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1

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 Zn 1-xCd xSe 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

2008-02-01

2

Synthesis and characterization of infrared quantum dots  

E-print Network

This thesis focuses on the development of synthetic methods to create application ready quantum dots (QDs) in the infrared for biological imaging and optoelectronic devices. I concentrated primarily on controlling the size ...

Harris, Daniel Kelly

2014-01-01

3

Facile synthesis and photoluminescence mechanism of graphene quantum dots  

NASA Astrophysics Data System (ADS)

We report a facile hydrothermal synthesis of intrinsic fluorescent graphene quantum dots (GQDs) with two-dimensional morphology. This synthesis uses glucose, concentrate sulfuric acid, and deionized water as reagents. Concentrated sulfuric acid is found to play a key role in controlling the transformation of as-prepared hydrothermal products from amorphous carbon nanodots to well-crystallized GQDs. These GQDs show typical absorption characteristic for graphene, and have nearly excitation-independent ultraviolet and blue intrinsic emissions. Temperature-dependent PL measurements have demonstrated strong electron-electron scattering and electron-phonon interactions, suggesting a similar temperature behavior of GQDs to inorganic semiconductor quantum dots. According to optical studies, the ultraviolet emission is found to originate from the recombination of electron-hole pairs localized in the C=C bonds, while the blue emission is from the electron transition of sp2 domains.

Yang, Ping; Zhou, Ligang; Zhang, Shenli; Wan, Neng; Pan, Wei; Shen, Wenzhong

2014-12-01

4

Synthesis and characterization of quantum dot–polymer composites†  

PubMed Central

In this study, we demonstrate a facile and simple synthesis of quantum dot (QD)–polymer composites. Highly fluorescent semiconducting CdSe/ZnS quantum dots were embedded in different commercially available polymers using one easy step. QD–polymer composite nanoparticles were also synthesized using template-assisted synthesis. In particular, we self-assembled lamellar micelles inside nanoporous alumina membranes which were used for the synthesis of mesoporous silica hollow nanotubes and solid nanorods. We observed that the addition of excess free octadecylamine (ODA) in the QD–silica solution resulted in gelation. The gelation time was found to be dependent on free ODA concentration. Similarly, the emission of QD–polymer composites was also found to be dependent on free ODA concentration. Highly purified QDs provided polymer composites that have a much lower emission compared to unpurified nanocomposites. This was attributed to passivation of the QD surfaces by amine, which reduced the surface defects and non-radiative pathways for excited QDs. Finally, highly fluorescent QD–polymer patterns were demonstrated on glass substrates which retained their emission in both polar and non-polar solvents. PMID:19936033

Weaver, Joe; Zakeri, Rashid; Aouadi, Samir

2009-01-01

5

Bioconjugated silicon quantum dots from one-step green synthesis  

NASA Astrophysics Data System (ADS)

Biofunctionalized silicon quantum dots were prepared through a one step strategy avoiding the use of chemical precursors. UV-Vis spectroscopy, Raman spectroscopy and HAADF-STEM prove oligonucleotide conjugation to the surface of silicon nanoparticle with an average size of 4 nm. The nanoparticle size results from the size-quenching effect during in situ conjugation. Photoemissive properties, conjugation efficiency and stability of these pure colloids were studied and demonstrate the bio-application potential, e.g. for nucleic acid vector delivery with semiconducting, biocompatible nanoparticles.Biofunctionalized silicon quantum dots were prepared through a one step strategy avoiding the use of chemical precursors. UV-Vis spectroscopy, Raman spectroscopy and HAADF-STEM prove oligonucleotide conjugation to the surface of silicon nanoparticle with an average size of 4 nm. The nanoparticle size results from the size-quenching effect during in situ conjugation. Photoemissive properties, conjugation efficiency and stability of these pure colloids were studied and demonstrate the bio-application potential, e.g. for nucleic acid vector delivery with semiconducting, biocompatible nanoparticles. Electronic supplementary information (ESI) available: Experimental details of sample preparation, sample characterizations. Additional results of UV-vis, HAADF-STEM, Raman spectroscopy of bioconjugated silicon dots and ICP-OES of deionized water used for the synthesis are presented in Fig. S1, S3, S2, and S4 and Table S2, respectively. See DOI: 10.1039/c2nr11763k

Intartaglia, Romuald; Barchanski, Annette; Bagga, Komal; Genovese, Alessandro; Das, Gobind; Wagener, Philipp; di Fabrizio, Enzo; Diaspro, Alberto; Brandi, Fernando; Barcikowski, Stephan

2012-02-01

6

Synthesis of CdSe quantum dots for quantum dot sensitized solar cell  

SciTech Connect

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

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

2014-04-24

7

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

Microsoft Academic Search

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

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

2005-01-01

8

Quantum Dot Solar Cells  

NASA Astrophysics Data System (ADS)

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

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

2002-10-01

9

Quantum Dot Solar Cells  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

10

Fluorescent quantum dots: Synthesis, biomedical optical imaging, and biosafety assessment.  

PubMed

The marriage of nanomaterials with biology has significantly promoted advancement of biological techniques, profoundly facilitating basic research and practical applications in biological and biomedical fields. Taking advantages of unique optical properties (e.g., strong fluorescence, robust photostability, size-tunable emission wavelengths, etc.), fluorescent quantum dots (QDs), appearing as high-performance biological fluorescent nanoprobes, have been extensively explored for a variety of biomedical optical imaging applications. In this review, we present representative synthetic strategies for preparation of QDs and their applications in biomedical optical imaging, as well as risk assessments in vitro and in vivo. Briefly, we first summarize recent progress in fabrication of QDs via two rudimentary approaches, i.e., organometallic route and aqueous synthesis. Next we present representative achievement in QDs-based in vitro and in vivo biomedical optical imaging applications. We further discuss the toxicity assessment of QDs, ranging from cell studies to animal models. In the final section, we discuss challenges and perspectives for the QDs-relative bioapplications in the future. PMID:25224376

Ji, Xiaoyuan; Peng, Fei; Zhong, Yiling; Su, Yuanyuan; He, Yao

2014-12-01

11

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

12

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

PubMed

This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using (1)H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales. PMID:21727983

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

2011-08-01

13

Improvement of the luminescent properties of cadmium sulfide quantum dots by a post-synthesis modification  

NASA Astrophysics Data System (ADS)

Here the improvement of the luminescent properties of CdS quantum dots by a post-synthesis modification with aqueous solutions of NaOH at different concentrations is presented. The CdS quantum dots were synthesized by a microwave-assisted method using citrate ions as stabilizer. The addition of the hydroxide ions increased the intensity of the orange-red emission by about 80%. Besides, a violet-blue emission was achieved by means of this post-synthesis modification. The hydroxide ions control the precipitation equilibria of the CdS and Cd(OH)2, dissolving and precipitating the surface of the quantum dots. The NaOH treatment increases the number of traps, which produces less band-edge and more deep-trap emission, which explains the decrease and increase in the intensity of the violet-blue and orange-red emissions, respectively.

López, Israel; Gómez, Idalia

2014-11-01

14

Microwave accelerated one-minute synthesis of luminescent ZnO quantum dots  

NASA Astrophysics Data System (ADS)

In this paper we present microwave assisted non-aqueous synthesis of ZnO quantum dots (QDs) by hydrolyzing zinc acetate with lithium hydroxide in ethanol under microwave heating. The processing time for QDs was reduced to few minutes when compared with time consuming sol-gel chemistry. The prepared QDs show good colloidal stability along with stable visible emission.

Asok, Adersh; Kulkarni, A. R.; Gandhi, Mayuri N.

2013-02-01

15

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

SciTech Connect

Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30?nm, and absorption peak from 475?nm to 510?nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO{sub 2} electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO{sub 2}'s to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO{sub 2}. The resulting green synthesized CdSe QDSCs with Cu{sub 2}S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn; Chen, Guorong, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Zhang, Bo [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China)

2014-05-21

16

Synthesis and application of quantum dots-based biosensor  

NASA Astrophysics Data System (ADS)

Trichlorfon (TF) is one of the organophosphorus pesticides used widely in agriculture. The content of this paper includes the exploitation of dominant optical properties of the quantum dots consisting of a core and multilayer shell CdSe/ZnSe/ZnS (QD). A biosensor was fabricated on the basis of this QD for rapidly detecting the residues of trichlofon pesticide with concentrations of 0.01 ppm to 5 ppm. The measurements were carried out to examine the morphology of the QD structure and fluorescent properties such as transmission electron microscopy, x-ray diffraction, absorption spectroscopy and fluorescence spectroscopy. The linking mechanism among biological agents and the specificity of the acetylcholinesterase enzymes in hydrolysis reaction of acetylthiolcholine was applied to create the changes in surroundings, affecting the fluorescence of the QD. In particular, the mechanism of bioluminescence resonance energy transfer (BRET) is discussed to clearly explain the recombination of electrons and holes in the QD.

Hai Nguyen, Ngoc; Giang Duong, Thi; Hoang, Van Nong; Thang Pham, Nam; Cao Dao, Tran; Nga Pham, Thu

2015-03-01

17

Synthesis and characterization of quantum dots designed for biomedical use.  

PubMed

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

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

2014-05-15

18

Synthesis of indium sulphide quantum dots in perfluoronated ionomer membrane  

SciTech Connect

In this paper, we demonstrate a simple and efficient method for synthesis of ?-indium sulphide (In{sub 2}S{sub 3}) nanoparticles embedded in an ionomer matrix (nafion membrane). The influence of reaction temperature on structural, compositional and optical properties of these films were analysed using X-Ray Diffraction, EDAX, UV-Vis absorption spectroscopy and photoluminescence studies. Average particle diameter was estimated using modified effective mass approximation method. Absorption spectra of In{sub 2}S{sub 3} nanoparticles show blue shift compared to bulk In{sub 2}S{sub 3}, indicating strong quantum size confinement effects. PL emission in the wavelength range 530–600 nm was recorded using a 488 nm line from an Ar{sup +} laser as the excitation source.

Sumi, R. [Centre for Nanotechnology Research, VIT University, Vellore (India); Warrier, Anita R.; Vijayan, C. [Department of Physics, Indian Institute of Technology, Chennai (India)

2014-01-28

19

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

PubMed

The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR)-active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intraband relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from the CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core-shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogeneous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe and the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation. PMID:25427007

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

2015-01-27

20

Review: three synthesis methods of CdX (X = Se, S or Te) quantum dots.  

PubMed

Quantum dots (QDs) are one of the first nanotechnologies to be integrated with the biological sciences that used for imaging or tracking macromolecules/cells in cell/tissue. Because of QDs are important in biomedical and biological applications, identify a variety of synthesis methods to produce QDs with different characteristics also is particularly important. Hence, in this review the authors discussed three methods for synthesis of heavy metal chalcogenide-based QDs for use in biomedical field: (i) Organometallic method for synthesis of QDs consists of three components: precursors, organic surfactants and solvents. The authors also discussed water-solubilisation strategies of synthesised QDs including encapsulation and ligand exchange. (ii) Aqueous synthesis technique using short-chain thiols as stabilising agents is a useful alternative to organometallic synthesis of CdSe, CdS and CdTe QDs. (iii) The third method discussed in this article for QDs synthesis involves the utilise of microorganisms to prepare QDs with controlled size, shape, chemical composition and functionality. The authors also discussed recently new methods for the synthesis of the appropriate QDs for use in biology. In addition, attachment of biomolecules such as antibodies, oligonucleotides on the surface of QDs for specific targeting and different opinions about toxicity of QD have been studied. PMID:25014077

Mussa Farkhani, Samad; Valizadeh, Alireza

2014-06-01

21

Microchemical systems for the synthesis of nanostructures : quantum dots  

E-print Network

We have developed a continuous multi-stage high-temperature and high-pressure microfluidic system. High-pressure conditions enabled the use low molecular weight solvents that have previously not been available for quantum ...

Baek, Jinyoung

2012-01-01

22

Gram-scale synthesis of single-crystalline graphene quantum dots with superior optical properties.  

PubMed

Graphene quantum dots (GQDs) have various alluring properties and potential applications, but their large-scale applications are limited by current synthetic methods that commonly produce GQDs in small amounts. Moreover, GQDs usually exhibit polycrystalline or highly defective structures and thus poor optical properties. Here we report the gram-scale synthesis of single-crystalline GQDs by a facile molecular fusion route under mild and green hydrothermal conditions. The synthesis involves the nitration of pyrene followed by hydrothermal treatment in alkaline aqueous solutions, where alkaline species play a crucial role in tuning their size, functionalization and optical properties. The single-crystalline GQDs are bestowed with excellent optical properties such as bright excitonic fluorescence, strong excitonic absorption bands extending to the visible region, large molar extinction coefficients and long-term photostability. These high-quality GQDs can find a large array of novel applications in bioimaging, biosensing, light emitting diodes, solar cells, hydrogen production, fuel cells and supercapacitors. PMID:25348348

Wang, Liang; Wang, Yanli; Xu, Tao; Liao, Haobo; Yao, Chenjie; Liu, Yuan; Li, Zhen; Chen, Zhiwen; Pan, Dengyu; Sun, Litao; Wu, Minghong

2014-01-01

23

Gram-scale synthesis of single-crystalline graphene quantum dots with superior optical properties  

NASA Astrophysics Data System (ADS)

Graphene quantum dots (GQDs) have various alluring properties and potential applications, but their large-scale applications are limited by current synthetic methods that commonly produce GQDs in small amounts. Moreover, GQDs usually exhibit polycrystalline or highly defective structures and thus poor optical properties. Here we report the gram-scale synthesis of single-crystalline GQDs by a facile molecular fusion route under mild and green hydrothermal conditions. The synthesis involves the nitration of pyrene followed by hydrothermal treatment in alkaline aqueous solutions, where alkaline species play a crucial role in tuning their size, functionalization and optical properties. The single-crystalline GQDs are bestowed with excellent optical properties such as bright excitonic fluorescence, strong excitonic absorption bands extending to the visible region, large molar extinction coefficients and long-term photostability. These high-quality GQDs can find a large array of novel applications in bioimaging, biosensing, light emitting diodes, solar cells, hydrogen production, fuel cells and supercapacitors.

Wang, Liang; Wang, Yanli; Xu, Tao; Liao, Haobo; Yao, Chenjie; Liu, Yuan; Li, Zhen; Chen, Zhiwen; Pan, Dengyu; Sun, Litao; Wu, Minghong

2014-10-01

24

Synthesis and unique photoluminescence properties of nitrogen-rich quantum dots and their applications.  

PubMed

Nitrogen-rich quantum dots (N-dots) were serendipitously synthesized in methanol or aqueous solution at a reaction temperature as low as 50?°C. These N-dots have a small size (less than 10?nm) and contain a high percentage of the element nitrogen, and are thus a new member of quantum-dot family. These N-dots show unique and distinct photoluminescence properties with an increasing percentage of nitrogen compared to the neighboring carbon dots. The photoluminescence behavior was adjusted from blue to green simply through variation of the reaction temperature. Furthermore, the detailed mechanism of N-dot formation was also proposed with the trapped intermediate. These N-dots have also shown promising applications as fluorescent ink and biocompatible staining in C.?elegans. PMID:25296956

Chen, Xiuxian; Jin, Qingqing; Wu, Lizhu; Tung, ChenHo; Tang, Xinjing

2014-11-10

25

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

E-print Network

We present a new class of polymeric ligands for quantum dot (QD) water solubilization to yield biocompatible and derivatizable QDs with compact size (10?12 nm diameter), high quantum yields (>50%), excellent stability ...

Liu, Wenhao

26

Facile synthesis of monodisperse Co3O4 quantum dots with efficient oxygen evolution activity.  

PubMed

Monodisperse, water-dispersible Co3O4 quantum dots with sizes of around 4.5 nm are prepared through a simple solution method. The resultant cobalt oxide quantum dots exhibit excellent visible-light-driven oxygen evolution activities in the [Ru(bpy)3](2+)-persulfate system under mild pH conditions. PMID:25485907

Shi, Nan; Cheng, Wei; Zhou, Han; Fan, Tongxiang; Niederberger, Markus

2014-12-01

27

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. PMID:21711922

2011-01-01

28

Tuning the Synthesis of Ternary Lead Chalcogenide Quantum Dots by Balancing Precursor Reactivity  

SciTech Connect

We report the synthesis and characterization of composition-tunable ternary lead chalcogenide alloys PbSe{sub x}Te{sub 1-x}, PbS{sub x}Te{sub 1-x}, and PbS{sub x}Se{sub 1-x}. This work explores the relative reaction rates of chalcogenide precursors to produce alloyed quantum dots (QDs), and we find the highly reactive bis(trimethylsilyl) (TMS{sub 2})-based precursors allow for the homogeneous incorporation of anions. By varying the Pb to oleic acid ratio, we demonstrate size control of similar composition alloys. We find the resulting QDs are Pb-rich but the Pb/anion ratio is size- and composition-dependent in all alloyed QD as well as in PbSe, PbTe, and PbS QDs and is consistent with the reaction rates of the anion precursors. A more reactive anion precursor results in a lower Pb/anion ratio.

Smith, Danielle K.; Luther, Joseph M; Semonin, Octavi Escala; Nozik, Arthur J; Beard, Matthew C

2010-01-01

29

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. PMID:22292028

Pérez-Donoso, José M.; Monrás, Juan P.; Bravo, Denisse; Aguirre, Adam; Quest, Andrew F.; Osorio-Román, Igor O.; Aroca, Ricardo F.; Chasteen, Thomas G.; Vásquez, Claudio C.

2012-01-01

30

Synthesis and enhanced fluorescence of Ag doped CdTe semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs.Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05731g

Ding, Si-Jing; Liang, Shan; Nan, Fan; Liu, Xiao-Li; Wang, Jia-Hong; Zhou, Li; Yu, Xue-Feng; Hao, Zhong-Hua; Wang, Qu-Quan

2015-01-01

31

Atomic structures and gram scale synthesis of three tetrahedral quantum dots.  

PubMed

Luminescent semiconducting quantum dots (QDs) are central to emerging technologies that range from tissue imaging to solid-state lighting. However, existing samples are heterogeneous, which has prevented atomic-resolution determination of their structures and obscured the relationship between their atomic and electronic structures. Here we report the synthesis, isolation, and structural characterization of three cadmium selenide QDs with uniform compositions (Cd35Se20(X)30(L)30, Cd56Se35(X)42(L)42, Cd84Se56(X)56(L)56; X = O2CPh, L = H2N-C4H9). Their UV-absorption spectra show a lowest energy electronic transition that decreases in energy (3.54 eV, 3.26 eV, 3.04 eV) and sharpens as the size of the QD increases (fwhm = 207 meV, 145 meV, 115 meV). The photoluminescence spectra of all three QDs are broad with large Stokes shifts characteristic of trap-luminescence. Using a combination of single-crystal X-ray diffraction and atomic pair distribution function analysis, we determine the structures of their inorganic cores, revealing a series of pyramidal nanostuctures with cadmium terminated {111} facets. Theoretical and experimental studies on these materials will open the door to a deeper fundamental understanding of structure-property relationships in quantum-confined semiconductors. PMID:25003618

Beecher, Alexander N; Yang, Xiaohao; Palmer, Joshua H; LaGrassa, Alexandra L; Juhas, Pavol; Billinge, Simon J L; Owen, Jonathan S

2014-07-30

32

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

33

6-Mercaptohexanoic acid assisted synthesis of high quality InP quantum dots for optoelectronic applications  

NASA Astrophysics Data System (ADS)

Indium phosphide semiconductor quantum dots are of significant heed as their applications encompass a spacious concatenation in LEDs and solar cells technologies. For improving their serviceable prominence, there is a real demand for a fashion that furnishes prompt and large mass production of mightily monodispersed nanoparticles. This study conveys an efficacious and fast recipe of generating substantially monodispersed InP quantum dots via water based route technique using a novel surfactant. Herein, InP QDs have been prepared using 6-mercaptohexanoic acid for achieving an effective surface passivation of monodispersed InP QDs with highly luminescence at temperature 50 °C. The as prepared quantum dots were investigated by transmission electron microscopy, luminescence spectroscopy, and X-ray diffraction. The XRD depicted that the InP quantum dots have a cubic zinc blend structure. TEM image revealed that the prepared quantum dots are monodispersed and their average particle size of about 4 nm. Energy dispersive X-ray spectroscopy confirmed the existence of organic ligand as a shell around InP nanoparticles. Time resolved spectra depicted that the capping agent passivated the InP QDs surface and enhanced the luminescence emission.

Mahmoud, Waleed E.; Chang, Y. C.; Al-Ghamdi, A. A.; Al-Marzouki, F.; Bronstein, Lyudmila M.

2013-04-01

34

Synthesis and characterization of intrinsically radiolabeled quantum dots for bimodal detection  

PubMed Central

A novel approach was developed to synthesize radioactive quantum dots (r-QDs) thereby enabling both optical and radionuclide signals to be detected from the same intrinsic bimodal probe. This proof-of-concept is exemplified by the incorporation of the radionuclide 109Cadmium into the core/shell of the nanoparticle. Green and near infrared (NIR) emission intrinsic r-QDs were synthesized and characterized. Zwitterionic and Poly-polyethlene glycol (PEGylated) ligands were synthesized and used to coat r-QDs. Zwitterionic NIR r-QDs (quantum yield = 11%) and PEGylated NIR r-QDs (quantum yield = 14%) with an average size of 13.8 nm and 16.8 nm were obtained respectively. The biodistribution of NIR zwitterionic and PEGylated r-QDs in nude mice was investigated and zwitterionic r-QDs showed longer blood circulation (t1/2 = 21.4±1.1 hrs) than their PEGylated counterparts (t1/2 = 6.4±0.5 min). Both zwitterionic and PEGylated r-QDs exhibited progressive accumulation in the liver and spleen, but the magnitude of the accumulation (%ID/g) was about 3-6 fold higher with the PEGylated r-QDs at all the time points. The results demonstrated the feasibility of r-QDs synthesis in quantitative yield and retention of fluorescence following incorporation of radioactivity into the core/shell of the nanoparticle. The gamma signal from the same fluorescent elemental material enabled quantitative and robust pharmacokinetic measurements and how these changed depended on the type of coating ligands used. This strategy for intrinsically radio-labeling the QDs is currently being implemented in our laboratory for the incorporation of other radiometals. PMID:23133807

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

2012-01-01

35

Low-temperature synthesis of polyethyleneimine-entrapped CdS quantum dots  

NASA Astrophysics Data System (ADS)

This Letter is focused on the one-pot formation of CdS nanoparticles in aqueous medium in presence of polyethyleneimine (PEI). Quantum dots can be obtained by adding a pre-cooled aqueous Na2S solution to a pre-cooled aqueous CdCl2 solution dropwise in presence of PEI. Field flow fractionation in combination with TEM experiments show a time dependent agglomeration of individual quantum dots from 1.6 nm up to 3.2 nm in size. The hyperbranched PEI of moderate molar mass (>20 000 g/mol) is an excellent polymer to prevent a further increase of the particle size. Therefore, stable fluorescent PEI-capped CdS quantum dots are available.

Kosmella, Sabine; Venus, Jane; Hahn, Jennifer; Prietzel, Claudia; Koetz, Joachim

2014-01-01

36

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.

37

Synthesis, characterization and application of luminescent quantum dots and microcrystalline phosphors  

NASA Astrophysics Data System (ADS)

A phosphor is a substance which emits light when excited by radiation. For traditional powder phosphors impurity elements are usually incorporated into the host material to act as the luminescent centers. The fluorescent quantum dot (QD) is a new kind of phosphor, "quantum phosphor", with an extremely small size of 1˜10 nm and size dependent tunable emission color from the same pure semiconductor material due to quantum confinement. In this research Si QDs embedded in SiOx or SiNx thin films, which could emit light in the entire visible range from 440 nm to 840 nm by controlling their size and/or their matrix, were synthesized by evaporation or plasma enhanced chemical vapor deposition (PECVD) techniques. Various shades of "white" could be obtained from multi-layered SiNx film structures by controlling the size of Si QDs and layer thickness. It was shown that the combination of these films can produce white emission spectra with superior color rendering properties compared to conventional fluorescent tubes. Such Si-based QDs can be used as down-converting phosphors to coat a blue/UV LED to generate white light, providing a less expensive fabrication process to obtain advanced solid state lighting devices that, compared to conventional fragile lamps, are more efficient, longer lived, and provide a full sunlight spectrum. As a supplement, free CdTe QDs with emission colors spanning 520˜700 nm and quantum efficiency (QE) up to 54%, were synthesized using a colloidal chemical method for white LED applications. White PL and a range of emission colors were obtained from mixed CdTe QD samples excited by a 420 nm blue LED. Another part of this research was to develop a new x-ray powder phosphor, ZnTe:O, for biological imaging applications used in CCD-based synchrotron x-ray detectors. As a lower band-gap semiconductor, ZnTe could theoretically achieve a higher x-ray luminescence efficiency than its counterpart, ZnSe, which is an x-ray phosphor host with the highest known x-ray conversion efficiency. However, ZnTe had not been developed as an efficient phosphor material, probably because it is very sensitive to moisture during synthesis. Conventional wet synthesis techniques used for ZnS and ZnSe phosphors fabrication are not applicable to ZnTe phosphor synthesis. In this research, a unique dry synthesis process, including gaseous dry doping and etching procedures, was developed to synthesize ZnTe:O phosphors. The excellent x-ray luminescence results of oxygen doped ZnTe, including high efficiency, high resolution, fast decay, low afterglow and an improved spectral match to the CCD detector, indicated that ZnTe:O is a promising phosphor candidate for x-ray imaging applications.

Kang, Zhitao

38

Quantum properties of spherical semiconductor quantum dots  

E-print Network

Quantum properties of spherical semiconductor quantum dots B. Billaud and T.-T. Truong Laboratoire of having a QD-LASER emitting in the range of visible light. Keywords spherical Quantum Dot, semiconductor.22.Dj. 1 Introduction Semiconductor quantum dots (QDs), as well as quantum wires or quantum wells, show

Paris-Sud XI, Université de

39

Synthesis and optical properties of cadmium selenide quantum dots for white light-emitting diode application  

SciTech Connect

Highlights: ? Stable CdSe QDs were synthesized by the one-step and two-level process respectively. ? The fabricated white LEDs show good white balance. ? CdSe QDs present well green to yellow band luminescence. ? CdSe QDs displayed a broad excitation band. - Abstract: Yellow light-emitting cadmium selenide quantum dots were synthesized using one-step and two-step methods in an aqueous medium. The structural luminescent properties of these quantum dots were investigated. The obtained cadmium selenide quantum dots displayed a broad excitation band suitable for blue or near-ultraviolet light-emitting diode applications. White light-emitting diodes were fabricated by coating the cadmium selenide samples onto a 460 nm-emitting indium gallium nitrite chip. Both samples exhibited good white balance. Under a 20 mA working current, the white light-emitting diode fabricated via the one-step and two-step methods showed Commission Internationale de l’Éclairage coordinates at (0.27, 0.23) and (0.27, 0.33), respectively, and a color rendering index equal to 41 and 37, respectively. The one-step approach was simpler, greener, and more effective than the two-step approach. The one-step approach can be enhanced by combining cadmium selenide quantum dots with proper phosphors.

Xu, Xianmei; Wang, Yilin; Gule, Teri; Luo, Qiang [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China); Zhou, Liya, E-mail: zhouliyatf@163.com [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China); Gong, Fuzhong [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China)

2013-03-15

40

Carbon Nanotube Quantum Dot  

E-print Network

Carbon Nanotube Quantum Dot with Superconducting Electrodes Bachelor of Science Thesis Faculty of march 2010. The study of the electrical properties of carbon nanotubes falls under meso- scopic physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Theory 8 3.1 Carbon Nanotubes . . . . . . . . . . . . . . . . . . . . . . . . 8 3

Nygård, Jesper

41

CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture  

NASA Astrophysics Data System (ADS)

This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ?500 and 700 nm with the luminescence quantum yield (LQY) of 30–85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml?1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3–50 ng ?l?1 with a detection limit of 3 ng ?L?1 has been performed based on the antibody-antigen recognition.

Dieu Thuy Ung, Thi; Tran, Thi Kim Chi; Nga Pham, Thu; Nghia Nguyen, Duc; Khang Dinh, Duy; Liem Nguyen, Quang

2012-12-01

42

Synthesis of biocompatible SiO2 coated ZnO quantum dots for cell imaging  

NASA Astrophysics Data System (ADS)

Quantum dots (QDs) is a promising candidate for biomedical imaging. However, the bio-toxicity of traditional quantum dots obstructed their further application seriously. In this work, a simple solution growth method was utilized to synthesize ZnO QDs. However, their self-assemble feature makes them unstable in aqueous solution. Furthermore, (3-Aminopropyl) triethoxysilane was selected as a capping agent to stabilize ZnO QDs and then ZnO@SiO2 nanoparticles were obtained. They dispersed excellently in water and exhibited favorable fluorescence properties owing to the protection of silane. The biocompatability of ZnO@SiO2 nanoparticles was verified by MTT assy. The cell affinity studies demonstrated that ZnO@SiO2 nanoparticles could be uptaken by cells efficiently. Therefore, the as-prepared ZnO@SiO2 nanoparticles is a promising candidate for applications in cell imaging.

Zhang, Min; Wang, Qian; Chen, Haiyan; Gu, Yueqing

2014-09-01

43

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

44

Spectroscopic characterization of streptavidin functionalized quantum dots  

Microsoft Academic Search

The spectroscopic properties of quantum dots can be strongly influenced by the conditions of their synthesis. In this work, we have characterized several spectroscopic properties of commercial, streptavidin functionalized quantum dots (QD525, lot 1005-0045, and QD585, lot 0905-0031, from Invitrogen). This is the first step in the development of calibration beads to be used in a generalizable quantification scheme of

Yang Wu; Gabriel P. Lopez; Larry A. Sklar; Tione Buranda

2007-01-01

45

Topic in Depth - Quantum Dots  

NSDL National Science Digital Library

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

2010-09-20

46

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

47

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

NASA Astrophysics Data System (ADS)

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.

Joung, Somyoung; Yoon, Sungwoo; Han, Chang-Soo; Kim, Youngjo; Jeong, Sohee

2012-01-01

48

Quantum Dot Light Emitting Diode  

SciTech Connect

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

Keith Kahen

2008-07-31

49

Quantum Dot Light Emitting Diode  

SciTech Connect

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

Kahen, Keith

2008-07-31

50

Synthesis and characterization of lead selenide nanocrystal quantum dots and wires.  

PubMed

Lead chalcogenide nanocrystalline materials offer possibilities of improving the efficiency of various optoelectric/thermoelectric applications, especially in solar cells, by generating more carriers with incoming photons, or by extending the bandgap toward the infra-red region. In this work, we suggest the synthetic approach of creating extended PbSe structures which shows better performances when incorporated into an electric device. Firstly, we synthesized monodisperse cubic-structured single-crystalline lead selenide nanocrystal quantum dots using lead acetate and oleic acid in non-coordinating solvent without additional surfactants. Also, single-crystal cubic PbSe nanowires were synthesized in a mixture of surfactants such as trioctylphosphine and phenyl ether. Morphologies of wires and dots were precisely controlled via reaction temperature and the surface ligands. Phenyl ether was found to facilitate the oriented attachment. Further, current-voltage characteristics of drop-casted 2D arrays of nanocrystalline materials were examined. PMID:21780455

Seo, Weonsik; Yun, Ju-Hyung; Park, Yun Chang; Han, Chang-Soo; Lee, Jihye; Jeong, Sohee

2011-05-01

51

Chiral quantum dot based materials  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

52

Functionalized silicon quantum dots by N-vinylcarbazole: synthesis and spectroscopic properties  

PubMed Central

Silicon quantum dots (Si QDs) attract increasing interest nowadays due to their excellent optical and electronic properties. However, only a few optoelectronic organic molecules were reported as ligands of colloidal Si QDs. In this report, N-vinylcarbazole - a material widely used in the optoelectronics industry - was used for the modification of Si QDs as ligands. This hybrid nanomaterial exhibits different spectroscopic properties from either free ligands or Si QDs alone. Possible mechanisms were discussed. This type of new functional Si QDs may find application potentials in bioimaging, photovoltaic, or optoelectronic devices. PMID:25147489

2014-01-01

53

Functionalized silicon quantum dots by N-vinylcarbazole: synthesis and spectroscopic properties  

NASA Astrophysics Data System (ADS)

Silicon quantum dots (Si QDs) attract increasing interest nowadays due to their excellent optical and electronic properties. However, only a few optoelectronic organic molecules were reported as ligands of colloidal Si QDs. In this report, N-vinylcarbazole - a material widely used in the optoelectronics industry - was used for the modification of Si QDs as ligands. This hybrid nanomaterial exhibits different spectroscopic properties from either free ligands or Si QDs alone. Possible mechanisms were discussed. This type of new functional Si QDs may find application potentials in bioimaging, photovoltaic, or optoelectronic devices.

