The electrical and optical properties of boron doped hydrogenated amorphous silicon thin films (a-Si) were investigated to determine the effect of boron and hydrogen incorporation on carrier transport. The a-Si thin films were grown by plasma enhanced chemical vapor deposition (PECVD) at various boron concentrations, hydrogen dilutions, and at differing growth temperatures. The temperature dependent conductivity generally follows the hopping conduction model. Above a critical temperature, the dominant conduction mechanism is Mott variable range hopping conductivity (M-VRH), where p = ¼, and the carrier hopping depends on energy. However, at lower temperatures, the coulomb interaction between charge carriers becomes important and Efros-Shklosvkii variable hopping (ES-VRH) conduction, where p=1/2, must be included to describe the total conductivity. To correlate changes in electrical conductivity to changes in the local crystalline order, the transverse optical (TO) and transverse acoustic (TA) modes of the Raman spectra were studied to relate changes in short- and mid-range order to the effects of growth temperature, boron, and hydrogen incorporation. With an increase of hydrogen and/or growth temperature, both short and mid-range order improve, whereas the addition of boron results in the degradation of short range order. It is seen that there is a direct correlation between the electrical conductivity and changes in the short and mid-range order resulting from the passivation of defects by hydrogen and the creation of trap states by boron. This work was done under the ARO grant W911NF-10-1-0410, William W. Clark Program Manager. The samples were provided by L-3 Communications.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-08-16T17:19:17Z No. of bitstreams: 1 CAROSSI_Lory_2017.pdf: 61131706 bytes, checksum: 687def06b5a758fcb457d49f53a494b1 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-16T17:19:27Z (GMT) No. of bitstreams: 1 CAROSSI_Lory_2017.pdf: 61131706 bytes, checksum: 687def06b5a758fcb457d49f53a494b1 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-16T17:19:33Z (GMT) No. of bitstreams: 1 CAROSSI_Lory_2017.pdf: 61131706 bytes, checksum: 687def06b5a758fcb457d49f53a494b1 (MD5) / Made available in DSpace on 2017-08-16T17:19:39Z (GMT). No. of bitstreams: 1 CAROSSI_Lory_2017.pdf: 61131706 bytes, checksum: 687def06b5a758fcb457d49f53a494b1 (MD5) Previous issue date: 2015-02-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nanoporous anodic alumina films (NAA) may present different behavior to reflectance and photoluminescence techniques, with Fabry-Pérot interferences and waveguide properties. This phenomenon makes possible the use of NAA as transducer signal in optical sensors. In this work, we investigated how the pre-treatment, the number of steps of anodizing, the anodizing electrolyte mode and temperature affect electrochemical characteristics, morphological and optical mainly NAA. As a result, it was noticeable that the realization of electropolishing is necessary for both the NAA with good regularity as to make it possible to obtain a spectrum with the Fabry-Pérot interference. If the fabrication of NAA is done in two steps, it is possible to obtain reflectance spectra and luminescence fringed with better amplitudes, areas and heights. Regarding the anodizing mode, both the NAA anodized in galvanostatic how potentiostatic showed similar morphologies and spectra with fringes, but the interferences were better defined when the galvanostatic mode was performed. Regarding the temperature, it was noticeable that the change of this parameter leads influences the porous oxide thickness. The spectrum of the luminescence and reflectance increasing the electrolyte temperature caused an increase in interference. However, the range and resolution of interference decreased with increasing temperature. The oxide thicknesses were estimated by energy variation (?E), graph slope between order and 1/? and fast Fourier transform (FFT) techniques. The ratio of film thickness and pore diameter (L/dp) was performed to validate the NAA films with better waveguides property. Moreover, the surface composition analysis of NAA films anodized in phosphoric acid, oxalic acid and mixtures thereof by backscattering spectroscopy Rutherford (RBS) was performed. From simulations it was possible to note that the amount of carbon in the porous oxide structure is practically zero, which may indicate that the origin of the