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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

Synthesis and applications of quantum dots and magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We have developed a new synthetic method for producing high-quality quantum dots (QDs) in aqueous solution for biological imaging applications. The glutathione-capped CdTe, ZnSe and 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 QDs is simple and cost-effective compared to the conventional organometallic approaches. It can be easily scaled up for the commercial production of alloyed nanocrystals of various compositions. We have also demonstrated the fabrication of magnetic quantum dots (MQDs) through a seed-mediated approach. The formation and assembly of these bifunctional nanocomposites have been elucidated by high-resolution transmission electron microscopy (HRTEM). The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components in this hybrid system. We have created biocompatible silica-coated MQDs that effectively target the cell membranes.

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

2008-03-01

3

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

2012-08-28

4

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

5

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

6

Plasma Synthesis of Luminescent Silicon Quantum Dots  

NASA Astrophysics Data System (ADS)

Semiconductor nanoparticles with photoluminescent properties are of interest for a wide range of applications from solid state lighting, to solid state lasers, to imaging biological systems. A wide range of compound semiconductor quantum dots has been produced with excellent photoluminescent properties such as, for instance, cadmium-selenide. However, many of these compound quantum dot materials are of environmental concerns due to their content of toxic heavy metals. Hence there is continued interest in silicon quantum dots as a luminescent material, since silicon is widely considered as environmentally benign. In this presentation we discuss a plasma process that is capable of producing crystalline, nonagglomerated silicon nanoparticles of less than 10 nm in size. The reactor is designed to be a flow through reactor which enables online analysis of the particle size distribution with a fast scanning nano-Differential Mobility Analyzer (DMA). The particles structural properties are studied with high resolution transmission electron microscopy. The luminescent properties of the particles are investigated by studying photoluminescence of the particles on illumination with UV radiation.

Thimsen, Elijah; Mangolini, Lorenzo; Kortshagen, Uwe

2004-09-01

7

Synthesis, biological targeting and photophysics of quantum dots  

Microsoft Academic Search

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

Samuel Jon Clarke

2009-01-01

8

Synthesis, Characterization and Application Of PbS Quantum Dots  

SciTech Connect

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

Sarma, Sweety; Datta, Pranayee [Department of Electronics Science, Gauhati University, Gnwahait-781014, Assam (India); Barua, Kishore Kr. [Department of Physics, Central University, Tezpur-784028, Assam (India); Karmakar, Sanjib [Department of Instrumentation and USIC, Gauhati University, Guwahati-781014, Assam (India)

2009-06-29

9

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

10

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

11

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

12

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

13

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

2011-09-15

14

Aqueous synthesis of Cu-doped ZnSe quantum dots  

Microsoft Academic Search

In this paper, we described a simple growth-doping approach for aqueous synthesis of Cu-doped ZnSe quantum dots (Cu:ZnSe d-dots) with mercaptopropionic acid as stabilizer. The influences of the ratios of precursors and the concentration of Cu dopant ions on Cu:ZnSe d-dots synthesis were studied in detail in this study. The Cu dopant ions had significant influence on the optical properties

Gao Xue; Wang Chao; Niu Lu; Su Xingguang

2011-01-01

15

Synthesis and characterization of aqueous quantum dots for biomedical applications  

Microsoft Academic Search

Quantum Dots (QDs) are semiconductor nanocrystals (1˜20 nm) exhibiting distinctive photoluminescence (PL) properties due to the quantum confinement effect. Having many advantages over organic dyes, such as broad excitation and resistance to photobleaching, QDs are widely used in bioapplications as one of most exciting nanobiotechnologies. To date, most commercial QDs are synthesized through the traditional organometallic method and contain toxic

Hui Li

2008-01-01

16

Synthesis and surface photochemistry of graphitized carbon quantum dots  

Microsoft Academic Search

Graphitized carbon quantum dots (CQDs) were synthesized by a simple hydrothermal process with cetyltrimethylammonium bromide (CTAB) as the starting material and nitric acid as surface oxidant. The photoluminescent quantum yield (QY) of CQDs could be greatly enhanced through surface esterification with glycol. Based on the structure characterization, we proposed that the CQDs consisted of the stack of graphene sheets sized

Yun Liu; Chun-yan Liu; Zhi-ying Zhang

2011-01-01

17

Synthesis and characterization of in-containing colloidal quantum dots  

Microsoft Academic Search

InP quantum dots (QDs) with zinc blende structure and InN QDs with hexagonal structure were synthesized from appropriate organometallic precursors in a noncoordinating solvent using myristic acid as a ligand. In2O3 nanospheres and quantum rods were synthesized under reflux conditions in a coordinating methyl imizadole (MeIm) solvent. The QDs were characterized by TEM, the associated energy dispersive spectroscopy (EDS), electron

Melisa R. Greenberg; Gennady A. Smolyakov; Ying-Bing Jiang; Timothy J. Boyle; Marek Osinski

2006-01-01

18

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

19

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

20

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

21

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

22

Synthesis and photoluminescence of fluorinated graphene quantum dots  

NASA Astrophysics Data System (ADS)

Fluorinated graphene quantum dots (F-GQDs) were synthesized by cutting fluorinated graphene through a hydrothermal approach. The F-GQDs with oxygen-rich functional groups have a F/C atomic ratio of ca. 23.68% and diameter of 1-7 nm. The photoluminescence (PL) properties of the F-GQDs were investigated. The results showed that besides exhibiting bright blue PL, the F-GQDs display a clear upconversion PL.

Feng, Qian; Cao, Qingqi; Li, Ming; Liu, Fuchi; Tang, Nujiang; Du, Youwei

2013-01-01

23

Synthesis and surface photochemistry of graphitized carbon quantum dots.  

PubMed

Graphitized carbon quantum dots (CQDs) were synthesized by a simple hydrothermal process with cetyltrimethylammonium bromide (CTAB) as the starting material and nitric acid as surface oxidant. The photoluminescent quantum yield (QY) of CQDs could be greatly enhanced through surface esterification with glycol. Based on the structure characterization, we proposed that the CQDs consisted of the stack of graphene sheets sized several nanometers and their excitation-dependent photoluminescence (PL) should be attributed to the n??* transition of CO bond of surface carboxylic groups. And the PL of CQDs was obviously enhanced by the esterification of carboxylic groups, possibly due to the increase of the molecular coplanarity or the rigidity. PMID:21306724

Liu, Yun; Liu, Chun-yan; Zhang, Zhi-ying

2011-01-25

24

Continuous-flow reactor–based synthesis of carbohydrate and dihydrolipoic acid–capped quantum dots  

Microsoft Academic Search

A detailed protocol for the large-scale synthesis of carbohydrate and dihydrolipoic acid (DHLA)-coated CdSe\\/ZnS and CdTe\\/ZnS nanoparticles using continuous flow reactors is described here. Three continuous flow microreaction systems, operating at three different temperatures, are used for the synthesis of mannose-, galactose- or DHLA-functionalized quantum dots (QDs). In the first step of synthesis, the CdSe and CdTe nanoparticles are prepared.

Paola Laurino; Raghavendra Kikkeri; Peter H Seeberger

2011-01-01

25

Controlled synthesis and characterization of ZnSe quantum dots.  

PubMed

Adopting improved metal-organic "Green method," Colloidal ZnSe quantum dots were synthesized by using cheap and low toxic zinc oxide (ZnO) in an organic solvent system of 1-hexadecylamine (HDA), lauric acid (LA) and tri-n-octylphosphine (TOP). The effects of HDA dosage, injection temperature, growth temperature and time on the microstructure and optical properties of ZnSe were studied by means of X-Ray diffraction(XRD), transmission electron microscopy (TEM), spectrofluorometers and ultraviolet spectrophotometer, respectively. The results showed that ZnSe quantum dots with the best range of the size evolution were obtained under the condition of injection at 280 degrees C and growth at 240 degrees C by choosing the optimal parameters of ZnO:HDA:LA= 1:2.1:5.2 and TOPSe = 1 mol/L. Its size became larger and the emission peak shifted obviously to red with increasing the growth time. Meanwhile, the obtained ZnSe was of the wurtzite structure, had good uniformity and fluorescent characteristics. PMID:21138039

Wang, X; Ma, X L; Feng, X; Zheng, Y F

2010-11-01

26

One-step synthesis of water-soluble ZnSe quantum dots via microwave irradiation  

Microsoft Academic Search

A facile strategy has been developed for the synthesis of glutathione-capped ZnSe quantum dots (QDs) in aqueous media. The reaction was carried out in air atmosphere with a single step by using Na2SeO3, a stable and commercial Se source, to replace the commonly adopted NaHSe or H2Se. Moreover, microwave irradiation improved the photoluminescence quantum yield (PLQY) as well as lowered

Liang Huang; Heyou Han

2010-01-01

27

Synthesis and upconversion luminescence of N-doped graphene quantum dots  

NASA Astrophysics Data System (ADS)

A hydrothermal approach was developed for the synthesis of N-doped graphene quantum dots (N-GQDs) by cutting N-doped graphene. The N-GQDs obtained have a N/C atomic ratio of ca. 5.6% and diameter of 1-7 nm. The photoluminescence (PL) properties of the N-GQDs were investigated. It was found that the N-GQDs possess bright blue PL and excellent upconversion PL properties.

Li, Ming; Wu, Wenbin; Ren, Wencai; Cheng, Hui-Ming; Tang, Nujiang; Zhong, Wei; Du, Youwei

2012-09-01

28

Synthesis and characterization of binary and ternary III–V quantum dots  

Microsoft Academic Search

Quantum dots of InP, GaP, GaInP2, and GaAs with diameters ranging from 20–80 Å can be synthesized as well-crystallized nanoparticles with bulk zinc blende structure. The synthesis is achieved by heating appropriate organometallic precursors with stabilizers in high boiling solvents for several days to produce QDs, which can then be dissolved in nonpolar organic solvents to form transparent colloidal QD

O. I. Mi?i?; A. J. Nozik

1996-01-01

29

Synthesis and exploitation of InP\\/ZnS quantum dots for bioimaging  

Microsoft Academic Search

Nano- and cytotoxicity becomes increasingly more important with an increasing number of potential bio-medical applications for semiconductor Quantum Dots (QDs). Therefore, the frequently used CdSe-based QDs are unsuitable per-se, since cadmium is a highly toxic heavy metal and may leach out of QDs. Cadmium-free QDs have not been available for a long time, because the synthesis of e.g. monodisperes and

Salam Massadeh; Shu Xu; Thomas Nann

2009-01-01

30

Colloidal chemical synthesis and characterization of InAs nanocrystal quantum dots  

SciTech Connect

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

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

1996-09-01

31

Quantum dots in nanobiotechnology  

Microsoft Academic Search

Research on semiconductor nanocristals (also known as quantum dots of QD) in the field of nanobiotechnology is rapidly evolving\\u000a thanks to progresses in their synthesis and their surface chemistry. Two types of materials, water soluble and biocompatible\\u000a single QD and beads containing QDs, are becoming available and exciting applications based on these new materials are developed.\\u000a We will present the

N. Lequeux; B. Dubertret

2005-01-01

32

Microwave-assisted low temperature synthesis of wurtzite ZnS quantum dots  

NASA Astrophysics Data System (ADS)

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 °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.

Shahid, Robina; Toprak, Muhammet S.; Muhammed, Mamoun

2012-03-01

33

Rapid synthesis of stable ZnO quantum dots  

Microsoft Academic Search

Zinc oxide nanocrystallites down to 1.5 nm in diameter were made by spray combustion of Zn\\/Si precursors. These crystallites exhibit a quantum size effect: blueshift of light absorption with decreasing crystallite size. X-ray diffraction, high-resolution transmission electron microscopy, and nitrogen adsorption showed that the addition of controlled amounts of silica prevented the growth and stabilized the ZnO crystals. The blue

L. Mädler; W. J. Stark; S. E. Pratsinis

2002-01-01

34

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

35

Quantum Computing with Quantum Dots  

Microsoft Academic Search

Our time at the Computing Beyond Silicon Summer School, hosted by Caltech, gave us a unique opportunity to explore new concepts and learn about advances in modern information processing that interest us. We chose to study quantum computation using quantum dot systems because of their potential for bringing forth a solid-sate quantum information processing system. Specifically we chose to investigate

Joon Ho Baek; Happy Hsin; Joshua LaForge; Daniel Nedelcu

36

Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots  

Microsoft Academic Search

Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained

Abhilash Sugunan; Yichen Zhao; Somak Mitra; Lin Dong; Shanghua Li; Sergei Popov; Saulius Marcinkevicius; Muhammet S. Toprak; Mamoun Muhammed

2011-01-01

37

Size-tunable polymeric nanoreactors for one-pot synthesis and encapsulation of quantum dots.  

PubMed

Hydrophilic polymeric nanoparticles are synthesized through a Bergman cyclization- mediated intramolecular chain collapse of structurally well-defined linear polymers, and then used as size-tunable nanoreactors to fabricate and encapsulate quantum dots in a one-pot reaction. Crystalline quantum dots are formed in all of these nanoreactors and visualized by transmission electron microscopy. Smaller nanoreactors produce one quantum dot each while larger nanoreactors form a number, resulting in fluorescence quenching. By controlling the molecular weight of the linear polymer precursor, a variable number of nanocrystals are fabricated and assembled in a single nanoreactor. PMID:22610539

Qian, Guannan; Zhu, Benchuan; Wang, Youfu; Deng, Sheng; Hu, Aiguo

2012-05-21

38

Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots  

PubMed Central

A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

2011-01-01

39

Continuous-flow reactor-based synthesis of carbohydrate and dihydrolipoic acid-capped quantum dots.  

PubMed

A detailed protocol for the large-scale synthesis of carbohydrate and dihydrolipoic acid (DHLA)-coated CdSe/ZnS and CdTe/ZnS nanoparticles using continuous flow reactors is described here. Three continuous flow microreaction systems, operating at three different temperatures, are used for the synthesis of mannose-, galactose- or DHLA-functionalized quantum dots (QDs). In the first step of synthesis, the CdSe and CdTe nanoparticles are prepared. The size and spectral properties of the CdSe core of the nanoparticles are controlled by adjustment of the residence time and the temperature. As a second step, the zinc sulfide capping under homogenous conditions is carried out at a substantially lower temperature than is required for nanoparticle growth in batch processes. Finally, the trioctylphosphine/oleic acid ligand is effectively replaced with either carbohydrate PEG-thiol moieties or DHLA at 60 °C. This new protocol allows the synthesis of biologically active fluorescent QDs in 4 d. PMID:21799489

Laurino, Paola; Kikkeri, Raghavendra; Seeberger, Peter H

2011-07-28

40

Biomimetic, Mild Chemical Synthesis of CdTe-GSH Quantum Dots with Improved Biocompatibility  

PubMed Central

Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility. In this study, a simple protocol for the chemical synthesis of glutathione (GSH)-capped CdTe QDs (CdTe-GSH) resembling conditions found in biological systems is described. Using only CdCl2, K2TeO3 and GSH, highly fluorescent QDs were obtained under pH, temperature, buffer and oxygen conditions that allow microorganisms growth. These CdTe-GSH NPs displayed similar size, chemical composition, absorbance and fluorescence spectra and quantum yields as QDs synthesized using more complicated and expensive methods. CdTe QDs were not freely incorporated into eukaryotic cells thus favoring their biocompatibility and potential applications in biomedicine. In addition, NPs entry was facilitated by lipofectamine, resulting in intracellular fluorescence and a slight increase in cell death by necrosis. Toxicity of the as prepared CdTe QDs was lower than that observed with QDs produced by other chemical methods, probably as consequence of decreased levels of Cd+2 and higher amounts of GSH. We present here the simplest, fast and economical method for CdTe QDs synthesis described to date. Also, this biomimetic protocol favors NPs biocompatibility and helps to establish the basis for the development of new, “greener” methods to synthesize cadmium-containing QDs.

Perez-Donoso, Jose M.; Monras, Juan P.; Bravo, Denisse; Aguirre, Adam; Quest, Andrew F.; Osorio-Roman, Igor O.; Aroca, Ricardo F.; Chasteen, Thomas G.; Vasquez, Claudio C.

2012-01-01

41

Review: Synthesis and properties of colloidal quantum dots: The evolving role of coordinating surface ligands  

Microsoft Academic Search

The review highlights developments in synthetic methods for colloidal quantum dots that have expanded the range of achievable sizes, shapes, materials, and surface chemistries over the past thirty years, and how these methods have enabled optimization of properties like photoluminescence quantum yield, monodisperse size distributions, and conductivity in the solid state.

Christopher M. Evans; Laura C. Cass; Kathryn E. Knowles; Daniel B. Tice; Robert P. H. Chang; Emily A. Weiss

2012-01-01

42

Synthesis and size dependent optical studies in CdSe quantum dots via inverse micelle technique  

Microsoft Academic Search

Cadmium selenide quantum dots (CdSe QDs) were successfully synthesized without using trioctylphosphine (TOP). The XRD pattern showed zinc-blend phase of the CdSe QDs. The absorption and PL spectra exhibit a strong blue shift as the QDs size decreases due to the quantum confinement effect. In addition, the quantum efficiency of CdSe QDs with TOP capping is higher than CdSe QDs

Nor Aliya Hamizi; Mohd Rafie Johan

2010-01-01

43

Synthesis and Characterization of a New Sensitizing Dye and Quantum Dots  

NASA Astrophysics Data System (ADS)

Quantum dots have demonstrated their conduction and luminescent abilities in solar cells, light emitting diodes and in vivo imaging [1]. The most intriguing of these is their potential as light absorbers in solar cells. The goal of this research was to dope copper indium sulfide (CIS, formula: CuInS2) quantum dots with aluminum (Al) or cerium (Ce) to determine if these dopants were able to shift the peak absorbance wavelength into the 300--750 nm range of the AM1.5 Solar Radiation Spectrum. Changing the CIS absorbance wavelengths would allow the solar cells to effectively absorb light in the ultraviolet (UV), visible and infrared (IR) regions of the solar spectrum. The Al doped quantum dots shifted the CIS absorbance from 284 nm to 307 nm. Transmission Electron Microscope (TEM) images of the Ce doped CIS quantum dots confirmed the crystallization and Energy Dispersive X-Ray Analysis (EDX) confirmed the chemical composition. This research has shown a new way to create rare earth doped CIS quantum dots and their commercial applications are only beginning to be realized.

Horst, Jason Michael

44

Phosphine-free synthesis of metal chalcogenide quantum dots by means of in situ-generated hydrogen chalcogenides  

Microsoft Academic Search

We proved that various organic solvents react with elemental chalcogens (sulfur and selenium) by liberating hydrogen chalcogenide\\u000a (H2X, X = S, Se) during the phosphine-free hot-matrix synthesis of quantum dots. The in situ-produced H2X reacts further with the metal salt to form the corresponding nanosized metal chalcogenide CdX. The effect of temperature\\u000a on the rate of H2X generation was quantitatively

Georgi G. Yordanov; Hideyuki Yoshimura; Ceco D. Dushkin

2008-01-01

45

Synthesis and characterization of InP, GaP, and GaInPâ quantum dots  

Microsoft Academic Search

Quantum dots (QDs) of InP, GaP, and GaInPâ with diameters ranging from 20 to 65 A were synthesized as well-crystallized nanoparticles with bulk zinc blende structure. The synthesis of InP, GaP, and GaInPâ QDs was achieved by heating appropriate organometallic precursors with stabilizers in high boiling solvents for several days to produce QDs which can be dissolved in nonpolar organic

O. I. Micic; J. R. Sprague; C. J. Curtis; K. M. Jones; J. L. Machol; A. J. Nozik; H. Giessen; B. Fluegel; G. Mohs; N. Peyghambarian

1995-01-01

46

Non-heavy-metal ZnS quantum dots with bright blue photoluminescence by a one-step aqueous synthesis  

Microsoft Academic Search

We have examined the aqueous synthesis of non-heavy-metal ZnS quantum dots (QDs) using 3-mercaptopropionic acid (MPA) as the capping molecule at various pH and MPA:Zn:S ratios. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) indicated that the aqueous ZnS QDs were 3-5 nm in size with a zinc blende structure. We showed that, at pH 12 with a MPA:Zn:S =

Hui Li; Wan Y. Shih; Wei-Heng Shih

2007-01-01

47

One-pot aqueous synthesis PbS quantum dots and their Hg2+ sensitive properties.  

PubMed

In this study, we report the synthesis and stability of PbS quantum dots (QDs) using an aqueous route with L-Cysteine (L-Cys) as the capping molecule. The as-synthesized L-Cys-capped PbS QDs were characterized by high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD), the results indicated that the QDs were about 4 nm in size and dispersed well with a rock salt crystalline structure, and there was L-Cys on the surface of QDs, which was confirmed by Fourier transform infrared (FT-IR) spectrometry. The influence of various experimental variables, including amounts of capping ligand, pH value and refluxing time, on the luminescent properties of the obtained QDs have been systematically investigated. The QDs exhibited optimal PL intensity when Pb: L-Cys: S = 1:2.2:0.3. In addition, the as-prepared QDs could be used as fluorescence probes to detect Hg2+ ions in aqueous media. The response of QDs fluorescence probes was linearly proportional to the concentration of Hg2+ ions ranging from 8 x 10(-9) to 2 x 10(-6) mol x L(-1) with a limit of detection of 2 x 10(-9) mol x L(-1). Furthermore, the method was successfully applied to the determine Hg2+ ions in different real samples. PMID:22755123

Yu, Yaxin; Zhang, Rui; Zhang, Kexin; Sun, Shuqing

2012-03-01

48

Synthesis of Highly Luminescent, Bio?Compatible ZnO Quantum Dots Doped with Na  

Microsoft Academic Search

Na doped ZnO quantum dots of average size 6 nm were prepared using wet chemical route at room temperature without any capping agents and the formation of nanoparticles is confirmed by transmission electron microscope (TEM) and x?ray diffraction (XRD) analysis. Optical band gap of ZnO: Na is found to be blue shifted with decrease in size due to quantum size effects.

B. Vinitha; K. Manzoor; R. S. Ajimsha; P. M. Aneesh; M. K. Jayaraj

2008-01-01

49

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

50

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.

51

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

52

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

53

Quantum Dots--From Synthesis to Applications in Biomedicine and Life Sciences  

PubMed Central

Imagine devices or particles so small that they are invisible to the naked eye. Imagine that such entities could be used to patrol our bodies and autonomously augment endogenous defense and repair mechanisms. Imagine the defeat of illness at a fraction of the current costs. Bionanotechnology is the field of science that deals with just that: the development of imaging, tracking, targeting, sensing, diagnostic, and eventually therapeutic capabilities based on particles in the nanometer range, i.e., “nanoparticles”. Within the extensive group of nanoparticles, semiconducting quantum dots play a central and prominent role. Quantum dots excel at a myriad of physical properties, most notably their fluorescent properties, such as high quantum yield, photo-stability, broad absorption spectra, and their remarkable size-dependent emission-tunability.

Drummen, Gregor P.C.

2010-01-01

54

Application of Synthesized Quantum Dots for Cell Imaging  

Microsoft Academic Search

Quantum dots (QDs) have received considerable attention due to their advantages and are widely used in biological studies, especially for multiplexed staining assays and immunological assays. Here we report an easy method for quantum dot synthesis and encapsulation, and use for efficient bioconjugation with secondary antibody. For the application of QDs-antibody conjugates, we approached a fast dot blotting immunological assay,

Hengyi Xu; Feng Xu; Yonghua Xiong; Cuixiang Wan; Jingfei Zhang; Hua Wei; Jiang Zhu

2009-01-01

55

Quantum dot intersublevel light emitters  

Microsoft Academic Search

Self-organized quantum dots have been used with great success in quantum dot infrared photodetectors (QDIPs), wherein intersublevel transitions between confined electron states are utilized. Many attributes make self-organized quantum dots attractive for the realization of intersublevel infrared light sources for the mid- to far-infrared wavelength range. Intersublevel electroluminescence has been demonstrated from both bipolar and quantum cascade unipolar structures, with

Pallab Bhattacharya; Carl Fischer; Sanjay Krishna; Zetian Mi; Xiaohua Su

2004-01-01

56

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

57

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

58

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

59

Aqueous synthesis and characterization of TGA-capped CdSe quantum dots at freezing temperature.  

PubMed

CdSe quantum dots (QDs) have traditionally been synthesized in organic phase and then transferred to aqueous solution by functionalizing their surface with silica, polymers, short-chain thiol ligands, or phospholipid micelles. However, a drastic increase in the hydrodynamic size and biotoxicity of QDs may hinder their biomedical applications. In this paper, the TGA-capped CdSe QDs are directly synthesized in aqueous phase at freezing temperature, and they prove to possess high QY (up to 14%). PMID:22785270

Sun, Qizhuang; Fu, Shasha; Dong, Tingmei; Liu, Shuxian; Huang, Chaobiao

2012-07-11

60

Synthesis, nonlinear optical properties and photoluminescence of ZnSe quantum dots in stable solutions  

Microsoft Academic Search

ZnSe quantum dots (QDs) were synthesized by using a novel oleic acid-controlled hydrothermal route. The as-synthesized QDs were easily dispersed in nonpolar solvents to form highly stable homogenous solutions, on the basis of which their optical properties were systematically investigated. It was found that the QDs had multiple optical properties of both obvious optical nonlinearity with a frequency-doubled Nd:YAG laser

Yang Jiao; Dabin Yu; Zirong Wang; Kun Tang; Xiaoquan Sun

2007-01-01

61

Synthesis and photophysical studies of CdTe quantum dot-monosubstituted zinc phthalocyanine conjugates  

Microsoft Academic Search

The linkage of unsymmetrically monosubstituted 4-aminophenoxy zinc phthalocyanine (ZnAPPc, 5) to CdTe quantum dots capped with mercaptopropionic acid (MPA), l-cysteine (l-cys) or thioglycolic acid (TGA) has been achieved using the coupling agents ethyl-N(3-dimethylaminopropyl) carbodiimide and N-hydroxy succinimide, which facilitate formation of an amide bond to form the QD–ZnAPPc-linked conjugate. The formation of the amide bond was confirmed using Raman and

Sarah D’ Souza; Edith Antunes; Tebello Nyokong

2011-01-01

62

Synthesis and characterization of InP and InN colloidal quantum dots  

Microsoft Academic Search

InP quantum dots (QDs) with zinc blende structure and InN QDs with hexagonal structure were synthesized from appropriate organometallic precursors in a noncoordinating solvent using myristic acid as a ligand. The QDs were characterized by TEM, the associated energy dispersive spectroscopy (EDS), electron diffraction, and steady state UV-VIS optical absorption and photoluminescence spectroscopy. To our best knowledge, this paper reports

Melissa R. Greenberg; Weiliang Chen; Ben N. Pulford; Gennady A. Smolyakov; Ying-Bing Jiang; Scott D. Bunge; Timothy J. Boyle; Marek Osinski

2005-01-01

63

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

64

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

65

Aqueous synthesis of CdTe/CdS/ZnS quantum dots and their optical and chemical properties.  

PubMed

In this paper, we described a strategy for synthesis of thiol-coated CdTe/CdS/ZnS (core-shell-shell) quantum dots (QDs) via aqueous synthesis approach. The synthesis conditions were systematically optimized, which included the size of CdTe core, the refluxing time and the number of monolayers and the ligands, and then the chemical and optical properties of the as-prepared products were investigated. We found that the mercaptopropionic acid (MPA)-coated CdTe/CdS/ZnS QDs presented highly photoluminescent quantum yields (PL QYs), good photostability and chemical stability, good salt tolerance and pH tolerance and favorable biocompatibility. The characterization of high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and fluorescence correlation spectroscopy (FCS) showed that the CdTe/CdS/ZnS QDs had good monodispersity and crystal structure. The fluorescence life time spectra demonstrated that CdTe/CdS/ZnS QDs had a longer lifetime in contrast to fluorescent dyes and CdTe QDs. Furthermore, the MPA-stabilized CdTe/CdS/ZnS QDs were applied for the imaging of cells. Compared with current synthesis methods, our synthesis approach was reproducible and simple, and the reaction conditions were mild. More importantly, our method was cost-effective, and was very suitable for large-scale synthesis of CdTe/CdS/ZnS QDs for future applications. PMID:20878652

Li, Zhong; Dong, Chaoqing; Tang, Lichuan; Zhu, Xin; Chen, Hongjin; Ren, Jicun

2010-09-27

66

Synthesis of mercaptosuccinic acid/MercaptoPolyhedral oligomeric silsesquioxane coated cadmium telluride quantum dots in cell labeling applications.  

PubMed

An aqueous synthesis method to obtain highly luminescent cadmium telluride nanocrystals is described. We have shown water-soluble semi-conductor quantum dots with high photoluminescence quantum yield have great potential for biological applications. The spectral properties of these nanocrystals can be easily tuned according to their particle size to yield multicolours simultaneously by a single excitation light source. A stable precursor material sodium tellurite is utilised instead of the traditional oxygen sensitive NaHTe or H2Te as Te source. We have introduced mercaptosuccinic acid and propylisobutyl polyhedral oligomeric silsesquioxane nanoparticles as novel capping agents to stabilize the nanocrystals, synthesized in borate-citrate buffering system. Inclusion of propylisobutyl polyhedral oligomeric silsesquioxane nanoparticles in the capping procedure showed enhanced stability and biocompatibility. The presence of mercaptosuccinic acid/propylisobutyl polyhedral oligomeric silsesquioxane coatings was confirmed by Fourier Transform Infrared spectroscopy and average sizes of 2-5 nm by transmission electron microscopy measurements. The functionalized and targeted quantum dots detected cancer cell death on exposure to some anticancer drugs. Studies have indicated that apoptotic cells can activate signaling pathways in dendritic cells via ligation of surface receptors. Cells treated with specific class of pro-apototic drug such as anthracyclines mount an anti-tumour immune response when introduced into mice. Apoptotic cells may be immunogenic or non-immunogenic depending on the presence of calreticulin on the plasma membrane of dying tumour cells. Here the confocal microscopy showed localization of conjugated mercaptosuccinic acid/propylisobutyl polyhedral oligomeric silsesquioxane cadmium telluride quantum dots on MCF-7 cells when exposed to cadmium ions at 50 microM, compared to coated quantum dots. We have used cadmium ions as a model drug as certain anticancer drugs (anthracyclines) induce translocation of calreticulin to the cell membrane, an indicator of apoptosis. Antibodies generated against a peptide to human calreticulin and conjugated to quantum dots detected the protein on cell membrane of stimulated cells were visualized by confocal microscopy. Stimulating natural immune response, against tumours has enormous potential to improve current regimens of cancer detection and therapy. PMID:22905553

Ghaderi, Shirin; Ramesh, Bala; Seifalian, Alexander M

2012-06-01

67

Quantum Dots as Cellular Probes  

SciTech Connect

Robust and bright light emitters, semiconductor nanocrystals[quantum dots (QDs)] have been adopted as a new class of fluorescent labels. Six years after the first experiments of their uses in biological applications, there have been dramatic improvements in understanding surface chemistry, biocompatibility, and targeting specificity. Many studies have shown the great potential of using quantum dots as new probes in vitro and in vivo. This review summarizes the recent advances of quantum dot usage at the cellular level, including immunolabeling, cell tracking, in situ hybridization, FRET, in vivo imaging, and other related technologies. Limitations and potential future uses of quantum dot probes are also discussed.

