Chemisorption of an organic monolayer to tune the surface properties of a transparent conductive oxide (TCO) electrode can improve the performance of organic electronic devices that rely on efficient charge transfer between an organic active layer and a TCO contact. Here, a series of perylene diimides (PDIs) was synthesized and used to study relationships between monolayer structure/properties and electron transfer kinetics at PDI-modified indium-tin oxide (ITO) electrodes. In these PDI molecules, one of the imide substituents is a benzene ring bearing a phosphonic acid (PA) and the other is a bulky aryl group that is twisted out of the plane of the PDI core. The size of the bulky aryl group and the substitution of the benzene ring bearing the PA were both varied, which altered the extent of aggregation when these molecules were absorbed as monolayer films (MLs) on ITO, as revealed by both attenuated total reflectance (ATR) and total internal reflection fluorescence spectra. Polarized ATR measurements indicate that, in these MLs, the long axis of the PDI core is tilted at an angle of 33-42 degrees relative to the surface normal; the tilt angle increased as the degree of bulky substitution increased. Rate constants for electron transfer (k(s,opt)) between these redox-active modifiers and ITO were determined by potential-modulated ATR spectroscopy. As the degree of PDI aggregation was reduced, k(s,opt) declined, which is attributed to a reduction in the lateral electron self-exchange rate between adsorbed PDI molecules, as well as the heterogeneous conductivity of the ITO electrode surface. Photoelectrochemical measurements using a dissolved aluminum phthalocyanine as an electron donor showed that ITO modified with any of these PDIs is a more effective electron-collecting electrode than bare ITO.

O óxido de índio dopado com estanho é um semicondutor degenerado de alta transparência no espectro visível e alta condutância elétrica. Por suas propriedades, ele é utilizado como eletrodo transparente em diversas aplicações. Algumas destas aplicações exigem que os filmes sejam depositados sobre substratos poliméricos, que degradam em temperaturas acima de 100 °C. Por este motivo, métodos de deposição que utilizam baixas temperaturas são necessários. O objetivo deste trabalho é o desenvolvimento de técnicas de deposição de filmes de óxido de índio dopado com estanho, em baixas temperaturas (< 100 °C), pelo método de magnetron sputtering de rádio fequência. Filmes foram obtidos sobre substratos de silício, vidro e policarbonato, e suas propriedades físicas, elétricas, ópticas, químicas e estruturais foram analisadas por perfilometria, elipsometria, curvas corrente-tensão, prova de quatro pontas, medidas de efeito Hall, difratometria de raios-X e espectrofotometria. Filmes depositados sobre silício e vidro tiveram resistividade elétrica mínima da ordem de 10^-4 Ohm.cm, enquanto a resistividade do filme obtido sobre policarbonato foi da ordem de 10^-3 Ohm.cm. A transmitância óptica média no espectro visível das amostras variou de 66 a 87 %. Do ponto de vista estrutural, as amostras tenderam a apresentar fase amorfa e cristalina, com orientação preferencial ao longo da direção [100]. De modo geral, as amostras obtidas de 75 a 125 W tiveram as melhores propriedades para serem utilizadas em aplicações que exijam eletrodos transparentes, considerando aspectos elétricos e ópticos. / Indium-tin oxide is a degenerate semiconductor that shows high transmittance in the visible region of the spectrum and high electrical conductance. Because of its properties, this material is used as transparent electrode in a wide variety of applications. Some of these applications demand the indium-tin oxide layer to be deposited over polymer substrates, which degrade at temperatures above 100 °C. Because of this degradation problem, deposition methods at low temperatures are needed. The purpose of this work is the development of low temperature (< 100 °C) indium-tin oxide deposition processes by radio frequency magnetron sputtering method. Thin films were deposited over silicon, glass and polycarbonate substrates, and their physical, electrical, optical, chemical and structural properties were analyzed by surface high step meter, ellipsometry, current-voltage curves, four-point probe analysis, Hall effect measurements, X-ray diffractometry and spectrophotometry. Films deposited over silicon and glass substrates showed minimal electrical resistivity in the order of 10^-4 Ohm.cm, while the resistivity of the film obtained over polycarbonate was in the order of 10^-3 Ohm.cm. The average transmittance in the visible spectrum varied over the range 66 to 87 %. According to the structural study, the films present both amorphous and crystalline phases, with crystallites showing preferential orientation along the [100] direction. In general, films deposited with power varying over the range 75 to 125 W showed the best results to be applied as transparent electrodes, considering electrical and optical aspects.

