This thesis explores colloidal semiconductor nanocrystal solutions as a feedstock for creating thin film semiconductor materials through printing processes. This thesis will span the synthesis of nanocrystals, ligand exchange chemistry, solution phase characterization methods, thin film device fabrication, thin film characterization methods, and device characteristics. We will focus extensively relating the structure of nanocrystals in solution and in thin films to their chemistry, optical properties and electronic properties. By way of introduction, the origin and nature of semiconductor nanocrystals will be explored. This discussion will place semiconductor nanocrystals in their historical context, namely the oil-shocks of the 1970s. The interest in II-VI semiconductor materials stemmed from a desire find photochemical synthetic routes to reduce the use of fossil fuels. As a result, II-VI semiconductor nanocrystal are far more developed synthetically. Additionally, our understanding of II-VI semiconductor nanocrystals is couched in the language of solid state physics rather than chemistry. This will lead into a discussion of their electronic structure and the iterative nature of nanocrystal synthetic development and our theoretical understanding of nanocrystals. The first chapter will discuss nanocrystal synthetic methods in a broad context, finally narrowing in on the synthesis chosen for this work. Following a description of the synthesis, we will then describe the ligand chemistry and the reactions which may be performed in the ligand shell. The final sections of the chapter will describe the synthetic routes to the three nanocrystal materials used in the rest of this work, namely CdSe-CdCl2/PBu3, CdSe-CdCl2/NH2Bu, and CdSe/NH2Bu. The second chapter will introduce the crystal structure of II-VI semiconductor nanocrystals and describe how the structure is measured. This will lead in to a discussion of pair distribution function analysis of X-ray data and examples of its application to the solution phase structure of semiconductor nanocrystals. Some size dependent structural properties, namely stain, will be demonstrated by PDF. At the end evidence for surface reconstruction in solution as ligands are removed will be presented. In the final chapter, techniques for film formation and ligand dissolution with be presented. Annealing of films produces electronic and structural changes which can be observed in the absorbance spectrum, electron microscopy, and X-ray scattering. I propose a three phase annealing model which includes 1) reversible desorption of the organic ligands, 2) irreversible particle fusion, and 3 ripening of grains. The temperature at which ripening occurs depends sensitively on the sample content, which increase chloride concentration decreasing the temperature at which ripening occurs. The ripening process is found to correlate with a phase transition from zinc blende to wurtzite, which indicates that grain boundary mobility is an important part of the ripening process. Finally thin film transistors are characterized electronically. Fused grains show superior electron mobility as high as 25 cm2/(Vs) and on/off ratios of 10\up5 and less than 0.5 V hysteresis in threshold voltage without the addition of indium. Surprisingly, the ripened grains show poorer transport characteristics. The manuscript concludes by noting the importance of the sintering process in achieving conductivity in thin films and discussing future directions to build upon this work.

Neste trabalho, se pretende caracterizar a morfologia de filmes finos poliméricos por meio de técnicas de processamento de imagens, utilizando principalmente a geometria computacional e técnicas de classificação de padrões. Os objetivos principais foram quantificar as grandezas geométricas das estruturas observadas nos filmes finos e descrever padrões de superfície formados nestes filmes. Foram estudadas imagens obtidas por microscopia de força atômica (AFM) de amostras de filmes finos SEBS [poliestireno-poli(etileno-co-butileno)-poliestireno], depositados sobre um substrato de mica por técnicas de imersão. Os filmes finos SEBS são considerados de grande interesse devido à formação de estruturas auto-organizadas na escala nanométrica. A caracterização e a obtenção da morfometria dos filmes são de relevância neste trabalho, pois contribuem para o entendimento da dinâmica de formação destes padrões nas nanoestruturas estudadas. Foram analisadas diferentes morfologias, como forma de gotículas com anéis concêntricos e forma de tiras e pontos regularmente espaçados. Os resultados obtidos permitem caracterizar os padrões observados. / In this work, we intend to characterize the morphology of polymer thin films by techniques of image processing, mainly using computational geometry and pattern classification. The main objectives were to quantify the geometrical structures observed in thin films and describe surface patterns formed in these films. Were studied images obtained by atomic force microscopy (AFM) of SEBS [polystyrene-poly(ethylene-co-butylene)-polystyrene] thin films samples, deposited on a mica substrate by dip-coating technique . SEBS thin film polymers have great interest due to the formation of self-organized structures on the nanometer scale. The characterization and obtaining measurements of the morphology of the thin films are of relevance in this work, because they contribute to the understanding of the formation dynamics of these patterns in nanostructures studied. We analyzed different morphologies, such as droplets form with concentric rings and stripe and regularly spaced points forms. The results allow to characterize the observed patterns.

