doping could effectively tailor the electronic properties and the chemical reactivity of carbon dots (CDs) for advanced potential applications. Herein, a one-step pyrolysis method was presented for synthesizing the NCDs with excellent water solubility, good stability and a high quantum yield of ca. 28%. The detection performance of NCDs for the antibacterial drugs was further explored, and it was proved to effectively enhance the fluorescence due to the strong interaction between the NCDs and antibacterial drugs. - Highlights: • A facile yet economic bottom-up pyrolysis method for synthesizing nitrogen (N)-doped carbon dots (NCDs) using glutamic acid as the precursor. • Glutamic acid was the only starting material and used as a source of carbon and nitrogen; the formation and functionalization of NCDs were accomplished simultaneously. • The NCDs possess bright blue emission (with a high quantum yield of ca. 28%) and excellent excitation dependent on PL properties. • NCDs were used for the determination of antibacterial drugs based on the fluorescence enhancement.

  3. Design and synthesis of heterostructured quantum dots with dual emission in the visible and infrared.

    Science.gov (United States)

    Lin, Qianglu; Makarov, Nikolay S; Koh, Weon-kyu; Velizhanin, Kirill A; Cirloganu, Claudiu M; Luo, Hongmei; Klimov, Victor I; Pietryga, Jeffrey M

    2015-01-27

    The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR)-active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intraband relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from the CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core-shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogeneous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe and the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation.

  4. 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.

  5. Spin-valley lifetimes in a silicon quantum dot with tunable valley splitting.

    Science.gov (United States)

    Yang, C H; Rossi, A; Ruskov, R; Lai, N S; Mohiyaddin, F A; Lee, S; Tahan, C; Klimeck, G; Morello, A; Dzurak, A S

    2013-01-01

    Although silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure the formation of well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3-0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin read-out and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 s. Spin relaxation occurs via phonon emission due to spin-orbit coupling between the valley states, a process not previously anticipated for silicon quantum dots. An analytical theory describes the magnetic field dependence of the relaxation rate, including the presence of a dramatic rate enhancement (or hot-spot) when Zeeman and valley splittings coincide.

  6. 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.

  7. [Spectral Characteristics of Si Quantum Dots Embedded in SiN(x) Thin Films Prepared by Magnetron Co-Sputtering].

    Science.gov (United States)

    Chen, Xiao-bo; Yang, Wen; Duan, Liang-fei; Zhang, Li-yuan; Yang, Pei-zhi; Song, Zhao-ning

    2015-07-01

    The silicon-rich SiN(x) films were fabricated on Si(100) substrate and quartz substrate at different substrate temperatures varying from room temperature to 400 degrees C by bipolar pulse ane RF magnetron co-sputtering deposition technique. After deposition, the films were annealed in a nitrogen atmosphere by rapid photothermal annealing at 1050 degrees C for 3 minutes. This thermal step allows the formation of the silicon quantum dots. Fourier transform infrared spectroscopy, Raman spectroscopy, grazing incidence X-ray diffraction and photoluminescence spectroscopy were used to analyze the bonding configurations, microstructures and luminescence properties of the films. The experimental results showed that: silicon-rich Si-N bonds were found in Fourier transform infrared spectra, suggesting that the silicon-rich SiN, films were successfully prepared; when the substrate temperature was not lower than 200 degrees C, the Raman spectra of the films showed the transverse optical mode of Si-Si vibration, while the significant diffraction peaks of Si(111) and Si(311) were shown in grazing incidence X-ray diffraction spectra, confirming the formation of silicon quantum dots; our work indicated that there was an optimal substrate temperature (300 degrees C), which could significantly increase the amount and the crystalline volume fraction of silicon quantum dots; three visible photoluminescence bands can be obtained for both 30 degrees C sample and 400 degrees C sample, and in combination with Raman results, the emission peaks were reasonably explained by using the quantum confinement effect and radiative recombination defect state of Si nanocrystals; the average size of the silicon quantum dots is 3.5 and 3.4 nm for the 300 degrees C sample and 400 degrees C sample, respectively. These results are useful for optimizing the fabrication parameters of silicon quantum dots embedded in SiN. thin films and have valuable implications for silicon based photoelectric device

  8. Trapping photon-dressed Dirac electrons in a quantum dot studied by coherent two dimensional photon echo spectroscopy

    Science.gov (United States)

    Roslyak, O.; Gumbs, Godfrey; Mukamel, S.

    2012-05-01

    We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated.

  9. Tunnel-coupled quantum dots: Atomistic Theory of Quantum Dot Molecules and Arrays

    Science.gov (United States)

    Bryant, Garnett W.; Aizpurua, J.; Jaskolski, W.; Zielinski, Michal

    2003-03-01

    Quantum dots are studied as artificial atoms for building novel artificial solids, as nanodevices in nanoelectronics, and as bio/nanohybrids. We present an atomistic tight-binding theory of coupled CdS nanocrystals and vertically and laterally coupled InAs self-assembled dots. Electron states of coupled dots follow the analogy of coupled dots as artificial molecules. Symmetric/antisymmetric pairs are formed with strongest coupling between states with high density at interdot interfaces. Complex coupling of hole states, with significant departures from the artificial molecule analogy, occurs because the coupling is determined by the hole envelope function and the hole atomic state. Some hole states couple to form symmetric/antisymmetric pairs. Other hole states couple through additional intermediate states to form two strongly split symmetric states and an antisymmetric state insensitive to coupling. These coupling effects lead to level reordering, changes in state symmetry, conversion of dark states to bright states and vice versa, and tailored polarization dependence.

  10. Fast synthesize ZnO quantum dots via ultrasonic method.

    Science.gov (United States)

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

    2016-05-01

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

  11. Single-photon superradiance from a quantum dot

    DEFF Research Database (Denmark)

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

    2016-01-01

    We report on the observation of single-photon superradiance from an exciton in a semiconductor quantum dot. The confinement by the quantum dot is strong enough for it to mimic a two-level atom, yet sufficiently weak to ensure superradiance. The electrostatic interaction between the electron and t...

  12. 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.

  13. Exciton dephasing in single InGaAs quantum dots

    DEFF Research Database (Denmark)

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

    2000-01-01

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

  14. Teaching Beginning Chemistry Students Simple Lewis Dot Structures

    Science.gov (United States)

    Nassiff, Peter; Czerwinski, Wendy A.

    2015-01-01

    Students beginning their initial study of chemistry often have a difficult time mastering simple Lewis dot structures. Textbooks show students how to manipulate Lewis structures by moving valence electron dots around the chemical structure so each atom has an octet or duet. However, an easier method of teaching Lewis structures for simple…

  15. Electron Energy Level Statistics in Graphene Quantum Dots

    NARCIS (Netherlands)

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

    2008-01-01

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

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

    DEFF Research Database (Denmark)

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

    2009-01-01

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

  17. Negative Trions Trapped by a Spherical Parabolic Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

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

  18. 49 CFR 41.119 - DOT regulated buildings.

    Science.gov (United States)

    2010-10-01

    ... and additions to existing buildings will ensure that each DOT regulated building is designed and... section pertains to all new building projects for which development of detailed plans and specifications.... (d) For DOT regulated buildings a certification of compliance with the seismic design...

  19. 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.

  20. ANISOTROPIC RADIATIVE DECAY OF InP SELF-ASSEMBLED QUANTUM DOTS

    OpenAIRE

    1998-01-01

    Strong optical anisotropy of the photoluminescence (PL) spectra and time resolvedPL spectra is observed in InP self-assembled quantum dots (SADs) embedded inGaInP matrix. From the TEM study, the origin of the optical anisotropy appearsto be due to the formation of composition modulation planes in GaInP matrix.We also studied the size dependence of the radiative decay time. In the vicinityof the PL peak from InP SADs, slowdown of the PL decay time was observed ondecreasing the detection energy...

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

    Energy Technology Data Exchange (ETDEWEB)

    Maksymov, Artur, E-mail: maxyartur@gmail.com [Advanced Materials Research Institute, University of New Orleans, LA 70148 (United States); Department of General Physics, Chernivtsi National University, Chernivtsi 58012 (Ukraine); Spinu, Leonard [Advanced Materials Research Institute, University of New Orleans, LA 70148 (United States); Department of Physics, University of New Orleans, New Orleans, LA 70148 (United States)

    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.