luminescence is related to the presence of more centers F. / Filmes de alumina anódica porosa (AAP) podem apresentar, espectros de reflectância e luminescência com interferências de Fabry-Pérot e propriedades de guias de onda. Esse fenômeno possibilita que a AAP possa ser utilizada como plataforma em sensores ópticos. Neste trabalho, foi investigado como o pré-tratamento, o número de etapas de anodização, o modo de anodização e a temperatura do eletrólito afetam características eletroquímicas, morfológicas e principalmente ópticas da AAP. Como resultado, foi possível notar que a realização do eletropolimento é necessário para obter tanto a AAP com boa regularidade como para que seja possível obter um espectro com as interferências Fabry-Pérot. Se a fabricação da AAP for feita em duas etapas, é possível obter espectros de reflectância e luminescência com franjas com melhores amplitudes, áreas e alturas. Com relação ao modo de anodização, tanto as AAPs anodizadas em modo galvanostático como potenciostático apresentaram morfologias semelhantes e espectros com franjas, mas as interferências foram melhor definidas quando o modo galvanostático foi realizado. Com relação à temperatura, foi possível notar que a mudança desse parâmetro ocasiona influencia na espessura do óxido poroso. Quanto aos espectros de luminescência e reflectância, o aumento da temperatura do eletrólito ocasionou um aumento no número de interferências. Entretanto, a amplitude e a resolução das interferências diminuíram com o aumento da temperatura. A espessura do filme poroso foi estimada pelas técnicas de variação de energia (?E), coeficiente angular do gráfico entre ordem da interferência e 1/? e através da transformada rápida de Fourier (FFT). E foi utilizada a razão entre a espessura do filme e diâmetro do poro (Esp/Dp) para averiguar os filmes de AAP com guias de onda que pudessem ser utilizadas como substratos para sensores ópticos. Além disso, foi realizada a análise de composição superficial dos filmes de AAP anodizados em ácido fosfórico, oxálico e mistura destes ácidos pela técnica de espectroscopia de retroespalhamento de Rutherford (RBS). A partir das simulações realizadas foi possível notar que a quantidade que carbono na estrutura do oxido poroso é praticamente nula, o que pode indicar que a origem da luminescência está relacionada à presença dos centros F.

Orientador: Julio Roberto Bartoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-04T22:28:46Z (GMT). No. of bitstreams: 1 Giacon_VirginiaMansanares_M.pdf: 2837652 bytes, checksum: cc8b7a2c68b1b5f694c6e06c1feb5bfb (MD5) Previous issue date: 2004 / Resumo: Materiais poliméricos são alternativas aos materiais inorgânicos na fabricação de dispositivos ópticos como guias de ondas e fibras ópticas (POF) para transmissão de luz ou sinal. Isso porque, a estrutura molecular dos polímeros pode ser modelada com versatilidade, contribuindo para obter materiais com índices de refração (?) distintos, baixo custo e fácil processamento. Esses dispositivos são constituídos basicamente de um núcleo e uma camada externa, casca ou cladding. Os materiais para casca são usualmente à base de polímeros fluorados. Neste trabalho estudou-se a modificação de superfície de filmes de poli (metacrilato de metila), PMMA, utilizando-se a técnica de Polimerização por Plasma de gás fluorado. Filmes de PMMA com espessuras de 60 µm foram obtidos por spin coating a partir de uma solução de MIBK e Xileno (30% em massa de PMMA). Seguindo dois planejamentos fatoriais, em diferentes condições de pressão (0,5 a 2 torr) e potência (60 a 150 W), os filmes foram expostos ao plasma de CHF3. As superfícies desses filmes foram caracterizadas através de espectroscopia no infravermelho (FTIR/ATR), ângulo de contato de molhamento, microscopia de força atômica (AFM), espectroscopia XPS e análise gravimétrica. A fluoração da superfície dos filmes de PMMA expostos ao plasma foi confirmada por análises de XPS (razão atômica F/C=1,12) e pelo aumento do ângulo de contato de 700(PMMA original) para 100°. O planejamento fatorial mostrou que a pressão é um fator significante (95% confiança) no seu nível mínimo (0,5 torr) para aumentar o ângulo de contato. Análises via FTIR-ATR mostraram alterações nas intensidades de absorção dos grupos C=O e C-O do PMMA, diminuindo significativamente a razão C=O/C-O após o plasma. Análises de AFM mostraram um tolerável aumento da rugosidade da superfície dos filmes após o tratamento. A espessura da camada