Orientador: Prof. Dr. Alexandre Jose de Castro Lanfredi / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2014. / Este trabalho dedica-se ao estudo da influencia das condicoes de deposicao de filmes finos de nitreto de titanio (TiN), observando o comportamento mecanico quando solicitados em um ensaio de tracao. Os filmes foram depositados utilizando a tecnica de deposicao fisica a vapor (PVD) Triodo Magnetron Sputtering (TMS) em substratos de Al. Atraves dos resultados dos ensaios mecanicos, estimou-se o espacamento maximo entre trincas a partir do valor de saturacao das mesmas, para cada condicao de sintese. Duas condicoes principais de sintese para obtencao dos filmes foram a variacao da tensao (bias) de polarizacao em -50, -100 e -150 V no substrato e o tempo de deposicao em 30, 60, 90 e 120 min, obtendo assim diferentes tensoes compressivas e espessura de filmes, respectivamente. Os filmes finos foram obtidos a partir de um alvo de uma liga de Ti6Al4V em atmosfera reagente de gas nitrogenio e foram utilizados substratos de aluminio comercial com 1 e 3 mm de espessura. Tanto os filmes quanto os substratos foram caracterizados pela tecnica do Ensaio de Tracao, Difracao de raios-X, Microscopia otica, Microscopia Eletronica de Varredura e Espectroscopia de Energia Dispersiva. Calculou-se o espacamento de saturacao de trincas utilizando o metodo proposto por Jeong, comparando esse espacamento entre as diferentes condicoes de deposicao e espessura dos filmes. A partir do metodo de sen2¿Õ (SSPP), que utiliza os resultados de difracao de raios-X obtidos em Angulos rasantes fixos (configuracao Seeman-Bohlin), calculou-se a tensao residual do filme apos a sintese com o intuito de estimar a tensao cisalhante interfacial pelo modelo proposto por Chou. Como resultado, os filmes com maior espessura tiveram um espacamento de saturacao das trincas maior quando comparados com os filmes de menor espessura. Os filmes depositados com a tensao de polarizacao negativa menor (-50V) tambem tiveram um espacamento de saturacao maior quando comparados com os filmes depositados com tensao de polarizacao negativa mais elevado (-100 e -150V). Tensoes de polarizacao tendem a gerar altas tensoes residuais compressivas no filme, o que podem levar ao destacamento do mesmo na interface. Tensoes de cisalhamento interfacial tambem estao diretamente relacionadas com tensoes residuais compressivas. Filmes com uma maior espessura podem ter uma menor tensao compressiva, mas ao mesmo tempo correm o risco de sofrerem destacamento do substrato. Assim, a escolha da amostra que obteve a melhor adesao foi aquela que ao mesmo tempo nao destacou e teve um alto valor de ¿É Sat. / This work presents a study of the influence of coating conditions on mechanical properties of titanium nitride (TiN) thin films, under tensile test. The films were deposited using a physical vapor deposition (PVD) technique, the Triode Magnetron Sputtering (TMS), on aluminum substrates. From interrupted mechanical testing results, the maximum inter-crack spacing of the cracked coating was obtained in the saturated situation (ë Sat), for each synthesis conditions applied. Two parameters used on the film deposition were the bias voltage polarization applied to the substrate (in -50, -100 and -150V) and the deposition time (30, 60, 90 and 120 min), leading to different compressive stress and film thickness, respectively. The thin films were obtained from a Ti6Al4V target in Ar and N2 atmosphere and the substrates were made from commercial laminated aluminum sheet with 1 and 3 mm thickness. The substrate and the films deposited were characterized by Tensile Test, x-ray diffraction, Optical Microscopy, Scanning Electron Microscopy and Energy Dispersive Spectrometry. The inter-crack spacing was calculated using the method proposed by Jeong and the results were compared between the several deposition conditions utilized and thickness obtained. From sen2ø (SSPP) method, obtained from x-ray diffraction pattern in grazing configuration (Seeman-Bohlin), the residual stress of the thin films was calculated and used to estimate the interfacial shear strength by the model proposed by Chou. As result, the samples with larger thickness had a saturated inter-crack spacing greater then thinner films. The deposited films using low negative bias voltage (-50V) also had a saturated inter-crack spacing greater when compared with the higher negative bias voltage (-100 and -150V). Higher negative bias voltage applied to the substrate leads to higher compressive residual stress and can induce to the detachment of the film. The interfacial shear stress is directly related with residual compressive stress. Films with higher thickness generally have lower compressive stresses, but with increase in the risk of detachment. Finally, the sample with best adhesion was the one that in same time not presented detachment and had a higher value of ëSat.

