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Charge Separation in Heterostructured Semiconductor NanocrystalsHewa-Kasakarage, Nishshanka Niroshan 03 August 2010 (has links)
No description available.
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Solution phase synthesis and characterization of III-V, II-VI and CdSe.₀₈Te.₉₂ semiconductor nanowiresFanfair, Dayne Dustan, 1978- 01 October 2012 (has links)
There are many advantages to the solution phase synthesis of semiconductor nanowires, the most notable of which are the ease of scalability and the production of nanowires in higher yields than those typically obtained in chemical vapor deposition (CVD) based processes. The solution phase synthesis of high quality, high aspect ratio (>100) narrow diameter semiconductor nanowires depends sensitively on three parameters: the diameter of the nanocrystals utilized to promote (seed) nanowire growth, molecular precursor decomposition kinetics and the choice of solvent in which the nanowires are grown. Bismuth is a low melting point (270 °C) semimetal and thus an ideal candidate for the solution-liquid-solid (SLS) growth of nanowires. A bismuth nanocrystal synthesis was developed that affords nanocrystals with average diameters from 4 - 20 nm. The nanocrystal diameter is controlled by varying the capping ligand (TOPO) to bismuth molar ratio. The synthesis of Au2Bi nanocrystals was also studied as it also affords small diameter (~ 2 nm) nanocrystals that are suitable for SLS nanowire growth. Molecular precursor decomposition kinetics can have a significant impact on nanowire yield and quality. Precursors that decompose too quickly can produce relatively large diameter nanowires, while precursors that decompose too slowly can produce nanowires with a highly tortuous morphology as a result of a high density of crystallographic defects. The choice of molecular precursor for the synthesis of III-V and II-VI nanowires was investigated. The solvent in which nanowires are grown can also have a significant effect on nanowire yield, quality and morphology. Coordinating solvents such as alkylphosphine oxides and alkylamines can interact with the atoms, or atomic complexes, that constitute nanowires and thus mediate the nanowire growth rate. In some instances, for example InAs nanowires grown in TOPO, this interaction can completely quench nanowire growth. This solvent effect has been investigated for the growth of III-V and II-VI nanowires. Solvents can also affect nanowire morphology. Branched ZnSe nanowires, i.e. hybrid nanostructures in which ZnSe nanorods grow epitaxially from the surface of ZnSe nanowires, are synthesized in trioctylamine whereas TOPO suppresses this branched growth. Finally, a mechanism which allows for the synthesis of narrow diameter nanowires seeded by much larger diameter nanocrystals is investigated. Bismuth nanocrystals with an average diameter of ~ 20 nm are utilized to promote the growth of narrow diameter (~ 6 nm) CdSe.₀₈Te.₉₂ nanowires. / text
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Semiconductor nanocrystals, nanorods, nanowires and applications in biomolecular integrationShieh, Felice 28 August 2008 (has links)
Not available / text
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Semiconductor nanocrystals, nanorods, nanowires and applications in biomolecular integrationShieh, Felice, January 1900 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.
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Solution phase synthesis and characterization of III-V, II-VI and CdSe.₀₈Te.₉₂ semiconductor nanowiresFanfair, Dayne Dustan, January 1900 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.
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Synthesis and characterization of Cu-based telluride semiconductor materials for application in photovoltaic cellsNtholeng, Nthabiseng January 2017 (has links)
Submitted to the Faculty of Science, School of Chemistry at University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 05 June 2017. / The colloidal method has extensively been used to synthesize ternary and quaternary copper
sulfides and selenides. Although tellurides form part of the chalcogenides, little has been
reported on them particularly the synthesis of these nanostructures. Achieving high-quality
nanocrystals through colloidal synthesis requires thorough monitoring of parameters such as
time, solvent, precursor as they affect nucleation and growth of the nanocrystals. Herein, we
report on the colloidal synthesis of ternary CuInTe2 and quaternary CuIn1-xGaxTe2
nanostructured semiconductor materials. A typical synthesis of CuInTe2 entailed varying
reaction temperature. At temperatures below 250 °C, no formation of CuInTe2 was seen. At
250 °C formation of CuInTe2 could be observed with the formation of binary impurities. A
change in the sequence in which precursors were added at 250 °C yielded pure CuInTe2.
Applying different surfactants aided in achieving differently structured morphologies of
CuInTe2 nanocrystals. Morphology varied from rods, cubes, nanosheets etc. Different
morphologies resulted in different optical properties with the high optical band gap of 1.22
eV measured for 1D rods. Different precursors were employed in the synthesis of quaternary
CuIn1-xGaxTe2. Precursor 2 (entailed the use of Cu (acac)2, In (acac)3 and Ga(acac)3) yielded
pure CuIn1-xGaxTe2 phase with no formation of impurities. Variation in reaction time
influenced the optical properties of the quaternary CuIn1-xGaxTe2 with high band gap
obtained at low reaction time (30 min). A change in Ga and In concentration resulted in
reduced lattice parameters a and c with lowest values obtained with the highest Ga
concentration. However, achieving the intended concentration proved challenging due to the
loss of the material during synthesis. Increasing the Ga concentration resulted in a high
optical band gap. Conducting the reaction with Hexadecylamine (HDA) resulted in a
relatively high optical band though the formation of impurities was evident. The obtained
band gap can be attributed to small sized particles as evident from TEM results.
