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1

Synthesis and applications of quantum dots and magnetic quantum dots  

Microsoft Academic Search

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

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

2008-01-01

2

Quantum dots: synthesis, bioapplications, and toxicity.  

PubMed

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

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

2012-01-01

3

Quantum dots: synthesis, bioapplications, and toxicity  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

4

Quantum dots: synthesis, bioapplications, and toxicity  

PubMed Central

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

2012-01-01

5

Germanium quantum dots: Optical properties and synthesis  

Microsoft Academic Search

Three different size distributions of Ge quantum dots (?200, 110, and 60 A?) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium\\/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray

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

1994-01-01

6

Synthesis of glutathione-coated quantum dots  

Microsoft Academic Search

This paper is focused on the preparation and characterization of glutathione (GSH) coated near infrared quantum dots (QDs). The preparation method is based on surface modification of hydrophobic core\\/shell CdSeTe\\/CdS by glutathione, which makes the QDs water-soluble. Moreover, tripeptide GSH provides a biocompatible barrier against toxic cadmium ions of QDs core. These GSH-coated NIR QDs are suitable for in vivo

Jana Chomoucka; Jana Drbohlavova; V. Adam; Rene Kizek; Jaromir Hubalek

2009-01-01

7

Synthesis of near-infrared quantum dots in cultured cancer cells.  

PubMed

Intracellular synthesis of near-infrared fluorescent silver sulfide quantum dots in HepG2 cancer cells is demonstrated. By delivering quantum dot precursors into cultured hepatoma carcinoma cells (HepG2 cells), silver sulfide quantum dots with emission efficiency qualified for in vivo imaging were successfully synthesized with the aid of endogenous glutathione in the cells. PMID:24344828

Tan, Lianjiang; Wan, Ajun; Li, Huili

2014-01-01

8

Quasi-periodic quantum dot arrays produced by electrochemical synthesis.  

National Technical Information Service (NTIS)

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

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

1994-01-01

9

Synthesis and Applications of Luminescent Quantum Dots in Bioassays  

Microsoft Academic Search

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

Venkata Ramana Kethineedi

2011-01-01

10

Synthesis of CdSe quantum dots: Effect of surfactant on the photoluminescence property  

Microsoft Academic Search

This paper reports the synthesis of highly lumimescence CdSe quantum dots via wet-chemical process and the study of the surfactant concentration effect on the improvement of the photoluminescence characteristic. Here, we also discussed in detail the quantum dots synthesis procedure and the mechanism for the improvement of the luminescence characteristic of CdSe quantum dots under a different surfactant concentration.

N. A. Bakar; A. A. Umar; T. H. T. Aziz; S. H. Abdullah; M. M. Salleh; M. Yahaya; B. Y. Majlis

2008-01-01

11

One pot synthesis of bi-linker stabilised CdSe quantum dots  

Microsoft Academic Search

In this study we exploited the classic Murray's synthesis for generating a hydrophilic CdSe quantum dot system in a single step procedure, with the aim of directly obtaining a material responding to the characteristic of polarity required in many end applications. 6-phosphonohexanoic acid was used as both ligand for generating the active monomer during the synthesis of the quantum dots

I. Concina; M. M. Natile; A. Braga; A. Vomiero; V. Morandi; L. Ortolani; M. Ferroni; G. Sberveglieri

2010-01-01

12

Encapsulated nanocrystals and quantum dots formed by ion beam synthesis  

SciTech Connect

High-dose ion implantation was used to synthesize a wide range of nanocrystals and quantum dots and to encapsulate them in host materials such as SiO{sub 2}, {alpha}-Al{sub 2}O{sub 3}, and crystalline Si. When Si nanocrystals are encapsulated in SiO{sub 2}, they exhibit dose dependent absorption and photoluminescence which provides insight into the luminescence mechanism. Compound semiconductor nanocrystals (both Group III-V and Group II-VI) can be formed in these matrices by sequential implantation of he individual constituents, and we discuss their synthesis and some of their physical and optical properties.

White, C.W.; Budai, J.D.; Withrow, S.P. [and others

1996-09-01

13

Synthesis of CdSe quantum dots for quantum dot sensitized solar cell  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

14

Quantum Dots  

NASA Astrophysics Data System (ADS)

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

Tartakovskii, Alexander

2012-07-01

15

Ion beam-induced quantum dot synthesis in glass  

NASA Astrophysics Data System (ADS)

Ion beam synthesis has played a significant role in fabricating metallic or semiconducting nanocrystal arrays in glass for their optical or magnetic properties, but basic questions remain unanswered. What are the microscopic mechanisms that control nanocluster growth, determine their density and size distributions? To what extent can we control these processes in order to tailor the properties? We demonstrate the role of chemistry (redox properties; charge state equilibrium modified by irradiation) in Ag nanocluster nucleation and growth processes in glasses and extend the conclusions to PbS nanocluster synthesis. In the latter case, we show how charge state differences affect diffusion and growth and devise a strategy that produces PbS quantum dots emitting intense photoluminescence at 1.5 ?m. In the course of this work, we also showed that the lognormal shape of cluster size distributions signals a loss of information as to the formation process and hence loss of property control.

Espiau de Lamaestre, R.; Bernas, H.

2007-04-01

16

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

Microsoft Academic Search

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

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

2011-01-01

17

The use of heat transfer fluids in the synthesis of high-quality CdSe quantum dots, core/shell quantum dots, and quantum rods  

NASA Astrophysics Data System (ADS)

Fluorescent semiconductor nanoparticles, or quantum dots, have potential uses as an optical material, in which the optoelectronic properties can be tuned precisely by particle size. Advances in chemical synthesis have led to improvements in size and shape control, cost, and safety. A limiting step in large-scale production is identified to be the raw materials cost, in which a common synthesis solvent, octadecene, accounts for most of the materials cost for a batch of CdSe quantum dots. Thus, less expensive solvents are needed. In this paper, we identify heat transfer fluids, a class of organic liquids commonly used in chemical process industries to transport heat between unit operations, as alternative solvents for quantum dot synthesis. We specifically show that two heat transfer fluids can be used successfully in the synthesis of CdSe quantum dots with uniform particle sizes. We show that the synthesis chemistry for CdSe/CdS core/shell quantum dots and CdSe quantum rods can also be performed in heat transfer fluids. With the aid of a population balance model, we interpret the effect of different HT fluids on QD growth kinetics in terms of solvent effects, i.e., solvent viscosity, CdSe bulk solubility in the solvent, and surface free energy.

Asokan, Subashini; Krueger, Karl M.; Alkhawaldeh, Ammar; Carreon, Alessandra R.; Mu, Zuze; Colvin, Vicki L.; Mantzaris, Nikos V.; Wong, Michael S.

2005-10-01

18

Synthesis of functionalized amphiphilic polymers for coating quantum dots.  

PubMed

Quantum dots (QDs) need to be attached to other chemical species if they are to be used as biomarkers, therapeutic agents or sensors. These materials also need to disperse well in water and have well-defined functional groups on their surfaces. QDs are most often synthesized in the presence of ligands such as trioctylphosphine oxide, which render the nanoparticle surfaces hydrophobic. We present a complete protocol for the synthesis and water solubilization of hydrophobic CdSe/ZnS QDs using designer amphiphilic polymeric coatings. The method is based on functionalization of an anhydride polymer backbone with nucleophilic agents. Small functional groups, bulky cyclic compounds and polymeric chains can be integrated into the coating prior to solubilization. We describe the preparation of acetylene- and azide-functionalized QDs for 'click' chemistry. The method is universal and applicable to any type of nanoparticle stabilized with hydrophobic ligands able to interact with the alkyl chains in the coating in water. PMID:21959237

Ja?czewski, Dominik; Tomczak, Nikodem; Han, Ming-Yong; Vancso, G Julius

2011-10-01

19

Electrochemical synthesis of quasi-periodic quantum dot arrays  

SciTech Connect

The conventional route to nanosynthesis involves beam nanolithography (electron beam, ion beam or-x-ray lithography). Exposure to these beams during pattern delineation however causes severe radiation damage to nanostructures which is further compounded during later post-processing such as reactive ion etching. Consequently, finished nanostructures become replete with traps, vacancies, spurious charges and surface states. To circumvent this problem, we are developing a ``gentle`` electrochemical technique for the fabrication of periodic quantum dot arrays. It does not damage the structures through harsh processing steps, offers a minimum feature size down to {approximately} 40 {Angstrom}, allows the fabrication of structures on non-planar surfaces (e.g. spherical or cylindrical substrates), is amenable to mass production (millions of wafers can be processed simultaneously) and is potentially orders of magnitude cheaper than conventional nanofabrication. This paper describes initial results and show that this technique bears significant promise for future applications in nanostructure synthesis.

Miller, A.E.; Yue, D.F.; Banerjee, G.; Bandyopadhyay, S. [Univ. of Notre Dame, Notre Dame, IN (United States). Dept. of Electrical Engineering; Ricker, R.E.; Jones, S. [National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Laboratory; Eastman, J.A. [Argonne National Lab., IL (United States)

1994-06-01

20

One pot synthesis of bi-linker stabilised CdSe quantum dots  

NASA Astrophysics Data System (ADS)

In this study we exploited the classic Murray's synthesis for generating a hydrophilic CdSe quantum dot system in a single step procedure, with the aim of directly obtaining a material responding to the characteristic of polarity required in many end applications. 6-phosphonohexanoic acid was used as both ligand for generating the active monomer during the synthesis of the quantum dots and final stabiliser. Diffraction measurements identified the cubic phase of cadmium selenide. Energy dispersive spectroscopy analysis revealed non-stoichiometric quantum dots, being the Cd/Se ratio 60/40. This feature suggests a configuration in which Cd2+ ions are present on the nanocrystal surface. Diffuse reflectance infrared Fourier transform analysis was applied in order to investigate the structure of the quantum dot system: the results indicate a configuration in which the carboxylic function of 6-phosphonohexanoic acid establishes only a partial interaction with the quantum dot surface, being set in a pseudo-ester configuration.

Concina, I.; Natile, M. M.; Braga, A.; Vomiero, A.; Morandi, V.; Ortolani, L.; Ferroni, M.; Sberveglieri, G.

2010-09-01

21

The use of heat transfer fluids in the synthesis of high-quality CdSe quantum dots, core\\/shell quantum dots, and quantum rods  

Microsoft Academic Search

Fluorescent semiconductor nanoparticles, or quantum dots, have potential uses as an optical material, in which the optoelectronic properties can be tuned precisely by particle size. Advances in chemical synthesis have led to improvements in size and shape control, cost, and safety. A limiting step in large-scale production is identified to be the raw materials cost, in which a common synthesis

Subashini Asokan; Karl M. Krueger; Ammar Alkhawaldeh; Alessandra R. Carreon; Zuze Mu; Vicki L. Colvin; Nikos V. Mantzaris; Michael S. Wong

2005-01-01

22

Quantum Dot Solar Cells  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

23

Quantum Dots  

NSDL National Science Digital Library

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

24

Quantum Dot Solar Cells  

Microsoft Academic Search

We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in

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

2002-01-01

25

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

26

Nearly Mono?disperse Quantum Dots of ZnSe: Synthesis and Characterization  

Microsoft Academic Search

Nearly mono?disperse high quality quantum dots (QDs) of zinc selenide have been synthesized by organometallic route that includes use of well known surfactants such as a carboxylic acid and trioctylphosphine (TOP). Single?step synthesis was performed at a temperature that is lower than many reported methods for such quantum dots of semiconductors. UV?Visible spectra of series of experiments showed steep absorption

K. Srinivas Rao; N. Singh; K. Gurunathan; R. Marimuthu; N. R. Munirathanam; T. L. Prakash; P. K. Khanna

2007-01-01

27

Biocompatible Hydrophilic CdSe Quantum Dots: Single-Step Synthesis  

Microsoft Academic Search

We herein present a simple one-step synthesis of CdSe quantum dots in aqueous medium using Na2SeSO3 as a source of Se and PVP and sodium succinate as the surfactant. The isolated orange to dark-red particles are re-dispersible in alcoholic and aq. medium. The optical spectra indicated blue shift of >150 nm. The hydrophilic quantum dots show excellent FWHM of approximately

P. K. Khanna; K. Dhanabalan; Priyesh More; Sowmya Viswanathan; V. Renugopalakrishnan

2012-01-01

28

Synthesis and Characterization of Manganese Doped CdSe Quantum Dots  

Microsoft Academic Search

The solution phase synthesis of high quality manganese doped CdSe quantum dot colloids is described. Single source manganese and selenium containing organometallic precursors such as Mn_2(mu-SeMe)_2(CO)8 are used as dopant sources. Exhaustive surface ligand exchange is performed on all samples to ensure that elemental analysis detects only Mn incorporated into the quantum dot inorganic core. Manganese concentrations determined by both

F. V. Mikulec; M. Kuno; M. Bennati; D. A. Hall; R. G. Griffin; M. G. Bawendi

1998-01-01

29

Synthesis and characterization of surface-modified colloidal CdTe Quantum Dots  

Microsoft Academic Search

The controlled synthesis of quantized colloidal CdTe nanocrystals (in aqueous solutions) with narrow size distributions and stabilized against rapid oxidation was achieved by capping the quantum dot particles with 3-mercapto-1,2-propanediol. Nanocrystals (i.e., quantum dots) with mean diameters of 20, 25, 35, and 40 A were produced. Optical absorption spectra showed strong excitonic peaks at the smallest size; the absorption coefficient

T. Rajh; O. I. Micic; A. J. Nozik

1993-01-01

30

Synthesis and characterization of luminescent cadmium selenide/zinc selenide/zinc sulfide cholinomimetic quantum dots  

NASA Astrophysics Data System (ADS)

Luminescent quantum dots conjugated with highly selective molecular recognition ligands are widely used for targeting and imaging biological structures. In this paper, water soluble cholinomimetic cadmium selenide (core), zinc selenide/zinc sulfide (shell) quantum dots were synthesized for targeting cholinergic sites. Cholinomimetic specificity was incorporated by conjugation of the quantum dots to an aminated analogue of hemicholinium-15, a well known competitive inhibitor of the high affinity choline uptake transporter. Detailed evaluation of the nanocrystal synthesis and characterization of the final product was conducted by 1H and 31P NMR, absorption and emission spectroscopy, as well as transmission electron microscopy.Luminescent quantum dots conjugated with highly selective molecular recognition ligands are widely used for targeting and imaging biological structures. In this paper, water soluble cholinomimetic cadmium selenide (core), zinc selenide/zinc sulfide (shell) quantum dots were synthesized for targeting cholinergic sites. Cholinomimetic specificity was incorporated by conjugation of the quantum dots to an aminated analogue of hemicholinium-15, a well known competitive inhibitor of the high affinity choline uptake transporter. Detailed evaluation of the nanocrystal synthesis and characterization of the final product was conducted by 1H and 31P NMR, absorption and emission spectroscopy, as well as transmission electron microscopy. Electronic supplementary information (ESI) available: NMR spectra supporting the synthesis of the HC-15 QDs are available. See DOI: 10.1039/c2nr30713h

Gégout, Claire; McAtee, Maria L.; Bennett, Nichole M.; Viranga Tillekeratne, L. M.; Kirchhoff, Jon R.

2012-07-01

31

Encapsulated nanocrystals and quantum dots formed by ion beam synthesis.  

National Technical Information Service (NTIS)

High-dose ion implantation was used to synthesize a wide range of nanocrystals and quantum dots and to encapsulate them in host materials such as SiO(sub 2), (alpha)-Al(sub 2)O(sub 3), and crystalline Si. When Si nanocrystals are encapsulated in SiO(sub 2...

C. W. White J. D. Budai S. P. Withrow

1996-01-01

32

Synthesis of high quality CdSe quantum dots through a mild solution-phase synthetic route  

Microsoft Academic Search

High quality CdSe quantum dots are synthesized through a solution-phase synthesis technique with Cd(CH3COO)2·2H2O and Na2SeSO3 as precursors. In this synthesis approach, the participation of a novel terpyridine derivative provides much better control over growth dynamics of CdSe quantum dots, resulting in the suppression of the Ostwald ripening process of the particle size distribution during growth. The CdSe quantum dots

Yuanhao Gao; Qian Zhang; Qiang Gao; Yupeng Tian; Wen Zhou; Lingxia Zheng; Shengyi Zhang

2009-01-01

33

A Safer, Easier, Faster Synthesis for CdSe Quantum Dot Nanocrystals  

ERIC Educational Resources Information Center

The synthesis for CdSe quantum dot nanocrystals that vary in color and are a visually engaging way to demonstrate quantum effects in chemistry is presented. CdSe nanocrystals are synthesized from CdO and elemental Se using a kinetic growth method where particle size depends on reaction time.

Boatman, Elizabeth M.; Lisensky, George C.; Nordell, Karen J.

2005-01-01

34

Quasi-periodic quantum dot arrays produced by electrochemical synthesis  

SciTech Connect

We discuss a ``gentle`` electrochemical technique for fabricating quasi-periodic quantum dot arrays. The technique exploits a self-organizing phenomenon to produce quasi-periodic arrangement of dots and provides excellent control over dot size and interdot spacing. Unlike conventional nanolithography, it does not cause radiation damage to the structures during exposure to pattern delineating beams (e-beam, ion-beam or x-ray). Moreover, it does not require harsh processing steps like reactive ion etching, offers a minimum feature size of {approximately}40 {angstrom}, allows the fabrication of structures on nonplanar surfaces (e.g. spherical or cylindrical substrates), is amenable to mass production (millions of wafers can be processed simultaneously) and is potentially orders of magnitude cheaper than conventional nanofabrication. In this paper, we describe our initial results and show the promise of this technique for low-cost and high-yield nanosynthesis.

Bandyopadhyay, S.; Miller, A.E.; Yue, D.F.; Banerjee, G. [Univ. of Notre Dame, Notre Dame, IN (United States). Dept. of Electrical Engineering; Ricker, R.E.; Jones, S. [National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Laboratory; Eastman, J.A. [Argonne National Lab., IL (United States); Baugher, E.; Chandrasekhar, M. [Univ. of Missouri-Columbia, Columbia, MS (United States). Dept. of Physics and Astronomy

1994-06-01

35

Synthesis, biological targeting and photophysics of quantum dots  

NASA Astrophysics Data System (ADS)

Quantum dots (QDs) are inorganic nanoparticles that have exceptional optical properties. Currently, QDs have failed to reach their potential as fluorescent probes in live cells, due to the nontrivial requirements for biological interfacing. The goal of this thesis is to address technical hurdles related to the reproducible synthesis of QDs, strategies for the specific targeting of QDs to biological cells and to understanding and exploitation of the photophysical properties. High quality QDs of varying composition (CdSe, CdTe and core/shell CdSe/ZnS) were synthesized with an organometallic method. To prepare biocompatible QDs, three strategies were used. The simplest strategy used small mercaptocarboxylic acids, while performance improvements were realized with engineered-peptide and lipid-micelle coatings. For specific biological targeting of the QDs, conjugation strategies were devised to attach biomolecules, while spectroscopic characterization methods were developed to assess conjugation efficiencies. To target gram-negative bacterial cells, an electrostatic self-assembly method was used to attach an antibiotic selective for this class of bacteria, polymyxin B. To target dopamine neurotransmitter receptor, a covalent conjugation method was used to attach dopamine, the endogenous ligand for that receptor. It was shown that dopamine molecule enabled electron transfer to QDs and the photophysics was studied in detail. A novel conjugation and targeting strategy was explored to enable the selective binding of QDs to polyhistidine epitopes on membrane proteins. Epifluorescence microscopy was used to evaluate the biological activity of the three QD probes. Combined, they add to the QD 'toolkit' for live-cell imaging. Finally, due to its negative implications in biological imaging, the fluorescent intermittency (blinking) of CdTe QDs was investigated. It was shown that mercaptocarboxylic acids contribute to the blinking suppression of the QDs, results that may aid in the design of nonblinking QDs. Overall, these findings should be useful in the future design of QDs for biological imaging and biosensing applications.

Clarke, Samuel Jon

36

Quantum Dots  

NSDL National Science Digital Library

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

Mishra, Gunjan

2008-07-07

37

Synthesis of MDMO-PPV capped PbS quantum dots and their application to solar cells  

Microsoft Academic Search

Poly[2-methoxy-5-(3?,7?-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) capped PbS quantum dots about 3–6nm in diameter were synthesized with a novel method. Unlike the synthesis of oleic acid capped PbS quantum dots, the reactions were carried out in solution at room temperature, with the presence of a capping ligand species, MDMO-PPV. The quantum dots were used to fabricate bulk heterojunction solar cells with an indium tin

Zhijie Wang; Shengchun Qu; Xiangbo Zeng; Changsha Zhang; Mingji Shi; Furui Tan; Zhanguo Wang; Junpeng Liu; Yanbing Hou; Feng Teng; Zhihui Feng

2008-01-01

38

Green synthesis of highly efficient CdSe quantum dots for quantum-dots-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30 nm, and absorption peak from 475 nm to 510 nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO2 electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO2's to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO2. The resulting green synthesized CdSe QDSCs with Cu2S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

Gao, Bing; Shen, Chao; Zhang, Bo; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia; Chen, Guorong

2014-05-01

39

Synthesis of luminescent 3D microstructures formed by carbon quantum dots and their self-assembly properties.  

PubMed

We report in this communication the synthesis of star-shaped carbon quantum dots-(poly-?-benzyl-l-glutamate) conjugates that self-assemble into microstructures and retain the characteristic emission properties of the native dots. Dots were used either as an initiator to give a daisy-like peptide-polymer structure or as capping agents towards more elaborated hybrid nanostructures. PMID:24824483

Mazzier, D; Favaro, M; Agnoli, S; Silvestrini, S; Granozzi, G; Maggini, M; Moretto, A

2014-05-27

40

Magnetic nanocrystals: Synthesis and properties of diluted magnetic semiconductor quantum dots  

Microsoft Academic Search

The chapters in this thesis describe the investigations into the synthesis and magnetic and electronic properties of diluted magnetic semiconductor quantum dots (DMS-QDs), specifically Co2+ and Mn2+-doped ZnO and Co2+:ZnSe. Homogeneous dopant incorporation and substitutional speciation of Co2+ and Mn2+ in ZnO QDs during solution synthesis at room temperature were confirmed by electronic absorption and electron paramagnetic resonance spectroscopy measurements.

Nicholas S. Norberg

2006-01-01

41

Microwave-assisted low temperature synthesis of wurtzite ZnS quantum dots  

SciTech Connect

In this work we report, for the first time, on microwave assisted synthesis of wurtzite ZnS quantum dots (QDs) in controlled reaction at temperature as low as 150 Degree-Sign C. The synthesis can be done in different microwave absorbing solvents with multisource or single source precursors. The QDs are less than 3 nm in size as characterized by transmission electron microscopy (TEM) using selected area electron diffraction (SAED) patterns to confirm the wurtzite phase of ZnS QDs. The optical properties were investigated by UV-Vis absorption which shows blue shift in absorption compared to bulk wurtzite ZnS due to quantum confinement effects. The photoluminescence (PL) spectra of QDs reveal point defects related emission of ZnS QDs. - Graphical abstract: Microwave assisted synthesis of wurtzite ZnS quantum dots (QDs) have been achieved in controlled reaction at temperature as low as 150 Degree-Sign C. The synthesis was performed in different microwave absorbing solvents with multisource or single source precursors for very short reaction periods due to effective heating with microwaves. Highlights: Black-Right-Pointing-Pointer Wurtzite a high temperature phase of ZnS was synthesized at low temperature. Black-Right-Pointing-Pointer Low temperature synthesis was possible because of the use of microwave absorbing solvents. Black-Right-Pointing-Pointer Capping agent was used to control the size of Quantum Dots. Black-Right-Pointing-Pointer Two different systems were developed using single molecular precursor and multisource precursors.

Shahid, Robina, E-mail: rkhan@kth.se [Division of Functional Materials, Royal Institute of Technology (KTH), 16440, Kista, Stockholm (Sweden); Toprak, Muhammet S., E-mail: toprak@kth.se [Division of Functional Materials, Royal Institute of Technology (KTH), 16440, Kista, Stockholm (Sweden); Muhammed, Mamoun [Division of Functional Materials, Royal Institute of Technology (KTH), 16440, Kista, Stockholm (Sweden)

2012-03-15

42

Guest Editorial: Quantum Dots.  

National Technical Information Service (NTIS)

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

J. Xu M. Gerhold

2009-01-01

43

Ligand and precursor effects on the synthesis and optical properties of PbS quantum dots.  

PubMed

We study how the as-received chemical reagents of a commonly used ligand oleylamine (C18-amine) and precursor PbCl2, each at two different purity statuses, affect the growth of PbS quantum dots in a solventless, relatively green, constant reaction-temperature synthesis system. It is found that the growth behavior of PbS quantum dots reflected from their absorption and photoluminescence spectra is quite sensitive to the purity status of the ligand and precursor under certain circumstances, while the lifetime and quantum yield of quantum dots exhibiting a monomodal or nearly monomodal photoluminescence band are not considerably affected. For instance, the effect of the ligand purity status is particularly evident when a higher PbCl2/S ratio is applied. The use of lower purity C18-amine leads to the growth showing much stronger temperature dependence and also facilitates the earlier entry of Ostwald process highlighted by a bimodal photoluminescence structure. Consistently, a 2 wt% increase in the PbCl2 purity from 98 wt% to 100 wt% (or the absence of 2 wt% of impurities) largely postpones the start of Ostwald process and thus significantly improves both absorption and photoluminescence spectra. These results imply that in order to produce PbS quantum dots with narrow absorption and photoluminescence peaks, one needs to optimize reaction parameters as well as select chemicals of appropriate purities. Moreover, the unintentional involvement of chemicals of different purity status may partially account for the irreproducibility problem often encountered in quantum dot synthesis. PMID:21125826

Zhao, Haiguang; Zhang, Teng; Chaker, Mohamed; Ma, Dongling

2010-08-01

44

Synthesis and characterization of quantum dots designed for biomedical use.  