Alivisatos, A. Paul; Gu, Weiwei; Larabell, Carolyn

2004-09-16

68

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

PubMed

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%. PMID:24013650

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

2013-09-06

69

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

70

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

71

A one-pot synthesis of reduced graphene oxide-Cu2S quantum dot hybrids for optoelectronic devices  

NASA Astrophysics Data System (ADS)

We demonstrate a facile one-pot approach for the synthesis of reduced graphene oxide (rGO)-cuprous sulfide quantum dot (Cu2S QD) hybrids, wherein the reduction of GO and the growth of Cu2S QDs on graphene occur simultaneously. The as-synthesized rGO-Cu2S QD hybrids exhibit an excellent photoelectric response and efficient electron transfer from the Cu2S QDs to the rGO sheets.We demonstrate a facile one-pot approach for the synthesis of reduced graphene oxide (rGO)-cuprous sulfide quantum dot (Cu2S QD) hybrids, wherein the reduction of GO and the growth of Cu2S QDs on graphene occur simultaneously. The as-synthesized rGO-Cu2S QD hybrids exhibit an excellent photoelectric response and efficient electron transfer from the Cu2S QDs to the rGO sheets. Electronic supplementary information (ESI) available: TGA curves of the GO and rGO-Cu2S QD hybrids, SEM images of the rGO-Cu2S QD hybrids with different Cu2S densities and typical I-V curves of pure Cu2S, with and without blue light irradiation. See DOI: 10.1039/c3nr02992a

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

2013-09-01

72

Surfactant-assisted synthesis of water-soluble and biocompatible semiconductor quantum dot micelles.  

PubMed

We report a simple, rapid approach to synthesize water-soluble and biocompatible fluorescent quantum dot (QD) micelles by encapsulation of monodisperse, hydrophobic QDs within surfactant/lipid micelles. Analyses of UV-vis and photo luminescence spectra, along with transmission electron microscopy, indicate that the water-soluble semiconductor QD micelles are monodisperse and retain the optical properties of the original hydrophobic QDs. The QD micelles were shown to be biocompatible and exhibited little or no aggregation when taken up by cultured rat hippocampal neurons. PMID:15826102

Fan, Hongyou; Leve, Erik W; Scullin, Chessa; Gabaldon, John; Tallant, David; Bunge, Scott; Boyle, Tim; Wilson, Michael C; Brinker, C Jeffrey

2005-04-01

73

Surfactant-assisted synthesis of water-soluble and biocompatible semiconductor quantum dot-micelles.  

SciTech Connect

We report a simple, rapid approach to synthesize water-soluble and biocompatible fluorescent quantum dot (QD) micelles by encapsulation of monodisperse, hydrophobic QDs within surfactant/lipid micelles. Analyses of UV-vis and photo luminescence spectra, along with transmission electron microscopy, indicate that the water-soluble semiconductor QD micelles are monodisperse and retain the optical properties of the original hydrophobic QDs. The QD micelles were shown to be biocompatible and exhibited little or no aggregation when taken up by cultured rat hippocampal neurons.

Brinker, C. Jeffrey; Bunge, Scott D.; Gabaldon, John (University of New Mexico, Albquerque, NM); Fan, Hongyou; Scullin, Chessa (University of New Mexico, Albquerque, NM); Leve, Erik W. (University of New Mexico, Albquerque, NM); Wilson, Michael C. (University of New Mexico, Albquerque, NM); Tallant, David Robert; Boyle, Timothy J.

2005-04-01

74

Quantum Dots for Infrared Devices  

Microsoft Academic Search

Tremendous progresses have been made in both fabrication and characterization of quantum dots, especially self-assembled dots grown by epitaxy. New physics has been discovered, e.g., unique luminescence section rules in the few-particle regime. Much efforts have been devoted to the research and development of quantum dot lasers relying on interband (conduction-to-valence) transitions and emitting in the near infrared to visible

H. C. Liu

2001-01-01

75

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

76

Clinical Potential of Quantum Dots  

PubMed Central

Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving sentinel lymph node mapping and identification in vivo studies. As the unique physical and chemical properties of these fluorescent probes are being unraveled, new potential methods of early cancer detection, rapid spread and therapeutic management, that is, photodynamic therapy are being explored. Encouraging results of optical and real time identification of sentinel lymph nodes and lymph flow using quantum dots in vivo models are emerging. Quantum dots have also superseded many of the limitations of organic fluorophores and are a promising alternative as a research tool. In this review, we examine the promising clinical potential of quantum dots, their hindrances for clinical use and the current progress in abrogating their inherent toxicity.

Iga, Arthur M.; Robertson, John H. P.; Winslet, Marc C.; Seifalian, Alexander M.

2007-01-01

77

Quantum dot composite light sources  

NASA Astrophysics Data System (ADS)

In this effort, we present the most recent progress towards fabrication and testing of quantum dot composite materials. These materials are important steps towards easy integration of a light source on silicon. Quantum dot composites are formed by incorporating quantum dots in a host material that acts to protect and maintain the characteristics of the quantum dots, as well as to act as a patternable matrix for lithography and etching. In this effort, commercially available IR emitting PbS quantum dots (Evident Technologies) were incorporated with PMMA and poly (hexyl methacrylate) and their photoluminescence spectra was examined over time. A large shift in the photoluminescence emission peak over the course of several days was observed in all composites. This could be due to oxidation despite being in a host.

Grund, David W., Jr.; Olbricht, Benjamin C.; Prather, Dennis W.

2011-02-01

78

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

2008-04-29

79

Green synthesis of well-defined spherical PbS quantum dots and its potential in biomedical imaging research and biosensing  

Microsoft Academic Search

In this research, we present a facile, effective and green route for the synthesis of well-defined spherical lead sulfide (PbS) quantum dots (QDs) through the reaction between lead nitrate and sodium sulphide by virtue of its strong reduction and selective interaction abilities without using any surfactant, and evaluate its potential for use in biomedical imaging and biosensing applications. The average

Masoud Mozafari; Fathollah Moztarzadeh

2011-01-01

80

Synthesis and characterization of hapten-quantum dots bioconjugates: Application to development of a melamine fluorescentimmunoassay.  

PubMed

A general and universal analytical strategy for characterization of hapten-BSA conjugates based on complementary optical spectroscopy and molecular mass spectrometry techniques is here described. The proposed procedure provides highly-valuable information about the molecular weight of the conjugate, its stoichiometry and the concentration of the precursors (hapten and BSA) in the conjugate; such information is of great analytical interest for further development of novel quantitative immunoassays. Further, due to great demand of new, simple and robust methodologies for the melamine analysis in milk infant formula, a new immunoprobe melamine-bovine serum albumin-quantum dot was synthetized, characterized and successfully applied in a competitive fluorescent quantum dot-based immunoassay. It should be highlighted that the limit of detection achieved without any sample pretreatment, 0.15 mg kg(-1) for melamine in milk infant formula, is one order of magnitude lower than the maximum concentration level allowed by international legislation in such type of samples. Finally, this simple approach was validated by the use of an alternative technique (HPLC-UV) for the analysis of melamine in contaminated milk infant formula, showing a good agreement between the results obtained by using both analytical methodologies. PMID:23598123

Trapiella-Alfonso, Laura; Costa-Fernandez, José M; Pereiro, Rosario; Sanz-Medel, Alfredo

2013-01-21

81

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

82

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

83

Stability of quantum dots in live cells  

Microsoft Academic Search

Quantum dots are highly fluorescent and photostable, making them excellent tools for imaging. When using these quantum dots in cells and animals, however, intracellular biothiols (such as glutathione and cysteine) can degrade the quantum dot monolayer, compromising function. Here, we describe a label-free method to quantify the intracellular stability of monolayers on quantum dot surfaces that couples laser desorption\\/ionization mass

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

2011-01-01

84

Quantum dots for multimodal molecular imaging of angiogenesis  

PubMed Central

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

Strijkers, Gustav J.; Nicolay, Klaas; Griffioen, Arjan W.

2010-01-01

85

Synthesis of amphiphilic triblock copolymers as multidentate ligands for biocompatible coating of quantum dots  

PubMed Central

One barrier to apply current tri-octylphosphine oxide (TOPO) based quantum dots (QDs) to biomedical imaging is that the TOPO on TOPO-QDs can be replaced by the proteins in living system, which may cause the degradation of QDs and/or deactivation of protein. In order to develop biocompatible optical imaging agents, a novel triblock copolymer, designed as a multidentate ligand, was synthesized to coat quantum dot nanocrystals (QDs). The copolymer consists of a polycarboxylic acid block at one end and a polythiol block at the other end with an intervening cross-linked poly(styrene-co-divinylbenzene) block bridging the ends. The multiple mercapto groups from the polythiol block act as multidentate ligands to stabilize QDs, while the polycarboxylic acid block improves the water solubility of QDs and offers reaction sites for surface modification or conjugation with bimolecules. The cross-linked poly(styrene-co-divinylbenzene) block provides a densely compacted hydrophobic shell. This shell will act as a barrier to inhibit the degradation of QDs by preventing the diffusion of ions and small molecules into the core of QDs. This new multidentate polymer coating facilitates the transfer of QDs from organic solvent into aqueous phase. The QDs directly bound to multidentate mercapto groups instead of TOPO are less likely to be affected by the mercapto or disulfide groups within proteins or other biomolecules. Therefore, this research will provide an alternative coating material instead of TOPO to produce QDs which could be more suitable for in vivo use under complex physiological conditions.

Wang, Tongxin; Sridhar, Rajagopalan; Korotcov, Alexandru; Ting, Andy Hai; Francis, Kyethann; Mitchell, James; Wang, Paul C.

2011-01-01

86

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

2013-08-13

87

Synthesis of blue emitting InP/ZnS quantum dots through control of competition between etching and growth  

NASA Astrophysics Data System (ADS)

Blue (<480 nm) emitting Cd-free quantum dots (QDs) are in great demand for various applications. However, their synthesis has been challenging. Here we present blue emitting InP/ZnS core/shell QDs with a band edge emission of 475 nm and a full width at half maximum of 39 nm (215 meV) from their quantum confined states. The drastic temperature drop immediately after mixing of the precursors and holding them at a temperature below 150?°C was the critical factor for the synthesis of blue emitting QDs, because the blue QDs are formed by the etching of ultra-small InP cores by residual acetic acid below 150?°C. Etching was dominant at temperatures below 150?°C, whereas growth was dominant at temperatures above 150?°C. ZnS shells were formed successfully at 150?°C, yielding blue emitting InP/ZnS QDs. The colour of the InP/ZnS QDs depicted on the CIE 1931 chromaticity diagram is located close to the edge, indicating a pure blue colour compared to other InP-based QDs.

Lim, Kipil; Jang, Ho Seong; Woo, Kyoungja

2012-12-01

88

Infrared emitting and photoconducting colloidal silver chalcogenide nanocrystal quantum dots from a silylamide-promoted synthesis.  

PubMed

Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region, making these materials promising as environmentally benign alternatives to established infrared active nanocrystals containing toxic metals such as Hg, Cd, and Pb. We present Ag(2)Se nanocrystals in detail, giving size-tunable luminescence with quantum yields above 1.7%. The luminescence, with a decay time on the order of 130 ns, was shown to improve due to the growth of a monolayer thick ZnSe shell. Photoconductivity with a quantum efficiency of 27% was achieved by blending the Ag(2)Se nanocrystals with a soluble fullerene derivative. The co-injection of lithium silylamide was found to be crucial to the synthesis of Ag chalcogenide nanocrystals, which drastically increased their nucleation rate even at relatively low growth temperatures. Because the same observation was made for the nucleation of Cd chalcogenide nanocrystals, we conclude that the addition of lithium silylamide might generally promote wet-chemical synthesis of metal chalcogenide nanocrystals, including in as-yet unexplored materials. PMID:21500803

Yarema, Maksym; Pichler, Stefan; Sytnyk, Mykhailo; Seyrkammer, Robert; Lechner, Rainer T; Fritz-Popovski, Gerhard; Jarzab, Dorota; Szendrei, Krisztina; Resel, Roland; Korovyanko, Oleksandra; Loi, Maria Antonietta; Paris, Oskar; Hesser, Günter; Heiss, Wolfgang

2011-04-22

89

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

90

Lateral Quantum Dots for Quantum Information Processing  

NASA Astrophysics Data System (ADS)

The possibility of building a computer that takes advantage of the most subtle nature of quantum physics has been driving a lot of research in atomic and solid state physics for some time. It is still not clear what physical system or systems can be used for this purpose. One possibility that has been attracting significant attention from researchers is to use the spin state of an electron confined in a semiconductor quantum dot. The electron spin is magnetic in nature, so it naturally is well isolated from electrical fluctuations that can a loss of quantum coherence. It can also be manipulated electrically, by taking advantage of the exchange interaction. In this work we describe several experiments we have done to study the electron spin properties of lateral quantum dots. We have developed lateral quantum dot devices based on the silicon metal-oxide-semiconductor transistor, and studied the physics of electrons confined in these quantum dots. We measured the electron spin excited state lifetime, which was found to be as long as 30 ms at the lowest magnetic fields that we could measure. We fabricated and characterized a silicon double quantum dot. Using this double quantum dot design, we fabricated devices which combined a silicon double quantum dot with a superconducting microwave resonator. The microwave resonator was found to be sensitive to two-dimensional electrons in the transistor channel, which we measured and characterized. We developed a new method for extracting information from random telegraph signals, which are produced when we observe thermal fluctuations of electrons in quantum dots. The new statistical method, based on the hidden Markov model, allows us to detect spin-dependent effects in such fluctuations even though we are not able to directly observe the electron spin. We use this analysis technique on data from two experiments involving gallium arsenide quantum dots and use it to measure spin-dependent tunneling rates. Our results advance the understanding of electron spin physics in lateral quantum dots, in silicon and in gallium arsenide.

House, Matthew Gregory

91

Stability of quantum dots in live cells  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

92

Synthesis and Optical Properties of Si-Rich Nitride Containing Silicon Quantum Dots  

NASA Astrophysics Data System (ADS)

Hydrogenated silicon-rich nitride films were deposited by plasma-enhanced chemical vapor deposition using NH3 and SiH4. As-deposited samples were thermally annealed under different conditions in argon ambient. Fourier-transform infrared spectroscopy was carried out to investigate the bonding configurations, and Raman scattering spectroscopy was used to study the microstructures and confirm the presence of Si quantum dots (QDs). We found that a near-stoichiometric silicon nitride matrix was formed after high-temperature processing. When the annealing temperature reached 1100°C, the degree of crystallinity (X c) increased to 51.6% for the 60-min sample compared with 46.1% for the 30-min sample. Red-light and yellow-light emission were obtained from the samples annealed at 1100°C for 30 min and 60 min, respectively. The emission mechanism is dominated by excitons confined within the Si QDs. The ultra-nanocrystals play an important role in the luminescence blue-shift. We measured the bandgap values from optical absorption studies. The increase of the optical bandgap from 1.80 eV to 1.90 eV with increase of the annealing temperature from 950°C to 1100°C is ascribed to the silicon clusters and nitride matrix.

Liao, Wugang; Zeng, Xiangbin; Wen, Xixing; Zheng, Wenjun; Yao, Wei

2013-10-01

93

Review of the synthesis and properties of colloidal quantum dots: the evolving role of coordinating surface ligands  

Microsoft Academic Search

This review highlights the developments in synthetic methods for colloidal quantum dots that have expanded the range of achievable sizes, shapes, materials, and surface chemistries over the past 30 years, and how these methods have enabled optimization of properties like photoluminescence quantum yield, monodisperse size distributions, and conductivity in the solid state.

Christopher M. Evans; Laura C. Cass; Kathryn E. Knowles; Daniel B. Tice; Robert P. H. Chang; Emily A. Weiss

2012-01-01

94

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

ERIC Educational Resources Information Center

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

Rice, Charles V.; Giffin, Guinevere A.

2008-01-01

95

Spectroscopic and structural characterization of electrochemically grown ZnO quantum dots  

Microsoft Academic Search

We report a novel method for the synthesis of stable, OH free zinc oxide quantum dots, using an electrochemical route. The optical properties of these quantum dots were studied at room temperature, by taking the optical absorption and luminescence spectra. The band gap luminescence is predominant in ZnO quantum dots synthesized by the present technique, while the green defect induced

Shailaja Mahamuni; Kavita Borgohain; B. S. Bendre; Valerie J. Leppert; Subhash H. Risbud

1999-01-01

96

One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels  

NASA Astrophysics Data System (ADS)

We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core-shell QDs) was used for passivating the defect emission (650 nm) and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530-600 nm). Moreover, the PL emission peak of CdSe/CdS core-shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core-shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol)-2-diphenyltertrazolium bromide (MTT) assay. The results showed the satisfactory (>80%) biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 ?g/ml.

Zhai, Chuanxin; Zhang, Hui; Du, Ning; Chen, Bingdi; Huang, Hai; Wu, Yulian; Yang, Deren

2010-12-01

97

Quantum entanglement and teleportation in quantum dot  

Microsoft Academic Search

We study the thermal entanglement and quantum teleportation using quantum dot as a resource. We first consider entanglement of the resource, and then focus on the effects of different parameters on the teleportation fidelity under different conditions. The critical temperature of disentanglement is obtained. Based on Bell measurements in two subspaces, we find the anisotropy measurements is optimal to the

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

2011-01-01

98

Synthesis and grafting of folate–PEG–PAMAM conjugates onto quantum dots for selective targeting of folate-receptor-positive tumor cells  

Microsoft Academic Search

We report the design and synthesis of folate–poly(ethylene glycol)–polyamidoamine (FPP)-functionalized CdSe\\/ZnS quantum dots (QDs), in which the QD plays a key role in imaging, whereas the folate–poly(ethylene glycol) (PEG) conjugates of the polyamidoamine (PAMAM) dendrimer serve as a system targeted to folate receptors in tumor cells. Dendrimer ligands such as folate–PEG grafted PAMAM of generation 3.5 are found to encapsulate

Yili Zhao; Sen Liu; Yapeng Li; Wei Jiang; Yulei Chang; Si Pan; Xuexun Fang; Y. Andrew Wang; Jingyuan Wang

2010-01-01

99

Growth and Characterization of Quantum Dots and Quantum Dots Devices  

SciTech Connect

Quantum dot nanostructures were investigated experimentally and theoretically for potential applications for optoelectronic devices. We have developed the foundation to produce state-of-the-art compound semiconductor nanostructures in a variety of materials: In(AsSb) on GaAs, GaSb on GaAs, and In(AsSb) on GaSb. These materials cover a range of energies from 1.2 to 0.7 eV. We have observed a surfactant effect in InAsSb nanostructure growth. Our theoretical efforts have developed techniques to look at the optical effects induced by many-body Coulombic interactions of carriers in active regions composed of quantum dot nanostructures. Significant deviations of the optical properties from those predicted by the ''atom-like'' quantum dot picture were discovered. Some of these deviations, in particular, those relating to the real part of the optical susceptibility, have since been observed in experiments.

CEDERBERG, JEFFREY G.; BIEFELD, ROBERT M.; SCHNEIDER, H.C.; CHOW, WENG W.

2003-04-01

100

Supercurrent reversal in quantum dots  

NASA Astrophysics Data System (ADS)

When two superconductors are electrically connected by a weak link-such as a tunnel barrier-a zero-resistance supercurrent can flow. This supercurrent is carried by Cooper pairs of electrons with a combined charge of twice the elementary charge, e. The 2e charge quantum is clearly visible in the height of voltage steps in Josephson junctions under microwave irradiation, and in the magnetic flux periodicity of h/2e (where h is Planck's constant) in superconducting quantum interference devices. Here we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Owing to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, that is, in a normal or a ?-junction, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions.

van Dam, Jorden A.; Nazarov, Yuli V.; Bakkers, Erik P. A. M.; de Franceschi, Silvano; Kouwenhoven, Leo P.

2006-08-01

101

Highly luminescent (ZnSe)ZnS core-shell quantum dots for blue to UV emission: synthesis and characterization  

Microsoft Academic Search

We synthesized nearly monodisperse bare ZnSe nanocrystallites having luminescence which ranges in wavelength from 340 to 430 nm via nucleation due to supersaturation and growth followed by size selective precipitation. Bare ZnSe dots' outermost surface is passivated with organic HDA\\/TOP. In order to enhance the radiative emission from the semiconductor nanocrystals, we capped the bare ZnSe quantum dots with ZnS

Keun-Kyu Song; Seonghoon Lee

2001-01-01

102

Intercalated synthesis of zinc oxide quantum dots between multilayered organic films: Preparation of 2D superlattices in colloidal solutions  

Microsoft Academic Search

Intercalation of ZnO quantum dots into two-dimensional (2D) laminated sodium lauryl sulfonate films in a colloidal solution was demonstrated. Without any substrates, hybrid films composed of a dispersed ZnO dots layer and organic films exhibit a high stability and regular 2D superlattice stacking after removal of cosurfactant molecules and water. The 2D superlattice films were characterized by transmission electron microscopy

Dazhi Wang; Chuanbao Cao; Fengqiu Ji; Hesun Zhu

2005-01-01

103

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

104

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

105

Mesoscopic cavity quantum electrodynamics with quantum dots  

SciTech Connect

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

Childress, L.; Soerensen, A.S.; Lukin, M.D. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA and ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States)

2004-04-01

106

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. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23060275

Yang, Fanghong; Yang, Ping; Zhang, Lipeng

2012-10-11

107

Aqueous, protein-driven synthesis of transition metal-doped ZnS immuno-quantum dots.  

PubMed

The intentional introduction of transition metal impurities in semiconductor nanocrystals is an attractive approach for tuning quantum dot 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 exhibit 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. PMID:21942544

Zhou, Weibin; Baneyx, François

2011-09-28

108

Green and facile synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots.  

PubMed

Water-soluble Cu-In-S/ZnS core/shell quantum dots with a photoluminescence quantum yield up to 38% and an emission peak tunable from 543 to 625 nm have been successfully synthesized. All of the synthetic procedures were conducted in an aqueous solution at 95 °C under open-air conditions. L-Glutathione and sodium citrate were used as the dual stabilizing agents to balance the reactivity between copper and indium ions. PMID:23805901

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

2013-06-27

109

Quantum-dot heterostructure lasers  

Microsoft Academic Search

Quantum-dot (QD) heterostructures are nanoscale coherent insertions of narrow-gap material in a single-crystalline matrix. These tiny structures provide unique opportunities to modify and extend all basic principles of heterostructure lasers and advance their applications. Despite early predictions, fabrication of QD heterostructure (QDHS) lasers appeared to be a much more challenging task, as compared to quantum well (QW) devices. The breakthrough

Nikolai N. Ledentsov; M. Grundmann; F. Heinrichsdorff; Dieter Bimberg; V. M. Ustinov; A. E. Zhukov; M. V. Maximov; Zh. I. Alferov; J. A. Lott

2000-01-01

110

Synthesis and characterization of a pegylated derivative of 3-(1,2,3,6-tetrahydro-pyridin-4yl)-1H-indole (IDT199): a high affinity SERT ligand for conjugation to quantum dots.  

PubMed

Quantum dots consisting of a cadmium selenide core encapsulated in a shell of cadmium doped zinc sulfide have the potential to revolutionize fluorescent imaging of live cell cultures. In order to utilize these fluorescent probes it is necessary to functionalize them with biologically active ligands. In this paper we report the design and synthesis of a ligand that has a high affinity for the serotonin transporter (SERT) that may be conjugated to quantum dots. PMID:17766114

Tomlinson, Ian D; Warnerment, Michael R; Mason, John N; Vergne, Matthew J; Hercules, David M; Blakely, Randy D; Rosenthal, Sandra J

2007-08-21

111

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

112

One-pot synthesis of colloidal silicon quantum dots and surface functionalization via thiol-ene click chemistry.  

PubMed

A solution method for preparing surface functionalized colloidal silicon quantum dots (SiQDs) is presented. SiQDs prepared by this method are reasonably monodispersed and can be further functionalized via thiol-ene click reactions to introduce specific functionalities (i.e. -NH(2), -COOH, -SO(3)(-), alkane, alkene). PMID:23125971

Cheng, Xiaoyu; Gondosiswanto, Richard; Ciampi, Simone; Reece, Peter J; Gooding, J Justin

2012-12-18

113

In situ synthesis of highly luminescent glutathione-capped CdTe/ZnS quantum dots with biocompatibility.  

PubMed

This paper focuses on the in situ synthesis of novel CdTe/ZnS core-shell quantum dots (QDs) in aqueous solution. Glutathione (GSH) was used as both capping reagent and sulfur source for in situ growth of ZnS shell on the CdTe core QDs. The maximum emission wavelengths of the prepared CdTe/ZnS QDs can be simply tuned from 569 nm to 630 nm. The PL quantum yield of CdTe/ZnS QDs synthesized is up to 84%, larger than the original CdTe QDs by around 1.7 times. The PL lifetime results reveal a triexponential decay model of exciton and trap radiation behavior. The average exciton lifetime at room temperature is 17.1 ns for CdTe (2.8 nm) and 27.4 ns for CdTe/ZnS (3.7 nm), respectively. When the solution of QDs is dialyzed for 3 h, 1.17 ppm of Cd(2+) is released from CdTe QDs and 0.35 ppm is released from CdTe/ZnS. At the dose of 120 microg/ml QDs, 9.5% of hemolysis was induced by CdTe QDs and 3.9% was induced by CdTe/ZnS QDs. These results indicate that the synthesized glutathione-capped CdTe/ZnS QDs are of less toxicity and better biocompatibility, so that are attractive for use in biological detection and related fields. PMID:20719328

Liu, Ying-Fan; Yu, Jun-Sheng

2010-07-23

114

Electroluminescence of colloidal ZnSe quantum dots  

Microsoft Academic Search

The article reports a green chemical synthesis of colloidal ZnSe quantum dots at a moderate temperature. The prepared colloid sample is characterised by UV–vis absorption spectroscopy and transmission electron microscopy. UV–vis spectroscopy reveals as-expected blue-shift with strong absorption edge at 400nm and micrographs show a non-uniform size distribution of ZnSe quantum dots in the range 1–4nm. Further, photoluminescence and electroluminescence

S. C. Dey; S. S. Nath

2011-01-01

115

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

116

Colloidal quantum dot solar cells  

NASA Astrophysics Data System (ADS)

Solar cells based on solution-processed semiconductor nanoparticles -- colloidal quantum dots -- have seen rapid advances in recent years. By offering full-spectrum solar harvesting, these cells are poised to address the urgent need for low-cost, high-efficiency photovoltaics.

Sargent, Edward H.

2012-03-01

117

Quantum dot-polypeptide hybrid assemblies: Synthesis, fundamental properties, and application  

NASA Astrophysics Data System (ADS)

We report the development of a multifunctional system that has the capability to target cancer cells, as well as simultaneously image and deliver therapeutics to these targeted cells. Such a "three-in-one" technology that has integrated targeting, imaging, and drug delivery capabilities is highly desirable in the field of cancer therapy. The material that we have developed for this application is a quantum dot (QD)-polypeptide hybrid assembly system that is spontaneously formed through the self-assembly of carboxyl-functionalized QDs and poly(diethylene glycol L-lysine)-poly(L-lysine) (PEGLL-PLL) diblock copolypeptide molecules. The hybrid assemblies could be modified to target a great variety of cancer biomarkers and have potential ability to carry therapeutic agents with diverse chemical and physical properties. In addition, the QD-polypeptide assemblies have the advantage of extensive tunability and versatility that allow their properties to be tailored and optimized for a broad range of applications. Cancer targeting can be achieved by modifying the QD-polypeptide hybrid assemblies with ligands that have affinity for certain biomarkers, which are overexpressed on cancer cells. Upon binding and uptake by the target cells through specific ligand-receptor mediated interactions, the assemblies could then allow for the simultaneous imaging of the cells and delivery of therapeutic agents to these cells. Imaging of the cells is done through detection of the QD fluorescence, and drug-delivery can be effected by loading the assembly with therapeutic agents and releasing them by means that disrupt the self-assembly. When compared to other dual imaging and drug-delivery systems, our QD-polypeptide hybrid assemblies have the advantage of extensive tunability and versatility. To showcase the tunability of the assembly, we demonstrated how its tumor-cell binding characteristics could be modulated and optimized by changing the PEGLL x-PLLy, architecture and the self-assembly conditions. First, we showed how the level of non-specific binding of the QD-polypeptide assemblies could be modulated by changing the PEGLLx-PLLy architecture that constitutes the assembly. The PEGLLx-PLLy architecture was found to affect the zeta-potential of the assembly, which in turn controls its level of non-specific binding. Second, we demonstrated that the level of integrin-mediated binding exhibited by the c(RGD)-assemblies could be modulated by varying the charge ratio (R'). R' is a parameter that is defined as the molar ratio of QD carboxyl functional groups to the lysine (PLL) residues. It was shown previously that the charge ratio controls the size of the assembly, and we believe that the assembly size in turn affects the ligand-receptor avidity effects. This work lays the foundation for further development of the QD-polypeptide hybrid assembly system such that we can achieve the ultimate goal of applying it as a highly tunable dual imaging and targeted drug-delivery agent. In the future, to allow for intracellular drug delivery, one can take advantage of the pH change that occurs in the endocytic pathway as the assemblies are internalized by the tumor cells. The change of pH to a relatively low value should then disrupt the electrostatic interaction that causes the self-assembly, which can in turn be expected to mediate the cytosolic delivery of the therapeutics cargo. (Abstract shortened by UMI.)

Thedjoisworo, Bayu Atmaja

118

A Novel Particle Detector: Quantum Dot Doped Liquid Scintillator  

NASA Astrophysics Data System (ADS)

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

Winslow, Lindley; Conrad, Janet; Jerry, Ruel

2010-02-01

119

Synthesis, encapsulation, purification and coupling of single quantum dots in phospholipid micelles for their use in cellular and in vivo imaging.  

PubMed

A detailed protocol for the synthesis of core/shell semiconductor nanocrystal, their encapsulation into phospholipid micelles, their purification and their coupling to a controlled number of small molecules is given. The protocol for the core/shell quantum dot (QD) CdSe/CdZnS synthesis has been specifically designed with two constraints in mind: green and reproducible core/shell QD synthesis with thick shell structure and QDs that can easily be encapsulated in poly(ethylene glycol)-phospholipid micelles with one QD per micelle. We present two procedures for the QD purification that are suitable for the use of QD micelles for in vivo imaging: ultracentrifugation and size-exclusion chromatography. We also discuss the different coupling chemistry for covalently linking a controlled number of molecules to the QD micelles. The total time durations for the different protocols are as follows: QD synthesis: 6 h; encapsulation: 15 min; purification: 1-4 h; coupling: reaction dependent. PMID:17947980

Carion, Olivier; Mahler, Benoît; Pons, Thomas; Dubertret, Benoit

2007-01-01

120

Investigation of confinement effects in ZnO quantum dots  

Microsoft Academic Search

We report a simple method for the synthesis of Na+ doped and stable zinc oxide quantum dots, using the quantum confinement atom method. An intense broad green photoluminescence (PL) was observed with a maximum located at ~535 nm when excited by UV radiation of 332 nm. The PL peak intensity is found to be highly dependent on the size of

D. Haranath; Sonal Sahai; Amish G. Joshi; Bipin K. Gupta; V. Shanker

2009-01-01

121

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

122

Synthesis and application of luminescent single CdS quantum dot encapsulated silica nanoparticles directed for precision optical bioimaging  

PubMed Central

This paper presents the synthesis of aqueous cadmium sulfide (CdS) quantum dots (QDs) and silica-encapsulated CdS QDs by reverse microemulsion method and utilized as targeted bio-optical probes. We report the role of CdS as an efficient cell tag with fluorescence on par with previously documented cadmium telluride and cadmium selenide QDs, which have been considered to impart high levels of toxicity. In this study, the toxicity of bare QDs was efficiently quenched by encapsulating them in a biocompatible coat of silica. The toxicity profile and uptake of bare CdS QDs and silica-coated QDs, along with the CD31-labeled, silica-coated CdS QDs on human umbilical vein endothelial cells and glioma cells, were investigated. The effect of size, along with the time-dependent cellular uptake of the nanomaterials, has also been emphasized. Enhanced, high-specificity imaging toward endothelial cell lines in comparison with glioma cells was achieved with CD31 antibody-conjugated nanoparticles. The silica-coated nanomaterials exhibited excellent biocompatibility and greater photostability inside live cells, in addition to possessing an extended shelf life. In vivo biocompatibility and localization study of silica-coated CdS QDs in medaka fish embryos, following direct nanoparticle exposure for 24 hours, authenticated the nanomaterials’ high potential for in vivo imaging, augmented with superior biocompatibility. As expected, CdS QD-treated embryos showed 100% mortality, whereas the silica-coated QD-treated embryos stayed viable and healthy throughout and after the experiments, devoid of any deformities. We provide highly cogent and convincing evidence for such silica-coated QDs as a model nanoparticle in practice, to achieve in vitro and in vivo precision targeted imaging.

