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Sample records for quantum dots synthesis

  1. Quantum dots: synthesis, bioapplications, and toxicity

    PubMed Central

    2012-01-01

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

  2. Facile synthesis and photoluminescence mechanism of graphene quantum dots

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  3. Facile synthesis and photoluminescence mechanism of graphene quantum dots

    SciTech Connect

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

    2014-12-28

    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 sp{sup 2} domains.

  4. Synthesis, Characterization and Application Of PbS Quantum Dots

    SciTech Connect

    Sarma, Sweety; Datta, Pranayee; Barua, Kishore Kr.; Karmakar, Sanjib

    2009-06-29

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

  5. Controllable Synthesis of Highly Luminescent Boron Nitride Quantum Dots.

    PubMed

    Li, Hongling; Tay, Roland Yingjie; Tsang, Siu Hon; Zhen, Xu; Teo, Edwin Hang Tong

    2015-12-01

    Boron nitride quantum dots (BNQDs), as a new member of heavy metal-free quantum dots, have aroused great interest in fundamental research and practical application due to their unique physical/chemical properties. However, it is still a challenge to controllably synthesize high-quality BNQDs with high quantum yield (QY), uniform size and strong fluorescent. In this work, BNQDs have been successfully fabricated by the liquid exfoliation and the subsequent solvothermal process with respect to its facileness and easy large scale up. Importantly, BNQDs with high-quality can be controllably obtained by adjusting the synthetic parameters involved in the solvothermal process including filling factor, synthesis temperature, and duration time. Encouragingly, the as-prepared BNQDs possess strong blue luminescence with QY as high as 19.5%, which can be attributed to the synergetic effect of size, surface chemistry and edge defects. In addition, this strategy presented here provides a new reference for the controllable synthesis of other heavy metal-free QDs. Furthermore, the as-prepared BNQDs are non-toxic to cells and exhibit nanosecond-scaled lifetimes, suggesting they have great potential biological and optoelectronic applications. PMID:26574683

  6. Synthesis and characterization of quantum dotpolymer composites

    PubMed Central

    Weaver, Joe; Zakeri, Rashid; Aouadi, Samir

    2009-01-01

    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. QDpolymer 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 QDsilica solution resulted in gelation. The gelation time was found to be dependent on free ODA concentration. Similarly, the emission of QDpolymer 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 QDpolymer patterns were demonstrated on glass substrates which retained their emission in both polar and non-polar solvents. PMID:19936033

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

    SciTech Connect

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

    2014-04-24

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

  8. Bioconjugated silicon quantum dots from one-step green synthesis

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    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

  9. Hydrothermal Synthesis and Photoluminescence of Boron Nitride Quantum Dots

    NASA Astrophysics Data System (ADS)

    Li, Hongling; Tay, Roland Yingjie; Tsang, Siu Hon; Teo, Edwin Hang Tong

    Boron nitride quantum dots (BNQDs), as a new member of heavy metal-free quantum dots, have attracted great interest owing to its unique structure as well as fascinating physical/chemical properties. However, it is still a challenge to controllably synthesize high quality BNQDs with high quantum yield (QY), uniform size and strong luminescence. Here we present a facile and effective approach to controllablly fabricate BNQDs by snoication-solvothermal technique. Encouragingly, the as-prepared BNQDs possess strong blue luminescence with high QY of up to 19.5%, which can be attributed to the synergic effect of size, surface chemistry and edge defects. In addition, the size of the BNQDs could be controlled with a narrow size distribution of 1.32 nm and the smallest average size achieved is 2.62 nm with an average thickness of ~3 atomic layers. Furthermore, the as-prepared BNQDs are non-toxic to cells and show nanosecond-scaled lifetimes and little photobleaching effect. Therefore, it is believed that BNQDs are promising as one of the novel heavy metal-free QDs for multi-purpose applications in a range of fields. Moreover, this synthesis concept is expected to open a new window to controllably prepare other heavy metal-free QDs, as well as to understand their luminescence mechanism.

  10. Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tartakovskii, Alexander

    2012-07-01

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

  11. Facile Synthesis, Silanization and Biodistribution of Biocompatible Quantum Dots

    PubMed Central

    Ma, Nan; Marshall, Ann F.; Gambhir, Sanjiv S.

    2016-01-01

    Here we report a facile strategy to the synthesis of silica-coated quantum dots (QDs) for in vivo imaging. All the QD synthesis and silanization steps are conducted in water and methanol under mild conditions without involving any organometallic precursors and high temperature, oxygen-free environments. The as-prepared silica-coated QDs possess high quantum yields and are extremely stable in mouse serum. In addition, the silanization method developed here produces nanoparticles (NPs) with small sizes that are difficult to achieve via conventional silanization methods. The silica coating helps to prevent the exposure of QD surface to the biological milieu and therefore increases the biocompatibility of QDs for in vivo applications. Interestingly, the silica-coated QDs exhibit a different biodistribution pattern than commercially available Invitrogen QD605 (carboxylate) with a similar size and emission wavelength. The Invitrogen QD605 exhibited predominant liver (57.2% ID g-1) and spleen (46.1% ID g-1) uptakes 30 mins after intravenous injection, whereas the silica-coated QDs exhibited much lower liver (16.2% ID g-1) and spleen (3.67% ID g-1) uptakes but higher kidney uptake (8.82% ID g-1), blood retention (15.0% ID g-1) and partial renal clearance. Overall, this straightforward synthetic strategy paves the way for routine and customized synthesis of silica-coated QDs for biological use. PMID:20564726

  12. Synthesis and characterization of aqueous quantum dots for biomedical applications

    NASA Astrophysics Data System (ADS)

    Li, Hui

    Quantum Dots (QDs) are semiconductor nanocrystals (120 nm) exhibiting distinctive photoluminescence (PL) properties due to the quantum confinement effect. Having many advantages over organic dyes, such as broad excitation and resistance to photobleaching, QDs are widely used in bioapplications as one of most exciting nanobiotechnologies. To date, most commercial QDs are synthesized through the traditional organometallic method and contain toxic elements, such as cadmium, lead, mercury, arsenic, etc. The overall goal of this thesis study is to develop an aqueous synthesis method to produce nontoxic quantum dots with strong emission and good stability, suitable for biomedical imaging applications. Firstly, an aqueous, simple, environmentally friendly synthesis method was developed. With cadmium sulfide (CdS) QDs as an example system, various processing parameters and capping molecules were examined to improve the synthesis and optimize the PL properties. The obtained water soluble QDs exhibited ultra small size (5 nm), strong PL and good stability. Thereafter, using the aqueous method, the zinc sulfide (ZnS) QDs were synthesized with different capping molecules, i.e., 3-mercaptopropionic acid (MPA) and 3-(mercaptopropyl)trimethoxysilane (MPS). Especially, via a newly developed capping molecule replacement method, the present ZnS QDs exhibited bright blue emission with a quantum yield of 75% and more than 60 days lifetime in the ambient conditions. Two cytotoxicity tests with human endothelial cells verified the nontoxicity of the ZnS QDs by cell counting with Trypan blue staining and fluorescence assay with Alamar Blue. Taking advantage of the versatile surface chemistry, several strategies were explored to conjugate the water soluble QDs with biomolecules, i.e., antibody and streptavidin. Accordingly, the imaging of Salmonella t. cells and biotinylated microbeads has been successfully demonstrated. In addition, polyethylenimine (PEI)-QDs complex was formed and delivered into PC12 neuronal cells for intracellular imaging with uniform distribution. The water soluble QDs were also embedded in electrospun polymer fibers as fluorescent nanocomposite. In summary, the ease of aqueous processing and the excellent PL properties of the nontoxic water soluble ZnS QDs provide great potential for various in vivo applications.

  13. Quantum Dot Solar Cells

    NASA Astrophysics Data System (ADS)

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

    2002-10-01

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

  14. Quantum Dot Solar Cells

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  15. Semiconductor Nanocrystal Quantum Dot Synthesis Approaches Towards Large-Scale Industrial Production for Energy Applications

    NASA Astrophysics Data System (ADS)

    Hu, Michael Z.; Zhu, Ting

    2015-12-01

    This paper reviews the experimental synthesis and engineering developments that focused on various green approaches and large-scale process production routes for quantum dots. Fundamental process engineering principles were illustrated. In relation to the small-scale hot injection method, our discussions focus on the non-injection route that could be scaled up with engineering stir-tank reactors. In addition, applications that demand to utilize quantum dots as "commodity" chemicals are discussed, including solar cells and solid-state lightings.

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

    ERIC Educational Resources Information Center

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

    2005-01-01

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

  17. Synthesis, biological targeting and photophysics of quantum dots

    NASA Astrophysics Data System (ADS)

    Clarke, Samuel Jon

    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.

  18. Quasi-periodic quantum dot arrays produced by electrochemical synthesis

    SciTech Connect

    Bandyopadhyay, S.; Miller, A.E.; Yue, D.F.; Banerjee, G.; Ricker, R.E.; Jones, S.; Eastman, J.A.; Baugher, E.; Chandrasekhar, M.

    1994-06-01

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

  19. Wet chemical synthesis of quantum dots for medical applications

    NASA Astrophysics Data System (ADS)

    Cepeda-Pérez, E. I.; López-Luke, T.; Pérez-Mayen, L.; Hidalgo, Alberto; de la Rosa, E.; Torres-Castro, Alejandro; Ceja-Fdez, Andrea; Vivero-Escoto, Juan; Gonzalez-Yebra, Ana L.

    2015-07-01

    In recent years the use of nanoparticles in medical applications has boomed. This is because the various applications that provide these materials like drug delivery, cancer cell diagnostics and therapeutics [1-5]. Biomedical applications of Quantum Dots (QDs) are focused on molecular imaging and biological sensing due to its optical properties. The size of QDs can be continuously tuned from 2 to 10 nm in diameter, which, after polymer encapsulation, generally increases to 5 - 20 nm diminishing the toxicity. The QDs prepared in our lab have a diameter between 2 to 7 nm. Particles smaller than 5 nm can interact with the cells [2]. Some of the characteristics that distinguish QDs from the commonly used fluorophores are wider range of emission, narrow and more sharply defined emission peak, brighter emission and a higher signal to noise ratio compared with organic dyes [6]. In this paper we will show our progress in the study of the interaction of quantum dots in live cells for image and Raman spectroscopy applications. We will also show the results of the interaction of quantum dots with genomic DNA for diagnostic purposes.

  20. Synthesis of Bi2S3 quantum dots for sensitized solar cells by reverse SILAR

    NASA Astrophysics Data System (ADS)

    Singh, Navjot; Sharma, J.; Tripathi, S. K.

    2016-05-01

    Quantum Dot Sensitized Solar cells (QDSSC) have great potential to replace silicon-based solar cells. Quantum dots of various materials and sizes could be used to convert most of the visible light into the electrical current. This paper put emphasis on the synthesis of Bismuth Sulphide quantum dots and selectivity of the anionic precursor by Successive Ionic Layer Adsorption Reaction (SILAR). Bismuth Sulfide (Bi2S3) (group V - Vi semiconductor) is strong contestant for cadmium free solar cells due to its optimum band gap for light harvesting. Optical, structural and electrical measurements are reported and discussed. Problem regarding the choice of precursor for anion extraction is discussed. Band gap of the synthesized quantum dots is 1.2 eV which does not match with the required energy band gap of bismuth sulfide that is 1.7eV.

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

    PubMed

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

    2011-08-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

    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 1H 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.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 1H 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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c1nr10458f

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

    NASA Astrophysics Data System (ADS)

    López, Israel; Gómez, Idalia

    2014-11-01

    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.

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

    SciTech Connect

    Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia E-mail: grchen@ecust.edu.cn; Chen, Guorong E-mail: grchen@ecust.edu.cn; Zhang, Bo

    2014-05-21

    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%.

  5. Silicon-based quantum dots: synthesis, surface and composition tuning with atmospheric pressure plasmas

    NASA Astrophysics Data System (ADS)

    Askari, Sadegh; Macias-Montero, Manuel; Velusamy, Tamilselvan; Maguire, Paul; Svrcek, Vladmir; Mariotti, Davide

    2015-08-01

    The synthesis of silicon and silicon-based quantum dots (diameter < 5 nm) is discussed. Specifically the synthesis of Si-based quantum dots (QDs) by atmospheric pressure plasmas is reviewed and the most recent developments are also reported. Atmospheric pressure plasmas are then compared with other synthesis methods that include low pressure plasmas, wet chemistry, electrochemical etching and laser-based methods. Finally, progress in the synthesis of alloyed silicon QDs is discussed where the nanoscale Si-Sn and Si-C systems are reported. The report also includes a theoretical analysis that highlights some fundamental differences offered by plasmas at atmospheric pressure and that may provide opportunities for novel materials with advantageous properties.

  6. Semiconductor Nanocrystal Quantum Dot Synthesis Approaches Towards Large-Scale Industrial Production for Energy Applications.

    PubMed

    Hu, Michael Z; Zhu, Ting

    2015-12-01

    This paper reviews the experimental synthesis and engineering developments that focused on various green approaches and large-scale process production routes for quantum dots. Fundamental process engineering principles were illustrated. In relation to the small-scale hot injection method, our discussions focus on the non-injection route that could be scaled up with engineering stir-tank reactors. In addition, applications that demand to utilize quantum dots as "commodity" chemicals are discussed, including solar cells and solid-state lightings. PMID:26637261

  7. Synthesis and application of quantum dots-based biosensor

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  8. Synthesis and characterization of quantum dots designed for biomedical use.

    PubMed

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

    2014-05-15

    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

  9. Synthesis of indium sulphide quantum dots in perfluoronated ionomer membrane

    SciTech Connect

    Sumi, R.; Warrier, Anita R.; Vijayan, C.

    2014-01-28

    In this paper, we demonstrate a simple and efficient method for synthesis of β-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.

  10. Synthesis of colloidal InAs/ZnSe quantum dots and their quantum dot sensitized solar cell (QDSSC) application

    NASA Astrophysics Data System (ADS)

    Lee, S. H.; Jung, C.; Jun, Y.; Kim, S.-W.

    2015-11-01

    We report the synthesis of colloidal InAs/ZnSe core/shell quantum dots (QDs) by the hot injection method. InAs nanocrystals have a narrow band gap of 0.38 eV, a high absorption coefficient, and multiple exciton generation; hence, they are promising candidates for application in solar cells. However, poor coverage of the titania layer causes a low solar efficiency of ∼1.74%. We synthesized type-I InAs/ZnSe core/shell QDs as an effective solution; they are expected to have enhanced solar cell efficiency because of the different wettability of the ZnSe shell and their superior stability as compared to that of the unstable InAs core. We characterized the QDs by powder X-ray diffraction, transmission electron microscopy, and absorption and emission spectroscopy. The particle size increased from 2.6 nm to 5 nm, whereas the absorption and emission spectra exhibited a slight red shift, which is typical of type-I structured core/shell QDs. We then fabricated QD-based solar cells and investigated the cell properties, obtaining an open-circuit voltage (VOC) of 0.51 V, a short-circuit current density (JSC) of 12.4 mA/cm2, and a fill factor (FF) of 44%; the efficiency of 2.7% shows an improvement of more than 50% as compared to the values in previous reports.

  11. Size control by rate control in colloidal PbSe quantum dot synthesis.

    PubMed

    Čapek, Richard Karel; Yanover, Dianna; Lifshitz, Efrat

    2015-03-12

    A recently demonstrated approach to control the size of colloidal nanoparticles, "size control by rate control", which was validated on the examples of colloidal CdSe- and CdS-quantum dot (CQD) synthesis, appears to be a general strategy for designing technically applicable CQD-syntheses. The "size control by rate control" concept allows full-yield syntheses of ensembles of CQDs with different sizes by tuning the solute formation rate. In this work, we extended this strategy to dialkylphosphine enhanced hot-injection synthesis of PbSe-CQDs. Furthermore, we provide new insight into the reaction mechanism of dialkylphosphine enhancement in TOPSe based CQD-syntheses. PMID:25721010

  12. Large-Scale Programmable Synthesis of PbS Quantum Dots.

    PubMed

    Preske, Amanda; Liu, Jin; Prezhdo, Oleg V; Krauss, Todd D

    2016-03-01

    The most common method of synthesizing colloidal quantum dots (QDs) relies on an increasing particle size through increasing reaction time. We demonstrate a synthesis where the QD size is programmable through the use of a secondary phosphine sulfide precursor. The reaction runs to thermodynamic completion, resulting in a desired PbS diameter for a given set of specific reaction conditions, with no need for reaction quenching or post-synthesis size-separation. Moreover, this method is shown to produce high-quality PbS QDs on the grams scale. PMID:26663537

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

    PubMed

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

    2008-05-20

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

  14. Colloidal Double Quantum Dots.

    PubMed

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

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon emission to classical emission. Dual emission also provides these NCs with more advanced functionalities than the isolated components. The ability to better tailor the emission spectrum can be advantageous for color designed LEDs in lighting and display applications. The different response of the two emission colors to external stimuli enables ratiometric sensing. Control over hot carrier dynamics within such structures allows for photoluminescence upconversion. This Account first provides a description of the main hurdles toward the synthesis of colloidal double QDs and an overview of the growing library of synthetic pathways toward constructing them. The main discoveries regarding their photophysical properties are then described in detail, followed by an overview of potential applications taking advantage of the double-dot structure. Finally, a perspective and outlook for their future development is provided. PMID:27108870

  15. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon emission to classical emission. Dual emission also provides these NCs with more advanced functionalities than the isolated components. The ability to better tailor the emission spectrum can be advantageous for color designed LEDs in lighting and display applications. The different response of the two emission colors to external stimuli enables ratiometric sensing. Control over hot carrier dynamics within such structures allows for photoluminescence upconversion. This Account first provides a description of the main hurdles toward the synthesis of colloidal double QDs and an overview of the growing library of synthetic pathways toward constructing them. The main discoveries regarding their photophysical properties are then described in detail, followed by an overview of potential applications taking advantage of the double-dot structure. Finally, a perspective and outlook for their future development is provided. PMID:27108870

  16. Synthesis of N, F and S co-doped graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Kundu, Sumana; Yadav, Ram Manohar; Narayanan, T. N.; Shelke, Manjusha V.; Vajtai, Robert; Ajayan, P. M.; Pillai, Vijayamohanan K.

    2015-07-01

    Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ~2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants.Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ~2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants. Electronic supplementary information (ESI) available: PLQY calculation, MWCNT synthetic details, TGA analysis and tabular format of GQD synthesis processes. See DOI: 10.1039/c5nr02427g

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

    PubMed

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

    2015-01-27

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

  18. Synthesis of cadmium selenide colloidal quantum dots in aquatic medium

    NASA Astrophysics Data System (ADS)

    Mazing, D. S.; Matyushkin, L. B.; Aleksandrova, O. A.; Mikhailov, I. I.; Moshnikov, V. A.; Tarasov, S. A.

    2014-12-01

    Cadmium selenide nanocrystals were prepared in water phase through facile wet chemistry technique with thioglycolic acid (TGA) acting as capping agent. Structures were characterized using X-ray diffraction (XRD), UV-vis absorption and photoluminescence spectroscopies. Depending on synthesis conditions nanoparticles exhibit photoluminescence with maximum in the region of 580 - 680 nm. Influence of technological parameters and component concentrations on nanocrystals average size and properties was studied.

  19. A general solid-state synthesis of chemically-doped fluorescent graphene quantum dots for bioimaging and optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Ma, Chong-Bo; Zhu, Zhen-Tong; Wang, Hang-Xing; Huang, Xiao; Zhang, Xiao; Qi, Xiaoying; Zhang, Hao-Li; Zhu, Yihan; Deng, Xia; Peng, Yong; Han, Yu; Zhang, Hua

    2015-05-01

    Graphene quantum dots (GQDs) have attracted increasing interest because of their excellent properties such as strong photoluminescence, excellent biocompatibility and low cost. Herein, we develop a general method for the synthesis of doped and undoped GQDs, which relies on direct carbonization of organic precursors in the solid state.Graphene quantum dots (GQDs) have attracted increasing interest because of their excellent properties such as strong photoluminescence, excellent biocompatibility and low cost. Herein, we develop a general method for the synthesis of doped and undoped GQDs, which relies on direct carbonization of organic precursors in the solid state. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01757b

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

    PubMed

    Mussa Farkhani, Samad; Valizadeh, Alireza

    2014-06-01

    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

  1. Synthesis of CdSe/CdS core/shell quantum dots for biological sensing applications

    NASA Astrophysics Data System (ADS)

    Xu, Yang; Mariam, Poojitha; Sethi, Varun; Jones, Mason; Meehan, Kathleen

    2006-02-01

    A simple, room temperature, one-pot method to produce biocompatible CdSe/CdS quantum dots (QDs) in aqueous solution is presented. CdCl II and NaSeSO 3 are the precursors for the CdSe core where gelatin is used as an inhibitor. A CdS shell is grown by injecting H IIS gas, generated by a reaction between sulfuric and sodium sulfide, into the solution. This fast, low cost synthesis approach is simple for scale-up production of QDs. Transmission electron microscopy shows that the bare CdSe quantum dots were 2-3 nm in diameter. The emission peak from the CdSe can be tuned over most of the visible wavelength (from 520nm to 600 nm) as the diameter of the QDs is allowed to increase before growth of the CdS shell. The core/shell structure was confirmed via UV-Vis absorption spectroscopy, PL studies, and structural characterization (XRD). The higher band gap CdS coatings significantly enhanced the photoluminescence (PL) of CdSe quantum dots by a factor of 2-3. However, the large lattice mismatch between the CdS coating and the CdSe core results in eventually quenched luminescence from CdSe with thicker CdS coatings. To increase the photochemical stability and biocompatibility of the CdSe/CdS QDs, a silica coating is grown directly on the QDs. Preliminary data indicates that the PL from CdSe/CdS QDs post-growth is affected as the applied electric field is altered. Efforts to functionalize the QDs with DNA and antibodies have begun. Studies have been initiated to demonstrate the feasibility of microinjecting the QDs into Xenopus embryo with minimal post-synthesis processing.

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

    PubMed

    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

    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

  3. Automated synthesis of photovoltaic-quality colloidal quantum dots using separate nucleation and growth stages.

    PubMed

    Pan, Jun; El-Ballouli, Ala'a O; Rollny, Lisa; Voznyy, Oleksandr; Burlakov, Victor M; Goriely, Alain; Sargent, Edward H; Bakr, Osman M

    2013-11-26

    As colloidal quantum dot (CQD) optoelectronic devices continue to improve, interest grows in the scaled-up and automated synthesis of high-quality materials. Unfortunately, all reports of record-performance CQD photovoltaics have been based on small-scale batch syntheses. Here we report a strategy for flow reactor synthesis of PbS CQDs and prove that it leads to solar cells having performance similar to that of comparable batch-synthesized nanoparticles. Specifically, we find that, only when using a dual-temperature-stage flow reactor synthesis reported herein, are the CQDs of sufficient quality to achieve high performance. We use a kinetic model to explain and optimize the nucleation and growth processes in the reactor. Compared to conventional single-stage flow-synthesized CQDs, we achieve superior quality nanocrystals via the optimized dual-stage reactor, with high photoluminescence quantum yield (50%) and narrow full width-half-maximum. The dual-stage flow reactor approach, with its versatility and rapid screening of multiple parameters, combined with its efficient materials utilization, offers an attractive path to automated synthesis of CQDs for photovoltaics and, more broadly, active optoelectronics. PMID:24131473

  4. Size control by rate control in colloidal PbSe quantum dot synthesis

    NASA Astrophysics Data System (ADS)

    Čapek, Richard Karel; Yanover, Dianna; Lifshitz, Efrat

    2015-03-01

    A recently demonstrated approach to control the size of colloidal nanoparticles, ``size control by rate control'', which was validated on the examples of colloidal CdSe- and CdS-quantum dot (CQD) synthesis, appears to be a general strategy for designing technically applicable CQD-syntheses. The ``size control by rate control'' concept allows full-yield syntheses of ensembles of CQDs with different sizes by tuning the solute formation rate. In this work, we extended this strategy to dialkylphosphine enhanced hot-injection synthesis of PbSe-CQDs. Furthermore, we provide new insight into the reaction mechanism of dialkylphosphine enhancement in TOPSe based CQD-syntheses.A recently demonstrated approach to control the size of colloidal nanoparticles, ``size control by rate control'', which was validated on the examples of colloidal CdSe- and CdS-quantum dot (CQD) synthesis, appears to be a general strategy for designing technically applicable CQD-syntheses. The ``size control by rate control'' concept allows full-yield syntheses of ensembles of CQDs with different sizes by tuning the solute formation rate. In this work, we extended this strategy to dialkylphosphine enhanced hot-injection synthesis of PbSe-CQDs. Furthermore, we provide new insight into the reaction mechanism of dialkylphosphine enhancement in TOPSe based CQD-syntheses. Electronic supplementary information (ESI) available: Additional data about the reaction and growth kinetics, NMR-data and exemplary TEM images of PbSe-CQDs prepared by the procedure described in this publication. See DOI: 10.1039/c5nr00028a

  5. A general solid-state synthesis of chemically-doped fluorescent graphene quantum dots for bioimaging and optoelectronic applications.

    PubMed

    Ma, Chong-Bo; Zhu, Zhen-Tong; Wang, Hang-Xing; Huang, Xiao; Zhang, Xiao; Qi, Xiaoying; Zhang, Hao-Li; Zhu, Yihan; Deng, Xia; Peng, Yong; Han, Yu; Zhang, Hua

    2015-06-14

    Graphene quantum dots (GQDs) have attracted increasing interest because of their excellent properties such as strong photoluminescence, excellent biocompatibility and low cost. Herein, we develop a general method for the synthesis of doped and undoped GQDs, which relies on direct carbonization of organic precursors in the solid state. PMID:25985855

  6. Synthesis of Luminescent Graphene Quantum Dots with High Quantum Yield and Their Toxicity Study

    PubMed Central

    Jiang, Dan; Chen, Yunping; Li, Na; Li, Wen; Wang, Zhenguo; Zhu, Jingli; Zhang, Hong; Liu, Bin; Xu, Shan

    2015-01-01

    High fluorescence quantum yield graphene quantum dots (GQDs) have showed up as a new generation for bioimaging. In this work, luminescent GQDs were prepared by an ameliorative photo-Fenton reaction and a subsequent hydrothermal process using graphene oxide sheets as the precursor. The as-prepared GQDs were nanomaterials with size ranging from 2.3 to 6.4 nm and emitted intense green luminescence in water. The fluorescence quantum yield was as high as 24.6% (excited at 340 nm) and the fluorescence was strongest at pH 7. Moreover, the influences of low-concentration (12.5, 25 μg/mL) GQDs on the morphology, viability, membrane integrity, internal cellular reactive oxygen species level and mortality of HeLa cells were relatively weak, and the in vitro imaging demonstrated GQDs were mainly in the cytoplasm region. More strikingly, zebrafish embryos were co-cultured with GQDs for in vivo imaging, and the results of heart rate test showed the intake of small amounts of GQDs brought little harm to the cardiovascular of zebrafish. GQDs with high quantum yield and strong photoluminescence show good biocompatibility, thus they show good promising for cell imaging, biolabeling and other biomedical applications. PMID:26709828

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

    PubMed Central

    2011-01-01

    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

  8. Large Scale Synthesis and Light Emitting Fibers of Tailor-Made Graphene Quantum Dots.

    PubMed

    Park, Hun; Noh, Sung Hyun; Lee, Ji Hye; Lee, Won Jun; Jaung, Jae Yun; Lee, Seung Geol; Han, Tae Hee

    2015-01-01

    Graphene oxide (GO), which is an oxidized form of graphene, has a mixed structure consisting of graphitic crystallites of sp(2) hybridized carbon and amorphous regions. In this work, we present a straightforward route for preparing graphene-based quantum dots (GQDs) by extraction of the crystallites from the amorphous matrix of the GO sheets. GQDs with controlled functionality are readily prepared by varying the reaction temperature, which results in precise tunability of their optical properties. Here, it was concluded that the tunable optical properties of GQDs are a result of the different fraction of chemical functionalities present. The synthesis approach presented in this paper provides an efficient strategy for achieving large-scale production and long-time optical stability of the GQDs, and the hybrid assembly of GQD and polymer has potential applications as photoluminescent fibers or films. PMID:26383257

  9. Convenient synthesis of stable silver quantum dots with enhanced photoluminescence emission by laser fragmentation

    NASA Astrophysics Data System (ADS)

    Shuang, Li; Ming, Chen

    2016-04-01

    A new strategy for the facile synthesis of very stable and mono-dispersed silver (Ag) quantum dots (QDs) is developed by laser fragmentation of bulk Ag in water using polysorbate 80 as a dispersing and stabilizing agent. The surfactant plays an important role in the formation of size-controlled Ag nano-structures. The Ag QDs have excellent photo-stability of ∼500 h and enhanced photoluminescence (PL) at 510 nm. This has significant implications for selective and ultrasensitive PL probes. Based on laser fragmentation in the biocompatible surfactant solution, our results have opened up a novel paradigm to obtain stable metal QDs directly from bulk targets. This is a breakthrough in the toxicity problems that arise from standard chemical fabrication. Project supported by the National Natural Science Foundation of China (Grant Nos. 11575102, 11105085, 11275116, and 11375108) and the Fundamental Research Funds of Shandong University, China (Grant No. 2015JC007).

  10. Large Scale Synthesis and Light Emitting Fibers of Tailor-Made Graphene Quantum Dots

    NASA Astrophysics Data System (ADS)

    Park, Hun; Hyun Noh, Sung; Hye Lee, Ji; Jun Lee, Won; Yun Jaung, Jae; Geol Lee, Seung; Hee Han, Tae

    2015-09-01

    Graphene oxide (GO), which is an oxidized form of graphene, has a mixed structure consisting of graphitic crystallites of sp2 hybridized carbon and amorphous regions. In this work, we present a straightforward route for preparing graphene-based quantum dots (GQDs) by extraction of the crystallites from the amorphous matrix of the GO sheets. GQDs with controlled functionality are readily prepared by varying the reaction temperature, which results in precise tunability of their optical properties. Here, it was concluded that the tunable optical properties of GQDs are a result of the different fraction of chemical functionalities present. The synthesis approach presented in this paper provides an efficient strategy for achieving large-scale production and long-time optical stability of the GQDs, and the hybrid assembly of GQD and polymer has potential applications as photoluminescent fibers or films.

  11. Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acid

    NASA Astrophysics Data System (ADS)

    Dickerson, B. D.; Irving, D. M.; Herz, E.; Claus, R. O.; Spillman, W. B.; Meissner, K. E.

    2005-04-01

    A diffusion-barrier model described the early evolution of size-dependent photoluminescence emission from CdSe quantum dots formed by organometallic synthesis. Emission peak widths, emission redshift rates, and nanocrystal growth rates all decreased to a minimum at a reaction completion time. Growth after the completion time by Ostwald ripening was marked by a doubling of the activation energy. The temperature dependence of both reaction completion rates and photoluminescence redshift rates followed Arrhenius behavior governed by activation energies that increased with solvent molecular weight, in this limited case. In stearic acid and in trioctylphosphine oxide, the typical activation energies were 0.6±0.1 and 0.92±0.26eV/molecule, respectively.

  12. Large Scale Synthesis and Light Emitting Fibers of Tailor-Made Graphene Quantum Dots

    PubMed Central

    Park, Hun; Hyun Noh, Sung; Hye Lee, Ji; Jun Lee, Won; Yun Jaung, Jae; Geol Lee, Seung; Hee Han, Tae

    2015-01-01

    Graphene oxide (GO), which is an oxidized form of graphene, has a mixed structure consisting of graphitic crystallites of sp2 hybridized carbon and amorphous regions. In this work, we present a straightforward route for preparing graphene-based quantum dots (GQDs) by extraction of the crystallites from the amorphous matrix of the GO sheets. GQDs with controlled functionality are readily prepared by varying the reaction temperature, which results in precise tunability of their optical properties. Here, it was concluded that the tunable optical properties of GQDs are a result of the different fraction of chemical functionalities present. The synthesis approach presented in this paper provides an efficient strategy for achieving large-scale production and long-time optical stability of the GQDs, and the hybrid assembly of GQD and polymer has potential applications as photoluminescent fibers or films. PMID:26383257

  13. Quantum Dots: Theory

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    This review covers the description of the methodologies typically used for the calculation of the electronic structure of self-assembled and colloidal quantum dots. These are illustrated by the results of their application to a selected set of physical effects in quantum dots.

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

    PubMed Central

    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

    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

  15. Lab-on-a-chip synthesis of inorganic nanomaterials and quantum dots for biomedical applications.

    PubMed

    Krishna, Katla Sai; Li, Yuehao; Li, Shuning; Kumar, Challa S S R

    2013-11-01

    The past two decades have seen a dramatic raise in the number of investigations leading to the development of Lab-on-a-Chip (LOC) devices for synthesis of nanomaterials. A majority of these investigations were focused on inorganic nanomaterials comprising of metals, metal oxides, nanocomposites and quantum dots. Herein, we provide an analysis of these findings, especially, considering the more recent developments in this new decade. We made an attempt to bring out the differences between chip-based as well as tubular continuous flow systems. We also cover, for the first time, various opportunities the tools from the field of computational fluid dynamics provide in designing LOC systems for synthesis inorganic nanomaterials. Particularly, we provide unique examples to demonstrate that there is a need for concerted effort to utilize LOC devices not only for synthesis of inorganic nanomaterials but also for carrying out superior in vitro studies thereby, paving the way for faster clinical translation. Even though LOC devices with the possibility to carry out multi-step syntheses have been designed, surprisingly, such systems have not been utilized for carrying out simultaneous synthesis and bio-functionalization of nanomaterials. While traditionally, LOC devices are primarily based on microfluidic systems, in this review article, we make a case for utilizing millifluidic systems for more efficient synthesis, bio-functionalization and in vitro studies of inorganic nanomaterials tailor-made for biomedical applications. Finally, recent advances in the field clearly point out the possibility for pushing the boundaries of current medical practices towards personalized health care with a vision to develop automated LOC-based instrumentation for carrying out simultaneous synthesis, bio-functionalization and in vitro evaluation of inorganic nanomaterials for biomedical applications. PMID:23726944

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  17. Facile synthesis and photoluminescence characteristics of blue-emitting nitrogen-doped graphene quantum dots.

    PubMed

    Gu, Jian; Zhang, Xiaoping; Pang, Aimin; Yang, Jun

    2016-04-22

    A one-step hydrothermal method for synthesizing nitrogen-doped graphene quantum dots (N-GQDs) from organic carbon sources is presented in this paper. The high-quality N-GQDs can be obtained via tuning the degree of dehydration/carbonization of citric acid and doping of nitrogen atoms into the graphene lattice. The micromorphology, chemical structure, composition and photoluminescence (PL) characteristics of the N-GQDs were characterized systematically. The size of the obtained N-GQDs is about 5-10 nm with typical topographic heights of 0.8-2.5 nm. There is intense blue emission and excitation-independent PL behavior when the N-GQDs are in aqueous solution. The most remarkable innovation is that the fluorescence quantum yield (FL QY) of our N-GQDs is up to 75.2%, which is much higher than that of most reported GQDs (less than 25%). Thus, it is initially believed that synthesis parameters, hydrothermal process and nitrogen doping may greatly influence the surface state and bandgap of the GQDs, which are important in determining the PL characteristics of the N-GQDs. PMID:26964866

  18. Two-step synthesis of luminescent MoS(2)-ZnS hybrid quantum dots.

    PubMed

    Clark, Rhiannon M; Carey, Benjamin J; Daeneke, Torben; Atkin, Paul; Bhaskaran, Madhu; Latham, Kay; Cole, Ivan S; Kalantar-Zadeh, Kourosh

    2015-10-28

    A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (<100 nm), of which, the latter show favorable optical properties. Two concurrent photoluminescent (PL) peaks are seen at 380 and 450 nm, which are assigned to MoS2 and ZnS components of QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing applications. PMID:26399979

  19. Facile synthesis and photoluminescence characteristics of blue-emitting nitrogen-doped graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Gu, Jian; Zhang, Xiaoping; Pang, Aimin; Yang, Jun

    2016-04-01

    A one-step hydrothermal method for synthesizing nitrogen-doped graphene quantum dots (N-GQDs) from organic carbon sources is presented in this paper. The high-quality N-GQDs can be obtained via tuning the degree of dehydration/carbonization of citric acid and doping of nitrogen atoms into the graphene lattice. The micromorphology, chemical structure, composition and photoluminescence (PL) characteristics of the N-GQDs were characterized systematically. The size of the obtained N-GQDs is about 5-10 nm with typical topographic heights of 0.8-2.5 nm. There is intense blue emission and excitation-independent PL behavior when the N-GQDs are in aqueous solution. The most remarkable innovation is that the fluorescence quantum yield (FL QY) of our N-GQDs is up to 75.2%, which is much higher than that of most reported GQDs (less than 25%). Thus, it is initially believed that synthesis parameters, hydrothermal process and nitrogen doping may greatly influence the surface state and bandgap of the GQDs, which are important in determining the PL characteristics of the N-GQDs.