fluorada, estimada por gravimetria, foi de aproximadamente 0,11 µm. Essa camada deve apresentar um índice de refração menor que o PMMA, inferido pelo alto teor de flúor na superfície dos filmes, determinado pelas análises XPS / Abstract: Polymeric materials are alternative to inorganic materials for production of optical devices as waveguides and optical fibers (POF) for light transmission. This because the molecular structure of polymers can be versatile modeled, giving materials with different refractive indices, low cost and easy processing. These devices are basically consisted by core with an external layer, cladding, of low refractive index (?) allowing light propagation into the core. The cladding materials are usually made of fluorinated polymers. In this work the surface modification of Poly (methylmethacrylate), PMMA, was studied using the plasma polymerization technique. Polymeric films of 60µm thickness were obtained by spin coating using a solution of MIBK and Xylene (30 wt% PMMA). The films were exposed to CHF3 plasma. The processing conditions followed two factorial experimental designs for gas pressure (0.5 - 2 torr) and plasma power (60 - 120 W). The surfaces of the films were characterized using infrared spectroscopy (FTIR/ A TR), contact angle of wetting, atomic force microscopy, XPS spectroscopy and gravimetry. The surface fluorination of PMMA films was confirmed by XPS analysis and also inferred due to the increase on contact angle from 70° (PMMA original) to 100°. The factorial analysis indicated that pressure is a significant factor to increase the contact angle at the lower level 0.5 torr (95% of confidence). FTIR/ATR analysis showed significant alteration on the absorbance intensity of the C=O/C-O groups after plasma. AFM topography analysis showed a tolerable increase on roughness of the surface of plasma exposed films. The thickness of the fluorinated layer was approximately 0.11 µm (estimated by gravimetry). This fluorinated layer should have lower refractive index than the PMMA, due to the high fluorine content on the film surface (F/C ratio), measured by XPS analysis / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

Orientador: Julio Roberto Bartoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-06T09:00:39Z (GMT). No. of bitstreams: 1 Padilha_GiovanadaSilva_M.pdf: 1555922 bytes, checksum: 035b74427e55cfdd28217830ff384c88 (MD5) Previous issue date: 2005 / Resumo: Dispositivos ópticos poliméricos têm sido promissores para aplicação em comunicações, principalmente na utilização em redes de curta distância devido ao fácil processamento e baixo custo quando comparado aos materiais ópticos fabricados com sílica. Na fabricação de um dispositivo óptico é imprescindível que o índice de refração do núcleo seja maior do que o da casca para que o sinal seja transmitido pelo dispositivo. Algumas técnicas de tratamento superficiais são muito comuns para obter diferentes índices de refração entre os materiais, entre elas a fluoração por plasma, seja por reações de deposição ou substituição, formando-se uma camada de polímero fluorado sobre um substrato polimérico com índice de refração modificado. Neste trabalho, estudou-se a modificação da superfície de filmes de poli (metacrilato de metila) (PMMA), usando a técnica de polimerização por plasma de gás fluorado. Filmes de PMMA com espessura de 1 O _m foram obtidos por Spin-Coating a partir de uma solução de clorofórmio (15,36% em massa de PMMA). Os filmes foram expostos ao plasma de CHF3 seguindo dois planejamentos fatoriais em diferentes níveis de pressão e tempo. A superfície dos filmes ópticos fluorados produzidos foi caracterizada através das técnicas: gravimetria, espectroscopia no infravermelho (FTIR-A TR), ângulo de contato de molhamento, microscopia óptica, microscopia eletrônica de varredura (MEV), microscopia de força atômica (AFM) e perfilometria. A fluoração da superfície dos filmes de PMMA pode ser inferida pelo aumento do ângulo de contato em todas as condições experimentais e confirmadas através das análises de FTIR-A TR. As análises gravimétricas apresentaram aumento da camada fluorada sobre o filme de PMMA em toàas as condições de processo, estimando a maior espessura próxima a 1,55 _m em 0,7 torr e 40 minutos de plasma. A análise estatística mostrou que a pressão e o tempo foram variáveis significativas (95% de confiança) para o crescimento de camada polimérica fluorada. Análises de MEV apresentaram uma camada fluorada bem definida e