Veeranarayanan, Srivani; Poulose, Aby Cheruvathoor; Mohamed, M Sheikh; Nagaoka, Yutaka; Iwai, Seiki; Nakagame, Yuya; Kashiwada, Shosaku; Yoshida, Yasuhiko; Maekawa, Toru; Kumar, D Sakthi

2012-01-01

123

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

124

One-step aqueous synthesis of graphene–CdTe quantum dot-composed nanosheet and its enhanced photoresponses  

Microsoft Academic Search

Although CdTe nanocrystal has been applied in quantum dot (QD)-based solar cells, there is no report on a graphene–CdTe QD hybrid system and its photoresponses. In this work, graphene–CdTe QD composed nanosheets were one-step synthesized in aqueous solution using a hydrothermal method and demonstrated enhanced photoresponses, rendering potentials in optoelectronics applications. This work could provide an environmental-friendly and universal approach

Zhisong Lu; Chun Xian Guo; Hong Bin Yang; Yan Qiao; Jun Guo; Chang Ming Li

125

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

126

Temperature dependence of optical properties and size tunability CdSe quantum dots via non-TOP synthesis  

Microsoft Academic Search

High-quality CdSe quantum dots with less common zinc blende structure were prepared in non-coordinating solvent 1-octadecene, with environment-friendly N,N-dimethyl-oleoyl amide as an alternative chemical to replace trioctylphoshine for Se powder, oleic acid as primary capping ligands, and benzophenone as secondary ligands. The temporal evolution of the optical properties of the nanocrystals with different growth temperature was monitored. Significant redshifts occurred

Chun Wang; Yang Jiang; Lanlan Chen; Shanying Li; Guohua Li; Zhongping Zhang

2009-01-01

127

Mechanochemical solid state synthesis of (Cd 0.8Zn 0.2)S quantum dots: Microstructure and optical characterizations  

Microsoft Academic Search

(Cd0.8Zn0.2)S quantum dots with a mixture of both cubic (Zinc-blende) and hexagonal (Wurtzite) phases have been prepared within 75min by mechanical alloying the stoichiometric mixture of Cd, Zn and S powders at room temperature in a planetary ball mill under Ar. The Rietveld analysis of X-ray powder diffraction data reveals relative phase abundances of both cubic and hexagonal phases and

S. Sain; S. K. Pradhan

2011-01-01

128

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

129

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

130

Copolymer nanosphere encapsulated CdS quantum dots prepared by RAFT copolymerization: synthesis, characterization and mechanism of formation  

Microsoft Academic Search

Cadmium sulfide (CdS) quantum dots (QDs) encapsulated in block copolymer spheres were synthesized by an aqueous emulsion polymerization\\u000a process. First, stable dispersions of CdS QDs in water were prepared using a polymer dispersant, either poly(acrylic acid)\\u000a or a random copolymer having an average of ten acrylic acid and five butyl acrylate units. These polymer dispersants were\\u000a prepared by reversible addition-fragmentation

Paramita Das; Weiheng Zhong; Jerome P. Claverie

131

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

132

Tunnel-Coupled Quantum Dots  

NASA Astrophysics Data System (ADS)

We consider a system of two quantum dots, coupled to each other and to separate leads by tunnel junctions with controllable barriers, in the regime where the Coulomb charging energy is large compared to the single-particle level spacing but small compared to the Fermi energy. When the dots are isolated from the leads, the interdot tunneling produces a shift in the groundstate energy which is a singular function of the system parameters. The shift is different for cases where the total number of electrons on the dots is even or odd, and depends also on any asymmetry between the dots. The tunneling strength may be independently determined from the conductivity measured when the dots are strongly coupled to the leads. Theoretical resultsfootnote J. M. Golden and B. I. Halperin, Phys. Rev. B (in press) and unpublished work^,footnote K. A. Matveev, L. I. Glazman, and H. U. Baranger, preprint may be compared with recent experiments by Waugh et alfootnote F. R. Waugh, M. J. Berry, D. J. Mar, R. M. Westervelt, K. C. Campman, and A. C. Gossard, Phys. Rev. Lett. 75, 705 (1995). This work has been supported by the NSF through the Harvard MRSEC, grant DMR94-00396.

Halperin, Bertrand I.

1996-03-01

133

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

134

The synthesis of highly water-dispersible and targeted CdS quantum dots and it is used for bioimaging by confocal microscopy  

NASA Astrophysics Data System (ADS)

Synthesis of a highly dispersed hydrophilic CdS nanocrystals and their use as fluorescence labeling for live cell imaging is reported here. By carefully manipulating the surface of CdS nanocrystals, the dispersions of CdS-MAA-PEI-FA nanocrystals with high photostability is prepared. The receptor-mediated delivery of folic acid conjugated quantum dots into folate-receptor-positive cell lines such as CBRH7919 liver cancer cells was demonstrated by confocal microscopy. In the future, the further modified CdS nanoparticles can be used for the tissue imaging in vivo studies.

Wei, Guangcheng; Yan, Miaomiao; Ma, Liying; Zhang, Huaibin

2012-01-01

135

Bandgap engineering of ZnSe quantum dots via a non-TOP green synthesis by use of organometallic selenium compound  

Microsoft Academic Search

Single-step green synthesis of ZnSe quantum dots (QDs) from 1,2,3-selenadiazole and zinc acetate resulted in formation of high-quality mono-disperse ZnSe with engineered band-gap. The present method is a non-TOP green route where oleic acid is used as a surfactant. The size quantization effect can be monitored by UV–visible spectroscopy which shows in the range 370–387nm (3.20–3.35eV), a blue shift of

Rupinder K. Beri; Priyesh More; B. G. Bharate; P. K. Khanna

2010-01-01

136

Electronic structure of quantum dots  

Microsoft Academic Search

The properties of quasi-two-dimensional semiconductor quantum dots are reviewed. Experimental techniques for measuring the electronic shell structure and the effect of magnetic fields are briefly described. The electronic structure is analyzed in terms of simple single-particle models, density-functional theory, and ``exact'' diagonalization methods. The spontaneous magnetization due to Hund's rule, spin-density wave states, and electron localization are addressed. As a

Stephanie M. Reimann; Matti Manninen

2002-01-01

137

Surface Functionalized Carbogenic Quantum Dots  

Microsoft Academic Search

Surface functionalized carbon-based quantum dots (C-QDs) are formed in-situ in a single-step process via thermal carbonization of suitable molecular precursors based on ammonium citrate salts. The as-synthesized nanoparticles have near spherical morphology and size around 7nm. Using different surface modifiers, we can form hydrophobic or hydrophilic capped C-QDs, which can be dispersed in organic or aqueous solvents, respectively. These C-QDs

A. B. Bourlinos; Andreas Stassinopoulos; A. Anglos; S. H. Anastasiadis; R. Zboril; M. Karakassides; E. P. Giannelis

2008-01-01

138

Applications of colloidal quantum dots  

Microsoft Academic Search

This paper addresses a number of major trends underlying the continuing effort to realize practical optoelectronic, electronic, and information-processing devices based on ensembles of quantum dots assembled in a variety of matrix materials. The great diversity of such structures makes it possible to fabricate numerous ensemble-based devices for applications underlying photoluminescent devices, light-emitting diodes, displays, photodetectors, photovoltaic devices, and solar

Ke Sun; Milana Vasudev; Hye-Son Jung; Jianyong Yang; Ayan Kar; Yang Li; Kitt Reinhardt; Preston Snee; Michael A. Stroscio; Mitra Dutta

2009-01-01

139

A facile synthesis route of size tunable CdS quantum dots with high photoluminescence yield.  

PubMed

Water soluble CdS nanoparticles were synthesized by reacting CdCl2 with sodium thiosulphate solutions as sulphur precursor. The facile one-pot synthetic route produced tunable (2-10 nm) high quality QDs with narrow particle size distribution and enhanced quantum yields (QY). PMID:21133124

Slipper, Ian J; Bhujval, Pranav; Rajaram, Sudha; Favretto, Marco E; Douroumis, Dennis

2010-09-01

140

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

2012-01-25

141

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

142

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

143

Ultrafast intraband relaxation in colloidal quantum dots  

Microsoft Academic Search

We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots using time-resolved luminescence and time-resolved TeraHertz spectroscopy. The rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This constitutes a direct proof of electron-to-hole energy transfer, the hypothesis behind the Auger cooling mechanism proposed in quantum dots,

J. J. H. Pijpers; E. Hendry; M. Bonn

2008-01-01

144

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

145

Lifetime blinking in nonblinking nanocrystal quantum dots.  

PubMed

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

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

2012-06-19

146

Carrier dynamics in quantum dot and gallium arsenide-based quantum dot cascade laser  

Microsoft Academic Search

Self-organized quantum dots provide unique atomic-like density of states and have important applications in semiconductor lasers. Energy relaxation of charge carriers in quantum dots is important for understanding the physics of devices fabricated from these artificially structured materials. Because the charge carriers relax through discrete energy levels, quantum dots provide a means to study the charge carrier interactions in the

Chuanshun Cao

2004-01-01

147

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

148

Highly luminescent polystyrene embedded CdSe quantum dots obtained through a modified colloidal synthesis route  

NASA Astrophysics Data System (ADS)

The present work describes a modified colloidal synthesis route for the preparation of CdSe nanocrystals, which were further embedded in a polystyrene matrix. Used as a reaction medium, glycerin makes it possible to obtain nanocrystals at lower temperatures in all process stages and an easier separation from the reaction mass. The influence of two different cadmium compounds used as primary cadmium sources over the quality of synthesized CdSe nanocrystals is established. Having a double role, namely in the formation of a cadmium precursor and that of a surface capping agent, three saturated monocarboxylic fatty acids are tested. The synthesis path is refined by evaluating the luminescent properties of CdSe nanocrystals resulting from each test. The obtained CdSe nanocrystals were further embedded in a polystyrene matrix, resulting in a highly luminescent composite. The solution-processed highly luminescent composite might be used as a conversion layer in various optoelectronic devices.

Stan, Corneliu S.; Secula, Marius S.; Sibiescu, Doina

2012-06-01

149

Synthesis and properties of CdSe Quantum Dot sensitized ZnO nanocomposites  

Microsoft Academic Search

In this work, zinc oxide nanocrystals with an average particle size of 13–22nm 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

Shefali Jain; Shailesh N. Sharma; Mahesh Kumar

150

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

151

Growth and Characterization of Quantum Dots and Quantum Dots Devices  

Microsoft Academic Search

Quantum dot nanostructures were investigated experimentally and theoretically for potential applications for optoelectronic devices. We have developed the foundation to produce state-of-the-art compound semiconductor nanostructures in a variety of materials: In(AsSb) on GaAs, GaSb on GaAs, and In(AsSb) on GaSb. These materials cover a range of energies from 1.2 to 0.7 eV. We have observed a surfactant effect in InAsSb

JEFFREY G. CEDERBERG; ROBERT M. BIEFELD; H. C. SCHNEIDER; WENG W. CHOW

2003-01-01

152

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

153

Single spins in semiconductor quantum dot microcavities  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots can be utilized to capture single electron or hole spins and they have therewith promise for various applications in fields like spintronics, spin based quantum information processing and chiral photonics. We integrate quantum dots into semiconductor microcavities to enhance light-matter interaction for ultrafast optical manipulation and read-out. Single electron and single hole spins can be statistically or deterministically loaded into the quantum dots and coherently controlled. Within the about ?s-coherence times of the spins about 105 complete single qubit rotations can be performed with ultrafast optical pulses. By utilizing a ?-type energy level system of a single quantum-dot electron spin in a magnetic field and ultrafast non-linear frequency conversion, quantum-dot spin-photon entanglement is observed.

Höfling, Sven; De Greve, Kristiaan; McMahon, Peter L.; Press, David; Yu, Leo; Pelc, Jason S.; Natarajan, Chandra M.; Kim, Na Young; Ladd, Thaddeus; Abe, Eisuke; Maier, Sebastian; Bisping, Dirk; Langer, Fabian; Schneider, Christian; Kamp, Martin; Hadfield, Robert H.; Forchel, Alfred; Fejer, M. M.; Yamamoto, Yoshihisa

2013-09-01

154

Colloidal quantum dot photovoltaics: the effect of polydispersity.  

PubMed

The size-effect tunability of colloidal quantum dots enables facile engineering of the bandgap at the time of nanoparticle synthesis. The dependence of effective bandgap on nanoparticle size also presents a challenge if the size dispersion, hence bandgap variability, is not well-controlled within a given quantum dot solid. The impact of this polydispersity is well-studied in luminescent devices as well as in unipolar electronic transport; however, the requirements on monodispersity have yet to be quantified in photovoltaics. Here we carry out a series of combined experimental and model-based studies aimed at clarifying, and quantifying, the importance of quantum dot monodispersity in photovoltaics. We successfully predict, using a simple model, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using this same experimentally tested model the implications of a broadened quantum dot population on device performance. We report that present-day colloidal quantum dot photovoltaic devices with typical inhomogeneous linewidths of 100-150 meV are dominated by surface traps, and it is for this reason that they see marginal benefit from reduction in polydispersity. Upon eliminating surface traps, achieving inhomogeneous broadening of 50 meV or less will lead to device performance that sees very little deleterious impact from polydispersity. PMID:22257205

Zhitomirsky, David; Kramer, Illan J; Labelle, André J; Fischer, Armin; Debnath, Ratan; Pan, Jun; Bakr, Osman M; Sargent, Edward H

2012-01-24

155

Quantum Confined Silicon Clathrate Quantum Dots  

NASA Astrophysics Data System (ADS)

Silicon (Si) allotropes can be synthesized in such a way that tetrahedrally bonded atoms form cage-like structures with bulk mechanical and opto-electronic properties distinct from those of diamond silicon (dSi). We use DFT, supplemented with many-body Green function analysis, to explore the structural stability of clathrate Si quantum dots (QDs) and to characterize their confinement as a function of crystal symmetry and size. Our results show that that there is a simple relationship between the confinement character of the QDs and the effective mass of the associated bulk crystals. Clathrate QDs and dSiQDs of the same size can exhibit differences of gap energies by as much as 2 eV. This offers the potential of synthesizing Si dots on the order of 1 nm that have optical gaps in the visible range but that do not rely on high-pressure routes such as those explored for the metastable BC8 and R8 phases. These results prompt the question as to how minimal quantum confinement can be in dots composed of Si. More broadly, clathrate QDs can in principle be synthesized for a wide range of semiconductors, and the design space can be further enriched via doping.

Lusk, Mark; Brawand, Nicholas

2013-03-01

156

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

2012-01-18

157

Aqueous synthesis of highly luminescent AgInS2-ZnS quantum dots and their biological applications  

NASA Astrophysics Data System (ADS)

Highly emissive and air-stable AgInS2-ZnS quantum dots (ZAIS QDs) with quantum yields of up to 20% have been successfully synthesized directly in aqueous media in the presence of polyacrylic acid (PAA) and mercaptoacetic acid (MAA) as stabilizing and reactivity-controlling agents. The as-prepared water-dispersible ZAIS QDs are around 3 nm in size, possess the tetragonal chalcopyrite crystal structure, and exhibit long fluorescence lifetimes (>100 ns). In addition, these ZAIS QDs are found to exhibit excellent optical and colloidal stability in physiologically relevant pH values as well as very low cytotoxicity, which render them particularly suitable for biological applications. Their potential use in biological labelling of baculoviral vectors is demonstrated.Highly emissive and air-stable AgInS2-ZnS quantum dots (ZAIS QDs) with quantum yields of up to 20% have been successfully synthesized directly in aqueous media in the presence of polyacrylic acid (PAA) and mercaptoacetic acid (MAA) as stabilizing and reactivity-controlling agents. The as-prepared water-dispersible ZAIS QDs are around 3 nm in size, possess the tetragonal chalcopyrite crystal structure, and exhibit long fluorescence lifetimes (>100 ns). In addition, these ZAIS QDs are found to exhibit excellent optical and colloidal stability in physiologically relevant pH values as well as very low cytotoxicity, which render them particularly suitable for biological applications. Their potential use in biological labelling of baculoviral vectors is demonstrated. Electronic supplementary information (ESI) available: Quantum yields, EDX spectrum and photoluminescence decay curves. See DOI: 10.1039/c3nr34159c

Regulacio, Michelle D.; Win, Khin Yin; Lo, Seong Loong; Zhang, Shuang-Yuan; Zhang, Xinhai; Wang, Shu; Han, Ming-Yong; Zheng, Yuangang

2013-02-01

158

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

159

Coherent photonic coupling of semiconductor quantum dots.  

PubMed

We report a new type of coupling between quantum dot excitons mediated by the strong single-photon field in a high-finesse micropillar cavity. Coherent exciton coupling is observed for two dots with energy differences of the order of the exciton-photon coupling. The coherent coupling mode is characterized by an anticrossing with a particularly large line splitting of 250 microeV. Because of the different dispersion relations with temperature, the simultaneous photonic coupling of quantum dot excitons can be easily distinguished from cases of sequential strong coupling of two quantum dots. PMID:16688279

Reitzenstein, S; Löffler, A; Hofmann, C; Kubanek, A; Kamp, M; Reithmaier, J P; Forchel, A; Kulakovskii, V D; Keldysh, L V; Ponomarev, I V; Reinecke, T L

2006-06-01

160

One-step aqueous synthesis of graphene-CdTe quantum dot-composed nanosheet and its enhanced photoresponses.  

PubMed

Although CdTe nanocrystal has been applied in quantum dot (QD)-based solar cells, there is no report on a graphene-CdTe QD hybrid system and its photoresponses. In this work, graphene-CdTe QD composed nanosheets were one-step synthesized in aqueous solution using a hydrothermal method and demonstrated enhanced photoresponses, rendering potentials in optoelectronics applications. This work could provide an environmental-friendly and universal approach to fabricate graphene-based hybrid nanomaterials for various applications. PMID:21035813

Lu, Zhisong; Guo, Chun Xian; Yang, Hong Bin; Qiao, Yan; Guo, Jun; Li, Chang Ming

2010-10-12

161

Synthesis and luminescence characteristics of DHLA-capped PbSe quantum dots with biocompatibility  

NASA Astrophysics Data System (ADS)

In this work, we report a facile aqueous route to prepare PbSe QDs with strong photoluminescent and near-infrared (NIR) emission using dihydrolipoic acid (DHLA) as the capping ligands. It was found that the synthesis parameters including the molar ratio of DHLA/Pb, the pH value and the reaction time have considerable influence on photoluminescent intensity (PL) of the PbSe QDs. The as-synthesized DHLA-capped PbSe QDs were characterized by high-resolution transmission electron microscopy (HRTEM), energy-dispersive analysis of X-ray (EDX) and X-ray diffraction (XRD), the results indicated that the QDs were about 8.0 ± 0.2 nm in size and had good monodisperse and a rock salt crystalline structure. Also, there was DHLA on the surface of QDs, which was confirmed by Fourier transform infrared (FT-IR) spectrometry. The PbSe QDs exhibited optimal PL intensity when Pb:Se:DHLA = 1:0.6:1 in weak alkaline aqueous. The as-synthesized QDs kept highly PL intensities when stored in the dark in normal air environment during the period of 60 days. In addition, the biocompatibility of these QDs was measured by hemolytic test, which indicated that DHLA-stabilized QDs are biocompatible. It is important for QDs as biomarkers in biological detection and diagnosis.

Yu, Yaxin; Zhang, Kexin; Li, Zhen; Sun, Shuqing

2012-03-01

162

Synthesis and characterization of Mn quantum dots by bioreduction with water hyacinth.  

PubMed

The bio-reduction method is reported as a part of a complimentary self-sustained technology, where bioremediation and metal particle production are related. The use of the characterization methods in this self sustainable technique open the expectative to be used for several other elements and with other plants, which will be discussed. However, the particular case of Mn nanoparticles involves an important option to generate nanoparticles in the range of 1-4 nanometers with a well controlled size and with a structure based on an fcc-like geometry for the smallest clusters and with more complex arrays for cluster greater than four shells, which involves magnetic moments significantly related to their atomistic configuration. At the same time, the use of the characterization methods establishes the dependence of the nanoparticle's size on the pH conditions used during the synthesis; small clusters in the range of 1-2 nm were generated using pH=5, and it was shown that for the smallest aggregates, simple polyhedron shapes are stable. PMID:16573087

Rosano-Ortega, G; Schabes-Retchkiman, P; Zorrilla, C; Liu, H B; Canizal, G; Avila-Pérez, P; Ascencio, J A

2006-01-01

163

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

2011-10-12

164

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

165

Nonradiative resonance energy transfer between quantum dots  

NASA Astrophysics Data System (ADS)

In the work we examined the mechanism of nonradiactive resonant energy transfer between quantum dots (QD), the probability of this process was calculated. The valence band has difficult structure due to the additional matrix element connected with another polarization of heavy holes. Dependences of transfer probability on distance between quantum dots and barrier heights for electrons were studied.

Stepashkina, A. S.; Samosvat, D. M.; Chikalova-Luzina, O. P.; Zegrya, G. G.

2013-08-01

166

Near-field magnetoabsorption of quantum dots  

Microsoft Academic Search

We investigate the effect of an external magnetic field of variable orientation and magnitude (up to 20T ) on the linear near-field optical absorption spectra of single and coupled III-V semiconductor quantum dots. We focus on the spatial as well as on the magnetic confinement, varying the dimensions of the quantum dots and the magnetic field. We show that the

Constantinos Simserides; Anna Zora; Georgios Triberis

2006-01-01

167

Phonon runaway in carbon nanotube quantum dots  

Microsoft Academic Search

We explore electronic transport in a nanotube quantum dot strongly coupled with vibrations and weakly with leads and the thermal environment. We show that the recent observation of anomalous conductance signatures in single-walled carbon nanotube quantum dots [B. J. LeRoy , Nature (London) 395, 371 (2004) and B. J. LeRoy , Phys. Rev. B 72, 075413 (2005)] can be understood

L. Siddiqui; A. W. Ghosh; S. Datta

2007-01-01

168

Quantum dots as handles for optical manipulation  

NASA Astrophysics Data System (ADS)

Individual colloidal quantum dots can be optically trapped and manipulated by a single infrared laser beam operated at low laser powers.1, 2 If the absorption spectrum and the emission wavelength of the trapping laser are appropriately chosen, the trapping laser light can act as a source for two-photon excitation of the trapped quantum dot. This eliminates the need for an additional excitation laser in experiments where individual quantum dots are used both as force transducers and for visualization of the system. To use quantum dots as handles for quantitative optical force transduction, it is crucial to perform a precise force calibration. Here, we present an Allan variance analysis3 of individual optically trapped quantum dots and show that the optimal measurement time for experiments involving individual quantum dots is on the order of 0.3 seconds. Due to their small size and strong illumination, quantum dots are optimal for single molecule assays where, optimally, the presence of the tracer particle should not dominate the dynamics of the system. As an example, we investigated the thermal fluctuations of a DNA tether using an individual colloidal quantum dot as marker, this being the smallest tracer for tethered particle method reported.

Jauffred, Liselotte; Sletmoen, Marit; Czerwinski, Fabian; Oddershede, Lene

2010-08-01

169

Spin noise spectroscopy of quantum dot molecules  

NASA Astrophysics Data System (ADS)

We discuss advantages and limitations of the spin noise spectroscopy for characterization of interacting quantum dot systems on specific examples of individual singly and doubly charged quantum dot molecules (QDMs). It is shown that all the relevant parameters of the QDMs, including tunneling amplitudes with spin-conserving and spin-nonconserving interactions, decoherence rates, Coulomb repulsions, anisotropic g factors and the distance between the dots, can be determined by measuring properties of the spin noise power spectrum.

Roy, Dibyendu; Li, Yan; Greilich, Alex; Pershin, Yuriy V.; Saxena, Avadh; Sinitsyn, Nikolai A.

2013-07-01

170

Ferritin-Templated Quantum-Dots for Quantum Logic Gates.  

National Technical Information Service (NTIS)

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

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

2005-01-01

171

Biocompatible Quantum Dots for Biological Applications  

PubMed Central

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

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

2011-01-01

172

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

173

Aqueous synthesis of highly luminescent AgInS?-ZnS quantum dots and their biological applications.  

PubMed

Highly emissive and air-stable AgInS2-ZnS quantum dots (ZAIS QDs) with quantum yields of up to 20% have been successfully synthesized directly in aqueous media in the presence of polyacrylic acid (PAA) and mercaptoacetic acid (MAA) as stabilizing and reactivity-controlling agents. The as-prepared water-dispersible ZAIS QDs are around 3 nm in size, possess the tetragonal chalcopyrite crystal structure, and exhibit long fluorescence lifetimes (>100 ns). In addition, these ZAIS QDs are found to exhibit excellent optical and colloidal stability in physiologically relevant pH values as well as very low cytotoxicity, which render them particularly suitable for biological applications. Their potential use in biological labelling of baculoviral vectors is demonstrated. PMID:23392168

Regulacio, Michelle D; Win, Khin Yin; Lo, Seong Loong; Zhang, Shuang-Yuan; Zhang, Xinhai; Wang, Shu; Han, Ming-Yong; Zheng, Yuangang

2013-03-21

174

The Coulomb Blockade in Coupled Quantum Dots  

NASA Astrophysics Data System (ADS)

Individual quantum dots are often referred to as ``artificial atoms''. Two tunnel-coupled quantum dots may be considered an ``artificial molecule''. One advantage of studying quantum dot molecules is that the amount of coupling between the dots may be experimentally varied. We present measurements of conductance through a double quantum dot with adjustable interdot tunneling rate that show the evolution from two separate ``atoms'' to one composite ``molecule''.(C. Livermore, C.H. Crouch, R.M. Westervelt, K.L. Campman, and A.C. Gossard, Science) 274, 1332 (1996). The quantum dots are defined in a two-dimensional electron gas in a GaAs/AlGaAs heterostructure by ten independent electrostatic surface gates. The gates are used to separately control the total induced charge on the double dot, the induced charge difference between the dots, and the interdot tunnel conductance. We measure the double dot conductance as a function of the total induced charge and the induced charge difference to measure the charging diagram and probe the minimum energy surface of the double dot; we repeat this measurement for a series of conductances ranging from near zero to 2e^2/h. For weak interdot tunneling each dot is individually governed by the Coulomb blockade. As interdot tunnel conductance increases, the charging diagram departs from simple Coulomb blockade theory and evolves to that of a single large dot. The evolution is controlled by quantum mechanical charge sharing between dots. The results are in excellent quantitative agreement with recent theory.(J.M. Golden and B.I. Halperin, Phys. Rev. B), in press (1996); K.A. Matveev, L.I. Glazman and H.U. Baranger, Phys. Rev. B 54, 5637 (1996).

Livermore, C.

1997-03-01

175

Synthesis and characterization of a pegylated derivative of 3-(1,2,3,6-tetrahydro-pyridin-4yl)-1 H-indole (IDT199): A high affinity SERT ligand for conjugation to quantum dots  

Microsoft Academic Search

Quantum dots consisting of a cadmium selenide core encapsulated in a shell of cadmium doped zinc sulfide have the potential to revolutionize fluorescent imaging of live cell cultures. In order to utilize these fluorescent probes it is necessary to functionalize them with biologically active ligands. In this paper we report the design and synthesis of a ligand that has a

Ian D. Tomlinson; Michael R. Warnerment; John N. Mason; Matthew J. Vergne; David M. Hercules; Randy D. Blakely; Sandra J. Rosenthal

2007-01-01

176

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

177

Seed-mediated synthesis, properties and application of ?-Fe2O3-CdSe magnetic quantum dots  

NASA Astrophysics Data System (ADS)

Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around ?-Fe2O3 magnetic cores was performed at high temperature (300 °C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells.

Lin, Alex W. H.; Yen Ang, Chung; Patra, Pranab K.; Han, Yu; Gu, Hongwei; Le Breton, Jean-Marie; Juraszek, Jean; Chiron, Hubert; Papaefthymiou, Georgia C.; Tamil Selvan, Subramanian; Ying, Jackie Y.

2011-08-01

178

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

PubMed

Silicon quantum dots (QDs) were prepared with a corona of di-n-octyl phosphine oxides, by performing hydrosilylation chemistry on the surface of hydrogen-terminated Si QDs. These novel Si QDs proved well-suited to serve as "ligands" for other semiconductor QDs, such as CdSe, by interaction of the phosphine oxide corona with the CdSe surface. A pronounced photoluminescence quenching of CdSe quantum dots was observed upon introduction of the phosphine oxide functionalized Si QDs to a CdSe QD solution. Surface functionalization of the Si QDs proved critically important to observing these effects, as conventional (alkane-covered) Si QD samples gave no evidence of electronic interactions with TOPO-covered CdSe. In a comparative system, phosphine oxide terminated oligo(phenylene vinylene) molecules acting as CdSe QD ligands provide a similar fluorescence quenching, with exciton decay kinetics supporting the formation of an electronically interacting hybrid materials system. PMID:19908857

Sudeep, P K; Emrick, Todd

2009-12-22

179

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

180

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

181

Development and characterization of silk fibroin coated quantum dots  

Microsoft Academic Search

Recent progress in the field of semiconductor nanocrystals or Quantum Dots (QDs) has seen them find wider acceptance as a tool in biomedical research labs. As produced, high quality QDs, synthesized by high temperature organometallic synthesis, are coated with a hydrophobic ligand. Therefore, they must be further processed to be soluble in water and to be made biocompatible. To accomplish

B. B. Nathwani; C. Needham; A. B. Mathur; K. E. Meissner

2008-01-01

182

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

183

Thermoelectromechanical effects in quantum dots  

NASA Astrophysics Data System (ADS)

Electromechanical effects are important in semiconductor nanostructures as most of the semiconductors are piezoelectric in nature. These nanostructures find applications in electronic and optoelectronic devices where they may face challenges for thermal management. Low dimensional semiconductor nanostructures, such as quantum dots (QD) and nanowires, are the nanostructures where such challenges must be particularly carefully addressed. In this contribution we report a study on thermoelectromechanical effects in QDs. For the first time a coupled model of thermoelectroelasticity has been applied to the analysis of quantum dots and the influence of thermoelectromechanical effects on bandstructures of low dimensional nanostructures has been quantified. Finite element solutions are obtained for different thermal loadings and their effects on the electromechanical properties and bandstructure of QDs are presented. Our model accounts for a practically important range of internal and external thermoelectromechanical loadings. Results are obtained for typical QD systems based on GaN/AlN and CdSe/CdS (as representatives of III-V and II-VI group semiconductors, respectively), with cylindrical and truncated conical geometries. The wetting layer effect on electromechanical quantities is also accounted for. The energy bandstructure calculations for various thermal loadings are performed. Electromechanical fields are observed to be more sensitive to thermal loadings in GaN/AlN QDs as compared to CdSe/CdS QDs. The results are discussed in the context of the effect of thermal loadings on the performance of QD-based nanosystems.

