Neste trabalho, foram produzidos filmes finos de carbono pela técnica de magnetron sputtering usando substratos monocristalinos de alumina com plano-c orientado em (0001) e substratos de Si (111) e Si (100), empregando Co, Ni e Cu como filmes intermediários (buffer-layers). As deposições foram conduzidas em três etapas, sendo primeiramente realizadas com buffer-layers de cobalto em substratos de alumina, onde somente após a produção de grande número de amostras, foram então realizadas as deposições usando buffer-layer de cobre em substratos de Si. Em seguida foram realizadas as deposições com buffer-layers de níquel em substratos de alumina. A cristalinidade dos filmes de carbono foi avaliada por meio da técnica de espectroscopia Raman e complementarmente por difração de raios X (DRX). A caracterização morfológica dos filmes foi feita por meio da microscopia eletrônica de varredura (MEV E FEG-SEM) e microscopia eletrônica de transmissão de alta resolução (HRTEM). Picos de DRX referentes aos filmes de carbono foram observados apenas nos resultados das amostras com buffer-layers de cobalto e de níquel. A espectroscopia Raman mostrou que os filmes de carbono com maior grau de cristalinidade foram os produzidos com substratos de Si (111) e buffers de Cu, e com substratos de alumina com buffer-layers de Ni e Co, tendo este último uma amostra com o maior grau de cristalinidade de todas as produzidas no trabalho. Foi observado que o cobalto possui menor recobrimento sobre os substratos de alumina quando comparado ao níquel. Foram realizados testes de absorção de íons de Ce pelos filmes de carbono em duas amostras e foi observado que a absorção não ocorreu devido, provavelmente, ao baixo grau de cristalinidade dos filmes de carbono em ambas amostras. / In this work, carbon thin films were produced by the magnetron sputtering technique using single crystal substrates of alumina c-plane (0001) and Si (111) and Si (100) substrates, employing Co, Ni and Cu as intermediate films (buffer-layers). The depositions were conducted in three stages, first with cobalt buffer-layers where only after the production of a large number of samples, the depositions using cooper buffer-layers were carried out on Si substrates. Then, depositions were performed with nickel buffer-layers using single-crystal alumina substrates. The crystallinity of the carbon films was evaluated by using the technique of Raman spectroscopy and, complementarily, by X-ray diffraction (XRD). The morphological characterization of the films was performed by scanning electron microscopy (SEM and FEG-SEM) and high-resolution transmission electron microscopy (HRTEM). The XRD peaks related to the carbon films were observed only in the results of the samples with cobalt and nickel buffer-layers. The Raman spectroscopy showed that the carbon films with the best degree of crystallinity were the ones produced with Si (111) substrates, for the Cu buffers, and sapphire substrates for the Ni and Co buffers, where the latter resulted in a sample with the best crystallinity of all the ones produced in this work. It was observed that the cobalt has low recovering over the alumina substrates when compared to the nickel. Sorption tests of Ce ions by the carbon films were conducted in two samples and it was observed that the sorption did not occur probably because of the low crystallinity of the carbon films in both samples.

