Contatos elétricos são aplicados na área de geração, manuseio e distribuição de energia elétrica, sendo fabricados em metais condutores como: cobre eletrolítico e suas ligas. Através de alguns métodos de brasagem, pastilhas com propriedades de condutividade, elétrica e térmica, mais apuradas são brasadas sobre estas bases condutoras. Em função da substituição do cádmio por um elemento menos nocivo ao homem e ao meio ambiente, o estanho vem se difundindo com rapidez, apoiado por iniciativas internacionais. O objetivo deste trabalho é avaliar a brasabilidade de um metal de adição na liga 40%Ag-21%Zn- 20%Cd-19%Cu, sobre metais de base em: cobre eletrolítico, latão (65%Cu-35%Zn), prata pura e prata-óxido de estanho (90%Ag-10%SnO2) através dos ensaios da gota séssil e da cunha. As amostras foram caracterizadas metalograficamente. Os resultados mostraram que a brasabilidade para todos os substratos empregados estava dentro de valores de ângulo de contato menores que 10o, com exceção do substrato prata-óxido de estanho. Para este material ocorreu o demolhamento, dificultando a caracterização da sua molhabilidade. / Electrical contacts are manufactured with conductive metals, like electrolytic copper and its alloys. These products are used in electric circuits to manage the electrical energy. Electrical contacts assemblies can be built up by brazing joining methods, which improves electrical and thermal conductivity in non-ferrous substrates. The cadmium oxide, present into electrical contact alloys, has been replaced by tin oxide due to environmental issues, to meet the actual internationals agreements. The objective of this work is to evaluate the brazeability of a filler metal 40%Ag-21%Zn-20%Cd-19%Cu, on non-ferrous substrates, like: electrolytic copper, brass (65%Cu-35%Zn), silver and silver tin-oxide (90%Ag- 10%SnO2) using sessile drop and edge tests. The results showed that the brazeability of all non-ferrous substrates depicted contact angles less than 10º, except for the silver-tin oxide substrate. For silver-tin oxide substrate dewetting took place and the measurement of contact angles was impossible.

The focus of this thesis involves development of highly transparent, n-channel, accumulation- mode thin-film transistors employing a zinc tin oxide (ZTO) channel layer. ZTO-based transparent thin-film transistors (TTFTs) show improved device performance compared to ZnO-based TTFTs. An estimated peak effective mobility for these devices as high as ~100 cm² V⁻¹sec⁻¹ has been observed, although effective mobilities in the range of 20-50 cm²V⁻¹sec⁻¹ are more common. This performance inconsistency may be due, in part, to the large device dimensions employed in developmental test structures and/or to shadow mask misalignment. Typical drain current on-to-off ratios are > 10⁶. Variation in the post-deposition annealing cycle is found to be an effective means to control the threshold voltage and to improve device performance. Optical characterization of these devices indicates ~84% transparency in the visible spectrum as viewed through the source/drain. Another aspect of this thesis research involves the utilization and extension of quantitative polycrystalline TFT device models with the intention of guiding the design and optimization of future TFTs. In particular, subthreshold conduction is assessed in order to estimate the bulk (and/or grain boundary) and interface trap densities. This leads to a consideration of threshold voltage and channel mobility extraction, as well as establishment of the turn-on voltage, V[subscript turn-on] Finally, a third aspect of this thesis research involves a new radio-frequency (RF) magnetron sputtering system, custom-designed and constructed at OSU by Chris Tasker. Contributions to the development of this tool include assisting in the design and implementation of the computer-controlled interlocks utilized for operation of the tool. The experimental flexibility of this new tool is discussed with respect to its applicability in the design and fabrication of future TTFTS. / Graduation date: 2004

One-dimensional and hierarchical nanostructures have acquired tremendous attention in the past decades due to their possible application. In spite of the rapid emergence of new morphologies, the underlying growth mechanism is still not well understood. The lack of effective p-type or n-type doping is another obstacle for many semiconducting nanomaterials. A deeper investigation into these structures and new methods to fabricate devices are of significant impact for nanoscience and nanotechnology. Motivated by a desire to understand the growth mechanism of nanostructures and investigate novel device fabrication method, the research described in this thesis carried out on the synthesis, characterization, and device fabrication of semiconducting nanostructures. The main focus of the research was on ZnO, SnO2, and Zn3P2 for their great capability for fundamental phenomena studying, promising applications in sensors and optoelectronics, and the potential generalization of results to other materials. Within this study the following goals have been achieved: 1) Improved understanding of polar-surface-induced growth mechanism in wurtzite-structured ZnO and generalization of this growth mechanism with the discovery and analysis of rutile ¨Cstructured SnO2, 2) observation of the significance of the transversal growth, which is usually ignored, in interpenetrative ZnO nanowires, 3) rational design and growth control over versatile nanostructures of ZnO and Zn3P2, and 4) conjunction of p-type Zn3P2 and n-type ZnO semiconducting nanostructures for device fabrications. The framework for the research is reviewed first in chapter 1. Chapter 2 gives the detailed experimental setup, synthesis procedure, and common growth mechanism for nanostructure growth. A detailed discussion on the growth of ZnO nanostructures in chapter 3 provides more insight into the polar-surface-induced growth, transversal growth, vapor-solid growth, and vapor-liquid-solid growth during the formation of nanostructures. Polar-surface-induced growth is also confirmed in the growth of SnO2 nanostructures, which is also included in chapter 2. Chapter 3 presents Zn3P2 nanostructures from the newly designed experiment setup and the device fabrication from ZnO and Zn3P2 crossed nanowires.