Patil, Sunil R.; Melnik, Roderick V. N.

2009-03-01

184

Dicke states in multiple quantum dots  

NASA Astrophysics Data System (ADS)

We present a theoretical study of the collective optical effects which can occur in groups of three and four quantum dots. We define conditions for stable subradiant (dark) states, rapidly decaying super-radiant states, and spontaneous trapping of excitation. Each quantum dot is treated like a two-level system. The quantum dots are, however, realistic, meaning that they may have different transition energies and dipole moments. The dots interact via a short-range coupling which allows excitation transfer across the dots, but conserves the total population of the system. We calculate the time evolution of single-exciton and biexciton states using the Lindblad equation. In the steady state the individual populations of each dot may have permanent oscillations with frequencies given by the energy separation between the subradiant eigenstates.

Sitek, Anna; Manolescu, Andrei

2013-10-01

185

Series-Coupled Triple Quantum Dot Molecules  

NASA Astrophysics Data System (ADS)

We present the electronic properties of a triple quantum dot molecule embedded inside a sub-micron mesa, made from a quadruple-barrier triple-quantum-well structure, and surrounded by a single gate electrode. We outline the design principles of the quadruple-barrier triple-quantum-well structure and calculate the energy of the three lowest states as a function of center well thickness. We observe regular and irregular shaped Coulomb diamond regions similar to those for double quantum dot devices. Variation in the Coulomb blockade region shape is introduced by fluctuation in the offset energies between the quantum dots likely associated with device processing and random impurity potential in the material. We also present Coulomb blockade patterns calculated with a constant interaction model for sequential tunneling through the three series-coupled quantum dots.

Amaha, Shinichi; Hatano, Tsuyoshi; Izumida, Wataru; Teraoka, Soichiro; Ono, Keiji; Kono, Kimitoshi; Tarucha, Seigo; Aers, Geof; Gupta, James; Austing, Guy

2012-02-01

186

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

187

New generation of chitosan-encapsulated ZnO quantum dots loaded with drug: synthesis, characterization and in vitro drug delivery response.  

PubMed

The objective of the study is to describe a new approach of combining quantum dots technology with anti-cancer drug therapy. In this regard, we communicate the preliminary research on the synthesis of blue-light emitting ZnO quantum dots (QDs) combined with biodegradable chitosan (N-acetylglucosamine) for tumor-targeted drug delivery. The results presented here indicate that the proposed new generation of QDs loaded with anti-cancer agents and encapsulated with biocompatible polymer represent a potential platform to deliver tumor-targeted drugs and document the delivery process, if desired. Non-toxic water-dispersed ZnO QDs with long-term fluorescence stability were synthesized by a chemical hydrolysis method, encapsulated with chitosan and loaded with anti-cancer drug. Chitosan enhanced the stability of the QDs because of the hydrophilicity and cationic charge of chitosan. The study points toward the application of water-dispersed ZnO QDs with long-term fluorescence stability for design of new drug release carrier. PMID:20100604

Yuan, Q; Hein, S; Misra, R D K

2010-01-25

188

Surface Termination Effects on Zinc Oxide Quantum Dots.  

NASA Astrophysics Data System (ADS)

We investigate the effects of surface terminations on the optical properties of 2-6 nm ZnO quantum dots. Nanocrystals were grown by wet chemical synthesis in a short-chain alcohol solvent from zinc acetate and sodium hydroxide. Quenching of particle growth with various capping agents is necessary to maintain and enhance the unique characteristics of the nanocrystals. We reproduce results of previous work and expand on characterization of naked and surface terminated ZnO quantum dots. The nanoparticle properties were investigated by UV absorption spectrophotometry, photoluminescence, infrared spectroscopy, scanning electron microscopy , and atomic force microscopy techniques.

Whitesell, Steve; Spalenka, Joe; Jack, Christopher; Allen, Cary; Collins, Reuben; Furtak, Thomas

2007-03-01

189

Layered double hydroxides as carriers for quantum dots@silica nanospheres.  

PubMed

Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists of using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties. PMID:22825338

Stoica, Georgiana; Castelló Serrano, Iván; Figuerola, Albert; Ugarte, Irati; Pacios, Roberto; Palomares, Emilio

2012-07-24

190

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

191

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.

192

Facile synthesis of water-soluble ZnS quantum dots with strong luminescent emission and biocompatibility  

NASA Astrophysics Data System (ADS)

ZnS quantum dots (QDs) are among the most promising emerging fluorescent materials for biolabeling. High-quality colloidal ZnS QDs were synthesized via a new facile chemical precipitation method using the mixture of ethylene glycol (EG) and water as the solvent. The phase structure and morphology of the ZnS QDs were characterized by X-ray powder diffraction and high resolution transmission electron microscopy. The synthesized ZnS QDs have a cubic zinc blende structure with monodispered and small particles. ZnS QDs easily dispersed in water to form stable and clear colloids and the strong tunable trap state emissions from 452 to 516 nm were achieved by varying the reaction time. The hemolysis assay was performed to evaluate the biocompatibility of the ZnS QDs.

Zhang, Rui; Liu, Yingbo; Sun, Shuqing

2013-10-01

193

Quantum dot-based theranostics  

PubMed Central

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

Ho, Yi-Ping; Leong, Kam W.

2010-01-01

194

Quantum dot-based theranostics  

NASA Astrophysics Data System (ADS)

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

Ho, Yi-Ping; Leong, Kam W.

2010-01-01

195

Quantum dot lasers: from promise to reality  

Microsoft Academic Search

Nanoscale coherent insertions of narrow gap material in a single-crystalline matrix, or Quantum Dot (QD) provide a possibility to extend the basic principles of heterostructure lasers. The idea to use heterostructures with dimensionality lower than two in semiconductor lasers appeared a quarter of a century ago, simultaneously with the proposal of a quantum well laser. However, fabrication of quantum wire-

Dieter Bimberg; Nikolai N. Ledentsov

2000-01-01

196

Triple quantum dots as charge rectifiers.  

PubMed

We theoretically analyze electronic spin transport through a triple quantum dot in series, attached to electrical contacts, where the drain contact is coupled to the central dot. We show that current rectification is observed in the device due to current blockade. The current blocking mechanism is originated by a destructive interference of the electronic wavefunction at the drain dot. There, the electrons are coherently trapped in a singlet two-electron dark state, which is a coherent superposition of the electronic wavefunction in the source dot and in the dot isolated from the contacts. Its formation gives rise to zero current and current rectification as the voltage is swept. We analyze this behavior analytically and numerically for both zero and finite magnetic dc fields. On top of that, we include phenomenologically a finite spin relaxation rate and calculate the current numerically. Our results show that triple dots in series can be designed to behave as quantum charge rectifiers. PMID:22442135

Busl, M; Platero, G

2012-03-23

197

CdS/CdSe quantum dot co-sensitized graphene nanocomposites via polymer brush templated synthesis for potential photovoltaic applications.  

PubMed

CdS/CdSe quantum dot (QDs) co-sensitized graphene sheets have been obtained via polymer brush templated synthesis. Firstly, the anionic functional polymer (polymethacrylate cadmium) was grafted via the surface initiated atomic transfer radical polymerization (ATRP) using a macromolecular initiator, which contains polymerized pyrene units for chemical anchoring on graphene surface and alkyl bromines to initiate ATRP. Then, the coordinated cadmium in the polymer chains can act as a source precursor for QDs. After reaction, polymer brushes can be recovered and act as the nanoreactor via the absorption of cadmium ions by carboxylate groups. So, high density QDs can be multiply uploaded onto the graphene surface by repeated steps. The as-prepared composite materials exhibited significantly enhanced visible light response compared to plain graphene, and have potential applications as the platform to build solar cell assembles. PMID:22349081

Yan, Junfeng; Ye, Qian; Wang, Xiaolong; Yu, Bo; Zhou, Feng

2012-02-21

198

CdS/CdSe quantum dot co-sensitized graphene nanocomposites via polymer brush templated synthesis for potential photovoltaic applications  

NASA Astrophysics Data System (ADS)

CdS/CdSe quantum dot (QDs) co-sensitized graphene sheets have been obtained via polymer brush templated synthesis. Firstly, the anionic functional polymer (polymethacrylate cadmium) was grafted via the surface initiated atomic transfer radical polymerization (ATRP) using a macromolecular initiator, which contains polymerized pyrene units for chemical anchoring on graphene surface and alkyl bromines to initiate ATRP. Then, the coordinated cadmium in the polymer chains can act as a source precursor for QDs. After reaction, polymer brushes can be recovered and act as the nanoreactor via the absorption of cadmium ions by carboxylate groups. So, high density QDs can be multiply uploaded onto the graphene surface by repeated steps. The as-prepared composite materials exhibited significantly enhanced visible light response compared to plain graphene, and have potential applications as the platform to build solar cell assembles.

Yan, Junfeng; Ye, Qian; Wang, Xiaolong; Yu, Bo; Zhou, Feng

2012-03-01

199

Open quantum dots: II. Probing the classical to quantum transition  

NASA Astrophysics Data System (ADS)

Open quantum dots provide a natural system in which to study both classical and quantum features of transport. From the classical point of view these dots possess a mixed phase space which yields families of closed, regular orbits as well as an expansive sea of chaos. An important question concerns the manner in which these classical states evolve into the set of quantum states that populate the dot in the quantum limit. In the reverse direction, the manner in which the quantum states evolve to the classical world is governed strongly by Zurek’s decoherence theory. This was discussed from the quantum perspective in an earlier review (Ferry et al 2011 Semicond. Sci. Technol. 26 043001). Here, we discuss the nature of the various classical states, how they are formed, how they progress to the quantum world, and the signatures that they create in magnetotransport and general conductance studies of these dots.

Brunner, R.; Ferry, D. K.; Akis, R.; Meisels, R.; Kuchar, F.; Burke, A. M.; Bird, J. P.

2012-08-01

200

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

201

Theory Of Alkyl Terminated Silicon Quantum Dots  

SciTech Connect

We have carried out a series of ab-initio calculations to investigate changes in the optical properties of Si quantum dots as a function of surface passivation. In particular, we have compared hydrogen passivated dots with those having alkyl groups at the surface. We find that, while on clusters with reconstructed surfaces a complete alkyl passivation is possible, steric repulsion prevents full passivation of Si dots with unreconstructed surfaces. In addition, our calculations show that steric repulsion may have a dominant effect in determining the surface structure, and eventually the stability of alkyl passivated clusters, with results dependent on the length of the carbon chain. Alkyl passivation weakly affects optical gaps of silicon quantum dots, while it substantially decreases ionization potentials and electron affinities and affect their excited state properties. On the basis of our results we propose that alkyl terminated quantum dots may be size selected taking advantage of the change in ionization potential as a function of the cluster size.

Reboredo, F; Galli, G

2004-08-19

202

Anticrossings in Förster coupled quantum dots  

Microsoft Academic Search

We consider two coupled generic quantum dots, each modelled by a simple\\u000apotential which allows the derivation of an analytical expression for the\\u000ainter-dot Foerster coupling, in the dipole-dipole approximation. We investigate\\u000athe energy level behaviour of this coupled two-dot system under the influence\\u000aof an external applied electric field and predict the presence of anticrossings\\u000ain the optical spectra

Ahsan Nazir; Brendon W. Lovett; Sean D. Barrett; John H. Reina; G. Andrew

2005-01-01

203

Nonlinear thermovoltage and thermocurrent in quantum dots  

NASA Astrophysics Data System (ADS)

Quantum dots are model systems for quantum thermoelectric behavior because of their ability to control and measure the effects of electron-energy filtering and quantum confinement on thermoelectric properties. Interestingly, nonlinear thermoelectric properties of such small systems can modify the efficiency of thermoelectric power conversion. Using quantum dots embedded in semiconductor nanowires, we measure thermovoltage and thermocurrent that are strongly nonlinear in the applied thermal bias. We show that most of the observed nonlinear effects can be understood in terms of a renormalization of the quantum-dot energy levels as a function of applied thermal bias and provide a theoretical model of the nonlinear thermovoltage taking renormalization into account. Furthermore, we propose a theory that explains a possible source of the observed, pronounced renormalization effect by the melting of Kondo correlations in the mixed-valence regime. The ability to control nonlinear thermoelectric behavior expands the range in which quantum thermoelectric effects may be used for efficient energy conversion.

Fahlvik Svensson, S.; Hoffmann, E. A.; Nakpathomkun, N.; Wu, P. M.; Xu, H. Q.; Nilsson, H. A.; Sánchez, D.; Kashcheyevs, V.; Linke, H.

2013-10-01

204

Facile synthesis and photophysical characterization of luminescent CdTe quantum dots for Forster resonance energy transfer based immunosensing of staphylococcal enterotoxin B.  

PubMed

Aqueous phase synthesis of CdTe quantum dots (QDs) with surface functionalization for bioconjugation remains the best approach for biosensing and bioimaging applications. We present a facile aqueous phase method to prepare CdTe QDs by adjusting precursor and ligand concentrations. CdTe QDs had photoluminescence quantum yield up to ?33% with a narrow spectral distribution. The powder X-ray diffraction profile elucidated characteristic broad peaks of zinc blende cubic CdTe nanoparticles with 2.5-3?nm average crystalline size having regular spherical morphology as revealed by transmission electron microscopy. Infra-red spectroscopy confirmed disappearance of characteristic absorptions for -SH thiols inferring thiol coordinated CdTe nanoparticles. The effective molar concentration of 1 : 2.5 : 0.5 respectively for Cd(2+) /3-mercaptopropionic acid/HTe(-) at pH 9?±?0.2 resulted in CdTe quantum dots of 2.2-3.06?nm having band gap in the range 2.74-2.26 eV respectively. Later, QD(523) and QD(601) were used for monitoring staphylococcal enterotoxin B (SEB; a bacterial superantigen responsible for food poisoning) using Forster resonance energy transfer based two QD fluorescence. QD(523) and QD(601) were bioconjugated to anti-SEB IgY antibody and SEB respectively according to carbodiimide protocol. The mutual affinity between SEB and anti-SEB antibody was relied upon to obtain efficient energy transfer between respective QDs resulting in fluorescence quenching of QD(523) and fluorescence enhancement of QD(601) . Presence of SEB in the range 1-0.05?µg varied the rate of fluorescence quenching of QD(523) , thereby demonstrating efficient use of QDs in the Forster resonance energy transfer based immunosensing method by engineering the QD size. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23192990

Vinayaka, Aaydha C; Thakur, Munna S

2012-11-29

205

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

2010-12-13

206

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

207

Quantum Dot Array Formation through Biomolecular Nanopatterning.  

National Technical Information Service (NTIS)

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

H. P. Gillis

1999-01-01

208

Quantum dots: Paradigm changes in semiconductor physics  

Microsoft Academic Search

Deposition of one or a few monolayers of a semiconductor having a lattice constant largely different from the underlying substrate\\u000a leads to formation of coherent “quantum dot arrays” of densities beyond 1011 cm?2 in a matter of seconds. Self-organization effects govern their massively parallel formation. Fundamental paradigms of semiconductor\\u000a physics must be changed in describing such quantum dots or their

D. Bimberg

1999-01-01

209

Quantum dots for fiber laser sources  

Microsoft Academic Search

In this invited paper, we will discuss the use of quantum dots as nonlinear optical elements in fiber laser sources. Furthemore, a review of the fabrication of the first low-loss (< 0.5 dB\\/cm) ion-exchanged waveguides in a quantum-dot-doped glass will be presented. We will discuss the coupling, propagation, absorption, and scattering losses in these waveguides. The near-field mode profile along

Jason M. Auxier; Axel Schülzgen; Michael M. Morrell; Brian R. West; Seppo Honkanen; Sabyasachi Sen; Nicholas F. Borrelli; Nasser N. Peyghambarian

2005-01-01

210

Magnetically-doped semiconductor quantum dots (nanocrystals)  

Microsoft Academic Search

Previously, we have shown how to use self-assembly and colloidal semiconductor quantum dots (or nanocrystals) to form semiconductor photonic crystals - structures that are three-dimensionally periodic on an optical-length scale. One route to further enhance the behavior of such structures is to modify the properties of the individual quantum dots prior to assembly. For example, properties may be altered by

David Norris

2001-01-01

211

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

212

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

2010-07-06

213

Quantum well and quantum dot energy harvesting devices  

Microsoft Academic Search

Quantum structured solar cells seek to harness a wide spectrum of photons at high voltages by embedding low energy-gap wells or dots within a high energy-gap matrix. Quantum well and quantum dot solar cells have the potential to deliver ultra-high power conversion efficiencies in single junction devices, efficiencies that in theory can approach 45% in un-concentrated sunlight over a wide

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

2011-01-01

214

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

215

Metamorphic quantum dots: Quite different nanostructures  

SciTech Connect

In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantum dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.

Seravalli, L.; Frigeri, P.; Nasi, L.; Trevisi, G.; Bocchi, C. [CNR-IMEM, Parco delle Scienze 37a, I-43100 Parma (Italy)

2010-09-15

216

Synthesis, biocompatibility and cell labeling of L-arginine-functional beta-cyclodextrin-modified quantum dot probes.  

PubMed

A series of quantum dots (QDs), CdSe, CdSe/CdS and CdSe/ZnSe, coated with L-arginine-modified beta-cyclodextrin (beta-CD-L-Arg) were prepared in a solution of H2O and hexane by ultrasonic method and characterized using PL, UV-vis, TEM, EDX and FTIR techniques. We observed that beta-CD-L-Arg-coated QDs are water-soluble and stable with high colloidal properties in water. Their photophysical properties are similar to those of trioctylphosphine oxide (TOPO)-coated nanocrystals. The quantum yield (QY) of beta-CD-L-Arg/CdSe/ZnSe QDs in water is 68%, which is much higher than those of beta-CD-L-Arg/CdSe/CdS (26%) and beta-CD-L-Arg/CdSe (13%). The in vitro cytotoxicity of these QDs was evaluated in ECV-304, SH-SY5Y and Hela cells and low cytotoxicity was observed. In particular, the beta-CD-L-Arg/CdSe/ZnSe QDs presented lower cytotoxicity to these cells (CC(50) value is 173 microg/mL in ECV-304 cells for 48h). This may be due to the presence of the ZnSe and beta-CD-L-Arg outlayer, which may improve the biocompatibility of QDs. The QDs were further investigated for biological labeling in ECV-304 cells using confocal laser scanning fluorescence microscopy. We found that these QDs were capable of localing to the cytoplasm of cells. These results demonstrate that the beta-CD-L-Arg-coated QDs could be used as a potential photoluminescent nanocrystal probing agent with good biocompatibility. PMID:20189641

Zhao, Mei-Xia; Xia, Qing; Feng, Xu-Dong; Zhu, Xu-Hui; Mao, Zong-Wan; Ji, Liang-Nian; Wang, Kui

2010-03-01

217

TOPICAL REVIEW: Labelling of cells with quantum dots  

Microsoft Academic Search

Colloidal quantum dots are semiconductor nanocrystals well dispersed in a solvent. The optical properties of quantum dots, in particular the wavelength of their fluorescence, depend strongly on their size. Because of their reduced tendency to photobleach, colloidal quantum dots are interesting fluorescence probes for all types of labelling studies. In this review we will give an overview on how quantum

Wolfgang J. Parak; Teresa Pellegrino; Christian Plank

2005-01-01

218

Hydrothermal Synthesis of High-Quality Thiol-Stabilized CdTexSe 1-x Alloyed Quantum Dots.  

PubMed

Alloyed semiconductor quantum dots (QDs) enriched the synthetic routes for engineering materials with unique structural and optical properties. High-quality thiol-stabilized CdTexSe1-x alloyed QDs were synthesized through a facile and economic hydrothermal method at 120 °C, a relatively low temperature. These water-soluble QDs were prepared using different capping agents including 3-mercaptopropionic acid (MPA) and L-cysteine (L-Cys). The photoluminescence (PL) intensity and stability of L-Cys-capped CdTexSe1-x QDs were found to be higher than that of MPA-stabilized ones. The molar ratios of Se-to-Te upon preparation were adjusted for investigating the effect of composition on the properties of the resulting QDs. We also investigated the effect of the pH value of the reaction solution on the growth kinetics of the alloyed CdTexSe1-x QDs. The resulting CdTexSe1-x QDs were characterized by UV-vis absorbance and PL spectroscopy, powder X-ray diffraction, and transmission electron microscopy. Being coated with a CdS inorganic shell, the PL intensity and stability of the CdTexSe1-x/CdS core-shell QDs were drastically enhanced, accompanied by the red-shift of the PL peak wavelength. Owing to the unique optical properties, the QDs hold great potential for application and have to be further exploited. PMID:23873206

Yang, Fanghong; Yang, Ping; Cao, Yongqiang

2013-07-20

219

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

220

Reverse-Micelle Synthesis of Electrochemically Encoded Quantum Dot Barcodes: Application to Electronic Coding of a Cancer Marker  

PubMed Central

Reproducible electrochemically encoded quantum dot (QD) barcodes were prepared by using the reverse-micelle synthetic approach. The encoding elements, Zn2+, Cd2+, Pb2+ were confined within a single QD, which eliminates the cumbersome encapsulation process used by other common nanoparticle-based barcode preparation schemes. The distinct voltammetric stripping patterns of Zn2+, Cd2+, Pb2+ at distinguishable potentials with controllable current intensities offer excellent encoding capability for the prepared electrochemical (EC) QDs. Additionally, the simultaneous modification of the QD barcode surface with organic ligands during the preparation process make them potentially useful in biomedical research. For proof of concept of their application in bioassays, the EC QD barcodes were further employed as tags for an immunoassay of a cancer marker, carcinoembryonic antigen (CEA). The voltammetric stripping response of the dissolved bardcode tags was proportional to log[CEA] in the range from 0.01 ng mL?1 to 80 ng mL?1, with a detection limit of 3.3 pg mL?1. The synthesized EC QD barcodes hold considerable potentials in biodetection, encrypted information and product tracking.

Xiang, Yun; Zhang, Yuyong; Chang, Yue; Chai, Yaqin; Wang, Joseph; Yuan, Ruo

2010-01-01

221

Reverse-micelle synthesis of electrochemically encoded quantum dot barcodes: application to electronic coding of a cancer marker.  

PubMed

Reproducible electrochemically encoded quantum dot (QD) barcodes were prepared using the reverse-micelle synthetic approach. The encoding elements, Zn(2+), Cd(2+), and Pb(2+), were confined within a single QD, which eliminates the cumbersome encapsulation process used by other common nanoparticle-based barcode preparation schemes. The distinct voltammetric stripping patterns of Zn(2+), Cd(2+) and Pb(2+) at distinguishable potentials with controllable current intensities offer excellent encoding capability for the prepared electrochemical (EC) QDs. Additionally, the simultaneous modification of the QD barcode surface with organic ligands during the preparation process make them potentially useful in biomedical research. For proof of concept of their application in bioassays, the EC QD barcodes were further employed as tags for an immunoassay of a cancer marker, carcinoembryonic antigen (CEA). The voltammetric stripping response of the dissolved bardcode tags was proportional to log[CEA] in the range from 0.01 to 80 ng mL(-1), with a detection limit of 3.3 pg mL(-1). The synthesized EC QD barcodes hold considerable potential in biodetection, encrypted information, and product tracking. PMID:20067269

Xiang, Yun; Zhang, Yuyong; Chang, Yue; Chai, Yaqin; Wang, Joseph; Yuan, Ruo

2010-02-01

222

CdS and CdTeS quantum dot decorated TiO2 nanowires. Synthesis and photoefficiency.  

PubMed

An easy process was developed to synthesize TiO(2) nanowires sensitized with CdS and CdTeS quantum dots (QDs) requiring no pretreatment of the TiO(2) nanowires prior to nanoparticle generation. CdS and CdTeS nanoparticles were firstly grown by an in situ colloidal method directly onto the TiO(2) surface, hence not requiring subsequent functionalization of the QDs. The resulting nanostructure assembly and composition was confirmed by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Successful decoration of the TiO(2) nanowires by the QDs was observed by TEM, while XPS spectra provided clear evidence for the coexistence of CdS and CdTeS QDs and TiO(2) nanowires. The electronic structure of the TiO(2) nanowires was preserved as indicated by Raman spectroscopy. Preliminary photocurrent measurements showed that inclusion of Te in CdS QDs improved the photocurrent efficiency. Compared to bare TiO(2) nanowires, CdS/TiO(2) nanoassemblies showed an enhancement in photocurrent efficiency of 300% while CdTeS/TiO(2) presented an improvement of 350%. This study indicates that the generation of strongly anchored CdS and CdTeS QDs on a TiO(2) nanowire surface is achievable without introduction of a linker molecule, whose presence is known to decrease the electron injection efficiency. PMID:21212494

Medina-Gonzalez, Yaocihuatl; Xu, William Z; Chen, Bo; Farhanghi, Nasrin; Charpentier, Paul A

2011-01-07

223

Detecting quantum and classical correlations using quantum dot system  

NASA Astrophysics Data System (ADS)

We investigate the thermal classical and quantum correlations in an isolated quantum dot system (QDS) including the effects of different parameters. The thermal density operator is generated by simplifying the Hamiltonian of the quantum dot to the nature Hamiltonian by integrating and finding the unitary matrix. We find that the quantum discord (QD) is more resistant against temperature effect and might be finite even for higher temperatures in the asymptotic limit. Furthermore, we show that there is an optimal value of temperature such that the different kinds of correlations are maximal. Our results show that QDS is a useful resource and may open new perspectives in different quantum information tasks.

Berrada, K.

2013-12-01

224

Quantum phase transition in a single-molecule quantum dot.  

PubMed

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

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

2008-05-29

225

Transient Currents Through Quantum Dots  

NASA Astrophysics Data System (ADS)

Kubo formula is used to get the time dependent current that flows through a quantum dot after switching on a small voltage bias. Technically, the calculation involves the evaluation of the linear response function for all frequencies and is, therefore, sensibly more expensive from the computational point of view than the evaluation of the d.c. conductance. Previous estimations of the transient current were done by Prigodin et al. in Phys. Rev. Lett. 72, 546 (1994) for chaotic mesoscopic systems. Our numerical results are completely different from the purely inductive results given in the mentioned paper. Both the regular and the chaotic system show initially a linear increase of the conductance that grows well beyond its static value. Afterwards, it decreases in an oscillating fashion towards its stationary value. While oscillations quickly attenuate in the chaotic model, a power law decay is obtained for the ideal system. Apart for the rapid oscillations, the result can be modelled by a classic circuit having resistive, inductive and also capacitive elements. In principle, our result opens a straightforward experimental way allowing a clear distinction between chaotic and regular systems.

Vergés, J. A.; Louis, E.

226

Probing relaxation times in graphene quantum dots.  

PubMed

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

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

2013-01-01

227

Novel multifunctional nanocomposites from titanate nanosheets and semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

A novel synthesis for a titanate nanosheets loaded nanocomposite has been developed. On this basis, a multifunctional material for optical applications has been fabricated with tunable refractive index, improved processing behavior and luminescent properties imparted by the incorporation of semiconductor quantum dots.Titanate synthesis, host material choice and quantum dots functionalization have been here addressed to obtain films with good optical quality and stable photoluminescence.In order to assess the potential application of the obtained nanocomposites, imprinting lithography and aerosol-based deposition techniques have been applied with promising results.The obtained nanocomposites have been characterized by UV-Vis, photoluminescence and FT-IR spectroscopy, X-ray diffraction and Transmission Electron Microscopy. The optical properties of the nanocomposite film have been tested by spectroscopic ellipsometry and M-line technique.

Antonello, A.; Brusatin, G.; Guglielmi, M.; Bello, V.; Perotto, G.; Mattei, G.; Maiwald, M.; Zöllmer, V.; Chiasera, A.; Ferrari, M.; Martucci, A.

2011-10-01

228

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

2013-05-27

229

Surface Termination Effects on Zinc Oxide Quantum Dots  

Microsoft Academic Search

We investigate the effects of surface terminations on the optical properties of 2-6 nm ZnO quantum dots. Nanocrystals were grown by wet chemical synthesis in a short-chain alcohol solvent from zinc acetate and sodium hydroxide. Quenching of particle growth with various capping agents is necessary to maintain and enhance the unique characteristics of the nanocrystals. We reproduce results of previous

Steve Whitesell; Joe Spalenka; Christopher Jack; Cary Allen; Reuben Collins; Thomas Furtak

2007-01-01

230

Thermometry and Refrigeration using Quantum Dots  

NASA Astrophysics Data System (ADS)

The 2D electron gas in GaAs/AlGaAs heterostructures has diverse applications at cryogenic temperatures, but is heated by unintended noise in the measurement set up. Our work involves the fabrication of a quantum dot refrigerator (QDR) which can cool the gas to below the ambient lattice temperature [1]. Lithographically defined gates define three quantum dots tunnel-coupled to an enclosed, macroscopic reservoir of electrons 100 ?m^2 in area. Energy selective transport of electrons via the discrete energy levels of two quantum dots through the electron reservoir modifies its Fermi-Dirac distribution, thus cooling it. The third quantum dot (the `thermometer') probes the temperature of the reservoir being cooled by monitoring the current flowing through an adjacent quantum point contact. We have demonstrated measuring electronic temperatures in the range 100 mK to 300 mK, with an estimated error of about 10%. We have also investigated the variation in electron temperature as a function of the energies of the entrance and exit dots. Our results are consistent with cooling an area of 64?m^2 by 30 mK, starting from 150mK, and agree qualitatively with theory [2].[1] Prance e. a. Phys. Rev. Lett. 102 146602 [2] Edwards e. a. Phys. Rev. B 52 5714

Mavalankar, Aquila; Smith, Charles; Chorley, Simon; Griffiths, Jonathan; Jones, Geb; Farrer, Ian; Ritchie, David

2013-03-01

231

Microwave-assisted aqueous synthesis: a rapid approach to prepare highly luminescent ZnSe(S) alloyed quantum dots.  

PubMed

In this paper, we present a new procedure for the rapid synthesis of luminescent ZnSe nanocrystals in aqueous phase by microwave irradiation with controllable temperature. The effects of microwave irradiation and experimental conditions on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of pH value of reaction solutions, molar ratio of precursors, and heating time of microwave irradiation on the optical properties of the ZnSe nanocrystals. A series of nanocrystals with different size was prepared in 1 h, and the photoluminescence quantum yield reached up to 17% at the optimal reaction condition. The results of HRTEM and XRD showed that the as-prepared nanocrystals had high crystallinity. The characterizations of EDS spectra and elemental analysis showed that the sulfur content of nanocrystals increased with the growth of nanocrystals. We speculated that the structure of nanocrystals was an alloy ZnSe(S) shell on the surface of the ZnSe particles core. Furthermore, we found that the oxygen from air in the reaction vessel played an important role in the decomposition of the thiol group under microwave irradiation. PMID:16671712

Qian, Huifeng; Qiu, Xin; Li, Liang; Ren, Jicun

2006-05-11

232

In-situ encapsulation of quantum dots into polymer microspheres.  