O presente trabalho possui como objetivo o estudo das propriedades dos filmes finos amorfos para aplicações em dispositivos fotônicos. Foram produzidos, por meio da técnica sputtering, filmes finos de telureto BWT, a partir de alvos cerâmicos com composição em peso de 54,6 TeO2 - 22,6 WO3 - 22,8 Bi2O3. A escolha dos vidros BWT se deve às qualidades elétricas e ópticas dos teluretos. Filmes com nanopartículas de ouro foram produzidos e a nucleação das nanopartículas se deu por tratamento térmico. Os filmes produzidos foram caracterizados pelas técnicas de elipsometria, perfilometria, espectrometria de fluorescência de raios-X por energia dispersiva, difração de raios-X, transmissão, absorção e microscopia eletrônica de transmissão e de varredura. Como etapa, final foram produzidos guias de onda do tipo rib por meio de procedimentos de corrosão e litografia, a fim de que fossem testados guiamentos de luz em 632,8 nm e em 1050 nm. Foram usados diferentes fluxos de SF6 para corrosão dos filmes, resultando em guias de diferentes valores de h_core. Os guias com h_core de 63 e 82 nm apresentaram perda de no máximo 3,5 dB/cm para guiamento em 632,8 e 1050 nm em guias com larguras que variaram de 6 a 10 m. As simulações realizadas mostraram guiamento multímodo para todos os casos. O material BWT é, portanto, promissor para aplicações em dispositivos fotônicos. / The objective of this present work is study the properties of amorphous thin films for applications in photonic devices. Thin films of tellurite BWT were produced by sputtering technique using targets whose compositions in weight are 54.6 TeO2 - 22.6 WO3 - 22.8 Bi2O3. BWT was chosen due to the electrical and optical properties of tellurite. Films with gold nanoparticles were produced and the nucleation of the nanoparticles was obtained by heat treatment. Films were characterized by the techniques of elipsometry, perfilometry, energy dispersive X-ray spectroscopy, X-ray diffraction, absorption, transmission, scanning electronic and transmission electronic microscopies. The final step was production of BWT rib waveguides using lithography and reactive-ion etching in order to test light guiding at 632.8 nm and 1050 nm. BWT rib waveguides were produced, using different flux of SF6 for the etching, resulting in waveguides with different values of h_core. Waveguides with 63 and 82 nm of h_core presented maximum loss of 3,5 dB/cm at 632.8 nm and 1050 nm wavelengths in guides with widths ranging from 6 to 10 m. All simulations showed multimode guiding. The BWT material is a potential candidate for applications in photonic devices.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Granular magnetic systems can be composed by magnetic particles or clusters with size of some nanometers. These magnetic nanoparticles present different magnetic order phases, as superparamagnetic, and they can be embedded in both, metallic or insulating matrix. These systems present several phenomena such as the giant magnetoresistance (GMR), tunnel magnetoresistance (TMR) and Coulomb blockade. That phenomena use to disappear when a small termal fluctuation is high enough to reverse the magnetization of the clusters leading the lost the magnetic information in a very short time range. When it occurs, the nano-particles are in superparamagnetic phase. In order to maintain the magnetic information at high values of temperature, or even to suppress the superparamagnetic limit, many works have tried to use an antiferromagnetic matrix, to induce the increase of the energy barrier among the two directions of magnetization easy by the exchange coupling in the grain(FM)/matrix(AFM) interfaces, with the purpose of stabilizing the nano-particles magnetization. In this work, we have produced Co granular samples inside an Al2O3/CoO insulating/antifferomagnetic matrix through a sequential deposition by magnetron sputtering. We aim to explore the couplingmechanisms among the ferromagnetic nanoparticles and the antiferromagnetic matrix. It has been performed measurements of Impedance Spectroscopy (IS), X-ray Difraction (XRD), and magnetization at function temperature analysed by zero-field cooling/field cooling curves (ZFC-FC) at some samples in order to obtain information about the magnetic and structural properties. The measurements of IS and XRD corroborate the formation of Co clusters and the magnetization versus temperature curves to some samples do not indicate evidence of the exchange coupling among the Co clusters and the CoO antiferromagnetic matrix. / Sistemas granulares magnéticos