  2. Growing InAs/GaAs quantum dots by droplet epitaxy under MOVPE conditions

    Science.gov (United States)

    Surnina, M. A.; Akchurin, R. Kh.; Marmalyuk, A. A.; Bagaev, T. A.; Sizov, A. L.

    2016-07-01

    Results of studying the formation of InAs quantum dots (QDs) on GaAs(100) substrates by droplet epitaxy using trimethylindium and arsine (AsH3) as precursors are presented. The growth process was carried out at temperatures within 230-400°C in a horizontal reactor for metalorganic vapor phase epitaxy (MOVPE) using high-purity hydrogen as the carrier gas. Data on the influence of process temperature on the QD size and the density of QD array and results of investigation of the low-temperature photoluminescence of obtained samples are presented.

  3. Strategy for synthesizing quantum dot-layered double hydroxide nanocomposites and their enhanced photoluminescence and photostability.

    Science.gov (United States)

    Cho, Seungho; Jung, Sungwook; Jeong, Sanghwa; Bang, Jiwon; Park, Joonhyuck; Park, Youngrong; Kim, Sungjee

    2013-01-08

    Layered double hydroxide-quantum dot (LDH-QD) composites are synthesized via a room temperature LDH formation reaction in the presence of QDs. InP/ZnS (core/shell) QD, a heavy metal free QD, is used as a model constituent. Interactions between QDs (with negative zeta potentials), decorated with dihydrolipoic acids, and inherently positively charged metal hydroxide layers of LDH during the LDH formations are induced to form the LDH-QD composites. The formation of the LDH-QD composites affords significantly enhanced photoluminescence quantum yields and thermal- and photostabilities compared to their QD counterparts. In addition, the fluorescence from the solid LDH-QD composite preserved the initial optical properties of the QD colloid solution without noticeable deteriorations such as red-shift or deep trap emission. Based on their advantageous optical properties, we also demonstrate the pseudo white light emitting diode, down-converted by the LDH-QD composites.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-07-01

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

  6. 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.

  7. Silicon Quantum Dots for Quantum Information Processing

    Science.gov (United States)

    2013-11-01

    A. J. Ferguson , A. S. Dzurak, and R. G. Clark. Gate-defined quantum dots in intrinsic silicon. Nano Letters, 7(7), 2051 (2007). 4, 21, 44, 68, 99 132...B, 80(7), 075310 (2009). 66 [105] M. Field, C. Smith, M. Pepper , D. Ritchie, J. Frost, G. Jones, and D. Hasko. Measurements of Coulomb blockade with a...transistor as an integrated charge sensor. Applied Physics Letters, 97(26), 262113 (2010). 68, 74 [111] G. Podd, S. Angus, D. Williams, and A. Ferguson

  8. Graphene Quantum Dots for Theranostics and Bioimaging.

    Science.gov (United States)

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

    2016-10-01

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

  9. 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.

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

    Science.gov (United States)

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

    2014-06-21

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

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

    Science.gov (United States)

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

    2016-08-01

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

  12. Colloidal-quantum-dot spasers and plasmonic amplifiers

    CERN Document Server

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

    2016-01-01

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

  13. Second-harmonic imaging of semiconductor quantum dots

    DEFF Research Database (Denmark)

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

    2000-01-01

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

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

    Science.gov (United States)

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

    2015-02-01

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

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

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg

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

  16. [The determination of the genotype of natural reassortant influenza A viruses according to the core protein genes by the methods of competitive dot hybridization and sequencing].

    Science.gov (United States)

    Grinbaum, E B; Zolotarev, F N; Petrov, N A; Litvinova, O M; Konovalenko, I B; Luzianina, T Ia; Golubev, D B

    1992-01-01

    Simultaneous circulation of different subtypes of influenza A viruses provides conditions for reassortant strains formation. A comparative investigation of genome of 47 influenza A virus strains (H1N1, H2N2, and H3N2) was carried out by competitive dot hybridization technique and sequence analysis of some of cDNA-copies of the virus genes. All the genes of 43 strains encoding nonglycolysed proteins corresponded to the serum subtype of surface glycoproteins. The reassortant pattern of genome for some genes of core proteins was revealed in 4 viruses. All the dot hybridization data were completely confirmed by sequence analysis of the genes.

  17. 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.

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

    DEFF Research Database (Denmark)

    Leosson, K.; Birkedal, Dan; Magnúsdóttir, Ingibjörg;

    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 ...

  19. DotFETs: MOSFETs strained by a Single SiGE dot in a Low-Temperature ELA Technology

    NARCIS (Netherlands)

    Biasotto, C.

    2011-01-01

    The work presented in this thesis was performed in the context of the European Sixth Framework Program FP6 project “Disposable Dot Field Effect Transistor for High Speed Si Integrated Circuits”, referred to as the D-DotFET project. The project had the goal of realizing strain-enhanced mobility in CM

  20. Galaxy formation

    CERN Document Server

    Silk, Joseph; Dvorkin, Irina

    2015-01-01

    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.

  1. Ultraviolet responses of a heterojunction Si quantum dot solar cell.

    Science.gov (United States)

    Lee, Seong Hyun; Kwak, Gyea Young; Hong, Songwoung; Kim, Chanhong; Kim, Sung; Kim, Ansoon; Kim, Kyung Joong

    2017-01-20

    We investigated the ultraviolet (UV) responses of a heterojunction Si quantum dot (QD) solar cell consisting of p-type Si-QDs fabricated on a n-type crystalline Si (p-Si-QD/n-c-Si HJSC). The UV responses were compared with a conventional n-type crystalline Si solar cell (n-c-Si SC). The external and internal quantum efficiency results of the p-Si-QD/n-c-Si HJSC exhibited a clear enhancement in the UV responses (300-400 nm), which was not observed in the n-c-Si SC. Based on the results of the cell reflectance and bias-dependent responses, we expect that almost all UV responses occur in the p-Si-QD layer, and the generated carriers can be transported via the Si-QD layer due to the formation of a sufficient electric filed. As a result, a high power conversion efficiency of 14.5% was achieved from the p-Si-QD/n-c-Si HJSC. By reducing the thickness of the n-Si substrate from 650 μm to 300 μm, more enhanced power conversion efficiency of 14.8% was obtained which is the highest value among the reported Si-QD based solar cells to date.

  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. Probing the kinetics of quantum dot-based proteolytic sensors.

    Science.gov (United States)

    Díaz, Sebastián A; Malonoski, Anthony P; Susumu, Kimihiro; Hofele, Romina V; Oh, Eunkeu; Medintz, Igor L

    2015-09-01

    As an enzyme superfamily, proteases are rivaled only by kinases in terms of their abundance within the human genome. Two ratiometric quantum dot (QD) Förster resonance energy transfer-based sensors designed to monitor the activity of the proteolytic enzymes collagenase and elastase are investigated here. Given the unique material constraints of these sensing constructs, assays are realized utilizing excess enzyme and fixed substrate in progress curve format to yield enzyme specificity or k cat/K m ratios. The range of k cat/Km values derived is 0.5-1.1 mM(-1) s(-1) for the collagenase sensor and 3.7-4.2 mM(-1) s(-1) for the elastase sensor. Of greater interest is the observation that the elastase sensor can be well represented by the Michaelis-Menten model while the collagenase sensor cannot. The latter demonstrates increased specificity at higher peptide substrate/QD loading values and an apparent QD-caused reversible inhibition as the reaction progresses. Understanding the detailed kinetic mechanisms that underpin these types of sensors will be important especially for their further quantitative utilization.

  4. 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.

  5. MBE growth of Ge quantum dot structures in oxide windows

    Energy Technology Data Exchange (ETDEWEB)

    Karmous, A; Kirfel, O; Oehme, M; Kasper, E; Schulze, J, E-mail: karmous@iht.uni-stuttgart.de [Institut fuer Halbleitertechnik - Universitaet Stuttgart, Pfaffenwaldring 47, D-70569 Stuttgart (Germany)

    2009-11-15

    The implementation of Quantum Dots (QDs) in devices allows novel electronic and opto-electronic functions. Strain driven Stranski-Krastanov growth mode enables the formation of nanometric islands (on wetting layer) whose density and geometry depend on growth conditions (temperature, rate) and surface structure (cleaning). The island positions are random. However, they can be influenced by surface patterning. In this work, the MBE growth of self-organized Ge QD structures in oxide windows is investigated. The studied Ge QD structures are composed by either a single Ge layer directly grown on a Si substrate, or double layer formed by a Ge QD layer on top of a Si buffer layer. Different surface preparation (dry etching with and without anisotropic wet etching) and cleaning (HF dip or RCA cleaning) schemes have been used. It is found that the cleaning and the Si buffer layer growth have strong influence on island nucleation. Preferred nucleation at the window edge and/or nucleation at the window center is observed under certain conditions. Interestingly, negligible influence (this is needed for most device works) is found only if Ge is grown directly on the RCA cleaned window.