  20. Synthesis of Zn-In-S Quantum Dots with Tunable Composition and Optical Properties.

    PubMed

    Wang, Xianliang; Damasco, Jossana; Shao, Wei; Ke, Yujie; Swihart, Mark T

    2016-03-01

    II-III-VI semiconductors are of interest due to their chemical stability and composition-tunable optical properties. Here, we report a methodology for the synthesis of monodisperse zinc-indium-sulfide (ZIS) alloy quantum dots (QDs, mean diameter from ∼2 to 3.5 nm) with an In content substantially below that of the stoichiometric ZnIn2 S4 compound. The effects of indium incorporation on the size, lattice constant, and optical properties of ZIS QDs are elucidated. In contrast to previous reports, we employ sulfur dissolved in oleic acid as the sulfur donor rather than thioacetamide (TAA). The size of the ZIS QDs and their crystal lattice constant increased with increasing In incorporation, but they maintained the cubic sphalerite phase of ZnS, rather than the hexagonal phase typical of ZnIn2 S4 . The QDs' absorbance onset at UV wavelengths red-shifts with increasing In content and the accompanying increase in NC size. The ZIS NCs and related materials, whose synthesis is enabled by the approach presented here, provide new opportunities to apply II-III-VI semiconductors in solution-processed UV optoelectronics. PMID:26541645

  1. Single-step synthesis of graphene quantum dots by femtosecond laser ablation of graphene oxide dispersions.

    PubMed

    Russo, Paola; Liang, Robert; Jabari, Elahe; Marzbanrad, Ehsan; Toyserkani, Ehsan; Zhou, Y Norman

    2016-04-21

    In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and laser power, it is possible to produce GQDs with average sizes of 2-5 nm, emitting a blue luminescence at 410 nm. We tested the feasibility of the synthesized GQDs as materials for electronic devices by aerosol-jet printing of an ink that is a mixture of water dispersion of laser synthesized GQDs and silver nanoparticle dispersion, which resulted in lower resistivity of the final printed patterns. Preliminary results showed that femtosecond laser synthesized GQDs can be mixed with silver nanoparticle dispersion to fabricate a hybrid material, which can be employed in printing electronic devices by either printing patterns that are more conductive and/or reducing costs of the ink by decreasing the concentration of silver nanoparticles (AgNPs) in the ink. PMID:27071944

  2. Diffusion-controlled synthesis of PbS and PbSe quantum dots with in situ halide passivation for quantum dot solar cells.

    PubMed

    Zhang, Jianbing; Gao, Jianbo; Miller, Elisa M; Luther, Joseph M; Beard, Matthew C

    2014-01-28

    We developed a simple non-hot-injection synthetic route that achieves in situ halide-passivated PbS and PbSe quantum dots (QDs) and simplifies the fabrication of Pb-chalcogenide QD solar cells. The synthesis mechanism follows a temperature-dependent diffusion growth model leading to strategies that can achieve narrow size distributions for a range of sizes. We show that PbS QDs can be produced with a diameter as small as 2.2 nm, corresponding to a 1.7 eV band gap, while the resulting size distribution (6-7%) is comparable to that of hot-injection syntheses. The in situ chloride surface passivation is demonstrated by X-ray photoelectron spectroscopy and an improved photostability of both PbS and PbSe QDs when stored under air. Additionally, the photoluminescence quantum yield of the PbS QDs is ∼30% higher compared to the traditional synthesis. We show that PbS QD solar cells with 6.5% power conversion efficiency (PCE) can be constructed. Finally, we fabricated PbSe QD solar cells in air (rather than in inert atmosphere), achieving a PCE of 2.65% using relatively large QDs with a corresponding band gap of 0.89 eV. PMID:24341705

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

    PubMed

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

    2014-01-01

    We report an electric pressure cooker for large-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots. Low-cost thioglycolic acid and sodium citrate were used as the dual stabilizers. ∼3 grams of quantum dots with a tunable emission from 545 to 610 nm and quantum yield up to 40% were obtained in a batch. PMID:24337019

  4. 6-Mercaptohexanoic acid assisted synthesis of high quality InP quantum dots for optoelectronic applications

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  5. Synthesis and characterization of intrinsically radiolabeled quantum dots for bimodal detection

    PubMed Central

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

    2012-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    PubMed

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

    2016-12-01

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

  8. Two-step synthesis of luminescent MoS2-ZnS hybrid quantum dots

    NASA Astrophysics Data System (ADS)

    Clark, Rhiannon M.; Carey, Benjamin J.; Daeneke, Torben; Atkin, Paul; Bhaskaran, Madhu; Latham, Kay; Cole, Ivan S.; Kalantar-Zadeh, Kourosh

    2015-10-01

    A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (<100 nm), of which, the latter show favorable optical properties. Two concurrent photoluminescent (PL) peaks are seen at 380 and 450 nm, which are assigned to MoS2 and ZnS components of QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing applications.A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (<100 nm), of which, the latter show favorable optical properties. Two concurrent photoluminescent (PL) peaks are seen at 380 and 450 nm, which are assigned to MoS2 and ZnS components of QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing applications. Electronic supplementary information (ESI) available: Additional XPS graphs, AFM image, PL spectra, SEM image, TEM images, EDX data, XRD patterns and quantum yield calculations included. See DOI: 10.1039/c5nr04790k

  9. Nitrogen and phosphorus co-doped graphene quantum dots: synthesis from adenosine triphosphate, optical properties, and cellular imaging.

    PubMed

    Ananthanarayanan, Arundithi; Wang, Yue; Routh, Parimal; Sk, Mahasin Alam; Than, Aung; Lin, Ming; Zhang, Jie; Chen, Jie; Sun, Handong; Chen, Peng

    2015-05-01

    Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells. PMID:25875153

  10. Redefining giant quantum dot functionality through synthesis and integration: from multifunctionality to directed photoluminescence (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Hollingsworth, Jennifer A.

    2015-09-01

    Thick-shell or "giant" core/shell nanocrystal quantum dots (gQDs) are efficient and stable emitters. Their characteristic properties of non-blinking and non-photobleaching emission, as well as suppressed non-radiative Auger recombination and minimal self-reabsorption (due to a large effective Stokes shift) make them relevant to both single-emitter and many-emitter applications, e.g., live-cell single-molecule tracking in the biosciences and down-conversion phosphors for solid-state lighting. Here, I will discuss how gQDs are also ideal "building blocks" for achieving additive functionalities through synthesis and modified emission properties through integration with fabricated photonic structures. gQDs have been synthetically incorporated into the interior of a gold shell, resulting in "plasmonic gQDs" that exhibit efficient photoluminescence combined with efficient photothermal transduction and thermometry. Furthermore, through direct patterning of gQDs into all-dielectric antennas, we show an approach for realizing emitter-antenna couples (toward controlling the motion of photons) that is both deterministic and reproducible.

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

    NASA Astrophysics Data System (ADS)

    Pan, Yi

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

  12. Single-step synthesis of graphene quantum dots by femtosecond laser ablation of graphene oxide dispersions

    NASA Astrophysics Data System (ADS)

    Russo, Paola; Liang, Robert; Jabari, Elahe; Marzbanrad, Ehsan; Toyserkani, Ehsan; Zhou, Y. Norman

    2016-04-01

    In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and laser power, it is possible to produce GQDs with average sizes of 2-5 nm, emitting a blue luminescence at 410 nm. We tested the feasibility of the synthesized GQDs as materials for electronic devices by aerosol-jet printing of an ink that is a mixture of water dispersion of laser synthesized GQDs and silver nanoparticle dispersion, which resulted in lower resistivity of the final printed patterns. Preliminary results showed that femtosecond laser synthesized GQDs can be mixed with silver nanoparticle dispersion to fabricate a hybrid material, which can be employed in printing electronic devices by either printing patterns that are more conductive and/or reducing costs of the ink by decreasing the concentration of silver nanoparticles (AgNPs) in the ink.In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and laser power, it is possible to produce GQDs with average sizes of 2-5 nm, emitting a blue luminescence at 410 nm. We tested the feasibility of the synthesized GQDs as materials for electronic devices by aerosol-jet printing of an ink that is a mixture of water dispersion of laser synthesized GQDs and silver nanoparticle dispersion, which resulted in lower resistivity of the final printed patterns. Preliminary results showed that femtosecond laser synthesized GQDs can be mixed with silver nanoparticle dispersion to fabricate a hybrid material, which can be employed in printing electronic devices by either printing patterns that are more conductive and/or reducing costs of the ink by decreasing the concentration of silver nanoparticles (AgNPs) in the ink. Electronic supplementary information (ESI) available: Supplementary SEM, AFM, TEM, XPS, size distributions and PL data. See DOI: 10.1039/c6nr01148a

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

    NASA Astrophysics Data System (ADS)

    Kang, Zhitao

    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.

  14. Synthesis of silane surface modified ZnO quantum dots with ultrastable, strong and tunable luminescence.

    PubMed

    Shi, Han-Qiao; Li, Wan-Nan; Sun, Li-Wei; Liu, Yu; Xiao, Hong-Mei; Fu, Shao-Yun

    2011-11-21

    Surface modified ZnO quantum dots (QDs) with ultrastable, strong and tunable luminescence have been successfully prepared via silanization during the growth process by (3-(2,3-epoxypropoxy)propyl)trimethoxysilane. The as-prepared ZnO QDs are demonstrated to be promising for anti-counterfeit applications in expensive high-end liquors, etc. PMID:21975866

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

    SciTech Connect

    Xu, Xianmei; Wang, Yilin; Gule, Teri; Luo, Qiang; Zhou, Liya; Gong, Fuzhong

    2013-03-15

    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.

  16. Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

    ERIC Educational Resources Information Center

    Pan, Yi; Li, Yue Ru; Zhao, Yu; Akins, Daniel L.

    2015-01-01

    A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a…

  17. Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

    ERIC Educational Resources Information Center

    Pan, Yi; Li, Yue Ru; Zhao, Yu; Akins, Daniel L.

    2015-01-01

    A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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 μl‑1 with a detection limit of 3 ng μL‑1 has been performed based on the antibody-antigen recognition.

  19. Quantum dot laser

    SciTech Connect

    Oraevsky, Anatolii N; Velichansky, Vladimir L; Scully, M O

    1998-03-31

    An analysis is made of the self-excitation condition for a laser in which the active medium is a 'quantum dot' and a whispering-gallery mode of a dielectric microsphere acts as the cavity. It is pointed out that the interaction of a quantum dot with an ensemble of degenerate or near-degenerate modes increases the laser excitation coefficient. A calculation is made of the dependence of the effective volume of a whispering-gallery mode on its index. It is shown that the field maximum of an E-type whispering-gallery mode lies on the surface of a sphere, whereas for an H-type mode this maximum is shifted along the radius into the sphere. Calculations suggest that it should be possible to construct a microlaser even on the basis of a single quantum dot. (lasers)

  20. Nitrogen and phosphorus co-doped graphene quantum dots: synthesis from adenosine triphosphate, optical properties, and cellular imaging

    NASA Astrophysics Data System (ADS)

    Ananthanarayanan, Arundithi; Wang, Yue; Routh, Parimal; Sk, Mahasin Alam; Than, Aung; Lin, Ming; Zhang, Jie; Chen, Jie; Sun, Handong; Chen, Peng

    2015-04-01

    Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells.Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells. Electronic supplementary information (ESI) available: Supplementary figures related to characterization, computational studies and protein conjugation. See DOI: 10.1039/c5nr01519g

  1. Synthesis of magnetofluorescence Gd-doped CuInS2/ZnS quantum dots with enhanced longitudinal relaxivity.

    PubMed

    Chang, Jia-Yaw; Chen, Guan-Rong; Li, Jyun-Dong

    2016-03-01

    In this paper, we describe the rapid microwave-assisted synthesis of Gd(3+)-doped CuInS2 (Gd:CIS) quaternary quantum dots (q-dots), which integrate the functions of optical fluorescence and magnetic resonance imaging. Through passivation of ZnS shells around Gd:CIS cores, high-quality and robust photostable Gd:CIS/ZnS core/shell q-dots with enhanced quantum yields were obtained. The intensity and peak-to-peak linewidth of the electron spin resonance (EPR) signal were found to vary depending on the Gd(3+) concentration of Gd:CIS/ZnS. Benefiting from the incorporation of paramagnetic Gd(3+) ions, the formed q-dots exhibited well-resolved and strong signals of electron paramagnetic resonance and provided significant contrast enhancement in T1-weighted images owing to the remarkably high longitudinal relaxivity (r1 = 55.90 mM(-1) s(-1)) and low r2/r1 ratio (1.42), which are significantly higher than those of commercially available T1 contrast agents. We expect that this facile one-pot synthetic strategy can be extended to the preparation of other Cu-based sulfide quaternary nanomaterials. PMID:26887889

  2. Emulsion Synthesis of Size-Tunable CH3NH3PbBr3 Quantum Dots: An Alternative Route toward Efficient Light-Emitting Diodes.

    PubMed

    Huang, Hailong; Zhao, Fangchao; Liu, Lige; Zhang, Feng; Wu, Xian-Gang; Shi, Lijie; Zou, Bingsuo; Pei, Qibing; Zhong, Haizheng

    2015-12-30

    We report a facile nonaqueous emulsion synthesis of colloidal halide perovskite quantum dots by controlled addition of a demulsifier into an emulsion of precursors. The size of resulting CH3NH3PbBr3 quantum dots can be tuned from 2 to 8 nm by varying the amount of demulsifier. Moreover, this emulsion synthesis also allows the purification of these quantum dots by precipitation from the colloidal solution and obtains solid-state powder which can be redissolved for thin film coating and device fabrication. The photoluminescence quantum yields of the quantum dots is generally in the range of 80-92%, and can be well-preserved after purification (∼80%). Green light-emitting diodes fabricated comprising a spin-cast layer of the colloidal CH3NH3PbBr3 quantum dots exhibited maximum current efficiency of 4.5 cd/A, power efficiency of 3.5 lm/W, and external quantum efficiency of 1.1%. This provides an alternative route toward high efficient solution-processed perovskite-based light-emitting diodes. In addition, the emulsion synthesis is versatile and can be extended for the fabrication of inorganic halide perovskite colloidal CsPbBr3 nanocrystals. PMID:26652661

  3. Aqueous Synthesis of PEGylated Quantum Dots with Increased Colloidal Stability and Reduced Cytotoxicity.

    PubMed

    Ulusoy, Mehriban; Jonczyk, Rebecca; Walter, Johanna-Gabriela; Springer, Sergej; Lavrentieva, Antonina; Stahl, Frank; Green, Mark; Scheper, Thomas

    2016-02-17

    Ligands used on the surface of colloidal nanoparticles (NPs) have a significant impact on physiochemical properties of NPs and their interaction in biological environments. In this study, we report a one-pot aqueous synthesis of 3-mercaptopropionic acid (MPA)-functionalized CdTe/CdS/ZnS quantum dots (Qdots) in the presence of thiol-terminated methoxy polyethylene glycol (mPEG) molecules as a surface coordinating ligand. The resulting mPEG-Qdots were characterized by using ζ potential, FTIR, thermogravimetric (TG) analysis, and microscale thermophoresis (MST) studies. We investigated the effect of mPEG molecules and their grafting density on the Qdots photophysical properties, colloidal stability, protein binding affinity, and in vitro cellular toxicity. Moreover, cellular binding features of the resulting Qdots were examined by using three-dimensional (3D) tumor-like spheroids, and the results were discussed in detail. Promisingly, mPEG ligands were found to increase colloidal stability of Qdots, reduce adsorption of proteins to the Qdot surface, and mitigate Qdot-induced side effects to a great extent. Flow cytometry and confocal microscopy studies revealed that PEGylated Qdots exhibited distinctive cellular interactions with respect to their mPEG grafting density. As a result, mPEG molecules demonstrated a minimal effect on the ZnS shell deposition and the Qdot fluorescence efficiency at a low mPEG density, whereas they showed pronounced effect on Qdot colloidal stability, protein binding affinity, cytotoxicity, and nonspecific binding at a higher mPEG grafting amount. PMID:26567697

  4. Quantum Dot Light Emitting Diode

    SciTech Connect

    Kahen, Keith

    2008-07-31

    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.

  5. Quantum Dot Light Emitting Diode

    SciTech Connect

    Keith Kahen

    2008-07-31

    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.

  6. Quantum dot device tunable from single to triple dot system

    SciTech Connect

    Rogge, M. C.; Haug, R. J.; Pierz, K.

    2013-12-04

    We present a lateral quantum dot device which has a tunable number of quantum dots. Depending on easily tunable gate voltages, one, two or three quantum dots are found. They are investigated in transport and charge detection.

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

    PubMed

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

    2015-04-01

    Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-angle X-ray scattering to experimentally monitor the formation of CdSe quantum dots synthesized in solution through the heating up of precursors in octadecene at 240 °C. Our experiment yields a complete movie of the structure of the solution from the self-assembly of the precursors to the formation of the quantum dots. We show that the initial cadmium precursor lamellar structure melts into small micelles at 100 °C and that the first CdSe nuclei appear at 218.7 °C. The size distributions and concentration in nanocrystals are measured in a quantitative fashion as a function of time. We show that a short nucleation burst lasting 30 s is followed by a slow decrease of nanoparticle concentration. The rate-limiting process of the quantum dot formation is found to be the thermal activation of selenium. PMID:25815414

  8. Optimization of the aqueous synthesis of Cu2S quantum dots with different surface ligands

    NASA Astrophysics Data System (ADS)

    Wang, Yue; Liu, Liwei; Wang, Qian; Hu, Siyi; Zou, Peng; Shi, Jing; Zhang, Xihe

    2016-01-01

    Surface functionalization of quantum dots (QDs) is one of the most important aspects of designing and preparing the desired QDs for intended optical and biomedical applications. In this paper, we synthesized aqueous-phase Cu2S quantum dots coating by three different stabilizers, i.e. mercaptoacetic acid, mercaptopropionic acid and glutathione (GSH). Different stabilizers can influence the coordination modes between Cu+ on the surface of Cu2S and S2- of the ligand. The Cu2S QDs were characterized by UV-vis spectroscopy, energy dispersive spectrometry, transmission electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction and Raman spectra. Then, we performed a systematic study to evaluate the colloidal stability and in vitro toxicity of the formulations of Cu2S QDs with different stabilizers. Our results show that Cu2S QDs modified with different stabilizers have distinct functional groups on their surface and these groups make Cu2S produce different vibrations according to Raman spectra. The Cu2S-GSH exhibit the best colloidal stability in all pH buffer solutions and the lowest toxicity compare to the other two stabilizers. These properties make the Cu2S-GSH quantum dots a candidate for bioapplications in the future.

  9. Chiral quantum dot based materials

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    PubMed

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

    2012-06-01

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

  11. C8-structured carbon quantum dots: Synthesis, blue and green double luminescence, and origins of surface defects

    NASA Astrophysics Data System (ADS)

    Xifang, Chen; Wenxia, Zhang; Qianjin, Wang; Jiyang, Fan

    Carbon quantum dots (CQDs) have attracted great attention in the past few years due to their low cytotoxicity, exploited various synthesis methods, unexampled abundance of raw materials on earth, and robust near-infrared to near-UV luminescence. Carbon nanoparticles have applications in biological labeling, delivery of drugs and biological molecules into cells, and light emitting diodes and lasing. CQDs generally exist as nanodiamonds or graphite quantum dots according to previous research reports. In this study, we report the first synthesis of the third-allotrope CQDs through carbonization of sucrose and study their luminescence properties. These CQDs have a body-centered cubic structure and each lattice point is composed of eight atoms which form a sub-cube (so called C8 crystal structure). High-resolution transmission electron microscopy and X-ray diffraction confirm the C8 structure of the synthesized carbon nanocrystallites with an average size of 2 nm. The C8 CQDs exhibit double-band luminescence with two peaks centered at around 432 and 520 nm. The study based on the photoluminescence, UV-Vis absorption, Fourier-transform infrared, and X-ray photoelectron spectroscopies reveals that the green emission originates from the C=O related surface defect.

  12. PREFACE: Quantum Dot 2010

    NASA Astrophysics Data System (ADS)

    Taylor, Robert A.

    2010-09-01

    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

  13. Synthesis and optical properties of water soluble CdSe/CdS quantum dots for biological applications

    NASA Astrophysics Data System (ADS)

    Chu, Viet Ha; Nghiem, Thi Ha Lien; Le, Tien Ha; Vu, Dinh Lam; Nhung Tran, Hong; Vu, Thi Kim Lien

    2012-06-01

    Water soluble CdSe/CdS quantum dots (QDs) have been synthesized directly in aqueous solution with sodium citrate as surfactant agent. The QDs are mono-dispersed in water and have strong luminescent emission intensity under excitation of ultraviolet light. The emission maxima of the QDs can be tuned in a wider range from 555 to 615 nm in water by changing synthesis conditions. The result of the synthesis of water-soluble CdSe and CdSe/CdS QDs shows the high quality of the QDs with the quite narrow luminescence emission band and photostability. The results show the strongest intensity of photoluminescence emission in media with pH value at about from 8-8.5, which are pH physiological environments. The luminescence intensity increases when the QDs are coated with a polyethylene glycol (PEG) or bovine serum albumin (BSA) protein layer, the lifetime also increases.

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

    PubMed Central

    Vinokurov, Alexander A; Lebedev, Oleg I; Kuznetsova, Tatiana A; Dorofeev, Sergey G

    2015-01-01

    Summary Zinc-doped InP(Zn) colloidal quantum dots (QDs) with narrow size distribution and low defect concentration were grown for the first time via a novel phosphine synthetic route and over a wide range of Zn doping. We report the influence of Zn on the optical properties of the obtained quantum dots. We propose a mechanism for the introduction of Zn in the QDs and show that the incorporation of Zn atoms into the InP lattice leads to the formation of Zn acceptor levels and a luminescence tail in the red region of the spectra. Using photochemical etching with HF, we confirmed that the Zn dopant atoms are situated inside the InP nanoparticles. Moreover, doping with Zn is accompanied with the coverage of the QDs by a zinc shell. During the synthesis Zn myristate covers the QD nucleus and inhibits the particle growth. At the same time the zinc shell leads to an increase of the luminescence quantum yield through the reduction of phosphorous dangling bonds. A scenario for the growth of the colloidal InP(Zn) QDs was proposed and discussed. PMID:26114082

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

    PubMed Central

    2014-01-01

    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

  16. Electrochromic nanocrystal quantum dots.

    PubMed

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

    2001-03-23

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

  17. Synthesis of CuInS2 quantum dots using polyetheramine as solvent.

    PubMed

    Shei, Shih-Chang; Chiang, Wen-Jui; Chang, Shoou-Jinn

    2015-01-01

    This paper presents a facile solvothermal method of synthesizing copper indium sulfide (CuInS2) quantum dots (QDs) via a non-coordinated system using polyetheramine as a solvent. The structural and optical properties of the resulting CuInS2 QDs were investigated using composition analysis, absorption spectroscopy, and emission spectroscopy. We employed molar ratios of I, III, and VI group elements to control the structure of CuInS2 QDs. An excess of group VI elements facilitated precipitation, whereas an excess of group I elements resulted in CuInS2 QDs with high photoluminescence quantum yield. The emission wavelength and photoluminescence quantum yield could also be modulated by controlling the composition ratio of Cu and In in the injection stock solution. An increase in the portion of S shifted the emission wavelength of the QDs to a shorter wavelength and increased the photoluminescence quantum yield. Our results demonstrate that the band gap of the CuInS2 QDs is tunable with size as well as the composition of the reactant. The photoluminescence quantum yield of the CuInS2 QDs ranged between 0.7% and 8.8% at 250°C. We also determined some important physical parameters such as the band gaps and energy levels of this system, which are crucial for the application of CuInS2 nanocrystals. PMID:25852415

  18. Quantum Dots Investigated for Solar Cells

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  19. Scalable noninjection phosphine-free synthesis and optical properties of tetragonal-phase CuInSe2 quantum dots.

    PubMed

    Liu, Feng; Zhu, Jun; Xu, Yafeng; Zhou, Li; Dai, Songyuan

    2016-05-21

    Phosphine-free synthesis of CISe quantum dots (QDs) is highly desirable, yet it has been challenging. The main difficulty lies in achieving phosphine-free Se precursors. Most reported protocols for the synthesis of size-confined CISe QDs highly depend on the use of air-sensitive, toxic, and expensive alkylphosphines to prepare reactive Se precursors and to confine particle growth. Herein, we present a new amine/thiol combination-based route to Se precursors that may enable a general synthesis of phosphine-free selenide QDs. What's more, instead of the traditional "hot-injection" method, we also report the first one-pot noninjection synthesis of high quality CISe QDs enabled by our strategy. A very high chemical yield of ∼95% is demonstrated, as well as the facile gram-scale production of monodisperse CISe QDs. By simply adjusting the amount of 1-dodecanethiol used in the synthesis, we are able to produce CISe QDs with continuous tunability of the particle size from ∼2 nm to ∼10 nm, and hence their intrinsic optical properties. PMID:27137673

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

    PubMed

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

    2016-05-11

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

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

    PubMed

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

    2013-03-15

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

  2. Quantum Dots as Cellular Probes

    SciTech Connect

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

    2004-09-16

    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.

  3. Quantum dots as cellular probes.

    PubMed

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

    2005-01-01

    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. PMID:16004566

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  5. In-situ synthesis of high stable CdS quantum dots and their application for photocatalytic degradation of dyes.

    PubMed

    Samadi-Maybodi, Abdolraouf; Sadeghi-Maleki, Mohammad-Rasool

    2016-01-01

    Photocatalysis based on semiconductor quantum dots, which utilize the solar energy can be used for elimination of pollutants from aqueous media and applied for water purification. In this paper, high stable CdS quantum dots (QDs) with good optical properties were successfully synthesized in a facile in-situ method, using Na2S2O3 as precursor and thioglycolic acid (TGA) as a catalyst, as well as capping agent in aqueous media. The synthesis process was optimized with a 2IV(7-3) fractional factorial design method. Then, we studied the degradation of some industrial dyes including: alizarin, acid violet, mordant red and thymol blue as a tool to check the photocatalytic activity of synthesized CdS QDs. Results specified that the synthesized CdS QDs are capable for degradation of organic dyes under visible light irradiation with good recycling stability during photocatalytic experiments. Structural and spectroscopic properties of the synthesized CdS QDs were studied by TEM, XRD and absorption and fluorescence spectroscopy techniques. The synthesized TGA-capped CdS QDs have sizes in the range of 2.65-2.93nm with cubic crystalline structures. PMID:26208270

  6. In-situ synthesis of high stable CdS quantum dots and their application for photocatalytic degradation of dyes

    NASA Astrophysics Data System (ADS)

    Samadi-Maybodi, Abdolraouf; Sadeghi-Maleki, Mohammad-Rasool

    2016-01-01

    Photocatalysis based on semiconductor quantum dots, which utilize the solar energy can be used for elimination of pollutants from aqueous media and applied for water purification. In this paper, high stable CdS quantum dots (QDs) with good optical properties were successfully synthesized in a facile in-situ method, using Na2S2O3 as precursor and thioglycolic acid (TGA) as a catalyst, as well as capping agent in aqueous media. The synthesis process was optimized with a 2IV7-3 fractional factorial design method. Then, we studied the degradation of some industrial dyes including: alizarin, acid violet, mordant red and thymol blue as a tool to check the photocatalytic activity of synthesized CdS QDs. Results specified that the synthesized CdS QDs are capable for degradation of organic dyes under visible light irradiation with good recycling stability during photocatalytic experiments. Structural and spectroscopic properties of the synthesized CdS QDs were studied by TEM, XRD and absorption and fluorescence spectroscopy techniques. The synthesized TGA-capped CdS QDs have sizes in the range of 2.65-2.93 nm with cubic crystalline structures.

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

    PubMed

    Tyrakowski, Christina Marie; Snee, Preston Todd

    2014-01-21

    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

  8. Quantum dot cascade laser

    PubMed Central

    2014-01-01

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

  9. Hydrothermal synthesis of CdTe quantum dots-TiO2-graphene hybrid

    NASA Astrophysics Data System (ADS)

    Liu, Jinghua; Li, Xin

    2014-01-01

    CdTe-TiO2-graphene nanocomposites were successfully synthesized via a simple and relatively general hydrothermal method. During the hydrothermal environment, GO was reduced to reduced graphene oxide (RGO), accompanying with the anchoring of TiO2 nanoparticles on the surface of RGO. In the following process, CdTe quantum dots (QDs) were then in situ grown on the carbon basal planes. The morphologies and structural properties of the as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and fluorescent spectroscopy. It is hoped that our current work could pave a way towards the fabrication of QDs-TiO2-RGO hybrid materials.

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

    PubMed

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

    2014-06-01

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

  11. General Method for the Synthesis of Ultrastable Core/Shell Quantum Dots by Aluminum Doping.

    PubMed

    Li, Zhichun; Yao, Wei; Kong, Long; Zhao, Yixin; Li, Liang

    2015-10-01

    Semiconductor quantum dots (QDs) have attracted extensive attention in various applications because of their unique optical and electronic properties. However, long-term photostability remains a challenge for their practical application. Here, we present a simple method to enhance the photostability of QDs against oxidation by doping aluminum into the shell of core/shell QDs. We demonstrate that Al in the coating shell can be oxidized to Al2O3, which can serve as a self-passivation layer on the surface of the core/shell QDs and effectively stop further photodegradation during long-term light irradiation. The prepared CdSe/CdS:Al QDs survived 24 h without significant degradation when they were subjected to intense illumination under LED light (450 nm, 0.35 W/cm(2)), whereas conventional CdSe/CdS QDs were bleached within 3 h. PMID:26389704

  12. Synthesis and optical properties of copper-doped ZnSe quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  13. Synthesis, modification, bioconjugation of silica coated fluorescent quantum dots and their application for mycotoxin detection.

    PubMed

    Goftman, Valentina V; Aubert, Tangi; Ginste, Dries Vande; Van Deun, Rik; Beloglazova, Natalia V; Hens, Zeger; De Saeger, Sarah; Goryacheva, Irina Yu

    2016-05-15

    To create bright and stable fluorescent biolabels for immunoassay detection of mycotoxin deoxynivalenol in food and feed, CdSe/CdS/ZnS core-shell quantum dots (QDs) were encapsulated in silica nanoparticles through a water-in-oil reverse microemulsion process. The optical properties and stability of the obtained silica coated QDs (QD@SiO2), modified with amino, carboxyl and epoxy groups and stabilized with polyethylene glycol fragments, were characterized in order to assess their bioapplicability. The developed co-condensation techniques allowed maintaining 80% of the initial fluorescent properties and yielded stable fluorescent labels that could be easily activated and bioconjugated. Further, the modified QD@SiO2 were efficiently conjugated with antibodies and applied as a novel label in a microtiter plate based immunoassay and a quantitative column-based rapid immunotest for deoxynivalenol detection with IC50 of 473 and 20ng/ml, respectively. PMID:26745794

  14. Scanning Quantum Dot Microscopy

    NASA Astrophysics Data System (ADS)

    Wagner, Christian; Green, Matthew F. B.; Leinen, Philipp; Deilmann, Thorsten; Krüger, Peter; Rohlfing, Michael; Temirov, Ruslan; Tautz, F. Stefan

    2015-07-01

    We introduce a scanning probe technique that enables three-dimensional imaging of local electrostatic potential fields with subnanometer resolution. Registering single electron charging events of a molecular quantum dot attached to the tip of an atomic force microscope operated at 5 K, equipped with a qPlus tuning fork, we image the quadrupole field of a single molecule. To demonstrate quantitative measurements, we investigate the dipole field of a single metal adatom adsorbed on a metal surface. We show that because of its high sensitivity the technique can probe electrostatic potentials at large distances from their sources, which should allow for the imaging of samples with increased surface roughness.

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

    PubMed Central

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

    2011-01-01

    One barrier to apply current tri-octylphosphine oxide (TOPO) based quantum dots (QDs) to biomedical imaging is that the TOPO on TOPO-QDs can be replaced by the proteins in living system, which may cause the degradation of QDs and/or deactivation of protein. In order to develop biocompatible optical imaging agents, a novel triblock copolymer, designed as a multidentate ligand, was synthesized to coat quantum dot nanocrystals (QDs). The copolymer consists of a polycarboxylic acid block at one end and a polythiol block at the other end with an intervening cross-linked poly(styrene-co-divinylbenzene) block bridging the ends. The multiple mercapto groups from the polythiol block act as multidentate ligands to stabilize QDs, while the polycarboxylic acid block improves the water solubility of QDs and offers reaction sites for surface modification or conjugation with bimolecules. The cross-linked poly(styrene-co-divinylbenzene) block provides a densely compacted hydrophobic shell. This shell will act as a barrier to inhibit the degradation of QDs by preventing the diffusion of ions and small molecules into the core of QDs. This new multidentate polymer coating facilitates the transfer of QDs from organic solvent into aqueous phase. The QDs directly bound to multidentate mercapto groups instead of TOPO are less likely to be affected by the mercapto or disulfide groups within proteins or other biomolecules. Therefore, this research will provide an alternative coating material instead of TOPO to produce QDs which could be more suitable for in vivo use under complex physiological conditions. PMID:21297870

  16. Large-scale synthesis of N-doped carbon quantum dots and their phosphorescence properties in a polyurethane matrix.

    PubMed

    Tan, Jing; Zou, Rui; Zhang, Jie; Li, Wang; Zhang, Liqun; Yue, Dongmei

    2016-02-18

    An easy, large-scale synthesis of N-doped carbon quantum dots (CQDs) was developed by using isophorone diisocyanate (IPDI) as a single carbon source under microwave irradiation. The yield of raw N-doped CQDs was about 83%, which is suitable for industrial-scale production. A detailed formation mechanism for N-doped CQDs involving self-polymerization and condensation of IPDI was demonstrated. Moreover, the obtained N-doped CQDs can be homogeneously dispersed in various organic monomers and do not need toxic organic solvents as dispersing agents. This advantage expands the range of applications of CQDs in composites. The N-doped CQDs dispersed in polyurethane (PU) matrixes emit not only fluorescence but also phosphorescence and delayed fluorescence at room temperature upon excitation with ultraviolet (UV) light. Furthermore, the phosphorescence of CQD/PU composites is sensitive to oxygen and therefore, the obtained-CQDs could be exploited in the development of novel oxygen sensors. PMID:26860279

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

    SciTech Connect

    Qian Huifeng; Li Liang; Ren Jicun . E-mail: jicunren@sjtu.edu.cn

    2005-10-06

    In this paper, we presented a seed-mediated approach for rapid synthesis of high quality alloyed quantum dots (CdSe-CdS) in aqueous phase by microwave irradiation with controllable temperature in 1 h. In the synthesis, CdSe seeds were first formed by the reaction of NaHSe and Cd{sup 2+}, and then alloyed quantum dots (CdSe-CdS) were rapidly produced by releasing of sulfide ions from 3-mercaptopropionic acid as sulfide source with microwave irradiation. The alloyed quantum dots synthesized had good optical properties, the quantum yield was up to 25%, and the full width at half maximum of the emission spectrum peak was about 28 nm. The as-prepared alloyed CdSe-CdS QDs were characterized by XRD, XPS and ICP-AES in order to explore the structure and component of the alloyed nanocrystals and the reaction mechanism. We speculate that the alloyed CdSe-CdS quantum dots may exist a gradient internal structure according to our preliminary results.

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

    SciTech Connect

    Micic, O.I.; Ahrenkiel, S.P.; Bertram, D.; Nozik, A.J.