podem ser formados por grãos ou aglomerados magnéticos cujo tamanho é de alguns nanômetros. Estes nano-grãos magnéticos apresentam diferentes fases de ordenamento magnético, como o superparamagnetismo, e podem estar envolvidos tanto por matrizes metálicas como matrizes isolantes. Estes sistemas possuem uma riqueza de fenômenos, como a magnetorresitência gigante (GMR), magnetorresistência túnel (TMR), bloqueio de coulomb entre outros. Estes fenômenos muitas vezes desaparecem quando uma flutuação térmica for suficiente para inverter a magnetização dos grãos, levando-os a perder informação magnética num intervalo de tempo muito curto. Quando isto ocorre dizemos que os nano-grãos estão na fase superparamagnética. Para reter a informação magnética a temperatura ambiente, ou até mesmo suprimir o superparamagnetismo, tem-se tentado o uso de uma matriz antiferromagnética (AFM) onde os nano-grãos ficam imersos, e o acoplamento de troca na interface grão (FM)/matriz (AFM) pode induzir um aumento na barreira de energia entre as duas direções de fácil magnetização e com isso estabilizar a magnetização dos nano-grãos. Neste trabalho foram produzidas amostras granulares de Co imersos em matriz isolante/antiferromagnética de Al2O3/CoO pela deposição alternada do metal e dos isolantes por magnetron sputtering , com a finalidade de explorar os mecanismos de acoplamento entre os nano-grãos ferromagnéticos e a matriz antiferromagnética. Foram realizadas medidas de Espectroscopia de Impedância (IS), Difração de raios-X (XRD), e magnetização em função da temperatura pelas técnicas ZFC-FC em algumas amostras, afim de se obter respostas quanto as propriedades estruturais e magnéticas. As medidas de IS e XRD, indicam a formação de nano-grãos Co e as medidas de magnetização em função da temperatura para algumas amostras, não mostraram com evidência o acoplamento de troca ( Exchange Bias ) entre os grãos de Co e a matriz antiferromagnética de CoO.

O presente trabalho possui como objetivo o estudo das propriedades dos filmes finos amorfos para aplicações em dispositivos fotônicos. Foram produzidos, por meio da técnica sputtering, filmes finos de telureto BWT, a partir de alvos cerâmicos com composição em peso de 54,6 TeO2 - 22,6 WO3 - 22,8 Bi2O3. A escolha dos vidros BWT se deve às qualidades elétricas e ópticas dos teluretos. Filmes com nanopartículas de ouro foram produzidos e a nucleação das nanopartículas se deu por tratamento térmico. Os filmes produzidos foram caracterizados pelas técnicas de elipsometria, perfilometria, espectrometria de fluorescência de raios-X por energia dispersiva, difração de raios-X, transmissão, absorção e microscopia eletrônica de transmissão e de varredura. Como etapa, final foram produzidos guias de onda do tipo rib por meio de procedimentos de corrosão e litografia, a fim de que fossem testados guiamentos de luz em 632,8 nm e em 1050 nm. Foram usados diferentes fluxos de SF6 para corrosão dos filmes, resultando em guias de diferentes valores de h_core. Os guias com h_core de 63 e 82 nm apresentaram perda de no máximo 3,5 dB/cm para guiamento em 632,8 e 1050 nm em guias com larguras que variaram de 6 a 10 m. As simulações realizadas mostraram guiamento multímodo para todos os casos. O material BWT é, portanto, promissor para aplicações em dispositivos fotônicos. / The objective of this present work is study the properties of amorphous thin films for applications in photonic devices. Thin films of tellurite BWT were produced by sputtering technique using targets whose compositions in weight are 54.6 TeO2 - 22.6 WO3 - 22.8 Bi2O3. BWT was chosen due to the electrical and optical properties of tellurite. Films with gold nanoparticles were produced and the nucleation of the nanoparticles was obtained by heat treatment. Films were characterized by the techniques of elipsometry, perfilometry, energy dispersive X-ray spectroscopy, X-ray diffraction, absorption, transmission, scanning electronic and transmission electronic microscopies. The final step was production of BWT rib waveguides using lithography and reactive-ion etching in order to test light guiding at 632.8 nm and 1050 nm. BWT rib waveguides were produced, using different flux of SF6 for the etching, resulting in waveguides with different values of h_core. Waveguides with 63 and 82 nm of h_core presented maximum loss of 3,5 dB/cm at 632.8 nm and 1050 nm wavelengths in guides with widths ranging from 6 to 10 m. All simulations showed multimode guiding. The BWT material is a potential candidate for applications in photonic devices.

