Foram estudados os filmes finos eletrocrômicos de WO3, MoO3 e PEDOT:PSS e aplicados em pequenos dispositivos eletrocrômicos. Os filmes finos de WO3 foram produzidos por meio do processo de eletrodeposição galvanostática a partir de um sol de ácido peroxotungstênico. Realizaram-se dois estudos de eletrodeposição dos filmes de WO3: 1º) produziu-se filmes em diferentes correntes -0,45 -0,50, -0,60 e -1,0 mA com tempo de 600 segundos; 2º) produziu-se filmes variando os tempos de eletrodeposição de 100, 200, 300, 400, 500 e 600 s com corrente de -0,45 mA. O tratamento térmico foi efetuado a 120 ºC por 1 hora. Os filmes de WO3 eletrodepositados com corrente -0,45 mA no tempo de 600 s foram estudados com maiores detalhes. Os filmes com espessura de 140 nm apresentaram mudança na coloração de transparente para azul em resposta a aplicação de potencial de -1,0 a 1,0 V. A variação em transmitância foi medida no visível (λ = 633 nm) resultando em ΔT = 61 %. A densidade de carga foi de 35 mC/cm2 e a estabilidade eletroquímica foi de até 3.000 ciclos. As medidas de difração de raios-X mostraram que a estrutura dos filmes de WO3 é amorfa e as imagens de microscopia eletrônica de varredura (MEV) evidenciaram uma superfície homogênea e sem rachaduras. O filme de PEDOT:PSS depositado por dip-coating apresentou uma espessura em torno de 400 nm, mudança de coloração de azul para transparente com a aplicação do potencial de -1,0 a 1,0 V e ΔT= 50 % para o filme de uma camada. Os filmes de MoO3 foram depositados pela técnica de spin-coating e avaliados conforme o número de camadas (1 a 10 camadas) sendo os melhores resultados foram obtidos para a amostra composta por 9 camadas. Este filme apresentou densidade de carga em torno de 25 mC/cm2 e uma mudança de cor de transparente (T= 80%) para azul (T=38%) após a aplicação de potencial de 1,5 e -1,5 V, respectivamente. Foram confeccionados e estudados dispositivos eletrocrômicos (ECDs) com os filmes finos de WO3 e PEDOT:PSS, eletrólitos poliméricos a base de hidroxipropilcelulose (HPC) e goma gelana (GGLA) e contra eletrodo de CeO2-TiO2. As melhores respostas óticas foram obtidas com o dispositivo eletrocrômico WO3/HPC/CeO2-TiO2, sendo ΔT=29% e a densidade de carga de 12 mC/cm2. A melhor estabilidade em função do número de ciclos de coloração/descoloração de 5.500 foi obtido com o dispositivo eletrocrômico WO3|GGLA-PVP-NHS|CeO2-TiO2 com glicerol. / Electrochromic WO3, MoO3 and PEDOT: PSS thin films were deposited and characterized. WO3 thin films were produced using the galvanostatic electrodeposition process from peroxotungstic acid sol. There were two studies of electrodeposition of WO3 films: 1) films were produced in different streams -0.45 -0.50, -0.60 and -1.0 mA with a time of 600 seconds, and 2) produced films were electrodeposited varying times 100, 200, 300, 400, 500 and 600 s with a current of -0.45 mA. The heat treatment was performed at 120 °C for 1 hour. The WO3 films electrodeposited with -0.45 mA current for 600 s were chosen and studied deeply. These films with a thickness of 140 nm showed change in color from transparent to blue in response to applied potential of -1.0 to 1.0 V. The variation in transmittance was measured at λ = 633 nm, resulting in ΔT = 61%, charge density of about 35 mC/cm2 and electrochemical stability up to 3,000 cycles. X-ray diffractograms showed that the structure of the films is amorphous and scanning electron microscopy (SEM) images showed a homogeneous surface without cracks. The film of PEDOT: PSS deposited by dip-coating had a thickness around 400 nm, color change from blue to transparent upon applied potential of -1.0 to 1.0 V and ΔT = 50% for the one layer film. The MoO3 films were deposited by spin-coating and evaluated as the number of layers (1 to 10 layers) appointing the best results for the sample with 9 layers. This displayed the charge density of around 25 mC/cm2 and a color change from transparent (T = 80%) to blue (T = 38%) after applying the potential of 1.5 and -1.5 V, respectively. Furthermore, the electrochromic devices containing WO3 and/or PEDOT: PSS thin films, polymer electrolytes based cellulose and/or gellan gum and counter electrode of CeO2-TiO2 were assembled and characterized. The best responses of ΔT = 29% and charge density of 12 mC/cm2 were obtained for the electrochromic device with WO3/cellulose/CeO2-TiO2 configuration. However, the best coloring/bleaching stability of 5,500 cycles was obtained with the electrochromic device WO3|GGLA-PVP-NHS|CeO2-TiO2 with glycerol configuration.

