No description available.

The thermal conductivity, thermopower, and electrical resistivity of (R1.5Ce0.5)RuSr2Cu2O10-delta (R=Gd, Eu) polycrystalline samples with different oxygen doping level are investigated in temperature range 1.8-300 K. Much attention is focused on the dependence of the effect of the annealing in high oxygen pressures as well as the effect of aging on transport coefficients in normal and superconducting states. It was found that the process of deoxydation goes faster for Ru-1222(Eu) samples than for Ru- 1222(Gd) samples, which results in more pronounced granular effects in Ru-1222(Eu) samples. The relative contribution to the thermal conductivity due to electrons and phonons was estimated by using the Wiedemann-Franz relation and the resistivity data. The calculation showed that the maximum electron contribution for Ru-1222(Eu) is about 0.75% and that for Ru-1222(Gd) samples is around 4 %.

Measurements on free standing films of the conductive polymer polyaniline (PANi) have revealed that charge transport within this material depends upon the level of intermolecular order. This factor is found to depend upon the method of sample preparation. PANi protonated by immersion of solid emeraldine base in aqueous methane sulphonic acid has low conductivity, 30-40 Scm(^-1). This can be enhanced, up to 250 Scm(^-1) if films are stretch oriented prior to protonation. Stretched samples have an electrical conductivity anisotropy factor of order 7 at 300 K, also revealed in their thermopower over the range 100 - 300 K. The behaviour of electrical conductivity with temperature is commensurate with charge transport in a disordered system. Protonation of PANi dissolved in meta cresol by addition of camphor sulphonic acid (CSA) yields material with conductivity of 250-300 Scm(^-1) Variation of the acid concentration has revealed a transition to a metallic response in conductivity (near 300 K) when 20-30% of polymer nitrogen sites are protonated. This character extends to progressively lower temperatures as protonation is increased to 60%. The metallic nature of this material is evident in the linear temperature dependence of thermopower and is ascribed to the presence of crystalhne regions within the polymer fihn, as revealed by an independent x-ray analysis The role of molecular order upon the properties of thin films of 3[2(S2-methylbutoxy)ethyl]-polythiophene has been investigated. Starting with polymer dissolved in 'good' solvent, quantities of nonsolvent lead to reorganisation of the sidechain groups when added. This promotes an increase in effective conjugation length which can be transferred to the solid state by the spin coating process as indicated by spectroscopic studies. With these films acting as the active layer in a field effect transistor the charge carrier mobility can be measured. It is found that as molecular order increases, mobility decreases from 10(^-5) cm(^2)V(^-1)s(^-1) to 710(^-8) cm(^2)V(^-1)s(^-1). This is ascribed to increased interchain separation and effects due to macroscopic aggregate grain boundaries.

No description available.

Two-dimensional (2D) carrier systems built from semiconductor heterostructures have been at the center of a wide variety of experimental and theoretical research over the past decades. The quality improvement of GaAs/AlGaAs systems has allowed the observation of several peculiar ground states stabilized by the subtle interplay between carrier-carrier interaction, disorder and magnetic field. More recently, 2D systems in semiconductor heterostructures have also been used as a prime substrate for further confinement of the carriers to mesoscopic systems of major interest for the emerging fields of quantum computing and spintronics. This thesis addresses both magnetotransport measurements in hole open quantum dots (QDs) and thermopower studies of 2D holes in (311)A GaAs heterostructures. In the first part of this thesis, we describe the fabrication process for hole GaAs open QDs and investigate their magnetotransport properties at very low temperature T. Below 500 mK, the magnetoconductance of the open QDs exhibits clear signatures of coherent transport, namely magnetoconductance fluctuations and weak anti-localization. From these effects, we extract a T dependence for the dephasing time, together with an upper limit for the spin-orbit scattering time using the random matrix theory. Both the dephasing time and the spin-orbit scattering time are found to be much smaller than for electrons in similar systems. In the second part of this work, we report low-T thermopower measurements in the parallel magnetic field-induced metal-insulator transition (MIT) of 2D GaAs hole heterojunctions with different interface-dependent mobilities. When the magnetic field is increased, the diffusion thermopower decreases across the MIT. The reduction of the diffusion thermopower is more pronounced for the lower mobility sample where it reverses its sign. This behaviour indicates that the system does not undergo any ground state modification through the MIT but rather that the parallel magnetic field induces a dramatic change of the dominant hole scattering mechanisms. Finally, the last part of this thesis is devoted to the thermopower study of the insulating phase (IP) observed in 2D GaAs bilayer hole systems around the total Landau level filling factor n = 1. Our measurements show that the diffusion thermopower diverges with decreasing T in the IP. This divergence of the diffusion thermopower at low T indicates the opening of an energy gap in the system's ground state and suggests the formation of a pinned bilayer hole Wigner crystal around n = 1.