  6. Ultraviolet responses of a heterojunction Si quantum dot solar cell

    Science.gov (United States)

    Lee, Seong Hyun; Kwak, Gyea Young; Hong, Songwoung; Kim, Chanhong; Kim, Sung; Kim, Ansoon; Kim, Kyung Joong

    2017-01-01

    We investigated the ultraviolet (UV) responses of a heterojunction Si quantum dot (QD) solar cell consisting of p-type Si-QDs fabricated on a n-type crystalline Si (p-Si-QD/n-c-Si HJSC). The UV responses were compared with a conventional n-type crystalline Si solar cell (n-c-Si SC). The external and internal quantum efficiency results of the p-Si-QD/n-c-Si HJSC exhibited a clear enhancement in the UV responses (300–400 nm), which was not observed in the n-c-Si SC. Based on the results of the cell reflectance and bias-dependent responses, we expect that almost all UV responses occur in the p-Si-QD layer, and the generated carriers can be transported via the Si-QD layer due to the formation of a sufficient electric filed. As a result, a high power conversion efficiency of 14.5% was achieved from the p-Si-QD/n-c-Si HJSC. By reducing the thickness of the n-Si substrate from 650 μm to 300 μm, more enhanced power conversion efficiency of 14.8% was obtained which is the highest value among the reported Si-QD based solar cells to date.

  7. Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots

    Directory of Open Access Journals (Sweden)

    Noor-Ul-Ain

    2016-11-01

    Full Text Available Tuning the emission energy of graphene quantum dots (GQDs and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped GQDs and (B-, Na-, and K-doped GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.

  8. 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.

  9. Soil formation.

    NARCIS (Netherlands)

    Breemen, van N.; Buurman, P.

    1998-01-01

    Soil Formation deals with qualitative and quantitative aspects of soil formation (or pedogenesis) and the underlying chemical, biological, and physical processes. The starting point of the text is the process - and not soil classification. Effects of weathering and new formation of minerals, mobilis

  10. Cost Effectiveness of DOTS and Non—DOTS Strategies for Smear—Positive Pulmonary Tuberculosis in Beijing

    Institute of Scientific and Technical Information of China (English)

    XU-QUN; JINSHUI-GAO; 等

    2000-01-01

    The cost-effectiveness of DOTS(Directly Observed Treatment,short course)and nonDOTS strategies for smear-positive pulmonary tuberculosis in Beijing was evaluated.Cost calculation was based on the experses of drugs ,chest X-ray films,sputm 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 tuberculsis;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.

  11. 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.

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

    CERN Document Server

    Tkach, N V; Zegrya, G G

    2002-01-01

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

  13. 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.

  14. 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.

  15. 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.

  16. 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...

  17. Application of Quantum Dots in Biological Imaging

    Directory of Open Access Journals (Sweden)

    Shan Jin

    2011-01-01

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

  18. Quantum dot imaging for embryonic stem cells

    Directory of Open Access Journals (Sweden)

    Gambhir Sanjiv S

    2007-10-01

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

  19. 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.

  20. Study of metallothionein-quantum dots interactions.

    Science.gov (United States)

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

    2014-05-01

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

  1. Kondo effects in triangular triple quantum dots

    Science.gov (United States)

    Oguri, Akira; Numata, Takahide; Nisikawa, Yunori; Hewson, A. C.

    2009-03-01

    We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. [4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496.

  2. 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.

  3. Polymersomes containing quantum dots for cellular imaging

    Directory of Open Access Journals (Sweden)

    Camblin M

    2014-05-01

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

  4. Using quantum dot photoluminescence for load detection

    Directory of Open Access Journals (Sweden)

    M. Moebius

    2016-08-01

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

  5. 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....

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

    Science.gov (United States)

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

    2016-10-01

    We define single quantum dots of lengths varying from 60 nm up to nearly half a micron in Ge-Si core-shell nanowires. The charging energies scale inversely with the quantum dot length between 18 and 4 meV. Subsequently, we split up a long dot into a double quantum dot with a separate control over the tunnel couplings and the electrochemical potential of each dot. Both single and double quantum dot configurations prove to be very stable and show excellent control over the electrostatic environment of the dots, making this system a highly versatile platform for spin-based quantum computing.

  7. 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.

  8. Self-assembled InAs/GaAs quantum dots and quantum dot laser

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Systematic study of molecular beam epitaxy-grown self-assembled In(Ga)As/GaAs, InAlAs/AlGaAs/GaAs, and InAs/InAlAs/InP quantum dots (QDs) is demonstrated. By adjusting growth conditions, surprising alignment, preferential elongation, and pronounced sequential coalescence of dots under the specific condition are realized. Room-temperature (RT) continuous-wave (CW) lasing at the wavelength of 960 nm with output power of 1 W is achieved from vertical coupled InAs/GaAs QDs ensemble. The RT threshold current density is 218 A/cm2. An RT CW output power of 0.53 W ensures at least 3 000 h lasing (only drops 0.83 db). This is one of the best results ever reported.

  9. Standardization of the dot enzyme-lynked immunosorbent assay (dot-ELISA for experimental plague

    Directory of Open Access Journals (Sweden)

    Silvia M. L. Montenegro

    1993-03-01

    Full Text Available A dot enzyme linked immunosorbent assay (dot-ELISA was previously developed to detect specific antibodies in rabbits sera immunized against FIA protein obtained from Yersina pestis. This antigen was covalently linked onto the surface of dacron (polyethyleneterephthalate. Here, standard conditions are described for the optimization of this procedure: an amount of 20 ng of FIA protein was fixed onto dacron; anti-rabbit IgG peroxidase conjugate diluted 1:8,000 and 30% non-fat instant milk as blocking substance were used throughout the method. This procedure was compared with that employing nitrocellulose as solid-phase which showed to be more sensitive. However, the method based on dacron did not show false positive reactions against non-immunized rabbits sera at low antigen amount and diluted anti-IgG peroxidase conjugate.

  10. Self-assembled InAs/GaAs quantum dots and quantum dot laser

    Institute of Scientific and Technical Information of China (English)

    王占国; 刘峰奇; 梁基本; 徐波

    2000-01-01

    Systematic study of molecular beam epitaxy-grown self-assembled ln(Ga)As/GaAs, In-AlAs/AlGaAs/GaAs, and InAs/InAIAs/lnP quantum dots (QDs) is demonstrated. By adjusting growth conditions, surprising alignment, preferential elongation, and pronounced sequential coalescence of dots under the specific condition are realized. Room-temperature (RT) continuous-wave (CW) lasing at the wavelength of 960 nm with output power of 1 W is achieved from vertical coupled InAs/GaAs QDs ensemble. The RT threshold current density is 218 A/cm2. An RT CW output power of 0.53 W ensures at least 3 000 h lasing (only drops 0.83 db). This is one of the best results ever reported.

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

    CERN Document Server

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

    2010-01-01

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

  12. Charge sensing of a few-donor double quantum dot in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Watson, T. F., E-mail: tfwatson15@gmail.com; Weber, B.; Büch, H.; Fuechsle, M.; Simmons, M. Y., E-mail: michelle.simmons@unsw.edu.au [Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, New South Wales 2052 (Australia)

    2015-12-07

    We demonstrate the charge sensing of a few-donor double quantum dot precision placed with atomic resolution scanning tunnelling microscope lithography. We show that a tunnel-coupled single electron transistor (SET) can be used to detect electron transitions on both dots as well as inter-dot transitions. We demonstrate that we can control the tunnel times of the second dot to the SET island by ∼4 orders of magnitude by detuning its energy with respect to the first dot.

  13. Computation of energy states of hydrogenic quantum dot with two-electrons

    Science.gov (United States)

    Yakar, Y.; Özmen, A.; ćakır, B.

    2016-03-01

    In this study we have investigated the electronic structure of the hydrogenic quantum dot with two electrons inside an impenetrable potential surface. The energy eigenvalues and wavefunctions of the ground and excited states of spherical quantum dot have been calculated by using the Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method, and the energies are investigated as a function of dot radius. The results show that as dot radius increases, the energy of quantum dot decreases.