Ji, Jianwei; Wang, Guan; You, Xiaozeng; Xu, Xiangxing

2014-08-01

54

Quantum dot devices  

Microsoft Academic Search

From a recent study of the growth and optical properties of quantum dots (QD's), we demonstrated that artificial atoms with sharp electronic shells can be fabricated with good control, using self-assembled QD's grown by molecular beam epitaxy. Size and shape engineering of the QD's during growth permits the tailoring of their intersublevel energy spacings. We demonstrate a much improved uniformity

Simon Fafard; Hui C. Liu; Z. R. Wasilewski; John P. McCaffrey; M. Spanner; Sylvain Raymond; C. N. Allen; K. Hinzer; Jean M. Lapointe; C. Struby; M. Gao; Pawel Hawrylak; C. Gould; A. Sachrajda; P. Zawadzki

2000-01-01

55

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

PubMed

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

Tyrakowski, Christina Marie; Snee, Preston Todd

2014-01-21

56

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

57

Biexcitons in semiconductor quantum dots  

Microsoft Academic Search

Theoretical and experimental results are reported which provide the first evidence for biexciton states in semiconductor quantum dots. The theory predicts an increasing biexciton binding energy with decreasing dot size. Unlike bulk semiconductors, quantum dots have excited biexciton states which are stable. These biexciton states are observed as pronounced induced absorption features on the high-energy side of the bleached exciton

Y. Z. Hu; S. W. Koch; M. Lindberg; N. Peyghambarian; E. L. Pollock; Farid F. Abraham

1990-01-01

58

Aqueous synthesis of highly luminescent glutathione-capped Mn²?-doped ZnS quantum dots.  

PubMed

In this paper, an aqueous-based route has been developed to prepare highly luminescent glutathione (GSH)-capped Mn-doped ZnS quantum dots (QDs). The dots obtained have an average diameter of 4.3 nm and exhibit the Mn(2+)-related orange luminescence with very low surface defect density. The highest photoluminescence was observed for a Mn(2+) to Zn(2+) molar ratio of 3%. Consecutive overcoating of the Mn:ZnS@GSH QDs by a ZnS shell was done, and the core/shell structured QDs exhibit a PL quantum yield of 23%. Transmission electron microscopy, X-ray powder diffraction, electron spin resonance, X-ray photoelectron spectroscopy, UV-visible spectroscopy and spectrofluorometry have been used to characterize the crystal structure, the doping status, and the optical properties of the doped-QDs. Our systematic investigation shows that Mn:ZnS/ZnS@GSH QDs are highly promising fluorescent labels in biological applications. PMID:25280675

Kolmykov, Oleksii; Coulon, Joël; Lalevée, Jacques; Alem, Halima; Medjahdi, Ghouti; Schneider, Raphaël

2014-11-01

59

Quantum dot cascade laser  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

60

Quantum Dots Investigated for Solar Cells  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

61

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

62

Colloidal silicon quantum dots: synthesis and luminescence tuning from the near-UV to the near-IR range  

NASA Astrophysics Data System (ADS)

This review describes a series of representative synthesis processes, which have been developed in the last two decades to prepare silicon quantum dots (QDs). The methods include both top-down and bottom-up approaches, and their methodological advantages and disadvantages are presented. Considerable efforts in surface functionalization of QDs have categorized it into (i) a two-step process and (ii) in situ surface derivatization. Photophysical properties of QDs are summarized to highlight the continuous tuning of photoluminescence color from the near-UV through visible to the near-IR range. The emission features strongly depend on the silicon nanostructures including QD surface configurations. Possible mechanisms of photoluminescence have been summarized to ascertain the future challenges toward industrial use of silicon-based light emitters.

Ghosh, Batu; Shirahata, Naoto

2014-02-01

63

PREFACE: Quantum Dot 2010  

NASA Astrophysics Data System (ADS)

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

Taylor, Robert A.

2010-09-01

64

Synthesis and optical properties of copper-doped ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

This paper reports a new method to synthesize Cu-doped ZnSe quantum dots (QDs). Emission properties are tuned from the blue to the green region simply by increasing the size of the QDs. A red shift in optical absorption of Cu:ZnSe QDs compared with undoped ZnSe QDs is observed. The increase in size of QDs is explained by a change in reaction kinematics. PL measurements revealed both a band edge as well as a copper-related emission. Delocalization of electronic wave functions leads to a shift in the copper-related emission with in size. PL excitation spectra recorded at Cu emission shows ZnSe energy levels along with a feature between 350–370 nm. This feature is assigned to excited energy levels of Cu ions. Variation in electron energy levels as a function of size and on Cu incorporation is mapped.

Rajesh, Ch; Phadnis, Chinmay V.; Sonawane, Kiran G.; Mahamuni, Shailaja

2015-01-01

65

Novel water-soluble chitosan derivatives/quantum dots nanocomposite: synthesis, characterization and photoluminescence properties.  

PubMed

Water-soluble biocompatible and monodisperse ZnS, CdS, CdSe quantum dots (QDs) were synthesized using natural chitosan derivatives as stabilizers. TEM, XRD, SAED and UV-vis confirmed the formation of nanoparticles with average size of 3-5 nm, and the resulted ZnS, CdS nanocrystals were shown to be of cubic and blended phase. It was found that the molecular structure of chitosan stabilizer had a large influence on the optical and crystalline properties of the QDs. Through refluxing, the surface defects of the nanoparticles were passivated and the photoluminescence were enhanced. The particle size and the photoluminescence intensity can be controlled through altering the concentration of precursor ions and stabilizer solution, the molar ratio of metal ions/[S2-] and refluxing time. The resulting biopolymer/QD composite can be potentially applied as biosensor or fluorescence tags in biological systems. PMID:19908691

Wang, Xiaohui; Li, Yan; Du, Yumin

2009-12-01

66

Investigation of the Emission Properties of Quantum Dot-thermoresponsive Polymer Nanocomposite Hydrogels with Temperature  

E-print Network

This thesis presents a novel method for the preparation of quantum dot-thermoresponsive polymer nanocomposite hydrogels. The quantum dots (QD’s) were synthesized in a microwave reactor using a high temperature organometallic synthesis procedure...

Juriani, Ameet Rajkumar

2011-08-08

67

Quantum Dots and Colors  

NSDL National Science Digital Library

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

2014-09-18

68

Quantum dot solar concentrators  

Microsoft Academic Search

The luminescent properties of core-shell quantum dots are being exploited in an unconventional solar concentrator, which promises\\u000a to reduce the cost of photovoltaic electricity. Luminescent solar collectors have advantages over geometric concentrators\\u000a in that tracking is unnecessary and both direct and diffuse radiation can be collected. However, development has been limited\\u000a by the performance of luminescent dyes. We present experimental

A. J. Chatten; K. W. J. Barnham; B. F. Buxton; N. J. Ekins-Daukes; M. A. Malik

2004-01-01

69

Quantum Dot Modulators  

Microsoft Academic Search

Mach-zender devices are an ideal modulation source for communication networks at 1.3 mum and 1.55 mum. Superlinear electro-optical effects are a desirable feature in mach-zender modulators since their large second order electro-optical coefficient would give complete signal extinction at a small voltage. Quantum dot devices show promise for such applications in the 1.3 mum band. In this project we performed

Brendan Turner; Manish Mehta; Ramesh Laghumavarapu; Diana Huffaker

2006-01-01

70

Si, Ge, and SiGe quantum wires and quantum dots  

NASA Astrophysics Data System (ADS)

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

Pearsall, T. P.

71

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

72

Zeno Quantum Gates in Semiconductor Quantum Dots  

E-print Network

We propose a scheme for a two-qubit conditional phase gate by quantum Zeno effect with semiconductor quantum dots. The system consists of two charged dots and one ancillary dot that can perform Rabi oscillations under a resonant laser pulse. The quantum Zeno effect is induced by phonon-assisted exciton relaxation between the ancillary dot and the charged dots, which is equivalent to a continuous measurement. We solve analytically the master equation and simulate the dynamics of the system using a realistic set of parameters. In contrast to standard schemes, larger phonon relaxation rates increase the fidelity of the operations.

K. J. Xu; Y. P. Huang; M. G. Moore; C. Piermarocchi

2008-10-24

73

Temperature-Dependent Electron Transport in Quantum Dot Photovoltaics  

E-print Network

Covalency in semiconductor quantum dots. Chemical SocietySemiconductor Properties Before examining quantum confinement effects in quantum dots,gap of the quantum dots. Besides semiconductor-semiconductor

Padilla, Derek

2013-01-01

74

Continuous-flow synthesis of CdSe quantum dots: a size-tunable and scalable approach.  

PubMed

In recent years, continuous-flow/microreactor processing for the preparation of colloidal nanocrystals has received considerable attention. The intrinsic advantages of microfluidic reactors have opened new opportunities for the size-controlled synthesis of nanocrystals either in the laboratory or on a large scale. Herein, an experimentally simple protocol for the size-tunable continuous-flow synthesis of rather monodisperse CdSe quantum dots (QDs) is presented. CdSe QDs are manufactured by using cadmium oleate as cadmium source, selenium dioxide as selenium precursor, and 1-octadecene as solvent. Exploiting selenium dioxide as selenium source and 1-octadecene as solvent allows execution of the complete process in open air without any requirement for air-free manipulations using a glove box or Schlenk line. Continuous-flow processing is performed with a stainless steel coil of 1.0?mm inner diameter pumping the combined precursor solution through the reactor by applying a standard HPLC pump. The effect of different reaction parameters, such as temperature, residence time, and flow rate, on the properties of the resulting CdSe QDs was investigated. A temperature increase from 240 to 260?°C or an extension of the residence time from 2 to 20?min affords larger nanocrystals (range 3-6?nm) whereas the size distribution does not change significantly. Longer reaction times and higher temperatures result in QDs with lower quantum yields (range 11-28?%). The quality of the synthesized CdSe QDs was confirmed by UV/Vis and photoluminescence spectroscopy, small-angle X-ray scattering, and high-resolution transmission electron microscopy. Finally, the potential of this protocol for large-scale manufacturing was evaluated and by operating the continuous-flow process for 87?min it was possible to produce 167?mg of CdSe QDs (with a mean diameter of 4?nm) with a quantum yield of 28?%. PMID:23857757

Mirhosseini Moghaddam, Mojtaba; Baghbanzadeh, Mostafa; Sadeghpour, Amin; Glatter, Otto; Kappe, C Oliver

2013-08-26

75

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

PubMed Central

Quantum dots (QDs) are luminescent semiconductor nanocrystals with great prospective for use in biomedical and environmental applications. Nonetheless, eliminating the potential cytotoxicity of the QDs made with heavy metals is still a challenge facing the research community. Thus, the aim of this work was to develop a novel facile route for synthesising biocompatible QDs employing carbohydrate ligands in aqueous colloidal chemistry with optical properties tuned by pH. The synthesis of ZnS QDs capped by chitosan was performed using a single-step aqueous colloidal process at room temperature. The nanobioconjugates were extensively characterised by several techniques, and the results demonstrated that the average size of ZnS nanocrystals and their fluorescent properties were influenced by the pH during the synthesis. Hence, novel 'cadmium-free’ biofunctionalised systems based on ZnS QDs capped by chitosan were successfully developed exhibiting luminescent activity that may be used in a large number of possible applications, such as probes in biology, medicine and pharmacy. PMID:24308633

2013-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

77

Nuclear Spins in Quantum Dots  

Microsoft Academic Search

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

S. I. Erlingsson

2003-01-01

78

Ambient synthesis and characterization of high-quality CdSe quantum dots by an aqueous route.  

PubMed

Herein, we report the ambient synthesis of CdSe nanoparticles of widely tunable particle size by a solution route. The proposed protocol uses hydrazine hydrate to form an air-stable complex of selenium. These nanoparticles are characterized by X-ray diffraction, FTIR, optical absorption, photoluminescence, and transmission electron microcopy measurements. By varying the molarities of Cd(2+) and Se(2-) ions in solution with 3-mercaptopropionic acid as the capping ligand, the method permits us to synthesize nanoparticles of size ranging from 1.58 to 3.42 nm (estimated from optical absorption edge measurements) by controlling the annealing time of the starting colloid at 100 degrees C. The extracted quantum dots are of high quality (40% photoluminescence quantum yield) and exhibit colors ranging from deep blue to red. The resulting colloids are very stable, and no precipitate is observed over a period of 6 months. Thus, the method is simple and easily scalable to synthesize fluorescent CdSe nanoparticles. PMID:19711933

Kalasad, M N; Rabinal, M K; Mulimani, B G

2009-11-01

79

Synthesis and in vitro evaluation of a hyaluronic acid-quantum dots-melphalan conjugate.  

PubMed

Polymer-drug conjugates have played an important role in improving tumor cell targeting and the selectivity of anticancer drugs. In this study, quantum dots and melphalan were attached to the backbone of hyaluronic acid to synthesize a polymer-drug conjugate. The physicochemical properties of the conjugate were characterized by FT-IR, XRD, (1)H NMR, UV-Vis spectra and DLS. The in vitro drug release profiles and cell evaluation were investigated. The results showed that the conjugate was synthesized and self-assembled into nanoparticles with a diameter of 115±2.3nm. The conjugate had a pH-sensitive drug controlled release property. It was an ideal receptor-mediated delivery system and can be internalized into the human breast cancer cell. It had a better inhibition effect on human breast cancer cell and a poorer inhibition effect on normal breast cell than melphalan. These results supported that the conjugate would be a promising candidate for cancer therapy. PMID:25659681

Xu, Haixing; He, Jingbo; Zhang, Yu; Fan, Lihong; Zhao, Yaqiong; Xu, Tengfei; Nie, Zhuang; Li, Xiangnan; Huang, Zhijun; Lu, Bo; Xu, Peihu

2015-05-01

80

Low temperature synthesis of CdSe capped 2-mercaptoethanol quantum dots  

NASA Astrophysics Data System (ADS)

Low temperature CdSe quantum dots are prepared by using 2-mercaptoethanol as capping agent for the first time. Cadmium chloride (CdCl2·5H2O) and sodium selenosulfate (Na2SeSO3) are used as a cadmium and selenium sources respectively. The resulting nanocrystals are characterized by X-ray diffraction, transmission electron microscopy (TEM), UV-vis absorption spectra and photoluminescence (PL) spectroscopy. The XRD pattern showed that the prepared CdSe has a cubic phase with zinc blende structure. The particle size was estimated from broadening of XRD peak using Scherrer's formula and also from TEM images. The size obtained from XRD and TEM are in agreement with each other. It is found that the size of CdSe nanoparticles increases with the increase of the reaction temperature. The optical absorption as a function of the wavelength for the prepared CdSe nanocrystals at different temperatures is investigated. The photoluminescence emission intensity for as-synthesized CdSe nanocrystals at different reaction temperatures depicted that, the emission peak wavelength of the CdSe QDs was larger than the absorption peak wavelength, indicating the presence of surface trap-state emissions. These surface crystal defect densities are increased with the increase of the reaction temperature.

Mahmoud, Waleed E.; Al-Amri, Amal M.; Yaghmour, S. J.

2012-05-01

81

Precise size control and synchronized synthesis of six colors of CdSe quantum dots in a slow-increasing temperature gradient.  

PubMed

The present study describes a simultaneous and highly reproducible large-scale synthesis of six (and more) colors of size-homogeneous and highly luminescent CdSe quantum dots in a single reaction, controlled by a slow-increasing temperature gradient. The described protocol allows a precise control and a synchronized isolation of aliquots of CdSe nanocrystals with defined sizes, avoiding disturbance of the growth of nanocrystals (existing in the reaction mixture) to the isolation of the next aliquot. The obtained quantum dot fractions are of high quality (in 95% size-homogeneous) and have sharp photoluminescence spectra (fwhm approximately 30 nm), quantum yields of 45-70% (in organic solvent), and a lack of aggregation in organic solvents. The method is environmentally friendly as it ensures almost complete utilization of the precursors and productive yield approximately 95%. PMID:17602608

Zlateva, Genoveva; Zhelev, Zhivko; Bakalova, Rumiana; Kanno, Iwao

2007-08-01

82

Quantum Dot Applications forQuantum Dot Applications for Flash Memory, SemiconductorFlash Memory, Semiconductor  

E-print Network

1 Quantum Dot Applications forQuantum Dot Applications for Flash Memory, SemiconductorFlash Memory cell #12;3 5 Quantum dots and highQuantum dots and high--K tunnelingK tunneling oxide reduce size and quantum dots 6 HighHigh--K tunneling layerK tunneling layer Replace current materials with a high

Lightsey, Glenn

83

Microwave-Assisted Aqueous Synthesis of Highly Luminescent Carboxymethyl Chitosan-Coated CdTe\\/CdS Quantum Dots as Fluorescent Probe for Live Cell Imaging  

Microsoft Academic Search

This paper describes the development of a simplified and rapid method for the aqueous synthesis of quantum dots (QDs) with\\u000a CdTe cores and gradient CdS external shells (CdTe\\/CdS QDs) aided by microwave irradiation. Several synthesis parameters, such\\u000a as molar ratio of reagents, pH, reaction temperature, and reaction time, were studied in details. Under the optimized conditions,\\u000a highly effective CdTe\\/CdS QDs

Zhenyu He; Honghao Zhu; Peijiang Zhou

84

Facile synthesis of N-acetyl-L-cysteine capped CdHgSe quantum dots and selective determination of hemoglobin  

NASA Astrophysics Data System (ADS)

Using N-acetyl-L-cysteine (NAC) as a stabilizer, well water-dispersed, high-quality and stable CdHgSe quantum dots were facilely synthesized via a simple aqueous phase method. The as-prepared NAC capped CdHgSe quantum dots were thoroughly characterized by fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. A novel method for the selective determination of hemoglobin (Hb) was developed based on fluorescence quenching of the NAC capped CdHgSe quantum dots. A number of key factors including pH value of phosphate buffer solution, quantum dots concentration, the adding sequence of reagents and reaction time that influence the analytical performance of the NAC capped CdHgSe quantum dots in Hb determination were investigated. Under the optimal experimental conditions, the change of fluorescence intensity (?I) was linearly proportional to the concentration of Hb in the range of 4.0 × 10-9-4.4 × 10-7 mol L-1 with a detection limit of 2.0 × 10-9 mol L-1. The developed method has been successfully employed to determine Hb in human urine samples.

Wang, Qingqing; Zhan, Guoqing; Li, Chunya

2014-01-01

85

Quantum transport in quantum dot cascade structures  

Microsoft Academic Search

In last years, a significant experimental and theoretical interest has been put into the possibility of development of intraband lasers based on quantum dots (1)-(5). Due to truly discrete electronic spectrum of quantum dots, most of the undesired scattering and relaxation processes are suppressed, and such devices are expected to have two orders of magnitude lower threshold currents than the

N. Vukmirovic; Z. Ikoni ´; D. Indjin; P. Harrison

86

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

87

Solvothermal, chloroalkoxide-based synthesis of monoclinic WO(3) quantum dots and gas-sensing enhancement by surface oxygen vacancies.  

PubMed

We report for the first time the synthesis of monoclinic WO3 quantum dots. A solvothermal processing at 250 °C in oleic acid of W chloroalkoxide solutions was employed. It was shown that the bulk monoclinic crystallographic phase is the stable one even for the nanosized regime (mean size 4 nm). The nanocrystals were characterized by X-ray diffraction, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis, Fourier transform infrared and Raman spectroscopy. It was concluded that they were constituted by a core of monoclinic WO3, surface covered by unstable W(V) species, slowly oxidized upon standing in room conditions. The WO3 nanocrystals could be easily processed to prepare gas-sensing devices, without any phase transition up to at least 500 °C. The devices displayed remarkable response to both oxidizing (nitrogen dioxide) and reducing (ethanol) gases in concentrations ranging from 1 to 5 ppm and from 100 to 500 ppm, at low operating temperatures of 100 and 200 °C, respectively. The analysis of the electrical data showed that the nanocrystals were characterized by reduced surfaces, which enhanced both nitrogen dioxide adsorption and oxygen ionosorption, the latter resulting in enhanced ethanol decomposition kinetics. PMID:25211288

Epifani, Mauro; Comini, Elisabetta; Díaz, Raül; Andreu, Teresa; Genç, Aziz; Arbiol, Jordi; Siciliano, Pietro; Faglia, Guido; Morante, Joan R

2014-10-01

88

Facile synthesis L-cysteine capped CdS:Eu quantum dots and their Hg2+ sensitive properties  

NASA Astrophysics Data System (ADS)

This paper described a facile aqueous route to prepare CdS: Eu quantum dots (QDs) with strong yellow emission using L-cysteine (L-Cys) as the capping ligands. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) confirm that the CdS:Eu QDs have a cubic structure with good crystallinity, the average diameter of the CdS:Eu QDs is about 8 nm. The traces of groups adsorbed on CdS:Eu QDs were confirmed via FT-IR spectra. In addition, the synthesis parameters including the concentration of doped Eu3+ ions, the pH value and the reaction time have influence on the optical properties of CdS:Eu QDs. The as-prepared L-Cys capped CdS:Eu QDs were used as a fluorescence probe to detect Hg2+ ions in aqueous media based on fluorescence quenching. The response of L-Cys capped CdS:Eu QDs as a fluorescence probe was linearly proportional to the concentration of Hg2+ ions in the range of 5 × 10-6 to 1 × 10-3 mol L-1 with a limit of detection of 2 × 10-6 mol L-1.

Zhang, Kexin; Yu, Yaxin; Sun, Shuqing

2013-07-01

89

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

2011-10-25

90

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

PubMed Central

The intentional introduction of transition metal impurities in semiconductor nanocrystals is an attractive approach for tuning quantum dot (QD) emission over a wide range of wavelengths. However, the development of effective doping strategies can be challenging, especially if one simultaneously requires a low toxicity crystalline core, a functional protein shell, and a “green”, single-step synthesis process. Here, we describe a simple and environmentally friendly route for the biofabrication of Cu-doped (blue-green) or Mn-doped (yellow-orange) ZnS nanocrystals surrounded by an antibody-binding protein shell. The ZnS:Mn hybrid particles obtained with this method exhibited a 60% enhancement in maximum photoluminescence intensity relative to undoped nanocrystals and have a hydrodynamic diameter inferior to 10 nm. They can be stored for months at 4°C, are stable over a physiological range of pH and salt concentrations, can be decorated with variable amounts of antibodies by direct mixing, and hold promise for biosensing and imaging applications. PMID:21942544

Zhou, Weibin; Baneyx, François

2011-01-01

91

Liquid-phase plasma synthesis of silicon quantum dots embedded in carbon matrix for lithium battery anodes  

SciTech Connect

Graphical abstract: - Highlights: • Silicon quantum dots embedded in carbon matrix (SiQDs/C) were fabricated. • SiQDs/C exhibits excellent battery performance as anode materials with high specific capacity. • The good performance was attributed to the marriage of small sized SiQDs and carbon. - Abstract: Silicon quantum dots embedded in carbon matrix (SiQDs/C) nanocomposites were prepared by a novel liquid-phase plasma assisted synthetic process. The SiQDs/C nanocomposites were demonstrated to show high specific capacity, good cycling life and high coulmbic efficiency as anode materials for lithium-ion battery.

Wei, Ying [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China); College of Chemistry and Chemical Engineering, Bohai University, Jinzhou 121000 (China); Yu, Hang; Li, Haitao; Ming, Hai; Pan, Keming; Huang, Hui [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China); Liu, Yang, E-mail: yangl@suda.edu.cn [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China); Kang, Zhenhui, E-mail: zhkang@suda.edu.cn [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China)

2013-10-15

92

Facile synthesis of CuInGaS? quantum dot nanoparticles for bilayer-sensitized solar cells.  

PubMed

CuIn(0.7)Ga(0.3)S2 quantum dots (QDs) with particle size of 2-5 nm were directly synthesised by a vacuum one-pot-nanocasting process and homogeneously anchored on TiO2 nanocrystals (<50 nm) for the first time. We further present CuIn(0.7)Ga(0.3)S2 quantum dots and dye bilayer-sensitized solar cells with a power conversion efficiency 36.3% higher than mono-dye sensitized solar cells. PMID:25300426

Zhao, Jinjin; Zhang, Jiangbin; Wang, Wenna; Wang, Peng; Li, Feng; Ren, Deliang; Si, Huanyan; Sun, Xiuguo; Ji, Fengqiu; Hao, Yanzhong

2014-11-28

93

Synthesis of radioactively labelled CdSe/CdS/ZnS quantum dots for in vivo experiments  

PubMed Central

Summary During the last decades of nanoparticles research, many nanomaterials have been developed for applications in the field of bio-labelling. For the visualization of transport processes in the body, organs and cells, luminescent quantum dots (QDs) make for highly useful diagnostic tools. However, intercellular routes, bio-distribution, metabolism during degradation or quantification of the excretion of nanoparticles, and the study of the biological response to the QDs themselves are areas which to date have not been fully investigated. In order to aid in addressing those issues, CdSe/CdS/ZnS QDs were radioactively labelled, which allows quantification of the QD concentration in the whole body or in ex vivo samples by ?-counting. However, the synthesis of radioactively labelled QDs is not trivial since the coating process must be completely adapted, and material availability, security and avoidance of radioactive waste must be considered. In this contribution, the coating of CdSe/CdS QDs with a radioactive 65ZnS shell using a modified, operator-safe, SILAR procedure is presented. Under UV illumination, no difference in the photoluminescence of the radioactive and non-radioactive CdSe/CdS/ZnS colloidal solutions was observed. Furthermore, a down-scaled synthesis for the production of very small batches of 5 nmol QDs without loss in the fluorescence quality was developed. Subsequently, the radio-labelled QDs were phase transferred by encapsulation into an amphiphilic polymer. ?-counting of the radioactivity provided confirmation of the successful labelling and phase transfer of the QDs.

Stachowski, Gordon M; Bauer, Christoph; Waurisch, Christian; Bargheer, Denise; Nielsen, Peter; Heeren, Jörg; Hickey, Stephen G

2014-01-01

94

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

95

Quantum optical phenomena in semiconductor quantum dots  

E-print Network

Quantum optical phenomena are explored in artificial atoms well known as semiconductor quantum dots, in the presence of excitons and biexcitons. The analytical results are obtained using the conventional time-dependent perturbation technique. Numerical estimations are made for arealistic sample of CdS quantum dots in a high-Q cavity. Quantum optical phenomena such as quantum Rabi oscillations, photon statistics and collapse and revival of population inversion in exciton and biexciton states are observed. In the presence of biexcitons the collapse and revival phenomenon becomes faster due to the strong coupling of biexciton with cavity field.

J. Thomas Andrews

2002-11-22

96

Aqueous Synthesis of Nontoxic Ag2Se/ZnSe Quantum Dots Designing as Fluorescence Sensors for Detection of Ag(I) and Cu(II) Ions.  

PubMed

We reported the synthesis of water-soluble and nontoxic Ag2Se/ZnSe Quantum Dots (QDs) using for fluorescence sensors. The influences of various experimental conditions including the synthesis pH, types of ligand, feed ratios, and the refluxed time on the growth process and fluorescence of QDs were investigated in detail. Under optimal conditions, Ag2Se/ZnSe QDs show a single emission peak around 490 nm with the maximal photoluminescence (PL) quantum yield (QYs) of 13.7 %. As-prepared Ag2Se/ZnSe QDs can be used for detection of Ag(II) and Cu(II). The detection limits are 1?×?10(-6) mol/L to 5?×?10(-5) mol/L for Ag (I), and 2?×?10(-6) mol/L to 1.10?×?10(-4) mol/L for Cu(II). PMID:25391903

Wang, Chunlei; Xu, Shuhong; Zhao, Zengxia; Wang, Zhuyuan; Cui, Yiping

2014-11-14

97

Transport through graphene quantum dots.  

PubMed

We review transport experiments on graphene quantum dots and narrow graphene constrictions. In a quantum dot, electrons are confined in all lateral dimensions, offering the possibility for detailed investigation and controlled manipulation of individual quantum systems. The recently isolated two-dimensional carbon allotrope graphene is an interesting host to study quantum phenomena, due to its novel electronic properties and the expected weak interaction of the electron spin with the material. Graphene quantum dots are fabricated by etching mono-layer flakes into small islands (diameter 60-350 nm) with narrow connections to contacts (width 20-75 nm), serving as tunneling barriers for transport spectroscopy. Electron confinement in graphene quantum dots is observed by measuring Coulomb blockade and transport through excited states, a manifestation of quantum confinement. Measurements in a magnetic field perpendicular to the sample plane allowed to identify the regime with only a few charge carriers in the dot (electron-hole transition), and the crossover to the formation of the graphene specific zero-energy Landau level at high fields. After rotation of the sample into parallel magnetic field orientation, Zeeman spin splitting with a g-factor of g ? 2 is measured. The filling sequence of subsequent spin states is similar to what was found in GaAs and related to the non-negligible influence of exchange interactions among the electrons. PMID:23144122

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

2012-12-01

98

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. PMID:22888233

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

99

Synthesis and mechanism study of CdS quantum dots in two-phase liquid/liquid interfaces via one-pot route  

NASA Astrophysics Data System (ADS)

The present letter reports a facile synthetic strategy in octadecene(ODE)/glycerol interfaces to prepare CdS quantum dots (QDs) with bright bandgap emission. In this synthesis, the precursors were not synthesized as a preceding step, but all chemicals were reacted simultaneously in a one-pot reaction. The monodispersed CdS QDs were synthesized in ODE/glycerol interfaces at 140, 160 and 180 °C, respectively. The thermodynamic equilibrium was proposed to explain the growth mechanism of CdS QDs in the ODE/glycerol interfaces.

Wang, Jidong; Guo, Kehong; Ke, Dandan; Han, Shumin

2015-01-01

100

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

PubMed

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

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

2012-10-22

101

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

PubMed

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

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

2012-02-01

102

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

103

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

PubMed

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

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

2010-06-25

104

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

105

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. PMID:22273747

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

2011-01-01

106

All inorganic colloidal quantum dot LEDs  

E-print Network

This thesis presents the first colloidal quantum dot light emitting devices (QD-LEDs) with metal oxide charge transport layers. Colloidally synthesized quantum dots (QDs) have shown promise as the active material in ...

Wood, Vanessa Claire

2007-01-01

107

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

108

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

109

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

PubMed Central

A continuous and compact CdS quantum dot-sensitive layer was synthesized on TiO2 nanorods by successive ionic layer adsorption and reaction (SILAR) and subsequent thermal annealing. The thickness of the CdS quantum dot layer was tuned by SILAR cycles, which was found to be closely related to light absorption and carrier transformation. The CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet–visible absorption spectroscopy, and photoelectrochemical property measurement. The optimum sample was fabricated by SILAR in 70 cycles and then annealed at 400°C for 1 h in air atmosphere. A TiO2/CdS core-shell structure was formed with a diameter of 35 nm, which presented an improvement in light harvesting. Finally, a saturated photocurrent of 3.6 mA/cm2 was produced under the irradiation of AM1.5G simulated sunlight at 100 mW/cm2. In particular, the saturated current density maintained a fixed value of approximately 3 mA/cm2 without decadence as time passed under the light conditions, indicating the steady photoelectronic property of the photoanode. PMID:23663590

2013-01-01

110

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

NASA Astrophysics Data System (ADS)

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

Hu, Yunxia; Wang, Baoyuan; Zhang, Jieqiong; Wang, Tian; Liu, Rong; Zhang, Jun; Wang, Xina; Wang, Hao

2013-05-01

111

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

112

Synthesis and Characterization of TiO2 Nanotubes Sensitized with CdS Quantum Dots Using a One-Step Method  

NASA Astrophysics Data System (ADS)

A novel one-step synthesis process was used to assemble CdS quantum dots (QDs) into TiO2 nanotube arrays (TNTAs). The sensitization time of the TiO2 nanotubes can be adjusted by controlling the CdS QD synthesis time. The absorption band of sensitized TNTAs red-shifted and broadened to the visible spectrum. The photoelectric conversion efficiency increased to 0.83%, the open-circuit voltage to 776 mV, and the short-circuit current density ( J SC) to 2.30 mA cm-2 with increased sensitization time. The conversion efficiency with this new sensitization method was five times that of nonsensitized TNTAs, providing novel ideas for study of TNTA solar cells.

Song, Jiahui; Zhang, Xinguo; Zhou, Chunyan; Lan, Yuwei; Pang, Qi; Zhou, Liya

2015-01-01

113

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

NASA Astrophysics Data System (ADS)

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

Coughlin, Kathleen M.

114

Quantum dot quantum cascade infrared photodetector  

SciTech Connect

We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3??m. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski–Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64?×?10{sup 11} and 4.83?×?10{sup 6} Jones at zero bias were obtained at 80?K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging.

Wang, Xue-Jiao; Zhai, Shen-Qiang; Zhuo, Ning; Liu, Jun-Qi, E-mail: jqliu@semi.ac.cn, E-mail: fqliu@semi.ac.cn; Liu, Feng-Qi, E-mail: jqliu@semi.ac.cn, E-mail: fqliu@semi.ac.cn; Liu, Shu-Man; Wang, Zhan-Guo [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences and Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, P.O. Box 912, Beijing 100083 (China)

2014-04-28

115

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

116

Large-scale synthesis of high quality InP quantum dots in a continuous flow-reactor under supercritical conditions.  

