Este trabalho tem por objetivo a investigação de atenuação de ondas acústicas superficiais (OAS) em filmes finos granulares supercondutores de PbO e Pb depositados por sputtering reativo em substratos piezoelétricos de LiNbO3 e quartzo (ST). As medidas de atenuação de OAS em função da temperatura foram efetuadas para diferentes potências de radiofreqüência, e em freqüência variando de 550 MHz a aproximadamente 700 MHz. A atenuação de OAS medida em filme granular de chumbo (550&#197), dotada de alta resistividade de filme (de 1000 &#937/&#9001) se manifesta piezoeletricamente induzida e proporcional à resistividade do filme. No estado supercondutor esta medida de atenuação excede esta simples relação. Esta atenuação excedente é atribuída à resistência local produzida pela presença de dipolos de vórtice-antivórtice / The subject of this work is the investigation of surface acoustic waves (SAW) on superconducting Pb and PbO granular thin films deposited by sputtering on piezoelectric substrate (LiNbO3 and quartz ST). The SAW attenuation was measured as a function of the temperature (1,3K to 20K) for different r.f. Power, in frequencies from 550 MHz to 700 MHz. The SAW attenuation, measured on granular lead film (550 &#197) with high sheet resistivity (1000 &#937/&#9001) appears to be piezoelectrically induced and should be proportional to the sheet resistivity. In the superconducting state the measured attenuation exceeds this simple relation. This excess attenuation is ascribed to the local resistance produced by the presence of vortex-antivortex dipoles

This study investigated localized corrosion behavior of austenitic stainless steels under stressed and unstressed conditions, as well as corrosion of metallic thin films. While austenitic stainless steels are widely used in corrosive environments, they are vulnerable to pitting and stress corrosion cracking (SCC), particularly in chloride-containing environments. The corrosion resistance of austenitic stainless steels is closely tied to the alloying elements chromium, nickel, and molybdenum. Polarization curves were measured for five commercially available austenitic stainless steels of varying chromium, nickel, and molybdenum content in 3.5 wt.% and 25 wt.% NaCl solutions. The alloys were also tested in tension at slow strain rates in air and in a chloride environment under different polarization conditions to explore the relationship between the extent of pitting corrosion and SCC over a range of alloy content and environment. The influence of alloy composition on corrosion resistance was found to be consistent with the pitting resistance equivalent number (PREN) under some conditions, but there were also conditions under which the model did not hold for certain commercial alloy compositions. Monotonic loading was used to generate SCC in in 300 series stainless steels, and it was possible to control the failure mode through adjusting environmental and polarization conditions. Metallic thin film systems of thickness 10-200 nm are being investigated for use as corrosion sensors and protective coatings, however the corrosion properties of ferrous thin films have not been widely studied. The effects of film thickness and substrate conductivity were examined using potentiodynamic polarization and scanning vibrating electrode technique (SVET) on iron thin films. Thicker films undergo more corrosion than thinner films in the same environment, though the corrosion mechanism is the same. Conductive substrates encourage general corrosion, similar to that of bulk iron, while insulating substrates supported only localized corrosion.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16883号 / 工博第3604号 / 新制||工||1544(附属図書館) / 29558 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 長谷川 博一, 教授 吉﨑 武尚, 教授 金谷 利治 / 学位規則第4条第1項該当

M.Sc. / As environmental and energy resource concerns have increased, greater emphasis has been placed on development of renewable energy resources such as photovoltaic electric generators. CuInSe 2/ZnO heterojunction solar cells are currently one of the most promising technologies to produce economically viable, clean electrical energy. The reaction of metallic alloys containing copper and indium to a selenium-containing atmosphere is by far the most promising industrial process. In this study ; copper-indium metallic precursors were prepared by electron-beam evaporation. The selenization process was conducted in vacuum in elemental Se vapour and in the presence of a H 2Se/Ar gas mixture at atmospheric pressure. Attention was given to the optimization of the structural features of the metallic alloys as well as the selenization parameters. Structural analysis revealed that the number of multilayers in , the precursor stack significantly influence the morphological features of the absorber films after selenization. The reaction temperature and reaction periods during the selenization process critically influenced the reaction kinetics of metallic phases. In the case of selenization in elemental Se vapour, temperatures as high as 550°C were required to convert the metallic alloys into fully reacted semiconductor thin films. Selenization in the presence of H2Se gas was more reactive and temperatures around 450°C resulted in the complete formation of CuInSe2. In the majority of cases, traces of CuSe were detected in the bulk of the material by XRD studies. The presence of the Cu-rich binary phases rendered solar cell devices useless. After removal of these detrimental segregated phases by KCN etching, glass/Mo/CuInSe2/CdS/ZnO solar cell devices reached conversion efficiencies around 8%.