PubMed

Semiconductor quantum dots (QDs) have become promising nanoparticles for a wide variety of biomedical applications. However, the major drawback of QDs is their potential toxicity. Here, we determined possible cytotoxic effects of a set of QDs by systematic photophysical evaluation in vitro as well as in vivo. QDs were synthesized by the hydrothermal aqueous route with sizes in the range of 2.0-3.5 nm. Cytotoxic effects of QDs were studied in the human pancreatic carcinoid cell line BON. Cadmium telluride QDs with or without zinc sulfide shell and coated with 3-mercaptopropionic acid (MPA) were highly cytotoxic even at nanomolar concentrations. Capping with l-glutathione (GSH) or thioglycolic acid (TGA) reduced the cytotoxicity of cadmium telluride QDs and cadmium selenide QDs. Determination of the toxicity of QDs revealed IC50 values in the micromolar range. In vivo studies showed good tolerability of CdSe QDs with ZnS shell and GSH capping. We could demonstrate that QDs with ZnS shell and GSH capping exhibit low toxicity and good tolerability in cell models and living organisms. These QDs appear to be promising candidates for biomedical applications such as drug delivery for enhanced chemotherapy or targeted delivery of light sensitive substances for photodynamic therapy. PMID:24657286

Kuzyniak, Weronika; Adegoke, Oluwasesan; Sekhosana, Kutloano; D'Souza, Sarah; Tshangana, Sesethu Charmaine; Hoffmann, Björn; Ermilov, Eugeny A; Nyokong, Tebello; Höpfner, Michael

2014-05-15

45

ESOP Transformation to Majority Gates for Quantum-dot Cellular Automata Logic Synthesis  

Microsoft Academic Search

We investigate the benefit of using ESOP minimization in the synthesis of quantum-dot cellular automata (QCA). We determine the size and delay of multi-input XOR and AND\\/OR gates when implemented in using 3-input majority gates that are easily realized in QCA, and use our results in our QCAexor estimator tool. We found that most benchmarks have at least one output

David Y. Feinstein; Mitchell A. Thornton

46

Synthesis and optical properties of colloidal core-shell semiconductor nanocrystals quantum dots for sensory application  

Microsoft Academic Search

We present results on the synthesis of core-shell CdSe\\/ZnS semiconductor nanocrystal quantum dots (NQDs) and their optical enhancement properties. A very strong and narrow photoluminescence is observed for sizes varying from 2 to 5 nm. Using an effective mass theory, we model the energy shift for the first excited state for core and core\\/shell NQDs. Core\\/shell heterostructure can be used

Pham Thu Nga; Nguyen Van Chuc; Vu Due Chinh; Nguyen Xuan Nghia; Phan Tien Dung; Pham Thai Cuong; Chu Viet Ha; Vu Hong Hanh; Vu Thi Kim Lien; Dao Nguyen Thuan; C. Barthou; P. Benalloul; M. Romanelli; A. Maitre

2006-01-01

47

Cd 1? x Mn x S quantum dots: new synthesis and characterization  

Microsoft Academic Search

We report on the synthesis of diluted magnetic semiconductor Cd1?xMnxS quantum dots (QDs) by the reverse micelle method using H2S as the sulfur source. The Cd1?xMnxS QDs size ranging from ?3.2 to ?4.2nm can be systematically controlled by the amount of H2S added and is characterized by high-resolution transmission electron microscopy. Manganese compositions in the QDs are estimated by energy

Q. Pang; B. C. Guo; C. L. Yang; S. H. Yang; M. L. Gong; W. K. Ge; J. N. Wang

2004-01-01

48

Long Fe 3O 4 nanowires decorated by CdTe quantum dots: Synthesis and magnetic–optical properties  

Microsoft Academic Search

This work describes the synthesis and magnetic–optical properties of Fe3O4 nanowires decorated by CdTe quantum dots. The composite nanowires with a length of 1?m and an average diameter of 23±3nm were prepared in a high yield through the preferential growth of Fe3O4 on CdTe quantum dots using ethylenediamine as template. Their growth mechanism was discussed based on the results of

Xianmei Lan; Xuebo Cao; Wenhu Qian; Weijian Gao; Cui Zhao; Yang Guo

2007-01-01

49

Green chemistry for large-scale synthesis of semiconductor quantum dots.  

PubMed

Large-scale synthesis of semiconductor nanocrystals or quantum dots (QDs) with high concentration and high yield through simultaneously increasing the precursor concentration was introduced. This synthetic route conducted in diesel has produced gram-scale CdSe semiconductor quantum dots (In optimal scale-up synthetic condition, the one-pot yield of QDs is up to 9.6g). The reaction has been conducted in open air and at relatively low temperature at 190-230 degrees C in the absence of expensive organic phosphine ligands, aliphatic amine and octadecene, which is really green chemistry without high energy cost for high temperature reaction and unessential toxic chemicals except for Cd, which is the essential building block for QDs. PMID:18399665

Liu, Jin-Hua; Fan, Jun-Bing; Gu, Zheng; Cui, Jing; Xu, Xiao-Bo; Liang, Zhi-Wu; Luo, Sheng-Lian; Zhu, Ming-Qiang

2008-05-20

50

Cluster-seeded synthesis of doped CdSe:Cu4 quantum dots.  

PubMed

We report here a method for synthesizing CdSe quantum dots (QDs) containing copper such that each QD is doped with four copper ions. The synthesis is a derivative of the cluster-seed method, whereby organometallic clusters act as nucleation centers for quantum dots. The method is tolerant of the chemical identity of the seed; as such, we have doped four copper ions into CdSe QDs using [Na(H2O)3]2[Cu4(SPh)6] as a cluster seed. The controlled doping allows us to monitor the photophysical properties of guest ions with X-ray spectroscopy, specifically XANES and EXAFS at the copper K-edge. These data reveal that copper can capture both electrons and holes from photoexcited CdSe QDs. When the dopant is oxidized, photoluminescence is quenched and the copper ions translocate within the CdSe matrix, which slows the return to an emissive state. PMID:23441602

Jawaid, Ali M; Chattopadhyay, Soma; Wink, Donald J; Page, Leah E; Snee, Preston T

2013-04-23

51

Synthesis and characterization of boron-doped Si quantum dots for all-Si quantum dot tandem solar cells  

Microsoft Academic Search

Multiple layers of Si quantum dots (QDs) in SiO2 with a narrow size distribution were synthesized by a co-sputtering technique. Structural, electrical and optical properties of Si QD\\/SiO2 multilayer films with various boron (B) concentrations introduced during the sputtering process were studied. X-ray photoelectron spectroscopy (XPS) revealed B–B\\/B–Si bonding, which suggests possible boron inclusion in the nanocrystals. The addition of

X. J. Hao; E. C. Cho; C. Flynn; Y. S. Shen; S. C. Park; G. Conibeer; M. A. Green

2009-01-01

52

Synthesis of colloidal SnSe quantum dots by electron beam irradiation  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

53

Ion beam-induced quantum dot synthesis in glass  

Microsoft Academic Search

Ion beam synthesis has played a significant role in fabricating metallic or semiconducting nanocrystal arrays in glass for their optical or magnetic properties, but basic questions remain unanswered. What are the microscopic mechanisms that control nanocluster growth, determine their density and size distributions? To what extent can we control these processes in order to tailor the properties? We demonstrate the

R. Espiau de Lamaestre; H. Bernas

2007-01-01

54

Ion Beam-induced Quantum Dot Synthesis in Glass  

Microsoft Academic Search

Irradiation-induced processes are often considered only in their nonequilibrium aspects. The purpose of this brief review is to show that chemistry, and particularly redox properties, play a major role in the thermal evolution of such systems and generally cannot, therefore, be neglected. This is exemplified by the synthesis of Ag nanoclusters in glasses and silica, under both low (gamma-ray) and

Harry Bernas; Roch Espiau

2007-01-01

55

Structural changes in R-phycoerythrin upon CdS quantum dot synthesis in tunnel cavities of protein molecules.  

PubMed

Structural changes in R-phycoerythrin used as a matrix for the synthesis of CdS quantum dots have been analyzed by circular dichroism spectrometry. In deionized water, quantum dot synthesis in the tunnel cavity of the R-phycoerythrin molecule proved to be accompanied by uncoiling of ?-helices and changes in the conformation of its chromophore groups, with consequent decay of protein fluorescence. Since R-phycoerythrin fluorescence is important for practical applications, conditions for quantum dot synthesis have been optimized by replacing deionized water with 0.01 M MES buffer, pH 5.7. Under such conditions, the size of the CdS quantum dots (determined from atomic force microscopy images) remains the same as in deionized water, but quantum dots cause only minor structural changes in protein molecules, as follows from circular dichroism and absorption spectra. The thermostability of R-phycoerythrin is enhanced, as indicated by an increase in the experimental activation energy for denaturation (from 140.8 to 149.9 kJ/mol) and the intensity of R-phycoerythrin fluorescence is also enhanced approximately twofold. PMID:24141070

Bekasova, O D; Shubin, V V; Safenkova, I V; Kovalyov, L I; Kurganov, B I

2013-11-01

56

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

Microsoft Academic Search

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

Yasukazu Hoshino

2002-01-01

57

Quantum computation with quantum dots  

Microsoft Academic Search

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

Daniel Loss; David P. Divincenzo

1998-01-01

58

Synthesis and spectroscopy of PbSe fused quantum-dot dimers.  

PubMed

We report the synthesis and characterization of Pb-chalcogenide fused quantum-dot (QD) dimer structures. The resulting QD dimers range in length from 6 to 16 nm and are produced by oriented attachment of single QD monomers with diameters of 3.1-7.8 nm. QD monomers with diameters exceeding about 5 nm appear to have the greatest affinity for QD dimer formation and, therefore, gave the greatest yields of fused structures. We find a new absorption feature in the first exciton QD dimer spectra and assign this to a splitting of the 8-fold degenerate 1S-level. The dimer splitting increases from 50 to 140 meV with decrease of the QD-monomer size, and we present a mechanism that accounts for this splitting. We also demonstrate the possibility of fusing two QDs with different sizes into a heterostructure. PMID:24564575

Hughes, Barbara K; Blackburn, Jeffrey L; Kroupa, Daniel; Shabaev, Andrew; Erwin, Steven C; Efros, Alexander L; Nozik, Arthur J; Luther, Joseph M; Beard, Matthew C

2014-03-26

59

Highly luminescent chitosan-L-cysteine functionalized CdTe quantum dots film: synthesis and characterization.  

PubMed

The present work describes synthesis of water soluble L-cysteine-functionalized CdTe quantum dots (QDs) with size tunable emission at different time intervals for chitosan based film. The characterization of the synthesized CdTe QDs-chitosan film was made by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and scanning electron microscope (SEM). The optical property of CdTe QDs-chitosan film was determined by UV-vis and photo-luminescence (PL) spectroscopy whereas their antibacterial activity was screened for Gram positive (Staphylococcus aureus) as well as Gram negative (Pseudomonas aurigionasa and Escherichia coli) bacteria by disc diffusion method. The loss of tunable light emission effect of QDs as well as the positive result of antibacterial study reveals that the synthesized QDs based chitosan film is a promising candidate for wide range of biomedical applications. PMID:23911453

Kumar, Hridyesh; Srivastava, Rohit; Dutta, P K

2013-09-12

60

Hydrogel templated CdS quantum dots synthesis and their characterization  

Microsoft Academic Search

This work reports a facile method for preparation of CdS quantum dots (Q-dots), using a crosslinked hydrophilic p(AMPS) hydrogel network by absorption of Cd(II) ions and sequential precipitation with aqueous Na2S within the network at room temperature. The TEM images revealed that prepared CdS Q-dots were distributed throughout the p(AMPS) hydrogel network and their sizes were about 5nm. The amount

Nurettin Sahiner; Kivanc Sel; Kadem Meral; Yavuz Onganer; Sultan Butun; Ozgur Ozay; Coskun Silan

2011-01-01

61

Synthesis of colloidal SnSe quantum dots by electron beam irradiation  

Microsoft Academic Search

Water-soluble orthorhombic colloidal SnSe quantum dots with an average diameter of 4nm 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 3.89eV, greatly blue shifted compared with that of bulk SnSe (1.0eV) due to the

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

2011-01-01

62

One-step and rapid synthesis of high quality alloyed quantum dots (CdSe–CdS) in aqueous phase by microwave irradiation with controllable temperature  

Microsoft Academic Search

In this paper, we presented a seed-mediated approach for rapid synthesis of high quality alloyed quantum dots (CdSe–CdS) in aqueous phase by microwave irradiation with controllable temperature in 1h. In the synthesis, CdSe seeds were first formed by the reaction of NaHSe and Cd2+, and then alloyed quantum dots (CdSe–CdS) were rapidly produced by releasing of sulfide ions from 3-mercaptopropionic

Huifeng Qian; Liang Li; Jicun Ren

2005-01-01

63

Low-cost and gram-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots in an electric pressure cooker  

NASA Astrophysics Data System (ADS)

We report an electric pressure cooker for large-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots. Low-cost thioglycolic acid and sodium citrate were used as the dual stabilizers. ~3 grams of quantum dots with a tunable emission from 545 to 610 nm and quantum yield up to 40% were obtained in a batch.We report an electric pressure cooker for large-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots. Low-cost thioglycolic acid and sodium citrate were used as the dual stabilizers. ~3 grams of quantum dots with a tunable emission from 545 to 610 nm and quantum yield up to 40% were obtained in a batch. Electronic supplementary information (ESI) available: Experimental details, PL decay curves, PL lifetimes, EDS spectra, chemical composition, cost analysis. See DOI: 10.1039/c3nr05014a

Chen, Yanyan; Li, Shenjie; Huang, Lijian; Pan, Daocheng

2014-01-01

64

Quantum Dots for Biophotonics  

PubMed Central

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

Yong, Ken-Tye

2012-01-01

65

Fluoroimmunoassays using antibody-conjugated quantum dots.  

PubMed

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

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

2005-01-01

66

Synthesis and properties of CdSe Quantum Dot sensitized ZnO nanocomposites  

NASA Astrophysics Data System (ADS)

In this work, zinc oxide nanocrystals with an average particle size of 13-22 nm are readily synthesized in aqueous medium by the wet synthesis method. Different sized nanocrystals obtained with change in calcination temperature are characterized by PL photoluminescence (PL) and UV-vis absorption spectroscopies, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The average crystal size of the as prepared ZnO nanopowder is determined by XRD and was found to be in good agreement with the UV-vis absorption analysis. The quality of different ZnO nanopowders is confirmed by XRD spectra. On the basis of different characterizations, ZnO calcined for 1 h (due to its large size and less agglomeration) is chosen for synthesis of ZnO-CdSe nanocomposites with variable sized CdSe QD's (Quantum Dots). Nano-composites are synthesized using bifunctional linker molecule Mercaptopropionic Acid (MPA), and by directly adsorbing CdSe QD's over the surface of ZnO nanocrystals. The difference in charge transfer mechanism in ZnO-CdSe nanocomposites due to different crystallite size of CdSe QD's is studied. Higher crystallinity of ZnO-CdSe nanocomposites can be determined from XRD characterization. Size and mode of attachment in various ZnO-CdSe nanocomposites are determined by SEM studies.

Jain, Shefali; Sharma, Shailesh N.; Kumar, Mahesh

2011-12-01

67

A one-pot synthesis of reduced graphene oxide-Cu?S quantum dot hybrids for optoelectronic devices.  

PubMed

We demonstrate a facile one-pot approach for the synthesis of reduced graphene oxide (rGO)-cuprous sulfide quantum dot (Cu?S QD) hybrids, wherein the reduction of GO and the growth of Cu?S QDs on graphene occur simultaneously. The as-synthesized rGO-Cu?S QD hybrids exhibit an excellent photoelectric response and efficient electron transfer from the Cu?S QDs to the rGO sheets. PMID:23907643

Su, Yanjie; Lu, Xiaonan; Xie, Minmin; Geng, Huijuan; Wei, Hao; Yang, Zhi; Zhang, Yafei

2013-10-01

68

Procedures for Controlling the Size, Structure and Optical Properties of CdS Quantum Dots during Synthesis in Aqueous Solution  

Microsoft Academic Search

We report an easy approach for the synthesis of CdS Quantum Dots (CdS QDs) with high luminescence and temporal stability through\\u000a the reaction of Cd2+ and S2- in the presence of mercaptoacetic acid (MAA) as a capping reagent in aqueous medium, under normal pressure and room temperature.\\u000a The influence of several experimental variables, including temperature, pH, the Cd\\/S ratio and

María-Jesús Almendral-Parra; Ángel Alonso-Mateos; Sara Sánchez-Paradinas; Juán F. Boyero-Benito; Emilio Rodríguez-Fernández; Julio J. Criado-Talavera

69

Sonochemical synthesis and bioconjugation of highly fluorescent, water soluble quantum dots for single molecule imaging on phospholipid membranes  

Microsoft Academic Search

The field of single molecule tracking based on gold and dye-labeled tracer molecules has been instrumental in changing the view about the structure-dynamics-function relationships in cellular membranes. However, these traditional probes are limited concerning their size and photostability, respectively. This work presents the successful development of a sonochemical synthesis method for high-quality CdSe\\/ZnS quantum dots, and their subsequent characterization. Also

Michael J Murcia

2006-01-01

70

Synthesis and characterization of intrinsically radiolabeled quantum dots for bimodal detection  

PubMed Central

A novel approach was developed to synthesize radioactive quantum dots (r-QDs) thereby enabling both optical and radionuclide signals to be detected from the same intrinsic bimodal probe. This proof-of-concept is exemplified by the incorporation of the radionuclide 109Cadmium into the core/shell of the nanoparticle. Green and near infrared (NIR) emission intrinsic r-QDs were synthesized and characterized. Zwitterionic and Poly-polyethlene glycol (PEGylated) ligands were synthesized and used to coat r-QDs. Zwitterionic NIR r-QDs (quantum yield = 11%) and PEGylated NIR r-QDs (quantum yield = 14%) with an average size of 13.8 nm and 16.8 nm were obtained respectively. The biodistribution of NIR zwitterionic and PEGylated r-QDs in nude mice was investigated and zwitterionic r-QDs showed longer blood circulation (t1/2 = 21.4±1.1 hrs) than their PEGylated counterparts (t1/2 = 6.4±0.5 min). Both zwitterionic and PEGylated r-QDs exhibited progressive accumulation in the liver and spleen, but the magnitude of the accumulation (%ID/g) was about 3-6 fold higher with the PEGylated r-QDs at all the time points. The results demonstrated the feasibility of r-QDs synthesis in quantitative yield and retention of fluorescence following incorporation of radioactivity into the core/shell of the nanoparticle. The gamma signal from the same fluorescent elemental material enabled quantitative and robust pharmacokinetic measurements and how these changed depended on the type of coating ligands used. This strategy for intrinsically radio-labeling the QDs is currently being implemented in our laboratory for the incorporation of other radiometals.

Sun, Minghao; Hoffman, David; Sundaresan, Gobalakrishnan; Yang, Likun; Lamichhane, Narottam; Zweit, Jamal

2012-01-01

71

Electrochromic Nanocrystal Quantum Dots  

Microsoft Academic Search

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

Congjun Wang; Moonsub Shim; Philippe Guyot-Sionnest

2001-01-01

72

Topic in Depth - Quantum Dots  

NSDL National Science Digital Library

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

2010-09-20

73

Synthesis, characterization, Raman, and surface enhanced Raman studies of semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The major contributions and discoveries of the dissertation include: (1) Homogeneous nucleation processes for the formation of nanocrystals can occur at low temperature and do not need to proceed at high temperature to overcome a high energy barrier. Monodisperse PbS quantum dots (QDs) obtained with nucleation and growth at 45°C support this finding. (2) Monodisperse single elemental Se QDs can be produced by simple solution crystallization from TDE (1-tetradecene) or ODE (1-octadecene). (3) TDE is a better non-coordinating solvent compare to ODE. STDE (S dissolved in TDE) and SeTDE (Se dissolved in TDE) are stable reagents with long storage time. They can be used as universal precursors for S-containing and Se-containing QDs. (4) QDs synthesis can be carried out at low temperature and relatively short reaction time using the simple, non-injection, one-pot synthetic method. (5) The one-pot method can be extended for the synthesis of QDs and graphene oxide nanocomposites and metal and graphene oxide nanocomposites. (6) PbCl2-OLA (oleylamine) is a universal system for the synthesis of Pb-chaclogenides QDs. (7) Surface enhanced Raman spectroscopy (SERS) is used to probe both size and wave length dependent quantum confinement effects (QCEs) of PbS QDs. (8) Raman spectroscopy is a powerful tool to elucidate crystal structure of Se nanoclusters with size of 1--2 nm. Semiconductor QDs have attracted considerable attention due to their potential for energy-efficient materials in optoelectronic and solar cell applications. When the radius of a QD is decreased to that of the exciton Bohr radius, the valence and conduction bands are known to split into narrower bands due to QCEs. QCEs are both size and wave length dependent. We have developed, synthesized and characterized a series of Pb-chaclogenide QDs, which all the sizes of the QDs are monodisperse and smaller than their respective exciton Bohr radius, to study the QCEs of these QDs. SERS is used as a crucial tool to investigate these QCEs. The QCEs are due to any of the following three resonances or a combination among them: interband resonance, molecular state resonance, and charge-transfer resonance.

Pan, Yi

74

Magnetic nanocrystals: Synthesis and properties of diluted magnetic semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The chapters in this thesis describe the investigations into the synthesis and magnetic and electronic properties of diluted magnetic semiconductor quantum dots (DMS-QDs), specifically Co2+ and Mn2+-doped ZnO and Co2+:ZnSe. Homogeneous dopant incorporation and substitutional speciation of Co2+ and Mn2+ in ZnO QDs during solution synthesis at room temperature were confirmed by electronic absorption and electron paramagnetic resonance spectroscopy measurements. Post-synthetic methods were shown to eliminate any dopants bound to the nanocrystal surfaces, resulting in high-quality, internally-doped ZnO DMS-QDs. The magneto-optical properties observed by MCD spectroscopy demonstrated the presence of sp-d exchange interactions that are characteristic of DMSs. The sensitivity of this technique allowed clear observation and assisted in the assignment of dopant charge transfer transitions in both materials. Ferromagnetism was activated in both Co2+:ZnO and Mn2+:ZnO nanocrystalline aggregates and thin films by addition of the proper defects, providing significant insight to the understanding of magnetic ordering in ZnO and other DMSs. The influence of post-synthetic treatments on the luminescent properties of ZnO nanocrystals were also investigated since surface defects identified as sources of trap state luminescence of ZnO could also potentially be incorporated into the nanocrystalline aggregates and thin films. Colloidal CO2+:ZnSe QDs were prepared from solution using the "hot injection method". Lower than expected Zeeman splittings in CO2+:ZnSe QDs, as measured by low temperature electronic absorption and MCD spectroscopies, were attributed to the presence of an undoped ZnSe core in the QDs, a result of a dopant-excluding nucleation event during the synthesis of these nanocrystals. Additionally, direct observation of a charge transfer transition by MCD spectroscopy showed experimental evidence that the dopant levels are pinned in energy as the valence and conduction bands of the semiconductor increase their energy gap with increasing quantum confinement. These studies highlight the utility of DMS-QDs as materials for studying DMS properties, and suggest opportunities for the use of these highly processable colloidal magnetic nanocrystals as potential building-block precursors for the construction of more advanced nanoscale DMS architectures.

Norberg, Nicholas S.

75

Self-organized ZnSe quantum dots: synthesis and characterization.  

PubMed

Self-organized ZnSe quantum dots (Q-ZnSe) were grown on indium tin oxide substrate using wet chemical technique without or in presence of copper and manganese dopants. The structural, morphological and luminescence properties of the as grown Q-dot films have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. Composition of the samples were analyzed using atomic absorption spectroscopy. The quantum dots have been shown to deposit in a compact, uniform and organized array on the indium tin oxide substrate. The size dependent blue shift in the experimentally determined absorption edge has been compared with the theoretical predictions based on the effective mass and tight binding approximations. It is shown that the experimentally determined absorption edges depart significantly from the theoretically calculated values. The photoluminescence properties of the undoped as well as doped Q-ZnSe have also been discussed. PMID:18468182

Kaushik, Diksha; Singh, R R; Sharma, A B; Gupta, D; Sharma, M; Pandey, R K

2008-03-01

76

Quantum-Dot Cellular Automata  

Microsoft Academic Search

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

Gregory Snider

2000-01-01

77

Synthesis and functionalization of epitaxial quantum dot nanostructures for nanoelectronic architectures  

Microsoft Academic Search

We describe methods for assembly of quantum dots (QDs) into arrays of any symmetry, and methods for nanoscale doping of individual QDs. We have previously shown how the Ga+ focused ion beam (FIB) can template Si(100) surfaces for controlled Ge QD nucleation. Local Ga-induced reduction of the wetting layer thickness also suppresses QD nucleation away from the templating sites. This

R. Hull; J. Floro; J. Graham; J. Gray; M. Gherasimova; A. Portavoce; F. M. Ross

2008-01-01

78

Synthesis and Adsorption Study of BSA Surface Imprinted Polymer on CdS Quantum Dots  

Microsoft Academic Search

A new bovine serum albumin (BSA) surface imprinting method was developed by the incorporation of quantum dots (QDs) into molecularly imprinted polymers (MIP), which can offer shape selectivity. Preparation and adsorption conditions were optimized. Physical appearance of the QDs and QDs-MIP particles was illustrated by scanning electron microscope images. Photoluminescence emission of CdS was quenched when rebinding of the template.

Ping-ping Tang; Ji-bao Cai; Qing-de Su

2010-01-01

79

Si, Ge, and SiGe quantum wires and quantum dots  

Microsoft Academic Search

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

T. P. Pearsall

2007-01-01

80

Quantum Dot Light Emitting Diode  

SciTech Connect

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

Kahen, Keith

2008-07-31

81

Quantum Dot Light Emitting Diode  

SciTech Connect

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

Keith Kahen

2008-07-31

82

Synthesis and Analysis of the Quantum Dot Core and Surface Structures Probed By Solid State Nuclear Magnetic Resonance  

Microsoft Academic Search

This dissertation outlines how the optical properties of InP quantum dots were improved by microwave synthetic techniques, how CdSSe alloy quantum dots were determined from a single source precursor, and how specific regions of CdSe quantum dots were identified by solid state nuclear magnetic resonance determining size dependent reconstruction.\\u000aHigh quantum yield (47%) InP nanocrystals can be prepared without the

Derek Dean Lovingood

2010-01-01

83

Quantum optics with single quantum dot devices  

Microsoft Academic Search

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

Valéry Zwiller; Thomas Aichele; Oliver Benson

2004-01-01

84

Quantum dots infrared photodetectors  

Microsoft Academic Search

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

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

2003-01-01

85

Quantum dot infrared photodetectors  

Microsoft Academic Search

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

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

2003-01-01

86

Quantum dot solar cells  

Microsoft Academic Search

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

A. J Nozik

2002-01-01

87

Plasmonic fluorescent quantum dots  

Microsoft Academic Search

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

Yongdong Jin; Xiaohu Gao

2009-01-01

88

Synthesis and optical characterisation of triphenylamine-based hole extractor materials for CdSe quantum dots.  

PubMed

We report the synthesis and optical characterisation of different triphenylamine-based hole capture materials able to anchor to CdSe quantum dots (QDs). Cyclic voltammetry studies indicate that these materials exhibit reversible electrochemical behaviour. Photoluminescence and transient absorption spectroscopy techniques are used to study interfacial charge transfer properties of the triphenylamine functionalized CdSe QDs. Specifically, we show that the functionalized QDs based on the most easily oxidised triphenylamine display efficient hole-extraction and long-lived charge separation. The present findings should help identify new strategies to control charge transfer QD-based optoelectronic devices. PMID:23591794

Planells, Miquel; Reynolds, Luke X; Bansode, Umesh; Chhatre, Shraddha; Ogale, Satishchandra; Robertson, Neil; Haque, Saif A

2013-05-28

89

Synthesis of Non-blinking Semiconductor Quantum Dots Emitting in the Near-Infrared  

SciTech Connect

Our previous work demonstrates that Quasi-Type II CdSe/CdS core-shell quantum dots with thick shells (3-5 nm) exhibit unique photophysical characteristics, including improved chemical robustness over typical thin-shelled core/shell systems and the elimination of blinking through suppression of nonradiative Auger recombination. Here we describe a new thick-shelled heterostructure, InP/CdS, which exhibits a Type II bandgap alignment producing near-infrared (NIR) emission. Samples with a range of shell thicknesses were synthesized, enabling shell-thickness-dependent study of the absorbance and emission spectra, fluorescence lifetimes, and quantum yields. InP/CdS/ZnS core/shell/shell structures were also synthesized to reduce cadmium exposure for applications in the biological environment. Single particle spectroscopy indicates reduced blinking and improved photostability with increasing shell thickness, resulting in thick-shelled dots that are appropriate for single-particle tracking measurements with NIR emission.