The purpose of the thesis is to investigate the improvement of single-crystal Si solar cell efficiency using porous Indium tin oxide (ITO)/ITO double layer antireflection(AR) coating. The resistivity, transmittance and refraction index of the porous ITO films prepared by supercritical CO2 treatment were investigated. At a 2000 psi pressure and 60¡CC, the resistivity of porous ITO films is 15 £[-cm, the average transmittance is better than 95 %, and the refraction index is 1.54. In addition, the resistivity of ITO thin films fabricated by reactive ratio-frequency magnetron sputtering is 7¡Ñ10-4 £[-cm, the average transmittance are 85 %, and the refraction index is 2.0. For the single crystal-Si solar cell with porous ITO/ITO double layer AR coating, the open circuit voltage, short circuit current, fill factor and efficiency are measured.

In this studing, application of the digital image correlation method (DIC) for determining the coefficient of thermal expansion (CTE) of Indium Tin Oxide/Polyethylene Terephthalate(ITO/PET) thin film/flexible substrate was proposed and the effects of thinkness variations of ITO and PET, respectively, on the CTE of the specimens was disscussed. The observation range of experimental temperature was chosen from room temperature to the glass transfer temperature of PET, 70¢J. A novel DIC experimental process for reducing the errors caused from the variations of the refractive index of the surrounding heated air was proposed. As a result, the experimental error of CTE measurement was reduced form 10~17% to less than 5%. The experimental results showed that the CTE of ITO/PET specimen is anisotropic. Futhermore, the CTE of an ITO/PET specimen will be increased by decreasing the thinkness of PET flexible substrate, and increased by increasing the thinkness of ITO film - which means decreasing the surface resistance of ITO film.

In the study, conductive distributed Bragg reflectors (DBRs) fabricated at room temperature based on porous indium tin oxide (ITO) on dense ITO bilayers were proposed for resonant cavity organic light emitting diodes (RCOLEDs). In the fabrication of the ITO DBRs, the low refractive index porous ITO films were obtained by applying supercritical CO2 treatment at different temperature and pressures on the spin-coated sol-gel ITO films. On the other hand, the high refractive index ITO films were grown at room temperature by long-throw reactive ratio-frequency magnetron sputtering. The refractive index of the porous ITO film and ITO films were 1.54 and 2.0, respectively. For the DBR with 4 pairs ITO bilayers, the optical reflectance of more than 70 % was achieved. The stop band and the average resistivity is 140 nm and 2.2¡Ñ10-3 £[-cm, respectively. Finally, electrical and optical characteristics of the RCOLEDs fabricated on the ITO DBR were investigated and compared with those of the conventional OLEDs. The maximum luminous efficiency of 3.79 cd/A was obtained at 347 mA/cm2 for the RCOLED. This luminous efficiency was 26 % higher than that of the conventional OLED.

In the present work, anatase and rutile titanium dioxide (TiO2) coated lustrous mica pigments were prepared by heterogeneous nucleation method. Anatase-rutile phase transformation of the TiO2 on mica substrate was achieved by coating very thin layers of tin (IV) oxide on mica surfaces prior to TiO2 deposition. Muscovite mica, which was used in the experiments was sieved, pre-treated with sodium bicarbonate and decantated before coating process. The surface morphology of mica titania pigments and anatase-rutile phase transformation were investigated by SEM and XRD analyse, respectively. Also, microwave-assisted synthesis of copper phthalocyanine and tetracarboxamide copper phthalocyanine pigments were carried out with phthalic anhydride and trimellitic anhydride precursors, respectively. Molecular structures of these pigments were confirmed by FT-IR and UV-visible spectroscopy analyse. Furthermore, combination pigments were obtained by the process of deposition of copper phthalocyanine pigments on mica-titania pigment substrate in dimethyl formamide solvent. FT-IR analysis and XRD analyse were performed to observe the transformations in the crystal forms of copper phthalocyanines on the substrate. The surface morphologies of copper phthalocyanines on the mica titania pigments were investigated by SEM analysis. Varying amounts of copper phthalocyanines were deposited on the mica surfaces, and nitrogen elemental analysis was performed to determine the amount of copper phthalocyanines. The resulting pigments were incorporated into alkyd based resin to prepare paint samples. L*a*b* values, gloss property, and hardness of the paint samples were determined by color measuring device, gloss meter and hardness measuring device, respectively. The resulting combination pigments obtained in this study showed improved luster, hue, and color intensity. Furthermore, in literature it was reported that these pigments have very high bleed resistance. This can be attributed to large macromolecular structure of copper phthalocyanine on the surface of mica titania pigment that prevents bleeding of the pigment from the paint. Moreover, the paint samples obtained from combination pigments showed higher hardness with respect to the paint sample of the mica titania pigment.