Um grande obstáculo a ser vencido para que se tenha uma maior utilização da tecnologia de membranas na purificação de líquidos é o fenômeno do fouling. Como consequência, o desenvolvimento de membranas menos propensas ao fouling é hoje objeto de inúmeras pesquisas. Dentre os processos estudados, tem-se o desenvolvimento de membranas de filme fino composto, que possui como vantagem a possibilidade de se melhorar cada camada de maneira independente, de forma a se aperfeiçoar o desempenho da membrana como um todo. O projeto de pesquisa foi desenvolvido no laboratório do Centro Internacional de Referência em Reúso de Água (CIRRA/IRCWR), uma entidade sem fins lucrativos, vinculado ao Departamento de Engenharia Hidráulica e Ambiental da Escola Politécnica da Universidade de São Paulo (USP). Este teve como objetivo a síntese e a caracterização de membranas de filme fino composto de polissulfona e quitosana reticulada com glutaraldeído. Embora o objetivo principal desse trabalho tenha sido o desenvolvimento de membranas menos propensa ao fouling, a susceptibilidade ao fouling das membranas produzidas foi avaliada de maneira indireta, através da avaliação de propriedades como hidrofilicidade e rugosidade da superfície. Membranas de ultrafiltração a base de polissulfona (PSF) foram produzidas, através do método de separação de fases via imersão-precipitação, para serem usadas como suporte poroso para a camada de quitosana. Nessa etapa, a influência da concentração de PSF na solução polimérica; da temperatura de síntese; da umidade relativa do ar; e do suporte (não-tecido) nas características da membrana foram estudadas. O efeito da aplicação de uma camada de álcool polivinílico, reticulada com glutaraldeído, entre as camadas de PSF e quitosana, como forma de melhorar a estabilidade estrutural da membrana, foi avaliado. Adicionalmente, analisou-se a influência da introdução do glutaraldeído como agente reticulante na solução de quitosana na seletividade; na taxa de permeação; na estabilidade química; e na toxicidade da membrana. Os resultados obtidos mostraram que o aumento da concentração de PSF na solução polimérica, a diminuição da temperatura de síntese e o aumento da umidade do ar levaram à formação de membranas menos porosas. Os suportes de poliéster avaliados, CU414 e CU424 (Crane Nonwovens), embora apresentem características adequadas à produção de membranas, não se mostraram adequados para a síntese de membranas de PSF nas condições avaliadas devido a sua alta porosidade. A solução de reticulação da camada de álcool polivinílico (PVA), composta de glutaraldeído em solução aquosa de acetona, atacou quimicamente o suporte de poliéster e a membrana de polissulfona, inviabilizando a aplicação da camada de PVA entre as camadas de PSF e quitosana. A introdução do glutaraldeído tornou a camada de quitosana menos rugosa e mais hidrofílica. Adicionalmente, o aumento da concentração de glutaraldeído na solução de quitosana levou a um decréscimo na permeabilidade da membrana, o qual foi atribuído à compactação da estrutura da membrana. A reticulação da quitosana com glutaraldeído não levou a uma melhora significativa da capacidade de separação das membranas. A rejeição de ions bivalentes (Mg2+ e SO4 2-) e monovalentes (Na+ e Cl-) não ultrapassou 25% e 12%, respectivamente. Análises de microscopia de eletrônica de varredura realizadas com as membranas reticuladas com glutaraldeído, antes e após sua imersão em solução de HCl, indicaram que a superfície das membranas reticuladas com 3% de glutaraldeído aparentemente