  14. UV Nano Lights - Nonlinear Quantum Dot-Plasmon Coupling

    Science.gov (United States)

    2016-06-20

    AFRL-AFOSR-JP-TR-2016-0072 UV Nano-Lights - Nonlinear Quantum Dot-Plasmon Coupling Eric Waclawik QUEENSLAND UNIVERSITY OF TECHNOLOGY Final Report 06...Final 3.  DATES COVERED (From - To)  03 Feb 2014 to 02 Feb 2016 4.  TITLE AND SUBTITLE UV Nano-Lights - Nonlinear Quantum Dot-Plasmon Coupling 5a...SUBJECT TERMS Quantum Dots, Energy Conversion, Up-conversion, Modeling 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES

  15. 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.

  16. Quantum dots microstructured optical fiber for x-ray detection

    Science.gov (United States)

    DeHaven, S. L.; Williams, P. A.; Burke, E. R.

    2016-02-01

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

  17. Imaging GABAc Receptors with Ligand-Conjugated Quantum Dots

    Directory of Open Access Journals (Sweden)

    Ian D. Tomlinson

    2007-01-01

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

  18. Infrared Focal Plane Arrays Based on Semiconductor Quantum Dots

    Science.gov (United States)

    2002-01-01

    studied in the framework of this, including the collaborating researchers in each of them, are detailed below: 1. “Ultra Small InAs/GaInP/ InP Quantum Dots ”: with...of detectors, which will be attached to Si based signal processors. D:\\FINAL REPORT.doc 4 Part 1 Ultra Small InAs/GaInP/ InP Quantum Dots The heights of...an ensemble of self-assembled InAs/GaAs or InAs/ InP quantum dots (QDs) are typically in the range of 10-30 monolayers [1]. Here, we report on InAs

  19. Temperature Studies of Single InP Quantum Dots

    Science.gov (United States)

    1999-06-18

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP012858 TITLE: Temperature Studies of Single InP Quantum Dots DISTRIBUTION...34 QWR/QD.07 St Petersburg, Russia, June 14-18, 1999 © 1999 loffe Institute Temperature studies of single InP quantum dots Valdry Zwiller, Mats-Erik...Information on the size and geometry of our self-assembled InP Quantum Dots grown on GamnP lattice matched to GaAs has been published elsewhere -I

  20. Solvothermal synthesis of InP quantum dots.

    Science.gov (United States)

    Nag, Angshuman; Sarma, D D

    2009-09-01

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

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer....... We notice that the emission spectra consist often of two peaks close in energy, which we explain with a comprehensive theory showing that the symmetry of the system plays a crucial role for the hole levels forming hybridized orbitals. Our results state that crystal phase quantum dots have promising...

  2. Emission redistribution from a quantum dot-bowtie nanoantenna

    OpenAIRE

    Regler, A.; Schraml, K.; Lyamkina, A.; Spiegl, M; Müller, K.; Vuckovic, J.; Finley, J. J.; Kaniber, M.

    2016-01-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby ($\\sim 25nm$) plasmonic antenna. Micro-photoluminescence spectroscopy shows a $\\sim 2.4\\times$ increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of $2.5\\mu W$ for both coupled and uncoupled quantum dot emission in polarization-resolved me...

  3. 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.

  4. PL Emission and Shape of Silicon Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-0-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet. The red-shifting of PL spectra on smaller silicon quantum dots can be explained by curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided in curved surface effect.About The Author: Zhong-Mei Huang,Master in Guizhou University.

  5. Magnetic quantum dot in two-dimensional topological insulators

    Science.gov (United States)

    Li, Guo; Zhu, Jia-Lin; Yang, Ning

    2017-03-01

    Magnetic quantum dots in two-dimensional band and topological insulators are studied by solving the modified Dirac model under nonuniform magnetic fields. The Landau levels split into discrete states with certain angular momentum. The states splitting from the zero Landau levels lie in the energy gap for topological insulators but are out of the gap for band insulators. It is found that the ground states oscillate between the spin-up and spin-down states when the magnetic field or the dot size changes. The oscillation manifests itself as changes of sign and strength of charge currents near the dot's edge.

  6. 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.

  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 (cotunneling....... Interestingly, the direction of the drag current is not determined by the drive current, but by an interplay between the energy-dependent lead couplings. Studying the drag mechanism in a graphene-based CQD heterostructure, we show that the predictions of our theory are consistent with recent experiments...

  8. [Fluorescent carbon dots and the application in biomedicine].

    Science.gov (United States)

    Zhang, Shuang; Gao, Hui-Le; Shen, Shun; Wang, Wei-Liang; Qian, Jun

    2014-09-01

    As a new type of carbon nanomaterials, fluorescent carbon dots (fluorescent CDs) have many advantages when compared with the traditional fluorescent probes. They are photoluminescence stable and resistance to photo bleaching. Moreover, they are excellent in biocompatibility, low-toxic and easy to modify. All these above make them a promising optical image material as a probe in optical image. This article reviews structure, the common carbon sources, the preparation methods, and the light-emitting principles of the carbon dots. We also introduce the research progress of fluorescent carbon dots in biomedicine, and the problems need to be resolved in the study of fluorescent CDs.

  9. Wafer scale integration of catalyst dots into nonplanar microsystems

    DEFF Research Database (Denmark)

    Gjerde, Kjetil; Kjelstrup-Hansen, Jakob; Gammelgaard, Lauge;

    2007-01-01

    In order to successfully integrate bottom-up fabricated nanostructures such as carbon nanotubes or silicon, germanium, or III-V nanowires into microelectromechanical systems on a wafer scale, reliable ways of integrating catalyst dots are needed. Here, four methods for integrating sub-100-nm...... diameter nickel catalyst dots on a wafer scale are presented and compared. Three of the methods are based on a p-Si layer utilized as an in situ mask, an encapsulating layer, and a sacrificial window mask, respectively. All methods enable precise positioning of nickel catalyst dots at the end...

  10. Realization of electrically tunable single quantum dot nanocavities

    Energy Technology Data Exchange (ETDEWEB)

    Hofbauer, Felix Florian Georg

    2009-03-15

    We investigated the design, fabrication and optical investigation of electrically tunable single quantum dot-photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light matter interaction. We demonstrate that the quantum confined Stark effect can be employed to quickly and reversibly switch the dot-cavity coupling, simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by up to {proportional_to}4 meV relative to the nanocavity mode, before the emission quenches due to carrier tunneling escape from the dots. We directly probe spontaneous emission, irreversible polariton decay and the statistics of the emitted photons from a single-dot nanocavity in the weak and strong coupling regimes. New information is obtained on the nature of the dot-cavity coupling in the weak coupling regime and electrical control of zero dimensional polaritons is demonstrated for the first time. The structures investigated are p-i-n photodiodes consisting of an 180nm thick free-standing GaAs membrane into which a two dimensional photonic crystal is formed by etching a triangular lattice of air holes. Low mode volume nanocavities (V{sub mode}<1.6 ({lambda}/n){sup 3}) are realized by omitting 3 holes in a line to form L3 cavities and a single layer of InGaAs self-assembled quantum dots is embedded into the midpoint of the membrane. The nanocavities are electrically contacted via 35 nm thick p- and n-doped contact layers in the GaAs membrane. In the weak coupling regime, time resolved spectroscopy reveals a {proportional_to}7 x shortening of the spontaneous emission lifetime as the dot is tuned through the nanocavity mode, due to the Purcell effect. Upon strongly detuning the same quantum dot transition from the nanocavity mode we observe an additional {proportional_to}8 x lengthening of the spontaneous emission lifetime. These observations unequivocally highlight two regimes of dot

  11. Graphene mediated Stark shifting of quantum dot energy levels

    Science.gov (United States)

    Kinnischtzke, Laura; Goodfellow, Kenneth M.; Chakraborty, Chitraleema; Lai, Yi-Ming; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Vamivakas, A. Nick

    2016-05-01

    We demonstrate an optoelectronic device comprised of single InAs quantum dots in an n-i-Schottky diode where graphene has been used as the Schottky contact. Deterministic electric field tuning is shown using Stark-shifted micro-photoluminescence from single quantum dots. The extracted dipole moments from the Stark shifts are comparable to conventional devices where the Schottky contact is a semi-transparent metal. Neutral and singly charged excitons are also observed in the well-known Coulomb-blockade plateaus. Our results indicate that graphene is a suitable replacement for metal contacts in quantum dot devices which require electric field control.

