published_or_final_version / abstract / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

Not available / text

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

No description available.

Thermally stimulated current measurements are carried out on as-grown TlGaS2, TlGaSe2 and TlInS2 layered single crystals with the current owing perpendiclar to the c-axis in the wide temperature range of 10-300 K with various heating rates. Experimental evidence is found for the presence of three, two and one trapping centers for TlGaS2 , TlGaSe2 and TlInS2 crystals with activation energies 6, 12 and 26 / 98 and 130 / 12 meV respectively. We have determined the trap parameters using varous methods of analyis, and these agree well with each other. The retrapping process is negligible for these levels, as confirmed by good agreement between the experimental results and theoretical predictions of the model that assumes slow retrapping. Also the calculated values of the capture cross sections, attempt to escape frequencies and the concentration of the traps are reported.

Orientador: Leinig Antônio Perazolli / Resumo: O presente trabalho buscou desenvolver fotocatalisadores cerâmicos por meio da produção de heterojunções inovadoras à base de SrTiO3, TiO2 e CaO, que tiveram suas fotoatividades avaliadas pela descoloração do corante Rodamina B (RhB) e pela obtenção de biodiesel, utilizando luz ultravioleta. As amostras TiO2, CaO e SrTiO3 foram obtidas pelo método de precursores poliméricos, método Pechini, e as heterojunções TiO2/SrTiO3, CaO/SrTiO3 e CaO/CaTiO3 foram preparados por rota sol-gel. Após síntese e tratamento térmico, as amostras foram caracterizadas por difração de Raios-X (DRX) para verificar as fases cristalinas formadas, por espectroscopia de infravermelho com transformada de fourier (FT-IR) e termogravimetria/análise térmica diferencial (TG/DTA) para verificar e quantificar a formação de CaCO3 e Ca(OH)2, por espectroscopia de refletância difusa (UV/Vis/NIR DRS) para determinar a energia de band gap, por Brunauer, Emmett e Teller (B.E.T.) para determinar a área específica, por microscopia eletrônica de varredura acoplada a espectroscopia de energia dispersiva de Raios-X (FE-SEMEDS) para estimar o tamanho das partículas, sua morfologia e composição elementar, por espectroscopia de fotoelétrons excitados por Raios-X (XPS) para conhecer a composição elementar presente na superfície da amostra e seus estados de oxidação, por espectroscopia de fotoluminescência (PL) para verificar a formação de defeitos estruturais, por microscopia eletrônica de transmissão de alta resolução (HRTE... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work aimed to develop ceramic photocatalysts through the production of innovative SrTiO3, TiO2 and CaO based heterojunctions, which had their photoactivities evaluated by the discoloration of Rhodamine B (RhB) dye and by obtaining biodiesel using UV light. TiO2, CaO and SrTiO3 samples were obtained by polymeric precursor method, Pechini method, and TiO2/SrTiO3, CaO/SrTiO3 and CaO/CaTiO3 heterojunctions were prepared by sol-gel route. After synthesis and heat treatment, the samples were characterized by X-ray diffraction (XRD) to verify the crystalline phases formed, fourier transform infrared spectroscopy (FT-IR) and thermogravimetry/differential thermal analysis (TG/DTA) to verify and quantify the formation of CaCO3 and Ca(OH)2, diffuse reflectance spectroscopy (UV/Vis/NIR DRS) to determine band gap energy, Brunauer, Emmett e Teller (B.E.T.) to determine specific area, field emission scanning electron microscopy coupled X-ray dispersive energy spectroscopy (FE-SEM-EDS) to estimate particle size, morphology and elemental composition, X-ray photoelectron spectroscopy (XPS) to know the elemental composition present on the sample surface and oxidation states, photoluminescence spectroscopy (PL) to verify the formation structural defects, high resolution transmission electron microscopy (HRTEM) to confirm the formation of heterojunction. Rhodamine B discoloration was measured by UV/Vis molecular absorption spectroscopy and the conversion of oil to biodiesel was analyz... (Complete abstract click electronic access below) / Doutor

Particle contamination control is a critical issue for the semiconductor industry. In the near future, this industry will be concerned with the chemical identities of contaminant particles as small as 0.01 pm in size. Therefore, analytical techniques with both high chemical sensitivity and spatial resolution are required. Transmission electron microscopy (TEM) provides excellent spatial resolution and yields structural and compositional information. It is rarely used, however, due to the difficulty of sample preparation. The goals of this research are to promote the use of TEM as an ultrafine particle analysis tool by developing new sample preparation methods, and to exploit the new TEM techniques for analysis of particles in semiconductor processing fluids. A TEM methodology for the analysis of particulate contaminants in fluids with an elemental detectability limit as low as 0.1 part per trillion (ppt), and a particle concentration detectability limit as low as 1 particle/ml for particles greater than 0.2 pm was developed and successfully applied to the analysis of particles in HF, H202, de-ionized (DI) water, and on the surface of an electronic device. HF samples from three manufacturers were examined. For HF (B), the maximum particle concentration was 8.3 x 103 particles/ml. Both a viscous material and lath-shaped particles were observed. The Sb concentration was less than 0.6 part per billion (ppb). HF (C) was the cleanest. CaF2 and TiO2 particles were identified in HF (D). For H2 02, iron and tin oxides and hydroxides were identified. The maximum particle concentration was 990 particles/ml. The Sn and Fe concentrations were less than 0.3 ppb. Spherical and dendritic particles were observed. For DI water, spherical and dendritic particles (<2 particles/ml), and particles containing Fe or Si with concentrations less than 0.1 ppt were observed. Contaminants on an electronic device surface were also analyzed. Clusters of small particles were determined to be a mixture of aluminum oxides and aluminum silicates.