PubMed

We have incorporated fluorescent quantum dots (QDs) into polystyrene microspheres using functionalized oligomeric phosphine (OP) ligands. We find that a uniform distribution of quantum dots is loaded inside each polymer bead. Some local close-packing of quantum dots in the beads is attributed to the self-polymerization of the functionalized ligands. The presence of quantum dots disturbs the nucleation and growth processes during the formation of polymer microspheres and results in a wider size distribution of the quantum dot-embedded polystyrene beads than for the control without dots. The change in quantum efficiency of the quantum dots before (approximately 20%) and after (12%) loading into the beads substantiates the protection of oligomeric phosphine ligands yet indicates that the properties of these quantum dots are still affected during processing. PMID:16584256

Sheng, Wenchao; Kim, Sungjee; Lee, Jinwook; Kim, Sang-Wook; Jensen, Klavs; Bawendi, Moungi G

2006-04-11

233

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

234

Magnetic quantum dots: synthesis, spectroscopy, and magnetism of Co2+ - and Ni2+-doped ZnO nanocrystals.  

PubMed

We report a method for the preparation of colloidal ZnO-diluted magnetic semiconductor quantum dots (DMS-QDs) by alkaline-activated hydrolysis and condensation of zinc acetate solutions in dimethyl sulfoxide (DMSO). Mechanistic studies reveal that Co(2+) and Ni(2+) dopants inhibit nucleation and growth of ZnO nanocrystals. In particular, dopants are quantitatively excluded from the critical nuclei but are incorporated nearly isotropically during subsequent growth of the nanocrystals. The smaller nanocrystal diameters that result upon doping are explained by the Gibbs-Thompson relationship between lattice strain and crystal solubility. We describe methods for cleaning the nanocrystal surfaces of exposed dopants and for redispersion of the final DMS-QDs. Homogeneous substitutional doping is verified by high-resolution low-temperature electronic absorption and magnetic circular dichroism (MCD) spectroscopies. A "giant Zeeman effect" is observed in the band gap transition of Co(2+):ZnO DMS-QDs. MCD and Zeeman spectroscopies are used to quantify the magnitude of the p-d exchange interaction (N(0)beta) that gives rise to this effect. N(0)beta values of -2.3 +/- 0.3 eV (-18 500 cm(-1)) for Co(2+):ZnO and -4.5 +/- 0.6 eV (-36 300 cm(-1)) for Ni(2+):ZnO have been determined. Ligand-to-metal charge-transfer transitions are observed in the MCD spectra of both Co(2+):ZnO and Ni(2+):ZnO DMS-QDs and are analyzed in the context of an optical electronegativity model. The importance of these charge-transfer states in determining N(0)beta is discussed. Ferromagnetism with T(C) > 350 K is observed in aggregated nanocrystals of Co(2+):ZnO that unambiguously demonstrates the existence of intrinsic high-T(C) ferromagnetism in this class of DMSs. PMID:14570496

Schwartz, Dana A; Norberg, Nick S; Nguyen, Quyen P; Parker, Jason M; Gamelin, Daniel R

2003-10-29

235

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

236

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

237

Quantum Dot-Based Cell Motility Assay  

SciTech Connect

Because of their favorable physical and photochemical properties, colloidal CdSe/ZnS-semiconductor nanocrystals (commonly known as quantum dots) have enormous potential for use in biological imaging. In this report, we present an assay that uses quantum dots as markers to quantify cell motility. Cells that are seeded onto a homogeneous layer of quantum dots engulf and absorb the nanocrystals and, as a consequence, leave behind a fluorescence-free trail. By subsequently determining the ratio of cell area to fluorescence-free track area, we show that it is possible to differentiate between invasive and noninvasive cancer cells. Because this assay uses simple fluorescence detection, requires no significant data processing, and can be used in live-cell studies, it has the potential to be a powerful new tool for discriminating between invasive and noninvasive cancer cell lines or for studying cell signaling events involved in migration.

Gu, Weiwei; Pellegrino, Teresa; Parak Wolfgang J; Boudreau,Rosanne; Le Gros, Mark A.; Gerion, Daniele; Alivisatos, A. Paul; Larabell, Carolyn A.

2005-06-06

238

Dynamics of Avalanche Quantum Dot Infrared Photodetectors  

NASA Astrophysics Data System (ADS)

Time and frequency response of an avalanche quantum dot infrared photodetector (A-QDIP) operating at long infrared (IR) wavelengths is calculated and the effect of its structure on the dynamic behavior is studied. For this purpose, the rate equations of different regions are numerically solved considering the boundary conditions. Results show that detector with long multiplication region has a slower time response. Also frequency analysis predicts a 3-dB bandwidth above 100 GHz for a device with multiplication length of 200 nm. Gain bandwidth product (GBP) is calculated and a value of about 1000 GHz is obtained. Effect of charge layer doping on dynamic response of detector is also studied and results show that increase in doping improves the GBP while the bandwidth is reduced. We also study the effect of quantum dots of absorption region on frequency response of device and results show that longer electron relaxation time into quantum dot decreases the bandwidth of detector.

Zavvari, Mahdi; Ahmadi, Vahid

2012-12-01

239

Exciton binding energy in semiconductor quantum dots  

SciTech Connect

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

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

2010-04-15

240

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

241

Quantum and semiclassical study of magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We study the energy level structure of two-dimensional charged particles in a circular quantum dot in inhomogeneous magnetic fields. In this system, the magnetic field is zero inside the dot and constant outside. Such a device can be fabricated with present-day technology. We present detailed semiclassical studies of such magnetic quantum dot systems and provide a comparison with exact quantum calculations. In the semiclassical approach we apply the Berry-Tabor formula for the density of states and the Borh-Sommerfeld quantization rules. In both cases we found good agreement with the exact spectrum in the weak magnetic field limit. The energy spectrum for a given missing flux quantum is classified in six possible classes of orbits and summarized in a so-called phase diagram. We also investigate the current flow patterns of different quantum states and show a clear correspondence with classical trajectories.

Kocsis, Bence; Palla, Gergely; Cserti, József

2005-02-01

242

Synergistic Tunability of Fluorescence Using Coupled Quantum Dots  

Microsoft Academic Search

Size and shape controlled semiconductor quantum dots have been widely adopted in tailoring nanomaterials properties, which basically utilize band edge engineering extending the band gap to larger values than the bulk. However, the long range electronic transition tunability is difficult to achieve using size or shape controlled quantum dots. Alternatively, chemically coupled quantum dots offer a novel route for tuning

Sucheta Sengupta; Somobrata Acharya

2011-01-01

243

Collective Excitations in Cylindrical Quantum Dots Chains  

NASA Astrophysics Data System (ADS)

We are interested in the study of collective excitations in quantum dot chains because these can be used to effectively transmit information at nano scale and to control spontaneous and stimulate electromagnetic emission in the quantum dots. [1] This work is centered in the study of semiconductor one-dimensional quantum dot arrays. Based on a tight-binding bandstructure calculation combined with a self consistent field approximation we obtain the dispersion relations and we analyze how the geometry of the dot affects the collective oscillation of charge and its propagation. We focus our study first on Coulomb interaction between charges as the main cause of the 1D plasmons neglecting tunneling to finally compare with the case where tunneling is allowed. We find out that Coulomb interaction plays an important role in these systems and that tunneling opens the energy spectrum permitting new excitations, which are good candidates to be used in nanometric devices. [1] A.V.Akimov, A.Mukherjee, C.L. Yu, D.E Chang, A.S.Zybrov, P.R. Hemmer, H Park and M.D Lukin, Generation of Single optical plasmons in metallic nanowires coupled to quantum dots, Nature 450, 402 (2007).

Vergara, Jimena; Camacho, Angela

2009-03-01

244

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

245

Resonant tunneling in graphene pseudomagnetic quantum dots.  

PubMed

Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction. PMID:23659203

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

2013-05-15

246

Resonant Tunneling in Graphene Pseudomagnetic Quantum Dots  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

247

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

248

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

249

Hydrothermal synthesis of GSH-TGA co-capped CdTe quantum dots and their application in labeling colorectal cancer cells.  

PubMed

We have successfully synthesized GSH and TGA co-capped CdTe quantum dots (QDs) with good biological compatibility and high fluorescence intensity. The effects of different reaction time, temperature, pH value, ligand concentration and the molar ratio of GSH/TGA were carefully investigated to optimize the synthesis condition. The optical properties of as-prepared CdTe QDs were studied by UV-visible absorption spectrum and fluorescence spectrum, meanwhile their structure and morphology were characterized using transmission electron microscope (TEM), Fourier transform infrared spectra (FT-IR) and X-ray powder diffraction (XRD). Compared with the CdTe QDs that are single-capped with either GSH or TGA, the GSH-TGA co-capped CdTe QDs demonstrated significantly improved fluorescence intensity and optical stability. In addition, GSH-TGA co-capped CdTe QDs were conjugated to amonoclonal antibody ND-1. The GSH-TGA co-capped CdTe QDs-antibody probe was successfully used to label colorectal cancer cells, CCL187, in vitro. PMID:22494668

Yu, Yongli; Xu, Linru; Chen, Jing; Gao, Huanyu; Wang, Shuo; Fang, Jin; Xu, Shukun

2012-03-28

250

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

251

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

252

Synthesis and grafting of folate-PEG-PAMAM conjugates onto quantum dots for selective targeting of folate-receptor-positive tumor cells.  

PubMed

We report the design and synthesis of folate-poly(ethylene glycol)-polyamidoamine (FPP)-functionalized CdSe/ZnS quantum dots (QDs), in which the QD plays a key role in imaging, whereas the folate-poly(ethylene glycol) (PEG) conjugates of the polyamidoamine (PAMAM) dendrimer serve as a system targeted to folate receptors in tumor cells. Dendrimer ligands such as folate-PEG grafted PAMAM of generation 3.5 are found to encapsulate and solubilize luminescent QDs through direct ligand-exchange reactions. Because of membrane expression of FA receptors in tumor cells, this class of ligand-exchanged QDs is able to target tumor cells. We have evaluated FPP-coated QDs and QDs without folate in HeLa cells and shown that cellular uptake of FPP-coated QDs is more significant than that non folate QDs in vivo imaging experiment. In particular, QDs coated with FPP are initially bound to tumor cell surfaces, followed by slow endosomal escape and release into the tumor cells. These insights are important for the design and development of nanoparticle agents for optical detection of tumor cells and bio-imaging. PMID:20624622

Zhao, Yili; Liu, Sen; Li, Yapeng; Jiang, Wei; Chang, Yulei; Pan, Si; Fang, Xuexun; Wang, Y Andrew; Wang, Jingyuan

2010-05-16

253

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

254

Nonlocal theory of collective excitations in quantum-dot arrays  

Microsoft Academic Search

We present a nonlocal theory of collective excitations in quantum-dot arrays. Selection rules, oscillator strengths, and Coulomb interactions inside a dot and between dots are discussed. The collective excitation energy is found to ``saturate'' for n0 (the number of electrons per dot) greater than 3. The depolarization energy shift in a quantum-dot array is found to be predominantly due to

Weiming Que; George Kirczenow; Eleuterio Castao

1991-01-01

255

Reconfigurable visible quantum dot microlasers integrated on a silicon chip  

NASA Astrophysics Data System (ADS)

Developing on-chip, dynamically reconfigurable visible lasers that can be integrated with additional optical and electronic components will enable adaptive optical components. In the present work, we demonstrate a reconfigurable quantum dot laser based on an integrated silica ultra high-Q microcavity. By attaching the quantum dot using a reversible, non-destructive bioconjugation process, the ability to remove and replace it with an alternative quantum dot without damaging the underlying microcavity device has been demonstrated. As a result of the absorption/emission characteristics of quantum dots, the same laser source can be used to excite quantum dots with distinct emission wavelengths.

Mehrabani, Simin; Hunt, Heather K.; Armani, Andrea M.

2012-02-01

256

Optical gain and stimulated emission in nanocrystal quantum dots.  

PubMed

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 the wavelength of the emitting transition for close-packed solids of these dots. Narrowband stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the nanocrystal was observed, as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility of nanocrystal quantum dot lasers. PMID:11030645

Klimov, V I; Mikhailovsky, A A; Xu, S; Malko, A; Hollingsworth, J A; Leatherdale, C A; Eisler, H; Bawendi, M G

2000-10-13

257

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

258

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

2013-09-10

259

Magnetic properties of graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

260

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

261

Resonant tunnelling features in quantum dots  

NASA Astrophysics Data System (ADS)

We present a systematic review of features due to resonant electron tunnelling, observable in transport spectroscopy experiments on quantum dots and single donors. The review covers features attributable to intrinsic properties of the dot (orbital, spin and valley states) as well as extrinsic effects (phonon/photon emission/absorption, features in the charge reservoirs, coupling to nearby charge centres). We focus on the most common operating conditions, neglecting effects due to strong coupling to the leads. By discussing the experimental signatures of each type of feature, we aim at providing practical methods to distinguish between their different physical origins. The correct classification of the resonant tunnelling features is an essential requirement to understand the details of the confining potential or to predict the performance of the dot for quantum information processing.

Escott, C. C.; Zwanenburg, F. A.; Morello, A.

2010-07-01

262

Interaction effects in coupled quantum dots.  

NASA Astrophysics Data System (ADS)

We study a linear array of coupled semiconductor quantum dots (``artificial molecules'') using an extended Hubbard Hamiltonian approach to account for the effects of intradot and interdot Coulomb interactions, as well as interdot tunneling. We obtain the electron addition spectrum from direct diagonalizations (C. A. Stafford and S. Das Sarma, Phys. Rev. Lett. 72), 3590 (1994) for identical double and triple quantum dots explaining qualitatively the splitting of the conductance peaks observed in recent experiments on these systems. We note that, depending on the number of particles in the system, the interdot Coulomb interaction gives rise to an interesting asymmetry in the conduction spectrum and is also responsible for splitting of the peaks even for weak coupling. We also consider dots of different sizes (``heteronuclear molecules'') and calculate the relevant many-body overlaps that enter in the calculation of the current in the nonlinear regime, to make contact with transport spectroscopy experiments.

Ramirez, F.; Cota, E.; Ulloa, S. E.

1996-03-01

263

Ligand exchange on the surface of cadmium telluride quantum dots with fluorosurfactant-capped gold nanoparticles: Synthesis, characterization and toxicity evaluation.  

PubMed

CdTe quantum dots (QDs) can provide high-intensity and photostable luminescent signals when they are used as labeling materials for sensing trace amounts of bioanalytes. However, a major concern is whether the capping ligands of CdTe QDs cause toxic effects in living systems. In the current study, we address this problem through the complete ligand transformation of CdTe QDs from toxic thiolglycolic acid (TGA) to green citrate, which is attributed to the CdS bond breaking and the AuS bond formation. The highly efficient depletion of S atom from the surface of the CdTe QDs occurs after the addition of fluorosurfactant (FSN)-capped gold nanoparticles into TGA-capped CdTe QDs, accompanying with the rapid aggregation of FSN-capped gold nanoparticles via noncrosslinking mechanism in the presence of high salt. After the ligand transformation, negligible differences are observed on both photoluminescence spectra and luminescent quantum yield. In addition, the cytotoxicity of the original and new-born CdTe QDs is detected by measuring cell viability after the nanoparticle treatment. In comparison with the original TGA-capped QDs, the new-born CdTe QDs can induce minimal cytotoxicity against human hepatocellular liver carcinoma (HepG2) cells even at high dosages. Our study indicates that the extremely simple method herein opens up novel pathways for the synthesis of green CdTe QDs, and the as-prepared citrate-capped CdTe QDs might have great potential for biological labeling and imaging applications. PMID:24183442

Wang, Lingyun; Zhang, Hongxia; Lu, Chao; Zhao, Lixia

2013-09-29

264

Quantum-dot infrared photodetectors: a review  

NASA Astrophysics Data System (ADS)

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

Stiff-Roberts, Adrienne D.

2009-04-01

265

Integrated photonics using colloidal quantum dots  

NASA Astrophysics Data System (ADS)

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 flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. Planar photonic devices consisting of vertically coupled microring resonators, microdisk emitters, active-passive integrated waveguide structures and coupled active microdisk resonators were realized using soft lithography, photo-lithography, and electron beam lithography, respectively. The gain medium in all these devices was a composite consisting of quantum dots embedded in SU8 matrix. Finally, the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements was determined. In addition to their specific functionalities, these novel device demonstrations and their development present a low-cost alternative to the traditional photonic device fabrication techniques.

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

2009-11-01

266

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

267

Charge pumping in carbon nanotube quantum dots  

Microsoft Academic Search

We investigate charge pumping in carbon nanotube quantum dots driven by the electric field of a surface acoustic wave. We find that at small driving amplitudes, the pumped current reverses polarity as the conductance is tuned through a Coulomb blockade peak using a gate electrode. We study the behavior as a function of wave amplitude, frequency and direction and develop

M. R. Buitelaar; V. Kashcheyevs; P. J. Leek; V. I. Talyanskii; C. G. Smith; D. Anderson; G. A. C. Jones; J. Wei; D. H. Cobden

268

Quantum dot lasers: Theory and experiment  

Microsoft Academic Search

Using of structures with size quantization in all three directions, or quantum dots (QD's) allows exciting possibilities in device engineering. Semiconductor heterostructures with self-organized QDs have experimentally exhibited properties expected for zero-dimensional systems. When used as active layer in the injection lasers, these advantages help to strongly increase material gain and differential gain, to improve temperature stability of the threshold

D. Bimberg; M. Grundmann; F. Heinrichsdorff; N. N. Ledentsov; Ch. Ribbat; R. Sellin; Zh. I. Alferov; P. S. Kop'ev; M. V. Maximov; V. M. Ustinov; A. E. Zhukov; J. A. Lott

2001-01-01

269

Quantum dot lasers: breakthrough in optoelectronics  

Microsoft Academic Search

Semiconductor heterostructures with self-organized quantum dots (QDs) have experimentally exhibited properties expected for zero-dimensional systems. When used as active layer in the injection lasers, these advantages help to strongly increase material gain and differential gain, to improve temperature stability of the threshold current, and to provide improved dynamic properties. Molecular beam epitaxy (MBE) represents a developed technology well suited for

D. Bimberg; M. Grundmann; F. Heinrichsdorff; N. N. Ledentsov; V. M. Ustinov; A. E. Zhukov; A. R. Kovsh; M. V. Maximov; Y. M. Shernyakov; B. V. Volovik; A. F. Tsatsul’nikov; P. S. Kop’ev; Zh. I. Alferov

2000-01-01

270

Optical processes in quantum dots and wires  

Microsoft Academic Search

Quantum wires and dots are unique condensed matter systems where electron and hole localization can be achieved by lateral confinement down to quasi 0-dimensions. Here we review how these nanostructures are realized and their optical properties, mainly from an experimental point of view. We discuss changes in the energy and momentum mechanisms as the lateral dimensions are reduced, such as

Clivia M. Sotomayor Torres; Pei D. Wang; N. N. Ledentsov; Yin-Sheng Tang

1994-01-01

271

Double Quantum Dots in Carbon Nanotubes.  

National Technical Information Service (NTIS)

We study the few-electron eigenspectrum of a carbon-nanotube double quantum dot with spin-orbit coupling. Exact calculation are combined with a simple model to provide an intuitive and accurate description of single- particle and interaction effects. For ...

A. M. Rey B. Wunsch E. Demler J. Von Stecher M. Lukin

2010-01-01

272

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

273

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

274

Nanocomposites of POC and quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

275

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

276

Optical properties of quantum-dot-doped liquid scintillators  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

277

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

278

Collective modes in quantum-dot arrays in magnetic fields  

Microsoft Academic Search

We study collective excitations in a model array of parabolically confined quantum dots in an applied magnetic field. Treating the interactions between electrons on the same dot exactly and those between electrons on different dots in a simple approximation, we find that the Hamiltonian separates into a term involving center-of-mass coordinates of the electrons on each dot and a term

Jed Dempsey; N. F. Johnson; L. Brey; B. I. Halperin

1990-01-01

279

Quantum dot circuits: Single-electron switch and few-electron quantum dots  

NASA Astrophysics Data System (ADS)

A strongly capacitively-coupled parallel double quantum dot was studied as a single-electron switch. The double dot was fabricated in a two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. An electrically-floating coupling gate increased capacitive-coupling between the dots, while an etched trench prevented tunnel-coupling between them. Split Coulomb blockade peaks were observed in each dot, and the Coulomb blockade conductance of the double dot formed a hexagonal pattern characteristic of coupled dots. A fractional peak splitting f = 0.34 was measured, which corresponds to a fractional capacitive-coupling alpha ? CINT/CSigma = 0.20. This is an order of magnitude larger than reported for similar lateral quantum dots, and shows that the coupling gate works. The strong capacitive-coupling in our device allowed the charge state of one dot to strongly influence the conductance of the other dot and enabled it to work as a single-electron switch. By moving in a combination of gate voltages, electrons are induced in one dot (the "trigger" dot) only. In response to the change in the charge state, the conductance of the other dot (the "switched" dot) is turned on and off. The abruptness of the conductance switching in gate voltage (the switching lineshape) is determined by how well charge is quantized on the trigger dot, and was found to follow tanh and arctan forms for (respectively) good and poor charge quantization in the trigger dot. A few-electron tunnel-coupled series double dot was studied for possible application to quantum computing. The device was fabricated in a square-well 2DEG in a GaAs/AlGaAs heterostructure. The dots were emptied of electrons in order to define the absolute number of electrons in the dot. Finite bias Coulomb blockade measurements on each dot showed that the last Coulomb blockade diamonds did not close and thus that both dots could be emptied. A three-dimensional conductance measurement of one dot in the one sidegate and the two quantum point contact voltages also showed that Coulomb blockade peaks ended, and corroborated that the dot could be emptied of electrons. The Zeeman energy of electrons in a few-electron dot, deduced from the Coulomb blockade peak spacings, was measured with an in-plane magnetic field of up to 7 T. The g-factor was found to be no different from that of bulk GaAs | g| = 0.44. Tunnel-coupling between the few-electron double dot was demonstrated, and a tunnel-coupling strength of 1.2e 2/h was estimated from the fractional peak splitting f = 0.3.

Chan, Ian Hin-Yun

280

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

281

Tuning of Long range Visible Emissions Using Coupled Quantum Dots  

Microsoft Academic Search

Size and shape controlled semiconductor quantum dots have been widely adopted in tailoring nanomaterials properties. Alternatively, chemically coupled quantum dots offer a novel route for tuning long range electronic transitions of semiconductors via band offset engineering at the material interface. We report on a simple route of tailoring visible emissions over long range by chemically designing coupled dots comprising of

Sucheta Sengupta; Nirmal Ganguli; I. Dasgupta; D. D. Sarma; Somobrata Acharya

2011-01-01

282

Mitigation of Quantum Dot Cytotoxicity by Microencapsulation  

PubMed Central

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

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

2011-01-01

283

Mitigation of quantum dot cytotoxicity by microencapsulation.  

PubMed

When CdSe/ZnS-polyethyleneimine (PEI) quantum dots (QDs) are microencapsulated in polymeric microcapsules, human fibroblasts are protected from acute cytotoxic effects. Differences in cellular morphology, uptake, and viability were assessed after treatment with either microencapsulated or unencapsulated dots. Specifically, QDs contained in microcapsules terminated with polyethylene glycol (PEG) mitigate contact with and uptake by cells, thus providing a tool to retain particle luminescence for applications such as extracellular sensing and imaging. The microcapsule serves as the "first line of defense" for containing the QDs. This enables the individual QD coating to be designed primarily to enhance the function of the biosensor. PMID:21814567

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

2011-07-21

284

Size dependence in tunneling spectra of PbSe quantum-dot arrays.  

PubMed

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 arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, the dependence of tunneling spectra on the sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored. PMID:19546498

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

2009-06-23

285

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

286

Principles of conjugating quantum dots to proteins via carbodiimide chemistry  

NASA Astrophysics Data System (ADS)

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

Song, Fayi; Chan, Warren C. W.

2011-12-01

287

Nonequilibrium transport through coupled quantum dots with electron phonon interaction  

NASA Astrophysics Data System (ADS)

We theoretically study transport properties of coupled quantum dots in parallel in the presence of electron phonon (e ph) interaction. Nonequilibrium transport under finite bias is calculated using the Keldysh Green function method. Firstly, we examine a double-dot interferometer with a penetrating magnetic flux (Aharonov Bohm phase phiv) between the two quantum dots. The differential conductance shows a sharp dip between double resonant peaks, as a function of energy levels in the quantum dots, when the two dots are equivalently coupled to external leads and 0 < phiv < ?. The e ph interaction significantly decreases the dip, reflecting an emission of phonons from one of the quantum dots. This dephasing effect is more prominent under larger bias voltage. Secondly, we study a T-shaped double-dot system in which one of the dots is connected to the external leads (dot 1) and the other is disconnected (dot 2). The differential conductance shows a dip between two resonant peaks, as in the double-dot interferometer. The dip is weakly reduced by an emission of phonons from dot 2. Phonon emission from dot 1 does not result in dephasing and hence does not influence the dip. Therefore the dip of the conductance is more robust against the e ph interaction in the T-shaped double-dot system than in the double-dot interferometer.

Ueda, Akiko; Eto, Mikio

2007-05-01

288

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

289

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

2012-12-23

290

Magneto-optical single dot spectroscopy of GaSb\\/GaAs type II quantum dots  

Microsoft Academic Search

We have investigated magneto-optical properties of GaSb\\/GaAs self-assemble type II quantum dots by single dot spectroscopy in magnetic field. We have observed clear Zeeman splitting and diamagnetic shift of GaSb\\/GaAs quantum dots. The diamagnetic coefficient ranges from 5 to 30?eV\\/T2. The large coefficient and their large distribution are attributed to the size inhomogeneity and electron localization outside the dot. The

Tomohiko Sato; Toshihiko Nakaoka; Makoto Kudo; Yasuhiko Arakawa

2006-01-01

291

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

292

Planar Dirac electrons in magnetic quantum dots.  

PubMed

In this paper, we explore the size- and mass-dependent energy spectra and the electronic correlation of two- and three-electron graphene magnetic quantum dots. It is found that only the magnetic dots with large size can well confine the electrons. For large graphene magnetic dots with massless (ultra-relativity) electrons, the energy level structures of two Dirac electrons and even the ground state spin and angular momentum of three electrons are quite different from those of the usual semiconductor quantum dots. Also we reveal that such differences are not due to the magnetic confinement but originate from the character of the Coulomb interaction of two-component electronic wavefunctions in graphene. We reveal that the increase of the mass leads to both the crossover of the energy spectrum structures from the ultra-relativity to non-relativity ones and the increasing of the crystallization. The results are helpful for the understanding of the mass and size effects and may be useful in controlling the few-electron states in graphene-based nanodevices. PMID:22543306

Yang, Ning; Zhu, Jia-Lin

2012-04-27

293

Ultra-small carbon-dot patterns for directed Ge quantum dot growth  

Microsoft Academic Search

The controlled growth of patterns of small quantum dots in the diameter range of 10 nm is critical for the application in quantum computer architectures. It is well known that Ge quantum dots with a diameter smaller than 10 nm nucleate on the Si(100) surface after carbon pre-adsorption in a random pattern 1. We follow this approach to generate ultimately

Olivier Guise; Hubertus Marbach; Sergey Mezhenny; Jeremy Levy; Joachim Ahner; J. R. Yates

2003-01-01

294

Quantum entanglement of excitons in coupled quantum dots  

Microsoft Academic Search

Optically controlled exciton dynamics in coupled quantum dots is studied. We show that the maximally entangled Bell states and Greenberger-Horne-Zeilinger (GHZ) states can be robustly generated by manipulating the system parameters to be at the avoided crossings in the eigenenergy spectrum. The analysis of population transfer is systematically carried out by using a dressed-state picture. In addition to the quantum

Ping Zhang; C. K. Chan; Qi-Kun Xue; Xian-Geng Zhao

2003-01-01

295

Rapid synthesis and luminescence of the Eu 3+ , Er 3+ codoped ZnO quantum-dot chain via chemical precipitation method  

NASA Astrophysics Data System (ADS)

ZnO quantum-dot chains codoped with Eu 3+ and Er 3+ are synthesized. Green emissions of Er 3+ are attributed to 2 H 11/2 ? 4 I 15/2 and 4 S 3/2 ? 4 I 15/2 transitions. Red emissions of Eu 3+ are attributed to 5 D 0 ? 7 F 1 and 5 D 0 ? 7 F 2 transitions. The doping concentration of Er 3+ ions influences the red emission of Eu 3+ ions.

Lang, Jihui; Li, Xue; Yang, Jinghai; Yang, Lili; Zhang, Yongjun; Yan, Yongsheng; Han, Qiang; Wei, Maobin; Gao, Ming; Liu, Xiaoyan; Wang, Rui

2011-09-01

296

Facile synthesis of N-acetyl- l-cysteine capped ZnS quantum dots as an eco-friendly fluorescence sensor for Hg 2+  

Microsoft Academic Search

This paper described an investigation of a novel eco-friendly fluorescence sensor for Hg2+ ions based on N-acetyl-l-cysteine (NAC)-capped ZnS quantum dots (QDs) in aqueous solution. By using safe and low-cost materials, ZnS QDs modified by NAC were easily synthesized in aqueous medium via a one-step method. The quantitative detection of Hg2+ ions was developed based on fluorescence quenching of ZnS

Junling Duan; Xiaochen Jiang; Shouqing Ni; Min Yang; Jinhua Zhan

2011-01-01

297

Synthesis and spectrum stability of high quality CdTe quantum dots capped with stearate groups in N-oleoylmorpholine solvent  

Microsoft Academic Search

The stearate-capped CdTe quantum dots (QDs) have been first prepared via direct reaction of cadmium stearate with Te powder in N-oleoylmorpholine solvent, which was a kind of clean, air-stable and conveniently synthesized acylamide, and can readily dissolve precursors cadmium stearate and Te powder at a relative low temperature. The as-prepared CdTe QDs exhibited size-dependent optical properties, steep absorbance edge and

Xinmei Liu; Yang Jiang; Chun Wang; Shanying Li; Xinzheng Lan; Yan Chen; Honghai Zhong

2010-01-01

298

Transport properties of graphene quantum dots  

NASA Astrophysics Data System (ADS)

In this work we present a theoretical study of transport properties of a double crossbar junction composed of segments of graphene ribbons with different widths forming a graphene quantum dot structure. The systems are described by a single-band tight binding Hamiltonian and the Green’s function formalism using real space renormalization techniques. We show calculations of the local density of states, linear conductance, and I-V characteristics. Our results depict a resonant behavior of the conductance in the quantum dot structures, which can be controlled by changing geometrical parameters such as the nanoribbon segment widths and the distance between them. By application of a gate voltage on determined regions of the structure, it is possible to modulate the transport response of the systems. We show that negative differential resistance can be obtained for low values of applied gate and bias voltages.

González, J. W.; Pacheco, M.; Rosales, L.; Orellana, P. A.

2011-04-01

299

Hyperspectral fluorescence tomography of quantum dots  

NASA Astrophysics Data System (ADS)

Hyperspectral excitation-resolved fluorescence tomography (HEFT) exploits the spectrally-dependent absorption properties of biological tissue for recovering the unknown three-dimensional (3D) fluorescent reporter distribution inside tissue. Only a single light source with macro-illumination and wavelength-discrimination is required for the purpose of light emission stimulation and 3D image reconstruction. HEFT is built on fluorescent sources with a relatively broad spectral absorption profile (quantum dots) and a light propagation model for strongly absorbing tissue between wavelengths 560 nm and 660 nm (simplified spherical harmonics - SPN, - equations). The measured partial current of fluorescence light is cast into an algebraic system of equations, which is solved for the unknown quantum dot distribution with an expectation-maximization (EM) method. HEFT requires no source-detector multiplexing for 3D image reconstruction and, hence, offers a technologically simple design.