PubMed

The synthesis of indium phosphide quantum dots (QDs) in toluene under supercritical conditions was carried out in a macroscopic continuous flow reaction system. The results of first experiments are reported in comparison with analogous reactions in octadecene. The reaction system is described and details are provided about special procedures that are enabled by the continuous flow system for the screening of reaction conditions. The produced QDs show very narrow emission peaks with full width at half maximum down to 45 nm and reasonable photoluminescence quantum yields. The subsequent purification process is facilitated by the ease of removal of toluene, and the productivity of the system is increased by high temperature and high pressure conditions. PMID:25656681

Ippen, Christian; Schneider, Benjamin; Pries, Christopher; Kröpke, Stefan; Greco, Tonino; Holländer, Andreas

2015-02-27

117

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

118

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. PMID:24084780

He, Xuewen; Gao, Li; Ma, Nan

2013-01-01

119

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

120

Synthesis of highly luminescent and biocompatible CdTe/CdS/ZnS quantum dots using microwave irradiation: a comparative study of different ligands.  

PubMed

We compared the effects of several ligands frequently used in aqueous synthesis, including L-cysteine, L-cysteine hydrochloride, N-acetyl-L-cysteine (NAC), glutathione and 3-mercaptopropionic acid, for microwave synthesis of CdTe quantum dots (QDs) in a sealed vessel with varied temperatures and times, and then developed a rapid microwave-assisted protocol for preparing highly luminescent, photostable and biocompatible CdTe/CdS/ZnS core-multishell QDs. The effects of molecular structures of these ligands on QD synthesis under high temperatures were explored. Among these ligands, NAC was found to be the optimal ligand in terms of the optical properties of resultant QDs and reaction conditions. The emission wavelength of NAC-capped CdTe QDs could reach 700 nm in 5 min by controlling the reaction temperature, and the resultant CdTe/CdS/ZnS core-multishell QDs could achieve the highest quantum yields up to 74% with robust photostability. In addition, the effects of temperature, growth time and shell-precursor ratio on shell growth were examined. Finally, cell culturing indicated the low cytotoxicity of CdTe/CdS/ZnS core-multishell QDs as compared to CdTe and CdTe/CdS QDs, suggesting their high potential for applications in biomedical imaging and diagnostics. PMID:24436082

He, Hua; Sun, Xing; Wang, Xiaojuan; Xu, Hai

2014-11-01

121

Colloidal quantum dots intraband photodetectors.  

PubMed

Photoconductivity is demonstrated with monodispersed HgSe colloidal quantum dots that are illuminated with radiation resonant with 1S(e)-1P(e) intraband electronic absorption, between 3 and 5 ?m. A doping of two electrons per dot gives the lowest dark current, and a detectivity of 8.5 × 10(8) Jones is obtained at 80 K. Photoluminescence of the intraband transition is also observed. The detector properties are discussed in terms of the measured photoluminescence quantum yield, the electron mobility in the 1P(e) state, and the responsivity. The intraband photoresponse allows to fully harness the quantum confined states in colloidal nanostructures, extending the prior limited use of interband transition. PMID:25343383

Deng, Zhiyou; Jeong, Kwang Seob; Guyot-Sionnest, Philippe

2014-11-25

122

Designing quantum dots for solotronics  

NASA Astrophysics Data System (ADS)

Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory.

Kobak, J.; Smole?ski, T.; Goryca, M.; Papaj, M.; Gietka, K.; Bogucki, A.; Koperski, M.; Rousset, J.-G.; Suffczy?ski, J.; Janik, E.; Nawrocki, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

2014-01-01

123

Designing quantum dots for solotronics  

PubMed Central

Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory. PMID:24463946

Kobak, J.; Smole?ski, T.; Goryca, M.; Papaj, M.; Gietka, K.; Bogucki, A.; Koperski, M.; Rousset, J.-G.; Suffczy?ski, J.; Janik, E.; Nawrocki, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

2014-01-01

124

Lifetime blinking in nonblinking nanocrystal quantum dots  

PubMed Central

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

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

2012-01-01

125

Semiconductor double quantum dot micromaser.  

PubMed

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

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

2015-01-16

126

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

PubMed Central

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

2012-01-01

127

Quantum dot ternary-valued full-adder: Logic synthesis by a multiobjective design optimization based on a genetic algorithm  

NASA Astrophysics Data System (ADS)

A methodology is proposed for designing a low-energy consuming ternary-valued full adder based on a quantum dot (QD) electrostatically coupled with a single electron transistor operating as a charge sensor. The methodology is based on design optimization: the values of the physical parameters of the system required for implementing the logic operations are optimized using a multiobjective genetic algorithm. The searching space is determined by elements of the capacitance matrix describing the electrostatic couplings in the entire device. The objective functions are defined as the maximal absolute error over actual device logic outputs relative to the ideal truth tables for the sum and the carry-out in base 3. The logic units are implemented on the same device: a single dual-gate quantum dot and a charge sensor. Their physical parameters are optimized to compute either the sum or the carry out outputs and are compatible with current experimental capabilities. The outputs are encoded in the value of the electric current passing through the charge sensor, while the logic inputs are supplied by the voltage levels on the two gate electrodes attached to the QD. The complex logic ternary operations are directly implemented on an extremely simple device, characterized by small sizes and low-energy consumption compared to devices based on switching single-electron transistors. The design methodology is general and provides a rational approach for realizing non-switching logic operations on QD devices.

Klymenko, M. V.; Remacle, F.

2014-10-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

129

Designed short RGD peptides for one-pot aqueous synthesis of integrin-binding CdTe and CdZnTe quantum dots.  

PubMed

We have designed a series of short RGD peptide ligands and developed one-pot aqueous synthesis of integrin-binding CdTe and CdZnTe quantum dots (QDs). We first examined the effects of different RGD peptides, including RGDS, CRGDS, Ac-CRGDS, CRGDS-CONH?, Ac-CRGDS-CONH?, RGDSC, CCRGDS, and CCCRGDS, on the synthesis of CdTe QDs. CRGDS were found to be the optimal ligand, providing the CdTe QDs with well-defined wavelength ranges (500-650 nm) and relatively high photoluminescence quantum yields (up to 15%). The key synthesis parameters (the pH value of the Cd²?-RGD precursors and the molar ratio of RGD/Cd²?) were assessed. In order to further improve the optical properties of the RGD-capped QDs, zinc was then incorporated by the simultaneous reaction of Cd²? and Zn²? with NaHTe. By using a mixture of CRGDS and cysteine as the stabilizer, the quantum yields of CdZnTe alloy QDs reached as high as 60% without any post-treatment, and they also showed excellent stability against time, pH, and salinity. Note that these properties could not be obtained with CRGDS or cysteine alone as the stabilizer. Finally, we demonstrated that the RGD-capped QDs preferentially bind to cell surfaces because of the specific recognition of the RGD sequence to cell surface integrin receptors. Our synthesis strategy based on RGD peptides thus represents a convenient route for opening up QD technologies for cell-specific tagging and labeling applicable to a wide range of diagnostics and therapy. PMID:23106442

He, Hua; Feng, Min; Hu, Jing; Chen, Cuixia; Wang, Jiqian; Wang, Xiaojuan; Xu, Hai; Lu, Jian R

2012-11-01

130

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

2010-07-01

131

A tunable few electron triple quantum dot  

NASA Astrophysics Data System (ADS)

We report on a new design to realize a fully tunable lateral triple quantum dot. The electrostatically defined quantum dots are arranged in series. The number of electrons in the quantum dots can be controlled and fundamental electronic configurations such as the (0,0,0) and (1,1,1) are obtained. Control of the number of electrons is important to perform quantum information processes using electron spins as qubits. Individual control of the tunnel barriers between the dots as well as resonant conditions called quadruple points where the chemical potential of the three quantum dots are aligned are achieved. A neighboring quantum point contact is used as a charge sensor to map out the charge stability diagram. We explore the back-action effects of the charge sensor on the triple quantum dot system and observe a series of additional resonances directly linked to the bias applied across the charge sensor.

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

2010-03-01

132

Quantum computation with quantum dot excitons  

Microsoft Academic Search

Potential application of elementary excitation in semiconductor quantum dot to quantum computation is discussed. We propose a scalable hardware and all optical implementation of a logic gate that exploits the discrete nature of electron-hole states and their well-concentrated oscillator strength for ultrafast gate operation. A multiple-bit gate function is based on the nearest neighbour dipole-dipole coupling. Rabi population oscillation and

H. Kamada; H. Gotoh

2004-01-01

133

Thermoelectric energy harvesting with quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

134

Thermoelectric energy harvesting with quantum dots.  

PubMed

We review recent theoretical work on thermoelectric energy harvesting in multi-terminal quantum-dot setups. We first discuss several examples of nanoscale heat engines based on Coulomb-coupled conductors. In particular, we focus on quantum dots in the Coulomb-blockade regime, chaotic cavities and resonant tunneling through quantum dots and wells. We then turn toward quantum-dot heat engines that are driven by bosonic degrees of freedom such as phonons, magnons and microwave photons. These systems provide interesting connections to spin caloritronics and circuit quantum electrodynamics. PMID:25549281

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

2015-01-21

135

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

136

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

SciTech Connect

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

Ameen, Tarek A.; El-Batawy, Yasser M.; Abouelsaood, A. A. [Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University, Giza (Egypt)

2014-02-14

137

Energy calculations of quantum dot  

NASA Astrophysics Data System (ADS)

We calculated the total energy of a semiconductor quantum dot formed in gate and etching defined devices. A 3D Poisson equation is solved self-consistently to obtain the electron density and potential profile. The total energies of electrons in the quantum dots with two different sizes are calculated with three different approximations by using the density and potential obtained from self-consistent procedure. In our calculation we used a recently developed energy functional called “orbital-free energy functional”, Thomas-Fermi approximation and standard local-density approximation within density functional theory. The comparison of these methods reveals the efficacy of the used newly developed orbital-free energy functional which facilitates the calculation of Hartree integral for treatment of electron-electron interaction.

Bilgeç Akyüz, G.; Akgüngör, K.; ?akiro?lu, S.; Siddiki, A.; Sökmen, ?.

2011-06-01

138

Generation of superradiation in quantum dot nanoheterostructures  

SciTech Connect

Conditions for the generation of Dicke supperradiation are studied for two types of quantum dot nanoheterostructures: a planar waveguide and a microdisk. The domain model for the generation of superradiation suggested earlier for quantum wells is generalized to inhomogeneous quantum dot arrays. Different scenarios of the generation of superradiation in a semiconductor microdisk are classified.

Savelyev, A. V., E-mail: savelev@mail.ioffe.ru; Karachinsky, L. Ya.; Novikov, I. I.; Gordeev, N. Yu.; Seisyan, R. P.; Zegrya, G. G. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2008-06-15

139

Electron counting in quantum dots  

Microsoft Academic Search

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

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

2009-01-01

140

Electron microscopy of quantum dots.  

PubMed

This brief review describes the different types of semiconductor quantum dot systems, their main applications and which types of microscopy methods are used to characterize them. Emphasis is put on the need for a comprehensive investigation of their size distribution, microstructure, chemical composition, strain state and electronic properties, all of which influence the optical properties and can be measured by different types of imaging, diffraction and spectroscopy methods in an electron microscope. PMID:25406030

Walther, T

2015-03-01

141

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

2012-02-01

142

Aqueous synthesis of highly luminescent surface Mn(2+) -doped CdTe quantum dots as a potential multimodal agent.  

PubMed

Mn(2+) -doped CdTe quantum dots (QDs) were synthesized directly via a facile surface doping strategy in aqueous solution. The best optical property emerged when the added amount of Mn(2+) was 5% compared to Cd(2+) in the CdTe nanoparticles and the reaction temperature was 60?°C. The fluorescence and magnetic properties of the QDs were studied. The as-prepared Mn(2+) -doped CdTe QDs have high quantum yield (48.13%) and a narrow distribution with an average diameter of 3.7?nm. The utility of biological imaging was also studied. Depending on the high quantum yield, cells in culture were illuminated and made more distinct from each other compared to results obtained with normal QDs. They also have a prominent longitudinal relaxivity value (r1 ?=?4.2?mM(-1) s(-1) ), which could indicate that the Mn(2+) -doped CdTe QDs can be used as a potential multimodal agent for fluorescence and magnetic resonance imaging. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24788557

Zhang, Fei; He, Fei; He, Xi-Wen; Li, Wen-You; Zhang, Yu-Kui

2014-12-01

143

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

NASA Astrophysics Data System (ADS)

The implantation and growth of metal nanoparticles on graphene nanosheets (GNS) leads directly to severe damage to the regular structure of the graphene sheets, which disrupts the extended ? conjugation, resulting in an impaired device performance. In this paper, we describe a facile approach for achieving the lossless formation of graphene composite decorated with tiny cadmium sulfide quantum dots (QDs) with excellent nonlinear optical properties by using benzyl mercaptan (BM) as the interlinker. The mercapto substituent of BM binds to the CdS QDs during their nucleation and growth process, and then the phenyl comes into contact with the GNS via the ?-? stacking interaction. Using this strategy, CdS QDs with an average diameter of 3 nm are uniformly dispersed over the surface of graphene, and the resulting QD-graphene composite exhibits excellent optical limiting properties, mainly contributed by nonlinear scattering and nonlinear absorption, upon both 532 and 1064 nm excitations, in the nanosecond laser pulse regime.

Feng, Miao; Sun, Ruiqing; Zhan, Hongbing; Chen, Yu

2010-02-01

144

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

145

Electron counting in quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

146

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

NASA Astrophysics Data System (ADS)

The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities up to 1400 mM-1 [QD] s-1 at 7 T and 300 K. We finally show that these QDs are suitable multimodal in vivo probes and demonstrate MRI and NIR fluorescence detection of regional lymph nodes in mice.The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities up to 1400 mM-1 [QD] s-1 at 7 T and 300 K. We finally show that these QDs are suitable multimodal in vivo probes and demonstrate MRI and NIR fluorescence detection of regional lymph nodes in mice. Electronic supplementary information (ESI) available: Determination of Mn content; magnetization measurements; additional TEM and spectroscopic data; additional NIR fluorescence image; MTT assay results. See DOI: 10.1039/c4nr02239d

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

2014-07-01

147

The quantum Hall effect in quantum dot systems  

NASA Astrophysics Data System (ADS)

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

Beltukov, Y. M.; Greshnov, A. A.

2014-12-01

148

Synthesis of cRGD-peptide conjugated near-infrared CdTe/ZnSe core-shell quantum dots for in vivo cancer targeting and imaging.  

PubMed

Cyclic RGD-peptide functionalized phospholipids micelle-encapsulated near-infrared CdTe/ZnSe quantum dots were synthesized as multifunctional probes for targeting and imaging tumors in live animals. PMID:20820500

Yong, Ken-Tye; Roy, Indrajit; Law, Wing-Cheung; Hu, Rui

2010-10-14

149

A facile synthesis of highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol in aqueous solution  

NASA Astrophysics Data System (ADS)

A facile bottom-up method for the synthesis of highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) has been developed via a one-step pyrolysis of citric acid and tris(hydroxymethyl)aminomethane. The obtained N-GQDs emitted strong blue fluorescence under 365 nm UV light excitation with a high quantum yield of 59.2%. They displayed excitation-independent behavior, high resistance to photobleaching and high ionic strength. In addition to the good linear relationship between the fluorescence intensity of the N-GQDs and pH in the range 2-7, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of 2,4,6-trinitrophenol (TNP). A sensitive approach has been developed for the detection of TNP with a detection limit of 0.30 ?M, and a linearity ranging from 1 to 60 ?M TNP could be obtained. The approach was highly selective and suitable for TNP analysis in natural water samples.A facile bottom-up method for the synthesis of highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) has been developed via a one-step pyrolysis of citric acid and tris(hydroxymethyl)aminomethane. The obtained N-GQDs emitted strong blue fluorescence under 365 nm UV light excitation with a high quantum yield of 59.2%. They displayed excitation-independent behavior, high resistance to photobleaching and high ionic strength. In addition to the good linear relationship between the fluorescence intensity of the N-GQDs and pH in the range 2-7, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of 2,4,6-trinitrophenol (TNP). A sensitive approach has been developed for the detection of TNP with a detection limit of 0.30 ?M, and a linearity ranging from 1 to 60 ?M TNP could be obtained. The approach was highly selective and suitable for TNP analysis in natural water samples. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr06365a

Lin, Liping; Rong, Mingcong; Lu, Sisi; Song, Xinhong; Zhong, Yunxin; Yan, Jiawei; Wang, Yiru; Chen, Xi

2015-01-01

150

Simple and greener synthesis of highly photoluminescence Mn2+-doped ZnS quantum dots and its surface passivation mechanism  

NASA Astrophysics Data System (ADS)

In this paper, we reported a simple synthetic method of highly photoluminescent (PL) and stable Mn2+-doped ZnS quantum dots (QDs) with glutathione (GSH) as the capping molecule and focused on mechanism of the surface passivation of QDs. The Mn2+-doped ZnS QDs that was synthesized in basic solution (pH 10) at 120 °C for 5 h exhibited blue trap-state emission around 418 nm and a strong orange-red emission at about 580 nm with an excitation wavelength of 330 nm. The optimum doping concentration is determined to be 1.5 at.%, and the present Mn2+-doped ZnS QDs synthesized under the optimal reaction condition exhibited a quantum yield of 48%. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) indicated that the Mn2+-doped ZnS QDs were 3-5 nm in size with a zinc blend structure. More importantly, the PL intensity and chemical stability can be improved using organic ligand modification strategies, it was found that GSH could passivate surface defects very efficiently by comparing and analyzing the results of the different organic ligands modification. The cadmium-free Mn2+-doped ZnS QDs well-passivated with GSH as capping molecule acquired the advantages of strong PL and excellent chemical stability, which are important to QD applications.

Wang, Yongbo; Liang, Xuhua; Ma, Xuan; Hu, Yahong; Hu, Xiaoyun; Li, Xinghua; Fan, Jun

2014-10-01

151

Photoluminescence of a quantum-dot molecule  

NASA Astrophysics Data System (ADS)

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

Kruchinin, Stanislav Yu.; Rukhlenko, Ivan D.; Baimuratov, Anvar S.; Leonov, Mikhail Yu.; Turkov, Vadim K.; Gun'ko, Yurii K.; Baranov, Alexander V.; Fedorov, Anatoly V.

2015-01-01

152

Charge state hysteresis in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which accounts for the observed hysteretic behaviour by extending the established description for transport in double dots coupled to two reservoirs. We demonstrate that this type of device operates like a single-electron memory latch.

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

2014-11-01

153

Creating atomic order in semiconductors quantum dots  

E-print Network

1 Creating atomic order in semiconductors quantum dots Peter Moeck Department of Physics (MC 273. Nanoscience and technology 3. Self-assembled semiconductor quantum dots: What are they? How are they made-8 ~ 0.01 diameter of a human hair #12;4 "for developing semiconductor heterostructures used in high

Moeck, Peter

154

Slow light using semiconductor quantum dots  

Microsoft Academic Search

A variable semiconductor optical buffer based on the electromagnetically induced transparency in a quantum dot waveguide is theoretically investigated with feasible parameters for applications to a 40 Gbps optical network. We show the refractive index and absorption spectra of the quantum dot waveguide at various pump levels, which exhibit an optimal pump power for maximum slow-down factor, in agreement with

J Kim; S L Chuang; P C Ku; C J Chang-Hasnain

2004-01-01

155

Thick-shell nanocrystal quantum dots  

DOEpatents

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

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

2011-05-03

156

QUANTUM DOTS: USING NANOTECHNOLOGY TO RESTORE VISION  

Microsoft Academic Search

Quantum dots are a newly developed nanotechnology that has the potential to restore impaired vision. We will explain what quantum dots are, how they operate, and how they are made, including the material makeup and fabrication processes. We will then proceed by giving brief background information about the composition of the eye and how it functions. Furthermore, we will explain

Catherine Nalesnik

157

Surface processes during purification of InP quantum dots  

PubMed Central

Summary Recently, a new simple and fast method for the synthesis of InP quantum dots by using phosphine as phosphorous precursor and myristic acid as surface stabilizer was reported. Purification after synthesis is necessary to obtain samples with good optical properties. Two methods of purification were compared and the surface processes which occur during purification were studied. Traditional precipitation with acetone is accompanied by a small increase in photoluminescence. It occurs that during the purification the hydrolysis of the indium precursor takes place, which leads to a better surface passivation. The electrophoretic purification technique does not increase luminescence efficiency but yields very pure quantum dots in only a few minutes. Additionally, the formation of In(OH)3 during the low temperature synthesis was explained. Purification of quantum dots is a very significant part of postsynthetical treatment that determines the properties of the material. But this subject is not sufficiently discussed in the literature. The paper is devoted to the processes that occur at the surface of quantum dots during purification. A new method of purification, electrophoresis, is investigated and described in particular. PMID:25161857

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

2014-01-01

158

Facile synthesis of analogous graphene quantum dots with sp2 hybridized carbon atom dominant structures and their photovoltaic application  

NASA Astrophysics Data System (ADS)

Graphene quantum dot (GQD) is an emerging class of zero-dimensional nanocarbon material with many novel applications. It is of scientific importance to prepare GQDs with more perfect structures, that is, GQDs containing negligible oxygenous defects, for both optimizing their optical properties and helping in their photovoltaic applications. Herein, a new strategy for the facile preparation of ``pristine'' GQDs is reported. The method we presented is a combination of a bottom-up synthetic and a solvent-induced interface separation process, during which the target products with highly crystalline structure were selected by the organic solvent. The obtained organic soluble GQDs (O-GQDs) showed a significant difference in structure and composition compared with ordinary aqueous soluble GQDs, thus leading to a series of novel properties. Furthermore, O-GQDs were applied as electron-acceptors in a poly(3-hexylthiophene) (P3HT)-based organic photovoltaic device. The performance highlights that O-GQD has potential to be a novel electron-acceptor material due to the sp2 hybridized carbon atom dominant structure and good solubility in organic solvents.Graphene quantum dot (GQD) is an emerging class of zero-dimensional nanocarbon material with many novel applications. It is of scientific importance to prepare GQDs with more perfect structures, that is, GQDs containing negligible oxygenous defects, for both optimizing their optical properties and helping in their photovoltaic applications. Herein, a new strategy for the facile preparation of ``pristine'' GQDs is reported. The method we presented is a combination of a bottom-up synthetic and a solvent-induced interface separation process, during which the target products with highly crystalline structure were selected by the organic solvent. The obtained organic soluble GQDs (O-GQDs) showed a significant difference in structure and composition compared with ordinary aqueous soluble GQDs, thus leading to a series of novel properties. Furthermore, O-GQDs were applied as electron-acceptors in a poly(3-hexylthiophene) (P3HT)-based organic photovoltaic device. The performance highlights that O-GQD has potential to be a novel electron-acceptor material due to the sp2 hybridized carbon atom dominant structure and good solubility in organic solvents. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03658a

Huang, Zhengcheng; Shen, Yongtao; Li, Yu; Zheng, Wenjun; Xue, Yunjia; Qin, Chengqun; Zhang, Bo; Hao, Jingxiang; Feng, Wei

2014-10-01

159

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

160

Semiconductor Fluorescent Quantum Dots: Efficient Biolabels in Cancer Diagnostics  

NASA Astrophysics Data System (ADS)

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

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

161

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

162

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

163

A facile synthesis of highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol in aqueous solution.  

PubMed

A facile bottom-up method for the synthesis of highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) has been developed via a one-step pyrolysis of citric acid and tris(hydroxymethyl)aminomethane. The obtained N-GQDs emitted strong blue fluorescence under 365 nm UV light excitation with a high quantum yield of 59.2%. They displayed excitation-independent behavior, high resistance to photobleaching and high ionic strength. In addition to the good linear relationship between the fluorescence intensity of the N-GQDs and pH in the range 2-7, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of 2,4,6-trinitrophenol (TNP). A sensitive approach has been developed for the detection of TNP with a detection limit of 0.30 ?M, and a linearity ranging from 1 to 60 ?M TNP could be obtained. The approach was highly selective and suitable for TNP analysis in natural water samples. PMID:25522688

Lin, Liping; Rong, Mingcong; Lu, Sisi; Song, Xinhong; Zhong, Yunxin; Yan, Jiawei; Wang, Yiru; Chen, Xi

2015-01-22

164

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

PubMed

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

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

2014-07-25

165

A facile cation exchange-based aqueous synthesis of highly stable and biocompatible Ag?S quantum dots emitting in the second near-infrared biological window.  

PubMed

Second near-infrared (NIR-II) emitting Ag2S quantum dots (QDs) with high stability and biocompatibility were synthesized and developed toward an ideal nanoprobe. This study reports a facile synthesis of NIR-II Ag2S QDs on the basis of cation exchange between visible-emitting CdS QDs and Ag(+) ions in aqueous solution. Experimental data testified that the cation exchange was quick and complete and that the resultant products were single monoclinic Ag2S without CdS QDs. The prepared Ag2S QDs were systematically characterized, showed typical NIR-II emission and high PL stability, and had small diameters (~3.5 nm) and a quantum yield up to 2.3%. The results of cytotoxicity assay suggested that the Ag2S QDs produced negligible effects in altering the cell proliferation or in generating reactive oxygen species, indicating an ultralow cytotoxicity and an excellent biocompatibility. These properties have opened up the possibility of using Ag2S QDs for effective bioimaging applications. PMID:25270003

Gui, Rijun; Sun, Jie; Liu, Dexiu; Wang, Yanfeng; Jin, Hui

2014-11-28

166

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots  

E-print Network

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ~170% and attained a saturation value after ~100 minutes of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200oC) and pressures (~120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright blue PL has been discussed. The results were supported by x-ray phase analysis, high-resolution electro...

Sahai, Sonal; Shanker, Virendra; Singh, Nahar; Haranath, D; 10.1016/j.jcis.2011.02.030

2012-01-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

168

High throughput synthesis of uniform biocompatible polymer beads with high quantum dot loading using microfluidic jet-mode breakup.  

PubMed

Uniform polymer microbeads with highly loaded quantum dots (QDs) are produced using high-throughput coherent jet breakup of a biocompatible poly(ethylene glycol) diacrylate (PEGDA) prepolymer resin, followed by in-line photopolymerization. A spiraling and gradually widening channel enables maximum absorption of radiated UV light for the in-line photopolymerization without coalescence and clogging issues. Although the dripping mode in general provides superior uniformity to the jet mode, our nozzle design with tapered geometry brings controlled jet breakup leading to 3% of uniform particle size distribution, comparable to dripping-mode performance. We achieve a maximum production rate of 2.32 kHz, 38 times faster than the dripping mode, at a same polymer flow rate. In addition, the jet-mode scheme provides better versatility with 3 times wider range of size control as well as the compatibility with viscous fluids that could cause pressure buildup in the microsystem. As a demonstration, a QD-doped prepolymer resin is introduced to create uniform biocompatible polymer beads with 10 wt % CdSe/ZnSe QD loading. In spite of this high loading, the resulting polymer beads exhibits narrow bandwidth of 28 nm to be used for the ultrasensitive bioimaging, optical coding, and sensing sufficiently with single bead. PMID:24506820

Lee, Seung-Kon; Baek, Jinyoung; Jensen, Klavs F

2014-03-01

169

Laser-assisted synthesis of Staphylococcus aureus protein-capped silicon quantum dots as bio-functional nanoprobes  

NASA Astrophysics Data System (ADS)

A novel approach for nanofabricating protein-functionalized luminescent silicon nanoparticles based on infrared ultrafast laser ablation of silicon in an aqueous solution of Staphylococcus aureus protein A is reported. It is demonstrated that 8 nm protein A-capped silicon quantum dots with blue-green photoemissive properties are generated. The conjugation efficiency studies reveal a high percentage of protein A attached to the Si nanoparticle surface through physical adsorption phenomena during the in situ laser process. The biological functionality of laser-generated Staphylococcus aureus protein A-capped Si nanoparticles is investigated. Confocal and electron microscopy together with energy dispersive x-ray spectroscopy analysis show that these Si-based bio-nanostructures selectively bind IgG in the cells. Cell viability studies reveal that these protein A-capped Si nanoparticles are suitable for biological applications, demonstrating their potential as universal secondary biomarkers for in vivo applications such as long-term, real-time cell labeling, cell staining and controlled drug delivery.

Bagga, K.; Barchanski, A.; Intartaglia, R.; Dante, S.; Marotta, R.; Diaspro, A.; Sajti, C. L.; Brandi, F.

2013-06-01

170

Facile synthesis of analogous graphene quantum dots with sp(2) hybridized carbon atom dominant structures and their photovoltaic application.  

PubMed

Graphene quantum dot (GQD) is an emerging class of zero-dimensional nanocarbon material with many novel applications. It is of scientific importance to prepare GQDs with more perfect structures, that is, GQDs containing negligible oxygenous defects, for both optimizing their optical properties and helping in their photovoltaic applications. Herein, a new strategy for the facile preparation of "pristine" GQDs is reported. The method we presented is a combination of a bottom-up synthetic and a solvent-induced interface separation process, during which the target products with highly crystalline structure were selected by the organic solvent. The obtained organic soluble GQDs (O-GQDs) showed a significant difference in structure and composition compared with ordinary aqueous soluble GQDs, thus leading to a series of novel properties. Furthermore, O-GQDs were applied as electron-acceptors in a poly(3-hexylthiophene) (P3HT)-based organic photovoltaic device. The performance highlights that O-GQD has potential to be a novel electron-acceptor material due to the sp(2) hybridized carbon atom dominant structure and good solubility in organic solvents. PMID:25247467

Huang, Zhengcheng; Shen, Yongtao; Li, Yu; Zheng, Wenjun; Xue, Yunjia; Qin, Chengqun; Zhang, Bo; Hao, Jingxiang; Feng, Wei

2014-11-01

171

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

PubMed

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. PMID:23282851

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

2013-02-01

172

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

PubMed

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

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

2013-11-29

173

Coherent optoelectronics with single quantum dots  

NASA Astrophysics Data System (ADS)

The optical properties of semiconductor quantum dots are in many respects similar to those of atoms. Since quantum dots can be defined by state-of-the-art semiconductor technologies, they exhibit long-term stability and allow for well-controlled and efficient interactions with both optical and electrical fields. Resonant ps excitation of single quantum dot photodiodes leads to new classes of coherent optoelectronic functions and devices, which exhibit precise state preparation, phase-sensitive optical manipulations and the control of quantum states by electrical fields.

Zrenner, A.; Ester, P.; Michaelis de Vasconcellos, S.; Hübner, M. C.; Lackmann, L.; Stufler, S.; Bichler, M.

2008-11-01

174

Hybrid superconductor-quantum dot devices.  

PubMed

Advances in nanofabrication techniques have made it possible to make devices in which superconducting electrodes are connected to non-superconducting nanostructures such as quantum dots. The properties of these hybrid devices result from a combination of a macroscopic quantum phenomenon involving large numbers of electrons (superconductivity) and the ability to control single electrons, offered by quantum dots. Here we review research into electron transport and other fundamental processes that have been studied in these devices. We also describe potential applications, such as a transistor in which the direction of a supercurrent can be reversed by adding just one electron to a quantum dot. PMID:20852639

De Franceschi, Silvano; Kouwenhoven, Leo; Schönenberger, Christian; Wernsdorfer, Wolfgang

2010-10-01

175

Photon assisted tunneling spectroscopy on a double quantum dot  

E-print Network

in a double-quantum-dot system. 1. Introduction Semiconductor quantum dots, in which charge states and singlePhoton assisted tunneling spectroscopy on a double quantum dot T Fujisawayz1 , T H Oosterkampy, W G quantum dots are often referred to as arti¯cial atoms since they contain well-de¯ned discrete levels. When

176

Electron Transport in Side Coupled Quantum Dots Fano Fano  

E-print Network

the detection of the spin polarization in a semiconductor using the side coupled quantum dot as a spin probeElectron Transport in Side Coupled Quantum Dots 21 12 #12;#12;Fano Fano Fermi Fermi Fermi Fermi dots. A quantum dot is an artificial quantum system to confine electrons in a small region. Different

Katsumoto, Shingo

177

Kondo Effect in Coupled Quantum Dots A. M. Chang+  

E-print Network

, with emphasis on the semiconductor quantum dot system. The rich variety of behaviors, such as distinct quantum and shapes, e.g. in semiconductor quantum dots [2­19], metallic quan- tum dots [20­23], tunnel junctionsKondo Effect in Coupled Quantum Dots A. M. Chang+ , J. C. Chen+ Department of Physics, Duke

Chang, Albert

178

Miniband formation in a quantum dot crystal Olga L. Lazarenkovaa)  

E-print Network

structure in a three-dimensional regimented array of semiconductor quantum dots using an envelope function of semiconductor quantum dots or multiple arrays, e.g., stacks of quantum dots, which are also referred regimented array of semiconductor quantum dots using an envelope function approximation. The regi- mentation

179

Optophononics with coupled quantum dots.  