    1999-07-01

    Colloidal chemistry was used to synthesize GaN quantum dots. A GaN precursor, polymeric gallium imide, {l_brace}Ga(NH){sub 3/2}{r_brace}{sub n}, which was prepared by the reaction of dimeric amidogallium with ammonia at room temperature, was heated in trioctylamine at 360&hthinsp;{degree}C for one day to produce GaN nanocrystals. The GaN particles were separated, purified, and partially dispersed in a nonpolar solvent to yield transparent colloidal solutions that consisted of individual GaN particles. The GaN nanocrystals have a spherical shape and mean diameter of about 30{plus_minus}12&hthinsp;{Angstrom}. The spectroscopic behavior of colloidal transparent dispersion has been investigated and shows that the band gap of the GaN nanocrystals shifts to slightly higher energy due to quantum confinement. The photoluminescence spectrum at 10 K (excited at 310 nm) shows band edge emission with several emission peaks in the range between 3.2 and 3.8 eV, while the photoluminescence excitation spectrum shows two excited-state transitions at higher energies. {copyright} {ital 1999 American Institute of Physics.}

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

    NASA Astrophysics Data System (ADS)

    Mićić, O. I.; Ahrenkiel, S. P.; Bertram, D.; Nozik, A. J.

    1999-07-01

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

  20. Synthesis and characterization of CdSe/ZnS quantum dots conjugated with poly (ethylene glycol) diamine

    NASA Astrophysics Data System (ADS)

    Bharti, Shivani; Kaur, Gurvir; Gupta, Shikha; Tripathi, S. K.

    2015-08-01

    Bio-functionalization or surface modification is an important technique to obtain biocompatibility in semiconductor nanoparticles for biomedical applications. In this study semiconductor core/shell quantum dots of CdSe/ZnS have been prepared by chemical reduction method and then further PEGylated using Poly(ethylene glycol) diamine of Mw 2000. They were characterized by UV-vis spectroscopy & Fourier transform infrared spectroscopy. The results reveals the successful PEGylation of CdSe/ZnS quantum dots.

  1. A Customizable Quantum-Dot Cellular Automata Building Block for the Synthesis of Classical and Reversible Circuits

    PubMed Central

    Moustafa, Ahmed; Younes, Ahmed; Hassan, Yasser F.

    2015-01-01

    Quantum-dot cellular automata (QCA) are nanoscale digital logic constructs that use electrons in arrays of quantum dots to carry out binary operations. In this paper, a basic building block for QCA will be proposed. The proposed basic building block can be customized to implement classical gates, such as XOR and XNOR gates, and reversible gates, such as CNOT and Toffoli gates, with less cell count and/or better latency than other proposed designs. PMID:26345412

  2. A Customizable Quantum-Dot Cellular Automata Building Block for the Synthesis of Classical and Reversible Circuits.

    PubMed

    Moustafa, Ahmed; Younes, Ahmed; Hassan, Yasser F

    2015-01-01

    Quantum-dot cellular automata (QCA) are nanoscale digital logic constructs that use electrons in arrays of quantum dots to carry out binary operations. In this paper, a basic building block for QCA will be proposed. The proposed basic building block can be customized to implement classical gates, such as XOR and XNOR gates, and reversible gates, such as CNOT and Toffoli gates, with less cell count and/or better latency than other proposed designs. PMID:26345412

  3. Synthesis and characterization of CdSe/ZnS quantum dots conjugated with poly (ethylene glycol) diamine

    SciTech Connect

    Bharti, Shivani; Tripathi, S. K.; Kaur, Gurvir; Gupta, Shikha

    2015-08-28

    Bio-functionalization or surface modification is an important technique to obtain biocompatibility in semiconductor nanoparticles for biomedical applications. In this study semiconductor core/shell quantum dots of CdSe/ZnS have been prepared by chemical reduction method and then further PEGylated using Poly(ethylene glycol) diamine of M{sub w} 2000. They were characterized by UV-vis spectroscopy & Fourier transform infrared spectroscopy. The results reveals the successful PEGylation of CdSe/ZnS quantum dots.

  4. One-pot noninjection route to CdS quantum dots via hydrothermal synthesis.

    PubMed

    Aboulaich, Abdelhay; Billaud, Denis; Abyan, Mouhammad; Balan, Lavinia; Gaumet, Jean-Jacques; Medjadhi, Ghouti; Ghanbaja, Jaafar; Schneider, Raphaël

    2012-05-01

    Water-dispersible CdS quantum dots (QDs) emitting from 510 to 650 nm were synthesized in a simple one-pot noninjection hydrothermal route using cadmium chloride, thiourea, and 3-mercaptopropionic acid (MPA) as starting materials. All these chemicals were loaded at room temperature in a Teflon sealed tube and the reaction mixture heated at 100 °C. The effects of CdCl(2)/thiourea/MPA feed molar ratios, pH, and concentrations of precursors affecting the growth of the CdS QDs, was monitored via the temporal evolution of the optical properties of the CdS nanocrystals. High concentration of precursors and high MPA/Cd feed molar ratios were found to lead to an increase in the diameter of the resulting CdS nanocrystals and of the trap state emission of the dots. The combination of moderate pH value, low concentration of precursors and slow growth rate plays the crucial role in the good optical properties of the obtained CdS nanocrystals. The highest photoluminescence achieved for CdS@MPA QDs of average size 3.5 nm was 20%. As prepared colloids show rather narrow particle size distribution, although all reactants were mixed at room temperature. CdS@MPA QDs were characterized by UV-vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry and MALDI TOF mass spectrometry. This noninjection one-pot approach features easy handling and large-scale production with excellent synthetic reproducibility. Surface passivation of CdS@MPA cores by a wider bandgap material, ZnS, led to enhanced luminescence intensity. CdS@MPA and CdS/ZnS@MPA QDs exhibit high photochemical stability and hold a good potential to be applied in optoelectronic devices and biological applications. PMID:22509818

  5. Quantum dots: Rethinking the electronics

    NASA Astrophysics Data System (ADS)

    Bishnoi, Dimple

    2016-05-01

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

  6. Thiol antioxidant-functionalized CdSe/ZnS quantum dots: synthesis, characterization, cytotoxicity.

    PubMed

    Zheng, Hong; Mortensen, Luke J; DeLouise, Lisa A

    2013-03-01

    Nanotechnology is a growing industry with wide ranging applications in consumer product and technology development. In the biomedical field, nanoparticles are finding increasing use as imaging agents for biomolecular labeling and tumor targeting. The nanoparticle physiochemical properties must be tailored for the specific application. For example, nanoparticle chemical and physical stability in the biological milieu (no oxidation, aggregation, agglomeration or toxicity) are often required. Nanoparticles used for biomolecular fluorescent imaging should also have high quantum yield (QY). The aim of this paper is to examine the QY, stability, and cell toxicity of a series of positive, negative and neutral surface charge quantum dot (QD) nanoparticles. Simple protocols are described to prepare water soluble QDs by modifying the surface with thiol containing antioxidant ligands and polymers keeping the QD core/shell composition constant. The ligands used to produce negatively charged QDs include glutathione (GSH), N-acetyl-L-cysteine (NAC), dihydrolipoic acid (DHLA), tiopronin (TP), bucilliamine (BUC), and mercaptosuccinic acid (MSA). Ligands used to produce positively charged QDs include cysteamine (CYS) and polyethylenimine (PEI). Dithiothreitol (DTT) was used to produce neutral charged QDs. Commercially available nonaqueous octadecylamine (ODA) capped QDs served as the starting material. Our results suggest that QD uptake and cytotoxicity are both dependent on surface ligand coating composition. The negative charged GSH coated QDs show superior performance exhibiting low cytotoxicity, high stability, high QY and therefore are best suited for bioimaging applications. PEI coated QD also show superior performance exhibiting high QY and stability. However, they are considerably more cytotoxic due to their high positive charge which is an advantageous property that can be exploited for gene transfection and/or tumor targeting applications. The synthetic procedures described are straightforward and can be easily adapted in most laboratory settings. PMID:23620993

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

    PubMed

    Liu, Ning; Yang, Ping

    2013-01-01

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

  8. Aqueous synthesis and biostabilization of CdS@ZnS quantum dots for bioimaging applications

    NASA Astrophysics Data System (ADS)

    Chen, L.; Liu, Y.; Lai, C.; Berry, R. M.; Tam, K. C.

    2015-10-01

    Bionanohybrids, combining biocompatible natural polymers with inorganic materials, have aroused interest because of their structural, functional, and environmental advantages. In this work, we report on the stabilization of CdS@ZnS core-shell quantum dots (QDs) using carboxylated cellulose nanocrytals (CNCs) as nanocarrieers in aqueous phase. The high colloidal stability was achieved with sufficient negative charge on CNC surface and the coordination of Cd2+ to carboxylate groups. This coordination allows the in-situ nucleation and growth of QDs on CNC surface. The influences of QD to CNC ratio, pH and ZnS coating on colloidal stability and photoluminescence property of CNC/QD nanohybirds were also studied. The results showed that products obtained at pH 8 with a CdS to CNC weight ratio of 0.19 and a ZnS/CdS molar ratio of 1.5 possessed excellent colloidal stability and highest photoluminescence intensity. By anchoring QDs on rigid bionanotemplates, CNC/CdS@ZnS exhibited long-term colloidal and optical stability. Using biocompatible CNC as nanocarriers, the products have been demonstrated to exhibit low cytotoxicity towards HeLa cells and can serve as promising red-emitting fluorescent bioimaging probes.

  9. Direct synthesis of aqueous quantum dots through 4,4'-bipyridine-based twin ligand strategy.

    PubMed

    Kalita, Mausam; Cingarapu, Sreeram; Roy, Santanu; Park, Seok Chan; Higgins, Daniel; Jankowiak, Ryszard; Chikan, Viktor; Klabunde, Kenneth J; Bossmann, Stefan H

    2012-04-16

    We report a new class of derivatized 4,4'-bipyridinium ligands for use in synthesizing highly fluorescent, extremely stable, water-soluble CdSe and CdTe quantum dots (QDs) for bioconjugation. We employed an evaporation-condensation technique, also known as solvated metal atom dispersion (SMAD), followed by a digestive ripening procedure. This method has been used to synthesize both metal nanoparticles and semiconductors in the gram scale with several stabilizing ligands in various solvents. The SMAD technique comprised evaporation condensation and stabilization of CdSe or CdTe in tetrahydrofuran. The as-prepared product was then digestively ripened in both water and dimethyl formamide, leading to narrowing of the particle size distributions. The ligands were synthesized by nucleophilic substitution (S(N)2) reactions using 4,4'-bipyridine as a nucleophile. Confocal microscopy images revealed the orange color of the nanocrystalline QDs with diameters of ~5 nm. The size has been confirmed by using transmission electron microscopy. As a part of our strategy, 85% of the 4,4'-bipyridinium salt was synthesized as propionic acid derivative and used to both stabilize the QDs in water and label basic amino acids and different biomarkers utilizing the carboxylic acid functional group. Fifteen percent of the 4,4'-bipyridinium salt was synthesized as N-propyl maleimide and used as a second ligand to label any protein containing the amino acid cysteine by means of a 1,4-Michael addition. PMID:22443511

  10. Synthesis, COSMO-RS analysis and optical properties of surface modified ZnS quantum dots using ionic liquids

    NASA Astrophysics Data System (ADS)

    Shahid, Robina; Muhammad, Nawshad; Gonfa, Girma; Toprak, Muhammet S.; Muhammed, Mamoun

    2015-10-01

    Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using the microwave assisted ionic liquid (MAIL) route. Three ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4]), trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl) amide ([P6,6,6,14][TSFA]) and trihexyl(tetradecyl) phosphonium chloride ([P6,6,6,14][Cl]) were used in this study. The size and structure of the QDs were characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern, respectively. The synthesized QDs were of wurtzite crystalline structure with size less than 5 nm. The QDs were more uniformly distributed while using the phosponium based ILs as a reaction medium during synthesis. The optical properties were investigated by UV-vis absorption and photoluminescence (PL) emission spectroscopy. The optical properties of QDs showed the quantum confinement effect in their absorption and the effect of cation and anion structural moiety was observed on their bandedge emission. The QDs emission intensity was measured higher for [P6,6,6,14][Cl] due to their better dispersion as well as high charge density of Cl anion. The capability of the ILs in stabilizing the QDs was interpreted by density functional theory (DFT) computations. The obtained results are in good agreement with the theoretical prediction.

  11. Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots

    NASA Astrophysics Data System (ADS)

    Bastos-Arrieta, Julio; Muñoz, Jose; Stenbock-Fermor, Anja; Muñoz, Maria; Muraviev, Dmitri N.; Céspedes, Francisco; Tsarkova, Larisa A.; Baeza, Mireia

    2016-04-01

    Intermatrix Synthesis (IMS) technique has proven to be a valid methodology for the in situ incorporation of quantum dots (QDs) in a wide range of nanostructured surfaces for the preparation of advanced hybrid-nanomaterials. In this sense, this communication reports the recent advances in the application of IMS for the synthesis of CdS-QDs with favourable distribution on sulfonated polyetherether ketone (SPEEK) membrane thin films (TFs), multiwall carbon nanotubes (MWCNTs) and nanodiamonds (NDs). The synthetic route takes advantage of the ion exchange functionality of the reactive surfaces for the loading of the QDs precursor and consequent QDs appearance by precipitation. The benefits of such modified nanomaterials were studied using CdS-QDs@MWCNTs hybrid-nanomaterials. CdS-QDs@MWCNTs has been used as conducting filler for the preparation of electrochemical nanocomposite sensors, which present electrocatalytic properties. Finally, the optical properties of the QDs contained on MWCNTs could allow a new procedure for the analytical detection of nanostructured carbon allotropes in water.

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

    PubMed Central

    2013-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  14. What future for quantum dot-based light emitters?

    NASA Astrophysics Data System (ADS)

    Nurmikko, Arto

    2015-12-01

    Synthesis of semiconductor colloidal quantum dots by low-cost, solution-based methods has produced an abundance of basic science. Can these materials be transformed to high-performance light emitters to disrupt established photonics technologies, particularly semiconductor lasers?

  15. Synthesis of Nitrogen-Doped Graphene Quantum Dots at Low Temperature for Electrochemical Sensing Trinitrotoluene.

    PubMed

    Cai, Zhewei; Li, Fumin; Wu, Ping; Ji, Lijuan; Zhang, Hui; Cai, Chenxin; Gervasio, Dominic F

    2015-12-01

    Nitrogen-doped graphene quantum dots (N-GQDs) are synthesized at low temperature as a new catalyst allowing electrochemical detection of 2,4,6-trinitrotoluene (TNT). N-GQDs are made by an oxidative ultrasonication of graphene oxide (GO) forming nanometer-sized species, which are then chemically reduced and nitrogen doped by reacting with hydrazine. The as-synthesized N-GQDs have an average diameter of ∼2.5 nm with an N/C atomic ratio of up to ∼6.4%. To detect TNT, TNT is first accumulated on N-GQDs modified glassy carbon (N-GQDs/GC) electrode by holding the electrode at a 0 V versus Ag/AgCl for 150 s in an aqueous TNT solution. Next, the N-GQDs/GC electrode with accumulated TNT is transferred to a fresh PBS solution (0.1 M, pH 7.0, without TNT), where the TNT reduction current at -0.36 V versus Ag/AgCl in a linear scan voltammogram (LSV) shows a linear response to TNT concentration in the aqueous solution from 1 to 400 ppb, with a correlation coefficient of 0.999, a detection limit of 0.2 ppb at a signal/noise (S/N) of 3, and a detection sensitivity of 363 ± 7 mA mM(-1) cm(-2). The detection limit of 0.2 ppb of TNT for this new method is much lower than 2 ppb set by the U.S. Environmental Protection Agency for drinking water. Therefore, N-GQDs allow an electrochemical method for assaying TNT in drinking water to determine if levels of TNT are safe or not. PMID:26545150

  16. Lateral Quantum Dots for Quantum Information Processing

    NASA Astrophysics Data System (ADS)

    House, Matthew Gregory

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

  17. Large-scale synthesis of N-doped carbon quantum dots and their phosphorescence properties in a polyurethane matrix

    NASA Astrophysics Data System (ADS)

    Tan, Jing; Zou, Rui; Zhang, Jie; Li, Wang; Zhang, Liqun; Yue, Dongmei

    2016-02-01

    An easy, large-scale synthesis of N-doped carbon quantum dots (CQDs) was developed by using isophorone diisocyanate (IPDI) as a single carbon source under microwave irradiation. The yield of raw N-doped CQDs was about 83%, which is suitable for industrial-scale production. A detailed formation mechanism for N-doped CQDs involving self-polymerization and condensation of IPDI was demonstrated. Moreover, the obtained N-doped CQDs can be homogeneously dispersed in various organic monomers and do not need toxic organic solvents as dispersing agents. This advantage expands the range of applications of CQDs in composites. The N-doped CQDs dispersed in polyurethane (PU) matrixes emit not only fluorescence but also phosphorescence and delayed fluorescence at room temperature upon excitation with ultraviolet (UV) light. Furthermore, the phosphorescence of CQD/PU composites is sensitive to oxygen and therefore, the obtained-CQDs could be exploited in the development of novel oxygen sensors.An easy, large-scale synthesis of N-doped carbon quantum dots (CQDs) was developed by using isophorone diisocyanate (IPDI) as a single carbon source under microwave irradiation. The yield of raw N-doped CQDs was about 83%, which is suitable for industrial-scale production. A detailed formation mechanism for N-doped CQDs involving self-polymerization and condensation of IPDI was demonstrated. Moreover, the obtained N-doped CQDs can be homogeneously dispersed in various organic monomers and do not need toxic organic solvents as dispersing agents. This advantage expands the range of applications of CQDs in composites. The N-doped CQDs dispersed in polyurethane (PU) matrixes emit not only fluorescence but also phosphorescence and delayed fluorescence at room temperature upon excitation with ultraviolet (UV) light. Furthermore, the phosphorescence of CQD/PU composites is sensitive to oxygen and therefore, the obtained-CQDs could be exploited in the development of novel oxygen sensors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08516k

  18. Transport through graphene quantum dots

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Galloway, Justin F.

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

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

    SciTech Connect

    Wei, Ying; Yu, Hang; Li, Haitao; Ming, Hai; Pan, Keming; Huang, Hui; Liu, Yang; Kang, Zhenhui

    2013-10-15

    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.

  2. Optically active quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  3. Chiral Quantum Dots

    NASA Astrophysics Data System (ADS)

    Balaz, Milan

    2015-03-01

    Chiral optically active semiconductor quantum dots (chiral QDs) represent appealing building blocks for assembly of nanomaterials with modular structural, electronic and chiroptical properties. Chirality in QDs can originate from several distinct phenomena that can concurrently modulate the observed chiroptical and optical properties (e.g. chiral surface, orbital hybridization). We will use our experimental and theoretical data to elaborate on the origin of capping ligand induced chirality in achiral colloidal QDs. We will present a simple method to prepare chiral QDs by post-synthetic chiral ligand functionalization of achiral QDs. Importantly, capping ligands can be used not only to induce but also to control chiroptical activity of QDs. Enantiomers of chiral ligands induce mirror-image chirality in QDs, and chiroptical properties of QDs can be further modulated by the chemical structure of capping ligands as well as the size of QDs. This work was supported by by U.S. Department of Energy (Award DE-FG02-10ER46728), National Science Foundation (awards CBET-1403947 and DGE-0948027) and University of Wyoming.

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

    ERIC Educational Resources Information Center

    Rice, Charles V.; Giffin, Guinevere A.

    2008-01-01

    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;

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

    ERIC Educational Resources Information Center

    Rice, Charles V.; Giffin, Guinevere A.

    2008-01-01

    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;…

  6. Preparation of chiral quantum dots.

    PubMed

    Moloney, Mícheál P; Govan, Joseph; Loudon, Alexander; Mukhina, Maria; Gun'ko, Yurii K

    2015-04-01

    Chiral quantum dots (QDs) are expected to have a range of potential applications in photocatalysis, as specific antibacterial and cytotoxic drug-delivery agents, in assays, as sensors in asymmetric synthesis and enantioseparation, and as fluorescent chiral nanoprobes in biomedical and analytical technologies. In this protocol, we present procedures for the synthesis of chiral optically active QD nanostructures and their quality control using spectroscopic studies and transmission electron microscopy imaging. We closely examine various synthetic routes for the preparation of chiral CdS, CdSe, CdTe and doped ZnS QDs, as well as of chiral CdS nanotetrapods. Most of these nanomaterials can be produced by a very fast (70 s) microwave-induced heating of the corresponding precursors in the presence of D- or L-chiral stabilizing coating ligands (stabilizers), which are crucial to generating optically active chiral QDs. Alternatively, chiral QDs can also be produced via the conventional hot injection technique, followed by a phase transfer in the presence of an appropriate chiral stabilizer. We demonstrate that the properties, structure and behavior of chiral QD nanostructures, as determined by various spectroscopic techniques, strongly depend on chiral stabilizers and that the chiral effects induced by them can be controlled via synthetic procedures. PMID:25741991

  7. Synthesis and characterization of InP, GaP, and GaInP{sub 2} quantum dots

    SciTech Connect

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

    1995-05-11

    Quantum dots (QDs) of InP, GaP, and GaInP{sub 2} with diameters ranging from 20 to 65 A were synthesized as well-crystallized nanoparticles with bulk zinc blende structure. The synthesis of InP, GaP, and GaInP{sub 2} QDs was achieved by heating appropriate organometallic precursors with stabilizers in high boiling solvents for several days to produce QDs which can be dissolved in nonpolar organic solvents, forming transparent colloidal QD dispersions. The high sample quality of the InP and GaP QDs results in excitonic features in the absorption spectra. Ternary QDs of GaInP{sub 2} were synthesized with a well-crystallized zinc blende structure and lattice spacing between InP and GaP. The QDs were characterized by TEM, powder x-ray diffraction, steady state optical absorption and photoluminescence spectroscopy, transient photoluminescence spectroscopy, and fs to ps pump-probe absorption (i.e., hole-burning) spectroscopy. 21 refs., 10 figs.

  8. Highly Photoluminescent Molybdenum Oxide Quantum Dots: One-Pot Synthesis and Application in 2,4,6-Trinitrotoluene Determination.

    PubMed

    Xiao, Sai Jin; Zhao, Xiao Jing; Hu, Ping Ping; Chu, Zhao Jun; Huang, Cheng Zhi; Zhang, Li

    2016-03-30

    As a well-studied transition-metal semiconductor material, MoOx has a wider band gap than molybdenum disulfide (MoS2), and its property varies dramatically for the existence of several different allotropes and suboxide phases of molybdenum oxides (MoOx, x < 3). In this manuscript, a one-pot method possessing the advantages of one pot, easily prepared, rapid, and environmentally friendly, has been developed for facile synthesis of highly photoluminescent MoOx quantum dots (MoOx QDs), in which commercial molybdenum disulfide (MoS2) powder and hydrogen peroxide (H2O2) are employed as the precursor and oxidant, respectively. The obtained MoOx QDs can be further utilized as an efficient photoluminescent probe, and a new turn-off sensor is developed for 2,4,6-trinitrotoluene (TNT) determination based on the fact that the photoluminescence of MoOx QDs can be quenched by the Meisenheimer complexes formed in the strong alkali solution through the inner filter effect (IFE). Under the optimal conditions, the decreased photoluminescence of MoOx QDs shows a good linear relationship to the concentration of TNT ranging from 0.5 to 240.0 μM, and the limit of detection was 0.12 μM (3σ/k). With the present turn-off sensor, TNT in river water samples can be rapidly and selectively detected without tedious sample pretreatment processes. PMID:26954663

  9. SnS Thin Film Prepared by Pyrolytic Synthesis as an Efficient Counter Electrode in Quantum Dot Sensitized Solar Cells.

    PubMed

    Dai, Xiaoyan; Shi, Chengwu; Zhang, Yanru; Liu, Feng; Fang, Xiaqin; Zhu, Jun

    2015-09-01

    The SnS thin films were successfully prepared by pyrolysis procedure for the counter electrodes in quantum dot sensitized solar cells (QDSCs) using the methanol solution containing stannous chloride dihydrate (0.40 mol x L(-1)) and thiourea (0.40 mol x L(-1)) as precursor solution at 300 degrees C in the air atmosphere. The electrochemical catalytic activity of the SnS thin films prepared by pyrolytic synthesis for the redox couple of S(2-)/S(2-) was investigated by electrochemical impedance spectroscopy. The result revealed that the charge transfer resistance of the as-prepared SnS thin film with the dipping-heating cycles of 5 was 106.4 Ω and the corresponded QDSCs gave a short circuit photocurrent density of 8.69 mA x cm(-2), open circuit voltage of 0.42 V, and fill factor of 0.43, yielding the photoelectric conversion efficiency of 1.57%, under the illumination of simulated AM 1.5 sunlight (100 mWx cm(-2)). PMID:26716249

  10. Quaternary Cu2ZnSnS4 quantum dot-sensitized solar cells: Synthesis, passivation and ligand exchange

    NASA Astrophysics Data System (ADS)

    Bai, Bing; Kou, Dongxing; Zhou, Wenhui; Zhou, Zhengji; Tian, Qingwen; Meng, Yuena; Wu, Sixin

    2016-06-01

    The quaternary Cu2ZnSnS4 (CZTS) QDs had been successfully introduced into quantum dot-sensitized solar cells (QDSC) via hydrolysis approach in our previous work [Green Chem. 2015, vol. 17, p. 4377], but the obtained cell efficiency was still limited by low open-circuit voltage and fill factor. Herein, we use 1-dodecanethiol (DDT) as capping ligand for fairly small-sized CZTS QDs synthesis to improve their intrinsic properties. Since this strong bonded capping ligand can not be replaced by 3-mercaptopropionic acid (MPA) directly, the nature cation (Cu, Zn or Sn)-DDT units of QDs are first exchanged by the preconjugated Cd-oleate via successive ionic layer adsorption and reaction (SILAR) procedure accompanied with the formation of a core/shell structure. The weak bonded oleic acid (OA) can be finally replaced by MPA and the constructed water soluble CZTS/CdSe QDSC achieves an impressive conversion efficiency of 4.70%. The electron transport and recombination dynamic processes are confirmed by intensity-modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS) measurements. It is found that the removal of long alkyl chain is conducive to improve the electron transport process and the type-II core/shell structure is beneficial to accelerate electron transport and retard charge recombination. This effective ligand removal strategy is proved to be more convenient for the applying of quaternary QDs in QDSC and would boost a more powerful efficiency in the future work.

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

    PubMed

    Yang, Fanghong; Yang, Ping; Zhang, Lipeng

    2013-01-01

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

  12. Peptide Coated Quantum Dots for Biological Applications

    PubMed Central

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

    2011-01-01

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

  13. Growth and Characterization of Quantum Dots and Quantum Dots Devices

    SciTech Connect

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

    2003-04-01

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

  14. Facile and green synthesis of CdSe quantum dots in protein matrix: tuning of morphology and optical properties.

    PubMed

    Ahmed, M; Guleria, A; Rath, M C; Singh, A K; Adhikari, S; Sarkar, S K

    2014-08-01

    Herein, we have demonstrated a facile and green approach for the synthesis of Cadmium selenide (CdSe) quantum dots (QDs). The process was mediated by bovine serum albumin (BSA) and it was found that BSA plays the dual role of reducing agent as well as a stabilizing agent. The QDs exhibited sharp excitonic absorption features at ~500 nm and subsequently showed reasonably good photoluminescence (PL) at room temperature. The PL is seen to be strongly dependent on the concentration of the precursors and hence, the luminescence of these QDs could be conveniently tuned across the visible spectrum simply by varying molar ratio of the precursors. It can be envisaged from the fact that a red-shift of about 100 nm in the PL peak position was observed when the molar ratio of the precursors ([Cd2+]:[Se2-], in mM) was varied from 10:5 to 10:40. Subsequently, the charge carrier relaxation dynamics associated with the different molar ratio of precursors has been investigated and very interesting information regarding the energy level structures of these QDs were revealed. Most importantly, in conjunction with the optical tuning, the nanomorphology of these nanoparticles was found to vary with the change in molar ratios of Se and Cd precursors. This aspect can provide a new direction of controlling the shape of CdSe nanoparticles. The possible mechanism of the formation as well as for the shape variation of these nanoparticles with the molar ratios of precursors has been proposed, taking into account the role of amino acid residues (present in BSA). Moreover, the QDs were water soluble and possessed fairly good colloidal stability therefore, can have potential applications in catalysis and bio-labeling. On the whole, the present methodology of protein assisted synthesis is relatively new especially for semiconducting nanomaterials and may provide some unique and interesting aspects to control and fine tune the morphology vis-à-vis, their optical properties. PMID:25935997

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

    PubMed

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

    2014-01-01

    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 γ-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 (65)ZnS 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. γ-counting of the radioactivity provided confirmation of the successful labelling and phase transfer of the QDs. PMID:25551066

  16. Two-step synthesis of highly emissive C/ZnO hybridized quantum dots with a broad visible photoluminescence

    NASA Astrophysics Data System (ADS)

    He, Liangjie; Mei, Shiliang; Chen, Qiuhang; Zhang, Wanlu; Zhang, Jie; Zhu, Jiatao; Chen, Guoping; Guo, Ruiqian

    2016-02-01

    In situ growth of ZnO layer on the surface of carbon dots was realized via a two-step method, which resulted in an enhancement of the broad visible emission with a high quantum yield. Influence of the refluxing time, the temperature and the oleylamine/octadecene ratio was investigated to address the key factors on the preparation of the carbon dots. Under the optimal conditions, the carbon dots with an average diameter of 3.4 ± 0.4 nm and a photoluminescence quantum yield of 29.3% were achieved. Remarkable improvements of photoluminescence were achieved by the hybridization of the ZnO layer, which can eliminate the surface-trap from the C cores and form the new centers of emission. The synergistic effect arising from the C/ZnO hybridized structure obviously broadened the visible emission and enhanced their photoluminescence quantum yield from 29.3% to 47.3%. The as-prepared highly emissive quantum dots exhibited a broad and stable emission with the Commission Internationaled 'E' clairage chromaticity coordinate of (0.23, 0.34), which could offer a promising solution for the future-generation white light emitting diodes.

  17. Size-controlled synthesis of SnO2 quantum dots and their gas-sensing performance

    NASA Astrophysics Data System (ADS)

    Du, Jianping; Zhao, Ruihua; Xie, Yajuan; Li, Jinping

    2015-08-01

    Tin dioxide quantum dots (TQDs) with controllable size were synthesized by changing the amount of alkaline reagent in the hydrothermal process. The gas-sensing properties were investigated by operating chemoresistor type sensor. The morphology and structure were characterized by X-ray diffraction, scanning/transmission electron microscopy, UV-vis and Raman spectrometry. The as-synthesized SnO2 shows the characteristics of quantum dots and the narrowest size distribution is about 2-3 nm. The gas-sensing results indicate that the responses are strongly dependent on the size of quantum dots. TQDs with different sizes exhibit different sensitivities and selectivities to volatile toxic chemicals such as aldehyde, acetone, methanol, ethanol and amine. Especially, when the sensors are exposed to 100 ppm triethylamine (TEA), the sensing response value of TQDs with small size is two times higher than that of the large-size TQDs. The maximum response values of TQDs to 1 ppm and 100 ppm TEA are 15 and 153, respectively. The response time is 1 s and the recovery time is 47 s upon exposure to 1 ppm TEA. The results suggest that it is an effective method by regulating the size of SnO2 quantum dots to detect low-concentration hazardous volatile compounds.

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

    SciTech Connect

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

    2012-05-15

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

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

    NASA Astrophysics Data System (ADS)

    Thedjoisworo, Bayu Atmaja

    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.)

  20. Quantum dot quantum cascade infrared photodetector

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  1. Quantum dot quantum cascade infrared photodetector

    SciTech Connect

    Wang, Xue-Jiao; Zhai, Shen-Qiang; Zhuo, Ning; Liu, Jun-Qi E-mail: fqliu@semi.ac.cn; Liu, Feng-Qi E-mail: fqliu@semi.ac.cn; Liu, Shu-Man; Wang, Zhan-Guo

    2014-04-28

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

  2. Chiral Graphene Quantum Dots.

    PubMed

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

    2016-02-23

    Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to l/d-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than l-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials. PMID:26743467

  3. Low Threshold Quantum Dot Lasers.

    PubMed

    Iyer, Veena Hariharan; Mahadevu, Rekha; Pandey, Anshu

    2016-04-01

    Semiconductor quantum dots have replaced conventional inorganic phosphors in numerous applications. Despite their overall successes as emitters, their impact as laser materials has been severely limited. Eliciting stimulated emission from quantum dots requires excitation by intense short pulses of light typically generated using other lasers. In this Letter, we develop a new class of quantum dots that exhibit gain under conditions of extremely low levels of continuous wave illumination. We observe thresholds as low as 74 mW/cm(2) in lasers made from these materials. Due to their strong optical absorption as well as low lasing threshold, these materials could possibly convert light from diffuse, polychromatic sources into a laser beam. PMID:26978011

  4. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

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

  5. The energy spectrum of parabolic quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Chin; Huang, Yung-Sheng

    2000-12-01

    We calculate the energy spectrum of hydrogen impurity located in the center of parabolic quantum dot. The energy levels under this model differ from the previous results for the case of spherical quantum dot. The degeneracy of the energy levels is quite different as well. However, compared with the spherical quantum dot, the energy plateau under this model is not obvious.

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

    PubMed

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

    2013-10-01

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

  7. Hydrophobin-Encapsulated Quantum Dots.

    PubMed

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

    2016-02-24

    The phase transfer of quantum dots to water is an important aspect of preparing nanomaterials that are suitable for biological applications, and although numerous reports describe ligand exchange, very few describe efficient ligand encapsulation techniques. In this report, we not only report a new method of phase transferring quantum dots (QDs) using an amphiphilic protein (hydrophobin) but also describe the advantages of using a biological molecule with available functional groups and their use in imaging cancer cells in vivo and other imaging applications. PMID:26824334

  8. Quantum dot/glycol chitosan fluorescent nanoconjugates

    NASA Astrophysics Data System (ADS)

    Mansur, Alexandra AP; Mansur, Herman S.

    2015-04-01

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

  9. Optical Fiber Sensing Using Quantum Dots

    PubMed Central

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

    2007-01-01

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

  10. Synthesis of blue-photoluminescent graphene quantum dots/polystyrenic anion-exchange resin for Fe(III) detection

    NASA Astrophysics Data System (ADS)

    Zhang, Wenjun; Gan, Jie

    2016-05-01

    A novel solid fluorescent sensor with millimeter size, based on graphene quantum dots/polystyrenic anion-exchange resin (GQDs/PS-AER) was obtained for the detection of Fe3+. The linear response range of Fe3+ was obtained from 1 μM to 7 μM and the detection limit was as low as 0.65 μM. In addition, the sensor could be regenerated by adding complexing agent EDTA and be separated by using simple filtration.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    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.

  14. Synthesis of highly photo-stable CuInS2/ZnS core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Ma, Jingwei; Liu, Mingming; Li, Zhichun; Li, Liang

    2015-09-01

    CuInS2 quantum dots are considered near-ideal fluorophores based on their bright emission and low toxicity. However, CuInS2 quantum dots are still bothered by their sensitivity to surface chemistry and chemical environment. Traditionally, the CIS QDs require an additional coating process to be encapsulated inside silica sphere or organic polymer. Up till now, few works have been made concerning improving the intrinsic stability of CIS QDs. In an effort to improve the stability of CuInS2 quantum dots, we came up with a new method by increasing the ZnS shell thickness. These QDs were characterized by photoluminescence, HRTEM, XRD and XRF analysis. We investigated the influence of ZnS shell thickness on the ambient stability of CIS/ZnS QDs. The results demonstrated that a thicker ZnS shell helped significantly improve both photostability and chemical stability of the QDs. Finally, the thick shell QDs were dispersed into transparent polymer matrix and fabricated into a LED device, which also gave much more stability compared with conventional QDs.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  16. Semiconductor double quantum dot micromaser

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  17. Semiconductor double quantum dot micromaser.

    PubMed

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

    2015-01-16

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

  18. Brightness-equalized quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  19. Brightness-equalized quantum dots

    PubMed Central

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

    2015-01-01

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices. PMID:26437175

  20. Designing quantum dots for solotronics

    PubMed Central

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

    2014-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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 μmol/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.