Klose, Alexander D.

2011-02-01

300

Conductance Peaks in Open Quantum Dots  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

301

Solution-processable graphene quantum dots.  

PubMed

This minireview describes recent progress in solution-processable graphene quantum dots (SGQDs). Advances in the preparation, modification, properties, and applications of SGQDs are highlighted in detail. As one of emerging nanostructured materials, possible ongoing research related to the precise control of the lateral size, edge structure and surface functionality; the manipulation and characterization; the relationship between the properties and structure; and interfaces with biological systems of SGQDs have been speculated upon. PMID:23733526

Zhou, Xuejiao; Guo, Shouwu; Zhang, Jingyan

2013-06-03

302

Quantum Dots with Perfectly Resonant Emission Energies  

Microsoft Academic Search

Semiconductor quantum dots (QDs) with excellent structural, optical and electronic properties can be easily fabricated by the self-assembled Stranski-Krastanow growth mode. However, in spite of numerous efforts and encouraging results, it has become clear that the bottom-up approach alone can not yield QDs with deterministically controllable electronic properties. Post-growth processing seems at present the only viable path to achieve this

A. Rastelli; Lijuan Wang; S. Kiravittaya; O. Schmidt

2007-01-01

303

Toxicity of carbon group quantum dots  

Microsoft Academic Search

Carbon group quantum dots (QDs) such as carbon, silicon and germanium, have potential for biomedical applications such as bio-imaging markers and drug delivery systems and are expected to demonstrate several advantages over conventional fluorescent QDs such as CdSe, especially in biocompatibility. We assessed biocompatibility of newly manufactured silicon QDs (Si-QDs), by means of both MTT assay and LDH assay for

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

2009-01-01

304

Luminescence properties of semiconductor quantum dots  

Microsoft Academic Search

Semiconductor quantum dot (QD) heterostructures created using self-ordering phenomena on crystal surfaces exhibit luminescence properties predicted for zero-dimensional systems, e.g. ultrasharp luminescence lines up to high temperatures, giantly increased material gain and practically complete temperature insensitivity of the laser threshold current. Faster than expected exciton capture and energy relaxation processes manifest minor role of the so-called phonon bottleneck effect. Formation

D. Bimberg; N. N. Ledentsov; M. Grundmann; R. Heitz; J. Böhrer; V. M. Ustinov; P. S. Kop'ev; Zh. I. Alferov

1997-01-01

305

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

306

Quantum-dot semiconductor disk lasers  

Microsoft Academic Search

We demonstrate quantum-dot (QD)-based, optically pumped semiconductor disk lasers (SDLs) for wavelengths ranging from 950 to 1210nm. QDs grown either in the submonolayer (SML) or in the Stranski–Krastanow (SK) regime are employed as active layers of the SDLs which are based on two different design concepts. Output power of up to 1.4W continuous wave (CW) is achieved with an InAs\\/GaAs-SML

T. D. Germann; A. Strittmatter; U. W. Pohl; D. Bimberg; J. Rautiainen; M. Guina; O. G. Okhotnikov

2008-01-01

307

Carrier Dynamics in Colloidal Graphene Quantum Dots  

Microsoft Academic Search

We describe carrier dynamics for single and multiple excitons in colloidal graphene quantum dots (GQDs). Strong confinement and corresponding size-tunable electronic structure make GQDs potentially useful sensitizers in photovoltaic devices. We have studied the optical response of GQDs consisting of 132 and 168 sp^2 hybridized carbon atoms dissolved in toluene with HOMO-LUMO transitions of 1.4-1.6 eV. From measurements of ultrafast

Cheng Sun; Xin Yan; Liang-Shi Li; John A. McGuire

2011-01-01

308

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

309

Quantum dot encapsulation in viral capsids.  

PubMed

Incorporation of CdSe/ZnS semiconductor quantum dots (QDs) into viral particles provides a new paradigm for the design of intracellular microscopic probes and vectors. Several strategies for the incorporation of QDs into viral capsids were explored; those functionalized with poly(ethylene glycol) (PEG) can be self-assembled into viral particles with minimal release of photoreaction products and enhanced stability against prolonged irradiation. PMID:16968014

Dixit, Suraj K; Goicochea, Nancy L; Daniel, Marie-Christine; Murali, Ayaluru; Bronstein, Lyudmila; De, Mrinmoy; Stein, Barry; Rotello, Vincent M; Kao, C Cheng; Dragnea, Bogdan

2006-09-01

310

Electron properties of open semiconductor quantum dots  

Microsoft Academic Search

The energy spectrum and lifetimes of electron states in an open semiconductor quantum dot (QD) have been studied using the\\u000a scattering S-matrix method. It is established that the lifetime of electron states in the QD is highly sensitive to changes in the QD\\u000a radius and the thickness of an external coating layer. As the coating layer thickness increases from one

N. V. Tkach; Yu. A. Seti; G. G. Zegrya

2007-01-01

311

Quantum-Dot Semiconductor Optical Amplifiers  

Microsoft Academic Search

This paper reviews the recent progress of quantum-dot semiconductor optical amplifiers developed as ultrawideband polarization-insensitive high-power amplifiers, high-speed signal regenerators, and wideband wavelength converters. A semiconductor optical amplifier having a gain of > 25 dB, noise figure of 20 dBm, over the record widest bandwidth of 90 nm among all kinds of optical amplifiers, and also having a penalty-free output

T. Akiyama; M. Sugawara; Y. Arakawa

2007-01-01

312

Engineered quantum dot single-photon sources  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

313

Examination of the stability of hydrophobic (CdSe)ZnS quantum dots in the digestive tract of rats.  

PubMed

Semiconductor quantum dots show promise as alternatives to organic dyes for biological labelling because of their bright and stable photoluminescence. The typical quantum dots is CdSe because colloidal synthesis for nanocrystals of this semiconductor is well established. CdSe is usually passivated with zinc sulfide. While the cytotoxicity of bulk CdSe is well documented, questions about (CdSe)ZnS potential toxicity and behaviour in vivo remain unanswered. The distribution and stability of (CdSe)ZnS quantum dots in Wistar line rats' digestive tract were investigated. Hydrophobic quantum dots were mixed with fat or sonificated in water and administered orally. The distribution and stability of quantum dots moving through the digestive system of rats was followed by fluorescence spectroscopy. In both ways prepared quantum dots were degraded in the digestive tract of animals. Quantum dots mixed with fat were more stable and degraded more slowly than quantum dots sonificated in water. The data obtained suggest possible toxicity of (CdSe)ZnS quantum dots due to the liberation of Cd(2+). PMID:18528558

Karabanovas, Vitalijus; Zakarevicius, Eugenijus; Sukackaite, Angele; Streckyte, Giedre; Rotomskis, Ricardas

2008-04-18

314

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

315

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

316

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

317

Molecular spintronics: Coherent spin transfer in coupled quantum dots  

Microsoft Academic Search

Time-resolved Faraday rotation has recently demonstrated coherent transfer of electron spin between quantum dots coupled by conjugated molecules. Using a transfer Hamiltonian ansatz for the coupled quantum dots, we calculate the Faraday rotation signal as a function of the probe frequency in a pump-probe setup using neutral quantum dots. Additionally, we study the signal of one spin-polarized excess electron in

Florian Meier; Veronica Cerletti; Oliver Gywat; Daniel Loss; D. D. Awschalom

2004-01-01

318

Growth and characterization of HgSe:Fe quantum dots  

Microsoft Academic Search

Applying three different sophisticated growth methods using MBE we succeeded in growing unburied and buried quantum-dot structures of HgSe:Fe on a ZnSe\\/GaAs buffer\\/substrate system in (001) orientation. For the buried quantum dots the buffer\\/substrate system was specially prepared by a thermal desorption process resulting in the generation of surface dips acting as a mould for the quantum dots. The advantage

T Tran-Anh; S Hansel; A Kirste; H. U Müller; M von Ortenberg; J Barner; J. P Rabe

2004-01-01

319

The development of a Quantum Dot Solar Concentrator  

Microsoft Academic Search

The aim of this study was to investigate the feasibility of Quantum Dot Solar Concentrators (QDSCs). Quantum Dots offer the advantages of having broad absorption specr4a, tunable emission and improved stability. A range of Cadmium Selenide\\/|Zince Sulphide Quantum Dots were characterized in solution and composite form using time-resolved and steady state spectroscopie techniques and the stability of the composite samples

Brenda Rowan

2007-01-01

320

Semiconductor quantum dot scintillation under gamma-ray irradiation  

SciTech Connect

We recently demonstrated the ability of semiconductor quantum dots to convert alpha radiation into visible photons. In this letter, we report on the scintillation of quantum dots under gamma-ray irradiation, and compare the energy resolution of the 59 keV line of Americium 241 obtained with our quantum dot-glass nanocomposite material to that of a standard sodium iodide scintillator. A factor 2 improvement is demonstrated experimentally and interpreted theoretically using a combination of energy-loss and photon transport models. These results demonstrate the potential of quantum dots for room-temperature gamma-ray detection, which has applications in medical imaging, environmental monitoring, as well as security and defense. Present technology in gamma radiation detection suffers from flexibility and scalability issues. For example, bulk Germanium provides fine energy resolution (0.2% energy resolution at 1.33 MeV) but requires operation at liquid nitrogen temperature. On the other hand, Cadmium-Zinc-Telluride is a good room temperature detector ( 1% at 662 keV) but the size of the crystals that can be grown is limited to a few centimeters in each direction. Finally, the most commonly used scintillator, Sodium Iodide (NaI), can be grown as large crystals but suffers from a lack of energy resolution (7% energy resolution at 662 keV). Recent advancements in nanotechnology6-10 have provided the possibility of controlling materials synthesis at the molecular level. Both morphology and chemical composition can now be manipulated, leading to radically new material properties due to a combination of quantum confinement and surface to volume ratio effects. One of the main consequences of reducing the size of semiconductors down to nanometer dimensions is to increase the energy band gap, leading to visible luminescence, which suggests that these materials could be used as scintillators. The visible band gap of quantum dots would also ensure both efficient photon counting (better coupling with photomultipliers optimized for the visible region), and high photon output (smaller individual photon energy results in more photons produced) at room temperature, which is essential for effective Poisson counting (the energy resolution {Delta}E/E is inversely proportional to the square root of the number of photons collected).

Letant, S E; Wang, T

2006-08-23

321

Highly tunable hybrid quantum dots with charge detection  

NASA Astrophysics Data System (ADS)

In order to employ solid state quantum dots as qubits, both a high degree of control over the confinement potential as well as sensitive charge detection are essential. We demonstrate that by combining local anodic oxidation with local Schottky-gates, these criteria are nicely fulfilled in the resulting hybrid device. To this end, a quantum dot with adjacent charge detector is defined. After tuning the quantum dot to contain only a single electron, we are able to observe the charge detector signal of the quantum dot state for a wide range of tunnel couplings.

Rössler, C.; Küng, B.; Dröscher, S.; Choi, T.; Ihn, T.; Ensslin, K.; Beck, M.

2010-10-01

322

Transparent non-volatile memory device using silicon quantum dots  

NASA Astrophysics Data System (ADS)

A transparent non-volatile memory device was fabricated using silicon quantum dots in silicon nitride film as a gate insulator. A silicon quantum dots were grown in-situ in the film by plasma-enhanced chemical vapor deposition. The silicon quantum dot film had a high optical transmittance of over 95% at 550 nm with a thickness of 50 nm. A large hysteresis curve was observed in a current-voltage measurement. When we increased the voltage sweep range, electrons were charged into the silicon quantum dots because of the electrical n-type channel in an oxide thin film transistor.

Park, Nae-Man; Shin, Jaeheon; Kim, Bosul; Kim, Kyung Hyun; Cheong, Woo-Seok

2013-07-01

323

Imaging ligand-gated ion channels with quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2007-02-01

324

Quantum transport through an array of quantum dots  

NASA Astrophysics Data System (ADS)

The transient current through an array of as many as 1000 quantum dots is simulated with two newly developed quantum mechanical methods. To our surprise, upon switching on the bias voltage, the current increases linearly with time before reaching its steady state value. And the time required for the current to reach its steady state value is proportional to the length of the array, and more interestingly, is exactly the time for a conducting electron to travel through the array at the Fermi velocity. These quantum phenomena can be understood by a simple analysis on the energetics of an equivalent classical circuit. An experimental design is proposed to confirm the numerical findings.

Chen, Shuguang; Xie, Hang; Zhang, Yu; Cui, Xiaodong; Chen, Guanhua

2012-12-01

325

[A facile colloid aqueous method for synthesis of water soluble ZnSe quantum dots with high fluorescence and stability characterization].  

PubMed

Highly fluorescent and stable ZnSe quantum dots were synthesized by a facile colloid aqueous phase route. It overcame the defects such as instability and low quantum yields of the quantum dots synthesized by early aqueous phase route. Optimum conditions were found. L-glutathione was used as the stabilizer, the molar ratio of L-glutathione, Se2- and Zn2+ is 5 : 1 : 5, the reaction media is pH 10.5, and the proper temperature is between 90 and 100 degrees C. Quantum yields (QYs) could reach to 50.1% without post irradiation in prime synthetical conditions. And the fluorescence intensity of ZnSe QDs almost didn't change after 3 months. Its water-soluble property is also excellent. The properties of ZnSe QDs were characterized by means of ultraviolet visible spectra, fluorescence spectra, and transmission electron microscopy. The synthesized ZnSe QDs emit blue-purple fluorescence (370 nm) when excited at 300 nm. And the excellent photochemical characteristics of the ZnSe QDs will be advantageous in the application in optothermal device manufacture and chemistry biology domain. PMID:20496695

Shi, Bao-Qin; Cai, Zhao-Xia; Ma, Mei-Hu

2010-03-01

326

Synthesis of aqueous CdTe quantum dots embedded silica nanoparticles and their applications as fluorescence probes  

Microsoft Academic Search

This paper presents the synthesis of aqueous CdTe QDs embedded silica nanoparticles by reverse microemulsion method and their applications as fluorescence probes in bioassay and cell imaging. With the aim of embedding more CdTe QDs in silica spheres, we use poly(dimethyldiallyl ammonium chloride) to balance the electrostatic repulsion between CdTe QDs and silica intermediates. By modifying the surface of CdTe\\/SiO2

Chao Wang; Qiang Ma; Wenchao Dou; Shamsa Kanwal; Guannan Wang; Pingfan Yuan; Xingguang Su

2009-01-01

327

Controllable synthesis of ZnS\\/PMMA nanocomposite hybrids generated from functionalized ZnS quantum dots nanocrystals  

Microsoft Academic Search

We reported controllable synthesis of ZnS nanocrystal-polymer transparent hybrids by using polymethylmethacrylate (PMMA) as\\u000a a polymer matrix. In a typical run, the appropriate amounts of zinc chloride (ZnCl2) and sodium sulfide (Na2S) in the presence of 2-mercaptoethanol (ME) as the organic ligand were well dispersed in H2O\\/dimethylformamide solution without any aggregation. In addition, the Mn-doped ZnS nanocrystals (NCs) were synthesized

Lei Guo; Su Chen; Li Chen

2007-01-01

328

Quantum dot lasers: from promise to reality  

NASA Astrophysics Data System (ADS)

Nanoscale coherent insertions of narrow gap material in a single-crystalline matrix, or Quantum Dot (QD) provide a possibility to extend the basic principles of heterostructure lasers. The idea to use heterostructures with dimensionality lower than two in semiconductor lasers appeared a quarter of a century ago, simultaneously with the proposal of a quantum well laser. However, fabrication of quantum wire- and, particularly, QD heterostructure (QDHS) lasers appeared to be much more difficult. The breakthrough occurred when techniques for self-organized growth of QDs allowed fabrication of dense arrays of uniform in shape and size coherent islands free from undesirable defects. Recently, some key parameters of QD lasers were significantly improved as compared to those for QW devices. High-power operation, record low threshold current densities, strongly reduced chirp and extension of the wavelength range on GaAs substrates up to 1.3 micrometer range were demonstrated. It also became clear that unique properties of QDs may give rise to a new generation of semiconductor lasers, such as far and middle infrared light emitters based on interlevel electron transitions in QDs or single quantum dot vertical-cavity surface-emitting lasers.

Bimberg, Dieter; Ledentsov, Nikolai N.

2000-07-01

329

Far-field patterns of Quantum Well, Quantum Dash, and Quantum Dot Laser Diodes  

Microsoft Academic Search

We perform measurements of far field pattern of various quantum-confined heterostructures namely quantum well (QW), quantum dash (Qdash), and quantum dot (Qdot) lasers to study the effect of different active gain mediums of semiconductor lasers on the optical beam quality and coupling efficiency. The beam pattern profile of the Qdash laser is similar to that of the QW laser (FWHM

Y. H. Ding; C. L. Tan; V. Hongpinyo; C. E. Dimas; Y. Wang; C. Chen; H. S. Djie; B. S. Ooi

2008-01-01

330

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

2011-03-21

331

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

332

Emission in Mn-Doped Quantum Dot  

NASA Astrophysics Data System (ADS)

We theoretically investigate the magneto-PL of Mn2+doped semiconductor core-shell colloidal quantum dot to explain the experiment result from a recent magnetophotoluminescence study of strongly confined diluted magnetic semiconductor (DMS) in Mn2+-doped ZnSe/CdSe core-shell colloidal nanocrystals. The yellow emission characterized for in Mn2+-which is associated with the d-d internal transition 4T1-6A1, was reported not suppressed in an applied B //z magnetic field and unpolarized as usual and instead, a Mn PL circular polarization has been observed. The in Mn2+- photoluminescence has been found to have a large splitting between ? + and ? {- }components which depends on the applied field. We show that this behavior, which has not been found in characteristics of the Mn2+ PL in bulks and other conventional DMS materials, is the result of the strong confinement of the nanocrystal and its properties. Our theory and calculation show that the reasons the yellow Mn2+ PL band in quantum dots is not suppressed under applied magnetic field originate due to the existence of the internal piezoelectric dipole moment and the Coulomb exchange interaction of the impurity ions with the confined electrons inside the dot.

Huong Nguyen, Que; Birman, Joseph L.

2013-03-01

333

Coulomb Oscillations in Partially Open Quantum Dots  

NASA Astrophysics Data System (ADS)

Coulomb blockade conductance oscillations in quantum dots are ordinarily observed with weak dot-to-lead tunneling. Recent theoryfootnote A. Furusaki and K.A. Matveev, Phys. Rev. Lett. 75 (1995), 709. examines the effect of strong tunneling on Coulomb oscillations. We have measured the zero magnetic field conductance through a 500 × 800 nm^2 quantum dot connected to leads through tunable tunnel barriers, defined in a high mobility near-surface two-dimensional electron gas by four independently tunable split gates on a GaAs/AlGaAs heterostructure. We set the conductance of one barrier much less than e^2/h and vary the conductance of the other (G_open) between e^2/h and 6e^2/h. We observe well-defined Coulomb oscillations at 50 mK for the entire range of G_open, except when G_open ? 2e^2/h, where the oscillations are suppressed. The temperature at which the oscillations disappear decreases with increasing G_open; for G_ open>2e^2/h, the oscillations are suppressed at temperatures above the single-particle level spacing.

Crouch, C. H.; Livermore, C.; Westervelt, R. M.; Campman, K. L.; Gossard, A. C.

1996-03-01

334

Multiple stack quantum dot infrared photodetectors  

NASA Astrophysics Data System (ADS)

Quantum dot infrared photodetectors (QDIP) have established themselves as promising devices for detecting infrared (IR) radiation for wavelengths <20?m due to their sensitivity to normal incidence radiation and long excited carrier lifetimes. A limiting factor of QDIPs at present is their relatively small absorption volume, leading to a lower quantum efficiency and detectivity than in quantum well infrared photodetectors and mercury cadmium telluride based detectors. One means of increasing the absorption volume is to incorporate a greater number of quantum dot (QD) stacks, thereby increasing the probability of photon capture. Growth of InAs/InGaAs dot-in-a-well (DWELL) QDIPs with greater than 10 stacks is challenging due to the increased strain between layers, leading to high dark current. It is known that strain can be reduced in QDIPs by reducing the width of the InGaAs well and incorporating a second well consisting of GaAs and barriers consisting of AlGaAs. A number of InAs/InGaAs/GaAs DWELL QDIPs with 30-80 stacks have been grown, fabricated and characterised. Dark current in these layers appears to be constant at given electric field, suggesting strain does not increase significantly if the number of QD stacks is increased. IR spectral measurements show well defined peaks at 5.5?m, 6.5?m and 8.4?m. In this work a comparison between dark current, noise, gain, responsivity and detectivity in these layers is presented and compared to existing data from conventional DWELL QDIPs.

Vines, P.; Tan, C. H.; David, J. P. R.; Attaluri, R. S.; Vandervelde, T. E.; Krishna, S.

2008-10-01

335

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

SciTech Connect

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

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

2011-12-23

336

Toward quantitatively fluorescent carbon-based ``quantum'' dots  

Microsoft Academic Search

Carbon-based ``quantum'' dots (or ``carbon dots'') are generally defined as surface-passivated small carbon nanoparticles that are brightly fluorescent. Apparently, the carbon particle surface passivation in carbon dots is critical to their fluorescence performance. An effective way to improve the surface passivation is to dope the surface of the precursor carbon nanoparticles with an inorganic salt, followed by the typical functionalization

Parambath Anilkumar; Xin Wang; Li Cao; Sushant Sahu; Jia-Hui Liu; Ping Wang; Katerina Korch; Kenneth N. Tackett II; Alexander Parenzan; Ya-Ping Sun

2011-01-01

337

Bipolar spin filter in a quantum dot molecule  

Microsoft Academic Search

We show that the tunable hybridization between two lateral quantum dots connected to a nonmagnetic current leads in a ``hanging-dot'' configuration that can be used to implement a bipolar spin filter. The competition between Zeeman, exchange interaction, and interdot tunneling (molecular hybridization) yields a singlet-triplet transition of the double dot ground state that allows spin filtering in Coulomb blockade experiments.

F. Mireles; S. E. Ulloa; F. Rojas; E. Cota

2006-01-01

338

Coherent Nonlinear Optical Response and Control of Single Quantum Dots.  

National Technical Information Service (NTIS)

Work on this program is aimed at developing and understanding nano- optical structures with emphasis on developing quantum optical-based devices. Specific work focused on semiconductor quantum dots. The major achievements include the first demonstration o...

D. G. Steel

2005-01-01

339

Quantum Dots: An Experiment for Physical or Materials Chemistry  

ERIC Educational Resources Information Center

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

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

2005-01-01

340

Controlling the Aspect Ratio of Quantum Dots: From Columnar Dots to Quantum Rods  

Microsoft Academic Search

We demonstrate the feasibility and flexibility of artificial shape engineering of epitaxial semiconductor nanostructures. Novel nanostructures including InGaAs quantum rods (QRs), nanocandles, and quantum dots (QDs)-in-rods were realized on a GaAs substrate. They were formed by depositing a short-period GaAs\\/InAs superlattice (SL) on a seed QD layer by molecular beam epitaxy growth. The InAs layer thickness in the SL plays

Lianhe Li; Gilles Patriarche; Nicolas Chauvin; Philipp Ridha; Marco Rossetti; Janusz Andrzejewski; Jan Misiewicz; Andrea Fiore

2008-01-01

341

Induced quantum dots and wires: electron storage and delivery.  

PubMed

We show that quantum dots and quantum wires are formed underneath metal electrodes deposited on a planar semiconductor heterostructure containing a quantum well. The confinement is due to the self-focusing mechanism of an electron wave packet interacting with the charge induced on the metal surface. Induced quantum wires guide the transfer of electrons along metal paths and induced quantum dots store the electrons in specific locations of the nanostructure. Induced dots and wires can be useful for devices operating on the electron spin. An application for a spin readout device is proposed. PMID:18517899

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

2008-03-28

342

Coherent Optical Spectroscopy of a Strongly Driven Quantum Dot  

Microsoft Academic Search

Quantum dots are typically formed from large groupings of atoms and thus may be expected to have appreciable many-body behavior under intense optical excitation. Nonetheless, they are known to exhibit discrete energy levels due to quantum confinement effects. We show that, like single-atom or single-molecule two- and three-level quantum systems, single semiconductor quantum dots can also exhibit interference phenomena when

Xiaodong Xu; Bo Sun; Paul R. Berman; Duncan G. Steel; Allan S. Bracker; Dan Gammon; L. J. Sham

2007-01-01

343

Nano-laser on silicon quantum dots  

NASA Astrophysics Data System (ADS)

A new conception of nano-laser is proposed in which depending on the size of nano-clusters (silicon quantum dots (QD)), the pumping level of laser can be tuned by the quantum confinement (QC) effect, and the population inversion can be formed between the valence band and the localized states in gap produced from the surface bonds of nano-clusters. Here we report the experimental demonstration of nano-laser on silicon quantum dots fabricated by nanosecond pulse laser. The peaks of stimulated emission are observed at 605 nm and 693 nm. Through the micro-cavity of nano-laser, a full width at half maximum of the peak at 693 nm can reach to 0.5 nm. The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of QD (d < 3 nm) can make the localized states into band gap. The emission energy of nano-laser will be limited in the range of 1.7-2.3 eV generally due to the position of the localized states in gap, which is in good agreement between the experiments and the theory.

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

2011-04-01

344

Energy level engineering in InAs quantum dot nanostructures  

NASA Astrophysics Data System (ADS)

We present an advanced method to tailor the optical and electrical properties of semiconductor quantum dot structures. By embedding vertically stacked quantum dots in a two-dimensional superlattice, the advantages of self-organized growth and of band structure engineering can be combined. The transition energies between the dot levels and the extended states of the superlattice can be adjusted by the period of the superlattice. We apply this scheme for photodetectors made of InAs quantum dots embedded in an AlAs/GaAs superlattice. The dark current of these devices is reduced by more than one order of magnitude compared to the devices without a superlattice.

Rebohle, L.; Schrey, F. F.; Hofer, S.; Strasser, G.; Unterrainer, K.

2002-09-01

345

Hybrid passivated colloidal quantum dot solids for photovoltaics  

NASA Astrophysics Data System (ADS)

Colloidal quantum dot (CQD) films are an attractive photovoltaic material due to their large-area-compatible solution processing and bandgap tuning through the quantum size effect. However, the large internal surface areas make CQD films prone to high trap state densities, leading to recombination of charge carriers. We quantify the density of midgap trap states in PbS CQD solids and show that the current photovoltaic performance is limited by these states. We 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 standard organic ligands, and combine this with an organic crosslinking strategy to form the film. 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.

Thon, Susanna M.; Ip, Alexander H.; 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.

2013-03-01

346

Mesoscopic thermodynamics and chaos in quantum dots  

NASA Astrophysics Data System (ADS)

In this thesis we present our work on the thermodynamic and transport properties of isolated or nearly isolated mesoscopic systems. These mesoscopic systems are phase coherent and their thermodynamic and transport properties do not self-average and exhibit sample-specific, reproducible fluctuations. Significant research in mesoscopic physics revealed the applicability of Random Matrix Theory (RMT), which is a statistical theory of electron eigenenergies and eigenfunctions in complex quantum systems. For the mesoscopic systems considered we assume the applicability of the RMT and calculate universal properties. The thermodynamics of isolated mesoscopic systems require the use of Canonical Ensemble because the number of electrons in each isolated sample must be constant in order to keep the samples charge neutral. We implement exact Canonical Ensemble techniques numerically and use RMT to calculate the mesoscopic averages and fluctuations for thermodynamic and transport properties. For an ensemble of metallic grains we calculate the average and fluctuations of spin magnetism, which is a fundamental thermodynamic quantity like the specific heat. We show the applicability of calculating mesoscopic corrections using an equivalent grand canonical ensemble, as proposed by Imry. We study the transport properties of chaotic quantum dots at temperatures that are comparable to the mean level spacing. Our results indicate the non-triviality of the well-known Landauer-Buttiker formula for such systems. In particular, the finite temperature conductance peak height distributions in quantum dots in Coulomb blockade regime clearly show the signatures of the charging energy. In addition, we calculate the temperature dependent peak-to-peak correlator. Our collaboration with experimentalists on the temperature dependence of peak height correlations demonstrates the scrambling of electronic levels as electrons are added to the dot.

Gokcedag, Mehmet

347

Solid-state tunneling spectroscopy of individual quantum dots  

Microsoft Academic Search

Quantum dots are gaining importance for their potential applications in the fields of energy harvesting, bio-labeling and treatment, in opto-electronic devices and in photonic devices. For all these applications, it is imperative to know their electronic structure. Although currently several spectroscopic techniques exist to study the electronic structure of these quantum dots, they are accompanied by other effects and do

Ramkumar Subramanian

2010-01-01

348

Visualization and Transport of Quantum Dot Nanomaterials in Porous Media  

Microsoft Academic Search

This paper presents our research on the visualization and transport phenomena of quantum dot nanomaterials in porous media. It includes the development of a non-intrusive, high spatial and temporal resolution method to visualize transport and measure quantum dot nanomaterials concentration in porous media, allowing to characterize the mechanisms that control the transport, or lack of mobility, of engineered nanomaterials ---

C. J. G. Darnault; S. M. C. Bonina; B. Uyusur; P. T. Snee

2009-01-01

349

Metallic carbon nanotube quantum dots under magnetic fields  

Microsoft Academic Search

Quantum dots made of individual metallic carbon nanotubes are theoretically studied under the influence of a magnetic field applied in the axial direction. After assessing the mechanical stability of the heterostructure by Monte Carlo simulations, the dependence of the electronic properties on the size of the nanotube quantum dot and applied magnetic field has been investigated within the Peierls approximation

C. G. Rocha; A. Latgé; L. Chico

2005-01-01

350

Integrated Quantum Dot Schottky Diodes for RECTENNA (Rectifying Antenna)  

Microsoft Academic Search

In this paper we will present our latest research results of integrated quantum dot Schottky diodes and integrated silicon antenna for RF applications. Both, the quantum dot Schottky diodes and the antenna are integrated on Si substrates forming a simple mm-wave detection system, the rectifying antenna (RECTENNA). Within this work a specific antenna design, 1-dimensional array (single line antenna), will

H. Xu; A. Karmous; M. Morschbach; O. Kirfel; S. Spiessberger; E. Kasper

2009-01-01

351

Spin and charge polarization in quantum dot arrays  

Microsoft Academic Search

The role of spin and charge distribution in a planar semiconductor quantum dot array (square geometry) with two electrons is studied in the presence of a driver cell and magnetic nanoparticles located near two quantum dots providing a local magnetic field. We use an extended Hubbard model to describe the electrons in the cell, taking into account intra and intercell

F. Rojas; E. Cota; F. Mireles; S. E. Ulloa

2005-01-01

352

Spin readout and initialization in semiconductor quantum dots  

US Patent & Trademark Office Database

A semiconductor quantum dot device converts spin information to charge information utilizing an elongated quantum dot having an asymmetric confining potential along its length so that charge movement occurs during orbital excitation. A single electron sensitive electrometer is utilized to detect the charge movement. Initialization and readout can be carried out rapidly utilizing RF fields at appropriate frequencies.