PubMed

Modern technology is founded on the intimate understanding of how to utilize and control electrons. Next to electrons, nature uses phonons, quantized vibrations of an elastic structure, to carry energy, momentum and even information through solids. Phonons permeate the crystalline components of modern technology, yet in terms of technological utilization phonons are far from being on par with electrons. Here we demonstrate how phonons can be employed to render a single quantum dot pair optically transparent. This phonon-induced transparency is realized via the formation of a molecular polaron, the result of a Fano-type quantum interference, which proves that we have accomplished making typically incoherent and dissipative phonons behave in a coherent and non-dissipative manner. We find the transparency to be widely tunable by electronic and optical means. Thereby we show amplification of weakest coupling channels. We further outline the molecular polaron's potential as a control element in phononic circuitry architecture. PMID:24534815

Kerfoot, Mark L; Govorov, Alexander O; Czarnocki, Cyprian; Lu, Davis; Gad, Youstina N; Bracker, Allan S; Gammon, Daniel; Scheibner, Michael

2014-01-01

180

Realization of quantum-dot cellular automata using semiconductor quantum dots  

Microsoft Academic Search

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

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

2003-01-01

181

Single to quadruple quantum dots with tunable tunnel couplings  

SciTech Connect

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

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

2014-03-17

182

Spin-based quantum computation in multielectron quantum dots  

Microsoft Academic Search

In a quantum computer the hardware and software are intrinsically connected because the quantum Hamiltonian (or more precisely its time development) is the code that runs the computer. We demonstrate this subtle and crucial relationship by considering the example of electron-spin-based solid-state quantum computer in semiconductor quantum dots. We show that multielectron quantum dots with one valence electron in the

Xuedong Hu; S. Das Sarma

2001-01-01

183

Quantum dots with single-atom precision.  

PubMed

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

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

2014-07-01

184

Quantum dots with single-atom precision  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

185

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

186

The confinement energy of quantum dots  

E-print Network

One of the most significant research interests in the field of electronics is that on quantum dot, because such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. Confinement energy is a very important property of quantum dot. In this study, quantum confinement energy of a quantum dot is concluded to be h2/8md2 (d being the diameter of the confinement) and not h2/8ma2 (a being the radius of the confinement), as reported in the available literature. This is in the light of a recent study [1]. This finding should have a significant impact in the understanding of the physics of quantum dot and its technological application.

Dey, Samrat; Chakraborty, kishan; Dasgupta, Debasmita; Bordoloi, Darsana; Saikia, Rituja; Neog, Darsana; Shimray, Shishila; Paul, Supriyanka; Brahma, Kabita; Dey, Joydeep; Choudhury, Saurav

2012-01-01

187

Fluorescent Quantum Dots for Biological Labeling  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

188

Amplification Without Inversion in Semiconductor Quantum Dot  

NASA Astrophysics Data System (ADS)

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

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

189

Phonon affected transport through molecular quantum dots.  

PubMed

To describe the interaction of molecular vibrations with electrons at a quantum dot contacted to metallic leads, we extend an analytical approach that we previously developed for the many-polaron problem. Our scheme is based on an incomplete variational Lang-Firsov transformation, combined with a perturbative calculation of the electron-phonon self-energy in the framework of generalized Matsubara functions. This allows us to describe the system at weak-to-strong coupling and intermediate-to-large phonon frequencies. We present results for the quantum dot spectral function and for the kinetic coefficient that characterizes the electron transport through the dot. With these results we critically examine the strengths and limitations of our approach, and discuss the properties of the molecular quantum dot in the context of polaron physics. We place particular emphasis on the importance of corrections to the concept of an anti-adiabatic dot polaron suggested by the complete Lang-Firsov transformation. PMID:21832393

Loos, J; Koch, T; Alvermann, A; Bishop, A R; Fehske, H

2009-09-30

190

Tuning the emission of CdSe quantum dots by controlled trap enhancement.  

PubMed

Ligand exchange with 3-mercaptopropionic acid (MPA) has been successfully used to tune the emission intensity of trioctylphosphineoxide/dodecylamine-capped CdSe quantum dots. Addition of 3-mercaptopropionic acid (MPA) to CdSe quantum dot suspension enhances the deep trap emission with concurrent quenching of the band edge emission. The smaller sized quantum dots, because of larger surface/volume ratio, create a brighter trap emission and are more easily tuned. An important observation is that the deep trap emission which is minimal after synthesis is brightened to have a quantum yield of 1-5% and can be tuned based on the concentration of MPA in solution with the quantum dots. Photoluminescence decay and transient absorption measurements reveal the role of surface bound MPA in altering the photophysical properties of CdSe quantum dots. PMID:20373780

Baker, David R; Kamat, Prashant V

2010-07-01

191

Quantum dots and prion proteins  

PubMed Central

A diagnostics of infectious diseases can be done by the immunologic methods or by the amplification of nucleic acid specific to contagious agent using polymerase chain reaction. However, in transmissible spongiform encephalopathies, the infectious agent, prion protein (PrPSc), has the same sequence of nucleic acids as a naturally occurring protein. The other issue with the diagnosing based on the PrPSc detection is that the pathological form of prion protein is abundant only at late stages of the disease in a brain. Therefore, the diagnostics of prion protein caused diseases represent a sort of challenges as that hosts can incubate infectious prion proteins for many months or even years. Therefore, new in vivo assays for detection of prion proteins and for diagnosis of their relation to neurodegenerative diseases are summarized. Their applicability and future prospects in this field are discussed with particular aim at using quantum dots as fluorescent labels. PMID:24055838

Sobrova, Pavlina; Blazkova, Iva; Chomoucka, Jana; Drbohlavova, Jana; Vaculovicova, Marketa; Kopel, Pavel; Hubalek, Jaromir; Kizek, Rene; Adam, Vojtech

2013-01-01

192

Magnetic anisotropies of quantum dots  

NASA Astrophysics Data System (ADS)

Magnetic anisotropies in quantum dots (QDs) doped by magnetic ions are discussed in terms of two frameworks: anisotropic g-factors and magnetocrystalline anisotropy energy [1]. Two examples, related to zinc-blende p-doped materials, are given of how these frameworks are utilized: four-level Hamiltonian of a flat QD and a cuboid infinite-well QD containing a single hole. The latter model, despite being an idealization of a real QD, displays a rich phenomenology of anisotropies. We quantify the anisotropy constants for ZnSe and CdTe QDs, confirming that the Ising-like effective Hamiltonians apply to magnetic QDs [2]. Compared to bulk systems, confinement tuning offers a new way to control easy axes in magnetic QDs. [1] K. Vyborny et al., preprint (2011). [2] C. Le Gall et al., Phys. Rev. Lett. 107, 057401 (2011).

Vyborny, Karel; Han, J. E.; Oszwaldowski, Rafal; Zutic, Igor; Petukhov, A. G.

2012-02-01

193

Multipolar interband absorption in a semiconductor quantum dot.  

E-print Network

Multipolar interband absorption in a semiconductor quantum dot. II. Magnetic dipole enhancement quantum dot. We find that electric dipole and magnetic dipole transitions are exclusive and therefore can- more, for various kinds of nanostructures (quantum dots, quantum wells, quantum wires) it has been

Novotny, Lukas

194

A facile synthesis of bimetallic AuPt nanoparticles as a new transparent counter electrode for quantum-dot-sensitized solar cells  

NASA Astrophysics Data System (ADS)

This study first reports the synthesis of AuPt bimetallic nanoparticles (AuPt-BNPs) on an FTO glass substrate using dry plasma reduction (DPR) and its application as an alternative transparent counter electrode (CE) for quantum-dot-sensitized solar cells (QDSCs) operated under bi-side illumination. DPR is an economically feasible and ecologically sustainable method. The formation of ultrafine crystalline AuPt-BNPs on an FTO substrate is confirmed through TEM, HRTEM with HAADF-STEM and HAADF-STEM-EDS analyses. The mechanism for controlling the size, mono-dispersity, and areal number density of nanoparticles on the substrate surface is suggested. The CE fabricated with AuPt-BNPs exhibits a high electro-catalytic activity without losing the optical transmittance of the FTO substrate. The QDSC employing the AuPt-BNP electrode reaches efficiencies of 2.4% under front-side illumination and 2.2% under back-side illumination. Bi-side illumination yields an efficiency of 3.4%, which is comparable to an efficiency of 3.7% obtained for the QDSC with the state-of-the-art CE.

Dao, Van-Duong; Choi, Youngwoo; Yong, Kijung; Larina, Liudmila L.; Shevaleevskiy, Oleg; Choi, Ho-Suk

2015-01-01

195

Synthesis of poly(ethylene glycol)-graft-chitosan and using as ligand for fabrication of water-soluble quantum dots.  

PubMed

The synthesis of water-soluble, stable and biocompatible quantum dots (QDs) is of crucial importance for nanobiotechnology. A chitosan derivative, poly(ethylene glycol)-graft-chitosan (PEG-g-CS), was successfully synthesized and employed as ligand for the growth of CdSe QDs in aqueous solution. The bivalent Cd(2+) ions can coordinate with multiple amino-groups, thus they act as both inter- and intramolecular cross-linking agents. When the concentration of Cd(2+) was 0.2 mmol/L, the CdSe/PEG-g-CS aggregates formed an irregular cross-linked network; when the concentration was 1 mmol/L, a phenomenon of micro-phase separation emerged as a result of enrichment of CS phase; when the concentration was 2 mmol/L, spherical nanohybrids with the size of 30-50 nm were obtained. Moreover, a possible mechanism was proposed for the formation of CdSe/PEG-g-CS aggregates. Meantime, in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests against HepG2 cells were carried out, the corresponding results suggested that the CdSe QDs prepared using PEG-g-CS as ligand displayed very low cytotoxicity. Therefore, these water-soluble QD-polymer hybrids are expected to find promising applications in medical field. PMID:24370850

Jiang, Zhenchao; Zhao, Chunbao; Liu, Xiaoheng

2014-03-01

196

Semiconductor Few-Electron Quantum Dots as Spin Qubits  

E-print Network

Semiconductor Few-Electron Quantum Dots as Spin Qubits J.M. Elzerman1,2 , R. Hanson1 , L.H.W. van the experimental steps we have taken towards using a single electron spin, trapped in a semiconductor quantum dot dot. This is done by J.M. Elzerman et al.: Semiconductor Few-Electron Quantum Dots as Spin Qubits

197

Excited-state spectroscopy on a quantum dot side coupled to a quantum wire  

E-print Network

.1063/1.2987424 Semiconductor quantum dots are promising candidates for quantum bits.1 In a conventional dot with two leadsExcited-state spectroscopy on a quantum dot side coupled to a quantum wire T. Otsuka,a E. Abe, Y report excited-state spectroscopy on a quantum dot side coupled to a quantum wire with accurate energy

Iye, Yasuhiro

198

SnO2 quantum dots and quantum wires: controllable synthesis, self-assembled 2D architectures, and gas-sensing properties.  

PubMed

SnO2 quantum dots (QDs) and ultrathin nanowires (NWs) with diameters of approximately 0.5-2.5 and approximately 1.5-4.5 nm, respectively, were controllably synthesized in a simple solution system. They are supposed to be ideal models for studying the continuous evolution of the quantum-confinement effect in SnO2 1D --> 0D systems. The observed transition from strong to weak quantum confinement in SnO2 QDs and ultrathin NWs is interpreted through the use of the Brus effective-mass approximation and the Nosaka finite-depth well model. Photoluminescence properties that were coinfluenced by size effects, defects (oxygen vacancies), and surface capping are discussed in detail. With the SnO2 QDs as building blocks, various 2D porous structures with ordered hexagonal, distorted hexagonal, and square patterns were prepared on silicon-wafer surfaces and exhibited optical features of 2D photonic crystals and enhanced gas sensitivity. PMID:18715007

Xu, Xiangxing; Zhuang, Jing; Wang, Xun

2008-09-17

199

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

200

Photodetectors based on colloidal quantum dots  

E-print Network

Inspired by recent work demonstrating photocurrent enhancement in quantum-dot (QD) solids via post-deposition chemical annealing and by recent successes incorporating single monolayers of QDs in light-emitting devices ...

Oertel, David C. (David Charles)

2007-01-01

201

Protein-directed synthesis of Mn-doped ZnS quantum dots: a dual-channel biosensor for two proteins.  

PubMed

Proteins typically have nanoscale dimensions and multiple binding sites with inorganic ions, which facilitates the templated synthesis of nanoparticles to yield nanoparticle-protein hybrids with tailored functionality, water solubility, and tunable frameworks with well-defined structure. In this work, we report a protein-templated synthesis of Mn-doped ZnS quantum dots (QDs) by exploring bovine serum albumin (BSA) as the template. The obtained Mn-doped ZnS QDs give phosphorescence emission centered at 590?nm, with a decay time of about 1.9?ms. A dual-channel sensing system for two different proteins was developed through integration of the optical responses (phosphorescence emission and resonant light scattering (RLS)) of Mn-doped ZnS QDs and recognition of them by surface BSA phosphorescent sensing of trypsin and RLS sensing of lysozyme. Trypsin can digest BSA and remove BSA from the surface of Mn-doped ZnS QDs, thus quenching the phosphorescence of QDs, whereas lysozyme can assemble with BSA to lead to aggregation of QDs and enhanced RLS intensity. The detection limits for trypsin and lysozyme were 40 and 3?nM, respectively. The selectivity of the respective channel for trypsin and lysozyme was evaluated with a series of other proteins. Unlike other protein sensors based on nanobioconjugates, the proposed dual-channel sensor employs only one type of QDs but can detect two different proteins. Further, we found the RLS of QDs can also be useful for studying the BSA-lysozyme binding stoichiometry, which has not been reported in the literature. These successful biosensor applications clearly demonstrate that BSA not only serves as a template for growth of Mn-doped ZnS QDs, but also impacts the QDs for selective recognition of analyte proteins. PMID:23576296

Wu, Peng; Zhao, Ting; Tian, Yunfei; Wu, Lan; Hou, Xiandeng

2013-06-01

202

Surface enhanced Raman scattering by CdS quantum dots  

Microsoft Academic Search

Surface enhanced Raman scattering is studied in nanostructures with CdS quantum dots formed using the Langmuir-Blodgett technology.\\u000a Features due to quantum dot longitudinal optical phonons are observed in the Raman spectra of both free CdS quantum dots and\\u000a such dots distributed in an organic matrix. The surface enhanced Raman scattering by nanostructures with CdS quantum dots\\u000a covered by an Ag

A. G. Milekhin; L. L. Sveshnikova; T. A. Duda; N. V. Surovtsev; S. V. Adichtchev; D. R. T. Zahn

2008-01-01

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

Electron Spin Dynamics in Semiconductor Quantum Dots  

SciTech Connect

An electron spin confined to a semiconductor quantum dot is not subject to the classical spin relaxation mechanisms known for free carriers but it strongly interacts with the nuclear spin system via the hyperfine interaction. We show in time resolved photoluminescence spectroscopy experiments on ensembles of self assembled InAs quantum dots in GaAs that this interaction leads to strong electron spin dephasing.

Marie, X.; Belhadj, T.; Urbaszek, B.; Amand, T. [Universite de Toulouse, LPCNO, INSA-CNRS-UPS, 135 avenue de Rangueil, 31077 Toulouse (France); Krebs, O.; Lemaitre, A.; Voisin, P. [Laboratoire de Photonique et Nanostructures, route de Nozay, 91460 Marcoussis (France)

2011-07-15

205

Far-infrared spectroscopy of quantum dots  

Microsoft Academic Search

Quantum dots on semiconductors are few-electron systems with discrete energy spectra. They are fabricated from semiconductor structures with two-dimensional electron gases like metal-oxide-semiconductor (MOS) capacitors or GaAs\\/GaAlAs heterostructures by laterally confining the electrons. Here some important fabrication schemes employing nanostructure technologies to create isolated quantum dots are outlined and the present status of far-infrared spectroscopy on these atomic-like systems is

Ulrich Merkt

1993-01-01

206

Synthesis of AS1411-aptamer-conjugated CdTe quantum dots with high fluorescence strength for probe labeling tumor cells.  

PubMed

In this paper, we report microwave-assisted, one-stage synthesis of high-quality functionalized water-soluble cadmium telluride (CdTe) quantum dots (QDs). By selecting sodium tellurite as the Te source, cadmium chloride as the Cd source, mercaptosuccinic acid (MSA) as the capping agent, and a borate-acetic acid buffer solution with a pH range of 5-8, CdTe nanocrystals with four colors (blue to orange) were conveniently prepared at 100 °C under microwave irradiation in less than one hour (reaction time: 10-60 min). The influence of parameters such as the pH, Cd:Te molar ratio, and reaction time on the emission range and quantum yield percentage (QY%) was investigated. The structures and compositions of the prepared CdTe QDs were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and X-ray powder diffraction experiments. The formation mechanism of the QDs is discussed in this paper. Furthermore, AS1141-aptamer-conjugated CdTe QDs in the U87MG glioblastoma cell line were assessed with a fluorescence microscope. The obtained results showed that the best conditions for obtaining a high QY of approximately 87% are a pH of 6, a Cd:Te molar ratio of 5:1, and a 30-min reaction time at 100 °C under microwave irradiation. The results showed that AS1141-aptamer-conjugated CdTe QDs could enter tumor cells efficiently. It could be concluded that a facile high-fluorescence-strength QD conjugated with a DNA aptamer, AS1411, which can recognize the extracellular matrix protein nucleolin, can specifically target U87MG human glioblastoma cells. The qualified AS1411-aptamer-conjugated QDs prepared in this study showed excellent capabilities as nanoprobes for cancer targeting and molecular imaging. PMID:25172439

Alibolandi, Mona; Abnous, Khalil; Ramezani, Mohammad; Hosseinkhani, Hossein; Hadizadeh, Farzin

2014-09-01

207

Facile one-pot synthesis of MoS2 quantum dots-graphene-TiO2 composites for highly enhanced photocatalytic properties.  

PubMed

We reported a simple one-pot solvothermal approach to fabricate a MoS2 quantum dots (QDs)-graphene-TiO2 (MGT) composite photocatalyst with significantly improved photocatalysis properties, which is caused by the increased charge separation, visible-light absorbance, specific surface area and reaction sites upon the introduction of MoS2 QDs. PMID:25514834

Gao, Weiyin; Wang, Minqiang; Ran, Chenxin; Li, Le

2015-01-15

208

Thermoelectric transport through strongly correlated quantum dots  

E-print Network

The thermoelectric properties of strongly correlated quantum dots, described by a single level Anderson model coupled to conduction electron leads, is investigated using Wilson's numerical renormalization group method. We calculate the electronic contribution, $K_{\\rm e}$, to the thermal conductance, the thermopower, $S$, and the electrical conductance, $G$, of a quantum dot as a function of both temperature, $T$, and gate voltage, ${\\rm v}_g$, for strong, intermediate and weak Coulomb correlations, $U$, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures $T_{1}({\\rm v}_g)$ and $T_{2}({\\rm v}_g)$ with $T_{1}< T_{2}$. Such sign changes in $S(T)$ are particularly sensitive signatures of strong correlations and Kondo physics. The relevance of this to recent thermopower measurements of Kondo correlated quantum dots is discussed. We discuss the figure of merit, power factor and the degree of violation of the Wiedemann-Franz law in quantum dots. The extent of temperature scaling in the thermopower and thermal conductance of quantum dots in the Kondo regime is also assessed.

T. A. Costi; V. Zlatic

2010-04-09

209

Electronic structure and photon absorption in semiconductor quantum dots  

Microsoft Academic Search

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

Gregory von Winckel

2006-01-01

210

Quantum dots for light emitting diodes.  

PubMed

In this article we discuss the development and key advantages of quantum dot based light emitting diode (QD-LED) and other applications based on their color purity, stability, and solution processibility. Analysis of quantum dot based LEDs and the main challenges faced in this field, such as the QD luminescence quenching, QD charging in thin films, and external quantum efficiency are discussed in detail. The description about how different optical down-conversion and structures enabled researchers to overcome these challenges and to commercialize the products. The recent developments about how to overcome these difficulties have also been discussed in this article. PMID:23858829

Qasim, Khan; Lei, Wei; Li, Qing

2013-05-01

211

Processing and characterization of monodisperse phosphine-free CdSe colloidal quantum dots  

NASA Astrophysics Data System (ADS)

In this research, mono-dispersed quantum dots of CdSe were produced using a phosphine-free approach to synthesis of colloidal quantum dots. Selenium precursor was selected as the main precursor. It was found that the initial concentration ratio of monomers critically controlled the size distribution of the nanoparticles through its influence on the growth kinetics of these particles. The best result was obtained using an initial Se/Cd ratio of 5 where CdSe quantum dots of a uniform size were synthesized. This was manifested in the absorption spectra of these particles by occurrence of sharp peaks at a wavelength of about 615 nm.

Maghsoudi, Hadi; Mahboub, Melika; Asgari, Sirous

2014-08-01

212

Qubit Protection in Nuclear-Spin Quantum Dot Memories  

E-print Network

We present a mechanism to protect quantum information stored in an ensemble of nuclear spins in a semiconductor quantum dot. When the dot is charged the nuclei interact with the spin of the excess electron through the ...

Taylor, J. M.

213

Electron tunneling and spin relaxation in a lateral quantum dot  

E-print Network

We report measurements that use real-time charge sensing to probe a single-electron lateral quantum dot. The charge sensor is a quantum point contact (QPC) adjacent to the dot and the sensitivity is comparable to other ...

Amasha, Sami

2008-01-01

214

Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field  

NASA Astrophysics Data System (ADS)

Semiconducting quantum dots - more fancifully dubbed artificial atoms - are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement - or the lack of any degree of freedom for the electrons (and/or holes) - in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines' random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level transitions are seen to be forbidden. The spherical quantum dots have an edge over the strictly two-dimensional quantum dots in that the additional (magnetic) quantum number makes the physics richer (but complex). A deeper grasp of the Coulomb blockade, quantum coherence, and entanglement can lead to a better insight into promising applications involving lasers, detectors, storage devices, and quantum computing.

Kushwaha, Manvir S.

2014-12-01

215

Study of the self-organization processes in lead sulfide quantum dots  

SciTech Connect

A procedure is described for the synthesis of nanoparticles based on lead chalcogenides. The procedure combines the synthesis of colloidal quantum dots (QDs) in aqueous solutions with simultaneous organization of the QDs into ordered arrays. The processes of the self-organization of QDs are analyzed at the nano- and microscopic levels by the photoluminescence method, atomic-force microscopy, and optical microscopy.

Tarasov, S. A., E-mail: SATarasov@mail.ru; Aleksandrova, O. A.; Maksimov, A. I.; Maraeva, E. V.; Matyushkin, L. B.; Men’kovich, E. A.; Moshnikov, V. A. [St. Petersburg Electrotechnical University LETI (Russian Federation); Musikhin, S. F. [St. Petersburg State Polytechnic University (Russian Federation)

2014-12-15

216

Electron cotunneling in a semiconductor quantum dot  

Microsoft Academic Search

We report transport measurements on a semiconductor quantum dot with a small\\u000anumber of confined electrons. In the Coulomb blockade regime, conduction is\\u000adominated by cotunneling processes. These can be either elastic or inelastic,\\u000adepending on whether they leave the dot in its ground state or drive it into an\\u000aexcited state, respectively. We are able to discriminate between these

S. De Franceschi; S. Sasaki; J. M. Elzerman; W. G. van der Wiel; S. Tarucha; L. P. Kouwenhoven

2001-01-01

217

Energy Transfer in CdSe Quantum Dot Solids  

Microsoft Academic Search

Dipole-dipole interdot interactions in close packed quantum dot solids lead to observed electronic energy transfer between close packed quantum dots. We use photoluminescence spectroscopies to study electronic energy transfer in optically thin and clear, close packed quantum dot solids prepared from samples of CdSe quantum dots tunable in size from 17-150 Åin diameter with standard deviations of <4.5%. High resolution

C. R. Kagan; C. B. Murray; M. Nirmal; M. G. Bawendi

1996-01-01

218

Mesoscopic spatiotemporal theory for quantum-dot lasers  

Microsoft Academic Search

We present a mesoscopic theory for the spatiotemporal carrier and light-field dynamics in quantum-dot lasers. Quantum-dot Maxwell-Bloch equations have been set up that mesoscopically describe the spatiotemporal light-field and interlevel\\/intralevel carrier dynamics in each quantum dot (QD) of a typical QD ensemble in quantum-dot lasers. In particular, this includes spontaneous luminescence, counterpropagation of amplified spontaneous emission, and induced recombination as

Edeltraud Gehrig; Ortwin Hess

2002-01-01

219

Sizes and fluorescence of cadmium sulfide quantum dots  

NASA Astrophysics Data System (ADS)

Cadmium sulfide quantum dots have been synthesized by wet chemical deposition from an aqueous solution. The sizes of the quantum dots determined by dynamic light scattering directly in the colloidal solution and by intermittent-contact atomic force microscopy in the dry sediment agree with each other. It has been found that splitting of the fluorescence peaks of the quantum dots can be affected by the disorder of the atomic structure of cadmium sulfide quantum dots.

Rempel', S. V.; Razvodov, A. A.; Nebogatikov, M. S.; Shishkina, E. V.; Shur, V. Ya.; Rempel', A. A.

2013-03-01

220

Quantum dot-based quantum buses for quantum computer hardware architecture  

Microsoft Academic Search

We propose a quantum bus based on semiconductor self-assembled quantum dots. This allows for transmission of qubits between the different quantum registers, and could be integrated in most of the present proposal for semiconductor quantum dot-based quantum computation.

Irene D’Amico

2006-01-01

221

Multipolar interband absorption in a semiconductor quantum dot.  

E-print Network

Multipolar interband absorption in a semiconductor quantum dot. I. Electric quadrupole enhancement a theoretical investigation of a semiconductor quantum dot interacting with a strongly localized optical field rates and selection rules. For a semiconductor quantum dot in the strong confinement limit we calcu

Novotny, Lukas

222

Magnetooptic properties of semiconductor quantum dots in glass composites  

Microsoft Academic Search

Low dimensional systems of semiconductor quantum dots in glass composites exhibit interesting physical properties arising from spatial confinement effects; an example is the discretization of the energy spectrum. In semiconductor quantum dots, electronic wave functions experience effects of quantum confinement arising from the dot-glass interface acting as an infinite potential barrier, effectively creating an infinite potential well. This leads to

Joseph H. Kratzer; John Schroeder

2004-01-01

223

Voltage-controlled motional narrowing in a semiconductor quantum dot  

E-print Network

Voltage-controlled motional narrowing in a semiconductor quantum dot A. Berthelot,1,2 G. Cassabois.1088/1367-2630/11/9/093032 #12;Voltage-controlled motional narrowing in a semiconductor quantum dot 2 Tunneling is one of the environment- induced decoherence in a semiconductor quantum dot (QD) embedded in a gated field- effect device

Paris-Sud XI, Université de

224

A molecular state of correlated electrons in a quantum dot  

E-print Network

by using inelastic light scattering16­18 in quantum dots containing four electrons19 . Spectra of lowLETTERS A molecular state of correlated electrons in a quantum dot SOKRATIS KALLIAKOS1 , MASSIMO in a semiconductor quantum dot1­3 , where at vanishing electron density the Coulomb interaction between electrons

Loss, Daniel

225

Controlling cavity reflectivity with a single quantum dot  

E-print Network

on direct probing of the cavity­quantum dot coupling, by means of resonant light scattering from stronglyLETTERS Controlling cavity reflectivity with a single quantum dot Dirk Englund1 *, Andrei Faraon1 nanocavities and semiconductor quantum dots have seen rapid progress. Recent experiments have allowed

Vuckovic, Jelena

226

Charge detection in graphene quantum dots J. Gttinger,a  

E-print Network

oxide top layer. Electron beam lithography EBL is used for patterning the isolated graphene flakesCharge detection in graphene quantum dots J. Güttinger,a C. Stampfer, S. Hellmüller, F. Molitor, T on a graphene quantum dot with an integrated graphene charge detector. The quantum dot device consists

Ihn, Thomas

227

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

228

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

PubMed

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

Das, Anirban; Wai, Chien M

2014-03-01

229

Quantum dot heterojunction solar cells: The mechanism of device operation and impacts of quantum dot oxidation  

NASA Astrophysics Data System (ADS)

This thesis explores the understanding of the chemistry and physics of colloidal quantum dots for practical solar energy photoconversion. Solar cell devices that make use of PbS quantum dots generally rely on constant and unchanged optical properties such that band gap energies remain tuned within the device. The design and development of unique experiments to ascertain mechanisms of optical band gap shifts occurring in PbS quantum dot thin-films exposed to air are discussed. The systematic study of the absorption properties of PbS quantum dot films exposed to air, heat, and UV illumination as a function of quantum dot size has been described. A method to improve the air-stability of films with atomic layer deposition of alumina is demonstrated. Encapsulation of quantum dot films using a protective layer of alumina results in quantum dot solids that maintain tuned absorption for 1000 hours. This thesis focuses on the use of atomic force microscopy and electrical variants thereof to study the physical and electrical characteristics of quantum dot arrays. These types of studies have broad implications in understanding charge transport mechanisms and solar cell device operation, with a particular emphasis on quantum dot transistors and solar cells. Imaging the channel potential of a PbSe quantum dot thin-film in a transistor showed a uniform distribution of charge coinciding with the transistor current voltage characteristics. In a second study, solar cell device operation of ZnO/PbS heterojunction solar cells was investigated by scanning active cross-sections with Kelvin probe microscopy as a function of applied bias, illumination and device architecture. This technique directly provides operating potential and electric field profiles to characterize drift and diffusion currents occurring in the device. SKPM established a field-free region occurring in the quantum dot layer, indicative of diffusion-limited transport. These results provide the path to optimization of future architectures that may employ drift-based transport in the quantum dot layer for enhanced charge extraction and power conversion efficiency.

Ihly, Rachelle

230

Scalable quantum computer architecture with coupled donor-quantum dot qubits  

DOEpatents

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

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

2014-08-26

231

Large scale synthesis of graphene quantum dots (GQDs) from waste biomass and their use as an efficient and selective photoluminescence on-off-on probe for Ag(+) ions.  

PubMed

Graphene quantum dots (GQDs) are synthesized from bio-waste and are further modified to produce amine-terminated GQDs (Am-GQDs) which have higher dispersibility and photoluminescence intensity than those of GQDs. A strong fluorescence quenching of Am-GQDs (switch-off) is observed for a number of metal ions, but only for the Ag(+) ions is the original fluorescence regenerated (switch-on) upon addition of L-cysteine. PMID:25162814

Suryawanshi, Anil; Biswal, Mandakini; Mhamane, Dattakumar; Gokhale, Rohan; Patil, Shankar; Guin, Debanjan; Ogale, Satishchandra

2014-10-21

232

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

233

Cavity quantum electrodynamics with quantum dot - photonic crystal nanocavities  

Microsoft Academic Search

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

Joshua R. Hendrickson

2010-01-01

234

Photodynamic antibacterial effect of graphene quantum dots.  

PubMed

Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD. PMID:24612819

Ristic, Biljana Z; Milenkovic, Marina M; Dakic, Ivana R; Todorovic-Markovic, Biljana M; Milosavljevic, Momir S; Budimir, Milica D; Paunovic, Verica G; Dramicanin, Miroslav D; Markovic, Zoran M; Trajkovic, Vladimir S

2014-05-01

235

Quantum optics with quantum dots. Towards semiconductor sources of quantum light for quantum information processing  

NASA Astrophysics Data System (ADS)

For the past fifteen years, single semiconductor quantum dots, often referred to as solid-state artificial atoms, have been at the forefront of various research direction lines for experimental quantum information science, in particular in the development of practical sources of quantum states of light. Here we review the research to date, on the tailoring of the emission properties from single quantum dots producing single photons, indistinguishable single photons and entangled photon pairs. Finally, the progress and future prospects for applications of single dots in quantum information processing is considered.

Beveratos, Alexios; Abram, Izo; Gérard, Jean-Michel; Robert-Philip, Isabelle

2014-12-01

236

Luminescence of a semiconductor quantum dot system  

Microsoft Academic Search

.  \\u000a A microscopic theory is used to study photoluminescence of\\u000a semiconductor quantum dots under the influence of Coulomb and carrier-photon correlation effects\\u000a beyond the Hartree-Fock level. We investigate the emission spectrum and the decay properties of the time-resolved luminescence\\u000a from initially excited quantum dots. The influence of\\u000a the correlations is included within a cluster expansion scheme up to the singlet-doublet

N. Baer; C. Gies; J. Wiersig; F. Jahnke

2006-01-01

237

Bilayer graphene quantum dot defined by topgates  

SciTech Connect

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

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

2014-06-21

238

Potential clinical applications of quantum dots  

PubMed Central

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

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

2008-01-01

239

Unconventional superconductivity in double quantum dots  

NASA Astrophysics Data System (ADS)

The formation of electron pairs is a prerequisite of superconductivity. The fermionic nature of electrons yields four classes of superconducting correlations with definite symmetry in spin, space, and time. Here, we suggest double quantum dots coupled to conventional s -wave superconductors in the presence of inhomogeneous magnetic fields as a model system exhibiting unconventional pairing. Due to their small number of degrees of freedom, tunable by gate voltages, quantum-dot systems are ideal to gain fundamental insight into unconventional pairing. We propose two detection schemes for unconventional superconductivity, based on either Josephson or Andreev spectroscopy.