Dennis, Allison M. [Los Alamos National Laboratory; Mangum, Benjamin D. [Los Alamos National Laboratory; Piryatinski, Andrei [Los Alamos National Laboratory; Park, Young-Shin [Los Alamos National Laboratory; Htoon, Han [Los Alamos National Laboratory; Hollingsworth, Jennifer A. [Los Alamos National Laboratory

2012-06-21

90

Synthesis and Adsorption Study of BSA Surface Imprinted Polymer on CdS Quantum Dots  

NASA Astrophysics Data System (ADS)

A new bovine serum albumin (BSA) surface imprinting method was developed by the incorporation of quantum dots (QDs) into molecularly imprinted polymers (MIP), which can offer shape selectivity. Preparation and adsorption conditions were optimized. Physical appearance of the QDs and QDs-MIP particles was illustrated by scanning electron microscope images. Photoluminescence emission of CdS was quenched when rebinding of the template. The quenching of photoluminescence emissions is presumably due to the fluorescence resonance energy transfer between quantum dots and BSA template molecules. The adsorption is compiled with Langmuir isotherm, and chemical adsorption is the rate-controlling step. The maximum adsorption capacity could reach 226.0 mg/g, which is 142.4 mg/g larger than that of undoped BSA MIP. This study demonstrates the validity of QDs coupled with MIP technology for analyzing BSA.

Tang, Ping-ping; Cai, Ji-bao; Su, Qing-de

2010-04-01

91

Quantum-dot cellular automata  

Microsoft Academic Search

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

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

1999-01-01

92

Synthesis and gas sensing properties of ZnO quantum dots  

Microsoft Academic Search

ZnO nanocrystals (2.5–4.5nm) were prepared by a wet chemical method based on alkaline-activated hydrolysis and condensation of zinc acetate solutions. Dropcasting of the nanocrystals onto alumina substrates allowed the fabrication of gas sensing devices, that were tested towards NO2, acetone and methanol and showed promising results. At low working temperature, the ZnO quantum dots based sensors are selective to nitrogen

A. Forleo; L. Francioso; S. Capone; P. Siciliano; P. Lommens; Z. Hens

2010-01-01

93

Synthesis of green CdSe\\/chitosan quantum dots using a polymer-assisted ?-radiation route  

Microsoft Academic Search

Chitosan-coated CdSe quantum dots (CdSe\\/CS QDs) were successfully synthesized in aqueous system through a ?-radiation route at room temperature under ambient pressure. The diameter of the resulting QDs was about 4nm with narrow size distribution. The synthesized QDs exhibited an absorption peak at 460nm and an emission peak at 535nm. These QDs were cubic zinc blende CdSe in core structure

Bin Kang; Shu-Quan Chang; Yao-Dong Dai; Da Chen

2008-01-01

94

Synthesis of green CdSe/chitosan quantum dots using a polymer-assisted ?-radiation route  

NASA Astrophysics Data System (ADS)

Chitosan-coated CdSe quantum dots (CdSe/CS QDs) were successfully synthesized in aqueous system through a ?-radiation route at room temperature under ambient pressure. The diameter of the resulting QDs was about 4 nm with narrow size distribution. The synthesized QDs exhibited an absorption peak at 460 nm and an emission peak at 535 nm. These QDs were cubic zinc blende CdSe in core structure and coated with chitosan on surface, with fine solubility in water.

Kang, Bin; Chang, Shu-Quan; Dai, Yao-Dong; Chen, Da

2008-07-01

95

Light emitting CdS quantum dots in PMMA: Synthesis and optical studies  

Microsoft Academic Search

Freshly prepared CdS-quantum dots (QDs) in DMF (clear pale solution) when loaded in polymethylmethacrylate (PMMA) lead to excellent optical properties. The tuning of the absorption and emission wavelengths via experimentally control parameters is considered novel and significant. The absorption band for CdS was observed at about 370nm in polymeric matrix. The blue, green and orange light emissions from such composite

P. K. Khanna; Narendra Singh

2007-01-01

96

Water-soluble multicolored fluorescent CdTe quantum dots: Synthesis and application for fingerprint developing  

Microsoft Academic Search

Multicolored water-soluble fluorescent CdTe quantum dots (QDs) have been synthesized by using Te, NaBH4, and CdCl2 as precursors and several mercapto-based compounds as modifiers. The effects of ratio of the precursor, type of modifier, refluxing time and initial pH value of the reaction on fluorescence intensity of CdTe QDs have been studied. XRD, HRTEM and fluorescence spectra were employed to

Jianjun Liu; Zhixia Shi; Yingchun Yu; Ruiqin Yang; Shengli Zuo

2010-01-01

97

‘One-pot’ synthesis of multifunctional GSH–CdTe quantum dots for targeted drug delivery  

NASA Astrophysics Data System (ADS)

A novel quantum dots-based multifunctional nanovehicle (DOX-QD-PEG-FA) was designed for targeted drug delivery, fluorescent imaging, tracking, and cancer therapy, in which the GSH–CdTe quantum dots play a key role in imaging and drug delivery. To exert curative effects, the antineoplastic drug doxorubicin hydrochloride (DOX) was loaded on the GSH–CdTe quantum dots through a condensation reaction. Meanwhile, a polyethylene glycol (PEG) shell was introduced to wrap the DOX-QD, thus stabilizing the structure and preventing clearance and drug release during systemic circulation. To actively target cancer cells and prevent the nanovehicles from being absorbed by normal cells, the nanoparticles were further decorated with folic acid (FA), allowing them to target HeLa cells that express the FA receptor. The multifunctional DOX-QD-PEG-FA conjugates were simply prepared using the ‘one pot’ method. In vitro study demonstrated that this simple, multifunctional nanovehicle can deliver DOX to the targeted cancer cells and localize the nanoparticles. After reaching the tumor cells, the FA on the DOX-QD-PEG surface allowed folate receptor recognition and increased the drug concentration to realize a higher curative effect. This novel, multifunctional DOX-QD-PEG-FA system shows great potential for tumor imaging, targeting, and therapy.

Chen, Xiaoqin; Tang, Yajun; Cai, Bing; Fan, Hongsong

2014-06-01

98

Synthesis and Resonance Energy Transfer in Conjugates of Luminescent Cadmium Selenide Quantum Dots and Chlorin e6 Molecules  

NASA Astrophysics Data System (ADS)

We synthesized a new type of conjugates of highly luminescent water soluble CdSe/ZnS colloidal quantum dots covalently bound to Chlorin e6 dye molecules. We observed a resonance energy transfer from quantum dots emitting at 660 nm to Chlorine e6 molecules in our conjugates which can be utilized for phototherapy. Contrary to that quantum dots emitting at 588 nm show non-resonance quenching of excitonic luminescence without the energy transfer to dye molecules.

Fedosyuk, A. A.; Artemyev, M. V.

2013-05-01

99

QUANTUM-DOT DEVICES AND QUANTUM-DOT CELLULAR AUTOMATA  

Microsoft Academic Search

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

WOLFGANG POROD

1997-01-01

100

Quantum-dot devices and Quantum-dot Cellular Automata  

Microsoft Academic Search

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

Wolfgang Porod

1997-01-01

101

Quantum-dot cellular automata: computing with coupled quantum dots  

Microsoft Academic Search

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

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

1999-01-01

102

Simple continuous-flow synthesis of Cu-In-Zn-S/ZnS and Ag-In-Zn-S/ZnS core/shell quantum dots  

NASA Astrophysics Data System (ADS)

We present a simple continuous-flow reaction for the synthesis of quaternary Cu-In-Zn-S/ZnS and Ag-In-Zn-S/ZnS core/shell quantum dots (QDs) using inexpensive and low-toxic precursors. The composition and band gap of Cu-In-Zn-S and Ag-In-Zn-S QDs were well controlled by changing the molar ratios of the starting materials. The PL quantum yields of Cu-In-Zn-S/ZnS core/shell quantum dots can reach as high as 40%.

Li, Shenjie; Chen, Yanyan; Huang, Lijian; Pan, Daocheng

2013-10-01

103

PREFACE: Quantum Dot 2010  

NASA Astrophysics Data System (ADS)

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

Taylor, Robert A.

2010-09-01

104

Synthesis and photoluminescence of water-soluble Mn 2+-doped ZnS quantum dots  

NASA Astrophysics Data System (ADS)

The water-soluble Mn 2+-doped ZnS quantum dots (Mn:ZnS d-dots) were synthesized by using thioglycolic acid (TGA) as stabilizer in aqueous solutions in air, and characterized by X-ray powder diffraction (XRD), UV-vis absorption spectra and photoluminescence (PL) emission spectroscopy. The sizes of Mn:ZnS d-dots were determined to be about 2 nm using XRD measurements and the UV-vis absorption spectra. It was found that the Mn 2+4T 1 ? 6A 1 emission intensity of Mn:ZnS d-dots significantly increased with the increase of Mn 2+ concentration, and showed a maximum when Mn 2+ doping content was 1.5%. If Mn 2+ concentration continued to increase, namely more than 1.5%, the Mn 2+4T 1 ? 6A 1 emission intensity would decrease. In addition, the effects of TGA/(Zn + Mn) molar ratio on PL were investigated. It was found that the peak intensity ratio of Mn 2+4T 1 ? 6A 1 emission to defect-states emission showed a maximum when the TGA/(Zn + Mn) molar ratio was equal to 1.8.

Xiao, Qi; Xiao, Chong

2008-08-01

105

Easily prepared high-quantum-yield CdS quantum dots in water using hyperbranched polyethylenimine as modifier  

Microsoft Academic Search

Some research has reported interaction between polyamidoamine dendrimers or polyethylenimine and quantum dots causing a quantum yield decrease of quantum dots. In this work, however, polyethylenimines of different molecular weight that were used to modify CdS quantum dots gave rise to the enhancement of CdS quantum yield to nearly 100%. Herein, we present the synthesis of a kind of easily

Jie Mao; Jun-Na Yao; Li-Na Wang; Wei-Sheng Liu

2008-01-01

106

Amphoteric Nanocrystalline Quantum Dots  

NASA Astrophysics Data System (ADS)

The Nanocrystalline Quantum Dot (NQDs) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the Dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied dc voltage across the pair, thin films of the Dots were deposited on both the positive and the negative electrodes. Extensive characterization including SEM, AFM, FTIR and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: 1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, 2) there are equal number of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited Dots is at least an order of magnitude higher than the number of initially charged Dots, indicating regeneration. Similar results were seen in maghemite (?-Fe2O3) NQDs. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of NQDs.

Islam, Mohammad

2007-03-01

107

Quantum Dots Investigated for Solar Cells  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

108

Facile synthesis of uniform large-sized InP nanocrystal quantum dots using tris(tert-butyldimethylsilyl)phosphine  

PubMed Central

Colloidal III-V semiconductor nanocrystal quantum dots [NQDs] have attracted interest because they have reduced toxicity compared with II-VI compounds. However, the study and application of III-V semiconductor nanocrystals are limited by difficulties in their synthesis. In particular, it is difficult to control nucleation because the molecular bonds in III-V semiconductors are highly covalent. A synthetic approach of InP NQDs was presented using newly synthesized organometallic phosphorus [P] precursors with different functional moieties while preserving the P-Si bond. Introducing bulky side chains in our study improved the stability while facilitating InP formation with strong confinement at a readily low temperature regime (210°C to 300°C). Further shell coating with ZnS resulted in highly luminescent core-shell materials. The design and synthesis of P precursors for high-quality InP NQDs were conducted for the first time, and we were able to control the nucleation by varying the reactivity of P precursors, therefore achieving uniform large-sized InP NQDs. This opens the way for the large-scale production of high-quality Cd-free nanocrystal quantum dots.

2012-01-01

109

Quantum Dots: Building Blocks of Quantum Devices?  

Microsoft Academic Search

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

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

2004-01-01

110

Quantum Dots and Colors  

NSDL National Science Digital Library

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

University Of Houston

111

Synthesis of positively charged CdTe quantum dots and detection for uric acid  

NASA Astrophysics Data System (ADS)

The CdTe dots (QDs) coated with 2-Mercaptoethylamine was prepared in aqueous solution and characterized with fluorescence spectroscopy, UV-Vis absorption spectra, high-resolution transmission electron microscopy and infrared spectroscopy. When the ?ex = 350 nm, the fluorescence peak of positively charged CdTe quantum dots is at 592 nm. The uric acid is able to quench their fluorescence. Under optimum conditions, the change of fluorescence intensity is linearly proportional to the concentration of uric acid in the range 0.4000-3.600 ?mol L -1, and the limit of detection calculated according to IUPAC definitions is 0.1030 ?mol L -1. Compared with routine method, the present method determines uric acid in human serum with satisfactory results. The mechanism of this strategy is due to the interaction of the tautomeric keto/hydroxyl group of uric acid and the amino group coated at the CdTe QDs.

Zhang, Tiliang; Sun, Xiangying; Liu, Bin

2011-09-01

112

Ultralow Noise Monolithic Quantum Dot Photonic Oscillators.  

National Technical Information Service (NTIS)

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

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

2013-01-01

113

Quantum Simulation in Quantum Dot Arrays.  

National Technical Information Service (NTIS)

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

L. Vandersypen

2013-01-01

114

Si, Ge, and SiGe quantum wires and quantum dots  

NASA Astrophysics Data System (ADS)

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

Pearsall, T. P.

115

Low temperature method for synthesis of ZnS quantum dots and its luminescence characterization studies  

NASA Astrophysics Data System (ADS)

Zinc Sulfide (ZnS) quantum dots of sizes 2.68-4.8 nm, embedded on polyvinyl alcohol (PVA) matrix, have been synthesized at 70° C by wet chemical method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), UV-vis spectroscopy and photoluminescence (PL) Spectroscopy has been adopted for sample characterization. Optical absorption spectra showed strong blue shift, which is an indication of strong quantum confinement. Photoluminescence spectra of the sample have been recorded at room temperature and observed two peaks centred around 415 nm and 440 nm. We have assigned the first peak due to band gap transitions while the later due to sulfur vacancy in the sample.

Senthilkumar, K.; Kalaivani, T.; Kanagesan, S.; Balasubramanian, V.

2013-01-01

116

Superradiance of quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2007-02-01

117

Synthesis and optical properties of core/shell ternary/ternary CdZnSe/ZnSeS quantum dots  

NASA Astrophysics Data System (ADS)

In this paper we report on the synthesis of ternary/ternary alloyed CdZnSe/ZnSeS core/shell quantum dots (QDs) by embryonic nuclei-induced alloying process. We synthesized CdZnSe core QDs emitting in the spectral range of 530-607 nm with various Cd/Zn ratios, depending on the core synthesis temperature. By shelling ZnSeS on the CdZnSe core QDs, the average luminescence quantum yield is increased by a typical factor of 2 up to 17, which we attribute to the reduction of number of non-emitting QDs. The single-photon emitter micro-photoluminescence study showed that the CdZnSe/ZnSeS core/shell QDs are good single-photon emitters and their blinking properties were improved compared to the CdZnSe core QDs. Quantum yields up to 25% were measured for the core/shell samples, demonstrating the potential for high-quality ternary/ternary QDs fabrication.

Nguyen, Hai Yen; de Marcillac, Willy Daney; Lethiec, Clotilde; Phan, Ngoc Hong; Schwob, Catherine; Maître, Agnès; Nguyen, Quang Liem; Le, Van Vu; Bénalloul, Paul; Coolen, Laurent; Thu Nga, Pham

2014-07-01

118

Quantum engineering of colloidal core-shell quantum dots: towards non blinking quantum dots and biexcitonic emission  

Microsoft Academic Search

In this paper, we show that the synthesis of thick shell enables to strongly reduce the blinking of colloidal quantum dots. It opens also new opportunities in terms of quantum engineering of the career wavefunctions. Modifying the Auger effect efficiency which is a crucial parameter to control the quantum optical properties of an individual nanocrystal fluorescence, we were able to

P. Spinicelli; B. Mahler; S. Buil; X. Quelin; B. Dubertret; J. P. Hermier

2009-01-01

119

A primer on the synthesis, water-solubilization, and functionalization of quantum dots, their use as biological sensing agents, and present status.  

PubMed

The use of nanomaterials, specifically fluorescent semiconductor quantum dots (QDs), for biological imaging and sensing has become very topical. Here we present a historical synopsis of research in this field to help elucidate the origins of the most recent advances in QD-based technology. We further aim to educate the novice researcher concerning many important aspects of QD synthesis, water-solubilization, functionalization, and usage in biological imaging and sensing that are generally not discussed in the literature. We will also summarize several recent transformative examples of using quantum dots for in vitro and in vivo studies. PMID:24296551

Tyrakowski, Christina Marie; Snee, Preston Todd

2014-01-21

120

Peptide Coated Quantum Dots for Biological Applications  

PubMed Central

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

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

2011-01-01

121

Assembling quantum dots in glasses and polymers  

Microsoft Academic Search

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

Subhash H. Risbud

2004-01-01

122

Quantum-dot cellular automata  

Microsoft Academic Search

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

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

1999-01-01

123

Surface-treated biocompatible ZnS quantum dots: Synthesis, photo-physical and microstructural properties  

NASA Astrophysics Data System (ADS)

In the present study, the ZnS semiconductor quantum dots were successfully synthesized via an aqueous method utilizing glutathione (GSH), thioglycolic acid (TGA) and polyvinyl pyrrolidone (PVP) as capping agents. The structural, morphological and photo-physical properties and biocompatibility were investigated using comprehensive characterization techniques such as x-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), dynamic light scattering (DLS), Fourier transform infrared spectrometry (FT-IR), UV-Vis optical absorption, photoluminescence (PL) spectrometer and MTT assay. The XRD patterns showed a cubic zinc blende crystal structure and a crystallite size of about 2-3 nm using Scherrer's equation confirmed by the electron micrographs and Effective Mass Approximation (EMA). The DLS and zeta-potential results revealed that GSH capped ZnS nanoparticles have the narrowest size distribution with an average size of 27 nm and relatively good colloidal stability. Also, the FT-IR spectrum confirmed the interaction of the capping agent groups with ZnS nanoparticles. According to the UV-Vis absorption results, optical bandgap of the spherical capped nanoparticles is higher compared to the uncapped sample and could be wider than 3.67 eV (corresponding to the bulk ZnS), which is due to the quantum confinement effect. From photoluminescence spectra, it was found that the emission becomes more intensive and shifts towards the shorter wavelengths in the presence of the capping agent. Moreover, the emission mechanism of uncapped and capped ZnS was discussed in detail. Finally, the MTT results revealed the satisfactory (>94%) biocompatibility of GSH capped ZnS quantum dots which would be a promising candidate applicable in fluorescent biological labels.

Taherian, M.; Sabbagh Alvani, A. A.; Shokrgozar, M. A.; Salimi, R.; Moosakhani, S.; Sameie, H.; Tabatabaee, F.

2014-03-01

124

Quantum dot micropatterning on si.  

PubMed

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

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

2008-06-01

125

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

PubMed Central

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

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

2011-01-01

126

Facile synthesis of soluble graphene quantum dots and its improved property in detecting heavy metal ions.  

PubMed

An effective approach to produce graphene quantum dots (GQDs) has been developed, which based on the cutting of graphene oxide (GO) powder into smaller pieces and being reduced by a green approach, using sodium polystyrene sulfonate (PSS) as a dispersant and l-ascorbic acid (l-AA) as the reducing agent, which is environmentally friendly. Then the as-prepared GQDs were further used for the detection of heavy metal ions Pb(2+). This kind of GQDs has greater solubility in water and is more biocompatible than GO that has been reduced by hydrazine hydrate. The few-layers of GQDs with defects and residual OH groups were shown to be particularly well suited for the determination of metal ions in the liquid phase using an electrochemical method, in which a remarkably low detection limit of 7×10(-9)M for Pb(2+) was achieved. PMID:24732395

Zhou, Chengfeng; Jiang, Wei; Via, Brian K

2014-06-01

127

Mesoscopic Theory for Quantum Dot Lasers  

Microsoft Academic Search

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

Ortwin Hess

128

TOPICAL REVIEW: Quantum dot micropillars  

Microsoft Academic Search

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

S. Reitzenstein; A. Forchel

2010-01-01

129

Biodetection using fluorescent quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2002-07-01

130

Facile synthesis of quantum dots/mesoporous silica/quantum dots core/shell/shell hybrid microspheres for ratiometric fluorescence detection of 5-fluorouracil in human serum.  

PubMed

Compared to single photoluminescence (PL) intensity-based sensors, dual-emitting-based ratiometric PL sensors are more preferable because the influence from PL fluctuation in the reagents and background PL can be reduced to a minimum. However, so far no report has been directed to the ratiometric PL detection of 5-fluorouracil (5-FU). In this study, for the first time, high-quality quantum dots (QD1)/mesoporous silica (SiO2)/quantum dots (QD2) core/shell/shell hybrid microspheres (QD1/SiO2/QD2) were prepared by self-assembly, and further developed toward a ratiometric PL sensor of 5-FU. The addition of 5-FU induced regular PL quenching of QD2, but hardly influenced on the PL of QD1 in the microspheres. Based on the linear relationship (R = -0.9994) between the ratiometric PL intensity (IQD2/IQD1) and the molar concentration of 5-FU (0-1 ?M), a ratiometric PL sensor for 5-FU was achieved and displays a low limit of detection (20 nM). Experimental results testified that this sensor for the detection of 5-FU in human serum samples was highly sensitive and selective over other inorganic ions and biological molecules. Compared with conventional analysis techniques and other spectrofluorimetric methods reported previously, this proposed ratiometric PL sensor could be a good candidate for the highly efficient detection of 5-FU. PMID:23939464

Gui, Rijun; Wan, Ajun; Jin, Hui

2013-10-21

131

The scalable quantum computation based on quantum dot systems  

Microsoft Academic Search

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

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

2011-01-01

132

Synthesis, structure, and optical properties of colloidal GaN quantum dots  

NASA Astrophysics Data System (ADS)

Colloidal chemistry was used to synthesize GaN quantum dots. A GaN precursor, polymeric gallium imide, {Ga(NH)3/2}n, which was prepared by the reaction of dimeric amidogallium with ammonia at room temperature, was heated in trioctylamine at 360 °C for one day to produce GaN nanocrystals. The GaN particles were separated, purified, and partially dispersed in a nonpolar solvent to yield transparent colloidal solutions that consisted of individual GaN particles. The GaN nanocrystals have a spherical shape and mean diameter of about 30+/-12 Å. The spectroscopic behavior of colloidal transparent dispersion has been investigated and shows that the band gap of the GaN nanocrystals shifts to slightly higher energy due to quantum confinement. The photoluminescence spectrum at 10 K (excited at 310 nm) shows band edge emission with several emission peaks in the range between 3.2 and 3.8 eV, while the photoluminescence excitation spectrum shows two excited-state transitions at higher energies.

Mi?i?, O. I.; Ahrenkiel, S. P.; Bertram, D.; Nozik, A. J.

1999-07-01

133

Compact biocompatible quantum dots via RAFT-mediated synthesis of imidazole-based random copolymer ligand  

PubMed Central

We present a new class of polymeric ligands for quantum dot (QD) water solubilization to yield biocompatible and derivatizable QDs with compact size (~10-12 nm diameter), high quantum yields (>50%), excellent stability across a large pH range (pH 5-10.5), and low nonspecific binding. To address the fundamental problem of thiol instability in traditional ligand exchange systems, the polymers here employ a stable multidentate imidazole binding motif to the QD surface. The polymers are synthesized via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization to produce molecular weight controlled monodisperse random copolymers from three types of monomers that feature imidazole groups for QD binding, polyethylene glycol (PEG) groups for water solubilization, and either primary amines or biotin groups for derivatization. The polymer architecture can be tuned by the monomer ratios to yield aqueous QDs with targeted surface functionalities. By incorporating amino-PEG monomers, we demonstrate covalent conjugation of a dye to form a highly efficient QD-dye energy transfer pair as well as covalent conjugation to streptavidin for high-affinity single molecule imaging of biotinylated receptors on live cells with minimal non-specific binding. The small size and low serum binding of these polymer-coated QDs also allow us to demonstrate their utility for in-vivo imaging of the tumor microenvironment in live mice.

Liu, Wenhao; Greytak, Andrew B.; Lee, Jungmin; Wong, Cliff R.; Park, Jongnam; Marshall, Lisa F.; Jiang, Wen; Curtin, Peter N.; Ting, Alice Y.; Nocera, Daniel G.; Fukumura, Dai; Jain, Rakesh K.; Bawendi, Moungi G.

2010-01-01

134

Self-assembly Drives Quantum Dot Photoluminescence  

Microsoft Academic Search

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

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

2009-01-01

135

Circuit Quantum Electrodynamics with Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

136

Coupled quantum dots as quantum gates  

Microsoft Academic Search

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

Guido Burkard; Daniel Loss; David P. Divincenzo

1999-01-01

137

Quantum optics with single nanowire quantum dots  

Microsoft Academic Search

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

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

2010-01-01

138

Quantum Dot Light Emitting Diode.  

National Technical Information Service (NTIS)

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

K. Kahen

2008-01-01

139

Investigation of Quantum Dot Lasers.  

National Technical Information Service (NTIS)

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

P. Bhattacharya

2004-01-01

140

Highly luminescent hybrid SiO2-coated CdTe quantum dots: synthesis and properties.  

PubMed

Novel hybrid SiO2-coated CdTe quantum dots (QDs) were created using CdTe QDs coated with a hybrid SiO2 shell containing Cd(2+) ions and a sulfur source via a sol-gel process in aqueous solution. Aqueous CdTe QDs with tunable emitting color created through a reaction between cadmium chloride and sodium hydrogen telluride was used as cores for the preparation of hybrid SiO2-coated CdTe QDs. In our experiments we found that the surface state of the cores and preparation conditions that affect the formation of the hybrid SiO2 shell also greatly affect photoluminescence of the hybrid SiO2-coated CdTe QDs. The generation of CdS-like clusters in the vicinity of the CdTe QDs, caused the quantum size effect of the QDs to be greatly reduced, which changes photoluminescence properties of the hybrid QDs fundamentally. Namely, the novel hybrid SiO2 shell played an important role in generating a series of specific optical properties. In addition, the novel hybrid SiO2 shell can be created if no CdTe QD is added. In order to gain an insight into the inter structure of the hybrid shell, we characterized the hybrid SiO2-coated CdTe QDs using X-ray diffraction analysis and discuss the formation mechanism of such a hybrid structure. This work is significant because the novel hybrid SiO2-coated CdTe QDs with its excellent properties can be used in many applications, such as biolabeling and optoelectronic devices. PMID:23460504

Liu, Ning; Yang, Ping

2013-01-01

141

Quantum Dots in Cell Biology  

PubMed Central

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

Barroso, Margarida M.

2011-01-01

142

Quantum-Dot Infrared Photodetectors  

Microsoft Academic Search

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

Joe C. Campbell; Anupam Madhukar

2007-01-01

143

Synthesis of CdSe Quantum Dots Using Micro-Flow Reactor and Their Optical Properties  

NASA Astrophysics Data System (ADS)

CdSe quantum dots (QDs) have been synthesized continuously at 200-320°C using a micro-flow reactor. Instead of the usual tri-n-octylphosphineoxide (TOPO)-tri-n-octylphosphine (TOP) solvent, octadecene (ODE)-oleic acid-TOP mixed solvent was used in the present study. Because the ODE-oleic acid-TOP solvent is in liquid form at room temperature, it enabled us to handle the reaction solution at room temperature. The particle size of the QDs synthesized at 250°C was controlled between 3.4 to 4.2 nm by changing the reaction time from 3 to 300 s. Clear photoluminescence was observed at 509 nm for 3.4 nm particles and at 578 nm for 4.2 nm particles. In comparison with the QDs synthesized using a small batch reactor, the particle size distribution of the QDs synthesized using the micro-flow reactor was distinctly sharp. The sharp particle distribution came from the accurate controllability of reaction temperature and time due to the short representative length of the micro-flow reactor.