presença do elemento flúor com a análise de EDS. A rugosidade dos filmes ópticos fluorados foi de 200 Á, bastante satisfatório para cladding com 1,55 _m de espessura / Abstract: Polymeric optical devices have been promising for application in communications, mainly for local networks due to easy processing and low cost compared to the optical materials made silica. In the production of an optical device it is indispensable the difference between the refraction index of the core and the cladding. The refractive index of the core should be larger than the one of the cladding so that the signal is transmitted by the device. Some techniques of surface treatment are very common to obtain different refractive index among the materials, among them plasma fluorination that either allow deposition reaction of a layer of fluorinated polymers the substrate with refractive index modified. In this work, it was studied the modification of the surface of poly (methyl methacrylate) (PMMA) films, with the technique of plasma polymerization. Films of PMMA with thickness of 1 O _m were obtained by Spin-Coating starting from a chloroform solution (15.36% wt% PMMA). The films were exposed to the plasma of CHF3 following two factorial experimental designs at different levels of pressure and time. The surface of the films was characterized through the techniques: gravimetry, infrared spectroscopy (FTIR-ATR), contact angle of wetting, optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and scan profile. The surface fluorination of PMMA films can be inferred by the increase of the contact angle in all of the experimental conditions and confirmed with the analyses of FTIR-ATR. Gravimetry showed an increase of the layer of fluorinated polymer onto PMMA films, being 1.55 _m the largest thickness at 0.7 torr and 40 minutes of plasma. The factorial analysis showed that pressure and time were significant (95% of confidence) for the growth of the fluorinated polymeric layer. Analyses of SEM showed a layer of fluorinated polymer well defined and presence of the fluorine element by EDS analysis. The roughness of the films fluorinated polymers was around of 200 A, quite satisfactory for cladding of 1.55 micro m of thickness / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

The present research work mainly focuses on the fabrication and characterization of single and multilayer thin films based on Bismuth Vanadate (BVO) and Bismuth Titanate (BTO). The multi-target laser ablation technique was used to fabricate single layer thin films of BVO, BVN and BTO; and multilayers composed of BVO and BTO in different structures. The fabricated thin films exhibited dense microstructure and a sharp interface with the substrate. The lattice strain, surface roughness and grain size could be varied as functions of composition and individual layer thickness in different structure fabricated. The optical properties were studied by spectroscopic ellipsometry and optical transmission spectra. The various models that were used for ellipsometric data analysis gave an excellent fitting to the experimental data. The optical constants were determined through multilayer analyses of the films. The band gap of these films was studied by spectroscopic ellipsometry and optical transmission. The optical studies carried out on BVO-BTO bilayer indicated the presence of an interfacial layer in between the BVO and BTO layer, whose refractive index was different from that of the individual layers and is attributed to different nature of the interfacial layer. The ferroelectric nature of BVO films was confirmed by P-E hysteresis loop studies under different applied fields and at various probing frequencies. The same was corroborated via the C-V measurements of these BVO films which exhibited butterfly shaped C-V characteristics. Fatigue studies in these films indicated that the switchable polarization is essentially constant through 105 cycles, after which it starts increasing probably due to the ionic conduction in BVO thin films. The dielectric response of undoped and Nb doped BVO as well as BVBT ML thin films were studied over a wide range of temperatures. The BVO films exhibited remarkable dielectric dispersion at low frequencies especially in the high temperature regime. Further, the frequency and temperature dependence of the dielectric, impedance, modulus and conductivity spectra of these films were investigated in detail. The ac conductivity was found to obey well the