  12. Second Bound State of Biexcitons in Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Eang

    2003-01-01

    The second bound state of the biexcitons in a quantum dot, with orbital angular momentum L = 1, is reported. By using the method of few-body physics, the binding energy spectra of the second bound state of a biexciton in a GaAs quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio and the quantum dot size. The fact that the biexcitons have a second bound state may aid in the better understanding of their binding mechanism.

  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. Long lived coherence in self-assembled quantum dots

    DEFF Research Database (Denmark)

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

    2001-01-01

    We report measurements of ultralong coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mu eV, which is significantly smaller than the linewidth observed in single-dot...... luminescence. Time-resolved luminescence measurements show a lifetime of the dot ground state of 800 ps, demonstrating the presence of pure dephasing at finite temperature. The homogeneous width is lifetime limited only at temperatures approaching 0 K....

  15. Thermal Rectification Effect of an Interacting Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    CHEN Xue-Ou; DONG Bing; LEI Xiao-Lin

    2008-01-01

    @@ We investigate the nonlinear thermal transport properties of a single interacting quantum dot with two energy levels tunnel-coupled to two electrodes using nonequilibrium Green function method and Hartree-Fock decoupling approximation. In the case of asymmetric tunnel-couplings to two electrodes, for example, when the upper level of the quantum dot is open for transport, whereas the lower level is blocked, our calculations predict a strong asymmetry for the heat (energy) current, which shows that the quantum dot system may act as a thermal rectifier in this specific situation.

  16. A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultra-trace chlortoluron in water.

    Science.gov (United States)

    Tao, Huilin; Liao, Xiufen; Sun, Chao; Xie, Xiangli; Zhong, Fuxin; Yi, Zhongsheng; Huang, Yipeng

    2015-02-05

    In this paper, a fluorescence resonance energy transfer (FRET) system between fluorescence carbon dots (CDs, donor) and CdTe quantum dots (CdTe, acceptor) was constructed, and a novel platform for sensitive and selective determination of chlortoluron was accordingly proposed. It was found that in Tris-HCl buffer solution at pH=8.7, energy transfer from CDs to CdTe occurred, which resulted in a great enhancement of the fluorescence intensity of CdTe. Upon the addition of chlortoluron, in terms of strong interaction between chlortoluron and CdTe QDs through the formation of chlortoluron-CdTe ground state complex, resulted in CdTe fluorescence quenching. Under optimal conditions, in range of 2.4×10(-10)molL(-1)-8.5×10(-8)molL(-1), the change of CdTe fluorescence intensity was in good linear relationship with the chlortoluron concentration, and the detection limit was 7.8×10(-11)molL(-1) (S/N=3). Most of common relevant substance, cations and anions did not interfere with the detection of chlortoluron. The proposed method was applied to determine chlortoluron in water samples with satisfactory results.

  17. Bio-nanohybrids of quantum dots and photoproteins facilitating strong nonradiative energy transfer.

    Science.gov (United States)

    Seker, Urartu Ozgur Safak; Mutlugun, Evren; Hernandez-Martinez, Pedro Ludwig; Sharma, Vijay K; Lesnyak, Vladimir; Gaponik, Nikolai; Eychmüller, Alexander; Demir, Hilmi Volkan

    2013-08-01

    Utilization of light is crucial for the life cycle of many organisms. Also, many organisms can create light by utilizing chemical energy emerged from biochemical reactions. Being the most important structural units of the organisms, proteins play a vital role in the formation of light in the form of bioluminescence. Such photoproteins have been isolated and identified for a long time; the exact mechanism of their bioluminescence is well established. Here we show a biomimetic approach to build a photoprotein based excitonic nanoassembly model system using colloidal quantum dots (QDs) for a new bioluminescent couple to be utilized in biotechnological and photonic applications. We concentrated on the formation mechanism of nanohybrids using a kinetic and thermodynamic approach. Finally we propose a biosensing scheme with an ON/OFF switch using the QD-GFP hybrid. The QD-GFP hybrid system promises strong exciton-exciton coupling between the protein and the quantum dot at a high efficiency level, possessing enhanced capabilities of light harvesting, which may bring new technological opportunities to mimic biophotonic events.

  18. Enzyme-Polymers Conjugated to Quantum-Dots for Sensing Applications

    Directory of Open Access Journals (Sweden)

    Alexandra Mansur

    2011-10-01

    Full Text Available In the present research, the concept of developing a novel system based on polymer-enzyme macromolecules was tested by coupling carboxylic acid functionalized poly(vinyl alcohol (PVA-COOH to glucose oxidase (GOx followed by the bioconjugation with CdS quantum-dots (QD. The resulting organic-inorganic nanohybrids were characterized by UV-visible spectroscopy, infrared spectroscopy, Photoluminescence spectroscopy (PL and transmission electron microscopy (TEM. The spectroscopy results have clearly shown that the polymer-enzyme macromolecules (PVA-COOH/GOx were synthesized by the proposed zero-length linker route. Moreover, they have performed as successful capping agents for the nucleation and constrained growth of CdS quantum-dots via aqueous colloidal chemistry. The TEM images associated with the optical absorption results have indicated the formation of CdS nanocrystals with estimated diameters of about 3.0 nm. The “blue-shift” in the visible absorption spectra and the PL values have provided strong evidence that the fluorescent CdS nanoparticles were produced in the quantum-size confinement regime. Finally, the hybrid system was biochemically assayed by injecting the glucose substrate and detecting the formation of peroxide with the enzyme horseradish peroxidase (HRP. Thus, the polymer-enzyme-QD hybrid has behaved as a nanostructured sensor for glucose detecting.

  19. Acoustically regulated carrier injection into a single optically active quantum dot

    Science.gov (United States)

    Schülein, Florian J. R.; Müller, Kai; Bichler, Max; Koblmüller, Gregor; Finley, Jonathan J.; Wixforth, Achim; Krenner, Hubert J.

    2013-08-01

    We study the carrier injection into a single InGaAs/GaAs quantum dot regulated by a radio frequency surface acoustic wave. We find that the time of laser excitation during the acoustic cycle programs both the emission intensities and time of formation of neutral (X0) and negatively charged (X-) excitons. We identify underlying, characteristic formation pathways of both few-particle states in the time-domain experiments and show that both exciton species can be formed either with the optical pump or at later times by injection of single electrons and holes “surfing” the acoustic wave. All experimental observations are in excellent agreement with calculated electron and hole trajectories in the plane of the two-dimensional wetting layer which is dynamically modulated by the acoustically induced piezoelectric potentials. Taken together, our findings provide insight on both the onset of acoustoelectric transport of electrons and holes and their conversion into the optical domain after regulated injection into a single quantum dot emitter.

  20. Effect of Intra-Dot Coulomb Interaction on Andreev Reflection in Normal-Metal/Quantum-Dot/Superconductor System

    Institute of Scientific and Technical Information of China (English)

    ZHU Yu; SUN Qing-Feng; LIN Tsung-Han

    2001-01-01

    We investigate the effect of intra-dot Coulomb interaction on the Andreev reflection in a normalmetal/quantum-dot/superconductor (N-QD-S) system with multiple levels in the quantum dot, in the regime where the intra-dot interacting constant is comparable to the energy gap of superconducting lead. By using nonequilibrium Green function method, the averaged occupation of electrons in the quantum dot and the Andreev reflection (AR) current are studied. Comparing to the case of non-interacting quantum dot, the system shows significant changes for the a two-step-like behavior; and the I-Vg shows two groups of peaks, separated by U and with equal heights, where Vg is the gate voltage and U denotes the intra-dot Coulomb interaction constant. (ii) For finite bias voltage, dips, superposed V ≥ U/2, extra AR current peaks occur between the two groups of the peaks. Besides, the properties of the heights of the AR current peaks are more complicated.``

  1. Silicon quantum dots for biological applications.

    Science.gov (United States)

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

    2014-01-01

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

  2. Quantum dots for next-generation photovoltaics

    Directory of Open Access Journals (Sweden)

    Octavi E. Semonin

    2012-11-01

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

  3. Preparation and Application of Fluorescent Carbon Dots

    Directory of Open Access Journals (Sweden)

    Jun Zuo

    2015-01-01

    Full Text Available Fluorescent carbon dots (CDs are a novel type of fluorescent nanomaterials, which not only possess the specific quantum confinement effects of nanomaterials due to the small size of nanomaterials, but also have good biocompatibility and high fluorescence. Meanwhile, fluorescence CDs overcome the shortcomings of high toxicity of traditional nanomaterials. Moreover, the preparation procedure of fluorescent CDs is simple and easy. Therefore, fluorescent CDs have great potential applied in photocatalysis, biochemical sensing, bioimaging, drug delivery, and other related areas. In this paper, recent hot researches on fluorescent CDs are reviewed and some problems in the progress of fluorescent CDs are also summarized. At last, a future outlook in this direction is presented.