Omata, Takahisa; Nose, Katsuhiro; Otsuka-Yao-Matsuo, Shinya; Nakamura, Hiroyuki; Maeda, Hideaki

2005-01-01

144

Synthesis of quantum dot-tagged submicrometer polystyrene particles by miniemulsion polymerization.  

PubMed

Submicrometer fluorescent polystyrene (PS) particles have been synthesized via miniemulsion polymerization using CdSe/ZnS core-shell quantum dots (QDs). The influence of QD concentration, QD coating (either trioctylphosphine oxide (TOPO)-coated or vinyl-functionalized), and surfactant concentration on the polymerization kinetics and the photoluminescence properties of the prepared particles has been analyzed. Polymerization kinetics were not altered by the presence of QDs, whatever their surface coating. Latexes exhibited particle sizes ranging from 100 to 350 nm, depending on surfactant concentration, and a narrow particle size distribution was obtained in all cases. The fluorescence signal of the particles increased with the number of incorporated TOPO-coated QDs. The slight red shift of the emission maximum was correlated with phase separation between PS and QDs, which occurred during the polymerization, locating the QDs in the vicinity of the particle/water interface. QD-tagged particles displayed higher fluorescence intensity with TOPO-coated QDs compared to those with the vinyl moiety. The obtained fluorescent particles open up new opportunities for a variety of applications in biotechnology. PMID:16460111

Joumaa, Nancy; Lansalot, Muriel; Théretz, Alain; Elaissari, Abdelhamid; Sukhanova, Alyona; Artemyev, Mikhail; Nabiev, Igor; Cohen, Jacques H M

2006-02-14

145

Synthesis and characterization of double-layer quantum-dots-tagged microspheres.  

PubMed

Quantum-dots-tagged poly (styrene-acrylamide-acrylic acid) microspheres (QDsAAMs) were synthesized and modified with hydrazine hydrate through hydrazinolysis. Azidocarbonyl groups, which can be rapidly coupled with proteins under mild conditions, were introduced onto the surface of QDsAAM using azido reaction. Bovine serum albumin (BSA) was selected as model protein to be covalently immobilized on the azidocarbonyl QDsAAM. Instruments such as fluorescence microscope, optical microscope, confocal laser scanning microscope, UV-visible spectrometer, Fourier transform infrared spectrometer, size analyzer, and fluorescence spectrophotometer were used to characterize QDsAAM. Results showed that QDsAAM had a regular double-layer spherical shape and an average diameter of 11.2 microm. It also displayed high fluorescence intensity (lambda(ex)/lambda(em) = 250 nm/370 nm), which showed linearity with concentrations ranging from 3.0 x10(-3) to 90.0 x10(-3) g.L(-1). In addition, external factors such as pH and ionic strength exerted little influence on fluorescent characteristic. BSA immobilization indicated that QDsAAM with azidocarbonyl groups could be covalently coupled with BSA at the rate of 40 x10(-3) g/g (BSA/QDsAAM), while fluorescence linearity correlation was also found. This functional azidocarbonyl QDsAAM with sensitive fluorescence and active azidocarbonyl groups could be used as a promising fluorescent probe for quantitative detection, protein immobilization, and early rapid clinical diagnostics. PMID:19304502

Pan, Xinghua; Lu, Maolin; Wu, Daocheng; Gai, Lili

2009-03-01

146

One-step colloidal synthesis of biocompatible water-soluble ZnS quantum dot/chitosan nanoconjugates  

NASA Astrophysics Data System (ADS)

Quantum dots (QDs) are luminescent semiconductor nanocrystals with great prospective for use in biomedical and environmental applications. Nonetheless, eliminating the potential cytotoxicity of the QDs made with heavy metals is still a challenge facing the research community. Thus, the aim of this work was to develop a novel facile route for synthesising biocompatible QDs employing carbohydrate ligands in aqueous colloidal chemistry with optical properties tuned by pH. The synthesis of ZnS QDs capped by chitosan was performed using a single-step aqueous colloidal process at room temperature. The nanobioconjugates were extensively characterised by several techniques, and the results demonstrated that the average size of ZnS nanocrystals and their fluorescent properties were influenced by the pH during the synthesis. Hence, novel 'cadmium-free' biofunctionalised systems based on ZnS QDs capped by chitosan were successfully developed exhibiting luminescent activity that may be used in a large number of possible applications, such as probes in biology, medicine and pharmacy.

Ramanery, Fábio P.; Mansur, Alexandra AP; Mansur, Herman S.

2013-12-01

147

Quantum dots investigated with charge detection techniques  

Microsoft Academic Search

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

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

2009-01-01

148

Novel Routes to Amphiphillic Ag Quantum Dots  

Microsoft Academic Search

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

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

2003-01-01

149

Peptide coated quantum dots for biological applications.  

PubMed

Quantum dots (QDOTs) have been widely recognized by the scientific community and the biotechnology industry, as witnessed by the exponential growth of this field in the past several years. We describe the synthesis and characterization of visible and near infrared QDots--a critical step for engineering organic molecules like proteins and peptides for building nanocomposite materials with multifunctional properties suitable for biological applications. PMID:17181021

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

2006-12-01

150

Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films  

SciTech Connect

Abstract:We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and uniform diameter (6.1 ( 0.7 nm). Simulations of the highly resolved X-and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 íB/Mn2+ and TC > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.

Norberg, Nicholas S.; Kittilstved, Kevin R.; Amonette, James E.; Kukkadapu, Ravi K.; Schwartz, Dana A.; Gamelin, Daniel R.

2004-08-04

151

Biological applications of quantum dots.  

PubMed

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

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

2007-11-01

152

Synthesis, solubilization, and surface functionalization of highly fluorescent quantum dots for cellular targeting through a small molecule  

NASA Astrophysics Data System (ADS)

To achieve long-term fluorescence imaging with quantum dots (QDs), a CdSe core/shell must first be synthesized. The synthesis of bright CdSe QDs is not trivial and as a consequence, the role of surfactant in nucleation and growth was investigated. It was found that the type of surfactant used, either phosphonic or fatty acid, played a pivotal role in the size of the CdSe core. The study of surfactant on CdSe synthesis, ultimately led to an electrical passivation method that utilized a short-chained phosphonic acid and highly reactive organometallic precursors to achieve high quantum yield (QY) as has been previously described. The synthesis of QDs using organometallic precursors and a phosphonic acid for passivation resulted in 4 out of 9 batches of QDs achieving QYs greater than 50% and 8 out of 9 batches with QYs greater than 35%. The synthesis of CdSe QDs was done in organic solutions rendering the surface of the particle hydrophobic. To perform cell-targeting experiments, QDs must be transferred to water. The transfer of QDs to water was successfully accomplished by using single acyl chain lipids. A systematic study of different lipid combinations and coatings demonstrated that 20-40 mol% single acyl chained lipids were able to transfer QDs to water resulting in monodispersed, stable QDs without adversely affecting the QY. The advantage to water solubilization using single acyl chain lipids is that the QD have a hydrodynamic radius less than 15 nm, QYs that can exceed 50% and additional surface functionalization can be down using the reactive sites incorporated into the lipid bilayer. QDs that are bright and stable in water were studied for the purpose of targeting G protein-coupled Receptors (GPCR). GPCRs are transmembrane receptors that internalize extracellular cues, and thus mediate signal transduction. The cyclic Adenosine Monophosphate Receptor 1 of the model organism Dictyostelium disodium was the receptor of interest. The Halo protein, a genetically modified dehalogenase, was added to the N-terminus of the cAR1 receptor without resulting in a phenotype. The Halo protein fused to cAR1 was then shown to bind an organic fluorophore by the cleavage of a chloroalkane bond. Though QDs functionalized with a chloroalkane were able to bind free Halo protein, no specific binding to the Halo protein fused to cAR1 was observed.

Galloway, Justin F.

153

Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices  

NASA Astrophysics Data System (ADS)

Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage (˜2.2 V) .The EL peak intensity was found to increase by increasing the operating current.

Bera, Susnata; Singh, Shashi B.; Ray, S. K.

2012-05-01

154

Aqueous, Protein-Driven Synthesis of Transition Metal-Doped ZnS Immuno-Quantum Dots  

PubMed Central

The intentional introduction of transition metal impurities in semiconductor nanocrystals is an attractive approach for tuning quantum dot (QD) emission over a wide range of wavelengths. However, the development of effective doping strategies can be challenging, especially if one simultaneously requires a low toxicity crystalline core, a functional protein shell, and a “green”, single-step synthesis process. Here, we describe a simple and environmentally friendly route for the biofabrication of Cu-doped (blue-green) or Mn-doped (yellow-orange) ZnS nanocrystals surrounded by an antibody-binding protein shell. The ZnS:Mn hybrid particles obtained with this method exhibited a 60% enhancement in maximum photoluminescence intensity relative to undoped nanocrystals and have a hydrodynamic diameter inferior to 10 nm. They can be stored for months at 4°C, are stable over a physiological range of pH and salt concentrations, can be decorated with variable amounts of antibodies by direct mixing, and hold promise for biosensing and imaging applications.

Zhou, Weibin; Baneyx, Francois

2011-01-01

155

Synthesis of CdSe quantum dots using selenium dioxide as selenium source and its interaction with pepsin  

NASA Astrophysics Data System (ADS)

A novel method has been developed for the synthesis of thioglycolic acid (TGA)-capped CdSe quantum dots (QDs) in an aqueous medium when selenium dioxide worked as a selenium source and sodium borohydride acted as a reductant. The interaction between CdSe QDs and pepsin was investigated by fluorescence spectroscopy. It was proved that the fluorescence quenching of pepsin by CdSe QDs was mainly a result of the formation of CdSe-pepsin complex. Based on the fluorescence quenching results, the Stern-Volmer quenching constant ( Ksv), binding constant ( KA) and binding sites ( n) were calculated. According to the Foster's non-radiative energy transfer theory, the binding distance ( r) between pepsin and CdSe QDs was obtained. The influence of CdSe QDs on the conformation of pepsin has been analyzed by synchronous fluorescence spectra, which provided that the secondary structure of pepsin has been changed by the interaction of CdSe QDs with pepsin.

Wang, Yilin; Mo, Yunchuan; Zhou, Liya

2011-09-01

156

Synthesis of near-infrared-emitting CdTeSe and CdZnTeSe quantum dots.  

PubMed

We exploited the synthesis of near-infrared (NIR) emitting ternary-alloyed CdTeSe and quaternary-alloyed CdZnTeSe quantum dots (QDs) with rod and tetrapod morphologies, which have tunable emission in the NIR electromagnetic spectrum. The morphologies of the QDs depended strongly on their growth kinetics, probably due to the coordinating ligands used in the preparation. Using oleic acid, stearic acid and hexadecylamine as ligands and keeping the same reaction parameters, QDs with tetrapod and rod morphologies were created. Not only had the capping ligands influenced the morphologies of QDs, but also they influenced the optical properties of QDs. The molar ratios of Cd/Zn and Te/Se upon preparation were adjusted for investigating the effect of composition on the properties of resulting QDs. By varying the composition of QDs, the photoluminescence (PL) wavelength of QDs was tuned from 650 nm to 800 nm. To enhance PL efficiency and stability, QDs were coated with a CdZnS shell. As NIR PL has numerous advantages in biological imaging detection, these QDs hold great potential for application. PMID:23060275

Yang, Fanghong; Yang, Ping; Zhang, Lipeng

2013-01-01

157

Quantum-Dot Cellular Automata  

NASA Astrophysics Data System (ADS)

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

Snider, Gregory

2000-03-01

158

Quantum dot quantum cascade infrared photodetector  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

159

Self-assembly drives quantum dot photoluminescence.  

PubMed

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

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

2009-03-01

160

Clocked molecular quantum-dot cellular automata  

Microsoft Academic Search

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

Craig S. Lent; Beth Isaksen

2003-01-01

161

Inkjet printing of light emitting quantum dots  

Microsoft Academic Search

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

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

2009-01-01

162

Applications of quantum dots in cell biology  

Microsoft Academic Search

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

Margarida Barroso; Roshanak Mehdibeigi; Louise Brogan

2006-01-01

163

Lossless synthesis of graphene nanosheets decorated with tiny cadmium sulfide quantum dots with excellent nonlinear optical properties  

Microsoft Academic Search

The implantation and growth of metal nanoparticles on graphene nanosheets (GNS) leads directly to severe damage to the regular structure of the graphene sheets, which disrupts the extended pi conjugation, resulting in an impaired device performance. In this paper, we describe a facile approach for achieving the lossless formation of graphene composite decorated with tiny cadmium sulfide quantum dots (QDs)

Miao Feng; Ruiqing Sun; Hongbing Zhan; Yu Chen

2010-01-01

164

Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices  

SciTech Connect

Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage ({approx}2.2 V) .The EL peak intensity was found to increase by increasing the operating current. - Graphical abstract: Light emitting diode was fabricated using CdSe quantum dots using olive oil as the capping agent, instead of toxic phosphine. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting device shows strong electroluminescence in the range 630-661 nm. Highlights: Black-Right-Pointing-Pointer CdSe Quantum dots were synthesized using olive oil as the capping agent. Black-Right-Pointing-Pointer Light emitting device was fabricated using CdSe QDs/P3HT polymer heterojunction. Black-Right-Pointing-Pointer The I-V characteristics study showed low turn on voltage at {approx}2.2 V. Black-Right-Pointing-Pointer The EL peak intensity increases with increasing the operating current.

Bera, Susnata, E-mail: susnata.bera@gmail.com [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Singh, Shashi B. [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Ray, S.K., E-mail: physkr@phy.iitkgp.ernet.in [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India)

2012-05-15

165

Analytical model for quantum well to quantum dot tunneling  

Microsoft Academic Search

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

Raphaël Clerc; Gérard Ghibaudo; Georges Pananakakis

2003-01-01

166

Quantum Dot-Encoded Fluorescent Beads for Biodetection and Imaging  

Microsoft Academic Search

\\u000a The need to analyze increasingly large panels of biomolecules for biomedical research and clinical diagnostics has greatly\\u000a stimulated the development of high-throughput screening technologies based on quantum dots. Herein, we describe recent advances\\u000a in the synthesis of quantum-dot-encoded beads and control of their fluorescence signatures. Compared with commercial beads\\u000a based on organic fluorophores, they exhibit significant advantages in terms of

Jian Yang; Mark P. Sena; Xiaohu Gao

167

Influence of Mn²? concentration on Mn²?-doped ZnS quantum dot synthesis: evaluation of the structural and photoluminescent properties.  

PubMed

The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn(2+) (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn(2+)-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn(2+) and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions. PMID:23921811

Sotelo-Gonzalez, Emma; Roces, Laura; Garcia-Granda, Santiago; Fernandez-Arguelles, Maria T; Costa-Fernandez, Jose M; Sanz-Medel, Alfredo

2013-10-01

168

Modeling the Role of Ligands in Controlling the Sizes, Shapes and Supramolecular Ordering of Quantum Dots  

Microsoft Academic Search

The density of electronic states controls many physical properties of a quantum dot and can be tuned by altering the dot's size, shape, or composition. In colloidal methods, ligands are used to control quantum dot size, shape, and polydispersity; however, there exists no a-priori means of describing specific conditions that will optimize the synthesis procedure. We apply a mean field

Michael Tambasco; Sanat Kumar; Igal Szleifer

2007-01-01

169

Quantum optics in coupled quantum dots  

NASA Astrophysics Data System (ADS)

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

Garrido, Mauricio

170

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

171

Quantum Dots for Molecular Pathology  

PubMed Central

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

True, Lawrence D.; Gao, Xiaohu

2007-01-01

172

Biological applications of quantum dots  

Microsoft Academic Search

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

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

2007-01-01

173

Optically Controlled Quantum Dot Spins for Scaleable Quantum Computing.  

National Technical Information Service (NTIS)

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

D. G. Steel

2005-01-01

174

Quantum optics in coupled quantum dots  

Microsoft Academic Search

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

Mauricio Garrido

2010-01-01

175

Microstructure-controlled aerosol-gel synthesis of ZnO quantum dots dispersed in SiO2 nanospheres.  

PubMed

ZnO quantum dots dispersed in a silica matrix were synthesized from a TEOS:Zn(NO(3))(2) solution by a one-step aerosol-gel method. It was demonstrated that the molar concentration ratio of Zn to Si (Zn/Si) in the aqueous solution was an efficient parameter with which to control the size, the degree of agglomeration, and the microstructure of ZnO quantum dots (QDs) in the SiO(2) matrix. When Zn/Si ? 0.5, unaggregated quantum dots as small as 2 nm were distributed preferentially inside SiO(2) spheres. When Zn/Si ? 1.0, however, ZnO QDs of ?7 nm were agglomerated and reached the SiO(2) surface. When decreasing the ratio of the Zn/Si, a blue shift in the band gap of ZnO was observed from the UV/Visible absorption spectra, representing the quantum size effect. The photoluminescence emission spectra at room temperature denoted two wide peaks of deep-level defect-related emissions at 2.2-2.8 eV. When decreasing Zn/Si, the first peak at ?2.3 eV was blue-shifted in keeping with the decrease in the size of the QDs. Interestingly, the second visible peak at 2.8 eV disappeared in the surface-exposed ZnO QDs when Zn/Si ? 1.0. PMID:22221080

Firmansyah, Dudi Adi; Kim, Sang-Gyu; Lee, Kwang-Sung; Zahaf, Riyan; Kim, Yong Ho; Lee, Donggeun

2012-02-01

176

Optically controlled spins in semiconductor quantum dots  

Microsoft Academic Search

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

Sophia Economou

2010-01-01

177

Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots.  

PubMed

Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core-shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 degrees C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on the solubility of the metal salts used to form shells; their inclusion in the precursor solutions, which use thiourea as a sulfur source, can lead to homogeneous and fully dissolved solutions. Upon addition to suspensions of quantum dot cores, these precursors deposit as uniform shells; the lowest temperature for shell growth (65 degrees C) yields the thinnest shells (d < 1 nm) while the same process at higher temperatures (180 degrees C) forms thicker shells (d approximately 1-2 nm). The growth of the shell structures, average particle size, size distribution, and shape were examined using optical spectroscopy, transmission electron microscopy, x-ray diffraction, and transmittance small angle x-ray scattering. The photoluminescence quantum yield (QY) of the as-prepared CdSe/ZnS quantum dots ranged from 26% to 46% as compared to 10% for the CdSe cores. This method was further generalized to CdZnS shells by mixing cadmium and zinc acetate precursors. The CdSe/CdZnS nanocrystals have a thicker shell and higher QY (40% versus 36%) as compared to the CdSe/ZnS prepared under similar conditions. These low temperature methods for shell growth are readily amenable to scale-up and can provide a route for economical and less energy intensive production of quantum dots. PMID:20516578

Zhu, Huiguang; Prakash, Arjun; Benoit, Denise N; Jones, Christopher J; Colvin, Vicki L

2010-06-25

178

Optimization of microwave-assisted synthesis of high-quality ZnSe/ZnS core/shell quantum dots using response surface methodology  

NASA Astrophysics Data System (ADS)

ZnSe/ZnS core/shell quantum dots were synthesized in aqueous phase using glutathione (GSH) as stabilizer via microwave irradiation. Box-Behnken design (BBD) and response surface methodology (RSM) were adopted to optimize the synthesis condition for maximizing the photoluminescence quantum yield (PLQY). The QDs obtained at the optimal conditions without any post-treatment present excellent fluorescent properties with a high quantum yield up to 41% and narrow full-width at half-maximum (FWHM) (20-25 nm). The as-prepared QDs exhibited homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM). The core/shell structure was confirmed by X-ray photoelectron spectra (XPS) and powder X-ray diffraction (XRD). A further characterization of Fourier Transform Infrared Spectroscopy proved the binding of glutathione on the surface of QDs by thiol ligands.

Ma, Rong; Zhou, Pei-Jiang; Zhan, Hong-Ju; Chen, Chi; He, Yu-Ning

2013-03-01

179

Protein-directed synthesis of NIR-emitting, tunable HgS quantum dots and their applications in metal-ion sensing.  

PubMed

The development of luminescent mercury sulfide quantum dots (HgS QDs) through the bio-mineralization process has remained unexplored. Herein, a simple, two-step route for the synthesis of HgS quantum dots in bovine serum albumin (BSA) is reported. The QDs are characterized by UV-vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, luminescence, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), circular dichroism (CD), energy dispersive X-ray analysis (EDX), and picosecond-resolved optical spectroscopy. Formation of various sizes of QDs is observed by modifying the conditions suitably. The QDs also show tunable luminescence over the 680-800 nm spectral regions, with a quantum yield of 4-5%. The as-prepared QDs can serve as selective sensor materials for Hg(II) and Cu(II), based on selective luminescence quenching. The quenching mechanism is found to be based on Dexter energy transfer and photoinduced electron transfer for Hg(II) and Cu(II), respectively. The simple synthesis route of protein-capped HgS QDs would provide additional impetus to explore applications for these materials. PMID:22826036

Goswami, Nirmal; Giri, Anupam; Kar, Shantimoy; Bootharaju, Megalamane Siddaramappa; John, Robin; Xavier, Paulrajpillai Lourdu; Pradeep, Thalappil; Pal, Samir Kumar

2012-10-22

180

One step, microwave assisted green synthesis of biocompatible carbon quantum dots and their composites with [?-PW12O403-] for visible light photocatalysis  

NASA Astrophysics Data System (ADS)

We report a simple, rapid and green route for synthesis of fluorescent carbon quantum dots (CQDs) by microwave assisted pyrolysis method using polyleucine polymer (Boc-L-Leu-HEMA) as precursor and self-passivating agent. The as synthesized CQDs were found to possess low cytotoxicity, thus making them suitable candidates for bioimaging and bio-labelling. Moreover, nanocomposites of as prepared CQDs with [?-PW12O403-] polyoxometalate were synthesized and were shown to possess excellent photocatalytic properties under visible light towards degradation of organic dye pollutants. Based on the control experiments, a suitable mechanism has been proposed to explain the remarkable photoactivity of the CQD/[?-PW12O403-] composites.

Sahasrabudhe, Atharva; Pant, Shashank; Chatti, Manjunath; Maiti, Binoy; De, Priyadarsi; Roy, Soumyajit

2014-04-01

181

A tunable few electron triple quantum dot  

Microsoft Academic Search

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

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

2010-01-01

182

CdSe\\/ZnS core\\/shell quantum dots for bio-application  

Microsoft Academic Search

Quantum dots, with functional group on surfaces, can be attached to bio-molecules to form quantum-dots\\/bio-molecule complex. With their excellent photo-electronic properties, quantum dots are now widely used to label the bio-molecules and highlight a cell's nucleus and microtubule fibers. They may also be used to control and operate the bio-molecules. We investigate the synthesis of the CdSe\\/ZnS core- shell quantum

N. Dai; J. Chen

2006-01-01

183

Electron spins in quantum dots for spintronics and quantum computation  

Microsoft Academic Search

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

Hans-Andreas Engel; Patrik Recher; Daniel Loss

2001-01-01

184

Quantum computing with quantum-dot cellular automata  

Microsoft Academic Search

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

Géza Tóth; Craig S. Lent

2001-01-01

185

Synthesis of green CdSe\\/chitosan quantum dots using a polymer-assisted gamma-radiation route  

Microsoft Academic Search

Chitosan-coated CdSe quantum dots (CdSe\\/CS QDs) were successfully synthesized in aqueous system through a gamma-radiation route at room temperature under ambient pressure. The diameter of the resulting QDs was about 4 nm with narrow size distribution. The synthesized QDs exhibited an absorption peak at 460 nm and an emission peak at 535 nm. These QDs were cubic zinc blende CdSe

Bin Kang; Shu-Quan Chang; Yao-Dong Dai; Da Chen

2008-01-01

186

Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots  

Microsoft Academic Search

Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core-shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 °C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on

Huiguang Zhu; Arjun Prakash; Denise N. Benoit; Christopher J. Jones; Vicki L. Colvin

2010-01-01

187

Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots  

Microsoft Academic Search

Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core–shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 °C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on

Huiguang Zhu; Arjun Prakash; Denise N Benoit; Christopher J Jones; Vicki L Colvin

2010-01-01

188

Quantum optics with quantum dots in microcavities  

NASA Astrophysics Data System (ADS)

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

Rakher, Matthew T.

189

Synthesis and photoelectrochemical response of CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes  

PubMed Central

A continuous and compact CdS quantum dot-sensitive layer was synthesized on TiO2 nanorods by successive ionic layer adsorption and reaction (SILAR) and subsequent thermal annealing. The thickness of the CdS quantum dot layer was tuned by SILAR cycles, which was found to be closely related to light absorption and carrier transformation. The CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet–visible absorption spectroscopy, and photoelectrochemical property measurement. The optimum sample was fabricated by SILAR in 70 cycles and then annealed at 400°C for 1 h in air atmosphere. A TiO2/CdS core-shell structure was formed with a diameter of 35 nm, which presented an improvement in light harvesting. Finally, a saturated photocurrent of 3.6 mA/cm2 was produced under the irradiation of AM1.5G simulated sunlight at 100 mW/cm2. In particular, the saturated current density maintained a fixed value of approximately 3 mA/cm2 without decadence as time passed under the light conditions, indicating the steady photoelectronic property of the photoanode.

2013-01-01

190

Large scale synthesis of highly crystallized SnO2 quantum dots at room temperature and their high electrochemical performance  

NASA Astrophysics Data System (ADS)

In this work, SnO2 quantum dots with high crystallinity were synthesized on a large scale under mild reaction conditions via an epoxide precipitation route. The SnO intermediate, which was produced in the reactions between epoxide and [Sn(H2O)6]2+, was converted to SnO2 quantum dots by the oxidation of H2O2. It is believed that the protonation and the following ring opening of epoxide promoted the hydrolysis and condensation of [Sn(H2O)6]2+ to form the intermediate. The obtained quantum dots had a maximum specific capacitance of 204.4 F g-1 at a scan rate of 5 mV s-1 in 1 mol l-1 KOH aqueous solution. The electrochemical measurements proved that this high specific capacitance of SnO2 resulted from the Faradaic reactions between SnO2 and the electrolyte. This demonstrates for the first time that SnO2 can be used as a pseudocapacitive electrode material.

Cui, Hongtao; Liu, Yan; Ren, Wanzhong; Wang, Minmin; Zhao, Yunan

2013-08-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

192

Room temperature synthesis of PbSe quantum dots in aqueous solution: Stabilization by interactions with ligands  

PubMed Central

An aqueous route of synthesis is described for rapid synthesis of lead selenide quantum dots (PbSe QDs) at room temperature in an attempt to produce water-soluble and stable nanocrystals. Several thiol-ligands, including thioglycolic acid (TGA), thioglycerol (TGC), 3-mercaptopropionic acid (MPA), 2-mercaptoethyleamine hydrochloride (MEA), 6-mercaptohexanoic acid (MHA), and L-cysteine (L-cys), were used for capping/stabilization of PbSe QDs. The effects of the ligands on the stability of PbSe QDs were evaluated for a period of two months at room temperature under normal light conditions and at 4 °C in dark. The TGA- and MEA-capped QDs exhibited the highest stability prior to purification, almost two months when kept in dark at 4 °C. However, the stability of TGA-capped QDs was reduced substantially after purification to about 5 days under same conditions, while MEA-capped QDs did not show any significant instability. The stabilization energies of Pb-thiolate complexes determined by theoretical DFT simulations supported the experimental results. The PbSe QDs capped with TGA, MPA and MEA were successfully purified and re-dispersed in water, while those stabilized with TGC, MHA and L-cys aggregated during purification attempts. The purified PbSe QDs possess very susceptible surface resulting in poor stability for about 30 – 45 min after re-dispersion in water. In the presence of an excess of free ligand, the stability increased up to 5 days for TGA-capped QDs at pH 7.19, 9 –12 days for MPA-capped QDs at pH 7.3–7.5 and 45–47 days for MEA-capped QDs at pH 7.35. X-Ray Diffraction (XRD) results showed that the QDs possess a cubic rock salt structure with the most intense peaks located at 2? = 25.3° (200) and 2? = 29.2° (100). TEM images showed that the size of the QDs ranges between 5 and 10 nm. ICP-MS results revealed that Pb:Se ratio was 1.26, 1.28, 3.85, 1.18, and 1.31 for the QDs capped with TGA, MPA, MEA, L-Cys, and TGC, respectively. The proposed method is inexpensive, simple and utilizes environmentally friendly chemicals and solvents.