Sothmann, Björn; Weiss, Stephan; Governale, Michele; König, Jürgen

2014-12-01

240

Single-dot optical emission from ultralow density well-isolated InP quantum dots  

SciTech Connect

We demonstrate a straightforward way to obtain single well-isolated quantum dots emitting in the visible part of the spectrum and characterize the optical emission from single quantum dots using this method. Self-assembled InP quantum dots are grown using gas-source molecular-beam epitaxy over a wide range of InP deposition rates, using an ultralow growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/{mu}m{sup 2} is realized. The resulting isolated InP quantum dots embedded in an InGaP matrix are individually characterized without the need for lithographical patterning and masks on the substrate. Such low-density quantum dots show excitonic emission at around 670 nm with a linewidth limited by instrument resolution. This system is applicable as a single-photon source for applications such as quantum cryptography.

Ugur, A.; Hatami, F.; Masselink, W. T. [Department of Physics, Humboldt-Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin (Germany); Vamivakas, A. N.; Lombez, L.; Atatuere, M. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2008-10-06

241

Quantum DotQuantum Dot SuperlatticesSuperlattices asas Perspective Materials forPerspective Materials for  

E-print Network

Perspective Materials for Thermoelectric ApplicationsThermoelectric Applications O.L. Lazarenkova, A.A. Balandin Y. Bao device it makes QDC very attractive as perspective materials for thermoelectric applications. [1]. OQuantum DotQuantum Dot SuperlatticesSuperlattices asas Perspective Materials for

242

Emission-tunable microwave synthesis of highly luminescent water soluble CdSe/ZnS quantum dots.  

PubMed

Water soluble CdSe/ZnS nanoparticles with emission maxima from 511 nm to 596 nm and quantum efficiencies ranging from 11% to 28% are synthesized in a facile two-step method in ambient atmospheric conditions using a commercially available microwave reactor. PMID:18438483

Roy, Marc D; Herzing, Andrew A; De Paoli Lacerda, Silvia H; Becker, Matthew L

2008-05-14

243

Spectroscopic Characterization of Streptavidin Functionalized Quantum dots1  

PubMed Central

The spectroscopic properties of quantum dots can be strongly influenced by the conditions of their synthesis. In this work we have characterized several spectroscopic properties of commercial, streptavidin functionalized quantum dots (QD525, lot#1005-0045 and QD585, Lot#0905-0031 from Invitrogen). This is the first step in the development of calibration beads, to be used in a generalizable quantification scheme of multiple fluorescent tags in flow cytometry or microscopy applications. We used light absorption, photoexcitation, and emission spectra, together with excited-state lifetime measurements to characterize their spectroscopic behavior, concentrating on the 400-500nm wavelength ranges that are important in biological applications. Our data show an anomalous dependence of emission spectrum, lifetimes, and quantum yield (QY) on excitation wavelength that is particularly pronounced in the QD525. For QD525, QY values ranged from 0.2 at 480nm excitation up to 0.4 at 450nm and down again to 0.15 at 350nm. For QD585, QY values were constant at 0.2 between 500nm and 400nm, but dropped to 0.1 at 350nm. We attribute the wavelength dependences to heterogeneity in size and surface defects in the QD525, consistent with characteristics previously described in the chemistry literature. The results are discussed in the context of bridging the gap between what is currently known in the physical chemistry literature of quantum dots, and the quantitative needs of assay development in biological applications. PMID:17368555

Wu, Yang; Lopez, Gabriel P.; Sklar, Larry A.; Buranda, Tione

2007-01-01

244

Quantum dots-in-a-well infrared photodetectors  

Microsoft Academic Search

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

Sanjay Krishna

2005-01-01

245

Resonant tunnelling features in quantum dots.  

PubMed

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. PMID:20571205

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

2010-07-01

246

Optical properties of quantum-dot-doped liquid scintillators  

PubMed Central

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. PMID:25392711

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

2014-01-01

247

Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals  

E-print Network

Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals Mehmet://jap.aip.org/about/rights_and_permissions #12;Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals in semiconductor quantum dots (QDs), which enables strongly size-dependent control of opti- cal properties

Demir, Hilmi Volkan

248

Electronic transient processes and optical spectra in quantum dots for quantum computing  

Microsoft Academic Search

Quantum dot systems are studied theoretically from the point of view of realization of quantum bit using the orbital state of electronic motion in a quantum dot. Attention is paid to several effects which can influence significantly the application of quantum dot electronic orbital states in quantum computing, for example, the effect of upconversion of the population and the incomplete

Karel Král; P. Zdenek; Z. Khas

2004-01-01

249

All quantum dot based femtosecond VECSEL  

Microsoft Academic Search

Using quantum well gain materials, ultrafast VECSELs have achieved higher output powers (2.1 W) and shorter pulses (60 fs) than any other semiconductor laser. Quantum dot (QD) gain materials offer a larger inhomogeneously broadened bandwidth, potentially supporting shorter pulse durations. We demonstrate the first femtosecond QD-based VECSEL using a QD-SESAM for modelocking, obtaining 63 mW at 3.2 GHz in 780-fs

M. Hoffmann; O. D. Sieber; W. P. Pallmann; V. J. Wittwer; I. L. Krestnikov; S. S. Mikhrin; D. A. Livshits; G. Malcolm; Y. Barbarin; T. Südmeyer; U. Keller

2011-01-01

250

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

251

Spin Relaxation Quenching in Semiconductor Quantum Dots  

Microsoft Academic Search

We have studied the spin dynamics in self-organized InAs\\/GaAs quantum dots by time-resolved photoluminescence performed under strictly resonant excitation. At low temperature, we observe strictly no decay of both the linear and the circular luminescence polarization. This demonstrates that the carrier spins are totally frozen on the exciton lifetime scale.

M. Paillard; X. Marie; P. Renucci; T. Amand; A. Jbeli; J. M. Gérard

2001-01-01

252

Excitonic Polarons in Semiconductor Quantum Dots  

Microsoft Academic Search

The discretization of the electronic spectrum in semiconductor quantum dots implies a strong coupling behavior between the optical phonons and the electron-hole pairs, despite the fact that a pair is electrically neutral. The excitonic polarons strongly modify the optical spectra. In particular, the ground excitonic polaron contains one or two phonon components, which leads to the existence of phonon replicas

O. Verzelen; R. Ferreira; G. Bastard

2002-01-01

253

New small quantum dots for neuroscience  

NASA Astrophysics Data System (ADS)

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

Selvin, Paul

2014-03-01

254

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

255

Biexciton and Triexciton States in Quantum Dots  

NASA Astrophysics Data System (ADS)

The formation, the binding energy and the structure of biexcitons and triexcitons in a strong magnetic field are studied within the method of hyperspherical harmonics. The magnetic field confines the excitons in quantum dots and results in formation of Wigner-crystal-like states of 4- and 6-particles.

Kezerashvili, R. Ya.; Tsiklauri, Sh. M.

2013-08-01

256

Producing Quantum Dots by Spray Pyrolysis  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

257

Electronic structure and photon absorption in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

Quantum dot structures have been the subject of intense investigation in recent years with the advances of molecular beam epitaxy growth technology. Quantum dot infrared photodetector (QDIP) which rely on intersubband transitions in quantum wells or quantum dots for infrared detection, as the three-dimensional confinement of electrons leads to a distribution of energy levels which impedes electron-phonon scattering. This suggests that such devices have the potential for higher operating temperatures in comparison with the traditional quantum well devices. However, the complexity of the QDIP geometry prevents closed-form solutions of the corresponding Schrodinger eigenvalue problems. We propose and demonstrate a numerically robust and efficient discretization scheme for one-dimensional and three-dimensional axisymmetric quantum structures using spectral elements. The variations in energy levels of isolated conical and lenticular InAs quantum dots are investigated with respect to changes in the dot dimension, as is the coupling between vertically stacked dots. Given measured distributions of quantum dot sizes, we give an uncertainty analysis for the range of energy levels. Finally we consider quantum dot-in-a-well (DWELL) structures and investigate dependence of eigenvalues and eigenfunctions on well width, dot size, and dot location. The effective quantum dot density-of-states and photon absorption oscillator strength are computed as functions of photon wavelength and polarization for a variety of configurations and applied electric fields.

von Winckel, Gregory

258

Electronic structure of quantum dots Stephanie M. Reimann  

E-print Network

III. Addition Energy Spectra 1293 A. Many-body effects in quantum dots 1294 B. Density with flattened bottom 1298 G. Three-dimensionality of the confinement 1299 H. Triangular quantum dots 1300 I spectroscopy of vertical dots 1313 2. Gated transport spectroscopy in magnetic fields 1314 3. B-N phase diagram

Wu, Zhigang

259

Progress towards single spin optoelectronics using quantum dot nanostructures  

Microsoft Academic Search

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

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

2005-01-01

260

Quantum Cascade of Photons in Semiconductor Quantum Dots  

Microsoft Academic Search

We have obtained pairs of correlated single photons from the emission cascade of an isolated InAs quantum dot. The cross-correlation function of the two photons in a pair exhibits the coexistence of asymmetric bunching and antibunching features, which is the signature for their sequential emission with a definite order. This observation opens the way to the use of semiconductor quantum

E. Moreau; I. Robert; L. Manin; V. Thierry-Mieg; J. M. Gérard; I. Abram

2001-01-01

261

Quantum criticality in a double-quantum-dot system.  

PubMed

We discuss the realization of the quantum-critical non-Fermi-liquid state, originally discovered within the two-impurity Kondo model, in double-quantum-dot systems. Contrary to common belief, the corresponding fixed point is robust against particle-hole and various other asymmetries and is unstable only to charge transfer between the two dots. We propose an experimental setup where such charge transfer processes are suppressed, allowing a controlled approach to the quantum-critical state. We also discuss transport and scaling properties in the vicinity of the critical point. PMID:17155422

Zaránd, Gergely; Chung, Chung-Hou; Simon, Pascal; Vojta, Matthias

2006-10-20

262

Elastic light scattering by semiconductor quantum dots of arbitrary shape  

Microsoft Academic Search

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

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

2007-01-01

263

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

264

Quantum Dot Platform for Single-Cell Molecular Profiling  

NASA Astrophysics Data System (ADS)

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

Zrazhevskiy, Pavel S.

265

Thermoelectric transport through strongly correlated quantum dots  

E-print Network

The thermoelectric properties of strongly correlated quantum dots, described by a single level Anderson model coupled to conduction electron leads, is investigated using Wilson's numerical renormalization group method. We calculate the electronic contribution, $K_{\\rm e}$, to the thermal conductance, the thermopower, $S$, and the electrical conductance, $G$, of a quantum dot as a function of both temperature, $T$, and gate voltage, ${\\rm v}_g$, for strong, intermediate and weak Coulomb correlations, $U$, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures $T_{1}({\\rm v}_g)$ and $T_{2}({\\rm v}_g)$ with $T_{1}< T_{2}$. Such sign changes in $S(T)$ are particularly sensitive signatures of strong correlations and Kondo physics. The relevance of this to recent thermopower measurements of Kondo correlated quantum dots is discussed. We discuss the figure of merit, power factor and the degree of violation of the Wiedemann-Franz law in ...

Costi, T A; 10.1103/PhysRevB.81.235127

2010-01-01

266

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. PMID:21814567

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

2011-01-01

267

Synthesis in aqueous solution and characterisation of a new cobalt-doped ZnS quantum dot as a hybrid ratiometric chemosensor  

Microsoft Academic Search

In this paper, cobalt (Co2+)-doped (CoD) ZnS quantum dots (QDs) are synthesised in aqueous solution and characterised for the first time. l-Cysteine (l-Cys) ligands on the surface of CoD ZnS QDs can bind 2,4,6-trinitrotoluene (TNT) to form Meisenheimer complexes (MHCs) mainly through acid–base pairing interactions between TNT and l-Cys and the assistance of hydrogen bonding and electrostatic co-interactions among l-Cys

Wen-sheng Zou; Jun-qin Qiao; Xin Hu; Xin Ge; Hong-zhen Lian

268

Aqueous synthesis of multidentate-polymer-capping Ag2Se quantum dots with bright photoluminescence tunable in a second near-infrared biological window.  

PubMed

A new strategy for fabricating water-dispersible Ag2Se quantum dots (QDs) is presented. A multidentate polymer (MDP) was synthesized and used as a capping agent for Ag2Se QDs. The MDP-capping Ag2Se QDs were synthesized in aqueous solution at room temperature, which are highly photoluminescent in a second near-infrared (NIR-II) biological window and possess good photostability. These readily prepared NIR-II fluorescent nanoprobes have great potential for biomedical applications, especially useful for in vivo imaging. PMID:24796941

Tan, Lianjiang; Wan, Ajun; Zhao, Tingting; Huang, Ran; Li, Huili

2014-05-14

269

Synthesis of a CdSe-graphene hybrid composed of CdSe quantum dot arrays directly grown on CVD-graphene and its ultrafast carrier dynamics.  

PubMed

We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices. PMID:23334263

Kim, Yong-Tae; Shin, Hee-Won; Ko, Young-Seon; Ahn, Tae Kyu; Kwon, Young-Uk

2013-02-21

270

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. PMID:21931483

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

2011-01-01

271

Mode Competition in Dual-Mode Quantum Dots Semiconductor Microlaser  

E-print Network

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

Chusseau, Laurent; Viktorovitch, P; Letartre, Xavier

2013-01-01

272

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

273

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

NASA Astrophysics Data System (ADS)

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

Elyasi, P.; SalmanOgli, A.

2014-05-01

274

Unveiling structural properties of self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

A better understanding of structural properties and growth kinetics of Stranski-Krastanov (SK) quantum dots is necessary for applying dot potential in optical and electronic applications. In fact, We have recently demonstrated theoretically and experimentally, the ability of reflection high energy electron diffraction (RHEED) tool in quantitative analysis such as extracting average dot size, facet orientation and average dot density and real time monitoring of dot size during growth .As an extended study, in this work for the first time we present the experimental evidence on onset epitaxial quantum dot average shape evolution and theoretical predictions on QD facet orientations.

Gunasekera, M.; Rajapaksha, C.; Freundlich, A.

2013-03-01

275

Aqueous synthesis and fluorescence-imaging application of CdTe/ZnSe core/shell quantum dots with high stability and low cytotoxicity.  

PubMed

CdTe/ZnSe core/shell quantum dots were directly synthesized in an aqueous condition by heating a mixed solution of ZnCI2, NaHSe and CdTe QDs in the presence of mercaptosuccinic acid as a stabilizer. By controlling the size and composition, the CdTe/ZnSe QDs with emission wavelength ranging from 540 to 630 nm, high quantum yield (44%) and narrow full width at half maximum (FWHM) could be obtained. Characterization results with HRTEM, XRD and EDX have shown that the synthesized CdTe/ZnSe QDs have good monodispersity and a nice crystal structure, and exhibited better stability and less cytotoxicity as compared with CdTe QDs. Furthermore, luminescent QD-IgG bioprobes were produced to detect the breast cancer marker Her2 on the surface of fixed MCF-7 cancer cells for their optical imaging. PMID:20355568

Fu, Tao; Qin, Hai-Yan; Hu, Hua-Jun; Hong, Zhi; He, Sailing

2010-03-01

276

Electric Field effects on quantum correlations in semiconductor quantum dots  

E-print Network

We study the effect of external electric bias on the quantum correlations in the array of optically excited coupled semiconductor quantum dots. The correlations are characterized by the quantum discord and concurrence and are observed using excitonic qubits. We employ the lower bound of concurrence for thermal density matrix at different temperatures. The effect of the F\\"orster interaction on correlations will be studied. Our theoretical model detects nonvanishing quantum discord when the electric field is on while concurrence dies, ensuring the existence of nonclassical correlations as measured by the quantum discord.

S. Shojaei; M. Mahdian; R. Yousefjani

2012-05-01

277

Electric Field effects on quantum correlations in semiconductor quantum dots  

E-print Network

We study the effect of external electric bias on the quantum correlations in the array of optically excited coupled semiconductor quantum dots. The correlations are characterized by the quantum discord and concurrence and are observed using excitonic qubits. We employ the lower bound of concurrence for thermal density matrix at different temperatures. The effect of the F\\"orster interaction on correlations will be studied. Our theoretical model detects nonvanishing quantum discord when the electric field is on while concurrence dies, ensuring the existence of nonclassical correlations as measured by the quantum discord.

Shojaei, S; Yosefjani, R

2012-01-01

278

Small bright charged colloidal quantum dots.  

PubMed

Using electrochemical charge injection, the fluorescence lifetimes of negatively charged core/shell CdTe/CdSe QDs are measured as a function of core size and shell thickness. It is found that the ensemble negative trion lifetimes reach a maximum (?4.5 ns) for an intermediate shell thickness. This leads to the smallest particles (?4.5 nm) with the brightest trion to date. Single dot measurements show that the negative charge suppresses blinking and that the trion can be as bright as the exciton at room temperature. In contrast, the biexciton lifetimes remain short and exhibit only a monotonous increase with shell thickness, showing no correlation with the negative trion decays. The suppression of the Auger process in small negatively charged CdTe/CdSe quantum dots is unprecedented and a significant departure from prior results with ultrathick CdSe/CdS core/shell or dot-in-rod structures. The proposed reason for the optimum shell thickness is that the electron-hole overlap is restricted to the CdTe core while the electron is tuned to have zero kinetic energy in the core for that optimum shell thickness. The different trend of the biexciton lifetime is not explained but tentatively attributed to shorter-lived positive trions at smaller sizes. These results improve our understanding of multiexciton recombination in colloidal quantum dots and may lead to the design of bright charged QDs for more efficient light-emitting devices. PMID:24350673

Qin, Wei; Liu, Heng; Guyot-Sionnest, Philippe

2014-01-28

279

Photoluminescence of silicon quantum dots in nanospheres  

NASA Astrophysics Data System (ADS)

Si quantum dots (SiQDs) based nanospheres (SiNSs) were prepared via a novel synthetic strategy. These SiNSs were demonstrated to possess unique dot spacing dependent photoluminescence (PL) up-conversion and surface dependent (N modified surface) down-converted PL. It was demonstrated that a small distance between SiQDs (<5 nm) is the necessary condition for the PL up-conversion of SiNSs, while the surface state of SiQDs will affect the maximum emission wavelength and the PL intensity. The as-prepared SiNSs feature excellent aqueous dispersibility, and their optical properties were found to be stable enough in a specified temperature and pH range.Si quantum dots (SiQDs) based nanospheres (SiNSs) were prepared via a novel synthetic strategy. These SiNSs were demonstrated to possess unique dot spacing dependent photoluminescence (PL) up-conversion and surface dependent (N modified surface) down-converted PL. It was demonstrated that a small distance between SiQDs (<5 nm) is the necessary condition for the PL up-conversion of SiNSs, while the surface state of SiQDs will affect the maximum emission wavelength and the PL intensity. The as-prepared SiNSs feature excellent aqueous dispersibility, and their optical properties were found to be stable enough in a specified temperature and pH range. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr32375c

Zhang, Yuxiao; Han, Xiao; Zhang, Jianming; Liu, Yang; Huang, Hui; Ming, Hai; Lee, Shuit-Tong; Kang, Zhenhui

2012-11-01

280

Photon-mediated interaction between distant quantum dot circuits.  

PubMed

Engineering the interaction between light and matter is an important goal in the emerging field of quantum opto-electronics. Thanks to the use of cavity quantum electrodynamics architectures, one can envision a fully hybrid multiplexing of quantum conductors. Here we use such an architecture to couple two quantum dot circuits. Our quantum dots are separated by 200 times their own size, with no direct tunnel and electrostatic couplings between them. We demonstrate their interaction, mediated by the cavity photons. This could be used to scale up quantum bit architectures based on quantum dot circuits or simulate on-chip phonon-mediated interactions between strongly correlated electrons. PMID:23360991

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

2013-01-01

281

Geometric spin manipulation in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We propose a method to flip the spin completely by an adiabatic transport of quantum dots. We show that it is possible to flip the spin by inducing a geometric phase on the spin state of a quantum dot. We estimate the geometric spin flip time (approximately 2 ps) which turned out to be much shorter than the experimentally reported decoherence time (approximately 100 ns) that would provide an alternative means of fliping the spin before reaching decoherence. It is important that both the Rashba coupling and the Dresselhaus coupling are present for inducing a phase necessary for spin flip. If one of them is absent, the induced phase is trivial and irrelevant for spin-flip.

Prabhakar, Sanjay; Melnik, Roderick; Inomata, Akira

2014-04-01

282

Separability and dynamical symmetry of Quantum Dots  

SciTech Connect

The separability and Runge–Lenz-type dynamical symmetry of the internal dynamics of certain two-electron Quantum Dots, found by Simonovi? et al. (2003), are traced back to that of the perturbed Kepler problem. A large class of axially symmetric perturbing potentials which allow for separation in parabolic coordinates can easily be found. Apart from the 2:1 anisotropic harmonic trapping potential considered in Simonovi? and Nazmitdinov (2013), they include a constant electric field parallel to the magnetic field (Stark effect), the ring-shaped Hartmann potential, etc. The harmonic case is studied in detail. -- Highlights: • The separability of Quantum Dots is derived from that of the perturbed Kepler problem. • Harmonic perturbation with 2:1 anisotropy is separable in parabolic coordinates. • The system has a conserved Runge–Lenz type quantity.

Zhang, P.-M., E-mail: zhpm@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Zou, L.-P., E-mail: zoulp@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Horvathy, P.A., E-mail: horvathy@lmpt.univ-tours.fr [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Laboratoire de Mathématiques et de Physique Théorique, Tours University (France); Gibbons, G.W., E-mail: G.W.Gibbons@damtp.cam.ac.uk [Department of Applied Mathematics and Theoretical Physics, Cambridge University, Cambridge (United Kingdom)

2014-02-15

283

Quantum dot behavior in bilayer graphene nanoribbons.  

PubMed

Bilayer graphene has recently earned great attention for its unique electronic properties and commendable use in electronic applications. Here, we report the observation of quantum dot (QD) behaviors in bilayer graphene nanoribbons (BL-GNRs). The periodic Coulomb oscillations indicate the formation of a single quantum dot within the BL-GNR because of the broad distribution function of the carrier concentration fluctuation at the charge neutrality point. The size of the QD changes as we modulate the relative position between the Fermi level and surface potential. Furthermore, the potential barriers forming the QD remain stable at elevated temperatures and external bias. In combination with the observation of transport gaps, our results suggest that the disordered surface potential creates QDs along the ribbon and governs the electronic transport properties in BL-GNRs. PMID:22017308

Wang, Minsheng; Song, Emil B; Lee, Sejoon; Tang, Jianshi; Lang, Murong; Zeng, Caifu; Xu, Guangyu; Zhou, Yi; Wang, Kang L

2011-11-22

284

Geometric spin manipulation in semiconductor quantum dots  

SciTech Connect

We propose a method to flip the spin completely by an adiabatic transport of quantum dots. We show that it is possible to flip the spin by inducing a geometric phase on the spin state of a quantum dot. We estimate the geometric spin flip time (approximately 2 ps) which turned out to be much shorter than the experimentally reported decoherence time (approximately 100 ns) that would provide an alternative means of fliping the spin before reaching decoherence. It is important that both the Rashba coupling and the Dresselhaus coupling are present for inducing a phase necessary for spin flip. If one of them is absent, the induced phase is trivial and irrelevant for spin-flip.

Prabhakar, Sanjay, E-mail: sprabhakar@wlu.ca; Melnik, Roderick [M2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada); Inomata, Akira [Department of Physics, State University of New York at Albany, Albany, New York 12222 (United States)

2014-04-07

285

Excitonic optical nonlinearity and exciton dynamics in semiconductor quantum dots  

Microsoft Academic Search

Two salient features of the excitonic state in semiconductor quantum dots are theoretically clarified. One is the enhanced excitonic optical nonlinearity arising from the state filling of discrete levels due to the quantum size effect. The calculated third-order nonlinear susceptibility explains successfully the recent experimental results. The other feature is the exciton dynamics in semiconductor quantum dots. A comprehensive interpretation

T. Takagahara

1987-01-01

286

Measurement back-action: Listening with quantum dots  

NASA Astrophysics Data System (ADS)

Single electrons in quantum dots can be disturbed by the apparatus used to measure them. The disturbance can be mediated by incoherent phonons -- literally, noise. Engineering acoustic interference could negate these deleterious effects and bring quantum dots closer to becoming a robust quantum technology.

Ladd, Thaddeus D.

2012-07-01

287

Deposition of colloidal quantum dots by microcontact printing for LED display technology  

E-print Network

This thesis demonstrates a new deposition method of colloidal quantum dots within a quantum dot organic light-emitting diode (QD-LED). A monolayer of quantum dots is microcontact printed as small as 20 ,Lm lines as well ...

Kim, LeeAnn

2006-01-01

288

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

289

Topological insulator quantum dot with tunable barriers.  

PubMed

Thin (6-7 quintuple layer) topological insulator Bi(2)Se(3) quantum dot devices are demonstrated using ultrathin (2-4 quintuple layer) Bi(2)Se(3) regions to realize semiconducting barriers which may be tuned from ohmic to tunneling conduction via gate voltage. Transport spectroscopy shows Coulomb blockade with large charging energy >5 meV and additional features implying excited states. PMID:22181853

Cho, Sungjae; Kim, Dohun; Syers, Paul; Butch, Nicholas P; Paglione, Johnpierre; Fuhrer, Michael S

2012-01-11

290

Multiple exciton generation in semiconductor quantum dots  

Microsoft Academic Search

A review is presented of recent work on (1) the origin of the concept of enhanced multiple electron–hole pair (i.e. exciton) production in semiconductor quantum dots (QDs), (2) various experiments based on time-resolved fs to ns spectroscopy (transient IR absorption, transient visible to near-IR bleaching due to state filling, terahertz spectroscopy, and time-resolved photoluminescence) that support the occurrence of highly

Arthur J. Nozik

2008-01-01

291

Coulomb effects in semiconductor quantum dots  

Microsoft Academic Search

Coulomb correlations in the optical spectra of semiconductor quantum dots are investigated using a full-diagonalization approach. The resulting multi-exciton spectra are discussed in terms of the symmetry of the involved states. Characteristic features of the spectra like the nearly equidistantly spaced s-shell emission lines and the approximately constant p-shell transition energies are explained using simplified Hamiltonians that are derived taking

Norman Baer; Paul Gartner; Frank Jahnke

2004-01-01

292

Red-Emitting Semiconductor Quantum Dot Lasers  

Microsoft Academic Search

Visible-stimulated emission in a semiconductor quantum dot (QD) laser structure has been demonstrated. Red-emitting, self-assembled QDs of highly strained InAlAs have been grown by molecular beam epitaxy on a GaAs substrate. Carriers injected electrically from the doped regions of a separate confinement heterostructure thermalized efficiently into the zero-dimensional QD states, and stimulated emission at ~707 nanometers was observed at 77

S. Fafard; K. Hinzer; S. Raymond; M. Dion; J. McCaffrey; Y. Feng; S. Charbonneau

1996-01-01

293

Dark pulse quantum dot diode laser.  

PubMed

We describe an operating regime for passively mode-locked quantum dot diode laser where the output consists of a train of dark pulses, i.e., intensity dips on a continuous background. We show that a dark pulse train is a solution to the master equation for mode-locked lasers. Using simulations, we study stability of the dark pulses and show they are consistent with the experimental results. PMID:20588468

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

2010-06-21

294

The pinning effect in quantum dots  

SciTech Connect

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

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

2014-04-24

295

Zeeman Effect in Parabolic Quantum Dots  

Microsoft Academic Search

An unprecedentedly well resolved Zeeman effect has been observed when confined carriers moving along a closed mesoscopic path experience an external magnetic field orthogonal to the orbit plane. Large Zeeman splitting of excited higher angular momentum states is observed in the magnetoluminescence spectrum of quantum dots induced by self-organized InP islands on InGaAs\\/GaAs. The measured effect is quantitatively reproduced by

R. Rinaldi; P. V. Giugno; R. Cingolani; H. Lipsanen; M. Sopanen; J. Tulkki; J. Ahopelto

1996-01-01

296

Optical study of Ge quantum dots and infrared photodetectors  

Microsoft Academic Search

Stacked Ge quantum dots were grown on Si(100) by ultra-high vacuum chemical vapor deposition (UHV\\/CVD). Obvious blueshift (87 meV) observed from PL spectrum under 10 K demonstrates strong quantum confinement in Ge dots. Based on the material, PIiN structure quantum dot infrared photodetectors (QDIPs) were fabricated. At room temperature, I-V measurement showed a low dark current density of 1.7 ×

Rongshan Wei; Ning Deng; Minsheng Wang; Shuang Zhang; Peiyi Chen

2005-01-01

297

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

298

Quantum Dot Charging By Means Of Temperature And Magnetic Field  

SciTech Connect

A micro-photoluminescence study of individual InAs/GaAs quantum dots is presented. It is demonstrated that by varying the strength of an applied magnetic field and/or the temperature, the charge state of a quantum dot can be tuned. The charge tuning mechanism is shown to be due to the modification of the electron and hole transport in the wetting layer plane prior to their capture into the quantum dot.

Larsson, L. A.; Holtz, P. O. [IFM, Semiconductor Materials, Linkoeping University, SE-58183 Linkoeping (Sweden); Moskalenko, E. S. [A. F. Ioffe Physical-Technical Institute, 194021, Polytechnicheskaya 26, St. Petersburg (Russian Federation)

2011-12-23

299

Carrier and spin dynamics in charged quantum dots  

Microsoft Academic Search

Carrier and spin dynamics are measured in meutral, positively and negatively charged quantum dots using polarization-sensitive time-resolved photoluminescence. Carrier capture rates are observed to be strongly enhanced in charged quantum dots, suggesting that electron-hole scattering dominates this process. For positive quantum dots, the enhanced spin-polarized electron capture rate eliminates loss of electron spin information in the GaAs barriers prior to

Kimberley C. Hall; Kenan Gundogdu; Thomas F. Boggess; Oleg B. Shchekin; Dennis G. Deppe

2004-01-01

300

Quantum dot dipole orientation and excitation efficiency of micropillar modes.  

PubMed

The relative intensity of photonic modes in microcavity pillars with embedded self-assembled quantum dots is shown to be a sensitive function of quantum dot dipole orientation and position. This is deduced from a comparison of experiment and calculated intensities of light emission for many nominally identical pillars. We are able to obtain the overall degree of in-plane polarization of the quantum dot ensemble and also to obtain information on the degree of polarization along the growth axis. PMID:19582012

Silva, A G; Parra-Murillo, C A; Valentim, P T; Morais, J S V; Plentz, F; Guimarães, P S S; Vinck-Posada, H; Rodriguez, B A; Skolnick, M S; Tahraoui, A; Hopkinson, M

2008-11-10

301

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

302

Quantum Computation Using Optically Coupled Quantum Dot Arrays  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

303

Quantum dot solar cells: The surface plays a core role  

NASA Astrophysics Data System (ADS)

Mastering the impact of surface chemistry on the electronic properties and stability of colloidal quantum dots enables the realization of architectures with enhanced photovoltaic performance and air stability.

Milliron, Delia J.

2014-08-01

304

One step, microwave assisted green synthesis of biocompatible carbon quantum dots and their composites with [??PW{sub 12}O{sub 40}{sup 3?}] for visible light photocatalysis  

SciTech Connect

We report a simple, rapid and green route for synthesis of fluorescent carbon quantum dots (CQDs) by microwave assisted pyrolysis method using polyleucine polymer (Boc-L-Leu-HEMA) as precursor and self-passivating agent. The as synthesized CQDs were found to possess low cytotoxicity, thus making them suitable candidates for bioimaging and bio-labelling. Moreover, nanocomposites of as prepared CQDs with [??PW{sub 12}O{sub 40}{sup 3?}] polyoxometalate were synthesized and were shown to possess excellent photocatalytic properties under visible light towards degradation of organic dye pollutants. Based on the control experiments, a suitable mechanism has been proposed to explain the remarkable photoactivity of the CQD/[??PW{sub 12}O{sub 40}{sup 3?}] composites.