não foi afetada pelo ácido, ao contrário das membranas reticuladas com 1% e 5% de glutaraldeído, que apresentaram aumento no tamanho de seus poros. Não foi observada toxicidade aguda e/ou crônica, em relação aos organismos teste Daphinia similis e Ceriodaphinia dubia, respectivamente, em amostras de água que permaneceram em contato com as membranas reticuladas com glutaraldeído. / A major obstacle to be overcome in order to have a greater use of membrane technology in liquids purification is the phenomenon of fouling. As a consequence, the development of membranes less prone to fouling is now the objective of numerous studies. Among the processes evaluated, the development of thin film composite membranes has been the focus of many researches since it is possible to improve each layer independently, in order to improve the membrane performance as a whole. This work aimed to study the synthesis and characterization of thin film composite chitosan, crosslinked with glutaraldehyde, and polysulfone (PSF) membranes. PSF ultrafiltration membranes were produced by phase inversion via immersion precipitation to be used as porous support for the chitosan layer. The influence of PSF concentration in the polymeric solution; temperature of synthesis; air humidity, and membrane nonwoven support, CU414 and CU424 (Crane Nonwovens), on the membrane characteristics and performance were studied. The effect polyvinyl alcohol (PVA), crosslinked with glutaraldehyde, between PSF and chitosan layers, on the cast membrane structural stability was investigated. The influence of glutaraldehyde as a chitosan crosslinking agent on membrane selectivity, permeability, chemical stability, and toxicity was also evaluated. The results showed that increasing PSF concentration, decreasing temperature and increasing air humidity resulted in less porous membranes. The support media used were not suitable for the production of PSF membranes under the conditions used in this work due to its high porosity. The solution used to crosslink the PVA layer, composed of glutaraldehyde in aqueous solution of acetone, attacked the support media and the PSF membrane, preventing the application of the PVA layer between the PSF and chitosan layers. The use of glutaraldehyde as a chitosan crosslinking agent made the membrane less rough and more hydrophilic. Additionally, increasing glutaraldehyde concentration in the chitosan solution led to a decrease in membrane permeability, which was attributed to a compaction of the membrane structure, leading to a decreased mobility of polymer chains and a decrease in the membrane void volume. Membranes separation capacity was evaluated using two different ionic solutions, magnesium sulphate (MgSO4 1,000 mg/L), and sodium chloride (NaCl 2,000 mg/L). Rejection of bivalent and monovalent ions did not exceed 25% and 12%, respectively. Scanning electron microscopy images showed that the membrane surface crosslinked with 3% glutaraldehyde apparently was not affected by immersion into HCl solution. However, the membranes crosslinked with 1% and 5% glutaraldehyde showed an increase in pore size after immersion, compared to the untreated membrane, suggesting an increased susceptibility to acid attack of the membrane. The potential for glutaraldehyde membrane releasing was evaluated through acute and chronic toxicity assays using Daphnia similis and Ceriodaphnia dubia, respectively. None of tested membranes induced acute or chronic toxicity to the water at which they remained in contact, under tested conditions.