Primera-Pedrozo, Oliva M.; Arslan, Zikri; Rasulev, Bakhtiyor; Leszczynski, Jerzy

2011-01-01

193

Room temperature synthesis of PbSe quantum dots in aqueous solution: stabilization by interactions with ligands.  

PubMed

An aqueous route of synthesis is described for rapid synthesis of lead selenide quantum dots (PbSe QDs) at room temperature in an attempt to produce water-soluble and stable nanocrystals. Several thiol-ligands, including thioglycolic acid (TGA), thioglycerol (TGC), 3-mercaptopropionic acid (MPA), 2-mercaptoethylamine hydrochloride (MEA), 6-mercaptohexanoic acid (MHA), and l-cysteine (l-cys), were used for capping/stabilization of PbSe QDs. The effects of the ligands on the stability of PbSe QDs were evaluated for a period of two months at room temperature under normal light conditions and at 4 °C in the dark. The TGA- and MEA-capped QDs exhibited the highest stability prior to purification, almost two months when kept in the dark at 4 °C. However, the stability of TGA-capped QDs was reduced substantially after purification to about 5 days under the same conditions, while MEA-capped QDs did not show any significant instability. The stabilization energies of Pb-thiolate complexes determined by theoretical DFT simulations supported the experimental results. The PbSe QDs capped with TGA, MPA and MEA were successfully purified and re-dispersed in water, while those stabilized with TGC, MHA and l-cys aggregated during purification attempts. The purified PbSe QDs possess very susceptible surface resulting in poor stability for about 30-45 min after re-dispersion in water. In the presence of an excess of free ligand, the stability increased up to 5 days for TGA-capped QDs at pH 7.19, 9-12 days for MPA-capped QDs at pH 7.3-7.5 and 45-47 days for MEA-capped QDs at pH 7.35. X-Ray diffraction (XRD) results showed that the QDs possess a cubic rock salt structure with the most intense peaks located at 2? = 25.3° (200) and 2? = 29.2° (100). TEM images showed that the size of the QDs ranges between 5 and 10 nm. ICP-MS results revealed that Pb?:?Se ratios were 1.26, 1.28, 3.85, 1.18, and 1.31 for the QDs capped with TGA, MPA, MEA, l-cys, and TGC, respectively. The proposed method is inexpensive, simple and utilizes environmentally friendly chemicals and solvents. PMID:22273747

Primera-Pedrozo, Oliva M; Arslan, Zikri; Rasulev, Bakhtiyor; Leszczynski, Jerzy

2012-02-21

194

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

Microsoft Academic Search

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

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

2008-01-01

195

Stark effect in parabolic quantum dot  

Microsoft Academic Search

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

S. JAZIRI; G. BASTARD; R. BENNACEUR

1993-01-01

196

Quantum Entanglement and Teleportation in a Vertical Quantum Dot  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

197

Hybrid passivated colloidal quantum dot solids  

NASA Astrophysics Data System (ADS)

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 electron-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.

Ip, Alexander H.; Thon, Susanna M.; Hoogland, Sjoerd; Voznyy, Oleksandr; Zhitomirsky, David; Debnath, Ratan; Levina, Larissa; Rollny, Lisa R.; Carey, Graham H.; Fischer, Armin; Kemp, Kyle W.; Kramer, Illan J.; Ning, Zhijun; Labelle, André J.; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H.

2012-09-01

198

Hybrid passivated colloidal quantum dot solids.  

PubMed

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 electron-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. PMID:22842552

Ip, Alexander H; Thon, Susanna M; Hoogland, Sjoerd; Voznyy, Oleksandr; Zhitomirsky, David; Debnath, Ratan; Levina, Larissa; Rollny, Lisa R; Carey, Graham H; Fischer, Armin; Kemp, Kyle W; Kramer, Illan J; Ning, Zhijun; Labelle, André J; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H

2012-09-01

199

Facile synthesis and characterization of water soluble ZnSe/ZnS quantum dots for cellar imaging  

NASA Astrophysics Data System (ADS)

Strong fluorescence and low cytotoxicity ZnSe/ZnS quantum dots (QDs) were synthesized by a facile aqueous phase route. It overcame the defects such as instability and low quantum yield of the quantum dots synthesized by early aqueous phase route. L-Glutathione (GSH) and 3-mercaptopropaonic acid (MPA) were used as mixture stabilizers to synthesize high quality ZnSe/ZnS QDs. The samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS) and their optical properties were investigated by using UV-vis spectrophotometer, fluorescence spectrophotometer (FL), IR spectrophotometer and confocal laser scanning microscope. The synthesized ZnSe/ZnS QDs illuminated blue fluorescence under ultraviolet lamp. Its water-soluble property is excellent and the fluorescence intensity of ZnSe/ZnS QDs almost did not change after 4 months at room temperature. The average diameter of ZnSe/ZnS nanocrystals is about 3 nm and quantum yield (QY) could reach to 70.6% after repeat determination. Low cytotoxicity was ensured by investigated SCG7901 and RAW264.7 cells. In comparison with cadmium based nanocrystals, ZnSe/ZnS QDs posed low cytotoxicity. The cells viability remained 96.7% when the QDs concentration was increased to 10 ?mol/L. The results in vitro indicate that ZnSe/ZnS QDs-based probes have good stability, low toxicity and biocompatibility for fluorescence imaging in cancer model system.

Shu, Chang; Huang, Bin; Chen, Xiangdong; Wang, Yan; Li, Xuequan; Ding, Li; Zhong, Wenying

2013-03-01

200

Quantum dot nanophotonics - from waveguiding to integration  

Microsoft Academic Search

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

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

2009-01-01

201

Renal clearance of quantum dots.  

PubMed

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

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

2007-10-01

202

Lifetime blinking in nonblinking nanocrystal quantum dots  

PubMed Central

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

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

2012-01-01

203

Electron counting in quantum dots  

Microsoft Academic Search

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

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

2009-01-01

204

High-Performance Quantum-Dot Solids via Elemental Sulfur Synthesis.  

PubMed

An elemental-sulfur-based synthesis is reported, which, combined with processing to improve the size dispersion and passivation, results in a low-cost high-quality platform for small-bandgap PbS-CQD-based devices. Size-selective precipitation and cadmium chloride passivation are used to improve the power conversion efficiency of 1 eV bandgap CQD photovoltaic devices dramatically, which leads to record power conversion efficiency for a 1 eV PbS CQD solar cell of 5.4%. PMID:24659303

Yuan, Mingjian; Kemp, Kyle W; Thon, Susanna M; Kim, Jin Young; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H

2014-06-01

205

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

206

Quantum Logic Using Excitonic Quantum Dots in External Optical Microcavities.  

National Technical Information Service (NTIS)

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

M. G. Raymer

2003-01-01

207

Influence of Mn2+ concentration on Mn2+-doped ZnS quantum dot synthesis: evaluation of the structural and photoluminescent properties  

NASA Astrophysics Data System (ADS)

The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn2+ (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn2+-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn2+ and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions.The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn2+ (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn2+-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn2+ and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions. Electronic supplementary information (ESI) available: Rietveld refinement parameters and plot for each sample are summarized in Fig. S1-S4 and Table S1. See DOI: 10.1039/c3nr02422a

Sotelo-Gonzalez, Emma; Roces, Laura; Garcia-Granda, Santiago; Fernandez-Arguelles, Maria T.; Costa-Fernandez, Jose M.; Sanz-Medel, Alfredo

2013-09-01

208

Aqueous Cadmium Chalcogenide Quantum Dots: Synthesis, Characterization, Spectroscopic Investigation of Electron Transfer Properties and Photovoltaic Device Performance  

NASA Astrophysics Data System (ADS)

The research presented in this thesis will focus on (1) synthesis and characterization of aqueous CdSe quantum dots (QDs) as alternatives to organic QDs; (2) the roles that linkers and capping groups play on the physical and optical properties of aqueous QDs; (3) performance of QD-sensitized solar cells (QDSSC) incorporating magic-sized clusters (MSCs) vs regular QDs (RQDs) and as a function of the molecular linkers between QDs and TiO2; and (4) the effect of the polysulfide electrolyte on QD-functionalized TiO 2 films and their performance in QDSSCs. The use of QDs as light harvesters has grown over the last few decades due to their unique properties. Water-dispersible QDs are of increasing interest because their syntheses are straightforward, environmentally-benign and more cost-effective. CdSe and CdS QDs were synthesized at room temperature under ambient conditions, by combining a Cd precursor and either Na2SeSO3 (for CdSe) or Na2S2O3 (for CdS), in basic aqueous reaction mixtures. Three different ligands were utilized as capping groups (cysteinate (Cys), mercaptopropionate (MP), and mercaptosuccinate (MS)). Changing the capping-agent, the reagent concentrations and the temperature changed the photophysical properties of the QDs. When Cys was used as the capping-agent, MSCs were formed. When high concentrations of Cys were used or when the reaction mixture was heated, RQDs were formed. When MP and MS were used in the synthesis of CdSe, RQDs were formed. In the synthesis of CdS, MS caused the formation of RQDs, and MP caused formation of a mixture of RQDs and MSCs. Transient absorption spectroscopy and photoelectrochemical experiments were performed to understand the influence of capping-agent and electronic properties (MSCs vs. RQDs) on the efficiency of electron transfer from photoexcited QDs to TiO2. The Cys-CdSe-functionalized TiO2 exhibited more efficient electron injection and/or slower recombination, leading to improved efficiency of QDSSCs. Devices made with Cys-CdSe RQDs exhibited higher efficiencies than QDSSCs with Cys-CdSe MSCs, indicating that the presence of Cys induces greater efficiency in QDSSCs. For QDSSCs, a polysulfide electrolyte is commonly used instead of I-/I3-. Effects of the polysulfide electrolyte and Na2S on CdSe-functionalized TiO2 films were explored to elucidate the chemistry that occurs when CdSe is exposed to the electrolyte in the QDSSCs. Photophysical changes to the CdSe-functionalized films occurred when exposed to the polysulfide electrolyte. Upon immersion of CdSe-functionalized TiO¬2 films into solutions of Na2S, an initial red shift in the absorption spectrum was observed, followed by a decrease and blue shift of the band. Based on XPS analysis of the films, it was determined that the S within the electrolyte (1) replaced Se or (2) bound to the CdSe-functionalized film without replacing Se. Photoelectrochemical measurements were acquired to analyze device performance with varying [S] within the electrolyte. Upon increase of S, the efficiency of the device increased and gave rise to a better fill factor in the photocurrent-photovoltage data collected.

Coughlin, Kathleen M.

209

Electron counting in quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

210

Facile ultrasonic synthesis of CoO quantum dot/graphene nanosheet composites with high lithium storage capacity.  

PubMed

In this paper, we report a facile ultrasonic method to synthesize well-dispersed CoO quantum dots (3-8 nm) on graphene nanosheets at room temperature by employing Co(4)(CO)(12) as cobalt precursor. The prepared CoO/graphene composites displayed high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity (1592 mAh g(-1) after 50 cycles), high Coulombic efficiency (over 95%), excellent cycling stability, and high rate capability (1008 mAh g(-1) with a total retention of 77.6% after 50 cycles at a current density of 1000 mA g(-1), dramatically increased from the initial 50 mA g(-1)). The extraordinary performance arises from the structure advantages of the composites: the nanosized CoO quantum dots with high dispersity on conductive graphene substrates supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions, which are beneficial for high capacity and rate capability. Meanwhile, the isolated CoO quantum dots anchored tightly on the graphene nanosheets can effectively circumvent the volume expansion/contraction associated with lithium insertion/extraction during discharge/charge processes, which is good for high capacity as well as cycling stability. Moreover, regarding the anomalous behavior of capacity increase with cycles (activation effect) observed, we proposed a tentative hypothesis stressing the competition between the conductivity increase and the amorphorization of the composite electrodes during cycling in determining the trends of the capacity, in the hope to gain a fuller understanding of the inner working of the novel nanostructured electrode-based lithium-ion batteries. PMID:22224549

Peng, Chengxin; Chen, Bingdi; Qin, Yao; Yang, Shihe; Li, Chunzhong; Zuo, Yuanhui; Liu, Siyang; Yang, Jinhu

2012-02-28

211

One-Step Instant Synthesis of Protein-Conjugated Quantum Dots at Room Temperature  

PubMed Central

We present a new general facile strategy for the preparation of protein-functionalized QDs in a single step at ambient conditions. We demonstrated that highly luminescent red to near-infrared (NIR) protein-functionalized QDs could be synthesized at room temperature in one second through a one-pot reaction that proceeds in aqueous solution. Herein protein-functionalized QDs were successfully constructed for a variety of proteins with a wide range of molecular weights and isoelectric points. The as-prepared protein-conjugated QDs exhibited high quantum yield, high photostabiliy and colloidal stability, and high functionalization efficiency. Importantly, the proteins attached to the QDs maintain their biological activities and are capable of catalyzing reactions and biotargeting. In particular, the as-prepared transferrin-QDs could be used to label cancer cells with high specificity. Moreover, we demonstrated that this synthetic strategy could be extended to prepare QDs functionalized with folic acids and peptides, which were also successfully applied to cancer cell imaging.

He, Xuewen; Gao, Li; Ma, Nan

2013-01-01

212

Raman-Controlled Quantum Dots for Quantum Computing.  

National Technical Information Service (NTIS)

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

L. J. Sham

2005-01-01

213

Synthesis and characterizations of ultra-small ZnS and Zn (1? x) Fe x S quantum dots in aqueous media and spectroscopic study of their interactions with bovine serum albumin  

Microsoft Academic Search

This work reports a new experimental methodology for the synthesis of ultra small zinc sulfide and iron doped zinc sulfide quantum dots in aqueous media. The nanoparticles were obtained using a simple procedure based on the precipitation of ZnS in aqueous solution in the presence of 2-mercaptoethanol as a capping agent, at room temperature. The effect of Fe3+ ion concentration

Omid Khani; Hamid Reza Rajabi; Mohammad Hasan Yousefi; Ali Azam Khosravi; Mohammad Jannesari; Mojtaba Shamsipur

2011-01-01

214

Stress Relaxation Phenomena in Buried Quantum Dots  

Microsoft Academic Search

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

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

215

Image simulations of quantum dots.  

SciTech Connect

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

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

2001-01-01

216

Large quantum dots with small oscillator strength  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

217

Semiconductor Quantum Dots for Biomedicial Applications  

PubMed Central

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

Shao, Lijia; Gao, Yanfang; Yan, Feng

2011-01-01

218

Quantum dots in biology and medicine  

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

219

Colloidal quantum dot photovoltaics: a path forward.  

PubMed

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. PMID:21967723

Kramer, Illan J; Sargent, Edward H

2011-11-22

220

CuInS2 quantum dot-sensitized TiO2 nanorod array photoelectrodes: synthesis and performance optimization  

NASA Astrophysics Data System (ADS)

CuInS2 quantum dots (QDs) were deposited onto TiO2 nanorod arrays for different cycles by using successive ionic layer adsorption and reaction (SILAR) method. The effect of SILAR cycles on the light absorption and photoelectrochemical properties of the sensitized photoelectrodes was studied. With optimization of CuInS2 SILAR cycles and introduction of In2S3 buffer layer, quantum dot-sensitized solar cells assembled with 3-?m thick TiO2 nanorod film exhibited a short-circuit current density ( I sc) of 4.51 mA cm-2, an open-circuit voltage ( V oc) of 0.56 V, a fill factor (FF) of 0.41, and a power conversion efficiency ( ?) of 1.06%, respectively. This study indicates that SILAR process is a very promising strategy for preparing directly anchored semiconductor QDs on TiO2 nanorod surface in a straightforward but controllable way without any complicated fabrication procedures and introduction of a linker molecule.

Zhou, Zhengji; Yuan, Shengjie; Fan, Junqi; Hou, Zeliang; Zhou, Wenhui; Du, Zuliang; Wu, Sixin

2012-11-01

221

CuInS2 quantum dot-sensitized TiO2 nanorod array photoelectrodes: synthesis and performance optimization.  

PubMed

CuInS2 quantum dots (QDs) were deposited onto TiO2 nanorod arrays for different cycles by using successive ionic layer adsorption and reaction (SILAR) method. The effect of SILAR cycles on the light absorption and photoelectrochemical properties of the sensitized photoelectrodes was studied. With optimization of CuInS2 SILAR cycles and introduction of In2S3 buffer layer, quantum dot-sensitized solar cells assembled with 3-?m thick TiO2 nanorod film exhibited a short-circuit current density (Isc) of 4.51 mA cm-2, an open-circuit voltage (Voc) of 0.56 V, a fill factor (FF) of 0.41, and a power conversion efficiency (?) of 1.06%, respectively. This study indicates that SILAR process is a very promising strategy for preparing directly anchored semiconductor QDs on TiO2 nanorod surface in a straightforward but controllable way without any complicated fabrication procedures and introduction of a linker molecule. PMID:23181940

Zhou, Zhengji; Yuan, Shengjie; Fan, Junqi; Hou, Zeliang; Zhou, Wenhui; Du, Zuliang; Wu, Sixin

2012-01-01

222

A quantum dot in topological insulator nanofilm.  

PubMed

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

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

2014-03-19

223

Synthesis of cadmium telluride quantum wires and the similarity of their band gaps to those of equidiameter cadmium telluride quantum dots  

SciTech Connect

High-quality colloidal CdTe quantum wires having purposefully controlled diameters in the range of 5-11 nm are grown by the solution-liquid-solid (SLS) method, using Bi-nanoparticle catalysts, cadmium octadecylphosphonate and trioctylphosphine telluride as precursors, and a TOPO solvent. The wires adopt the wurtzite structure, and grow along the [002] direction (parallel to the c axis). The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to the experimental results for high-quality CdTe quantum dots. In contrast to the predictions of an effective-mass approximation, particle-in-a-box model, and previous experimental results from CdSe and InP dot-wire comparisons, the band gaps of CdTe dots and wires of like diameter are found to be experimentally indistinguishable. The present results are analyzed using density functional theory under the local-density approximation by implementing a charge-patching method. The higher-level theoretical analysis finds the general existence of a threshold diameter, above which dot and wire band gaps converge. The origin and magnitude of this threshold diameter is discussed.

Wang, Lin-Wang; Sun, Jianwei; Wang, Lin-Wang; Buhro, William E.

2008-07-11

224

Silicon quantum dots: surface matters.  

PubMed

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

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

2014-04-30

225

Silicon quantum dots: surface matters  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

226

Magneto Electronics with Quantum Dots  

NASA Astrophysics Data System (ADS)

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

Datta, Subhadeep

2013-03-01

227

Quantum dot photonic crystal detectors  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

228

Nonlinear Optical Properties of Quantum Dot Composites  

Microsoft Academic Search

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

Anthony Kolodzinski

2010-01-01

229

Intraband transitions in colloidal quantum dots  

Microsoft Academic Search

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

Philippe Guyot-Sionnest; Congjun Wang

2002-01-01

230

Theory of random population for quantum dots  

Microsoft Academic Search

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

M. Grundmann; D. Bimberg

1997-01-01

231

Molecular quantum-dot cellular automata  

Microsoft Academic Search

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

Beth Isaksen; Craig S. Lent

2003-01-01

232

Thick-shell nanocrystal quantum dots  

DOEpatents

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

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

2011-05-03

233

Charging colloidal quantum dots by electrochemistry  

Microsoft Academic Search

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

Philippe Guyot-Sionnest

2008-01-01

234

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

Microsoft Academic Search

Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine

X. Michalet; F. F. Pinaud; L. A. Bentolila; J. M. Tsay; S. Doose; J. J. Li; G. Sundaresan; A. M. Wu; S. S. Gambhir; S. Weiss

2005-01-01

235

Stable functionalized PEGylated quantum dots micelles with a controlled stoichiometry.  

PubMed

Here we report the synthesis of monofunctional PEGylated amide ligands that were used to prepare bioactivable quantum dots of a 20 nm diameter with a controlled mean number of the covalently grafted ligands. They are stable in aqueous medium of high salinity including a large pH domain. PMID:21103558

Amela-Cortes, Marian; Roullier, Victor; Wolpert, Cécile; Neubauer, Stefanie; Kessler, Horst; Bedel, Olivier; Mignani, Serge; Marchi-Artzner, Valérie

2011-01-28

236

Ultranarrow Luminescence Lines from Single Quantum Dots  

Microsoft Academic Search

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

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

1995-01-01

237

Polymer-coated quantum dots.  

PubMed

Quantum Dots (QDs) are semiconductor nanocrystals with distinct photophysical properties finding applications in biology, biosensing, and optoelectronics. Polymeric coatings of QDs are used primarily to provide long-term colloidal stability to QDs dispersed in solutions and also as a source of additional functional groups used in further chemical derivatization of the nanoparticles. We review the coating methods, including multidentate and amphiphilic polymeric coatings, and grafting-to and grafting-from approaches. We highlight the most commonly used polymers and discuss how their chemical structure influences the coating properties. PMID:24136705

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

2013-12-21

238

DNA-based programing of quantum dot properties.  

PubMed

Nucleic acid molecules can serve as robust ligands for aqueous synthesis of semiconductor nanocrystals or quantum dots (QDs). QD properties including size, morphology, dispersity, emission maximum, and quantum yield are highly dependent on the sequences and structures of nucleic acids used for the synthesis. This synthetic strategy provides a novel facile means of constructing compact, stable, and biofunctionalized QDs in one step, which is of particular interest for a variety of applications such as biosensing, bioimaging, and self-assembly. This article summarizes recent advances in nucleic acid-templated QD synthesis with an emphasis on the nucleic acids-based programing of quantum dots properties. A variety of applications based on DNA-passivated QDs are also discussed. PMID:22965762

Ma, Nan; Kelley, Shana O

2013-01-01

239

Biocompatible Quantum Dots for Biological Applications  

SciTech Connect

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

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

2011-01-01

240

Quantum dot - polymer nanocomposites: New materials for dispersion, encapsulation, and electronic applications  

Microsoft Academic Search

Tremendous advances in the synthesis and functionalization of nanoparticles over the past twenty years have resulted in remarkable discoveries in the field of nanotechnology. One such development is found in quantum dots, semiconductor nanoparticles that exhibit unique optical and electronic properties not found in the bulk. Research efforts associated with the combination of quantum dots and polymers center on uniting

Kevin N. Sill

2006-01-01

241

Nanometer Distance Measurements Between Multicolor Quantum Dots  

PubMed Central

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

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

2009-01-01

242

Quantum dots as luminescent probes in biological systems  

Microsoft Academic Search

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

Andrew J Sutherland

2002-01-01

243

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

Microsoft Academic Search

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

Richard J. Warburton

244

Quantum dot loaded immunomicelles for tumor imaging  

Microsoft Academic Search

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

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

2010-01-01

245

Realization of quantum-dot cellular automata using semiconductor quantum dots  

Microsoft Academic Search

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

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

2003-01-01

246

Semiconductor Fluorescent Quantum Dots: Efficient Biolabels in Cancer Diagnostics  

NASA Astrophysics Data System (ADS)

We present and discuss results and features related to the synthesis of water-soluble semiconductor quantum dots and their application as fluorescent biomarkers in cancer diagnostics. We have prepared and applied different core-shell quantum dots, such as cadmium telluride-cadmium sulfide, CdTe-CdS, and cadmium sulfide-cadmium hydroxide, CdS/Cd(OH)2, in living healthy and neoplastic cells and tissues samples. The CdS/Cd(OH)2 quantum dots presented the best results, maintaining high levels of luminescence as well as high photostability in cells and tissues. Labeled tissues and cells were analyzed by their resulting fluorescence, via conventional fluorescence microscopy or via laser scanning confocal microscopy. The procedure presented in this work was shown to be efficient as a potential tool for fast and precise cancer diagnostics.

Farias, Patricia M. A.; Santos, Beate S.; Fontes, Adriana

247

Quantum dots with single-atom precision.  

PubMed

Quantum dots are often called artificial atoms because, like real atoms, they confine electrons to quantized states with discrete energies. However, although real atoms are identical, most quantum dots comprise hundreds or thousands of atoms, with inevitable variations in size and shape and, consequently, unavoidable variability in their wavefunctions and energies. Electrostatic gates can be used to mitigate these variations by adjusting the electron energy levels, but the more ambitious goal of creating quantum dots with intrinsically digital fidelity by eliminating statistical variations in their size, shape and arrangement remains elusive. We used a scanning tunnelling microscope to create quantum dots with identical, deterministic sizes. By using the lattice of a reconstructed semiconductor surface to fix the position of each atom, we controlled the shape and location of the dots with effectively zero error. This allowed us to construct quantum dot molecules whose coupling has no intrinsic variation but could nonetheless be tuned with arbitrary precision over a wide range. Digital fidelity opens the door to quantum dot architectures free of intrinsic broadening-an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies of confined electrons. PMID:24974937

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

2014-07-01

248

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

National Technical Information Service (NTIS)

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

A. Harju

1999-01-01

249

On-chip quantum optics with quantum dot microcavities.  

PubMed

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

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

2013-02-01

250

Solvothermal synthesis of InP quantum dots and their enhanced luminescent efficiency by post-synthetic treatments.  

PubMed

InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH(3))(2))(3) instead of highly toxic P(TMS)(3) widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)(3). Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure. PMID:21194707

Byun, Ho-June; Lee, Ju Chul; Yang, Heesun

2011-03-01

251

Amplification Without Inversion in Semiconductor Quantum Dot  

NASA Astrophysics Data System (ADS)

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

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

252

Inkjet printing of light emitting quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

253

Fluorescent Quantum Dots for Biological Labeling  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

254

Magneto-Absorption in Ellipsoidal Quantum Dot  

NASA Astrophysics Data System (ADS)

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

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

255

CNT Quantum dots as Terahertz detectors  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

256

Single to quadruple quantum dots with tunable tunnel couplings  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

257

Transient nonlinear spectroscopy of single quantum dots  

Microsoft Academic Search

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

Todd Harry Stievater

2001-01-01

258

Purification of functionalized quantum dots.  