Orientador: Luís Augusto Sousa Marques da Rocha / Resumo: O titânio (Ti) é um material que apresenta boa resistência à fadiga e à corrosão. Ainda que seja utilizado na fabricação de próteses ortopédicas e implantes dentários, o titânio metálico não é bioativo, ou seja, não é capaz de provocar reações que favoreçam a fixação de implantes, biocolonização ou a regeneração de tecidos, além de apresentar alguns inconvenientes relacionados a propriedades de superfície, que podem levar à sua degradação. Para fins biomédicos, essa degradação se dá principalmente por processos de tribocorrosão, que ocorre quando ações mecânicas e químicas acontecem de formas concomitantes. Diante deste cenário, superfícies de titânio (Ti) foram recobertas com filmes finos de óxido de titânio (TiO2) por meio da técnica de Sputtering reativo. O principal objetivo do trabalho foi entender como as fases anatase e rutilo dos filmes de TiO2, produzidos por sputtering reativo, podem influenciar na resistência dessas superfícies de titânio, recobertas, à tribocorrosão. São apresentadas análises estruturais e de composição desses filmes, a partir de difração de raios-X e espectroscopia Raman, que confirmam a obtenção de filmes finos compostos de diferentes proporções entre as fases anatase e rutilo, além de uma análise detalhada da forma de crescimento, a partir de microscopia eletrônica de transmissão (MET). O trabalho apresenta uma análise da resistência dos filmes finos de TiO2 no que diz respeito aos mecanismos de tribocorrosão, em meios fisiológicos. Nesse senti... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Titanium (Ti) is a material that has good resistance to fatigue and corrosion. Although it is used in the manufacture of orthopedic prostheses and dental implants, metallic titanium is not bioactive, that is, it is not capable of causing reactions that favor the fixation of implants, biocolonization or tissue regeneration, in addition to presenting some inconveniences related to surface properties, which can lead to its degradation. For biomedical purposes, this degradation occurs mainly through tribocorrosion processes, which occur when mechanical and chemical actions occur in concomitant ways. In view of this scenario, titanium (Ti) surfaces were covered with thin films of titanium oxide (TiO2) using the reactive Sputtering technique. The main objective ofthe work was to understand how the different phases present in TiO2films, anatase and rutile, can influence the resistance of these surfaces relatedto tribocorrosion.Structural and composition analyzes of these films are presented, using X-ray diffraction and Raman spectroscopy, which confirm the achievement of thin films composed of different proportions between the anatase and rutile phases. Inaddition, a detailed analysis of the growth morphology was performed using transmission electron microscopy (TEM). The work presents an analysis of the resistance of TiO2thin films with respect to tribocorrosion mechanisms, in physiological media. In this sense, the tribocorrosion tests were carried out, the electrochemical data ar... (Complete abstract click electronic access below) / Doutor

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Thins films play a critical role in many technical fields today, such as optics, semiconductor, and tool manufacturing. A widely used method for thin film deposition is magnetron sputtering, with Direct-Current Magnetron Sputtering (DCMS) being the most conventional approach. DCMS is very capable at depositing pure metallic (e.g. Al, Ti) or non-metallic (e.g. C, B) films, but encounters problems when depositing compound films, such as oxides or nitrides, in a process known as reactive DCMS (R-DCMS). The process tends to drift into either metallic mode, characterized by high deposition rate but lacking compound formation, or poisoned mode, where compound forms, but with significantly lower deposition rate. Ideally, the process