Heterojunction ZnO/CIT and ZnO/CIGT solar cell devices were fabricated through a simple
solution approach. The performance of ZnO/CIGT device was superior to that of ZnO/CIT in
which efficiency increased from 0.26-0.78%. In the ZnO/CIT device, high Voc of 880 mV
was recorded while 573.66 mV was measured for ZnO/CIGT device. Chemical and thermal
treatments were performed on the ZnO/CIGT devices. The efficiency increased from 0.78
1.25% when the device was chemically treated with a short-chain EDT ligand. A high
conversion efficiency of 2.14% was recorded for devices annealed at 300 °C. High annealing
temperatures resulted in poor device performance with the lowest efficiency of 0.089%
obtained at annealing temperatures of 500 °C attributed to the leaching out of In and Ga into
the ZnO layer. / LG2017
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Electronic properties of low dimensional carbon materialsSanders, Kirsty Gail January 2016 (has links)
A Dissertation submitted to the Faculty of Science, University of the Witwatersrand,
Johannesburg, in ful lment of the requirements for the degree of Master of Science. Johannesburg 2016. / Low dimensional carbon systems are of immense interest in condensed matter physics
due to their exceptional and often startling electric and magnetic properties. In this
dissertation we consider two of these materials - graphene and nanocrystalline diamond.
The effect of synthesis parameters on the quality of graphene is examined and
it is found that controlling the partial pressure of the synthesis gases plays a critical
role in determining the quality of the sample. Superconductivity in Boron doped
nanocrystalline diamond (B-NCD) is considered and weak localisation along with a
Berezinsky-Kosterlitz-Thouless (BKT) transition is identified in the samples. Furthermore
we explore theoretically the problem of electric transport through a double quantum
dot system coupled to a nanomechanical resonator. We find resonant tunnelling
when the difference between the energy levels of the dots equals an integer multiple of
the resonator frequency, and that while initially increasing the electron phonon coupling
(g) increases the current through the sample further increase in g inhibits electric
transport through the quantum dots. / LG2017
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Preparation and characterisation of biocompatible semiconductor nanocrystalsLees, Emma E. January 2009 (has links)
Semiconductor nanocrystals exhibit unique optical and physical properties that make them an attractive alternative to organic dyes for fluorescent bioapplications. Although significant advances have been made since their first reported use in biology a decade ago, it still remains a challenge to prepare high quality, biocompatible semiconductor nanocrystals. / In this thesis, studies are described with the aim to prepare robust, biocompatible semiconductor nanocrystals that exhibit each of the properties necessary for their implementation in biological applications. Two different approaches were investigated: ligand exchange and polymer encapsulation, and advances in each are presented. A heterobifunctional ligand suitable for bioconjugation, carboxyl terminated dihydrolipoic acid poly(ethylene glycol) (DHLA-PEG-COOH), was synthesised and characterised to prepare water-soluble, biocompatible semiconductor nanocrystals via ligand exchange. It was found that nanocrystals transferred into water using DHLA-PEG-COOH exhibit the same optical properties and colloidal stability as those prepared using DHLA-PEG. It was demonstrated that the surface charge of the nanocrystals may be controlled by altering the ratio of DHLA-PEG:DHLA-PEG- COOH ligands. In a different approach, colloidally stable, biocompatible nanocrystals were prepared via polymer encapsulation. It was found that by employing a low molecular weight polymer, biocompatible nanocrystals that exhibit a small hydrodynamic diameter could be realised. / Experimental results are presented on the conjugation of biocompatible nanocrystals to protein targets. It was found that while standard coupling chemistries yield protein-dye conjugates, these chemistries did not result in protein-nanocrystal conjugates. In order to overcome the drawbacks of standard coupling chemistries, which are susceptible to hydrolysis, a novel conjugation scheme utilising copper-free click chemistry is proposed. / Finally, the success of nanocrystals in bioapplications depends on the ability to characterise nanocrystal-protein conjugates. By means of analytical ultracentrifugation, data on the sedimentation properties of nanocrystals and nanocrystal-protein conjugates was obtained. Analysis of these data provided information on fundamental physical properties of biocompatible nanocrystals and nanocrystal-protein conjugates, in particular the core crystal size, hydrodynamic size, number of surface ligands and nanocrystal:protein stoichiometry. Such a precise, comprehensive characterisation of nanocrystals in general, and nanocrystal-protein conjugates in particular, will greatly facilitate their use in bioapplications.
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Preparation and characterisation of biocompatible semiconductor nanocrystals /Lees, Emma E. January 2009 (has links)
Thesis (Ph.D.)--University of Melbourne, School of Chemistry, 2010. / Typescript. Includes bibliographical references.
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Synthesis, spectroscopy, and magnetism of diluted magnetic semiconductor nanocrystals /Radovanovic, Pavle V. January 2004 (has links)
Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 155-170).
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