This work has analyzed the complex interfaces of GaN and InGaN grown by sputter deposition and GaN grown by metal-organic chemical vapor deposition (MOCVD) with CdTe and CdS. First, the GaN and InGaN films were characterized by AFM and XRD, and it has been shown that the MOCVD samples have a very smooth surface and are single crystalline with growth in the (002) direction. On the other hand, the sputter deposited samples have rougher surfaces and are polycrystalline. Furthermore, complete interface studies have been performed using in-situ XPS and deposition between GaN grown by sputter deposition and MOCVD and CdTe and CdS to determine the band alignments, conduction and valence band offsets, and Fermi level positions. These interface studies will help determine basic properties to see if these GaN films can be incorporated in a CdTe solar cell to improve its efficiency. It was determined that all the interfaces between the sputtered GaN/InGaN and CdTe/CdS have small conduction band offsets of less than 0.1 eV that do not significantly prevent electron flow across the interface. However, the valence band offsets were much more significant, as they ranged from 0.43 eV to over 1.8 eV. For purposes of the desired positions of the GaN in the CdTe solar cell, the conduction band offsets are much more crucial, and very small conduction band offsets are desired. An interesting effect was that the interfaces between InGaN/CdTe and InGaN/CdS showed In migration into the CdTe and CdS, causing a rise in the Fermi level for the CdTe and CdS, which has been known to worsen the performance of the CdTe solar cell. The MOCVD GaN/CdTe and CdS interfaces showed a slightly higher conduction band offset of about 0.15 eV, but this barrier still should not significantly prevent current flow. / Master of Science

No description available.

No description available.

No description available.

No description available.

A major gene controlling grain cadmium (Cd) concentration, designated as Cdu-B1, has been mapped to the long arm of chromosome 5B, but the genetic factor(s) conferring the low Cd phenotype are currently unknown. Genetic mapping of markers linked to Cdu-B1 in a population of recombinant inbred substitution lines (RSLs) revealed that the gene(s) associated with variation in Cd concentration reside(s) in wheat deletion bin 5BL9 between fraction breakpoints 0.76 and 0.79, and linked to two candidate genes; PCS2 (phytochelatin synthetase) and Xwg644, which codes for a known ABC (ATP-binding cassette) protein. Genetic mapping and quantitative trait locus (QTL) analysis of grain Cd concentration was performed in a doubled haploid (DH) population and revealed that these genes were not associated with Cdu-B1. Two expressed sequence markers (ESMs), and five sequence tagged site (STS) markers were identified that co-segregated with Cdu-B1, and explained >80% of the phenotypic variation in grain Cd concentration. A gene coding for a P1B-ATPase, designated as OsHMA3 (heavy metal associated), has recently been associated with phenotypic variation in grain Cd concentration in rice. Mapping of the orthologous gene to OsHMA3 in the DH population revealed complete linkage with Cdu-B1 and was designated as HMA3-B1. Fine mapping of Cdu-B1 in >4000 F2 plants localized Cdu-B1 to a 0.14 cM interval containing HMA3-B1. Two bacterial artificial chromosomes (BACs) containing full-length coding sequence for HMA3-B1 and HMA3-A1 (homoeologous copy from the A genome) were identified and sequenced. Sequencing of HMA3-B1 from high and low Cd accumulators of durum wheat revealed a 17 bp duplication in high accumulators that results in predicted pre-mature stop codon and thus, a severely truncated protein. Several DNA markers linked to Cdu-B1, including HMA3-B1, were successfully converted to high throughput markers and were evaluated for practical use in breeding programs. These markers were successful at classifying a collection of 96 genetically diverse cultivars and breeding lines into high and low Cd accumulators and will have broad application in breeding programs targeting selection for low grain Cd concentrations. Current results support HMA3-B1 as a candidate gene responsible for phenotypic differences in grain Cd concentrations in durum wheat.

The thesis describes an electrochemical investigation of different types of nickel electrode used in nickel-cadmium cells, which are available commercially or currently under development. Impedance spectroscopy has been used to determine the electrochemical characteristics of these electrodes. The electrochemistry of the nickel electrodes was modelled by the electrical analogue method. Allowance was made within the model for porosity and adsorption effects. Component values were initially estimated by graphical techniques and the computer fitting procedure was then completed by an iterative process to provide kinetic parameters which were used to compare and contrast the characteristics of the nickel sintered, pocket and plastic bonded electrodes. The technological target of this work was establish a possible method by which the residual capacity remaining within nickel-cadmium cells could be determined. The kinetic parameters generated by the electrical analogue technique have provided data on which to base a measurement for the prediction of the state of charge in nickel-cadmium cells.