PubMed

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

Courty, Sébastien; Dahan, Maxime

2013-10-01

259

Comparison of quantum confinement effects between quantum wires and dots  

SciTech Connect

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

Li, Jingbo; Wang, Lin-Wang

2004-03-30

260

Spatio-temporal fluctuations and disorder in quantum dot lasers  

Microsoft Academic Search

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

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

2004-01-01

261

Quantum Dots-in-a-Well Focal Plane Arrays  

Microsoft Academic Search

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

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

2008-01-01

262

Electric field control of exciton states in quantum dot molecules  

Microsoft Academic Search

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

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

2004-01-01

263

Short-wave infrared colloidal quantum dot photodetectors on silicon  

NASA Astrophysics Data System (ADS)

In this paper, two kinds of colloidal quantum dots, PbS and HgTe, are explored for SWIR photodetectors application. The colloidal dots are prepared by hot injection chemical synthesis, with organic ligands around the dots keeping them stable in solution. For the purpose of achieving efficient carrier transport between the dots in a film, these long organic ligands are replaced by shorter, inorganic ligands. We report uniform, ultra-smooth colloidal QD films without cracks realized by dip-coating and corresponding ligand exchange on a silicon substrate. Metal-free inorganic ligands, such as OH- and S2-, are investigated to facilitate the charge carrier transport in the film. Both PbS and HgTe-based quantum dot photoconductors were fabricated on interdigitated gold electrodes. For PbS-based detectors a responsivity of 200A/W is measured at 1.5?m, due to the large internal photoconductive gain. A 2.2?m cut-off wavelength for PbS photodetectors and 2.8?m for HgTe quantum dot photodetectors are obtained.

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

2013-01-01

264

Optical Signatures of Coupled Quantum Dots  

Microsoft Academic Search

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

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

2006-01-01

265

Eco-friendly synthesis of size-controllable amine-functionalized graphene quantum dots with antimycoplasma properties  

NASA Astrophysics Data System (ADS)

Size-controllable amine-functionalized graphene quantum dots (GQDs) are prepared by an eco-friendly method with graphene oxide sheets, ammonia and hydrogen peroxide as starting materials. Using a Sephadex G-25 gel column for fine separation, for the first time we obtain GQDs with either single or double layers. By atomic force microscopy characterization, we confirm that hydrogen peroxide and ammonia play a synergistic role on graphene oxide (GO), in which the former cuts the GO into small pieces and the latter passivates the active surface to give amine-modified GQDs. Due to the low cytotoxicity and excellent biocompatibility of the obtained amine-functionalized GQDs, besides the multiwavelength imaging properties of GQDs, for the first time we find that this kind of GQD exhibits good antimycoplasma properties. Given the superior antimycoplasma effect of the GQDs and their eco-friendly mass production with low cost, these new GQDs may offer opportunities for the development of new antimycoplasma agents, thus extending their widespread application in biomedicine.Size-controllable amine-functionalized graphene quantum dots (GQDs) are prepared by an eco-friendly method with graphene oxide sheets, ammonia and hydrogen peroxide as starting materials. Using a Sephadex G-25 gel column for fine separation, for the first time we obtain GQDs with either single or double layers. By atomic force microscopy characterization, we confirm that hydrogen peroxide and ammonia play a synergistic role on graphene oxide (GO), in which the former cuts the GO into small pieces and the latter passivates the active surface to give amine-modified GQDs. Due to the low cytotoxicity and excellent biocompatibility of the obtained amine-functionalized GQDs, besides the multiwavelength imaging properties of GQDs, for the first time we find that this kind of GQD exhibits good antimycoplasma properties. Given the superior antimycoplasma effect of the GQDs and their eco-friendly mass production with low cost, these new GQDs may offer opportunities for the development of new antimycoplasma agents, thus extending their widespread application in biomedicine. Electronic supplementary information (ESI) available: Experimental details and additional characterization data. See DOI: 10.1039/c2nr33191h

Jiang, Feng; Chen, Daiqin; Li, Ruimin; Wang, Yucheng; Zhang, Guoqiang; Li, Shumu; Zheng, Junpeng; Huang, Naiyan; Gu, Ying; Wang, Chunru; Shu, Chunying

2013-01-01

266

Final Report, Quantum Dot Light Emitting Diode.  

National Technical Information Service (NTIS)

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

K. Kahen R. Egidi

2012-01-01

267

Towards registered single quantum dot photonic devices  

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

268

Towards registered single quantum dot photonic devices.  

PubMed

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

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

2008-11-12

269

Quantum Dots and the Harkess Method  

NSDL National Science Digital Library

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

Vu Bioengineering Ret Program

270

Nanomaterials: Earthworms lit with quantum dots  

NASA Astrophysics Data System (ADS)

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

Tilley, Richard D.; Cheong, Soshan

2013-01-01

271

Carbon Nanotube Quantum Dots as THz Detectors.  

National Technical Information Service (NTIS)

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

P. Barbara

2012-01-01

272

Wavelength agile superlattice quantum dot infrared photodetector  

Microsoft Academic Search

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

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

2009-01-01

273

Semiconductor clusters nanocrystals, and quantum dots  

Microsoft Academic Search

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

A. P. Alivisatos

1996-01-01

274

Integrated photonics using colloidal quantum dots  

Microsoft Academic Search

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

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

2009-01-01

275

Photon-Assisted Tunneling in Quantum Dots  

Microsoft Academic Search

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

Enrico Prati; Rossella Latempa; Marco Fanciulli

2009-01-01

276

Submonolayer Quantum Dot Infrared Photodetector  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

277

Positioning of quantum dots on metallic nanostructures.  

PubMed

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

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

2010-04-01

278

Quantum dots and spin qubits in graphene.  

PubMed

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

Recher, Patrik; Trauzettel, Björn

2010-07-30

279

Synthesis and Optical Properties of Thiol Functionalized CdSe/ZnS (Core/Shell) Quantum Dots by Ligand Exchange  

SciTech Connect

The colloidal photoluminescent quantum dots (QDs) of CdSe (core) and CdSe/ZnS (core/shell) were synthesized at different temperatures with different growth periods. The optical properties (i.e., UV/Vis spectra and photoluminescent emission spectra) of the resulting QDs were investigated. The CdSe/ZnS QDs exhibited higher photoluminescent (PL) efficiency and stability than their corresponding CdSe core QDs. Ligand exchange with various thiol molecules was performed to replace the initial surface passivation ligands, that is, trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), and the optical properties of the surface-modified QDs were studied. The thiol ligand molecules used included 1,4-benzenedimethanethiol, 1,16-hexadecanedithiol, 1,11-undecanedithiol, 11-mercapto-1-undecanol, and 1,8 octanedithiol. After the thiol functionalization, the CdSe/ZnS QDs exhibited significantly enhanced PL efficiency and storage stability. Besides surface passivation effect, such enhanced performance of thiol-functionalized QDs could be due to self-assembly formation of dimer/trimer clusters, in which QDs are linked by dithiol molecules. Effects of ligand concentration, type of ligand, and heating on the thiol stabilization of QDs were also discussed.

Zhu, Huaping [ORNL] [ORNL; Hu, Michael Z. [ORNL] [ORNL; Shao, Lei [ORNL] [ORNL; Yu, Kui [SIMS, NRC of Canada] [SIMS, NRC of Canada; Dabestani, Reza T [ORNL] [ORNL; Zaman, Md. Badruz [SIMS, NRC of Canada] [SIMS, NRC of Canada; Liao, Dr. Shijun [South China University of Technology, Guangzhou, PR China] [South China University of Technology, Guangzhou, PR China

2014-01-01

280

Bioinspired, direct synthesis of aqueous CdSe quantum dots for high-sensitive copper(II) ion detection.  

PubMed

Luminescent CdSe semiconductor quantum dots (QDs), which are coated with a denatured bovine serum albumin (dBSA) shell, have been directly synthesized via a bioinspired approach. The dBSA coated CdSe QDs are ultrasmall (d < 2.0 nm) with a narrow size distribution and exhibit a strong green fluorescent emission at about 525 nm. They can be stored for months at room temperature and possess excellent stability against ultraviolet irradiation, high salt concentration, and a wide physiological range of pH. Systematic experimental investigations have shown the contribution of dBSA with free cysteine residues for both their effective ion chelating and surface passivating interactions during the formation and stabilization of CdSe QDs. The luminescent QDs are used for copper(II) ion detection due to their highly sensitive and selective fluorescence quenching response to Cu(2+). The concentration dependence of the quenching effect can be best described by the typical Stern-Volmer equation in a linearly proportional concentration of Cu(2+) ranging from 10 nM to 7.5 ?M with a detection limit of 5 nM. As confirmed by various characterization results, a possible quenching mechanism is given: Cu(2+) ions are first reduced to Cu(+) by the dBSA shell and then chemical displacement between Cu(+) and Cd(2+) is performed at the surface of the ultrasmall metallic core to impact the fluorescence performance. PMID:24013872

Bu, Xiaohai; Zhou, Yuming; He, Man; Chen, Zhenjie; Zhang, Tao

2013-11-21

281

Synthesis of water-dispersible zinc oxide quantum dots with antibacterial activity and low cytotoxicity for cell labeling.  

PubMed

Typical photoluminescent semiconductor nanoparticles, called quantum dots (QDs), have potential applications in biological labeling. When used to label stem cells, QDs may impair the differentiation capacity of the stem cells. In this study, we synthesized zinc oxide (ZnO) QDs in methanol with an average size of ?2 nm. We then employed two different types of polyethylene glycol (PEG) molecules (SH-PEG-NH2 and NH2-PEG-NH2) to conjugate ZnO QDs and made them water-dispersible. Fourier transform infrared spectroscopy spectra indicated the attachment of PEG molecules on ZnO QDs. No obvious size alteration was observed for ZnO QDs after PEG conjugation. The water-dispersible ZnO QDs still retained the antibacterial activity and fluorescence intensity. The cytotoxicity evaluation revealed that ZnO QDs at higher concentrations decreased cell viability but were generally safe at 30 ppm or below. Cell lines of hepatocytes (HepG2), osteoblasts (MC3T3-E1) and mesenchymal stem cells (MSCs) were successfully labeled by the water-dispersible ZnO QDs at 30 ppm. The ZnO QD-labeled MSCs maintained their stemness and differentiation capacity. Therefore, we conclude that the water-dispersible ZnO QDs developed in this study have antibacterial activity, low cytotoxicity, and proper labeling efficiency, and can be used to label a variety of cells including stem cells. PMID:24177451

Hsu, Shan-hui; Lin, Ying Yi; Huang, Sherry; Lem, Kwok Wai; Nguyen, Dinh Huong; Lee, Dai Soo

2013-11-29

282

Synthesis of CdSe quantum dots using various long-chain fatty acids and their phase transfer.  

PubMed

Monodispersed colloidal photoluminescent CdSe quantum dots (QDs) were synthesized via an organic approach by using cadmium oxide and elemental selenium as precursors, and long-chain fatty acids as surface ligands. The hydrocarbon chain length of the fatty acid was adjusted to investigate the effect on CdSe QDs. The fatty acid ligands with different hydrocarbon chain lengths showed an apparent effect on the nanocrystal nucleation and growth which is the key controlling the size, size distribution and crystal structure of resulting CdSe QDs. This effect was attributable to the steric hindrance of different hydrocarbon length of the fatty acids, which affected the reactivity of the monomers and nanocrystals during the nanocrystal nucleation and growth. The water-soluble CdSe QDs were obtained by encapsulating the CdSe ODs in oil phase with amphiphilic poly(styrene-co-maleic anhydride) (PSMA)-ethanolamine (EA) polymers, which made it possible for further applications of the CdSe QDs in aqueous environment such as surface functionalization for biological labeling and application in photocatalysis and photosensitization. PMID:23862479

Zhang, Qiang; Zhang, Aiyu; Yang, Ping; Shen, Jianxing

2013-06-01

283

One-pot synthesis of highly luminescent carbon quantum dots and their nontoxic ingestion by zebrafish for in vivo imaging.  

PubMed

Photoluminescent carbon and/or silicon-based nanodots have attracted ever increasing interest. Accordingly, a myriad of synthetic methodologies have been developed to fabricate them, which unfortunately, however, frequently involve relatively tedious steps, such as initial surface passivation and subsequent functionalization. Herein, we describe a green and sustainable synthetic strategy to combine these procedures into one step and to produce highly luminescent carbon quantum dots (CQDs), which can also be easily fabricated into flexible thin films with intense luminescence for future roll-to-roll manufacturing of optoelectronic devices. The as-synthesized CQDs exhibited enhanced cellular permeability and low or even noncytotoxicity for cellular applications, as corroborated by confocal fluorescence imaging of HeLa cells as well as cell viability measurements. Most strikingly, zebrafish were directly fed with CQDs for in vivo imaging, and mortality and morphologic analysis indicated ingestion of the CQDs posed no harm to the living organisms. Hence, the multifunctional CQDs potentially provide a rich pool of tools for optoelectronic and biomedical applications. PMID:24677275

Huang, Yi-Fan; Zhou, Xin; Zhou, Rong; Zhang, Hong; Kang, Kai-Bin; Zhao, Min; Peng, Yong; Wang, Qiang; Zhang, Hao-Li; Qiu, Wen-Yuan

2014-05-01

284

Synthesis of Nanocrystalline CdS Quantum Dots via Paraffin Liquid as Solvent and Oleic Acid as the Reacting Media  

NASA Astrophysics Data System (ADS)

Fluorescent semiconductor nanocrystals have been widely used as fluorescent materials in chemical sensors, biotechnology, medical diagnostics, biological imaging and many other fields. Compared to the conventional organic fluorophores, the inorganic quantum dots (QDs) have many advantages, including broad absorption spectra, narrow emission spectra, good photostability and long fluorescent lifetime after excitation. Here, the high quality CdS QDs were synthesized directly from sulfur and CdO using the paraffin liquid as solvent and the oleic acid as the reacting media. The synthesized CdS QDs with a zinc blende (cubic) crystal structure were proved by X-ray diffraction. HRTEM observation revealed that the CdS QDs were uniform and the average grain size was about 4 nm. The optical properties of the CdS QDs were characterized by using photoluminescence (PL) spectrophotometer and Ultraviolet-visible (UV-Vis) absorption spectrophotometer. The formation mechanism of CdS QDs in the paraffin liquid and oleic acid system was proposed.

Li, Wenjiang; Wang, Mingrui; Xie, Fei; Zhu, Sha; Zhao, Yue

2012-12-01

285

Toward quantum entanglement in a quantum-dot nanocavity  

Microsoft Academic Search

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

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

1999-01-01

286

Cation-inverting-injection: a novel method for synthesis of aqueous ZnSe quantum dots with bright excitionic emission and suppressed trap emission.  

PubMed

In the conventional synthesis of aqueous ZnSe quantum dots (QDs), highly reactive Se monomers are rapidly injected into a Zn-thiol complexes solution at room temperature, resulting in a poor excitionic luminescence and a serious trap emission of as-prepared ZnSe QDs. In this paper, we develop a novel cation-inverting-injection method to prepare aqueous ZnSe QDs with a bright excitionic luminescence. In this method, highly reactive Se monomers are first diluted in the reaction solution, followed by low-reaction Zn-thiol complexes slowly dropped at a high reaction temperature (90 °C). The inverting monomer injection order, the suppressed monomer reactivity and the high nucleation temperature in the cation-inverting-injection method can contribute to low-concentration but high-quality ZnSe nuclei, thereby promoting the formation of ZnSe QDs with large-sized particles, a high excitionic emission and a weak trap emission. As-prepared ZnSe QDs exhibit an intense deep-blue excitionic emission, which is the first reported case of a visible excitionic emission instead of a trap emission resulting from ZnSe QDs that are directly synthesized in an aqueous media. Using three types of dyes, via two measuring methods, the accurate photoluminescence quantum yield of the as-prepared ZnSe QDs is measured as 15%, which is a new record for mercaptocarboxylic acid stabilized ZnSe QDs synthesized in an aqueous media. PMID:24981918

Wang, Yanbin; Wang, Chunlei; Xu, Shuhong; Wang, Zhuyuan; Cui, Yiping

2014-07-25

287

The Glutathione Synthesis Gene Gclm Modulates Amphiphilic Polymer-Coated CdSe/ZnS Quantum Dot-Induced Lung Inflammation in Mice  

PubMed Central

Quantum dots (QDs) are unique semi-conductor fluorescent nanoparticles with potential uses in a variety of biomedical applications. However, concerns exist regarding their potential toxicity, specifically their capacity to induce oxidative stress and inflammation. In this study we synthesized CdSe/ZnS core/shell QDs with a tri-n-octylphosphine oxide, poly(maleic anhydride-alt-1-tetradecene) (TOPO-PMAT) coating and assessed their effects on lung inflammation in mice. Previously published in vitro data demonstrated these TOPO-PMAT QDs cause oxidative stress resulting in increased expression of antioxidant proteins, including heme oxygenase, and the glutathione (GSH) synthesis enzyme glutamate cysteine ligase (GCL). We therefore investigated the effects of these QDs in vivo in mice deficient in GSH synthesis (Gclm +/? and Gclm ?/? mice). When mice were exposed via nasal instillation to a TOPO-PMAT QD dose of 6 µg cadmium (Cd) equivalents/kg body weight, neutrophil counts in bronchoalveolar lavage fluid (BALF) increased in both Gclm wild-type (+/+) and Gclm heterozygous (+/?) mice, whereas Gclm null (?/?) mice exhibited no such increase. Levels of the pro-inflammatory cytokines KC and TNF? increased in BALF from Gclm +/+ and +/? mice, but not from Gclm ?/? mice. Analysis of lung Cd levels suggested that QDs were cleared more readily from the lungs of Gclm ?/? mice. There was no change in matrix metalloproteinase (MMP) activity in any of the mice. However, there was a decrease in whole lung myeloperoxidase (MPO) content in Gclm ?/? mice, regardless of treatment, relative to untreated Gclm +/+ mice. We conclude that in mice TOPO-PMAT QDs have in vivo pro-inflammatory properties, and the inflammatory response is dependent on GSH synthesis status. Because there is a common polymorphism in humans that influences GCLM expression, these findings imply that humans with reduced GSH synthesis capabilities may be more susceptible to the pro-inflammatory effects of QDs.

White, Collin C.; Weldy, Chad S.; Wilkerson, Hui-Wen; Yu, Jianbo; Dills, Russell; Yu, Xiaozhong; Griffith, William C.; Faustman, Elaine M.; Farin, Federico M.; Gill, Sean E.; Parks, William C.; Hu, Xiaoge; Gao, Xiaohu; Eaton, David L.; Kavanagh, Terrance J.

2013-01-01

288

The glutathione synthesis gene Gclm modulates amphiphilic polymer-coated CdSe/ZnS quantum dot-induced lung inflammation in mice.  

PubMed

Quantum dots (QDs) are unique semi-conductor fluorescent nanoparticles with potential uses in a variety of biomedical applications. However, concerns exist regarding their potential toxicity, specifically their capacity to induce oxidative stress and inflammation. In this study we synthesized CdSe/ZnS core/shell QDs with a tri-n-octylphosphine oxide, poly(maleic anhydride-alt-1-tetradecene) (TOPO-PMAT) coating and assessed their effects on lung inflammation in mice. Previously published in vitro data demonstrated these TOPO-PMAT QDs cause oxidative stress resulting in increased expression of antioxidant proteins, including heme oxygenase, and the glutathione (GSH) synthesis enzyme glutamate cysteine ligase (GCL). We therefore investigated the effects of these QDs in vivo in mice deficient in GSH synthesis (Gclm +/- and Gclm -/- mice). When mice were exposed via nasal instillation to a TOPO-PMAT QD dose of 6 µg cadmium (Cd) equivalents/kg body weight, neutrophil counts in bronchoalveolar lavage fluid (BALF) increased in both Gclm wild-type (+/+) and Gclm heterozygous (+/-) mice, whereas Gclm null (-/-) mice exhibited no such increase. Levels of the pro-inflammatory cytokines KC and TNF? increased in BALF from Gclm +/+ and +/- mice, but not from Gclm -/- mice. Analysis of lung Cd levels suggested that QDs were cleared more readily from the lungs of Gclm -/- mice. There was no change in matrix metalloproteinase (MMP) activity in any of the mice. However, there was a decrease in whole lung myeloperoxidase (MPO) content in Gclm -/- mice, regardless of treatment, relative to untreated Gclm +/+ mice. We conclude that in mice TOPO-PMAT QDs have in vivo pro-inflammatory properties, and the inflammatory response is dependent on GSH synthesis status. Because there is a common polymorphism in humans that influences GCLM expression, these findings imply that humans with reduced GSH synthesis capabilities may be more susceptible to the pro-inflammatory effects of QDs. PMID:23724032

McConnachie, Lisa A; Botta, Dianne; White, Collin C; Weldy, Chad S; Wilkerson, Hui-Wen; Yu, Jianbo; Dills, Russell; Yu, Xiaozhong; Griffith, William C; Faustman, Elaine M; Farin, Federico M; Gill, Sean E; Parks, William C; Hu, Xiaoge; Gao, Xiaohu; Eaton, David L; Kavanagh, Terrance J

2013-01-01

289

Multimodal Mn-doped I-III-VI quantum dots for near infrared fluorescence and magnetic resonance imaging: from synthesis to in vivo application.  

PubMed

The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities up to 1400 mM(-1) [QD] s(-1) at 7 T and 300 K. We finally show that these QDs are suitable multimodal in vivo probes and demonstrate MRI and NIR fluorescence detection of regional lymph nodes in mice. PMID:24980473

Sitbon, Gary; Bouccara, Sophie; Tasso, Mariana; Francois, Aurélie; Bezdetnaya, Lina; Marchal, Frédéric; Beaumont, Marine; Pons, Thomas

2014-07-10

290

Molecular states in graphene double quantum dots  

NASA Astrophysics Data System (ADS)

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

Xiong, Yong-Jian

2013-12-01

291

Engineered quantum dot structures: fabrication and applications  

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

292

Advancements in the Field of Quantum Dots  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

293

Thermoelectric properties of hexagonal graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

294

Searching for spin coherence in single quantum dots  

Microsoft Academic Search

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

Petru Fodor; Gilberto Medeiros-Ribeiro; Jeremy Levy

2004-01-01

295

Electronic structure and photon absorption in semiconductor quantum dots  

Microsoft Academic Search

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

Gregory von Winckel

2006-01-01

296

Evaluation of the fundamental properties of quantum dot infrared detectors  

Microsoft Academic Search

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

Jamie Phillips

2002-01-01

297

Full-colour quantum dot displays fabricated by transfer printing  

Microsoft Academic Search

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

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

2011-01-01

298

The quantum dot molecule from an optical point of view  

Microsoft Academic Search

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

Daniel Gammon

2009-01-01

299

Quantum dot nanoscale heterostructures for solar energy conversion.  

PubMed

Quantum dot nanoscale semiconductor heterostructures (QDHs) are a class of materials potentially useful for integration into solar energy conversion devices. However, realizing the potential of these heterostructured systems requires the ability to identify and synthesize heterostructures with suitably designed materials, controlled size and morphology of each component, and structural control over their shared interface. In this review, we will present the case for the utility and advantages of chemically synthesized QDHs for solar energy conversion, beginning with an overview of various methods of heterostructured material synthesis and a survey of heretofore reported materials systems. The fundamental charge transfer properties of the resulting materials combinations and their basic design principles will be outlined. Finally, we will discuss representative solar photovoltaic and photoelectrochemical devices employing QDHs (including quantum dot sensitized solar cells, or QDSSCs) and examine how QDH synthesis and design impacts their performance. PMID:23229593

Selinsky, Rachel S; Ding, Qi; Faber, Matthew S; Wright, John C; Jin, Song

2013-04-01

300

Microwave-assisted aqueous synthesis of new quaternary-alloyed CdSeTeS quantum dots; and their bioapplications in targeted imaging of cancer cells.  

PubMed

In this study, we report for the first time a one-pot approach for the synthesis of new CdSeTeS quaternary-alloyed quantum dots (QDs) in aqueous phase by microwave irradiation. CdCl2 was used as a Cd precursor during synthesis, NaHTe and NaHSe were used as Te and Se precursors and mercaptopropionic acid (MPA) was used as a stabilizer and source of sulfur. A series of quaternary-alloyed QDs of different sizes were prepared. CdSeTeS QDs exhibited a wide emission range from 549 to 709 nm and high quantum yield (QY) up to 57.7 %. Most importantly, the quaternary-alloyed QDs possessed significantly long fluorescence lifetimes > 100 ns as well as excellent photostability. Results of high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (XRD) spectroscopy showed that the nanocrystals possessed a quaternary alloy structure with good crystallinity. Fluorescence correlation spectroscopy (FCS) showed that QDs possessed good water solubility and monodispersity in aqueous solution. Furthermore, CdSeTeS QDs were modified with alpha-thio-omega-carboxy poly(ethylene glycol) (HS-PEG-COOH) and the modified QDs were linked to anti-epidermal growth factor receptor (EGFR) antibodies. QDs with the EGFR antibodies as labeling probes were successfully applied to targeted imaging for EGFR on the surface of SiHa cervical cancer cells. We believe that CdSeTeS QDs can become useful probes for in vivo targeted imaging and clinical diagnosis. PMID:22696455

Yang, Fengzhao; Xu, Zhancheng; Wang, Jinjie; Zan, Feng; Dong, Chaoqing; Ren, Jicun

2013-01-01

301

Optical properties of charged semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

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

Jha, Praket P.

302

Synthesis, characterization and target protein binding of drug-conjugated quantum dots in vitro and in living cells  

NASA Astrophysics Data System (ADS)

Elucidation of unknown target proteins of a drug is of great importance in understanding cell biology and drug discovery. There have been extensive studies to discover and identify target proteins in the cell. Visualization of targets using drug-conjugated probes has been an important approach to gathering mechanistic information of drug action at the cellular level. As quantum dot (QD) nanocrystals have attracted much attention as a fluorescent probe in the bioimaging area, we prepared drug-conjugated QD to explore the potential of target discovery. As a model drug, we selected a well-known anticancer drug, methotrexate (MTX), which has been known to target dihydrofolate reductase (DHFR) with high affinity binding (Kd = 0.54 nM). MTX molecules were covalently attached to amino-PEG-polymer-coated QDs. Specific interactions of MTX-conjugated QDs with DHFR were identified using agarose gel electrophoresis and fluorescence microscopy. Cellular uptake of the MTX-conjugated QDs in living CHO cells was investigated with regard to their localization and distribution pattern. MTX-QD was found to be internalized into the cells via caveolae-medicated endocytosis without significant sequestration in endosomes. A colocalization experiment of the MTX-QD conjugate with antiDHFR-TAT-QD also confirmed that MTX-QD binds to the target DHFR. This study showed the potential of the drug-QD conjugate to identify or visualize drug-target interactions in the cell, which is currently of great importance in the area of drug discovery and chemical biology.

Choi, Youngseon; Kim, Minjung; Cho, Yoojin; Yun, Eunsuk; Song, Rita

2013-02-01

303

Quantum Dots: Fundamentals, Applications, and Frontiers  

Microsoft Academic Search

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

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

2005-01-01

304

Universal quantum computing with nanowire double quantum dots  

NASA Astrophysics Data System (ADS)

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

Xue, Peng

2011-10-01

305

Quantum dot-nanocavity devices for information processing  

Microsoft Academic Search

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

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

2011-01-01

306

Pulse-gated quantum dot hybrid qubit  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

307

Quantum Dots: Fundamentals, Applications, and Frontiers  

NASA Astrophysics Data System (ADS)

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

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

308

Experimental demonstration of quantum-dot cellular automata  

Microsoft Academic Search

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

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

1998-01-01

309

Cavity quantum electrodynamics with quantum dot - photonic crystal nanocavities  

NASA Astrophysics Data System (ADS)

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

Hendrickson, Joshua R.

310

Imaging a coupled quantum dot-quantum point contact system  

Microsoft Academic Search

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

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

2007-01-01

311

Probing relaxation times in graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

312

Probing relaxation times in graphene quantum dots  

PubMed Central

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

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

2013-01-01

313

Dot-in-Well Quantum-Dot Infrared Photodetectors  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

314

Synthesis and applications of crack-free SiO2 monolith containing CdSe/ZnS quantum dots as passive lighting sources.  

