Bismuth telluride based compounds is known to be the best thermoelectric materials within the low temperature regime. In this study, the P-type Bi0.5Sb1.5Te3 thermoelectric alloy was synthesized by ceramic processing method. The Bi0.5Sb1.5Te3 thermoelectric materials were prepared via the ball milling, cold pressing, and sintering processes. The effects of sintering time and temperature on the microstructures and thermoelectric properties were investigated and discussed. The X-ray diffraction patterns of Bi0.5Sb1.5Te3 reveal that the compounds have the oxides after the sintering processes and the heat treatment process causes grain growth by the increased sintering temperature and time. The results of thermoelectric properties show that the optimal Seebeck coefficient 300(£gV/K) was obtained as the sample was sintered at 350¢XC for 3h and the resistivity will reach the maximum. The figure of merit of 0.15 was obtained at room temperature as the sample was sintered at 375¢XC for 3h.

The purpose of this thesis is to fabricate 12-layer InxGa1-xAs quantum dots grown on 2-nm In0.1Ga0.9As quantum wells (DWell) laser structures grown by molecular-beam epitaxy (MBE) on GaAs substrats. We expect to optimum the lasers performance by tune the epitaxial recipe and fabrication condition. For the carrier injection efficiency, DWell structure of quantum dots grown on quantum wells is proposed to enhance the carrier capture rate. So we analyze a series of DWell structure in this work. In the epitaxial recipe, we investigate the influences of p-type doping and change the quantum wells growth temperature for the laser structures. In the laser fabrication, to transport the light wave in smaller dispersion loss single mode waveguide, dry etching photolithography processes are adapted in this study to fabricate 2.2mm width ridge waveguide. The as-cleaved facets are used as Fabry-Perot laser mirrors in ridge waveguide lasers. The pattern can be transferred effectively with less under-cut by dry etching compare with wet etching. Finally, the P-type doping DWell laser exhibits high power/facet of 24mW, slope efficiency of 0.209W/A. The maximum power/facet of PWell580 laser reach to 24mW, slope efficiency of 0.238W/A after raising the growth temperature to 580oC.

In this thesis, we investigate the synthesis of CuAlO2 on sapphire (0001) substrate by rapid thermal annealing of an Al2O3/Cu2O/sapphire structure above 1000oC. We examine the effects of growth conditions on the structural, formation mechanism, and optical and electrical properties of CuAlO2 thin film. The film prepared at 1100 oC in air was with epitaxial structure as verified by X-ray diffraction methods. Gas ambient, temperature ramp rate and reaction temperature are crucial parameters for the formation of CuAlO2 film. We found that single-phase CuAlO2 thin films formed in air ambient by a rapid temperature ramp rate above 1000oC. A slow temperature ramp rate and a pure oxygen ambient might lead to the appearance of second phase such as CuAl2O4. Optical gap of our films were determined to be 3.75 eV. Optical transmittance depended on the temperature of thin film reaction. The best transmittance obtained was 60 % by annealing at 1100 oC in air. Photoluminescence and cathodoluminescence measurements showed that the two peaks obtained are around 3.4 eV and 1.8 eV corresponding to UV and red emission. As a result of CuAlO2 has an indirect gap about 1.8 eV. The electrical conductivity of the film related to the oxygen content was investigated by the annealing experiments in oxygen-deficient (vacuum) and oxygen-excess (air) ambient. The sheet resistance of CuAlO2 increases consistently with an increase in the duration of the vacuum annealing. Further annealing in air restores the sheet resistance to the original value. The highest conductivity obtained in this work was 0.57 S/cm. Metal contacts to CuAlO2 were also studied in this work. The current-voltage characteristics showed that Cu, Al, Ni or Au could form Ohmic contact to CuAlO2. The lowest contact resistance was using Al metal. However, when the contacts were post-annealed above 300oC, the contact resistance was increased.