1. The digestive gland of the scallop Pecten maximus naturally contains a very high concentration of cadmium (100 ppm wet weight), which does not show individual or seasonal variations. 2. About 60% of the tissue cadmium is soluble (i.e. is found in the supernatant when homogenate is centrifuged for 1 hour at 100,000g) and is bound to three main types of macromolecule. Most (about 60%) of this metal is associated with a component of molecular weight 55,000, the rest being bound to a low molecular weight species and, probably non-specifically, to components of very high molecular weight (greater than 100,000 molecular weight). The latter components were not further characterised. 3 The major binding component complexes the Cd2+ via sulphydryl groups, and so has a high cysteine content, but the binding is weaker than that of cadmium to metallothionein. The component has a high content of glutamate and aspartate (or their amides) and contains aromatic amino acids. It may also have a small carbohydrate content.4. The major cadmium binding component was susceptible to degradation by endogenous proteolytic enzymes. A major digestive enzyme was identified as a chymotrypsin which could be inactivated with phenylmethanesulphonylfluoride. Addition of PMSF to the homogenate reduced the total proteolytic activity of the digestive gland cytosol by up to 75%. Attempts to further inhibit, or remove, the remaining protease activity were largely unsuccessful. Probably as a result of the action of the proteolytic enzymes on the major cadmium component efforts to isolate the latter were characterised by irreproducibility, and satisfactory purification was not achieved. 5. The low molecular weight cadmium binding component binds 10-15% of the total soluble cadmium and exhibits many of the characteristics of a metallothionein. It has an apparent molecular weight of 10,000 on gel exclusion chromatography, high cadmium and cysteine contents and a high A250/A280 ratio. It is also heat stable and contains copper and zinc as well as cadmium. It can be detected by the metallothionein assay of Eaton & Toal (1982). 6. Preparations of both the major Cd binding component and metallo-thionein-like component contained relatively large amounts of carbohydrate, but the latter was probably not associated with these proteins. Its origin is unknown.

The synthesis of n-alkylamine-bound CdSe-NH2Rʹ nanocrystals from carboxylateterminated CdSe-Cd(O2CR)2/HO2CR requires the removal of acidic impurities prior to the addition of primary amine. Otherwise, the formation and subsequent tight binding of n-alkylammonium carboxylate ion pairs prevents quantitative removal of carboxylate species. Dimethylcadmium and diethylzinc were used as reagents to deprotonate acidic impurities, which either causes methylation (with a surface density of 0.04−0.22 nm−2) and photoinduced reduction of the nanocrystal core or X-type ligand exchange with ethyl species, respectively. The acid-scavenged nanocrystals could be completely isolated from displaced carboxylate ligands (≤ 0.01 carboxylates nm-2). In addition to traditional selective precipitation procedures, gel permeation and silica chromatography were investigated as alternative purification methods for the isolation of CdSe-NH2Rʹ. Both demonstrated no improvement compared to the more convenient precipitation process. Thin films fabricated from CdSe-NH2C4H9 show little to no grain growth upon thermal annealing at 250 ºC, maintaining domains (~10 nm) despite complete desorption of n-butylamine from the nanocrystal surface above 150 ºC. Despite no passivation of the surface and a high density of grain boundaries, thin film transistors of CdSe-NH2C4H9 fabricated on thermally grown silicon dioxide gate dielectrics produce field-effect transistors with an average electron mobility of 12 ± 1 cm2 V-1s-1, a low threshold voltage hysteresis (4.0 ± 0.6 Vth), and an on/off ratio of 8x104. Colloidal dispersions of amine bound nanocrystals (CdSe−NH2Rʹ) are indefinitely stable at amine concentrations of 0.1 M or higher and slowly aggregate at lower concentrations. Dissociation and evaporation of the amine ligands in 4-ethylpyridine, tri-n-butylphosphine, or molten tri-n-octylphosphine oxide solution results in nanocrystal aggregation. Greater stability can be achieved using dimethyl-n-octadecylphosphine as the L-type ligand, yielding soluble CdSe- PMe2C18H37 nanocrystals with a phosphine coverage of 1.8 nm-2. CdSe-PMe2C18H37 is the first stable nanocrystal sample bound solely by neutral phosphines. Z-type rebinding was investigated with metal oleate species (Mn+(O2CR)n, M = Cd2+, Zn2+, Pb2+, In3+), and a relative binding affinity of these complexes can be established. Rebinding of metal oleate species at 25 ºC yield lower coverages, yet can reach saturation upon heating to 100 ºC. The rebinding of cadmium chloride to aggregated CdSe-PBu3 stabilizes the particle and aids in their redissolution. L-type ligand exchange and subsequent Z-type rebinding was employed towards the synthesis of a new model compound passivated by dimethyl-n-octadecylphosphine and cadmium trifluoroacetate ligands, CdSe-Cd(O2CCF3)2/PMe2C18H37, which is characterized by UV-Vis, 1H, 19F, and 31P NMR spectroscopies. The findings of this dissertation demonstrate the importance of ion-pair species in the colloidal stabilization of colloidal nanocrystal systems. It also indicates the utility of stoichiometric, amine and phosphine-bound CdSe-L to act as both reporter complexes and as a clean reactive reagent for synthesis of novel CdSe-MX2/L systems to study the molecular interactions at nanocrystal surfaces.