Magistro studijų baigiamojo darbo tikslas-- įvertinant esamą situacija bei atliekant reikalingus tyrimus, nustatyti Klaipėdos šiluminės elektrinės teritorijos konversijos galimybes, pateikti projektinius pasiūlymus. Atlikus architektūrinę ir urbanistinę analizę nuspręsta plėtoti visuomeninės ir komercinės infrastruktūros teritorijoją, integruojant ja į miesto planinę- erdvinę struktūrą. Planuojamą teritoriją siūloma išvalyti, paliekant architektūrinę ir konstrukcinę vertę turinčius pastatus. Šiluminės elektrinės pastatas tampa teritorijos ir miesto dalies akcentu, turintis glaudų ryšį su senamiesčiu. Trijų tūrių kompozicija racionaliai pritaikoma šiuolaikinio meno centro funkcijai, kuriame projektuojamos ekspozicijų erdvės, konferencijų salės, vestibiuliai, viešojo maitinimo, techninės patalpos ir kt. Rengiant projektą naudojamos netradicinės konstrukcinės sistemos. Darbą sudaro grafinė medžiaga ir tekstinė dalis: įvadas, analitinė dalis, duomenų apie pastatą apibendrinimas, pastato architektūrinis ir konstrukcijų techninės būklės įvertinimas, tyrimo medžiagos apdorojimas, architekturiniai ir konstrukciniai pastato renovacijos siulymai, literatūros sąrašas. Atskirai pridedami darbo priedai – grafinės medžiagos sumažintos kopijos, maketo nuotraukos. / The aim of the final work of MA – identify the teritory conversion opportunities of Klaipeda thermopower station, evaluating the current situation and taking the relevant research methods . Develop comercial and public infrastructure area by using architectural and urbanistical analysis and integrating it into the target –spacial structure of the city. It is suggested to empty the target area, except the buildings that have architectural and structural value. The Thermopower station is going to be the accent of the teritory and the part of town, and have a close relation with the architecture of the oldtown. Three solids composition is adopted for the function of the modern art center, where exposition spaces, conference halls, lobbies, restaurants, technical rooms are being established. Untraditional constuctive systems were adjusted to prepare this project. The work contains graphic matereal and text part: introduction, analytical part, the summary of the building data, the evaluation of the building‘s architectural and constructive technical condition, processing of the research matereal, architectural and contructive renovation suggestions, bibliography. Appedixes: graphic matereal copies, photos of the model of the project.