M.Sc. / As environmental and energy resource concerns have increased, greater stress has been placed on development of renewable energy resources such as photovoltaic electric generators. CuInSe2/ZnO heterojunction solar cells are currently one of the most promising technologies. CuInSe2 and its related alloys such as Cu(In,Ga)Se2 have been deposited by a number of techniques, including methods which have been demonstrated to be scalable to mass production volumes. In this study, attention was focused on (i) developing a relatively simple deposition technology for the production of chalcopyrite absorber films, (ii) detailed characterization of the semiconductor thin films in terms of the experimental parameters and (iii) production of completed CuInSe2/CdS/ZnO solar cell devices. A new two-stage growth process was developed which involved a low temperature precursor formation step and a subsequent high temperature selenization step. Selenium containing Cu-In-Ga and Cu-In-Ga-Se precursors were deposited by a thermal process in which the constituent elements were evaporated from a single graphite crucible onto heated substrates in presence of a selenium overpressure. These precursors were subsequently reacted in vacuum to elemental selenium vapour or to H2Se/Ar at atmospheric pressure in a separate diffusion reactor. In order to investigate the growth kinetics of the respective processes, the precursors were reacted to the Se in the temperature range between 300„aC and 600„aC. The structural features (morphology, presence of crystalline phases, bulk and in-depth compositional uniformity) of the respective films were compared and correlated against the growth parameters. From this systematic study, optimum growth parameters were determined for the production of completed solar cell devices. / Prof. V. Alberts

Ph.D. / The two-step growth process, involving the selenization and sulfurization of sputter deposited CuInGa alloys has been identified as a commercially viable method to produce large area Cu(In1-xGax)(Se1-ySy)2 absorber films for solar cell application. The success of this method is however limited by insufficient control over the lattice parameters and band gap of the compound due to phase segregation associated with non-uniform Ga and S incorporation. This study provides an approach to overcome this limitation by investigating the influence of process parameters on the structural features of the Cu(In1-xGax)(Se1-ySy)2 films. In this approach, films were partially selenized in optimum H2Se/Ar flow to produce composite alloys comprising of a mixture of binary selenides (InSe, CuSe and GaSe) and at least one group I-III-VI ternary alloy. The subsequent reaction step in H2S/Ar produced homogeneous Cu(In1-xGax)(Se1-ySy)2 films. The lattice constants of the resulting films varied linearly with an increase in the S/(S+Se) ratio in accordance with Vegard’s law. The Raman spectra of the films were characterized by the presence of the A1-Se mode near 180 cm-1 and a low intensity, A1-S mode around 290 cm-1. With an increase in the S/(S+Se) ratio of the films, the FWHM of the A1-Se mode increased and its frequency shifted linearly towards that of A1-S mode. A corresponding increase in the value of the Urbach energy, attributed to an increase in chalcopyrite crystal alloy disorder, was observed from the analysis of the transmission and reflectance data. 0.45 cm2 area devices with conversion efficiencies between 12% and 15%, were fabricated from absorber layers with the (112) x-ray diffraction peak position between 27.1°and 27.2°, corresponding to the S/(S+Se) ratio of about 0.18 to 0.20. The process scale up was demonstrated by the fabrication of large area, (30 x 40) cm2 modules, with conversion efficiencies of 10%.

Thin-film photovoltaics are of great interest due to decreased manufacturing costs, improved environmental sustainability and the potential for flexible, semi-transparent, and light-weight modules. The scientific literature contains a plethora of work incorporating wavelength scale nanostructures within thin-film solar cells to increase power conversion efficiency by trapping light inside solar cell absorbing layers. One category of nanostructures, namely plasmonic nanoparticles, theoretically show great promise for their light-trapping abilities but experimental success has been limited. In this work, solar cells were designed and fabricated to incorporate multiple light-trapping mechanisms, including optical cavity resonances, waveguide mode excitation, and plasmonic effects. Due to our novel design considerations, we demonstrate a 33% increase in Jsc originating from plasmon-based enhancement mechanisms. The experimental results are complemented and confirmed by well-matching simulations which are used to further investigate the light-trapping mechanisms. The concepts demonstrated in this work can be directly translated to next-generation transition metal dichalcogenide photovoltaic devices. / Graduate / 2018-12-14

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This thesis concerns itself with the scientific study of the recently discovered organic magnetoresistance (OMAR) whose underlying mechanism is currently not known with certainty. As an introduction, we briefly review the major findings from prior work done by my colleagues. They found that OMAR can be as large as ~10% magnetoresistance at 10 mT magnetic fields at room temperature. Both OMAR and other kinds of magnetic field effect data in organics can be fitted using the empirical laws B^2/(B^2+B_0^2) or B^2/(|B|+B_0)^2, dependent on material. The fitting parameter B_0 is a measure of the characteristic magnetic field strength of OMAR. We explore the dependence of B_0 on material parameters to clarify the origin of OMAR. Various pi-conjugated semiconductor OMAR devices were studied to explore the possibility that hyperfine interaction causes OMAR. For a quantitative analysis of the experiments, we developed a theoretical fitting formula to relate B_0 to the hyperfine coupling strength. In addition, organic materials with different spin-orbit coupling strengths were also measured. Fluorescence and phosphorescence spectroscopies were used to estimate the spin-orbit coupling strength from the measured spectra. For analyzing our measurements, we developed a fitting formula from the time-dependent Schrodinger equation that takes into account the combined effect of hyperfine and spin-orbit coupling on spin-dynamics. We found that in the case of strong spin-orbit coupling, it dominates the behavior, resulting in magnetic field effect traces that are much wider than those in ordinary organics. However, a small cone remains at zero field with a width equal to the hyperfine coupling strength. We find qualitative agreement between the experimental results and the model. We also investigated the question whether OMAR is related to an excitonic effect, or is primarily a transport effect. We measured the magnetic field effects on current, photocurrent and electroluminescence to address this question. By varying the injection efficiency of the minority carriers, we show that OMAR most likely is not an excitonic effect. Our results provide strong evidence in support of the claim that OMAR is caused by spin-dynamics. However, further study is required to study the mechanism connecting spin-dynamics and conductivity.