Sahasrabudhe, Atharva, E-mail: atharva19101991@gmail.com; Pant, Shashank, E-mail: atharva19101991@gmail.com; Chatti, Manjunath, E-mail: atharva19101991@gmail.com; Maiti, Binoy, E-mail: atharva19101991@gmail.com; De, Priyadarsi, E-mail: atharva19101991@gmail.com; Roy, Soumyajit, E-mail: atharva19101991@gmail.com [Department of Chemical Sciences, Indian Institute of Science Education and Research-Kolkata, Mohanpur-741252, W.B. (India)

2014-04-24

305

Far infrared spectroscopy of quantum-dots and antidot arrays  

Microsoft Academic Search

Advances in submicron technology make it possible to realize man-made low-dimensional electronic systems with quantum confined energy states, i.e., quantum wires, quantum dots and antidots. With typical confinement energies in the meV regime far-infrared spectroscopy gives the most direct access to the quantum confined energy levels in these systems. One is now approaching the limit to prepare quantum dots with

Detlef Heitmann

1995-01-01

306

Effect of shells on photoluminescence of aqueous CdTe quantum dots  

SciTech Connect

Graphical abstract: Size-tunable CdTe coated with several shells using an aqueous solution synthesis. CdTe/CdS/ZnS quantum dots exhibited high PL efficiency up to 80% which implies the promising applications for biomedical labeling. - Highlights: • CdTe quantum dots were fabricated using an aqueous synthesis. • CdS, ZnS, and CdS/ZnS shells were subsequently deposited on CdTe cores. • Outer ZnS shells provide an efficient confinement of electron and hole inside the QDs. • Inside CdS shells can reduce the strain on the QDs. • Aqueous CdTe/CdS/ZnS QDs exhibited high stability and photoluminescence efficiency of 80%. - Abstract: CdTe cores with various sizes were fabricated in aqueous solutions. Inorganic shells including CdS, ZnS, and CdS/ZnS were subsequently deposited on the cores through a similar aqueous procedure to investigate the effect of shells on the photoluminescence properties of the cores. In the case of CdTe/CdS/ZnS quantum dots, the outer ZnS shell provides an efficient confinement of electron and hole wavefunctions inside the quantum dots, while the middle CdS shell sandwiched between the CdTe core and ZnS shell can be introduced to obviously reduce the strain on the quantum dots because the lattice parameters of CdS is situated at the intermediate-level between those of CdTe and ZnS. In comparison with CdTe/ZnS core–shell quantum dots, the as-prepared water-soluble CdTe/CdS/ZnS quantum dots in our case can exhibit high photochemical stability and photoluminescence efficiency up to 80% in an aqueous solution, which implies the promising applications in the field of biomedical labeling.

Yuan, Zhimin; Yang, Ping, E-mail: mse_yangp@ujn.edu.cn

2013-07-15

307

Characterization of InGaAs quantum dot lasers with a single quantum dot layer as an active region  

Microsoft Academic Search

Quantum dot lasers with an active region consisting of just a single quantum dot layer have been grown using molecular beam epitaxy and characterized from 80 to 300K. The quantum dot lasers lase from excited states over the entire temperature range. The characteristic temperature is 185±10K over the temperature range 80–141K and decreases to 111±2K from 141–304K. The effects of

Richard P Mirin; Arthur C Gossard; John E Bowers

1998-01-01

308

Characterization of InGaAs quantum dot lasers with a single quantum dot layer as an active region  

Microsoft Academic Search

Quantum dot lasers with an active region consisting of just a single quantum dot layer have been grown using molecular beam epitaxy and characterized from 80 to 300 K. The quantum dot lasers lase from excited states over the entire temperature range. The characteristic temperature is 185+\\/-10 K over the temperature range 80-141 K and decreases to 111+\\/-2 K from

Richard P. Mirin; Arthur C. Gossard; John E. Bowers

1998-01-01

309

Enhanced performance of quantum dot solar cells based on type II quantum dots  

SciTech Connect

The characteristics of quantum dot solar cells (QDSCs) based on type II QDs are investigated theoretically. Based on a drift-diffusion model, we obtained a much higher open circuit voltage (V{sub oc}) as well as conversion efficiency in a type II QDSC, compared to type I QDSCs. The improved V{sub oc} and efficiency are mainly attributed to the much longer Auger recombination lifetime in type II QDs. Moreover, the influence of the carrier lifetime on devices' performance is discussed and clarified. In addition, an explicit criterion to determine the role of quantum dots in solar cells is put forward.

Xu, Feng; Yang, Xiao-Guang; Luo, Shuai; Lv, Zun-Ren; Yang, Tao, E-mail: tyang@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China)

2014-10-07

310

Enhanced performance of quantum dot solar cells based on type II quantum dots  

NASA Astrophysics Data System (ADS)

The characteristics of quantum dot solar cells (QDSCs) based on type II QDs are investigated theoretically. Based on a drift-diffusion model, we obtained a much higher open circuit voltage (Voc) as well as conversion efficiency in a type II QDSC, compared to type I QDSCs. The improved Voc and efficiency are mainly attributed to the much longer Auger recombination lifetime in type II QDs. Moreover, the influence of the carrier lifetime on devices' performance is discussed and clarified. In addition, an explicit criterion to determine the role of quantum dots in solar cells is put forward.

Xu, Feng; Yang, Xiao-Guang; Luo, Shuai; Lv, Zun-Ren; Yang, Tao

2014-10-01

311

Coherent population transfer in coupled semiconductor quantum dots  

Microsoft Academic Search

We propose a solid-state implementation of stimulated Raman adiabatic passage in two coupled semiconductor quantum dots. Proper combination of two pulsed laser fields allows the coherent carrier transfer between the two nanostructures without suffering significant losses due to environment coupling. By use of a general solution scheme for the carrier states in the double-dot structure, we identify the pertinent dot

Ulrich Hohenester; Filippo Troiani; Elisa Molinari; Giovanna Panzarini; Chiara Macchiavello

2000-01-01

312

Hyperfine-induced decay in triple quantum dots  

NASA Astrophysics Data System (ADS)

We analyze the effects of hyperfine interactions on coherent control experiments in triple quantum dots. By exploiting Hamiltonian symmetries and the SU(3) structure of the triple-dot system under pseudoexchange and longitudinal hyperfine couplings, we provide analytic formulas for the hyperfine decay of triple-dot Rabi and dephasing experiments.

Ladd, Thaddeus D.

2012-09-01

313

Synthesis of Honeycomb-like Mesoporous Pyrite FeS2 Microspheres as Efficient Counter Electrode in Quantum Dots Sensitized Solar Cells.  

PubMed

Honeycomb-like mesoporous pyrite FeS2 microspheres, with diameters of 500-800 nm and pore sizes of 25-30 nm, are synthesized by a simple solvothermal approach. The mesoporous FeS2 microspheres are demonstrated to be an outstanding counter electrode (CE) material in quantum dot sensitized solar cells (QDSSCs) for electrocatalyzing polysulfide electrolyte regeneration. The cell using mesoporous FeS2 microspheres as CE shows 86.6% enhancement in power conversion efficiency (PCE) than the cell using traditional noble Pt CE. Furthermore, it also shows 11.4% enhancement in PCE than the cell using solid FeS2 microspheres as CE, due to the mesoporous structure facilitating better contact with polysulfide electrolyte and fast diffusion of redox couple species in electrolyte. PMID:24986216

Xu, Jun; Xue, Hongtao; Yang, Xia; Wei, Huaixin; Li, Wenyue; Li, Zhangpeng; Zhang, Wenjun; Lee, Chun-Sing

2014-11-01

314

Synthesis of Fluorinated and Nonfluorinated Graphene Quantum Dots through a New Top-Down Strategy for Long-Time Cellular Imaging.  

PubMed

Herein, a new strategy has been developed through combining a microwave-assisted technique with hydrothermal treatment to reduce graphene waste and improve production yield of graphene quantum dots (GQDs) prepared by top-down methods. By using fluorinated graphene oxide (FGO) as a raw material, fluorinated GQDs and nonfluorinated GQDs can be synthesized. Additionally, in the fluorinated GQDs, the protective shell supplied by fluorine improves the pH stability of photoluminescence and the strong electron-withdrawing group, ?F, reduces the ?- electron density of the aromatic structure; thus inhibiting reactivity toward singlet oxygen produced during irradiation and improving the photostability. Therefore, the as-prepared fluorinated GQDs with excellent photo- and pH stability are suitable for long-term cellular imaging. PMID:25614445

Sun, Hanjun; Ji, Haiwei; Ju, Enguo; Guan, Yijia; Ren, Jinsong; Qu, Xiaogang

2015-02-23

315

Cadmium-free quantum dots in aqueous solution: Potential for fingermark detection, synthesis and an application to the detection of fingermarks in blood on non-porous surfaces.  

PubMed

The use of quantum dots (QDs) in the area of fingermark detection is currently receiving a lot of attention in the forensic literature. Most of the research efforts have been devoted to cadmium telluride (CdTe) quantum dots often applied as powders to the surfaces of interests. Both the use of cadmium and the nano size of these particles raise important issues in terms of health and safety. This paper proposes to replace CdTe QDs by zinc sulphide QDs doped with copper (ZnS:Cu) to address these issues. Zinc sulphide-copper doped QDs were successfully synthesized, characterized in terms of size and optical properties and optimized to be applied for the detection of impressions left in blood, where CdTe QDs proved to be efficient. Effectiveness of detection was assessed in comparison with CdTe QDs and Acid Yellow 7 (AY7, an effective blood reagent), using two series of depletive blood fingermarks from four donors prepared on four non-porous substrates, i.e. glass, transparent polypropylene, black polyethylene and aluminium foil. The marks were cut in half and processed separately with both reagents, leading to two comparison series (ZnS:Cu vs. CdTe, and ZnS:Cu vs. AY7). ZnS:Cu proved to be better than AY7 and at least as efficient as CdTe on most substrates. Consequently, copper-doped ZnS QDs constitute a valid substitute for cadmium-based QDs to detect blood marks on non-porous substrates and offer a safer alternative for routine use. PMID:23246071

Moret, Sébastien; Bécue, Andy; Champod, Christophe

2013-01-10

316

Production and Targeting of Monovalent Quantum Dots  

PubMed Central

The multivalent nature of commercial quantum dots (QDs) and the difficulties associated with producing monovalent dots have limited their applications in biology, where clustering and the spatial organization of biomolecules is often the object of study. We describe here a protocol to produce monovalent quantum dots (mQDs) that can be accomplished in most biological research laboratories via a simple mixing of CdSe/ZnS core/shell QDs with phosphorothioate DNA (ptDNA) of defined length. After a single ptDNA strand has wrapped the QD, additional strands are excluded from the surface. Production of mQDs in this manner can be accomplished at small and large scale, with commercial reagents, and in minimal steps. These mQDs can be specifically directed to biological targets by hybridization to a complementary single stranded targeting DNA. We demonstrate the use of these mQDs as imaging probes by labeling SNAP-tagged Notch receptors on live mammalian cells, targeted by mQDs bearing a benzylguanine moiety. PMID:25407345

Southard, Kade; Jun, Young-wook; Gartner, Zev J.

2014-01-01

317

Predicted Ultrafast Single Qubit Operations in Semiconductor Quantum Dots  

E-print Network

Several recently proposed implementations of scalable quantum computation rely on the ability to manipulate the spin polarization of individual electrons in semiconductors. The most rapid single-spin-manipulation technique to date relies on the generation of an effective magnetic field via a spin-sensitive optical Stark effect. This approach has been used to split spin states in colloidal CdSe quantum dots and to manipulate ensembles of spins in ZnMnSe quantum wells with femtosecond optical pulses. Here we report that the process will produce a coherent rotation of spin in quantum dots containing a single electron. The calculated magnitude of the effective magnetic field depends on the dot bandgap and the strain. We predict that in InAs/InP dots, for reasonable experimental parameters, the magnitude of the rotation is sufficient and the intrinsic error is low enough for them to serve as elements of a quantum dot based quantum computer.

C. E. Pryor; M. E. Flatté

2002-11-25

318

Design and fabrication of quantum-dot lasers  

E-print Network

Semiconductor lasers using quantum-dots in their active regions have been reported to exhibit significant performance advantages over their bulk semiconductor and quantum-well counterparts namely: low threshold current, ...

Nabanja, Sheila

2008-01-01

319

Increased normal incidence photocurrent in quantum dot infrared photodetectors  

NASA Astrophysics Data System (ADS)

We have increased the ratio of s-polarization (normal incidence) to p-polarization photocurrent to 50% in a quantum dot-in-a-well based infrared photodetector form the typical s-p polarization ratio about 20%. This improvement was achieved by engineering the dot geometry and the quantum confinement via post growth capping materials of the Stranski Krastanov growth mode quantum dots (QDs). The TEM images show that the height to base ratio of shape engineered QDs was increased to 8 nm/12 nm from the control sample's ratio 4 nm/17 nm. The dot geometry correlates with the polarized photocurrent measurements of the detector.

Shao, Jiayi; Vandervelde, Thomas E.; Barve, Ajit; Stintz, Andreas; Krishna, Sanjay

2012-12-01

320

Power-law photoluminescence decay in quantum dots  

SciTech Connect

Some quantum dot samples show a long-time (power-law) behavior of their luminescence intensity decay. This effect has been recently explained as being due to a cooperation of many tunneling channels transferring electrons from small quantum dots with triplet exciton to quantum dots at which the electrons can recombine with the holes in the valence band states. In this work we show that the long-time character of the sample luminescence decay can also be caused by an intrinsic property of a single dot, namely, by a non-adiabatic effect of the electron occupation up-conversion caused by the electron-phonon multiple scattering mechanism.

Král, Karel [Institute of Physics, Academy of Sciences of Czech Republic, v.v.i., Na Slovance 2, 18221 Prague 8 (Czech Republic); Menšík, Miroslav [Institute of Macromolecular Chemistry, Academy of Sciences of Czech Republic, v.v.i., Heyrovského nám. 2, 162 06 Prague 6 (Czech Republic)

2014-05-15

321

PREFACE: Quantum dots as probes in biology  

NASA Astrophysics Data System (ADS)

The recent availability of nanostructured materials has resulted in an explosion of research focused on their unique optical, thermal, mechanical and magnetic properties. Optical imagining, magnetic enhancement of contrast and drug delivery capabilities make the nanoparticles of special interest in biomedical applications. These materials have been involved in the development of theranostics—a new field of medicine that is focused on personalized tests and treatment. It is likely that multimodal nanomaterials will be responsible for future diagnostic advances in medicine. Quantum dots (QD) are nanoparticles which exhibit luminescence either through the formation of three-dimensional excitons or excitations of the impurities. The excitonic luminescence can be tuned by changing the size (the smaller the size, the higher the frequency). QDs are usually made of semiconducting materials. Unlike fluorescent proteins and organic dyes, QDs resist photobleaching, allow for multi-wavelength excitations and have narrow emission spectra. The techniques to make QDs are cheap and surface modifications and functionalizations can be implemented. Importantly, QDs could be synthesized to exhibit useful optomagnetic properties and, upon functionalization with an appropriate biomolecule, directed towards a pre-selected target for diagnostic imaging and photodynamic therapy. This special issue on Quantum dots in Biology is focused on recent research in this area. It starts with a topical review by Sreenivasan et al on various physical mechanisms that lead to the QD luminescence and on using wavelength shifts for an improvement in imaging. The next paper by Szczepaniak et al discusses nanohybrids involving QDs made of CdSe coated by ZnS and combined covalently with a photosynthetic enzyme. These nanohybrids are shown to maintain the enzymatic activity, however the enzyme properties depend on the size of a QD. They are proposed as tools to study photosynthesis in isolated photosynthetic systems. The next paper, by Olejnik et al, discussed metallic QDs which enhance photosynthetic function in light-harvesting biomolecular complexes. Such hybrid structures with gold QDs are shown to exhibit a strong increase in the fluorescence quantum yield. The next two papers, by Sikora et al and Kaminska et al deal with the ZnO nanoparticles passivated by MgO. In the first of these two papers, the authors describe the behavior of ZnO/MgO when introduced to human cancer cells. In the second, the authors describe the QDs with an extra outer layer of Fe2O3 which makes the nanoparticles superparamagnetic and also capable of generation of reactive oxygen species which could be applied to form localized centers of toxicity for cancer treatment. Finally, in the last paper by Yatsunenko et al, the authors discuss several semiconducting QDs like ZnO with various rare-earth dopands. They propose a microwave-driven hydrothermal technology to make them, characterize their luminescence and demonstrate their usefulness in the early recognition of cancer tissues. Quantum dots as probes in biology contents Quantum dots as probes in biologyMarek Cieplak Luminescent nanoparticles and their applications in the life sciencesVarun K A Sreenivasan, Andrei V Zvyagin and Ewa M Goldys Ferredoxin:NADP+ oxidoreductase in junction with CdSe/ZnS quantum dots: characteristics of an enzymatically active nanohybrid Krzysztof Szczepaniak, Remigiusz Worch and Joanna Grzyb Spectroscopic studies of plasmon coupling between photosynthetic complexes and metallic quantum dotsMaria Olejnik, Bartosz Krajnik, Dorota Kowalska, Guanhua Lin and Sebastian Mackowski Luminescence of colloidal ZnO nanoparticles synthesized in alcohols and biological application of ZnO passivated by MgOBo?ena Sikora, Krzysztof Fronc, Izabela Kami?ska, Kamil Koper, Piotr St?pie? and Danek Elbaum Novel ZnO/MgO/Fe2O3 composite optomagnetic nanoparticles I Kami?ska, B Sikora, K Fronc, P Dziawa, K Sobczak, R Minikayev, W Paszkowicz and D Elbaum Impact of yttria stabilization on Tb3+ intra-shell luminescence efficiency in

Cieplak, Marek

2013-05-01

322

Quantum dot lipid oligonucleotide bioconjugates: toward a new anti-microRNA nanoplatform.  

PubMed

The construction of new nanotools is presented here using the example of fluorescent semiconductor nanocrystals, quantum dots (QDs). In this study, the implementation of the new lipid oligonucleotide conjugate-functionalized quantum dots (LON-QDs) is realized in four steps: (i) the synthesis of the lipid oligonucleotide conjugates (LONs), (ii) the encapsulation of QDs by nucleolipids and LONs, (iii) the study of the duplex formation of LON-QDs with the complementary ON partners, and (iv) the cellular uptake of the LON-QD platform and hybridization with the target ONs (microRNA and miR-21). PMID:23888900

Aimé, Ahissan; Beztsinna, Nataliia; Patwa, Amit; Pokolenko, Alexander; Bestel, Isabelle; Barthélémy, Philippe

2013-08-21

323

Visible single-photon generation from semiconductor quantum dots  

Microsoft Academic Search

In this paper we report recent results on single-photon generation with single InP and CdSe quantum dots. These dots produce single-photons on demand in the visible spectral range 510 690 nm. The emitted photoluminescence was characterized by measuring the autocorrelation function and by performing Fourier spectroscopy on several transitions in the quantum dot. We present the observation and interpretation of

Thomas Aichele; Valéry Zwiller; Oliver Benson

2004-01-01

324

Elastic light scattering by semiconductor quantum dots of arbitrary shape  

Microsoft Academic Search

Elastic light scattering by low-dimensional quantum objects without a change in the frequency is theoretically investigated\\u000a in terms of the quantum perturbation theory. The differential cross section of resonance light scattering from any excitons\\u000a in any quantum dots is calculated. It is demonstrated that, when the light wavelengths considerably exceed the quantum-dot\\u000a size, the polarization and angular distribution of the

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

2007-01-01

325

Long-range radiative interaction between semiconductor quantum dots  

Microsoft Academic Search

We develop a Maxwell-Schrödinger formalism in order to describe the radiative interaction mechanism between semiconductor quantum dots. We solve the Maxwell equations for the electromagnetic field coupled to the polarization field of a quantum dot ensemble through a linear nonlocal susceptibility and compute the polariton resonances of the system. The radiative coupling, mediated by both radiative and surface photon modes,

Gaetano Parascandolo; Vincenzo Savona

2005-01-01

326

Coherent Acoustic Phonons in a Semiconductor Quantum Dot  

Microsoft Academic Search

The electronic and optical properties of semiconductor quantum dots (QD's) have attracted much attention re- cently due to their interesting physical properties and po- tential utility in applications. Exciton-phonon coupling is a crucial issue in nanocrystal physics, and this has moti- vated much of the previous work on the vibrational modes of quantum dots. The coupling to optical modes pro-

Todd D. Krauss; Frank W. Wise

1997-01-01

327

Spin Readout and Initialization in a Semiconductor Quantum Dot  

Microsoft Academic Search

Electron spin qubits in semiconductors are attractive from the viewpoint of long coherence times. However, single spin measurement is challenging. Several promising schemes incorporate ancillary tunnel couplings that may provide unwanted channels for decoherence. Here, we propose a novel spin-charge transduction scheme, converting spin information to orbital information within a single quantum dot by microwave excitation. The same quantum dot

Mark Friesen; Charles Tahan; Robert Joynt; M. A. Eriksson

2004-01-01

328

Mannosylated semiconductor quantum dots for the labeling of macrophages  

Microsoft Academic Search

Quantum dots show strong fluorescence emission and long stability compared with classical organic fluorescent dyes; therefore, quantum dots take the place of other dyes in Western blot, immunostaining and bioimaging. Since macrophage plays crucial roles in many pathophysiological processes, tracking macrophage migration, homing and fate is important for understanding the complex roles of macrophages in disease or developing disease diagnosis.

Yuriko Higuchi; Machiko Oka; Shigeru Kawakami; Mitsuru Hashida

2008-01-01

329

BCD computing structures in quantum- dot cellular automata  

Microsoft Academic Search

This paper proposes a detailed design analysis of BCD computing circuit for quantum-dot cellular automata (QCA). QCA is attracting a lot of attentions due to its very small sizes and low power consumption. The primary device, a quantum-dot cell, can be used to make gates, wires, and memories as such it is the basic building block of nanotechnology circuits. Because

Maryam Taghizadeh; Mehdi Askari; Khossro Fardad

2008-01-01

330

Modified Quantum Dots Could Lead to Improved Treatments for Cancer  

NSDL National Science Digital Library

This online article from Carnegie Mellon Today, discusses how chemists are researching quantum dots to evaluate their effectiveness in treating diseases such as cancer. Readers can discover how the scientists were able to produce quantum dots that fluoresced for an unprecedented eight months, and how they might be useful in locating diseases like cancer.

Pavlak, Amy

331

Study of exciton transfer in dense quantum dot nanocomposites  

E-print Network

Study of exciton transfer in dense quantum dot nanocomposites Burak Guzelturk,ab Pedro Ludwig. Govorov,c Xiao Wei Sun,b Qihua Xiongb and Hilmi Volkan Demir*ab Nanocomposites of colloidal quantum dots, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites

Demir, Hilmi Volkan

332

Quantum-Dot Cellular Automata SPICE Macro Model Northeastern University  

E-print Network

Quantum-Dot Cellular Automata SPICE Macro Model Rui Tang Northeastern University 360 Huntington Ave describes a SPICE model development method- ology for Quantum-Dot Cellular Automata (QCA) cells and presents a SPICE model for QCA cells. The model is val- idated by simulating the basic logic gates such as inverter

Ayers, Joseph

333

Minimized deterioration of ultrashort pulses in quantum dot optical amplifiers  

Microsoft Academic Search

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

Edeltraud Gehrig; Ortwin G. Hess

2004-01-01

334

Monovalent, reduced-size quantum dots for imaging  

E-print Network

Monovalent, reduced-size quantum dots for imaging receptors on living cells Mark Howarth1,3, Wenhao Bawendi1 & Alice Y Ting1 We describe a method to generate monovalent quantum dots (QDs) using agarose gel particles or latex beads allow stable single-particle tracking via their scattering, but are generally very

335

Molecular-Scale Quantum Dots from Carbon Nanotube Heterojunctions  

E-print Network

Molecular-Scale Quantum Dots from Carbon Nanotube Heterojunctions Bhupesh Chandra,,#,¶ Joydeep chiralities. These measurements reveal asymmetric IV-characteristics and the presence of a quantum dot (QD deposition across open slits (100 µm wide) on Si/SiO2 wafers,7 then characterized using Rayleigh scattering

Heinz, Tony F.

336

Quantum dot infrared photodetector enhanced by surface plasma wave excitation  

E-print Network

Quantum dot infrared photodetector enhanced by surface plasma wave excitation S. C. Lee, S. Krishna: Up to a thirty-fold detectivity enhancement is achieved for an InAs quantum dot infrared photodetector (QDIP) by the excitation of surface plasma waves (SPWs) using a metal photonic crystal (MPC

Krishna, Sanjay

337

Photosensitive quantum dot composites and their applications in optical structures  

E-print Network

Photosensitive quantum dot composites and their applications in optical structures Lin Pang,a Kevin poly methyl methacrylate PMMA -quantum-dot QD positive composite via a prepolymerization processing and an electron beam and ultraviolet UV light sensitive SU-8-QD negative composite via a direct dispersion

Fainman, Yeshaiahu

338

Evidence for transfer of polarization in a quantum dot cellular automata cell consisting of semiconductor quantum dots  

Microsoft Academic Search

We present evidence for quantum dot cellular automata action in a cell consisting of four dots defined by submicron metal gates on the top surface of a molecular-beam-epitaxy-grown GaAs\\/AlGaAs heterostructure in which a two-dimensional electron gas layer was formed approximately 70 nm below the surface. The four-dot cell is separated by a strong barrier in two double-dot sets. We show

S. Gardelis; C. G. Smith; J. Cooper; D. A. Ritchie; E. H. Linfield; Y. Jin

2003-01-01

339

Synthesis of highly fluorescent nitrogen-doped graphene quantum dots for sensitive, label-free detection of Fe (III) in aqueous media.  

PubMed

Heteroatom doping can drastically alter the electronic characteristics of graphene quantum dots (GQDs), thus resulting in unusual properties and related applications. Herein, we develop a simple and low-cost synthetic strategy to prepare nitrogen-doped GQDs (N-GQDs) through hydrothermal treatment of GQDs with hydrazine. The obtained N-GQDs with oxygen-rich functional groups exhibit a strong blue emission with 23.3% quantum yield (QY). Compared to GQDs, the N-GQDs exhibit enhanced fluorescence with blue-shifted energy. Due to the selective coordination to Fe(3+), the N-GQDs can be used as a green and facile sensing platform for label-free sensitive and selective detection of Fe (III) ions in aqueous solution and real water samples. The N-GQDs fluorescence probe shows a sensitive response to Fe(3+) in a wide concentration range of 1-1945?M with a detection limit of 90nM (s/N=3). Interestingly, it is also found that both dynamic and static quenching processes occur for the detection of Fe(3+) by N-GQDs, while the quenching effect of Fe(3+) on the fluorescence of GQDs is achieved by affecting the surface states of GQDs. PMID:24650437

Ju, Jian; Chen, Wei

2014-08-15

340

Numerical simulation of optical feedback on a quantum dot lasers  

SciTech Connect

We use multi-population rate equations model to study feedback oscillations in the quantum dot laser. This model takes into account all peculiar characteristics in the quantum dots such as inhomogeneous broadening of the gain spectrum, the presence of the excited states on the quantum dot and the non-confined states due to the presence of wetting layer and the barrier. The contribution of quantum dot groups, which cannot follow by other models, is simulated. The results obtained from this model show the feedback oscillations, the periodic oscillations which evolves to chaos at higher injection current of higher feedback levels. The frequency fluctuation is attributed mainly to wetting layer with a considerable contribution from excited states. The simulation shows that is must be not using simple rate equation models to express quantum dots working at excited state transition.

Al-Khursan, Amin H., E-mail: ameen_2all@yahoo.com [Thi-Qar University, Nassiriya Nanotechnology Research Laboratory (NNRL), Science College (Iraq); Ghalib, Basim Abdullattif [Babylon University, Laser Physics Department, Science College for Women (Iraq); Al-Obaidi, Sabri J. [Al-Mustansiriyah University, Physics Department, Science College (Iraq)

2012-02-15

341

Impurity position effect on optical properties of various quantum dots  

NASA Astrophysics Data System (ADS)

In this work, we have investigated the effect of impurity position on optical properties of a pyramid and a cone like quantum dot. For this goal, we first obtain the energy levels and wave functions using finite element method (FEM) in the presence of impurity. Then, we have studied the influence of impurity location on refractive index changes and absorption coefficients of the two quantum dots. We found that there is a maximum value for total refractive index changes and absorption coefficients at a special impurity position. Also, we have found that the refractive index changes and absorption coefficients of a cone like quantum dot are greater than a pyramid quantum dot in same volume and height. According to the results, it is deduced that the impurity location plays an important and considerable role in the electronic and optical properties of a pyramid and a cone like quantum dot.

Khordad, R.; Bahramiyan, H.

2015-02-01

342

Synthesis in aqueous solution and characterisation of a new cobalt-doped ZnS quantum dot as a hybrid ratiometric chemosensor.  

PubMed

In this paper, cobalt (Co(2+))-doped (CoD) ZnS quantum dots (QDs) are synthesised in aqueous solution and characterised for the first time. L-Cysteine (L-Cys) ligands on the surface of CoD ZnS QDs can bind 2,4,6-trinitrotoluene (TNT) to form Meisenheimer complexes (MHCs) mainly through acid-base pairing interactions between TNT and L-Cys and the assistance of hydrogen bonding and electrostatic co-interactions among L-Cys intermolecules. The aggregation of inter-dots induced by MHCs greatly influenced the light scattering property of the QDs in aqueous solution, and Rayleigh scattering (RS) enhancement at the defect-related emission wavelengths as well as its left side was observed with the excitation of CoD ZnS QDs by violet light. RS enhancement, combining with the quenching of the orange transition emission induced by TNT anions, resulted in a change in the ratiometric visualisation of the system being investigated. A novel CoD ZnS QD-based hybrid ratiometric chemosensor has therefore been developed for simple and sensitive analysis of TNT in water. This ratiometric probe can assay down to 25 nM TNT in solution without interference from a matrix of real water sample and other nitroaromatic compounds. Because of the excellent electron-accepting ability and strong affinity of TNT to L-Cys on the surface of CoD ZnS QDs, the CoD photoluminescent nanomaterials reported here are well suited for detecting ultra-trace TNT and for distinguishing different nitro-compounds in aqueous solution. PMID:22093356

Zou, Wen-sheng; Qiao, Jun-qin; Hu, Xin; Ge, Xin; Lian, Hong-zhen

2011-12-01

343

Hyperfine interactions in silicon quantum dots  

E-print Network

We present an all-electron calculation of the hyperfine parameters for conduction electrons in Si, showing that: (i) all parameters scale linearly with the spin density at a $^{29}$Si site; (ii) the isotropic term is over 30 times larger than the anisotropic part; (iii) conduction electron charge density at a Si nucleus is consistent with experimental estimates; (iv) Overhauser fields in natural Si quantum dots (QDs) are two orders of magnitude smaller than in GaAs QDs. This reinforces the outstanding performance of Si in keeping spin coherence and opens access to reliable quantitative information aiming at spintronic applications.

Lucy V. C. Assali; Helena M. Petrilli; Rodrigo B. Capaz; Belita Koiller; Xuedong Hu; S. Das Sarma

2010-07-06

344

Hyperfine interactions in silicon quantum dots  

E-print Network

We present an all-electron calculation of the hyperfine parameters for conduction electrons in Si, showing that: (i) all parameters scale linearly with the spin density at a $^{29}$Si site; (ii) the isotropic term is over 30 times larger than the anisotropic part; (iii) conduction electron charge density at a Si nucleus is consistent with experimental estimates; (iv) Overhauser fields in natural Si quantum dots (QDs) are two orders of magnitude smaller than in GaAs QDs. This reinforces the outstanding performance of Si in keeping spin coherence and opens access to reliable quantitative information aiming at spintronic applications.

Assali, Lucy V C; Capaz, Rodrigo B; Koiller, Belita; Hu, Xuedong; Sarma, S Das

2010-01-01

345

Mesoscopic admittance of a double quantum dot  

SciTech Connect

We calculate the mesoscopic admittance G({omega}) of a double quantum dot (DQD), which can be measured directly using microwave techniques. This quantity reveals spectroscopic information on the DQD and is also directly sensitive to a Pauli spin blockade effect. We then discuss the problem of a DQD coupled to a high quality photonic resonator. When the photon correlation functions can be developed along a random-phase-approximation-like scheme, the response of the resonator gives an access to G({omega}).

Cottet, Audrey; Mora, Christophe; Kontos, Takis [Laboratoire Pierre Aigrain, Ecole Normale Superieure, CNRS (UMR 8551), Universite P. et M. Curie, Universite D. Diderot, 24 rue Lhomond, F-75231 Paris Cedex 05 (France)

2011-03-15

346

Vacancy clusters in graphane as quantum dots.  

PubMed

Complementary electronic properties and a tendency to form sharp graphene-graphane interfaces open tantalizing possibilities for two-dimensional nanoelectronics. First-principles density functional and tight-binding calculations show that graphane can serve as natural host for graphene quantum dots, clusters of vacancies in the hydrogen sublattice. Their size n, shape, and stability are governed by the aromaticity and interfaces, resulting in formation energies approximately 1/ radicaln eV/atom and preference to hexagonal clusters congruent with lattice hexagons (i.e., with armchair edge). Clusters exhibit large gaps approximately 15/ radicaln eV with size dependence typical for confined Dirac fermions. PMID:20465240

Singh, Abhishek K; Penev, Evgeni S; Yakobson, Boris I

2010-06-22

347

Holonomic quantum computation with electron spins in quantum dots  

SciTech Connect

With the help of the spin-orbit interaction, we propose a scheme to perform holonomic single-qubit gates on the electron spin confined to a quantum dot. The manipulation is done in the absence (or presence) of an applied magnetic field. By adiabatic changing the position of the confinement potential, one can rotate the spin state of the electron around the Bloch sphere in semiconductor heterostructures. The dynamics of the system is equivalent to employing an effective non-Abelian gauge potential whose structure depends on the type of the spin-orbit interaction. As an example, we find an analytic expression for the electron spin dynamics when the dot is moved around a circular path (with radius R) on the two dimensional electron gas (2DEG) and show that all single-qubit gates can be realized by tuning the radius and orientation of the circular paths. Moreover, using the Heisenberg exchange interaction, we demonstrate how one can generate two-qubit gates by bringing two quantum dots near each other, yielding a scalable scheme to perform quantum computing on arbitrary N qubits. This proposal shows a way of realizing holonomic quantum computers in solid-state systems.