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

    PubMed

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

    2012-02-01

    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

  3. The emission wavelength dependent photoluminescence lifetime of the N-doped graphene quantum dots

    SciTech Connect

    Deng, Xingxia; Sun, Jing; Yang, Siwei; Ding, Guqiao; Shen, Hao; Zhou, Wei; Lu, Jian; Wang, Zhongyang

    2015-12-14

    Aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques. The PL lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum, which is different from most semiconductor quantum dots and fluorescent dyes. This result shows the synergy and competition between the quantum confinement effect and edge functional groups, which may have the potential to guide the synthesis and expand the applications of graphene quantum dots.

  4. Thermoelectric energy harvesting with quantum dots.

    PubMed

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

    2015-01-21

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

  5. A highly reactive chalcogenide precursor for the synthesis of metal chalcogenide quantum dots

    NASA Astrophysics Data System (ADS)

    Jiang, Peng; Zhu, Dong-Liang; Zhu, Chun-Nan; Zhang, Zhi-Ling; Zhang, Guo-Jun; Pang, Dai-Wen

    2015-11-01

    Metal chalcogenide semiconductor nanocrystals (NCs) are ideal inorganic materials for solar cells and biomedical labeling. In consideration of the hazard and instability of alkylphosphines, the phosphine-free synthetic route has become one of the most important trends in synthesizing selenide QDs. Here we report a novel phase transfer strategy to prepare phosphine-free chalcogenide precursors. The anions in aqueous solution were transferred to toluene via electrostatic interactions between the anions and didodecyldimethylammonium bromide (DDAB). The obtained chalcogenide precursors show high reactivity with metal ions in the organic phase and could be applied to the low-temperature synthesis of various metal chalcogenide NCs based on a simple reaction between metal ions (e.g. Ag+, Pb2+, Cd2+) and chalcogenide anions (e.g. S2-) in toluene. In addition to chalcogenide anions, other anions such as BH4- ions and AuCl4- ions can also be transferred to the organic phase for synthesizing noble metal NCs (such as Ag and Au NCs).Metal chalcogenide semiconductor nanocrystals (NCs) are ideal inorganic materials for solar cells and biomedical labeling. In consideration of the hazard and instability of alkylphosphines, the phosphine-free synthetic route has become one of the most important trends in synthesizing selenide QDs. Here we report a novel phase transfer strategy to prepare phosphine-free chalcogenide precursors. The anions in aqueous solution were transferred to toluene via electrostatic interactions between the anions and didodecyldimethylammonium bromide (DDAB). The obtained chalcogenide precursors show high reactivity with metal ions in the organic phase and could be applied to the low-temperature synthesis of various metal chalcogenide NCs based on a simple reaction between metal ions (e.g. Ag+, Pb2+, Cd2+) and chalcogenide anions (e.g. S2-) in toluene. In addition to chalcogenide anions, other anions such as BH4- ions and AuCl4- ions can also be transferred to the organic phase for synthesizing noble metal NCs (such as Ag and Au NCs). Electronic supplementary information (ESI) available: Experimental details and additional figures as described in the text. See DOI: 10.1039/c5nr05747g

  6. A highly reactive chalcogenide precursor for the synthesis of metal chalcogenide quantum dots.

    PubMed

    Jiang, Peng; Zhu, Dong-Liang; Zhu, Chun-Nan; Zhang, Zhi-Ling; Zhang, Guo-Jun; Pang, Dai-Wen

    2015-12-01

    Metal chalcogenide semiconductor nanocrystals (NCs) are ideal inorganic materials for solar cells and biomedical labeling. In consideration of the hazard and instability of alkylphosphines, the phosphine-free synthetic route has become one of the most important trends in synthesizing selenide QDs. Here we report a novel phase transfer strategy to prepare phosphine-free chalcogenide precursors. The anions in aqueous solution were transferred to toluene via electrostatic interactions between the anions and didodecyldimethylammonium bromide (DDAB). The obtained chalcogenide precursors show high reactivity with metal ions in the organic phase and could be applied to the low-temperature synthesis of various metal chalcogenide NCs based on a simple reaction between metal ions (e.g. Ag(+), Pb(2+), Cd(2+)) and chalcogenide anions (e.g. S(2-)) in toluene. In addition to chalcogenide anions, other anions such as BH4(-) ions and AuCl4(-) ions can also be transferred to the organic phase for synthesizing noble metal NCs (such as Ag and Au NCs). PMID:26531253

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

    NASA Astrophysics Data System (ADS)

    Coughlin, Kathleen M.

    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 TiO2 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.

  8. Electron transport through double quantum dots

    NASA Astrophysics Data System (ADS)

    van der Wiel, W. G.; de Franceschi, S.; Elzerman, J. M.; Fujisawa, T.; Tarucha, S.; Kouwenhoven, L. P.

    2002-12-01

    Electron transport experiments on two lateral quantum dots coupled in series are reviewed. An introduction to the charge stability diagram is given in terms of the electrochemical potentials of both dots. Resonant tunneling experiments show that the double dot geometry allows for an accurate determination of the intrinsic lifetime of discrete energy states in quantum dots. The evolution of discrete energy levels in magnetic field is studied. The resolution allows one to resolve avoided crossings in the spectrum of a quantum dot. With microwave spectroscopy it is possible to probe the transition from ionic bonding (for weak interdot tunnel coupling) to covalent bonding (for strong interdot tunnel coupling) in a double dot artificial molecule. This review is motivated by the relevance of double quantum dot studies for realizing solid state quantum bits.

  9. Quantitative multiplexed quantum dot immunohistochemistry

    SciTech Connect

    Sweeney, E.; Ward, T.H.; Gray, N.; Womack, C.; Jayson, G.; Hughes, A.; Dive, C.; Byers, R.

    2008-09-19

    Quantum dots are photostable fluorescent semiconductor nanocrystals possessing wide excitation and bright narrow, symmetrical, emission spectra. These characteristics have engendered considerable interest in their application in multiplex immunohistochemistry for biomarker quantification and co-localisation in clinical samples. Robust quantitation allows biomarker validation, and there is growing need for multiplex staining due to limited quantity of clinical samples. Most reported multiplexed quantum dot staining used sequential methods that are laborious and impractical in a high-throughput setting. Problems associated with sequential multiplex staining have been investigated and a method developed using QDs conjugated to biotinylated primary antibodies, enabling simultaneous multiplex staining with three antibodies. CD34, Cytokeratin 18 and cleaved Caspase 3 were triplexed in tonsillar tissue using an 8 h protocol, each localised to separate cellular compartments. This demonstrates utility of the method for biomarker measurement enabling rapid measurement of multiple co-localised biomarkers on single paraffin tissue sections, of importance for clinical trial studies.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  11. Lifetime blinking in nonblinking nanocrystal quantum dots

    PubMed Central

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

    2012-01-01

    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

  12. Electron counting in quantum dots

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

    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.

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

    SciTech Connect

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

    2014-02-14

    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.

  14. Synthetic Developments of Nontoxic Quantum Dots.

    PubMed

    Das, Adita; Snee, Preston T

    2016-03-01

    Semiconductor nanocrystals, or quantum dots (QDs), are candidates for biological sensing, photovoltaics, and catalysis due to their unique photophysical properties. The most studied QDs are composed of heavy metals like cadmium and lead. However, this engenders concerns over heavy metal toxicity. To address this issue, numerous studies have explored the development of nontoxic (or more accurately less toxic) quantum dots. In this Review, we select three major classes of nontoxic quantum dots composed of carbon, silicon and Group I-III-VI elements and discuss the myriad of synthetic strategies and surface modification methods to synthesize quantum dots composed of these material systems. PMID:26548450

  15. The quantum Hall effect in quantum dot systems

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

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

    SciTech Connect

    Klymenko, M. V.; Remacle, F.

    2014-10-28

    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.

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

    NASA Astrophysics Data System (ADS)

    Klymenko, M. V.; Remacle, F.

    2014-10-01

    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.

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

    PubMed Central

    2012-01-01

    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-μm 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 (η) 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

  19. Seed-mediated synthesis, properties and application of ?-Fe 2O 3-CdSe magnetic quantum dots

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

    Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around ?-Fe 2O 3 magnetic cores was performed at high temperature (300 C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells.

  20. Synthesis and characterization of zinc sulfide quantum dots and their interaction with snake gourd (Trichosanthes anguina) seed lectin.

    PubMed

    Ayaz Ahmed, Khan Behlol; Ahalya, Pichaikkannu; Sengan, Megarajan; Kamlekar, Ravikanth; Veerappan, Anbazhagan

    2015-12-01

    Owing to the use of quantum dots in biological labeling, and the specific interaction of lectins with tumor cells, studies on lectin-QDs interaction are of potential interest. Herein, we report a facile method to prepare zinc sulfide quantum dots (ZnS QDs) using pectin as a capping agent and studied their interaction with snake gourd seed lectin (SGSL) by fluorescence spectroscopy. The QDs were characterized by X-ray diffraction, high-resolution transmission electron microscopy, UV-Vis absorption and fluorescence spectroscopy. The thermodynamic forces governing the interaction between ZnS-QDs and SGSL have been delineated from the temperature dependent association constant. These results suggest that the binding between ZnS QDs and SGSL is governed by enthalpic forces with negative entropic contribution. The red shift of synchronous fluorescence spectra showed that the microenvironment around the tryptophan residues of SGSL was perturbed by ZnS-QDs. The obtained results suggest that the development of optical bioimaging agents by using the conjugated lectin-QDs would be possible to diagnose cancerous tissues. PMID:26172461

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

    PubMed

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

    2014-11-01

    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

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

    SciTech Connect

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

    2008-07-11

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

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

    PubMed

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

    2014-11-01

    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

  4. Photoluminescence of a quantum-dot molecule

    SciTech Connect

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

    2015-01-07

    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.

  5. Facile synthesis of N-rich carbon quantum dots by spontaneous polymerization and incision of solvents as efficient bioimaging probes and advanced electrocatalysts for oxygen reduction reaction.

    PubMed

    Lei, Zhouyue; Xu, Shengjie; Wan, Jiaxun; Wu, Peiyi

    2016-01-21

    In this study, uniform nitrogen-doped carbon quantum dots (N-CDs) were synthesized through a one-step solvothermal process of cyclic and nitrogen-rich solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethyl-imidazolidinone (DMEU), under mild conditions. The products exhibited strong light blue fluorescence, good cell permeability and low cytotoxicity. Moreover, after a facile post-thermal treatment, it developed a lotus seedpod surface-like structure of seed-like N-CDs decorating on the surface of carbon layers with a high proportion of quaternary nitrogen moieties that exhibited excellent electrocatalytic activity and long-term durability towards the oxygen reduction reaction (ORR). The peak potential was -160 mV, which was comparable to or even lower than commercial Pt/C catalysts. Therefore, this study provides an alternative facile approach to the synthesis of versatile carbon quantum dots (CDs) with widespread commercial application prospects, not only as bioimaging probes but also as promising electrocatalysts for the metal-free ORR. PMID:26739885

  6. Colloidal quantum dot photovoltaics: a path forward.

    PubMed

    Kramer, Illan J; Sargent, Edward H

    2011-11-22

    Colloidal quantum dots (CQDs) offer a path toward high-efficiency photovoltaics based on low-cost materials and processes. Spectral tunability via the quantum size effect facilitates absorption of specific wavelengths from across the sun's broad spectrum. CQD materials' ease of processing derives from their synthesis, storage, and processing in solution. Rapid advances have brought colloidal quantum dot photovoltaic solar power conversion efficiencies of 6% in the latest reports. These achievements represent important first steps toward commercially compelling performance. Here we review advances in device architecture and materials science. We diagnose the principal phenomenon-electronic states within the CQD film band gap that limit both current and voltage in devices-that must be cured for CQD PV devices to fulfill their promise. We close with a prescription, expressed as bounds on the density and energy of electronic states within the CQD film band gap, that should allow device efficiencies to rise to those required for the future of the solar energy field. PMID:21967723

  7. Silicon quantum dots: surface matters.

    PubMed

    Dohnalová, K; Gregorkiewicz, T; Kůsová, K

    2014-04-30

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

  8. A quantum dot in topological insulator nanofilm.

    PubMed

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

    2014-03-19

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

  9. Charge state hysteresis in semiconductor quantum dots

    SciTech Connect

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

    2014-11-03

    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.

  10. Imaging a single-electron quantum dot.

    PubMed

    Fallahi, Parisa; Bleszynski, Ania C; Westervelt, Robert M; Huang, Jian; Walls, Jamie D; Heller, Eric J; Hanson, Micah; Gossard, Arthur C

    2005-02-01

    Images of a single-electron quantum dot were obtained in the Coulomb blockade regime at liquid He temperatures using a cooled scanning probe microscope (SPM). The charged SPM tip shifts the lowest energy level in the dot and creates a ring in the image corresponding to a peak in the Coulomb-blockade conductance. Fits to the line shape of the ring determine the tip-induced shift of the energy of the electron state in the dot. SPM manipulation of electrons in quantum dots promises to be useful in understanding, building, and manipulating circuits for quantum information processing. PMID:15794600

  11. STED nanoscopy with fluorescent quantum dots

    PubMed Central

    Hanne, Janina; Falk, Henning J.; Görlitz, Frederik; Hoyer, Patrick; Engelhardt, Johann; Sahl, Steffen J.; Hell, Stefan W.

    2015-01-01

    The widely popular class of quantum-dot molecular labels could so far not be utilized as standard fluorescent probes in STED (stimulated emission depletion) nanoscopy. This is because broad quantum-dot excitation spectra extend deeply into the spectral bands used for STED, thus compromising the transient fluorescence silencing required for attaining super-resolution. Here we report the discovery that STED nanoscopy of several red-emitting commercially available quantum dots is in fact successfully realized by the increasingly popular 775 nm STED laser light. A resolution of presently ∼50 nm is demonstrated for single quantum dots, and sub-diffraction resolution is further shown for imaging of quantum-dot-labelled vimentin filaments in fibroblasts. The high quantum-dot photostability enables repeated STED recordings with >1,000 frames. In addition, we have evidence that the tendency of quantum-dot labels to blink is largely suppressed by combined action of excitation and STED beams. Quantum-dot STED significantly expands the realm of application of STED nanoscopy, and, given the high stability of these probes, holds promise for extended time-lapse imaging. PMID:25980788

  12. STED nanoscopy with fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Hanne, Janina; Falk, Henning J.; Görlitz, Frederik; Hoyer, Patrick; Engelhardt, Johann; Sahl, Steffen J.; Hell, Stefan W.

    2015-05-01

    The widely popular class of quantum-dot molecular labels could so far not be utilized as standard fluorescent probes in STED (stimulated emission depletion) nanoscopy. This is because broad quantum-dot excitation spectra extend deeply into the spectral bands used for STED, thus compromising the transient fluorescence silencing required for attaining super-resolution. Here we report the discovery that STED nanoscopy of several red-emitting commercially available quantum dots is in fact successfully realized by the increasingly popular 775 nm STED laser light. A resolution of presently ~50 nm is demonstrated for single quantum dots, and sub-diffraction resolution is further shown for imaging of quantum-dot-labelled vimentin filaments in fibroblasts. The high quantum-dot photostability enables repeated STED recordings with >1,000 frames. In addition, we have evidence that the tendency of quantum-dot labels to blink is largely suppressed by combined action of excitation and STED beams. Quantum-dot STED significantly expands the realm of application of STED nanoscopy, and, given the high stability of these probes, holds promise for extended time-lapse imaging.

  13. Thick-shell nanocrystal quantum dots

    DOEpatents

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

    2011-05-03

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

  14. Large-Scale and Controllable Synthesis of Graphene Quantum Dots from Rice Husk Biomass: A Comprehensive Utilization Strategy.

    PubMed

    Wang, Zhaofeng; Yu, Jingfang; Zhang, Xin; Li, Na; Liu, Bin; Li, Yanyan; Wang, Yuhua; Wang, Weixing; Li, Yezhou; Zhang, Lichun; Dissanayake, Shanka; Suib, Steven L; Sun, Luyi

    2016-01-20

    In this work, rice husk biomass was utilized as an abundant source to controllably prepare high-quality graphene quantum dots (GQDs) with a yield of ca. 15 wt %. The size, morphology, and structure of the rice-husk-derived GQDs were determined by high-resolution transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. The as-fabricated GQDs can be stably dispersed in water, exhibiting bright and tunable photoluminescence. A cell viability test further confirmed that the GQDs possess excellent biocompatibility, and they can be easily adopted for cell imaging via a facile translocation into the cytoplasm. It is worth noting that mesoporous silica nanoparticles were also synthesized as a byproduct during the fabrication of GQDs. As such, our strategy achieves a comprehensive utilization of rice husks, exhibiting tremendous benefits on both the economy and environment. PMID:26710249

  15. Synthesis of a Neutral Mixed-Valence Diferrocenyl Carborane for Molecular Quantum-Dot Cellular Automata Applications.

    PubMed

    Christie, John A; Forrest, Ryan P; Corcelli, Steven A; Wasio, Natalie A; Quardokus, Rebecca C; Brown, Ryan; Kandel, S Alex; Lu, Yuhui; Lent, Craig S; Henderson, Kenneth W

    2015-12-14

    The preparation of 7-Fc(+) -8-Fc-7,8-nido-[C2 B9 H10 ](-) (Fc(+) FcC2 B9 (-) ) demonstrates the successful incorporation of a carborane cage as an internal counteranion bridging between ferrocene and ferrocenium units. This neutral mixed-valence Fe(II) /Fe(III) complex overcomes the proximal electronic bias imposed by external counterions, a practical limitation in the use of molecular switches. A combination of UV/Vis-NIR spectroscopic and TD-DFT computational studies indicate that electron transfer within Fc(+) FcC2 B9 (-) is achieved through a bridge-mediated mechanism. This electronic framework therefore provides the possibility of an all-neutral null state, a key requirement for the implementation of quantum-dot cellular automata (QCA) molecular computing. The adhesion, ordering, and characterization of Fc(+) FcC2 B9 (-) on Au(111) has been observed by scanning tunneling microscopy. PMID:26516063

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

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Liu, Yingbo; Sun, Shuqing

    2013-10-01

    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.

  17. Biocompatible Quantum Dots for Biological Applications

    SciTech Connect

    Rosenthal, Sandra; Chang, Jerry; Kovtun, Oleg; McBride, James; Tomlinson, Ian

    2011-01-01

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

  18. Quantum-dot supercrystals for future nanophotonics

    PubMed Central

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

    2013-01-01

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

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

    PubMed

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

    2015-04-01

    The emerging graphene quantum dots (GQDs) and carbon dots (C-dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications. PMID:25521301

  20. Fluorescent carbon 'quantum' dots from thermochemical functionalization of carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Rednic, Monica I.; Lu, Zhuomin; Wang, Ping; LeCroy, Gregory E.; Yang, Fan; Liu, Yun; Qian, Haijun; Terec, Anamaria; Veca, L. Monica; Lu, Fushen; Sun, Ya-Ping

    2015-10-01

    Fluorescent carbon 'quantum' dots are generally obtained by deliberate chemical functionalization of carbon nanoparticles or by 'one-pot' carbonization processing. For brightly fluorescent carbon dots with optoelectronic polymers, a hybrid approach was developed to use pre-processed and selected carbon nanoparticles as precursor for surface passivation by poly(9-vinylcarbazole) (PVK) in one-pot thermochemical processing, thus taking advantage of the more controllable feature from the deliberate functionalization and also the versatility associated with the one-pot synthesis. The PVK-carbon dots were characterized by optical spectroscopy, microscopy, and other techniques. The broad applicability of the hybrid approach is discussed.

  1. Acid-free and oxone oxidant-assisted solvothermal synthesis of graphene quantum dots using various natural carbon materials as resources.

    PubMed

    Shin, Yonghun; Park, Jintaek; Hyun, Daesun; Yang, Junghee; Lee, Jae-Hyeok; Kim, Jae-Ho; Lee, Hyoyoung

    2015-03-19

    To prepare carbon-based fluorescent materials such as graphene quantum dots (GQDs), new and effective methods are needed to convert one-dimensional (1D) or two-dimensional (2D) carbon materials to 0D GQDs. Here, we report a novel acid-free and oxone oxidant-assisted solvothermal synthesis of GQDs using various natural carbon resources including graphite (G), multiwall carbon nanotubes (M), carbon fibers (CF), and charcoal (C). This acid-free method, not requiring the neutralization process of strong acids, exhibits a simple and eco-friendly purification process and also represents a recycling production process, together with mass production and high yield. Newly synthesized GQDs exhibited a strong blue photoluminescence (PL) under 365 nm UV light illumination. The PL emission peaks of all the recycled GQDs did not change. PMID:25757839

  2. Acid-free and oxone oxidant-assisted solvothermal synthesis of graphene quantum dots using various natural carbon materials as resources

    NASA Astrophysics Data System (ADS)

    Shin, Yonghun; Park, Jintaek; Hyun, Daesun; Yang, Junghee; Lee, Jae-Hyeok; Kim, Jae-Ho; Lee, Hyoyoung

    2015-03-01

    To prepare carbon-based fluorescent materials such as graphene quantum dots (GQDs), new and effective methods are needed to convert one-dimensional (1D) or two-dimensional (2D) carbon materials to 0D GQDs. Here, we report a novel acid-free and oxone oxidant-assisted solvothermal synthesis of GQDs using various natural carbon resources including graphite (G), multiwall carbon nanotubes (M), carbon fibers (CF), and charcoal (C). This acid-free method, not requiring the neutralization process of strong acids, exhibits a simple and eco-friendly purification process and also represents a recycling production process, together with mass production and high yield. Newly synthesized GQDs exhibited a strong blue photoluminescence (PL) under 365 nm UV light illumination. The PL emission peaks of all the recycled GQDs did not change.To prepare carbon-based fluorescent materials such as graphene quantum dots (GQDs), new and effective methods are needed to convert one-dimensional (1D) or two-dimensional (2D) carbon materials to 0D GQDs. Here, we report a novel acid-free and oxone oxidant-assisted solvothermal synthesis of GQDs using various natural carbon resources including graphite (G), multiwall carbon nanotubes (M), carbon fibers (CF), and charcoal (C). This acid-free method, not requiring the neutralization process of strong acids, exhibits a simple and eco-friendly purification process and also represents a recycling production process, together with mass production and high yield. Newly synthesized GQDs exhibited a strong blue photoluminescence (PL) under 365 nm UV light illumination. The PL emission peaks of all the recycled GQDs did not change. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00814j

  3. Spintronics with graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Droth, Matthias; Burkard, Guido

    2016-01-01

    Thanks to its intrinsic ability to preserve spin coherence, graphene is a prime material for spintronics. In this review article, we summarize recent achievements related to spintronics in graphene quantum dots and motivate this field from a spintronics and a materials science point of view. We focus on theory but also discuss recent experiments. The main sources of spin decoherence are interactions with lattice excitations and the hyperfine interaction with present nuclear spins. We explain effective spin-phonon coupling in detail and present a generic power law for the spin relaxation time T1 as a function of the magnetic field. For specific cases, we discuss spin relaxation in detail. The Heisenberg exchange interaction is paramount for coherent spin qubit operation and addressed in the context of magnetism in graphene nano flakes. Nuclear spins in the host and surrounding material can be considered by several means and the influence of 13C nuclei has been studied in detail. Impressive advances in general spintronics and the fabrication of graphene devices are likely to spark significant advances in spintronics with graphene quantum dots in the near future.

  4. Hydrothermal synthesis of highly luminescent blue-emitting ZnSe(S) quantum dots exhibiting low toxicity.

    PubMed

    Mirnajafizadeh, Fatemeh; Ramsey, Deborah; McAlpine, Shelli; Wang, Fan; Reece, Peter; Stride, John Arron

    2016-07-01

    Highly luminescent quantum dots (QDs) that emit in the visible spectrum are of interest to a number of imaging technologies, not least that of biological samples. One issue that hinders the application of luminescent markers in biology is the potential toxicity of the fluorophore. Here we show that hydrothermally synthesized ZnSe(S) QDs have low cytotoxicity to both human colorectal carcinoma cells (HCT-116) and human skin fibroblast cells (WS1). The QDs exhibited a high degree of crystallinity, with a strong blue photoluminescence at up to 29% quantum yield relative to 4',6-diamidino-2-phenylindole (DAPI) without post-synthetic UV-irradiation. Confocal microscopy images obtained of HCT-116 cells after incubation with the QDs highlighted the stability of the particles in cell media. Cytotoxicity studies showed that both HCT-116 and WS1 cells retain 100% viability after treatment with the QDs at concentrations up to 0.5g/L, which makes them of potential use in biological imaging applications. PMID:27127041

  5. Synthesis and characterization of novel molecularly imprinted polymer - coated Mn-doped ZnS quantum dots for specific fluorescent recognition of cocaine.

    PubMed

    Chantada-Vázquez, María Pilar; Sánchez-González, Juan; Peña-Vázquez, Elena; Tabernero, María Jesús; Bermejo, Ana María; Bermejo-Barrera, Pilar; Moreda-Piñeiro, Antonio

    2016-01-15

    Mn-doped ZnS quantum dots (QDs) coated with a molecularly imprinted polymer (MIP) material selective toward cocaine and its metabolites have been prepared and applied to cocaine (COC) and metabolites assessment by spectrofluorimetry. Ultrasound irradiation (37kHz) was novelty used for performing the Mn-doped ZnS QDs synthesis as well as for preparing the QD based MIP-coated composite by precipitation polymerization (imprinting process). This fact allowed the synthesis to be accomplished in four hours. In addition, the use of ultrasound irradiation during MIP-QDs synthesis increased the homogeneity of the QDs size, and reduced nanoparticles agglomeration. MIP was synthesized using COC as a template molecule, ethylene dimethacrylate (EDMA) as a functional monomer, divinylbenzene (DVB) as a cross-linker, and 2,2'-azobisisobutyronitrile (AIBN) as an initiator. The fluorescence of MIP-coated QDs was quenched by the template (COC) and also by metabolites from COC such as benzoylecgonine (BZE), and ecgonine methyl ester (EME). Quenching was not observed when performing experiments with non-imprinted polymer (NIP)-coated QDs; and also, fluorescence quenching of MIP-coated QDs was not observed by other drugs of abuse and metabolites (heroin and cannabis abuse). This fact indicates that the prepared material recognize only COC (template) and metabolites. PMID:26319164

  6. Quantum dots with single-atom precision.

    PubMed

    Flsch, Stefan; Martnez-Blanco, Jess; Yang, Jianshu; Kanisawa, Kiyoshi; Erwin, Steven C

    2014-07-01

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

  7. Quantum dots with single-atom precision

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    PubMed

    Stoica, Georgiana; Castell Serrano, Ivn; Figuerola, Albert; Ugarte, Irati; Pacios, Roberto; Palomares, Emilio

    2012-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Stoica, Georgiana; Castell Serrano, Ivn.; Palomares, Emilio

    2013-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Stoica, Georgiana; Castell Serrano, Ivn; Figuerola, Albert; Ugarte, Irati; Pacios, Roberto; Palomares, Emilio

    2012-08-01

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

  11. Semiconductor Fluorescent Quantum Dots: Efficient Biolabels in Cancer Diagnostics

    NASA Astrophysics Data System (ADS)

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

    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.

  12. Semiconductor fluorescent quantum dots: efficient biolabels in cancer diagnostics.

    PubMed

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

    2009-01-01

    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. PMID:19488715

  13. Charge transport and localization in atomically coherent quantum dot solids

    NASA Astrophysics Data System (ADS)

    Whitham, Kevin; Yang, Jun; Savitzky, Benjamin H.; Kourkoutis, Lena F.; Wise, Frank; Hanrath, Tobias

    2016-05-01

    Epitaxial attachment of quantum dots into ordered superlattices enables the synthesis of quasi-two-dimensional materials that theoretically exhibit features such as Dirac cones and topological states, and have major potential for unprecedented optoelectronic devices. Initial studies found that disorder in these structures causes localization of electrons within a few lattice constants, and highlight the critical need for precise structural characterization and systematic assessment of the effects of disorder on transport. Here we fabricated superlattices with the quantum dots registered to within a single atomic bond length (limited by the polydispersity of the quantum dot building blocks), but missing a fraction (20%) of the epitaxial connections. Calculations of the electronic structure including the measured disorder account for the electron localization inferred from transport measurements. The calculations also show that improvement of the epitaxial connections will lead to completely delocalized electrons and may enable the observation of the remarkable properties predicted for these materials.

  14. Charge transport and localization in atomically coherent quantum dot solids.

    PubMed

    Whitham, Kevin; Yang, Jun; Savitzky, Benjamin H; Kourkoutis, Lena F; Wise, Frank; Hanrath, Tobias

    2016-05-01

    Epitaxial attachment of quantum dots into ordered superlattices enables the synthesis of quasi-two-dimensional materials that theoretically exhibit features such as Dirac cones and topological states, and have major potential for unprecedented optoelectronic devices. Initial studies found that disorder in these structures causes localization of electrons within a few lattice constants, and highlight the critical need for precise structural characterization and systematic assessment of the effects of disorder on transport. Here we fabricated superlattices with the quantum dots registered to within a single atomic bond length (limited by the polydispersity of the quantum dot building blocks), but missing a fraction (20%) of the epitaxial connections. Calculations of the electronic structure including the measured disorder account for the electron localization inferred from transport measurements. The calculations also show that improvement of the epitaxial connections will lead to completely delocalized electrons and may enable the observation of the remarkable properties predicted for these materials. PMID:26901512

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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

  16. Spatially resolved photoluminescence spectroscopy of quantum dots

    NASA Astrophysics Data System (ADS)

    Dybiec, Maciej

    Recent advancements in nanotechnology create a need for a better understanding of the underlying physical processes that lead to the different behavior of nanoscale structures in comparison to bulk materials. The influence of the surrounding environment on the physical and optical properties of nanoscale objects embedded inside them is of particular interest. This research is focused on the optical properties of semiconductor quantum dots which are zero-dimensional nanostructures. There are many investigation techniques for measuring the local parameters and structural characteristics of Quantum Dot structures. They include X-ray diffraction, Transmission Electron Microscopy, Wavelength Dispersive Spectroscopy, etc. However, none of these is suitable for the study of large areas of quantum dots matrices and substrates. The existence of spatial inhomogeneity in the quantum dots allows for a deeper and better understanding of underlying physical processes responsible in particular for the observed changes in photoluminescence (PL) characteristics. Spectroscopic PL mapping can reveal areas of improved laser performance of InAs - InGaAs quantum dots structures. Establishing physical mechanisms responsible for two different types of spatial PL inhomogeneity in InAs/InGaAs quantum dots structures for laser applications was the first objective of this research. Most of the bio-applications of semiconductor quantum dots utilize their superior optical properties over organic fluorophores. Therefore, optimization of QD labeling performance with biomolecule attachment was another focus of this research. Semiconductor quantum dots suspended in liquids were investigated, especially the influence of surrounding molecules that may be attached or bio-conjugated to the quantum dots for specific use in biological reactions on the photoluminescence spectrum. Provision of underlying physical mechanisms of optical property instability of CdSe/ZnS quantum dots used for biological applications was in the scope of this research. Bio-conjugation and functionalization are the fundamental issues for bio-marker tagging application of semiconductor quantum dots. It was discovered that spatially resolved photoluminescence spectroscopy and PL photo-degradation kinetics can confirm the bio-conjugation. Development of a methodology that will allow the spectroscopic confirmation of bio-conjugation of quantum dot fluorescent tags and optimization of their performance was the final goal for this research project.

  17. Fluorescent Quantum Dots for Biological Labeling

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  18. Magnetic anisotropies of quantum dots

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    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).

  19. Quantum dots and prion proteins

    PubMed Central

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

    2013-01-01

    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

  20. Facile synthesis of N-rich carbon quantum dots by spontaneous polymerization and incision of solvents as efficient bioimaging probes and advanced electrocatalysts for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Lei, Zhouyue; Xu, Shengjie; Wan, Jiaxun; Wu, Peiyi

    2016-01-01

    In this study, uniform nitrogen-doped carbon quantum dots (N-CDs) were synthesized through a one-step solvothermal process of cyclic and nitrogen-rich solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethyl-imidazolidinone (DMEU), under mild conditions. The products exhibited strong light blue fluorescence, good cell permeability and low cytotoxicity. Moreover, after a facile post-thermal treatment, it developed a lotus seedpod surface-like structure of seed-like N-CDs decorating on the surface of carbon layers with a high proportion of quaternary nitrogen moieties that exhibited excellent electrocatalytic activity and long-term durability towards the oxygen reduction reaction (ORR). The peak potential was -160 mV, which was comparable to or even lower than commercial Pt/C catalysts. Therefore, this study provides an alternative facile approach to the synthesis of versatile carbon quantum dots (CDs) with widespread commercial application prospects, not only as bioimaging probes but also as promising electrocatalysts for the metal-free ORR.In this study, uniform nitrogen-doped carbon quantum dots (N-CDs) were synthesized through a one-step solvothermal process of cyclic and nitrogen-rich solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethyl-imidazolidinone (DMEU), under mild conditions. The products exhibited strong light blue fluorescence, good cell permeability and low cytotoxicity. Moreover, after a facile post-thermal treatment, it developed a lotus seedpod surface-like structure of seed-like N-CDs decorating on the surface of carbon layers with a high proportion of quaternary nitrogen moieties that exhibited excellent electrocatalytic activity and long-term durability towards the oxygen reduction reaction (ORR). The peak potential was -160 mV, which was comparable to or even lower than commercial Pt/C catalysts. Therefore, this study provides an alternative facile approach to the synthesis of versatile carbon quantum dots (CDs) with widespread commercial application prospects, not only as bioimaging probes but also as promising electrocatalysts for the metal-free ORR. Electronic supplementary information (ESI) available: Digital photographs of DMF, DMSO, DMEU, NMP after the solvothermal treatment, time-resolved AFM images of N-CDs, time-resolved FTIR spectra, XPS spectra and NMR spectrum of the N-CDs, time-resolved PL spectra of the N-CDs, cell viabilities of the N-CDs, XRD patterns of the N-CDs and the post-treated sample, CV curves of the N-CDs and Pt/C commercial catalysts, a summary of ORR performances of the CDs and other N-doped carbon materials, the electrochemical stability and methanol-tolerant ability of the post-treated N-CDs. See DOI: 10.1039/c5nr07335a

  1. Comparison of quantum confinement effects between quantum wires and dots

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2004-03-30

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

  2. Rapid microwave-assisted synthesis of molecularly imprinted polymers on carbon quantum dots for fluorescent sensing of tetracycline in milk.

    PubMed

    Hou, Juan; Li, Huiyu; Wang, Long; Zhang, Ping; Zhou, Tianyu; Ding, Hong; Ding, Lan

    2016-01-01

    In this paper, a novel, selective and eco-friendly sensor for the detection of tetracycline was developed by grafting imprinted polymers onto the surface of carbon quantum dots. A simple microwave-assisted approach was utilized to fabricate the fluorescent imprinted composites rapidly for the first time, which could shorten the polymerization time and simplify the experimental procedure dramatically. The novel composites not only demonstrated excellent fluorescence stability and special binding sites, but also could selectively accumulate target analytes. Under optimal conditions, the relative fluorescence intensity of the composites decreased linearly with increasing the concentration of tetracycline from 20 nM to 14 µM. The detection limit of tetracycline was 5.48 nM. The precision and reproducibility of the proposed sensor were also acceptable. Significantly, the practicality of this ultrasensitive sensor for tetracycline detection in milk was further validated, revealing the advantages of simplicity, sensitivity, selectivity and low cost. This approach combines the high selective adsorption property of molecular imprinted polymers and the sensitivity of fluorescence detection. It is envisioned that the development of fluorescent molecularly imprinted composites will offer a new way of thinking for rapid analysis in complex samples. PMID:26695231

  3. Controlled synthesis of Eu2+ and Eu3+ doped ZnS quantum dots and their photovoltaic and magnetic properties

    NASA Astrophysics Data System (ADS)

    Horoz, Sabit; Yakami, Baichhabi; Poudyal, Uma; Pikal, Jon M.; Wang, Wenyong; Tang, Jinke

    2016-04-01

    Eu-doped ZnS quantum dots (QDs) have been synthesized by wet-chemical method and found to form in zinc blende (cubic) structure. Both Eu2+ and Eu3+ doped ZnS can be controllably synthesized. The Eu2+ doped ZnS QDs show broad photoluminescence emission peak around 512 nm, which is from the Eu2+ intra-ion transition of 4f6d1 - 4f7, while the Eu3+ doped samples exhibit narrow emission lines characteristic of transitions between the 4f levels. The investigation of the magnetic properties shows that the Eu3+ doped samples exhibit signs of ferromagnetism, on the other hand, Eu2+ doped samples are paramagnetic of Curie-Weiss type. The incident photon to electron conversion efficiency is increased with the Eu doping, which suggests the QD solar cell efficiency can be enhanced by Eu doping due to widened absorption windows. This is an attractive approach to utilize benign and environmentally friendly wide band gap ZnS QDs in solar cell technology.

