Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 43-44).

Thesis (Ph. D.)--University of Idaho, 2005. / Also available online in PDF format. Abstract. "July, 2005." Includes bibliographical references (leaves 94-98).

A systematic study has been made of the electrical conduction processes through electrically etched porous silicon (PS) films sandwiched between two metal electrodes. The PS layers were formed by anodisation of p-type silicon wafers in a hydrofluoric (HF) acid solution. The effect of fabrication conditions on the structural and electrical properties of PS have been investigated. The thickness of PS layers was found to depend on the anodisation time, whereas porosity was regarded to be controlled by the current density and HF acid concentration. The dark current-voltage I(V) characteristics at fixed temperature and the variation of current as a function of temperature have been established. The characteristics for all devices, regardless the metal contact, show a rectifying behaviour with ideality factor close to unity. It was found that PS films fabricated from p-type silicon substrates behave like n-type silicon due to the depletion of electronic holes. The results suggest that a pn heterojunction between PS and p-Si is responsible for the rectifying behaviour. A value of 0.7 eV was obtained for the barrier height at the interface between PS and p-Si at room temperature. The barrier height was found to increase with rising temperature. Recombination conduction process was found to be dominant at low temperatures as the activation energy did not exceed 0.22 eV. At high temperatures, thermionic emission diffusion process was found to be responsible for the current transport in the PS structures. A band model was proposed for metal/PS/p-Si/metal structures in order to explain the observed characteristics. A.c. dark current measurements revealed that the a.c. conductivity varies as ws where w is the angular frequency and s' is an index which depends on temperature and having a value less than unity. A.c. activation energy was interpreted in terms of hopping conduction at low temperatures (less than 200 K) and diffusion transport of charge carriers through PS layers at higher temperatures. Measurements of capacitance as a function of frequency and temperature showed a decrease with increasing frequency and increase with increasing temperature. The photoconduction behaviour of PS was characterised by high dark resistivity, a clear photosensitivity for visible light, and a bias voltage dependence of the spectral response.

Orientador: Anna Silvia Palcheco Peixoto / Banca: Roger Augusto Rodrigues / Banca: Paulo José Rocha de Albuquerque / Resumo: Os estudos de técnicos modernas na investigação geotécnica vêm avançando a cada ano com o objetivo de obter resultados mais rápidos e práticos com maior precisão. A resistividade elétrica vem ganhando atenção devido ao seu apelo ambiental, visto que, a obtenção desta medida se dá por meio da imposição de um fluxo de corrente elétrica em um dado material. Porém a interpretação dos resultados em solo tropical é dificultada pelas variáveis envolvidas, como a não saturação e os argilo-minerais. O objetivo desta dissertação de mestrado é verificar a influência que a sucção, presente em solos não saturados, têm sobre os valores de resistividade/condutividade elétrica. Também foi possível analisar as curvas de retenção de água dos solos obtidos pelas diferentes trajetórias, secagem e umedecimento, observando sua interferência nos valores de Resistividade elétrica. Essas trajetórias representam o fluxo de água no solo durante o ano, como as estações secas e úmidas. Esse estudo tem importância em regiões de clima árido e tropical em que solos têm como característica principal baixa umidade próxima à superfície, podendo sofrer ciclos alternados de secagem e umedecimento, e assim, constante mudança dos valores de sucção. Utilizaram-se três solos: areia argilosa de origem residual do Arenito Bauru, retirada do Aterro de Resíduos Sólidos de Bauru; argila arenosa residual de diabásio, proveniente do Aeroporto Estadual de Piracicaba; e uma areia fina com pouca argila, retirada do processo erosivo ao longo do córrego Água Comprida. Em cada ensaio foram obtidos: resistividade elétrica, temperatura do solo e do fluido, teor de umidade, grau de saturação e índice de vazios. Para a curva de retenção de água no solo, foi utilizado o método do Papel Filtro sob trajetóriade secagem e de umedecimento. O formato da curva de retenção depende, dentre outros fatores, do tipo de solo e do tamanho... / Mestre

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