O óxido de índio dopado com estanho é um semicondutor degenerado de alta transparência no espectro visível e alta condutância elétrica. Por suas propriedades, ele é utilizado como eletrodo transparente em diversas aplicações. Algumas destas aplicações exigem que os filmes sejam depositados sobre substratos poliméricos, que degradam em temperaturas acima de 100 °C. Por este motivo, métodos de deposição que utilizam baixas temperaturas são necessários. O objetivo deste trabalho é o desenvolvimento de técnicas de deposição de filmes de óxido de índio dopado com estanho, em baixas temperaturas (< 100 °C), pelo método de magnetron sputtering de rádio fequência. Filmes foram obtidos sobre substratos de silício, vidro e policarbonato, e suas propriedades físicas, elétricas, ópticas, químicas e estruturais foram analisadas por perfilometria, elipsometria, curvas corrente-tensão, prova de quatro pontas, medidas de efeito Hall, difratometria de raios-X e espectrofotometria. Filmes depositados sobre silício e vidro tiveram resistividade elétrica mínima da ordem de 10^-4 Ohm.cm, enquanto a resistividade do filme obtido sobre policarbonato foi da ordem de 10^-3 Ohm.cm. A transmitância óptica média no espectro visível das amostras variou de 66 a 87 %. Do ponto de vista estrutural, as amostras tenderam a apresentar fase amorfa e cristalina, com orientação preferencial ao longo da direção [100]. De modo geral, as amostras obtidas de 75 a 125 W tiveram as melhores propriedades para serem utilizadas em aplicações que exijam eletrodos transparentes, considerando aspectos elétricos e ópticos. / Indium-tin oxide is a degenerate semiconductor that shows high transmittance in the visible region of the spectrum and high electrical conductance. Because of its properties, this material is used as transparent electrode in a wide variety of applications. Some of these applications demand the indium-tin oxide layer to be deposited over polymer substrates, which degrade at temperatures above 100 °C. Because of this degradation problem, deposition methods at low temperatures are needed. The purpose of this work is the development of low temperature (< 100 °C) indium-tin oxide deposition processes by radio frequency magnetron sputtering method. Thin films were deposited over silicon, glass and polycarbonate substrates, and their physical, electrical, optical, chemical and structural properties were analyzed by surface high step meter, ellipsometry, current-voltage curves, four-point probe analysis, Hall effect measurements, X-ray diffractometry and spectrophotometry. Films deposited over silicon and glass substrates showed minimal electrical resistivity in the order of 10^-4 Ohm.cm, while the resistivity of the film obtained over polycarbonate was in the order of 10^-3 Ohm.cm. The average transmittance in the visible spectrum varied over the range 66 to 87 %. According to the structural study, the films present both amorphous and crystalline phases, with crystallites showing preferential orientation along the [100] direction. In general, films deposited with power varying over the range 75 to 125 W showed the best results to be applied as transparent electrodes, considering electrical and optical aspects.

<p>When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.<br /> &nbsp / </p>

<p>When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.<br /> &nbsp / </p>

For polymer-matrix composites (PMCs) that contain insulating matrices and conducting fillers, the electrical properties of the PMCs are especially sensitive to the local concentration of the fillers in the matrix. For PMCs that have phase-segregated microstructures, better prediction of the properties is possible since enhanced control over the distribution of the filler in the matrix can be achieved. In this research, PMMA-ITO nanocomposites were chosen as the composite system in which to explore alternative microstructures, specifically highly phase-segregated microstructures. The microstructures were primarily controlled by varying the ITO particle size and concentration, and the fabrication parameters used to form the nanocomposites. The motivation for this research was to develop correlations between the microstructure and non-destructive measurements in order to improve the predictability of properties in percolating PMCs. As a result of this work, a novel phase-segregated microstructure was discovered, where ITO aggregate-wire structures self-assembled during the composite forming process. Structural analysis of the specimens was conducted primarily using transmission optical microscopy and scanning electron microscopy (SEM). Impedance spectroscopy and optical spectroscopy were the primary NDE characterization tools used for analyzing the variations among the specimens. Ultra-small angle x-ray scattering (USAXS) and stereological techniques were also used to describe the dimensions of the ITO aggregate-wire structures that self-assembled in the PMMA-ITO nanocomposites.