Titanium dioxide, TiO2, has potential applications as a photoelectrode for photoelectrochemical generation of hydrogen by splitting water using solar energy and as a photocatalyst for water purification. This study is part of the UNSW research program to process TiO2-based oxide semiconductors as high-performance photoelectrodes and photocatalysts. This study investigates the effect of defect disorder on semiconducting properties of polycrystalline TiO2. This study involved the processing of high-purity polycrystalline TiO2 and determination of its semiconducting properties through measurement of electrical conductivity and thermoelectric power at elevated temperatures (1073-1323K) in controlled oxygen activities [1x10-13 Pa < p(O2) < 75 kPa]. The study included two types of experiments: Determination of electrical properties under conditions of gas/solid equilibrium. The data obtained was used to derive defect disorder and related semiconducting properties Monitoring of electrical properties during equilibration. This data was used to determine the chemical diffusion coefficient. The data obtained under equilibrium conditions indicates that oxygen may be used as a dopant to impose controlled semiconducting properties. In reduced conditions TiO2 is an n-type semiconductor and under oxidizing conditions TiO2 is a p-type semiconductor. The n-type behaviour is associated with oxygen vacancies as the predominant defects and titanium interstitials as the minority defects. The p-type behaviour is closely related to titanium vacancies that are formed during prolonged oxidation. Charge transport at elevated temperature was shown to involve substantial contribution from ions. Analysis of electrical properties enabled determination of several defect-related quantities including the activation enthalpy for oxygen vacancy formation, and the activation energy of the electrical conductivity components related to electrons, holes and ions. The kinetic data obtained during gas/solid equilibration enabled determination of the chemical diffusion coefficient which exhibited a complex dependence on nonstoichiometry. In addition, prolonged oxidation showed that equilibration occurred in two kinetic regimes. One for highly mobile oxygen vacancies and titanium interstitials which quickly reached an ??operational equilibrium?? within hours and another slow kinetic regime for equilibration of titanium vacancies over many thousand hours. The determined chemical diffusion coefficient data may be used to select the processing conditions required to impose uniform concentration of defects within a TiO2.

Carbon nanotubes are made into films or bulks, their surface or junction morphology in the networks can be modified to obtain desired electrical transport properties by various surface modification methods. The methods include incorporation of organic molecules or inorganic nanoparticles, debundling of nanotubes by dispersing agents, and microwave irradiation. Because carbon nanotubes have unique carrier transport characteristics along a sheet of graphite in a cylindrical shape, the properties can be dramatically changed by the modification. This is ideal for developing high-performance materials for thermoelectric and photovoltaic energy conversion applications. In this research, decoration of various organic/inorganic nanomaterials on carbon nanotubes was employed to enhance their electrical conductivity, to improve thermoelectric power factor by modulating their electrical conductance and thermopower, or to obtain n-type converted carbon nanotube. The electrical conductivity of double-wall nanotubes (DWNTs) decorated with tetrafluoro-tetracyanoquinodimethane (F4TCNQ) was increased up to 5.9 × 10^5 S/m. The sheet resistances were measured to be 42 Ω/sq at 75% of transmittance for HNO3/SOCl2-treated DWNT films, making their electrical conductivities 200~300% better than those of the pristine DWNT films. A series of experiments at different ion concentrations and reaction time periods were systematically performed in order to find optimum nanomaterial formation conditions and corresponding electronic transport changes for better thermoelectric power factor. For example, the thermoelectric power factors were improved by ~180% with F4TCNQ on DWNTs, ~200% with Cu on SWNTs, and ~140% with Fe on single-walled nanotubes (SWNTs). Also SWNTs was converted from p-type to n-type with a large thermopower (58 μV/K) by using polyethyleneimine (PEI) without vacuum or controlled environment. This transport behavior is believed to be from charge interactions resulted from the difference between the work functions/reduction potentials of nanotubes and nanomaterials. In addition, different dispersing agents were utilized with DWNT and SWNTs to see a debundling effect in a film network. The highest electrical conductivity of ~1.72×10^6 S/m was obtained from DWNT film which was fabricated with a nanotube solution dispersed by chlorosulfonic acid. Debundling of nanotubes in the film network has been demonstrated to be a critical parameter in order to get such high electrical property. In the last experiment, Au nanoparticle decoration on carbon nanotube bundle was performed and a measurement of themophysical properties has done before and after modifying carbon nanotube surface. Carbon nanotube bundle, herein, was bridged on microdevice to enable the measurement work. This study demonstrates a first step toward a breakthrough in order to extract the potential of carbon nanotubes regarding electron transport properties.