PubMed

A reverse microemulsion technique has been used to synthesize quantum dot nanocomposites within a SiO2 surface coating. With this approach, the unique optical properties of the CdSe/ZnS quantum dots were preserved. CdSe/ZnS/SiO2 nanoparticles were homogeneously distributed in a tetramethyl orthosilicate ethanol solution and gelation process was initiated within a 10 min, and was left over night at room temperature and dried fully to achieve a solid SiO, monolith. The resulting monolith was transparent and fluorescent under ultraviolet (UV) lamp. Moreover the monolith produced was crack-free. Further studies on the photo stability of the monolith were performed using a high power UV LED device. Remarkably, quantum dots in the SiO, monolith showed better photo stability compared with those dispersed in a polymer matrix. PMID:19049053

Yi, Dong Kee

2008-09-01

315

Fabrication of Novel Germanium Oxide-cladded Germanium Quantum Dots and Quantum Dot Gate Nonvolatile Memory using Germanium Oxide-Germanium Qd's  

NASA Astrophysics Data System (ADS)

In this dissertation, the floating gate type quantum dot gate nonvolatile memory device has been investigated. The electrical characterization and simulation of the fabricated quantum dot nonvolatile memory (QD-NVM) devices is presented. The electrical characterization includes program, erase, and read operations and the memory retention and endurance measurements. In addition, QD synthesis and their incorporation as the floating gate (along with material characterization) is presented in fabricated QD-NVM devices. The synthesis of the germanium oxide cladding on the germanium quantum dots is one of the key interests in this research. Owing to the electrical and physical isolation of the quantum dots due to germanium oxide cladding, it provides a larger threshold voltage shift due to tight packing and higher density of quantum dots. GeOx cladding on the QDs enhances the data retention by avoiding the lateral dot-to-dot conduction, thereby reducing charge leakage. A threshold voltage of 1.5 V was observed in the first GeOx-Ge QD-NVM device when pulsed with a 20 micros stress pulse. The experimental data indicates that there is about a 0.1 V shift in the threshold voltage of that device over a period of one year. Similarly, 1.6 V of threshold voltage shift was observed in the second device and the retention data indicates negligible shift in the threshold voltage over a period of one year. Similar results were observed in the II-VI based QD-NVM devices.

Gogna, Mukesh

316

Optically Detected Magnetic Resonance of Semiconductor Quantum Dots.  

National Technical Information Service (NTIS)

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

A. Glozman E. Lifshitz I. D. Litvin

2000-01-01

317

Quantum-dot Cellular Automata Devices and Architectures.  

National Technical Information Service (NTIS)

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

W. Porod

1998-01-01

318

Energy transfer from CdSe quantum dots to graphene  

NASA Astrophysics Data System (ADS)

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

Liao, Chunyan; Zhu, Xiuhong

2013-12-01

319

Quantum Dots: The New Little Nanosemiconductors  

NASA Astrophysics Data System (ADS)

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

Harenza, Chance

2006-10-01

320

Cavity quantum electrodynamics with quantum dot - photonic crystal nanocavities  

Microsoft Academic Search

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

Joshua R. Hendrickson

2010-01-01

321

Controlled Population Transfer in a Double Quantum Dot System  

SciTech Connect

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

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

2007-12-26

322

Microscopic study of relaxation oscillations in quantum-dot VCSELs  

Microsoft Academic Search

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

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

2011-01-01

323

Bound states in continuum: Quantum dots in a quantum well  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

324

Successive and large-scale synthesis of InP/ZnS quantum dots in a hybrid reactor and their application to white LEDs  

NASA Astrophysics Data System (ADS)

We report successive and large-scale synthesis of InP/ZnS core/shell nanocrystal quantum dots (QDs) using a customized hybrid flow reactor, which is based on serial combination of a batch-type mixer and a flow-type furnace. InP cores and InP/ZnS core/shell QDs were successively synthesized in the hybrid reactor in a simple one-step process. In this reactor, the flow rate of the solutions was typically 1 ml min-1, 100 times larger than that of conventional microfluidic reactors. In order to synthesize high-quality InP/ZnS QDs, we controlled both the flow rate and the crystal growth temperature. Finally, we obtained high-quality InP/ZnS QDs in colors from bluish green to red, and we demonstrated that these core/shell QDs could be incorporated into white-light-emitting diode (LED) devices to improve color rendering performance.

Kim, Kyungnam; Jeong, Sohee; Woo, Ju Yeon; Han, Chang-Soo

2012-02-01

325

One-pot synthesis of water-dispersible Ag2S quantum dots with bright fluorescent emission in the second near-infrared window  

NASA Astrophysics Data System (ADS)

The second near-infrared window (NIR-II, wavelength of 1.0-1.4 ?m) is optimal for the bioimaging of live animals due to their low albedo and endogenous autofluorescence. Herein, we report a facile and one-pot biomimetic synthesis approach to prepare water-dispersible NIR-II-emitting ultrasmall Ag2S quantum dots (QDs). Photoluminescence spectra showed that the emission peaks could be tuned from 1294 to 1050 nm as the size of the Ag2S QDs varied from 6.8 to 1.6 nm. The x-ray diffraction patterns and x-ray photoelectron spectra confirmed that the products were monoclinic ?-Ag2S. Fourier transform infrared spectrograph analysis indicated that the products were protein-conjugated Ag2S QDs. Examination of cytotoxicity and the hemolysis test showed that the obtained Ag2S QDs had good biocompatibility, indicating that such a nanomaterial could be a new kind of fluorescent label for in vivo imaging.

Yang, Hua-Yan; Zhao, Yu-Wei; Zhang, Zheng-Yong; Xiong, Huan-Ming; Yu, Shao-Ning

2013-02-01

326

Poly(glycidyl methacrylate) grafted CdSe quantum dots by surface-initiated atom transfer radical polymerization: Novel synthesis, characterization, properties, and cytotoxicity studies  

NASA Astrophysics Data System (ADS)

A novel approach for the synthesis of poly(glycidyl methacrylate) grafted CdSe quantum dot (QDs) (PGMA-g-CdSe) was developed. The PGMA-g-CdSe nanohybrids were synthesized by the surface-initiated atom transfer radical polymerization of glycidyl methacrylate from the surface of the strategic initiator, CdSe-BrIB QDs prepared by the interaction of 2-bromoisobutyryl bromide (BrIB) and CdSe-OH QDs. The structure, morphology, and optical property of the PGMA-g-CdSe nanohybrids were analyzed by FT-IR, XPS, TGA, XRD, TEM, and PL. The as-synthesized PGMA-g-CdSe nanohybrids having multi-epoxide groups were employed for the direct coupling of biotin via ring-opening reaction of the epoxide groups to afford the Biotin-f-PGMA-g-CdSe nanobioconjugate. The covalent immobilization of biotin onto PGMA-g-CdSe was confirmed by FT-IR, XPS, and EDX. Biocompatibility and imaging properties of the Biotin-f-PGMA-g-CdSe were investigated by MTT bioassay and PL analysis, respectively. The cell viability study suggested that the biocompatibility was significantly enhanced by the functionalization of CdSe QDs by biotin and PGMA.

Bach, Long Giang; Islam, Md. Rafiqul; Lee, Doh Chang; Lim, Kwon Taek

2013-10-01

327

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

Microsoft Academic Search

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

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

2009-01-01

328

Functional microspheres of graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

329

Exotic Kondo States in GaAs Quantum Dots  

Microsoft Academic Search

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

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

2005-01-01

330

Quantum Dot Research: Current State and Future Prospects  

Microsoft Academic Search

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

Tracie J. Bukowski; Joseph H. Simmons

2002-01-01

331

A device architecture for computing with quantum dots  

Microsoft Academic Search

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

CRAIG S. LENT; P. DOUGLAS TOUGAW

1997-01-01

332

Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots  

Microsoft Academic Search

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

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

2000-01-01

333

Experimental studies of clocked quantum-dot cellular automata devices  

Microsoft Academic Search

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

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

2000-01-01

334

Computing with Quantum-dot Cellular Automata: Adiabatic Switching  

Microsoft Academic Search

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

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

1997-01-01

335

Spin states in graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

Ensslin, Klaus

2011-03-01

336

Red light emitting solid state hybrid quantum dot near-UV GaN LED devices  

Microsoft Academic Search

We produced core-shell (CdSe)ZnSe quantum dots by direct colloidal chemical synthesis and the surface-passivation method---an overcoating of the core CdSe with a larger-bandgap material ZnSe. The (CdSe)ZnSe quantum dots(QDs) play the role of a colour conversion centre. We call these quantum dots nanophosphors. We fabricated red light emitting hybrid devices of (CdSe)ZnSe QDs and a near-UV GaN LED by combining

Hongjoo Song; Seonghoon Lee

2007-01-01

337

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

PubMed

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

Pai, Yi-Hao; Lin, Gong-Ru

2011-01-17

338

High-efficiency InN-based quantum dot solar cells for defense applications  

NASA Astrophysics Data System (ADS)

Nitride semiconductors possess a number of unique material properties applicable to energy harvesting photovoltaic devices, including a large range of energy gaps, superior radiation resistance, and tolerance to high temperatures. We present here our experimental results related to the self-assembled InN quantum dots formed on Si substrates. We have been successful at synthesizing InN quantum dots using the metal-organic chemical vapor deposition (MOCVD) process. We demonstrate the synthesis of a high density of InN dots exhibiting excellent structural and optical properties. An unprecedented range of absorption energies, ranging from the infrared to the ultraviolet, can be obtained by embedding InN-based quantum dots in a wide band gap GaN barrier. The combination of energy-gaps accessible to III-V nitride materials may be used to reap the benefits of advance quantum dot device concepts involving hot carrier effects or multiple carrier generation processes.

Welser, Roger E.; Sood, Ashok K.; Puri, Yash R.; Laboutin, Oleg A.; Guido, Louis J.; Dhar, Nibir K.; Wijewarnasuriya, Priyalal S.

2010-04-01

339

Single-step noninjection synthesis of highly luminescent water soluble Cu+ doped CdS quantum dots: application as bio-imaging agents.  

PubMed

Novel highly luminescent Cu(+) doped CdS quantum dots (QDs) were directly synthesized in aqueous phase through a facile single-step noninjection method. Due to their bright red fluorescence, ultrasmall size, and good biocompatibility, as-prepared CdS:Cu(+) QDs have potential as probes in bio-imaging. PMID:23986122

Xuan, Tongtong; Wang, Song; Wang, Xiaojun; Liu, Jiaqing; Chen, Jiyao; Li, Huili; Pan, Likun; Sun, Zhuo

2013-10-11

340

Compact quantum-dot-based ultrafast lasers  

NASA Astrophysics Data System (ADS)

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

Sibbett, W.; Rafailov, E. U.

2008-03-01

341

Potential clinical applications of quantum dots  

PubMed Central

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

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

2008-01-01

342

Circular polarization memory in single Quantum Dots  

SciTech Connect

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

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

2010-01-04

343

Bilayer graphene quantum dot defined by topgates  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

344

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

Microsoft Academic Search

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

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

1999-01-01

345

Size dependence in tunneling spectra of PbSe quantum-dot arrays  

Microsoft Academic Search

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

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

2009-01-01

346

Full-colour quantum dot displays fabricated by transfer printing  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

347

Quantum dots-in-a-well infrared photodetectors  

Microsoft Academic Search

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

Sanjay Krishna

2005-01-01

348

Mid infrared quantum dots in a well infrared photodetectors  

Microsoft Academic Search

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

S. Krishna

2005-01-01

349

Coherent nonlinear optical spectroscopy of coupled quantum dots  

Microsoft Academic Search

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

Elizabeth Tabak Batteh

2003-01-01

350

Quantum Information Processing Using Quantum Dot Spins and Cavity QED  

Microsoft Academic Search

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

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

1999-01-01

351

Hyperfine interactions and quantum information processing in quantum dots  

Microsoft Academic Search

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

Jacob Mason Taylor

2006-01-01

352

Spectral and threshold performance of patterned quantum dot lasers  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

353

Coherent spin manipulation with a triple quantum dot  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

354

Nuclear spin effects in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

355

Anisotropic Spin Exchange in Coupled Quantum Dots  

NASA Astrophysics Data System (ADS)

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

Foster, Kerwin; Hormozi, Layla

2005-03-01

356

Synthesis and characterization of CdTe/CdS and CdTe/CdSe core/shell type-II quantum dots in a noncoordinating solvent  

NASA Astrophysics Data System (ADS)

A synthetic route to CdTe/CdS and CdTe/CdSe core/shell type-II quantum dots in noncoordinating solvents (1-octadecene) was obtained. The results showed redshift in the emission spectra of CdTe/CdS and CdTe/CdSe compared with the CdTe core nanocrystals. This phenomenon is believed to indicate the formation of core/shell nanostructures. Transmission electron microscopy and powder x-ray diffraction were also consistent with nanocrystals containing a core of nearly monodisperse CdTe with CdS or CdSe capping. The photoluminescence quantum yield was enhanced by epitaxial growth of CdS or CdSe shells. Stepwise increasing concentration of sulfur or selenium monomers into the CdTe core solution allowed the examination of monomer activities, which are very relevant for synthesizing core/shell quantum dots.

Chang, Jia-Yaw; Wang, Shiuann-Ren; Yang, Cheng-Hsien

2007-08-01

357

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

Microsoft Academic Search

In this thesis, we study solution-processed lead sulfide quantum dots for near-infrared quantum information and communication applications. Quantum dots processed through synthetic routes and colloidally suspended in solution offer far-reaching device application possibilities that are unparalelled in traditional self-assembled quantum dots. Lead sulfide quantum dots are especially promising for near-infrared quantum optics due to their optical emission at the wavelengths

Ranojoy Bose

2009-01-01

358

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

Microsoft Academic Search

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

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

2000-01-01

359

Noise spectra of an interacting quantum dot  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

360

Adiabatic description of nonspherical quantum dot models  

SciTech Connect

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

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

2012-10-15

361

Quantum dots in biology and medicine  

Microsoft Academic Search

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

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

2004-01-01

362

Solution-Processed Quantum Dot Photodetectors  

Microsoft Academic Search

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

Gerasimos Konstantatos; Edward H. Sargent

2009-01-01

363

Magnetic Polarons in Anisotropic Quantum Dots  

Microsoft Academic Search

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

Rafal Oszwaldowski; Andre Petukhov; Igor Zutic

2010-01-01

364

Spin Fluctuations in Magnetic Quantum Dots  

Microsoft Academic Search

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

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

2009-01-01

365

Optical Signatures of Coupled Quantum Dots.  

National Technical Information Service (NTIS)

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

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

2006-01-01

366

Positioning of quantum dots on metallic nanostructures  

Microsoft Academic Search

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

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

2010-01-01

367

Spin relaxation in graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

Burkard, Guido; Struck, Philipp

2010-03-01

368

Spin qubits in graphene quantum dots  

Microsoft Academic Search

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

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

2007-01-01

369

Quantum Dot Based Infrared Focal Plane Arrays  

Microsoft Academic Search

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

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

2007-01-01

370

Triggered Single Photons from a Quantum Dot  

Microsoft Academic Search

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

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

2001-01-01

371

Producing Quantum Dots by Spray Pyrolysis  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

372

Applications of quantum dots in cell biology  

NASA Astrophysics Data System (ADS)

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

Barroso, Margarida; Mehdibeigi, Roshanak; Brogan, Louise

2006-03-01

373

PLAs in Quantum-dot Cellular Automata  

Microsoft Academic Search

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

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

2006-01-01

374

Interacting electrons in parabolic quantum dots  

Microsoft Academic Search

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

Michael Schreiber; Jens Siewert; Thomas Vojta

2001-01-01

375

Protease-activated quantum dot probes  

Microsoft Academic Search

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

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

2005-01-01

376

Quantum-Dot Cellular Automata Design Guideline  

Microsoft Academic Search

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

Kyosun Kim; Kaijie Wu; Ramesh Karri

2006-01-01

377

New small quantum dots for neuroscience  

NASA Astrophysics Data System (ADS)

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

Selvin, Paul

2014-03-01

378

Theoretical analysis of quantum dot infrared photodetectors  

Microsoft Academic Search

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

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

2003-01-01

379

Dark Current in Quantum Dot Infrared Photodetectors  

Microsoft Academic Search

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

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

2000-01-01

380

Controlling cavity reflectivity with a single quantum dot  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

381

Controlling cavity reflectivity with a single quantum dot.  

PubMed

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

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

2007-12-01

382

Nonlocal quantum cloning via quantum dots trapped in distant cavities  

NASA Astrophysics Data System (ADS)

A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed. By modulating the parameters of the system, the optimal 1 ? 2 universal quantum cloning machine, 1 ? 2 phase-covariant cloning machine, and 1 ? 3 economical phase-covariant cloning machine are constructed. The present scheme, which is attainable with current technology, saves two qubits compared with previous cloning machines.

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

2012-05-01

383

Elastic light scattering by semiconductor quantum dots of arbitrary shape  

Microsoft Academic Search

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

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

2007-01-01

384

Spontaneous emission and optical control of spins in quantum dots  

Microsoft Academic Search

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

Sophia E. Economou

2006-01-01

385

Phase coherent transport in two coupled quantum dots  

Microsoft Academic Search

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

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

2003-01-01

386

Vertical quantum dot with a vertically coupled charge detector  

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

387

Using a quantum dot system to realize perfect state transfer  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

388

Vertical quantum dot with a vertically coupled charge detector  

Microsoft Academic Search

We fabricated a vertical quantum dot equipped with a charge detector. The dot current flows vertically between the top and bottom contacts. The charge detector is formed at the bottom contact layer with a current channel constricted to the region just under the dot. This channel current is reduced by addition of an extra electron onto the dot due to

Koichiro Zaitsu; Yosuke Kitamura; Keiji Ono; Seigo Tarucha

2008-01-01

389

Improved photoluminescence efficiency of patterned quantum dots incorporating a dots-in-the-well structure  

Microsoft Academic Search

InAs quantum dots embedded in InGaAs quantum well (DWELL: dots-in-the-well) structures grown on nanopatterned GaAs pyramids and planar GaAs(001) surface are comparatively investigated. Photoluminescence (PL) measurements demonstrate that the DWELL structure grown on the GaAs pyramids exhibits a broad quantum well PL band (full width at half-maximum ~ 90 meV) and a higher quantum dot emission efficiency than the DWELL

P. S. Wong; B. L. Liang; V. G. Dorogan; J. Tatebayashi; X. He; N. Nuntawong; Yu I. Mazur; G. J. Salamo; S. R. J. Brueck; D. L. Huffaker

2008-01-01

390

Laterally-biased quantum dot infrared photodetector  

NASA Astrophysics Data System (ADS)

At the Air Force Research Laboratory, Space Vehicles Directorate, we are interested in improving the performance of or modifying the capabilities of infrared detectors in order to locate and identify dim and/or distant objects in space. One characteristic we are very interested in is multicolor detection. To this end, we have turned to a novel detector design that we have come to call a Lateral Quantum Dot Infrared Photodetector (LQDIP). In this design, InAs quantum dots are buried in a GaAs quantum well, which in turn is tunnel-coupled to another GaAs quantum well. Photoexcited electrons from the quantum dots tunnel over to the second well and are then swept out via a lateral (perpendicular to the growth direction) bias voltage. This architecture should exhibit the ability to tune to select infrared frequencies with reduced dark current and unity gain. The lateral photocurrent is directed by a vertical (parallel to the growth direction) gate voltage. We will discuss this detector architecture and the LQDIP operating principles and conditions, and we will present some preliminary results of current-voltage, photocurrent, differential conductance, and spectral measurements.

Cardimona, D. A.; Morath, C. P.; Guidry, D. H.; Cowan, V. M.

2013-07-01

391

Progress towards single spin optoelectronics using quantum dot nanostructures  

Microsoft Academic Search

We summarise recent progress in our understanding of the physics of fundamental charge and spin excitations in quantum dot semiconductor nanostructures. Many novel potential applications of these nanostructures have arisen from the strong optical non-linearities that exist in the few-particle quantum dot absorption spectrum. By comparison, the interaction of the electron spin with other localised charges in the dot and

Domink Heiss; Miro Kroutvar; Jonathan J. Finley; Gerhard Abstreiter

2005-01-01

392

Quantum-dot cellular automata at a molecular scale  

Microsoft Academic Search

ABSTRACT: Quantum - dot cellular automata (QCA) is a scheme for molecular electronics in which information is transmitted and processed through electro - static interactions between charges in an array of quantum dots QCA wires, majority gates, clocked cell operation, and (recently) true power gain between QCA cells has been demonstrated in a metal - dot prototype system at cryogenic

M. Lieberman

2002-01-01

393

Quantum optics with quantum dots in microcavities  

Microsoft Academic Search

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

Matthew T. Rakher

2008-01-01

394

Barrier engineered superlattice and quantum dot detectors for HOT operation  

Microsoft Academic Search

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

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

2011-01-01

395

InP\\/GalnP Quantum Dot Lasers  

Microsoft Academic Search

\\u000a Over the last decade self-assembled semiconductor quantum dots have become a major issue in semiconductor physics [1–3] — both from a fundamental point of view as well as in respect to applications such as the quantum dot laser. Originally,\\u000a the quantum dot laser was proposed to outperform the well-established quantum well laser on the basis of properties such as\\u000a material

Oliver G. Schmidt; Yvonne M. Manz; Karl Eber

396

Investigation of potential profile effects in quantum dot and onion-like quantum dot-quantum well on optical properties  

NASA Astrophysics Data System (ADS)

This paper investigates GaAs/AlGaAs modified quantum dot nanocrystal and GaAs/AlGaAs/GaAs/AlGaAs quantum dot-quantum well heteronanocrystal. These quantum dots have been analyzed by the finite element numerical methods. Simulations carried out for state n=1, l=0, and m=0 which are original, orbital, and magnetic state of quantum numbers. The effects of variation in radius layers such as total radius, GaAs core, shell and AlGaAs barriers radius on the wavelength and emission coefficient are studied. For the best time, it has also investigated the effect of mole fraction on emission coefficient. Meanwhile, one of the problems in biological applications is alteration of the emission wavelength of a quantum dot by changing in its dimension. This problem will be resolved by changing in potential profile.

Elyasi, P.; SalmanOgli, A.

2014-05-01

397

Ultrasound-assisted synthesis of PbS quantum dots stabilized by 1,2-benzenedimethanethiol and attachment to single-walled carbon nanotubes.  

PubMed

Lead sulfide (PbS) quantum dots stabilized by 1,2-benzenedimethanethiol can be synthesized by mixing Pb(NO3)2 and Na2S solutions in ethanol under ultrasound irradiation. The PbS quantum dots (2.7 and 3.6 nm in diameter) are characterized by their absorption and fluorescence spectra in the near infrared region and by other surface analytical techniques. With addition of single-walled carbon nanotubes (SWNT) to the system, this ultrasound-assisted procedure allows attachment of PbS nanoparticles to SWNT surface via ?-? stacking, thus providing a simple one-pot method for preparation of SWNT-PbS nanoparticle composite materials. Using the ultrasound-assisted method for synthesizing silica composites containing PbS nanoparticles by a sol-gel process is also described. PMID:24074959

Das, Anirban; Wai, Chien M

2014-03-01

398

Quantum Dot Platform for Single-Cell Molecular Profiling  

NASA Astrophysics Data System (ADS)

In-depth understanding of the nature of cell physiology and ability to diagnose and control the progression of pathological processes heavily rely on untangling the complexity of intracellular molecular mechanisms and pathways. Therefore, comprehensive molecular profiling of individual cells within the context of their natural tissue or cell culture microenvironment is essential. In principle, this goal can be achieved by tagging each molecular target with a unique reporter probe and detecting its localization with high sensitivity at sub-cellular resolution, primarily via microscopy-based imaging. Yet, neither widely used conventional methods nor more advanced nanoparticle-based techniques have been able to address this task up to date. High multiplexing potential of fluorescent probes is heavily restrained by the inability to uniquely match probes with corresponding molecular targets. This issue is especially relevant for quantum dot probes---while simultaneous spectral imaging of up to 10 different probes is possible, only few can be used concurrently for staining with existing methods. To fully utilize multiplexing potential of quantum dots, it is necessary to design a new staining platform featuring unique assignment of each target to a corresponding quantum dot probe. This dissertation presents two complementary versatile approaches towards achieving comprehensive single-cell molecular profiling and describes engineering of quantum dot probes specifically tailored for each staining method. Analysis of expanded molecular profiles is achieved through augmenting parallel multiplexing capacity with performing several staining cycles on the same specimen in sequential manner. In contrast to other methods utilizing quantum dots or other nanoparticles, which often involve sophisticated probe synthesis, the platform technology presented here takes advantage of simple covalent bioconjugation and non-covalent self-assembly mechanisms for straightforward probe preparation and specimen labeling, requiring no advanced technical skills and being directly applicable for a wide range of molecular profiling studies. Utilization of quantum dot platform for single-cell molecular profiling promises to greatly benefit both biomedical research and clinical diagnostics by providing a tool for addressing phenotypic heterogeneity within large cell populations, opening access to studying low-abundance events often masked or completely erased by batch processing, and elucidating biomarker signatures of diseases critical for accurate diagnostics and targeted therapy.

Zrazhevskiy, Pavel S.

399

Aqueous Synthesis of CdTe\\/CdSe Core\\/Shell Quantum Dots as pH-Sensitive Fluorescence Probe for the Determination of Ascorbic Acid  

Microsoft Academic Search

By controlling the reflux time and the quantity of the shell materials, different sizes of thioglycollic acid (TGA) modified\\u000a CdTe\\/CdSe core\\/shell quantum dots were synthesized in aqueous solution. This type of QDs was used for sensitive and selective\\u000a determination of ascorbic acid in commercial tablets. Under optimal conditions, a good linearity was observed between the\\u000a relative fluorescence (FL) intensity and

Shan-Shan Yang; Cui-Ling Ren; Zhen-Yang Zhang; Jun-Jie Hao; Qin Hu; Xing-Guo Chen

2011-01-01

400

Entrapment in phospholipid vesicles quenches photoactivity of quantum dots  

PubMed Central

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

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

2011-01-01

401

Biosynthesis of luminescent quantum dots in an earthworm  

NASA Astrophysics Data System (ADS)

The synthesis of designer solid-state materials by living organisms is an emerging field in bio-nanotechnology. Key examples include the use of engineered viruses as templates for cobalt oxide (Co3O4) particles, superparamagnetic cobalt-platinum alloy nanowires and gold-cobalt oxide nanowires for photovoltaic and battery-related applications. Here, we show that the earthworm's metal detoxification pathway can be exploited to produce luminescent, water-soluble semiconductor cadmium telluride (CdTe) quantum dots that emit in the green region of the visible spectrum when excited in the ultraviolet region. Standard wild-type Lumbricus rubellus earthworms were exposed to soil spiked with CdCl2 and Na2TeO3 salts for 11 days. Luminescent quantum dots were isolated from chloragogenous tissues surrounding the gut of the worm, and were successfully used in live-cell imaging. The addition of polyethylene glycol on the surface of the quantum dots allowed for non-targeted, fluid-phase uptake by macrophage cells.

Stürzenbaum, S. R.; Höckner, M.; Panneerselvam, A.; Levitt, J.; Bouillard, J.-S.; Taniguchi, S.; Dailey, L.-A.; Khanbeigi, R. Ahmad; Rosca, E. V.; Thanou, M.; Suhling, K.; Zayats, A. V.; Green, M.