double power law in case of ML, indicating the different contributions to the conductivity, the low frequency conductivity being due to the short range translational hopping and the high frequency conductivity is due to the localized or reorientational hopping motion. DC leakage conduction in BVO, BVN and BVBT ML thin films was studied over a wide range of temperatures and applied electric fields. The experimental data were analyzed in light of different models to investigate the dc conduction mechanism in these films which were broadly classified into electrode limited and bulk limited conduction processes. In the case of BVO thin films the dc leakage current exhibited an ohmic nature at low electric fields followed by an onset of the space charge limited conduction (>1). Further in case of BVN films, three distinct regions were observed in I-V characteristics signifying different types of conduction processes in these films. In case of BVBT ML thin films, bulk limited PF mechanism was found to determine the conduction behavior at moderate electric fields. At higher electric fields, a trap filled region was observed which was followed by SCL conduction at higher fields. Therefore the present observation indicates the presence of more than one bulk limited conduction process in BVBT ML thin films. BVO thin films exhibiting good structure and dense morphology were successfully prepared on p-type Si by chemical solution decomposition technique. The C-V characteristics were evaluated for Au/BVO/Si MFS structure which showed a typical high frequency feature of a conventional MFIS structure.

Chalcogenide glasses have attracted considerable attention due to their infrared transparency, low phonon energy, and high non linear optical properties. They have been explored as promising candidate for optical memories, gratings, switching devices etc. Because of their low phonon energy and high refractive indices, now a days these are used for high efficiency fibre amplifiers. Nevertheless, the availability of amorphous semiconductors in the form of high quality multilayers provides potential applications in the field of micro and optoelectronics. Among amorphous multilayers, chalcogenide multilayers are attractive because of the prominent photoinduced effects. Studies in chalcogenide amorphous multilayer have been directed towards two phenomena. One is photoinduced interdiffusion in short period multilayer systems which finds potential applications in holographic recording and fabrication of phase gratings . The other is photo darkening or photobleaching which is also known in thick films. These multilayers exhibit prominent photoinduced effects, similar to those exhibited by uniform thin films. In spite of its practical usefulness, the mechanism of photoinduced interdiffusion is not properly understood. Since most structural transformations are related to atomic diffusion, understanding of the structural transformation must be based on the diffusion process. The main aim of this thesis is to study the photoinduced diffusion in Sb/As2S3 multilayered films and (As2S3)1-xSbx thin films. In literature, there are reports about the photoinduced interdiffusion in Se/As2S3 and Bi/As2S3 multilayered films, but the mechanisms of photoinduced interdiffusion of these elements are not very clear. Raman scattering and infrared spectroscopy techniques have been used to study the photoinduced interdiffusion in Se/As2S3 and Bi/As2S3 multilayered films by Malyovanik et al. (M. Malyovanik, M. Shiplyak, V. Cheresnya, T. Remeta, S. Ivan, and A. Kikineshi, J. Optoelectron. Adv. Mater. 5, 397 (2003). But many questions remain unanswered. The characteristic spectra of components in the multilayer and those of the diffused layer were rather similar. In the present thesis, photoinduced interdiffusion in Sb/As2S3 multilayered samples are studied by Fourier Transform Infrared spectroscopy (FTIR) at room and low temperature and X-ray photoelectron spectroscopy (XPS). The photoinduced effects in (As2S3)1-xSbx thin films are studied by FTIR, XPS and Raman Spectroscopy. The detailed information about the distribution of electronic states in the absorption edge, localized states and the new bonds formed between the components due to photoinduced interdiffusion elucidated from the above studies will give more insight into the mechanism and kinetics of photoinduced interdiffusion. The thesis consists of seven chapters. References are given at the end of each chapter.