An aim of this work is a research of a deposition process of indium tin oxide by plasma assisted methods. The thesis deals with plasma diagnostics, e.g. Langmuir probe diagnostics and optical emission spectroscopy, as well as describes experiments of film deposition including their diagnostics, e.g. absorption spectroscopy, X-ray diffractometry and atomic force microscopy.

Made available in DSpace on 2016-06-02T20:15:21Z (GMT). No. of bitstreams: 1 3005.pdf: 10668736 bytes, checksum: 8ec8cb21968edc4feb09cb7616b0e9b2 (MD5) Previous issue date: 2010-05-07 / Universidade Federal de Minas Gerais / The structural and transport features of oxide nanostructures synthesized by a vapour phase aproach: the VLS and VS methods were investigated in this work. ITO and In2O3 nanowires were characterized by using XRD, HRTEM and FEG-SEM techniques. Both nanostructures were found to be body-centered cubic (bixbyite, point group Ia3) single crystals with a well defined growth direction. Raman spectroscopy was used in order to study the nanowires composition, crystalline character and the role of tin atoms in the In2O3 lattice (ITO) was studied as well. The influence of the structural disorder induced by doping was pointed as the main cause of the break of the selection rules in ITO and it was promptly recognized in the Raman spectrum. The metallic character observed in In2O3 micrometric wires was assigned to the electron-phonon scattering in agreement with the Bloch-Grüneisen theory. ITO samples with different sizes were analysed in the framework of the Bloch-Grüneisen theory and at high temperatures (T > 77 K) they were found to present a typical metallic character. It was observed at low temperatures (T < 77 K) and in small samples a negative temperature coefficient of resistance which is an evidence that quantum interference processes are present. A weak localized character was found in these samples as detected in magnetoresistance measurements. The electron s phase break was associated to the electronelectron scattering (T < 77 K) and the electron-phonon scattering (T > 77 K). The transport measurements in one-nanowire based FET provided data on the electron s mobility and density. Tin oxide nanobelts were also studied and their structural and electrical characterizations were obtained. In this case the association of several structural measurements provided that the samples are rutile-like single crystals (point group P42/mnm) grown by the VS mechanism. The transport measurements provided data on the nanobelts gap energy (3.8 eV) and on the transport mechanisms acting in different temperature ranges. An activated-like process and the variable range hopping were found to be present in different temperature range and additionally the localization length was determined. The influence of additional levels inside the gap caused by oxygen vacancies was studied by performing light and atmosphere-dependent experiments and as a result a photo-activated character was detected. Thermally stimulated current measurements provided evidence that only one level associated to the oxygen vacancies at 1.8 eV seems to contribute to the transport in SnO2 nanobelts. Triclinic single crystalline nanobelts were identified as the Sn3O4 phase and were analyzed by transport measurements. The samples were wide band gap semiconductors and the role of oxygen vacancies was identified by using PL and PC measurements. The semiconductor behavior was confirmed by the electron transport data, which pointed to the variable range hopping process as the main conduction mechanism (55 K < T < 398 K) and data on localization length and on the hopping distance were obtained. The presence of additional levels due to oxygen vacancies and tin interstitials was recognized in the samples by performing photo-activated and thermally stimulated current measurements. / Neste trabalho foram investigadas características estruturais e de transporte eletrônico em nanoestruturas óxidas sintetizadas por métodos baseados em fase de vapor: os métodos VLS e VS. Amostras de In2O3 e ITO foram caracterizadas quanto às suas características estruturais usando-se técnicas experimentais como XRD, HRTEM e FEG-SEM e comprovou-se que são monocristais cúbicos de corpo centrado (bixbyite) pertencentes ao grupo puntual Ia3 com direção preferencial de crescimento bem