2013-01-01

402

Biosynthesis of luminescent quantum dots in an earthworm.  

PubMed

The synthesis of designer solid-state materials by living organisms is an emerging field in bio-nanotechnology. Key examples include the use of engineered viruses as templates for cobalt oxide (Co(3)O(4)) particles, superparamagnetic cobalt-platinum alloy nanowires and gold-cobalt oxide nanowires for photovoltaic and battery-related applications. Here, we show that the earthworm's metal detoxification pathway can be exploited to produce luminescent, water-soluble semiconductor cadmium telluride (CdTe) quantum dots that emit in the green region of the visible spectrum when excited in the ultraviolet region. Standard wild-type Lumbricus rubellus earthworms were exposed to soil spiked with CdCl(2) and Na(2)TeO(3) salts for 11 days. Luminescent quantum dots were isolated from chloragogenous tissues surrounding the gut of the worm, and were successfully used in live-cell imaging. The addition of polyethylene glycol on the surface of the quantum dots allowed for non-targeted, fluid-phase uptake by macrophage cells. PMID:23263722

Stürzenbaum, S R; Höckner, M; Panneerselvam, A; Levitt, J; Bouillard, J-S; Taniguchi, S; Dailey, L-A; Ahmad Khanbeigi, R; Rosca, E V; Thanou, M; Suhling, K; Zayats, A V; Green, M

2013-01-01

403

Lateral conduction quantum dot infrared photodetectors using photoionization of holes in InAs quantum dots  

Microsoft Academic Search

We report on mid-infrared photoconductivity of Be-doped p-type lateral conduction quantum dot infrared photodetectors and electronic states of the valence band in InAs self-assembled quantum dots. We have observed a broad photocurrent signal in a photon energy range of 100-400 meV (lambda~3-10 µm) due to bound-to-continuum intersublevel absorption of normal incidence radiation in the valence band of InAs self-assembled quantum

S.-W. Lee; K. Hirakawa

2006-01-01

404

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

NASA Astrophysics Data System (ADS)

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 electromagnetic field has no influence on the generated CdSe QDs. The resulting CdSe NCs prepared using either conductive or microwave dielectric heating exhibited the same primary crystallite size, shape, quantum yield and size distribution regardless of the heating mode.

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

2012-11-01

405

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

PubMed

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 electromagnetic field has no influence on the generated CdSe QDs. The resulting CdSe NCs prepared using either conductive or microwave dielectric heating exhibited the same primary crystallite size, shape, quantum yield and size distribution regardless of the heating mode. PMID:23085887

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

2012-12-01

406

Quantum-dot-induced phase shift in a pillar microcavity  

SciTech Connect

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

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

2011-07-15

407

Quantum Computation Using Optically Coupled Quantum Dot Arrays  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

408

InAs Based Quantum Dots for Quantum Information Processing:. from Fundamental Physics to 'plug and Play' Devices  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots have attracted much interest in implementing solid-state quantum information processing. Using InAs based quantum dots, we demonstrate quantum coupling between two stacked quantum dot molecules in electroluminescence, controlling Stark shifts of single quantum dots in electroluminescence, and 'plug and play' single photon emission at telecommunication wavelengths.

Xu, Xiulai; Andreev, Aleksey; Brossard, Frederic; Hammura, Kiyotaka; Williams, David

2009-06-01

409

InAs Based Quantum Dots for Quantum Information Processing:. from Fundamental Physics to 'plug and Play' Devices  

Microsoft Academic Search

Semiconductor quantum dots have attracted much interest in implementing solid-state quantum information processing. Using InAs based quantum dots, we demonstrate quantum coupling between two stacked quantum dot molecules in electroluminescence, controlling Stark shifts of single quantum dots in electroluminescence, and 'plug and play' single photon emission at telecommunication wavelengths.

Xiulai Xu; Aleksey Andreev; Frederic Brossard; Kiyotaka Hammura; David Williams

2009-01-01

410

Timing matters: the underappreciated role of temperature ramp rate for shape control and reproducibility of quantum dot synthesis  

NASA Astrophysics Data System (ADS)

Understanding the coupled kinetic and thermodynamics factors governing colloidal nanocrystals nucleation and growth are critical factors in the predictable and reproducible synthesis of advanced nanomaterials. We show that the temporal temperature profile is decisive in tuning the particle shape from pseudo-spherical to monodisperse cubes. The shape of the nanocrystals was characterized by transmission electron microscopy and X-ray diffraction. We introduce a mechanism for the shape controlled synthesis in the context of temperature-dependent nucleation and growth and provide experimental evidence to support it.Understanding the coupled kinetic and thermodynamics factors governing colloidal nanocrystals nucleation and growth are critical factors in the predictable and reproducible synthesis of advanced nanomaterials. We show that the temporal temperature profile is decisive in tuning the particle shape from pseudo-spherical to monodisperse cubes. The shape of the nanocrystals was characterized by transmission electron microscopy and X-ray diffraction. We introduce a mechanism for the shape controlled synthesis in the context of temperature-dependent nucleation and growth and provide experimental evidence to support it. Electronic supplementary information (ESI) available: Experimental details, temperature dip experiments, and water content experiments. See DOI: 10.1039/c2nr31054f

Baumgardner, William J.; Quan, Zewei; Fang, Jiye; Hanrath, Tobias

2012-05-01

411

Photon-mediated interaction between distant quantum dot circuits.  

PubMed

Engineering the interaction between light and matter is an important goal in the emerging field of quantum opto-electronics. Thanks to the use of cavity quantum electrodynamics architectures, one can envision a fully hybrid multiplexing of quantum conductors. Here we use such an architecture to couple two quantum dot circuits. Our quantum dots are separated by 200 times their own size, with no direct tunnel and electrostatic couplings between them. We demonstrate their interaction, mediated by the cavity photons. This could be used to scale up quantum bit architectures based on quantum dot circuits or simulate on-chip phonon-mediated interactions between strongly correlated electrons. PMID:23360991

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

2013-01-01

412

Photon-mediated interaction between distant quantum dot circuits  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

413

A functional cell for quantum-dot cellular automata  

Microsoft Academic Search

We present experimental demonstration of a basic cell of Quantum-dot Cellular Automata, a transistorless computation paradigm which addresses the issues of device density and interconnection. The devices presented consist of four and six-dot quantum-dot cellular systems where the metal dots are connected by capacitors and tunnel junctions. The operation of a basic cell is confirmed by the externally controlled polarization

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

1998-01-01

414

Bound states in the continuum in quantum-dot pairs  

SciTech Connect

It is shown that for two open quantum dots connected by a wire, ''bound states in the continuum'' of a single electron are formed at nearly periodic distances between the dots. This is due to Fabry-Perot interference between quasibound states in each dot. The bound states are nonlocal, describing the electron trapped in both dots at the same time. Theoretical and numerical results show that trapped states exist even if the wire connecting the dots is relatively long.

Ordonez, Gonzalo; Na, Kyungsun; Kim, Sungyun [Center for Studies in Statistical Mechanics and Complex Systems, University of Texas at Austin, Austin, Texas 78712 (United States); Max-Planck Institute for Physics of Complex Systems, Noethnizter Str. 38, 01187 Dresden (Germany)

2006-02-15

415

Detection of the relaxation rates of an interacting quantum dot by a capacitively coupled sensor dot  

NASA Astrophysics Data System (ADS)

We present a theoretical study of the detection of the decay time scales for a single-level quantum dot by means of a capacitively coupled sensor dot, which acts as an electrometer. We investigate the measurement back-action on the quantum-dot decay rates and elucidate its mechanism. We explicitly show that the setup can be used to measure the bare quantum-dot relaxation rates by choosing gate pulses that minimize the back-action. Interestingly, we find that besides the charge relaxation rate, also the rate associated to the fermion parity in the dot can be accessed with this setup.

Schulenborg, Jens; Splettstoesser, Janine; Governale, Michele; Contreras-Pulido, L. Debora

2014-05-01

416

Small bright charged colloidal quantum dots.  

PubMed

Using electrochemical charge injection, the fluorescence lifetimes of negatively charged core/shell CdTe/CdSe QDs are measured as a function of core size and shell thickness. It is found that the ensemble negative trion lifetimes reach a maximum (?4.5 ns) for an intermediate shell thickness. This leads to the smallest particles (?4.5 nm) with the brightest trion to date. Single dot measurements show that the negative charge suppresses blinking and that the trion can be as bright as the exciton at room temperature. In contrast, the biexciton lifetimes remain short and exhibit only a monotonous increase with shell thickness, showing no correlation with the negative trion decays. The suppression of the Auger process in small negatively charged CdTe/CdSe quantum dots is unprecedented and a significant departure from prior results with ultrathick CdSe/CdS core/shell or dot-in-rod structures. The proposed reason for the optimum shell thickness is that the electron-hole overlap is restricted to the CdTe core while the electron is tuned to have zero kinetic energy in the core for that optimum shell thickness. The different trend of the biexciton lifetime is not explained but tentatively attributed to shorter-lived positive trions at smaller sizes. These results improve our understanding of multiexciton recombination in colloidal quantum dots and may lead to the design of bright charged QDs for more efficient light-emitting devices. PMID:24350673

Qin, Wei; Liu, Heng; Guyot-Sionnest, Philippe

2014-01-28

417

Quantum Dots with Built-in Charge for Enhancing Quantum Dot Solar Cells and Infrared Photodetectors  

NASA Astrophysics Data System (ADS)

We present theoretical and experimental results of electron kinetics and transport in quantum dot structures with potential barriers created around dots via intentional or unintentional doping. Monte Carlo simulations demonstrate that photoelectron capture is substantially enhanced in strong fields and electron kinetics can be controlled by potential barriers. Therefore, by creating potential barriers around dots, we found that our novel quantum dots with built-in charge (Q-BIC) solar cells and infrared (IR) photodectors enhance electron intersubband transitions and suppress fast electron capture processes. These factors lead to a 60% increase in the photocurrent of the Q-BIC solar cells (without degradation of the open circuit voltage) and ~25 times increase in the photoresponse of the Q-BIC photodetectors.

Sablon, Kimberly A.; Mitin, V.; Little, J. W.; Sergeev, A.; Vagidov, N.

418

Multicolor quantum dots-in-a-well focal plane arrays  

Microsoft Academic Search

This paper discusses recent and future advancements in the field of quantum dots-in-a-well (DWELL) focal plane arrays (FPAs). Additionally, for clarity sake, the fundamentals of FPA figures of merit are reviewed. The DWELL detector represents a hybrid between a conventional quantum well photodetector (QWIP) and a quantum dot (QD) photodetector (QDIP). This hybridization, where the active region consists of QDs

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

2008-01-01

419

Logic Gate Implementations for Quantum Dot Cellular Automata  

Microsoft Academic Search

Quantum dot cellular automata (QCA) is a novel and potentially advanced technology for implementing computing architecture at nano scale. QCA is a promising successor for CMOS transistor technology, while allowing the implementation of logic circuits using quantum devices, such as quantum dot or single domain nano magnets, a new set of tools must be developed to assist the design and

Sanjay Modi; Abhineet S. Tomar

2010-01-01

420

Classical behavior of few-electron parabolic quantum dots  

Microsoft Academic Search

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

O. Ciftja

2009-01-01

421

Light amplification in semiconductor nanocrystals: Quantum rods versus quantum dots  

NASA Astrophysics Data System (ADS)

We perform side-by-side comparison of optical gain properties of spherical and elongated nanocrystals (quantum dots and quantum rods, respectively). This comparison indicates that elongated nanoparticles provide several features beneficial for lasing applications, such as enhanced absorption cross sections (and hence reduced lasing threshold and improved photostability), increased optical gain lifetime, and extended optical gain spectral range through the use of transitions that involve both ground and excited electronic states.

Htoon, H.; Hollingworth, J. A.; Malko, A. V.; Dickerson, R.; Klimov, V. I.

2003-06-01

422

Vector solitons in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

A theory of an optical vector soliton of self-induced transparency in an ensemble of semiconductor quantum dots is considered. By using the perturbative reduction method, the system of the Maxwell-Liouville equations is reduced to the two-component coupled nonlinear Schrödinger equations. It is shown that a distribution of transition dipole moments of the quantum dots and phase modulation changes significantly the pulse parameters. The shape of the optical two-component vector soliton with the sum and difference of the frequencies in the region of the carrier frequency is presented. The vector soliton can be reduced to the breather solution of self-induced transparency with a different profile. Explicit analytical expressions in the presence of single-excitonic and biexcitonic transitions for the optical vector soliton are obtained with realistic parameters which can be reached in current experiments.

Adamashvili, G. T.

2012-09-01

423

Scanning photoluminescent spectroscopy of bioconjugated quantum dots  

NASA Astrophysics Data System (ADS)

We report on the application of the bio-conjugated quantum dots (QDs) for a "sandwich" enzyme-linked immunosorbent assay (ELISA) cancer testing technique. Quantum dot ELISA detection of the cancer PSA antigen at concentrations as low as 0.01 ng/ml which is ˜50 times lower than the classic "sandwich" ELISA was demonstrated. Scanning photoluminescence (PL) spectroscopy was performed on dried ELISA wells and the results compared with the same QD samples dried on a solid substrate. We confirmed a "blue" up to 37 nm PL spectral shift in a case of QDs conjugated to PSA antibodies. Increasing of the "blue" spectral shift was observed at lower PSA antigen concentrations. The results can be used to improve sensitivity of "sandwich" ELISA cancer antigen detection.

Chornokur, G.; Ostapenko, S.; Oleynik, E.; Phelan, C.; Korsunska, N.; Kryshtab, T.; Zhang, J.; Wolcott, A.; Sellers, T.

2009-04-01

424

Quantum dot behavior in bilayer graphene nanoribbons.  

PubMed

Bilayer graphene has recently earned great attention for its unique electronic properties and commendable use in electronic applications. Here, we report the observation of quantum dot (QD) behaviors in bilayer graphene nanoribbons (BL-GNRs). The periodic Coulomb oscillations indicate the formation of a single quantum dot within the BL-GNR because of the broad distribution function of the carrier concentration fluctuation at the charge neutrality point. The size of the QD changes as we modulate the relative position between the Fermi level and surface potential. Furthermore, the potential barriers forming the QD remain stable at elevated temperatures and external bias. In combination with the observation of transport gaps, our results suggest that the disordered surface potential creates QDs along the ribbon and governs the electronic transport properties in BL-GNRs. PMID:22017308

Wang, Minsheng; Song, Emil B; Lee, Sejoon; Tang, Jianshi; Lang, Murong; Zeng, Caifu; Xu, Guangyu; Zhou, Yi; Wang, Kang L

2011-11-22

425

Geometric spin manipulation in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We propose a method to flip the spin completely by an adiabatic transport of quantum dots. We show that it is possible to flip the spin by inducing a geometric phase on the spin state of a quantum dot. We estimate the geometric spin flip time (approximately 2 ps) which turned out to be much shorter than the experimentally reported decoherence time (approximately 100 ns) that would provide an alternative means of fliping the spin before reaching decoherence. It is important that both the Rashba coupling and the Dresselhaus coupling are present for inducing a phase necessary for spin flip. If one of them is absent, the induced phase is trivial and irrelevant for spin-flip.

Prabhakar, Sanjay; Melnik, Roderick; Inomata, Akira

2014-04-01

426

Nonlinear optical properties of semiconductor quantum dots  

Microsoft Academic Search

The crystallite radius R that is ascertained by X-ray techniques is noted to exert an influence on the shift of the lowest quantized state in quantum dots (QDs). On the basis of the Stokes shift of absorption and emission, and their half-widths, an upper limit is obtained for the Huang-Rhys factor S. Pump and probe beam measurements exhibit absorption structure

A. Uhrig; A. Woerner; C. Klingshirn; L. Banyai; S. Gaponenko; I. Lacis; N. Neuroth; B. Speit; K. Remitz

1992-01-01

427

InAs quantum dots infrared photodetectors  

Microsoft Academic Search

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

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

2003-01-01

428

Inverted colloidal quantum dot solar cells.  

PubMed

An inverted architecture of quantum dot solar cells is demonstrated by introducing a novel ZnO method on top of the PbS CQD film. Improvements in device characteristics stem from constructive optical interference from the ZnO layer that enhances absorption in the PbS CQD layer. Outstanding diode characteristics arising from a superior PbS/ZnO junction provide a further electronic advantage. PMID:24677118

Kim, Gi-Hwan; Walker, Bright; Kim, Hak-Beom; Kim, Jin Young; Sargent, Edward H; Park, Jongnam; Kim, Jin Young

2014-05-01

429

Template-assembly of quantum dot molecules.  

PubMed

Semiconductor quantum dots (QDs) have been called artificial atoms because of their discrete electronic structures. Assembling them into artificial molecules may greatly expand our capability in controlling physical properties on the nanoscale. Here we show the successful assembly and size control of colloidal PbSe QD clusters into large-scale templates defined by block-copolymer patterns. Following the exchange of capping molecules, the QD clusters behave as artificial molecules due to enhanced and local electronic interactions. PMID:23075221

Lei, Kin Wai; West, Tyler; Zhu, X-Y

2013-04-25

430

Quantum-dot cellular automata adders  

Microsoft Academic Search

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

Wei Wang; Konrad Walus; G. A. Jullien

2003-01-01

431

Electrical properties of semiconductor quantum dots  

SciTech Connect

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

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

2013-04-15

432

Photoluminescence of Silicon-Germanium Quantum Dots  

NSDL National Science Digital Library

This presentation, given at the Arizona Nanotechnology Cluster Symposium, introduces the topic of the photoluminescence of silicon-germainium quantum dots. Dr. James Kolodzey, of University of Delaware, presents the topic in powerpoint format. The presentation is loaded with helpful diagrams and images that capture the essence of Kolodzey's research. Overall, while the topic is advanced, the presentations allows users to better understand due to the helpful resources it contains.

Kolodzey, James

2008-10-27

433

Controlling blinking in multilayered quantum dots  

NASA Astrophysics Data System (ADS)

The fluorescence intermittency of multilayered quantum dots (QDs) is experimentally investigated. The measured blinking statistical probabilities for QDs of different shell structures and at different excitation powers are compared with the diffusion controlled electron transfer model. The results show that the power law statistics for the ``on'' and ``off'' events depend strongly on the structure and thicknesses of the shells. Strongly suppressed blinking behavior is observed in the CdSe/CdS/ZnCdS/ZnS QDs.

Wang, Ruimin; Zhang, Yanpeng; Gan, Chenli; Muhammad, Javed; Xiao, Min

2010-04-01

434

Ab initio computation of circular quantum dots  

Microsoft Academic Search

We perform coupled-cluster and diffusion Monte Carlo calculations of the\\u000aenergies of circular quantum dots up to 20 electrons. The coupled-cluster\\u000acalculations include triples corrections and a renormalized Coulomb interaction\\u000adefined for a given number of low-lying oscillator shells. Using such a\\u000arenormalized Coulomb interaction brings the coupled-cluster calculations with\\u000atriples correlations in excellent agreement with the diffusion Monte Carlo

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

2010-01-01

435

Quantum Dot Superlattice Thermoelectric Materials and Devices  

Microsoft Academic Search

PbSeTe-based quantum dot superlattice structures grown by molecular beam epitaxy have been investigated for applications in thermoelectrics. We demonstrate improved cooling values relative to the conventional bulk (Bi,Sb)2(Se,Te)3 thermoelectric materials using a n-type film in a one-leg thermoelectric device test setup, which cooled the cold junction 43.7 K below the room temperature hot junction temperature of 299.7 K. The typical

T. C. Harman; P. J. Taylor; M. P. Walsh; B. E. LaForge

2002-01-01

436

Quantum Dot Nanotechnology for Prostate Cancer Research  

Microsoft Academic Search

Quantum dots (QDs), tiny light-emitting particles on the nanometer scale, are emerging as a new class of fluorescent probes\\u000a for cancer cell imaging and molecular profiling. In comparison with organic dyes and fluorescent proteins, QDs have unique\\u000a optical and electronic properties, such as size-tunable light emission, improved signal brightness, resistance against photobleaching,\\u000a and simultaneous excitation of multiple fluorescence colors. These

Xiaohu Gao; Yun Xing; Leland W. K. Chung; Shuming Nie

437

Spin Polarizing Neutral Excitons In Quantum Dots  

NASA Astrophysics Data System (ADS)

A high degree of spin polarization for the neutral exciton in individual InAs quantum dots, without any external magnetic field applied, is demonstrated. The polarization mechanism is shown to be due to the difference in capture time into the QD for the electrons and holes after photo excitation in the wetting layer. This leads to optical pumping of the QD nuclei by spin polarized electrons and hence suppression of the anisotropic electron--hole exchange interaction.

Larsson, L. A.; Moskalenko, E. S.; Holtz, P. O.

2011-12-01

438

The pinning effect in quantum dots  

NASA Astrophysics Data System (ADS)

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

Monisha, P. J.; Mukhopadhyay, Soma

2014-04-01

439

Outlook on quantum dot infrared photodetectors  

Microsoft Academic Search

This paper reviews the present status and gives outlook on future developments of quantum dot infrared photodetectors (QDIPs).\\u000a At the beginning the paper summarizes the fundamental properties of QDIPs. Next, an emphasize is put on their potential developments.\\u000a Investigations of the performance of QDIPs as compared to other types of infrared photodetectors are presented. A model is\\u000a based on fundamental

A. Rogalski

2009-01-01

440

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

Microsoft Academic Search

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

Jed Dempsey

1991-01-01

441

Synthesis and characterizations of ultra-small ZnS and Zn(1-x)Fe(x)S quantum dots in aqueous media and spectroscopic study of their interactions with bovine serum albumin.  

PubMed

This work reports a new experimental methodology for the synthesis of ultra small zinc sulfide and iron doped zinc sulfide quantum dots in aqueous media. The nanoparticles were obtained using a simple procedure based on the precipitation of ZnS in aqueous solution in the presence of 2-mercaptoethanol as a capping agent, at room temperature. The effect of Fe(3+) ion concentration as dopant on the optical properties of ZnS was studied. The size of quantum dots was determined to be about 1nm, using scanning tunneling microscopy. The synthesized nanoparticles were characterized by X-ray diffraction, UV-Vis absorption and photoluminescence emission spectroscopies. The presence and amount of iron impurity in the structure of Zn((1-x))Fe(x)S nanocrystals were confirmed by atomic absorption spectrometry. A blue shift in band-gap of ZnS was observed upon increasing incorporation of Fe(3+) ion in the iron doped zinc sulfide quantum dots. The photoluminescence investigations showed that, in the case of iron doped ZnS nanoparticles, the emission band of pure ZnS nanoparticles at 427nm shifts to 442nm with appearance of a new sharp emission band around 532nm. The X-ray diffraction analysis indicated that the iron doped nanoparticles are crystalline, with cubic zinc blend structure, having particle diameters of 1.7±022nm. Finally, the interaction of the synthesized nanoparticles with bovine serum albumin was investigated at pH 7.2. The UV-Vis absorption and fluorescence spectroscopic methods were applied to compare the optical properties of pure and iron doped ZnS quantum dots upon interaction with BSA. It was proved that, in both cases, the fluorescence quenching of BSA by the quantum dots is mainly a result of the formation of QDs-BSA complex in solution. In the steady-state fluorescence studies, the interaction parameters including binding constants (K(a)), number of binding sites (n), quenching constants ( [Formula: see text] ), and bimolecular quenching rate constants (k(q)) were determined at three different temperatures and the results were then used to evaluate the corresponding thermodynamic parameters ?H, ?S and ?G. PMID:21482179

Khani, Omid; Rajabi, Hamid Reza; Yousefi, Mohammad Hasan; Khosravi, Ali Azam; Jannesari, Mohammad; Shamsipur, Mojtaba

2011-07-01

442

Synthesis and characterizations of ultra-small ZnS and Zn (1- x) Fe xS quantum dots in aqueous media and spectroscopic study of their interactions with bovine serum albumin  

NASA Astrophysics Data System (ADS)

This work reports a new experimental methodology for the synthesis of ultra small zinc sulfide and iron doped zinc sulfide quantum dots in aqueous media. The nanoparticles were obtained using a simple procedure based on the precipitation of ZnS in aqueous solution in the presence of 2-mercaptoethanol as a capping agent, at room temperature. The effect of Fe 3+ ion concentration as dopant on the optical properties of ZnS was studied. The size of quantum dots was determined to be about 1 nm, using scanning tunneling microscopy. The synthesized nanoparticles were characterized by X-ray diffraction, UV-Vis absorption and photoluminescence emission spectroscopies. The presence and amount of iron impurity in the structure of Zn (1- x) Fe xS nanocrystals were confirmed by atomic absorption spectrometry. A blue shift in band-gap of ZnS was observed upon increasing incorporation of Fe 3+ ion in the iron doped zinc sulfide quantum dots. The photoluminescence investigations showed that, in the case of iron doped ZnS nanoparticles, the emission band of pure ZnS nanoparticles at 427 nm shifts to 442 nm with appearance of a new sharp emission band around 532 nm. The X-ray diffraction analysis indicated that the iron doped nanoparticles are crystalline, with cubic zinc blend structure, having particle diameters of 1.7 ± 022 nm. Finally, the interaction of the synthesized nanoparticles with bovine serum albumin was investigated at pH 7.2. The UV-Vis absorption and fluorescence spectroscopic methods were applied to compare the optical properties of pure and iron doped ZnS quantum dots upon interaction with BSA. It was proved that, in both cases, the fluorescence quenching of BSA by the quantum dots is mainly a result of the formation of QDs-BSA complex in solution. In the steady-state fluorescence studies, the interaction parameters including binding constants ( Ka), number of binding sites ( n), quenching constants ( KSV), and bimolecular quenching rate constants ( kq) were determined at three different temperatures and the results were then used to evaluate the corresponding thermodynamic parameters ? H, ? S and ? G.

Khani, Omid; Rajabi, Hamid Reza; Yousefi, Mohammad Hasan; Khosravi, Ali Azam; Jannesari, Mohammad; Shamsipur, Mojtaba

2011-07-01

443

Diamagnetic Exciton Properties in Quantum Dot Molecules  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

444

Quantum-dot infrared photodetector with lateral carrier transport  

Microsoft Academic Search

In this letter, we present a normal-incident quantum-dot infrared photodetector. The detection principle is based on intersubband transition between the p states and the wetting-layer subband in the conduction band of self-assembled In(Ga)As\\/GaAs quantum dots. Carrier transport takes place in a channel next to the quantum-dot layers. The photoresponse is peaked at lambda=6.65 mum (186 meV) and reaches a maximum

L. Chu; A. Zrenner; M. Bichler; G. Abstreiter

2001-01-01

445

Ultrafast Coherent Spectroscopy of Single Semiconductor Quantum Dots  

Microsoft Academic Search

This chapter summarizes our recent work—performed within the project B6 of the Sonderforschungsbereich 296—on combining ultrafast\\u000a spectroscopy and near-field microscopy to probe the nonlinear optical response of a single quantum dot and of a pair of dipole-coupled\\u000a quantum dots on a femtosecond time scale. We demonstrate coherent control of both amplitude and phase of the coherent quantum\\u000a dot polarization by

Christoph Lienau; Thomas Elsaesser

446

Optical Spectroscopy on Single Quantum Dots: Charged Excitons  

Microsoft Academic Search

Single self-assembled quantum dots are among the most widely studied systems in the field of modern solid state spectroscopy.\\u000a Neutral multi-exciton complexes have been investigated in quantum dots by power dependent photoluminescence spectroscopy.\\u000a The experimental preparation of specific charged exciton states in a single quantum dot can be realized by bias controlled\\u000a si