Nanoestructuras de alumina anódica porosa (AAP) têm sido tradicionalmente fabricadas por duas etapas de anodização a temperaturas relativamente baixas (de 0 até 5°C), e usadas como máscaras ideais para formação de vários materiais nanoestruturados. Neste sentido, o objetivo do trabalho foi estudar sistematicamente a formação e a fabricação de nanoestruturas de AAP autoorganizadas por uma só etapa de anodização e posterior aplicação na síntese de nanopartículas e nanofios metálicos. As nanoestruturas auto-organizadas de AAP foram obtidas por apenas uma etapa de anodização em ácido oxálico (H2C2O4) a temperatura ambiente; diferentemente dos processos convencionais onde são utilizados duas ou mais etapas de anodização. As características estruturais dos filmes de AAP foram moduladas através do controle dos parâmetros da concentração da solução, temperatura e potencial de polarização. O procedimento principal, para a obtenção de AAP auto-organizadas apenas por uma etapa de anodização, foi o pós-processamento de abertura dos poros através de um processo de corrosão química. Os resultados obtidos neste trabalho mostraram que o diâmetro médio dos poros apresentou uma dependência linear com a temperatura, potencial e tempo de corrosão química e foi constante em relação à concentração da solução eletrolítica. No entanto, a análise estrutural via microscopia eletrônica de varredura (MEV), mostrou que a circularidade e a ordem dos nanoporos sobre a superfície anodizada melhoraram com o aumento da concentração do eletrólito. A estrutura de AAP com um arranjo hexagonal de poros regularmente distribuídos foi obtida quando a anodização foi realizada em 0,3M de H2C2O4, a 45V e 20°C de temperatura seguido de uma corrosão química a temperatura de 17°C por 102 minutos. Adicionalmente foram obtidos nanopartículas e nanofios metálicos utilizando-se as nanoestruturas de AAP como moldes. Como os filmes de AAP são isolantes a obtenção das nanopartículas e nanofios foi realizado através de um processo de eletrodeposição de corrente alternada (CA). Os resultados deste trabalho mostraram que nanoestruturas de AAP autoorganizadas podem ser fabricadas por uma etapa de anodização controlando o tempo de corrosão química. Os resultados apresentados neste trabalho mostram-se vantajosos em relação aos reportados na literatura, já que normalmente as nanoestruturas de AAP são obtidas mediante processos de anodização em duas etapas e tempos longos de anodização. / Nanostructures of porous anodic alumina (PAA) have been traditionally manufactured by two steps anodization at relatively low temperatures (0 to 5°C) and used as templates suitable for the formation of various nanostructured materials. In this sense, the goal of this work was the fabrication of self-organized porous Anodic alumina nanostructures (AAP) by a one anodization step and subsequent application in the synthesis of metal nanowires and nanoparticles. The self-organized nanostructures of PAA were obtained by just one anodization step in oxalic acid (H2C2O4) at ambient temperature unlike to conventional processes where they are used two or more anodization steps. The structural characteristics of PAA films were modulated through control of the solution concentration, temperature and potential of polarization. The key procedure to obtain the periodic organized PAA by only one step anodization was the post-processing of pore opening through a process of corrosion chemistry. The results of this work showed that the average diameter of pores presented a linear dependence with temperature, time of chemical corrosion, polarization potential and it was constant relative to the concentration of the electrolyte solution. However, the structural analysis via scanning electron microscopy (SEM) showed that the roundness and the order of nanoporos over the anodized surface improved with the electrolyte concentration increasing. The PAA structure with a hexagonal arrangement of pores was obtained when the anodization was held in 0.3 M of H2C2O4, 45V, and 20°C of temperature followed by a chemical corrosion at 17°C of temperature for 102 minutes. Additionally it was obtained nano particles and nano metal wires using the PAA structures as molds. Since the PAA films are insulating, the nanoparticles and nanowire were obtained through an electrodeposition process using alternating current. The results of this work have shown that self-organized PAA nanostructures can be fabricated by one anodization step controlling the time of chemical etching process. The results presented in this work are advantageous in relation to reported in the literature, since normally the structures of PAA are obtained by two step anodization and for long anodization time.