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

    PubMed

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

    2014-11-01

    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

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

    SciTech Connect

    Zhu, Huaping; Hu, Michael Z.; Shao, Lei; Yu, Kui; Dabestani, Reza T; Zaman, Md. Badruz; Liao, Dr. Shijun

    2014-03-20

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

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

    PubMed

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

    2013-11-21

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

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

    PubMed

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

    2014-05-01

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

  8. Synthesis and formation mechanistic investigation of nitrogen-doped carbon dots with high quantum yields and yellowish-green fluorescence.

    PubMed

    Hou, Juan; Wang, Wei; Zhou, Tianyu; Wang, Bo; Li, Huiyu; Ding, Lan

    2016-06-01

    Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A possible formation mechanism has thus been proposed including dehydration, polymerization and carbonization. Furthermore, the N-CDs could serve as a facile and label-free probe for the detection of iron and fluorine ions with detection limits of 50 nmol L(-1) and 75 nmol L(-1), respectively. PMID:27180833

  9. Understanding electronic systems in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Ciftja, Orion

    2013-11-01

    Systems of confined electrons are found everywhere in nature in the form of atoms where the orbiting electrons are confined by the Coulomb attraction of the nucleus. Advancement of nanotechnology has, however, provided us with an alternative way to confine electrons by using artificial confining potentials. A typical structure of this nature is the quantum dot, a nanoscale system which consists of few confined electrons. There are many types of quantum dots ranging from self-assembled to miniaturized semiconductor quantum dots. In this work we are interested in electrostatically confined semiconductor quantum dot systems where the electrostatic confining potential that traps the electrons is generated by external electrodes, doping, strain or other factors. A large number of semiconductor quantum dots of this type are fabricated by applying lithographically patterned gate electrodes or by etching on two-dimensional electron gases in semiconductor heterostructures. Because of this, the whole structure can be treated as a confined two-dimensional electron system. Quantum confinement profoundly affects the way in which electrons interact with each other, and external parameters such as a magnetic field. Since a magnetic field affects both the orbital and the spin motion of the electrons, the interplay between quantum confinement, electron-electron correlation effects and the magnetic field gives rise to very interesting physical phenomena. Thus, confined systems of electrons in a semiconductor quantum dot represent a unique opportunity to study fundamental quantum theories in a controllable atomic-like setup. In this work, we describe some common theoretical models which are used to study confined systems of electrons in a two-dimensional semiconductor quantum dot. The main emphasis of the work is to draw attention to important physical phenomena that arise in confined two-dimensional electron systems under various quantum regimes.

  10. Single to quadruple quantum dots with tunable tunnel couplings

    SciTech Connect

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

    2014-03-17

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

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

    PubMed

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

    2013-01-01

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

  12. Ag2Te quantum dots with compact surface coatings of multivalent polymers: ambient one-pot aqueous synthesis and the second near-infrared bioimaging.

    PubMed

    Yang, Min; Gui, Rijun; Jin, Hui; Wang, Zonghua; Zhang, Feifei; Xia, Jianfei; Bi, Sai; Xia, Yanzhi

    2015-02-01

    In this study, we described a facile ambient one-pot aqueous synthesis of fluorescent Ag2Te quantum dots (QDs) adopting multivalent polymers (poly(maleic anhydride) homopolymers) as stabilizers. In experiments, Ag2Te QDs were synthesized via a stepwise addition of the stabilizers, precursors (AgNO3/Na2TeO3) and promoters (NaBH4/N2H4 · H2O) in ambient one-pot aqueous solution. By regulating the compositions of raw materials, water-dispersed Ag2Te QDs (3.8-4.7 nm) were achieved and exhibited tunable photoluminescence (PL) emission (995-1068 nm) in the second near-infrared (NIR-II) region, accompanying with the minimized surface coating thickness (1.5-1.9 nm). Such compact coating of multivalent polymers promoted PL emission of Ag2Te QDs, so showing high PL quantum yields (PLQYs: 13.1-15.2%). In addition to compact sizes and high PLQYs, experimental results testified that the Ag2Te QDs demonstrated high photo-/colloidal stability and ultralow cytotoxicity, which implied their promising applications, especially serving as an effective nanoprobe for bioimaging in the NIR-II biological window. PMID:25546835

  13. Nanomaterials: Earthworms lit with quantum dots

    NASA Astrophysics Data System (ADS)

    Tilley, Richard D.; Cheong, Soshan

    2013-01-01

    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.

  14. Submonolayer Quantum Dot Infrared Photodetector

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  15. First principle thousand atom quantum dot calculations

    SciTech Connect

    Wang, Lin-Wang; Li, Jingbo

    2004-03-30

    A charge patching method and an idealized surface passivation are used to calculate the single electronic states of IV-IV, III-V, II-VI semiconductor quantum dots up to a thousand atoms. This approach scales linearly and has a 1000 fold speed-up compared to direct first principle methods with a cost of eigen energy error of about 20 meV. The calculated quantum dot band gaps are parametrized for future references.

  16. Renormalization in Periodically Driven Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eissing, A. K.; Meden, V.; Kennes, D. M.

    2016-01-01

    We report on strong renormalization encountered in periodically driven interacting quantum dots in the nonadiabatic regime. Correlations between lead and dot electrons enhance or suppress the amplitude of driving depending on the sign of the interaction. Employing a newly developed flexible renormalization-group-based approach for periodic driving to an interacting resonant level we show analytically that the magnitude of this effect follows a power law. Our setup can act as a non-Markovian, single-parameter quantum pump.

  17. Renormalization in Periodically Driven Quantum Dots.

    PubMed

    Eissing, A K; Meden, V; Kennes, D M

    2016-01-15

    We report on strong renormalization encountered in periodically driven interacting quantum dots in the nonadiabatic regime. Correlations between lead and dot electrons enhance or suppress the amplitude of driving depending on the sign of the interaction. Employing a newly developed flexible renormalization-group-based approach for periodic driving to an interacting resonant level we show analytically that the magnitude of this effect follows a power law. Our setup can act as a non-Markovian, single-parameter quantum pump. PMID:26824557

  18. Final Progress Report for Project Entitled: Quantum Dot Tracers for Use in Engineered Geothermal Systems

    SciTech Connect

    Rose, Peter; Bartl, Michael; Reimus, Paul; Williams, Mark; Mella, Mike

    2015-09-12

    The objective of this project was to develop and demonstrate a new class of tracers that offer great promise for use in characterizing fracture networks in EGS reservoirs. From laboratory synthesis and testing through numerical modeling and field demonstrations, we have demonstrated the amazing versatility and applicability of quantum dot tracers. This report summarizes the results of four years of research into the design, synthesis, and characterization of semiconductor nanocrystals (quantum dots) for use as geothermal tracers.

  19. Quantum Dots in Gated Nanowires and Nanotubes

    NASA Astrophysics Data System (ADS)

    Churchill, Hugh Olen Hill

    This thesis describes experiments on quantum dots made by locally gating one-dimensional quantum wires. The first experiment studies a double quantum dot device formed in a Ge/Si core/shell nanowire. In addition to measuring transport through the double dot, we detect changes in the charge occupancy of the double dot by capacitively coupling it to a third quantum dot on a separate nanowire using a floating gate. We demonstrate tunable tunnel coupling of the double dot and quantify the strength of the tunneling using the charge sensor. The second set of experiments concerns carbon nanotube double quantum dots. In the first nanotube experiment, spin-dependent transport through the double dot is compared in two sets of devices. The first set is made with carbon containing the natural abundance of 12C (99%) and 13C (1%), the second set with the 99% 13C and 1% 12C. In the devices with predominantly 13C, we find evidence in spin-dependent transport of the interaction between the electron spins and the 13C nuclear spins that was much stronger than expected and not present in the 12C devices. In the second nanotube experiment, pulsed gate experiments are used to measure the timescales of spin relaxation and dephasing in a two-electron double quantum dot. The relaxation time is longest at zero magnetic field and goes through a minimum at higher field, consistent with the spin-orbit-modified electronic spectrum of carbon nanotubes. We measure a short dephasing time consistent with the anomalously strong electron-nuclear interaction inferred from the first nanotube experiment.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

    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.

  1. Metamorphic quantum dots: Quite different nanostructures

    SciTech Connect

    Seravalli, L.; Frigeri, P.; Nasi, L.; Trevisi, G.; Bocchi, C.

    2010-09-15

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

  2. Quantum-dot-in-perovskite solids.

    PubMed

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H

    2015-07-16

    Heteroepitaxy-atomically aligned growth of a crystalline film atop a different crystalline substrate-is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned 'dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics. PMID:26178963

  3. Quantum-dot-in-perovskite solids

    NASA Astrophysics Data System (ADS)

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H.

    2015-07-01

    Heteroepitaxy--atomically aligned growth of a crystalline film atop a different crystalline substrate--is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned `dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  4. Spectroscopy characterization and quantum yield determination of quantum dots

    NASA Astrophysics Data System (ADS)

    Contreras Ortiz, S. N.; Mejía Ospino, E.; Cabanzo, R.

    2016-02-01

    In this paper we show the characterization of two kinds of quantum dots: hydrophilic and hydrophobic, with core and core/shell respectively, using spectroscopy techniques such as UV-Vis, fluorescence and Raman. We determined the quantum yield in the quantum dots using the quinine sulphate as standard. This salt is commonly used because of its quantum yield (56%) and stability. For the CdTe excitation, we used a wavelength of 549nm and for the CdSe/ZnS excitation a wavelength of 527nm. The results show that CdSe/ZnS (49%) has better fluorescence, better quantum dots, and confirm the fluorescence result. The quantum dots have shown a good fluorescence performance, so this property will be used to replace dyes, with the advantage that quantum dots are less toxic than some dyes like the rhodamine. In addition, in this work we show different techniques to find the quantum dots emission: fluorescence spectrum, synchronous spectrum and Raman spectrum.

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

    SciTech Connect

    Bouravleuv, Alexei; Sapega, Victor; Nevedomskii, Vladimir; Khrebtov, Artem; Samsonenko, Yuriy; Cirlin, George

    2014-12-08

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

  6. Optically controlled spins in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Economou, Sophia

    2010-03-01

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

  7. Quantum Dots for quantitative flow cytometry

    PubMed Central

    Buranda, Tione; Wu, Yang; Sklar, Larry A.

    2014-01-01

    Summary In flow cytometry, the quantitation of fluorophore-tagged ligands and receptors on cells or at particulate surfaces is achieved by the use of standard beads of known calibration. To the best of our knowledge, only those calibration beads based on fluorescein, EGFP, phycoerythyrin and allophycocyanine are readily available from commercial sources. Because fluorophore based standards are specific to the selected fluorophore tag, their applicability is limited to the spectral region of resonance. Since quantum dots can be photo-excited over a continuous and broad spectral range governed by their size, it is possible to match the spectral range and width (absorbance and emission) of a wide range of fluorophores with appropriate quantum dots. Accordingly, quantitation of site coverage of the target fluorophores can be readily achieved using quantum dots whose emission spectra overlaps with the target fluorophore. This chapter will focus on the relevant spectroscopic concepts and molecular assembly of quantum dot fluorescence calibration beads. We will first examine the measurement and applicability of spectroscopic parameters, ε, φ, and %T to fluorescence calibration standards. Where, ε is the absorption coefficient of the fluorophore, φ is the quantum yield of the fluorophore and %T is the percent fraction of emitted light that is transmitted by the bandpass filter at the detector PMT. The modular construction of beads decorated with discrete quantities of quantum dots with defined spectroscopic parameters is presented in the context of a generalizable approach to calibrated measurements of fluorescence in flow cytometry. PMID:21116979

  8. Colloidal quantum dot materials for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Arinze, Ebuka S.; Nyirjesy, Gabrielle; Cheng, Yan; Palmquist, Nathan; Thon, Susanna M.

    2015-09-01

    Colloidal quantum dots (CQDs) are an attractive material for optoelectronic applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Specifically, the bandgap of films composed of arrays of CQDs can be tuned via the quantum confinement effect for tailored spectral utilization. PbS-based CQDs can be tuned throughout the near and mid-infrared wavelengths and are a promising materials system for photovoltaic devices that harvest non-visible solar radiation. The performance of CQD solar cells is currently limited by an absorption-extraction compromise, whereby photon absorption lengths in the near infrared spectral regime exceed minority carrier diffusion lengths in the bulk films. Several light trapping strategies for overcoming this compromise and increasing the efficiency of infrared energy harvesting will be reviewed. A thin-film interference technique for creating multi-colored and transparent solar cells will be presented, and a discussion of designing plasmonic nanomaterials based on earth-abundant materials for integration into CQD solar cells is developed. The results indicate that it should be possible to achieve high absorption and color-tunability in a scalable nanomaterials system.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  10. Quantum Dot Single-Photon Sources

    NASA Astrophysics Data System (ADS)

    Michler, Peter

    In this contribution, we briefly recall basic concepts of quantum optics and semiconductor quantum-dot physics which are necessary to understand the physics of single-photon generation with single quantum dots. The classification of light states and the photon statistics as well as the electronic and optical properties of the quantum dots are discussed. We then review the recent progress on extending the wavelength range and show how polarization control and high repetition rates have been realized. New generations of electrically driven single-photon LEDs lead to ultralow pump currents, high repetition rates, high collection efficiencies, and elevated temperature operation. Furthermore, new developments on coherent state preparation and single photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for practical single-photon sources are also discussed.

  11. Dot-in-Well Quantum-Dot Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Wu, Jiang; Chen, Siming; Seeds, Alwyn; Liu, Huiyun

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

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

    PubMed

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

    2014-09-01

    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

  17. Highly photoluminescent MoOx quantum dots: Facile synthesis and application in off-on Pi sensing in lake water samples.

    PubMed

    Xiao, Sai Jin; Zhao, Xiao Jing; Zuo, Jun; Huang, Hai Qing; Zhang, Li

    2016-02-01

    Molybdenum oxide (MoOx) is a well-studied transition-metal semiconductor material, and has a wider band gap than MoS2 which makes it become a promising versatile probe in a variety of fields, such as gas sensor, catalysis, energy storage ect. However, few MoOx nanomaterials possessing photoluminescence have been reported until now, not to mention the application as photoluminescent probes. Herein, a one-pot method is developed for facile synthesis of highly photoluminescent MoOx quantum dots (MoOx QDs) in which commercial molybdenum disulfide powder and hydrogen peroxide (H2O2) are involved as the precursor and oxidant, respectively. Compared with current synthesis methods, the proposed one has the advantages of rapid, one-pot, easily prepared, environment friendly as well as strong photoluminescence. The obtained MoOx QDs is further utilized as an efficient photoluminescent probe, and a new off-on sensor has been constructed for phosphate (Pi) determination in complicated lake water samples, attributed to the fact that the binding affinity of Eu(3+) ions to the oxygen atoms from Pi is much higher than that from the surface of MoOx QDs. Under the optimal conditions, a good linear relationship was found between the enhanced photoluminescence intensity and Pi concentration in the range of 0.1-160.0 μM with the detection limit of 56 nM (3σ/k). The first application of the photoluminescent MoOx nanomaterials for ion photochemical sensing will open the gate of employing MoOx nanomaterials as versatile probes in a variety of fields, such as chemi-/bio-sensor, cell imaging, biomedical and so on. PMID:26772134

  18. Quantum efficiency of a double quantum dot microwave photon detector

    NASA Astrophysics Data System (ADS)

    Wong, Clement; Vavilov, Maxim

    Motivated by recent interest in implementing circuit quantum electrodynamics with semiconducting quantum dots, we study charge transfer through a double quantum dot (DQD) capacitively coupled to a superconducting cavity subject to a microwave field. We analyze the DQD current response using input-output theory and determine the optimal parameter regime for complete absorption of radiation and efficient conversion of microwave photons to electric current. For experimentally available DQD systems, we show that the cavity-coupled DQD operates as a photon-to-charge converter with quantum efficiencies up to 80% C.W. acknowledges support by the Intelligence Community Postdoctoral Research Fellowship Program.

  19. Imaging a coupled quantum dot-quantum point contact system

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

    We have quantitatively studied the effect of charge traps on the electrical conductance of a quantum dot and a capacitively coupled quantum point contact. Using the sharp metallic tip of a low-temperature scanning force microscope as a scanned gate, we could localize the traps. The quantum point contact served as a charge detector and allowed us to distinguish single electron charging events in several traps from charging events on the dot. We used the quantum dot to analyze the tip-induced potential quantitatively and found its shape to be independent of the voltage applied to the tip within a certain range of parameters. We estimate that the trap density is below 0.1% of the doping density, that the charging energy of a trap is three times higher than that of the quantum dot, and that the interaction energy between the quantum dot and a trap is a significant portion of the dot's charging energy. Possibly, such charge traps are the reason for frequently observed parametric charge rearrangements.

  20. Energy transfer from CdSe quantum dots to graphene

    NASA Astrophysics Data System (ADS)

    Liao, Chunyan; Zhu, Xiuhong

    2013-12-01

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

  1. Surface treatment of nanocrystal quantum dots after film deposition

    DOEpatents

    Sykora, Milan; Koposov, Alexey; Fuke, Nobuhiro

    2015-02-03

    Provided are methods of surface treatment of nanocrystal quantum dots after film deposition so as to exchange the native ligands of the quantum dots for exchange ligands that result in improvement in charge extraction from the nanocrystals.

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

    PubMed

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

    2015-01-31

    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

  3. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    DOEpatents

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

    2014-08-26

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

  4. Three-terminal quantum-dot refrigerators

    NASA Astrophysics Data System (ADS)

    Zhang, Yanchao; Lin, Guoxing; Chen, Jincan

    2015-05-01

    Based on two capacitively coupled quantum dots in the Coulomb-blockade regime, a model of three-terminal quantum-dot refrigerators is proposed. With the help of the master equation, the transport properties of steady-state charge current and energy flow between two quantum dots and thermal reservoirs are revealed. It is expounded that such a structure can be used to construct a refrigerator by controlling the voltage bias and temperature ratio. The thermodynamic performance characteristics of the refrigerator are analyzed, including the cooling power, coefficient of performance (COP), maximum cooling power, and maximum COP. Moreover, the optimal regions of main performance parameters are determined. The influence of dissipative tunnel processes on the optimal performance is discussed in detail. Finally, the performance characteristics of the refrigerators operated in two different cases are compared.

  5. Three-terminal quantum-dot refrigerators.

    PubMed

    Zhang, Yanchao; Lin, Guoxing; Chen, Jincan

    2015-05-01

    Based on two capacitively coupled quantum dots in the Coulomb-blockade regime, a model of three-terminal quantum-dot refrigerators is proposed. With the help of the master equation, the transport properties of steady-state charge current and energy flow between two quantum dots and thermal reservoirs are revealed. It is expounded that such a structure can be used to construct a refrigerator by controlling the voltage bias and temperature ratio. The thermodynamic performance characteristics of the refrigerator are analyzed, including the cooling power, coefficient of performance (COP), maximum cooling power, and maximum COP. Moreover, the optimal regions of main performance parameters are determined. The influence of dissipative tunnel processes on the optimal performance is discussed in detail. Finally, the performance characteristics of the refrigerators operated in two different cases are compared. PMID:26066130

  6. Quantum and semiclassical study of magnetic quantum dots

    NASA Astrophysics Data System (ADS)

    Kocsis, Bence; Palla, Gergely; Cserti, József

    2005-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Ihly, Rachelle

    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.

  8. Quantum well and quantum dot energy harvesting devices

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    Quantum structured solar cells seek to harness a wide spectrum of photons at high voltages by embedding low energy-gap wells or dots within a high energy-gap matrix. Quantum well and quantum dot solar cells have the potential to deliver ultra-high power conversion efficiencies in single junction devices, efficiencies that in theory can approach 45% in un-concentrated sunlight over a wide range of environmental conditions. In this paper, we will briefly review the theoretical underpinnings of quantum well and quantum dot photovoltaic devices, and summarize recent experimental efforts developing quantum-structured solar cell devices. In a specific example, test devices utilizing radiation-hard, III-V nitride materials have been built using both bulk and multiple quantum well (MQW) structures. Photovoltaic devices with an InGaN MQW structure are shown to outperform devices employing a thicker, bulk InGaN layer. These results, along with the underlying theoretical foundations, suggest that quantum well and quantum dot structures can enhance the performance of photovoltaic devices for a variety of defense applications.

  9. Ambipolar quantum dots in intrinsic silicon

    SciTech Connect

    Betz, A. C. Gonzalez-Zalba, M. F.; Podd, G.; Ferguson, A. J.

    2014-10-13

    We electrically measure intrinsic silicon quantum dots with electrostatically defined tunnel barriers. The presence of both p- and n-type ohmic contacts enables the accumulation of either electrons or holes. Thus, we are able to study both transport regimes within the same device. We investigate the effect of the tunnel barriers and the electrostatically defined quantum dots. There is greater localisation of charge states under the tunnel barriers in the case of hole conduction, leading to higher charge noise in the p-type regime.

  10. Bilayer graphene quantum dot defined by topgates

    SciTech Connect

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

    2014-06-21

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

  11. CNT Quantum dots as Terahertz detectors

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    We study Carbon Nanotube (CNT) quantum dots as detectors of THz radiation via photon assisted single electron tunneling. Although successful detection was recently demonstrated, the coupling between the CNT and THz radiations was very weak. Here, we implement a novel device design where the radiation is effectively coupled to the CNT quantum dot through broad band on-chip antennas. We show that the enhanced coupling yields a highly sensitive broad band Terahertz sensor. Funded by Airforce office of Scientific Research, Grant #FA9550-09-1-0697.

  12. Bright quantum-dot-sized single-chain conjugated polyelectrolyte nanoparticles: synthesis, characterization and application for specific extracellular labeling and imaging.

    PubMed

    Liu, Jie; Feng, Guangxue; Liu, Rongrong; Tomczak, Nikodem; Ma, Lin; Gurzadyan, Gagik G; Liu, Bin

    2014-08-13

    We report a simple method to fabricate quantum-dot-sized nanoparticles (NPs) from poly[9,9-bis((6-N,N,N-trimethylammonium)hexyl)fluorene-alt-co-2,1,3-benzo-xadiazole dibromide] (PFBD). The transmission electron microscope results reveal that the obtained NPs have a mean diameter of ?4 nm, which is composed of a single PFBD chain. The NPs show bright fluorescence with an emission maximum at ?636 nm and a quantum yield of ?26% in water. The fluorescence properties of the NPs are characterized by steady fluorescence microscopy, fluorescence dynamic study and single nanoparticle microscopy, which show superior brightness over commercial quantum dots QD655. The NPs are further conjugated with streptavidin to yield PFBD-SA NPs, which serve as a specific extracellular labeling and imaging probe with high specificity and good photostability. PMID:24729391

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

    PubMed

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

    2013-02-01

    CdSe Quantum dots (Q-dots) and CdSe/ZnS core/shell have been synthesized by wet chemical route using mercaptoethanol (ME) as cappant. The synthesized Q-dots and core/shell were characterized using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDS), Dynamic Light Scattering (DLS), Optical absorption and luminescence spectroscopy. The core/shell formation was confirmed by both XRD and TEM analysis. The luminescence was shown to be considerably enhanced in the core/shell sample. Effect of dialysis process on the optical properties of the Q-dots and core/shell has also been discussed. Cytotoxicity studies have been carried out for Q-dots and core/shell. CdSe/ZnS core/shell was found to be non-cytotoxic as compared to CdSe Q-dots up to a certain concentration range. Polyethylene glycol (PEG) coating enhances the non-cytotoxic nature of CdSe/ZnS core/shell when compared with bare core/shell. PMID:23627052

  14. Resonance fluorescence and cavity quantum electrodynamics with quantum dots

    NASA Astrophysics Data System (ADS)

    Muller, Andreas

    2007-05-01

    Next-generation information technology is expected to rely on discrete two-state quantum systems that can deterministically emit single photons. Quantum dots are mesoscopic (10,000 atoms large) semiconductor islands grown in a host crystal of larger band-gap that make well-defined two-level quantum systems and are very attractive due to stability, record coherence times, and the possibility of integrating them into larger structures, such as optical microcavities. This work presents experimental progress towards understanding the coherent optical processes that occur in single quantum dots, particularly such phenomena that might be one day utilized for quantum communication applications. High resolution low temperature optical spectroscopy is used in conjunction with first order (amplitude) and second-order (intensity) correlation measurements of the emitted field. A novel technique is introduced that is capable of harvesting the fluorescence of single dots at the same frequency as the laser, previously impossible due to insurmountable scattering. This technique enables the observation, for the first time, of single quantum dot resonance fluorescence, in both the weak and strong excitation regimes, which forms the basis for deterministic generation of single photons. Guided by the rich theoretical description available from quantum optics with atoms we obtain insight into the complex dynamics of this driven system. Quantum dots confined to novel optical microcavities were further investigated using micro photoluminescence. An optical microcavity properly coupled to a two-level system can profoundly modify its emission characteristics via quantum electrodynamical effects, which are highly attractive for single photon sources. The all-epitaxial structures we probe are distinguished by a bulk morphology that overcomes the fragility problems of existing approaches, and provides high quality factors as well as small mode volumes. Lasing is obtained with larger structures. Additionally, isolation of individual dots is further realized in smaller cavities and the Purcell effect observed in time-resolved photon counting experiments.

  15. Doping silicon nanocrystals and quantum dots

    NASA Astrophysics Data System (ADS)

    Oliva-Chatelain, Brittany L.; Ticich, Thomas M.; Barron, Andrew R.

    2016-01-01

    The ability to incorporate a dopant element into silicon nanocrystals (NC) and quantum dots (QD) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications. Unlike doping of traditional bulk semiconductor materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping) or within the surrounding matrix (m-doping). A review of the various synthetic strategies for doping silicon NCs and QDs is presented, concentrating on the efficacy of the synthetic routes, both in situ and post synthesis, with regard to the structural location of the dopant and the doping level. Methods that have been applied to the characterization of doped NCs and QDs are summarized with regard to the information that is obtained, in particular to provide researchers with a guide to the suitable techniques for determining dopant concentration and location, as well as electronic and photonic effectiveness of the dopant.

  16. Photodynamic antibacterial effect of graphene quantum dots.

    PubMed

    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

    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

  17. Quantum Optical Signature of Plasmonically Coupled Nanocrystal Quantum Dots.

    PubMed

    Wang, Feng; Karan, Niladri S; Nguyen, Hue Minh; Mangum, Benjamin D; Ghosh, Yagnaseni; Sheehan, Chris J; Hollingsworth, Jennifer A; Htoon, Han

    2015-10-01

    Small clusters of two to three silica-coated nanocrystals coupled to plasmonic gap-bar antennas can exhibit photon antibunching, a characteristic of single quantum emitters. Through a detailed analysis of their photoluminescence emissions characteristics, it is shown that the observed photon antibunching is the evidence of coupled quantum dot formation resulting from the plasmonic enhancement of dipole-dipole interaction. PMID:26140499

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

    NASA Astrophysics Data System (ADS)

    Kushwaha, Manvir S.

    2014-12-01

    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.

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

    SciTech Connect

    Kushwaha, Manvir S.

    2014-12-15

    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.

  20. Biomedical and biological applications of quantum dots.

    PubMed

    Abbasi, Elham; Kafshdooz, Tayebeh; Bakhtiary, Mohsen; Nikzamir, Nasrin; Nikzamir, Nasim; Nikzamir, Mohammad; Mohammadian, Mozhdeh; Akbarzadeh, Abolfazl

    2016-05-01

    Quantum dots (QDs) as colloidal nanocrystalline semiconductors have exceptional photophysical properties, due to their quantum confinement effects. Depending on their sizes and chemical compositions, QDs emit different wavelengths over a broad range of the light spectrum, from visible to infrared. QDs are typically extensively used for optical applications due to their high extinction coefficient. This article reviews biomedical applications of QDs, especially the application of QDs in cell targeting, delivery, diagnostics, cancer therapy, and imaging for cancer research. PMID:25615877

  1. Adiabatic description of nonspherical quantum dot models

    SciTech Connect

    Gusev, A. A. Chuluunbaatar, O.; Vinitsky, S. I.; Dvoyan, K. G.; Kazaryan, E. M.; Sarkisyan, H. A.; Derbov, V. L.; Klombotskaya, A. S.; Serov, V. V.

    2012-10-15

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

  2. Silicon based quantum dot hybrid qubits

    NASA Astrophysics Data System (ADS)

    Kim, Dohun

    2015-03-01

    The charge and spin degrees of freedom of an electron constitute natural bases for constructing quantum two level systems, or qubits, in semiconductor quantum dots. The quantum dot charge qubit offers a simple architecture and high-speed operation, but generally suffers from fast dephasing due to strong coupling of the environment to the electron's charge. On the other hand, quantum dot spin qubits have demonstrated long coherence times, but their manipulation is often slower than desired for important future applications. This talk will present experimental progress of a `hybrid' qubit, formed by three electrons in a Si/SiGe double quantum dot, which combines desirable characteristics (speed and coherence) in the past found separately in qubits based on either charge or spin degrees of freedom. Using resonant microwaves, we first discuss qubit operations near the `sweet spot' for charge qubit operation. Along with fast (>GHz) manipulation rates for any rotation axis on the Bloch sphere, we implement two independent tomographic characterization schemes in the charge qubit regime: traditional quantum process tomography (QPT) and gate set tomography (GST). We also present resonant qubit operations of the hybrid qubit performed on the same device, DC pulsed gate operations of which were recently demonstrated. We demonstrate three-axis control and the implementation of dynamic decoupling pulse sequences. Performing QPT on the hybrid qubit, we show that AC gating yields π rotation process fidelities higher than 93% for X-axis and 96% for Z-axis rotations, which demonstrates efficient quantum control of semiconductor qubits using resonant microwaves. We discuss a path forward for achieving fidelities better than the threshold for quantum error correction using surface codes. This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), DOE (DE-FG02-03ER46028), and by the Laboratory Directed Research and Development program at Sandia National Laboratories under contract DE-AC04-94AL85000.

  3. Nanocomposites of POC and quantum dots

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

    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.

  4. Imaging Live Cells Using Quantum Dots.

    PubMed

    Jaiswal, Jyoti K; Simon, Sanford M

    2015-07-01

    Quantum dots (QDs) are nanoparticles with fluorescent properties that offer advantages over organic fluorophores. As a result, QDs have found wide application in biological imaging. In this introduction we discuss the approaches for using QDs for labeling and imaging individual cells and cellular processes in live cells both in vivo and in culture. PMID:26134913

  5. Incipient Wigner localization in circular quantum dots

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

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

  6. Quantum-dot infrared photodetectors: a review

    NASA Astrophysics Data System (ADS)

    Stiff-Roberts, Adrienne D.

    2009-04-01

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

  7. Producing Quantum Dots by Spray Pyrolysis

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  8. The luminescence properties of colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Mikhailov, I. I.; Tarasov, S. A.; Lamkin, I. I.; Y Andreev, M.; Solomonov, A. V.

    2015-11-01

    Luminescent properties of systems containing lead sulfide (PbS) nanoparticles deposited on substrates of porous silicon (p-Si), oxidized porous silicon (OPS) and have been studied. It was shown that structure of the matrix and its composition are of crucial importance affecting luminescence spectra of colloidal quantum dots by setting their radiation wavelength.

  9. Unraveling the Mesoscopic Character of Quantum Dots in Nanophotonics.

    PubMed

    Tighineanu, P; Sørensen, A S; Stobbe, S; Lodahl, P

    2015-06-19

    We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. The deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, where a strong variation of the multipolar moments across the emission spectrum of quantum dots is observed. Our work enriches the physical understanding of quantum dots and is of significance for the fields of nanophotonics, quantum photonics, and quantum-information science, where quantum dots are actively employed. PMID:26197011

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

    SciTech Connect

    Ugur, A.; Hatami, F.; Masselink, W. T.; Vamivakas, A. N.; Lombez, L.; Atatuere, M.

    2008-10-06

    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.

  11. Hybrid quantum-state joining and splitting assisted by quantum dots in one-side optical microcavities

    NASA Astrophysics Data System (ADS)

    Luo, Ming-Xing; Ma, Song-Ya; Chen, Xiu-Bo; Wang, Xiaojun

    2015-04-01

    Quantum state joining has been recently experimentally demonstrated [C. Vitelli et al., Nat. Photon. 7, 521 (2013), 10.1038/nphoton.2013.107] which can transfer two input photonic qubits into a photonic ququart. Here, we revisit these processes from a hybrid point of view. By exploring the giant optical circular birefringence induced by quantum-dot spins in one-sided optical microcavities, we introduce some deterministic joining schemes including two quantum-dot spin joining, hybrid photon and quantum-dot spin joining, and two-photon joining. The input quantum information is represented by one photon with polarization and spatial mode degrees of freedom (DOFs). These schemes are also adapted to the inverse processes called quantum state splitting because all the joining procedures are unitary and do not require projection and feed-forward steps. The fused photon is convenient for realizing elementary logic gates such as the controlled-not (cnot) gate, swap gate, and Toffoli gate. These hybrid fusion and splitting schemes provide flexible synthesis of the quantum-dot spin and photon in quantum applications. The transmission superiority of photons and storage superiority of the quantum-dot spin may be combined for quantum network communication or quantum computations.

  12. Optical properties of quantum-dot-doped liquid scintillators

    PubMed Central

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

    2014-01-01

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO. PMID:25392711

  13. Sono-chemical successive ionic layer adsorption and reaction for the synthesis of CdS quantum dots onto mesoporous TiO2 photoanodes

    NASA Astrophysics Data System (ADS)

    Kim, Jae Ho; Kim, Geon Yang; Sohn, Sang Ho

    2015-07-01

    Aiming at high efficiency of quantum dot-sensitized solar cells (QDSCs) with CdS quantum dots (QDs)/mesoporous TiO2 (mp-TiO2) photoanodes, physical properties of CdS QDs/mp-TiO2 grown by sono-chemical successive ionic layer adsorption and reaction (SC-SILAR) process were studied. It is found that SC-SILAR process has less growth time and larger absorbance of CdS QDs besides a uniform penetration into mp-TiO2 films, compared with the conventional SILAR process. Experimental results show that SC-SILAR is an effective method for growing CdS QDs with high efficiency due to an extra sono-chemical energy of acoustic cavitation.

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

    PubMed

    Das, Anirban; Wai, Chien M

    2014-03-01

    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 π-π 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

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

    SciTech Connect

    Tarasov, S. A. Aleksandrova, O. A.; Maksimov, A. I.; Maraeva, E. V.; Matyushkin, L. B.; Men’kovich, E. A.; Moshnikov, V. A.; Musikhin, S. F.

    2014-12-15

    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.

  16. Non-Markovian full counting statistics in quantum dot molecules

    PubMed Central

    Xue, Hai-Bin; Jiao, Hu-Jun; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-01-01

    Full counting statistics of electron transport is a powerful diagnostic tool for probing the nature of quantum transport beyond what is obtainable from the average current or conductance measurement alone. In particular, the non-Markovian dynamics of quantum dot molecule plays an important role in the nonequilibrium electron tunneling processes. It is thus necessary to understand the non-Markovian full counting statistics in a quantum dot molecule. Here we study the non-Markovian full counting statistics in two typical quantum dot molecules, namely, serially coupled and side-coupled double quantum dots with high quantum coherence in a certain parameter regime. We demonstrate that the non-Markovian effect manifests itself through the quantum coherence of the quantum dot molecule system, and has a significant impact on the full counting statistics in the high quantum-coherent quantum dot molecule system, which depends on the coupling of the quantum dot molecule system with the source and drain electrodes. The results indicated that the influence of the non-Markovian effect on the full counting statistics of electron transport, which should be considered in a high quantum-coherent quantum dot molecule system, can provide a better understanding of electron transport through quantum dot molecules. PMID:25752245

  17. Efficient Luminescence from Perovskite Quantum Dot Solids.

    PubMed

    Kim, Younghoon; Yassitepe, Emre; Voznyy, Oleksandr; Comin, Riccardo; Walters, Grant; Gong, Xiwen; Kanjanaboos, Pongsakorn; Nogueira, Ana F; Sargent, Edward H

    2015-11-18

    Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids. PMID:26529572

  18. Probing the quantum-classical connection with open quantum dots

    NASA Astrophysics Data System (ADS)

    Ferry, D. K.; Akis, R.; Brunner, R.