The thin film deposition system using ultrasonic nebulization was adopted in this study. SnCl4.5H2O, SbCl3, and TaCl5 were used as solutes. Ethanol was used as the solvent. Solutions of different Sn4+ concentration, Sb concentration (Sb/Sn atomic ratio) in Sn, and Ta concentration (Ta/Sn atomic ratio) in Sn were mixed. The mist was generated from a solution by the agitation of an ultrasonic device operating at about 1.65MHz. The mist was carried to the heated substrate (corning 7059 glass) by the flow of nitrogen gas so that it was decomposed by heat. SnO2-x films were deposited on the substrate due to the pyrolysis reaction. The experiment included six series: Sn4+ concentration series, Sb-doping series, temperature series, Ta-doping series, aging time series and nebulization rate series. SnO2-x films were analyzed by XRD, UV-Visible, SEM, and Hall-measurement. The optimum deposition conditions were obtained through analyses of these six series. The film deposition rate of nonaged solution was faster than aged solution. When the nebulization rate of solution was 1.6 ml/min, the resistivity of undoped SnO2 film obtained with the substrate kept at 450 oC is 2.364¡Ñ10-2£[-cm and the maximum transmittance of the visible light is 78.7%. When Sb/Sn atomic ratio in the solution was 2%, the resistivity of Sb doped SnO2 film obtained with the substrate kept at 525 oC is 2.77¡Ñ10-3£[-cm and the maximum transmittance of the visible light is 71% . When Ta/Sn atomic ratio in the solution was 0.1%, the resistivity of Ta doped SnO2 film obtained with the substrate kept at 450 oC is 3.917¡Ñ10-2£[-cm and the maximum transmittance of the visible light is 85% In this study, the electro-optical properties of Sb and Ta doped SnO2 thin films derived from an ultrasonic nebulization process were reported and discussed carefully through film characterizations.

Carbon-based materials are currently used for anodes in commercial lithium ion secondary batteries. The theoretical capacity for carbon is only 372mAh/g, and new materials are being developed for anodes to raise the electrical capacity and cycling times. One of the most promising materials is tin oxide that has 50% more electrical capacity and has been studied extensively in the industrial and academic institutions. While most studies have been concentrated on the electrochemical behavior in the charge-discharge process, microstructure evolution along with phase transformation have been emphasized in this work. Tin oxide films are deposited on stainless steel substrate by sputtering and spray. A cell consists of a pure lithium foil as anode and tin oxide film as cathode along with 1M LiClO4 in DMC/EC mixture as electrolyte is fabricated and employed in the charge-discharge test and Cyclic Voltammetry. In the charge-discharge test, we use a constant current of 0.09mA to charge or discharge to the voltage that we need. In the Cyclic Voltammetry test, we change the scanning rate and scanning range. Microstructures developed and phase transformation in different stages of the charge-discharge or CV test process are examined by XRD, SEM and TEM.

Glass matrix composites containing a conducting filler such as antimony tin oxide (ATO) or silicon carbide whiskers (SiCw) have the potential for applications such as transparent electrodes, heating elements, and electromagnetic shielding. For these applications, the composite performance is highly dependent on the microstructure of the composite and the interactions the added filler has with one another. In this research, borosilicate glass-matrix composites were fabricated using a processing method that creates segregated percolated networks at low concentrations of conducting fillers. The conducting fillers were hot pressed with the glass microspheres at temperatures near the glass transition temperature (550°C) using various pressures. Upon hot-pressing at these low temperatures, the glass microspheres deformed into faceted polyhedra and the fillers were displaced to the edges of the glass particles, resulting in percolation. The processing method used in this study was able to bypass many of the current composition and densification issues associated with the creation of percolated networks in glass composites. In some cases, the formation of these percolated networks resulted in a 12-13 orders of magnitude decrease in the resistivity. Using a non-destructive electrical measurement technique, ac impedance spectroscopy (IS), the changes in the electrical properties were tracked as the conducting networks developed. Using IS in conjunction with other techniques, correlations were made between the electrical properties, the filler interfaces, and the influence the processing parameters had on the development of the percolation networks within these composites.