Neste trabalho, é apresentado um estudo sobre a influência de aditivos em banhos de eletrodeposição de Au, análise da morfologia dos depósitos de Au e o crescimento de multicamadas da liga AuxSny por deposição eletroquímica. Os banhos de eletrodeposição estudados são baseados em uma composição, comum na literatura, formada por tetraclorourato(III) de potássio (KAuCl4), cloreto de estanho(II) (SnCl2), sulfito de sódio (Na2SO3), e citrato de amônio [(NH4)HC6H5O7]. Os contatos de solda da liga AuxSny, aplicáveis em diversos dispositivos microeletrônicos, podem ser formadas de maneira mais econômica a partir de banhos eletroquímicos. Banhos ácidos e reagentes de baixa toxicidade são exigências comuns dos novos banhos de eletrodeposição. A formação de multicamadas permite, ainda, ampliar o uso do metal de solda em dispositivos sensíveis a altas temperaturas, devido ao baixo ponto de fusão da liga. A obtenção das ligas AuxSny utilizando deposição eletroquímica, foi feita com base no estudo sobre banho de eletrodeposição e seus depósitos, a partir de um banho para deposição da liga AuxSny já conhecido. O aprimoramento do banho de eletrodeposição foi focado no banho de eletrodeposição de Au, com três opções de aditivos, buscando avaliar as características dos depósitos e o tempo de estabilidade do banho. Os aditivos utilizados foram hipofosfito de sódio (NaH2PO2), metanal (HCHO) e tiossulfato de sódio (Na2S2O3), separadamente. Esses banhos foram analisados por voltametria cíclica, e os depósitos obtidos a partir de eletrodeposições foram caracterizados por Espectrometria por Retroespalhamento de Rutherford (RBS), Microscopia Eletrônica de Varredura (SEM) e, em alguns casos, por Espectrometria de Energia Dispersiva de Raios X (EDS). Análises de dimensão fractal e de escalamento dinâmico da rugosidade forneceram detalhes importantes sobre a morfologia superficial dos depósitos. .A adição de Na2S2O3 ao banho permitiu o desenvolvimento de um novo banho de eletrodeposição para a co-deposição de Au AuxSny. O Na2S2O3 atua como um complexante dos íons de Au(I) juntamente com o sulfito de sódio. O emprego de 3 g L-1 de Na2S2O3 evita a degradação do banho durante as eletrodeposições. Finalmente, o estudo da eletrodeposição de multicamadas foi feito por controle do potencial aplicado e por controle da corrente aplicada. As multicamadas obtidas apresentaram camadas da liga AuxSny com a concentração de Sn incorporado, variando entre 6 % e 49 % (em porcentagem atômica). / It is shown in this work a study about the influence of additives in baths for electrodeposition of Au, analysis of morphology of gold deposits and the growth of multilayered AuxSny alloys from improved electrodeposition baths based on a common composition of the literature containing potassium gold(III) chloride (KAuCl4), tin(II) chloride (SnCl2), sodium sulfite (Na2SO3) and ammonium citrate dibasic [(NH4)HC6H5O7]. The AuxSny solders are commonly used in microelectronic devices. These solders can be applied in a number of ways, and electrochemical deposition is an attractive alternative due to the low cost process. Acidic baths and low toxicity reagents are common requirements of new electrochemical baths. The multilayered AuxSny alloys are applicable to temperature sensitive materials due to its reduced melting point temperature. Therefore, the study of electrodeposition of AuxSny alloys began with an already known bath and aiming its improvement. The focus of interest was the gold bath, which received additives to improve control of the deposits and their stability. The additives used were sodium hypophosphite (NaH2PO2), methanal (HCHO) and sodium thiosulfate (Na2S2O3), one of each time. These baths were analyzed by cyclic voltammetry and the deposits obtained from these baths were analyzed by Rutherford Backscattering Spectrometry (RBS), Scanning Electron Microscopy (SEM) and, in some cases, Energy Dispersive Spectrometry (EDS). Fractal dimension and dynamic scaling of the surface width analysis allowed one to quantify the surface morphology details. The addition of Na2S2O3 to the bath allowed the development of a new electrodeposition bath for co-deposition of AuxSny. The Na2S2O3 acts as complexing agent of Au(I) ions together with sodium sulfite. The use of 3 g L-1 of Na2S2O3 avoids bath degradation during the electrodepositions. Potential-controlled and current-controlled electrodepositions were employed to obtain multilayers of AuxSny alloys. The multilayer deposits obtained presented between 6 atomic % and 49 atomic % of tin.

O estudo do eletrorrevestimento de tântalo sobre aço e sobre cobre foi realizado na mistura eutética FLINAK (29,2% LiF - 11,7% NaF - 59,1% KF - % em massa) contendo 15% em massa de K2TaF7. Foram estudadas as influências da densidade de corrente catódica, do tempo de eletrólise, da temperatura e da natureza do substrato sobre as eficiências de correntes catódicas e a morfologia dos revestúnentos. Depósitos de tântalo lisos, brilhantes, aderentes e uniformes foram obtidos com alta eficiência de corrente catódica usando os seguintes parâmetros: densidade de corrente catódica de 23 mA/cm2 a 50 mA/cm2, temperatura de 750°C e tempo de eletrólise de 30 minutos a 120 minutos. Os revestimentos obtidos nestas condições possuem espessuras de 18 µm a 41 µm. Os depósitos de tântalo sobre aço e sobre cobre são constituídos de tântalo puro, sem formação de camada de difusão. Ensaios de eletrodeposição de camadas delgadas de tântalo em catodos de formas e geometrias complexas mostraram o bom poder de cobertura do tântalo. Curvas potencial de circuito aberto x tempo, feitas à temperatura ambiente em soluções de ácido nítrico a 40%, a 50% e a 60% em massa, ácido clorídrico a 3,6% em massa e ácido sulfúrico a 80% em massa, mostraram ótima concordância entre o potencial de circuito aberto estacionário do tântalo maciço comercial e dos revestimentos de tântalo sobre cobre nestes meios. Curvas potencial de circuito aberto x tempo feitas à temperatura ambiente em meio de ácido clorídrico a 3,6% em massa, para revestimentos sobre