Neste trabalho, são discutidas as características de transistores de filmes finos (TFTs) nos quais nanopartículas de óxido de zinco (ZnO) são empregadas como material ativo na camada semicondutora. O crescimento contínuo do interesse por este componente está associado à busca pelo desenvolvimento da tecnologia de dispositivos eletrônicos flexíveis, transparentes e de baixo custo. TFTs integrados com nanopartículas de ZnO são apresentados, e uma extensa rotina de caracterização elétrica transiente é realizada para avaliar como estes dispositivos se comportam e degradam ao longo do tempo. Foram medidas, ao total, 80 amostras de transistores integrados em duas configurações distintas: inverted staggered e inverted coplanar. A partir das medidas analisadas foram identificados dois grupos de comportamentos elétricos dominantes, os quais foram classificados em: efeitos abruptos e efeitos de memória. A partir dos dados coletados, foram formuladas hipóteses para modelar o comportamento típico observado. Para tanto, utiliza-se dos mecanismos de atividade de traps, de interação da camada semicondutora com o meio ambiente, de polarização de dipolos e difusão de cargas móveis no dielétrico, de formação de caminhos percolados paralelos pelas nanopartículas e de difusão de vacâncias de oxigênio e íons metálicos que podem estar associados ao comportamento elétrico observado. / In this work, the characteristics of thin-film transistors (TFTs) employing nanoparticulated zinc oxide (ZnO) as the active semiconductor channel layer are discussed. The growing interest in this component is associated to the development of low-cost, flexible and transparent electronic devices. The TFTs integrated with ZnO nanoparticles are presented and an extensive transient electrical characterization campaign was performed in order to evaluate how these devices behave and degrade over time. The measurement was performed for 80 samples of two different integration setups: inverted staggered and inverted coplanar. In the performed tests two main disturbances were identified, which were classified as abrupt and memory effects. From the collected data, hypothesis to model the observed typical behavior are formulated. Trapping activity, ambient interaction, dielectric dipoles, mobile charges, formed parallel-paths, oxygen vacancies and metallic ions diffusion are mechanisms that may be associated to the observed behavior.

Cette thèse démontre le potentiel dont dispose l’exfoliation en phase liquide du graphite dans le but d’obtenir des feuillets de graphène dispersés dans un solvant organique. Ainsi le mécanisme d’exfoliation a été étudié en profondeur, en particulier, l’influence de plusieurs paramètres (température, puissance et solvants). Le choix de ses paramètres se montre crucial dans le contrôle du procédé, et pour l’obtention des feuillets de graphène ayant une taille ciblée. Il est donc possible de fabriquer des nano-feuillets de quelques dizaines de nanomètre qui en plus possèdent des propriétés de photoluminescence.Dans le but de comprendre le mécanisme d’exfoliation en phase liquide assistée par des molécules, une nouvelle approche a été mise au point : l’approche supramoléculaire. Cette approche se base sur l’utilisation de surfactants d’un nouveau type. En effet, les molécules sélectionnées possèdent une longue chaine alkyle. Cette chaine s’adsorbe sur la surface du graphène et permet de stabiliser les feuillets lors de l’exfoliation. L’influence de la taille de la chaine alkyle de ces molécules lors de l’exfoliation a été vérifiée. De plus, ces molécules ont été équipées de différentes fonctions supramoléculaires afin qu’elles puissent former des dimères sur la surface du graphène. L’ajout de ces molécules augmente non seulement le rendement d’exfoliation mais aussi le nombre de mono-feuillets présents dans ces dispersions. Ces dispersions présentent des propriétés conductrices lorsqu’elles sont déposées sur des substrats. Une nouvelles méthode de déposition a été mise au point afin d’améliorer et d’augmenter la conductivité mais aussi le pourcentage de transparence. / This thesis demonstrates the potential of exfoliation of the graphite in the liquid phase in order to obtain graphene sheets dispersed in an organic solvent. Thus the exfoliation mechanism has been studied, in particular, the influence of several parameters (temperature, power and solvents). The choice of parameters is actually crucial for the control of the process, and to obtain graphene sheets having a targeted size. It is therefore possible to manufacture nanosheets of several tens of nanometers, which in addition exhibit photoluminescence properties.In order to understand the exfoliation mechanism in liquid phase assisted by molecules, a new approach has been developed: the supramolecular approach. This approach is based on using a new type of surfactant. Indeed, the selected molecules carry a long alkyl chain. This chain is adsorbed on the surface of graphene and can stabilize the sheets during exfoliation. The influence of the size of the alkyl chain of these molecules during exfoliation was verified. Furthermore, these molecules have been equipped with various supramolecular functions, which can form dimers on the surface of graphene. The addition of these molecules not only increases exfoliation performance but also the number of mono-layers present in these dispersions. These dispersions have conductive properties when deposited on substrates. A new deposition method was developed to enhance and increase conductivity but also the percentage of transparency.