    2015-10-01

    Open quantum dots provide a natural system in which to study both classical and quantum features of transport. From the classical point of view these dots possess a mixed phase space which yields families of closed, regular orbits as well as an expansive sea of chaos. As a closed test bed, they provide a natural system with a very rich set of eigen-states. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which eventually couple to the classical states discussed above. The manner of this connection is governed strongly by decoherence theory. The remaining coherent states possess all the properties of pointer states. Here, we discuss the quantum-classical connection and how it appears within the experimental world.

  19. Elastic fields of quantum dots in subsurface layers

    NASA Astrophysics Data System (ADS)

    Romanov, A. E.; Beltz, G. E.; Fischer, W. T.; Petroff, P. M.; Speck, J. S.

    2001-04-01

    In this work, models based on conventional small-strain elasticity theory are developed to evaluate the stress fields in the vicinity of a quantum dot or an ordered array of quantum dots. The models are based on three different approaches for solving the elastic boundary value problem of a misfitting inclusion embedded in a semi-infinite space. The first method treats the quantum dot as a point source of dilatation. In the second approach we approximate the dot as a misfitting oblate spheroid, for which exact analytic solutions are available. Finally, the finite element method is used to study complex, but realistic, quantum dot configurations such as cuboids and truncated pyramids. We evaluate these three levels of approximation by comparing the hydrostatic stress component near a single dot and an ordered array of dots in the presence of a free surface, and find very good agreement except in the immediate vicinity of an individual quantum dot.

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

    NASA Astrophysics Data System (ADS)

    Chan, Ian Hin-Yun

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

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

    NASA Astrophysics Data System (ADS)

    Elyasi, P.; SalmanOgli, A.

    2014-05-01

    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.

  2. Mitigation of Quantum Dot Cytotoxicity by Microencapsulation

    PubMed Central

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

    2011-01-01

    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

  3. Interface optical phonons in spheroidal quantum dots

    NASA Astrophysics Data System (ADS)

    Comas, F.; Trallero-Giner, C.; Studart, N.; Marques, G. E.

    2002-07-01

    Interface optical phonons are studied in the case of a quantum dot (QD) with prolate and oblate spheroidal geometries within the dielectric continuum approach. We considered CdSe or CdS QDs imbedded in a host material which is modelled as an infinite medium. The surface optical phonon modes, the corresponding frequencies, and the electron-phonon interaction Hamiltonian are reported. Comparison is made with previous works which only considered strictly spherical dots. We conclude that deviations from the perfect spherical shape could be responsible for observable physical effects in Raman spectra.

  4. Quantum dot molecules realized with modulated quantum wire heterostructrues

    NASA Astrophysics Data System (ADS)

    Zhu, Qing; Karlsson, Fredrik; Rudra, Alok; Pelucchi, Emanuele; Kapon, Eli

    2008-04-01

    We report on double-quantum dot (QD) molecules realized with modulated quantum wire (QWR) heterostructures by self-limiting growth of AlGaAs alloys in inverted tetrahedral pyramids. The QWR barriers connecting the dots facilitate the tunnel-coupling between the confined carriers. Evidences for the presence of such coupling are provided by conventional micro-photoluminescence measurements and theoretical modeling. Systematically tuning the relative QD sizes in the QD molecules reveals spectral line splitting consistent with the expected level splitting due to carrier hybridization. Prospects for extension of these structures to larger QD superlattices are discussed.

  5. Functional surface engineering of quantum dot hydrogels for selective fluorescence imaging of extracellular lactate release.

    PubMed

    Zhang, Xiaomeng; Ding, Shushu; Cao, Sumei; Zhu, Anwei; Shi, Guoyue

    2016-06-15

    Selective and sensitive detection of extracellular lactate is of fundamental significance for studying the metabolic alterations in tumor progression. Here we report the rational design and synthesis of a quantum-dot-hydrogel-based fluorescent probe for biosensing and bioimaging the extracellular lactate. By surface engineering the destabilized quantum dot sol with Nile Blue, the destabilized Nile-Blue-functionalized quantum dot sol cannot only self-assemble forming quantum dot hydrogel but also monitor lactate in the presence of nicotinamide adenine dinucleotide cofactor and lactate dehydrogenase through fluorescence resonance energy transfer. Notably, the surface engineered quantum dot hydrogel show high selectivity toward lactate over common metal ions, amino acids and other small molecules that widely coexist in biological system. Moreover, the destabilized Nile-Blue-functionalized quantum dots can encapsulate isolated cancer cells when self-assembled into a hydrogel and thus specifically detect and image the extracellular lactate metabolism. By virtue of these properties, the functionalized quantum dot hydrogel was further successfully applied to monitor the effect of metabolic agents. PMID:26852200

  6. Quantum Dot Platform for Single-Cell Molecular Profiling

    NASA Astrophysics Data System (ADS)

    Zrazhevskiy, Pavel S.

    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.

  7. Biosynthesis of luminescent quantum dots in an earthworm

    NASA Astrophysics Data System (ADS)

    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

    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.

  8. Theory of the Quantum Dot Hybrid Qubit

    NASA Astrophysics Data System (ADS)

    Friesen, Mark

    2015-03-01

    The quantum dot hybrid qubit, formed from three electrons in two quantum dots, combines the desirable features of charge qubits (fast manipulation) and spin qubits (long coherence times). The hybridized spin and charge states yield a unique energy spectrum with several useful properties, including two different operating regimes that are relatively immune to charge noise due to the presence of optimal working points or ``sweet spots.'' In this talk, I will describe dc and ac-driven gate operations of the quantum dot hybrid qubit. I will analyze improvements in the dephasing that are enabled by the sweet spots, and I will discuss the outlook for quantum hybrid qubits in terms of scalability. This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), the USDOD, and the Intelligence Community Postdoctoral Research Fellowship Program. The views and conclusions contained in this presentation are those of the authors and should not be interpreted as representing the official policies or endorsements, either expressed or implied, of the US government.

  9. Nanoscale optimization of quantum dot solar sells

    NASA Astrophysics Data System (ADS)

    Li, Yanshu; Sergeev, Andrei; Vagidov, Nizami; Mitin, Vladimir; Sablon, Kimberly; State Univ of NY-Buffalo Team; Army Research Laboratory Team

    2015-03-01

    Quantum dots (QDs) offer possibilities for nanoscale control of photoelectron processes via engineering the band structure and potential profile. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AlGaAs atomically thin barriers) effectively suppress the photoelectron capture to QDs. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons that excited by high-energy photons. To study the effects of the band structure engineering and nanoscale potential barriers on the photovoltaic performance we fabricated 3- μm base GaAs devices with various InAs quantum dot media and selective doping. All quantum dot devices show improvement in conversion efficiency compared with the reference cell. Quantum efficiency measurements allow us to associate the spectral characteristics of photoresponse enhancement with nanoscale structure of QD media. The dark current analysis provides valuable information about recombination in QD solar cells. The two-diode model well fit the scope of data and recovers the measured open circuit voltage.

  10. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    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.

  11. Systematic optimization of quantum junction colloidal quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Huan; Zhitomirsky, David; Hoogland, Sjoerd; Tang, Jiang; Kramer, Illan J.; Ning, Zhijun; Sargent, Edward H.

    2012-10-01

    The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum junction solar cell that leverages an improved aluminum zinc oxide electrode for a stable contact to the n-side of the quantum junction and silver doping of the p-layer that greatly enhances the photocurrent by expanding the depletion region in the n-side of the device. These improvements result in greater stability and a power conversion efficiency of 6.1% under AM1.5 simulated solar illumination.

  12. Charge-tunable indium gallium nitride quantum dots

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Teng, Chu-Hsiang; Ku, Pei-Cheng; Deng, Hui

    2016-02-01

    III-Nitride quantum dots have emerged as a new chip-scale system for quantum information science, which combines electrical and optical interfaces on a semiconductor chip that is compatible with noncryogenic operating temperatures. Yet most work has been limited to optical excitations. To enable single-spin-based quantum optical and quantum information research, we demonstrate here quantized charging in optically active, site-controlled III-nitride quantum dots. Single-electron charging was confirmed by the voltage dependence of the energy, dipole moment, fine structures, and polarization properties of the exciton states in the quantum dots. The fundamental energy structures of the quantum dots were identified, including neutral and charged excitons, fine structures of excitons, and A and B excitons. The results lay the ground for coherent control of single charges in III-nitride quantum dots, opening a door to III-nitride-based spintronics and spin-qubit quantum information processing.

  13. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

    PubMed Central

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

    2011-01-01

    Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers. PMID:21931483

  14. One-pot aqueous synthesis of gadolinium doped CdTe quantum dots with dual imaging modalities.

    PubMed

    Jiang, Chunli; Shen, Zhitao; Luo, Chunhua; Lin, Hechun; Huang, Rong; Wang, Yiting; Peng, Hui

    2016-08-01

    A facile one-pot strategy has been developed for the aqueous synthesis of Gd doped CdTe (Gd:CdTe) QDs as fluorescence and magnetic resonance imaging dual-modal agent. The prepared Gd:CdTe QDs showed narrow size distribution and the average size was less than 5nm. The amount of Gd(3+) dopant in Gd:CdTe QDs significantly affected the optical properties of obtained QDs. The highest PL QY for the prepared Gd:CdTe QDs was up to 42.5%. The QDs showed the weak toxicity and significant enhancement in MRI signal. The specific relaxivity value (r1) was determined to be 4.22mM(-1)s(-1). These properties make the prepared Gd:CdTe QDs be an effective dual-modal imaging agent and have great potential applications in biomedical field. PMID:27216651

  15. Direct water-phase synthesis of lead sulfide quantum dots encapsulated by β-lactoglobulin for in vivo second near infrared window imaging with reduced toxicity.

    PubMed

    Chen, Jun; Kong, Yifei; Wang, Wei; Fang, Hongwei; Wo, Yan; Zhou, Dejian; Wu, Ziying; Li, Yunxia; Chen, Shiyi

    2016-03-01

    Compared to conventional fluorescence imaging in the visible (400-700 nm) and NIR-I regions (700-900 nm), optical fluorescence imaging in the second near infrared window (NIR-II, 1000-1400 nm) offers reduced photon scattering, deeper tissue penetration and lower auto-fluorescence. Despite excellent imaging capabilities, current NIR-II probes have not yet reached their full potential due to weak quantum yield, low water solubility and suboptimal biocompatibility. To address these problems, we report herein a new NIR-II fluorescent PbS quantum dots (QDs) that are fabricated in water using β-lactoglobulin (LG) as a biological template. The LG-PbS QDs exhibit satisfactory dispersibility, relatively high quantum yield and favorable biocompatibility, and therefore are suitable for high-resolution in vivo imaging applications. PMID:26888668

  16. Biosynthesis of luminescent CdS quantum dots using plant hairy root culture

    NASA Astrophysics Data System (ADS)

    Borovaya, Mariya N.; Naumenko, Antonina P.; Matvieieva, Nadia A.; Blume, Yaroslav B.; Yemets, Alla I.

    2014-12-01

    CdS nanoparticles have a great potential for application in chemical research, bioscience and medicine. The aim of this study was to develop an efficient and environmentally-friendly method of plant-based biosynthesis of CdS quantum dots using hairy root culture of Linaria maroccana L. By incubating Linaria root extract with inorganic cadmium sulfate and sodium sulfide we synthesized stable luminescent CdS nanocrystals with absorption peaks for UV-visible spectrometry at 362 nm, 398 nm and 464 nm, and luminescent peaks at 425, 462, 500 nm. Transmission electron microscopy of produced quantum dots revealed their spherical shape with a size predominantly from 5 to 7 nm. Electron diffraction pattern confirmed the wurtzite crystalline structure of synthesized cadmium sulfide quantum dots. These results describe the first successful attempt of quantum dots synthesis using plant extract.

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

    PubMed

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

    2011-07-01

    This work reports a new experimental methodology for the synthesis of ultra small zinc sulfide and iron doped zinc sulfide quantum dots in aqueous media. The nanoparticles were obtained using a simple procedure based on the precipitation of ZnS in aqueous solution in the presence of 2-mercaptoethanol as a capping agent, at room temperature. The effect of Fe(3+) ion concentration as dopant on the optical properties of ZnS was studied. The size of quantum dots was determined to be about 1nm, using scanning tunneling microscopy. The synthesized nanoparticles were characterized by X-ray diffraction, UV-Vis absorption and photoluminescence emission spectroscopies. The presence and amount of iron impurity in the structure of Zn((1-x))Fe(x)S nanocrystals were confirmed by atomic absorption spectrometry. A blue shift in band-gap of ZnS was observed upon increasing incorporation of Fe(3+) ion in the iron doped zinc sulfide quantum dots. The photoluminescence investigations showed that, in the case of iron doped ZnS nanoparticles, the emission band of pure ZnS nanoparticles at 427nm shifts to 442nm with appearance of a new sharp emission band around 532nm. The X-ray diffraction analysis indicated that the iron doped nanoparticles are crystalline, with cubic zinc blend structure, having particle diameters of 1.7±022nm. Finally, the interaction of the synthesized nanoparticles with bovine serum albumin was investigated at pH 7.2. The UV-Vis absorption and fluorescence spectroscopic methods were applied to compare the optical properties of pure and iron doped ZnS quantum dots upon interaction with BSA. It was proved that, in both cases, the fluorescence quenching of BSA by the quantum dots is mainly a result of the formation of QDs-BSA complex in solution. In the steady-state fluorescence studies, the interaction parameters including binding constants (K(a)), number of binding sites (n), quenching constants ( [Formula: see text] ), and bimolecular quenching rate constants (k(q)) were determined at three different temperatures and the results were then used to evaluate the corresponding thermodynamic parameters ΔH, ΔS and ΔG. PMID:21482179

  18. Separability and dynamical symmetry of Quantum Dots

    SciTech Connect

    Zhang, P.-M.; Zou, L.-P.; Horvathy, P.A.; Gibbons, G.W.

    2014-02-15

    The separability and Runge–Lenz-type dynamical symmetry of the internal dynamics of certain two-electron Quantum Dots, found by Simonović 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 Simonović 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.

  19. The pinning effect in quantum dots

    SciTech Connect

    Monisha, P. J.; Mukhopadhyay, Soma

    2014-04-24

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

  20. Electrical properties of semiconductor quantum dots

    SciTech Connect

    Kharlamov, V. F. Korostelev, D. A.; Bogoraz, I. G.; Milovidova, O. A.; Sergeyev, V. O.

    2013-04-15

    A method, which makes it possible to obtain semiconductor particles V Almost-Equal-To 10{sup -20} cm{sup 3} in volume (quantum dots) with a concentration of up to 10{sup 11} cm{sup -2} and electrical contacts to each of them, is suggested. High variability in the electrical properties of such particles from a metal oxide (CuO or NiO) after the chemisorption of gas molecules is found.

  1. Floquet Majorana fermions in superconducting quantum dots

    NASA Astrophysics Data System (ADS)

    Benito, Mónica; Platero, Gloria

    2015-11-01

    We consider different configurations of ac driven quantum dots coupled to superconductor leads where Majorana fermions can exist as collective quasiparticles. The main goal is to tune the existence, localization and properties of these zero energy quasiparticles by means of periodically driven external gates. In particular, we analyze the relevance of the system and driving symmetry. We predict the existence of different sweet spots with Floquet Majorana fermions in configurations where they are not present in the undriven system.

  2. Inverted colloidal quantum dot solar cells.

    PubMed

    Kim, Gi-Hwan; Walker, Bright; Kim, Hak-Beom; Kim, Jin Young; Sargent, Edward H; Park, Jongnam; Kim, Jin Young

    2014-05-28

    An inverted architecture of quantum dot solar cells is demonstrated by introducing a novel ZnO method on top of the PbS CQD film. Improvements in device characteristics stem from constructive optical interference from the ZnO layer that enhances absorption in the PbS CQD layer. Outstanding diode characteristics arising from a superior PbS/ZnO junction provide a further electronic advantage. PMID:24677118

  3. Solution-processable graphene quantum dots.

    PubMed

    Zhou, Xuejiao; Guo, Shouwu; Zhang, Jingyan

    2013-08-26

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

  4. Synthesis of eco-friendly CuInS2 quantum dot-sensitized solar cells by a combined ex situ/in situ growth approach.

    PubMed

    Chang, Chia-Chan; Chen, Jem-Kun; Chen, Chih-Ping; Yang, Cheng-Hsien; Chang, Jia-Yaw

    2013-11-13

    A cadmium-free CuInS2 quantum dot (QD)-sensitized solar cell (QDSC) has been fabricated by taking advantage of the ex situ synthesis approach for fabricating highly crystalline QDs and the in situ successive ionic-layer adsorption and reaction (SILAR) approach for achieving high surface coverage of QDs. The ex situ synthesized CuInS2 QDs can be rendered water soluble through a simple and rapid two-step method under the assistance of ultrasonication. This approach allows a stepwise ligand change from the insertion of a foreign ligand to ligand replacement, which preserves the long-term stability of colloidal solutions for more than 1 month. Furthermore, the resulting QDs can be utilized as sensitizers in QDSCs, and such a QDSC can deliver a power conversion efficiency (PCE) of 0.64%. Using the SILAR process, in situ CuInS2 QDs could be preferentially grown epitaxially on the pre-existing seeds of ex situ synthesized CuInS2 QDs. The results indicated that the CuInS2 QDSC fabricated by the combined ex situ/in situ growth process exhibited a PCE of 1.84% (short-circuit current density = 7.72 mA cm(-2), open-circuit voltage = 570 mV, and fill factor = 41.8%), which is higher than the PCEs of CuInS2 QDSCs fabricated by ex situ and in situ growth processes, respectively. The relative efficiencies of electrons injected by the combined ex situ/in situ growth approach were higher than those of ex situ synthesized CuInS2 QDs deposited on TiO2 films, as determined by emission-decay kinetic measurements. The incident photon-to-current conversion efficiency has been determined, and electrochemical impedance spectroscopy has been carried out to investigate the photovoltaic behavior and charge-transfer resistance of the QDSCs. The results suggest that the combined synergetic effects of in situ and ex situ CuInS2 QD growth facilitate more electron injection from the QD sensitizers into TiO2. PMID:24095097

  5. Water-soluble, luminescent ZnTe quantum dots: supersaturation-controlled synthesis and self-assembly into nanoballs, nanonecklaces and nanowires.

    PubMed

    Patra, Sovan Kumar; Bhushan, Bhavya; Priyam, Amiya

    2016-02-18

    A supersaturation-controlled aqueous synthesis route has been developed for ZnTe quantum dots (QDs) with high monodispersity, size tunability, stability, band-edge luminescence (full-width at half-maximum (FWHM) 10-12 nm) and negligibly small Stokes' shift (2-4 nm). The degree of supersaturation of the initial reaction mixture was varied by increasing the reagent concentration, but keeping the molar ratio Zn(2+) : thioglycolic acid : Te(2-) constant at 1 : 2.5 : 0.5. For a 10× increase in supersaturation, the photoluminescence (PL) peak underwent a 50 nm blue shift from 330 to 280 nm at pH 6. The effect was more pronounced at pH 12, where the PL peak blue-shifted by 100 nm from 327 to 227 nm. Concomitantly, the FWHM was also reduced to a low value of 10 nm, indicating high monodispersity. For a 10× change in supersaturation, the particle size decreased by 63% (from 2.2 to 0.8 nm) at pH 12, whereas it changed by 19% (from 2.1 to 1.7 nm) at pH 6. High-resolution transmission electron microscopy and selected area electron diffraction data further revealed that the QDs synthesized at higher supersaturation had a better crystallinity. These QDs exhibited the unique property of undergoing isotropic and anisotropic self-assembly, which resulted in a blue shift and a red shift in the absorption and PL spectra, respectively. Isotropic assembly into spherical nanoballs (100 nm diameter, 1 nm inter-QD separation) occurred when the QDs were stored at pH 12 for 3 weeks at room temperature. The nanoballs further self-assembled into a 'pearl necklace' arrangement. On the partial removal of the capping agents, the QDs self-organized anisotropically into nanowires (1.3 μm long and 4.6 nm in diameter). The self-assembled nanostructures showed exciton-exciton coupling and excellent PL properties, which may be useful in enhanced optoelectronics, photovoltaics and biochemical sensing. PMID:26830257

  6. Quantum phase transition in a multilevel dot.

    PubMed

    Hofstetter, Walter; Schoeller, Herbert

    2002-01-01

    We discuss electronic transport through a lateral quantum dot close to the singlet-triplet degeneracy in the case of a single conduction channel per lead. By applying the numerical renormalization group, we obtain rigorous results for the linear conductance and the density of states. A new quantum phase transition of the Kosterlitz-Thouless-type is found, with an exponentially small energy scale T(*) close to the degeneracy point. Below T(*), the conductance is strongly suppressed, corresponding to a universal dip in the density of states. This explains recent transport measurements. PMID:11800978

  7. Relaxation dynamics in correlated quantum dots

    SciTech Connect

    Andergassen, S.; Schuricht, D.; Pletyukhov, M.; Schoeller, H.

    2014-12-04

    We study quantum many-body effects on the real-time evolution of the current through quantum dots. By using a non-equilibrium renormalization group approach, we provide analytic results for the relaxation dynamics into the stationary state and identify the microscopic cutoff scales that determine the transport rates. We find rich non-equilibrium physics induced by the interplay of the different energy scales. While the short-time limit is governed by universal dynamics, the long-time behavior features characteristic oscillations as well as an interplay of exponential and power-law decay.

  8. Silicon quantum dots for optical applications

    NASA Astrophysics Data System (ADS)

    Wu, Jeslin J.

    Luminescent silicon quantum dots (SiQDs) are emerging as attractive materials for optoelectronic devices, third generation photovoltaics, and bioimaging. Their applicability in the real world is contingent on their optical properties and long-term environmental stability; and in biological applications, factors such as water solubility and toxicity must also be taken into consideration. The aforementioned properties are highly dependent on the QDs' surface chemistry. In this work, SiQDs were engineered for the respective applications using liquid-phase and gas-phase functionalization techniques. Preliminary work in luminescent downshifting for photovoltaic systems are also reported. Highly luminescent SiQDs were fabricated by grafting unsaturated hydrocarbons onto the surface of hydrogen-terminated SiQDs via thermal and photochemical hydrosilylation. An industrially attractive, all gas-phase, nonthermal plasma synthesis, passivation (aided by photochemical reactions), and deposition process was also developed to reduce solvent waste. With photoluminescence quantum yields (PLQYs) nearing 60 %, the alkyl-terminated QDs are attractive materials for optical applications. The functionalized SiQDs also exhibited enhanced thermal stability as compared to their unfunctionalized counterparts, and the photochemically-hydrosilylated QDs further displayed photostability under UV irradiation. These environmentally-stable SiQDs were used as luminescent downshifting layers in photovoltaic systems, which led to enhancements in the blue photoresponse of heterojunction solar cells. Furthermore, the QD films demonstrated antireflective properties, improving the coupling efficiency of sunlight into the cell. For biological applications, oxide, amine, or hydroxyl groups were grafted onto the surface to create water-soluble SiQDs. Luminescent, water-soluble SiQDs were produced in by microplasma treating the QDs in water. Stable QYs exceeding 50 % were obtained. Radical-based and catalytic hydrosilylation reactions were also investigated to engineer individually-dispersed SiQDs in water. The results of this dissertation demonstrate the potential of SiQDs in optical applications. In the future, their application may lead to improvements in the efficiencies of photovoltaic devices and perhaps allow the cells to exceed the Shockley-Queisser limit. In biology, the stability of the SiQDs may allow long-term monitoring of biomolecules and perhaps lead to new discoveries.

  9. TOPICAL REVIEW: Quantum dots: lasers and amplifiers

    NASA Astrophysics Data System (ADS)

    Bimberg, Dieter; Ledentsov, Nikolai

    2003-06-01

    Continuous wave room-temperature output power of ~ 3 W for edge emitters and of 1.2 mW for vertical-cavity surface-emitting lasers is realized for GaAs-based devices using InAs quantum dots (QDs) operating at 1.3 µm. Characteristic temperatures up to 170 K below 330 K are realized. Simultaneously, differential efficiency exceeds 80% for these devices. Lasers emitting up to 12 W at 1140 1160 nm are useful as pump sources for Tm3+-doped fibres for frequency up-conversion to 470 nm. Both types of lasers show transparency current densities of 6 A cm-2 per dot layer, ηint = 98% and αi around 1.5 cm-1. Long operation lifetimes (above 3000 h at 50 °C heatsink temperature at 1.5 W CW) and improved radiation hardness as compared to quantum well (QW) devices are manifested. Cut-off frequencies of about 10 GHz at 1100 nm and 6 GHz at 1300 nm and low α factors resulting in reduced filamentation and improved M2 values in single-mode operation are realized. Quantum dot semiconductor optical amplifiers (QD SOAs) demonstrate gain recovery times of 120 140 fs, 4 7 times faster than bulk/QW SOAs. The breakthrough became possible due to the development of self-organized growth in QD technology.

  10. Quantum dot spectroscopy using a single phosphorus donor

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  11. Optical resonators and quantum dots: An excursion into quantum optics, quantum information and photonics

    NASA Astrophysics Data System (ADS)

    Bianucci, Pablo

    Modern communications technology has encouraged an intimate connection between Semiconductor Physics and Optics, and this connection shows best in the combination of electron-confining structures with light-confining structures. Semiconductor quantum dots are systems engineered to trap electrons in a mesoscopic scale (the are composed of ? 10000 atoms), resulting in a behavior resembling that of atoms, but much richer. Optical microresonators are engineered to confine light, increasing its intensity and enabling a much stronger interaction with matter. Their combination opens a myriad of new directions, both in fundamental Physics and in possible applications. This dissertation explores both semiconductor quantum dots and microresonators, through experimental work done with semiconductor quantum dots and microsphere resonators spanning the fields of Quantum Optics, Quantum Information and Photonics; from quantum algorithms to polarization converters. Quantum Optics leads the way, allowing us to understand how to manipulate and measure quantum dots with light and to elucidate the interactions between them and microresonators. In the Quantum Information area, we present a detailed study of the feasibility of excitons in quantum dots to perform quantum computations, including an experimental demonstration of the single-qubit Deutsch-Jozsa algorithm performedin a single semiconductor quantum dot. Our studies in Photonics involve applications of microsphere resonators, which we have learned to fabricate and characterize. We present an elaborate description of the experimental techniques needed to study microspheres, including studies and proof of concept experiments on both ultra-sensitive microsphere sensors and whispering gallery mode polarization converters.

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

    PubMed

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

    2014-05-14

    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

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

    PubMed

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

    2013-02-21

    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

  14. Terahertz transmission through rings of quantum dots-nanogap

    NASA Astrophysics Data System (ADS)

    Tripathi, Laxmi-Narayan; Bahk, Young-Mi; Choi, Geunchang; Han, Sanghoon; Park, Namkyoo; Kim, Dai-Sik

    2016-03-01

    We report resonant funneling of terahertz (THz) waves through (9 ± 1) nm wide quantum dots-nanogap of cadmium selenide quantum dots silver nanogap metamaterials. We observed a giant THz intensity enhancement (∼104) through the quantum dots-nanogap at the resonant frequency. We, further report the experimentally measured effective mode indices for these metamaterials. A finite difference time domain simulation of the nanogap enabled by the quantum dots supports the experimentally measured THz intensity enhancement across the nanogap. We propose that these low effective mode index terahertz resonators will be useful as bio/chemical sensors, gain-enhanced antennas, and wave guides.

  15. Electron-Hole Confinement Symmetry in Silicon Quantum Dots.

    PubMed

    Mueller, Filipp; Konstantaras, Georgios; Spruijtenburg, Paul C; van der Wiel, Wilfred G; Zwanenburg, Floris A

    2015-08-12

    We report electrical transport measurements on a gate-defined ambipolar quantum dot in intrinsic silicon. The ambipolarity allows its operation as either an electron or a hole quantum dot of which we change the dot occupancy by 20 charge carriers in each regime. Electron-hole confinement symmetry is evidenced by the extracted gate capacitances and charging energies. The results demonstrate that ambipolar quantum dots offer great potential for spin-based quantum information processing, since confined electrons and holes can be compared and manipulated in the same crystalline environment. PMID:26134900

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

    SciTech Connect

    See, Gloria G.; Xu, Lu; Nuzzo, Ralph G.; Sutanto, Erick; Alleyne, Andrew G.; Cunningham, Brian T.

    2015-08-03

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

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

    NASA Astrophysics Data System (ADS)

    See, Gloria G.; Xu, Lu; Sutanto, Erick; Alleyne, Andrew G.; Nuzzo, Ralph G.; Cunningham, Brian T.

    2015-08-01

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

  18. Imaging ligand-gated ion channels with quantum dots

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

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

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

    SciTech Connect

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

    2014-10-07

    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.

  20. Silicon quantum dots: fine-tuning to maturity.

    PubMed

    Morello, Andrea

    2015-12-18

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science. PMID:26584678

  1. Silicon quantum dots: fine-tuning to maturity

    NASA Astrophysics Data System (ADS)

    Morello, Andrea

    2015-12-01

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science.

  2. In situ synthesis of binary cobalt-ruthenium nanofiber alloy counter electrode for electrolyte-free cadmium sulfide quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Du, Nan; Ren, Lei; Sun, Weifu; Jin, Xiao; Zhao, Qing; Cheng, Yuanyuan; Wei, Taihuei; Li, Qinghua

    2015-06-01

    A facile, low-cost and low-temperature fabrication approach of counter electrode is essential for pursuing robust photovoltaic devices. Herein, we develop a hydrothermal in situ growth of Cobalt-Ruthenium (Co-Ru) alloy nanofiber electrode for quantum dot solar cell (QDSC) applications. Colloidal CdS QDs with tunable absorption band edge are synthesized and used as light absorber. After optimizing the QDs with the highest photoluminescence quantum yield accompanied by considerable solar light absorption ability, QDSC based on Co-Ru alloy electrode delivers a much higher power conversion efficiency than its counterparts, i.e., either pure Co or Ru metal electrodes. In detail, Co-Ru alloy electrode exhibits high specific area, excellent electrical behavior, intimate interface contact, and good stability, thus leading to notable improved device performances. The impressive robust function of Co-Ru alloy with simple manufacturing procedure highlights its potential applications in robust QDSCs.

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  4. 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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.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. Electronic supplementary information (ESI) available: HRTEM images, GQD SAED patterns and EDAX analysis of Am-GQD@Ag. See DOI: 10.1039/c4nr02494j

  5. Quantum dot spin cellular automata for realizing a quantum processor

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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 (10 ns) deterministic coherent singlet-triplet filtering, as opposed to current incoherent tunneling/slow-adiabatic based quantum gates (operation time 300 ns), can be employed to produce a two-qubit gate through capacitive (electrostatic) couplings that can operate over significant distances. This is the coherent version of the widely discussed charge and nano-magnet cellular automata, and would increase speed, reduce dissipation, and perform quantum computation while interfacing smoothly with its classical counterpart. This combines the best of two worldsthe coherence of spin pairs known from quantum technologies, and the strength and range of electrostatic couplings from the charge-based classical cellular automata. Significantly our system has zero electric dipole moment during the whole operation process, thereby increasing its charge dephasing time.

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

    ERIC Educational Resources Information Center

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

    2005-01-01

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

  7. Measurement Back-Action in Stacked Graphene Quantum Dots.

    PubMed

    Bischoff, D; Eich, M; Zilberberg, O; Rössler, C; Ihn, T; Ensslin, K

    2015-09-01

    We present an electronic transport experiment in graphene where both classical and quantum mechanical charge detector back-action on a quantum dot are investigated. The device consists of two stacked graphene quantum dots separated by a thin layer of boron nitride. This device is fabricated by van der Waals stacking and is equipped with separate source and drain contacts to both dots. By applying a finite bias to one quantum dot, a current is induced in the other unbiased dot. We present an explanation of the observed measurement-induced current based on strong capacitive coupling and energy dependent tunneling barriers, breaking the spatial symmetry in the unbiased system. This is a special feature of graphene-based quantum devices. The experimental observation of transport in classically forbidden regimes is understood by considering higher-order quantum mechanical back-action mechanisms. PMID:26280388

  8. Charge transport in strongly coupled quantum dot solids.

    PubMed

    Kagan, Cherie R; Murray, Christopher B

    2015-12-01

    The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design. PMID:26551016

  9. Charge transport in strongly coupled quantum dot solids

    NASA Astrophysics Data System (ADS)

    Kagan, Cherie R.; Murray, Christopher B.

    2015-12-01

    The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design.

  10. Electrostatically defined silicon quantum dots with counted antimony donor implants

    NASA Astrophysics Data System (ADS)

    Singh, M.; Pacheco, J. L.; Perry, D.; Garratt, E.; Ten Eyck, G.; Bishop, N. C.; Wendt, J. R.; Manginell, R. P.; Dominguez, J.; Pluym, T.; Luhman, D. R.; Bielejec, E.; Lilly, M. P.; Carroll, M. S.

    2016-02-01

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

  11. Bioinspired inimitable cadmium telluride quantum dots for bioimaging purposes.

    PubMed

    Pawar, Vinay; Kumar, Ameeta Ravi; Zinjarde, Smita; Gosavi, Suresh

    2013-06-01

    Synthesis of quantum nanoparticles of specific size, shape and composition are an aspect important in nanotechnology research. Although these nanostructures are routinely synthesized by chemical routes, the use of microorganisms has emerged as a promising option. The synthesis of cadmium telluride (CdTe) quantum dots by two hitherto unreported marine bacteria (Bacillus pumilus and Serratia marcescens) is reported here. Ultraviolet-visible (UV-vis) spectroscopy indicated the synthesis of CdTe nanoparticles and X-ray diffraction (XRD) patterns implicated their crystalline face-centered cubic nature. The size of the synthesized CdTe nanostructures estimated by XRD and dynamic light scattering (DLS) analysis was found to be approximately 10 nm. Photoluminescence (PL) studies were used to confirm the fluorescence properties of these semi-conducting nanoparticles. Scanning electron microscope (SEM) analysis showed the presence of well-defined nanostructures and energy dispersive spectra (EDS) confirmed the microbial synthesis of these nanoparticles. These bio-inspired CdTe nanostructures could be effectively used in imaging of yeast and animal cells. This work thus describes a cost-effective green method for synthesizing highly fluorescent biocompatible CdTe nanoparticles suitable for bio-labeling purposes. PMID:23862414

  12. Nano-laser on silicon quantum dots

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  13. Effect of shells on photoluminescence of aqueous CdTe quantum dots

    SciTech Connect

    Yuan, Zhimin; Yang, Ping

    2013-07-15

    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.

  14. Controlling quantum dot energies using submonolayer bandstructure engineering

    SciTech Connect

    Yu, L.; Law, S.; Wasserman, D.; Jung, D.; Lee, M. L.; Shen, J.; Cha, J. J.

    2014-08-25

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  16. Quantum Dot Device Design Optimization for Resonator Coupling

    NASA Astrophysics Data System (ADS)

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

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

  17. Power-law photoluminescence decay in quantum dots

    SciTech Connect

    Král, Karel; Menšík, Miroslav

    2014-05-15

    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.

  18. Unilamellar vesicles from amphiphilic graphene quantum dots.

    PubMed

    Nandi, Sukhendu; Kolusheva, Sofiya; Malishev, Ravit; Trachtenberg, Alexander; Vinod, T P; Jelinek, Raz

    2015-05-18

    Graphene quantum dots (GQDs) have attracted considerable interest due to their unique physicochemical properties and various applications. For the first time it is shown that GQDs surface-functionalized with hydrocarbon chains (i.e., amphiphilic GQDs) self-assemble into unilamellar spherical vesicles in aqueous solution. The amphiphilic GQD vesicles exhibit multicolor luminescence that can be readily exploited for membrane studies by fluorescence spectroscopy and microscopy. The GQD vesicles were used for microscopic analysis of membrane interactions and disruption by the peptide beta-amyloid. PMID:25800814

  19. Quantum Dots for Molecular Diagnostics of Tumors

    PubMed Central

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

    2011-01-01

    Semiconductor quantum dots (QDs) are a new class of fluorophores with unique physical and chemical properties, which allow to appreciably expand the possibilities for the current methods of fluorescent imaging and optical diagnostics. Here we discuss the prospects of QD application for molecular diagnostics of tumors ranging from cancer-specific marker detection on microplates to non-invasive tumor imagingin vivo. We also point out the essential problems that require resolution in order to clinically promote QD, and we indicate innovative approaches to oncology which are implementable using QD. PMID:22649672

  20. Quantum dot intermixing using excimer laser irradiation

    SciTech Connect

    Djie, H. S.; Ooi, B. S; Gunawan, O.