aço mostraram que a semelhança com o tântalo maciço só é observada em depósitos recentes, o que foi atribuído à difusão do ferro do substrato para a superficie do revestimento. Ensaios gravimétricos mostraram que a velocidade de corrosão dos revestimentos é comparável com a do tântalo comercial, em meios de ácido nítrico a 40% e a 50% em massa, à temperatura de ebulição. / The study of tantalum electroplating on copper and carbon steel has been carried out in FLINAK eutectic (29.2% LiF -11.7% NaF -59.1% KF - wt%) containing 15wt% K2TaF7. The effects of current cathodic density, time of electrolysis, temperature and substrate kind have been studied in relation to the cathodic current efficiencies and the coating morphology. Tantalum deposits, with good smoothness, brightness, adherence and uniformity were obtained with high cathodic efficiency, using the following conditions: 23 mA/cm2 to 50 mA/cm2 cathodic current densities, 30 minutes to 120 minutes electrolysis time interval and 750°C temperature. Under these conditions the coatings are about 18 µm to 41 µm thick. The deposits obtained on carbon steel and copper are both constituted of pure tantalum without formation of interdiffusion layer. The results of tantalum thin coatings electrodeposition on cathodes of complex geometrics and shapes showed the good throwing power of tantalum. Open circuit potential x time curves have been recorded for massive tantalum and for tantalum coatings on copper in 40 wt%, 50 wt% and 60 wt% nitric acid, 3.6 wt% hydrochloric acid and 80 wt% sulfurie acid at room temperature. They showed similar stationary open-circuit poteutial values for both the massive tantalum and the tantalum coatings. Open circuit potential x time curves for tantalum coatings on carbon steel performed in 3.6%wt hydrochloric acid at room temperature showed that the similarity with massive tantalum exists only with recent deposits, because of iron diffusion from substrate to coating surface. Gravimetric tests showed comparable corrosion rate values for massive tantalum and tantalum coatings in boiling 40wt% and 50wt% nitric acid.

Orientador: Kleber Roberto Pirota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T03:13:48Z (GMT). No. of bitstreams: 1 Carvalho_PetersonGrandinide_M.pdf: 8255135 bytes, checksum: 51addf2df8b7383dc2ab652f85205ea2 (MD5) Previous issue date: 2013 / Resumo: Redes de nanofios (NF) magnéticos têm atraído muita atenção devido suas possíveis aplicações tecnológicas. Do ponto de vista tecnológico tais redes poderiam ser utilizadas em diversas aplicações tais como dispositivos spintrônicos, sistemas de armazenamento de memória magnética, elementos sensores de campo magnético e em diversas aplicações biológicas. Por outro lado, do ponto de vista da ciência de base é fundamental compreender o efeito da baixa dimensionalidade nas propriedades magnéticas dos materiais. Muitas das propriedades magnéticas dos NF decorrem simplesmente de sua geometria. Neles, há uma forte anisotropia magnética de forma que tende a manter os momentos magnéticos alinhados ao eixo principal dos NF. No cobalto com estrutura hexagonal compacta (hcp), os momentos magnéticos tendem a se alinhar em uma direção cristalina preferencial (eixo c), ou seja, há uma anisotropia magnetocristalina. Tal anisotropia é da mesma ordem de grandeza da anisotropia de forma de NF ideias (cujo comprimento é muito maior que o diâmetro). Nanofios de cobalto hcp são interessantes basicamente porque suas propriedades magnéticas dependerão fortemente da estrutura cristalina (tamanho do grão e orientação do cristal em relação ao eixo principal dos nanofios). Como as duas contribuições de anisotropia são da mesma ordem de grandeza, pode-se controlar a anisotropia efetiva ao longo do NF através do controle da direção cristalina. Neste trabalho foram produzidas redes de NF de Co via eletrodeposição em moldes de membrana nanoporosa de alumínio anodizado (MNPAA). Alterou-se a estrutura cristalina dos NF através do pH de eletrodeposição (1,9; 3,9 e 5,5). Os NF possuem diâmetro de 35 nm, comprimento de ~10 ?m e a distância entre eles na rede é de 110 nm . A estrutura cristalina foi estudada através de técnicas de microscopia eletrônica (de varredura e de transmissão) e por difração de raios-X. As propriedades magnéticas foram inferidas através de técnicas de magnetometria. Foram obtidas curvas de histerese em função da temperatura e do ângulo entre o campo magnético aplicado e o eixo principal dos NF. Também foram obtidas curvas de magnetização inicial com o campo aplicado paralelo e perpendicular aos NF, e após diferentes ciclos de desmagnetização. Também foram feitos alguns breves estudos sobre o efeito do tratamento térmico nas propriedades magnéticas dos NF; sobre a dieletroforese, que é uma técnica de separação dos NF removidos da MNPAA e dispersos em solução, e sobre as alterações morfológicas e grau de oxidação dos nanofios quando retirados da MNPAA. Observou-se que para pH¿s baixos o eixo c é perpendicular ao eixo principal e os grãos são pequenos. O aumento do pH tende a tornar o eixo c paralelo ao eixo principal dos nanofios, o que aumenta a anisotropia magnética efetiva da rede. O tamanho dos grãos também aumenta com o pH, tornando o meio cristalino local mais expressivo no processo de inversão da magnetização. Também se observou que, dependendo da direção do eixo c, a diminuição da temperatura pode inverter a direção fácil de anisotropia efetiva dos nanofios, devido ao aumento da anisotropia magnetocristalina / Abstract: Magnetic nanowire (NW) arrays have been attracting great attention due to their possible technological applications. Such arrays are promising candidates for different applications, such as spintronic devices, magnetic memory storage systems, magnetic field sensors and in several biological systems. On the other hand, from a basic science point of view, it is fundamental to understand the low dimensionality effect on materials magnetic properties. Many of the NW magnetic properties simply occur due to its elongated geometry. It creates a