Lam, Ngai Sze. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Lam, Ngai Sze. / Abstract --- p.i / Acknowledgements --- p.iii / Table of contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.1.1 --- Properties of CdSe --- p.1 / Chapter 1.1.2 --- Synthesis of CdSe one-dimensional (ID) nanostructure --- p.5 / Chapter 1.1.3 --- Application of CdSe nanostructures --- p.8 / Chapter 1.1.4 --- Significance of surface engineering --- p.10 / Chapter 1.1.4.1 --- Surface passivation --- p.11 / Chapter 1.1.4.2 --- Surface functionalization --- p.11 / Chapter 1.1.4.3 --- Modulation of optical/electrical properties --- p.12 / Chapter 1.2 --- Present study --- p.14 / Chapter 1.2.1 --- Objective --- p.14 / Chapter 1.2.2 --- General methodology --- p.14 / Chapter Chapter 2 --- Instrumentation --- p.19 / Chapter 2.1 --- Introduction --- p.19 / Chapter 2.2 --- Setup of Sample Preparation --- p.19 / Chapter 2.2.1 --- Synthesis --- p.19 / Chapter 2.2.1.1 --- Thermal evaporation apparatus --- p.19 / Chapter 2.2.1.2 --- Microwave assisted chemical synthesis --- p.21 / Chapter 2.2.2 --- Sample handling --- p.22 / Chapter 2.2.3 --- Other treatments --- p.22 / Chapter 2.3 --- X-ray photoelectron spectrometer (XPS) --- p.22 / Chapter 2.3.1 --- Basic Principle --- p.22 / Chapter 2.3.2 --- Instrumentation --- p.24 / Chapter 2.3.3 --- Charging problem --- p.27 / Chapter 2.3.4 --- Qualitative analysis --- p.27 / Chapter 2.3.5 --- Quantitative analysis --- p.28 / Chapter 2.3.5.1 --- Curve fitting --- p.28 / Chapter 2.3.5.2 --- Atomic percentage --- p.29 / Chapter 2.3.5.3 --- Thickness determination --- p.29 / Chapter 2.4 --- Photoluminescence --- p.30 / Chapter 2.4.1 --- Basic principle --- p.30 / Chapter 2.4.2 --- Instrumentation --- p.31 / Chapter 2.5 --- Other equipments --- p.32 / Chapter Chapter 3 --- Synthesis of CdSe Nanorods --- p.34 / Chapter 3.1 --- Introduction --- p.34 / Chapter 3.2 --- Thermal evaporation --- p.34 / Chapter 3.2.1 --- Experimental procedures --- p.34 / Chapter 3.2.2 --- Characterization --- p.35 / Chapter 3.3 --- Microwave assisted method --- p.41 / Chapter 3.3.1 --- Experimental procedures --- p.41 / Chapter 3.3.2 --- Characterization --- p.42 / Chapter 3.4 --- Summary --- p.47 / Chapter Chapter 4 --- Surface Treatment of CdSe Nanorods --- p.49 / Chapter 4.1 --- Introduction --- p.49 / Chapter 4.2 --- Experimental procedures --- p.50 / Chapter 4.3 --- Results and Discussion --- p.51 / Chapter 4.3.1 --- Formation of Se-coated CdSe NRs --- p.51 / Chapter 4.3.2 --- Desorption and thinning --- p.56 / Chapter 4.3.3 --- Surface degradation --- p.67 / Chapter 4.4 --- Summary --- p.69 / Chapter Chapter 5 --- Surface Capping of CdSe Nanorods --- p.73 / Chapter 5.1 --- Introduction --- p.73 / Chapter 5.2 --- Experimental procedures --- p.73 / Chapter 5.3 --- Results and Discussion --- p.74 / Chapter 5.3.1 --- Capping of thiol with halo-functional group --- p.74 / Chapter 5.3.1.1 --- Compositional analysis --- p.75 / Chapter 5.3.1.2 --- PL analysis --- p.79 / Chapter 5.3.2 --- Capping of DNA --- p.81 / Chapter 5.3.2.1 --- Compositional analysis --- p.81 / Chapter 5.3.2.2 --- PL analysis --- p.83 / Chapter 5.4 --- Summary --- p.92 / Chapter Chapter 6 --- Conclusions and Future Work --- p.94 / Chapter 6.1 --- Conclusions --- p.94 / Chapter 6.2 --- Future work --- p.95