Golovach, Vitaly N. [Arnold Sommerfeld Center for Theoretical Physics and Center for Nanoscience Department of Physics, Ludwig-Maximilians-Universitaet, Theresienstrasse 37, D-80333 Munich (Germany); Borhani, Massoud [Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland); Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260-1500 (United States); Loss, Daniel [Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland)

2010-02-15

348

Optical properties of excitons in quantum dots: diffraction of an electromagnetic plane wave by a spherical quantum dot  

Microsoft Academic Search

We show how to compute the optical spectra resulting from the scattering of a plane electromagnetic wave on a quantum dot (QD) in the region of the excitonic resonances. The method uses the microscopic calculation of quantum dot eigenfunctions and the macroscopic Stahl's density matrix approach to compute the electromagnetic field within and outside the QD, taking into account the

L. Silvestri; F. Bassani; G. Czajkowski

2000-01-01

349

The Procedure to Realize Two-Dimensional Quantum Dot Superlattices: From Incoherently Coupled to Coherently Coupled Quantum Dot Arrays  

Microsoft Academic Search

We will describe, from both the theoretical and experimental points of view, a procedure leading to the realization of two-dimensional quantum dot superlattices (2D QDSLs). Two kinds of laterally coupled quantum dot arrays in which the exciton motions are coherent and incoherent are studied by photoluminescence (PL) measurements. The formation of minibands with coherent exciton motion is demonstrated in the

Sheng Lan; Kouichi Akahane; Kee-Youn Jang; Takahiro Kawamura; Yoshitaka Okada; Mitsuo Kawabe

1999-01-01

350

A novel silica-coated multiwall carbon nanotube with CdTe quantum dots nanocomposite.  

PubMed

A novel silica-coated multiwall carbon nanotube (MWNTs) with CdTe quantum dots nanocomposite was synthesized in this paper. Here, we show the in situ growth of crystalline CdTe quantum dots on the surfaces of oxidized MWNTs. The approach proposed herein differs from previous attempts to synthesize nanotube assemblies in that we mix the oxidized MWNTs into CdCl(2) solution of CdTe nanocrystals synthesized in aqueous solution. Reinforced the QD-MWNTs heterostructures with silica coating, this method is not invasive and does not introduce defects to the structure of carbon nanotubes (CNTs), and it ensures high stability in a range of organic solvents. Furthermore, a narrow SiO(2) layer on the MWNT-CdTe heterostructures can eliminate the biological toxicity of quantum dots and carbon nanotubes. This is not only a breakthrough in the synthesis of one-dimensional nanostructures, but also taking new elements into bio-nanotechnology. PMID:19660982

Fei, Qiang; Xiao, Dehai; Zhang, Zhiquan; Huan, Yanfu; Feng, Guodong

2009-10-01

351

Subtle leakage of a Majorana mode into a quantum dot  

NASA Astrophysics Data System (ADS)

We investigate quantum transport through a quantum dot connected to source and drain leads and side coupled to a topological superconducting nanowire (Kitaev chain) sustaining Majorana end modes. Using a recursive Green's-function approach, we determine the local density of states of the system and find that the end Majorana mode of the wire leaks into the dot, thus, emerging as a unique dot level pinned to the Fermi energy ?F of the leads. Surprisingly, this resonance pinning, resembling, in this sense, a "Kondo resonance," occurs even when the gate-controlled dot level ?dot(Vg) is far above or far below ?F. The calculated conductance G of the dot exhibits an unambiguous signature for the Majorana end mode of the wire: In essence, an off-resonance dot [?dot(Vg)??F], which should have G =0, shows, instead, a conductance e2/2h over a wide range of Vg due to this pinned dot mode. Interestingly, this pinning effect only occurs when the dot level is coupled to a Majorana mode; ordinary fermionic modes (e.g., disorder) in the wire simply split and broaden (if a continuum) the dot level. We discuss experimental scenarios to probe Majorana modes in wires via these leaked/pinned dot modes.

Vernek, E.; Penteado, P. H.; Seridonio, A. C.; Egues, J. C.

2014-04-01

352

Quantum Dot Spin Cellular Automata for Realizing a Quantum Processor  

E-print Network

We show how "single" quantum dots, each hosting a singlet-triplet qubit, can be placed in arrays to build a spin quantum cellular automaton. A fast ($\\sim 10$ ns) deterministic coherent singlet-triplet filtering, as opposed to current incoherent tunneling/slow-adiabatic based quantum gates (operation time $\\sim 300$ ns), can be employed to produce a two-qubit gate through capacitive (electrostatic) coupling that can operate over significant distances. This is the coherent version of the widely discussed charge and nano-magnet cellular automata and would offer speed, reduce dissipation, perform quantum computation, while interfacing smoothly with its classical counterpart. This combines the best of two worlds -- the coherence of spin pairs known from quantum technologies, and the strength and range of electrostatic couplings from the charge based classical cellular automata.

Abolfazl Bayat; Charles E. Creffield; John H. Jefferson; Michael Pepper; Sougato Bose

2013-10-16

353

Manipulating Single Spins in Quantum Dots Coupled to Ferromagnetic Leads  

NASA Astrophysics Data System (ADS)

We discuss the possibility to generate, manipulate, and probe single spins in single-level quantum dots coupled to ferromagnetic leads. The spin-polarized currents flowing between dot and leads lead to a non-equilibrium spin accumulation, i.e., a finite polarization of the dot spin. Both the magnitude and the direction of the dot's spin polarization depends on the magnetic properties of leads and their coupling to the dot. They can be, furthermore, manipulated by either an externally applied magnetic field or an intrinsically present exchange field that arises due to the tunnel coupling of the strongly-interacting quantum-dot states to spin-polarized leads. The exchange field can be tuned by both the gate and bias voltage, which, therefore, provide convenient handles to manipulate the quantum-dot spin. Since the transmission through the quantum-dot spin valve sensitively depends on the state of the quantum-dot spin, all the dynamics of the latter is reflected in the transport properties of the device.

König, Jürgen; Braun, Matthias; Martinek, Jan

354

Structural Transformations in self-assembled Semiconductor Quantum Dots as inferred by Transmission Electron Microscopy  

E-print Network

Structural Transformations in self-assembled Semiconductor Quantum Dots as inferred by Transmission of self-assembled semiconductor quantum dots are reported. III-V and II-VI quantum dots as grown and controlling structural transformations in self-assembled semiconductor quantum dots may also offer

Moeck, Peter

355

Discrete quantum Fourier transform in coupled semiconductor double quantum dot molecules  

E-print Network

In this Letter, we present a physical scheme for implementing the discrete quantum Fourier transform in a coupled semiconductor double quantum dot system. The main controlled-R gate operation can be decomposed into many simple and feasible unitary transformations. The current scheme would be a useful step towards the realization of complex quantum algorithms in the quantum dot system.

Ping Dong; Ming Yang; Zhuo-Liang Cao

2008-11-28

356

Photovoltaic quantum dot quantum cascade infrared photodetector A. V. Barve and S. Krishna  

E-print Network

Photovoltaic quantum dot quantum cascade infrared photodetector A. V. Barve and S. Krishna Citation subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions #12;Photovoltaic) Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared

Krishna, Sanjay

357

Universal Braess paradox in open quantum dots  

NASA Astrophysics Data System (ADS)

We present analytical and numerical results that demonstrate the presence of the Braess paradox in chaotic quantum dots. The paradox that we identify, originally perceived in classical networks, shows that the addition of more capacity to the network can suppress the current flow in the universal regime. We investigate the weak localization term, showing that it presents the paradox encoded in a saturation minimum of the conductance, under the presence of hyperflow in the external leads. In addition, we demonstrate that the weak localization suffers a transition signal depending on the overcapacity lead and presents an echo on the magnetic crossover before going to zero due to the full time-reversal symmetry breaking. We also show that the quantum interference contribution can dominate the Ohm term in the presence of constrictions and that the corresponding Fano factor engenders an anomalous behavior.

Barbosa, A. L. R.; Bazeia, D.; Ramos, J. G. G. S.

2014-10-01

358

Electron states in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

359

Universal Braess paradox in open quantum dots.  

PubMed

We present analytical and numerical results that demonstrate the presence of the Braess paradox in chaotic quantum dots. The paradox that we identify, originally perceived in classical networks, shows that the addition of more capacity to the network can suppress the current flow in the universal regime. We investigate the weak localization term, showing that it presents the paradox encoded in a saturation minimum of the conductance, under the presence of hyperflow in the external leads. In addition, we demonstrate that the weak localization suffers a transition signal depending on the overcapacity lead and presents an echo on the magnetic crossover before going to zero due to the full time-reversal symmetry breaking. We also show that the quantum interference contribution can dominate the Ohm term in the presence of constrictions and that the corresponding Fano factor engenders an anomalous behavior. PMID:25375575

Barbosa, A L R; Bazeia, D; Ramos, J G G S

2014-10-01

360

Semiconductor quantum dot-sensitized solar cells  

PubMed Central

Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future. PMID:24191178

Tian, Jianjun; Cao, Guozhong

2013-01-01

361

Biosensing with Luminescent Semiconductor Quantum Dots  

PubMed Central

Luminescent semiconductor nanocrystals or quantum dots (QDs) are a recently developed class of nanomaterial whose unique photophysical properties are helping to create a new generation of robust fluorescent biosensors. QD properties of interest for biosensing include high quantum yields, broad absorption spectra coupled to narrow size-tunable photoluminescent emissions and exceptional resistance to both photobleaching and chemical degradation. In this review, we examine the progress in adapting QDs for several predominantly in vitro biosensing applications including use in immunoassays, as generalized probes, in nucleic acid detection and fluorescence resonance energy transfer (FRET) - based sensing. We also describe several important considerations when working with QDs mainly centered on the choice of material(s) and appropriate strategies for attaching biomolecules to the QDs.

Sapsford, Kim E.; Pons, Thomas; Medintz, Igor L.; Mattoussi, Hedi

2006-01-01

362

Quantum-Dot Photodetectors: High Sensitivity due to Controllable Kinetics  

NASA Astrophysics Data System (ADS)

Comparing to the quantum wells, the quantum-dot structures provide more opportunities to control electron kinetics and to optimize operating regimes of quantum-dot photodetectors. At room temperatures, the photoelectron capture in quantum-dot structures is determined by the electron diffusion in the potential of intentionally or unintentionally charged quantum dots1. Therefore, the capture time can be drastically increased by a proper choice of geometry of the quantum-dot structure and modulation doping. Suppression of capture processes provides longer lifetimes of photoelectrons, thus increasing the photoconductive gain and responsivity. Here we exploit a model of the QD detectors operating at room temperatures and study electron diffusion in the self-consistent field of potential barriers surrounding quantum dots. Using the Monte-Carlo method and analytical evaluations, we investigate photoelectron capture and transit processes as functions of the quantum dot positions, sensor geometry, and external electric field applied. Finally, we calculate the photoconductive gain and discuss the optimal structures and regimes. [1] A. Sergeev, V. Mitin, and M. Stroscio, Physica B 316-317, 369 (2002).

Sergeev, Andrei; Chien, Li-Hsin; Vagidov, Nizami; Mitin, Vladimir

2008-03-01

363

Fractional Josephson effect in a quadruple quantum dot  

NASA Astrophysics Data System (ADS)

A double quantum dot coupled to an s-wave superconductor and subject to an inhomogeneous magnetic field can host a pair of zero-energy Majorana fermions when the dot properties are tuned appropriately. Here, we demonstrate the possibility of generating a fractional 4? Josephson effect in two such double dots tunnel-coupled to each other. We discuss the robustness of this effect with respect to perturbations away from the special point in parameter space where the uncoupled double dots host Majorana fermions. We demonstrate the possibility of generating Josephson effects with a period of 8? and 12? in strongly coupled double dots.

Sothmann, Björn; Li, Jian; Büttiker, Markus

2013-08-01

364

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

365

Quantum and classical thermoelectric transport in quantum dot nanocomposites  

Microsoft Academic Search

Quantum dot nanocomposites are potentially high-efficiency thermoelectric materials, which could outperform superlattices and random nanocomposites in terms of manufacturing cost-effectiveness and material properties because of the reduction of thermal conductivity due to the phonon-interface scattering, the enhancement of Seebeck coefficient due to the formation of minibands, and the enhancement of electrical conductivity due to the phonon-bottleneck effect in electron-phonon scattering

Jun Zhou; Ronggui Yang

2011-01-01

366

Optically programmable electron spin memory using semiconductor quantum dots  

Microsoft Academic Search

The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled

Miro Kroutvar; Yann Ducommun; Dominik Heiss; Max Bichler; Dieter Schuh; Gerhard Abstreiter; Jonathan J. Finley

2004-01-01

367

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

368

Colloidal quantum dot light-emitting devices  

PubMed Central

Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs - optical excitation, Förster energy transfer, and direct charge injection - that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs. PMID:22110863

Wood, Vanessa; Bulovi?, Vladimir

2010-01-01

369

Competing interactions in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free-induction decay and spin-echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin-echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the nondecaying fraction previously observed for zero-field free-induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.

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

2014-10-01

370

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. PMID:22916072

Zhang, Yi; Wang, Tza-Huei

2012-01-01

371

Behavior of optical bistability in multifold quantum dot molecules  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

372

Electronic transport properties of coupled quantum dots on carbon nanotubes.  

PubMed

We investigate the electronic transport properties of coupled quantum dots, controlled by local gates on carbon nanotubes. The inter-dot coupling can be tuned from weak to strong by changing gate voltages, and oscillates in short and long period with the distance between two gates. We introduce a one-dimensional scattering model to describe the mechanism of the electron transport through the carbon nanotube quantum dots. We show that pi and PI* channels contribute differently to the inter-dot coupling and the transport phase plays a key role in the oscillations of the coupling. PMID:21125895

Qian, Haiyun; Lu, Jun-Qiang

2010-08-01

373

Nitrogen-doped carbon quantum dots: facile synthesis and application as a "turn-off" fluorescent probe for detection of Hg2+ ions.  

PubMed

A facile, economical and straightforward hydrothermal strategy is used to prepare highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) by using folic acid as both carbon and nitrogen sources. The as-prepared N-CQDs have an average size of 4.5 ± 1.0 nm and exhibit excitation wavelength-dependent fluorescence with the maximum emission and excitation at 390 and 470 nm, respectively. Furthermore, due to the effective quenching effect of Hg(2+) ions, such N-CQDs are found to serve as an effective fluorescent sensing platform for lable-free sensitive detection of Hg(2+) ions with a detection limit of 0.23 ?M. The selectivity experiments reveal that the fluorescent sensor is specific for Hg(2+) even with interference by high concentrations of other metal ions. Most importantly, the N-CQDs-based Hg(2+) ions sensor can be successfully applied to the determination of Hg(2+) in tap water and real lake water samples. With excellent sensitivity and selectivity, such stable and cheap carbon materials are potentially suitable for monitoring of Hg(2+) in environmental application. PMID:24365697

Zhang, Ruizhong; Chen, Wei

2014-05-15

374

Synthesis of CdTe quantum dot-conjugated CC49 and their application for in vitro imaging of gastric adenocarcinoma cells  

NASA Astrophysics Data System (ADS)

The purpose of this experiment was to investigate the visible imaging of gastric adenocarcinoma cells in vitro by targeting tumor-associated glycoprotein 72 (TAG-72) with near-infrared quantum dots (QDs). QDs with an emission wavelength of about 550 to 780 nm were conjugated to CC49 monoclonal antibodies against TAG-72, resulting in a probe named as CC49-QDs. A gastric adenocarcinoma cell line (MGC80-3) expressing high levels of TAG-72 was cultured for fluorescence imaging, and a gastric epithelial cell line (GES-1) was used for the negative control group. Transmission electron microscopy indicated that the average diameter of CC49-QDs was 0.2 nm higher compared with that of the primary QDs. Also, fluorescence spectrum analysis indicated that the CC49-QDs did not have different optical properties compared to the primary QDs. Immunohistochemical examination and in vitro fluorescence imaging of the tumors showed that the CC49-QDs probe could bind TAG-72 expressed on MGC80-3 cells.

Zhang, Yun-Peng; Sun, Peng; Zhang, Xu-Rui; Yang, Wu-Li; Si, Cheng-Shuai

2013-06-01

375

Synthesis and application of a targeting diagnosis system via quantum dots coated by amphiphilic polymer for the detection of liver cancer cells.  

PubMed

Water-soluble quantum dots (QDs) for liver cancer diagnosis were prepared using QDs with oleylamine ligand coated with poly(aspartate)-graft-poly(ethylene glycol)-dodecylamine (PASP-Na-g-PEG-DDA). Dynamic light scattering and transmission electron microscopy imaging showed that the novel QDs have an ellipsoidal morphology with a size of ~ 45 nm which could be used for biomedical application. Furthermore, the PASP-Na-g-PEG-DDA was then modified with anti-(vascular endothelial growth factor) (VEGF antibody), and a 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) assay showed that the novel anti-VEGF-targeting QDs in vitro had low toxicity. Confocal laser scanning microscopy observations revealed an intracellular (HepG2) distribution of the novel anti-VEGF-targeting QDs and the targeting efficiency of anti-VEGF. These novel QDs could be used as a probe for liver cancer cell imaging because of anti-VEGF targeting. PMID:24403213

Sun, Xiaoran; Li, Yapeng; Huang, Hailong; Yang, Bohan; Wang, Yuzhen

2014-11-01

376

Aqueous synthesis of thiol-capped CdTe quantum dots and its photoluminescence enhancement via room temperature treatment with alkyl chain diamines  

NASA Astrophysics Data System (ADS)

In this study the CdTe quantum dots (QDs) are synthesized in aqueous solution with three thiol-contained capping ligands of thioglycollic acid (TGA), 3-mercaptopropionic acid (MPA), and L-cysteine (LCys). The photoluminescence (PL) enhancement of the as-prepared QDs is also conducted via room temperature treatment with alkyl chain diamines. Our measurements on the ultraviolet-visible (UV-vis) absorption and fluorescence emission reveal that both the growth kinetics and the PL efficiency of the QDs vary a lot with the molecular structures of the three involved ligands. In comparison with TGA and LCys, MPA endows the QDs with a wide color tuning range from cyan to deep red and strong PL emission while its full width at half maximum (FWHM) is regretfully large. Notable enhancement on PL emission is achieved for the TGA and MPA capped QDs via room temperature treatment with diamines solutions while in the case of the QDs capped by LCys the enhancement is practically meaningless.

Liu, Xiangming; Tian, Jintao; Dai, Jinhui; Wang, Xin

2014-03-01

377

Nondestructive chemical functionalization of MWNTs by poly(2-dimethylaminoethyl methacrylate) and their conjugation with CdSe quantum dots: Synthesis, properties, and cytotoxicity studies  

NASA Astrophysics Data System (ADS)

Multi-walled carbon nanotubes (MWNTs) were functionalized with poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) in a nondestructive manner by UV-driven surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization. The RAFT agent having benzophenone groups was initially synthesized, and anchored to MWNTs through UV-triggered photoreaction. The subsequent RAFT polymerization of DMAEMA from the surface of MWNTs afforded PDMAEMA grafted MWNTs (MWNTs-g-PDMAEMA). The successful grafting of PDMAEMA on MWNTs via chemical linkage was confirmed by FT-IR, 1H NMR, XPS, EDX, TGA, TEM, and SEM analyses. A reversible dispersion phenomenon was observed in an aqueous solution of MWNTs-g-PDMAEMA as induced either by temperature or pH. The CdSe quantum dots (CdSe QDs) were attached to quaternized MWNTs-g-PDMAEMA to produce MWNTs-g-PDMAEMA-MeI/CdSe nanohybrids via electrostatic self-assembly. The formation of the nanohybrids was elucidated by EDS, TEM, and XRD. The cell viability assessment of the nanohybrids suggested their biocompatible character. The photoluminescence spectra of the nanohybrids indicated that the CdSe QDs significantly preserved its optical property after conjugation with MWNTs-g-PDMAEMA.

Islam, Md. Rafiqul; Bach, Long Giang; Vo, Thanh-Sang; Tran, Thi-Nga; Lim, Kwon Taek

2013-12-01

378

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

NASA Astrophysics Data System (ADS)

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 narrow photoluminescence full width at half maximum. The high-resolution transmission electron microscopy images and X-ray diffraction revealed that the highly monodisperse CdTe QDs were of regular spherical morphology with zinc blende crystal structure displaying mean sizes of about 4 nm. The energy dispersed spectrometry measurement indicated the presence of Cd and Te, with the Cd:Te ratio being close to 1:1. Fourier transform infrared transmission spectra confirmed the existence of stearate on the CdTe QDs surfaces. The experimental results also demonstrated that the stearate-capped CdTe QDs had an unexpected good stability.

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

2010-09-01

379

Scalable single-step noninjection synthesis of high-quality core/shell quantum dots with emission tunable from violet to near infrared.  

PubMed

The common two-step "hot-injection" methods are not suitable for reproducible production of core/shell quantum dots (QDs) at large scale for practical applications. Herein we develop a scalable, reproducible, and low-cost synthetic approach for high-quality core/shell QDs (CdS/Zn(x)Cd(1-x)S, CdSe/Zn(x)Cd(1-x)S, and CdTe/Zn(x)Cd(1-x)S) with shell material composed of gradient alloy structure by directly heating commercial available, air-stable CdO, Zn(NO(3))(2), and chalcogenide elements in octadecene media at air. With simple variation of reaction recipe (reactants and feeding ratio), luminescence color of the resulting QDs can be conveniently tuned from violet to near-infrared (400-820 nm). The emission efficiency of the as-prepared QDs can be up to 80%. Moreover, the high emission efficiency can be preserved after QDs transferred into aqueous media via ligand exchange. The structure, chemical composition, and optical properties of the obtained QDs have been characterized with use of transmission electron microscopy, elemental analysis, and optical spectroscopy. The scalability of the reported approach has been demonstrated by the facile preparation of gram-scaled QD product in one batch reaction. PMID:23234382

Zhang, Wenjin; Zhang, Hua; Feng, Yaoyu; Zhong, Xinhua

2012-12-21

380

Nonequilibrium electron transport in quantum dot and quantum point contact systems  

Microsoft Academic Search

Much experimental research has been performed in the equilibrium regime on individual quantum dots and quantum point contacts (QPCs). The focus of the research presented here is electron transport in the nonequilibrium regime in coupled quantum dot and QPC systems fabricated on AlGaAs\\/GaAs material using the split gate technique. Near equilibrium magnetoconductance measurements were performed on a quantum dot and

Anasuya Erin Krishnaswamy

1999-01-01

381

A novel route to photoluminescent, water-soluble Mn-doped ZnS quantum dots via photopolymerization initiated by the quantum dots  

Microsoft Academic Search

We design a photopolymerization, in which Mn-doped ZnS quantum dots (ZnS:Mn2+) initiate the polymerization of acrylic acid, to convert the non-cytotoxic quantum dots to water-soluble ones for biological chromophores The prepared quantum dots are nearly monodispersed in water and the resulting solution shows long-term stability for months. The water-soluble ZnS:Mn2+ quantum dots exhibit high quantum efficiency of fluorescence. The polymerization

Xufeng Liu; Xiuyuan Ni; Jiao Wang; Xinghai Yu

2008-01-01

382

Frequency cavity pulling induced by a single semiconductor quantum dot  

E-print Network

We investigate the emission properties of a single semiconductor quantum dot deterministically coupled to a confined optical mode in the weak coupling regime. A strong pulling, broadening and narrowing of the cavity mode emission is evidenced when changing the spectral detuning between the emitter and the cavity. These features are theoretically accounted for by considering the phonon assisted emission of the quantum dot transition. These observations highlight a new situation for cavity quantum electrodynamics involving spectrally broad emitters.

Daniel Valente; Jan Suffczy?ski; Tomasz Jakubczyk; Adrien Dousse; Aristide Lemaître; Isabelle Sagnes; Loïc Lanco; Paul Voisin; Alexia Auffeves; Pascale Senellart

2013-07-23

383

Resonant Raman scattering by strained and relaxed germanium quantum dots  

Microsoft Academic Search

This paper reports on the results of resonant Raman scattering investigations of the fundamental vibrations in Ge\\/Si structures\\u000a with strained and relaxed germanium quantum dots. Self-assembled strained Ge\\/Si quantum dots are grown by molecular-beam epitaxy\\u000a on Si(001) substrates. An ultrathin SiO2 layer is grown prior to the deposition of a germanium layer with the aim of forming relaxed germanium quantum

A. G. Milekhin; A. I. Nikiforov; M. Yu. Ladanov; O. P. Pchelyakov; S. Schulze; D. R. T. Zahn

2004-01-01

384

Bioconjugated Quantum Dots for In Vivo Molecular and Cellular Imaging  

PubMed Central

Semiconductor quantum dots (QDs) are tiny light-emitting particles on the nanometer scale, and are emerging as a new class of fluorescent labels for biology and medicine. In comparison with organic dyes and fluorescent proteins, they have unique optical and electronic properties, with size-tunable light emission, superior signal brightness, resistance to photobleaching, and broad absorption spectra for simultaneous excitation of multiple fluorescence colors. QDs also provide a versatile nanoscale scaffold for designing multifunctional nanoparticles with both imaging and therapeutic functions. When linked with targeting ligands such as antibodies, peptides or small molecules, QDs can be used to target tumor biomarkers as well as tumor vasculatures with high affinity and specificity. Here we discuss the synthesis and development of state-of-the-art QD probes and their use for molecular and cellular imaging. We also examine key issues for in vivo imaging and therapy, such as nanoparticle biodistribution, pharmacokinetics, and toxicology. PMID:18495291

Smith, Andrew M.; Duan, Hongwei; Mohs, Aaron M.; Nie, Shuming

2008-01-01

385

Quantum Dot-Based Nanoprobes for In Vivo Targeted Imaging  

PubMed Central

Fluorescent semiconductor quantum dots (QDs) have attracted tremendous attention over the last decade. The superior optical properties of QDs over conventional organic dyes make them attractive labels for a wide variety of biomedical applications, whereas their potential toxicity and instability in biological environment has puzzled scientific researchers. Much research effort has been devoted to surface modification and functionalization of QDs to make them versatile probes for biomedical applications, and significant progress has been made over the last several years. This review article aims to describe the current state-of-the-art of the synthesis, modification, bioconjugation, and applications of QDs for in vivo targeted imaging. In addition, QD-based multifunctional nanoprobes are also summarized. PMID:24206136

Zhu, Yian; Hong, Hao; Xu, Zhi Ping; Li, Zhen; Cai, Weibo

2013-01-01

386

Quantum dot quantum computation in III-V type semiconductor  

NASA Astrophysics Data System (ADS)

Among recent proposals for next-generation, non-charge-based logic is the notion that a single electron can be trapped and spin of the electron can be manipulated through the application of gate potentials. In the thesis, there are two major contributions of the manipulation of electron spin. In regard to the first contribution, we present numerical simulations of such a spin in single electron devices for realistic asymmetric potentials in electrostatically confined quantum dot. Using analytical and numerical techniques we show that breaking in-plane rotational symmetry of the confining potential by applied gate voltage leads to a significant effect on the tuning of the electron g-factor. In particular, we find that anisotropy extends the tunability to larger quantum dots in the GaAs case. Although the same extension of tunability exists in the InAs quantum dot case, we find a new effect in the InAs case. The new discovery is that broken in-plane rotational symmetry due to the Rashba spin-orbit coupling in an asymmetric potential results in a significant reverse effect in the tuning of the electron g-factor. This effect can not be observed in symmetric case. The derivative of the g-factor with respect to the electric field has the opposite sign in the above two potentials. The manipulation of Berry phases of spin in nano-scale devices is a topic that has received recent attention as a promising candidate for solid state quantum computation and non-charge-based logic devices. A single electron in an electrostatically defined quantum dot located in a 2 dimensional electron gas (2DEG), for example, can be trapped and the spin can be manipulated by simply moving the center of mass of the quantum dot adiabatically along a closed loop in the 2D plane via the application of gate potentials. In relation to the second contribution, we present numerical simulations and analytical expressions for the spin-dependent electron propagator (a matrix-valued function of position) for an electron trapped in a quantum dot, while the center of mass of the quantum dot is adiabatically moved in the 2D plane in the presence of the Rashba and Dresselhaus spin-orbit interactions. We apply the Feynman disentangling technique to determine the non-abelian matrix Berry phase, we find exact analytical expression for the propagator in three cases: (a) pure Rashba coupling; (b) pure Dresselhaus coupling; and (c) a combination of equally strong Rashba and Dresselhaus couplings. For other cases of interest where the solution of the propagator can not be found analytically, we present results obtained by numerically solving the Riccati equation resulting from the disentangling procedure. We also find that the presence of both spin-orbit couplings leads to a larger spin-flip probability than what would result from either mechanism considered separately.

Prabhakar, Sanjay Kumar

387

Electronic structure and optical properties of quantum dots  

NASA Astrophysics Data System (ADS)

Because of complete (three dimensional) confinement, quantum dots have a most dramatic quantum size effect. Due to the finite size of the dot, the conduction and valence bands of semiconductor dots are quantized and quantum dot spectra exhibit a series of discrete electronic transitions and depend strongly on the size of the nanocrystal. In this thesis we study the electronic structure and the optical properties of semiconductor quantum dots and semiconductor quantum dot systems. Different properties and different dots and dot systems are described. The first topic is the electric polarization in a semiconductor dot (II-VI compound). A simple theoretical model for the origin of spontaneous polarization in single nanocrystals is developed, based on the proposal that the origin of the spontaneous polarization is in the strained layer between "cap" and the nanocrystal. The internal electric field in the dot is due to the piezoelectric effect caused by the strain existing in the interface region of material with different lattice constants. Based on spherical rotation symmetry without inversion SO(3), the model employs a distribution of polarization with symmetry which is a subgroup of SO(3), consistent with the hexagonal structure of wurtzite structure. The second topic we study is a distribution of many quantum dots, which are arranged together in an array. We present a new model to implement organic exciton-inorganic (semiconductor) exciton hybridization. We consider embedding a quantum dot array into an organic medium. A Wannier-Mott transfer exciton is formed when the exciton in each semiconductor dot interacts via multipole-multipole coupling with other excitons in the different semiconductor dots of the array. A new hybrid exciton appears in the system owing to strong dipole-dipole interaction of the Frenkel exciton of organic molecules with the Wannier Mott transfer exciton of the quantum dot array. This hybrid exciton has both a large oscillator strength (Frenkel-like) and a large exciton Bohr radius (Wannier-like). At resonance between these two types of excitons, the optical non-linearity is very high and can be controlled by changing parameters of the system such as dot radius and dot-dot spacing. As the third topic, which differs from the pure nanocrystal in the above study, we also present our study on Mn-doped semiconductor nanocrystals such as the ZnS:Mn quantum dot. The effect of an extra electron "injected" into the doped quantum dot with a substitutional Mn 2+ at the center is considered. The electron confined in the dot will be strongly coupled by exchange interaction with the Mn ion, and will split and mix Mn crystal-field energy levels. As a result, this will strongly break the previous selection rules. The optical transition of interest is the 4T1 - 6 A1 transition. Using this model we evaluate the energy structure, wavefunctions, luminescent efficiency and transition life time of a Mn doped quantum dot and compare our results with experimental data.