strong magnetic anisotropy which tends to maintain the magnetic moments aligned to the NW¿s main axis. In bulk cobalt with a hexagonal compact structure (hcp), the magnetic moments tend to align in a preferential crystalline direction, i.e. there is a magnetocrystalline anisotropy. Such anisotropy is of the same order of magnitude than NW¿s shape anisotropy (when the length is much bigger than the diameter). Hcp cobalt nanowires are mainly interesting because their magnetic properties strongly depend on their crystalline structure (grain size and crystal orientation with respect to the NW main axis). Since the two anisotropy contributions are of the same order of magnitude, we can control the effective anisotropy along the NW by controlling the crystalline structure orientation. In this study were produced Co NW arrays through eletrodeposition in aluminum nanoporous templates. The NW crystalline structure was altered by the pH during the eletrodeposition process. The NW present a diameter of 35 nm, length of ~10 ?m and an interwire distance of 110 nm. The crystalline structure was investigated through electronic microscopy techniques (scanning and transmission) and X-ray diffraction. The magnetic properties were inferred through magnetometry techniques. Hysteresis curves were obtained as a function of temperature and of the angle between the applied magnetic field and the NW¿s main axis. Initial magnetization curves with the applied field parallel and perpendicular to the NW, and after different demagnetization cycles, were also obtained. Finally, some brief studies have also been made about the effect of heat treatment on the NW magnetic properties; about dielectrophoresis, which is a separation technique for the NW removed from the alumina template and dispersed in solution; and about the morphological changes and the NW oxidation degree when removed from the alumina template / Mestrado / Física / Mestre em Física

In the recent years, there has been a growing interest in micro- and nano-structured composite systems due to their wide use in microelectronics, optoelectronics, magneto-optical devices, high-density data storage, sensors, biomedical devices, and many other areas. Of particular interest is application in the integrated circuit (IC) industry. Here the need for miniaturization has led to new architectures that combine disparate technologies. This has been achieved through innovations in packaging technologies such as 3D integration for high interconnection density, low power, high data throughput, good signal integrity and reliability, and low cost. One of the key active manufacturing technologies for 3D integration is through silicon vias (TSVs), which involves etching of deep vias in a silicon substrate that are filled with an electrodeposited metal, and subsequent removal of excess metal by chemical mechanical planarization (CMP). Electrodeposition often results in undesired voids in the TSV metal fill as well as a thick overburden layer. These via plating defects can severely degrade interconnect properties and lead to variation in via resistance, electrically open vias, and trapped plating chemicals that present a reliability hazard. Thick overburden layers result in lengthy and expensive CMP processing. We are proposing a technique that pursues a viable method of depositing a high quality metal inside vias with true bottom-up filling, using an additive-free deposition solution. The mechanism is based on a novel concept of electrochemical oxidation of backside silicon that releases electrons, and subsequent chemical etching of silicon dioxide for regeneration of the surface. Electrons are transported through the bulk silicon to the interface of the via bottom and the deposition solution, where the metal ions accept these electrons and electrodeposit resulting in the bottom-up filling of the large aspect ratio vias. With regions outside the vias covered bydielectric, no metal electrodeposition should occur in these regions, which minimizes the metal CMP step and reduces the overall processing times and costs. Hence, inherent bottom-up filling is financially advantageous because it will eliminate a large portion of the metal overburden and associated planarization costs. Additive-free deposition is preferable from both lower production cost and quality management perspectives since it results in higher reliability of deposited metal. Our new bottom-up technique was initially examined and successfully demonstrated on blanket silicon wafers and shown to supply electrons to provide bottom-up filling advantage of through-hole plating and the depth tailorability of blind vias. In order to understand the driving mechanism and limits of this process, we have also conducted a fundamental study that investigated the effect of various process parameters on the characteristics of deposited Cu and Ni and established correlations between metal filling properties and various electrochemical and solution variables. A copper sulfate solution with temperature of about 65 °C was shown to be suitable for achieving stable and high values of current density that translated to copper deposition rates of ~2.4 μm/min with good deposition uniformity. The importance of backside silicon oxidation and subsequent oxide etching on the kinetics of metal deposition on front side silicon has also been highlighted. Further, a process model was also developed to simulate the through silicon via copper filling process using conventional and contactless electrodeposition methods with no additives being used in the electrolyte solution. A series of electrochemical measurements were employed and integrated in the development of the comprehensive process simulator. The experimental data not only provided the necessary parameters for the model but also validated the simulation accuracy. From the simulation results, the “pinch-off” effect was observed for the additive-free conventional deposition process, which further causes partial filling and void formation. By contrast, a void-free filling with higher deposition