The layered iridates such as Sr2IrO4 and Sr3Ir2O7, have attracted substantial attention due to their novel electronic states originating from strong spin-orbit coupling and electron-correlation. Recent studies have revealed the possibilities of novel phases such as topological insulators, Weyl semimetals, and even a potential high-Tc superconducting state with a d-wave gap. However, there are still controversial issues regarding the fundamental electronic structure of these systems: the origin of the insulating gap is disputed as arising either from an antiferromagnetic ordering, i.e. Slater scheme or electron-correlation, i.e. Mott scheme. Moreover, it is a formidable task to unveil the physics of layered iridates due to the limited number of available materials for experimental characterizations. One way to overcome this limit and extend our investigation of the layered iridates is using metastable materials. These materials which are far from their equilibrium state, often have mechanical, electronic, and magnetic properties that different from their thermodynamically stable phases. However, these materials cannot be synthesized using thermodynamic equilibrium processes. One way to synthesize these materials is by using pulsed laser deposition (PLD). PLD is able to generate nonequilibrium material phases through the use of substrate strain and deposition conditions. Using this method, we have synthesized several thermodynamically metastable iridate thin-films and have investigated their electronic and optical properties. Synthesizing and investigating metastable iridates opens a path to expand the tunability further than the ability of the bulk methods. This thesis consists of four studies on metastable layered iridate thin film systems. In the first study, three-dimensional Mott variable-range hopping transport with decreased characteristic temperatures under lattice strain or isovalent doping has been observed in Sr2IrO4 thin films. Application of lattice strain or isovalent doping exerts metastable chemical pressure in the compounds, which changes both the bandwidth and electronic hopping. The variation of the characteristic temperature under lattice strain or isovalent doping implies that the density of states near the Fermi energy is reconstructed. The increased density of states in the Sr2IrO4 thin films with strain and isovalent doping could facilitate a condition to induce unprecedented electronic properties, opening a way for electronic device applications. In the second study, the effects of tuning the bandwidth via chemical pressure (i.e., Ca and Ba doping) on the optical properties of Sr2IrO4 epitaxial thin films has been investigated. Substitution of Sr by Ca and Ba ions exerts metastable chemical pressure in the system, which changes both the bandwidth and electronic hopping. The optical conductivity results of these thin films suggest that the two-peak-like optical conductivity spectra of the layered iridates originates from the overlap between the optically-forbidden spin-orbit exciton and the inter-site optical transitions within the Jeff = ½ band, which is consistent with the results obtained from a multi-orbital Hubbard model calculation. In the third study, thermodynamically metastable Ca2IrO4 thin- films have been synthesized. Since the perovskite structure of Ca2IrO4 is not thermodynamically stable, its bulk crystals do not exist in nature. We have synthesized the layered perovskite phase Ca2IrO4 thin- films from a polycrystalline hexagonal bulk crystal using an epitaxial stabilization technique. The smaller A-site in this compound compared to Sr2IrO4 and Ba2IrO4, increases the octahedral rotation and tilting, which enhance electron-correlation. The enhanced electron-correlation is consistent with the observation of increased gap energy in this compound. This study suggest that the epitaxial stabilization of metastable-phase thin-films can be used effectively for investigating complex-oxide systems. Finally, structural, transport, and optical properties of tensile strained (Sr1-xLax)3Ir2O7 (x = 0, 0.025, 0.05) thin-films have been investigated. While high-Tc superconductivity is predicted in the system, all of the samples are insulating. The insulating behavior of the La-doped Sr3Ir2O7 thin-films is presumably due to disorder-induced localization and ineffective electron-doping of La, which brings to light the intriguing difference between epitaxial thin films and bulk single crystals of the iridates. These studies thoroughly investigate a wide array of novel electronic and optical phenomena via tuning the relative strengths of electron correlation, electronic bandwidth, and spin-orbit coupling using perturbations such as chemical doping, and the stabilization of metastable phases in the layered iridates.