2006-11-14

353

Quantum Dots for Molecular Diagnostics of Tumors  

PubMed Central

Semiconductor quantum dots (QDs) are a new class of fluorophores with unique physical and chemical properties, which allow to appreciably expand the possibilities for the current methods of fluorescent imaging and optical diagnostics. Here we discuss the prospects of QD application for molecular diagnostics of tumors ranging from cancer-specific marker detection on microplates to non-invasive tumor imagingin vivo. We also point out the essential problems that require resolution in order to clinically promote QD, and we indicate innovative approaches to oncology which are implementable using QD.

Zdobnova, T.A.; Lebedenko, E.N.; Deyev, S.?.

2011-01-01

354

Mollow quintuplets from coherently excited quantum dots.  

PubMed

Charge-neutral excitons in semiconductor quantum dots (QDs) have a small finite energy separation caused by the anisotropic exchange splitting. Coherent excitation of neutral excitons will generally excite both exciton components, unless the excitation is parallel to one of the dipole axes. We present a polaron master equation model to describe two-exciton pumping using a coherent continuous wave pump field in the presence of a realistic anisotropic exchange splitting. We predict a five-peak incoherent spectrum, namely a Mollow quintuplet under general excitation conditions. We experimentally confirm such spectral quintuplets for In(Ga)As QDs and obtain very good agreement with theory. PMID:23938913

Ge, Rong-Chun; Weiler, S; Ulhaq, A; Ulrich, S M; Jetter, M; Michler, P; Hughes, S

2013-05-15

355

Stability of Quantum Dots in Live Cells  

PubMed Central

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

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

2011-01-01

356

Quantum dot loaded immunomicelles for tumor imaging  

PubMed Central

Background Optical imaging is a promising method for the detection of tumors in animals, with speed and minimal invasiveness. We have previously developed a lipid coated quantum dot system that doubles the fluorescence of PEG-grafted quantum dots at half the dose. Here, we describe a tumor-targeted near infrared imaging agent composed of cancer-specific monoclonal anti-nucleosome antibody 2C5, coupled to quantum dot (QD)-containing polymeric micelles, prepared from a polyethylene glycol/phosphatidylethanolamine (PEG-PE) conjugate. Its production is simple and involves no special equipment. Its imaging potential is great since the fluorescence intensity in the tumor is twofold that of non-targeted QD-loaded PEG-PE micelles at one hour after injection. Methods Para-nitrophenol-containing (5%) PEG-PE quantum dot micelles were produced by the thin layer method. Following hydration, 2C5 antibody was attached to the PEG-PE micelles and the QD-micelles were purified using dialysis. 4T1 breast tumors were inoculated subcutaneously in the flank of the animals. A lung pseudometastatic B16F10 melanoma model was developed using tail vein injection. The contrast agents were injected via the tail vein and mice were depilated, anesthetized and imaged on a Kodak Image Station. Images were taken at one, two, and four hours and analyzed using a methodology that produces normalized signal-to-noise data. This allowed for the comparison between different subjects and time points. For the pseudometastatic model, lungs were removed and imaged ex vivo at one and twenty four hours. Results The contrast agent signal intensity at the tumor was double that of the passively targeted QD-micelles with equally fast and sharply contrasted images. With the side views of the animals only tumor is visible, while in the dorsal view internal organs including liver and kidney are visible. Ex vivo results demonstrated that the agent detects melanoma nodes in a lung pseudometastatic model after a 24 hours wash-out period, while at one hour, only a uniform signal is detected. Conclusions The targeted agent produces ultrabright tumor images and double the fluorescence intensity, as rapidly and at the same low dose as the passively targeted agents. It represents a development that may potentially serve to enhance early detection for metastases.

2010-01-01

357

Minimal Self-Contained Quantum Refrigeration Machine Based on Four Quantum Dots  

NASA Astrophysics Data System (ADS)

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

Venturelli, Davide; Fazio, Rosario; Giovannetti, Vittorio

2013-06-01

358

Interaction of porphyrins with CdTe quantum dots  

NASA Astrophysics Data System (ADS)

Porphyrins may be used as photosensitizers for photodynamic therapy, photocatalysts for organic pollutant dissociation, agents for medical imaging and diagnostics, applications in luminescence and electronics. The detection of porphyrins is significantly important and here the interaction of protoporphyrin-IX (PPIX) with CdTe quantum dots was studied. It was observed that the luminescence of CdTe quantum dots was quenched dramatically in the presence of PPIX. When CdTe quantum dots were embedded into silica layers, almost no quenching by PPIX was observed. This indicates that PPIX may interact and alter CdTe quantum dots and thus quench their luminescence. The oxidation of the stabilizers such as thioglycolic acid (TGA) as well as the nanoparticles by the singlet oxygen generated from PPIX is most likely responsible for the luminescence quenching. The quenching of quantum dot luminescence by porphyrins may provide a new method for photosensitizer detection.

Zhang, Xing; Liu, Zhongxin; Ma, Lun; Hossu, Marius; Chen, Wei

2011-05-01

359

Growth and photoluminescence study of ZnSe quantum dots  

SciTech Connect

The authors report detailed photoluminescence (PL) studies of ZnSe quantum dots grown by controlling the flow duration of the precursors in a metal-organic chemical vapor deposition system. The growth time of the quantum dots determines the amount of blue shift observed in the PL measurements. Blue shift as large as 320 meV was observed, and the emission was found to persist up to room temperature. It is found that changing the flow rate and the total number of quantum dot layers also affect the peak PL energy. The temperature dependence of the peak PL energy follows the Varshni relation. From analyzing the temperature-dependent integrated intensity of the photoluminescence spectra, it is found that the activation energy for the quenching of photoluminescence increases with decreasing quantum dot size, and is identified as the binding energy of the exciton in ZnSe quantum dot.

Chang, Y.H.; Chieng, M.H.; Tsai, C.C.; Harris Liao, M.C.; Chen, Y.F.

2000-01-01

360

Enhanced intratumoral uptake of quantum dots concealed within hydrogel nanoparticles  

NASA Astrophysics Data System (ADS)

Effective nanomedical devices for tumor imaging and drug delivery are not yet available. In an attempt to construct a more functional device for tumor imaging, we have embedded quantum dots (which have poor circulatory behavior) within hydrogel nanoparticles made of poly-N-isopropylacrylamide. We found that the hydrogel encapsulated quantum dots are more readily taken up by cultured tumor cells. Furthermore, in a melanoma model, hydrogel encapsulated quantum dots also preferentially accumulate in the tumor tissue compared with normal tissue and have ~16-fold greater intratumoral uptake compared to non-derivatized quantum dots. Our results suggest that these derivatized quantum dots, which have greatly improved tumor localization, may enhance cancer monitoring and chemotherapy.

Nair, Ashwin; Shen, Jinhui; Thevenot, Paul; Zou, Ling; Cai, Tong; Hu, Zhibing; Tang, Liping

2008-12-01

361

Prospects for Spin-Based Quantum Computing in Quantum Dots  

NASA Astrophysics Data System (ADS)

Experimental and theoretical progress toward quantum computation with spins in quantum dots (QDs) is reviewed, with particular focus on QDs formed in GaAs heterostructures, on nanowire-based QDs, and on self-assembled QDs. We report on a remarkable evolution of the field, where decoherence—one of the main challenges for realizing quantum computers—no longer seems to be the stumbling block it had originally been considered. General concepts, relevant quantities, and basic requirements for spin-based quantum computing are explained; opportunities and challenges of spin-orbit interaction and nuclear spins are reviewed. We discuss recent achievements, present current theoretical proposals, and make several suggestions for further experiments.

Kloeffel, Christoph; Loss, Daniel

2013-04-01

362

Controlling cavity reflectivity with a single quantum dot  

Microsoft Academic Search

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

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

2007-01-01

363

Luminescence upconversion in colloidal double quantum dots  

NASA Astrophysics Data System (ADS)

Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved.

Deutsch, Zvicka; Neeman, Lior; Oron, Dan

2013-09-01

364

Backaction dephasing by a quantum dot detector  

NASA Astrophysics Data System (ADS)

We derive an analytical expression for the backaction dephasing rate, which characterizes the disturbance induced by coupling with an environment containing a quantum dot detector (QDD). In this paper, we show in an explicit form that the charge noise induces backaction dephasing. In equilibrium, this backaction dephasing induced by the charge noise can be explained as a relaxation by an inelastic electron-electron scattering in Fermi-liquid theory. Unlike the quantum point contact, the backaction dephasing rate increases or decreases with the bias at low bias and finite-temperature condition. This behavior depends on the QDD energy level with respect to the Fermi energy and the asymmetry of the QDD coupling to the reservoirs. In the high bias voltage regime, the dephasing rate becomes insensitive to the bias because of the saturation of the charge noise.

Kubo, Toshihiro; Tokura, Yasuhiro

2013-10-01

365

FAST TRACK COMMUNICATION: Graphene based quantum dots  

NASA Astrophysics Data System (ADS)

Laterally localized electronic states are identified on a single layer of graphene on ruthenium by low temperature scanning tunneling spectroscopy (STS). The individual states are separated by 3 nm and comprise regions of about 90 carbon atoms. This constitutes a highly regular quantum dot-array with molecular precision. It is evidenced by quantum well resonances (QWRs) with energies that relate to the corrugation of the graphene layer. The dI/dV conductance spectra are modeled by a layer height dependent potential-well with a delta-function potential that describes the barrier for electron penetration into graphene. The resulting QWRs are strongest and lowest in energy on the isolated 'hill' regions with a diameter of 2 nm, where the graphene is decoupled from the surface.

Zhang, H. G.; Hu, H.; Pan, Y.; Mao, J. H.; Gao, M.; Guo, H. M.; Du, S. X.; Greber, T.; Gao, H.-J.

2010-08-01

366

Luminescence upconversion in colloidal double quantum dots.  

PubMed

Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved. PMID:23912060

Deutsch, Zvicka; Neeman, Lior; Oron, Dan

2013-08-04

367

In Vivo Imaging of Quantum Dots  

NASA Astrophysics Data System (ADS)

Noninvasive whole-body near-infrared fluorescence imaging is now acknowledged as a powerful method for the molecular mapping of biological events in live small animals such as mouse models. With outstanding optical properties such as high fluorescence quantum yields and low photobleaching rates, quantum dots (QDs) are labels of choice in the near-infrared domain. The main applications described in the literature for in vivo imaging of mice after injection of QDs encompass imaging of lymph nodes and tumors and cell tracking. Standard methods for the preparation, the purification, and the in vivo fluorescence whole-body imaging of QDs in the live mouse are described. Nanoparticles coated by PEG chains of different sizes and terminal groups are prepared using 705-nm-emitting commercial QDs. Their biodistribution after intravenous or intradermal injections in tumor-bearing mice is reported here.

Texier, Isabelle; Josser, Véronique

368

Stepwise fluorescence changes of quantum dots: single-molecule spectroscopic studies on the properties of turn-on quantum dots.  

PubMed

Single-molecule spectroscopy of turn-on quantum dots induced by NADPH-dependent biocatalyzed transformations reveals that the fluorescence intensities of quantum dots functionalized with Nile Blue are stepwisely and reversibly changed in the presence of NADPH. PMID:22117202

Kim, Yea Seul; Kim, Min Young; Song, Jae Kyu; Kim, Tae Jung; Kim, Young Dong; Hah, Sang Soo

2011-11-25

369

CdTe/CdS-MPA quantum dots as fluorescent probes to label yeast cells: synthesis, characterization and conjugation with Concanavalin A  

NASA Astrophysics Data System (ADS)

Candida albicans is the most frequent human opportunistic pathogenic fungus and one of the most important causes of nosocomial infections. In fact, diagnosis of invasive candidiasis presents unique problems. The aim of this work was to evaluate, by fluorescence image analysis, cellular labeling of C. albicans with CdTe/CdS quantum dots conjugated or not to concanavalin A (ConA). Yeast cells were incubated with CdTe/CdS quantum dots (QD) stabilized with mercaptopropionic acid (MPA) (emission peak at 530 nm) for 1 hour. In the overall study we observed no morphological alterations. The fluorescence microscopic analysis of the yeast cells showed that the non-functionalized QDs do not label C. albicans cells, while for the QD conjugated to ConA the cells showed a fluorescence profile indicating that the membrane was preferentially marked. This profile was expected since Concanavalin A is a protein that binds specifically to terminal carbohydrate residues at the membrane cell surface. The results suggest that the QD-labeled Candida cells represent a promising tool to open new possibilities for a precise evaluation of fungal infections in pathological conditions.

Kato, Ilka T.; Santos, Camila C.; Benetti, Endi; Tenório, Denise P. L. A.; Cabral Filho, Paulo E.; Sabino, Caetano P.; Fontes, Adriana; Santos, Beate S.; Prates, Renato A.; Ribeiro, Martha S.

2012-02-01

370

Fast and efficient photodetection in nanoscale quantum-dot junctions.  

PubMed

We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another. PMID:23094869

Prins, Ferry; Buscema, Michele; Seldenthuis, Johannes S; Etaki, Samir; Buchs, Gilles; Barkelid, Maria; Zwiller, Val; Gao, Yunan; Houtepen, Arjan J; Siebbeles, Laurens D A; van der Zant, Herre S J

2012-10-26

371

Fast and Efficient Photodetection in Nanoscale Quantum-Dot Junctions  

NASA Astrophysics Data System (ADS)

We report on a photodetector in which colloidal quantum-dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum-efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another.

Prins, Ferry; Buscema, Michele; Seldenthuis, Johannes S.; Etaki, Samir; Buchs, Gilles; Barkelid, Maria; Zwiller, Val; Gao, Yunan; Houtepen, Arjan J.; Siebbeles, Laurens D. A.; van der Zant, Herre S. J.

2012-11-01

372

Self-Organized Formation of Quantum Dots: New Physics, New Chemistry, New Technology  

Microsoft Academic Search

This LDRD initiative proposed to seize a unique opportunity to make major advances in nanoscale science, engineering, and technology by solving one persistent bottleneck problem of the field: mass production of quantum dots (QDs) with narrow size and uniform spatial distributions. The project was focused on demonstrating the wide applicability of a conceptually new synthesis method conceived at ORNL that

Zhenyu Zhang; John Wendelken; Jian Shen; Kalman Varga; Frank Flack; Max Lagally

373

In situ activation of Mn in semiconductor quantum dots in the presence of a biopolymer matrix  

Microsoft Academic Search

We report the synthesis and characterization of zinc sulphide quantum dots (QDs) in the presence of Mn and a chitosan environment, which results in the formation of novel chitosan–zinc oxide QD nanocomposites containing Mn in traces. The location of Mn in these composites has been especially considered. The optical properties revealed that, instead of doping, activation by Mn occurs at

Preyas Ankit; V. S. Tripathi; M. C. Chattopadhyaya

2010-01-01

374

Highly red luminescence properties from ternary ZnCdTe quantum dots  

Microsoft Academic Search

This paper reports the synthesis of ternary ZnCdTe quantum dots (QD) system with highly luminescent in the red region. The ternary QD system was prepared by quick injection of trioctylphosphine telluride (TOPTe) into a reactor that contains a hot mixed cadmium and zinc precursors, trioctylphosphine oxide and oleic acid at temperature of as low as 300°C. After the injection of

Norhayati Abu Bakar; Akrajas Ali Umar; Muhamad Mat Salleh; Muahamad Yahaya; Burhanuddin Yeop Majlis

2009-01-01

375

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

Microsoft Academic Search

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

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

2005-01-01

376

Chaos and interactions in quantum dots  

NASA Astrophysics Data System (ADS)

Random-matrix theory has proved to be a successful tool in understanding the statistics of transport measurements in mesoscopic systems. Fluctuations of conductance peak-heights due to the transfer of single electrons through diffusive and chaotic ballistic quantum dots in the Coulomb-blockade regime can be modeled by fluctuations of random-matrix wavefunctions at low temperatures in the simple constant interaction model. On the other hand, statistics of the spacing between successive peaks do not show the behaviour predicted by the simple model, indicating that interactions beyond constant charging energy play an important role. The central theme of this thesis is the study of interaction effects on the mesoscopic fluctuations in a weakly disordered or chaotic ballistic quantum dot. Mean-field calculations suggest that upon addition of electrons into the dot, single-particle wavefunctions are not significantly altered while their eigenvalues "scramble" with the change in the self-consistent potential, thus affecting the peak-spacing statistics. We model this variation in the mean field by an extension of random-matrix theory: Gaussian processes, where the ensemble of random matrices depends on a discrete parameter, the number of electrons. Using a Gaussian process we can explain the saturation of the peak-to-peak correlator versus temperature. Another experimental signature of interactions is the enhanced peak-height correlation length versus an experimental magnetic field. We calculate the parametric peak-height correlator in the random interaction matrix model whose single-particle Hamiltonian is modeled by a Gaussian process. We find an increase in peak-height correlation length with the interaction fluctuation strength, that explains qualitatively the experimental observations. A microscopic understanding of the peak-spacing distribution requires the inclusion of the spin degrees of freedom. We introduce the Hartree-Fock-Koopmans approach for electrons with spin and calculate the Coulomb-blockade spacing statistics in quantum dots with a large number of electrons and at low temperatures. We account for the exchange interaction, as well as the fluctuations of interaction matrix elements to leading order in inverse Thouless conductance. We explain various features of the experimental peak-spacing distributions, including the absence of bimodality.

Khandelwal, Swati

377

Coulomb blockade spectroscopy of tunnel-coupled quantum dots  

NASA Astrophysics Data System (ADS)

This thesis presents experimental studies of interactions in systems of coupled quantum dots. Quantum dots are often referred to as "artificial atoms" because the number of electrons on a dot is quantized, and those electrons occupy quantized energy levels. Two quantum dots coupled together by interdot electron tunneling may be considered an "artificial molecule". In this thesis we study artificial molecules composed of two quantum dots connected in series and use Coulomb blockade spectroscopy to measure the analog of a molecular binding energy. These measurements reveal how the effects of charge quantization on each individual dot are destroyed as interdot electron tunneling increases in both zero and strong magnetic fields. In one set of experiments, we use transport measurements to monitor the double dot charge configuration as interdot electron tunneling is increased from near zero, where the dots are almost completely separated, to strong tunneling, where they are entirely joined by quantum mechanical charge sharing. These measurements demonstrate that in zero magnetic field, charge quantization effects on the two individual dots are destroyed when the interdot tunnel conductance is exactly 2esp2/h. The charging diagram is shown to evolve in quantitative agreement with recent many body theories. In other experiments, we study double quantum dots in the quantum Hall regime by applying a strong perpendicular magnetic field to the sample. We find that charge quantization weakens as the quantum Hall edge states on the two dots join, with quantization effects completely destroyed at esp2/h of interdot tunnel conductance. Finally, we find that as the magnetic field is varied, the electron distribution readjusts to minimize the energy. The adjustments form a pattern that repeats with magnetic field and with the addition of electrons.

Livermore, Carol

378

Quantum Dot Enabled Molecular Sensing and Diagnostics  

PubMed Central

Since its emergence, semiconductor nanoparticles known as quantum dots (QDs) have drawn considerable attention and have quickly extended their applicability to numerous fields within the life sciences. This is largely due to their unique optical properties such as high brightness and narrow emission band as well as other advantages over traditional organic fluorophores. New molecular sensing strategies based on QDs have been developed in pursuit of high sensitivity, high throughput, and multiplexing capabilities. For traditional biological applications, QDs have already begun to replace traditional organic fluorophores to serve as simple fluorescent reporters in immunoassays, microarrays, fluorescent imaging applications, and other assay platforms. In addition, smarter, more advanced QD probes such as quantum dot fluorescence resonance energy transfer (QD-FRET) sensors, quenching sensors, and barcoding systems are paving the way for highly-sensitive genetic and epigenetic detection of diseases, multiplexed identification of infectious pathogens, and tracking of intracellular drug and gene delivery. When combined with microfluidics and confocal fluorescence spectroscopy, the detection limit is further enhanced to single molecule level. Recently, investigations have revealed that QDs participate in series of new phenomena and exhibit interesting non-photoluminescent properties. Some of these new findings are now being incorporated into novel assays for gene copy number variation (CNV) studies and DNA methylation analysis with improved quantification resolution. Herein, we provide a comprehensive review on the latest developments of QD based molecular diagnostic platforms in which QD plays a versatile and essential role.

Zhang, Yi; Wang, Tza-Huei

2012-01-01

379

Nanotwinning in CdS quantum dots  

NASA Astrophysics Data System (ADS)

High resolution transmission electron microscopy, X-ray diffraction and photoluminescence measurements are carried out in order to study the defects in CdS quantum dots (QDs), synthesized in cubic phase by chemical co-precipitation method. The nanotwinning structures in CdS quantum dots (˜2.7 nm) are reported for the first time. Mostly CdS QDs are characterized by existence of nanotwin structures. The twinning structures are present together with stacking faults in some QDs while others exist with grain boundaries. Raman spectroscopy analysis shows intense and broad peaks corresponding to fundamental optical phonon mode (LO) and the first over tone mode (2LO) of CdS at 302 cm-1 and 605 cm-1 respectively. A noticeable shift is observed in Raman lines indicating the effect of phonon confinement. Fourier transform infrared spectroscopy analysis confirms the presence of Cd-S stretching bands at 661 cm-1 and 706 cm-1. The photoluminescence spectrum shows emission in yellow and red regions of visible spectrum. The presence of stacking faults and other defects are explained on the basis of X-rays diffraction patterns and are correlated with photoluminescence spectrum. These nanotwinning and microstructural defects are responsible for different emissions from CdS QDs.

Kumar, Pragati; Saxena, Nupur; Singh, F.; Agarwal, Avinash

2012-09-01

380

Nonlinear thermoelectric response of quantum dots  

NASA Astrophysics Data System (ADS)

The thermoelectric transport properties of nanostructured devices continue to attract attention from theorists and experimentalist alike as the spatial confinement allows for a controlled approach to transport properties of correlated matter. Most of the existing work, however, focuses on thermoelectric transport in the linear regime despite the fact that the nonlinear conductance of correlated quantum dots has been studied in some detail throughout the last decade. To go beyond the linear response regime, we use a recently developed scheme [1], to address the low-energy behavior near the strong-coupling fixed point at finite bias voltage and finite temperature drop at the quantum dot. We test the reliability of the method against the numerical renormalization group [2] and determine the charge, energy, and heat current through the nanostructure. This allows us to determine the nonlinear transport coefficients, the entropy production, and the fate of the Wiedemann-Franz law in the non-thermal steady-state [3].[4pt] [1] E. Munoz et al, arXiv:1111.4076.[0pt] [2] L. Merker et al, in preparation.[0pt] [3] S. Kirchner, F. Zamani, and E. Munoz, in ``New Materials for Thermoelectric Applications: Theory and Experiment,'' Springer (2012).

Kirchner, Stefan; Zamani, Farzaneh; Munoz, Enrique; Merker, Lukas; Costi, Theo

2013-03-01

381

Electrical transport phenomena in systems of semiconductor quantum dots.  

PubMed

While a fairly good understanding of optical and transport properties that are associated with single quantum dots has emerged in recent years the understanding of the relation between these properties and the observed macroscopic optical and electrical properties of solid ensembles of such dots is still at a very rudimentary level. This is in particular so in regard to the transport properties where the interplay between inter-dot conduction and the connectivity of the dots network determines the macroscopic observations. Reviewing the basic concepts and issues associated with these two essential ingredients, and considering some recent experimental observations on quantum dot ensembles of CdSe and Si, an effort is made here to derive a whole-but-simple physical basis for the understanding of the transport and the optoelectronic properties of solid state ensemble of semiconductor quantum dots. PMID:18464401

Balberg, Isaac

2008-02-01

382

Open quantum dots in graphene: Scaling relativistic pointer states  

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

383

Optically induced entanglement of excitons in a single quantum Dot  

PubMed

Optically induced entanglement is identified by the spectrum of the phase-sensitive homodyne-detected coherent nonlinear optical response in a single gallium arsenide quantum dot. The electron-hole entanglement involves two magneto-excitonic states differing in transition energy and polarization. The strong coupling needed for entanglement is provided through the Coulomb interaction involving the electrons and holes. The result presents a first step toward the optical realization of quantum logic operations using two or more quantum dots. PMID:10988065

Chen; Bonadeo; Steel; Gammon; Katzer; Park; Sham

2000-09-15

384

Spin-resolved quantum-dot resonance fluorescence  

Microsoft Academic Search

Confined spins in self-assembled semiconductor quantum dots promise to serve both as probes for studying mesoscopic physics in the solid state and as stationary qubits for quantum-information science. Moreover, the excitations of self-assembled quantum dots can interact with near-infrared photons, providing an interface between stationary and `flying' qubits. Here, we report the observation of spin-selective photon emission from a resonantly

A. Nick Vamivakas; Yong Zhao; Chao-Yang Lu; Mete Atatüre

2009-01-01

385

Tuning of Long range Visible Emissions Using Coupled Quantum Dots  

NASA Astrophysics Data System (ADS)

Size and shape controlled semiconductor quantum dots have been widely adopted in tailoring nanomaterials properties. Alternatively, chemically coupled quantum dots offer a novel route for tuning long range electronic transitions of semiconductors via band offset engineering at the material interface. We report on a simple route of tailoring visible emissions over long range by chemically designing coupled dots comprising of ZnSe and CdS quantum dots. Long range tunability of visible emissions originated from strong interdot dispersion, which can not be realized from individual quantum dots. The first principles electronic structure calculations based on density functional theory reveals the type-II nature of chemical bonding at CdS/ZnSe interface which plays a crucial role in tailoring the long range emissions.

Sengupta, Sucheta; Ganguli, Nirmal; Dasgupta, I.; Sarma, D. D.; Acharya, Somobrata

2011-07-01

386

Electrospray organometallic chemical vapor deposition—A novel technique for preparation of II–VI quantum dot composites  

Microsoft Academic Search

A novel technique combining electrospray and organometallic chemical vapor deposition (OMCVD) has been developed for the synthesis of new II–VI quantum dot composites. CdSe nanocrystals (quantum dots) of selected size are dispersed in a pyridine\\/acetonitrile mixture. The nanocrystals are transferred by electrospray into the growth zone of an OMCVD reactor and codeposited on a ZnSe matrix grown from hydrogen selenide

M. Danek; K. F. Jensen; C. B. Murray; M. G. Bawendi

1994-01-01

387

Quantum-Dot Cellular Automata: Line and Majority Logic Gate  

NASA Astrophysics Data System (ADS)

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 devices presented are QCA cells where the dots are metal islands, coupled by capacitors and tunnel junctions. A line of three two-dot cells is presented, which demonstrates that there are no metastable states in a QCA line. The final experiment presented is a QCA majority gate, a programmable AND/OR logic gate.

Snider, Gregory; Orlov, Alexei; Amlani, Islamshah; Bernstein, Gary; Lent, Craig; Merz, James; Porod, Wolfgang

1999-12-01

388

Luminescence properties of In(Zn)P alloy core\\/ZnS shell quantum dots  

Microsoft Academic Search

Chemically synthesized InP\\/ZnS core\\/shell quantum dots (QDs) are studied using time-resolved photoluminescence spectroscopy and x-ray diffraction. Zinc stearate, which is added during the synthesis of the InP core, significantly improves the optical characteristics of the QDs. The luminescence quantum yield (QY) reaches 60%-70% and the emission is tunable from 485 to 586 nm by varying the Zn2+:In3+ molar ratio and

Ung Thi Dieu Thuy; Peter Reiss; Nguyen Quang Liem

2010-01-01

389

Luminescence properties of In(Zn)P alloy core\\/ZnS shell quantum dots  

Microsoft Academic Search

Chemically synthesized InP\\/ZnS core\\/shell quantum dots (QDs) are studied using time-resolved photoluminescence spectroscopy and x-ray diffraction. Zinc stearate, which is added during the synthesis of the InP core, significantly improves the optical characteristics of the QDs. The luminescence quantum yield (QY) reaches 60%–70% and the emission is tunable from 485 to 586 nm by varying the Zn2+:In3+ molar ratio and

Ung Thi Dieu Thuy; Peter Reiss; Nguyen Quang Liem

2010-01-01

390

Photoluminescence of ZnO quantum dots produced by a sol–gel process  

Microsoft Academic Search

We report synthesis and spectroscopic characterization of sol–gel derived zinc oxide (ZnO) quantum dots (Qdots) of 3–8nm size. The Qdots exhibited a broad and strong visible emission peak centered near 520nm with a quantum efficiency of approximately 5%. A weak ultraviolet (UV) emission peak was also observed near the band gap at 370nm. The integrated area under the curve for

Debasis Bera; Lei Qian; Subir Sabui; Swadeshmukul Santra; Paul H. Holloway

2008-01-01

391

Determination of the size of quantum dots by fluorescence spectroscopy.  

PubMed

There has been a lack of quick, simple and reliable methods for determination of nanoparticle size. An investigation of the size of hydrophobic (CdSe) and hydrophilic (CdSe/ZnS) quantum dots was performed by using the maximum position of the corresponding fluorescence spectrum. It has been found that fluorescence spectroscopy is a simple and reliable methodology to estimate the size of both quantum dot types. For a given solution, the homogeneity of the size of quantum dots is correlated to the relationship between the fluorescence maximum position (FMP) and the quantum dot size. This methodology can be extended to the other fluorescent nanoparticles. The employment of evolving factor analysis and multivariate curve resolution-alternating least squares for decomposition of the series of quantum dots fluorescence spectra recorded by a specific measuring procedure reveals the number of quantum dot fractions having different diameters. The size of the quantum dots in a particular group is defined by the FMP of the corresponding component in the decomposed spectrum. These results show that a combination of the fluorescence and appropriate statistical method for decomposition of the emission spectra of nanoparticles may be a quick and trusted method for the screening of the inhomogeneity of their solution. PMID:21491050

Mutavdži?, Dragosav; Xu, Jianmin; Thakur, Garima; Triulzi, Robert; Kasas, Sandor; Jeremi?, Milorad; Leblanc, Roger; Radoti?, Ksenija

2011-04-14

392

Single spins in self-assembled quantum dots.  

PubMed

Self-assembled quantum dots have excellent photonic properties. For instance, a single quantum dot is a high-brightness, narrow-linewidth source of single photons. Furthermore, the environment of a single quantum dot can be tailored relatively easily using semiconductor heterostructure and post-growth processing techniques, enabling electrical control of the quantum dot charge and control over the photonic modes with which the quantum dot interacts. A single electron or hole trapped inside a quantum dot has spintronics applications. Although the spin dephasing is rather rapid, a single spin can be manipulated using optical techniques on subnanosecond timescales. Optical experiments are also providing new insights into old issues, such as the central spin problem. This Review provides a snapshot of this active field, with some indications for the future. It covers the basic materials and optical properties of single quantum dots, techniques for initializing, manipulating and reading out single spin qubits, and the mechanisms that limit the electron-spin and hole-spin coherence. PMID:23695745

Warburton, Richard J

2013-06-01

393

Single spins in self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

Self-assembled quantum dots have excellent photonic properties. For instance, a single quantum dot is a high-brightness, narrow-linewidth source of single photons. Furthermore, the environment of a single quantum dot can be tailored relatively easily using semiconductor heterostructure and post-growth processing techniques, enabling electrical control of the quantum dot charge and control over the photonic modes with which the quantum dot interacts. A single electron or hole trapped inside a quantum dot has spintronics applications. Although the spin dephasing is rather rapid, a single spin can be manipulated using optical techniques on subnanosecond timescales. Optical experiments are also providing new insights into old issues, such as the central spin problem. This Review provides a snapshot of this active field, with some indications for the future. It covers the basic materials and optical properties of single quantum dots, techniques for initializing, manipulating and reading out single spin qubits, and the mechanisms that limit the electron-spin and hole-spin coherence.