rates was achieved by the use of the contactless technique. Moreover, experimental results of contactless electrodeposition on patterned wafers showed fast rate bottom-up filling (~3.3 μm/min) in vias of 4 μm diameter and 50 μm depth (aspect ratio = 12.5) without void formation and no copper overburden in the regions outside the vias. Efforts were also made to extend the use of the contactless technique to other applications such as synthesis of porous silicon, which is known to be an excellent material with fascinating physical and chemical properties. We were able to fabricate porous silicon with a morphological gradient using a novel design of the experimental cell. The resulted porous silicon layers show a large distribution in porosity, pore size and depth along the radius of the samples. Symmetrical arrangements were attributed to decreasing current density radially inward on the silicon surface exposed to surfactant containing HF based etchant solution. The formation mechanism as well as morphological properties and their dependence on different process parameters, such as HF concentration, solution pH, surfactant concentration, current density and wafer resistivity, has been investigated in detail. In the presence of surfactants, an increase in the distribution range of porosity, pore diameter and depth was observed by increasing HF concentration or lowering pH of the etchant solution, as the formation of pores was considered to be limited by the etch rates of silicon dioxide. Gradient porous silicon was also found to be successfully formulated both at high and low current densities. Interestingly, the morphological gradient was not developed when dimethyl sulfoxide (instead of surfactants) was used in etchant solution potentially due to limitations in the availability of oxidizing species at the silicon-etchant solution interface. In the last part of the dissertation, we have discussed the gradient bottom up filling of Cu in porous silicon substrates using the contactless electrochemical method. The radially symmetric current that gradually varied across the radius of the sample area was achieved by utilizing the modified cell design, which resulted in gradient filling in the vias. Effect of different deposition parameters such as applied current density, copper sulfate concentration and etching to deposition area ratio has been examined and discussed. Increasing the current density from 10 to 15 mA/cm2 resulted in bottom up deposition with less sharp gradients. Further, the study on the effect of copper sulfate concentration highlighted the importance of mass transfer in this process, as either bottom-up deposition or gradient filling could not be achieved at lower CuSO4 concentrations (0.1 and 0.25 M). Additionally, the filling gradient of deposited Cu was obtained with etching to deposition area ratio of 1.6 and 2.7, while a more uniform deposition was observed when the ratio was increased to 3.8. This suggested that the gradient filling may only be accomplished within a certain range of the etching to deposition area ratios.

L'élaboration d'un revêtement submicronique est réalisée par électrodéposition de nanoparticules de silice (EPD = ElectrophoreticDeposition). Cette approche permet de contrôler l'épaisseur des dépôts, qui est un paramètre à ajuster pour élaborer un revêtement sélectif absorbeur de type capteur photothermique. La nature du revêtement recherché est un co-dépôt de silice et de carbone. Pour la compréhension et le contrôle des mécanismes de dépôt par EPD, le dépôt de silice seule est étudié. Deux systèmes ont été investigués : de la silice déposée sur du wafer de silicium ou sur du platine, notés respectivement SiO2/Si et SiO2/Pt. Une suspension colloïdale commerciale, le Ludox® HS-40, est utilisée pour permettre la dilution de sols stables de nanoparticules de silice monodisperses (12 nm de diamètre), chargées négativement. Un EPD anodique est réalisé en milieu aqueux grâce à ce sol.Le potentiel, la concentration initiale en nanoparticules et la durée de dépôt ont été explorés. Lorsque le potentiel appliqué est trop élevé, le phénomène d'électrolyse de l'eau est observé. Plus particulièrement, le système à base de platine se trouve limité par ce phénomène à partir d'un potentiel de +2V. La forte conductivité de ce substrat favorise le phénomène de dégagement gazeux. Ce bullage subséquent, dégrade la cohésion du revêtement. Néanmoins, l'application d'un potentiel inférieur au potentiel d'électrolyse de l'eau permet de bonnes conditions de dépôt. Des phénomènes similaires ont également été observés avec le système SiO2/Si. Les propriétés semi-conductrices du wafer de silicium permettent cependant d'appliquer des potentiels plus élevés (jusqu'à +40 V), en limitant le phénomène d'électrolyse. L'optimisation des conditions de dépôt sur ces deux systèmes ont permis d'obtenir des conditions expérimentales de dépôt compatibles avec l'objectif fixé, à savoir : un potentiel de +1 V pour le système SiO2/Pt et de +3 ou +30 V pour le système SiO2/Si, une concentration comprise entre 1 et 10 %mass, et une durée de dépôt de 1h.Dans les conditions optimales définies précédemment, les propriétés physico-chimiques de la suspension initiale ont été modifiées par l'ajout d'un co-solvant (EtOH), d'un sel (Na2SO4) ou d'un polymère (PAA out PVA) afin d'étudier l'influence du milieu dispersant, de la conductivité de la suspension ou du potentiel zêta des nanoparticules sur l'épaisseur des dépôts. Ces ajouts ont permis d'augmenter l'épaisseur des revêtements, notamment pour le système SiO2(EtOH)/Pt et les systèmes à base de PAA. L'ajout d'un composé carboné (PVA, PAA) dans la suspension a également été étudié afin d'obtenir après calcination (500°C) un revêtement présentant des caractéristiques intéressantes pour l'application envisagée. Les revêtements de type SiO2(PAA)/Pt présentent une certaine sélectivité optique. Toutefois les valeurs du ratio alpha/epsilon restent inférieures à 7, ce qui est plus faible que les valeurs obtenues pour le même type de système, avec des