should be maintained in the transition region in-between the two, but this mode is very unstable and further complicated by a hysteresis effect when switching between metallic and poisoned modes. An alternative approach is High-Power Impulse Magnetron Sputtering (HiPIMS) which has been shown to mitigate or remove the instability and hysteresis seen in R-DCMS, as well as improving film density, adhesion and film uniformity on complex geometries. In many cases however, feedback control is needed to stabilize the transition region in reactive HiPIMS (R-HiPIMS). This thesis presents a novel, non-invasive control method for R-HiPIMS using Plasma Emission Monitoring (PEM) to automatically adjust the HiPIMS pulse repetition rate to maintain the delicate transition region. The method was tested on growth of titanium oxide (TiOx) using an industrially relevant deposition system. It was bench-marked against deposition in poisoned mode, and against a control method based on peak discharge current. Results are promising, with higher deposition rate than poisoned mode deposition, and better process stability than peak current control. Challenges remain in making the controller more robust to changes in plasma characteristics due to moving parts, in this case a moving substrate carrier.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Ta-Al-N thin films were prepared using reactive magnetron sputtering, in order to verify the influence of the aluminum content on the crystalline structure, hardness and oxidation resistance. The samples were characterized by Grazing Incidence X-ray Diffraction (GIXRD), Energy Dispersive Spectroscopy (EDS), Rutherford Backscattering Spectrometry (RBS), nanohardness analysis and oxidation tests at 500°C, 600°C and 700°C. First, it was necessary to define deposition parameters of stoichiometric TaN with face centered cubic structure. From this, TaAlN thin films were prepared and present at concentration of 2, 5, 7, 14, 24 and 41 at.%. The crystal phase for the TaAlN films was only present with addition up to 5 at.%, increasing the Al concentration the coatings will tend to be amorphous. From the SEM analysis was possible to observe the surface of the film after oxidation, all thin films showed irregularities, however the amount of such failures was lower in samples with low aluminum content. Moreover, the addition of aluminum does not result in significant gains for oxidation resistance. The highest hardness value obtained was 29 GPa for the sample containing 14 at.%. / Filmes finos de Ta-Al-N foram depositados por magnetron sputtering reativo, com o intuito de verificar a influência da variação do teor de alumínio na estrutura cristalina, na dureza e na resistência à oxidação desse revestimento. As amostras foram caracterizadas por Difração de Raios X em ângulo rasante (GAXRD), Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Energia Dispersiva (EDS), Espectroscopia por Retroespalhamento Rutherford (RBS), análises de nanodureza e testes de oxidação a temperaturas de 500°C, 600°C e 700°C. Primeiro foi necessário definir os parâmetros de deposição de filmes finos de TaN estequiométrico e com estrutura cubica de face centrada. A partir disso, filmes finos de TaAlN foram depositados e apresentaram concentração de 2, 5, 7, 14, 24 e 41 at.% de Al. A fase cristalina obtida para os filmes de TaAlN se apresentou constate com a adição de até 5 at.% de Al, com o aumento da concentração de Al o filme passa a ter uma tendência a ser amorfo. A partir das análises de MEV foi possível observar a superfície dos filmes após a oxidação, todos os filmes apresentaram irregularidades na superfície, entretanto a quantidade dessas falhas foi menor nas amostras com menores concentrações de alumínio. Além disso, a adição de alumínio não trouxe ganhos significativos para a resistência à oxidação desse revestimento. O maior valor de dureza obtido foi de 29 GPa para as amostras contendo 14 at.%.