  4. Quantum Dot Devices for Optical Signal Processing

    DEFF Research Database (Denmark)

    Chen, Yaohui

    . Additional to the static linear amplication properties, we focus on exploring the gain dynamics on the time scale ranging from sub-picosecond to nanosecond. In terms of optical signals that have been investigated, one is the simple sinusoidally modulated optical carrier with a typical modulation frequency...... range of 1-100 gigahertz. Our simulations reveal the role of ultrafast intradot carrier dynamics in enhancing modulation bandwidth of quantum dot semiconductor optical ampliers. Moreover, the corresponding coherent gain response also provides rich dispersion contents over a broad bandwidth. One...... important implementation is recently boosted by the research in slow light. The idea is to migrate such dynamical gain knowledge for the investigation of microwave phase shifter based on semiconductor optical waveguide. Our study reveals that phase shifting based on the conventional semiconductor optical...

  5. Wet electron microscopy with quantum dots.

    Science.gov (United States)

    Timp, Winston; Watson, Nicki; Sabban, Alon; Zik, Ory; Matsudaira, Paul

    2006-09-01

    Wet electron microscopy (EM) is a new imaging method with the potential to allow higher spatial resolution of samples. In contrast to most EM methods, it requires little time to perform and does not require complicated equipment or difficult steps. We used this method on a common murine macrophage cell line, IC-21, in combination with various stains and preparations, to collect high resolution images of the actin cytoskeleton. Most importantly, we demonstrated the use of quantum dots in conjunction with this technique to perform light/electron correlation microscopy. We found that wet EM is a useful tool that fits into a niche between the simplicity of light microscopy and the high spatial resolution of EM.

  6. Coherent spin dynamics in semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-05-01

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

  7. 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)

    CERN Document Server

    Hasegawa, M; Suzuki, M; Tang, Z; Yubuta, K

    2003-01-01

    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) ...

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

    Directory of Open Access Journals (Sweden)

    Liang BL

    2007-01-01

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

  9. Strain fields and chemical composition maps of Si Ge:Si(001) quantum dot molecules

    Energy Technology Data Exchange (ETDEWEB)

    Leite, Marina Soares; Medeiros-Ribeiro, Gilberto [Laboratorio Nacional de Luz Sincrotron (LNLS), Campinas, SP (Brazil); Gray, Jeniffer L.; Hull, Robert [University of Virginia, Charlottesville, VA (United States); Floro, Jerrold A. [Sandia National Laboratories, NM (United States); Magalhaes-Paniago, Rogerio [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Fisica

    2006-07-01

    Depending on kinetic and thermodynamic factors, numerous interesting structures can be created starting from epitaxially grown Si Ge:Si(001). In a regime of relatively low growth temperatures (about 550 degree C), a cooperative nucleation process takes place: pyramidal pits are formed preferentially, followed by the nucleation of {l_brace}105{r_brace} elongated islands, leading to Quantum Dot Molecules (QDMs), where the islands can interact electronically with each other. A thorough understanding of the formation of these structures requires knowledge of their strain and compositional fields. Recently, Grazing Incidence Anomalous X ray Diffraction (GIXRD) has been used to understand these issues. The purpose of the measurements taken on the XD1 beam line of the LNLS was to investigate compositional inhomogeneities in QDMs, which helped to elucidate their mechanisms of formation. (author)

  10. Influence of phase separation for surfactant driven pattern formation during ion beam erosion

    Energy Technology Data Exchange (ETDEWEB)

    Hofsaess, Hans; Zhang, Kun; Vetter, Ulrich; Bobes, Omar; Pape, Andre; Gehrke, Hans-Gregor; Broetzmann, Marc [II. Physikalisches Institut, Goettingen Univ. (Germany)

    2012-07-01

    We will present results on metal surfactant driven self-organized pattern formation on surfaces by ion beam erosion, with a focus on the role of phase separation for the initial steps of pattern formation. Si substrates were irradiated with 5 keV Xe ions at normal incidence and ion fluences up to 5.10{sup 17} Xe/cm{sup 2} under continuous deposition of surfactant atoms. In the absence of such surfactants uniform flat surfaces are obtained, while in the presence of Fe and Mo surfactants pronounced patterns like dots, combinations of dots and ripples with wavelengths around 100 nm are generated. The surfactant coverage and deposition direction determine the pattern type and the pattern orientation, respectively. A critical steady-state coverage for onset of dot formation and onset of ripple formation is in the range of 10{sup 15} and 5.10{sup 15} Xe/cm{sup 2}. The steady-state surface region consists of a thin amorphous metal silicide layer with high metal concentration in the ripple and dot regions. Pattern formation is explained by ion induced diffusion and phase separation of the initially flat amorphous silicide layer and subsequent ion beam erosion with composition dependent sputter yield. To investigate the role of initial phase separation we additionally compare the pattern formation for different other metal surfactants.

  11. 78 FR 48868 - Proposed Cercla Administrative Cost Recovery Settlement; MassDOT, MassDOT Route 1 Right-of-Way...

    Science.gov (United States)

    2013-08-12

    ... AGENCY Proposed Cercla Administrative Cost Recovery Settlement; MassDOT, MassDOT Route 1 Right-of-Way...), concerning the MassDOT Route 1 Right-of-Way Site in Chelsea, Massachusetts with the following Settling Party... should refer to: In re: MassDOT Route 1 Right-of- Way Site, U.S. EPA Docket No.01-2013-0031. FOR...

  12. Charge-extraction strategies for colloidal quantum dot photovoltaics

    KAUST Repository

    Lan, Xinzheng

    2014-02-20

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

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

    Data.gov (United States)

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

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

    Science.gov (United States)

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

    2010-04-13

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

  15. A fast "hybrid" silicon double quantum dot qubit

    CERN Document Server

    Shi, Zhan; Prance, J R; Gamble, John King; Koh, Teck Seng; Shim, Yun-Pil; Hu, Xuedong; Savage, D E; Lagally, M G; Eriksson, M A; Friesen, Mark; Coppersmith, S N

    2011-01-01

    We propose a quantum dot qubit architecture that has an attractive combination of speed and fabrication simplicity. It consists of a double quantum dot with one electron in one dot and two electrons in the other. The qubit itself is a set of two states with total spin quantum numbers $S^2=3/4$ ($S=\\half$) and $S_z = -\\half$, with the two different states being singlet and triplet in the doubly occupied dot. The architecture is relatively simple to fabricate, a universal set of fast operations can be implemented electrically, and the system has potentially long decoherence times. These are all extremely attractive properties for use in quantum information processing devices.

  16. Probing individual quantum dots: noise in self-assembled systems.

    Science.gov (United States)

    Vicaro, K O; Gutiérrez, H R; Seabra, A C; Schulz, P A; Cotta, M A

    2009-11-01

    In this work we explore the noise characteristics in lithographically-defined two terminal devices containing self-assembled InAs/InP quantum dots. The experimental ensemble of InAs dots show random telegraph noise (RTN) with tuneable relative amplitude-up to 150%-in well defined temperature and source-drain applied voltage ranges. Our numerical simulation indicates that the RTN signature correlates with a very low number of quantum dots acting as effective charge storage centres in the structure for a given applied voltage. The modulation in relative amplitude variation can thus be associated to the altered electrostatic potential profile around such centres and enhanced carrier scattering provided by a charged dot.

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

    Science.gov (United States)

    Ferry, D. K.; Huang, L.; Yang, R.; Lai, Y.-C.; Akis, R.

    2010-04-01

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

  18. Berry phase jumps and giant nonreciprocity in Dirac quantum dots

    Science.gov (United States)

    Rodriguez-Nieva, Joaquin F.; Levitov, Leonid S.