Titanium dioxide, TiO2, has potential applications as a photoelectrode for photoelectrochemical generation of hydrogen by splitting water using solar energy and as a photocatalyst for water purification. This study is part of the UNSW research program to process TiO2-based oxide semiconductors as high-performance photoelectrodes and photocatalysts. This study investigates the effect of defect disorder on semiconducting properties of polycrystalline TiO2. This study involved the processing of high-purity polycrystalline TiO2 and determination of its semiconducting properties through measurement of electrical conductivity and thermoelectric power at elevated temperatures (1073-1323K) in controlled oxygen activities [1x10-13 Pa < p(O2) < 75 kPa]. The study included two types of experiments: Determination of electrical properties under conditions of gas/solid equilibrium. The data obtained was used to derive defect disorder and related semiconducting properties Monitoring of electrical properties during equilibration. This data was used to determine the chemical diffusion coefficient. The data obtained under equilibrium conditions indicates that oxygen may be used as a dopant to impose controlled semiconducting properties. In reduced conditions TiO2 is an n-type semiconductor and under oxidizing conditions TiO2 is a p-type semiconductor. The n-type behaviour is associated with oxygen vacancies as the predominant defects and titanium interstitials as the minority defects. The p-type behaviour is closely related to titanium vacancies that are formed during prolonged oxidation. Charge transport at elevated temperature was shown to involve substantial contribution from ions. Analysis of electrical properties enabled determination of several defect-related quantities including the activation enthalpy for oxygen vacancy formation, and the activation energy of the electrical conductivity components related to electrons, holes and ions. The kinetic data obtained during gas/solid equilibration enabled determination of the chemical diffusion coefficient which exhibited a complex dependence on nonstoichiometry. In addition, prolonged oxidation showed that equilibration occurred in two kinetic regimes. One for highly mobile oxygen vacancies and titanium interstitials which quickly reached an ??operational equilibrium?? within hours and another slow kinetic regime for equilibration of titanium vacancies over many thousand hours. The determined chemical diffusion coefficient data may be used to select the processing conditions required to impose uniform concentration of defects within a TiO2.

abstract: The challenging search for clean, reliable and environmentally friendly energy sources has fueled increased research in thermoelectric materials, which are capable of recovering waste heat. Among the state-of-the-art thermoelectric materials &beta;-Zn4Sb3 is outstanding because of its ultra-low glass-like thermal conductivity. Attempts to explore ternary phases in the Zn-Sb-In system resulted in the discovery of the new intermetallic compounds, stable Zn5Sb4In2-&delta; (&delta;=0.15) and metastable Zn9Sb6In2. Millimeter-sized crystals were grown from molten metal fluxes, where indium metal was employed as a reactive flux medium.Zn5Sb4In2-&delta; and Zn9Sb6In2 crystallize in new structure types featuring complex framework and the presence of structural disorder (defects and split atomic positions). The structure and phase relations between ternary Zn5Sb4In2-&delta;, Zn9Sb6In2 and binary Zn4Sb3 are discussed. To establish and understand structure-property relationships, thermoelectric properties measurements were carried out. The measurements suggested that Zn5Sb4In2-&delta; and Zn9Sb6In2 are narrow band gap semiconductors, similar to &beta;-Zn4Sb3. Also, the peculiar low thermal conductivity of Zn4Sb3 (1 W/mK) is preserved. In the investigated temperature range 10 to 350 K Zn5Sb4In2-&delta; displays higher thermoelectric figure of merits than Zn4Sb3, indicating a potential significance in thermoelectric applications. Finally, the glass-like thermal conductivities of binary and ternary antimonides with complex structures are compared and the mechanism behind their low thermal conductivities is briefly discussed. / Dissertation/Thesis / Ph.D. Chemistry 2011