procédés sol-gel classiques. / The development of a submicron coating was carried out by electrophoretic deposition (EPD)of silica nanoparticles. This approach allows controlling the thickness of the deposits which is a parameter to adjust to develop a selective absorber coating dedicated to a photothermal sensor. The composition of the desired coating is a co-deposition of silica and carbon. For the understanding and the control of EPD deposition mechanisms, silica deposit is first studied. Two systems were investigated: silica deposited on a silicon wafer or platinum substrate, respectively noted SiO2/Si and SiO2/Pt. A commercial colloidal suspension, Ludox® HS-40, is used to realize stable diluted sols of monodispersed silica nanoparticles (12 nm diameter), negatively charged. Anodic EPD is performed in aqueous medium from this sol.The applied potential, the initial concentration of nanoparticles and the deposition time are investigated. When the applied potential is too high, the water electrolysis phenomenon occurs. More particularly, the platinum-based system is limited by this phenomenon, from a potential of +2 V. The high conductivity of this substrate promotes gassing phenomenon. This subsequent bubbling degrades the cohesion of the coating. However, an applied potential lower than the electrolysis potential gives some good deposition conditions. Similar phenomena were also observed with SiO2/Si system. However, the semiconductor properties of the silicon wafer enable to apply higher potential (up to +40 V) by reducing the phenomenon of electrolysis. Optimizations of the deposition conditions on these two systems have yielded experimental deposition conditions consistent with the objective, namely: a potential of +1 V to SiO2/Pt system and of +3 and +30 V for SiO2/Si system, a concentration between 1 and 10 %mass, and a deposition time of 1 hour.Under optimum conditions defined above, the physicochemical properties of the initial suspension are modified by adding a co-solvent (EtOH), a salt (Na2SO4) or a polymer (PAA or PVA) in order to study the influence of the dispersing medium, the conductivity of the suspension or the zeta potential of the nanoparticles on the thickness of the deposits. These additions have increased the thicknesses of coatings, especially for SiO2(EtOH)/Pt system and systems based on PAA. The addition of some carbon compounds (PVA or PAA) in the suspension was also studied to obtain after calcinations (500 °C) a coating with interesting characteristics for the intended application. Coating obtained with SiO2(PAA)/Pt system exhibit a significant optical selectivity. However, the value of the alpha/epsilon ratio remains below 7, which is lower than the values obtained for the same type of system with conventional sol-gel processes.

Les cellules solaires en couches minces à base de Cu(In,Ga)(S,Se)2 (CIGS) représentent une technologie à fort potentiel et aux performances photovoltaïques élevées. La couche finale de l'empilement, appelée couche fenêtre, est principalement composée d'une bi-couche d'oxyde de zinc (ZnO) non dopé et dopé de type n - généralement à l'aluminium - et déposée par un procédé sous vide : la pulvérisation cathodique. Cependant, cette technique demande des investissements importants et un intérêt croissant s'est porté sur le développement de techniques alternatives atmosphériques en vue d'une réduction des coûts. L'objectif de ce travail a été d'étudier la réalisation d'une couche fenêtre fonctionnelle de ZnO par un procédé d'électrodépôt photo-assisté en milieu aqueux sur des substrats de grandes dimensions. Pour y parvenir, différentes études ont été réalisées afin de déterminer les propriétés du ZnO électrodéposé et optimiser le procédé de dépôt. Dans un premier temps, l'influence de la composition de trois solutions électrolytiques sur les propriétés et le dopage du ZnO a été étudiée : le milieu chlorure (Cl-), le milieu perchlorate (ClO4-) et un milieu mixte à base de perchlorate et d’acide borique (H3BO3). Dans un second temps, la synthèse électrochimique du ZnO comme couche fenêtre a été réalisée sur des substrats de CIGS/CdS. Son étude a permis de montrer que la réalisation in situ d'une couche d'accroche facilite la croissance d'une couche finale dense et compacte. Cette méthode de synthèse en deux étapes a conduit à l'obtention de performances photovoltaïques élevées sur grandes surfaces avec des rendements allant jusqu'à 14,3 % pour une cellule solaire entièrement réalisée par des procédés atmosphériques. / Cu(In,Ga)(S,Se)2 (CIGS) thin films based solar cells are a promising technology for high efficiency energy conversion. A window layer completes the stack of the cell. It is commonly constituted by an intrinsic and aluminum doped bi-layer of zinc oxide (ZnO) deposited by magnetron sputtering, an expensive vacuum process. Alternative processes, using low cost and atmospheric techniques, have been developed in order to reduce the costs. The aim of this work was to achieve a functional window layer of ZnO by a photo-assisted electrodeposition process on large scale substrates of CIGS/CdS in aqueous medium and replace the sputtered one. For this purpose, several studies have been carried out in order to determine the optoelectronic properties such as doping level and mobilities of the electrodeposited ZnO and optimize the deposition process. Firstly, the effect of three different electrolytes on the zinc oxide properties and doping has been studied on metallic substrate: chloride medium (Cl-), perchlorate medium (ClO4-) and a mixed medium of perchlorate with boric acid (H3BO3). Then, electrochemical synthesis of zinc oxide as window layer has been performed on CIGS/ CdS substrates. This study allowed to establish the need to synthesize an in situ seed layer which promotes the growth and the compactness of the final layer of zinc oxide. This two-step method has led to the achievement of high photovoltaic performances on large scale with promising efficiencies up to 14.3 % for a solar cell made entirely by atmospheric processes.