    2016-12-01

    We predict that a strong nonreciprocity in the resonance spectra of Dirac quantum dots can be induced by the Berry phase. The nonreciprocity arises in relatively weak magnetic fields and is manifest in anomalously large field-induced splittings of quantum dot resonances which are degenerate at B =0 due to time-reversal symmetry. This exotic behavior, which is governed by field-induced jumps in the Berry phase of confined electronic states, is unique to quantum dots in Dirac materials and is absent in conventional quantum dots. The effect is strong for gapless Dirac particles and can overwhelm the B -induced orbital and Zeeman splittings. A finite Dirac mass suppresses the effect. The nonreciprocity, predicted for generic two-dimensional Dirac materials, is accessible through Faraday and Kerr optical rotation measurements and scanning tunneling spectroscopy.

  19. Photolithographic process for the patterning of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-09-15

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

  20. Hydrogenic Donor in a Spherical Quantum Dot with Different Confinements

    Institute of Scientific and Technical Information of China (English)

    A. John Peter; K. Navaneethakrishnan

    2009-01-01

    Binding energies of a hydrogenic donor in a spherical GaAs quantum dot surrounded by Ga1-xAlxAs matrix are calculated. The results are presented for realistic barrier heights corresponding to different values of x (x < 0.4). The calculations are performed under two different conditions: (i) a spherical dot with square well confinement and (ii) a dot with parabolic potential well confinement. The results show that (i) the donor ionization energies are always higher under parabolic confinement as compared to a dot of the same radius under square well confinement and (ii) the oscillator strengths coupling ground state with excited states are two orders larger under parabolic confinement. Our results are in agreement with the results of other researchers.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-14

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

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

    Science.gov (United States)

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

    2005-01-01

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

  3. Type 2 quantum dots in Ge/Si system

    CERN Document Server

    Dvurechenskij, A V

    2001-01-01

    The results on the electronic structure of spatially indirect excitons, multiparticle excitonic complexes, and negative interband photoconductivity in arrays of Ge/Si type 2 quantum dots are presented. These data have been compared with the well known results for type 2 A sup I sup I sup I B sup V and A sup I sup I B sup V sup I -based heterostructures with quantum dots. Fundamental physical phenomena are found to be the result of an increase in the binding energy of excitons in quantum dots as compared with that of free excitons in bulk homogeneous materials; the shortwave shift of exciton transition energy at multiparticle complexes production (charges excitons, biexcitons), as well as the trapping of equilibrium carrier by localized states induced by the charged quantum dot electric field

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

    DEFF Research Database (Denmark)

    Grodecka-Grad, Anna; Foerstner, Jens

    2011-01-01

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

  5. Dephasing and hyperfine interaction in carbon nanotubes double quantum dots

    DEFF Research Database (Denmark)

    Reynoso, Andres Alejandro; Flensberg, Karsten

    2012-01-01

    We study theoretically the return probability experiment, which is used to measure the dephasing time T-2*, in a double quantum dot (DQD) in semiconducting carbon nanotubes with spin-orbit coupling and disorder-induced valley mixing. Dephasing is due to hyperfine interaction with the spins of the C......-13 nuclei. Due to the valley and spin degrees of freedom, four bounded states exist for any given longitudinal mode in the quantum dot. At zero magnetic field, the spin-orbit coupling and the valley mixing split those four states into two Kramers doublets. The valley-mixing term for a given dot...... is determined by the intradot disorder; this leads to (i) states in the Kramers doublets belonging to different dots being different, and (ii) nonzero interdot tunneling amplitudes between states belonging to different doublets. We show that these amplitudes give rise to new avoided crossings, as a function...

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

    Science.gov (United States)

    Winslow, Lindley; Conrad, Janet; Jerry, Ruel

    2010-02-01

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

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

    DEFF Research Database (Denmark)

    Wölfle, Peter; Paaske, Jens; Rosch, Achim;

    2005-01-01

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

  8. Carbon nanotube quantum dots as highly sensitive THz spectrometers

    Science.gov (United States)

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

    2012-02-01

    We show that carbon nanotube quantum dots (CNT-Dots) coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors. Their response is due to photon-assisted single-electron tunneling (PASET)[1], but cannot be fully understood with orthodox PASET models[2]. We consider intra-dot excitations and non-equilibrium cooling to explain the anomalous response. REFERENCES: [1] Y. Kawano, S. Toyokawa, T. Uchida and K. Ishibashi, THz photon assisted tunneling in carbon-nanotube quantum dots, Journal of Applied Physics 103, 034307 (2008). [2] P. K. Tien and J. P. Gordon, Multiphoton Process Observed in the Interaction of Microwave Fields with the Tunneling between Superconductor Films, Phys. Rev. 129, 647 (1963).

  9. Non-Markovian spontaneous emission from a single quantum dot

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg; Ates, Serkan; Lund-Hansen, Toke;

    2011-01-01

    We observe non-Markovian dynamics of a single quantum dot when tuned into resonance with a cavity mode. Excellent agreement between experiment and theory is observed providing the first quantitative description of such a system....

  10. Kondo effect for electron transport through an artificial quantum dot

    Institute of Scientific and Technical Information of China (English)

    Sun Ke-Wei; Xiong Shi-Jie

    2006-01-01

    We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper.We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases.The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case.It increases as the external magnetic field increases.We obtain the relation between the coupling coefficient and conductance.If the interaction is big enough to prevent conduction electrons from tunnelling through the dot,the dispersion effect is dominant in this case.In the Kondo temperature regime,we obtain the conductivity of a quantum dot system with Kondo correlation.

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

  12. Calculation of hyperfine interaction in spherical quantum dot

    Science.gov (United States)

    Yakar, Yusuf; Çakır, Bekir; Özmen, Ayhan

    2015-10-01

    In this study, we have calculated the unperturbed wavefunctions and energy eigenvalues of the ground and excited states of a spherical quantum dot, GaAs/AlxGa1-xAs, by using quantum genetic algorithm and Hartree-Fock Roothaan method. Hyperfine coupling constant and hyperfine energy of 1s, 2p, 3d and 4f levels are carried out as a function of dot radius. The results show that the hyperfine constant and hyperfine energy varies rapidly in the strong and medium confining regions as dot radius decreases. It is worth pointing out that dot radius, impurity charge and angular momentum have a strong influence on the hyperfine energy. It is also found that hyperfine energy and hyperfine splitting vary with aluminium concentration ratio x.

  13. [Louis Braille (1809-1852)--inventor of raised dots system].

    Science.gov (United States)

    Maciejewicz, Piotr; Kopacz, Dorota

    2005-01-01

    Louis Braille was born on January 4th 1809 in Coupvray, France. An injury to his eye at the age of three, resulted in total loss of vision. In 1819 he entered the Institute for Blind Youth in Paris. There he would live, study, and later teach. When he was fifteen, he developed system of reading and writing by means of raised dots, which is known today as Braille. The basis of the Braille system is known as a Braille cell. The cell is comprised of six dots numbered in a specific order. Each dot or combination of dots represents a letter of the alphabet. This Braille system has established itself internationally and formed the basic Braille for all languages.

  14. Carbon Dot Based Sensing of Dopamine and Ascorbic Acid

    Directory of Open Access Journals (Sweden)

    Upama Baruah

    2014-01-01

    Full Text Available 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 ascorbic acid, respectively. The quenching constants determined from Stern-Volmer plot were determined to be 5 × 10−4 and 1 × 10−4 for dopamine and ascorbic acid, respectively. A probable mechanism of quenching has been discussed in the paper.

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

    Science.gov (United States)

    Abdelsalam, Hazem; Talaat, Mohamed H.; Lukyanchuk, Igor; Portnoi, M. E.; Saroka, V. A.

    2016-07-01

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

  16. Fabrication of quantum-dot devices in graphene

    Directory of Open Access Journals (Sweden)

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

    2010-01-01

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

  17. Probing of Unembedded Metallic Quantum Dots with Positrons

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, C G; Denison, A B; Weber, M H; Wilcoxon, J P; Woessner, S; Lynn, K G

    2003-08-01

    We employed the two detector coincident Doppler Broadening Technique (coPAS) to investigate Ag, Au and Ag/Au alloy quantum dots of varying sizes which were deposited in thin layers on glass slides. The Ag quantum dots range from 2 to 3 nm in diameter, while the Ag/Au alloy quantum dots exhibit Ag cores of 2 nm and 3 nm and Au shells of varying thickness. We investigate the possibility of positron confinement in the Ag core due to positron affinity differences between Ag and Au. We describe the results and their significance to resolving the issue of whether positrons annihilate within the quantum dot itself or whether surface and positron escape effects play an important role.

  18. Solution-Processed Nanocrystal Quantum Dot Tandem Solar Cells

    KAUST Repository

    Choi, Joshua J.