Nguyen, Thique Huong

388

Shape, strain, and ordering of lateral InAs quantum dot molecules  

Microsoft Academic Search

The results of an x-ray study on freestanding, self-assembled InAs\\/GaAs quantum dots grown by molecular beam epitaxy are presented. The studied samples cover the range from statistically distributed single quantum dots to quantum dot bimolecules, and finally to quantum dot quadmolecules. The x-ray diffraction data of the single quantum dots and the bimolecules, obtained in grazing incidence geometry, have been

B. Krause; T. H. Metzger; A. Rastelli; R. Songmuang; S. Kiravittaya; O. G. Schmidt

2005-01-01

389

Quantum dot nanoparticle conjugation, characterization, and applications in neuroscience  

NASA Astrophysics Data System (ADS)

Quantum dot are semiconducting nanoparticles that have been used for decades in a variety of applications such as solar cells, LEDs and medical imaging. Their use in the last area, however, has been extremely limited despite their potential as revolutionary new biological labeling tools. Quantum dots are much brighter and more stable than conventional fluorophores, making them optimal for high resolution imaging and long term studies. Prior work in this area involves synthesizing and chemically conjugating quantum dots to molecules of interest in-house. However this method is both time consuming and prone to human error. Additionally, non-specific binding and nanoparticle aggregation currently prevent researchers from utilizing this system to its fullest capacity. Another critical issue that has not been addressed is determining the number of ligands bound to nanoparticles, which is crucial for proper interpretation of results. In this work, methods to label fixed cells using two types of chemically modified quantum dots are studied. Reproducible non-specific artifact labeling is consistently demonstrated if antibody-quantum dot conditions are less than optimal. In order to explain this, antibodies bound to quantum dots were characterized and quantified. While other groups have qualitatively characterized antibody functionalized quantum dots using TEM, AFM, UV spectroscopy and gel electrophoresis, and in some cases have reported calculated estimates of the putative number of total antibodies bound to quantum dots, no quantitative experimental results had been reported prior to this work. The chemical functionalization and characterization of quantum dot nanocrystals achieved in this work elucidates binding mechanisms of ligands to nanoparticles and allows researchers to not only translate our tools to studies in their own areas of interest but also derive quantitative results from these studies. This research brings ease of use and increased reliability to nanoparticles in medical imaging.

Pathak, Smita

390

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

SciTech Connect

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

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

2014-07-01

391

Magneto-optical studies of quantum dots  

NASA Astrophysics Data System (ADS)

Significant effort in condensed matter physics has recently been devoted to the field of "spintronics" which seeks to utilize the spin degree of freedom of electrons. Unlike conventional electronics that rely on the electron charge, devices exploiting their spin have the potential to yield new and novel technological applications, including spin transistors, spin filters, and spin-based memory devices. Any such application has the following essential requirements: 1) Efficient electrical injection of spin-polarized carriers; 2) Long spin lifetimes; 3) Ability to control and manipulate electron spins; 4) Effective detection of spin-polarized carriers. Recent work has demonstrated efficient electrical injection from ferromagnetic contacts such as Fe and MnAs, utilizing a spin-Light Emitting Diode (spin-LED) as a method of detection. Semiconductor quantum dots (QDs) are attractive candidates for satisfying requirements 2 and 3 as their zero dimensionality significantly suppresses many spin-flip mechanisms leading to long spin coherence times, as well as enabling the localization and manipulation of a controlled number of electrons and holes. This thesis is composed of three projects that are all based on the optical properties of QD structures including: I) Intershell exchange between spin-polarized electrons occupying adjacent shells in InAs QDs; II) Spin-polarized multiexitons in InAs QDs in the presence of spin-orbit interactions; III) The optical Aharonov-Bohm effect in AlxGa1-xAs/AlyGa1-yAs quantum wells (QWs). In the following we introduce some of the basic optical properties of quantum dots, describe the main tool (spin-LED) employed in this thesis to inject and detect spins in these QDs, and conclude with the optical Aharonov-Bohm effect (OAB) in type-II QDs.

Russ, Andreas Hans

392

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

NASA Technical Reports Server (NTRS)

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

Qiu, Y.; Uhl, D.

2002-01-01

393

Full counting statistics of quantum dot resonance fluorescence  

PubMed Central

The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding. PMID:24810097

Matthiesen, Clemens; Stanley, Megan J.; Hugues, Maxime; Clarke, Edmund; Atatüre, Mete

2014-01-01

394

Full counting statistics of quantum dot resonance fluorescence.  

PubMed

The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding. PMID:24810097

Matthiesen, Clemens; Stanley, Megan J; Hugues, Maxime; Clarke, Edmund; Atatüre, Mete

2014-01-01

395

Full counting statistics of quantum dot resonance fluorescence  

NASA Astrophysics Data System (ADS)

The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding.

Matthiesen, Clemens; Stanley, Megan J.; Hugues, Maxime; Clarke, Edmund; Atatüre, Mete

2014-05-01

396

Entanglement creation in semiconductor quantum dot charge qubit  

E-print Network

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

Fabrizio Buscemi; Paolo Bordone; Andrea Bertoni

2010-06-03

397

Entanglement creation in semiconductor quantum dot charge qubit  

E-print Network

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

Buscemi, Fabrizio; Bertoni, Andrea

2010-01-01

398

Semiconductor Quantum Dots in Chemical Sensors and Biosensors  

PubMed Central

Quantum dots are nanometre-scale semiconductor crystals with unique optical properties that are advantageous for the development of novel chemical sensors and biosensors. The surface chemistry of luminescent quantum dots has encouraged the development of multiple probes based on linked recognition molecules such as peptides, nucleic acids or small-molecule ligands. This review overviews the design of sensitive and selective nanoprobes, ranging from the type of target molecules to the optical transduction scheme. Representative examples of quantum dot-based optical sensors from this fast-moving field have been selected and are discussed towards the most promising directions for future research. PMID:22423206

Frasco, Manuela F.; Chaniotakis, Nikos

2009-01-01

399

Hyper-parallel photonic quantum computation with coupled quantum dots  

NASA Astrophysics Data System (ADS)

It is well known that a parallel quantum computer is more powerful than a classical one. So far, there are some important works about the construction of universal quantum logic gates, the key elements in quantum computation. However, they are focused on operating on one degree of freedom (DOF) of quantum systems. Here, we investigate the possibility of achieving scalable hyper-parallel quantum computation based on two DOFs of photon systems. We construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on both the spatial-mode and the polarization DOFs of a two-photon system simultaneously, by exploiting the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics (QED). This hyper-CNOT gate is implemented by manipulating the four qubits in the two DOFs of a two-photon system without auxiliary spatial modes or polarization modes. It reduces the operation time and the resources consumed in quantum information processing, and it is more robust against the photonic dissipation noise, compared with the integration of several cascaded CNOT gates in one DOF.

Ren, Bao-Cang; Deng, Fu-Guo

2014-04-01

400

Hyper-parallel photonic quantum computation with coupled quantum dots  

PubMed Central

It is well known that a parallel quantum computer is more powerful than a classical one. So far, there are some important works about the construction of universal quantum logic gates, the key elements in quantum computation. However, they are focused on operating on one degree of freedom (DOF) of quantum systems. Here, we investigate the possibility of achieving scalable hyper-parallel quantum computation based on two DOFs of photon systems. We construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on both the spatial-mode and the polarization DOFs of a two-photon system simultaneously, by exploiting the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics (QED). This hyper-CNOT gate is implemented by manipulating the four qubits in the two DOFs of a two-photon system without auxiliary spatial modes or polarization modes. It reduces the operation time and the resources consumed in quantum information processing, and it is more robust against the photonic dissipation noise, compared with the integration of several cascaded CNOT gates in one DOF. PMID:24721781

Ren, Bao-Cang; Deng, Fu-Guo

2014-01-01

401

Coherent population transfer in coupled semiconductor quantum dots  

E-print Network

We propose a solid-state implementation of stimulated Raman adiabatic passage in two coupled semiconductor quantum dots. Proper combination of two pulsed laser fields allows the coherent carrier transfer between the two nanostructures without suffering significant losses due to environment coupling. By use of a general solution scheme for the carrier states in the double-dot structure, we identify the pertinent dot and laser parameters.

Ulrich Hohenester; Giovanna Panzarini; Filippo Troiani; Elisa Molinari; Chiara Macchiavello

2000-08-03

402

Swapping Kondo resonances in coupled double quantum dots  

Microsoft Academic Search

Strong electron and spin correlations are studied in parallel-coupled double quantum dots with interdot spin superexchange J . In the Kondo regime with degenerate dot energy levels, coherent transport occurs at zero temperature, where two entangled (bonding and antibonding) resonances are formed near the Fermi energy. When increasing J or the dot-lead parallel-coupling asymmetry ratio Gamma2\\/Gamma1 , a swap between

Guang-Ming Zhang; Rong Lü; Zhi-Rong Liu; Lu Yu

2005-01-01

403

New Theoretical Approach to Quantum Size Effects of Interactive Electron-hole in Spherical Semiconductor Quantum Dots  

E-print Network

Semiconductor Quantum Dots B. Billaud and M. Picco Laboratoire de Physique Th´eorique et Hautes Energies (LPTHE semiconductor quantum dots is put to question. A sharper theoretical approach is suggested based on a new pseudo on their dimensionality, these structures are called quantum dots (0D), quantum wires (1D) or quantum wells (2D

Paris-Sud XI, Université de

404

Nonequilibrium transport through a Josephson quantum dot  

NASA Astrophysics Data System (ADS)

We study the electronic current through a quantum dot coupled to two superconducting leads which is driven by either a voltage V or temperature ?T bias. Finite biases beyond the linear response regime are considered. The local two-particle interaction U on the dot is treated using an approximation scheme within the functional renormalization group approach set up in Keldysh-Nambu space with U being the small parameter. For V >0, we compare our renormalization group enhanced results for the dc component of the current to earlier weak coupling approaches such as the Hartree-Fock approximation and second-order perturbation theory in U. We show that in parameter regimes in which finite-bias-driven multiple Andreev reflections prevail, small-|U| approaches become unreliable for interactions of appreciable strength. In the complementary regime, the convergence of the current with respect to numerical parameters becomes an issue, but can eventually be achieved, and interaction effects turn out to be smaller than expected based on earlier results. For ?T >0, we find a surprising increase of the current as a function of the superconducting phase difference in the regime which at T =0 becomes the ? (doublet) phase.

Rentrop, J. F.; Jakobs, S. G.; Meden, V.

2014-06-01

405

Ferritin-Templated Quantum-Dots for Quantum Logic Gates  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

406

Spectroscopy and energy level statistics in a disordered quantum dot  

Microsoft Academic Search

The spectrum of heavily doped quantum dots is found to be discrete only in close vicinity to the Fermi energy. Levels further away are broadened beyond the average level spacing and merge to form a quasi-continuous spectrum. This breakdown of a single particle picture is consistent with electron-electron interaction in the dot. For the discrete part of the spectrum, level

U. Sivan; F. P. Milliken; K. Milkove; S. Rishton; Y. Lee; J. M. Hong; V. Boegli; D. Kern; M. de Franza

1993-01-01

407

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

408

Fractal behavior in magnetoconductance in coupled quantum dot systems  

Microsoft Academic Search

Fractal behavior in magnetoconductance fluctuations in coupled quantum dots has been studied by means of exact and statistical self-similarity. The fractal dimensions from the different features are not coincident exactly but show the similar gate voltage dependences, where the values increase with increasing negative gate voltage. Moreover, results of statistical fractal dimensions obtained from two types of dot-array samples show

Nobuyuki Aoki; Li-Hung Lin; Takahiro Morimoto; Takahiko Sasaki; Jun-Feng Song; Koji Ishibashi; Jonathan P. Bird; Agung Budiyono; Katsuhiro Nakamura; Takahisa Harayama; Yuichi Ochiai

2004-01-01

409

Spectroscopy of electronic states in InSb quantum dots  

Microsoft Academic Search

Arrays of quantum dots on InSb have been realized, and intraband transitions between their discrete (zero-dimensional) electronic states have been observed with far-infrared magnetospectroscopy. In the devices, the number of electrons can be adjusted by a gate voltage, and less than five electrons per dot are detectable.

Ch. Sikorski; U. Merkt

1989-01-01

410

Quantum Circuit based on Electron Spins in Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

In this thesis, I present a microscopic theory of quantum circuits based on interacting electron spins in quantum dot molecules. We use the Linear Combination of Harmonic Orbitals-Configuration Interaction (LCHO-CI) formalism for microscopic calculations. We then derive effective Hubbard, t-J, and Heisenberg models. These models are used to predict the electronic, spin and transport properties of a triple quantum dot molecule (TQDM) as a function of topology, gate configuration, bias and magnetic field. With these theoretical tools and fully characterized TQDMs, we propose the following applications: 1. Voltage tunable qubit encoded in the chiral states of a half-filled TQDM. We show how to perform single qubit operations by pulsing voltages. We propose the "chirality-to-charge" conversion as the measurement scheme and demonstrate the robustness of the chirality-encoded qubit due to charge fluctuations. We derive an effective qubit-qubit Hamiltonian and demonstrate the two-qubit gate. This provides all the necessary operations for a quantum computer built with chirality-encoded qubits. 2. Berry's phase. We explore the prospect of geometric quantum computing with chirality-encoded qubit. We construct a Herzberg circuit in the voltage space and show the accumulation of Berry's phase. 3. Macroscopic quantum states on a semiconductor chip. We consider a linear chain of TQDMs, each with 4 electrons, obtained by nanostructuring a metallic gate in a field effect transistor. We theoretically show that the low energy spectrum of the chain maps onto that of a spin-1 chain. Hence, we show that macroscopic quantum states, protected by a Haldane gap from the continuum, emerge. In order to minimize decoherence of electron spin qubits, we consider using electron spins in the p orbitals of the valence band (valence holes) as qubits. We develop a theory of valence hole qubit within the 4-band k.p model. We show that static magnetic fields can be used to perform single qubit operations. We also show that the qubit-qubit interactions are sensitive to the geometry of a quantum dot network. For vertical qubit arrays, we predict that there exists an optimal qubit separation suitable for the voltage control of qubit-qubit interactions.

Hsieh, Chang-Yu

411

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

2013-09-01

412

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

2012-03-28

413

Correlation energy of anisotropic quantum dots  

SciTech Connect

We study the D-dimensional high-density correlation energy E{sub c} of the singlet ground state of two electrons confined by a harmonic potential with Coulombic repulsion. We allow the harmonic potential to be anisotropic and examine the behavior of E{sub c} as a function of the anisotropy {alpha}{sup -1}. In particular, we are interested in the limit where the anisotropy goes to infinity ({alpha}{yields}0) and the electrons are restricted to a lower-dimensional space. We show that tuning the value of {alpha} from 0 to 1 allows a smooth dimensional interpolation and we demonstrate that the usual model, in which a quantum dot is treated as a two-dimensional system, is inappropriate. Finally, we provide a simple function which reproduces the behavior of E{sub c} over the entire range of {alpha}.

Zhao Yan; Loos, Pierre-Francois; Gill, Peter M. W. [Research School of Chemistry, Australian National University, Canberra, ACT 0200 (Australia)

2011-09-15

414

Highly Fluorescent Noble Metal Quantum Dots  

PubMed Central

Highly fluorescent, water-soluble, few-atom noble metal quantum dots have been created that behave as multi-electron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near IR. 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 that 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. PMID:17105412

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

2009-01-01

415

Electronic confinement in modulation doped quantum dots  

SciTech Connect

Modulation doping, an effective way to dope quantum dots (QDs), modifies the confinement energy levels in the QDs. We present a self-consistent full multi-grid solver to analyze the effect of modulation doping on the confinement energy levels in large-area structures containing Si QDs in SiO{sub 2} and Si{sub 3}N{sub 4} dielectrics. The confinement energy was found to be significantly lower when QDs were in close proximity to dopant ions in the dielectric. This effect was found to be smaller in Si{sub 3}N{sub 4}, while smaller QDs in SiO{sub 2} were highly susceptible to energy reduction. The energy reduction was found to follow a power law relationship with the QD size.

Puthen Veettil, B., E-mail: b.puthen-veettil@unsw.edu.au; König, D.; Patterson, R.; Smyth, S.; Conibeer, G. [Australian Centre for Advanced Photovoltaics, UNSW, Sydney 2052 (Australia)

2014-04-14

416

Subdiffusive exciton transport in quantum dot solids.  

PubMed

Colloidal quantum dots (QDs) are promising materials for use in solar cells, light-emitting diodes, lasers, and photodetectors, but the mechanism and length of exciton transport in QD materials is not well understood. We use time-resolved optical microscopy to spatially visualize exciton transport in CdSe/ZnCdS core/shell QD assemblies. We find that the exciton diffusion length, which exceeds 30 nm in some cases, can be tuned by adjusting the inorganic shell thickness and organic ligand length, offering a powerful strategy for controlling exciton movement. Moreover, we show experimentally and through kinetic Monte Carlo simulations that exciton diffusion in QD solids does not occur by a random-walk process; instead, energetic disorder within the inhomogeneously broadened ensemble causes the exciton diffusivity to decrease over time. These findings reveal new insights into exciton dynamics in disordered systems and demonstrate the flexibility of QD materials for photonic and optoelectronic applications. PMID:24807586

Akselrod, Gleb M; Prins, Ferry; Poulikakos, Lisa V; Lee, Elizabeth M Y; Weidman, Mark C; Mork, A Jolene; Willard, Adam P; Bulovi?, Vladimir; Tisdale, William A

2014-06-11

417

Coherent control and decoherence of single semiconductor quantum dots in a microcavity  

Microsoft Academic Search

Semiconductor quantum dots tightly confine excited electron-hole pairs, called excitons, resulting in discrete energy levels similar to those of single atoms. Transition energies in the visible or near-infrared make quantum dots suitable for many applications in quantum optics and quantum information science, but to take advantage of all the properties of quantum dot emission, it is necessary to excite them

Edward B. Flagg II

2008-01-01

418

Elastic analysis of an inhomogeneous quantum dot in multilayered semiconductors using a boundary element method  

E-print Network

Elastic analysis of an inhomogeneous quantum dot in multilayered semiconductors using a boundary examine the elastostatic field due to a buried quantum dot QD in multilayered semiconductors using quasizero- dimensional dots or quantum dots QDs and quasione- dimensional wires on the nanoscale

Pan, Ernie

419

Polarons in semiconductor quantum dots and their role in the quantum kinetics of carrier relaxation  

Microsoft Academic Search

While time-dependent perturbation theory shows inefficient carrier-phonon scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic description of carrier-phonon interaction predicts fast carrier capture and relaxation. The considered processes do not fulfill energy conservation in terms of free-carrier energies because polar coupling of localized quantum-dot states strongly modifies this picture.

J. Seebeck; T. R. Nielsen; P. Gartner; F. Jahnke

2005-01-01

420

Effect of Coulomb correlation on electron transport through a concentric quantum ring-quantum dot structure  

Microsoft Academic Search

We study transfer of a single-electron through a quantum ring capacitively coupled to the charged quantum dot placed in its center. For this purpose we solve the time-dependent Schrödinger equation for the pair of particles: the electron traveling through the ring and the other carrier confined within the quantum dot. The correlation effects due to the interaction between the charge

T. Chwiej; K. Kutorasinski

2010-01-01

421

Quantum Monte Carlo study of quantum dots in magnetic fields  

NASA Astrophysics Data System (ADS)

We have studied the ground state energies and quantum numbers of confined two-dimensional (2D) electrons in weak and intermediate magnetic field strengths using quantum Monte Carlo methods. These 2D quantum dots are of theoretical interest, because it is possible to go from a weakly to a strongly correlated system by tuning the relative strength of the external potential to the electron-electron interaction. The accuracy of current spin density functional theory, and of the variational and diffusion Monte Carlo methods using single and multi configuration wave functions, is studied by comparison with results obtained by exact diagonalization. Using optimized trial wave functions, we calculate pair correlation functions as a function of the magnetic field and confinement strength. (Supported by the DOE and NSF)

Geist, Wolfgang; Zeng, Lang; Chou, Mei-Yin

2004-03-01

422

Continuous flow purification of nanocrystal quantum dots  

NASA Astrophysics Data System (ADS)

Colloidal quantum dot (QD) purification is typically conducted via repeating precipitation-redispersion involving massive amounts of organic solvents and has been the main obstacle in mass production of QDs with dependable surface properties. Our results show that the electric field apparently affects the streamlining of QDs and that we could continuously collect stably dispersed QDs by the electrophoretic purification process. The purification yield increases as the electric potential difference increases or the flow rate decreases, but reaches an asymptotic value. The yield can be further improved by raising the absolute magnitude of the mobility of QDs with the addition of solvents with high dielectric constants. The continuous purification process sheds light on industrial production of colloidal nanomaterials.Colloidal quantum dot (QD) purification is typically conducted via repeating precipitation-redispersion involving massive amounts of organic solvents and has been the main obstacle in mass production of QDs with dependable surface properties. Our results show that the electric field apparently affects the streamlining of QDs and that we could continuously collect stably dispersed QDs by the electrophoretic purification process. The purification yield increases as the electric potential difference increases or the flow rate decreases, but reaches an asymptotic value. The yield can be further improved by raising the absolute magnitude of the mobility of QDs with the addition of solvents with high dielectric constants. The continuous purification process sheds light on industrial production of colloidal nanomaterials. Electronic supplementary information (ESI) available: Additional figures on the microfluidic chip fabrication, QD size analysis, and the effect of the solution environment (dilution) on removal of ligands. See DOI: 10.1039/c4nr04351k

Kim, Duckjong; Park, Hye Kyung; Choi, Hyekyoung; Noh, Jaehong; Kim, Kyungnam; Jeong, Sohee

2014-11-01

423

Annealing-induced change in quantum dot chain formation mechanism  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

424

Coherent radiation by quantum dots and magnetic nanoclusters  

SciTech Connect

The assemblies of either quantum dots or magnetic nanoclusters are studied. It is shown that such assemblies can produce coherent radiation. A method is developed for solving the systems of nonlinear equations describing the dynamics of such assemblies. The method is shown to be general and applicable to systems of different physical nature. Despite mathematical similarities of dynamical equations, the physics of the processes for quantum dots and magnetic nanoclusters is rather different. In a quantum dot assembly, coherence develops due to the Dicke effect of dot interactions through the common radiation field. For a system of magnetic clusters, coherence in the spin motion appears due to the Purcell effect caused by the feedback action of a resonator. Self-organized coherent spin radiation cannot arise without a resonator. This principal difference is connected with the different physical nature of dipole forces between the objects. Effective dipole interactions between the radiating quantum dots, appearing due to photon exchange, collectivize the dot radiation. While the dipolar spin interactions exist from the beginning, yet before radiation, and on the contrary, they dephase spin motion, thus destroying the coherence of moving spins. In addition, quantum dot radiation exhibits turbulent photon filamentation that is absent for radiating spins.

Yukalov, V. I. [Bogolubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Yukalova, E. P. [Laboratory of Information Technologies, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation)

2014-03-31

425

Ultrafast nonlinear silicon waveguides and quantum dot semiconductor optical amplifiers.  

E-print Network

??In this book, nonlinear silicon-organic hybrid waveguides and quantum dot semiconductor optical amplifiers are investigated. Advantageous applications are identified, and corresponding proof-of-principle experiments are performed.… (more)

Vallaitis, Thomas

2011-01-01

426

Heterovalent cation substitutional doping for quantum dot homojunction solar cells.  

PubMed

Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%. PMID:24346430

Stavrinadis, Alexandros; Rath, Arup K; de Arquer, F Pelayo García; Diedenhofen, Silke L; Magén, César; Martinez, Luis; So, David; Konstantatos, Gerasimos

2013-01-01

427

Electronic structure of double Ge quantum dots in Si  

NASA Astrophysics Data System (ADS)

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

Yakimov, A. I.

2012-09-01

428

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

429

Study of field driven electroluminescence in colloidal quantum dot solids  

E-print Network

Semiconductor nanocrystals, or quantum dots(QDs), promise to drive advances in electronic light generation. It was recently shown that long range transport of charge, which is typically required for electric excitation and ...

Bozyigit, Deniz

430

Coal as an abundant source of graphene quantum dots  

NASA Astrophysics Data System (ADS)

Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

Ye, Ruquan; Xiang, Changsheng; Lin, Jian; Peng, Zhiwei; Huang, Kewei; Yan, Zheng; Cook, Nathan P.; Samuel, Errol L. G.; Hwang, Chih-Chau; Ruan, Gedeng; Ceriotti, Gabriel; Raji, Abdul-Rahman O.; Martí, Angel A.; Tour, James M.

2013-12-01

431

Entanglement switching via the Kondo effect in triple quantum dots  

NASA Astrophysics Data System (ADS)

We consider a triple quantum dot system in a triangular geometry with one of the dots connected to metallic leads. Using Wilson's numerical renormalization group method, we investigate quantum entanglement and its relation to the thermodynamic and transport properties in the regime where each of the dots is singly occupied on average, but with non-negligible charge fluctuations. It is shown that even in the regime of significant charge fluctuations the formation of the Kondo singlets induces switching between separable and perfectly entangled states. The quantum phase transition between unentangled and entangled states is analyzed quantitatively and the corresponding phase diagram is explained by exactly solvable spin model. In the framework of an effective model we also explain smearing of the entanglement transition for cases when the symmetry of the triple quantum dot system is relaxed.

Tooski, S. B.; Bu?ka, Bogdan R.; Žitko, Rok; Ramšak, Anton

2014-06-01

432

Heterovalent cation substitutional doping for quantum dot homojunction solar cells  

PubMed Central

Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%. PMID:24346430

Stavrinadis, Alexandros; Rath, Arup K.; de Arquer, F. Pelayo García; Diedenhofen, Silke L.; Magén, César; Martinez, Luis; So, David; Konstantatos, Gerasimos

2013-01-01

433

CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms  

PubMed Central

Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

2011-01-01

434

Computational study of confined states in quantum dots by an efficient finite difference method.  

E-print Network

??Semiconductor quantum dot systems have gained more attention in quantum computation and optoelectronic applications due to the ease of bandstructure tailoring and three-dimensional quantum confinement.… (more)

Butt, Salman

2010-01-01

435

Optical control of single excitons in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The fundamental building block of quantum information processing technologies is the quantum-bit a ‘qubit.’ These technologies require the ability to prepare, control, and read out a qubit state. Spins confined in self-assembled quantum dots are promising candidates for a quantum bit, because semiconductors are compatible with mature modern opto- and micro-electronics. These quantum dot systems offer two more advantages: they are excellent interfaces between the spin state—an anchored qubit and a photon—a ‘flying qubit’ and they provide means to coherently control the spin qubit by ultrashort optical pulses. In this review, we thoroughly discuss the qubit provided by an optically-excited electron in a quantum dot-the exciton qubit. We demonstrate its spin state initialization, coherent control and read-out using ultrashort optical pulses.

Kodriano, Y.; Schmidgall, E. R.; Benny, Y.; Gershoni, D.

2014-05-01

436

Optimal tunneling enhances the quantum photovoltaic effect in double quantum dots  

NASA Astrophysics Data System (ADS)

We investigate the quantum photovoltaic effect in double quantum dots by applying the nonequilibrium quantum master equation. A drastic suppression of the photovoltaic current is observed near the open circuit voltage, which leads to a large filling factor. We find that there always exists an optimal inter-dot tunneling that significantly enhances the photovoltaic current. Maximal output power will also be obtained around the optimal inter-dot tunneling. Moreover, the open circuit voltage behaves approximately as the product of the eigen-level gap and the Carnot efficiency. These results suggest a great potential for double quantum dots as efficient photovoltaic devices.

Wang, Chen; Ren, Jie; Cao, Jianshu

2014-04-01

437

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

438

Ultrafast optical properties of lithographically defined quantum dot amplifiers  

SciTech Connect

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

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

2014-02-10

439

Theory of relaxation oscillations in semiconductor quantum dot lasers  

Microsoft Academic Search

A microscopic approach combining rate equations for photon and electron\\/hole occupations with kinetic equations for Coulomb scattering rates involving quantum dot and wetting layer states in InAs\\/GaAs quantum dot lasers is presented. The authors find strong damping of relaxation oscillations on a picosecond to nanosecond time scale depending on the type of the initial perturbation, similar to the damping observed

Ermin Malic; Kwang J. Ahn; Moritz J. P. Bormann; Philipp Hövel; Eckehard Schöll; Andreas Knorr; Matthias Kuntz; Dieter Bimberg

2006-01-01

440

Coulomb Damped Relaxation Oscillations in Semiconductor Quantum Dot Lasers  

Microsoft Academic Search

We present a theoretical simulation of the turn-on dynamics of InAs\\/GaAs quantum dot semiconductor lasers driven by electrical current pulses. Our approach goes beyond standard phenomenological rate equations. It contains microscopically calculated Coulomb scattering rates, which describe Auger transitions between quantum dots and the wetting layer. In agreement with the experimental results, we predict a strong damping of relaxation oscillations

Ermin Malic; Moritz J. P. Bormann; P. Hovel; M. Kuntz; D. Bimberg; Andreas Knorr; Eckehard Scholl

2007-01-01

441

Single electron charging effects in semiconductor quantum dots  

Microsoft Academic Search

We have studied charging effects in a lateral split-gate quantum dot defined by metal gates in the two dimensional electron gas (2 DEG) of a GaAs\\/AlGaAs heterostructure. The gate structure allows an independent control of the conductances of the two tunnel barriers separating the quantum dot from the two 2 DEG leads, and enables us to vary the number of

L. P. Kouwenhoven; N. C. van der Vaart; A. T. Johnson; W. Kool; C. J. P. M. Harmans; J. G. Williamson; A. A. M. Staring; C. T. Foxon

1991-01-01

442

Binding of semiconductor quantum dots to cellular integrins  

Microsoft Academic Search

There is currently a major international effort aimed at integrating semiconductor nanostructures with biological structures. This paper reports the functionalization of cadmium sulfide quantum dots with peptides that facilitate the selective binding of these quantum-dot-peptide complexes to integrins in the membranes of cancer cells of the MDA-MB-435 cell line. In addition, this paper focuses on the roles that biological environments

Dimitri Alexson; Yang Li; Dinakar Ramadurai; Peng Shi; Leena George; M. Uddin; P. Thomas; S. Rufo; M. Dutta; M. A. Stroscio

2004-01-01

443

Colloidal semiconductor quantum dots: Potential tools for new diagnostic methods  

NASA Astrophysics Data System (ADS)

We present and discuss the application of colloidal semiconductor quantum dots for diagnostic purposes, with special emphasis for cancer. We prepared and applied core-shell cadmium sulfide-cadmium hydroxide (CdS/Cd(OH) 2) semiconductor quantum dots in aqueous medium. Tissue and cells labeling was evaluated by laser scanning confocal microscopy as well as by conventional fluorescence microscopy. The procedure presented in this work, shown to be a promising tool for fast, low-cost and precise cancer diagnostic protocols.

Farias, P. M. A.; Santos, B. S.; Fontes, A.; Vieira, A. A. S.; Silva, D. C. N.; Castro-Neto, A. G.; Chaves, C. R.; Da Cunha, A. H. G. B.; Scordo, D.; Amaral, J. C. O. F.; Moura-Neto, V.

2008-11-01

444

Mesoscopic Theory and Simulation of Quantum Dot Lasers  

Microsoft Academic Search

We present results of extensive numerical simulations on the ultrafast spatio-temporal dynamics of quantum dot lasers and amplifiers. The simulations are based on quantum-dot Maxwell-Bloch equations (QD-MBE) (1). Our mesoscopic QD-MBE theory bridges theoretical descriptions of microscopic material properties of QDs with macroscopic phenomenological laser theories. The QD-MBEs consist of coupled spatio- temporally resolved wave equations and QD-Bloch equations for

Ortwin Hess

445

Theory of Non-Adiabatic Optical Effects in Quantum Dots  

Microsoft Academic Search

Quantum dots continue to be an area of intense scientific activity, because they have a number of advantages as the `building blocks' for advanced semiconductor devices with three-dimensional band-structure engineering. Considerable effort is being devoted to the investigation of effects due to the exciton-phonon interaction on the optical properties of quantum dots. Our theory of photoluminescence and Raman scattering in

J. T. Devreese

2002-01-01

446

Terahertz detection with tunneling quantum dot intersublevel photodetector  

Microsoft Academic Search

The characteristics of a tunnel quantum dot intersublevel photodetector, designed for the absorption of terahertz radiation, are described. The absorption region consists of self-organized In0.6Al0.4As\\/GaAs quantum dots with tailored electronic properties. Devices exhibit spectral response from 20 to 75 mum (~4 THz) with peak at ~50 mum. The peak responsivity and specific detectivity of the device are 0.45 A\\/W and

X. H. Su; J. Yang; P. Bhattacharya; G. Ariyawansa; A. G. U. Perera

2006-01-01

447

Towards quantum dot arrays of entangled photon emitters  

E-print Network

We show that with a new family of pyramidal site-controlled InGaAsN quantum dots it is possible to obtain areas containing as much as 15% of polarization-entangled photon emitters - a major improvement if compared to the small fraction achievable by other quantum dot systems. Entanglement is attested by a two-photon polarization state density matrix and the parameters obtained from it. Emitters showing fidelities up to 0.721+-0.043 were found.

Gediminas Juska; Valeria Dimastrodonato; Lorenzo O. Mereni; Agnieszka Gocalinska; Emanuele Pelucchi

2014-02-07

448

Superconducting tunneling spectroscopy of a carbon nanotube quantum dot  

NASA Astrophysics Data System (ADS)

We report results on superconducting tunneling spectroscopy of a carbon nanotube quantum dot. Using a three-probe technique that includes a superconducting tunnel probe, we map out changes in conductance due to band structure, excited states, and end-to-end bias. The superconducting probe allows us to observe enhanced spectroscopic features, such as robust signals of both elastic and inelastic cotunneling. We also see evidence of inelastic scattering processes inside the quantum dot.

Dirks, Travis; Chen, Yung-Fu; Birge, Norman O.; Mason, Nadya

2009-11-01

449