This dissertation investigates the growth of high quality GaN and InN thin films by plasma assisted molecular beam epitaxy (PAMBE). It also explores the growth of self-seeded GaN branching nanowires and p-type doping of InN, two topics of particular interest at present. The growth of high quality III-Nitride semiconductor thin films have been shown to be dependent on the group-III (metal) to nitrogen ratio. A metal-rich growth environment enhances the diffusion of the group-III adatoms through the formation of a group-III adlayer. By using a metal-rich growth environment, determined by growth rate studies using laser reflection interferometry or RHEED analysis of the surface, both GaN and InN films have been grown with a smooth surface morphology. Additionally the smooth surface morphology has beneficial effects on the electrical and optical properties of both materials. However, with the growth using a metal-rich environment, group-III droplets are present on all film surfaces, which can be an issue for device fabrication, as they produce facets in the crystal structure due to enhanced growth rates. MBE growth of GaN nanowires via the vapour liquid solid (VLS) and vapour solid (VS) growth techniques have so far been based on the N-rich growth regime. However, we have shown that the Ga-rich growth regime can be used to grow self-seeded one dimensional and hierarchical GaN nanowires. 7 µm long hierarchical GaN nanowires with at least three branches were grown and shown to have a high crystalline quality. The suggested growth mechanism is a self-seeding VLS process driven by liquid phase epitaxy at the nanoscale, while the branching growth was nucleated due to the Ga-rich growth regime by excess Ga droplets forming on the trunk during growth. The growth of vertical GaN nanowires has also been achieved using the same self-seeding process and the critical parameter seems to be the Ga to N ratio. Also, the growth rate of the Ga-rich grown GaN nanowires can supersede the growth rates reported from N-rich grown GaN nanowires by at least a factor of two. The fabrication of vertical and planar GaN nanowire devices has been demonstrated in this study. Two point and three point contacts were fabricated to the branching GaN nanowires in the planar direction with resistive measurements ranging from 200 - 900 kΩ, similar to chemical vapour deposition and MBE grown GaN nanowires. The nonlinear current-voltage characteristics from the three point contacts may lead to unique nano-devices. The planar nanowires have also shown to have potential as UV detectors. Schottky diodes were fabricated on the vertical nanowires, with values for the barrier heights consistent with bulk diodes. Mg and Zn doping studies of InN were also performed. Both InN:Mg and InN:Zn have strong photoluminescence only at low doping concentrations. However, the InN:Mg films have reduced mobilities with increased Mg content, whereas the mobility determined from the InN:Zn films is independent of Zn. When the InN:Zn film quality was improved by growing under the In-rich growth regime, electrochemical capacitance-voltage results suggest n{type conductivity, and strong photoluminescence was obtained from all of the films with four features seen at 0.719 eV, 0.668 eV, 0.602 eV and 0.547 eV. The features at 0.719 eV and 0.668 eV are possibly due to a near band edge to valence band or shallow acceptor transition, while the 0.547 eV has an activation energy of 60 meV suggesting a deep level acceptor.

No description available.

No description available.