The increasing energy demand, combined with the use of harmful non-renewable energy sources calls for the search of alternative methods to cover our energy need.Renewable energy can be harvested in different ways, through the movement of wind and water, biomass, or directly from the rays of the sun, as in the case of photovoltaic (PV) devices. Whilst crystalline silicon (c-Si) is the most common absorber used for solar cells, other technologies are emerging. Solar cells with copper indium gallium diselenide (CIGS) as an absorber have the possibility of being flexible, which is an advantage due to the many more application possibilities that appear compared to the rigid and heavy c-Si solar cells. CIGS solar cells have some long-term stability issues, especially regarding ingression of atmospheric species through the front contact layer. This calls for further research in the front contact of the CIGS solar cell, exploring alternative materials to prevent degradation. The front contact of a solar cell must be both optically transparent and conduct electricity. Transparent conductive oxides (TCO) are materials characterized by the ability to conduct electricity, while also possessing a certain degree of optical transparency. The combination of conductivity and transparency makes TCOs ideal as front contacts in solar cells. A very common TCO for front contacts in CIGS solar cells is aluminum-doped zinc oxide (AZO) due to its low cost, good electrical conductivity and optical transparency. Because of its low resistance to degradation in humid environments more robust TCO alternatives, such as indium-doped tin oxide (ITO), are being investigated. Indium-doped tin oxide possesses similar electrical and optical properties as AZO, but better stability in humid environments.The ITO was deposited through RF magnetron sputtering, on a glass substrate to be able to measure optical properties. Initially, experiments focusing on oxygen content in the deposition atmosphere were done, together with a reproducibility experiment. This gave useful information about sputtering parameters and stability of the deposition. Thereon, an experiment was done varying three parameters: oxygen content in deposition atmosphere, sputtering power and temperature of substrate. A statistical software was used to analyze the data, identifying the effects of the changing parameters. The best performing samples were made with an oxygen content of 0,4-0,6 vol%. A high sensibility for oxygen in the system was also observed, as a result of the initial reproducibility experiments. This led to the introduction of a sacrificial deposition step after the machine had been shut down. Optimal substrate temperature was around 150°Cand it was not possible to go higher due to sensibility of the underlying solar cell layers.A lower threshold for the film thickness, located somewhere between 125 and 175 nm, was observed. Films with thickness below this threshold experienced a large resistivityincrease. Further depositions with higher oxygen content are advised to see if the properties of the films further improve.

Si3N4 thin films were prepared by RF magnetron sputtering using N2 or Ar as the sputtering gas. The films were amorphous, with the deposition rate for Ar-sputtered films increasing with RF power and Ar pressure. Sandwich samples having both Al and Au electrodes were prepared. Capacitancevoltage measurements indicated that the contacts for Nj-sputtcred samples were ohmic, while Ar-sputtered samples with Al electrodes exhibited depletion regions. Values of the relative permittivity of 6.3 (AI electrodes) and 6.8 (Au electrodes) were determined from geometric capacitance variations in Ny-sputrered films. Current density-voltage characteristics normally showed ohmic and space charge limited conductivity with trap levels distributed exponentially within the insulator band gap, but exceptionally in N2-sputtered films with Au electrodes electroforming behaviour was observed, with Poole-Frenkel conductivity in the preformed region. Hopping was dominant at low temperatures. AC conductivity was higher for Ar-sputtering, and with Au electrodes. These effects were related to the possible structure of the films, and the diffusion of Au. AC conductivity increased with increasing frequency and temperature, appearing to be via a free band process at high temperatures and hopping at low temperatures. Plausible values of the density of localised states were deri ved using Elliott's model, but this could not be considered uni versally applicable. Loss tangent was also frequency and temperature dependent in Ny-sputtered films, showing a minimum value which shifted towards higher frequencies with increasing temperature. In Ar-sputtered samples minima were not observed in the frequency range covered. The model of Goswami and Goswami appears consistent with these results, particularly in the former case. Variations in the loss tangent values with the sputtering gas and electrode species were consistent with the observed conducti vity variations. Optical properties were also investigated. In Ar-sputtered films, the optical band-gap appeared narrower and the optical absorption higher than for Ny-sputtered films, and a direct transition was also identified. Values of the electrical properties determined for such sputtered films are comparable to those prepared using more sophisticated methods, particularly in the case of Nj-sputtered films. Sputtering may therefore prove useful in semiconductor processing, where a relatively inexpensive method of deposition is required.