definida. A espectroscopia Raman foi utilizada como ferramenta fundamental para o estudo da composição destes materiais, confirmando a fase, o caráter monocristalino bem como a presença de dopantes na estrutura do In2O3 como no caso do ITO. Estudou-se ainda a influência da desordem estrutural causada pela dopagem nas estruturas já que esta se reflete diretamente em uma quebra na regra de seleção do material e portanto, no espectro Raman. O estudo dos mecanismos de transporte eletrônico em microfios de In2O3 mostrou uma característica essencialmente metálica nestes materiais, comprovada pela identificação do espalhamento elétron-fônon (teoria de Bloch-Grüneisen) como a principal fonte de espalhamento. Amostras de ITO com diferentes tamanhos também foram estudadas e observou-se, acima de 77 K, o aumento da resistência com o aumento da temperatura também caracterizado pela interação elétron-fônon. A observação de um coeficiente negativo de temperatura da resistência observado na amostra nanométrica e em baixas temperaturas aponta para a presença de processos quânticos de interferência originados principalmente da redução da dimensionalidade da amostra. De fato, a aplicação de um campo magnético mostrou a supressão desse comportamento em função da temperatura, comprovando assim que a chamada localização fraca encontra-se presente no nanofio de ITO. Nesse caso, a destruição da fase do elétron foi associada ao espalhamento elétron-elétron (T < 77 K) e ao espalhamento elétron-fônon (T > 77 K). O uso das referidas amostras como transistores de efeito de campo permitiu ainda a obtenção de parâmetros importantes como a mobilidade e a densidade de portadores nas amostras. Nanofitas de SnO2 também foram estudadas e suas propriedades estruturais e de transporte eletrônico foram obtidas. Nesse caso encontrou-se através de técnicas de medida variadas que as amostras são monocristais com estrutura do tipo rutila (grupo puntual P42/mnm) sintetizadas pelo método VS. Diferentes experimentos de transporte eletrônico permitiram a determinação do gap de energia deste material em 3.8 eV e ainda permitiram identificar a presença de diferentes mecanismos de transporte atuando em intervalos de temperatura bem determinados. De fato observou-se a transição de um comportamento de ativação térmica para um comportamento localizado e também ativado por fônons, o hopping donde se determinou o comprimento de localização eletrônico. A presença de níveis adicionais ao gap de energia foi estudada através de experimentos feitos em diferentes atmosferas e sob ação de luz ultravioleta visando explorar o caráter foto-ativado detectado nas amostras. Foi observado de medidas termicamente estimuladas a emissão termiônica de portadores através dos contatos elétricos o que indica que o único nível que parece contribuir com portadores livres nas nanofitas de SnO2 é aquele detectado em 1.8 eV. Amostras monocristalinas com estrutura triclínica, com morfologia de fita e cuja fase foi identificada como sendo Sn3O4 foram também investigadas. A presença de vacâncias de oxigênio e de um gap largo de energia foram observadas através de experimentos de PL e PC. O hopping foi identificado em um grande intervalo de temperaturas (55 K < T < 398 K) como o principal mecanismo de transporte eletrônico observado nas amostras o que comprova a presença de localização e também indica que as amostras se comportam como um semicondutor. Adicionalmente, parâmetros como o comprimento de localização e a distância de pulo dos elétrons foram calculadas. A presença de vacâncias de oxigênio nestas amostras foi ainda estudada através de medidas foto-ativadas pela luz ultravioleta e em diferentes atmosferas de medida, e também por experimentos de TSC donde obteve-se evidências adicionais sobre a presença de outras fontes de elétrons livres como vacâncias superficiais ou interstícios de estanho, contribuindo para o transporte nestas amostras.

Philosophiae Doctor - PhD / When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity. / South Africa

Philosophiae Doctor - PhD / When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell.A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon.In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity.The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped.A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.