Warburton, Richard J.

2013-06-01

394

Quantum dot: magic nanoparticle for imaging, detection and targeting.  

PubMed

Quantum dots (QDs) are one of the nanoparticles that use in Imaging, Detection and Targeting. Quantum dots are nanometer-size luminescent semiconductor crystals and have unique chemical and physical properties due to their size and their highly compact structure. They emit different wavelengths over a broad range of the light spectrum from visible to infrared, depending on their size and chemical composi tion. Eventual use of quantum dots to dramatically improve clinical diagnostic tests for the early detection of cancer. The use of quantum dots heralds a revolution in biological imaging. The current and widely used organic fluorophores have two shortcomings associated with their fluorescence. Signals from the labeled molecules can be obscured by cell autofluorescence, occurring in the visible spectrum and by photobleaching which seriously limits observation time. Colloidal quantum dots are bright, photostable fluorophores of a few nanometers in diameter. Because their size approximates that of individual biomolecules, water-solubl quantum dot complex have been used to target and image tumor cells. Despite their advantages the best materials for quantum dots; cadmium sulfide, CdS and cadmium selenide, CdSe can be highly toxic. While enhancing the biocompatibility of this nanoparticle various encapsulation techniques have also aided in their water-dispersibility and functionalization. QDs were introduced to cell biology as alternative fluorescent probes in recent years. Traditional fluorophores, e.g. organic dyes and fluorescent proteins are limited by thei narrow absorption range, broad emission spectra and short fluorescent lifetime. PMID:19848055

Ghasemi, Younes; Peymani, Payam; Afifi, Saba

2009-08-01

395

Spintronics and Quantum Dots for Quantum Computing and Quantum Communication  

Microsoft Academic Search

Control over electron-spin states, such as coherent manipulation, filtering and measurement promises access to new technologies in conventional as well as in quantum computation and quantum communication. We review our proposal of using electron spins in quantum confined structures as qubits and discuss the requirements for implementing a quantum computer. We describe several realizations of one- and two-qubit gates and

Guido Burkard; Hans-Andreas Engel; Daniel Loss

2000-01-01

396

Electron-spin resonance in a quantum dot  

NASA Astrophysics Data System (ADS)

We discuss electron-spin resonance in a single quantum dot at filling factor ?<~2. The exchange interaction leads to an enhanced effective g*eff factor, which in turn gives rise to spatially separated regions of compressible and incompressible states with different spin orientations in the dot. These can be treated as electrostatically coupled dot systems within the original dot. Transport measurements under microwave radiation provide an experimental tool to induce spin transitions between these dots. Measurements indicating a spin-flip transition are presented.

Blick, Robert H.; Gudmundsson, Vidar; Haug, Rolf J.; von Klitzing, Klaus; Eberl, Karl

1998-05-01

397

Minimized deterioration of ultrashort pulses in quantum dot optical amplifiers  

NASA Astrophysics Data System (ADS)

The dynamics of ultrashort pulses propagating in a quantum dot amplifier is determined by a complex nonlinear coupling and dynamic interplay of light fields and carriers in the spatially inhomogeneous quantum dot ensemble. Computational modeling shows that in spite of the large complexity the strong localization of the carrier inversion and the low amplitude phase coupling may allow the amplification and transmission of ultrahort light pulses with minimum deterioration of the pulse properties (e.g. pulse shape, duration). The theoretical description is based on spatially resolved Quantum Dot Maxwell-Bloch equations that describe the spatio-temporal light field and inter-/intra-level carrier dynamics in each quantum dot of a typical quantum dot ensemble. In particular, this includes spontaneous luminescence, counterpropagation of amplified spontaneous emission and induced recombination as well as carrier diffusion in the wetting layer of the laser. Intradot scattering via emission and absorption of phonons, as well as the scattering with the carriers and phonons of the surrounding wetting layer are dynamically included on a mesoscopic level. Spatial fluctuations in size and energy levels of the quantum dots and irregularities in the spatial distribution of the quantum dots in the active layer are simulated via statistical methods. Simulation results of the nonlinear pulse propagation in quantum dot optical amplifiers allow visualization and interpretation of fundamental nonlinear processes such as selective depletion and re-filling of quantum dot energy levels leading to a complex gain and index dynamics that affect the amplitude and phase of a propagating light pulse. Computational modelling thus may lay the foundation for an optimization and tayloring of pulse properties.

Gehrig, Edeltraud; Hess, Ortwin G.

2004-09-01

398

GaSb quantum dot growth using InAs quantum dot stressors  

Microsoft Academic Search

Metalorganic vapor phase epitaxy of GaSb quantum dots (QDs) grown on top of a layer of InAs seed QDs shows a vertically aligned correlation if thin GaAs spacer layers deposited at low temperature are used. Introduction of an annealing step after spacer deposition strongly improves the crystalline quality of the spacer layer. Vertically anticorrelated ordering is found on annealed spacers

L. Müller-Kirsch; N. N. Ledentsov; R. Sellin; U. W. Pohl; D. Bimberg; I. Häusler; H. Kirmse; W. Neumann

2003-01-01

399

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

NASA Astrophysics Data System (ADS)

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 of fiber-optic communications (1.3--1.5 microm). The broad absorption spectrum of these quantum dots can be used for solar light-harvesting applications, to which end the results of Chapter 2---where we study Forster resonance energy transfer in quantum dot solids---provide remarkable insights into photon emission from quantum-dot based solar cells. In subsequent chapters, we explore quantum-dot photonic crystal applications, where exciton-photon interactions in the cavity environment remarkably allow for the emission of indistinguishable single photons that are important for distribution of high-security quantum keys---being highly sensitive to 'eavesdropping'. Particularly, the suggestion of the solution-processed QED system is novel compared to traditional self-assembled systems, and as we will discuss, offer integration and processing capabilities that are unprecedented, and perform well at wavelength ranges where standard QED systems scale poorly. The results of chapters 3--6 are therefore significant in the general field of cavity quantum electrodynamics.

Bose, Ranojoy

400

Energy levels in self-assembled quantum arbitrarily shaped dots.  

PubMed

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

Tablero, C

2005-02-01

401

Tracking bio-molecules in live cells using quantum dots  

PubMed Central

Single particle tracking (SPT) techniques were developed to explore bio-molecules dynamics in live cells at single molecule sensitivity and nanometer spatial resolution. Recent developments in quantum dots (Qdots) surface coating and bio-conjugation schemes have made them most suitable probes for live cell applications. Here we review recent advancements in using quantum dots as SPT probes for live cell experiments. The trajectory of single quantum dot bound to avidin-GPI (in black) is overlaid with the mean intensity of caveolin-1-EGFP (in green) to allow colocalization studies of avidin-GPI with caveolae.

Chang, Yun-Pei; Pinaud, Fabien; Antelman, Joshua; Weiss, Shimon

2009-01-01

402

Size-Dependent Photoluminescence and Electroluminescence of Colloidal CdSe Quantum Dots  

NASA Astrophysics Data System (ADS)

Here we adopt a convenient green chemical route for synthesis of CdSe quantum dots, their characterization by UV/Vis absorption spectroscopy, X-ray diffraction study and transmission electron microscopy. We carry out photoluminescence and electroluminescence spectroscopy to investigate the variation in electro-optical property with size. By UV/Vis spectroscopy, blue shift is revealed and bandgap is also calculated. X-ray diffraction spectrum reveals cubic structure and transmission electron micrographs show quantum dots of different size distributions (in the range 2-8 nm). Both the luminescence spectroscopies reveal green-orange luminescence depending upon the size distribution and indicate the possibility of using CdSe quantum dots as light emitting devices with better compatibility and faster response.

Dey, S. C.; Nath, S. S.

2013-04-01

403

Synthesis of crystalline Si quantum dots by millisecond laser irradiation of SiO{sub x}N{sub y} layers  

SciTech Connect

We demonstrated that the timescale for Si quantum dot (Si-QD) formation in a SiO{sub x}N{sub y} layer is a few milliseconds by IR laser irradiation. The amount of Si agglomerated into QD in a laser irradiated SiO{sub x}N{sub y} layer is comparable to that calculated after furnace annealing at 1250 deg. C for 30 min. However, we found that crystalline Si-QD can be formed by laser only if the amount of Si atoms in excess is as high as 1x10{sup 22}/cm{sup 3}. The Si-QD contains impurities like N and O that prevent luminescence at 900 nm. The photoluminescence (PL) signal is recorded only after an additional annealing after laser irradiation at temperatures above 1000 deg. C when diffusion-assisted replacement of N and O occurs.

Mannino, Giovanni; Spinella, Corrado; Bongiorno, Corrado; Nicotra, Giuseppe; Mercorillo, Flora; Privitera, Vittorio [CNR-IMM, VIII Strada n deg. 5, 95121 Catania (Italy); Franzo, Giorgia; Piro, Alberto Maria; Grimaldi, MariaGrazia [CNR-INFM-MATIS, Via Santa Sofia 64, 95124 Catania (Italy); Di Stefano, Maria Ausilia; Di Marco, Silvestra [STMicroelectronics, Stradale Primosole 50, 95121 Catania (Italy)

2010-01-15

404

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

NASA Astrophysics Data System (ADS)

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 red light emitting (CdSe)ZnSe quantum dots (as a colour conversion centre) with a near-UV(NUV) GaN LED chip (as an excitation source). A few good red phosphors have been known for UV excitation wavelengths, and red phosphors for UV excitation have been sought for a long time. Here we tested the possibility of using (CdSe)ZnSe QDs as red nanophosphors for UV excitation. The fabricated red light emitting hybrid device of (CdSe)ZnSe and a NUV GaN LED chip showed a good luminance. We demonstrated that the (CdSe)ZnSe quantum dots were promising red nanophosphors for NUV excitation and that a red LED made of QDs and a NUV excitation source was a highly efficient hybrid device.

Song, Hongjoo; Lee, Seonghoon

2007-06-01

405

Highly Fluorescent Noble-Metal Quantum Dots  

NASA Astrophysics Data System (ADS)

Highly fluorescent, water-soluble, few-atom noble-metal quantum dots have been created that behave as multielectron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near infrared. These molecular metals exhibit highly polarizable transitions and scale in size according to the simple relation EFermi/N1/3, predicted by the free-electron model of metallic behavior. This simple scaling indicates that fluorescence arises from intraband transitions of free electrons, and these conduction-electron transitions are the low-number limit of the plasmon—the collective dipole oscillations occurring when a continuous density of states is reached. Providing the missing link between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy-transfer pairs, and light-emitting sources in nanoscale optoelectronics.

Zheng, Jie; Nicovich, Philip R.; Dickson, Robert M.

2007-05-01

406

Self-Formation of Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

We reviewed the self-formation control of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. Uniform InAs/GaAs QDs were demonstrated by self-size-limiting effect, the optimized capping growth, and the closely stacked growth using the nanoholes. High-density InAs QDs were achieved by Sb-mediated growth. In addition, an intermittent growth method was presented for ultralow density InAs QDs. Furthermore, the vertical and in-plane arrangements of InAs/GaAs QDs were attempted by using the strain-controlled underlying layers. One-dimensional QD chains were spontaneously formed along the [1-10] direction on the GaAs/InGaAs/GaAs(001) buffer layers. Two-dimensional arrangement of InAs QDs was demonstrated by using GaAsSb/GaAs(001) buffer layers.

Yamaguchi, Koichi

407

Self-Formation of Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

We reviewed the self-formation control of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. Uniform InAs/GaAs QDs were demonstrated by self size-limiting effect, the optimized capping growth, and the closely-stacked growth using the nanoholes. High-density InAs QDs were achieved by Sb-mediated growth. In addition, an intermittent growth method was presented for ultra-low density InAs QDs. Furthermore, the vertical and in-plane arrangements of InAs/GaAs QDs were attempted by using the strain-controlled underlying layers. One-dimensional QD chains were spontaneously formed along the [1-10] direction on the GaAs/InGaAs/GaAs(001) buffer layers. Two-dimensional arrangement of InAs QDs was demonstrated by using GaAsSb/GaAs(001) buffer layers.

Yamaguchi, Koichi

408

Antimony-based quantum dot memories  

NASA Astrophysics Data System (ADS)

As a type-II heterostructure with exclusive hole confinement GaSb/(Al,Ga)As QDs are an ideal candidate for a QD based memory device operating at room temperature. We investigated different Antimony-based QDs in respect of localization energies and storage times with 8-band-k•p calculations as well as time-resolved capacitance spectroscopy. In addition, we present a memory concept based on self-organized quantum dots (QDs) which could fuse the advantages of today's main semiconductor memories DRAM and Flash. First results on the performance of such a memory cell are shown and a closer look at Sb-based QDs as a storage unit is taken.

Bimberg, Dieter; Marent, Andreas; Nowozin, Tobias; Schliwa, Andrei

2011-02-01

409

Semiconductor quantum dot-inorganic nanotube hybrids.  

PubMed

A synthetic route for preparation of inorganic WS(2) nanotube (INT)-colloidal semiconductor quantum dot (QD) hybrid structures is developed, and transient carrier dynamics on these hybrids are studied via transient photoluminescence spectroscopy utilizing several different types of QDs. Measurements reveal efficient resonant energy transfer from the QDs to the INT upon photoexcitation, provided that the QD emission is at a higher energy than the INT direct gap. Charge transfer in the hybrid system, characterized using QDs with band gaps below the INT direct gap, is found to be absent. This is attributed to the presence of an organic barrier layer due to the relatively long-chain organic ligands of the QDs under study. This system, analogous to carbon nanotube-QD hybrids, holds potential for a variety of applications, including photovoltaics, luminescence tagging and optoelectronics. PMID:22354096

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

2012-02-21

410

[Application of quantum dots in biomedical detection].  

PubMed

Semiconductor quantum dots (QDs) are a new kind of biological fluorescence material, which has many advantages, such as broad excitation spectra, tunable emission spectra and good photostability. In the field of biomedical detection, the problems encountered in the traditional organic dye-based biomedical detections, such as short fluorescence lifetime and failure to simultaneous excitation of multiple colors, can be solved by using QDs. Water-soluble QDs combined with specific bio-molecules can label targeting bio-compound, which is useful in bio-molecule detection, cell labeling, tissue imaging, and can be used in fluorescence resonance energy transfer (FRET) technology. Combining QDs and protein chip technology to develop a new technology to detect multiple kinds of tumor markers will be one of the promising clinical applications of QDs with greater sensitivity, specificity, rapidity and convenience. PMID:21774239

Zhang, Luyao; Niu, Wanting; Yang, Hao; Pan, Min

2011-06-01

411

Carrier Dynamics in Colloidal Graphene Quantum Dots  

NASA Astrophysics Data System (ADS)

We describe carrier dynamics for single and multiple excitons in colloidal graphene quantum dots (GQDs). Strong confinement and corresponding size-tunable electronic structure make GQDs potentially useful sensitizers in photovoltaic devices. We have studied the optical response of GQDs consisting of 132 and 168 sp^2 hybridized carbon atoms dissolved in toluene with HOMO-LUMO transitions of 1.4-1.6 eV. From measurements of ultrafast (˜100 fs) transient absorption over nanosecond timescales, we extract the single-photon absorption cross-section and observe carrier-induced Stark shifts of the order of 0.1 eV indicating strong carrier-carrier interactions, as expected for the relatively weak screening of a two-dimensional nanostructure. Multiexcitons are observed to decay nonradiatively on ˜1 to 20 ps timescales, while single excitons display dynamics on multiple timescales due to carrier cooling, singlet-to-triplet intersystem crossing, and, on nanosecond to microsecond timescales, radiative recombination.

Sun, Cheng; Yan, Xin; Li, Liang-Shi; McGuire, John A.

2011-03-01

412

Multifunctional Quantum Dots for Personalized Medicine  

PubMed Central

Successes in biomedical research and state-of-the-art medicine have undoubtedly improved the quality of life. However, a number of diseases, such as cancer, immunodeficiencies, and neurological disorders, still evade conventional diagnostic and therapeutic approaches. A transformation towards personalized medicine may help to combat these diseases. For this, identification of disease molecular fingerprints and their association with prognosis and targeted therapy must become available. Quantum dots (QDs), semiconductor nanocrystals with unique photo-physical properties, represent a novel class of fluorescence probes to address many of the needs of personalized medicine. This review outlines the properties of QDs that make them a suitable platform for advancing personalized medicine, examines several proof-of-concept studies showing utility of QDs for clinically relevant applications, and discusses current challenges in introducing QDs into clinical practice.

Zrazhevskiy, Pavel; Gao, Xiaohu

2009-01-01

413

Luminescence studies of individual quantum dot photocatalysts.  

PubMed

Using far-field optical microscopy we report the first measurements of photoluminescence from single nanoparticle photocatalysts. Fluence-dependent luminescence is investigated from metal-semiconductor heterojunction quantum dot catalysts exposed to a variety of environments, ranging from gaseous argon to liquid water containing a selection of hole scavengers. The catalysts each exhibit characteristic nonlinear fluence dependence. From these structurally and environmentally sensitive trends, we disentangle the separate rate-determining steps in each particle across the very wide range of time scales, which follow the initial light absorption process. This information will significantly benefit the design of effective artificial photocatalytic systems for renewable direct solar-to-fuel energy conversion. PMID:23895591

Amirav, Lilac; Alivisatos, A Paul

2013-08-26

414

Efficient electron spin detection using positively charged quantum dots  

Microsoft Academic Search

The efficient detection of spin polarized carriers is a crucial issue for the design of semiconductor based spintronics devices. Spin detection using the degree of circular polarization of the luminescence from a quantum well has been demonstrated[1]. Quantum dots (QDs) are especially attractive for detection of spin polarized carriers[2] owing to their long spin lifetimes and large internal quantum efficiency[3].

Kenan Gundogdu; Kimberley Hall; Lin Zhang; Thomas Boggess; Dennis Deppe; Oleg Shchekin

2003-01-01

415

Broad-band superluminescent light-emitting diodes incorporating quantum dots in compositionally modulated quantum wells  

Microsoft Academic Search

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

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

2006-01-01

416

Wavelet analysis of quantum transient transport in a quantum dot  

NASA Astrophysics Data System (ADS)

We investigate effects of switching speed of a bias voltage on a time-dependent current in a quantum dot with a single energy level, weakly coupled with two electrodes. Our simulations based on non-equilibrium Green's function formalism show that the transient current in the case of the high speed oscillates around the value of the stationary current. On the other hand, the current in the opposite case monotonically changes with time. This difference is explained in terms of the wavelet spectra of the currents, which mainly consist of two time-frequency domains with high intensities.

Sasaoka, Kenji; Yamamoto, Takahiro; Watanabe, Satoshi

2013-06-01

417

Precise Ge quantum dot placement for quantum tunneling devices.  

PubMed

This study demonstrates the precise placement of Ge quantum dots (QDs) in an SiO2 or Si3N4 matrix in a self-organized manner by thermally oxidizing SiGe in nanostructures. The effectiveness of this method is shown by a variety of geometries including nanotrenches, nanorods and polygonal nanocavities. Modulating the structural geometry and peripheral spacer materials effectively places a single Ge QD in the center of an oxidized SiGe nanostructure or individual QDs at the corners (edges). This study also reports the fabrication of Ge QD single-electron devices that exhibit clear Coulomb staircases and differential conductance oscillations at room temperature. PMID:20032557

Chen, Kuan-Hung; Chien, Chung-Yen; Li, Pei-Wen

2009-12-24

418

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

NASA Astrophysics Data System (ADS)

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

SalmanOgli, A.; Rostami, R.

2013-10-01

419

In a "nutshell": intrinsically radio-labeled quantum dots.  

PubMed

Quantum dots (QDs) have many intriguing properties suitable for biomedical imaging applications. The poor tissue penetration of optical imaging in general, including those using QDs, has motivated the development of various QD-based dual-modality imaging agents. In this issue of AJNMMI (http://www.ajnmmi.us), Sun et al. reported the synthesis and in vitro/in vivo characterization of intrinsically radio-labeled QDs (r-QDs), where (109)Cd was incorporated into the core/shell of QDs of various compositions. These r-QDs emit in the near-infrared range, have long circulation half-life, are quite stable with low cytotoxicity, exhibit small size and low accumulation in the reticuloendothelial system, and can allow for accurate measurement of their biodistribution in mice. With these desirable features demonstrated in this study, future development and optimization will further enhance the biomedical potential of intrinsically radio-labeled QDs. PMID:23133808

Cai, Weibo; Hong, Hao

2012-03-28

420

Quantum dots for live cells, in vivo imaging, and diagnostics.  

PubMed

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 receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics. PMID:15681376

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

2005-01-28

421

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

PubMed Central

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 receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.

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

2005-01-01

422

In a "nutshell": intrinsically radio-labeled quantum dots  

PubMed Central

Quantum dots (QDs) have many intriguing properties suitable for biomedical imaging applications. The poor tissue penetration of optical imaging in general, including those using QDs, has motivated the development of various QD-based dual-modality imaging agents. In this issue of AJNMMI (http://www.ajnmmi.us), Sun et al. reported the synthesis and in vitro/in vivo characterization of intrinsically radio-labeled QDs (r-QDs), where 109Cd was incorporated into the core/shell of QDs of various compositions. These r-QDs emit in the near-infrared range, have long circulation half-life, are quite stable with low cytotoxicity, exhibit small size and low accumulation in the reticuloendothelial system, and can allow for accurate measurement of their biodistribution in mice. With these desirable features demonstrated in this study, future development and optimization will further enhance the biomedical potential of intrinsically radio-labeled QDs.

Cai, Weibo; Hong, Hao

2012-01-01

423

Photoluminescence polarization of single InP quantum dots  

SciTech Connect

The linear polarization dependence of photoluminescence emission was measured on single self-assembled InP quantum dots. The dots were obtained by Stranski-Krastanow growth on Ga{sub 0.5}In{sub 0.5}P. The highest-intensity emission occurred for light polarized parallel to the elongation of the dots in agreement with theoretical calculations. The excitation intensity was varied to obtain the polarization dependence of higher (state-filled) levels.

Zwiller, Valery; Jarlskog, Linda; Pistol, Mats-Erik; Pryor, Craig; Castrillo, Pedro; Seifert, Werner; Samuelson, Lars

2001-06-15

424

Long-wavelength infrared quantum-dot based interband photodetectors  

Microsoft Academic Search

We report on the design and fabrication of (Al)GaAs(Sb)\\/InAs tensile strained quantum-dot (QD) based detector material for thermal infrared imaging applications in the long-wavelength infrared (LWIR) regime. The detection is based on transitions between confined dot states and continuum states in a type-II band lineup, and we therefore refer to it as a dot-to-bulk (D2B) infrared photodetector with expected benefits

O. Gustafsson; J. Berggren; U. Ekenberg; A. Hallén; M. Hammar; L. Höglund; A. Karim; B. Noharet; Q. Wang; A. Gromov; S. Almqvist; A. Zhang; S. Junique; J. Y. Andersson; C. Asplund; R. Marcks von Würtemberg; H. Malm; H. Martijn

2011-01-01

425

Quantum theory of dynamic nuclear polarization in quantum dots  

NASA Astrophysics Data System (ADS)

Nuclear spins play a major role in the dynamics of spin qubits in III-V semiconductor quantum dots. Although the hyperfine interaction between nuclear and electron (or hole) spins is typically viewed as the leading source of decoherence in these qubits, understanding how to experimentally control the nuclear spin polarization can not only ameliorate this problem, but in fact turn the nuclear spins into a valuable resource for quantum computing. Beyond extending decoherence times, control of this polarization can enable universal quantum computation as shown in singlet-triplet qubits and, in addition, offers the possibility of repurposing the nuclear spins into a robust quantum memory. In [1], we took a first step toward taking advantage of this resource by developing a general, fully quantum theory of non-unitary electron-nuclear spin dynamics with a periodic train of delta-function pulses as the external control driving the electron spin. Here, we extend this approach to other types of controls and further expand on the predictions and physical insights that emerge from the theory. [1] Edwin Barnes and Sophia E. Economou, Phys. Rev. Lett. 107, 047601 (2011)

Economou, Sophia; Barnes, Edwin

2013-03-01

426

Open quantum dots—probing the quantum to classical transition  

NASA Astrophysics Data System (ADS)

Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zurek's decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.

Ferry, D. K.; Burke, A. M.; Akis, R.; Brunner, R.; Day, T. E.; Meisels, R.; Kuchar, F.; Bird, J. P.; Bennett, B. R.

2011-04-01

427

Engineering of absorbing medium for quantum dot infrared photodetectors  

NASA Astrophysics Data System (ADS)

Quantum well infrared photodetectors are widely used in focal plane arrays operating at liquid nitrogen temperatures. Compared to quantum-well structures, quantum dot (QD) nanomaterials are more flexible to control photoelectron processes by engineering of the nanoscale potential profiles formed by charged quantum dots. Quantum dots with builtin charge (Q-BIC) suppress capture of photoelectrons by QDs and provide strong coupling to infrared radiation. We review design approaches, fabrication and characterization of photodetectors based on Q-BIC media with strong selective doping to increase the built-in dot charge. Characterization of Q-BIC media includes the structural, spectral (photoluminescence measurements) and electrical characterization (dark current, I-V measurements). After several design-growth-characterization cycles we reached relatively high density of quantum dots, small concentration of defects related to quantum dot growth, and suppressed carrier capture by QDs. Optimized Q-BIC media were used for fabrication of Q-BIC IR photodetectors. We studied spectral and temperature dependences of photoresponse and also its dependences on bias voltage and parameters of Q-BIC medium.

Yakimov, M.; Sergeev, A.; Pogrebnyak, V.; Varghese, A.; Tokranov, V.; Thomain, G.; Vagidov, N.; Mitin, V.; Oktyabrsky, S.

2013-09-01

428

Mid-Infrared Quantum Dot Emitters Utilizing Planar Photonic Crystal Technology.  

National Technical Information Service (NTIS)

The three-dimensional confinement inherent in InAs self-assembled quantum dots (SAQDs) yields vastly different optical properties compared to one-dimensionally confined quantum well systems. Intersubband transitions in quantum dots can emit light normal t...

B. Passmore E. A. Shaner G. Subramania J. Cederberg S. K. Lyo

2008-01-01

429

Dynamical localization of double quantum dots with two levels  

Microsoft Academic Search

We study the dynamics of a two-level double quantum dot system under the action of ac electric field, in which two electrons are confined. The results show that, although these electrons always transit between different energy levels, they can be localized in one dot with appropriate parameters. The localization can be significantly influenced by the external parameters, which provides an

Zhe Jiang; Duan Suqing; Xian-Geng Zhao

2005-01-01

430

Interferometric Rayleigh Scattering by Excitons in a Single Quantum Dot  

Microsoft Academic Search

Considerable progress in realizing various regimes of cou- pling between the electromagnetic field and semiconductor quantum dots (QDs) has been achieved recently. Observations of phenomena related to interaction of photons with discrete states in self-assembled dots such as ground state Rabi oscil- lations (1), weak (2, 3, 4) and strong (5, 6) coupling regimes in various microcavity structures have strengthened

Benito Alen; Alexander Hogele; Martin Kroner; Stefan Seidl; Khaled Karrai; Richard J. Warburton; Antonio Badolato; Gilberto Medeiros-Ribeiro; Pierre M. Petroff

2005-01-01

431

Anomalous Kondo Effect in a Quantum Dot at Nonzero Bias  

Microsoft Academic Search

We present measurements on the Kondo effect in a small quantum dot connected strongly to one lead and weakly to the other. The conductance of the dot reveals an offset of the Kondo resonance at zero magnetic field. While the resonance persists in the negative bias regime, it is suppressed in the opposite direction. This demonstrates the pinning of the

F. Simmel; R. H. Blick; J. P. Kotthaus; W. Wegscheider; M. Bichler

1999-01-01

432

Reversible computation with quantum-dot cellular automata (QCA)  

Microsoft Academic Search

Quantum-dot cellular automata (QCA) is a strategy in which binary data is represented by charge configuration within a multi-dot cell. Data is transmitted to nearest neighbors by the Coulombic interaction. An electric field acts as a clock and imposes directionality on circuits. We have explored the connection between logical reversibility and physical reversibility in the context of a QCA system,

Craig S. Lent; Sarah E. Frost; Peter M. Kogge

2005-01-01

433

Spin-Dependent Transport through an Interacting Quantum Dot  

Microsoft Academic Search

We study the nonequilibrium spin transport through a quantum dot coupled to the magnetic electrodes. A formula for the spin-dependent current is obtained and is applied to discuss the linear conductance and magnetoresistance in the interacting regime. We show that the Kondo resonance and the correlation-induced spin splitting of the dot levels may be systematically controlled by internal magnetization in

Ping Zhang; Qi-Kun Xue; Yupeng Wang; X. C. Xie

2002-01-01

434

Characterizing quantum-dot blinking using noise power spectra  

Microsoft Academic Search

Fluctuations in the fluorescence from macroscopic ensembles of colloidal semiconductor quantum dots have the spectral form of 1\\/f noise. The measured power spectral density reflects the fluorescence intermittency of individual dots with power-law distributions of ``on'' and ``off'' times, and can thus serve as a simple method for characterizing such blinking behavior.

Matthew Pelton; David G. Grier; Philippe Guyot-Sionnest

2004-01-01

435

Characterizing quantum-dot blinking using noise power spectra  

NASA Astrophysics Data System (ADS)

Fluctuations in the fluorescence from macroscopic ensembles of colloidal semiconductor quantum dots have the spectral form of 1/f noise. The measured power spectral density reflects the fluorescence intermittency of individual dots with power-law distributions of ``on'' and ``off'' times, and can thus serve as a simple method for characterizing such blinking behavior.

Pelton, Matthew; Grier, David G.; Guyot-Sionnest, Philippe

2004-08-01

436

Effect of strain anisotropies on RHEED patterns of quantum dots  

NASA Astrophysics Data System (ADS)

The strain distributions and of reflection high-energy electron diffraction (RHEED) patterns of uncapped pyramidal shape InAs Stranski Krastanov quantum dots fabricated on GaAs(0 0 1) substrate are investigated theoretically. Three-dimensional strain anisotropy is computed with an atomistic elasticity approach, using inter-atomic Keating potentials and the strain energy is minimized using the conjugate gradient numerical method. RHEED images are predicted in the framework of the kinematical theory, by taking into account the refraction of the electron beam at the quantum dot/vacuum interface. Clear correlation between RHEED image features and quantum dot structural properties is established showing that even rather small strain anisotropies imply noticeable changes in RHEED images stressing the potential of RHEED in detecting and deciphering real-time strain distributions in quantum dots.

Feltrin, A.; Freundlich, A.

2007-04-01

437

Probing of Unembedded Metallic Quantum Dots with Positrons  

SciTech Connect

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

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

2003-08-01

438

Colloidal Quantum Dot Absorption Enhancement in Flexible Fano Filters.  

National Technical Information Service (NTIS)

We report here modified absorption property of colloidal quantum dots (CQDs) inside flexible Fano filters-made of patterned single crystalline silicon nanomembrane transferred onto flexible plastic substrates. Enhanced optical absorption was obtained both...

H. Pang H. Yang L. Chen L. Sun Z. Qiang

2010-01-01

439

Growth of cubic GaN quantum dots  

SciTech Connect

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

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

2010-11-01

440

Quantum Dot Array Formation through Biomolecular Nanopatterning. Phase 1.  

National Technical Information Service (NTIS)

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

H. P. Gillis

1999-01-01