    2006-08-21

    The authors report a spatial control of the band gap in InGaAs/GaAs quantum dots (QDs) using the combined effects of pulsed excimer laser irradiation and impurity-free dielectric cap induced intermixing technique. A large band gap shift of up to 180 meV has been obtained under laser irradiation of 480 mJ/cm{sup 2} and 150 pulses to the SiO{sub 2} capped shallow QD structure, while the nonirradiated SiO{sub 2} and Si{sub x}N{sub y} capped QDs only exhibit band gap shifts of 18 and 91 meV, respectively.

  1. A Nanowire-Based Plasmonic Quantum Dot Laser.

    PubMed

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

    2016-04-13

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

  2. Fast synthesize ZnO quantum dots via ultrasonic method.

    PubMed

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

    2016-05-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots. PMID:26611814

  3. Spin storage and readout in self-organized quantum dots

    NASA Astrophysics Data System (ADS)

    Warming, T.; Wieczorek, W.; Geller, M.; Bimberg, D.; Cirlin, G. E.; Zhukov, A. E.; Ustinov, V. M.

    2007-04-01

    We demonstrate optical charging of spectrally selected subensembles of self-organized quantum dots with single charge carriers. By circularly polarized excitation in an applied magnetic field, we are able to address the spin of single electron in the quantum dot. A spin-flip of the electron is observed after excitation in the upper Zeeman level.

  4. Implementing of Quantum Cloning with Spatially Separated Quantum Dot Spins

    NASA Astrophysics Data System (ADS)

    Wen, Jing-Ji; Yeon, Kyu-Hwang; Du, Xin; Lv, Jia; Wang, Ming; Wang, Hong-Fu; Zhang, Shou

    2016-02-01

    We propose some schemes for implementing optimal symmetric (asymmetric) 1 → 2 universal quantum cloning, optimal symmetric (asymmetric) 1 → 2 phase-covariant cloning, optimal symmetric 1 → 3 economical phase-covariant cloning and optimal symmetric 1 → 3 economical real state cloning with spatially separated quantum dot spins by choosing the single-qubit rotation angles appropriately. The decoherences of the spontaneous emission of QDs, cavity decay and fiber loss are suppressed since the effective long-distance off-resonant interaction between two distant QDs is mediated by the vacuum fields of the fiber and cavity, and during the whole process no system is excited.

  5. Double quantum dot in a quantum dash: Optical properties

    SciTech Connect

    Kaczmarkiewicz, Piotr Machnikowski, Paweł; Kuhn, Tilmann

    2013-11-14

    We study the optical properties of highly elongated, highly flattened quantum dot structures, also referred to as quantum dashes, characterized by the presence of two trapping centers located along the structure. Such a system can exhibit some of the properties characteristic for double quantum dots. We show that sub- and super-radiant states can form for certain quantum dash geometries, which is manifested by a pronounced transfer of intensity between spectral lines, accompanied by the appearance of strong electron-hole correlations. We also compare exciton absorption spectra and polarization properties of a system with a single and double trapping center and show how the geometry of multiple trapping centers influences the optical properties of the system. We show that for a broad range of trapping geometries the relative absorption intensity of the ground state is larger than that of the lowest excited states, contrary to the quantum dash systems characterized by a single trapping center. Thus, optical properties of these structures are determined by fine details of their morphology.

  6. 3D super-resolution imaging with blinking quantum dots

    PubMed Central

    Wang, Yong; Fruhwirth, Gilbert; Cai, En; Ng, Tony; Selvin, Paul R.

    2013-01-01

    Quantum dots are promising candidates for single molecule imaging due to their exceptional photophysical properties, including their intense brightness and resistance to photobleaching. They are also notorious for their blinking. Here we report a novel way to take advantage of quantum dot blinking to develop an imaging technique in three-dimensions with nanometric resolution. We first applied this method to simulated images of quantum dots, and then to quantum dots immobilized on microspheres. We achieved imaging resolutions (FWHM) of 8–17 nm in the x-y plane and 58 nm (on coverslip) or 81 nm (deep in solution) in the z-direction, approximately 3–7 times better than what has been achieved previously with quantum dots. This approach was applied to resolve the 3D distribution of epidermal growth factor receptor (EGFR) molecules at, and inside of, the plasma membrane of resting basal breast cancer cells. PMID:24093439

  7. Quantum dots find their stride in single molecule tracking

    PubMed Central

    Bruchez, Marcel P.

    2011-01-01

    Thirteen years after the demonstration of quantum dots as biological imaging agents, and nine years after the initial commercial introduction of bioconjugated quantum dots, the brightness and photostability of the quantum dots has enabled a range of investigations using single molecule tracking. These materials are being routinely utilized by a number of groups to track the dynamics of single molecules in reconstituted biophysical systems and on living cells, and are especially powerful for investigations of single molecules over long timescales with short exposure times and high pointing accuracy. New approaches are emerging where the quantum dots are used as “hard-sphere” probes for intracellular compartments. Innovations in quantum dot surface modification are poised to substantially expand the utility of these materials. PMID:22055494

  8. Quantum Dots in Diagnostics and Detection: Principles and Paradigms

    PubMed Central

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

    2014-01-01

    Quantum dots are semiconductor nanocrystals that exhibit exceptional optical and electrical behaviors not found in their bulk counterparts. Following seminal work in the development of water-soluble quantum dots in the late 1990's, researchers have sought to develop interesting and novel ways of exploiting the extraordinary properties of quantum dots for biomedical applications. Since that time, over 10,000 articles have been published related to the use of quantum dots in biomedicine, many of which regard their use in detection and diagnostic bioassays. This review presents a didactic overview of fundamental physical phenomena associated with quantum dots and paradigm examples of how these phenomena can and have been readily exploited for manifold uses in nanobiotechnology with a specific focus on their implementation in in vitro diagnostic assays and biodetection. PMID:24770716

  9. Interaction of porphyrins with CdTe quantum dots

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

  10. Hyper-parallel photonic quantum computation with coupled quantum dots

    PubMed Central

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-01-01

    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

  11. Hyper-parallel photonic quantum computation with coupled quantum dots.

    PubMed

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-01-01

    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

  12. Universal Braess paradox in open quantum dots.

    PubMed

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

    2014-10-01

    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

  13. Electron states in semiconductor quantum dots

    SciTech Connect

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

    2014-11-28

    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.

  14. Silicon quantum dots for biological applications.

    PubMed

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

    2014-01-01

    Semiconductor nanoparticles (or quantum dots, QDs) exhibit unique optical and electronic properties such as size-controlled fluorescence, high quantum yields, and stability against photobleaching. These properties allow QDs to be used as optical labels for multiplexed imaging and in drug delivery detection systems. Luminescent silicon QDs and surface-modified silicon QDs have also been developed as potential minimally toxic fluorescent probes for bioapplications. Silicon, a well-known power electronic semiconductor material, is considered an extremely biocompatible material, in particular with respect to blood. This review article summarizes existing knowledge related to and recent research progress made in the methods for synthesizing silicon QDs, as well as their optical properties and surface-modification processes. In addition, drug delivery systems and in vitro and in vivo imaging applications that use silicon QDs are also discussed. PMID:23949967

  15. Semiconductor quantum dot-sensitized solar cells

    PubMed Central

    Tian, Jianjun; Cao, Guozhong

    2013-01-01

    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

  16. Biosensing with Luminescent Semiconductor Quantum Dots

    PubMed Central

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

    2006-01-01

    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.

  17. Universal Braess paradox in open quantum dots

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  18. Luminescence upconversion in colloidal double quantum dots.

    PubMed

    Deutsch, Zvicka; Neeman, Lior; Oron, Dan

    2013-09-01

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

  19. Microwave-Assisted Synthesis of Glutathione-Capped CdTe/CdSe Near-Infrared Quantum Dots for Cell Imaging.

    PubMed

    Chen, Xiaogang; Li, Liang; Lai, Yongxian; Yan, Jianna; Tang, Yichen; Wang, Xiuli

    2015-01-01

    These glutathione (GSH)-conjugated CdTe/CdSe core/shell quantum dot (QD) nanoparticles in aqueous solution were synthesized using a microwave-assisted approach. The prepared type II core/shell QD nanoparticles were characterized by UV-Vis absorption, photoluminescence (PL) spectroscopy, X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). Results revealed that the QD nanoparticles exhibited good dispersity, a uniform size distribution and tunable fluorescence emission in the near-infrared (NIR) region. In addition, these nanoparticles exhibited good biocompatibility and photoluminescence in cell imaging. In particular, this type of core/shell NIR QDs may have potential applications in molecular imaging. PMID:25997004

  20. Chemically grown vertically aligned 1D ZnO nanorods with CdS coating for efficient quantum dot sensitized solar cells (QDSSC): a controlled synthesis route.

    PubMed

    Mali, Sawanta S; Kim, Hyungjin; Patil, Pramod S; Hong, Chang Kook

    2013-12-28

    In the present article, vertically aligned ZnO nanorod arrays were synthesized by an aqueous chemical growth (ACG) route on a fluoride doped tin oxide (FTO) coated glass substrate. These nanorods were further sensitized with cadmium sulfide (CdS) quantum dots (QDs) by a successive ionic layer adsorption and reaction (SILAR) technique. The synthesized CdS coated ZnO nanorods were characterized for their structural and morphological properties with X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). Finally, prepared CdS coated 1D ZnO photoelectrodes were tested for their photoelectrochemical performance. Our results show that the sample deposited after 40 SILAR cycles shows 5.61 mA cm(-2) short current density (JSC) with ? = 1.61% power conversion efficiency. PMID:24097343

  1. Nucleation temperature-controlled synthesis and in vitro toxicity evaluation of l-cysteine-capped Mn:ZnS quantum dots for intracellular imaging.

    PubMed

    Pandey, Vivek; Pandey, Gajanan; Tripathi, Vinay Kumar; Yadav, Sapna; Mudiam, Mohana Krishna Reddy

    2016-03-01

    Quantum dots (QDs), one of the fastest developing and most exciting fluorescent materials, have attracted increasing interest in bioimaging and biomedical applications. The long-term stability and emission in the visible region of QDs have proved their applicability as a significant fluorophore in cell labelling. In this study, an attempt has been made to explore the efficacy of l-cysteine as a capping agent for Mn-doped ZnS QD for intracellular imaging. A room temperature nucleation strategy was adopted to prepare non-toxic, water-dispersible and biocompatible Mn:ZnS QDs. Aqueous and room temperature QDs with l-cysteine as a capping agent were found to be non-toxic even at a concentration of 1500 µg/mL and have wide applications in intracellular imaging. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26179189

  2. Microwave-Assisted Synthesis of Glutathione-Capped CdTe/CdSe Near-Infrared Quantum Dots for Cell Imaging

    PubMed Central

    Chen, Xiaogang; Li, Liang; Lai, Yongxian; Yan, Jianna; Tang, Yichen; Wang, Xiuli

    2015-01-01

    These glutathione (GSH)-conjugated CdTe/CdSe core/shell quantum dot (QD) nanoparticles in aqueous solution were synthesized using a microwave-assisted approach. The prepared type II core/shell QD nanoparticles were characterized by UV–Vis absorption, photoluminescence (PL) spectroscopy, X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). Results revealed that the QD nanoparticles exhibited good dispersity, a uniform size distribution and tunable fluorescence emission in the near-infrared (NIR) region. In addition, these nanoparticles exhibited good biocompatibility and photoluminescence in cell imaging. In particular, this type of core/shell NIR QDs may have potential applications in molecular imaging. PMID:25997004

  3. Solid-phase synthesis of graphene quantum dots from the food additive citric acid under microwave irradiation and their use in live-cell imaging.

    PubMed

    Zhuang, Qianfen; Wang, Yong; Ni, Yongnian

    2016-05-01

    The work demonstrated that solid citric acid, one of the most common food additives, can be converted to graphene quantum dots (GQDs) under microwave heating. The as-prepared GQDs were further characterized by various analytical techniques like transmission electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, fluorescence and UV-visible spectroscopy. Cytotoxicity of the GQDs was evaluated using HeLa cells. The result showed that the GQDs almost did not exhibit cytotoxicity at concentrations as high as 1000 µg mL(-1) . In addition, it was found that the GQDs showed good solubility, excellent photostability, and excitation-dependent multicolor photoluminescence. Subsequently, the multicolor GQDs were successfully used as a fluorescence light-up probe for live-cell imaging. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26310294

  4. 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

    Moret, Sébastien; Bécue, Andy; Champod, Christophe

    2013-01-10

    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

  5. Seed-mediated synthesis, properties and application of {gamma}-Fe{sub 2}O{sub 3}-CdSe magnetic quantum dots

    SciTech Connect

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

    2011-08-15

    Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around {gamma}-Fe{sub 2}O{sub 3} magnetic cores was performed at high temperature (300 deg. C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells. - Graphical abstract: (a) HRTEM image of oleic acid capped MPs. The size of MPs ranges from 8 to 10 nm. (b) XRD pattern of {gamma}-Fe{sub 2}O{sub 3} MPs. Highlights: > The fabrication of MQDs through a seed-mediated approach has been demonstrated. > The formation and assembly of these bi-functional nanocomposites have been elucidated. > The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components. > MQDs with thin silica coating were successfully employed in the labeling of cancer cell membranes.

  6. Synthesis of Cu2O Octadecahedron/TiO2 Quantum Dot Heterojunctions with High Visible Light Photocatalytic Activity and High Stability.

    PubMed

    Xu, Xu; Gao, Zhonghui; Cui, Zhenduo; Liang, Yanqin; Li, Zhaoyang; Zhu, Shengli; Yang, Xianjin; Ma, Jianmin

    2016-01-13

    Since p-n heterojunction photocatalysts with higher energy facets exposed usually possess greatly enhanced photocatalytic activities than single-phase catalysts, a novel Cu2O octadecahedron/TiO2 quantum dot (Cu2O-O/TiO2-QD) p-n heterojunctions composite was designed and synthesized in this study. Cu2O octadecahedra (Cu2O-O) with {110} facets and {100} facets exposed were synthesized first, then highly dispersed TiO2 quantum dots (TiO2-QDs) were loaded on Cu2O-O by the precipitation of TiO2-QDs sol in the presence of absolute ethanol. The morphology, crystal structure, chemical composition, optical properties, photocatalytic activity, and stability of Cu2O-O/TiO2-QD heterojunctions were characterized and investigated. It was found that TiO2-QDs were firmly anchored on Cu2O-O single crystals with good dispersibility. The Cu2O-O/TiO2-QD heterojunctions with partial coverage of TiO2-QDs showed a strong absorbance of visible light and exhibited an effective transfer of photoexcited electrons. The degradation of methyl orange (MO) under visible light irradiation indicated that the photocatalytic activity of Cu2O-O/TiO2-QD heterojunctions was significantly enhanced compared with that of Cu2O-O. This Cu2O-O/TiO2-QD heterojunctions composite exhibited high stability in MO degradation process and after storage in air. The high visible light photocatalytic activity and good stability were attributed to high utilization of light, effective separation of photoexcited electron-hole pairs, and instant scavenging of holes in the unique heterojunction structure. PMID:26651845

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

    SciTech Connect

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

    2014-04-24

    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 [α−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/[α−PW{sub 12}O{sub 40}{sup 3−}] composites.

  8. Competing interactions in semiconductor quantum dots

    SciTech Connect

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

    2014-10-14

    In this study, 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 non-decaying 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.

  9. Excitation transfer in stacked quantum dot chains

    NASA Astrophysics Data System (ADS)

    Kanjanachuchai, Songphol; Xu, Ming; Jaffré, Alexandre; Jittrong, Apichart; Chokamnuai, Thitipong; Panyakeow, Somsak; Boutchich, Mohamed

    2015-05-01

    Stacked InAs quantum dot chains (QDCs) on InGaAs/GaAs cross-hatch pattern (CHP) templates yield a rich emission spectrum with an unusual carrier transfer characteristic compared to conventional quantum dot (QD) stacks. The photoluminescent spectra of the controlled, single QDC layer comprise multiple peaks from the orthogonal QDCs, the free-standing QDs, the CHP, the wetting layers and the GaAs substrate. When the QDC layers are stacked, employing a 10 nm GaAs spacer between adjacent QDC layers, the PL spectra are dominated by the top-most stack, indicating that the QDC layers are nominally uncoupled. Under high excitation power densities when the high-energy peaks of the top stack are saturated, however, low-energy PL peaks from the bottom stacks emerge as a result of carrier transfers across the GaAs spacers. These unique PL signatures contrast with the state-filling effects in conventional, coupled QD stacks and serve as a means to quickly assess the presence of electronic coupling in stacks of dissimilar-sized nanostructures.

  10. Fourier transform spectra of quantum dots

    NASA Astrophysics Data System (ADS)

    Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

    2009-09-01

    Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

  11. Fourier transform spectra of quantum dots

    NASA Astrophysics Data System (ADS)

    Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

    2010-05-01

    Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

  12. Competing interactions in semiconductor quantum dots

    DOE PAGESBeta

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

    2014-10-14

    In this study, 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 atmore » 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 non-decaying 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.« less

  13. Colloidal quantum dot light-emitting devices

    PubMed Central

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

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

  14. Quantum Dot Enabled Molecular Sensing and Diagnostics

    PubMed Central

    Zhang, Yi; Wang, Tza-Huei

    2012-01-01

    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

  15. Study of metallothionein-quantum dots interactions.

    PubMed

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

    2014-05-01

    Nanoparticles have gained increasing interest in medical and in vivo applications. Metallothionein (MT) is well known as a maintainer of metal ions balance in intracellular space. This is due to high affinity of this protein to any reactive species including metals and reactive oxygen species. The purpose of this study was to determine the metallothionein-quantum dots interactions that were investigated by spectral and electrochemical techniques. CuS, CdS, PbS, and CdTe quantum dots (QDs) were analysed. The highest intensity was shown for CdTe, than for CdS measured by fluorescence. These results were supported by statistical analysis and considered as significant. Further, these interactions were analysed using gel electrophoresis, where MT aggregates forming after interactions with QDs were detected. Using differential pulse voltammetry Brdicka reaction, QDs and MT were studied. This method allowed us to confirm spectral results and, moreover, to observe the changes in MT structure causing new voltammetric peaks called X and Y, which enhanced with the prolonged time of interaction up to 6 h. PMID:24703633

  16. Electron Spin Qubits in Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eriksson, Mark

    2010-10-01

    It is intriguing that silicon, the central material of modern classical electronics, also has properties well suited to quantum electronics. Recent advances in Si/SiGe quantum devices have enabled the creation of high-quality silicon quantum dots, also known as artificial atoms. Motivated in part by the potential for very long spin coherence times in this material, we are pursuing the development of individual electron spin qubits in silicon quantum dots. I will discuss recent demonstrations of single-shot spin measurement in a Si/SiGe quantum dot spin qubit, and the demonstration of spin-relaxation times longer than one second in such a system. These and similar measurements depend on a knowledge of tunnel rates between quantum dots and nearby reservoirs or between pairs of quantum dots. Measurements of such rates provide an opportunity to revisit classic experiments in quantum mechanics. At the same time, the unique features of the silicon conduction band lead to novel and unexpected effects, demonstrating that Si/SiGe quantum dots provide a highly controlled experimental system in which to study ideas at the heart of quantum physics.

  17. Charge-extraction strategies for colloidal quantum dot photovoltaics.

    PubMed

    Lan, Xinzheng; Masala, Silvia; Sargent, Edward H

    2014-03-01

    The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p- and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction. PMID:24553652

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

    PubMed

    Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal; Patriarche, Gilles; Harmand, Jean-Christophe; Akopian, Nika; Zwiller, Val

    2016-02-10

    We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width. We notice that the emission spectra consist often of two peaks close in energy, which we explain with a comprehensive theory showing that the symmetry of the system plays a crucial role for the hole levels forming hybridized orbitals. Our results state that crystal phase quantum dots have promising quantum optical properties for single photon application and quantum optics. PMID:26806321

  19. Coherent control of energy transfer in a quantum dot strongly coupled to a photonic crystal molecule

    NASA Astrophysics Data System (ADS)

    Cai, Tao; Bose, Ranojoy; Choudhury, Kaushik R.; Solomon, Glenn S.; Waks, Edo

    2015-03-01

    Vacuum Rabi oscillation is a damped oscillation in which energy can transfer between an atomic excitation and a photon when an atom is strongly coupled to a photonic cavity. This process is challenging to be coherently controlled due to the fact that interaction between the atom and the electromagnetic resonator needs to be modulated in a quick manner compared to vacuum Rabi frequency. This control has been achieved at microwave frequencies, but has remained challenging to be implemented in the optical domain. Here we demonstrated coherent control of energy transfer in a semiconductor quantum dot strongly coupled to a photonic crystal molecule by manipulating the vacuum Rabi oscillation of the system. Instead of using a single photonic crystal cavity, we utilized a photonic crystal molecule consisting two coupled photonic crystal defect cavities to obtain both strong quantum dot-cavity coupling and cavityenhanced AC stark shift. In our system the AC stark shift modulates the coupling interaction between the quantum dot and the cavity by shifting the quantum dot resonance, on timescales (picosecond) shorter than the vacuum Rabi period. We demonstrated the ability to transfer excitation between a quantum dot and cavity, and performed coherent control of light-matter states. Our results provides an ultra-fast approach for probing and controlling light-matter interactions in an integrated nanophotonic device, and could pave the way for gigahertz rate synthesis of arbitrary quantum states of light at optical frequencies.

  20. Size controlled near-infrared high-quality PbSe quantum dots

    NASA Astrophysics Data System (ADS)

    Kalasad, M. N.; Rabinal, M. K.; Mulimani, B. G.; Greenham, N. C.

    2015-06-01

    Herein, we report the size controlled preparation of PbSe quantum dots (QDs) by non coordinating solvent route using oleic acid as surfactant molecules. The particles size is controlled by varying temperature and time of reaction. The present method of synthesis gives highly stable colloids, spherical in shape, better size tunability, narrow size distribution, extremely small size, monodisperse and exhibit strong near-infrared emission. The estimated particles sizes are in the range of 2 to 8 nm. These PbSe quantum dots are used for applications in optoelectronics and biological imaging.

  1. Manipulating Single Spins in Quantum Dots Coupled to Ferromagnetic Leads

    NASA Astrophysics Data System (ADS)

    König, Jürgen; Braun, Matthias; Martinek, Jan

    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.

  2. Ferritin-Templated Quantum-Dots for Quantum Logic Gates

    NASA Technical Reports Server (NTRS)

    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

    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.

  3. Isolated single quantum dot emitters in all-epitaxial microcavities.

    PubMed

    Muller, Andreas; Shih, Chih-Kang; Ahn, Jaemin; Lu, Dingyuan; Deppe, Dennis G

    2006-02-15

    Data are presented on a fabrication approach that places an isolated single quantum dot at the center of a semiconductor microcavity. The microcavity is based on an all-epitaxial mesa-confined design that is mechanically robust and provides the thermal dissipation needed for a single photon source device technology. Microphotoluminescence is used to reveal single quantum dot emission with the essential optical properties of single quantum emitters. PMID:16496909

  4. Synthesis of Cu-Deficient and Zn-Graded Cu-In-Zn-S Quantum Dots and Hybrid Inorganic-Organic Nanophosphor Composite for White Light Emission.

    PubMed

    Ilaiyaraja, P; Mocherla, Pavana S V; Srinivasan, T K; Sudakar, C

    2016-05-18

    Cu-deficient graded-zinc Cu-In-Zn-S (CIZS) quantum dots (QDs) were synthesized by a two-step solvothermal method. These CIZS QDs exhibited size and composition tunable photoluminescence characteristics with emission color tunable from greenish-yellow to orange to red with a relatively high quantum yield between 45 and 60%. Novel white-light-emitting (WLE) hybrid composite is fabricated by integrating the blue-emissive 1,4-bis-2-(5-phenyl oxazolyl)-benzene (POPOP) organic fluorophore and quaternary CIZS inorganic QDs. Integrating CIZS QDs with POPOP fluorophore resulted in series of tunable emission colors with CIE coordinates lying in a straight line between the coordinates of the end member. WLE was shown for hybrid mixture comprising 0.5 nM of POPOP and 3 mg/mL of CIZS QDs with color coordinates (0.3312, 0.3324). Thin films of this hybrid mixture in PMMA matrix coated on UV-LED or on glass substrates with UV backlit light also showed broadband WLE with ideal CIE color coordinates of (0.34, 0.33), high color-rendering index value of 92, and correlated color temperature value of 5143 K. The hybrid composite exhibit Forster resonance energy transfer cascading from POPOP to CIZS which results in emission covering the entire visible spectral range. POPOP and CIZS QDs hybrid composite is a versatile material for WLED applications. PMID:27135154

  5. [Synthesis and bioactivity of the folate receptor targeted gamma-cyclodextrin-folate inclusion-coated CdSe/ZnS quantum dots].

    PubMed

    Zhao, Mei-Xia; Li, Yang; Wang, Chao-Jie

    2013-04-01

    The gamma-cyclodextrin-folate (gamma-CD/FA) inclusion-coated CdSe/ZnS quantum dots (QDs) with folate-receptor (FR) targeted were synthesized by simple and convenient sonochemical method. The products were studied using Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), utraviolet-visible spectrometry (UV-vis), fluorescence spectrum and transmission electron micrographs (TEM). The results showed that the gamma-CD/FA-coated CdSe/ZnS QDs not only have good monodispersity and smaller size, but also have good optical performance, such as higher quantum yield (QY) and a long fluorescence lifetime. The cytotoxicity experiments showed that the gamma-CD/FA-coated CdSe/ZnS QDs have lower cytotoxicity and could more effectively enter cancer cells with FR over-expression. The QDs with 4-5 nm in diameter were relatively easy to enter the cell and to be removed through kidneys, so it is more suitable for biomedical applications for bioprobes and bioimaging. PMID:23833947

  6. Low-Temperature Hydrothermal Synthesis of Green Luminescent Carbon Quantum Dots (CQD), and Optical Properties of Blends of the CQD with Poly(3-hexylthiophene)

    NASA Astrophysics Data System (ADS)

    Feng, Xiaoting; Zhao, Yongqiang; Yan, Lingpeng; Zhang, Yi; He, Yuheng; Yang, Yongzhen; Liu, Xuguang

    2015-10-01

    Carbon quantum dots (CQD) emitting green photoluminescence (PL; emission peak at 500 nm) with satisfactory quantum yield (12.1%) were synthesized by a low-temperature hydrothermal method (90°C for 2 h) with l-ascorbic acid as carbon source and ethanediamine as catalyst. The as-prepared CQD dispersed readily in aqueous media, were of average diameter 6.2 nm, and their PL performance was excitation-independent. The photoluminescence wavelength of the CQD was pH-independent but the photoluminescence intensity was pH-dependent. Films of the composite materials poly(3-hexylthiophene) (P3HT) and the CQD were prepared by spin-coating and characterized by ultraviolet-visible absorption spectrophotometry and fluorescence spectrometry. The results revealed enhanced ultraviolet-visible absorption of the P3HT-CQD film compared with pure P3HT and substantially reduced PL intensity of the blend film. Experimental and theoretical results indicate the feasibility of using the CQD as a new acceptor material in polymeric photovoltaic devices.

  7. Glycerol-regulated facile synthesis and targeted cell imaging of highly luminescent Ag2Te quantum dots with tunable near-infrared emission.

    PubMed

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

    2016-07-01

    In this work, highly luminescent and emission tunable Ag2Te quantum dots (QDs) were facilely prepared by using water-dispersed glycerol as viscous solvent and CH3COOAg/Na2TeO3 as Ag/Te precursors. Viscous glycerol was utilized to slow the nucleation and growth of QDs at 200°C, and enabled the isolation of QDs with different emission wavelengths. Experimental results revealed that the as-prepared Ag2Te QDs exhibited tunable near-infrared emission from 930 to 1084nm, high photoluminescence (PL) quantum yields (QYs, more than 20%), good photostability and low cytotoxicity. After surface coating of a thin silica shell (∼1.4nm), the resulting NH2 terminated Ag2Te@SiO2-NH2 displayed enhanced PL QYs, higher photostability and biocompatibility when compared with the original Ag2Te QDs. Through a facile carboxy-amine coupling, folic acid (FA) was grafted with Ag2Te@SiO2-NH2 to form Ag2Te@SiO2-FA nanocomposites, which were used for targeted PL imaging of folate receptor over-expressed tumor cells. PMID:26998873

  8. Microwave assisted one-pot synthesis of graphene quantum dots as highly sensitive fluorescent probes for detection of iron ions and pH value.

    PubMed

    Zhang, Chunfang; Cui, Yanyan; Song, Li; Liu, Xiangfeng; Hu, Zhongbo

    2016-04-01

    Recently, carbon nanomaterials have received considerable attention as fluorescent probes owing to their low toxicity, water solubility and stable photochemical properties. However, the development of graphene quantum dots (GQDs) is still on its early stage. In this work, GQDs were successfully synthesized by one-step microwave assisted pyrolysis of aspartic acid (Asp) and NH4HCO3 mixture. The as-prepared GQDs exhibited strongly blue fluorescence with high quantum yield up to 14%. Strong fluorescence quenching effect of Fe(3+) on GQDs can be used for its high selectivity detection among of general metal ions. The probe exhibited a wide linear response concentration range (0-50μM) to Fe(3+) and the limit of detection (LOD) was calculated to be 0.26μM. In addition, GQDs are also sensitive to the pH value in the range from 2 to 12 indicating a great potential as optical pH sensors. More importantly, the GQDs possess lower cellular toxicity and high photostability and can be directly used as fluorescent probes for cell imaging. PMID:26838381

  9. A fast synthesis of near-infrared emitting CdTe/CdSe quantum dots with small hydrodynamic diameter for in vivo imaging probes.

    PubMed

    Hu, Dehong; Zhang, Pengfei; Gong, Ping; Lian, Shuhong; Lu, Yangyang; Gao, Duyang; Cai, Lintao

    2011-11-01

    Highly luminescent near-infrared (NIR) emitting CdTe/CdSe quantum dots (QDs) were prepared through a fast and convenient method, and a new type of multivalent polymer ligands was used as the surface substituents to prepare highly stable hydrophilic QDs with small sizes. The well-defined CdTe/CdSe QDs were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and photoluminescence (PL) spectroscopy, respectively. The as-prepared CdTe/CdSe QDs were photostable with high PL quantum yields (QYs) (up to 66% at room temperature), low toxicity to cells at experimental dosages, and the QDs' fluorescence emissions were tunable between 700 and 820 nm. Furthermore, fluorescence imaging using CdTe/CdSe QDs conjugated with the AS1411 aptamer (targeting nucleolin) probe in cancer cells was reported, and the CdTe/CdSe QDs were also successfully applied for the fluorescence imaging of living animals. Our preliminary results illustrated that the CdTe/CdSe NIR-QDs with small sizes would be an alternative probe for ultrasensitive, multicolor, and multiplex applications, especially for in vivo imaging applications. PMID:21989776

  10. A fast synthesis of near-infrared emitting CdTe/CdSe quantum dots with small hydrodynamic diameter for in vivo imaging probes

    NASA Astrophysics Data System (ADS)

    Hu, Dehong; Zhang, Pengfei; Gong, Ping; Lian, Shuhong; Lu, Yangyang; Gao, Duyang; Cai, Lintao

    2011-11-01

    Highly luminescent near-infrared (NIR) emitting CdTe/CdSe quantum dots (QDs) were prepared through a fast and convenient method, and a new type of multivalent polymer ligands was used as the surface substituents to prepare highly stable hydrophilic QDs with small sizes. The well-defined CdTe/CdSe QDs were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and photoluminescence (PL) spectroscopy, respectively. The as-prepared CdTe/CdSe QDs were photostable with high PL quantum yields (QYs) (up to 66% at room temperature), low toxicity to cells at experimental dosages, and the QDs' fluorescence emissions were tunable between 700 and 820 nm. Furthermore, fluorescence imaging using CdTe/CdSe QDs conjugated with the AS1411 aptamer (targeting nucleolin) probe in cancer cells was reported, and the CdTe/CdSe QDs were also successfully applied for the fluorescence imaging of living animals. Our preliminary results illustrated that the CdTe/CdSe NIR-QDs with small sizes would be an alternative probe for ultrasensitive, multicolor, and multiplex applications, especially for in vivo imaging applications.

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

    PubMed

    Ju, Jian; Chen, Wei

    2014-08-15

    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 1-1945μM 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

  12. Magneto-optical studies of quantum dots

    NASA Astrophysics Data System (ADS)

    Russ, Andreas Hans

    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.

  13. Behavior of optical bistability in multifold quantum dot molecules

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Heine, A. W.; Tutuc, D.; Zwicknagl, G.; Schuh, D.; Wegscheider, W.; Haug, R. J.

    2013-12-01

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

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

    SciTech Connect

    Heine, A. W.; Tutuc, D.; Haug, R. J.; Zwicknagl, G.; Schuh, D.; Wegscheider, W.

    2013-12-04

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

    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.

  17. Defects related emission and nanosecond optical power limiting in CuS quantum dots

    NASA Astrophysics Data System (ADS)

    Ann Mary, K. A.; Unnikrishnan, N. V.; Philip, Reji

    2015-11-01

    We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm-2, and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices.

  18. Indium, tin, and gallium doped cadmium selenide quantum dots

    NASA Astrophysics Data System (ADS)

    Tuinenga, Christopher J.

    Doping quantum dots to increase conductivity is a crucial step towards being able to fabricate a new generation of electronic devices built on the "bottom-up" platform that are smaller and more efficient than currently available. Indium, tin, and gallium have been used to dope CdSe in both the bulk and thin film regimes and introduce n-type electron donation to the conduction band. CdSe quantum dots have been successfully doped with indium, tin, and gallium using the Li4[Cd10Se4 (SPh16)] single source precursor combined with metal chloride compounds. Doping CdSe quantum dots is shown to effect particle growth dynamics in the "heterogeneous growth regime." Doping with indium, tin, and gallium introduce donor levels 280, 100, and 50 meV below the conduction band minimum, respectively. Thin films of indium and tin doped quantum dots show improved conductivity over films of undoped quantum dots. Transient Absorption spectroscopy indicates that indium doping introduces a new electron energy level in the conduction band that results in a 70 meV blue shift in the 1Se absorption bleach position. Novel characterization methods such as in-situ fluorescence growth monitoring, single quantum dot EDS acquisition, static and time-resolved temperature dependant fluorescence spectroscopy were developed in the course of this work as well. These results show that doping CdSe quantum dots with indium, tin, and gallium has not only been successful but has introduced new electronic properties to the quantum dots that make them superior to traditional CdSe quantum dots.

  19. Hybrid Circuit QED with Double Quantum Dots

    NASA Astrophysics Data System (ADS)

    Petta, Jason

    2014-03-01

    Cavity quantum electrodynamics explores quantum optics at the most basic level of a single photon interacting with a single atom. We have been able to explore cavity QED in a condensed matter system by placing a double quantum dot (DQD) inside of a high quality factor microwave cavity. Our results show that measurements of the cavity field are sensitive to charge and spin dynamics in the DQD.[2,3] We can explore non-equilibrium physics by applying a finite source-drain bias across the DQD, which results in sequential tunneling. Remarkably, we observe a gain as large as 15 in the cavity transmission when the DQD energy level detuning is matched to the cavity frequency. These results will be discussed in the context of single atom lasing.[4] I will also describe recent progress towards reaching the strong-coupling limit in cavity-coupled Si DQDs. In collaboration with Manas Kulkarni, Yinyu Liu, Karl Petersson, George Stehlik, Jacob Taylor, and Hakan Tureci. We acknowledge support from the Sloan and Packard Foundations, ARO, DARPA, and NSF.

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

    NASA Astrophysics Data System (ADS)

    Pozner, R.; Lifshitz, E.; Peskin, U.

    2015-09-01

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

  1. Gate-controlled electromechanical backaction induced by a quantum dot

    PubMed Central

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-01-01

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter. PMID:27063939

  2. Gate-controlled electromechanical backaction induced by a quantum dot

    NASA Astrophysics Data System (ADS)

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-04-01

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter.