    2011-06-03

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

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

    OpenAIRE

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

    2010-01-01

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

  20. Lindblad theory of dynamical decoherence of quantum-dot excitons

    OpenAIRE

    Eastham, P. R.; Spracklen, A O; Keeling, Jonathan Mark James

    2013-01-01

    We use the Bloch-Redfield-Wangsness theory to calculate the effects of acoustic phonons in coherent control experiments where quantum-dot excitons are driven by shaped laser pulses. This theory yields a generalized Lindblad equation for the density operator of the dot, with time-dependent damping and decoherence due to phonon transitions between the instantaneous dressed states. It captures similar physics to the form recently applied to Rabi oscillation experiments [Ramsay et al., Phys. Rev....

  1. Coupled quantum dot-ring structures by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-05-06

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

  2. Progress in the toxicological researches for quantum dots

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Quantum dots (QDs) have received more and more attention as a novel example of nanomaterials. Due to their unique fluorescent characteristics,quantum dots have been successfully applied in biotech-nology and medicine applications. Recently,the toxicity and the potential environmental effects of QDs have become a research hotspot. In this paper,toxicological effects of QDs are reviewed,and the prospects and research directions are given based on the analysis of this research field.

  3. Quantum Optics with Quantum Dots in Photonic Nanowires

    DEFF Research Database (Denmark)

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

    2011-01-01

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

  4. Yellowish dots in the retina: a finding of ocular syphilis?

    OpenAIRE

    Renan Albert Mendonça Rodrigues; Heloisa Moraes do Nascimento; Cristina Muccioli

    2014-01-01

    Here we report the occurrence of pale yellowish perivascular preretinal dots in 12 patients with ocular syphilis. A case series of these patients was examined between March and October 2012 at the Uveitis Sector of Universidade Federal de São Paulo. After diagnostic confirmation of syphilis, fundus photographs and optical coherence tomography (OCT) were performed to verify the localization of the dots, and patients were treated with IV crystalline penicillin for 14 days. The study comprised 1...

  5. Ultrafast optical signal processing using semiconductor quantum dot amplifiers

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Mørk, Jesper

    2002-01-01

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

  6. Solution-processed nanocrystal quantum dot tandem solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Joshua J.; Lim, Yee-Fun [School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853 (United States); Wenger, Whitney N.; Hoffman, Rachel S.; Hanrath, Tobias [School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853 (United States); Luria, Justin; Marohn, John A. [Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853 (United States); Jasieniak, Jacek [CSIRO Materials Science and Engineering, Bayview Ave, Clayton, Victoria 3168 (Australia)

    2011-07-26

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

  7. Optical phonons in Ge quantum dots obtained on Si(111)

    CERN Document Server

    Talochkin, A B

    2002-01-01

    The light combination scattering on the optical phonons in the Ge quantum dots, obtained on the Si surface of the (111) orientation through the molecular-beam epitaxy, is studied. The series of lines, connected with the phonon spectrum quantization, was observed. It is shown, that the phonon modes frequencies are well described by the elastic properties and dispersion of the voluminous Ge optical phonons. The value of the Ge quantum dots deformation is determined

  8. Quantum Entanglement of Quantum Dot Spin Using Flying Qubits

    Science.gov (United States)

    2015-05-01

    previously to optically isolate single quantum dots, and adopted a high NA confocal fiber setup that allows for single quantum dot resolution and the...960nm, to telecom wavelength (1.55 microns) for long distance transmission in fibers . Work toward these goals began with non QuEST support from...been to advance the frontier of quantum entangled semiconductor electrons using ultrafast optical techniques. The approach is based on

  9. Intraband Relaxation and Its Influences on Quantum Dot Lasers

    Institute of Scientific and Technical Information of China (English)

    DENG Sheng-Ling; HUANG Yong-Zhen; YU Li-Juan

    2005-01-01

    @@ A comprehensive two-level numerical model is developed to describe carrier distribution in a quantum-dot laser. Light-emission spectra with different intraband relaxation rates (2ps, 7.5ps and 20ps) are calculated and analysed to investigate the influence of relaxation rates on performance of the quantum-dot laser. The results indicate that fast intraband relaxation favours not only the ground state single mode operation but also the higher injection efficiency.

  10. Dynamical symmetries in Kondo tunneling through complex quantum dots.

    Science.gov (United States)

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-07

    Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4).

  11. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

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

  12. THz Electro-absorption Effect in Quantum Dots

    DEFF Research Database (Denmark)

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

    2011-01-01

    Instantaneous electro-absorption effect in quantum dots, induced by electric field of THz pulse with 3 THz bandwidth is demonstrated in THz pump - optical probe experiment. This effect may be promising for Tbit/s wireless transmission systems.......Instantaneous electro-absorption effect in quantum dots, induced by electric field of THz pulse with 3 THz bandwidth is demonstrated in THz pump - optical probe experiment. This effect may be promising for Tbit/s wireless transmission systems....

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

    DEFF Research Database (Denmark)

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

    2011-01-01

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

  14. Progress in the toxicological researches for quantum dots

    Institute of Scientific and Technical Information of China (English)

    LI HongCheng; ZHOU QunFang; LIU Wei; YAN Bing; ZHAO Yibing; JIANG GuiBin

    2008-01-01

    Quantum dots (QDs) have Received more and more attention as a novel example of nanomaterials. Due to their unique fluorescent characteristics, quantum dots have been successfully applied in biotech-nology and medicine applications. Recently, the toxicity and the potential environmental effects of QDs have become a research hotspot. In this paper, toxicological effects of QDs are reviewed, and the prospects and research directions are given based on the analysis of this research field.

  15. Semiconductor Quantum Dots in Chemical Sensors and Biosensors

    OpenAIRE

    Nikos Chaniotakis; Frasco, Manuela F.

    2009-01-01

    Quantum dots are nanometre-scale semiconductor crystals with unique optical properties that are advantageous for the development of novel chemical sensors and biosensors. The surface chemistry of luminescent quantum dots has encouraged the development of multiple probes based on linked recognition molecules such as peptides, nucleic acids or small-molecule ligands. This review overviews the design of sensitive and selective nanoprobes, ranging from the type of target molecules to the optical ...

  16. Growth and characterization of InP/In{sub 0.48}Ga{sub 0.52}P quantum dots optimized for single-photon emission

    Energy Technology Data Exchange (ETDEWEB)

    Ugur, Asli

    2012-08-28

    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 In{sub 0.48}Ga{sub 0.52}P, 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/μm{sup 2} 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{sup (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 In{sub 0.48}Ga{sub 0.52}P 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 In{sub 0.48}Ga{sub 0.52}P 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. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    Science.gov (United States)

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

    2014-08-26

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

  18. Colloidal quantum dot photovoltaics: The effect of polydispersity

    KAUST Repository

    Zhitomirsky, David

    2012-02-08

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

  19. Emission redistribution from a quantum dot-bowtie nanoantenna

    Science.gov (United States)

    Regler, Armin; Schraml, Konrad; Lyamkina, Anna A.; Spiegl, Matthias; Müller, Kai; Vuckovic, Jelena; Finley, Jonathan J.; Kaniber, Michael

    2016-07-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby (˜25 nm) plasmonic antenna. Microphotoluminescence spectroscopy shows a ˜2.4× increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of 2.5 μW for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell enhancement of the quantum dot coupled to the antenna as compared with an uncoupled dot, yielding comparable exciton lifetimes of τ˜0.5 ns. This observation is supported by numerical simulations, suggesting only minor Purcell-effects of antenna separations >25 nm. The observed increased emission from a coupled quantum dot-plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding of light-matter coupling in such semiconductor-plasmonic hybrid systems.

  20. Emission redistribution from a quantum dot-bowtie nanoantenna

    CERN Document Server

    Regler, A; Lyamkina, A; Spiegl, M; Müller, K; Vuckovic, J; Finley, J J; Kaniber, M

    2016-01-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby ($\\sim 25nm$) plasmonic antenna. Micro-photoluminescence spectroscopy shows a $\\sim 2.4\\times$ increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of $2.5\\mu W$ for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell-enhancement of the quantum dot coupled to the antenna as compared to an uncoupled dot, yielding comparable exciton lifetimes of $\\tau\\sim0.5ns$. This observation is supported by numerical simulations, suggesting only minor Purcell-effects of $25nm$. The observed increased emission from a coupled quantum dot-plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding o...