Previous work done at Cal Poly has shown that thin-film nickel-titanium (NiTi) can be easily sputtered onto silicon wafers and annealed to create a crystallized shape memory alloy (SMA) film. Initial work on creating devices yielded cantilevers that were highly warped due to thin-film stress created during the sputtering process. The objective of this work was to create a thin-film NiTi SMA device that could be better characterized. A membrane was selected due to the simplicity of fabrication and testing which would also oppose the thin-film stress due to the increase in attachment points to the substrate. Silicon wafers were etched through the majority of the thickness (~75%) creating square etch pits of varying sizes varying from 1294 µm to 4394 µm. The wafers were then sputtered with an approximate NiTi film of 5 µm followed by a thin chromium film. The chromium film would act as a diffusion barrier and prevent oxygen from diffusing into the NiTi and reacting with the titanium and forming titanium dioxide. These wafers were then annealed in a custom built vacuum annealing chamber at 550 °C for 1 hour with a pressure around 77 kPa. The chromium was then etched away followed by the remaining silicon. This left a thin membrane of shape memory NiTi which was packaged in order for characterization. The devices were glued to an aluminum substrate using polydimethylsiloxane (PDMS) and sealed with a small Tygon tube leading to the sealed chamber. This packaged device was then able to be pressurized using a nitrogen tank and the resulting NiTi membrane deflection was measured using a profilometer. Due to the differences in elastic moduli of the room temperature phase (martensite) and the high temperature phase (austenite) a difference of deflection was expected. The austenite finish (Af) temperature of bulk NiTi films was found to be around 60 °C so the devices were tested at both room temperature and at 60 °C. After testing seven separate devices of varying sizes, a regression model was used to analyze the final data. It was found that pressure, membrane size and theoretical versus actual deflection all affected the maximum deflection, but temperature did not. Higher pressures and larger membranes led to higher deflections as membrane deflection models from fundamental principles indicated. Some devices showed inferior performance when compared to the model due to incomplete silicon etching which caused lower deflection due to the much higher modulus of the remaining silicon. Thickness could also limit the amount of deflection measured with a thicker film leading to less deflection, but this is likely not the case due to the high uniformity of the sputtering system. Other devices showed superior performance over the model most likely due to either local delamination or lateral silicon etching. Both these would create a membrane that was larger than expected leading to a higher deflection. Unforutnaly, differential scanning calorimetry (DSC) analysis showed no shape memory behavior on a test wafer which was anneald at 550 ˚C for 1 hour. A design of experiments was conducted in order to find a heat treatment that would anneal the NiTi film and ensure that shape memory behavior could be obtained. An annealing at 650 °C for 1 hour showed a sharper and clearer Af phase transformation at around the target temperature of 60 °C. Annealing a full wafer at this temperature and time also showed that no delamination would occur which has also been linked to nonideal behavior of the NiTi membranes which has also been linked to meaningful behavior of the NiTi membranes.

The motivation of this study is to investigate the size dependent properties of Gadolinium silicide nanoparticles and their potential applications in Biomedicine. We use two approaches in our investigation - size dependence and possible exchange interaction in a core-shell structure. Past results showed Gd5Si4 NPs exhibit significantly reduced echo time compared to superparamagnetic iron oxide nanoparticles (SPION) when measured in a 7 T magnetic resonance imaging (MRI) system. This indicates potential use of Gd5Si4 ferromagnetic nanoparticles as T2 contrast agents for MRI. Until recently most contrast agents (CA) that are used in Magnetic Resonance Imaging (MRI) studies have been paramagnetic. However, ferromagnetic CAs are potentially more sensitive as T2 CAs than T1 paramagnetic compounds due to their large magnetic moments. Furthermore, the need for better MRI images without the need of upgrading to the higher magnetic field strength can be achieved using better CA such as Gd5Si4 NP. The quality of the image contrast in MRI is improved by shortening T1 and T2 relaxation times at the site or close proximity to the CA. In this study, effect of Gd5Si4 NP of varying sizes and with different concentrations are investigated on T1, T2 and T2* (effective/observed T2) relaxations times. Further study was carried out on possible exchange interaction between Fe3O4 and Gd5Si4 to enhance the magnetic properties of the Gd5Si4 which could be later used to synthesize core-shell structures. Exchange interaction / bias is a phenomena associated with the exchange anisotropy created at the interface between the two magnetic materials. Therefore, thin films of varying thickness was deposited and studied for their magnetic properties.

No description available.