  3. Gate-controlled electromechanical backaction induced by a quantum dot.

    PubMed

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-01-01

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter. PMID:27063939

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

    SciTech Connect

    Pozner, R.; Lifshitz, E.; Peskin, U.

    2015-09-14

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

  5. What Quantum Dots Can Do for You

    NASA Astrophysics Data System (ADS)

    Salamo, Gregory

    2008-03-01

    Recent clever techniques for fabricating nanosize materials, one-atomic-layer-at-a-time, have simultaneously opened a door to a fantastic adventure at the frontier of physics, chemistry, biology, and engineering. Nanosize materials simply do not behave as the bulk. Indeed, the rules that govern the growth and behavior of these tiny structures are unexplored. In this talk we will discuss our recent efforts to be the architect of their shape, size, density, and position of nanostructures and along the way, the interactions between them that lead to their optical and electrical behavior. While self-assembly is providing exciting quantum dot (QD) structures to explore, like the QD molecules shown here, it is equally exciting to try to use the rules we uncover to encourage QD formation to take a desired path. Can we understand the formation of faceted nanostructures? Can we encourage or seed dot structures to form specific arrays? Is it possible to engineer greater homogeneity of dot shape and size? Can we design both the optical and electrical behavior of either individual or arrays of nanostructures to mimic those we find in nature? In this talk we will review our progress to answer these questions and discuss the possibilities and challenges ahead. For example, we will discuss the formation of individual faceted nanostructures as well as the fabrication of a vertically and laterally ordered QD stacks forming three-dimensional QD arrays. As another example, we will discuss the importance of surfaces with high Miller indices, as a template to the formation of nanostructures as well as their potential role in determining the shape and increased size uniformity of the confined structures. Importantly, these observations lead to an even more basic question of when and why high index surfaces are stable. Indeed, we have found that in order to understand the origin of high index surfaces that bound nanostructures we have to study them directly.

  6. PREFACE: Quantum dots as probes in biology

    NASA Astrophysics Data System (ADS)

    Cieplak, Marek

    2013-05-01

    The recent availability of nanostructured materials has resulted in an explosion of research focused on their unique optical, thermal, mechanical and magnetic properties. Optical imagining, magnetic enhancement of contrast and drug delivery capabilities make the nanoparticles of special interest in biomedical applications. These materials have been involved in the development of theranostics—a new field of medicine that is focused on personalized tests and treatment. It is likely that multimodal nanomaterials will be responsible for future diagnostic advances in medicine. Quantum dots (QD) are nanoparticles which exhibit luminescence either through the formation of three-dimensional excitons or excitations of the impurities. The excitonic luminescence can be tuned by changing the size (the smaller the size, the higher the frequency). QDs are usually made of semiconducting materials. Unlike fluorescent proteins and organic dyes, QDs resist photobleaching, allow for multi-wavelength excitations and have narrow emission spectra. The techniques to make QDs are cheap and surface modifications and functionalizations can be implemented. Importantly, QDs could be synthesized to exhibit useful optomagnetic properties and, upon functionalization with an appropriate biomolecule, directed towards a pre-selected target for diagnostic imaging and photodynamic therapy. This special issue on Quantum dots in Biology is focused on recent research in this area. It starts with a topical review by Sreenivasan et al on various physical mechanisms that lead to the QD luminescence and on using wavelength shifts for an improvement in imaging. The next paper by Szczepaniak et al discusses nanohybrids involving QDs made of CdSe coated by ZnS and combined covalently with a photosynthetic enzyme. These nanohybrids are shown to maintain the enzymatic activity, however the enzyme properties depend on the size of a QD. They are proposed as tools to study photosynthesis in isolated 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 MgOBożena Sikora, Krzysztof Fronc, Izabela Kamińska, Kamil Koper, Piotr Stępień and Danek Elbaum Novel ZnO/MgO/Fe2O3 composite optomagnetic nanoparticles I Kamińska, 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 zirconium dioxide nanopowdersS Yatsunenko, J Kaszewski, J Grzyb, I Pełech, M M Godlewski, E Mijowska, U Narkiewicz and M Godlewski

  7. Reconfigurable Quantum-Dot Molecules Created by Atom Manipulation.

    PubMed

    Pan, Yi; Yang, Jianshu; Erwin, Steven C; Kanisawa, Kiyoshi; Flsch, Stefan

    2015-08-14

    Quantum-dot molecules were constructed on a semiconductor surface using atom manipulation by scanning tunneling microscopy (STM) at 5 K. The molecules consist of several coupled quantum dots, each of which comprises a chain of charged adatoms that electrostatically confines intrinsic surface-state electrons. The coupling takes place across tunnel barriers created reversibly using the STM tip. These barriers have an invariant, reproducible atomic structure and can be positioned-and repeatedly repositioned-to create a series of reconfigurable quantum-dot molecules with atomic precision. PMID:26317740

  8. Carbon nanotube+graphene quantum dots complex for biomedical applications

    NASA Astrophysics Data System (ADS)

    Glukhova, Olga E.; Saliy, Igor N.; Kolesnikova, Anna S.; Kossovich, Elena L.; Slepchenkov, Michael M.

    2013-02-01

    Different types of carbon nanotube + graphene quantum dot composites were investigated. Stable configuration of carbon nanotube + graphene quantum dot composites with the van der Waals and the chemical interactions were established. It was shown that a peapod + graphene quantum dot (GQD) composite is a stable configuration at the chemical interaction. Investigation of the stability were performed by means of the empirical method based on Brenner's potential. The ionization potential of the peapod + GQD composite decreases by 0.5% in comparison with the ionization potential of the hollow nanotubes.

  9. Energy levels in self-assembled quantum arbitrarily shaped dots.

    PubMed

    Tablero, C

    2005-02-01

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

  10. Semiconductor Quantum Dots in Chemical Sensors and Biosensors

    PubMed Central

    Frasco, Manuela F.; Chaniotakis, Nikos

    2009-01-01

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

  11. Quantum Dots Microstructured Optical Fiber for X-Ray Detection

    NASA Technical Reports Server (NTRS)

    DeHaven, Stan; Williams, Phillip; Burke, Eric

    2015-01-01

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

  12. Reconfigurable Quantum-Dot Molecules Created by Atom Manipulation

    NASA Astrophysics Data System (ADS)

    Pan, Yi; Yang, Jianshu; Erwin, Steven C.; Kanisawa, Kiyoshi; Fölsch, Stefan

    2015-08-01

    Quantum-dot molecules were constructed on a semiconductor surface using atom manipulation by scanning tunneling microscopy (STM) at 5 K. The molecules consist of several coupled quantum dots, each of which comprises a chain of charged adatoms that electrostatically confines intrinsic surface-state electrons. The coupling takes place across tunnel barriers created reversibly using the STM tip. These barriers have an invariant, reproducible atomic structure and can be positioned—and repeatedly repositioned—to create a series of reconfigurable quantum-dot molecules with atomic precision.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  14. Bioconjugated Quantum Dots for In Vivo Molecular and Cellular Imaging

    PubMed Central

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

    2008-01-01

    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

  15. Quantum Dot-Based Nanoprobes for In Vivo Targeted Imaging

    PubMed Central

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

    2013-01-01

    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

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

    PubMed

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

    2016-01-25

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

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

    NASA Astrophysics Data System (ADS)

    Song, Hongjoo; Lee, Seonghoon

    2007-06-01

    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.

  18. Polaronic effects in a Gaussian quantum dot

    NASA Astrophysics Data System (ADS)

    Yanar, Sonay; Sevim, Ata; Boyacioglu, B.; Saglam, Mesude; Mukhopadhyaya, Soma; Chatterjee, Ashok

    2008-03-01

    The problem of an electron interacting with longitudinal-optical (LO) phonons is investigated in an N-dimensional quantum dot with symmetric Gaussian confinement in all directions using the Rayleigh-Schrödinger perturbation theory, a variant of the canonical transformation method of Lee-Low-Pines, and the sophisticated apparatus of the Feynman-Haken path-integral technique for the entire range of the coupling parameters and the results for N=2 and N=3 are obtained as special cases. It is shown that the polaronic effects are quite significant for small dots with deep confining potential well and the parabolic potential is only a poor approximation of the Gaussian confinement. The Feynman-Haken path-integral technique in general gives a good upper bound to the ground state energy for all values of the system parameters and therefore is used as a benchmark for comparison between different methods. It is shown that the perturbation theory yields for the ground state polaron self-energy a simple closed-form analytic expression containing only Gamma functions and in the weak-coupling regime it provides the lowest energy because of an efficient partitioning of the Gaussian potential and the subsequent use of a mean-field kind of treatment. The polarization potential, the polaron radius and the number of virtual phonons in the polaron cloud are obtained using the Lee-Low-Pines-Huybrechts method and their variations with respect to different parameters of the system are discussed.

  19. Quantum dots as a possible oxygen sensor.

    PubMed

    Ziółczyk, Paulina; Kur-Kowalska, Katarzyna; Przybyt, Małgorzata; Miller, Ewa

    2014-05-21

    Results of studies on optical properties of low toxicity quantum dots (QDs) obtained from copper doped zinc sulfate are discussed in the paper. The effect of copper admixture concentration and solution pH on the fluorescence emission intensity of QDs was investigated. Quenching of QDs fluorescence by oxygen was reported and removal of the oxygen from the environment by two methods was described. In the chemical method oxygen was eliminated by adding sodium sulfite, in the other method oxygen was removed from the solution using nitrogen gas. For elimination of oxygen by purging the solution with nitrogen the increase of fluorescence intensity with decreasing oxygen concentration obeyed Stern-Volmer equation indicating quenching. For the chemical method Stern-Volmer equation was not fulfilled. The fluorescence decays lifetimes were determined and the increase of mean lifetimes at the absence of oxygen support hypothesis that QDs fluorescence is quenched by oxygen. PMID:24568848

  20. Quantum Dots Confined in Nanoporous Alumina Membranes

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Xia, Jianfeng; Wang, Jun; Shinar, Joseph; Lin, Zhiqun

    2007-03-01

    Precise control over the dispersion and lateral distribution of quantum dots (QDs) within nanoscopic porous media provides a unique route to manipulate the optical and/or electronic properties of QDs in a very simple and controllable manner for applications related to light emitting, optoelectronic, and sensor devices. Here we filled nanoporous alumina membranes (PAMs) with CdSe/ZnS core/shell QDs by dip coating. The deposition of QDs induced changes in the refractive index of PAMs. The amount of absorbed QDs was quantified by fitting the reflection and transmission spectra observed experimentally with one side open and freestanding (i.e., with two sides open) PAMs employed, respectively. The fluorescence of the QDs was found to be retained within the cylindrical nanopores of PAMs.

  1. Nanosecond colloidal quantum dot lasers for sensing.

    PubMed

    Guilhabert, B; Foucher, C; Haughey, A-M; Mutlugun, E; Gao, Y; Herrnsdorf, J; Sun, H D; Demir, H V; Dawson, M D; Laurand, N

    2014-03-24

    Low-threshold, gain switched colloidal quantum dot (CQD) distributed-feedback lasers operating in the nanosecond regime are reported and proposed for sensing applications for the first time to the authors' knowledge. The lasers are based on a mechanically-flexible polymeric, second order grating structure overcoated with a thin-film of CQD/PMMA composite. The threshold fluence of the resulting lasers is as low as 0.5 mJ/cm² for a 610 nm emission and the typical linewidth is below 0.3 nm. The emission wavelength of the lasers can be set at the design stage and laser operation between 605 nm and 616 nm, while using the exact same CQD gain material, is shown. In addition, the potential of such CQD lasers for refractive index sensing in solution is demonstrated by immersion in water. PMID:24664078

  2. Multifunctional Quantum Dots for Personalized Medicine

    PubMed Central

    Zrazhevskiy, Pavel; Gao, Xiaohu

    2009-01-01

    Successes in biomedical research and state-of-the-art medicine have undoubtedly improved the quality of life. However, a number of diseases, such as cancer, immunodeficiencies, and neurological disorders, still evade conventional diagnostic and therapeutic approaches. A transformation towards personalized medicine may help to combat these diseases. For this, identification of disease molecular fingerprints and their association with prognosis and targeted therapy must become available. Quantum dots (QDs), semiconductor nanocrystals with unique photo-physical properties, represent a novel class of fluorescence probes to address many of the needs of personalized medicine. This review outlines the properties of QDs that make them a suitable platform for advancing personalized medicine, examines several proof-of-concept studies showing utility of QDs for clinically relevant applications, and discusses current challenges in introducing QDs into clinical practice. PMID:20161004

  3. Continuous flow purification of nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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

  4. Quantum theory of dynamic nuclear polarization in quantum dots

    NASA Astrophysics Data System (ADS)

    Economou, Sophia; Barnes, Edwin

    2013-03-01

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

  5. Undoped accumulation-mode Si/SiGe quantum dots.

    PubMed

    Borselli, M G; Eng, K; Ross, R S; Hazard, T M; Holabird, K S; Huang, B; Kiselev, A A; Deelman, P W; Warren, L D; Milosavljevic, I; Schmitz, A E; Sokolich, M; Gyure, M F; Hunter, A T

    2015-09-18

    We report on a quantum dot device design that combines the low disorder properties of undoped SiGe heterostructure materials with an overlapping gate stack in which each electrostatic gate has a dominant and unique function-control of individual quantum dot occupancies and of lateral tunneling into and between dots. Control of the tunneling rate between a dot and an electron bath is demonstrated over more than nine orders of magnitude and independently confirmed by direct measurement within the bandwidth of our amplifiers. The inter-dot tunnel coupling at the [Formula: see text] charge configuration anti-crossing is directly measured to quantify the control of a single inter-dot tunnel barrier gate. A simple exponential dependence is sufficient to describe each of these tunneling processes as a function of the controlling gate voltage. PMID:26302871

  6. Tunable Quantum Dot Solids: Impact of Interparticle Interactions on Bulk Properties

    SciTech Connect

    Sinclair, Michael B.; Fan, Hongyou; Brener, Igal; Liu, Sheng; Luk, Ting S.; Li, Binsong

    2015-09-01

    QD-solids comprising self-assembled semiconductor nanocrystals such as CdSe are currently under investigation for use in a wide array of applications including light emitting diodes, solar cells, field effect transistors, photodetectors, and biosensors. The goal of this LDRD project was develop a fundamental understanding of the relationship between nanoparticle interactions and the different regimes of charge and energy transport in semiconductor quantum dot (QD) solids. Interparticle spacing was tuned through the application of hydrostatic pressure in a diamond anvil cell, and the impact on interparticle interactions was probed using x-ray scattering and a variety of static and transient optical spectroscopies. During the course of this LDRD, we discovered a new, previously unknown, route to synthesize semiconductor quantum wires using high pressure sintering of self-assembled quantum dot crystals. We believe that this new, pressure driven synthesis approach holds great potential as a new tool for nanomaterials synthesis and engineering.

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

    NASA Astrophysics Data System (ADS)

    SalmanOgli, A.; Rostami, R.

    2013-10-01

    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.

  8. Synthesis and Optical Properties of CdTe(x)Se(1-x)-Based Red to Near-Infrared Emitting Quantum Dots.

    PubMed

    Ma, Qian; Yue, Hanxiao; Zhu, Yuanna; Wang, Junpeng; Che, Quande; Shi, Ruixia; Yang, Ping

    2015-06-01

    A series of red to near-infrared (NIR) emitting quantum dots (QDs) with spherical morphologies and tunable photoluminescence (PL) properties have been synthesized by a facile organic route using octadecene (ODE) as solvent and oleic acid (OA) as single capping agent. CdSe cores with the average size of 4.5 nm display the typical optical behaviors with the PL emission peak around 610 nm. The coating CdZnS shells are introduced on the surface of CdSe cores for improving the photostability and PL efficiency of the initial QDs. As the thickness of CdZnS shells increasing, the gradual red-shift of emission wavelength varying from 617 to 634 nm of the resulting QDs can be observed, along with the remarkable increase of PL quantum yield (QY). The composition-dependent CdTe(x)Se(1-x) (CdTeSe) cores with the emission in NIR region are easily carried out by adjusting the molar ratio of Se/Te. The abnormal variation of optical bowling effect is mainly ascribed to the composition effect of alloyed QDs. Compared with CdTe0.1Se0.9/CdZnS core/shell QDs, the introducing of CdZnS shells on CdTe0.05Se0.95 cores can exhibit better passivation effect on surface status, consequently leading to the red-shifted emission peaks in the range of 739-752 nm with the maximum PL QY reaching up to 45.09%. The unique PL properties of CdTeSe-based QDs in the red to NIR range make these core/shell QDs attractive for future biological sensing and labeling applications. PMID:26369063

  9. Synthesis and Characterization of Anti-HER2 Antibody Conjugated CdSe/CdZnS Quantum Dots for Fluorescence Imaging of Breast Cancer Cells

    PubMed Central

    Tiwari, Dhermendra K.; Tanaka, Shin-Ichi; Inouye, Yasushi; Yoshizawa, Keiko; Watanabe, Tomonobu M.; Jin, Takashi

    2009-01-01

    The early detection of HER2 (human epidermal growth factor receptor 2) status in breast cancer patients is very important for the effective implementation of anti-HER2 antibody therapy. Recently, HER2 detections using antibody conjugated quantum dots (QDs) have attracted much attention. QDs are a new class of fluorescent materials that have superior properties such as high brightness, high resistance to photo-bleaching, and multi-colored emission by a single-light source excitation. In this study, we synthesized three types of anti-HER2 antibody conjugated QDs (HER2Ab-QDs) using different coupling agents (EDC/sulfo-NHS, iminothiolane/sulfo-SMCC, and sulfo-SMCC). As water-soluble QDs for the conjugation of antibody, we used glutathione coated CdSe/CdZnS QDs (GSH-QDs) with fluorescence quantum yields of 0.23∼0.39 in aqueous solution. Dispersibility, hydrodynamic size, and apparent molecular weights of the GSH-QDs and HER2Ab-QDs were characterized by using dynamic light scattering, fluorescence correlation spectroscopy, atomic force microscope, and size-exclusion HPLC. Fluorescence imaging of HER2 overexpressing cells (KPL-4 human breast cancer cell line) was performed by using HER2Ab-QDs as fluorescent probes. We found that the HER2Ab-QD prepared by using SMCC coupling with partially reduced antibody is a most effective probe for the detection of HER2 expression in KPL-4 cells. We have also studied the size dependency of HER2Ab-QDs (with green, orange, and red emission) on the fluorescence image of KPL-4 cells. PMID:22291567

  10. Quantum computing with quantum dots using the Heisenberg exchange interaction

    NASA Astrophysics Data System (ADS)

    Dewaele, Nick J.

    One of the most promising systems for creating a working quantum computer is the triple quantum dots in a linear semiconductor. One of the biggest advantages is that we are able to perform Heisenberg exchange gates on the physical qubits. These exchanges are both fast and relatively low energy. Which means that they would be excellent for producing fast and accurate operations. In order to prevent leakage errors we use a 3 qubit DFS to encode a logical qubit. Here we determine the theoretical time dependent affects of applying the Heisenberg exchange gates in the DFS basis as well as the effect of applying multiple exchange gates at the same time. we also find that applying two heisenberg exchange gates at the same time is an effective way of implementing a leakage elimination operator.

  11. Photoluminescence polarization of single InP quantum dots

    SciTech Connect

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

    2001-06-15

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

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

    PubMed

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

    2014-11-01

    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

  13. Wet chemical synthesis and self-assembly of SnS2 nanoparticles on TiO2 for quantum dot-sensitized solar cells.

    PubMed

    Tsukigase, Hiroki; Suzuki, Yoshikazu; Berger, Marie-Hélène; Sagawa, Takashi; Yoshikawa, Susumu

    2011-04-01

    SnS2 nanoparticles were synthesized through a simple wet chemical process at room temperature. The SnS2 nanoparticles were approximately spherical in shape and had diameter about 3-4 nm. SnS2-sensitized TiO2 electrodes were fabricated by the immersion of chemically modified TiO2 to well-dispersed SnS2 solution for 72 h (i.e., self-assembly method.) SnS2-sensitized TiO2 electrodes were applied in quantum dot-sensitized solar cells (QDSSCs). Under AM1.5 irradiation with 100 mW/cm2 light intensity (at 1 sun), the short-circuit current density (J(sc)), the open-circuit voltage (V(oc)), the fill factor (FF), and the energy conversion efficiency (eta) were 0.47 mA/cm2, 0.29 V, 0.58 and 0.081%, respectively. PMID:21776689

  14. One-Step Synthesis of Water-Soluble MoS2 Quantum Dots via a Hydrothermal Method as a Fluorescent Probe for Hyaluronidase Detection.

    PubMed

    Gu, Wei; Yan, Yinghan; Zhang, Cuiling; Ding, Caiping; Xian, Yuezhong

    2016-05-11

    In this work, a bottom-up strategy is developed to synthesize water-soluble molybdenum disulfide quantum dots (MoS2 QDs) through a simple, one-step hydrothermal method using ammonium tetrathiomolybdate [(NH4)2MoS4] as the precursor and hydrazine hydrate as the reducing agent. The as-synthesized MoS2 QDs are few-layered with a narrow size distribution, and the average diameter is about 2.8 nm. The resultant QDs show excitation-dependent blue fluorescence due to the polydispersity of the QDs. Moreover, the fluorescence can be quenched by hyaluronic acid (HA)-functionalized gold nanoparticles through a photoinduced electron-transfer mechanism. Hyaluronidase (HAase), an endoglucosidase, can cleave HA into proangiogenic fragments and lead to the aggregation of gold nanoparticles. As a result, the electron transfer is blocked and fluorescence is recovered. On the basis of this principle, a novel fluorescence sensor for HAase is developed with a linear range from 1 to 50 U/mL and a detection limit of 0.7 U/mL. PMID:27082278

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    We present the results of the simulation of a quantum neural network based on quantum dots using numerical method of path integral calculation. In the proposed implementation of the quantum neural network using an array of single-electron quantum dots with dipole-dipole interaction, the coherence is shown to survive up to 0.1 nanosecond in time and up to the liquid nitrogen temperature of 77K.We study the quantum correlations between the quantum dots by means of calculation of the entanglement of formation in a pair of quantum dots on the GaAs based substrate with dot size of 100 ÷ 101 nanometer and interdot distance of 101 ÷ 102 nanometers order.

  17. Nitrogen-Doped Carbon Dots for "green" Quantum Dot Solar Cells

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Sun, Pengfei; Cong, Shan; Wu, Jiang; Gao, Lijun; Wang, Yun; Dai, Xiao; Yi, Qinghua; Zou, Guifu

    2016-01-01

    Considering the environment protection, "green" materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots' excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed "green" nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79 % under AM 1.5 G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells.

  18. Nitrogen-Doped Carbon Dots for "green" Quantum Dot Solar Cells.

    PubMed

    Wang, Hao; Sun, Pengfei; Cong, Shan; Wu, Jiang; Gao, Lijun; Wang, Yun; Dai, Xiao; Yi, Qinghua; Zou, Guifu

    2016-12-01

    Considering the environment protection, "green" materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots' excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed "green" nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79 % under AM 1.5 G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells. PMID:26781285

  19. Energy levels of hybrid monolayer-bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; Ketabi, S. A.; da Costa, D. R.; Peeters, F. M.

    2016-04-01

    Often real samples of graphene consist of islands of both monolayer and bilayer graphene. Bound states in such hybrid quantum dots are investigated for (i) a circular single-layer graphene quantum dot surrounded by an infinite bilayer graphene sheet and (ii) a circular bilayer graphene quantum dot surrounded by an infinite single-layer graphene. Using the continuum model and applying zigzag boundary conditions at the single-layer-bilayer graphene interface, we obtain analytical results for the energy levels and the corresponding wave spinors. Their dependence on perpendicular magnetic and electric fields are studied for both types of quantum dots. The energy levels exhibit characteristics of interface states, and we find anticrossings and closing of the energy gap in the presence of a bias potential.

  20. Correlation studies in weakly confining quantum dot potentials

    NASA Astrophysics Data System (ADS)

    Kimani, Peter; Jones, Preston; Winkler, Peter

    We investigate the electron correlation in few-electron closed-shell atomic systems and similarly in few-electron quantum dots under weak confinement. As usual we start with restricted Hartree-Fock (HF) calculations and add electron correlation in steps in a series of approximations based on the single particle Green's function approach: (i) second-order Green function (GF); (ii) 2ph-Tamm-Dancoff approximation (TDA); and (iii) an extended version thereof which introduces ground-state correlation into the TDA. Our studies exhibit similarities and differences between weakly confined quantum dots and standard atomic systems. The calculations support the application of HF, GF, and TDA techniques in the modeling of three-dimensional quantum dot systems. The observed differences emphasize the significance of confinement and electronic features unique to quantum dots, such as the increased binding of electrons with higher angular momentum and thus - compared to atomic systems - modified shell-filling sequences.

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

    DOEpatents

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

    2008-07-29

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

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

    DOEpatents

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

    2010-04-13

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

  3. Prospects for thermoelectricity in quantum dot hybrid arrays

    NASA Astrophysics Data System (ADS)

    Urban, Jeffrey J.

    2015-12-01

    The electronic, chemical and mechanical properties of quantum dot structures may lead to thermoelectric devices with a range of advantages with respect to existing ones based on bulk polycrystalline materials.

  4. Air-stable n-type colloidal quantum dot solids.

    PubMed

    Ning, Zhijun; Voznyy, Oleksandr; Pan, Jun; Hoogland, Sjoerd; Adinolfi, Valerio; Xu, Jixian; Li, Min; Kirmani, Ahmad R; Sun, Jon-Paul; Minor, James; Kemp, Kyle W; Dong, Haopeng; Rollny, Lisa; Labelle, André; Carey, Graham; Sutherland, Brandon; Hill, Ian; Amassian, Aram; Liu, Huan; Tang, Jiang; Bakr, Osman M; Sargent, Edward H

    2014-08-01

    Colloidal quantum dots (CQDs) offer promise in flexible electronics, light sensing and energy conversion. These applications rely on rectifying junctions that require the creation of high-quality CQD solids that are controllably n-type (electron-rich) or p-type (hole-rich). Unfortunately, n-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure. Here we report high-performance, air-stable n-type CQD solids. Using density functional theory we identify inorganic passivants that bind strongly to the CQD surface and repel oxidative attack. A materials processing strategy that wards off strong protic attack by polar solvents enabled the synthesis of an air-stable n-type PbS CQD solid. This material was used to build an air-processed inverted quantum junction device, which shows the highest current density from any CQD solar cell and a solar power conversion efficiency as high as 8%. We also feature the n-type CQD solid in the rapid, sensitive, and specific detection of atmospheric NO2. This work paves the way for new families of electronic devices that leverage air-stable quantum-tuned materials. PMID:24907929

  5. Coherent spin transport through dynamic quantum dots.

    PubMed

    Stotz, James A H; Hey, Rudolf; Santos, Paulo V; Ploog, Klaus H

    2005-08-01

    Spin transport and manipulation in semiconductors have been studied intensively with the ultimate goal of realizing spintronic devices. Previous work in GaAs has focused on controlling the carrier density, crystallographic orientation and dimensionality to limit the electron spin decoherence and allow transport over long distances. Here, we introduce a new method for the coherent transport of spin-polarized electronic wave packets using dynamic quantum dots (DQDs) created by the piezoelectric field of coherent acoustic phonons. Photogenerated spin carriers transported by the DQDs in undoped GaAs (001) quantum wells exhibit a spin coherence length exceeding 100 microm, which is attributed to the simultaneous control of the carrier density and the dimensionality by the DQDs during transport. In the absence of an applied magnetic field, we observe the precession of the electron spin induced by the internal magnetic field associated with the spin splitting of the conduction band (Dresselhaus term). The coherent manipulation of the precession frequency is also achieved by applying an external magnetic field. PMID:16041380

  6. Spin Qubits with Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tarucha, Seigo; Yamamoto, Michihisa; Oiwa, Akira; Choi, Byung-Soo; Tokura, Yasuhiro

    This section describes recent progresses on the research of spin qubits realized in semiconductor quantum dot (QD) systems. After we argue the scheme of initialization and detection of individual spin states, we discuss the key idea of the universal gates constituted with QDs proposed by D. Loss and D. P. DiVincenzo. In order to achieve universal quantum gate operations, we need single qubit coherent manipulations and two qubit controlled-NOT or control-Z gates. For the first type of gate, instead of the standard rf magnetic field driven electron spin resonance (ESR), we proposed and implemented electric dipole induced spin resonance (EDSR), which has various advantages over ESR, including low dissipation, individual access to the spins and integrability. We describes recent progress in the fast Rabi oscillations. The second type of gate can be realized by the exchange coupling between nearby QDs. We also discuss the experiments combining single- and two-qubit operations. Finally, we argue the progress of the coupling of the spins in QDs with the "flying qubits", namely, photons of visible or microwave and itinerant electrons in the wave guides.

  7. Lead selenide quantum dot polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Waldron, Dennis L.; Preske, Amanda; Zawodny, Joseph M.; Krauss, Todd D.; Gupta, Mool C.

    2015-02-01

    Optical absorption and fluorescence properties of PbSe quantum dots (QDs) in an Angstrom Bond AB9093 epoxy polymer matrix to form a nanocomposite were investigated. To the authors’ knowledge, this is the first reported use of AB9093 as a QD matrix material and it was shown to out-perform the more common poly(methyl methacrylate) matrix in terms of preserving the optical properties of the QD, resulting in the first reported quantum yield (QY) for PbSe QDs in a polymer matrix, 26%. The 1-s first excitonic absorption peak of the QDs in a polymer matrix red shifted 65 nm in wavelength compared to QDs in a hexane solution, while the emission peak in the polymer matrix red shifted by 38 nm. The fluorescence QY dropped from 55% in hexane to 26% in the polymer matrix. A time resolved fluorescence study of the QDs showed single exponential lifetimes of 2.34 and 1.34 μs in toluene solution and the polymer matrix respectively.

  8. Lead selenide quantum dot polymer nanocomposites.

    PubMed

    Waldron, Dennis L; Preske, Amanda; Zawodny, Joseph M; Krauss, Todd D; Gupta, Mool C

    2015-02-20

    Optical absorption and fluorescence properties of PbSe quantum dots (QDs) in an Angstrom Bond AB9093 epoxy polymer matrix to form a nanocomposite were investigated. To the authors' knowledge, this is the first reported use of AB9093 as a QD matrix material and it was shown to out-perform the more common poly(methyl methacrylate) matrix in terms of preserving the optical properties of the QD, resulting in the first reported quantum yield (QY) for PbSe QDs in a polymer matrix, 26%. The 1-s first excitonic absorption peak of the QDs in a polymer matrix red shifted 65 nm in wavelength compared to QDs in a hexane solution, while the emission peak in the polymer matrix red shifted by 38 nm. The fluorescence QY dropped from 55% in hexane to 26% in the polymer matrix. A time resolved fluorescence study of the QDs showed single exponential lifetimes of 2.34 and 1.34 μs in toluene solution and the polymer matrix respectively. PMID:25629463

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

    NASA Technical Reports Server (NTRS)

    Qiu, Y.; Uhl, D.

    2002-01-01

    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.

  10. Coupling capacitance between double quantum dots tunable by the number of electrons in Si quantum dots

    SciTech Connect

    Uchida, Takafumi Arita, Masashi; Takahashi, Yasuo; Fujiwara, Akira

    2015-02-28

    Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD.

  11. Coherent radiation by quantum dots and magnetic nanoclusters

    SciTech Connect

    Yukalov, V. I.; Yukalova, E. P.

    2014-03-31

    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.

  12. Quantum Phase Transitions in Cavity Coupled Dot systems

    NASA Astrophysics Data System (ADS)

    Kasisomayajula, Vijay; Russo, Onofrio

    2011-03-01

    We investigate a Quantum Dot System, in which the transconductance, in part, is due to spin coupling, with each dot subjected to a biasing voltage. When this system is housed in a QED cavity, the cavity dot coupling alters the spin coupling of the coupled dots significantly via the Purcell Effect. In this paper we show the extent to which one can control the various coupling parameters: the inter dot coupling, the individual dots coupling with the cavity and the coupled dots coupling with the cavity as a single entity. We show that the dots coupled to each other and to the cavity, the spin transport can be controlled selectively. We derive the conditions for such control explicitly. Further, we discuss the Quantum phase transition effects due to the charge and spin transport through the dots. The electron transport through the dots, electron-electron spin interaction and the electron-photon interaction are treated using the Non-equilibrium Green's Function Formalism. http://publish.aps.org/search/field/author/Trif_Mircea (Trif Mircea), http://publish.aps.org/search/field/author/Golovach_Vitaly_N (Vitaly N. Golovach), and http://publish.aps.org/search/field/author/Loss_Daniel (Daniel Loss), Phys. Rev. B 75, 085307 (2007)

  13. Whispering-gallery mode microcavity quantum-dot lasers

    SciTech Connect

    Kryzhanovskaya, N V; Maximov, M V; Zhukov, A E

    2014-03-28

    This review examines axisymmetric-cavity quantum-dot microlasers whose emission spectrum is determined by whisperinggallery modes. We describe the possible designs, fabrication processes and basic characteristics of the microlasers and demonstrate the possibility of lasing at temperatures above 100 °C. The feasibility of creating multichannel optical sources based on a combination of a broadband quantum-dot laser and silicon microring modulators is discussed. (review)

  14. Ultrafast optical properties of lithographically defined quantum dot amplifiers

    SciTech Connect

    Miaja-Avila, L.; Verma, V. B.; Mirin, R. P.; Silverman, K. L.; Coleman, J. J.

    2014-02-10

    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.

  15. Dissipative laser bullets in dielectric media containing quantum dots

    NASA Astrophysics Data System (ADS)

    Gubin, M. Yu.; Leksin, A. Yu.; Gladush, M. G.; Arakelian, S. M.; Prokhorov, A. V.

    2015-09-01

    The formation of three-dimensional spatiotemporal dissipative solitons (laser bullets) in a dense ensemble of two-level quantum dots imbedded into a dielectric host is analyzed theoretically taking into account complex local field corrections. The possibility of satisfying stability conditions for laser bullets in a wide range of concentration and quantum dot size parameters is demonstrated. Substantial increase in dimensions of the found areas of stability when choosing all-dielectric metamaterials as a host medium is revealed.

  16. Colloidal semiconductor quantum dots: Potential tools for new diagnostic methods

    NASA Astrophysics Data System (ADS)

    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

    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.

  17. Optimal excitation conditions for indistinguishable photons from quantum dots

    NASA Astrophysics Data System (ADS)

    Huber, Tobias; Predojević, Ana; Föger, Daniel; Solomon, Glenn; Weihs, Gregor

    2015-12-01

    In this paper, we present a detailed, all optical study of the influence of different excitation schemes on the indistinguishability of single photons from a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel interference of consecutive photons from the spontaneous emission of an InAs quantum dot state under various excitation schemes and different excitation conditions and give a comparison.

  18. Propagating surface plasmon induced photon emission from quantum dots.

    PubMed

    Wei, Hong; Ratchford, Daniel; Li, Xiaoqin Elaine; Xu, Hongxing; Shih, Chih-Kang

    2009-12-01

    We investigate the interaction between propagating surface plasmons in silver nanowires and excitons generated in quantum dots. We show propagating surface plasmons can excite excitons, which results in quantum dot emission. In this process, the energy is directly transferred from the propagating surface plasmons to the excitons without converting to photons. Furthermore, we demonstrate the reverse process where the decay of excitons generates surface plasmons. PMID:19821597

  19. Charge and spin storage in self-organized quantum dots

    NASA Astrophysics Data System (ADS)

    Wieczorek, W.; Warming, T.; Geller, M.; Bimberg, D.; Cirlin, G. E.; Zhukov, A. E.; Ustinov, V. M.

    2006-05-01

    We demonstrate optical charging of spectrally selected subensembles of self-organized quantum dots with single charge carriers. In spectral hole burning experiments negative and positive trions are observed, representing quantum dots charged with single electrons and holes. By circularly polarized excitation in an applied magnetic field we are able to address the spin of single electrons. A spin flip of the electron is observed after excitation in the upper Zeeman level.

  20. Los Alamos Quantum Dots for Solar, Display Technology

    SciTech Connect

    Klimov, Victor

    2015-04-13

    Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.