The thermoelectric properties and microstructure of two families of misfit type layered structure cobaltites were investigated for thermoelectric applications. Firstly, Bismuth strontium cobaltite ceramics with the formulations Bi2+xSr2Co2Oy (x=0, 0.1 and 0.2), Bi1.74Sr2Co1.8Oy and Bi2Sr2Co1.8Oy were produced using solid-state reaction (MO) method. The same powders were also used to produce ceramics by Spark Plasma Sintering (SPS) fabrication technique. SEM, high resolution XRD and HRTEM techniques has been employed to characterise the microstructure and crystal structures of the ceramics. Figure of merit (ZT) was also determined from measurement of electrical resistivity, Seebeck coefficient and thermal conductivity. Together with the above, calcium cobaltite of formulation Ca3-xBixCo3O9 (x=0 and 0.3) was also produced via MO and SPS routes. The same characterisation techniques were used for characterisation of calcium cobaltite. For Bi2+xSr2Co2Oy ceramics, it was found that SPS fabrication is essential to obtain high density samples. Excess bismuth has a major role in the adjustment of the microstructure and thermoelectric properties. The room temperature microstructure contains two minor phases with compositions of CoO and Bi0.75Sr0.25O1.26. The crystal structure of the main phase was successfully indexed and refined as misfit type structure having monoclinic symmetry with I2/a space group. A high ZT of 0.12 was achieved in both x=0.1 and 0.2 MO samples. For Bi2Sr2Co1.8Oy ceramics, the microstructure contains only one minor phase, Bi0.75Sr0.25O1.26. A high ZT of 0.16 was obtained at 900 K for this composition. For Bi1.74Sr2Co1.8Oy, it was not possible to obtain high density ceramics by MO route and SPS fabrication was necessary. However, SPS sample showed a low ZT of 0.04 at 900 K.For ceramics of formulation Ca3-xBixCo3O9 (x=0 and 0.3), it was difficult to obtain high density calcium cobaltite ceramics by MO route and SPS fabrication was found to be essential. In addition to improved density, SPS produced textured microstructure. Similar to bismuth strontium cobaltite, excess bismuth played a major role in microstructure development and thermoelectric properties. Single phase and high density Ca3Co4O9 ceramics were obtained by SPS. A minor phase of Bi2Ca2Co2Oy was found in the microstructure of Ca3-xBixCo3O4 (x=0.3) samples. A high ZT of 0.25 was obtained for Ca3Co4O9 SPS samples at 900 K through improvement of power factor. In-situ synchrotron XRD in the temperature range of 300-1223 K was performed on both Bi2Sr2Co2Oy and Ca3Co4O9 to obtain their high temperature structural characteristics. The crystal structure of both compounds remains unchanged till 1223 K. For, Bi2Sr2Co2Oy the CoO and Bi0.75Sr0.25O1.26 minor phases disappear above 1073 K and a new minor phase containing (Bi-Sr-O) or (Bi-Co-O) starts forming. On heating, the lattice volume and coefficient of thermal expansion change linearly for both compounds. Thermal expansion coefficient was found to be 0.0000353-0.0000343 and 0.0000296-0.0000288 K-1 over the temperature range of 300-1223 K for Bi2Sr2Co2Oy and Ca3Co4O9 respectively.

A TPases do tipo P são proteínas integrais de membrana que usam a energia química contida na molécula de ATP para o transporte de cátions através de membranas. O nosso trabalho apresenta a clonagem e o sequenciamento de um gene (BePAT2) e a caracterização da expressão de dois genes (BePAT1 e BePAT2) codificando isoformas de uma ATPase do tipo P no fungo aquático Blastocladiella emersonii. As proteínas codificadas por estes genes, surpreendentemente se mostraram mais similares às Na+/K+ e H+/K+-ATPases de eucariotos superiores do que a outras ATPases de fungos. Experimentos de \"Northern blot\", imunoprecipitação e \"Western blot\" demonstraram que as ATPases (BePAT1 e BePAT2) são diferencialmente expressas durante o desenvolvimento de B. emersonii. Os resultados obtidos mostraram que o aumento da transcrição dos genes refletiu em um aumento da síntese e do acúmulo das ATPases, sugerindo um controle pré-traducional da expressão de BePAT1/2. Estudos de formação de fosfoenzima na presença de diferentes íons e inibidores, utilizando as enzimas imunopurificadas, sugerem que as proteínas codificadas por estes genes tenham uma atividade semelhante às Na+/K+-ATPases. Os nossos resultados de expressão e atividade mostram pela primeira vez, evidências da funcionalidade de genes codificando uma proteína similar às Na+/K+-ATPases em um eucarioto inferior. / P- type A TPases are integral membrane proteins which use the energy stored in the A TP molecule to drive the transport of cations through biological membranes. In this work we report the cloning and sequencing of the BePAT2 gene and the characterization and expression of two genes (BePAT1 and BePAT2) encoding isoforms of a P-Type ATPase in the aquatic fungus Blastocladiella emersonii. Surprisingly the putative BePAT1 and BePAT2 proteins are more similar to Na+/K+and H+/K+-ATPases from animal cells than to other P-type ATPases from fungi. Northern blot, immunoprecipitation and Western blot experiments demonstrated that these ATPases (BePAT1 and BePAT2) are developmentally regulated in B. emersonii. The results showed that the increase in the BePAT1/2 transcription reflects in an increase in the synthesis and accumulation of the proteins, suggesting a transcriptional control of the BePAT1/2 expression. Studies of phosphoenzyme formation using the immunopurified enzymes in the presence of different ions and inhibitors suggested a Na/K-ATPase like activity. Our results demonstrate for the first time biochemical evidences of functionality of genes encoding a Na+ /K+-ATPase like protein in an eucaryotic microorganism.

In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.

In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.