L'oxyde de zinc (ZnO) est un semi-conducteur à large gap direct (3,37 eV) qui possède de nombreuses propriétés intéressantes (piézoélectrique, optique, catalytique, chimique…). Un large champs d'applications fait de lui l'un des matériaux les plus étudiés de la dernière décennie, notamment sous forme nanostructurée. Dans ce travail, nous nous intéressons à la synthèse par électrochimie des couches minces, des micro- & nano-plots, et des nanofils de ZnO. Deux méthodes ont été utilisées : la première dite Template consiste à la fabrication des micro- et nanopores en réseau ordonné à l'aide de la technique lithographique dans lesquels a lieu la croissance du ZnO ; la seconde consiste à la croissance libre de réseau de nanofils. Les caractérisations structurales, morphologiques et optiques du ZnO ainsi élaboré ont été réalisées par diffractométrie des rayons-X (DRX), microscopie électronique à balayage (MEB), microscopie électronique en transmission (MET), spectroscopie Raman, spectroscopie UV et photoluminescence (PL). Les propriétés électriques des couches minces et des réseaux de nanofils (sous l'effet collectif) de ZnO ont été étudiées par des mesures «courant tension» (I-V) à température ambiante dans la configuration métal/semi-conducteur/métal à l'aide d'un réseau de micro-électrodes métalliques déposé en surface du ZnO. Cette étude nous a permis de déterminer qualitativement la conductivité électrique du ZnO et les différents paramètres de la jonction Schottky entre le ZnO et le substrat doré. Celle-ci est fondamentale et indispensable pour la réalisation d'un dispositif de récupération d'énergie tel que le nanogénérateur de courant piézoélectrique à base de nanofils de ZnO / Abstract Zinc oxide (ZnO) is direct wide band gap semiconductor (3.37 eV) with many interesting properties (piezoelectric, optical, catalytic, chemical …). A wide range of applications makes it one of the most studied materials in the past decade, particularly when elaborated as nanostructures. In this work, we focus on electrochemical synthesis of ZnO thin films, micro- and nano-pillars as well as nanowires. Two methods were used: the first, called “Template”, consists of growing ZnO into organized arrays of micro- and nanopores made by lithographic methods ; the second consists of the free growth of nanowires array. The morphological and optical characterizations of the obtained ZnO were carried out using scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), Raman and UV spectroscopy, and photoluminescence (PL). Electrical properties of the electrodeposited ZnO (thin films and nanowire networks) were studied using I-V measurements at room temperature in metal/semiconductor/metal configuration, by the use of an array of metallic micro-electrodes deposited on the surface of ZnO. This allows determining qualitatively the electrical conductivity of ZnO and the different parameters of the Schottky junction between ZnO and the substrate (Au). This study is necessary for future applications based on ZnO nanowires array such as the solar cell and the piezoelectric nanogenerator

abstract: Lateral programmable metallization cells (PMC) utilize the properties of electrodeposits grown over a solid electrolyte channel. Such devices have an active anode and an inert cathode separated by a long electrodeposit channel in a coplanar arrangement. The ability to transport large amount of metallic mass across the channel makes these devices attractive for various More-Than-Moore applications. Existing literature lacks a comprehensive study of electrodeposit growth kinetics in lateral PMCs. Moreover, the morphology of electrodeposit growth in larger, planar devices is also not understood. Despite the variety of applications, lateral PMCs are not embraced by the semiconductor industry due to incompatible materials and high operating voltages needed for such devices. In this work, a numerical model based on the basic processes in PMCs – cation drift and redox reactions – is proposed, and the effect of various materials parameters on the electrodeposit growth kinetics is reported. The morphology of the electrodeposit growth and kinetics of the electrodeposition process are also studied in devices based on Ag-Ge30Se70 materials system. It was observed that the electrodeposition process mainly consists of two regimes of growth – cation drift limited regime and mixed regime. The electrodeposition starts in cation drift limited regime at low electric fields and transitions into mixed regime as the field increases. The onset of mixed regime can be controlled by applied voltage which also affects the morphology of electrodeposit growth. The numerical model was then used to successfully predict the device kinetics and onset of mixed regime. The problem of materials incompatibility with semiconductor manufacturing was solved by proposing a novel device structure. A bilayer structure using semiconductor foundry friendly materials was suggested as a candidate for solid electrolyte. The bilayer structure consists of a low resistivity oxide shunt layer on top of a high resistivity ion carrying oxide layer. Devices using Cu2O as the low resistivity shunt on top of Cu doped WO3 oxide were fabricated. The bilayer devices provided orders of magnitude improvement in device performance in the context of operating voltage and switching time. Electrical and materials characterization revealed the structure of bilayers and the mechanism of electrodeposition in these devices. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2020